TY - CONF TI - New Observations of Elements with 70 < A < 90 AU - Roederer, I.U. T2 - Torino Workshop on Nucleosynthesis in AGB Stars C2 - 2014/// C3 - Torino Workshop on Nucleosynthesis in AGB Stars CY - Bad Honnef, Germany DA - 2014/// PY - 2014/// ER - TY - CONF TI - New Observations of r-process Material in Metal-Poor Stars AU - Roederer,, I.U. T2 - Workshop on the Status and Challenges of the r-process C2 - 2014/// C3 - Workshop on the Status and Challenges of the r-process, INT CY - Seattle, WA DA - 2014/// PY - 2014/// ER - TY - JOUR TI - HUBBLE SPACE TELESCOPENEAR-ULTRAVIOLET SPECTROSCOPY OF THE BRIGHT CEMP-NO STAR BD+44°493 AU - Placco, Vinicius M. AU - Beers, Timothy C. AU - Roederer, Ian U. AU - Cowan, John J. AU - Frebel, Anna AU - Filler, Dan AU - Ivans, Inese I. AU - Lawler, James E. AU - Schatz, Hendrik AU - Sneden, Christopher AU - Sobeck, Jennifer S. AU - Aoki, Wako AU - Smith, Verne V. T2 - The Astrophysical Journal AB - We present an elemental-abundance analysis, in the near-ultraviolet (NUV) spectral range, for the extremely metal-poor star BD+44 493, a 9th magnitude sub-giant with [Fe/H] = -3.8 and enhanced carbon, based on data acquired with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. This star is the brightest example of a class of objects that, unlike the great majority of carbon-enhanced metal-poor (CEMP) stars, does not exhibit over-abundances of heavy neutron-capture elements (CEMP-no). In this paper, we validate the abundance determinations for a number of species that were previously studied in the optical region, and obtain strong upper limits for beryllium and boron, as well as for neutron-capture elements from zirconium to platinum, many of which are not accessible from ground-based spectra. The boron upper limit we obtain for BD+44 493, logeps(B) < -0.70, the first such measurement for a CEMP star, is the lowest yet found for very and extremely metal-poor stars. In addition, we obtain even lower upper limits on the abundances of beryllium, logeps(Be) < -2.3, and lead, logeps(Pb) < -0.23 ([Pb/Fe] < +1.90), than those reported by previous analyses in the optical range. Taken together with the previously measured low abundance of lithium, the very low upper limits on Be and B suggest that BD+44 493 was formed at a very early time, and that it could well be a bona-fide second-generation star. Finally, the Pb upper limit strengthens the argument for non-s-process production of the heavy-element abundance patterns in CEMP-no stars. DA - 2014/6/30/ PY - 2014/6/30/ DO - 10.1088/0004-637x/790/1/34 VL - 790 IS - 1 SP - 34 J2 - ApJ OP - SN - 0004-637X 1538-4357 UR - http://dx.doi.org/10.1088/0004-637x/790/1/34 DB - Crossref ER - TY - JOUR TI - Chemical abundances in bright giants of the globular cluster M62 (NGC 6266)★ AU - Yong, David AU - Alves Brito, Alan AU - Da Costa, Gary S. AU - Alonso-García, Javier AU - Karakas, Amanda I. AU - Pignatari, Marco AU - Roederer, Ian U. AU - Aoki, Wako AU - Fishlock, Cherie K. AU - Grundahl, Frank AU - Norris, John E. T2 - Monthly Notices of the Royal Astronomical Society AB - With the exception of Terzan 5, all the Galactic globular clusters that possess significant metallicity spreads, such as omega Cen and M22, are preferentially the more luminous clusters with extended horizontal branches. Here we present radial velocities and chemical abundances for seven bright giants in the globular cluster M62, a previously little-studied cluster. With M_V = -9.18, M62 is the ninth most luminous Galactic globular cluster and has an extended horizontal branch. Within our sample, we find (i) no evidence for a dispersion in metallicity, [Fe/H], beyond the measurement uncertainties, (ii) star-to-star abundance variations for C, O, Na and Al with the usual correlations between these elements as seen in other globular clusters, and (iii) a global enrichment for the elements Zr, Ba and La at the level [X/Fe] = +0.4 dex. For elements heavier than La, the abundance ratios are consistent with the scaled-solar $r$-process distribution. Below La, the abundances are anomalous when compared to the scaled-solar s-process or r-process distributions. For these elements, the abundance signature in M62 is in agreement with predictions of the s-process from fast-rotating massive stars, although the high [Rb/Y] ratio we measure may be a challenge to this scenario. DA - 2014/2/15/ PY - 2014/2/15/ DO - 10.1093/mnras/stu118 VL - 439 IS - 3 SP - 2638-2650 LA - en OP - SN - 1365-2966 0035-8711 UR - http://dx.doi.org/10.1093/mnras/stu118 DB - Crossref ER - TY - JOUR TI - NEUTRON-CAPTURE NUCLEOSYNTHESIS IN THE FIRST STARS AU - Roederer, Ian U. AU - Preston, George W. AU - Thompson, Ian B. AU - Shectman, Stephen A. AU - Sneden, Christopher T2 - The Astrophysical Journal AB - Recent studies suggest that metal-poor stars enhanced in carbon but containing low levels of neutron-capture elements may have been among the first to incorporate the nucleosynthesis products of the first generation of stars. We have observed 16 stars with enhanced carbon or nitrogen using the MIKE Spectrograph on the Magellan Telescopes at Las Campanas Observatory and the Tull Spectrograph on the Smith Telescope at McDonald Observatory. We present radial velocities, stellar parameters, and detailed abundance patterns for these stars. Strontium, yttrium, zirconium, barium, europium, ytterbium, and other heavy elements are detected. In four stars, these heavy elements appear to have originated in some form of r-process nucleosynthesis. In one star, a partial s-process origin is possible. The origin of the heavy elements in the rest of the sample cannot be determined unambiguously. The presence of elements heavier than the iron group offers further evidence that zero-metallicity rapidly-rotating massive stars and pair instability supernovae did not contribute substantial amounts of neutron-capture elements to the regions where the stars in our sample formed. If the carbon- or nitrogen-enhanced metal-poor stars with low levels of neutron-capture elements were enriched by products of zero-metallicity supernovae only, then the presence of these heavy elements indicates that at least one form of neutron-capture reaction operated in some of the first stars. DA - 2014/3/18/ PY - 2014/3/18/ DO - 10.1088/0004-637x/784/2/158 VL - 784 IS - 2 SP - 158 J2 - ApJ OP - SN - 0004-637X 1538-4357 UR - http://dx.doi.org/10.1088/0004-637x/784/2/158 DB - Crossref ER - TY - JOUR TI - Detailed abundance analysis of the brightest star in Segue 2, the least massive galaxy★ AU - Roederer, Ian U. AU - Kirby, Evan N. T2 - Monthly Notices of the Royal Astronomical Society AB - We present the first high resolution spectroscopic observations of one red giant star in the ultra-faint dwarf galaxy Segue 2, which has the lowest total mass (including dark matter) estimated for any known galaxy. These observations were made using the MIKE spectrograph on the Magellan II Telescope at Las Campanas Observatory. We perform a standard abundance analysis of this star, SDSS J021933.13+200830.2, and present abundances of 21 species of 18 elements as well as upper limits for 25 additional species. We derive [Fe/H] = -2.9, in excellent agreement with previous estimates from medium resolution spectroscopy. Our main result is that this star bears the chemical signatures commonly found in field stars of similar metallicity. The heavy elements produced by neutron-capture reactions are present, but they are deficient at levels characteristic of stars in other ultra-faint dwarf galaxies and a few luminous dwarf galaxies. The otherwise normal abundance patterns suggest that the gas from which this star formed was enriched by metals from multiple Type II supernovae reflecting a relatively well-sampled IMF. This adds to the growing body of evidence indicating that Segue 2 may have been substantially more massive in the past. DA - 2014/4/9/ PY - 2014/4/9/ DO - 10.1093/mnras/stu491 VL - 440 IS - 3 SP - 2665-2675 LA - en OP - SN - 1365-2966 0035-8711 UR - http://dx.doi.org/10.1093/mnras/stu491 DB - Crossref ER - TY - JOUR TI - Iron and neutron-capture element abundance variations in the globular cluster M2 (NGC 7089)★ AU - Yong, David AU - Roederer, Ian U. AU - Grundahl, Frank AU - Da Costa, Gary S. AU - Karakas, Amanda I. AU - Norris, John E. AU - Aoki, Wako AU - Fishlock, Cherie K. AU - Marino, A. F. AU - Milone, A. P. AU - Shingles, Luke J. T2 - Monthly Notices of the Royal Astronomical Society AB - We present CN and CH indices and CaII triplet metallicities for 34 giant stars and chemical abundances for 33 elements in 14 giants in the globular cluster M2. Assuming the program stars are cluster members, our analysis reveals (i) an extreme variation in CN and CH line strengths, (ii) a metallicity dispersion with a dominant peak at [Fe/H] = -1.7 and smaller peaks at -1.5 and -1.0, (iii) star-to-star abundance variations and correlations for the light elements O, Na, Al and Si and (iv) a large (and possibly bimodal) distribution in the abundances of all elements produced mainly via the s-process in solar system material. Following Roederer et al. (2011), we define two groups of stars, "r+s" and "r-only", and subtract the average abundances of the latter from the former group to obtain a "s-process residual". This s-process residual is remarkably similar to that found in M22 and in M4 despite the range in metallicity covered by these three systems. With recent studies identifying a double subgiant branch in M2 and a dispersion in Sr and Ba abundances, our spectroscopic analysis confirms that this globular cluster has experienced a complex formation history with similarities to M22, NGC 1851 and omega Centauri. DA - 2014/5/31/ PY - 2014/5/31/ DO - 10.1093/mnras/stu806 VL - 441 IS - 4 SP - 3396-3416 LA - en OP - SN - 1365-2966 0035-8711 UR - http://dx.doi.org/10.1093/mnras/stu806 DB - Crossref ER - TY - JOUR TI - NEW DETECTIONS OF ARSENIC, SELENIUM, AND OTHER HEAVY ELEMENTS IN TWO METAL-POOR STARS AU - Roederer, Ian U. AU - Schatz, Hendrik AU - Lawler, James E. AU - Beers, Timothy C. AU - Cowan, John J. AU - Frebel, Anna AU - Ivans, Inese I. AU - Sneden, Christopher AU - Sobeck, Jennifer S. T2 - The Astrophysical Journal AB - We use the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope to obtain new high-quality spectra covering the 1900 ⩽λ ⩽ 2360 Å wavelength range for two metal-poor stars, HD 108317 and HD 128279. We derive abundances of Cu ii, Zn ii, As i, Se i, Mo ii, and Cd ii, which have not been detected previously in either star. Abundances derived for Ge i, Te i, Os ii, and Pt i confirm those derived from lines at longer wavelengths. We also derive upper limits from the non-detection of W ii, Hg ii, Pb ii, and Bi i. The mean [As/Fe] ratio derived from these two stars and five others in the literature is unchanged over the metallicity range −2.8 < [Fe/H] <−0.6, 〈[As/Fe]〉 = +0.28 ± 0.14 (σ = 0.36 dex). The mean [Se/Fe] ratio derived from these two stars and six others in the literature is also constant, 〈[Se/Fe]〉 = +0.16 ± 0.09 (σ = 0.26 dex). The As and Se abundances are enhanced relative to a simple extrapolation of the iron-peak abundances to higher masses, suggesting that this mass region (75 ⩽A ⩽ 82) may be the point at which a different nucleosynthetic mechanism begins to dominate the quasi-equilibrium α-rich freezeout of the iron peak. 〈[Cu ii/Cu i]〉 = +0.56 ± 0.23 in HD 108317 and HD 128279, and we infer that lines of Cu i may not be formed in local thermodynamic equilibrium in these stars. The [Zn/Fe], [Mo/Fe], [Cd/Fe], and [Os/Fe] ratios are also derived from neutral and ionized species, and each ratio pair agrees within the mutual uncertainties, which range from 0.15 to 0.52 dex. DA - 2014/7/23/ PY - 2014/7/23/ DO - 10.1088/0004-637x/791/1/32 VL - 791 IS - 1 SP - 32 J2 - ApJ OP - SN - 0004-637X 1538-4357 UR - http://dx.doi.org/10.1088/0004-637x/791/1/32 DB - Crossref ER - TY - JOUR TI - Nine new metal-poor stars on the subgiant and red horizontal branches with high levels of r-process enhancement★ AU - Roederer, Ian U. AU - Cowan, John J. AU - Preston, George W. AU - Shectman, Stephen A. AU - Sneden, Christopher AU - Thompson, Ian B. T2 - Monthly Notices of the Royal Astronomical Society AB - We report the discovery of nine metal-poor stars with high levels of r-process enhancement (+0.81<[Eu/Fe]<+1.13), including six subgiants and three stars on the red horizontal branch. We also analyze four previously-known r-process-enhanced metal-poor red giants. From this sample of 13 stars, we draw the following conclusions. (1) High levels of r-process enhancement are found in a broad range of stellar evolutionary states, reaffirming that this phenomenon is not associated with a chemical peculiarity of red giant atmospheres. (2) Only 1 of 10 stars observed at multiple epochs shows radial velocity variations, reaffirming that stars with high levels of r-process enhancement are not preferentially found among binaries. (3) Only 2 of the 13 stars are highly-enhanced in C and N, indicating that there is no connection between high levels of r-process enhancement and high levels of C and N. (4) The dispersions in [Sr/Ba] and [Sr/Eu] are larger than the dispersions in [Ba/Eu] and [Yb/Eu], suggesting that the elements below the second r-process peak do not always scale with those in the rare earth domain, even within the class of highly-r-process-enhanced stars. (5) The light-element (12-1.0, the [P/Fe] ratio decreases toward the solar value with increasing metallicity, in agreement with previous observational studies. In stars with [Fe/H]<-1.0, <[P/Fe]>=+0.04+/-0.10, which overlaps with the [P/Fe] ratios found in several high-redshift damped Lyman-alpha systems. This behavior hints at a primary origin in massive stars. DA - 2014/11/24/ PY - 2014/11/24/ DO - 10.1088/0004-637X/797/1/69 VL - 797 IS - 1 SP - 69 ER - TY - JOUR TI - A SEARCH FOR STARS OF VERY LOW METAL ABUNDANCE. VI. DETAILED ABUNDANCES OF 313 METAL-POOR STARS AU - Roederer, Ian U. AU - Preston, George W. AU - Thompson, Ian B. AU - Shectman, Stephen A. AU - Sneden, Christopher AU - Burley, Gregory S. AU - Kelson, Daniel D. T2 - The Astronomical Journal AB - We present radial velocities, equivalent widths, model atmosphere parameters, and abundances or upper limits for 53 species of 48 elements derived from high resolution optical spectroscopy of 313 metal-poor stars. A majority of these stars were selected from the metal-poor candidates of the HK Survey of Beers, Preston, and Shectman. We derive detailed abundances for 61% of these stars for the first time. Spectra were obtained during a 10-year observing campaign using the Magellan Inamori Kyocera Echelle spectrograph on the Magellan Telescopes at Las Campanas Observatory, the Robert G. Tull Coude Spectrograph on the Harlan J. Smith Telescope at McDonald Observatory, and the High Resolution Spectrograph on the Hobby-Eberly Telescope at McDonald Observatory. We perform a standard LTE abundance analysis using MARCS model atmospheres, and we apply line-by-line statistical corrections to minimize systematic abundance differences arising when different sets of lines are available for analysis. We identify several abundance correlations with effective temperature. A comparison with previous abundance analyses reveals significant differences in stellar parameters, which we investigate in detail. Our metallicities are, on average, lower by approx. 0.25 dex for red giants and approx. 0.04 dex for subgiants. Our sample contains 19 stars with [Fe/H] < -3.5, 84 stars with [Fe/H] < -3.0, and 210 stars with [Fe/H] < -2.5. Detailed abundances are presented here or elsewhere for 91% of the 209 stars with [Fe/H] < -2.5 as estimated from medium resolution spectroscopy by Beers, Preston, and Shectman. We will discuss the interpretation of these abundances in subsequent papers. DA - 2014/5/2/ PY - 2014/5/2/ DO - 10.1088/0004-6256/147/6/136 VL - 147 IS - 6 SP - 136 ER - TY - CONF TI - Nanodiamond-based nanolubricants: Experiment and modeling AU - Brenner, D. AU - Mahbooba, Z. AU - Saberi-Movahed, F. AU - Krim, J. AU - Liu, Z. AU - Ivanov, M.G. AU - Osawa, E. AU - Shenderova, O. C2 - 2014/// C3 - Materials Research Society Symposium Proceedings DA - 2014/// DO - 10.1557/opl.2014.840 VL - 1703 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84924359244&partnerID=MN8TOARS ER - TY - SOUND TI - Simulations of signal and background for an NNbar Experiment with Free Neutrons AU - Young, A. R. AU - Phillips, D. G., II AU - Pattie, R.W., Jr. DA - 2014/6// PY - 2014/6// ER - TY - SOUND TI - Fundamental Symmetries Experiments: Neutron and Nuclear Beta Decay AU - Young, A.R. DA - 2014/9/28/ PY - 2014/9/28/ ER - TY - SOUND TI - Progress at Los Alamos: The Current Status of CN and UCN Beta-decay Studies AU - Young, A.R. DA - 2014/9// PY - 2014/9// ER - TY - CONF TI - Spallation-Driven Ultracold Neutron Sources: Concepts for a Next Generation Source AU - Young, A.R. AU - Muhrer, G. T2 - J-PARC2014 Symposium C2 - 2014/7// C3 - J-PARC2014 Symposium CY - J-PARC Center, Ibaraki Prefecture, Japan DA - 2014/7// PY - 2014/7// ER - TY - SOUND TI - Progress at Los Alamos: The Current Status of UCN Beta-decay Studies AU - Young, A.R. DA - 2014/6// PY - 2014/6// ER - TY - JOUR TI - Order and disorder control the functional rearrangement of influenza hemagglutinin AU - Lin, Xingcheng AU - Eddy, Nathanial R. AU - Noel, Jeffrey K. AU - Whitford, Paul C. AU - Wang, Qinghua AU - Ma, Jianpeng AU - Onuchic, José N. T2 - Proceedings of the National Academy of Sciences AB - Significance Influenza hemagglutinin (HA), a viral surface glycoprotein, undergoes a critical and large conformational rearrangement to promote fusion of the viral membrane with the host membrane. Unlike the variable receptor binding domain HA 1 , the coiled-coil domain HA 2 is highly conserved, making HA 2 a promising target for therapeutics. Furthermore, the structural similarity between influenza HA 2 and other viral fusion proteins, including that of HIV, makes HA 2 a valuable model system. We build a model using information from only the prefusion and postfusion configurations of HA 2 and use molecular dynamics simulations to characterize the structural ensembles found during the conformational transition. We find that local unfolding facilitates interaction of HA 2 with the host membrane and enables a quasi-stable asymmetric intermediate during the transition. DA - 2014/7/31/ PY - 2014/7/31/ DO - 10.1073/pnas.1412849111 VL - 111 IS - 33 SP - 12049-12054 J2 - Proc. Natl. Acad. Sci. U.S.A. LA - en OP - SN - 0027-8424 1091-6490 UR - http://dx.doi.org/10.1073/pnas.1412849111 DB - Crossref ER - TY - JOUR TI - Enhancement of single particle rare earth doped NaYF4: Yb, Er emission with a gold shell AU - Li, Ling AU - Green, Kory AU - Hallen, Hans AU - Lim, Shuang Fang T2 - Nanotechnology AB - Upconversion of infrared light to visible light has important implications for bioimaging. However, the small absorption cross-section of rare earth dopants has limited the efficiency of these anti-Stokes nanomaterials. We present enhanced excitation absorption and single particle fluorescent emission of sodium yttrium fluoride, NaYF4: Yb, Er based upconverting nanoparticles coated with a gold nanoshell through surface plasmon resonance. The single gold-shell coated nanoparticles show enhanced absorption in the near infrared, enhanced total emission intensity, and increased green relative to red emission. We also show differences in enhancement between single and aggregated gold shell nanoparticles. The surface plasmon resonance of the gold-shell coated nanoparticle is shown to be dependent on the shell thickness. In contrast to other reported results, our single particle experimental observations are corroborated by finite element calculations that show where the green/red emission enhancement occurs, and what portion of the enhancement is due to electromagnetic effects. We find that the excitation enhancement and green/red emission ratio enhancement occurs at the corners and edges of the doped emissive core. DA - 2014/12/17/ PY - 2014/12/17/ DO - 10.1088/0957-4484/26/2/025101 VL - 26 IS - 2 SP - 025101 J2 - Nanotechnology OP - SN - 0957-4484 1361-6528 UR - http://dx.doi.org/10.1088/0957-4484/26/2/025101 DB - Crossref KW - bioimaging KW - upconversion KW - near infrared ER - TY - JOUR TI - TRF1 and TRF2 use different mechanisms to find telomeric DNA but share a novel mechanism to search for protein partners at telomeres AU - Lin, Jiangguo AU - Countryman, Preston AU - Buncher, Noah AU - Kaur, Parminder AU - Longjiang, E AU - Zhang, Yiyun AU - Gibson, Greg AU - You, Changjiang AU - Watkins, Simon C AU - Piehler, Jacob AU - others T2 - Nucleic acids research DA - 2014/// PY - 2014/// VL - 42 IS - 4 SP - 2493-2504 ER - TY - CONF TI - The cosmic dawn and epoch of reionization with the square kilometre array AU - Koopmans, L.V.E. AU - Pritchard, J. AU - Mellema, G. AU - Abdalla, F. AU - Aguirre, J. AU - Ahn, K. AU - Barkana, R. AU - Van Bemmel, I. AU - Bernardi, G. AU - Bonaldi, A. AU - Briggs, F. AU - De Bruyn, A.G. AU - Chang, T.C. AU - Chapman, E. AU - Chen, X. AU - Ciardi, B. AU - Datta, K.K. AU - Dayal, P. AU - Ferrara, A. AU - Fialkov, A. AU - Fiore, F. AU - Ichiki, K. AU - Illiev, I.T. AU - Inoue, S. AU - Jeli?, V. AU - Jones, M. AU - Lazio, J. AU - Maio, U. AU - Majumdar, S. AU - Mack, K.J. AU - Mesinger, A. AU - Morales, M.F. AU - Parsons, A. AU - Pen, U.-L. AU - Santos, M. AU - Schneider, R. AU - Semelin, B. AU - De Souza, R.S. AU - Subrahmanyan, R. AU - Takeuchi, T. AU - Trott, C. AU - Vedantham, H. AU - Wagg, J. AU - Webster, R. AU - Wyithe, S. C2 - 2014/// C3 - Proceedings of Science DA - 2014/// VL - 9-13-June-2014 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84978955020&partnerID=MN8TOARS ER - TY - CONF TI - 21cm Forest with the SKA AU - Ciardi, B. AU - Inoue, S. AU - Mack, K.J. AU - Xu, Y. AU - Bernardi, G. C2 - 2014/// C3 - Proceedings of Science DA - 2014/// VL - 9-13-June-2014 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84978929471&partnerID=MN8TOARS ER - TY - CHAP TI - Logic from Dynamics AU - Ditto, William L. AU - Miliotis, Abraham AU - Murali, K. AU - Sinha, Sudeshna T2 - Chaotic Signal Processing A2 - Leung, Henry T3 - Applied mathematics, OT PY - 2014/// SP - 102–127 PB - Higher Education Press SN - 9781611973259 SV - 136 ER - TY - JOUR TI - QCD in magnetic field, Landau levels and double-life of unbroken center-symmetry AU - Anber, Mohamed M. AU - Ünsal, Mithat T2 - Journal of High Energy Physics AB - We study the thermal confinement/deconfinement and non-thermal quantum phase transitions or rapid cross-overs in QCD and QCD-like theories in external magnetic fields. At large magnetic fields, while the contribution of gauge fluctuations to Wilson-line potential remains unaltered at one-loop order, the contribution of fermions effectively becomes two lower dimensional and is enhanced by the density of states of the lowest Landau level (LLL). In a spatial compactification and for heavy adjoint fermions, this enhancement leads to a calculable zero temperature quantum phase transition on R^3*S^1 driven by a competition between the center-destabilizing gauge contribution and center-stabilizing LLL fermions. We also show that at a (formal) asymptotically large magnetic field, the adjoint fermions with arbitrarily large but fixed mass stabilize the center symmetry. This is an exotic case of simultaneous non-decoupling of large mass fermions (due to the enhancement by the LLL density of states) and decoupling from the low energy effective field theory. This observation has important implications for both Hosotani mechanism, for which gauge symmetry "breaking" occurs, and large-N volume independence (Eguchi-Kawai reduction), for which gauge structure is never "broken". Despite sounding almost self-contradictory, we carefully explain the physical scales entering the problem, double-meaning of unbroken center symmetry and how a clash is avoided. We also identify, for both thermal and spatial compactification, the jump in magnetic susceptibility as an order parameter for the deconfinement transition. The predictions of our analysis are testable by using current lattice techniques. DA - 2014/12// PY - 2014/12// DO - 10.1007/JHEP12(2014)107 VL - 2014 IS - 12 SP - 107 SN - 1029-8479 UR - http://dx.doi.org/10.1007/JHEP12(2014)107 KW - Confinement KW - Field Theories in Lower Dimensions KW - Phase Diagram of QCD KW - Nonperturbative Effects ER - TY - JOUR TI - Cu-Deficiency in the p-Type Semiconductor Cu5–xTa11O30: Impact on Its Crystalline Structure, Surfaces, and Photoelectrochemical Properties AU - Sullivan, Ian AU - Sahoo, Prangya P. AU - Fuoco, Lindsay AU - Hewitt, Andrew S. AU - Stuart, Sean AU - Dougherty, Daniel AU - Maggard, Paul A. T2 - Chemistry of Materials AB - The p-type semiconductor Cu5Ta11O30 has been investigated for the effect of Cu extrusion on its crystalline structure, surface chemistry, and photoelectrochemical properties. The Cu5Ta11O30 phase was prepared in high purity using a CuCl-mediated flux synthesis route, followed by heating the products in air from 250 to 750 °C in order to investigate the effects of its reported film preparation conditions as a p-type photoelectrode. At 650 °C and higher temperatures, Cu5Ta11O30 is found to decompose into CuTa2O6 and Ta2O5. At lower temperatures of 250 to 550 °C, nanosized CuIIO surface islands and a Cu-deficient Cu5–xTa11O30 crystalline structure (i.e., x ∼ 1.8(1) after 450 °C for 3 h in air) is found by electron microscopy and Rietveld structural refinement results, respectively. Its crystalline structure exhibits a decrease in the unit cell volume with increasing reaction temperature and time, owing to the increasing removal of Cu(I) ions from its structure. The parent structure of Cu5Ta11O30 is conserved up to ∼50% Cu vacancies but with one notably shorter Cu–O distance (by ∼0.26 Å) and concomitant changes in the Ta–O distances within the pentagonal bipyramidal TaO7 layers (by ∼0.29 Å to ∼0.36 Å). The extrusion and oxidation of Cu(I) to Cu(II) cations at its surfaces is found by X-ray photoelectron spectroscopy, while magnetic susceptibility data are consistent with the oxidation of Cu(I) within its structure, as given by CuI(5–2x)CuIIxTa11O30. Polycrystalline films of Cu5–xTa11O30 were prepared under similar conditions by sintering, followed by heating in air at temperatures of 350 °C, 450 °C, and 550 °C, each for 15, 30, and 60 min. An increasing amount of copper deficiency in the Cu5–xTa11O30 structure and CuIIO surface islands are found to result in significant increases in its p-type visible-light photocurrent at up to −2.5 mA/cm2 (radiant power density of ∼500 mW/cm2). Similarly high p-type photocurrents are also observed for Cu5Ta11O30 films with an increasing amount of CuO nanoparticles deposited onto their surfaces, showing that the enhancement primarily arises from the presence of the CuO nanoparticles which provide a favorable band-energy offset to drive electron–hole separation at the surfaces. By contrast, negligible photocurrents are observed for Cu-deficient Cu5–xTa11O30 without the CuO nanoparticles. Electronic structure calculations show that an increase in Cu vacancies shifts the Fermi level to lower energies, resulting in the depopulation of primarily Cu 3d10-orbitals as well as O 2p orbitals. Thus, these findings help shed new light into the role of Cu-deficiency and CuIIO surface islands on the p-type photoelectrode films for solar energy conversion systems. DA - 2014/11/24/ PY - 2014/11/24/ DO - 10.1021/CM502891T VL - 26 IS - 23 SP - 6711-6721 J2 - Chem. Mater. LA - en OP - SN - 0897-4756 1520-5002 UR - http://dx.doi.org/10.1021/CM502891T DB - Crossref ER - TY - JOUR TI - Copper Deficiency in the p-Type Semiconductor Cu1–xNb3O8 AU - King, Nacole AU - Sahoo, Prangya Parimita AU - Fuoco, Lindsay AU - Stuart, Sean AU - Dougherty, Daniel AU - Liu, Yi AU - Maggard, Paul A. T2 - Chemistry of Materials AB - The p-type semiconductor CuNb3O8 has been synthesized by solid-state and flux reactions and investigated for the effects of copper extrusion from its structure at 250–750 °C in air. High purity CuNb3O8 could be prepared by solid-state reactions at 750 °C at reaction times of 15 min and 48 h, and within a CuCl flux (10:1 molar ratio) at 750 °C at reaction times of 15 min and 12 h. The CuNb3O8 phase grows rapidly into well-faceted micrometer-sized crystals under these conditions, even with the use of Cu2O and Nb2O5 nanoparticle reactants. Heating CuNb3O8 in air to 450 °C for 3 h yields Cu-deficient Cu0.79(2)Nb3O8 that was characterized by powder X-ray Rietveld refinements (Sp. Grp. P21/a, Z = 4, a = 15.322(2) Å, b = 5.0476(6) Å, c = 7.4930(6) Å, β = 107.07(1)o, and V = 554.0(1) Å3). The parent structure of CuNb3O8 is maintained with ∼21% copper vacancies but with notably shorter Cu–O distances (by 0.16–0.27 Å) within the Cu–O–Nb1 zigzag chains down its b-axis. Copper is extruded at high temperatures in air and is oxidized to form ∼100–200 nm CuO islands on the surfaces of Cu1–xNb3O8, as characterized by electron microscopy and X-ray photoelectron spectroscopy (XPS) techniques. XPS measurements show only the Cu(II) oxidation state at the surfaces after heating in air at 450 and 550 °C. Magnetic susceptibility of the bulk powders after heating to 350 and 450 °C is consistent with the percentage of Cu(II) in the compound. Electronic structure calculations find that an increase in Cu vacancies from 0 to 25% shifts the Fermi level to lower energies, resulting in the partial oxidation of Cu(I) to Cu(II). However, higher amounts of Cu vacancies lead to a significant increase in the energy of the O 2p contributions, and which cross the Fermi level and become partially oxidized at the top of the valence band. These oxygen contributions occur over the bridging Cu–O–Nb neighbors when the Cu site is vacant. After heating to 550 °C, XPS data show the formation of a new higher energy O 1s peak that corresponds to the formation of “O–” species at this higher concentration of Cu vacancies. Light-driven bandgap transitions between the valence and conduction band edges are predicted to occur between regions of the structure having Cu vacancies to regions of the structure without Cu vacancies, respectively. This perturbation of the electronic structure of Cu-deficient Cu1–xNb3O8 could serve to drive a more effective separation of excited electron/hole pairs. Thus, these findings help shed new light on p-type Cu(I)-niobate photoelectrode films, i.e., CuNb3O8 and CuNbO3, that exhibit significant increases in their cathodic photocurrents after being heated to increasing temperatures in air. DA - 2014/3/13/ PY - 2014/3/13/ DO - 10.1021/CM404147J VL - 26 IS - 6 SP - 2095-2104 J2 - Chem. Mater. LA - en OP - SN - 0897-4756 1520-5002 UR - http://dx.doi.org/10.1021/CM404147J DB - Crossref ER - TY - JOUR TI - Partial Cross Sections of Neutron-Induced Reactions on natCu at En = 6, 8, 10, 12, 14, and 16 MeV for 0νββ Background Studies AU - Gooden, M.E. AU - Fallin, B.A. AU - Finch, S.W. AU - Kelley, J.H. AU - Howell, C.R. AU - Rusev, G. AU - Tonchev, A.P. AU - Tornow, W. AU - Stanislav, V. T2 - Nuclear Data Sheets AB - Partial cross-section measurements of (n,n'γ) reactions on natCu were carried out at tunl using monoenergetic neutrons at six energies of En = 6, 8, 10, 12, 14, 16 MeV. These studies were performed to provide accurate cross-section data on materials abundant in experimental setups involving HPGe detectors used to search for rare events, like the neutrino-less double-beta decay of 76Ge. Spallation and (α,n) neutrons are expected to cause the largest source of external background in the energy region of interest. At tunl pulsed neutron beams were produced via the 2H(d,n)3He reaction and the deexcitation γ rays from the reaction natCu(n,xγ) were detected with clover HPGe detectors. Cross-section results for the strongest transtions in 63Cu and 65Cu will be reported, and will compared to model calculations and to data recently obtained at lanl with a white neutron beam. DA - 2014/5// PY - 2014/5// DO - 10.1016/J.NDS.2014.08.034 VL - 119 SP - 121-123 J2 - Nuclear Data Sheets LA - en OP - SN - 0090-3752 UR - http://dx.doi.org/10.1016/J.NDS.2014.08.034 DB - Crossref ER - TY - JOUR TI - Light-front quantum chromodynamics: A framework for the analysis of hadron physics AU - Bakker, B.L.G. AU - Bassetto, A. AU - Brodsky, S.J. AU - Broniowski, W. AU - Dalley, S. AU - Frederico, T. AU - Głazek, S.D. AU - Hiller, J.R. AU - Ji, C.-R. AU - Karmanov, V. AU - Kulshreshtha, D. AU - Mathiot, J.-F. AU - Melnitchouk, W. AU - Miller, G.A. AU - Papavassiliou, J. AU - Polyzou, W.N. AU - Stefanis, N.G. AU - Vary, J.P. AU - Ilderton, A. AU - Heinzl, T. T2 - Nuclear Physics B - Proceedings Supplements AB - An outstanding goal of physics is to find solutions that describe hadrons in the theory of strong interactions, Quantum Chromodynamics (QCD). For this goal, the light-front Hamiltonian formulation of QCD (LFQCD) is a complementary approach to the well-established lattice gauge method. LFQCD offers access to the hadrons' nonperturbative quark and gluon amplitudes, which are directly testable in experiments at existing and future facilities. We present an overview of the promises and challenges of LFQCD in the context of unsolved issues in QCD that require broadened and accelerated investigation. We identify specific goals of this approach and address its quantifiable uncertainties. DA - 2014/6// PY - 2014/6// DO - 10.1016/J.NUCLPHYSBPS.2014.05.004 VL - 251-252 SP - 165–174 SN - 0920-5632 UR - http://dx.doi.org/10.1016/J.NUCLPHYSBPS.2014.05.004 ER - TY - JOUR TI - Kinematic Issues of GPDs in DVCS AU - Ji, Chueng-Ryong AU - Bakker, Bernard L.G. T2 - Nuclear Physics B - Proceedings Supplements AB - Generalized Parton Distributions (GPDs) in Deeply Virtual Compton Scattering (DVCS) have been widely recognized and used as a useful tool to explore the quark and gluon structure of the target hadrons. However, we recently pointed out treacherous kinematic issues in analyzing DVCS in terms of GPDs. We present our key findings in the simplest possible level of complete amplitude including the lepton current. We also discuss an implication on theoretical frameworks to cover the kinematic region of DVCS experiment with the 12 GeV upgrade at Jefferson Lab. DA - 2014/6// PY - 2014/6// DO - 10.1016/J.NUCLPHYSBPS.2014.04.013 VL - 251-252 SP - 75-80 J2 - Nuclear Physics B - Proceedings Supplements LA - en OP - SN - 0920-5632 UR - http://dx.doi.org/10.1016/J.NUCLPHYSBPS.2014.04.013 DB - Crossref KW - Deeply Virtual Compton Scattering (DVCS) KW - Generalized Parton Distributions (GPDs) ER - TY - JOUR TI - Sensitivity studies forr-process nucleosynthesis in three astrophysical scenarios AU - Surman, R. AU - Mumpower, M. AU - Cass, J. AU - Bentley, I. AU - Aprahamian, A. AU - McLaughlin, G.C. T2 - EPJ Web of Conferences AB - In rapid neutron capture, or r-process, nucleosynthesis, heavy elements are built up via a sequence of neutron captures and β decays that involves thousands of nuclei far from stability. Though we understand the basics of how the r process proceeds, its astrophysical site is still not conclusively known. The nuclear network simulations we use to test potential astrophysical scenarios require nuclear physics data (masses, β decay lifetimes, neutron capture rates, fission probabilities) for all of the nuclei on the neutron-rich side of the nuclear chart, from the valley of stability to the neutron drip line. Here we discuss recent sensitivity studies that aim to determine which individual pieces of nuclear data are the most crucial for r-process calculations. We consider three types of astrophysical scenarios: a traditional hot r process, a cold r process in which the temperature and density drop rapidly, and a neutron star merger trajectory. DA - 2014/// PY - 2014/// DO - 10.1051/EPJCONF/20146607024 VL - 66 SP - 07024 J2 - EPJ Web of Conferences OP - SN - 2100-014X UR - http://dx.doi.org/10.1051/EPJCONF/20146607024 DB - Crossref ER - TY - CHAP TI - Synthetic Computation: Chaos Computing, Logical Stochastic Resonance, and Adaptive Computing AU - Kia, Behnam AU - Murali, K. AU - Jahed Motlagh, Mohammad-Reza AU - Sinha, Sudeshna AU - Ditto, William L. T2 - International Conference on Theory and Application in Nonlinear Dynamics (ICAND 2012) A2 - Palacios, V. A. A2 - Longhini, P. AB - Nonlinearity and chaos can illustrate numerous behaviors and patterns, and one can select different patterns from this rich library of patterns. In this paper we focus on synthetic computing, a field that engineers and synthesizes nonlinear systems to obtain computation. We explain the importance of nonlinearity, and describe how nonlinear systems can be engineered to perform computation. More specifically, we provide an overview of chaos computing, a field that manually programs chaotic systems to build different types of digital functions. Also we briefly describe logical stochastic resonance (LSR), and then extend the approach of LSR to realize combinational digital logic systems via suitable concatenation of existing logical stochastic resonance blocks. Finally we demonstrate how a chaotic system can be engineered and mated with different machine learning techniques, such as artificial neural networks, random searching, and genetic algorithm, to design different autonomous systems that can adapt and respond to environmental conditions. PY - 2014/12/14/ DO - 10.1007/978-3-319-02925-2_5 SP - 51–65 PB - Springer International Publishing SN - 9783319029245 9783319029252 UR - http://dx.doi.org/10.1007/978-3-319-02925-2_5 ER - TY - CONF TI - Examining the Diffusion of Research-Based Instructional Strategies Using Social Network Analysis: A Case Study of SCALE-UP AU - Neumeyer, X. AU - Foote, K.T. AU - Beichner, R. AU - Dancy, M.H. AU - Henderson, C. T2 - 121st ASEE Annual Conference & Exposition C2 - 2014/// C3 - Proceedings of the 2014 ASEE Annual Conference CY - Indianapolis, IN DA - 2014/// PY - 2014/6/15/ ER - TY - JOUR TI - Magnetic properties of periodically organized cobalt frameworks AU - Hukic-Markosian, Golda AU - Zhai, Yaxin AU - Montanari, Danielle E. AU - Ott, Steven AU - Braun, Adrianne AU - Sun, Dali AU - Vardeny, Zeev V. AU - Bartl, Michael H. T2 - Journal of Applied Physics AB - Periodically organized magnetic cobalt frameworks have been fabricated by a combination of colloidal self-assembly and electrochemical deposition. The ordered cobalt frameworks have a closed-packed face-centered-cubic inverse opal structure and are fabricated as micrometer-thick films. The size and density of the cobalt crystallites that compose the cobalt frameworks can be modified by a thermal annealing step following the electrodeposition. Comparison of the magnetic properties (studied by magneto-optical Kerr effect (MOKE) spectroscopy) of as-deposited and annealed samples reveals strong impact of the annealing process. Fitting the obtained MOKE response to a modified Langevin model reveals optimum values of coercivity, pinning site density, and inter-domain coupling for samples that are thermally annealed at 440 °C. DA - 2014/7/7/ PY - 2014/7/7/ DO - 10.1063/1.4883537 VL - 116 IS - 1 SP - 013906 J2 - Journal of Applied Physics LA - en OP - SN - 0021-8979 1089-7550 UR - http://dx.doi.org/10.1063/1.4883537 DB - Crossref ER - TY - JOUR TI - The first decade of organic spintronics research AU - Sun, Dali AU - Ehrenfreund, Eitan AU - Valy Vardeny, Z. T2 - Chem. Commun. AB - The significant milestones in organic spintronics achieved during the first decade of research are reviewed. DA - 2014/// PY - 2014/// DO - 10.1039/C3CC47126H VL - 50 IS - 15 SP - 1781-1793 J2 - Chem. Commun. LA - en OP - SN - 1359-7345 1364-548X UR - http://dx.doi.org/10.1039/C3CC47126H DB - Crossref ER - TY - JOUR TI - Active control of magnetoresistance of organic spin valves using ferroelectricity AU - Sun, Dali AU - Fang, Mei AU - Xu, Xiaoshan AU - Jiang, Lu AU - Guo, Hangwen AU - Wang, Yanmei AU - Yang, Wenting AU - Yin, Lifeng AU - Snijders, Paul C. AU - Ward, T. Z. AU - Gai, Zheng AU - Zhang, X.-G. AU - Lee, Ho Nyung AU - Shen, Jian T2 - Nature Communications AB - Organic spintronic devices have been appealing because of the long spin lifetime of the charge carriers in the organic materials and their low cost, flexibility and chemical diversity. In previous studies, the control of resistance of organic spin valves is generally achieved by the alignment of the magnetization directions of the two ferromagnetic electrodes, generating magnetoresistance. Here we employ a new knob to tune the resistance of organic spin valves by adding a thin ferroelectric interfacial layer between the ferromagnetic electrode and the organic spacer: the magnetoresistance of the spin valve depends strongly on the history of the bias voltage, which is correlated with the polarization of the ferroelectric layer; the magnetoresistance even changes sign when the electric polarization of the ferroelectric layer is reversed. These findings enable active control of resistance using both electric and magnetic fields, opening up possibility for multi-state organic spin valves. DA - 2014/7/10/ PY - 2014/7/10/ DO - 10.1038/NCOMMS5396 VL - 5 IS - 1 J2 - Nat Commun LA - en OP - SN - 2041-1723 UR - http://dx.doi.org/10.1038/NCOMMS5396 DB - Crossref ER - TY - JOUR TI - Observation of the energy transfer sequence in an organic host–guest system of a luminescent polymer and a phosphorescent molecule AU - Basel, Tek AU - Sun, Dali AU - Gautam, Bhoj AU - Valy Vardeny, Z. T2 - Journal of Luminescence AB - We used steady state optical spectroscopies such as photoluminescence and photoinduced absorption (PA), and magnetic-field PA (MPA) for studying the energy transfer dynamics in films and organic light emitting diodes (OLED) based on host–guest blends with different guest concentrations of the fluorescent polymer poly-[2-methoxy, 5-(2′-ethyl-hexyloxy)phenylene vinylene] (MEHPPV-host), and phosphorescent molecule PtII-tetraphenyltetrabenzoporphyrin [Pt(tpbp); guest]. We show that the energy transfer process between the excited states of the host polymer and guest molecule takes a ‘ping-pong’ type sequence, because the lowest guest triplet exciton energy, ET(guest), lies higher than that of the host, ET(host). Upon photon excitation the photogenerated singlet excitons in the host polymer chains first undergo a Förster resonant energy transfer process to the guest singlet manifold, which subsequently reaches ET(guest) by intersystem crossing. Because ET(guest)>ET(host) there is a subsequent Dexter type energy transfer from ET(guest) to ET(host). This energy transfer sequence has profound influence on the photoluminescence and electroluminescence emission spectra in both films and OLED devices based on the MEHPPV-Pt(tpbp) system. DA - 2014/11// PY - 2014/11// DO - 10.1016/J.JLUMIN.2014.06.015 VL - 155 SP - 89-94 J2 - Journal of Luminescence LA - en OP - SN - 0022-2313 UR - http://dx.doi.org/10.1016/J.JLUMIN.2014.06.015 DB - Crossref KW - Fluorescence KW - Phosphorescence KW - Photo-induced absorption KW - Energy transfer KW - Organic light emitting diode ER - TY - JOUR TI - Investigation of Calcein for Reporting Content Mixing During Viral Membrane Fusion Experiments AU - Wessels, Laura AU - Weninger, Keith T2 - Biophysical Journal AB - Simultaneous diagnosis of lipid mixing and content mixing during fusion of enveloped virus particle with a target liposome is critical for thorough understanding of the completeness of the membrane fusion reaction. Here we have investigated calcein for fluorescence detection of content mixing in virus fusion experiments. Calcein was encapsulated into target liposomes and lipophilic fluorescent dyes were incorporated into virus samples, both at self-quenching concentrations, to allow hemifusion and full fusion to be distinguished by the relative timing of the dequenching signals. We report that osmotic balancing of the interior and exterior of the calcein-loaded vesicles is essential for these experiments to reproduce native virus fusion behaviors. DA - 2014/1// PY - 2014/1// DO - 10.1016/J.BPJ.2013.11.3922 VL - 106 IS - 2 SP - 707a J2 - Biophysical Journal LA - en OP - SN - 0006-3495 UR - http://dx.doi.org/10.1016/J.BPJ.2013.11.3922 DB - Crossref ER - TY - JOUR TI - PULSATION PERIOD VARIATIONS IN THE RRc LYRAE STAR KIC 5520878 AU - Hippke, Michael AU - Learned, John G. AU - Zee, A. AU - Edmondson, William H. AU - Lindner, John F. AU - Kia, Behnam AU - Ditto, William L. AU - Stevens, Ian R. T2 - The Astrophysical Journal AB - Learned et. al. proposed that a sufficiently advanced extra-terrestrial civilization may tickle Cepheid and RR Lyrae variable stars with a neutrino beam at the right time, thus causing them to trigger early and jogging the otherwise very regular phase of their expansion and contraction. This would turn these stars into beacons to transmit information throughout the galaxy and beyond. The idea is to search for signs of phase modulation (in the regime of short pulse duration) and patterns, which could be indicative of intentional, omnidirectional signaling. We have performed such a search among variable stars using photometric data from the Kepler space telescope. In the RRc Lyrae star KIC 5520878, we have found two such regimes of long and short pulse durations. The sequence of period lengths, expressed as time series data, is strongly auto correlated, with correlation coefficients of prime numbers being significantly higher ($p=99.8$\%). Our analysis of this candidate star shows that the prime number oddity originates from two simultaneous pulsation periods and is likely of natural origin. Simple physical models elucidate the frequency content and asymmetries of the KIC 5520878 light curve. Despite this SETI null result, we encourage testing other archival and future time-series photometry for signs of modulated stars. This can be done as a by-product to the standard analysis, and even partly automated. DA - 2014/12/18/ PY - 2014/12/18/ DO - 10.1088/0004-637X/798/1/42 VL - 798 IS - 1 SP - 42 J2 - ApJ OP - SN - 1538-4357 UR - http://dx.doi.org/10.1088/0004-637X/798/1/42 DB - Crossref KW - stars: variables: Cepheids KW - stars: variables: RR Lyrae ER - TY - JOUR TI - Solution-state conformation and stoichiometry of yeast Sir3 heterochromatin fibres AU - Swygert, Sarah G. AU - Manning, Benjamin J. AU - Senapati, Subhadip AU - Kaur, Parminder AU - Lindsay, Stuart AU - Demeler, Borries AU - Peterson, Craig L. T2 - Nature Communications AB - Heterochromatin is a repressive chromatin compartment essential for maintaining genomic integrity. A hallmark of heterochromatin is the presence of specialized nonhistone proteins that alter chromatin structure to inhibit transcription and recombination. It is generally assumed that heterochromatin is highly condensed. However, surprisingly little is known about the structure of heterochromatin or its dynamics in solution. In budding yeast, formation of heterochromatin at telomeres and the homothallic silent mating type loci require the Sir3 protein. Here, we use a combination of sedimentation velocity, atomic force microscopy and nucleosomal array capture to characterize the stoichiometry and conformation of Sir3 nucleosomal arrays. The results indicate that Sir3 interacts with nucleosomal arrays with a stoichiometry of two Sir3 monomers per nucleosome. We also find that Sir3 fibres are less compact than canonical magnesium-induced 30 nm fibres. We suggest that heterochromatin proteins promote silencing by ‘coating’ nucleosomal arrays, stabilizing interactions between nucleosomal histones and DNA. Heterochromatin is a ‘repressed’ chromatin state involved in the generation of centromeres, the protection of telomeres and the maintenance of genome integrity. Here Swygert et al.show that Sir3 - a key factor in the formation of heterochromatin - promotes a chromatin structure distinct from the canonical 30 nm fibre. DA - 2014/8/28/ PY - 2014/8/28/ DO - 10.1038/NCOMMS5751 VL - 5 IS - 1 J2 - Nat Commun LA - en OP - SN - 2041-1723 UR - http://dx.doi.org/10.1038/NCOMMS5751 DB - Crossref ER - TY - JOUR TI - Precision calculation of the quartet-channelp−dscattering length AU - König, Sebastian AU - Hammer, H.-W. T2 - Physical Review C AB - We present a fully perturbative calculation of the quartet-channel proton-deuteron scattering length up to next-to-next-to-leading order in pionless effective field theory. We use a framework that consistently extracts the Coulomb-modified effective-range function for a screened Coulomb potential in momentum space and allows for a clear linear extrapolation back to the physical limit without screening. Our result of ${{}^{4}a}_{p\text{\ensuremath{-}}d}=(10.9\ifmmode\pm\else\textpm\fi{}0.4)$ fm agrees with older experimental determinations of this quantity but deviates from potential-model calculations and a more recent result from Black et al., which find larger values around 14 fm. As a possible resolution to this discrepancy, we discuss the scheme dependence of Coulomb subtractions in a three-body system. DA - 2014/9// PY - 2014/9// DO - 10.1103/physrevc.90.034005 VL - 90 IS - 3 ER - TY - JOUR TI - He3andpdscattering to next-to-leading order in pionless effective field theory AU - Vanasse, Jared AU - Egolf, David A. AU - Kerin, John AU - König, Sebastian AU - Springer, Roxanne P. T2 - Physical Review C AB - We study the three-body systems of $^{3}\mathrm{He}$ and $pd$ scattering and demonstrate, both analytically and numerically, that a new $pd$ three-body force is needed at next-to-leading order in pionless effective field theory. We also show that at leading order these observables require no new three-body force beyond what is necessary to describe $nd$ scattering. We include electromagnetic effects by iterating only diagrams that involve a single photon exchange in the three-body sector. DA - 2014/6// PY - 2014/6// DO - 10.1103/physrevc.89.064003 VL - 89 IS - 6 UR - http://dx.doi.org/10.1103/physrevc.89.064003 ER - TY - JOUR TI - Ultraviolet extrapolations in finite oscillator bases T2 - Physical Review C AB - The use of finite harmonic oscillator spaces in many-body calculations introduces both infrared (IR) and ultraviolet (UV) errors. The IR effects are well approximated by imposing a hard-wall boundary condition at a properly identified radius L_eff. We show that duality of the oscillator implies that the UV effects are equally well described by imposing a sharp momentum cutoff at a momentum Lambda_eff complementary to L_eff. By considering two-body systems with separable potentials, we show that the UV energy corrections depend on details of the potential, in contrast to the IR energy corrections, which depend only on the S-matrix. An adaptation of the separable treatment to more general interactions is developed and applied to model potentials as well as to the deuteron with realistic potentials. The previous success with a simple phenomenological form for the UV error is also explained. Possibilities for controlled extrapolations for A > 2 based on scaling arguments are discussed. DA - 2014/12/29/ PY - 2014/12/29/ DO - 10.1103/PhysRevC.90.064007 ER - TY - JOUR TI - Constraints on a possible dineutron state from pionless EFT AU - Hammer, H.-W. AU - König, Sebastian T2 - Physics Letters B AB - We investigate the sensitivity of the three-nucleon system to changes in the neutron-neutron scattering length to next-to-leading order in the pionless effective field theory, focusing on the the triton-3He binding energy difference and neutron-deuteron elastic scattering. Due to the appearance of an electromagnetic three-body counterterm at this order, the triton-3He binding energy difference remains consistent with the experimental value even for large positive neutron-neutron scattering lengths while the elastic neutron-deuteron scattering phase shifts are insensitive. We conclude that a bound dineutron cannot be excluded to next-to-leading order in pionless EFT. DA - 2014/9// PY - 2014/9// DO - 10.1016/j.physletb.2014.07.015 VL - 736 SP - 208-213 ER - TY - CONF TI - A silicon integrated BaTiO3 electro-optic modulator AU - Xiong, C. AU - Pernice, W.H.P. AU - Ngai, J.H. AU - Reiner, J.W. AU - Kumah, D. AU - Walker, F.J. AU - Ahn, C.H. AU - Tang, H.X. C2 - 2014/// C3 - Conference on Lasers and Electro-Optics Europe - Technical Digest DA - 2014/// VL - 2014-January UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84944698664&partnerID=MN8TOARS ER - TY - JOUR TI - The Majorana Demonstrator: Progress towards showing the feasibility of a tonne-scale 76Ge neutrinoless double-beta decay experiment AU - Finnerty, P. AU - Aguayo, E. AU - Amman, M. AU - Avignone, F.T. AU - Barabash, A.S. AU - Barton, P.J. AU - Beene, J.R. AU - Bertrand, F.E. AU - Boswell, M. AU - Brudanin, V. AU - Busch, M. AU - Chan, Y.-D. AU - Christofferson, C.D. AU - Collar, J.I. AU - Combs, D.C. AU - Cooper, R.J. AU - Detwiler, J.A. AU - Doe, P.J. AU - Efremenko, Y. AU - Egorov, V. AU - Ejiri, H. AU - Elliott, S.R. AU - Esterline, J. AU - Fast, J.E. AU - Fields, N. AU - Fraenkle, F.M. AU - Galindo-Uribarri, A. AU - Gehman, V.M. AU - Giovanetti, G.K. AU - Green, M.P. AU - Guiseppe, V.E. AU - Gusey, K. AU - Hallin, A.L. AU - Hazama, R. AU - Henning, R. AU - Hoppe, E.W. AU - Horton, M. AU - Howard, S. AU - Howe, M.A. AU - Johnson, R.A. AU - Keeter, K.J. AU - Kidd, M.F. AU - Knecht, A. AU - Kochetov, O. AU - Konovalov, S.I. AU - Kouzes, R.T. AU - Laferriere, B.D. AU - Leon, J. AU - Leviner, L.E. AU - Loach, J.C. AU - Luke, P.N. AU - Macmullin, S. AU - Marino, M.G. AU - Martin, R.D. AU - Merriman, J.H. AU - Miller, M.L. AU - Mizouni, L. AU - Nomachi, M. AU - Orrell, J.L. AU - Overman, N.R. AU - Perumpilly, G. AU - Phillips, D.G. AU - Poon, A.W.P. AU - Radford, D.C. AU - Rielage, K. AU - Robertson, R.G.H. AU - Ronquest, M.C. AU - Schubert, A.G. AU - Shima, T. AU - Shirchenko, M. AU - Snavely, K.J. AU - Steele, D. AU - Strain, J. AU - Timkin, V. AU - Tornow, W. AU - Varner, R.L. AU - Vetter, K. AU - Vorren, K. AU - Wilkerson, J.F. AU - Yakushev, E. AU - Yaver, H. AU - Young, A.R. AU - Yu, C.-H. AU - Yumatov, V. T2 - Journal of Physics: Conference Series AB - The Majorana Demonstrator will search for the neutrinoless double–beta decay (0vββ) of the 76Ge isotope with a mixed array of enriched and natural germanium detectors. The observation of this rare decay would indicate the neutrino is its own anti–particle, demonstrate that lepton number is not conserved, and provide information on the absolute mass–scale of the neutrino. The Demonstrator is being assembled at the 4850 foot level of the Sanford Underground Research Facility in Lead, South Dakota. The array will be contained in a low–background environment and surrounded by passive and active shielding. The goals for the Demonstrator are: demonstrating a background rate less than 3 t−1 y−1 in the 4 keV region of interest (ROI) surrounding the 2039 keV 76Ge endpoint energy; establishing the technology required to build a tonne–scale germanium based double–beta decay experiment; testing the recent claim of observation of 0vββ [1]; and performing a direct search for light WIMPs (3-10 GeV/c2). DA - 2014/// PY - 2014/// DO - 10.1088/1742-6596/485/1/012042 VL - 485 IS - 1 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84899864081&partnerID=MN8TOARS ER - TY - CONF TI - The Majorana Demonstrator: A search for neutrinoless double-beta decay of germanium-76 AB - The Majorana collaboration is searching for neutrinoless double beta decay using 76Ge, which has been shown to have a number of advantages in terms of sensitivities and backgrounds. The observation of neutrinoless double-beta decay would show that lepton number is violated and that neutrinos are Majorana particles and would simultaneously provide information on neutrino mass. Attaining sensitivities for neutrino masses in the inverted hierarchy region, 15 - 50 meV, will require large, tonne-scale detectors with extremely low backgrounds, at the level of ∼1 count/t-y or lower in the region of the signal. The Majorana collaboration, with funding support from DOE Office of Nuclear Physics and NSF Particle Astrophysics, is constructing the Demonstrator, an array consisting of 40 kg of p-type point-contact high-purity germanium (HPGe) detectors, of which ∼30 kg will be enriched to 87% in 76Ge. The Demonstrator is being constructed in a clean room laboratory facility at the 4850' level (4300 m.w.e.) of the Sanford Underground Research Facility (SURF) in Lead, SD. It utilizes a compact graded shield approach with the inner portion consisting of ultra-clean Cu that is being electroformed and machined underground. The primary aim of the Demonstrator is to show the feasibility of a future tonne-scale measurement in terms of backgrounds and scalability. C2 - 2014/// C3 - AIP Conference Proceedings DA - 2014/// DO - 10.1063/1.4856546 VL - 1572 SP - 45-48 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84904130282&partnerID=MN8TOARS KW - neutrino KW - double-beta KW - germanium ER - TY - CONF TI - Status of the Majorana Demonstrator experiment AU - Martin, R. D. AU - Abgrall, N. AU - Aguayo, E. AU - Avignone III, F. T. AU - Barabash, A. S. AU - Bertrand, F. E. AU - Boswell, M. AU - Brudanin, V. AU - Busch, M. AU - Caldwell, A. S. AU - Chan, Y-D. AU - Christofferson, C. D. AU - Combs, D. C. AU - Detwiler, J. A. AU - Doe, P. J. AU - Efremenko, Yu. AU - Egorov, V. AU - Ejiri, H. AU - Elliott, S. R. AU - Esterline, J. AU - Fast, J. E. AU - Finnerty, P. AU - Fraenkle, F. M. AU - Galindo-Uribarri, A. AU - Giovanetti, G. K. AU - Goett, J. AU - Green, M. P. AU - Gruszko, J. AU - Guiseppe, V. E. AU - Gusev, K. AU - Hallin, A. L. AU - Hazama, R. AU - Hegai, A. AU - Henning, R. AU - Hoppe, E. W. AU - Howard, S. AU - Howe, M. A. AU - Keeter, K. J. AU - Kidd, M. F. AU - Kochetov, O. AU - Konovalov, S. I. AU - Kouzes, R. T. AU - LaFerriere, B. D. AU - Leon, J. AU - Leviner, L. E. AU - Loach, J. C. AU - MacMullin, J. AU - MacMullin, S. AU - Mertens, S. AU - Mizouni, L. AU - Nomachi, M. AU - Orrell, J. L. AU - O'Shaughnessy, C. AU - Overman, N. R. AU - Phillips II, D. G. AU - Poon, A. W. P. AU - Pushkin, K. AU - Radford, D. C. AU - Rielage, K. AU - Robertson, R. G. H. AU - Romero-Romero, E. AU - Ronquest, M. C. AU - Schubert, A. G. AU - Shanks, B. AU - Shima, T. AU - Shirchenko, M. AU - Snavely, K. J. AU - Snyder, N. AU - Soin, A. AU - Suriano, A. M. AU - Thompson, J. AU - Timkin, V. AU - Tornow, W. AU - Varner, R. L. AU - Vasilyev, S. AU - Vetter, K. AU - Vorren, K. AU - White, B. R. AU - Wilkerson, J. F. AU - Xu, W. AU - Yakushev, E. AU - Young, A. R. AU - Yu, C.-H. AU - Yumatov, V. T2 - WORKSHOP ON DARK MATTER, NEUTRINO PHYSICS AND ASTROPHYSICS CETUP* 2013: VIIth International Conference on Interconnections between Particle Physics and Cosmology PPC* 2013 AB - Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation R. D. Martin, N. Abgrall, E. Aguayo, F. T. Avignone III, A. S. Barabash, F. E. Bertrand, M. Boswell, V. Brudanin, M. Busch, A. S. Caldwell, Y-D. Chan, C. D. Christofferson, D. C. Combs, J. A. Detwiler, P. J. Doe, Yu. Efremenko, V. Egorov, H. Ejiri, S. R. Elliott, J. Esterline, J. E. Fast, P. Finnerty, F. M. Fraenkle, A. Galindo-Uribarri, G. K. Giovanetti, J. Goett, M. P. Green, J. Gruszko, V. E. Guiseppe, K. Gusev, A. L. Hallin, R. Hazama, A. Hegai, R. Henning, E. W. Hoppe, S. Howard, M. A. Howe, K. J. Keeter, M. F. Kidd, O. Kochetov, S. I. Konovalov, R. T. Kouzes, B. D. LaFerriere, J. Leon, L. E. Leviner, J. C. Loach, J. MacMullin, S. MacMullin, S. Mertens, L. Mizouni, M. Nomachi, J. L. Orrell, C. O'Shaughnessy, N. R. Overman, D. G. Phillips II, A. W. P. Poon, K. Pushkin, D. C. Radford, K. Rielage, R. G. H. Robertson, E. Romero-Romero, M. C. Ronquest, A. G. Schubert, B. Shanks, T. Shima, M. Shirchenko, K. J. Snavely, N. Snyder, A. Soin, A. M. Suriano, J. Thompson, V. Timkin, W. Tornow, R. L. Varner, S. Vasilyev, K. Vetter, K. Vorren, B. R. White, J. F. Wilkerson, W. Xu, E. Yakushev, A. R. Young, C.-H. Yu, V. Yumatov; Status of the Majorana Demonstrator experiment. AIP Conf. Proc. 24 June 2014; 1604 (1): 413–420. https://doi.org/10.1063/1.4883459 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioAIP Conference Proceedings Search Advanced Search |Citation Search C2 - 2014/// C3 - AIP Conference Proceedings CY - Lead/Deadwood, South Dakota DA - 2014/// PY - 2013/6/24/ DO - 10.1063/1.4883459 VL - 1604 SP - 413-420 PB - AIP Publishing LLC SN - 9780735412385 UR - http://dx.doi.org/10.1063/1.4883459 KW - Neutrinoless double beta-decay KW - germanium KW - PPC ER - TY - JOUR TI - Stochastic resonance and 1/f noise at coupled phase transitions AU - Koverda, V.P. AU - Skokov, V.N. T2 - Physica A: Statistical Mechanics and its Applications AB - The system of two nonlinear stochastic equations simulating 1/f fluctuations during the interaction of nonequilibrium phase transitions in the presence of an external periodic action has been studied by numerical methods. It is shown that in the system there appears stochastic resonance, which leads to an amplification of the output periodic signal under the action of noise. To a random process with a 1/f power spectrum corresponds the maximum Gibbs–Shannon informational entropy. At stochastic resonance the informational entropy is minimum. A new behavior of a two-dimensional system at stochastic resonance has been revealed: at low frequencies of a periodic action with an increased white noise intensity the system trajectories are limited by two mutually perpendicular directions—anisotropic stochastic resonance. With a further increase in the white noise intensity in the system one can observe “ordinary” stochastic resonance, when the increasing intensity of fluctuations in the vicinity of the driving frequency is smeared in the directions. DA - 2014/// PY - 2014/// DO - 10.1016/j.physa.2013.09.050 VL - 393 SP - 173-181 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84886593380&partnerID=MN8TOARS KW - Stochastic resonance KW - 1/f noise KW - Stochastic equations KW - Nonequilibrium phase transitions KW - Informational entropy ER - TY - JOUR TI - Stochastic resonant response in the transient boiling regime with periodic heat release AU - Vinogradov, A.V. AU - Skokov, V.N. AU - Koverda, V.P. T2 - Doklady Physics DA - 2014/// PY - 2014/// DO - 10.1134/S1028335814100097 VL - 59 IS - 10 SP - 449-452 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84920288373&partnerID=MN8TOARS ER - TY - JOUR TI - Stochastic resonance in a nonlinear system with a 1/f spectrum AU - Skokov, V.N. AU - Koverda, V.P. T2 - Technical Physics DA - 2014/// PY - 2014/// DO - 10.1134/S1063784214050296 VL - 59 IS - 5 SP - 637-641 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84901438339&partnerID=MN8TOARS ER - TY - JOUR TI - Coupled phase transitions under periodic perturbation AU - Koverda, V.P. AU - Skokov, V.N. T2 - Doklady Physics DA - 2014/// PY - 2014/// DO - 10.1134/S1028335814070039 VL - 59 IS - 7 SP - 291-294 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84920803996&partnerID=MN8TOARS ER - TY - JOUR TI - Li dust injection experiments into T-10 tokamak AU - Skokov, V.G. AU - Sergeev, V.Y. AU - Bykov, A.S. AU - Krylov, S.V. AU - Kuteev, B.V. AU - Timokhin, V.M. AU - Wagner, F. T2 - Fusion Engineering and Design AB - An improved 0D transport model has been applied to model the deuterium, lithium and carbon densities of T-10 plasmas during Li dust injection. The deuterium recycling coefficient is found to drop from 0.92 to 0.80 during Li dust injection at the expense of higher Zeff values. The dust injection results are compared with the alternative techniques, Li pellet injection and Li evaporation. Dust injection provides the best recycling conditions at the lowest levels of Li consumption. DA - 2014/// PY - 2014/// DO - 10.1016/j.fusengdes.2014.02.065 VL - 89 IS - 12 SP - 2816-2821 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84914167494&partnerID=MN8TOARS KW - Lithium injection technologies KW - Deuterium recycling KW - Effective charge ER - TY - JOUR TI - Formation of gas hydrate during crystallization of ethane-saturated amorphous ice AU - Faizullin, M.Z. AU - Vinogradov, A.V. AU - Skokov, V.N. AU - Koverda, V.P. T2 - Russian Journal of Physical Chemistry A DA - 2014/// PY - 2014/// DO - 10.1134/S0036024414100124 VL - 88 IS - 10 SP - 1706-1711 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84906872134&partnerID=MN8TOARS KW - amorphous ice KW - vitrification KW - crystallization KW - gas hydrates ER - TY - JOUR TI - Fission Product Yield Study of 235U, 238U and 239Pu Using Dual-Fission Ionization Chambers AU - Bhatia, C. AU - Fallin, B. AU - Howell, C. AU - Tornow, W. AU - Gooden, M. AU - Kelley, J. AU - Arnold, C. AU - Bond, E. AU - Bredeweg, T. AU - Fowler, M. AU - Moody, W. AU - Rundberg, R. AU - Rusev, G. AU - Vieira, D. AU - Wilhelmy, J. AU - Becker, J. AU - Macri, R. AU - Ryan, C. AU - Sheets, S. AU - Stoyer, M. AU - Tonchev, A. T2 - Nuclear Data Sheets AB - Abstract To resolve long-standing differences between LANL and LLNL regarding the correct fission basis for analysis of nuclear test data [M.B. Chadwick et al., Nucl. Data Sheets 111, 2891 (2010); H. Selby et al., Nucl. Data Sheets 111, 2891 (2010)], a collaboration between TUNL/LANL/LLNL has been established to perform high-precision measurements of neutron induced fission product yields. The main goal is to make a definitive statement about the energy dependence of the fission yields to an accuracy better than 2-3% between 1 and 15 MeV, where experimental data are very scarce. At TUNL, we have completed the design, fabrication and testing of three dual-fission chambers dedicated to 235U, 238U, and 239Pu. The dual-fission chambers were used to make measurements of the fission product activity relative to the total fission rate, as well as for high-precision absolute fission yield measurements. The activation method was employed, utilizing the mono-energetic neutron beams available at TUNL. Neutrons of 4.6, 9.0, and 14.5 MeV were produced via the 2H(d,n)3He reaction, and for neutrons at 14.8 MeV, the 3H(d,n)4He reaction was used. After activation, the induced γ-ray activity of the fission products was measured for two months using high-resolution HPGe detectors in a low-background environment. Results for the yield of seven fission fragments of 235U, 238U, and 239Pu and a comparison to available data at other energies are reported. For the first time results are available for neutron energies between 2 and 14 MeV. DA - 2014/5// PY - 2014/5// DO - 10.1016/J.NDS.2014.08.089 VL - 119 SP - 324-327 J2 - Nuclear Data Sheets LA - en OP - SN - 0090-3752 UR - http://dx.doi.org/10.1016/J.NDS.2014.08.089 DB - Crossref ER - TY - JOUR TI - Force on spindle microtubule minus ends moves chromosomes AU - Elting, Mary Williard AU - Hueschen, Christina L. AU - Udy, Dylan B. AU - Dumont, Sophie T2 - The Journal of Cell Biology AB - The spindle is a dynamic self-assembling machine that coordinates mitosis. The spindle's function depends on its ability to organize microtubules into poles and maintain pole structure despite mechanical challenges and component turnover. Although we know that dynein and NuMA mediate pole formation, our understanding of the forces dynamically maintaining poles is limited: we do not know where and how quickly they act or their strength and structural impact. Using laser ablation to cut spindle microtubules, we identify a force that rapidly and robustly pulls severed microtubules and chromosomes poleward, overpowering opposing forces and repairing spindle architecture. Molecular imaging and biophysical analysis suggest that transport is powered by dynein pulling on minus ends of severed microtubules. NuMA and dynein/dynactin are specifically enriched at new minus ends within seconds, reanchoring minus ends to the spindle and delivering them to poles. This force on minus ends represents a newly uncovered chromosome transport mechanism that is independent of plus end forces at kinetochores and is well suited to robustly maintain spindle mechanical integrity. DA - 2014/7/14/ PY - 2014/7/14/ DO - 10.1083/JCB.201401091 VL - 206 IS - 2 SP - 245-256 LA - en OP - SN - 1540-8140 0021-9525 UR - http://dx.doi.org/10.1083/JCB.201401091 DB - Crossref ER - TY - JOUR TI - Probing Forces on Newly Generated Spindle Microtubule Minus-Ends AU - Hueschen, Christina L. AU - Elting, Mary W. AU - Udy, Dylan B. AU - Dumont, Sophie T2 - Biophysical Journal AB - The mitotic spindle is a dynamic self-organizing machine that coordinates cell division and preserves genomic stability. The ability to focus microtubule minus-ends into poles is crucial to spindle structure and function. However, our understanding of pole-focusing forces has been limited by the challenges of labeling and imaging microtubule minus-ends in established spindles. Here, we used laser ablation to sever kinetochore-fiber microtubules in mammalian cells and probe how the cell detects and organizes newly generated microtubule minus-ends. Within a few seconds of ablation, the cell recognizes new minus-ends and begins pulling them poleward. These pole-focusing forces exist throughout metaphase and anaphase and can move chromosomes rapidly, dominating other spindle forces. Opposing forces on chromosomes from the other half-spindle are able to slow, though not stop, the pole-focusing response, as indicated by faster pole-focusing speeds in monopolar spindles and during anaphase than in metaphase bipolar spindles. Together, our data indicate that microtubule minus-end focusing forces operate broadly and rapidly and are of similar magnitude to other spindle forces. These pole-focusing forces are thus well-suited to robustly maintain spindle structural integrity despite rapid turnover of spindle components and mechanical challenges. DA - 2014/1// PY - 2014/1// DO - 10.1016/J.BPJ.2013.11.4314 VL - 106 IS - 2 SP - 787a J2 - Biophysical Journal LA - en OP - SN - 0006-3495 UR - http://dx.doi.org/10.1016/J.BPJ.2013.11.4314 DB - Crossref ER - TY - JOUR TI - Probing Forces on Newly Generated Spindle Microtubule Minus-Ends AU - Elting, Mary W. AU - Hueschen, Christina L. AU - Udy, Dylan B. AU - Dumont, Sophie T2 - Biophysical Journal AB - The mitotic spindle is a dynamic self-organizing machine that coordinates cell division and preserves genomic stability. The ability to focus microtubule minus-ends into poles is crucial to spindle structure and function. However, our understanding of pole-focusing forces has been limited by the challenges of labeling and imaging microtubule minus-ends in established spindles. Here, we used laser ablation to sever kinetochore-fiber microtubules in mammalian cells and probe how the cell detects and organizes newly generated microtubule minus-ends. Within a few seconds of ablation, the cell recognizes new minus-ends and begins pulling them poleward. These pole-focusing forces exist throughout metaphase and anaphase and can move chromosomes rapidly, dominating other spindle forces. Opposing forces on chromosomes from the other half-spindle are able to slow, though not stop, the pole-focusing response, as indicated by faster pole-focusing speeds in monopolar spindles and during anaphase than in metaphase bipolar spindles. Together, our data indicate that microtubule minus-end focusing forces operate broadly and rapidly and are of similar magnitude to other spindle forces. These pole-focusing forces are thus well-suited to robustly maintain spindle structural integrity despite rapid turnover of spindle components and mechanical challenges. DA - 2014/1// PY - 2014/1// DO - 10.1016/J.BPJ.2013.11.100 VL - 106 IS - 2 SP - 9a-10a J2 - Biophysical Journal LA - en OP - SN - 0006-3495 UR - http://dx.doi.org/10.1016/J.BPJ.2013.11.100 DB - Crossref ER - TY - JOUR TI - Correction to Classical Electrostatics for Biomolecular Simulations AU - Cisneros, G. Andrés AU - Karttunen, Mikko AU - Ren, Pengyu AU - Sagui, Celeste T2 - Chemical Reviews AB - ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionORIGINAL ARTICLEThis notice is a correctionCorrection to Classical Electrostatics for Biomolecular SimulationsG. Andrés Cisneros, Mikko Karttunen, Pengyu Ren, and Celeste Sagui*Cite this: Chem. Rev. 2014, 114, 9, 5116Publication Date (Web):April 8, 2014Publication History Published online8 April 2014Published inissue 14 May 2014https://doi.org/10.1021/cr500124kCopyright © 2014 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views1078Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (120 KB) Get e-Alerts Get e-Alerts DA - 2014/4/8/ PY - 2014/4/8/ DO - 10.1021/CR500124K VL - 114 IS - 9 SP - 5116-5116 J2 - Chem. Rev. LA - en OP - SN - 0009-2665 1520-6890 UR - http://dx.doi.org/10.1021/CR500124K DB - Crossref ER - TY - JOUR TI - Investigating rare events with nonequilibrium work measurements. II. Transition and reaction rates AU - Moradi, Mahmoud AU - Sagui, Celeste AU - Roland, Christopher T2 - The Journal of Chemical Physics AB - We present a formalism for investigating transition pathways and transition probabilities for rare events in biomolecular systems. The formalism is based on combining Transition Path Theory with the results of nonequilibrium work relations, and shows that the equilibrium and nonequilibrium transition rates are in fact related. Aside from its fundamental importance, this allows for the calculation of relative equilibrium reaction rates with driven nonequilibrium simulations such as Steered Molecular Dynamics. The workings of the formalism are illustrated with a few typical numerical examples. DA - 2014/1/21/ PY - 2014/1/21/ DO - 10.1063/1.4861056 VL - 140 IS - 3 SP - 034115 J2 - The Journal of Chemical Physics LA - en OP - SN - 0021-9606 1089-7690 UR - http://dx.doi.org/10.1063/1.4861056 DB - Crossref ER - TY - JOUR TI - Investigating rare events with nonequilibrium work measurements. I. Nonequilibrium transition path probabilities AU - Moradi, Mahmoud AU - Sagui, Celeste AU - Roland, Christopher T2 - The Journal of Chemical Physics AB - We have developed a formalism for investigating transition pathways and transition probabilities for rare events in biomolecular systems. In this paper, we set the theoretical framework for employing nonequilibrium work relations to estimate the relative reaction rates associated with different classes of transition pathways. Particularly, we derive an extension of Crook's transient fluctuation theorem, which relates the relative transition rates of driven systems in the forward and reverse directions, and allows for the calculation of these relative rates using work measurements (e.g., in Steered Molecular Dynamics). The formalism presented here can be combined with Transition Path Theory to relate the equilibrium and driven transition rates. The usefulness of this framework is illustrated by means of a Gaussian model and a driven proline dimer. DA - 2014/1/21/ PY - 2014/1/21/ DO - 10.1063/1.4861055 VL - 140 IS - 3 SP - 034114 J2 - The Journal of Chemical Physics LA - en OP - SN - 0021-9606 1089-7690 UR - http://dx.doi.org/10.1063/1.4861055 DB - Crossref ER - TY - JOUR TI - Organic Solar Cells: On the Efficiency of Charge Transfer State Splitting in Polymer:Fullerene Solar Cells (Adv. Mater. 16/2014) AU - Albrecht, Steve AU - Vandewal, Koen AU - Tumbleston, John R. AU - Fischer, Florian S. U. AU - Douglas, Jessica D. AU - Fréchet, Jean M. J. AU - Ludwigs, Sabine AU - Ade, Harald AU - Salleo, Alberto AU - Neher, Dieter T2 - Advanced Materials AB - A so called “energy river” originates in the active layer of a bulk-heterojunction solar cell as described in work by D. Neher, K. Vandewal, and co-workers on page 2533. This river contains polymer chains and cools down from its hot origin to a cold front. The riverbank is created by “fullerene walls” with different heights. Flashes create hot electrons in the energy river. These electrons need to decrease in temperature during their refrigerating evolution in the river. The cold electrons on the right side cannot escape the river, hidden by the big fullerene wall, and get lost. The cold electrons on the left side are the “good guys”. They are able to splash out of the river and generate electrical power. DA - 2014/4// PY - 2014/4// DO - 10.1002/ADMA.201470107 VL - 26 IS - 16 SP - 2607-2607 J2 - Adv. Mater. LA - en OP - SN - 0935-9648 UR - http://dx.doi.org/10.1002/ADMA.201470107 DB - Crossref ER - TY - JOUR TI - On the Efficiency of Charge Transfer State Splitting in Polymer:Fullerene Solar Cells AU - Albrecht, Steve AU - Vandewal, Koen AU - Tumbleston, John R. AU - Fischer, Florian S. U. AU - Douglas, Jessica D. AU - Fréchet, Jean M. J. AU - Ludwigs, Sabine AU - Ade, Harald AU - Salleo, Alberto AU - Neher, Dieter T2 - Advanced Materials AB - The field dependence and yield of free charge carrier generation in polymer:fullerene blends with varying energetic offsets is not affected when the excitation energy is varied from above band-gap to direct CT state excitation. Instead, the ability of the CT state to split is dictated by the energetic offset between the relaxed CT state and the charge separated (CS) state. DA - 2014/2/27/ PY - 2014/2/27/ DO - 10.1002/ADMA.201305283 VL - 26 IS - 16 SP - 2533-2539 J2 - Adv. Mater. LA - en OP - SN - 0935-9648 UR - http://dx.doi.org/10.1002/ADMA.201305283 DB - Crossref KW - organic solar cells KW - charge generation KW - geminate recombination KW - charge transfer states KW - driving force KW - excess energy KW - morphology KW - spectroelectrochemistry ER - TY - JOUR TI - Accretion in supergiant High Mass X-ray Binaries AU - Manousakis, Antonios AU - Walter, Roland AU - Blondin, John T2 - EPJ Web of Conferences AB - Supergiant High Mass X-ray Binary systems (sgHMXBs) consist of a massive, late type, star and a neutron star. The massive stars exhibits strong, radiatively driven, stellar winds. Wind accretion onto compact object triggers X-ray emission, which alters the stellar wind significantly. Hydrodynamic simulation has been used to study the neutron star - stellar wind interaction it two sgHMXBs: i) A heavily obscured sgHMXB (IGR J17252-3616) discovered by INTEGRAL. To account for observable quantities (i.e., absorbing column density) we have to assume a very slow wind terminal velocity of about 500 km/s and a rather massive neutron star. If confirmed in other obscured systems, this could provide a completely new stellar wind diagnostics. ii) A classical sgHMXB (Vela X-1) has been studied in depth to understand the origin of the off-states observed in this system. Among many models used to account for this observed behavior (clumpy wind, gating mechanism) we propose that self-organized criticality of the accretion stream is the likely reason for the observed behavior. In conclusion, the neutron star, in these two examples, acts very efficiently as a probe to study stellar winds. DA - 2014/// PY - 2014/// DO - 10.1051/EPJCONF/20136402006 VL - 64 SP - 02006 J2 - EPJ Web of Conferences OP - SN - 2100-014X UR - http://dx.doi.org/10.1051/EPJCONF/20136402006 DB - Crossref ER - TY - CONF TI - Flavor evolution of supernova neutrinos in turbulent matter AU - Lund, Tina AU - Kneller, James P. T2 - WORKSHOP ON DARK MATTER, NEUTRINO PHYSICS AND ASTROPHYSICS CETUP* 2013: VIIth International Conference on Interconnections between Particle Physics and Cosmology PPC* 2013 AB - The neutrino signal from the next galactic supernova carries with it an enormous amount of information on the explosion mechanism of a core-collapse supernova, as well as on the stellar progenitor and on the neutrinos themselves. In order to extract this information we need to know how the neutrino flavor evolves over time due to the interplay of neutrino self-interactions and matter effects. Additional turbulence in the supernova matter may impart its own signatures on the neutrino spectrum, and could partly obscure the imprints of collective and matter effects. We investigate the neutrino flavor evolution due to neutrino self-interactions, matter effects due to the shock wave propagation, and turbulence in three progenitors with masses of 8.8 M⊙, 10.8 M⊙ and 18.0 M⊙. In the lightest progenitor we find that the impact of moderate turbulence of the order 10% is limited and occurs only briefly early on. This makes the signatures of collective and matter interactions relatively straightforward to interpret. Similarly, with moderate turbulence the two heavier progenitors exhibit only minor changes in the neutrino spectrum, and collective and matter signatures persists. However, when the turbulence is increased to 30% and 50% the high density matter resonance features in the neutrino spectrum get obscured, while new features arise in the low density resonance channel and in the non-resonant channels. We conclude that with moderate amounts of turbulence spectral features of collective and matter interactions survive in all three progenitors. For the larger amounts of turbulence in the 10.8 M⊙ and 18.0 M⊙ progenitor new features arise, as others disappear. C2 - 2014/// C3 - DA - 2014/// DO - 10.1063/1.4883435 VL - 1604 SP - 225-232 PB - AIP Publishing LLC UR - http://dx.doi.org/10.1063/1.4883435 DB - Crossref KW - neutrino flavor oscillations KW - supernovae KW - turbulence ER - TY - JOUR TI - Oklo reactors and implications for nuclear science AU - Davis, E. D. AU - Gould, C. R. AU - Sharapov, E. I. T2 - International Journal of Modern Physics E AB - We summarize the nuclear physics interests in the Oklo natural nuclear reactors, focusing particularly on developments over the past two decades. Modeling of the reactors has become increasingly sophisticated, employing Monte Carlo simulations with realistic geometries and materials that can generate both the thermal and epithermal fractions. The water content and the temperatures of the reactors have been uncertain parameters. We discuss recent work pointing to lower temperatures than earlier assumed. Nuclear cross sections are input to all Oklo modeling and we discuss a parameter, the $^{175}$Lu ground state cross section for thermal neutron capture leading to the isomer $^{176\mathrm{m}}$ Lu, that warrants further investigation. Studies of the time dependence of dimensionless fundamental constants have been a driver for much of the recent work on Oklo. We critically review neutron resonance energy shifts and their dependence on the fine structure constant $\alpha$ and the ratio $X_q=m_q/\Lambda$ (where $m_q$ is the average of the $u$ and $d$ current quark masses and $\Lambda$ is the mass scale of quantum chromodynamics). We suggest a formula for the combined sensitivity to $\alpha$ and $X_q$ that exhibits the dependence on proton number $Z$ and mass number $A$, potentially allowing quantum electrodynamic and quantum chromodynamic effects to be disentangled if a broader range of isotopic abundance data becomes available. DA - 2014/4// PY - 2014/4// DO - 10.1142/s0218301314300070 VL - 23 IS - 04 SP - 1430007 J2 - Int. J. Mod. Phys. E LA - en OP - SN - 0218-3013 1793-6608 UR - http://dx.doi.org/10.1142/s0218301314300070 DB - Crossref KW - Oklo KW - natural nuclear reactors KW - Monte Carlo simulation KW - neutron/gamma fluxes KW - core temperature KW - nuclear data KW - nuclear waste depository KW - time variation fundamental constants ER - TY - JOUR TI - Phase structure of SU (3) gauge-Higgs unification models at finite temperature AU - Kashiwa, Kouji AU - Tanizaki, Yuya T2 - Phys.Rev.D AB - Five-dimensional $SU(3)$ gauge-Higgs unification models are studied at finite temperature in the warped extra dimension $S^1/\mathbb{Z}_2$. In order to investigate the phase structure, we developed a technique to compute the one-loop effective potential with the nontrivial Polyakov loop phase and with the nontrivial Wilson line phase along the extra dimension. Effective potentials as functions of two gauge-field condensations are shown for several simple matter contents, including fundamental, sextet, and adjoint representational Dirac fermions. Possible extensions and applications of our formalism are also briefly discussed. DA - 2014/// PY - 2014/// DO - 10.1103/PhysRevD.89.116013 VL - 89 IS - 11 SP - 116013 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84903692266&partnerID=MN8TOARS ER - TY - CONF TI - Many-Body Composite Bosons from the Viewpoint of Functional Renormalization AU - Tanizaki, Yuya C2 - 2014/// C3 - Bulg.J.Phys. DA - 2014/// VL - 41 SP - 180-186 M1 - 2 UR - http://inspirehep.net/record/1337529 ER - TY - CONF TI - Functional renormalization group approach to conventional theory of superfluidity and beyond AU - Tanizaki, Yuya AU - Fejős, Gergely AU - Hatsuda, Tetsuo AB - Fermionic functional renormalization group (FRG) is applied to describe the superfluid phase transition of the two-component fermionic system with attractive contact interaction. Connection between the fermionic FRG approach and the Bardeen-Cooper- Schrieffer (BCS) theory with its Gorkov and Melik-Barkhudarov (GMB) correction is made clear, and the FRG flow of the fermion self-energy is also studied to go beyond the BCS+GMB theory. The superfluid transition temperature and the associated chemical potential are calculated in the region of the negative scattering length using fermionic FRG. C2 - 2014/// C3 - Journal of Physics: Conference Series DA - 2014/// DO - 10.1088/1742-6596/529/1/012027 VL - 529 SP - 012027 M1 - 1 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84906690155&partnerID=MN8TOARS ER - TY - JOUR TI - Fermionic functional renormalization group approach to superfluid phase transition AU - Tanizaki, Yuya AU - Fejős, Gergely AU - Hatsuda, Tetsuo T2 - PTEP AB - Fermionic functional renormalization group (FRG) is applied to describe the superfluid phase transition of the two-component fermionic system with attractive contact interaction. Connection between the fermionic FRG approach and the conventional Bardeen-Cooper-Schrieffer (BCS) theory with Gorkov and Melik-Barkhudarov (GMB) correction are clarified in details in the weak coupling region by using the renormalization group flow of the fermionic four-point vertex with particle-particle and particle-hole scattering contributions. To go beyond the BCS+GMB theory, coupled FRG flow equations of the fermion self-energy and the four-point vertex are studied under an Ansatz concerning their frequency/momentum dependence. We found that the fermion self-energy turns out to be substantial even in the weak couping region, and the frequency dependence of the four-point vertex is essential to obtain the correct asymptotic-ultraviolet behavior of the flow for the self-energy. The superfluid transition temperature and the associated chemical potential are calculated in the region of negative scattering lengths. DA - 2014/// PY - 2014/// DO - 10.1093/ptep/ptu035 VL - 2014 IS - 4 SP - 043I01 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84898483737&partnerID=MN8TOARS ER - TY - JOUR TI - Fermionic functional renormalization group approach to Bose-Einstein condensation of dimers AU - Tanizaki, Yuya T2 - PTEP AB - Fermionic functional renormalization group (f-FRG) is applied to describe Bose-Einstein condensation (BEC) of dimers for a two-component fermionic system with attractive contact interaction. In order to describe the system of dimers without introducing auxiliary bosonic fields (bosonization), we propose a new exact evolution-equation of the effective action in f-FRG with an infrared regulator for the fermion vertex. Then we analyze its basic properties in details. We show explicitly that the critical temperature of the free Bose gas is obtained naturally by this method without bosonization. Methods to make systematic improvement from the deep BEC limit are briefly discussed. DA - 2014/// PY - 2014/// DO - 10.1093/ptep/ptu009 VL - 2014 IS - 2 SP - 023A04 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84898490553&partnerID=MN8TOARS ER - TY - JOUR TI - Real-time path integral with Picard-Lefschetz theory and its applications to quantum tunneling AU - Tanizaki, Yuya AU - Koike, Takayuki T2 - Annals of Physics AB - Picard–Lefschetz theory is applied to path integrals of quantum mechanics, in order to compute real-time dynamics directly. After discussing basic properties of real-time path integrals on Lefschetz thimbles, we demonstrate its computational method in a concrete way by solving three simple examples of quantum mechanics. It is applied to quantum mechanics of a double-well potential, and quantum tunneling is discussed. We identify all of the complex saddle points of the classical action, and their properties are discussed in detail. However a big theoretical difficulty turns out to appear in rewriting the original path integral into a sum of path integrals on Lefschetz thimbles. We discuss generality of that problem and mention its importance. Real-time tunneling processes are shown to be described by those complex saddle points, and thus semi-classical description of real-time quantum tunneling becomes possible on solid ground if we could solve that problem. DA - 2014/9/16/ PY - 2014/9/16/ DO - 10.1016/j.aop.2014.09.003 VL - 351 SP - 250-274 UR - http://dx.doi.org/10.1016/j.aop.2014.09.003 KW - Real-time dynamics KW - Path integral KW - Picard-Lefschetz theory KW - Lefschetz thimble KW - Quantum tunneling ER - TY - CONF TI - Many-body composite bosons from the viewpoint of functional renormalization C2 - 2014/10// C3 - Bulgarian Journal of Physics DA - 2014/10// UR - http://www.bjp-bg.com/paper.php?id=698 ER - TY - JOUR TI - Noise tolerant spatiotemporal chaos computing AU - Kia, Behnam AU - Kia, Sarvenaz AU - Lindner, John F. AU - Sinha, Sudeshna AU - Ditto, William L. T2 - Chaos: An Interdisciplinary Journal of Nonlinear Science AB - We introduce and design a noise tolerant chaos computing system based on a coupled map lattice (CML) and the noise reduction capabilities inherent in coupled dynamical systems. The resulting spatiotemporal chaos computing system is more robust to noise than a single map chaos computing system. In this CML based approach to computing, under the coupled dynamics, the local noise from different nodes of the lattice diffuses across the lattice, and it attenuates each other's effects, resulting in a system with less noise content and a more robust chaos computing architecture. DA - 2014/12// PY - 2014/12// DO - 10.1063/1.4897168 VL - 24 IS - 4 SP - 043110 J2 - Chaos LA - en OP - SN - 1054-1500 1089-7682 UR - http://dx.doi.org/10.1063/1.4897168 DB - Crossref ER - TY - JOUR TI - Watch your step: Integrating nonlinear dynamical flows by stepping through space and time AU - Kia, B. AU - Lindner, J.F. AU - Ditto, W.L. T2 - International Journal of Bifurcation and Chaos AB - Nonlinear dynamical flows are often solved approximately by numerical integration based on advancing the independent variable, typically time. Here, we present a unified framework for numerical integration of differential equations based on advancing either the dependent variable, often space, or the independent variable, or any combination of the two. Spacetime stepping unifies and extends previous work. In particular, dependent variable stepping can produce better numerical results and also more faithfully describe the underlying physics, thereby providing both practical and conceptual benefits. We indicate extensions to higher dimensions. DA - 2014/// PY - 2014/// DO - 10.1142/S0218127414501454 VL - 24 IS - 11 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84928336406&partnerID=MN8TOARS KW - Nonlinear flows KW - numerical integration KW - spacetime KW - time KW - arc length ER - TY - JOUR TI - Time-dependent generalization of the Nosé-Hoover thermostatting technique for molecular dynamics simulations AU - Davis, Edward D AU - Zaher, Ashraf A T2 - Journal of Physics: Conference Series AB - The Nosé-Hoover scheme demonstrates that molecular dynamics simulations can be used to calculate the properties of systems at constant temperature (i.e. canonical ensemble averages). There is interest in deterministic generalizations of Nosé-Hoover dynamics which are ergodic even for simple systems like the harmonic oscillator. Prompted by parallels with studies of the Duffing oscillator within control theory, we have investigated a non-autonomous version of the Nosé-Hoover oscillator in which the temperature is replaced by a weakly time-dependent function. This function is chosen so that its average over time coincides with the temperature desired. Calculations are facilitated by graphical programming with a MATLAB-Simulink platform. A time series analysis of our simple non-autonomous system yields the position and momentum distributions expected for the harmonic oscillator. DA - 2014/3/11/ PY - 2014/3/11/ DO - 10.1088/1742-6596/490/1/012101 VL - 490 SP - 012101 J2 - J. Phys.: Conf. Ser. OP - SN - 1742-6596 UR - http://dx.doi.org/10.1088/1742-6596/490/1/012101 DB - Crossref ER - TY - JOUR TI - Implications of the Oklo Phenomenon in a Chiral Approach to Nuclear Matter AU - Davis, Edward D. T2 - Few-Body Systems AB - It has been customary to use data from the Oklo natural nuclear reactor to place bounds on the change that has occurred in the electromagnetic fine structure constant α over the last 2 billion years. Alternatively, an analysis could be based on a recently proposed expression for shifts in resonance energies which relates them to changes in both α and the average m q of the u and d current quark masses, and which makes explicit the dependence on mass number A and atomic number Z. (Recent model independent results on hadronic $${\sigma}$$ -terms suggest sensitivity to the strange quark mass is negligible.) The most sophisticated analysis, to date, of the quark mass term invokes a calculation of the nuclear mean-field within the Walecka model of quantum hadrodynamics. We comment on this study and consider an alternative in which the link to low-energy quantum chromodynamics and its pattern of chiral symmetry-breaking is more readily discernible. Specifically, we investigate the sensitivity to changes in the pion mass $${M_\pi}$$ of a single nucleon potential determined by an in-medium chiral perturbation theory ( $${\chi}$$ PT) calculation which includes virtual $${{\Delta}}$$ -excitations. Subject to some reasonable assumptions about low-energy constants, we confirm that the m q -contribution to resonance shifts is enhanced by a factor of 10 or so relative to the $${\alpha}$$ -term and deduce that the Oklo data for Sm imply that $${|m_q({\rm Oklo})- m_q({\rm now})| \lesssim 10^{-9}m_q({\rm now})}$$ . DA - 2014/9/30/ PY - 2014/9/30/ DO - 10.1007/s00601-014-0909-0 VL - 56 IS - 6-9 SP - 431-437 J2 - Few-Body Syst LA - en OP - SN - 0177-7963 1432-5411 UR - http://dx.doi.org/10.1007/s00601-014-0909-0 DB - Crossref ER - TY - JOUR TI - THE HARD X-RAY VIEW OF THE YOUNG SUPERNOVA REMNANT G1.9+0.3 AU - Zoglauer, Andreas AU - Reynolds, Stephen P. AU - An, Hongjun AU - Boggs, Steven E. AU - Christensen, Finn E. AU - Craig, William W. AU - Fryer, Chris L. AU - Grefenstette, Brian W. AU - Harrison, Fiona A. AU - Hailey, Charles J. AU - Krivonos, Roman A. AU - Madsen, Kristin K. AU - Miyasaka, Hiromasa AU - Stern, Daniel AU - Zhang, William W. T2 - The Astrophysical Journal AB - NuSTAR observed G1.9+0.3, the youngest known supernova remnant in the Milky Way, for 350 ks and detected emission up to $\sim$30 keV. The remnant's X-ray morphology does not change significantly across the energy range from 3 to 20 keV. A combined fit between NuSTAR and CHANDRA shows that the spectrum steepens with energy. The spectral shape can be well fitted with synchrotron emission from a power-law electron energy distribution with an exponential cutoff with no additional features. It can also be described by a purely phenomenological model such as a broken power-law or a power-law with an exponential cutoff, though these descriptions lack physical motivation. Using a fixed radio flux at 1 GHz of 1.17 Jy for the synchrotron model, we get a column density of N$_{\rm H}$ = $(7.23\pm0.07) \times 10^{22}$ cm$^{-2}$, a spectral index of $\alpha=0.633\pm0.003$, and a roll-off frequency of $\nu_{\rm rolloff}=(3.07\pm0.18) \times 10^{17}$ Hz. This can be explained by particle acceleration, to a maximum energy set by the finite remnant age, in a magnetic field of about 10 $\mu$G, for which our roll-off implies a maximum energy of about 100 TeV for both electrons and ions. Much higher magnetic-field strengths would produce an electron spectrum that was cut off by radiative losses, giving a much higher roll-off frequency that is independent of magnetic-field strength. In this case, ions could be accelerated to much higher energies. A search for $^{44}$Ti emission in the 67.9 keV line results in an upper limit of $1.5 \times 10^{-5}$ $\,\mathrm{ph}\,\mathrm{cm}^{-2}\,\mathrm{s}^{-1}$ assuming a line width of 4.0 keV (1 sigma). DA - 2014/12/31/ PY - 2014/12/31/ DO - 10.1088/0004-637X/798/2/98 VL - 798 IS - 2 SP - 98 KW - ISM: supernova remnants KW - X-rays: individual (G1.9+0.3) ER - TY - JOUR TI - NuSTAR STUDY OF HARD X-RAY MORPHOLOGY AND SPECTROSCOPY OF PWN G21.5–0.9 AU - Nynka, Melania AU - Hailey, Charles J. AU - Reynolds, Stephen P. AU - An, Hongjun AU - Baganoff, Frederick K. AU - Boggs, Steven E. AU - Christensen, Finn E. AU - Craig, William W. AU - Gotthelf, Eric V. AU - Grefenstette, Brian W. AU - Harrison, Fiona A. AU - Krivonos, Roman AU - Madsen, Kristin K. AU - Mori, Kaya AU - Perez, Kerstin AU - Stern, Daniel AU - Wik, Daniel R. AU - Zhang, William W. AU - Zoglauer, Andreas T2 - The Astrophysical Journal AB - We present NuSTAR high energy X-ray observations of the pulsar wind nebula (PWN)/supernova remnant G21.5-0.9. We detect integrated emission from the nebula up to ~40 keV, and resolve individual spatial features over a broad X-ray band for the first time. The morphology seen by NuSTAR agrees well with that seen by XMM-Newton and Chandra below 10 keV. At high energies NuSTAR clearly detects non-thermal emission up to ~20 keV that extends along the eastern and northern rim of the supernova shell. The broadband images clearly demonstrate that X-ray emission from the North Spur and Eastern Limb results predominantly from non-thermal processes. We detect a break in the spatially integrated X-ray spectrum at ~9 keV that cannot be reproduced by current SED models, implying either a more complex electron injection spectrum or an additional process such as diffusion compared to what has been considered in previous work. We use spatially resolved maps to derive an energy-dependent cooling length scale, $L(E) \propto E^{m}$ with $m = -0.21 \pm 0.01$. We find this to be inconsistent with the model for the morphological evolution with energy described by Kennel & Coroniti (1984). This value, along with the observed steepening in power-law index between radio and X-ray, can be quantitatively explained as an energy-loss spectral break in the simple scaling model of Reynolds (2009), assuming particle advection dominates over diffusion. This interpretation requires a substantial departure from spherical magnetohydrodynamic (MHD), magnetic-flux-conserving outflow, most plausibly in the form of turbulent magnetic-field amplification. DA - 2014/6/17/ PY - 2014/6/17/ DO - 10.1088/0004-637X/789/1/72 VL - 789 IS - 1 SP - 72 KW - ISM: individual objects (G21.5-0.9) KW - ISM: supernova remnants KW - radiation mechanisms: general KW - stars: neutron KW - X-rays: ISM ER - TY - JOUR TI - Effect of Surface Termination on the Electronic Properties of LaNiO3 Films AU - Kumah, Divine P. AU - Malashevich, Andrei AU - Disa, Ankit S. AU - Arena, Dario A. AU - Walker, Frederick J. AU - Ismail-Beigi, Sohrab AU - Ahn, Charles H. T2 - Physical Review Applied AB - Tailoring the microscopic structures of oxide interfaces and surfaces to realize desired electronic properties is of intense interest. The authors modulate the conductivity of LaNiO${}_{3}$ films as thin as three unit cells by precisely controlling the composition of the topmost atomic layer. Three-dimensional x-ray imaging combined with first-principles theory exposes the correlation between surface termination and electrical conductivity, which could be widely exploited in logic, memory, or sensor applications. DA - 2014/11/6/ PY - 2014/11/6/ DO - 10.1103/physrevapplied.2.054004 VL - 2 IS - 5 SP - 054004 SN - 2331-7019 UR - http://dx.doi.org/10.1103/physrevapplied.2.054004 ER - TY - JOUR TI - Tuning the Structure of Nickelates to Achieve Two-Dimensional Electron Conduction AU - Kumah, Divine P. AU - Disa, Ankit S. AU - Ngai, Joseph H. AU - Chen, Hanghui AU - Malashevich, Andrei AU - Reiner, James W. AU - Ismail-Beigi, Sohrab AU - Walker, Frederick J. AU - Ahn, Charles H. T2 - Advanced Materials AB - Metallic electronic transport in nickelate heterostructures can be induced and confined to two dimensions (2D) by controlling the structural parameters of the nickel–oxygen planes. DA - 2014/2/3/ PY - 2014/2/3/ DO - 10.1002/adma.201304256 VL - 26 IS - 12 SP - 1935-1940 J2 - Adv. Mater. LA - en OP - SN - 0935-9648 UR - http://dx.doi.org/10.1002/adma.201304256 DB - Crossref KW - thin films KW - complex oxides KW - structure-property relationships KW - 2D conductivity ER - TY - JOUR TI - Active Silicon Integrated Nanophotonics: Ferroelectric BaTiO3 Devices AU - Xiong, Chi AU - Pernice, Wolfram H. P. AU - Ngai, Joseph H. AU - Reiner, James W. AU - Kumah, Divine AU - Walker, Frederick J. AU - Ahn, Charles H. AU - Tang, Hong X. T2 - Nano Letters AB - The integration of complex oxides on silicon presents opportunities to extend and enhance silicon technology with novel electronic, magnetic, and photonic properties. Among these materials, barium titanate (BaTiO3) is a particularly strong ferroelectric perovskite oxide with attractive dielectric and electro-optic properties. Here we demonstrate nanophotonic circuits incorporating ferroelectric BaTiO3 thin films on the ubiquitous silicon-on-insulator (SOI) platform. We grow epitaxial, single-crystalline BaTiO3 directly on SOI and engineer integrated waveguide structures that simultaneously confine light and an RF electric field in the BaTiO3 layer. Using on-chip photonic interferometers, we extract a large effective Pockels coefficient of 213 ± 49 pm/V, a value more than six times larger than found in commercial optical modulators based on lithium niobate. The monolithically integrated BaTiO3 optical modulators show modulation bandwidth in the gigahertz regime, which is promising for broadband applications. DA - 2014/2/4/ PY - 2014/2/4/ DO - 10.1021/nl404513p VL - 14 IS - 3 SP - 1419-1425 J2 - Nano Lett. LA - en OP - SN - 1530-6984 1530-6992 UR - http://dx.doi.org/10.1021/nl404513p DB - Crossref KW - Complex oxide KW - BaTiO3 KW - optical modulator KW - silicon integrated optics KW - ferroelectrics ER - TY - JOUR TI - Hysteretic electrical transport in BaTiO3/Ba1−xSrxTiO3/Ge heterostructures AU - Ngai, J. H. AU - Kumah, D. P. AU - Ahn, C. H. AU - Walker, F. J. T2 - Applied Physics Letters AB - We present electrical transport measurements of heterostructures comprised of BaTiO3 and Ba1−xSrxTiO3 epitaxially grown on Ge. Sr alloying imparts compressive strain to the BaTiO3, which enables the thermal expansion mismatch between BaTiO3 and Ge to be overcome to achieve c-axis oriented growth. The conduction bands of BaTiO3 and Ba1−xSrxTiO3 are nearly aligned with the conduction band of Ge, which facilitates electron transport. Electrical transport measurements through the dielectric stack exhibit rectifying behavior and hysteresis, where the latter is consistent with ferroelectric switching. DA - 2014/2/10/ PY - 2014/2/10/ DO - 10.1063/1.4864648 VL - 104 IS - 6 SP - 062905 J2 - Appl. Phys. Lett. LA - en OP - SN - 0003-6951 1077-3118 UR - http://dx.doi.org/10.1063/1.4864648 DB - Crossref ER - TY - CONF TI - Core Collapse Supernova Models For Nucleosynthesis AU - Casanova, Jordi AU - Frohlich, C. AU - Perego, A. AU - Hempel, M. C2 - 2014/1// C3 - American Astronomical Society Meeting Abstracts #223 DA - 2014/1// ER - TY - CONF TI - 3D Simulations of Supernova Remnants from Type Ia Supernova Models AU - Johnson, Heather AU - Reynolds, S. P. AU - Frohlich, C. AU - Blondin, J. M. C2 - 2014/1// C3 - American Astronomical Society Meeting Abstracts #223 DA - 2014/1// ER - TY - CONF TI - The Effects of Collective Neutrino Oscillations on Supernova Nucleosynthesis AU - Seadrow, Shaquann AU - Frohlich, C. AU - Duan, H. AU - Friedland, A. AU - McLaughlin, G. AU - Keohane, J. W. C2 - 2014/1// C3 - American Astronomical Society Meeting Abstracts #223 DA - 2014/1// ER - TY - CONF TI - Parametrized Spherically Symmetric Core Collapse Supernova Simulations: Push AU - Ebinger, K. AU - Perego, A. AU - Hempel, M. AU - Frohlich, C. AU - Eichler, M. AU - Casanova, J. AU - Liebendörfer, M. AU - Thielemann, F. K. C2 - 2014/// C3 - XIII Nuclei in the Cosmos (NIC XIII) DA - 2014/// ER - TY - CONF TI - Core-collapse supernovae and nucleosynthesis AU - Frohlich, Carla C2 - 2014/9// C3 - APS Division of Nuclear Physics Meeting Abstracts DA - 2014/9// ER - TY - CHAP TI - Origin of the Elements AU - Heger, A. AU - Fröhlich, C. AU - Truran, J. W. T2 - Planets, Asteriods, Comets and The Solar System, Volume 2 of Treatise on Geochemistry (Second Edition). Edited by Andrew M. Davis. Elsevier, 2014., p.1-14 A2 - Davis, Andrew M. PY - 2014/// VL - 2 SP - 1-14 ER - TY - JOUR TI - New source for ultracold neutrons at the Institut Laue-Langevin AU - Piegsa, F. M. AU - Fertl, M. AU - Ivanov, S. N. AU - Kreuz, M. AU - Leung, K. K. H. AU - Schmidt-Wellenburg, P. AU - Soldner, T. AU - Zimmer, O. T2 - Physical Review C AB - A new intense superthermal source for ultracold neutrons (UCN) was installed at a dedicated beam line at the Institut Laue-Langevin. Incident neutrons with a wavelength of 0.89 nm are converted to UCN in a 5-liter volume filled with superfluid $^{4}\mathrm{He}$ at a temperature of about 0.7 K. The UCN can be extracted to room temperature experiments. We present the cryogenic setup of the source, a characterization of the cold neutron beam, and UCN production measurements, where a UCN density in the production volume of at least 55 per ${\mathrm{cm}}^{3}$ was determined. DA - 2014/7/23/ PY - 2014/7/23/ DO - 10.1103/physrevc.90.015501 VL - 90 IS - 1 J2 - Phys. Rev. C LA - en OP - SN - 0556-2813 1089-490X UR - http://dx.doi.org/10.1103/PhysRevC.90.015501 DB - Crossref ER - TY - CONF TI - A Comparison of Two Magnetic Ultra-Cold Neutron Trapping Concepts Using a Halbach-Octupole Array AU - Leung, K. AU - Ivanov, S. AU - Martin, F. AU - Rosenau, F. AU - Simson, M. AU - Zimmer, O. T2 - Next Generation Experiments to Measure the Neutron Lifetime AB - This paper describes a new magnetic trap for ultra-cold neutrons (UCNs) made from a 1.2 m long Halbach-octupole array of permanent magnets with an inner bore radius of 47 mm combined with an assembly of superconducting end coils and bias field solenoid. The use of the trap in a vertical, magneto-gravitational and a horizontal setup are compared in terms of the effective volume and ability to control key systematic effects that need to be addressed in high precision neutron lifetime measurements. C2 - 2014/3/27/ C3 - Next Generation Experiments to Measure the Neutron Lifetime DA - 2014/3/27/ DO - 10.1142/9789814571678_0015 PB - WORLD SCIENTIFIC SN - 9789814571661 9789814571678 UR - http://dx.doi.org/10.1142/9789814571678_0015 DB - Crossref ER - TY - CONF TI - Deconfinement transition at weak coupling in Yang-Mills theory on a torus AU - Schäfer, Thomas C2 - 2014/10// C3 - PoS DA - 2014/10// DO - 10.22323/1.187.0217 VL - LATTICE2013 SP - 217 UR - http://inspirehep.net/record/1262712 ER - TY - JOUR TI - Second order fluid dynamics for the unitary Fermi gas from kinetic theory AU - Schaefer, Thomas T2 - Phys.Rev.A AB - We compute second-order transport coefficients of the dilute Fermi gas at unitarity. The calculation is based on kinetic theory and the Boltzmann equation at second order in the Knudsen expansion. The second-order transport coefficients describe the shear stress relaxation time, nonlinear terms in the strain-stress relation, and nonlinear couplings between vorticity and strain. An exact calculation in the dilute limit gives ${\ensuremath{\tau}}_{R}=\ensuremath{\eta}/P$, where ${\ensuremath{\tau}}_{R}$ is the shear stress relaxation time, $\ensuremath{\eta}$ is the shear viscosity, and $P$ is pressure. This relation is identical to the result obtained using the Bhatnagar-Gross-Krook approximation to the collision term, but other transport coefficients are sensitive to the exact collision integral. DA - 2014/10/29/ PY - 2014/10/29/ DO - 10.1103/PhysRevA.90.043633 VL - 90 IS - 4 SP - 043633 UR - http://inspirehep.net/record/1292847 ER - TY - CONF TI - Fermi liquid theory: A brief survey in memory of Gerald E. Brown AU - Schäfer, Thomas AB - I present a brief review of Fermi liquid theory, and discuss recent work on Fermi liquid theory in dilute neutron matter and cold atomic gases. I argue that renewed interest in transport properties of quantum fluids provides fresh support for Landau's approach to Fermi liquid theory, which is based on kinetic theory rather than effective field theory and the renormalization group. I also discuss work on non-Fermi liquids, in particular dense quark matter. C2 - 2014/8// C3 - Nucl.Phys.A CY - Stony Brook , United States DA - 2014/8// DO - 10.1016/j.nuclphysa.2014.04.006 VL - 928 SP - 180-189 UR - http://inspirehep.net/record/1287668 KW - Many-body physics KW - Transport theory ER - TY - JOUR TI - Viscosity spectral function of a scale invariant nonrelativistic fluid from holography AU - Schaefer, Thomas T2 - Phys.Rev.D AB - We study the viscosity spectral function of a holographic 2+1 dimensional fluid with Schroedinger symmetry. The model is based on a twisted compactification of $Ads_5\times S_5$. We numerically compute the spectral function of the stress tensor correlator for all frequencies, and analytically study the limits of high and low frequency. We compute the shear viscosity, the viscous relaxation time, and the quasi-normal mode spectrum in the shear channel. We find a number of unexpected results: The high frequency behavior is governed by a fractional 1/3 power law, the viscous relaxation time is negative, and the quasi-normal mode spectrum in the shear channel is not doubled. DA - 2014/11/25/ PY - 2014/11/25/ DO - 10.1103/PhysRevD.90.106008 VL - 90 IS - 10 SP - 106008 UR - http://inspirehep.net/record/1311648 ER - TY - CONF TI - Remote aerosol species-identification using IR scattering spectroscopy AU - Niu, Shupeng AU - Philbrick, C.R. AU - Hallen, H.D. AB - Identification of atmospheric aerosol species and their chemical composition may help to trace their source and better estimate their impact on climate and environment. Optical scattering of aerosols depends primarily on aerosol chemical composition, size distribution, particle shape and the wavelength used. Extraction of features due to the aerosol complex refractive index from scattering spectroscopy at a single angle of observation allows composition identification via the spectral fingerprint, as shown computationally with Mie calculations of the optical scattering. Size-dependent scattering effects are eliminated by using near-forward scattering, such as in the scattering aureole. The only features of the aerosol aureole scattering spectra that very rapidly with wavelength are associated with the composition, so the aureole can give a reliable identification of aerosol composition. C2 - 2014/// C3 - Proc. SPIE, Int. Soc. Opt. Eng. DA - 2014/// DO - 10.1117/12.2050689 VL - 9080 SP - 908010 (12 pp.) - UR - http://dx.doi.org/10.1117/12.2050689 KW - aerosol scattering KW - Mie calculation KW - size distribution KW - complex refractive index ER - TY - CONF TI - Laser remote sensing of species concentrations and dynamical processes AU - Philbrick, C.R. AU - Hallen, H.D. AB - A review of current lidar techniques summarizes present capabilities to: (1) measure atmospheric concentrations of most major and several minor molecular species using Raman scattering and DIAL techniques, (2) detect and measure concentrations of certain trace level species, (3) characterize active dynamical processes in the troposphere based upon using water vapor as a tracer, and (4) describe interesting thermodynamic properties based upon rotational Raman temperature profiles, multi-wavelength aerosol distributions, and changes in the phase states of water. Advances in lasers and detectors have extended the range of wavelengths available through the ultraviolet, visible, and infrared spectrum by using tunable laser techniques and supercontinuum broad spectrum lasers. Prior studies are reviewed, several applications for the technology are suggested which extend the techniques proposed to future investigations. In particular, the extension of tunable laser sources into the ultraviolet region has opened opportunities to use resonance Raman techniques, which provide greatly increased sensitivity for certain molecular species, such as hydrocarbons. The developments of supercontinuum lasers and tunable OPO lasers has enabled long-path trace concentration measurements of molecular spectra lines to detect and measure the concentrations of many species, as well as to distinguish any interfering species. C2 - 2014/// C3 - Proc. SPIE, Int. Soc. Opt. Eng. DA - 2014/// DO - 10.1117/12.2050696 VL - 9080 SP - 90800Z (15 pp.) - UR - http://dx.doi.org/10.1117/12.2050696 KW - Raman Lidar KW - DIAL KW - Supercontinuum Absorption Lidar KW - Resonance Raman KW - Atmospheric Chemistry KW - Atmospheric Dynamics KW - Optical Extinction ER - TY - JOUR TI - Unconfined, melt edge electrospinning from multiple, spontaneous, self-organized polymer jets AU - Wang, Qingqing AU - Curtis, Colin K AU - Thoppey, Nagarajan Muthuraman AU - Bochinski, Jason R AU - Gorga, Russell E AU - Clarke, Laura I T2 - Materials Research Express AB - Commercial grade polyethylene is melt electrospun from a thin film of unconfined molten polymer on a heated, electrically-grounded plate. Under the influence of an applied electric field, the melt spontaneously forms fingering perturbations at the plate edge which then evolve into emitting fiber-forming jets. Jet-to-jet spacing (∼5 mm), which is dependent on the applied voltage amplitude, is in agreement with estimates from a simple theoretical treatment. The broad applicability of the approach is verified by spinning a second polymer—polycaprolactone. In both cases, the fabricated fibers are similar in quality to those obtained under needle melt electrospinning; however for this method, there are no nozzles to clog and an enhanced production rate up to 80 mg min−1 is achieved from approximately 20–25 simultaneous parallel jets. The process of jet formation, effective flow rates, cone-jet diameters, as well as limits on jet density and differences with polymer type are compared with theoretical models. This particular approach allows facile, high throughput micro- and nano-fiber formation from a wide variety of thermoplastics and other high viscosity fluids without the use of solvents or the persistent issues of clogging and pumping that hamper traditional methods, resulting in mechanically strong meso-scale fibers highly desirable for industrial applications. DA - 2014/11// PY - 2014/11// DO - 10.1088/2053-1591/1/4/045304 VL - 1 IS - 4 SP - 045304 KW - melt electrospinning KW - mesofibers KW - scale up KW - polyethylene KW - polycaprolactone ER - TY - CONF TI - A new class of strongly coupled plasmas inspired by sonoluminescence AU - Bataller, Alexander AU - Plateau, Guillaume AU - Kappus, Brian AU - Putterman, Seth C2 - 2014/// C3 - APS Meeting Abstracts DA - 2014/// ER - TY - BOOK TI - Exploring the Universality of Sonoluminescence AU - Bataller, Alexander William DA - 2014/// PY - 2014/// PB - University of California, Los Angeles ER - TY - JOUR TI - The zCOSMOS redshift survey: evolution of the light in bulges and discs since z̃ 0.8 AU - Tasca, LAM AU - Tresse, L AU - Le Fèvre, O AU - Ilbert, O AU - Lilly, SJ AU - Zamorani, G AU - López-Sanjuan, C AU - Ho, LC AU - Bardelli, S AU - Cattaneo, A AU - others T2 - Astronomy & Astrophysics DA - 2014/// PY - 2014/// VL - 564 SP - L12 ER - TY - JOUR TI - the COS-Dwarfs survey: the carbon reservoir around sub-L* galaxies AU - Bordoloi, Rongmon AU - Tumlinson, Jason AU - Werk, Jessica K AU - Oppenheimer, Benjamin D AU - Peeples, Molly S AU - Prochaska, J Xavier AU - Tripp, Todd M AU - Katz, Neal AU - Davé, Romeel AU - Fox, Andrew J AU - others T2 - The Astrophysical Journal DA - 2014/// PY - 2014/// VL - 796 IS - 2 SP - 136 ER - TY - JOUR TI - The dependence of Galactic outflows on the properties and orientation of zCOSMOS galaxies at z~ 1 AU - Bordoloi, R AU - Lilly, Simon J AU - Hardmeier, E AU - Contini, T AU - Kneib, J-P AU - Le Fevre, O AU - Mainieri, V AU - Renzini, A AU - Scodeggio, M AU - Zamorani, G AU - others T2 - The Astrophysical Journal DA - 2014/// PY - 2014/// VL - 794 IS - 2 SP - 130 ER - TY - JOUR TI - The COS-halos survey: physical conditions and baryonic mass in the low-redshift circumgalactic medium AU - Werk, Jessica K AU - Prochaska, J Xavier AU - Tumlinson, Jason AU - Peeples, Molly S AU - Tripp, Todd M AU - Fox, Andrew J AU - Lehner, Nicolas AU - Thom, Christopher AU - O’Meara, John M AU - Ford, Amanda Brady AU - others T2 - The Astrophysical Journal DA - 2014/// PY - 2014/// VL - 792 IS - 1 SP - 8 ER - TY - JOUR TI - How Galaxy Mergers Affect Their Environment: Mapping the Multiphase Circumgalactic Medium of Close Kinematic Pairs AU - Bordoloi, Rongmon T2 - HST Proposal DA - 2014/// PY - 2014/// ER - TY - JOUR TI - The CGM in HD: New Maps of Galactic Accretion, Quenching, and Chemical Feedback in the Circumgalactic Medium AU - Tumlinson, Jason AU - Bordoloi, Rongmon AU - O’Meara, John AU - Werk, Jessica T2 - NOAO Proposal DA - 2014/// PY - 2014/// ER - TY - CONF TI - The CGM around Dwarf Galaxies AU - Tumlinson, Jason AU - Bordoloi, R AU - Team, COS-Halos C2 - 2014/// C3 - American Astronomical Society Meeting Abstracts# 223 DA - 2014/// VL - 223 ER - TY - CONF TI - The CGM around dwarf galaxies AU - Bordoloi, Rongmon AU - Tumlinson, J AU - Werk, J AU - Thom, C AU - Prochaska, JX AU - Tripp, TM AU - Katz, N AU - Dave, R AU - Oppenheimer, B AU - Ford, A Brady AU - others C2 - 2014/// C3 - American Astronomical Society Meeting Abstracts# 223 DA - 2014/// VL - 223 ER - TY - JOUR TI - Modeling the distribution of Mg II absorbers around galaxies using background galaxies and quasars AU - Bordoloi, Rongmon AU - Lilly, Simon J AU - Kacprzak, Glenn G AU - Churchill, Christopher W T2 - The Astrophysical Journal DA - 2014/// PY - 2014/// VL - 784 IS - 2 SP - 108 ER - TY - JOUR TI - A high density two-dimensional electron gas in an oxide heterostructure on Si (001) AU - Jin, E. N. AU - Kornblum, L. AU - Kumah, D. P. AU - Zou, K. AU - Broadbridge, C. C. AU - Ngai, J. H. AU - Ahn, C. H. AU - Walker, F. J. T2 - APL Materials AB - We present the growth and characterization of layered heterostructures comprised of LaTiO3 and SrTiO3 epitaxially grown on Si (001). Magnetotransport measurements show that the sheet carrier densities of the heterostructures scale with the number of LaTiO3/SrTiO3 interfaces, consistent with the presence of an interfacial 2-dimensional electron gas (2DEG) at each interface. Sheet carrier densities of 8.9 × 1014 cm−2 per interface are observed. Integration of such high density oxide 2DEGs on silicon provides a bridge between the exceptional properties and functionalities of oxide 2DEGs and microelectronic technologies. DA - 2014/11/1/ PY - 2014/11/1/ DO - 10.1063/1.4902433 VL - 2 IS - 11 SP - 116109 UR - https://doi.org/10.1063/1.4902433 ER - TY - JOUR TI - Performance improvements for nuclear reaction network integration AU - Longland, R. AU - Martin, D. AU - José, J. T2 - Astronomy & Astrophysics AB - Aims. The aim of this work is to compare the performance of three reaction network integration methods used in stellar nucleosynthesis calculations. These are the Gear’s backward differentiation method, Wagoner’s method (a 2nd-order Runge-Kutta method), and the Bader-Deuflehard semi-implicit multi-step method. DA - 2014/3// PY - 2014/3// DO - 10.1051/0004-6361/201321958 VL - 563 SP - A67 KW - methods: numerical KW - nuclear reactions, nucleosynthesis, abundances ER - TY - JOUR TI - Nuclear astrophysics in the laboratory and in the universe AU - Champagne, A. E. AU - Iliadis, C. AU - Longland, R. T2 - AIP Advances AB - Nuclear processes drive stellar evolution and so nuclear physics, stellar models and observations together allow us to describe the inner workings of stars and their life stories. This Information on nuclear reaction rates and nuclear properties are critical ingredients in addressing most questions in astrophysics and often the nuclear database is incomplete or lacking the needed precision. Direct measurements of astrophysically-interesting reactions are necessary and the experimental focus is on improving both sensitivity and precision. In the following, we review recent results and approaches taken at the Laboratory for Experimental Nuclear Astrophysics (LENA, http://research.physics.unc.edu/project/nuclearastro/Welcome.html). DA - 2014/4// PY - 2014/4// DO - 10.1063/1.4864794 VL - 4 IS - 4 SP - 041006 ER - TY - JOUR TI - Ultrathin Polyaniline-based Buffer Layer for Highly Efficient Polymer Solar Cells with Wide Applicability AU - Zhao, Wenchao AU - Ye, Long AU - Zhang, Shaoqing AU - Fan, Bin AU - Sun, Mingliang AU - Hou, Jianhui T2 - Scientific Reports AB - Interfacial buffer layers often attribute the improved device performance in organic optoelectronic device. Herein, a water-soluble hydrochloric acid doped polyanilines (HAPAN) were utilized as p-type electrode buffer layer in highly efficient polymer solar cells (PSC) based on PBDTTT-EFT and several representative polymers. The PBDTTT-EFT-based conventional PSC featuring ultrathin HAPAN (1.3 nm) delivered high PCE approximately 9%, which is one of the highest values among conventional PSC devices. Moreover, ultrathin HAPAN also exhibited wide applicability in a variety of efficient photovoltaic polymers including PBDTTT-C-T, PTB7, PBDTBDD, PBTTDPP-T, PDPP3T and P3HT. The excellent performances were originated from the high transparency, small film roughness and suitable work function. DA - 2014/// PY - 2014/// DO - 10.1038/srep06570 VL - 4 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000343082600001&KeyUID=WOS:000343082600001 ER - TY - JOUR TI - Side Chain Selection for Designing Highly Efficient Photovoltaic Polymers with 2D-Conjugated Structure AU - Zhang, Shaoqing AU - Ye, Long AU - Zhao, Wenchao AU - Liu, Delong AU - Yao, Huifeng AU - Hou, Jianhui T2 - Macromolecules AB - Recently, the benzodithiophene- (BDT-) based polymers with conjugated side groups attracted considerable attention due to their superior properties in polymer solar cells (PSCs), so the investigation of the side chain effects on the photovoltaic properties of this type of polymers is an interesting and important topic for molecular design. Herein, three conjugated polymers based on BDT and thieno[3,4-b]thiophene units with furan, thiophene and selenophene as side groups, named as PBDTTT-EFF, PBDTTT-EFT, and PBDTTT-EFS, were synthesized and applied in polymer solar cells. The polymers were characterized in parallel by absorption spectroscopy, thermogravimetric analysis (TGA), density functional theory (DFT), ultraviolet photoemission spectroscopy (UPS), X-ray diffraction (XRD), and photovoltaic measurements. The results show that the dihedral angles between the BDT and conjugated side groups play important roles in affecting the absorption bands, HOMO levels, crystallinities, and aggregation sizes of the polymers. The photovoltaic results indicate that PBDTTT-EFT and PBDTTT-EFS show similar photovoltaic characteristics in device, and PCEs of 9.0% and 8.78% were obtained, respectively. The device of PBDTTT-EFF shows a Voc of 0.69 V and a Jsc of 11.77 mA/cm2, which are lower than those in the devices based on the other two polymers. Overall, this work suggests that the photovoltaic properties of the BDT-based polymers can be effectively tuned by introducing conjugated side groups with varied steric hindrance. DA - 2014/// PY - 2014/// DO - 10.1021/ma500829r VL - 47 IS - 14 SP - 4653-4659 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84904648056&partnerID=MN8TOARS ER - TY - JOUR TI - Selecting a Donor Polymer for Realizing Favorable Morphology in Efficient Non-fullerene Acceptor-based Solar Cells AU - Ye, Long AU - Jiang, Wei AU - Zhao, Wenchao AU - Zhang, Shaoqing AU - Qian, Deping AU - Wang, Zhaohui AU - Hou, Jianhui T2 - Small AB - A highly efficient non-fullerene small molecule-based polymer solar cell (n-PSC) is realized by employing PBDTBDD as donor polymer and singly linked perylene bisimide (SDIPBI) as acceptor with PCE up to 4.4%, which is one of the outstanding values among n-PSCs so far. In particular, high Voc of 0.87 V and FF over 60% are achieved for PBDTBDD: SDIPBI based PSCs. DA - 2014/// PY - 2014/// DO - 10.1002/smll.201401082 VL - 10 IS - 22 SP - 4658-4663 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000345366800016&KeyUID=WOS:000345366800016 KW - polymer solar cells KW - nano-morphology KW - non-fullerene acceptors KW - ternary solvents KW - donor polymers ER - TY - JOUR TI - Photovoltaics: Quantification of Nano- and Mesoscale Phase Separation and Relation to Donor and Acceptor Quantum Efficiency,Jsc, and FF in Polymer:Fullerene Solar Cells (Adv. Mater. 25/2014) AU - Ma, Wei AU - Tumbleston, John R. AU - Ye, Long AU - Wang, Cheng AU - Hou, Jianhui AU - Ade, Harald T2 - Advanced Materials AB - On page 4234, J. Hou, H. Ade, and co-workers quantify the composition variations in a complex three-phase, hierarchical morphology of polymer/fullerene devices and establish novel structure–function relations by combining different X-ray scattering techniques. Anti-correlated composition variations between meso- and nanoscale separation are observed and impacted by the solvent mixture. DA - 2014/7// PY - 2014/7// DO - 10.1002/ADMA.201470171 VL - 26 IS - 25 SP - 4399-4399 J2 - Adv. Mater. LA - en OP - SN - 0935-9648 UR - http://dx.doi.org/10.1002/ADMA.201470171 DB - Crossref ER - TY - JOUR TI - Molecular Design toward Highly Efficient Photovoltaic Polymers Based on Two-Dimensional Conjugated Benzodithiophene AU - Ye, Long AU - Zhang, Shaoqing AU - Huo, Lijun AU - Zhang, Maojie AU - Hou, Jianhui T2 - Accounts of Chemical Research AB - As researchers continue to develop new organic materials for solar cells, benzo[1,2-b:4,5-b']dithiophene (BDT)-based polymers have come to the fore. To improve the photovoltaic properties of BDT-based polymers, researchers have developed and applied various strategies leading to the successful molecular design of highly efficient photovoltaic polymers. Novel polymer materials composed of two-dimensional conjugated BDT (2D-conjugated BDT) have boosted the power conversion efficiency of polymer solar cells (PSCs) to levels that exceed 9%. In this Account, we summarize recent progress related to the design and synthesis of 2D-conjugated BDT-based polymers and discuss their applications in highly efficient photovoltaic devices. We introduce the basic considerations for the construction of 2D-conjugated BDT-based polymers and systematic molecular design guidelines. For example, simply modifying an alkoxyl-substituted BDT to form an alkylthienyl-substituted BDT can improve the polymer hole mobilities substantially with little effect on their molecular energy level. Secondly, the addition of a variety of chemical moieties to the polymer can produce a 2D-conjugated BDT unit with more functions. For example, the introduction of a conjugated side chain with electron deficient groups (such as para-alkyl-phenyl, meta-alkoxyl-phenyl, and 2-alkyl-3-fluoro-thienyl) allowed us to modulate the molecular energy levels of 2D-conjugated BDT-based polymers. Through the rational design of BDT analogues such as dithienobenzodithiophene (DTBDT) or the insertion of larger π bridges, we can tune the backbone conformations of these polymers and modulate their photovoltaic properties. We also discuss the influence of 2D-conjugated BDT on polymer morphology and the blends of these polymers with phenyl-C61 (or C71)-butyric acid methyl ester (PCBM). Finally, we summarize the various applications of the 2D-conjugated BDT-based polymers in highly efficient PSC devices. Overall, this Account correlates the molecular structures of the 2D-conjugated BDT-based polymers with their photovoltaic properties. As a result, this Account can guide the molecular design of organic photovoltaic materials and the development of organic materials for other types of optoelectronic devices. DA - 2014/// PY - 2014/// DO - 10.1021/ar5000743 VL - 47 IS - 5 SP - 1595-1603 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84901270303&partnerID=MN8TOARS ER - TY - JOUR TI - Investigations of the Conjugated Polymers Based on Dithienogermole (DTG) Units for Photovoltaic Applications AU - Wang, Qi AU - Zhang, Shaoqing AU - Ye, Long AU - Cui, Yong AU - Fan, Huili AU - Hou, Jianhui T2 - Macromolecules AB - Conjugated polymers based on the dithienogermole (DTG) units showed promising properties for the applications in polymer solar cells (PSCs), so that the investigations of the natures and photovoltaic properties of the DTG-based polymers with varied backbone structures would be of great interest. In this work, four DTG-based polymers named as PDTG-BDD, PDTG-IID, PDTG-BT, and PDTG-DPP were synthesized and characterized. The results indicate that the DTG-based polymers show varied absorption bands and molecular energy levels. In X-ray diffraction measurements, these polymers show different laminar packing and π–π stacking distances in solid films. The PSC devices based on the four DTG-based polymers were fabricated, and their photovoltaic properties were characterized. The results show that different device fabrication conditions are needed to get optimal photovoltaic performance of these four polymers. The device of PDTG-BDD shows a PCE of 6.3% with a high Voc of 0.935 V, a FF of 65.0%, and a Jsc of 10.3 mA/cm2, which is the highest one in these four polymers; the devices of PDTG-DPP showed a miserably low Jsc of 3.19 mA/cm2 due to the unfavorable morphologies of the polymer:PC71BM blend. Overall, the comparisons among these four polymers provide fundamental information for understanding the correlations among molecular structures and photovoltaic properties of the DTG-based polymers, and how to control or modulate the bandgaps, molecular energy levels, and morphologies of the DTG-polymers will be the key to fully explore their potentials as photovoltaic materials. DA - 2014/// PY - 2014/// DO - 10.1021/ma500831z VL - 47 IS - 16 SP - 5558-5565 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84906675984&partnerID=MN8TOARS ER - TY - JOUR TI - Highly Efficient 2D-Conjugated Benzodithiophene-Based Photovoltaic Polymer with Linear Alkylthio Side Chain AU - Ye, Long AU - Zhang, Shaoqing AU - Zhao, Wenchao AU - Yao, Huifeng AU - Hou, Jianhui T2 - Chemistry of Materials AB - ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTHighly Efficient 2D-Conjugated Benzodithiophene-Based Photovoltaic Polymer with Linear Alkylthio Side ChainLong Ye†‡, Shaoqing Zhang†, Wenchao Zhao†, Huifeng Yao†‡, and Jianhui Hou*†View Author Information† State Key Laboratory of Polymer Physics and Chemistry, Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China‡ University of Chinese Academy of Sciences, Beijing 100049, China*E-mail: [email protected]Cite this: Chem. Mater. 2014, 26, 12, 3603–3605Publication Date (Web):June 12, 2014Publication History Received18 April 2014Revised8 June 2014Published online12 June 2014Published inissue 24 June 2014https://doi.org/10.1021/cm501513nCopyright © 2014 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views8298Altmetric-Citations512LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. 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Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (1002 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Absorption,Conjugated polymers,Photovoltaics,Polymers,Power conversion efficiency Get e-Alerts DA - 2014/// PY - 2014/// DO - 10.1021/cm501513n VL - 26 IS - 12 SP - 3603-3605 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000338089500004&KeyUID=WOS:000338089500004 ER - TY - JOUR TI - Binary additives synergistically boost the efficiency of all-polymer solar cells up to 3.45% AU - Cheng, Pei AU - Ye, Long AU - Zhao, Xingang AU - Hou, Jianhui AU - Li, Yongfang AU - Zhan, Xiaowei T2 - Energy & Environmental Science AB - Binary additives synergistically boost the power conversion efficiency of all-polymer solar cells up to 3.45%. The nonvolatile additive PDI-2DTT suppresses aggregation of the acceptor PPDIDTT and enhances donor/acceptor mixing, while the additive DIO facilitates aggregation and crystallization of the donor PBDTTT-C-T as well as improves phase separation. Combination of DIO and PDI-2DTT leads to suitable phase separation and improved and balanced charge transport, which is beneficial to efficiency enhancement. DA - 2014/// PY - 2014/// DO - 10.1039/c3ee43041c VL - 7 IS - 4 SP - 1351-1356 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84894031115&partnerID=MN8TOARS ER - TY - JOUR TI - Bay-linked perylene bisimides as promising non-fullerene acceptors for organic solar cells AU - Jiang, Wei AU - Ye, Long AU - Li, Xiangguang AU - Xiao, Chengyi AU - Tan, Fang AU - Zhao, Wenchao AU - Hou, Jianhui AU - Wang, Zhaohui T2 - Chemical Communications AB - A series of bay-linked perylene bisimides as non-fullerene acceptors for organic solar cells are designed. The best power conversion efficiency up to 3.63% based on s-diPBI (1b) is demonstrated by fine-tuning optoelectronic properties resulting from different degrees of twisting and flexibility by bay-linkages. DA - 2014/// PY - 2014/// DO - 10.1039/c3cc47204c VL - 50 IS - 8 SP - 1024-1026 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84890848848&partnerID=MN8TOARS ER - TY - JOUR TI - Collision Time Measurements in a Sonoluminescing Microplasma with a Large Plasma Parameter AU - Bataller, A. AU - Kappus, B. AU - Camara, C. AU - Putterman, S. T2 - Physical Review Letters AB - The plasma which forms inside of a micron-sized sonoluminescing bubble in water for under a nanosecond has been probed with 3 ns long laser pulses. A comparison of the response to 532 and 1064 nm light indicates that the plasma number density is about 2×10(21) cm(-3) and that transport properties are dominated by strong screening and correlation effects. The spherical shape, well-defined atomic density, and blackbody temperature make the sonoluminescing plasma a test bed for theories of strongly coupled plasmas. The plasma in this experiment distinguishes between competing theories of strong, intermediate, and weak effective screening. DA - 2014/7/7/ PY - 2014/7/7/ DO - 10.1103/PhysRevLett.113.024301 VL - 113 IS - 2 SP - 024301 J2 - Phys. Rev. Lett. LA - en OP - SN - 0031-9007 1079-7114 UR - http://dx.doi.org/10.1103/PhysRevLett.113.024301 DB - Crossref ER - TY - JOUR TI - Blackbody Emission from Laser Breakdown in High-Pressure Gases AU - Bataller, A. AU - Plateau, G. R. AU - Kappus, B. AU - Putterman, S. T2 - Physical Review Letters AB - Laser induced breakdown of pressurized gases is used to generate plasmas under conditions where the atomic density and temperature are similar to those found in sonoluminescing bubbles. Calibrated streak spectroscopy reveals that a blackbody persists well after the exciting femtosecond laser pulse has turned off. Deviation from Saha's equation of state and an accompanying large reduction in ionization potential are observed at unexpectedly low atomic densities---in parallel with sonoluminescence. In laser breakdown, energy input proceeds via excitation of electrons whereas in sonoluminescence it is initiated via the atoms. The similar responses indicate that these systems are revealing the thermodynamics and transport of a strongly coupled plasma. DA - 2014/8/15/ PY - 2014/8/15/ DO - 10.1103/PhysRevLett.113.075001 VL - 113 IS - 7 SP - 075001 J2 - Phys. Rev. Lett. LA - en OP - SN - 0031-9007 1079-7114 UR - http://dx.doi.org/10.1103/PhysRevLett.113.075001 DB - Crossref ER - TY - JOUR TI - Nanosecond high-power dense microplasma switch for visible light AU - Bataller, A. AU - Koulakis, J. AU - Pree, S. AU - Putterman, S. T2 - Applied Physics Letters AB - Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation A. Bataller, J. Koulakis, S. Pree, S. Putterman; Nanosecond high-power dense microplasma switch for visible light. Appl. Phys. Lett. 1 December 2014; 105 (22): 223501. https://doi.org/10.1063/1.4902914 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioApplied Physics Letters Search Advanced Search |Citation Search DA - 2014/12// PY - 2014/12// DO - 10.1063/1.4902914 VL - 105 IS - 22 SP - 223501 J2 - Appl. Phys. Lett. LA - en OP - SN - 0003-6951 1077-3118 UR - http://dx.doi.org/10.1063/1.4902914 DB - Crossref ER - TY - JOUR TI - Diffusion of research-based instructional strategies: the case of SCALE-UP AU - Foote, Kathleen T AU - Neumeyer, Xaver AU - Henderson, Charles AU - Dancy, Melissa H AU - Beichner, Robert J T2 - International Journal of STEM Education AB - Many innovative teaching strategies have been developed under the assumption that documenting successful student learning outcomes at the development site is enough to spread the innovation successfully to secondary sites. Since this ‘show them and they will adopt’ model has yet to produce the desired large-scale transformation, this study examines one innovative teaching strategy that has demonstrated success in spreading. This instructional strategy, Student-Centered Active Learning Environment with Upside-down Pedagogies (SCALE-UP), modifies both the pedagogy and classroom design to maximize interaction and activity-based learning. A web survey was used to develop a census of instructors who have been influenced by SCALE-UP. SCALE-UP, which started in large enrollment university physics, has spread widely across disciplines and institutions. The survey identified that SCALE-UP style instruction is currently used in over a dozen disciplines at a minimum of 314 departments in at least 189 higher education institutions in 21 countries. Many more respondents indicated learning about SCALE-UP via interpersonal channels, such as talks/workshops and colleagues, than via mass media channels, such as the Internet and publications. We estimate the dissemination of SCALE-UP in physics may be at the tipping point between adoption by adventurous early users and the more mainstream majority. Implementers demonstrate pedagogical and structural variation in their use of SCALE-UP. Leveraging interpersonal networks can help accelerate dissemination of educational innovations and should be used more prominently in change strategies. Since SCALE-UP may be nearing a tipping point within the discipline of physics, now may be the time to modify change strategies to appeal to more typical faculty rather than the early adopters. This may include using successful secondary implementers as like-minded intermediaries to reach out to people considering the use of the innovation in different institutional settings for more practical and relatable advice. For SCALE-UP, having a specialized classroom may improve the likelihood of continued use at an institution. We also hypothesize that having a special classroom may start departmental conversations about innovative teaching and may make instructors less likely to revert back to traditional methods. DA - 2014/11/26/ PY - 2014/11/26/ DO - 10.1186/s40594-014-0010-8 VL - 1 IS - 1 J2 - IJ STEM Ed LA - en OP - SN - 2196-7822 UR - http://dx.doi.org/10.1186/s40594-014-0010-8 DB - Crossref ER - TY - JOUR TI - History and Evolution of Active Learning Spaces AU - Beichner, Robert J. T2 - New Directions for Teaching and Learning AB - This chapter examines active learning spaces as they have developed over the years. Consistently well‐designed classrooms can facilitate active learning even though the details of implementing pedagogies may differ. DA - 2014/3// PY - 2014/3// DO - 10.1002/tl.20081 VL - 2014 IS - 137 SP - 9-16 J2 - New Directions for Teaching and Learning LA - en OP - SN - 0271-0633 UR - http://dx.doi.org/10.1002/tl.20081 DB - Crossref ER - TY - JOUR TI - Known unknowns of dark matter annihilation over cosmic time AU - Mack, Katherine J. T2 - Monthly Notices of the Royal Astronomical Society AB - Dark matter self-annihilation holds promise as one of the most robust mechanisms for the identification of the particle responsible for the Universe's missing mass. In this work, I examine the evolution of the dark matter annihilation power produced by smooth and collapsed structures over cosmic time, taking into account uncertainties in the structure of dark matter haloes. As we search for observational signatures of annihilation, an understanding of this time evolution will help us to best direct our observational efforts, either with local measurements or investigation of the effects of annihilation on the intergalactic medium at high redshift. As I show in this work, there are several key sources of uncertainty in our ability to estimate the dark matter annihilation from collapsed structures, including: the density profile of dark matter haloes; the small-scale cut-off in the dark matter halo mass function; the redshift-dependent mass–concentration relation for small haloes; and the particle-velocity dependence of the dark matter annihilation process. Varying assumptions about these quantities can result in annihilation power predictions that differ by several orders of magnitude. These uncertainties must be resolved, through a combination of observation and modelling, before robust estimations of the cosmological annihilation signal can be made. DA - 2014/2/20/ PY - 2014/2/20/ DO - 10.1093/mnras/stu129 VL - 439 IS - 3 SP - 2728-2735 LA - en OP - SN - 1365-2966 0035-8711 UR - http://dx.doi.org/10.1093/mnras/stu129 DB - Crossref KW - galaxies: formation KW - dark matter KW - large-scale structure of Universe ER - TY - JOUR TI - Dynamic competition between spin-density wave order and superconductivity in underdoped Ba1−xKxFe2As2 AU - Yi, M. AU - Zhang, Y. AU - Liu, Z.-K. AU - Ding, X. AU - Chu, J.-H. AU - Kemper, A.F. AU - Plonka, N. AU - Moritz, B. AU - Hashimoto, M. AU - Mo, S.-K. AU - Hussain, Z. AU - Devereaux, T.P. AU - Fisher, I.R. AU - Wen, H.H. AU - Shen, Z.-X. AU - Lu, D.H. T2 - Nat Comms AB - An intriguing aspect of unconventional superconductivity is that it always appears in the vicinity of other competing phases, whose suppression brings the full emergence of superconductivity. In the iron-pnictides, these competing phases are marked by a tetragonal-to-orthorhombic structural transition and a collinear spin-density-wave (SDW) transition. There has been macroscopic evidence for competition between these phases and superconductivity as the magnitude of both the orthorhombicity and magnetic moment are suppressed in the superconducting state. Here, using angle-resolved photoemission spectroscopy on detwinned underdoped $Ba_{1-x}K_xFe_2As_2$, we observe a coexistence of both the SDW gap and superconducting gap in the same electronic structure. Furthermore, our data reveal that following the onset of superconductivity, the SDW gap decreases in magnitude and shifts in a direction consistent with a reduction of the orbital anisotropy. This observation provides direct spectroscopic evidence for the dynamic competition between superconductivity and both SDW and electronic nematic orders in these materials. DA - 2014/4// PY - 2014/4// DO - 10.1038/ncomms4711 VL - 5 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000335223100002&KeyUID=WOS:000335223100002 ER - TY - JOUR TI - Balancing Act: Evidence for a Strong Subdominant d -Wave Pairing Channel in Ba 0.6 K 0.4 Fe 2 As 2 AU - Böhm, T. AU - Kemper, A. F. AU - Moritz, B. AU - Kretzschmar, F. AU - Muschler, B. AU - Eiter, H.-M. AU - Hackl, R. AU - Devereaux, T. P. AU - Scalapino, D. J. AU - Wen, Hai-Hu T2 - Phys. Rev. X AB - High-temperature superconductivity may arise from competing or cooperating mechanisms. Researchers show that Raman light scattering can be used to characterize competing superconducting channels in the iron-based compound Ba${}_{0.6}$K${}_{0.4}$Fe${}_{2}$As${}_{2}$. DA - 2014/// PY - 2014/// DO - 10.1103/physrevx.4.041046 VL - 4 IS - 4 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000349072800001&KeyUID=WOS:000349072800001 ER - TY - JOUR TI - Ultrafast electron dynamics in the topological insulator Bi2Se3 studied by time-resolved photoemission spectroscopy AU - Sobota, J.A. AU - Yang, S.-L. AU - Leuenberger, D. AU - Kemper, A.F. AU - Analytis, J.G. AU - Fisher, I.R. AU - Kirchmann, P.S. AU - Devereaux, T.P. AU - Shen, Z.-X. T2 - Journal of Electron Spectroscopy and Related Phenomena AB - We characterize the topological insulator Bi2Se3 using time- and angle-resolved photoemission spectroscopy. By employing two-photon photoemission, a complete picture of the unoccupied electronic structure from the Fermi level up to the vacuum level is obtained. We demonstrate that the unoccupied states host a second Dirac surface state which can be resonantly excited by 1.5 eV photons. We then study the ultrafast relaxation processes following optical excitation. We find that they culminate in a persistent non-equilibrium population of the first Dirac surface state, which is maintained by a meta-stable population of the bulk conduction band. Finally, we perform a temperature-dependent study of the electron–phonon scattering processes in the conduction band, and find the unexpected result that their rates decrease with increasing sample temperature. We develop a model of phonon emission and absorption from a population of electrons, and show that this counter-intuitive trend is the natural consequence of fundamental electron–phonon scattering processes. This analysis serves as an important reminder that the decay rates extracted by time-resolved photoemission are not in general equal to single electron scattering rates, but include contributions from filling and emptying processes from a continuum of states. DA - 2014/8// PY - 2014/8// DO - 10.1016/j.elspec.2014.01.005 VL - 195 SP - 249-257 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000342872800036&KeyUID=WOS:000342872800036 KW - Topological insulator KW - Time- and angle-resolved photoemission KW - Two-photon photoemission KW - Electron-phonon scattering ER - TY - JOUR TI - Publisher's Note: Effect of dynamical spectral weight redistribution on effective interactions in time-resolved spectroscopy [Phys. Rev. B 90, 075126 (2014)] AU - Kemper, A. F. AU - Sentef, M. A. AU - Moritz, B. AU - Freericks, J. K. AU - Devereaux, T. P. T2 - Phys. Rev. B DA - 2014/8// PY - 2014/8// DO - 10.1103/physrevb.90.079905 VL - 90 IS - 7 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000341299800010&KeyUID=WOS:000341299800010 ER - TY - JOUR TI - Bandgap closure and reopening in CsAuI3 at high pressure AU - Wang, Shibing AU - Kemper, Alexander F. AU - Baldini, Maria AU - Shapiro, M. C. AU - Riggs, Scott C. AU - Zhao, Zhao AU - Liu, Zhenxian AU - Devereaux, Thomas P. AU - Geballe, Ted H. AU - Fisher, Ian R. AU - Mao, Wendy L. T2 - Phys. Rev. B AB - Results of high-pressure infrared (IR) and Raman spectroscopy measurements are presented for the mixed valence compound ${\mathrm{CsAuI}}_{3}$, where Au adopts ${\mathrm{Au}}^{\mathrm{I}}$ and ${\mathrm{Au}}^{\mathrm{III}}$ valency. Raman spectroscopy shows softening with pressure of the vibration modes in the ${\mathrm{Au}}^{\mathrm{III}}$-${\mathrm{I}}_{4}$ square planar units in the tetragonal phase, indicating a similar pressure-induced lattice distortion as found for the closely related compounds ${\mathrm{CsAuCl}}_{3}$ and ${\mathrm{CsAuBr}}_{3}$. Multiple features in the higher pressure spectra confirm that the high-pressure phase has a lower symmetry than the ambient pressure tetragonal structure, consistent with an orthorhombic structure discovered recently by x-ray diffraction measurements. From IR spectroscopy, we observed rapid bandgap closure at a rate of 0.2 eV/GPa in the tetragonal phase of ${\mathrm{CsAuI}}_{3}$, close to the tetragonal-orthorhombic phase transition. The IR reflectivity shows a Drude-like behavior implying metallic conductivity. However, as the compound fully transforms to the orthorhombic phase, the bandgap reopens and the Drude behavior in the reflectivity disappears. DA - 2014/6// PY - 2014/6// DO - 10.1103/physrevb.89.245109 VL - 89 IS - 24 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000336976400003&KeyUID=WOS:000336976400003 ER - TY - JOUR TI - Manipulation of Gap Nodes by Uniaxial Strain in Iron-Based Superconductors AU - Kang, Jian AU - Kemper, Alexander F. AU - Fernandes, Rafael M. T2 - Phys. Rev. Lett. AB - In the iron pnictides and chalcogenides, multiple orbitals participate in the superconducting state, enabling different gap structures to be realized in distinct materials. Here we argue that the spectral weights of these orbitals can in principle be controlled by a tetragonal symmetry-breaking uniaxial strain, due to the enhanced nematic susceptibility of many iron-based superconductors. By investigating multi-orbital microscopic models in the presence of orbital order, we show that not only $T_{c}$ can be enhanced, but pairs of accidental gap nodes can be annihilated and created in the Fermi surface by an increasing external strain. We explain our results as a mixture of nearly-degenerate superconducting states promoted by strain, and show that the annihilation and creation of nodes can be detected experimentally via anisotropic penetration depth measurements. Our results provide a promising framework to externally control the superconducting properties of iron-based materials. DA - 2014/11// PY - 2014/11// DO - 10.1103/physrevlett.113.217001 VL - 113 IS - 21 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000345356900006&KeyUID=WOS:000345356900006 ER - TY - JOUR TI - Exact solution for high harmonic generation and the response to an ac driving field for a charge density wave insulator AU - Shen, Wen AU - Kemper, A. F. AU - Devereaux, T. P. AU - Freericks, J. K. T2 - Phys. Rev. B AB - We develop and exactly solve a model for electrons driven by pulsed or continuous ac fields. The theory includes both the photoexcitation process as well as the subsequent acceleration of the electrons. In the case of an ac response, we examine both the nonequilibrium density of states and the current. In the case of pulsed light for high harmonic generation, we find the radiated light assumes a nearly universal behavior, with only limited dependence on the parameters of the system, except for the amplitude of the driving field, which determines the range of high harmonics generated and a tendency toward a narrowing of the peaks in a charge density wave versus a metal. This type of high harmonic generation can potentially be used for the creation of solid-state-based ultrafast light sources. DA - 2014/9// PY - 2014/9// DO - 10.1103/physrevb.90.115113 VL - 90 IS - 11 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000341259600002&KeyUID=WOS:000341259600002 ER - TY - JOUR TI - Effect of dynamical spectral weight redistribution on effective interactions in time-resolved spectroscopy AU - Kemper, A. F. AU - Sentef, M. A. AU - Moritz, B. AU - Freericks, J. K. AU - Devereaux, T. P. T2 - Phys. Rev. B AB - The redistribution of electrons in an ultrafast pump-probe experiment causes significant changes to the spectral distribution of the retarded interaction between electrons and bosonic modes. We study the influence of these changes on pump-probe photoemission spectroscopy for a model electron-phonon coupled system using the nonequilibrium Keldysh formalism. We show that spectral rearrangement due to the driving field preserves an overall sum rule for the electronic self-energy, but modifies the effective electron-phonon scattering as a function of energy. Experimentally, this pump-modified scattering can be tracked by analyzing the fluence or excitation energy dependence of population decay rates and transient changes in dispersion kinks. DA - 2014/8// PY - 2014/8// DO - 10.1103/physrevb.90.075126 VL - 90 IS - 7 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000341256600003&KeyUID=WOS:000341256600003 ER - TY - JOUR TI - Distinguishing Bulk and Surface Electron-Phonon Coupling in the Topological Insulator Bi2Se3 Using Time-Resolved Photoemission Spectroscopy AU - Sobota, J. A. AU - Yang, S.-L. AU - Leuenberger, D. AU - Kemper, A. F. AU - Analytis, J. G. AU - Fisher, I. R. AU - Kirchmann, P. S. AU - Devereaux, T. P. AU - Shen, Z.-X. T2 - Phys. Rev. Lett. AB - We report time- and angle-resolved photoemission spectroscopy measurements on the topological insulator Bi(2)Se(3). We observe oscillatory modulations of the electronic structure of both the bulk and surface states at a frequency of 2.23 THz due to coherent excitation of an A(1g) phonon mode. A distinct, additional frequency of 2.05 THz is observed in the surface state only. The lower phonon frequency at the surface is attributed to the termination of the crystal and thus reduction of interlayer van der Waals forces, which serve as restorative forces for out-of-plane lattice distortions. Density functional theory calculations quantitatively reproduce the magnitude of the surface phonon softening. These results represent the first band-resolved evidence of the A(1g) phonon mode coupling to the surface state in a topological insulator. DA - 2014/10// PY - 2014/10// DO - 10.1103/physrevlett.113.157401 VL - 113 IS - 15 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000344052200011&KeyUID=WOS:000344052200011 ER - TY - JOUR TI - Somites Without a Clock AU - Dias, Ana S. AU - Almeida, Irene AU - Belmonte, Julio M. AU - Glazier, James A. AU - Stern, Claudio D. T2 - Science AB - The formation of body segments (somites) in vertebrate embryos is accompanied by molecular oscillations (segmentation clock). Interaction of this oscillator with a wave traveling along the body axis (the clock-and-wavefront model) is generally believed to control somite number, size, and axial identity. Here we show that a clock-and-wavefront mechanism is unnecessary for somite formation. Non-somite mesoderm treated with Noggin generates many somites that form simultaneously, without cyclic expression of Notch-pathway genes, yet have normal size, shape, and fate. These somites have axial identity: The Hox code is fixed independently of somite fate. However, these somites are not subdivided into rostral and caudal halves, which is necessary for neural segmentation. We propose that somites are self-organizing structures whose size and shape is controlled by local cell-cell interactions. DA - 2014/// PY - 2014/// DO - 10.1126/science.1247575 VL - 343 IS - 6172 SP - 791-795 ER - TY - JOUR TI - The rapidity dependence of the average transverse momentum in p + Pb collisions at the LHC: The Color Glass Condensate versus hydrodynamics AU - Bozek, Piotr AU - Bzdak, Adam AU - Skokov, Vladimir T2 - Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics AB - We show that in proton–lead (p + Pb) collisions at the LHC, the Color Glass Condensate (CGC) and hydrodynamics lead to qualitatively different behavior of the average transverse momentum, 〈p⊥〉, with the particle rapidity. In hydrodynamics, the 〈p⊥〉 decreases as one goes from zero rapidity, y=0, to the proton fragmentation region since the number of particles decreases. In contrast, in the CGC the saturation momentum increases as one goes from y=0 to the proton fragmentation region, and so the 〈p⊥〉 increases. At the LHC, the difference between the two models may be large enough to be tested experimentally. DA - 2014/// PY - 2014/// DO - 10.1016/j.physletb.2013.12.034 VL - 728 IS - 1 SP - 662-665 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84903641379&partnerID=MN8TOARS ER - TY - JOUR TI - Production of dilepton/photon in semi-quark gluon plasma AU - Hidaka, Yoshimasa AU - Lin, Shu AU - Pisarski, Robert D. AU - Satow, Daisuke AU - Skokov, Vladimir V. T2 - Nuclear Physics A AB - We consider the production of dilepton/photon in deconfined Quark Gluon Plasma (QGP). In the region of semi-QGP, effective color degrees of freedom are suppressed by a small value of the Polyakov loop. We find that the effect of the Polyakov loop leads to modest enhancement in the dilepton production rate but strong suppression in the photon production rate. The suppression of photon production in the QGP phase offers a possible explanation to the puzzle of photon elliptic flow. DA - 2014/// PY - 2014/// DO - 10.1016/j.nuclphysa.2014.10.014 VL - 931 SP - 681-685 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84922282044&partnerID=MN8TOARS KW - Semi-QGP KW - Polyakov loop KW - Electromagnetic radiation KW - Elliptic flow ER - TY - JOUR TI - Net baryon number probability distribution near the chiral phase transition AU - Morita, Kenji AU - Skokov, Vladimir AU - Friman, Bengt AU - Redlich, Krzysztof T2 - European Physical Journal C AB - We discuss the properties of the net baryon number probability distribution near the chiral phase transition to explore the effect of critical fluctuations. Our studies are performed within Landau theory, where the coefficients of the polynomial potential are parametrized, so as to reproduce the mean-field (MF), the $$Z(2)$$ , and the $$O(4)$$ scaling behaviors of the cumulants of the net baryon number. We show that in the critical region the structure of the probability distribution changes, depending on the values of the critical exponents. In the MF approach, as well as in the $$Z(2)$$ universality class, the contribution of the singular part of the thermodynamic potential tends to broaden the distribution. By contrast, in the model with $$O(4)$$ scaling, the contribution of the singular part results in a narrower net baryon number probability distribution with a wide tail. DA - 2014/// PY - 2014/// DO - 10.1140/epjc/s10052-013-2706-1 VL - 74 IS - 1 SP - 1-9 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84896715086&partnerID=MN8TOARS ER - TY - CONF TI - Describing pair production in inhomogeneous external fields with the Dirac-Heisenberg-Wigner formalism AU - Berényi, Dániel AU - Varró, Sándor AU - Lévai, Péter AU - Skokov, Vladimir V. A2 - Varró, S. A2 - Ádám, P. AB - In this contribution we present results on pair production from vacuum in QED in case of inhomogeneous external electric fields. The central tool of our description is the relativistic one particle single-time Wigner-function, that describes the evolution of the e+e− densities in phase-space. We compare the influence of homogeneous and inhomogeneous external fields, and find that the inhomogeneity near the Compton-scale increases particle production proportionally to the duration of the electric pulse. We also find, that when the inhomogeneity is restricted to a single direction, a significant component of the pair yield originates from the edge or surface where the electric field gradients are large, in agreement with the prediction of Heisenberg. C2 - 2014/// C3 - EPJ Web of Conferences DA - 2014/// DO - 10.1051/epjconf/20147803001 VL - 78 SP - 03001 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84907483884&partnerID=MN8TOARS ER - TY - JOUR TI - Comments about the electromagnetic field in heavy-ion collisions AU - McLerran, L. AU - Skokov, V. T2 - Nuclear Physics A AB - In this article we discuss the properties of electromagnetic fields in heavy-ion collisions and consequences for observables. We address quantitatively the issue of the magnetic field lifetime in a collision including the electric and chiral magnetic conductivities. We show that for reasonable parameters, the magnetic field created by spectators in a collision is not modified by the presence of matter. DA - 2014/// PY - 2014/// DO - 10.1016/j.nuclphysa.2014.05.008 VL - 929 SP - 184-190 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84918804088&partnerID=MN8TOARS KW - Magnetic field KW - Electromagnetic probes KW - Chiral magnetic wave ER - TY - JOUR TI - Collisional energy loss above the critical temperature in QCD AU - Lin, Shu AU - Pisarski, Robert D. AU - Skokov, Vladimir V. T2 - Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics AB - We compute the collisional energy loss for a heavy quark above the critical temperature in Quantum ChromoDynamics (QCD). We work in the semi Quark–Gluon Plasma, which assumes that this region is dominated by the non-trivial holonomy of the thermal Wilson line. Relative to the result of leading order in perturbation theory, at a fixed value of the coupling constant we generically find that collisional energy loss is suppressed by powers of the Polyakov loop, l<1. For small values of the loop, this suppression is linear when the heavy quark scatters off of light quarks, and quadratic when the heavy quark scatters off of gluons, or for Compton scattering. DA - 2014/// PY - 2014/// DO - 10.1016/j.physletb.2014.01.043 VL - 730 SP - 236-242 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84893613460&partnerID=MN8TOARS ER - TY - CONF TI - Video: Spatiotemporal dynamics of surfactant monolayers on Faraday waves AU - Strickland, Stephen AU - Shearer, Michael AU - Daniels, Karen C2 - 2014/11// C3 - 67th Annual Meeting of the APS Division of Fluid Dynamics - Gallery of Fluid Motion DA - 2014/11// DO - 10.1103/aps.dfd.2014.gfm.v0069 PB - American Physical Society ER - TY - JOUR TI - Surfactant spreading on a thin liquid film: reconciling models and experiments AU - Swanson, Ellen R. AU - Strickland, Stephen L. AU - Shearer, Michael AU - Daniels, Karen E. T2 - Journal of Engineering Mathematics AB - The spreading dynamics of surfactant molecules on a thin fluid layer is of both fundamental and practical interest. A mathematical model formulated by Gaver and Grotberg [J Fluid Mech 235:399–414, 1992] describing the spreading of a single layer of insoluble surfactant has become widely accepted, and several experiments on axisymmetric spreading have confirmed its predictions for both the height profile of the free surface and the spreading exponent (the radius of the circular area covered by surfactant grows as $$t^{1/4}$$ ). However, these prior experiments utilized primarily surfactant quantities exceeding (sometimes far exceeding) a monolayer. In this paper, we report that this regime is characterized by a mismatch between the timescales of the experiment and model and, additionally, find that the spatial distribution of surfactant molecules differs substantially from the model prediction. For experiments performed in the monolayer regime for which the model was developed, the surfactant layer is observed to have a spreading exponent of less than $$1/10$$ , far below the predicted value, and the surfactant distribution is also in disagreement. These findings suggest that the model is inadequate for describing the spreading of insoluble surfactants on thin fluid layers. DA - 2014/10// PY - 2014/10// DO - 10.1007/s10665-014-9735-0 VL - 94 IS - 1 SP - 63-79 KW - Experiment KW - Model KW - Surfactant KW - Thin liquid film ER - TY - JOUR TI - Pushing on a Nonlinear Material AU - Daniels, Karen T2 - Physics AB - Understanding how materials bend, stretch, or compress under an applied force (or “load”) is essential in the design of buildings, vehicles, and machines. These deformations can be straightforwardly calculated for materials like aluminum, glass, or carbon fiber, which tend to deform little and can therefore, to a good approximation, be treated as linear: doubling the load doubles the effect, like pulling on a spring. In contrast, scientists are still looking for the right way to perform the equivalent calculations on stretchy materials like rubbers and foams, and disconnected “granular” materials, such as soil, sand, and cereals. All of these materials share a common property that they are easy to deform by large amounts, and therefore, the linear approximation no longer applies. Corentin Coulais, now at the University of Leiden, the Netherlands, and his colleagues report experiments on a model “soil” in which they carefully tracked the soil’s elastic response to a force exerted on it via a series of very gradual steps [1]. By comparing their results to predictions of an idealized theory of granular materials, they were able to identify the theory’s strengths and limitations. The work could therefore help researchers develop more reliable methods for predicting the behavior of granular materials. Physicists have been working on a number of models to understand how granular materials cross the boundary between being able to support a load to failing completely—a problem of considerable importance for engineers who need to know if a soil can serve as a foundation for a house or bridge. A promising route is to describe this boundary as a “jamming transition” [2, 3]. In this picture, particles are collectively “jammed” into place by their neighbors. However, under an applied stress, they can dislodge from those cages and give way—an “unjamming” transition that is analogous to the melting of an ordinary solid. Similar to the thermodynamic equations of state, where compressibility is a known function of state variables like pressure or temperature, the theory behind jamming can predict material properties of granular materials, such as how they stiffen as a function of particle packing density. But, so far, most of these predictions assume that the particles are frictionless, leaving it unclear which aspects of the theory apply to real situations in which friction is present. Coulais and his colleagues focused their study on two key predictions from the jamming framework [2, 3] that had not been tested for real, frictional particles. The first is the values of the critical exponents that describe how elasticity and dilatancy (the tendency to decrease packing density under shear [4]) vary as the material is sheared near the jamming transition. The second is to measure how characteristic lengths, in this case the one that characterizes the onset of nonlinearity as a function of distance from a disturbance, depend on the proximity of the material to the jamming/unjamming transition. To test these predictions, they used an experimental technique that allowed them to measure the force on each particle as they pushed grains in a jammed state outward from the center of the material. Instead of actual grains of sand, they used 5-millimeter-diameter polymer disks, laying 8000 of these disks in a single, densely packed layer. The polymer disks are photoelastic, meaning they rotate the polarization of light passing through them by an amount that depends on how much stress they experience. When properly calibrated [5, 6], these patterns of birefringence (Fig. 1) can measure the force at each individual contact. To generate shear within the layer of disks, Coulais and his colleagues slowly inflated a 26-millimeter “balloon” at the center of the packed layer. They then observed the progressive changes in the particle-scale stress, strain, dilation, and pressure resulting from each inflation step. For the tiniest steps possible, the researchers observed that the grain-scale stresses (forces between particles) were a nonlinear function of the local strain (the amount the aggregate deformed). But with each subsequent step, the packing experienced a dilatancy-associated pressure rise and a decreased in stiffness. This dilatancy softening DA - 2014/11/3/ PY - 2014/11/3/ DO - 10.1103/Physics.7.113 VL - 7 J2 - Physics LA - en OP - SN - 1943-2879 UR - http://dx.doi.org/10.1103/Physics.7.113 DB - Crossref ER - TY - CONF TI - Ideas of four-fermion operators in electromagnetic form factor calculations AU - Ji, Chueng-Ryong AU - Bakker, Bernard L.G. AU - Choi, Ho-Meoyng AU - Suzuki, Alfredo T. T2 - MENU 2013 – 13th International Conference Meson-Nucleon Physics and the Structure of the Nucleon A2 - Battaglieri, M. A2 - D'Angelo, A. A2 - De Vita, R. A2 - Pascolini, A. A2 - Salmè, G. AB - Four-fermion operators have been utilized in the past to link the quark-exchange processes in the interaction of hadrons with the effective meson-exchange amplitudes. In this presentation, we apply the similar idea of Fierz rearrangement to the electromagnetic processes and focus on the electromagnetic form factors of nucleon and electron. We explain the motivation of using four-fermion operators and discuss the advantage of this method in computing electromagnetic processes. C2 - 2014/// C3 - EPJ Web of Conferences CY - Rome, Italy DA - 2014/// PY - 2013/9/30/ DO - 10.1051/EPJCONF/20147306006 VL - 73 SP - 06006 PB - EDP Sciences UR - http://dx.doi.org/10.1051/EPJCONF/20147306006 ER - TY - CONF TI - Kinematic Issues of GPDs in DVCS AU - Ji, C. R. AU - Bakker, B. L. G. C2 - 2014/// C3 - Nuclear Physics. B, Proceedings, Supplements DA - 2014/// VL - 251 SP - 75-80 ER - TY - JOUR TI - Topographic measurement of buried thin-film interfaces using a grazing resonant soft x-ray scattering technique AU - Gann, Eliot AU - Watson, Anne AU - Tumbleston, John R. AU - Cochran, Justin AU - Yan, Hongping AU - Wang, Cheng AU - Seok, Jaewook AU - Chabinyc, Michael AU - Ade, Harald T2 - PHYSICAL REVIEW B AB - The internal structures of thin films, particularly interfaces between different materials, are critical to system properties and performance across many disciplines, but characterization of buried interface topography is often unfeasible. In this work, we demonstrate that grazing resonant soft x-ray scattering (GRSoXS), a technique measuring diffusely scattered soft x rays from grazing incidence, can reveal the statistical topography of buried thin-film interfaces. By controlling and predicting the x-ray electric field intensity throughout the depth of the film and simultaneously the scattering contrast between materials, we are able to unambiguously identify the microstructure at different interfaces of a model polymer bilayer system. We additionally demonstrate the use of GRSoXS to selectively measure the topography of the surface and buried polymer-polymer interface in an organic thin-film transistor, revealing different microstructure and markedly differing evolution upon annealing. In such systems, where only indirect control of interface topography is possible, accurate measurement of the structure of interfaces for feedback is critically important. While we demonstrate the method here using organic materials, we also show that the technique is readily extendable to any thin-film system with elemental or chemical contrasts exploitable at absorption edges. DA - 2014/12/15/ PY - 2014/12/15/ DO - 10.1103/physrevb.90.245421 VL - 90 IS - 24 SP - SN - 1550-235X ER - TY - JOUR TI - Nuclear Data and the Oklo Natural Nuclear Reactors AU - Gould, C. R. AU - Sharapov, E. I. AU - Sonzogni, A. A. T2 - NUCLEAR DATA SHEETS AB - Data from the Oklo natural nuclear reactors have enabled some of the most sensitive terrestrial tests of time variation of dimensionless fundamental constants. The constraints on variation of αEM, the fine structure constant are particular good, but depend on the reliability of the nuclear data, and on the reliability of the modeling of the reactor environment. We briefly review the history of these tests and discuss our recent work in 1) attempting to better bound the temperatures at which the reactors operated, 2) investigating whether the γ-ray fluxes in the reactors could have contributed to changing lutetium isotopic abundances and 3) determining whether lanthanum isotopic data could provide an alternate estimate of the neutron fluence. DA - 2014/4// PY - 2014/4// DO - 10.1016/j.nds.2014.04.142 VL - 118 SP - 585-587 SN - 1095-9904 ER - TY - JOUR TI - Fluid Dynamics and Viscosity in Strongly Correlated Fluids AU - Schaefer, Thomas T2 - ANNUAL REVIEW OF NUCLEAR AND PARTICLE SCIENCE, VOL 64 AB - We review the modern view of fluid dynamics as an effective low-energy, long-wavelength theory of many-body systems at finite temperature. We introduce the concept of a nearly perfect fluid, defined by a ratio η/s of shear viscosity to entropy density of order ℏ/k B or less. Nearly perfect fluids exhibit hydrodynamic behavior at all distances down to the microscopic length scale of the fluid. We summarize arguments that suggest that there is fundamental limit to fluidity, and we review the current experimental situation of measurements of η/s in strongly coupled quantum fluids. DA - 2014/// PY - 2014/// DO - 10.1146/annurev-nucl-102313-025439 VL - 64 SP - 125-148 SN - 1545-4134 UR - http://inspirehep.net/record/1283620 KW - nonequilibrium physics KW - kinetic theory KW - holographic duality ER - TY - JOUR TI - Fermion-dimer scattering using an impurity lattice Monte Carlo approach and the adiabatic projection method AU - Elhatisari, Serdar AU - Lee, Dean T2 - PHYSICAL REVIEW C AB - We present lattice Monte Carlo calculations of fermion-dimer scattering in the limit of zero-range interactions using the adiabatic projection method. The adiabatic projection method uses a set of initial cluster states and Euclidean time projection to give a systematically improvable description of the low-lying scattering cluster states in a finite volume. We use L\"uscher's finite-volume relations to determine the s-wave, p-wave, and d-wave phase shifts. For comparison, we also compute exact lattice results using Lanczos iteration and continuum results using the Skorniakov-Ter-Martirosian equation. For our Monte Carlo calculations we use a new lattice algorithm called impurity lattice Monte Carlo. This algorithm can be viewed as a hybrid technique which incorporates elements of both worldline and auxiliary-field Monte Carlo simulations. DA - 2014/12/1/ PY - 2014/12/1/ DO - 10.1103/physrevc.90.064001 VL - 90 IS - 6 SP - SN - 1089-490X ER - TY - JOUR TI - Systematics of Scissors Mode in Gd Nuclei from Experiments with the DANCE Detector AU - Kroll, J. AU - Agvaanluvsan, U. AU - Baramsai, B. AU - Becker, J. A. AU - Becvar, F. AU - Bredeweg, T. A. AU - Chyzh, A. AU - Couture, A. AU - Dashdorj, D. AU - Haight, R. C. AU - Jandel, M. AU - Keksis, A. L. AU - Krticka, M. AU - Mitchell, G. E. AU - O'Donnell, J. M. AU - Parker, W. AU - Rundberg, R. S. AU - Ullmann, J. L. AU - Valenta, S. AU - Vieira, D. J. AU - Walker, C. L. AU - Wilhelmy, J. B. AU - Wouters, J. M. AU - Wu, C. Y. T2 - NUCLEAR DATA SHEETS AB - Multi-step cascade γ-ray spectra from neutron capture at isolated resonances of 152,154−158Gd nuclei were measured at the LANSCE/DANCE time-of-flight facility in Los Alamos National Laboratory. The main objective of these experiments was to obtain new information on photon strength functions with emphasis on the role of the M1 scissors mode vibration. An analysis of the data obtained shows that the scissors mode plays a significant role in the ground state transitions, as well as in the transitions populating all excited states of the studied nuclei. The estimates of the scissors mode strength indicate that for 157,159Gd this strength is significantly higher than in neighboring even–even nuclei 156,158Gd. The results are compared with the (γ,γ′) data for the ground-state scissors mode and the results from 3He-induced reactions. DA - 2014/5// PY - 2014/5// DO - 10.1016/j.nds.2014.08.044 VL - 119 SP - 158-161 SN - 1095-9904 ER - TY - JOUR TI - Spin measurements of n+Sr-87 for level density studies AU - Gunsing, F. AU - Fraval, K. AU - Mathelie, M. AU - Valenta, S. AU - Becvar, F. AU - Rusev, G. AU - Tonchev, A. P. AU - Mitchell, G. AU - Baramsai, B. AU - Altstadt, S. AU - Andrzejewski, J. AU - Audouin, L. AU - Barbagallo, M. AU - Becares, V. AU - Belloni, F. AU - Berthoumieux, E. AU - Billowes, J. AU - Boccone, V. T2 - Nuclear Data Sheets DA - 2014/// PY - 2014/// VL - 119 SP - E132-136 ER - TY - JOUR TI - Partial cross sections of neutron-induced reactions on Cu-nat at E-n=6, 8, 10, 12, 14, and 16 MeV for 0 nu beta beta background studies AU - Gooden, M. E. AU - Fallin, B. A. AU - Finch, S. W. AU - Kelley, J. H. AU - Howell, C. R. AU - Rusev, G. AU - Tonchev, A. P. AU - Tornow, W. AU - Stanislav, V. T2 - Nuclear Data Sheets DA - 2014/// PY - 2014/// VL - 119 SP - E121-123 ER - TY - JOUR TI - Neutron Capture Cross Sections and Gamma Emission Spectra from Neutron Capture on U-234,U-236,U-238 Measured with DANCE AU - Ullmann, J. L. AU - Mosby, S. AU - Bredeweg, T. A. AU - Couture, A. J. AU - Haight, R. C. AU - Jandel, M. AU - Kawano, T. AU - O'Donnell, J. M. AU - Rundberg, R. S. AU - Vieira, D. J. AU - Wilhelmy, J. B. AU - Wu, C. -Y. AU - Becker, J. A. AU - Chyzh, A. AU - Baramsai, B. AU - Mitchell, G. E. AU - Krticka, M. T2 - NUCLEAR DATA SHEETS DA - 2014/5// PY - 2014/5// DO - 10.1016/j.nds.2014.08.008 VL - 119 SP - 22-25 SN - 1095-9904 ER - TY - JOUR TI - Measurements of the (n,2n) Reaction Cross Section of Ta-181 from 8 to 15 MeV AU - Bhatia, C. AU - Gooden, M. E. AU - Tornow, W. AU - Tonchev, A. P. T2 - NUCLEAR DATA SHEETS AB - The cross section for the reaction 181Ta(n,2n)180Tag was measured from 8 to 15 MeV in small energy steps to resolve inconsistencies in the existing databases. The activation technique was used, and the 93.4 keV γ-ray from the decay of the 180Tag ground state was recorded with a HPGe detector. In addition, the γ-rays from the monitor reactions 27Al(n,α)24Na and 197Au(n,2n)196Au were measured for neutron fluence determination. As a cross check, a calibrated neutron detector was also used. The ENDF/B-VII.1 and TENDL-2011 evaluations are in considerable disagreement with the present data, which in turn agree very well with the majority of the existing data in the 14 MeV energy region. DA - 2014/5// PY - 2014/5// DO - 10.1016/j.nds.2014.08.049 VL - 119 SP - 176-178 SN - 1095-9904 ER - TY - JOUR TI - Ion distributions around left- and right-handed DNA and RNA duplexes: a comparative study AU - Pan, Feng AU - Roland, Christopher AU - Sagui, Celeste T2 - NUCLEIC ACIDS RESEARCH AB - The ion atmosphere around nucleic acids is an integral part of their solvated structure. However, detailed aspects of the ionic distribution are difficult to probe experimentally, and comparative studies for different structures of the same sequence are almost non-existent. Here, we have used large-scale molecular dynamics simulations to perform a comparative study of the ion distribution around (5′-CGCGCGCGCGCG-3′)2 dodecamers in solution in B-DNA, A-RNA, Z-DNA and Z-RNA forms. The CG sequence is very sensitive to ionic strength and it allows the comparison with the rare but important left-handed forms. The ions investigated include Na+, K+ and Mg2 +, with various concentrations of their chloride salts. Our results quantitatively describe the characteristics of the ionic distributions for different structures at varying ionic strengths, tracing these differences to nucleic acid structure and ion type. Several binding pockets with rather long ion residence times are described, both for the monovalent ions and for the hexahydrated Mg[(H2O)6]2+ ion. The conformations of these binding pockets include direct binding through desolvated ion bridges in the GpC steps in B-DNA and A-RNA; direct binding to backbone oxygens; binding of Mg[(H2O)6]2+ to distant phosphates, resulting in acute bending of A-RNA; tight ‘ion traps’ in Z-RNA between C-O2 and the C-O2′ atoms in GpC steps; and others. DA - 2014/12/16/ PY - 2014/12/16/ DO - 10.1093/nar/gku1107 VL - 42 IS - 22 SP - 13981-13996 SN - 1362-4962 ER - TY - JOUR TI - Fission product yield study of U-235, U-238 and Pu-239 using dual-fission ionization chambers AU - Bhatia, C. AU - Fallin, B. AU - Howell, C. AU - Tornow, W. AU - Gooden, M. AU - Kelley, J. AU - Arnold, C. AU - Bond, E. AU - Bredeweg, T. AU - Fowler, M. AU - Moody, W. AU - Rundberg, R. AU - Rusev, G. AU - Vieira, D. AU - Wilhelmy, J. AU - Becker, J. AU - Macri, R. AU - Ryan, C. AU - Sheets, S. AU - Stoyer, M. T2 - Nuclear Data Sheets DA - 2014/// PY - 2014/// VL - 119 SP - E324-327 ER - TY - JOUR TI - Additive-assisted supramolecular manipulation of polymer:fullerene blend phase morphologies and its influence on photophysical processes AU - Buchaca-Domingo, E. AU - Ferguson, A. J. AU - Jamieson, F. C. AU - McCarthy-Ward, T. AU - Shoaee, S. AU - Tumbleston, J. R. AU - Reid, O. G. AU - Yu, L. AU - Madec, M.-B. AU - Pfannmöller, M. AU - Hermerschmidt, F. AU - Schröder, R. R. AU - Watkins, S. E. AU - Kopidakis, N. AU - Portale, G. AU - Amassian, A. AU - Heeney, M. AU - Ade, H. AU - Rumbles, G. AU - Durrant, J. R. AU - Stingelin, N. T2 - Mater. Horiz. AB - The role of intermixed phases in organic solar cell blends is evaluated through manipulation of their number of phases. DA - 2014/// PY - 2014/// DO - 10.1039/C3MH00125C VL - 1 IS - 2 SP - 270-279 J2 - Mater. Horiz. LA - en OP - SN - 2051-6347 2051-6355 UR - http://dx.doi.org/10.1039/C3MH00125C DB - Crossref ER - TY - CONF TI - Ab initio nuclear structure from lattice effective field theory AU - Lee, D. C2 - 2014/// C3 - Xxxvi brazilian workshop on nuclear physics DA - 2014/// VL - 1625 SP - 3-9 ER - TY - JOUR TI - Thermonuclear reaction rate of Ne-18(alpha, p)Na-21 from Monte Carlo calculations AU - Mohr, P. AU - Longland, R. AU - Iliadis, C. T2 - PHYSICAL REVIEW C AB - The $^{18}\mathrm{Ne}(\ensuremath{\alpha},p)^{21}\mathrm{Na}$ reaction impacts the break-out from the hot CNO cycles to the $rp$ process in type-I x-ray bursts. We present a revised thermonuclear reaction rate, which is based on the latest experimental data. The new rate is derived from Monte Carlo calculations, taking into account the uncertainties of all nuclear physics input quantities. In addition, we present the reaction rate uncertainty and probability density versus temperature. Our results are also consistent with estimates obtained using different indirect approaches. DA - 2014/12/19/ PY - 2014/12/19/ DO - 10.1103/physrevc.90.065806 VL - 90 IS - 6 SP - SN - 1089-490X ER - TY - JOUR TI - Surface-Energy-Assisted Perfect Transfer of Centimeter-Scale Mono layer and Few-Layer MoS2 Films onto Arbitrary Substrates AU - Gurarslan, Alper AU - Yu, Yifei AU - Su, Liqin AU - Yu, Yiling AU - Suarez, Francisco AU - Yao, Shanshan AU - Zhu, Yong AU - Ozturk, Mehmet AU - Zhang, Yong AU - Cao, Linyou T2 - ACS NANO AB - The transfer of synthesized 2D MoS2 films is important for fundamental and applied research. However, it is problematic to translate the well-established transfer processes for graphene to MoS2 due to different growth mechanisms and surface properties. Here we demonstrate a surface-energy-assisted process that can perfectly transfer centimeter-scale monolayer and few-layer MoS2 films from original growth substrates onto arbitrary substrates with no observable wrinkles, cracks, and polymer residues. The unique strategies used in this process include leveraging the penetration of water between hydrophobic MoS2 films and hydrophilic growth substrates to lift off the films and dry transferring the film after the lift off. This is in stark contrast with the previous transfer process for synthesized MoS2 films, which explores the etching of the growth substrate by hot base solutions to lift off the films. Our transfer process can effectively eliminate the mechanical force caused by bubble generations, the attacks from chemical etchants, and the capillary force induced when transferring the film outside solutions as in the previous transfer process, which consists of the major causes for the previous unsatisfactory transfer. Our transfer process also benefits from using polystyrene (PS), instead of poly(methyl methacrylate) (PMMA) that was widely used previously, as the carrier polymer. PS can form more intimate interaction with MoS2 films than PMMA and is important for maintaining the integrity of the film during the transfer process. This surface-energy-assisted approach can be generally applied to the transfer of other 2D materials, such as WS2. DA - 2014/11// PY - 2014/11// DO - 10.1021/nn5057673 VL - 8 IS - 11 SP - 11522-11528 SN - 1936-086X KW - molybdenum disulfide KW - 2D materials KW - tungsten disulfide KW - surface energy KW - large scale ER - TY - JOUR TI - Spectroscopic ellipsometry - Past, present, and future AU - Aspnes, D. E. T2 - THIN SOLID FILMS AB - Since its initial development in the early 1970s, spectroscopic ellipsometry (SE) has evolved to become the primary technique for determining the intrinsic and structural properties of homogeneous and inhomogeneous materials in bulk and thin-film form, including properties of surfaces and interfaces. As an indispensible nondestructive approach for determining critical dimensions in integrated-circuit technology, its economic impact has been enormous. I review the development of theory as well as instrumentation, from the perspective of someone who has worked in SE essentially from its beginning. I provide comments about its present state, note some unresolved issues, then consider possible improvements and predict how the field is likely to evolve. DA - 2014/11/28/ PY - 2014/11/28/ DO - 10.1016/j.tsf.2014.03.056 VL - 571 SP - 334-344 SN - 0040-6090 KW - Spectroscopic KW - Ellipsometry KW - Critical dimension KW - Dielectric function KW - Optical properties ER - TY - JOUR TI - Medium effects and the shear viscosity of the dilute Fermi gas away from the conformal limit AU - Bluhm, M. AU - Schaefer, T. T2 - PHYSICAL REVIEW A AB - We study the shear viscosity of a dilute Fermi gas as a function of the scattering length in the vicinity of the unitarity limit. The calculation is based on kinetic theory, which provides a systematic approach to transport properties in the limit in which the fugacity $z=n\lambda^3/2$ is small. Here, $n$ is the density of the gas and $\lambda$ is the thermal wave length of the fermions. At leading order in the fugacity expansion the shear viscosity is independent of density, and the minimum shear viscosity is achieved at unitarity. At the next order medium effects modify the scattering amplitude as well as the quasi-particle energy and velocity. We show that these effects shift the minimum of the shear viscosity to the Bose-Einstein condensation (BEC) side of the resonance, in agreement with the result of recent experiments. DA - 2014/12/8/ PY - 2014/12/8/ DO - 10.1103/PhysRevA.90.063615 VL - 90 IS - 6 SP - SN - 1094-1622 UR - http://inspirehep.net/record/1321574 ER - TY - JOUR TI - Loop Electrostatics Modulates the Intersubunit Interactions in Ferritin AU - Bernacchioni, Caterina AU - Ghini, Veronica AU - Pozzi, Cecilia AU - Di Pisa, Flavio AU - Theil, Elizabeth C. AU - Turano, Paola T2 - ACS CHEMICAL BIOLOGY AB - Functional ferritins are 24-mer nanocages that self-assemble with extended contacts between pairs of 4-helix bundle subunits coupled in an antiparallel fashion along the C2 axes. The largest intersubunit interaction surface in the ferritin nanocage involves helices, but contacts also occur between groups of three residues midway in the long, solvent-exposed L-loops of facing subunits. The anchor points between intersubunit L-loop pairs are the salt bridges between the symmetry-related, conserved residues Asp80 and Lys82. The resulting quaternary structure of the cage is highly soluble and thermostable. Substitution of negatively charged Asp80 with a positively charged Lys in homopolymeric M ferritin introduces electrostatic repulsions that inhibit the oligomerization of the ferritin subunits. D80K ferritin was present in inclusion bodies under standard overexpressing conditions in E. coli, contrasting with the wild type protein. Small amounts of fully functional D80K nanocages formed when expression was slowed. The more positively charged surface results in a different solubility profile and D80K crystallized in a crystal form with a low density packing. The 3D structure of D80K variant is the same as wild type except for the side chain orientations of Lys80 and facing Lys82. When three contiguous Lys groups are introduced in D80KI81K ferritin variant the nanocage assembly is further inhibited leading to lower solubility and reduced thermal stability. Here, we demonstrate that the electrostatic pairing at the center of the L-loops has a specific kinetic role in the self-assembly of ferritin nanocages. DA - 2014/11// PY - 2014/11// DO - 10.1021/cb500431r VL - 9 IS - 11 SP - 2517-2525 SN - 1554-8937 ER - TY - JOUR TI - Design and performance of a cryogenic apparatus for magnetically trapping ultracold neutrons AU - Huffman, P. R. AU - Coakley, K. J. AU - Doyle, J. M. AU - Huffer, C. R. AU - Mumm, H. P. AU - O'Shaughnessy, C. M. AU - Schelhammer, K. W. AU - Seo, P-N. AU - Yang, L. T2 - CRYOGENICS AB - The cryogenic design and performance of an apparatus used to magnetically confine ultracold neutrons (UCN) is presented. The apparatus is part of an effort to measure the beta-decay lifetime of the free neutron and is comprised of a high-current superconducting magnetic trap that surrounds ∼21 l of isotopically pure 4He cooled to approximately 250 mK. A 0.89 nm neutron beam can enter the apparatus from one end of the magnetic trap and a light collection system allows visible light generated within the helium by decays to be transported to detectors at room temperature. Two cryocoolers are incorporated to reduce liquid helium consumption. DA - 2014/// PY - 2014/// DO - 10.1016/j.cryogenics.2014.09.008 VL - 64 SP - 40-50 SN - 1879-2235 KW - Neutron lifetime KW - Magnetic trap KW - Cryocooler KW - Ultracold neutrons ER - TY - JOUR TI - Combined direct- and reciprocal-space approach for converting spectra to energy scales with negligible loss of information AU - Aspnes, D. E. AU - Choi, S. G. T2 - THIN SOLID FILMS AB - Extracting information from spectra is best done in reciprocal space, provided that baseline effects, information, and noise can be localized in low-, intermediate-, and high-index coefficients, respectively. In optical spectroscopy this occurs if data are equally spaced in energy E. We develop and quantify a procedure to generate such spectra from any initial distribution of wavelengths λ. Reciprocal-space analysis shows that this transformation can be accomplished with negligible loss of information. The procedure can be applied to any system where the Fourier coefficients of the result can be separated as noted above. DA - 2014/11/28/ PY - 2014/11/28/ DO - 10.1016/j.tsf.2013.11.028 VL - 571 SP - 506-508 SN - 1879-2731 KW - Ellipsometry KW - Interpolation KW - Optical spectra KW - Wavelength KW - Fourier analysis ER - TY - JOUR TI - Blending with Non-responsive Polymers to Incorporate Nanoparticles into Shape-Memory Materials and Enable Photothermal Heating: The Effects of Heterogeneous Temperature Distribution AU - Abbott, David B. AU - Maity, Somsubhra AU - Burkey, Mary T. AU - Gorga, Russell E. AU - Bochinski, Jason R. AU - Clarke, Laura I. T2 - MACROMOLECULAR CHEMISTRY AND PHYSICS AB - Blending a shape‐memory polymer (SMP) (e.g., thermoplastic polyurethane) with an immiscible carrier polymer (e.g., poly(ethylene oxide) (PEO) or poly(vinyl alcohol) (PVA)) containing dispersed metal nanoparticles (AuNPs) is a simple approach to enable actuation via photothermal heating. For blends containing up to 90% carrier polymer, the shape‐memory capability can be thermally triggered either conventionally or utilizing internal heating via application of light that is resonant with the particle's surface plasmon resonance. When incorporating nanoparticles in this manner, neither chemical modification of the shape‐memory moiety nor solvation of the SMP is necessary. Actuation times are determined by the particular heterogeneous temperature distribution, which generally occurs under both conventional and photothermal heating methods, but with different spatial patterns. Blending an SMP with PEO containing AuNPs imposes a higher transition temperature (the melting point of PEO), enabling heat generated within the nanoparticle‐containing regions to equilibrate throughout the sample, resulting in performance under photothermal conditions comparable with that achieved in a conventional heating approach. SMP:PVA blends actuate at the SMP transition temperature and the response depends on the size of phase segregation between the PVA and SMP; when decreasing the characteristic size of the segregated regions, heat is efficiently transferred and optimal photothermal performance is observed. image DA - 2014/12// PY - 2014/12// DO - 10.1002/macp.201400386 VL - 215 IS - 23 SP - 2345-2356 SN - 1521-3935 KW - blends KW - metal nanoparticles KW - photothermal heating KW - polymeric materials KW - shape-memory materials ER - TY - JOUR TI - Viscosity spectral function of a scale invariant nonrelativistic fluid from holography AU - Schafer, T. T2 - Physical Review. D, Particles, Fields, Gravitation, and Cosmology DA - 2014/// PY - 2014/// VL - 90 IS - 10 ER - TY - CONF TI - Hidden color AU - Ji, C. R. C2 - 2014/// C3 - 1st tensor polarized solid target workshop DA - 2014/// VL - 543 ER - TY - JOUR TI - Determination of freeze-out conditions from fluctuation observables measured at RHIC AU - Bluhm, M. AU - Alba, P. AU - Alberico, W. AU - Bellwied, R. AU - Sarti, V. Mantovani AU - Nahrgang, M. AU - Ratti, C. T2 - NUCLEAR PHYSICS A AB - We extract chemical freeze-out conditions via a thermal model approach from fluctuation observables measured at RHIC and compare with results from lattice QCD and statistical hadronization model fits. The possible influence of additional critical and non-critical fluctuation sources not accounted for in our analysis is discussed. DA - 2014/11// PY - 2014/11// DO - 10.1016/j.nuclphysa.2014.08.016 VL - 931 SP - 814-819 SN - 1873-1554 KW - Chemical freeze-out KW - Fluctuations KW - QCD phase diagram ER - TY - CONF TI - Ultrafast valley relaxation dynamics in single layer semiconductors AU - Barrette, A. AU - Mai, C. AU - Yu, Y. F. AU - Semenov, Y. AU - Jin, Z. H. AU - Kim, K. W. AU - Cao, L. Y. AU - Gundogdu, K. C2 - 2014/// C3 - Ultrafast nonlinear imaging and spectroscopy ii DA - 2014/// VL - 9198 ER - TY - JOUR TI - Ultracold neutron source at the PULSTAR reactor: Engineering design and cryogenic testing AU - Korobkina, E. AU - Medlin, G. AU - Wehring, B. AU - Hawari, A. I. AU - Huffman, P. R. AU - Young, A. R. AU - Beaumont, B. AU - Palmquist, G. T2 - NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT AB - Construction is completed and commissioning is in progress for an ultracold neutron (UCN) source at the PULSTAR reactor on the campus of North Carolina State University. The source utilizes two stages of neutron moderation, one in heavy water at room temperature and the other in solid methane at ~40K, followed by a converter stage, solid deuterium at 5 K, that allows a single down scattering of cold neutrons to provide UCN. The UCN source rolls into the thermal column enclosure of the PULSTAR reactor, where neutrons will be delivered from a bare face of the reactor core by streaming through a graphite-lined assembly. The source infrastructure, i.e., graphite-lined assembly, heavy-water system, gas handling system, and helium liquefier cooling system, has been tested and all systems operate as predicted. The research program being considered for the PULSTAR UCN source includes the physics of UCN production, fundamental particle physics, and material surface studies of nanolayers containing hydrogen. In the present paper we report details of the engineering and cryogenic design of the facility as well as results of critical commissioning tests without neutrons. DA - 2014/12/11/ PY - 2014/12/11/ DO - 10.1016/j.nima.2014.08.016 VL - 767 SP - 169–175 SN - 1872-9576 KW - Ultracold neutrons KW - Moderation KW - Nuclear reactor KW - Ortho-para conversion KW - Raman spectroscopy ER - TY - CONF TI - Time and neighbor interaction in resonance Raman spectroscopy AU - Hallen, Hans AU - Niu, Shupeng AU - Li, Ling AB - We study systems in which the resonance Raman process is fast due to the requirement for phonon involvement in the absorption. The resonance enhancement is found to track the isolated molecule, or vapor phase, absorption since the molecule does not have time to exchange energy with its neighbors. This corroborates with studies of pre-resonance, where Heisenberg’s uncertainty principle enforces a rapid process, but differs from resonance on electronically allowed transitions, where the resonance allows a relatively prolonged interaction. High resolution excitation spectroscopy reveals large gains and narrow features usually associated with the isolated molecule. Vibration energies shift as the resonance is approached and the excited state vibration levels are probed. Several multiplets and overtone modes are enhanced along with the strongly coupled ring-breathing mode in aromatic molecules. C2 - 2014/// C3 - Proc. SPIE DA - 2014/// DO - 10.1117/12.2062001 VL - 9198 SP - 91980F (8 pp.) - UR - http://dx.doi.org/10.1117/12.2062001 N1 - – An invited paper RN - – An invited paper KW - Resonance Raman KW - plasmon enhancement KW - gradient field Raman KW - nano-antenna KW - phonon allowed transitions KW - tunable excitation KW - excited state spectroscopy ER - TY - JOUR TI - REVERSE AND FORWARD SHOCK X-RAY EMISSION IN AN EVOLUTIONARY MODEL OF SUPERNOVA REMNANTS UNDERGOING EFFICIENT DIFFUSIVE SHOCK ACCELERATION AU - Lee, Shiu-Hang AU - Patnaude, Daniel J. AU - Ellison, Donald C. AU - Nagataki, Shigehiro AU - Slane, Patrick O. T2 - ASTROPHYSICAL JOURNAL AB - We present new models for the forward and reverse shock thermal X-ray emission from core-collapse and Type Ia supernova remnants (SNRs) that include the efficient production of cosmic rays (CR) via nonlinear diffusive shock acceleration (DSA). Our CR-hydro-NEI code takes into account non-equilibrium ionization, hydrodynamic effects of efficient CR production on the SNR evolution, and collisional temperature equilibration among heavy ions and electrons in both the shocked supernova (SN) ejecta and the shocked circumstellar material. While X-ray emission is emphasized here, our code self-consistently determines both thermal and non-thermal broadband emission from radio to TeV energies. We include Doppler broadening of the spectral lines by thermal motions of the ions and by the remnant expansion. We study, in general terms, the roles that the ambient environment, progenitor models, temperature equilibration, and processes related to DSA have on the thermal and non-thermal spectra. The study of X-ray line emission from young SNRs is a powerful tool for determining specific SN elemental contributions and for providing critical information that helps to understand the type and energetics of the explosion, the composition of the ambient medium in which the SN exploded, and the ionization and dynamics of the hot plasma in the shocked SN ejecta and interstellar medium. With the approaching launch of the next-generation X-ray satellite Astro-H, observations of spectral lines with unprecedented high resolution will become a reality. Our self-consistent calculations of the X-ray spectra from various progenitors will help interpret future observations of SNRs. DA - 2014/8/20/ PY - 2014/8/20/ DO - 10.1088/0004-637x/791/2/97 VL - 791 IS - 2 SP - SN - 1538-4357 KW - acceleration of particles KW - ISM: supernova remnants KW - shock waves ER - TY - JOUR TI - Quantum Monte Carlo study of one-dimensional transition-metal organometallic cluster systems and their suitability as spin filters AU - Horvathova, L. AU - Derian, R. AU - Mitas, L. AU - Stich, I. T2 - PHYSICAL REVIEW B AB - We present calculations of electronic and magnetic structures of vanadium-benzene multidecker clusters V$_{n}$Bz$_{n+1}$ ($n$ = 1 - 3) using advanced quantum Monte Carlo methods. These and related systems have been identified as prospective spin filters in spintronic applications, assuming that their ground states are half-metallic ferromagnets. Although we find that magnetic properties of these multideckers are consistent with ferromagnetic coupling, their electronic structures do not appear to be half-metallic as previously assumed. In fact, they are ferromagnetic insulators with large and broadly similar $\uparrow$-/$\downarrow$-spin gaps. This makes the potential of these and related materials as spin filtering devices very limited, unless they are further modified or functionalized. DA - 2014/9/11/ PY - 2014/9/11/ DO - 10.1103/physrevb.90.115414 VL - 90 IS - 11 SP - SN - 2469-9969 ER - TY - JOUR TI - Quantum Monte Carlo for noncovalent interactions: an efficient protocol attaining benchmark accuracy AU - Dubecky, Matus AU - Derian, Rene AU - Jurecka, Petr AU - Mitas, Lubos AU - Hobza, Pavel AU - Otyepka, Michal T2 - PHYSICAL CHEMISTRY CHEMICAL PHYSICS AB - A benchmark quantum Monte Carlo protocol with a favorable scaling is reported and extensively tested. DA - 2014/// PY - 2014/// DO - 10.1039/c4cp02093f VL - 16 IS - 38 SP - 20915-20923 SN - 1463-9084 ER - TY - JOUR TI - Morphology linked to miscibility in highly amorphous semi-conducting polymer/fullerene blends AU - Tumbleston, John R. AU - Yang, Liqiang AU - You, Wei AU - Ade, Harald T2 - POLYMER AB - Molecular miscibility is a defining property of mixtures of electron-donating polymers and electron-accepting fullerenes used in the photoactive layer of bulk heterojunction (BHJ) organic solar cells. Even though miscibility of fullerene in the polymer is a commonly observed property, quantitative measurements have unknown connections with other morphological properties such as domain size and domain purity. By varying the amount of fullerene loading in BHJ thin films, we show that morphological properties are related to miscibility via straightforward relationships. In particular, miscibility influences the sensitivity of domain spacing to fullerene loading and determines the domain volume fractions and the residual fullerene content in the mixed polymer-rich phase in devices. Not only does this work show the relationships between miscibility and morphology, but it also highlights the general importance in determining miscibility levels in BHJ systems in order to target optimum morphologies and domain purities. DA - 2014/9/15/ PY - 2014/9/15/ DO - 10.1016/j.polymer.2014.07.051 VL - 55 IS - 19 SP - 4884-4889 SN - 1873-2291 KW - Organic solar cells KW - X-ray scattering KW - Bulk heterojunction ER - TY - JOUR TI - Magnetic dipole strength in Xe-128 and Xe-134 in the spin-flip resonance region AU - Massarczyk, R. AU - Rusev, G. AU - Schwengner, R. AU - Doenau, F. AU - Bhatia, C. AU - Gooden, M. E. AU - Kelley, J. H. AU - Tonchev, A. P. AU - Tornow, W. T2 - PHYSICAL REVIEW C AB - The magnetic dipole strength in the energy region of the spin-flip resonance is investigated in $^{128}\mathrm{Xe}$ and $^{134}\mathrm{Xe}$ using quasimonoenergetic and linearly polarized $\ensuremath{\gamma}$-ray beams at the High-Intensity $\ensuremath{\gamma}$-Ray Source facility in Durham, North Carolina, USA. Absorption cross sections were deduced for the magnetic and electric and dipole strength distributions separately for various intervals of excitation energy, including the strength of states in the unresolved quasicontinuum. The magnetic dipole strength distributions show structures resembling a resonance in the spin-flip region around an excitation energy of 8 MeV. The electric dipole strength distributions obtained from the present experiments are in agreement with the ones deduced from an earlier experiment using broad-band bremsstrahlung instead of a quasimonoenergetic beam. The experimental magnetic and electric dipole strength distributions are compared with phenomenological approximations and with predictions of a quasiparticle random phase approximation in a deformed basis. DA - 2014/11/10/ PY - 2014/11/10/ DO - 10.1103/physrevc.90.054310 VL - 90 IS - 5 SP - SN - 1089-490X ER - TY - JOUR TI - Interplay of Solvent Additive Concentration and Active Layer Thickness on the Performance of Small Molecule Solar Cells AU - Love, John A. AU - Collins, Samuel D. AU - Nagao, Ikuhiro AU - Mukherjee, Subhrangsu AU - Ade, Harald AU - Bazan, Guillermo C. AU - Nguyen, Thuc-Quyen T2 - ADVANCED MATERIALS AB - A relationship between solvent additive concentration and active layer thickness in small-molecule solar cells is investigated. Specifically, the additive concentration must scale with the amount of semiconductor material and not as absolute concentration in solution. Devices with a wide range of active layers with thickness up to 200 nm can readily achieve efficiencies close to 6% when the right concentration of additive is used. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article. DA - 2014/11/19/ PY - 2014/11/19/ DO - 10.1002/adma.201402403 VL - 26 IS - 43 SP - 7308-7316 SN - 1521-4095 ER - TY - JOUR TI - HIGH-ENERGY X-RAY IMAGING OF THE PULSAR WIND NEBULA MSH 15-52: CONSTRAINTS ON PARTICLE ACCELERATION AND TRANSPORT AU - An, Hongjun AU - Madsen, Kristin K. AU - Reynolds, Stephen P. AU - Kaspi, Victoria M. AU - Harrison, Fiona A. AU - Boggs, Steven E. AU - Christensen, Finn E. AU - Craig, William W. AU - Fryer, Chris L. AU - Grefenstette, Brian W. AU - Hailey, Charles J. AU - Mori, Kaya AU - Stern, Daniel AU - Zhang, William W. T2 - ASTROPHYSICAL JOURNAL AB - We present the first images of the pulsar wind nebula (PWN) MSH 15-52 in the hard X-ray band (>8 keV), as measured with the Nuclear Spectroscopic Telescope Array (NuSTAR). Overall, the morphology of the PWN as measured by NuSTAR in the 3-7 keV band is similar to that seen in Chandra high-resolution imaging. However, the spatial extent decreases with energy, which we attribute to synchrotron energy losses as the particles move away from the shock. The hard-band maps show a relative deficit of counts in the northern region towards the RCW 89 thermal remnant, with significant asymmetry. We find that the integrated PWN spectra measured with NuSTAR and Chandra suggest that there is a spectral break at 6 keV which may be explained by a break in the synchrotron-emitting electron distribution at ~200 TeV and/or imperfect cross calibration. We also measure spatially resolved spectra, showing that the spectrum of the PWN softens away from the central pulsar B1509-58, and that there exists a roughly sinusoidal variation of spectral hardness in the azimuthal direction. We discuss the results using particle flow models. We find non-monotonic structure in the variation with distance of spectral hardness within 50" of the pulsar moving in the jet direction, which may imply particle and magnetic-field compression by magnetic hoop stress as previously suggested for this source. We also present 2-D maps of spectral parameters and find an interesting shell-like structure in the NH map. We discuss possible origins of the shell-like structure and their implications. DA - 2014/10/1/ PY - 2014/10/1/ DO - 10.1088/0004-637x/793/2/90 VL - 793 IS - 2 SP - SN - 1538-4357 KW - ISM: individual objects (G320.4-1.2) KW - ISM: jets and outflows KW - ISM: supernova remnants KW - pulsars: individual (PSR B1509-58) KW - stars: neutron KW - X-rays: ISM ER - TY - JOUR TI - Gas source molecular beam epitaxy of scandium nitride on silicon carbide and gallium nitride surfaces AU - King, Sean W. AU - Davis, Robert F. AU - Nemanich, Robert J. T2 - JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A AB - Scandium nitride (ScN) is a group IIIB transition metal nitride semiconductor with numerous potential applications in electronic and optoelectronic devices due to close lattice matching with gallium nitride (GaN). However, prior investigations of ScN have focused primarily on heteroepitaxial growth on substrates with a high lattice mismatch of 7%–20%. In this study, the authors have investigated ammonia (NH3) gas source molecular beam epitaxy (NH3-GSMBE) of ScN on more closely lattice matched silicon carbide (SiC) and GaN surfaces (&lt;3% mismatch). Based on a thermodynamic analysis of the ScN phase stability window, NH3-GSMBE conditions of 10−5–10−4 Torr NH3 and 800–1050 °C where selected for initial investigation. In-situ x-ray photoelectron spectroscopy (XPS) and ex-situ Rutherford backscattering measurements showed all ScN films grown using these conditions were stoichiometric. For ScN growth on 3C-SiC (111)-(√3 × √3)R30° carbon rich surfaces, the observed attenuation of the XPS Si 2p and C 1s substrate core levels with increasing ScN thickness indicated growth initiated in a layer-by-layer fashion. This was consistent with scanning electron microscopy (SEM) images of 100–200 nm thick films that revealed featureless surfaces. In contrast, ScN films grown on 3C-SiC (111)-(3 × 3) and 3C-SiC (100)-(3 × 2) silicon rich surfaces were found to exhibit extremely rough surfaces in SEM. ScN films grown on both 3C-SiC (111)-(√3 × √3)R30° and 2H-GaN (0001)-(1 × 1) epilayer surfaces exhibited hexagonal (1 × 1) low energy electron diffraction patterns indicative of (111) oriented ScN. X-ray diffraction ω-2θ rocking curve scans for these same films showed a large full width half maximum of 0.29° (1047 arc sec) consistent with transmission electron microscopy images that revealed the films to be poly-crystalline with columnar grains oriented at ≈15° to the [0001] direction of the 6H-SiC (0001) substrate. In-situ reflection electron energy loss spectroscopy measurements determined the band-gap for the NH3-GSMBE ScN films to be 1.5 ± 0.3 eV, and thermal probe measurements indicated all ScN films to be n-type. The four point probe sheet resistance of the ScN films was observed to increase with decreasing growth temperature and decreased with unintentional oxygen incorporation. Hg probe capacitance–voltage measurements indicated ND-NA decreased with decreasing growth temperature from 1019 to 1020/cm3 for the lowest resistivity films to ≅5 × 1016/cm3 for the highest resistivity films. In-situ ultraviolet photoelectron spectroscopy measurements additionally showed the valence band maximum moving from 1.4 to 0.8 eV below the Fermi level with decreasing growth temperature consistent with the increased resistivity and reduction in carrier concentration. These results suggest that additional reductions in ScN carrier concentrations can be achieved via continued optimization of ScN growth conditions and selection of substrate orientation and surface termination. DA - 2014/11// PY - 2014/11// DO - 10.1116/1.4894816 VL - 32 IS - 6 SP - SN - 1520-8559 ER - TY - JOUR TI - Desorption and sublimation kinetics for fluorinated aluminum nitride surfaces AU - King, Sean W. AU - Davis, Robert F. AU - Nemanich, Robert J. T2 - JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A AB - The adsorption and desorption of halogen and other gaseous species from surfaces is a key fundamental process for both wet chemical and dry plasma etch and clean processes utilized in nanoelectronic fabrication processes. Therefore, to increase the fundamental understanding of these processes with regard to aluminum nitride (AlN) surfaces, temperature programmed desorption (TPD) and x-ray photoelectron spectroscopy (XPS) have been utilized to investigate the desorption kinetics of water (H2O), fluorine (F2), hydrogen (H2), hydrogen fluoride (HF), and other related species from aluminum nitride thin film surfaces treated with an aqueous solution of buffered hydrogen fluoride (BHF) diluted in methanol (CH3OH). Pre-TPD XPS measurements of the CH3OH:BHF treated AlN surfaces showed the presence of a variety of Al-F, N-F, Al-O, Al-OH, C-H, and C-O surfaces species in addition to Al-N bonding from the AlN thin film. The primary species observed desorbing from these same surfaces during TPD measurements included H2, H2O, HF, F2, and CH3OH with some evidence for nitrogen (N2) and ammonia (NH3) desorption as well. For H2O, two desorption peaks with second order kinetics were observed at 195 and 460 °C with activation energies (Ed) of 51 ± 3 and 87 ± 5 kJ/mol, respectively. Desorption of HF similarly exhibited second order kinetics with a peak temperature of 475 °C and Ed of 110 ± 5 kJ/mol. The TPD spectra for F2 exhibited two peaks at 485 and 585 °C with second order kinetics and Ed of 62 ± 3 and 270 ± 10 kJ/mol, respectively. These values are in excellent agreement with previous Ed measurements for desorption of H2O from SiO2 and AlFx from AlN surfaces, respectively. The F2 desorption is therefore attributed to fragmentation of AlFx species in the mass spectrometer ionizer. H2 desorption exhibited an additional high temperature peak at 910 °C with Ed = 370 ± 10 kJ/mol that is consistent with both the dehydrogenation of surface AlOH species and H2 assisted sublimation of AlN. Similarly, N2 exhibited a similar higher temperature desorption peak with Ed = 535 ± 40 kJ/mol that is consistent with the activation energy for direct sublimation of AlN. DA - 2014/9// PY - 2014/9// DO - 10.1116/1.4891650 VL - 32 IS - 5 SP - SN - 1520-8559 ER - TY - JOUR TI - Unraveling secrets of telomeres: One molecule at a time AU - Lin, Jiangguo AU - Kaur, Parminder AU - Countryman, Preston AU - Opresko, Patricia L. AU - Wang, Hong T2 - DNA REPAIR AB - Telomeres play important roles in maintaining the stability of linear chromosomes. Telomere maintenance involves dynamic actions of multiple proteins interacting with long repetitive sequences and complex dynamic DNA structures, such as G-quadruplexes, T-loops and t-circles. Given the heterogeneity and complexity of telomeres, single-molecule approaches are essential to fully understand the structure-function relationships that govern telomere maintenance. In this review, we present a brief overview of the principles of single-molecule imaging and manipulation techniques. We then highlight results obtained from applying these single-molecule techniques for studying structure, dynamics and functions of G-quadruplexes, telomerase, and shelterin proteins. DA - 2014/8// PY - 2014/8// DO - 10.1016/j.dnarep.2014.01.012 VL - 20 SP - 142-153 SN - 1568-7856 KW - Telomeres KW - Single-molecule imaging KW - Atomic force microscopy KW - Fluorescence microscopy KW - FRET KW - Laser tweezers KW - Magnetic tweezers KW - Protein DNA interactions ER - TY - JOUR TI - Turbulence and its effects upon neutrinos AU - Kneller, J. P. AU - McLaughlin, G. C. AU - Patton, K. M. T2 - WORKSHOP ON DARK MATTER, NEUTRINO PHYSICS AND ASTROPHYSICS CETUP 2013: VIITH INTERNATIONAL CONFERENCE ON INTERCONNECTIONS BETWEEN PARTICLE PHYSICS AND COSMOLOGY PPC 2013 AB - As a neutrino passes through turbulent matter, large amplitude transitions between its eigenstates can occur. These transitions can be modeled as like those of an irradiated polarized atom and we investigate this connection both analytically and numerically. We find a simple theory that makes use of the Rotating Wave Approximation can make predictions for the amplitudes and wavelengths of the transitions that agree very well with those from the numerical solutions. DA - 2014/// PY - 2014/// DO - 10.1063/1.4883432 VL - 1604 SP - 204-209 SN - 0094-243X UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84903938255&partnerID=MN8TOARS KW - neutrinos KW - turbulence ER - TY - JOUR TI - Single molecule studies of DNA mismatch repair AU - Erie, Dorothy A. AU - Weninger, Keith R. T2 - DNA REPAIR AB - DNA mismatch repair, which involves is a widely conserved set of proteins, is essential to limit genetic drift in all organisms. The same system of proteins plays key roles in many cancer related cellular transactions in humans. Although the basic process has been reconstituted in vitro using purified components, many fundamental aspects of DNA mismatch repair remain hidden due in part to the complexity and transient nature of the interactions between the mismatch repair proteins and DNA substrates. Single molecule methods offer the capability to uncover these transient but complex interactions and allow novel insights into mechanisms that underlie DNA mismatch repair. In this review, we discuss applications of single molecule methodology including electron microscopy, atomic force microscopy, particle tracking, FRET, and optical trapping to studies of DNA mismatch repair. These studies have led to formulation of mechanistic models of how proteins identify single base mismatches in the vast background of matched DNA and signal for their repair. DA - 2014/8// PY - 2014/8// DO - 10.1016/j.dnarep.2014.03.007 VL - 20 SP - 71-81 SN - 1568-7856 KW - Mismatch repair KW - One-dimensional diffusion KW - Single-molecule fluorescence KW - FRET KW - Atomic force microscopy KW - AFM KW - Single particle tracking KW - Protein-DNA interactions ER - TY - JOUR TI - Nonlinear elasticity of microsphere heaps AU - Ortiz, C. P. AU - Daniels, K. E. AU - Riehn, R. T2 - Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics AB - Thermal fluctuations, geometric exclusion, and external driving all govern the mechanical response of dense particulate suspensions. Here, we measure the stress-strain response of quasi-two-dimensional flow-stabilized microsphere heaps in a regime in which all three effects are present using a microfluidic device. We observe that the elastic modulus and the mean interparticle separation of the heaps are tunable via the confining stress provided by the fluid flow. Furthermore, the measured stress-strain curves exhibit a universal nonlinear shape, which can be predicted from a thermal van der Waals equation of state with excluded volume. This analysis indicates that many-body interactions contribute a significant fraction of the stress supported by the heap. DA - 2014/// PY - 2014/// DO - 10.1103/physreve.90.022304 VL - 90 IS - 2 SP - 9 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000341301600006&KeyUID=WOS:000341301600006 ER - TY - JOUR TI - Neutrinos and nucleosynthesis in core-collapse supernovae AU - Froehlich, C. AU - Casanova, J. AU - Hempel, M. AU - Liebendoerfer, M. AU - Melton, C. A. AU - Perego, A. T2 - WORKSHOP ON DARK MATTER, NEUTRINO PHYSICS AND ASTROPHYSICS CETUP 2013: VIITH INTERNATIONAL CONFERENCE ON INTERCONNECTIONS BETWEEN PARTICLE PHYSICS AND COSMOLOGY PPC 2013 AB - Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation C. Fröhlich, J. Casanova, M. Hempel, M. Liebendörfer, C. A. Melton, A. Perego; Neutrinos and nucleosynthesis in core-collapse supernovae. AIP Conf. Proc. 24 June 2014; 1604 (1): 178–184. https://doi.org/10.1063/1.4883428 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioAIP Conference Proceedings Search Advanced Search |Citation Search DA - 2014/// PY - 2014/// DO - 10.1063/1.4883428 VL - 1604 SP - 178-184 SN - 0094-243X KW - nucleosynthesis KW - core collapse supernovae ER - TY - JOUR TI - Mobility-Controlled Performance of Thick Solar Cells Based on Fluorinated Copolymers AU - Li, Wentao AU - Abrecht, Steve AU - Yang, Liqiang AU - Roland, Steffen AU - Tumbleston, John R. AU - McAfee, Terry AU - Yan, Liang AU - Kelly, Mary Allison AU - Ade, Harald AU - Neher, Dieter AU - You, Wei T2 - JOURNAL OF THE AMERICAN CHEMICAL SOCIETY AB - Developing novel materials and device architectures to further enhance the efficiency of polymer solar cells requires a fundamental understanding of the impact of chemical structures on photovoltaic properties. Given that device characteristics depend on many parameters, deriving structure–property relationships has been very challenging. Here we report that a single parameter, hole mobility, determines the fill factor of several hundred nanometer thick bulk heterojunction photovoltaic devices based on a series of copolymers with varying amount of fluorine substitution. We attribute the steady increase of hole mobility with fluorine content to changes in polymer molecular ordering. Importantly, all other parameters, including the efficiency of free charge generation and the coefficient of nongeminate recombination, are nearly identical. Our work emphasizes the need to achieve high mobility in combination with strongly suppressed charge recombination for the thick devices required by mass production technologies. DA - 2014/11/5/ PY - 2014/11/5/ DO - 10.1021/ja5067724 VL - 136 IS - 44 SP - 15566-15576 SN - 0002-7863 ER - TY - JOUR TI - High-Efficiency All-Polymer Solar Cells Based on a Pair of Crystalline Low-Bandgap Polymers AU - Mu, Cheng AU - Liu, Peng AU - Ma, Wei AU - Jiang, Kui AU - Zhao, Jingbo AU - Zhang, Kai AU - Chen, Zhihua AU - Wei, Zhanhua AU - Yi, Ya AU - Wang, Jiannong AU - Yang, Shihe AU - Huang, Fei AU - Facchetti, Antonio AU - Ade, Harald AU - Yan, He T2 - ADVANCED MATERIALS AB - All-polymer solar cells based on a pair of crystalline low-bandgap polymers (NT and N2200) are demonstrated to achieve a high short-circuit current density of 11.5 mA cm-2 and a power conversion efficiency of up to 5.0% under the standard AM1.5G spectrum with one sun intensity. The high performance of these NT:N2200-based cells can be attributed to the low optical bandgaps of the polymers and the reasonably high and balanced electron and hole mobilities of the NT:N2200 blends due to the crystalline nature of the two polymers. DA - 2014/11/12/ PY - 2014/11/12/ DO - 10.1002/adma.201402473 VL - 26 IS - 42 SP - 7224-7230 SN - 1521-4095 KW - low bandgap polymer KW - all polymer solar cell KW - domain size KW - resonant soft X-ray scattering ER - TY - JOUR TI - Fermi liquid theory: A brief survey in memory of Gerald E. Brown AU - Schafer, T. T2 - Nuclear Physics. A DA - 2014/// PY - 2014/// VL - 928 SP - 180-189 ER - TY - JOUR TI - Elastocapillary deformations on partially-wetting substrates: rival contact-line models AU - Bostwick, Joshua B. AU - Shearer, Michael AU - Daniels, Karen E. T2 - Soft Matter AB - A partially-wetting liquid can deform the underlying elastic substrate upon which it rests. This situation requires the development of theoretical models to describe the wetting forces imparted by the drop onto the solid substrate, particularly those at the contact-line. We construct a general solution using a displacement potential function for the elastic deformations within a finite elastic substrate associated with these wetting forces, and compare the results for several different contact-line models. Our work incorporates internal contributions to the surface stress from both liquid/solid Σls and Σsg solid/gas solid surface tensions (surface stress), which results in a non-standard boundary-value problem that we solve using a dual integral equation. We compare our results to relevant experiments and conclude that the generalization of solid surface tension Σls ≠ Σsg is an essential feature in any model of partial-wetting. The comparisons also allow us to systematically eliminate some proposed contact-line models. DA - 2014/7// PY - 2014/7// DO - 10.1039/c4sm00891j VL - 10 IS - 37 SP - 7361 ER - TY - JOUR TI - Correlated Donor/Acceptor Crystal Orientation Controls Photocurrent Generation in All-Polymer Solar Cells AU - Schubert, Marcel AU - Collins, Brian A. AU - Mangold, Hannah AU - Howard, Ian A. AU - Schindler, Wolfram AU - Vandewal, Koen AU - Roland, Steffen AU - Behrends, Jan AU - Kraffert, Felix AU - Steyrleuthner, Robert AU - Chen, Zhihua AU - Fostiropoulos, Konstantinos AU - Bittl, Robert AU - Salleo, Alberto AU - Facchetti, Antonio AU - Laquai, Frédéric AU - Ade, Harald W. AU - Neher, Dieter T2 - Advanced Functional Materials AB - New polymers with high electron mobilities have spurred research in organic solar cells using polymeric rather than fullerene acceptors due to their potential of increased diversity, stability, and scalability. However, all‐polymer solar cells have struggled to keep up with the steadily increasing power conversion efficiency of polymer:fullerene cells. The lack of knowledge about the dominant recombination process as well as the missing concluding picture on the role of the semi‐crystalline microstructure of conjugated polymers in the free charge carrier generation process impede a systematic optimization of all‐polymer solar cells. These issues are examined by combining structural and photo‐physical characterization on a series of poly(3‐hexylthiophene) (donor) and P(NDI2OD‐T2) (acceptor) blend devices. These experiments reveal that geminate recombination is the major loss channel for photo‐excited charge carriers. Advanced X‐ray and electron‐based studies reveal the effect of chloronaphthalene co‐solvent in reducing domain size, altering domain purity, and reorienting the acceptor polymer crystals to be coincident with those of the donor. This reorientation correlates well with the increased photocurrent from these devices. Thus, efficient split‐up of geminate pairs at polymer/polymer interfaces may necessitate correlated donor/acceptor crystal orientation, which represents an additional requirement compared to the isotropic fullerene acceptors. DA - 2014/4/17/ PY - 2014/4/17/ DO - 10.1002/ADFM.201304216 VL - 24 IS - 26 SP - 4068-4081 J2 - Adv. Funct. Mater. LA - en OP - SN - 1616-301X UR - http://dx.doi.org/10.1002/ADFM.201304216 DB - Crossref ER - TY - JOUR TI - Controlling Molecular Weight of a High Efficiency Donor-Acceptor Conjugated Polymer and Understanding Its Significant Impact on Photovoltaic Properties AU - Li, Wentao AU - Yang, Liqiang AU - Tumbleston, John R. AU - Yan, Liang AU - Ade, Harald AU - You, Wei T2 - ADVANCED MATERIALS AB - The molecular weight (MW) of PBnDT-FTAZ can be precisely controlled by adjusting the stoichiometric ratio of the two monomers, following the Carothers equation. The study of a set of PBnDT-FTAZ polymers with different MWs reveals that the MW significantly influences the morphology and structural order of PBnDTFTAZ in its bulk heterojunction solar cells, with the highest efficiency (over 7%) achieved with the use of a MW of 40 000 g mol(-1) . DA - 2014/7/9/ PY - 2014/7/9/ DO - 10.1002/adma.201305251 VL - 26 IS - 26 SP - 4456-+ SN - 1521-4095 ER - TY - JOUR TI - Breaking and restoration of rotational symmetry on the lattice for bound state multiplets AU - Lu, Bing-Nan AU - Laehde, Timo A. AU - Lee, Dean AU - Meissner, Ulf-G. T2 - PHYSICAL REVIEW D AB - We explore the breaking of rotational symmetry on the lattice for bound state energies and practical methods for suppressing this breaking. We demonstrate the general problems associated with lattice discretization errors and finite-volume errors using an $\ensuremath{\alpha}$ cluster model for $^{8}\mathrm{Be}$ and $^{12}\mathrm{C}$. We consider the two and three $\ensuremath{\alpha}$-particle systems and focus on the lowest states with nonzero angular momentum which split into multiplets corresponding to different irreducible representations of the cubic group. We examine the dependence of such splittings on the lattice spacing and box size. We find that lattice spacing errors are closely related to the commensurability of the lattice with the intrinsic length scales of the system. We also show that rotational symmetry breaking effects can be significantly reduced by using improved lattice actions, and that the physical energy levels are accurately reproduced by the weighted averages of the spin multiplets. DA - 2014/8/26/ PY - 2014/8/26/ DO - 10.1103/physrevd.90.034507 VL - 90 IS - 3 SP - SN - 1550-2368 ER - TY - JOUR TI - Analysis and Control of Beliefs in Social Networks AU - Wang, Tian AU - Krim, Hamid AU - Viniotis, Yannis T2 - IEEE TRANSACTIONS ON SIGNAL PROCESSING AB - In this paper, we investigate the problem of how beliefs diffuse among members of social networks. We propose an information flow model (IFM) of belief that captures how interactions among members affect the diffusion and eventual convergence of a belief. The IFM model includes a generalized Markov Graph (GMG) model as a social network model, which reveals that the diffusion of beliefs depends heavily on two characteristics of the social network characteristics, namely degree centralities and clustering coefficients. We apply the IFM to both converged belief estimation and belief control strategy optimization. The model is compared with an IFM including the Barabási-Albert model, and is evaluated via experiments with published real social network data. DA - 2014/11/1/ PY - 2014/11/1/ DO - 10.1109/tsp.2014.2352591 VL - 62 IS - 21 SP - 5552-5564 SN - 1941-0476 KW - Complex networks KW - information flow KW - machine learning ER - TY - JOUR TI - A Polythiophene Derivative with Superior Properties for Practical Application in Polymer Solar Cells AU - Zhang, Maojie AU - Guo, Xia AU - Ma, Wei AU - Ade, Harald AU - Hou, Jianhui T2 - ADVANCED MATERIALS AB - A polythiophene derivative called PDCBT, which has a backbone of thiophene units and just carboxylate functional groups to modulate its properties, exhibits properties superior to those of poly(3-hexylthiophene), the classic polythiophene derivative, when used as an electron donor in polymer solar cells (PSCs). The best device, based on PDCBT/PC71BM (1:1), develops a good power conversion efficiency of 7.2%. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article. DA - 2014/9/3/ PY - 2014/9/3/ DO - 10.1002/adma.201401494 VL - 26 IS - 33 SP - 5880-5885 SN - 1521-4095 KW - polythiophenes KW - carboxylates KW - energy level KW - polymer solar cells ER - TY - JOUR TI - Valence and conduction band alignment at ScN interfaces with 3C-SiC (111) and 2H-GaN (0001) AU - King, Sean W. AU - Nemanich, Robert J. AU - Davis, Robert F. T2 - APPLIED PHYSICS LETTERS AB - In order to understand and predict the behavior of future scandium nitride (ScN) semiconductor heterostructure devices, we have utilized in situ x-ray and ultra-violet photoelectron spectroscopy to determine the valence band offset (VBO) present at ScN/3C-SiC (111) and 2H-GaN (0001)/ScN (111) interfaces formed by ammonia gas source molecular beam epitaxy. The ScN/3C-SiC (111) VBO was dependent on the ScN growth temperature and resistivity. VBOs of 0.4 ± 0.1 and 0.1 ± 0.1 eV were, respectively, determined for ScN grown at 925 °C (low resistivity) and 800 °C (high resistivity). Using the band-gaps of 1.6 ± 0.2 and 1.4 ± 0.2 eV previously determined by reflection electron energy loss spectroscopy for the 925 and 800 °C ScN films, the respective conduction band offsets (CBO) for these interfaces were 0.4 ± 0.2 and 0.9 ± 0.2 eV. For a GaN (0001) interface with 925 °C ScN (111), the VBO and CBO were similarly determined to be 0.9 ± 0.1 and 0.9 ± 0.2 eV, respectively. DA - 2014/8/25/ PY - 2014/8/25/ DO - 10.1063/1.4894010 VL - 105 IS - 8 SP - SN - 1077-3118 ER - TY - JOUR TI - Spatial temperature mapping within polymer nanocomposites undergoing ultrafast photothermal heating via gold nanorods AU - Maity, Somsubhra AU - Wu, Wei-Chen AU - Xu, Chao AU - Tracy, Joseph B. AU - Gundogdu, Kenan AU - Bochinski, Jason R. AU - Clarke, Laura I. T2 - NANOSCALE AB - Polarized fluorescence temperature measurements combined with direct detection of nanorod rotation within the polymer melt regions reveal the steady-state temperature gradient on the nanoscale. DA - 2014/// PY - 2014/// DO - 10.1039/c4nr05179c VL - 6 IS - 24 SP - 15236-15247 SN - 2040-3372 ER - TY - JOUR TI - Spallation-driven ultracold neutron sources: concepts for a next generation source AU - Young, A. R. AU - Huegle, T. AU - Makela, M. AU - Morris, C. AU - Muhrer, G. AU - Saunders, A. T2 - ESS SCIENCE SYMPOSIUM ON NEUTRON PARTICLE PHYSICS AT LONG PULSE SPALLATION SOURCES (NPPATLPS 2013) AB - We present concepts for a next-generation, spallation-driven ultracold neutron source. Our source is based on a 40 liter volume of liquid He held at 1.6 K, with heat removed by “sub-cooled” He technology developed for the Large Hadron Collider's magnet systems. We report on neutronics modeling for two geometries which utilize well-vetted scattering and absorption data developed for the Lujan Center Mark-3 target, as well as promising moderator materials for the cold neutron “pre-moderator” for this source. DA - 2014/// PY - 2014/// DO - 10.1016/j.phpro.2013.12.021 VL - 51 SP - 93–97 SN - 1875-3892 KW - ultracold neutron KW - spallation KW - source KW - moderator ER - TY - CONF TI - Single-molecule imaging reveals DNA-binding properties of cohesin proteins SA1 and SA2. AU - Lin, J. AU - Kaur, P. AU - Chen, H. AU - Countryman, P. AU - Roushan, M. AU - Flaherty, D. AU - Brennan, E. AU - You, C. AU - Piehler, J. AU - Riehn, R. AU - Tao, Y. J. AU - Wang, H. C2 - 2014/// C3 - Environmental and Molecular Mutagenesis DA - 2014/// VL - 55 SP - S29-29 ER - TY - JOUR TI - Second-order fluid dynamics for the unitary Fermi gas from kinetic theory AU - Schafer, T. T2 - Physical Review. A DA - 2014/// PY - 2014/// VL - 90 IS - 4 ER - TY - JOUR TI - More stable and more efficient alternatives of Z-907: carbazole-based amphiphilic Ru(II) sensitizers for dye-sensitized solar cells AU - Cheema, Hammad AU - Islam, Ashraful AU - Younts, Robert AU - Gautam, Bhoj AU - Bedja, Idriss AU - Gupta, Ravindra Kumar AU - Han, Liyuan AU - Gundogdu, Kenan AU - El-Shafei, Ahmed T2 - PHYSICAL CHEMISTRY CHEMICAL PHYSICS AB - Here we report two novel amphiphilic Ru(II) heteroleptic bipyridyl complexes, HD-14 and HD-15, compared to previously reported NCSU-10. We have combined the strong electron donor characteristics of carbazole and the hydrophobic nature of different long alkyl chains, C7, C18 and C2 (NCSU-10), tethered to N-carbazole to study their influence on photocurrent, photovoltage and long term stability for dye-sensitized solar cells. Photon harvesting efficiency and electron donating characteristics of carbazole-based ancillary ligands were found to be unaffected by different alkyl chain lengths. However, a slight drop in the Voc of HD-14 and HD-15 was observed compared to that of NCSU-10. It was found by nanosecond flash photolysis transient absorption (TA) measurements that the faster the dye regeneration the higher the photocurrent density response, and the dye regeneration time was found to be 2.6, 3.6, and 3.7 μs for HD-14, HD-15, and N719 dyes, respectively. The difference in the amplitude of the transient absorption (TA) signal of the oxidized dye as measured by femtosecond TA studies is in excellent agreement with the photocurrent generated, which was in the following order HD-14 > HD-15 > N719. Under 1000 h light soaking conditions, HD-15 maintained up to 98% (only 2% loss) of the initial power conversion efficiency compared to 8% loss for HD-14 and 22% loss in the power conversion efficiency for NCSU-10. HD-15 was strikingly stable to light soaking conditions when employed in the presence of an ionic liquid electrolyte, which paves the way for widespread applications of dye-sensitized solar cells with long term stability. The total power conversion efficiency (η) was 9.27% for HD-14 and 9.17% for HD-15 compared to 8.92% for N719. DA - 2014/// PY - 2014/// DO - 10.1039/c4cp04120h VL - 16 IS - 48 SP - 27078-27087 SN - 1463-9084 ER - TY - JOUR TI - Molecular Electronic Level Alignment at Weakly Coupled Organic Film/Metal Interfaces AU - Zhao, Jin AU - Feng, Min AU - Dougherty, Daniel Barker AU - Sun, Hao AU - Petek, Hrvoje T2 - ACS NANO AB - Electronic level alignment at interfaces of molecular materials with inorganic semiconductors and metals controls many interfacial phenomena. How the intrinsic properties of the interacting systems define the electronic structure of their interface remains one of the most important problems in molecular electronics and nanotechnology that can be solved through a combination of surface science experimental techniques and theoretical modeling. In this article, we address this fundamental problem through experimental and computational studies of molecular electronic level alignment of thin films of C6F6 on noble metal surfaces. The unoccupied electronic structure of C6F6 is characterized with single molecule resolution using low-temperature scanning tunneling microscopy-based constant-current distance-voltage spectroscopy. The experiments are performed on several noble metal surfaces with different work functions and distinct surface-normal projected band structures. In parallel, the electronic structures of the quantum wells (QWs) formed by the lowest unoccupied molecular orbital state of the C6F6 monolayer and multilayer films and their alignment with respect to the vacuum level of the metallic substrates are calculated by solving the Schrödinger equation for a semiempirical one-dimensional (1D) potential of the combined system using input from density functional theory. Our analysis shows that the level alignment for C6F6 molecules bound through weak van der Waals interactions to noble metal surfaces is primarily defined by the image potential of metal, the electron affinity of the molecule, and the molecule surface distance. We expect the same factors to determine the interfacial electronic structure for a broad range of molecule/metal interfaces. DA - 2014/10// PY - 2014/10// DO - 10.1021/nn5049969 VL - 8 IS - 10 SP - 10988-10997 SN - 1936-086X KW - energy level alignment KW - image potential KW - quantum well state ER - TY - JOUR TI - Intrinsic and extrinsic effects on the electrostatic field at the surface of Bi2Se3 AU - Xu, Chao AU - Hewitt, Andy AU - Wang, Jingying AU - Guan, Tianshuai AU - Boltersdorf, Jonathan AU - Maggard, Paul A. AU - Dougherty, Daniel B. AU - Gundogdu, Kenan T2 - Journal of Applied Physics AB - The time evolution of electrostatic fields near a Bi2Se3 surface after a mechanical cleave was observed using Second Harmonic Generation. By comparing samples with different bulk doping levels and samples cleaved in different gas environments, these observations indicate multiple contributions to electric field evolution. These include the intrinsic process of Se vacancy diffusion as well as extrinsic processes due to both reactive and nonreactive surface adsorbates. DA - 2014/7/28/ PY - 2014/7/28/ DO - 10.1063/1.4891719 VL - 116 IS - 4 SP - 043519 J2 - Journal of Applied Physics LA - en OP - SN - 0021-8979 1089-7550 UR - http://dx.doi.org/10.1063/1.4891719 DB - Crossref ER - TY - JOUR TI - Influence of mono versus bis-electron-donor ancillary ligands in heteroleptic Ru(II) bipyridyl complexes on electron injection from the first excited singlet and triplet states in dye-sensitized solar cells AU - Cheema, Hammad AU - Islam, Ashraful AU - Han, Liyuan AU - Gautam, Bhoj AU - Younts, Robert AU - Gundogdu, Kenan AU - El-Shafei, Ahmed T2 - JOURNAL OF MATERIALS CHEMISTRY A AB - A novel Ru(ii) bipyridyl complex was designed for DSCs. DA - 2014/// PY - 2014/// DO - 10.1039/c4ta01942c VL - 2 IS - 34 SP - 14228-14235 SN - 2050-7496 ER - TY - JOUR TI - Fullerene-Free Polymer Solar Cells with Highly Reduced Bimolecular Recombination and Field-Independent Charge Carrier Generation AU - Roland, Steffen AU - Schubert, Marcel AU - Collins, Brian A. AU - Kurpiers, Jona AU - Chen, Zhihua AU - Facchetti, Antonio AU - Ade, Harald AU - Neher, Dieter T2 - The Journal of Physical Chemistry Letters AB - Photogeneration, recombination, and transport of free charge carriers in all-polymer bulk heterojunction solar cells incorporating poly(3-hexylthiophene) (P3HT) as donor and poly([N,N'-bis(2-octyldodecyl)-naphthelene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)) (P(NDI2OD-T2)) as acceptor polymer have been investigated by the use of time delayed collection field (TDCF) and time-of-flight (TOF) measurements. Depending on the preparation procedure used to dry the active layers, these solar cells comprise high fill factors (FFs) of up to 67%. A strongly reduced bimolecular recombination (BMR), as well as a field-independent free charge carrier generation are observed, features that are common to high performance fullerene-based solar cells. Resonant soft X-ray measurements (R-SoXS) and photoluminescence quenching experiments (PQE) reveal that the BMR is related to domain purity. Our results elucidate the similarities of this polymeric acceptor with the superior recombination properties of fullerene acceptors. DA - 2014/8/4/ PY - 2014/8/4/ DO - 10.1021/JZ501506Z VL - 5 IS - 16 SP - 2815-2822 J2 - J. Phys. Chem. Lett. LA - en OP - SN - 1948-7185 UR - http://dx.doi.org/10.1021/JZ501506Z DB - Crossref ER - TY - JOUR TI - Freeze-out conditions from net-proton and net-charge fluctuations at RHIC AU - Alba, Paolo AU - Alberico, Wanda AU - Bellwied, Rene AU - Bluhm, Marcus AU - Sarti, Valentina Mantovani AU - Nahrgang, Marlene AU - Ratti, Claudia T2 - PHYSICS LETTERS B AB - We calculate ratios of higher-order susceptibilities quantifying fluctuations in the number of net protons and in the net-electric charge using the Hadron Resonance Gas (HRG) model. We take into account the effect of resonance decays, the kinematic acceptance cuts in rapidity, pseudo-rapidity and transverse momentum used in the experimental analysis, as well as a randomization of the isospin of nucleons in the hadronic phase. By comparing these results to the latest experimental data from the STAR collaboration, we determine the freeze-out conditions from net-electric charge and net-proton distributions and discuss their consistency. DA - 2014/11/10/ PY - 2014/11/10/ DO - 10.1016/j.physletb.2014.09.052 VL - 738 SP - 305-310 SN - 1873-2445 ER - TY - JOUR TI - Exciton valley relaxation in a single layer of WS2 measured by ultrafast spectroscopy AU - Mai, Cong AU - Semenov, Yuriy G. AU - Barrette, Andrew AU - Yu, Yifei AU - Jin, Zhenghe AU - Cao, Linyou AU - Kim, Ki Wook AU - Gundogdu, Kenan T2 - PHYSICAL REVIEW B AB - We measured the lifetime of optically created valley polarization in single layer WS2 using transient absorption spectroscopy. The electron valley relaxation is very short (< 1ps). However the hole valley lifetime is at least two orders of magnitude longer and exhibits a temperature dependence that cannot be explained by single carrier spin/valley relaxation mechanisms. Our theoretical analysis suggests that a collective contribution of two potential processes may explain the valley relaxation in single layer WS2. One process involves direct scattering of excitons from K to K' valleys with a spin flip-flop interaction. The other mechanism involves scattering through spin degenerate Gamma valley. This second process is thermally activated with an Arrhenius behavior due to the energy barrier between Gamma and K valleys. DA - 2014/7/31/ PY - 2014/7/31/ DO - 10.1103/physrevb.90.041414 VL - 90 IS - 4 SP - SN - 2469-9969 ER - TY - JOUR TI - Control of the electric field-polymer solution interaction by utilizing ultra-conductive fluids AU - Thoppey, N. M. AU - Gorga, R. E. AU - Clarke, L. I. AU - Bochinski, J. R. T2 - POLYMER AB - Dramatically raising the conductivity of a polymer solution by using a salt additive allows control over the electric field-induced jet feed rate when electrospinning from an unconfined fluid without altering the applied voltage. As the solution conductivity increases, the flow rate drops by an order of magnitude. At a high voltage level and fluid conductivity value, the jets undergo a whipping instability over almost the entire path from the source to the collector experiencing only a negligibly short linear region which, along with the flow rate data, indicates that the jet narrows due to the high conductivity. Under these conditions, even while possessing relatively large individual jet feed rates, thin diameter nanofibers (200–300 nm) are readily produced. In contrast with other approaches to obtain narrow fibers from unconfined fluids (e.g., voltage reduction to control feed rate), here the fiber forming jets are present indefinitely. Continuous, scaled up nanofiber production rate of >125× over the traditional single needle electrospinning method is observed from the presence of multiple jets, each possessing a relatively high solution feed rate. These fundamental experiments reveal new pathways for exploring novel electrospinning configurations where the jet feed rate can be controlled by manipulating the solution conductivity. DA - 2014/11/18/ PY - 2014/11/18/ DO - 10.1016/j.polymer.2014.10.007 VL - 55 IS - 24 SP - 6390-6398 SN - 1873-2291 KW - Unconfined electrospinning KW - Electric field interactions KW - Nanofibers ER - TY - JOUR TI - Coexisting Bi and Se surface terminations of cleaved Bi2Se3 single crystals AU - Hewitt, A. S. AU - Wang, J. Y. AU - Boltersdorf, J. AU - Maggard, P. A. AU - Dougherty, D. B. T2 - Journal of Vacuum Science & Technology. B, Microelectronics and Nanometer Structures DA - 2014/// PY - 2014/// VL - 32 IS - 4 ER - TY - JOUR TI - Beta decay measurements with ultracold neutrons: a review of recent measurements and the research program at Los Alamos National Laboratory AU - Young, A. R. AU - Clayton, S. AU - Filippone, B. W. AU - Geltenbort, P. AU - Ito, T. M. AU - Liu, C-Y AU - Makela, M. AU - Morris, C. L. AU - Plaster, B. AU - Saunders, A. AU - Seestrom, S. J. AU - Vogelaar, R. B. T2 - JOURNAL OF PHYSICS G-NUCLEAR AND PARTICLE PHYSICS AB - We present a review of the motivation and results of recent experiments which utilize ultracold neutrons for measurements of neutron beta decay. Because these experiments hinge critically on the available ultracold neutron source technology, we also review the status of ultracold neutron source development, emphasizing the Los Alamos ultracold neutron facility and the ongoing beta decay research program sited there. DA - 2014/11// PY - 2014/11// DO - 10.1088/0954-3899/41/11/114007 VL - 41 IS - 11 SP - 114007 SN - 1361-6471 KW - fundamental symmetries KW - neutron decay KW - ultracold neutrons ER - TY - JOUR TI - Aggregation and morphology control enables multiple cases of high-efficiency polymer solar cells AU - Liu, Yuhang AU - Zhao, Jingbo AU - Li, Zhengke AU - Mu, Cheng AU - Ma, Wei AU - Hu, Huawei AU - Jiang, Kui AU - Lin, Haoran AU - Ade, Harald AU - Yan, He T2 - NATURE COMMUNICATIONS AB - Although the field of polymer solar cell has seen much progress in device performance in the past few years, several limitations are holding back its further development. For instance, current high-efficiency (>9.0%) cells are restricted to material combinations that are based on limited donor polymers and only one specific fullerene acceptor. Here we report the achievement of high-performance (efficiencies up to 10.8%, fill factors up to 77%) thick-film polymer solar cells for multiple polymer:fullerene combinations via the formation of a near-ideal polymer:fullerene morphology that contains highly crystalline yet reasonably small polymer domains. This morphology is controlled by the temperature-dependent aggregation behaviour of the donor polymers and is insensitive to the choice of fullerenes. The uncovered aggregation and design rules yield three high-efficiency (>10%) donor polymers and will allow further synthetic advances and matching of both the polymer and fullerene materials, potentially leading to significantly improved performance and increased design flexibility. DA - 2014/11// PY - 2014/11// DO - 10.1038/ncomms6293 VL - 5 SP - SN - 2041-1723 ER - TY - JOUR TI - The Hoyle state in nuclear lattice effective field theory AU - Laehde, Timo A. AU - Epelbaum, Evgeny AU - Krebs, Hermann AU - Lee, Dean AU - Meissner, Ulf-G AU - Rupak, Gautam T2 - PRAMANA-JOURNAL OF PHYSICS AB - We review the calculation of the Hoyle state of 12C in nuclear lattice effective field theory (NLEFT) and its anthropic implications in the nucleosynthesis of 12C and 16O in red giant stars. We also analyse the extension of NLEFT to the regime of medium-mass nuclei, with emphasis on the determination of the ground-state energies of the α nuclei 16O, 20Ne, 24Mg, and 28Si by Euclidean time projection. Finally, we discuss recent NLEFT results for the spectrum, electromagnetic properties, and α-cluster structure of 16O. DA - 2014/11// PY - 2014/11// DO - 10.1007/s12043-014-0861-z VL - 83 IS - 5 SP - 651-659 SN - 0973-7111 KW - Nuclear structure KW - chiral effective field theory KW - lattice Monte Carlo ER - TY - JOUR TI - Measurement of the Half-Life of the T=1/2 Mirror Decay of Ne-19 and its Implication on Physics Beyond the Standard Model AU - Broussard, L. J. AU - Back, H. O. AU - Boswell, M. S. AU - Crowell, A. S. AU - Dendooven, P. AU - Giri, G. S. AU - Howell, C. R. AU - Kidd, M. F. AU - Jungmann, K. AU - Kruithof, W. L. AU - Mol, A. AU - Onderwater, C. J. G. AU - Pattie, R. W., Jr. AU - Shidling, P. D. AU - Sohani, M. AU - Hoek, D. J. AU - Rogachevskiy, A. AU - Traykov, E. AU - Versolato, O. O. AU - Willmann, L. AU - Wilschut, H. W. AU - Young, A. R. T2 - PHYSICAL REVIEW LETTERS AB - The ${\frac{1}{2}}^{+}\ensuremath{\rightarrow}{\frac{1}{2}}^{+}$ superallowed mixed mirror decay of $^{19}\mathrm{Ne}$ to $^{19}\mathrm{F}$ is excellently suited for high precision studies of the weak interaction. However, there is some disagreement on the value of the half-life. In a new measurement we have determined this quantity to be ${T}_{1/2}=17.2832\ifmmode\pm\else\textpm\fi{}0.005{1}_{\text{(stat)}}\ifmmode\pm\else\textpm\fi{}0.006{6}_{\text{(syst)}}\text{ }\text{ }\mathrm{s}$, which differs from the previous world average by 3 standard deviations. The impact of this measurement on limits for physics beyond the standard model such as the presence of tensor currents is discussed. DA - 2014/5/27/ PY - 2014/5/27/ DO - 10.1103/physrevlett.112.212301 VL - 112 IS - 21 SN - 1079-7114 ER - TY - JOUR TI - Dielectric functions and interband transitions of InxAl1 (-) P-x alloys AU - Kim, T. J. AU - Hwang, S. Y. AU - Byun, J. S. AU - Aspnes, D. E. AU - Lee, E. H. AU - Song, J. D. AU - Liang, C. -T. AU - Chang, Y. -C. AU - Park, H. G. AU - Choi, J. AU - Kim, J. Y. AU - Kang, Y. R. AU - Park, J. C. AU - Kim, Y. D. T2 - CURRENT APPLIED PHYSICS AB - We report pseudodielectric functions <ε> from 1.5 to 6.0 eV of InxAl1 − xP ternary alloy films. Data were obtained by spectroscopic ellipsometry on 1.2 μm thick films grown on (001) GaAs substrates by molecular beam epitaxy. Artifacts were minimized by real-time assessment of overlayer removal, leading to accurate representations of the bulk dielectric responses of these materials. Critical-point (CP) energies were obtained from numerically calculated second energy derivatives, and their Brillouin-zone origins identified by band-structure calculations using the linear augmented Slater-type orbital method. DA - 2014/9// PY - 2014/9// DO - 10.1016/j.cap.2014.06.026 VL - 14 IS - 9 SP - 1273-1276 SN - 1878-1675 KW - Ellipsometry KW - InAlP KW - Dielectric function KW - Critical point ER - TY - JOUR TI - An X-ray scatter system for material identification in cluttered objects: A Monte Carlo simulation study AU - Lakshmanan, Manu N. AU - Kapadia, Anuj J. AU - Sahbaee, Pooyan AU - Wolter, Scott D. AU - Harrawood, Brian P. AU - Brady, David AU - Samei, Ehsan T2 - NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS AB - The analysis of X-ray scatter patterns has been demonstrated as an effective method of identifying specific materials in mixed object environments, for both biological and non-biological applications. Here we describe an X-ray scatter imaging system for material identification in cluttered objects and investigate its performance using a large-scale Monte Carlo simulation study of one-thousand objects containing a broad array of materials. The Geant4 Monte Carlo source code for Rayleigh scatter physics was modified to model coherent scatter diffraction in bulk materials based on experimentally measured form factors for 33 materials. The simulation was then used to model coherent scatter signals from a variety of targets and clutter (background) materials in one thousand randomized objects. The resulting scatter images were used to characterize four parameters of the imaging system that affected its ability to identify target materials: (a) the arrangement of materials in the object, (b) clutter attenuation, (c) type of target material, and (d) the X-ray tube current. We found that the positioning of target materials within the object did not significantly affect their detectability; however, a strong negative correlation was observed between the target detectability and the clutter attenuation of the object. The imaging signal was also found to be relatively invariant to increases in X-ray tube current above 1 mAs for most materials considered in the study. This work is the first Monte Carlo study to our knowledge of a large population of cluttered object of an X-ray scatter imaging system for material identification and lays the foundation for large-scale studies of the effectiveness of X-ray scatter imaging systems for material identification in complex samples. DA - 2014/9/15/ PY - 2014/9/15/ DO - 10.1016/j.nimb.2014.05.021 VL - 335 SP - 31-38 SN - 1872-9584 KW - Coherent scatter KW - X-ray imaging KW - Suitcase clutter KW - Material identification ER - TY - JOUR TI - A quantum Monte Carlo study of zinc-porphyrin: Vertical excitation between the singlet ground state and the lowest-lying singlet excited state AU - Kulahlioglu, A.H. AU - Mitas, L. T2 - Computational and Theoretical Chemistry AB - We have calculated the vertical excitation energy between the singlet ground state (11Ag) and the lowest-lying singlet excited state (11Eu) of Zn-porphyrin employing the fixed-node diffusion Monte Carlo technique. The determinantal parts of trial wave functions were constructed using results from Configuration Interaction and time-dependent Density Functional Theory. DA - 2014/10// PY - 2014/10// DO - 10.1016/J.COMPTC.2014.07.006 VL - 1046 SP - 6-9 J2 - Computational and Theoretical Chemistry LA - en OP - SN - 2210-271X UR - http://dx.doi.org/10.1016/J.COMPTC.2014.07.006 DB - Crossref KW - Quantum Monte Carlo KW - Fixed-node approximation KW - Zinc porphyrin KW - Excited states ER - TY - JOUR TI - Understanding the Morphology of PTB7: PCBM Blends in Organic Photovoltaics AU - Liu, Feng AU - Zhao, Wei AU - Tumbleston, John R. AU - Wang, Cheng AU - Gu, Yu AU - Wang, Dong AU - Briseno, Alejandro L. AU - Ade, Harald AU - Russell, Thomas P. T2 - ADVANCED ENERGY MATERIALS AB - The structure–property relationships of PTB7‐phenyl‐C 61 ‐butyric acid methyl ester (PCBM)‐based organic photovoltaics are investigated. The morphology is investigated in an active layer setting where a multi‐length‐scale morphology is observed using a solvent additive‐assisted film processing. This multi‐length‐scale structure consists of a phase separated morphology with a characteristic length scale of ≈30 nm, which is critical for producing large currents in devices; a second length scale of ≈130 nm, arises from face‐on PTB7 crystalline aggregates. This latter morphological feature is also observed in films prepared without the use of an additive. By observing the structure formation in situ during solvent evaporation for blade coated thin films, the additive is found to promote the formation of ordered domains of the PTB7 at an earlier stage during the solvent evaporation, which is critical in the development of the final morphology. In studies on PTB7/PCBM bilayers, PCBM is found to diffuse into the PTB7 layer. However, the performance of devices prepared in this manner is low. This diffusion leads to a swelling of the PTB7 and a reduction in the crystallinity of the PTB7, reflecting the strong miscibility of PCBM with PTB7. The morphology resulting from the interdiffusion is single‐length‐scale with slightly large phase separation. This leads to devices with poor performance. DA - 2014/4// PY - 2014/4// DO - 10.1002/aenm.201301377 VL - 4 IS - 5 SP - SN - 1614-6840 KW - organic photovoltaics KW - structure-property relationships KW - morphology KW - low bandgap polymers KW - crystallization KW - diffusion ER - TY - JOUR TI - Stimulated neutrino transformation through turbulence AU - Patton, Kelly M. AU - Kneller, James P. AU - McLaughlin, Gail C. T2 - PHYSICAL REVIEW D AB - We derive an analytical solution for the flavor evolution of a neutrino through a turbulent density profile which is found to accurately predict the amplitude and transition wavelength of numerical solutions on a case-by-case basis. The evolution is seen to strongly depend upon those Fourier modes in the turbulence which are approximately the same as the splitting between neutrino eigenvalues. Transitions are strongly enhanced by those Fourier modes in the turbulence which are approximately the same as the splitting between neutrino eigenvalues. We also find a suppression of transitions due to the long wavelength modes when the ratio of their amplitude and the wave number is of order, or greater than, the first root of the Bessel function ${J}_{0}$. DA - 2014/4/30/ PY - 2014/4/30/ DO - 10.1103/physrevd.89.073022 VL - 89 IS - 7 SP - SN - 1550-2368 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84899723375&partnerID=MN8TOARS ER - TY - JOUR TI - Single-molecule analysis reveals human UV-damaged DNA-binding protein (UV-DDB) dimerizes on DNA via multiple kinetic intermediates AU - Ghodke, Harshad AU - Wang, Hong AU - Hsieh, Ching L. AU - Woldemeskel, Selamawit AU - Watkins, Simon C. AU - Rapic-Otrin, Vesna AU - Van Houten, Bennett T2 - PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA AB - How human DNA repair proteins survey the genome for UV-induced photoproducts remains a poorly understood aspect of the initial damage recognition step in nucleotide excision repair (NER). To understand this process, we performed single-molecule experiments, which revealed that the human UV-damaged DNA-binding protein (UV-DDB) performs a 3D search mechanism and displays a remarkable heterogeneity in the kinetics of damage recognition. Our results indicate that UV-DDB examines sites on DNA in discrete steps before forming long-lived, nonmotile UV-DDB dimers (DDB1-DDB2)2 at sites of damage. Analysis of the rates of dissociation for the transient binding molecules on both undamaged and damaged DNA show multiple dwell times over three orders of magnitude: 0.3-0.8, 8.1, and 113-126 s. These intermediate states are believed to represent discrete UV-DDB conformers on the trajectory to stable damage detection. DNA damage promoted the formation of highly stable dimers lasting for at least 15 min. The xeroderma pigmentosum group E (XP-E) causing K244E mutant of DDB2 found in patient XP82TO, supported UV-DDB dimerization but was found to slide on DNA and failed to stably engage lesions. These findings provide molecular insight into the loss of damage discrimination observed in this XP-E patient. This study proposes that UV-DDB recognizes lesions via multiple kinetic intermediates, through a conformational proofreading mechanism. DA - 2014/5/6/ PY - 2014/5/6/ DO - 10.1073/pnas.1323856111 VL - 111 IS - 18 SP - E1862-E1871 SN - 0027-8424 KW - DNA damage recognition KW - single-molecule tracking KW - DNA tightrope KW - human nucleotide excision repair ER - TY - JOUR TI - Remote plasma-processing (RPP), medium range order, and precursor sites for dangling bond defects in "amorphous-Si(H)" alloys: Photovoltaic and thin film transistor devices AU - Lucovsky, G. AU - Zeller, D. J. AU - Cheng, C. AU - Zhang, Y. T2 - SURFACE & COATINGS TECHNOLOGY AB - Remote plasma processing (RPP) provides pathways to the formation of photovoltaic (PV) and thin-film-transistor (TFT) devices that include buried interfaces. This is made possible by separate and independent control of (i) plasma excited O- and N-atom deposition precursors in a up-stream plasma chamber, combined with (ii) down-stream injection of Si- and Ge-atoms with control gas flow rates providing control of buried interface bonding at monolayer levels. Devices with intrinsic, B p-type and P n-type “a-Si(H)” & “a-Si,Ge(H)” layers require 10% bonded H in monolayer (SiH arrangements) and deposition and/or annealing at temperatures between 240 and 275 °C. Deposition from SiH4 with either PH3 or B2H6 dopant gasses provides spectrally reflecting films which can be annealed yielding fine-grain films for gate, or source and drain regions for TFTs or FETs. DA - 2014/3/15/ PY - 2014/3/15/ DO - 10.1016/j.surfcoat.2013.06.104 VL - 242 SP - 183-186 SN - 0257-8972 KW - Hydrogenated amorphous Si KW - Photovoltaic applications KW - Thin film transistors KW - Fine grain polycrystalline Si KW - Medium range order ER - TY - JOUR TI - Quantifying Charge Extraction in Organic Solar Cells: The Case of Fluorinated PCPDTBT AU - Albrecht, Steve AU - Tumbleston, John R. AU - Janietz, Silvia AU - Dumsch, Ines AU - Allard, Sybille AU - Scherf, Ullrich AU - Ade, Harald AU - Neher, Dieter T2 - JOURNAL OF PHYSICAL CHEMISTRY LETTERS AB - We introduce a new and simple method to quantify the effective extraction mobility in organic solar cells at low electric fields and charge carrier densities comparable to operation conditions under one sun illumination. By comparing steady-state carrier densities at constant illumination intensity and under open-circuit conditions, the gradient of the quasi-Fermi potential driving the current is estimated as a function of external bias and charge density. These properties are then related to the respective steady-state current to determine the effective extraction mobility. The new technique is applied to different derivatives of the well-known low-band-gap polymer PCPDTBT blended with PC70BM. We show that the slower average extraction due to lower mobility accounts for the moderate fill factor when solar cells are fabricated with mono- or difluorinated PCPDTBT. This lower extraction competes with improved generation and reduced nongeminate recombination, rendering the monofluorinated derivative the most efficient donor polymer. DA - 2014/4/3/ PY - 2014/4/3/ DO - 10.1021/jz500457b VL - 5 IS - 7 SP - 1131-1138 SN - 1948-7185 ER - TY - JOUR TI - Phase coexistence in Ti6Sn5 intermetallics AU - Oni, A. A. AU - Hook, D. AU - Maria, J. P. AU - LeBeau, J. M. T2 - INTERMETALLICS AB - Here we report the structural characterization of a complex Ti–Sn intermetallic compound, Ti6Sn5. From X-ray diffraction, the resulting compound was observed to exist in both orthorhombic and hexagonal phases. Analysis by electron microscopy revealed that “planar-like” defects form throughout the material. Atomic resolution aberration-corrected scanning transmission electron microscopy reveals that these “planar-like” defects represent the coexistence of the orthorhombic and hexagonal phases within single grains. The resulting interwoven phases range in thickness from a fraction to multiple unit cells and exhibit coherent phase boundaries with the matrix grain. DA - 2014/8// PY - 2014/8// DO - 10.1016/j.intermet.2014.03.002 VL - 51 SP - 48-52 SN - 1879-0216 KW - Intermetallics,miscellaneous KW - Phase interfaces KW - Defects: planar faults KW - Electron microscopy,transmission KW - Diffraction ER - TY - JOUR TI - Patient-based estimation of organ dose for a population of 58 adult patients across 13 protocol categories AU - Sahbaee, Pooyan AU - Segars, W. Paul AU - Samei, Ehsan T2 - MEDICAL PHYSICS AB - Purpose: This study aimed to provide a comprehensive patient-specific organ dose estimation across a multiplicity of computed tomography (CT) examination protocols. Methods: A validated Monte Carlo program was employed to model a common CT system (LightSpeed VCT, GE Healthcare). The organ and effective doses were estimated from 13 commonly used body and neurological CT examination. The dose estimation was performed on 58 adult computational extended cardiac-torso phantoms (35 male, 23 female, mean age 51.5 years, mean weight 80.2 kg). The organ dose normalized by CTDIvol (h factor) and effective dose normalized by the dose length product (DLP) (k factor) were calculated from the results. A mathematical model was derived for the correlation between the h and k factors with the patient size across the protocols. Based on this mathematical model, a dose estimation iPhone operating system application was designed and developed to be used as a tool to estimate dose to the patients for a variety of routinely used CT examinations. Results: The organ dose results across all the protocols showed an exponential decrease with patient body size. The correlation was generally strong for the organs which were fully or partially located inside the scan coverage (Pearson sample correlation coefficient (r) of 0.49). The correlation was weaker for organs outside the scan coverage for which distance between the organ and the irradiation area was a stronger predictor of dose to the organ. For body protocols, the effective dose before and after normalization by DLP decreased exponentially with increasing patient's body diameter (r > 0.85). The exponential relationship between effective dose and patient's body diameter was significantly weaker for neurological protocols (r < 0.41), where the trunk length was a slightly stronger predictor of effective dose (0.15 < r < 0.46). Conclusions: While the most accurate estimation of a patient dose requires specific modeling of the patient anatomy, a first order approximation of organ and effective doses from routine CT scan protocols can be reasonably estimated using size specific factors. Estimation accuracy is generally poor for organ outside the scan range and for neurological protocols. The dose calculator designed in this study can be used to conveniently estimate and report the dose values for a patient across a multiplicity of CT scan protocols. DA - 2014/7// PY - 2014/7// DO - 10.1118/1.4883778 VL - 41 IS - 7 SP - SN - 2473-4209 KW - CT KW - computed tomography KW - Monte Carlo KW - radiation KW - dose KW - patient-specific KW - dose calculator KW - iOS app ER - TY - JOUR TI - Optical Enhancement in Heteroleptic Ru(II) Polypyridyl Complexes Using Electron-Donor Ancillary Ligands AU - Dong, Rui AU - Calzolari, Arrigo AU - Felice, Rosa AU - El-Shafei, Ahmed AU - Hussain, Maqbool AU - Nardelli, Marco Buongiorno T2 - JOURNAL OF PHYSICAL CHEMISTRY C AB - Organic dyes are a viable alternative to silicon for energy conversion. Using simulations from first-principles, we show that chemical manipulation is a powerful tool for tuning the optical absorption spectra of a special class of dyes in a way that is convenient for exploitation in dye-sensitized solar cells. Specifically, we have carried out density functional theory calculations on three Ru(II) polypyridyl complexes with electron-donor ancillary ligands. These complexes were recently developed to study how different electron-donor ancillary ligands affect the photophysical and electrochemical properties of these dyes for light harvesting and photon-to-electron conversion efficiency. We found that the electron-donor ancillary ligands significantly enhance the light harvesting in the visible and the near-infrared regions relative to the reference dye N3. Furthermore, we detected a decrease in the ionization potential, which improves the energy alignment with the redox potentials of the electrolyte. These findings demonstrated that better organic materials for energy applications were developed. DA - 2014/5/1/ PY - 2014/5/1/ DO - 10.1021/jp409733a VL - 118 IS - 17 SP - 8747-8755 SN - 1932-7455 ER - TY - JOUR TI - Lattice effective field theory for medium-mass nuclei AU - Laehde, Timoa A. AU - Epelbaum, Evgeny AU - Krebs, Hermann AU - Lee, Dean AU - Meissner, Ulf-G. AU - Rupak, Gautam T2 - PHYSICS LETTERS B AB - We extend Nuclear Lattice Effective Field Theory (NLEFT) to medium-mass nuclei, and present results for the ground states of alpha nuclei from 4He to 28Si, calculated up to next-to-next-to-leading order (NNLO) in the EFT expansion. This computational advance is made possible by extrapolations of lattice data using multiple initial and final states. For our soft two-nucleon interaction, we find that the overall contribution from multi-nucleon forces must change sign from attractive to repulsive with increasing nucleon number. This effect is not produced by three-nucleon forces at NNLO, but it can be approximated by an effective four-nucleon interaction. We discuss the convergence of the EFT expansion and the broad significance of our findings for future ab initio calculations. DA - 2014/5/1/ PY - 2014/5/1/ DO - 10.1016/j.physletb.2014.03.023 VL - 732 SP - 110-115 SN - 1873-2445 KW - Nuclear structure KW - Chiral effective field theory KW - Lattice Monte Carlo ER - TY - JOUR TI - High-Molecular-Weight Insulating Polymers Can Improve the Performance of Molecular Solar Cells AU - Huang, Ye AU - Wen, Wen AU - Mukherjee, Subhrangsu AU - Ade, Harald AU - Kramer, Edward J. AU - Bazan, Guillermo C. T2 - ADVANCED MATERIALS AB - The addition of small quantities of polystyrene (PS) is a simple and economically viable process that improves the power conversion efficiency of one of the most efficient small molecule donors. Addition of PS increases the solution viscosity, thereby providing thicker layers, and allows the formation of a desirable bulk heterojunction morphology. Moreover, the PS spontaneously accumulates as phase separated domains, away from the electrodes, so as not to interfere with charge extraction. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article. DA - 2014/6/25/ PY - 2014/6/25/ DO - 10.1002/adma.201400497 VL - 26 IS - 24 SP - 4168-4172 SN - 1521-4095 KW - organic solar cells KW - morphology KW - non-conductive polystyrene KW - small molecules KW - processing ER - TY - JOUR TI - Extrinsic origins of electronic disorder in 2D organic crystals AU - Wang, Jiuyang AU - Dougherty, Daniel B. T2 - JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B AB - The dominant impact of extrinsic electronic disorder was observed in α-sexithiophene (α-6T) films grown on C60/Au(111) substrates by scanning tunneling microscopy and spectroscopy measurements. Sexithiophene molecules adopt an upright orientation with a structure that reflects both bulklike α-6T packing and C60 substrate templating effects. Apparent height variations in these films are assigned as molecular sliding defects but are observed to have negligible impact on the energy of the highest occupied molecular orbital. This orbital energy varies more significantly in response to random changes in probe tip, implying that the dominant origin of electronic disorder in two-dimensional organic crystals can be extrinsic to the film. DA - 2014/5// PY - 2014/5// DO - 10.1116/1.4869196 VL - 32 IS - 3 SP - SN - 2166-2746 ER - TY - JOUR TI - Enhanced Photovoltaic Performance by Modulating Surface Composition in Bulk Heterojunction Polymer Solar Cells Based on PBDTTT-C-T/PC71BM AU - Guo, Xia AU - Zhang, Maojie AU - Ma, Wei AU - Ye, Long AU - Zhang, Shaoqing AU - Liu, Shengjian AU - Ade, Harald AU - Huang, Fei AU - Hou, Jianhui T2 - ADVANCED MATERIALS AB - For the blend film of PBDTTT-C-T:PC71 BM, the use of 1,8-diiodooctane as the solvent additive enriches the polymer at the top surface, so that a power conversion efficiency of 9.13% is recorded in the inverted polymer solar cell based on the blend, which is much higher than that of the device with conventional structure. DA - 2014/6/25/ PY - 2014/6/25/ DO - 10.1002/adma.201400411 VL - 26 IS - 24 SP - 4043-4049 SN - 1521-4095 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84903160839&partnerID=MN8TOARS KW - solvent additives KW - morphology KW - polymer solar cells KW - surface composition ER - TY - JOUR TI - Coverage-dependent surface magnetism of iron phthalocyanine on an O-Fe(110) surface AU - Dougherty, Daniel B. AU - Sandin, Andreas AU - Vescovo, Elio AU - Rowe, J. E. T2 - PHYSICAL REVIEW B AB - Iron phthalocyanine adsorbed on an oxygen covered Fe(110) surface shows a complex coverage-dependent spin polarization during growth of a molecular monolayer. Spin polarization is modified at low submonolayer coverages, absent at intermediate submonolayer coverages, and reappears in modified form for a complete monolayer. This is attributed to coverage-dependent adsorption configurations from a random adsorption system to a packed monolayer with a well-defined interfacial spin polarization. In addition, we report on the observation of a rotation of the spin direction of photoelectrons in the presence of molecules which is attributed to molecular modifications of surface magnetic anisotropy. DA - 2014/7/14/ PY - 2014/7/14/ DO - 10.1103/physrevb.90.045406 VL - 90 IS - 4 SP - SN - 2469-9969 ER - TY - JOUR TI - Correlations between electrical and mechanical signals during granular stick-slip events AU - Daniels, Karen E. AU - Bauer, Caroline AU - Shinbrot, Troy T2 - GRANULAR MATTER AB - Powders and grains exhibit unpredictable jamming-to-flow transitions that manifest themselves on geophysical scales in catastrophic slip events such as landslides and earthquakes, and on laboratory/industrial scales in profound processing difficulties. Over the past few years, insight into these transitions has been provided by new evidence that slip events may be accompanied, or even preceded, by electrical effects. In the present work, we quantify the correlation between slip and the separation of electrical charges, using an archetypal granular material: photoelastic polymers. We measure a strong correlation between material displacement, acoustic emissions, and voltage. We find that the generation of voltage is associated with surface, rather than bulk properties of the granular materials. While voltage precursors are only occasionally observed in this system, there is some asymmetry in the cross-correlation between the slip and voltage signals that indicates differences between the pre- and post-slip dynamics. DA - 2014/4// PY - 2014/4// DO - 10.1007/s10035-013-0471-3 VL - 16 IS - 2 SP - 217-222 SN - 1434-7636 KW - Sheared granular materials KW - Stick-slip KW - Electrical charging ER - TY - JOUR TI - Coordinating subdomains of ferritin protein cages with catalysis and biomineralization viewed from the C (4) cage axes AU - Theil, Elizabeth C. AU - Turano, Paola AU - Ghini, Veronica AU - Allegrozzi, Marco AU - Bernacchioni, Caterina T2 - JOURNAL OF BIOLOGICAL INORGANIC CHEMISTRY AB - Integrated ferritin protein cage function is the reversible synthesis of protein-caged, solid Fe2O3·H2O minerals from Fe2+ for metabolic iron concentrates and oxidant protection; biomineral order differs in different ferritin proteins. The conserved 432 geometric symmetry of ferritin protein cages parallels the subunit dimer, trimer, and tetramer interfaces, and coincides with function at several cage axes. Multiple subdomains distributed in the self-assembling ferritin nanocages have functional relationships to cage symmetry such as Fe2+ transport though ion channels (threefold symmetry), biomineral nucleation/order (fourfold symmetry), and mineral dissolution (threefold symmetry) studied in ferritin variants. On the basis of the effects of natural or synthetic subunit dimer cross-links, cage subunit dimers (twofold symmetry) influence iron oxidation and mineral dissolution. 2Fe2+/O2 catalysis in ferritin occurs in single subunits, but with cooperativity (n = 3) that is possibly related to the structure/function of the ion channels, which are constructed from segments of three subunits. Here, we study 2Fe2+ + O2 protein catalysis (diferric peroxo formation) and dissolution of ferritin Fe2O3·H2O biominerals in variants with altered subunit interfaces for trimers (ion channels), E130I, and external dimer surfaces (E88A) as controls, and altered tetramer subunit interfaces (L165I and H169F). The results extend observations on the functional importance of structure at ferritin protein twofold and threefold cage axes to show function at ferritin fourfold cage axes. Here, conserved amino acids facilitate dissolution of ferritin-protein-caged iron biominerals. Biological and nanotechnological uses of ferritin protein cage fourfold symmetry and solid-state mineral properties remain largely unexplored. DA - 2014/6// PY - 2014/6// DO - 10.1007/s00775-014-1103-z VL - 19 IS - 4-5 SP - 615-622 SN - 1432-1327 KW - Ferritin KW - Protein nanocage KW - Ferric oxo KW - Di-iron protein KW - Nanobiomineral ER - TY - JOUR TI - The influence of neutrinos on the nucleosynthesis of accretion disc outflows AU - Caballero, O. L. AU - Malkus, A. C. AU - McLaughlin, G. C. AU - Surman, R. A. T2 - JOURNAL OF PHYSICS G-NUCLEAR AND PARTICLE PHYSICS AB - We present a short review of recent progress on the influence of neutrinos on the nucleosynthesis from black hole accretion disc outflows. Discs that form from the end of life of rapidly rotating massive stars as well as discs that form from mergers will produce large numbers of neutrinos. These neutrinos influence the nucleosynthesis that occurs in hot accretion disc outflows. A variety of nucleosynthesis products can be produced in these outflows. We review work on nickel, p-process and r-process elements. DA - 2014/4// PY - 2014/4// DO - 10.1088/0954-3899/41/4/044004 VL - 41 IS - 4 SP - SN - 1361-6471 KW - neutrinos KW - nucleosynthesis KW - accretion disc ER - TY - JOUR TI - The influence of molecular orientation on organic bulk heterojunction solar cells AU - Tumbleston, John R. AU - Collins, Brian A. AU - Yang, Liqiang AU - Stuart, Andrew C. AU - Gann, Eliot AU - Ma, Wei AU - You, Wei AU - Ade, Harald T2 - NATURE PHOTONICS DA - 2014/5// PY - 2014/5// DO - 10.1038/nphoton.2014.55 VL - 8 IS - 5 SP - 385-391 SN - 1749-4893 ER - TY - JOUR TI - Supernovae, neutrinos, and nucleosynthesis AU - Froehlich, Carla T2 - JOURNAL OF PHYSICS G-NUCLEAR AND PARTICLE PHYSICS AB - Core-collapse supernovae are the violent explosions at the end of the life of massive stars (? 8 ? 10?M?). In these explosions a wide range of elements are synthesized and ejected: low-mass elements (O and Mg) from the hydrostatic evolution, intermediate-mass elements and Fe-group elements from explosive nucleosynthesis, and elements heavier than iron from the ?p-process and potentially an r-process. However, supernova nucleosynthesis predictions are hampered by the not yet fully understood supernova explosion mechanism. In addition, recent progress in observational astronomy paints a fascinating picture for the origin of heavy elements, which is more complicated than the traditional s-, r-, and ?-processes. In this paper, we summarize the status of core-collapse supernova nucleosynthesis. DA - 2014/4// PY - 2014/4// DO - 10.1088/0954-3899/41/4/044003 VL - 41 IS - 4 SP - SN - 1361-6471 UR - http://dx.doi.org/10.1088/0954-3899/41/4/044003 KW - nucleosynthesis KW - novae and supernovae KW - neutrinos interactions KW - chemical composition of stars ER - TY - JOUR TI - Self-consistent covariant description of vector meson decay constants and chirality-even quark-antiquark distribution amplitudes up to twist 3 in the light-front quark model AU - Choi, Ho-Meoyng AU - Ji, Chueng-Ryong T2 - PHYSICAL REVIEW D AB - Although the meson decay amplitude described by a two-point function may be regarded as one of the simplest possible physical observables, it is interesting that this apparently simple amplitude bears abundant fundamental information on QCD vacuum dynamics and chiral symmetry. The light-front zero-mode issue of the vector meson decay constant ${f}_{V}$ is in this respect highly nontrivial and deserves careful analysis. We discuss the zero-mode issue in the light-front quark model (LFQM) prediction of ${f}_{V}$ from the perspective of the vacuum fluctuation consistent with the chiral symmetry of QCD. We extend the exactly solvable, manifestly covariant Bethe-Salpeter model calculation to the more phenomenologically accessible, realistic light-front quark model and present a self-consistent covariant description of ${f}_{V}$, analyzing the twist-2 and twist-3 quark-antiquark distribution amplitudes with even chirality. DA - 2014/2/19/ PY - 2014/2/19/ DO - 10.1103/physrevd.89.033011 VL - 89 IS - 3 SP - SN - 1550-2368 ER - TY - JOUR TI - SPITZER OBSERVATIONS OF THE TYPE IA SUPERNOVA REMNANT N103B: KEPLER'S OLDER COUSIN? AU - Williams, Brian J. AU - Borkowski, Kazimierz J. AU - Reynolds, Stephen P. AU - Ghavamian, Parviz AU - Raymond, John C. AU - Long, Knox S. AU - Blair, William P. AU - Sankrit, Ravi AU - Winkler, P. Frank AU - Hendrick, Sean P. AU - al., T2 - ASTROPHYSICAL JOURNAL AB - We report results from Spitzer observations of SNR 0509-68.7, also known as N103B, a young Type Ia supernova remnant in the Large Magellanic Cloud that shows interaction with a dense medium in its western hemisphere. Our images show that N103B has strong IR emission from warm dust in the post-shock environment. The post-shock gas density we derive, 45 cm$^{-3}$, is much higher than in other Type Ia remnants in the LMC, though a lack of spatial resolution may bias measurements towards regions of higher than average density. This density is similar to that in Kepler's SNR, a Type Ia interacting with a circumstellar medium. Optical images show H$\alpha$ emission along the entire periphery of the western portion of the shock, with [O III] and [S II] lines emitted from a few dense clumps of material where the shock has become radiative. The dust is silicate in nature, though standard silicate dust models fail to reproduce the "18 $\mu$m" silicate feature that peaks instead at 17.3 $\mu$m. We propose that the dense material is circumstellar material lost from the progenitor system, as with Kepler. If the CSM interpretation is correct, this remnant would become the second member, along with Kepler, of a class of Type Ia remnants characterized by interaction with a dense CSM hundreds of years post-explosion. A lack of N enhancement eliminates symbiotic AGB progenitors. The white dwarf companion must have been relatively unevolved at the time of the explosion. DA - 2014/8/1/ PY - 2014/8/1/ DO - 10.1088/0004-637x/790/2/139 VL - 790 IS - 2 SP - SN - 1538-4357 KW - dust, extinction KW - ISM: supernova remnants ER - TY - JOUR TI - Production of Ni-56 in black hole-neutron star merger accretion disc outflows AU - Surman, R. AU - Caballero, O. L. AU - McLaughlin, G. C. AU - Just, O. AU - Janka, H-Th T2 - JOURNAL OF PHYSICS G-NUCLEAR AND PARTICLE PHYSICS AB - The likely outcome of a compact object merger event is a central black hole surrounded by a rapidly accreting torus of debris. This disk of debris is a rich source of element synthesis, the outcome of which is needed to predict electromagnetic counterparts of individual events and to understand the contribution of mergers to galactic chemical evolution. Here we study disk outflow nucleosynthesis in the context of a two-dimensional, time-dependent black hole-neutron star merger accretion disk model. We use two time snapshots from this model to examine the impact of the evolution of the neutrino fluxes from the disk on the element synthesis. While the neutrino fluxes from the early-time disk snapshot appear to favor neutron-rich outflows, by the late-time snapshot the situation is reversed. As a result we find copious production of Nickel-56 in the outflows. DA - 2014/4// PY - 2014/4// DO - 10.1088/0954-3899/41/4/044006 VL - 41 IS - 4 SP - SN - 1361-6471 KW - nuclear reactions KW - nucleosynthesis KW - accretion discs KW - abundances ER - TY - JOUR TI - Probing transient protein-mediated DNA linkages using nanoconfinement AU - Roushan, Maedeh AU - Kaur, Parminder AU - Karpusenko, Alena AU - Countryman, Preston J. AU - Ortiz, Carlos P. AU - Fang Lim, Shuang AU - Wang, Hong AU - Riehn, Robert T2 - Biomicrofluidics AB - We present an analytic technique for probing protein-catalyzed transient DNA loops that is based on nanofluidic channels. In these nanochannels, DNA is forced in a linear configuration that makes loops appear as folds whose size can easily be quantified. Using this technique, we study the interaction between T4 DNA ligase and DNA. We find that T4 DNA ligase binding changes the physical characteristics of the DNA polymer, in particular persistence length and effective width. We find that the rate of DNA fold unrolling is significantly reduced when T4 DNA ligase and ATP are applied to bare DNA. Together with evidence of T4 DNA ligase bridging two different segments of DNA based on AFM imaging, we thus conclude that ligase can transiently stabilize folded DNA configurations by coordinating genetically distant DNA stretches. DA - 2014/5// PY - 2014/5// DO - 10.1063/1.4882775 VL - 8 IS - 3 SP - 034113 J2 - Biomicrofluidics LA - en OP - SN - 1932-1058 UR - http://dx.doi.org/10.1063/1.4882775 DB - Crossref ER - TY - JOUR TI - Molecular Doping Control at a Topological Insulator Surface: F-4-TCNQ on Bi2Se3 AU - Wang, J. AU - Hewitt, A. S. AU - Kumar, R. AU - Boltersdorf, J. AU - Guan, T. AU - Hunte, F. AU - Maggard, P. A. AU - Brom, J. E. AU - Redwing, J. M. AU - Dougherty, D. B. T2 - JOURNAL OF PHYSICAL CHEMISTRY C AB - Recent electrical measurements have accessed transport in the topological surface state band of thin exfoliated samples of Bi2Se3 by removing the bulk n-type doping by contact with thin films of the molecular acceptor F4-TCNQ. Here we report on the film growth and interfacial electronic characterization of F4-TCNQ grown on Bi2Se3. Atomic force microscopy shows wetting layer formation followed by 3D island growth. X-ray photoelectron spectroscopy is consistent with this picture and also shows that charge transferred to the molecular layer is localized on nitrogen atoms. Ultraviolet photoelectron spectroscopy shows a work function increase and an upward shift of the valence band edge that suggest significant reduction in carrier density at the Bi2Se3 surface. DA - 2014/7/10/ PY - 2014/7/10/ DO - 10.1021/jp412690h VL - 118 IS - 27 SP - 14860-14865 SN - 1932-7447 ER - TY - JOUR TI - MAGNETIC FIELD AMPLIFICATION IN THE THIN X-RAY RIMS OF SN 1006 AU - Ressler, Sean M. AU - Katsuda, Satoru AU - Reynolds, Stephen P. AU - Long, Knox S. AU - Petre, Robert AU - Williams, Brian J. AU - Winkler, P. Frank T2 - ASTROPHYSICAL JOURNAL AB - Several young supernova remnants (SNRs), including SN1006, emit synchrotron X-rays in narrow filaments, hereafter thin rims, along their periphery. The widths of these rims imply 50 to 100 $\mu$G fields in the region immediately behind the shock, far larger than expected for the interstellar medium compressed by unmodified shocks, assuming electron radiative losses limit rim widths. However, magnetic-field damping could also produce thin rims. Here we review the literature on rim width calculations, summarizing the case for magnetic-field amplification. We extend these calculations to include an arbitrary power-law dependence of the diffusion coefficient on energy, $D \propto E^{\mu}$. Loss-limited rim widths should shrink with increasing photon energy, while magnetic-damping models predict widths almost independent of photon energy. We use these results to analyze Chandra observations of SN 1006, in particular the southwest limb. We parameterize the full widths at half maximum (FWHM) in terms of energy as FWHM $\propto E^{m_E}_{\gamma}$. Filament widths in SN1006 decrease with energy; $m_E \sim -0.3$ to $-0.8$, implying magnetic field amplification by factors of 10 to 50, above the factor of 4 expected in strong unmodified shocks. For SN 1006, the rapid shrinkage rules out magnetic damping models. It also favors short mean free paths (small diffusion coefficients) and strong dependence of $D$ on energy ($\mu \ge 1$). DA - 2014/8/1/ PY - 2014/8/1/ DO - 10.1088/0004-637x/790/2/85 VL - 790 IS - 2 SP - SN - 1538-4357 KW - acceleration of particles KW - ISM: individual objects (SN 1006) KW - ISM: magnetic fields KW - ISM: supernova remnants KW - X-rays: ISM ER - TY - JOUR TI - Lewis Worth Seagondollar Obituary AU - Gould, Chris AU - Haase, David T2 - PHYSICS TODAY AB - Lewis Worth Seagondollar, longtime secretary of the Southeast Section of the American Physical Society, influential president of the physics student honor society Sigma Pi Sigma, and emeritus professor of physics at North Carolina State University, died at his home in Raleigh on 20 September 2013.Lewis Worth SeagondollarBRAND FORTNER, NCSU PHYSICS DEPARTMENTPPT|High resolutionBorn in Emporia, Kansas, on 30 September 1920, Worth graduated from what is now Emporia State University in 1941. He enrolled soon after in graduate school at the University of Wisconsin–Madison and began working with Raymond Herb on accelerator construction. In 1944 he went to Los Alamos to join the Manhattan Project, and he found himself in the spring of 1944 as part of a three-person team that measured the critical mass of plutonium-239.As the junior member of the team, Worth worked the overnight shift. In an episode that encapsulates his unfailing optimism that every problem has a solution, he succeeded in hammering out a small dent in one of the plutonium hemispheres after it was dropped on a table. Stationed nine miles away in Alamogordo, New Mexico, Worth witnessed the first nuclear test, and his experiences formed the basis of a memorable presentation he gave hundreds of times to civic and student groups over the following 50 years.Worth returned to Wisconsin in 1948 and, as the first student of Heinz Barschall, completed a dissertation in 1947 on fast-neutron cross sections on aluminum. He then participated in the installation of the research Van de Graaff accelerator at the University of Kansas. Worth worked as a professor of physics at Kansas before moving in 1965 to NC State, where he served as head of the physics department for 10 years. While at NC State, he cofounded the Triangle Universities Nuclear Laboratory and measured nuclear cross sections with secondary neutron beams and with cryogenic polarized targets. After retiring in 1991, he remained as professor emeritus; younger researchers gratefully remember his willingness to help and advise them.Worth offered years of dedicated service to ΣΠΣ and to the Society of Physics Students (SPS). It was during Worth’s tenure as ΣΠΣ president that the honor society merged with the American Institute of Physics (AIP) to form SPS. According to ΣΠΣ’s official history, as the presiding officer, Worth “allowed everyone to have his say and yet kept to the agenda (while he ‘chain-smoked 75 cigars!’).” Needing a two-thirds majority to pass, the articles of agreement between AIP and ΣΠΣ were approved with one vote to spare, 181 out of 270 (see Donald Cunningham and coauthors, Physics Today, September 1968, page 59). The honor society later instituted the Worth Seagondollar Service Award to recognize an exemplary level of commitment and service to SPS and ΣΠΣ. He was the first recipient.Worth’s 23 years as secretary of the Southeast Section of the American Physical Society was the longest tenure of anyone in that position. He steered the section through a period of rapid growth in the physics departments and research facilities in the Southeast and associated growth in participation at section meetings. He received two of the section’s highest awards, one for excellence in teaching physics in the Southeast and the other for service to the section.In retirement, and well into his eighties, Worth remained an active speaker and was invited to give many talks; he felt particularly honored to speak at the ΣΠΣ quadrennial meeting in Albuquerque in 2004. For many years he also set his scientific and managerial skills to planning and executing yard-sale shopping trips. He was known for his early use of GPS to optimize shopping routes. Worth was one of only a few people to ever buy a used, working Mercedes-Benz at a yard sale. He also found many pieces of semi-antique scientific equipment in similar unlikely venues.© 2014 American Institute of Physics. DA - 2014/3// PY - 2014/3// DO - 10.1063/pt.3.2319 VL - 67 IS - 3 SP - 64-66 SN - 1945-0699 ER - TY - JOUR TI - Isospin properties of electric dipole excitations in Ca-48 AU - Derya, V. AU - Savran, D. AU - Endres, J. AU - Harakeh, M. N. AU - Hergert, H. AU - Kelley, J. H. AU - Papakonstantinou, P. AU - Pietralla, N. AU - Ponomarev, V. Y. AU - Roth, R. AU - Rusev, G. AU - Tonchev, A. P. AU - Tornow, W. AU - Wortche, H. J. AU - Zilges, A. T2 - Physics Letters. B AB - Two different experimental approaches were combined to study the electric dipole strength in the doubly-magic nucleus 48Ca below the neutron threshold. Real-photon scattering experiments using bremsstrahlung up to 9.9 MeV and nearly mono-energetic linearly polarized photons with energies between 6.6 and 9.51 MeV provided strength distribution and parities, and an (\alpha,\alpha'\gamma) experiment at E_{\alpha}=136 MeV gave cross sections for an isoscalar probe. The unexpected difference observed in the dipole response is compared to calculations using the first-order random-phase approximation and points to an energy-dependent isospin character. A strong isoscalar state at 7.6 MeV was identified for the first time supporting a recent theoretical prediction. DA - 2014/// PY - 2014/// DO - 10.1016/j.physletb.2014.01.050 VL - 730 SP - 288-292 ER - TY - JOUR TI - From square-well to Janus: Improved algorithm for integral equation theory and comparison with thermodynamic perturbation theory within the Kern-Frenkel model AU - Giacometti, A. AU - Gogelein, C. AU - Lado, F. AU - Sciortino, F. AU - Ferrari, S. AU - Pastore, G. T2 - Journal of Chemical Physics DA - 2014/// PY - 2014/// VL - 140 IS - 9 ER - TY - JOUR TI - Dynamics of MutS-Mismatched DNA Complexes Are Predictive of Their Repair Phenotypes AU - DeRocco, Vanessa C. AU - Sass, Lauryn E. AU - Qiu, Ruoyi AU - Weninger, Keith R. AU - Erie, Dorothy A. T2 - BIOCHEMISTRY AB - MutS recognizes base–base mismatches and base insertions/deletions (IDLs) in newly replicated DNA. Specific interactions between MutS and these errors trigger a cascade of protein–protein interactions that ultimately lead to their repair. The inability to explain why different DNA errors are repaired with widely varying efficiencies in vivo remains an outstanding example of our limited knowledge of this process. Here, we present single-molecule Förster resonance energy transfer measurements of the DNA bending dynamics induced by Thermus aquaticus MutS and the E41A mutant of MutS, which is known to have error specific deficiencies in signaling repair. We compared three DNA mismatches/IDLs (T-bulge, GT, and CC) with repair efficiencies ranging from high to low. We identify three dominant DNA bending states [slightly bent/unbent (U), intermediately bent (I), and significantly bent (B)] and find that the kinetics of interconverting among states varies widely for different complexes. The increased stability of MutS–mismatch/IDL complexes is associated with stabilization of U and lowering of the B to U transition barrier. Destabilization of U is always accompanied by a destabilization of B, supporting the suggestion that B is a “required” precursor to U. Comparison of MutS and MutS-E41A dynamics on GT and the T-bulge suggests that hydrogen bonding to MutS facilitates the changes in base–base hydrogen bonding that are required to achieve the U state, which has been implicated in repair signaling. Taken together with repair propensities, our data suggest that the bending kinetics of MutS–mismatched DNA complexes may control the entry into functional pathways for downstream signaling of repair. DA - 2014/4/1/ PY - 2014/4/1/ DO - 10.1021/bi401429b VL - 53 IS - 12 SP - 2043-2052 SN - 0006-2960 ER - TY - JOUR TI - An Easy and Effective Method to Modulate Molecular Energy Level of the Polymer Based on Benzodithiophene for the Application in Polymer Solar Cells AU - Zhang, Maojie AU - Guo, Xia AU - Ma, Wei AU - Zhang, Shaoqing AU - Huo, Lijun AU - Ade, Harald AU - Hou, Jianhui T2 - ADVANCED MATERIALS AB - Attaching meta-alkoxy-phenyl groups as conjugated side chains is an easy and effective way to modulate the molecular energy level of D-A polymer for photovoltaic application, and the polymer solar cells based on the polymer consisting meta-alkoxy-phenyl groups as conjugated side chain, PBT-OP, shows an enhanced open circuit voltage and thus higher efficiency of 7.50%, under the illumination of AM 1.5G, 100 mW/cm(2) . DA - 2014/4// PY - 2014/4// DO - 10.1002/adma.201304631 VL - 26 IS - 13 SP - 2089-2095 SN - 1521-4095 KW - molecular energy level KW - polymer solar cell KW - polymer KW - efficiency ER - TY - JOUR TI - A role for iron and oxygen chemistry in preserving soft tissues, cells and molecules from deep time AU - Schweitzer, M. H. AU - Zheng, W. X. AU - Cleland, T. P. AU - Goodwin, M. B. AU - Boatman, E. AU - Theil, E. AU - Marcus, M. A. AU - Fakra, S. C. T2 - Proceedings of the Royal Society of London. Series B DA - 2014/// PY - 2014/// VL - 281 IS - 1775 ER - TY - JOUR TI - A method for measuring coherent elastic neutrino-nucleus scattering at a far off-axis high-energy neutrino beam target AU - Brice, S. J. AU - Cooper, R. L. AU - DeJongh, F. AU - Empl, A. AU - Garrison, L. M. AU - Hime, A. AU - Hungerford, E. AU - Kobilarcik, T. AU - Loer, B. AU - Mariani, C. AU - Mocko, M. AU - Muhrer, G. AU - Pattie, R. AU - Pavlovic, Z. AU - Ramberg, E. AU - Scholberg, K. AU - Tayloe, R. AU - Thornton, R. T. AU - Yoo, J. AU - Young, A. T2 - PHYSICAL REVIEW D AB - We present a new experimental method for measuring the process of Coherent Elastic Neutrino Nucleus Scattering (CENNS). This method uses a detector situated transverse to a high energy neutrino beam production target. This detector would be sensitive to the low energy neutrinos arising from pion decays-at-rest in the target. We discuss the physics motivation for making this measurement and outline the predicted backgrounds and sensitivities using this approach. We report a measurement of neutron backgrounds as found in an off-axis surface location of the Fermilab Booster Neutrino Beam (BNB) target. The results indicate that the Fermilab BNB target is a favorable location for a CENNS experiment. DA - 2014/4/3/ PY - 2014/4/3/ DO - 10.1103/physrevd.89.072004 VL - 89 IS - 7 SN - 1550-2368 ER - TY - JOUR TI - Visualizations of coastal terrain time series AU - Tateosian, Laura AU - Mitasova, Helena AU - Thakur, Sidharth AU - Hardin, Eric AU - Russ, Emily AU - Blundell, Bruce T2 - INFORMATION VISUALIZATION AB - In coastal regions, water, wind, gravitation, vegetation, and human activity continuously alter landscape surfaces. Visualizations are important for understanding coastal landscape evolution and its driving processes. Visualizing change in highly dynamic coastal terrain poses a formidable challenge; the combination of natural and anthropogenic forces leads to cycles of retreat and recovery and complex morphology of landforms. In recent years, repeated high-resolution laser terrain scans have generated a time series of point cloud data that represent landscapes at snapshots in time, including the impacts of major storms. In this article, we build on existing approaches for visualizing spatial–temporal data to create a collection of perceptual visualizations to support coastal terrain evolution analysis. We extract terrain features and track their migration; we derive temporal summary maps and heat graphs that quantify the pattern of elevation change and sediment redistribution and use the space–time cube concept to create visualizations of terrain evolution. The space–time cube approach allows us to represent shoreline evolution as an isosurface extracted from a voxel model created by stacking time series of digital elevation models. We illustrate our approach on a series of Light Detection and Ranging surveys of sandy North Carolina barrier islands. Our results reveal terrain changes of shoreline and dune ridge migration, dune breaches and overwash, the formation of new dune ridges, and the construction and destruction of homes, changes which are due to erosion and accretion, hurricanes, and human activities. These events are all visualized within their geographic and temporal contexts. DA - 2014/7// PY - 2014/7// DO - 10.1177/1473871613487086 VL - 13 IS - 3 SP - 266-282 SN - 1473-8724 KW - Visualization of time series KW - temporal visualization KW - geovisualization KW - visual perception KW - visual exploration KW - visualize changes KW - geospatial data KW - three-dimensional visualization KW - spatial data KW - visual exploration KW - space-time cube KW - geographic information systems KW - LiDAR KW - time series KW - terrain elevation KW - land surfaces KW - GIS GRASS ER - TY - JOUR TI - The Role of Regioregularity, Crystallinity, and Chain Orientation on Electron Transport in a High-Mobility n-Type Copolymer AU - Steyrleuthner, Robert AU - Di Pietro, Riccardo AU - Collins, Brian A. AU - Polzer, Frank AU - Himmelberger, Scott AU - Schubert, Marcel AU - Chen, Zhihua AU - Zhang, Shiming AU - Salleo, Alberto AU - Ade, Harald AU - Facchetti, Antonio AU - Neher, Dieter T2 - JOURNAL OF THE AMERICAN CHEMICAL SOCIETY AB - We investigated the correlation between the polymer backbone structural regularity and the charge transport properties of poly{[N,N'-bis(2-octyldodecyl)-1,4,5,8-naphthalenediimide-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} [P(NDI2OD-T2)], a widely studied semiconducting polymer exhibiting high electron mobility and an unconventional micromorphology. To understand the influence of the chemical structure and crystal packing of conventional regioregular P(NDI2OD-T2) [RR-P(NDI2OD-T2)] on the charge transport, the corresponding regioirregular polymer RI-P(NDI2OD-T2) was synthesized. By combining optical, X-ray, and transmission electron microscopy data, we quantitatively characterized the aggregation, crystallization, and backbone orientation of all of the polymer films, which were then correlated to the electron mobilities in electron-only diodes. By carefully selecting the preparation conditions, we were able to obtain RR-P(NDI2OD-T2) films with similar crystalline structure along the three crystallographic axes but with different orientations of the polymer chains with respect to the substrate surface. RI-P(NDI2OD-T2), though exhibiting a rather similar LUMO structure and energy compared with the regioregular counterpart, displayed a very different packing structure characterized by the formation of ordered stacks along the lamellar direction without detectible π-stacking. Vertical electron mobilities were extracted from the space-charge-limited currents in unipolar devices. We demonstrate the anisotropy of the charge transport along the different crystallographic directions and how the mobility depends on π-stacking but is insensitive to the degree or coherence of lamellar stacking. The comparison between the regioregular and regioirregular polymers also shows how the use of large planar functional groups leads to improved charge transport, with mobilities that are less affected by chemical and structural disorder with respect to classic semicrystalline polymers such as poly(3-hexylthiophene). DA - 2014/3/19/ PY - 2014/3/19/ DO - 10.1021/ja4118736 VL - 136 IS - 11 SP - 4245-4256 SN - 0002-7863 ER - TY - JOUR TI - TRF1 and TRF2 use different mechanisms to find telomeric DNA but share a novel mechanism to search for protein partners at telomeres AU - Lin, Jiangguo AU - Countryman, Preston AU - Buncher, Noah AU - Kaur, Parminder AU - Longjiang, E. AU - Zhang, Yiyun AU - Gibson, Greg AU - You, Changjiang AU - Watkins, Simon C. AU - Piehler, Jacob AU - Opresko, Patricia L. AU - Kad, Neil M. AU - Wang, Hong T2 - NUCLEIC ACIDS RESEARCH AB - Human telomeres are maintained by the shelterin protein complex in which TRF1 and TRF2 bind directly to duplex telomeric DNA. How these proteins find telomeric sequences among a genome of billions of base pairs and how they find protein partners to form the shelterin complex remains uncertain. Using single-molecule fluorescence imaging of quantum dot-labeled TRF1 and TRF2, we study how these proteins locate TTAGGG repeats on DNA tightropes. By virtue of its basic domain TRF2 performs an extensive 1D search on nontelomeric DNA, whereas TRF1's 1D search is limited. Unlike the stable and static associations observed for other proteins at specific binding sites, TRF proteins possess reduced binding stability marked by transient binding (∼ 9-17 s) and slow 1D diffusion on specific telomeric regions. These slow diffusion constants yield activation energy barriers to sliding ∼ 2.8-3.6 κ(B)T greater than those for nontelomeric DNA. We propose that the TRF proteins use 1D sliding to find protein partners and assemble the shelterin complex, which in turn stabilizes the interaction with specific telomeric DNA. This 'tag-team proofreading' represents a more general mechanism to ensure a specific set of proteins interact with each other on long repetitive specific DNA sequences without requiring external energy sources. DA - 2014/2// PY - 2014/2// DO - 10.1093/nar/gkt1132 VL - 42 IS - 4 SP - 2493-2504 SN - 1362-4962 ER - TY - JOUR TI - Storage of ultracold neutrons in the magneto-gravitational trap of the UCN tau experiment AU - Salvat, D. J. AU - Adamek, E. R. AU - Barlow, D. AU - Bowman, J. D. AU - Broussard, L. J. AU - Callahan, N. B. AU - Clayton, S. M. AU - Cude-Woods, C. AU - Currie, S. AU - Dees, E. B. AU - Fox, W. AU - Geltenbort, P. AU - Hickerson, K. P. AU - Holley, A. T. AU - Liu, C. -Y. AU - Makela, M. AU - Medina, J. AU - Morley, D. J. AU - Morris, C. L. AU - Penttilae, S. I. AU - Ramsey, J. AU - Saunders, A. AU - Seestrom, S. J. AU - Sharapov, E. I. AU - Sjue, S. K. L. AU - Slaughter, B. A. AU - Vanderwerp, J. AU - VornDick, B. AU - Walstrom, P. L. AU - Wang, Z. AU - Womack, T. L. AU - Young, A. R. T2 - PHYSICAL REVIEW C AB - A precise value for the neutron lifetime (about 880 s) is needed for nuclear astrophysics predictions of Big-Bang nucleosynthesis and solar neutrino production, as well as in precision searches for new physics beyond the Standard Model. This work reports on a new type of magnetic neutron trap that has the potential to resolve the present 4-sigma inconsistency in measurements of the neutron lifetime, and suggests that a next generation of measurements with less than one second uncertainty is possible. DA - 2014/5/23/ PY - 2014/5/23/ DO - 10.1103/physrevc.89.052501 VL - 89 IS - 5 SN - 1089-490X ER - TY - JOUR TI - Sensitivity studies for the weak r process: neutron capture rates AU - Surman, R. AU - Mumpower, M. AU - Sinclair, R. AU - Jones, K. L. AU - Hix, W. R. AU - McLaughlin, G. C. T2 - AIP ADVANCES AB - Rapid neutron capture nucleosynthesis involves thousands of nuclear species far from stability, whose nuclear properties need to be understood in order to accurately predict nucleosynthetic outcomes. Recently sensitivity studies have provided a deeper understanding of how the r process proceeds and have identified pieces of nuclear data of interest for further experimental or theoretical study. A key result of these studies has been to point out the importance of individual neutron capture rates in setting the final r-process abundance pattern for a ‘main’ (A ∼ 130 peak and above) r process. Here we examine neutron capture in the context of a ‘weak’ r process that forms primarily the A ∼ 80 r-process abundance peak. We identify the astrophysical conditions required to produce this peak region through weak r-processing and point out the neutron capture rates that most strongly influence the final abundance pattern. DA - 2014/4// PY - 2014/4// DO - 10.1063/1.4867191 VL - 4 IS - 4 SP - SN - 2158-3226 ER - TY - JOUR TI - Scattering Amplitudes Interpolating Between Instant Form and Front Form of Relativistic Dynamics AU - Ji, Chueng-Ryong AU - Bakker, Bernard L. G. AU - Li, Ziyue AU - Suzuki, Alfredo T. T2 - FEW-BODY SYSTEMS DA - 2014/6// PY - 2014/6// DO - 10.1007/s00601-013-0796-9 VL - 55 IS - 5-7 SP - 425-434 SN - 1432-5411 ER - TY - JOUR TI - Progress in ZnO Acceptor Doping: What Is the Best Strategy? AU - Reynolds, Judith G. AU - Reynolds, C. Lewis T2 - ADVANCES IN CONDENSED MATTER PHYSICS AB - This paper reviews the recent progress in acceptor doping of ZnO that has been achieved with a focus toward the optimum strategy. There are three main approaches for generating p-type ZnO: substitutional group IA elements on a zinc site, codoping of donors and acceptors, and substitution of group VA elements on an oxygen site. The relevant issues are whether there is sufficient incorporation of the appropriate dopant impurity species, does it reside on the appropriate lattice site, and lastly whether the acceptor ionization energy is sufficiently small to enable significant p-type conduction at room temperature. The potential of nitrogen doping and formation of the appropriate acceptor complexes is highlighted although theoretical calculations predict that nitrogen on an oxygen site is a deep acceptor. We show that an understanding of the growth and annealing steps to achieve the relevant acceptor defect complexes is crucial to meet requirements. DA - 2014/// PY - 2014/// DO - 10.1155/2014/457058 VL - 2014 SP - SN - 1687-8124 ER - TY - JOUR TI - Parameterization of the dielectric functions of InGaSb alloys AU - Kim, Tae Jung AU - Byun, Jun Seok AU - Hwang, Soon Yong AU - Park, Han Gyeol AU - Kang, Yu Ri AU - Park, Jae Chan AU - Kim, Young Dong AU - Aspnes, David E. T2 - CURRENT APPLIED PHYSICS AB - Analytic expressions are presented that accurately represent the dielectric functions ε = ε1 + iε2 of In1−xGaxSb from 1.5 to 6 eV. We used the parametric model, which portrays ε as a sum of polynomials and can accommodate the asymmetric nature of critical point transitions. The ε spectra were obtained previously by spectroscopic ellipsometry for x = 0.000, 0.102, 0.305, 0.473, 0.684, and 1.000. The ε data are successfully reconstructed and parameterized by eight polynomials. With the interpolation of parameters of ε spectra, we can determine ε as a continuous function of Ga composition and energy over the entire composition range 0 ≤ x ≤ 1. These results should be useful for device design and in situ monitoring of deposition. DA - 2014/5// PY - 2014/5// DO - 10.1016/j.cap.2014.03.010 VL - 14 IS - 5 SP - 768-771 SN - 1878-1675 KW - InGaSb KW - Dielectric function KW - Parametric model KW - Ellipsometry ER - TY - JOUR TI - Organic photovoltaic cells with controlled polarization sensitivity AU - Awartani, Omar AU - Kudenov, Michael W. AU - Brendan T. O'Connor, T2 - APPLIED PHYSICS LETTERS AB - In this study, we demonstrate linearly polarized organic photovoltaic cells with a well-controlled level of polarization sensitivity. The polarized devices were created through the application of a large uniaxial strain to the bulk heterojunction poly(3-hexylthiophene):Phenyl-C61-butyric acid methyl ester (P3HT:PCBM) film and printing the plastically deformed active layer onto a PEDOT:PSS and indium tin oxide coated glass substrate. The P3HT:PCBM layer is processed such that it is able to accommodate high strains (over 100%) without fracture. After printing the strained films, thermal annealing is used to optimize solar cell performance while maintaining polarization sensitivity. A dichroic ratio and short circuit current ratio of ≈6.1 and ≈1.6 were achieved, respectively. DA - 2014/3/3/ PY - 2014/3/3/ DO - 10.1063/1.4868041 VL - 104 IS - 9 SP - SN - 1077-3118 ER - TY - JOUR TI - Optical second-harmonic generation induced by electric current in graphene on Si and SiC substrates AU - An, Yong Q. AU - Rowe, J. E. AU - Dougherty, Daniel B. AU - Lee, Ji Ung AU - Diebold, Alain C. T2 - PHYSICAL REVIEW B AB - We find that the flow of direct electric current (dc) through graphene on substrate enhances surface optical second-harmonic generation (SHG) from the graphene/substrate system. The current can enhance surface SHG by about 300% for a chemical-vapor-deposition (CVD) graphene monolayer on a SiO${}_{2}/\mathrm{Si}(001)$ substrate, and by about 25% for an epitaxial four-layer-graphene film on a 3.5\ifmmode^\circ\else\textdegree\fi{}-miscut vicinal SiC(0001) substrate. The enhancement in both the CVD and epitaxial graphene samples is due to electric field-induced SHG, which is produced by the current-associated vertical electric field at the SiO${}_{2}/$Si interface or at the graphene/SiC interface. Measurements of rotational-anisotropy SHG (RA-SH) from both samples revealed that the current-induced SHG varies strongly with the measurement location along the current flow direction. By measuring RA-SH from the vicinal SiC(0001) substrate, we determined all three second-order susceptibility tensor elements (${d}_{33}$ = \ensuremath{-}52.0 pm/V, ${d}_{15}$ = 20.0 pm/V, and ${d}_{31}$ = 18.7 pm/V) that characterize the SHG response of hexagonal SiC at the fundamental wavelength of 740 nm. We further determined the three effective susceptibility tensor elements (${d}_{33}$ = \ensuremath{-}135.8 pm/V, ${d}_{15}$ = 18.5 pm/V, and ${d}_{31}$ = 14.6 pm/V) that characterize the surface SHG from the graphene/vicinal-SiC(0001) sample and finally showed that the current-dependent tensor element ${d}_{33}$ can be enhanced to a large value of ${d}_{33}$ = \ensuremath{-}199.0 pm/V by electric current in epitaxial graphene. DA - 2014/3/12/ PY - 2014/3/12/ DO - 10.1103/physrevb.89.115310 VL - 89 IS - 11 SP - SN - 2469-9969 ER - TY - JOUR TI - Moving Fe2+ from ferritin ion channels to catalytic OH centers depends on conserved protein cage carboxylates AU - Behera, Rabindra K. AU - Theil, Elizabeth C. T2 - PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA AB - Ferritin biominerals are protein-caged metabolic iron concentrates used for iron-protein cofactors and oxidant protection (Fe(2+) and O2 sequestration). Fe(2+) passage through ion channels in the protein cages, like membrane ion channels, required for ferritin biomineral synthesis, is followed by Fe(2+) substrate movement to ferritin enzyme (Fox) sites. Fe(2+) and O2 substrates are coupled via a diferric peroxo (DFP) intermediate, λmax 650 nm, which decays to [Fe(3+)-O-Fe(3+)] precursors of caged ferritin biominerals. Structural studies show multiple conformations for conserved, carboxylate residues E136 and E57, which are between ferritin ion channel exits and enzymatic sites, suggesting functional connections. Here we show that E136 and E57 are required for ferritin enzyme activity and thus are functional links between ferritin ion channels and enzymatic sites. DFP formation (Kcat and kcat/Km), DFP decay, and protein-caged hydrated ferric oxide accumulation decreased in ferritin E57A and E136A; saturation required higher Fe(2+) concentrations. Divalent cations (both ion channel and intracage binding) selectively inhibit ferritin enzyme activity (block Fe(2+) access), Mn(2+) << Co(2+) < Cu(2+) < Zn(2+), reflecting metal ion-protein binding stabilities. Fe(2+)-Cys126 binding in ferritin ion channels, observed as Cu(2+)-S-Cys126 charge-transfer bands in ferritin E130D UV-vis spectra and resistance to Cu(2+) inhibition in ferritin C126S, was unpredicted. Identifying E57 and E136 links in Fe(2+) movement from ferritin ion channels to ferritin enzyme sites completes a bucket brigade that moves external Fe(2+) into ferritin enzymatic sites. The results clarify Fe(2+) transport within ferritin and model molecular links between membrane ion channels and cytoplasmic destinations. DA - 2014/6/3/ PY - 2014/6/3/ DO - 10.1073/pnas.1318417111 VL - 111 IS - 22 SP - 7925-7930 SN - 0027-8424 KW - iron traffic KW - oxidoreductase enzyme activity KW - antioxidant KW - ferrihydrite KW - BioIron ER - TY - JOUR TI - Light-Front Zero-Mode Issue on the Vector Meson Decay Constant AU - Choi, Ho-Meoyng AU - Ji, Chueng-Ryong T2 - FEW-BODY SYSTEMS AB - We discuss the light-front zero-mode issue in the light-front quark model (LFQM) prediction of a vector meson decay constant from the perspective of the vacuum fluctuation consistent with the chiral symmetry of QCD. We extend the exactly solvable manifestly covariant Bethe–Salpeter model calculation to the more phenomenologically accessible realistic LFQM and present a self-consistent covariant description of the vector meson decay constant analyzing the twist-2 and twist-3 quark-antiquark distribution amplitudes with even chirality. DA - 2014/6// PY - 2014/6// DO - 10.1007/s00601-013-0789-8 VL - 55 IS - 5-7 SP - 435-440 SN - 1432-5411 ER - TY - JOUR TI - High Performance All-Polymer Solar Cell via Polymer Side-Chain Engineering AU - Zhou, Yan AU - Kurosawa, Tadanori AU - Ma, Wei AU - Guo, Yikun AU - Fang, Lei AU - Vandewal, Koen AU - Diao, Ying AU - Wang, Chenggong AU - Yan, Qifan AU - Reinspach, Julia AU - Mei, Jianguo AU - Appleton, Anthony Lucas AU - Koleilat, Ghada I. AU - Gao, Yongli AU - Mannsfeld, Stefan C. B. AU - Salleo, Alberto AU - Ade, Harald AU - Zhao, Dahui AU - Bao, Zhenan T2 - ADVANCED MATERIALS AB - An average PCE of 4.2% for all-polymer solar cells from 20 devices with an average J SC of 8.8 mA cm−2 are obtained with a donor-acceptor pair despite a low LUMO-LUMO energy offset of less than 0.1 eV. Incorporation of polystyrene side chains into the donor polymer is found to assist in reducing the phase separation domain length scale, and results in more than 20% enhancement of PCE. We observe a direct correlation between the short circuit current (J SC) and the length scale of BHJ phase separation, which is obtained by resonance soft X-ray scattering. The performance of organic solar cells has rapidly improved over the past few years.1 Major efforts have been focused on developing a variety of donor materials to collect a broader wavelength range of the solar spectrum, to tune their energy levels, and to improve hole transport.2-4 On the other hand, the most widely used acceptors are still those from the fullerene family, including [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM), PC71BM and indene C60 bis-adduct (ICBA).3, 5 The high cost of fullerenes and their potential lack of morphological stability will potentially hinder the future commercialization of fullerene-based organic solar cells.6 All-polymer solar cells, consisting of polymers for both the donor and acceptor, gained significantly increased interests recently, because of their ease of solution processing, potentially low cost, versatility in molecular design, and their potential for good chemical and morphological stability due to entanglement of polymers.7, 8 Unlike small molecular fullerene acceptors, polymer acceptors can benefit from the high mobility of intra-chain charge transport9, 10 and exciton generation by both donor and acceptor.11 Moreover, all-polymer bulk heterojunction (BHJ) systems are considered less likely to have “dead island” formation and the associated charge recombination.7 Despite extensive efforts on all-polymer solar cells in the past decade, however, only a few systems had reported power conversion efficiencies (PCE) over 2%.12-15 In early 2013, there have been two new reports with PCEs up to 3.3%16 and 3.6%.17-19 More recently, a PCE of 4.1% was reported.19 Additionally, Poly­era released an announcement of achieving a PCE as high as 6.47%, demonstrating the potential for high efficiency with all-polymer solar cells.7 Controlling phase separation is one of the most critical issues in all-polymer solar cells as it limits the generation of free charge carriers and subsequently the device performance.7 Tuning processing parameters during device fabrication has been used to optimize phase separation.20, 21 However, limited success has been achieved in this regard. Recently, we introduced the use of polystyrene (PS) side-chains for conjugated polymers.22 The solubility and processibility were improved for the resulting polymers with <10 mol% PS-containing repeating units, yet, the thin film transistor mobility and solar cell performance with fullerene acceptors were the same or better than without PS side chains.22 In this paper, we report high performance all-polymer solar cells employing isoindigo-containing donor polymers and perylene tetracarboxlic di-imide (PTCDI)-containing acceptor polymers. Incorporation of polystyrene side chains into the donor polymer22 is found to assist in reducing the phase separation domain length scale. A direct correlation between the short circuit current (JSC) and the length scale of BHJ phase separation is observed. An average PCE of 4.2% from 20 devices with an average JSC of 8.8 mA cm−2 are obtained. The highest PCE is 4.4%, with a JSC as high as 9.0 mA cm−2, and VOC of 1.04 V. This result represents one of the highest performance in published literature for all-polymer solar cells.7, 16, 17, 19 The chemical structures and energy diagrams of the donor and acceptor polymers employed herein are shown in Scheme 1. The isoindigo polymers are selected as the donor polymers because of their low bandgaps, strong absorption, good hole charge transport, deep HOMO for potentially high VOC and good BHJ solar cell performance when combined with PCBM acceptors.23-26 A swallow-tail substituted PTCDI polymer is chosen as the acceptor polymer due to its good electron transporting property and good solubility.15, 27, 28 All the polymer samples were synthesized from Stille coupling polymerization reactions and purified by Soxhlet followed by preparative Size Exclusion Chromatography (SEC) fractionation. The molecular weight and polydispersity index (PDI) are listed in Table S1. As shown in Figure 1 and Table S1, the optical band gaps of the isoindigo polymers are close to 1.6 eV while PiI-BDT gives an optical gap of 1.7 eV. The thin films of polymeric donors show two major absorption bands at around 700 nm and 650 nm, respectively. The maximum absorption peak of P(TP) is centered at 563 nm, hence complementing the absorption profile of the polymeric donors. The energy levels of these active materials were measured by Ultraviolet Photoemission Spectroscopy (UPS) and Inverse Photoemission Spectroscopy (IPES). The LUMO levels of the donor polymers are all similar to each other at around −3.70 eV, despite the different aromatic co-monomers. The HOMO level of P(TP) was measured to be −5.72 eV by UPS, while the LUMO level was −3.80 eV by IPES. Based on the IPES measured LUMO levels, the LUMO-LUMO offset [(−3.70 eV) − (−3.80 eV)] between the donors and the acceptor is less than 0.1 eV, lower than the often mentioned empirical value of 0.3 eV needed for efficient exciton dissociation.29 It can be seen later that despite of this very low offset, the relatively high PCE can still be achieved. Grazing incident X-ray diffraction (GIXRD) is used to obtain the crystalline order and polymer orientation information in the polymeric donors. As shown in Figure S1, crystalline structures are found in all the donors in the thin film state while no crystalline order is observed for the acceptor polymer (data not shown). The d-spacing does not change between the neat films and blend films, for both the lamellar (100) distance and the π−π (010) distance, but the intensities of those diffraction patterns were notably lower. This data indicates that the crystallinity of the donor polymers was reduced by blending with the acceptor polymer, but the orientation of the crystalline regions remained unchanged. Our all-polymer solar cell is constructed in an inverted BHJ structure, in which an electron transporting layer of ZnO is at the bottom and the hole transporting layer of MoO3 is at the top. The various donor polymers with small changes in their chemical structures exhibited drastically different photovoltaic characteristics (Table 1). From the external quantum efficiencies (EQE) shown in Figure 2b, we clearly observed that features at wavelength shorter than 550 nm are overlapping with the acceptor polymer absorption region, which indicates that excitons generated on the acceptor polymer also contributed to the overall performance of the device. Normalizing the EQE over the double-pass absorption of the devices, the internal quantum efficiencies (IQEs) from 500 nm to 720 nm (Figure S2) are almost the same within each cells with different donor, suggesting that the excitons generated from donor and acceptor split with equal probability in these blends. Interestingly, although the energy levels and absorption coefficients of the employed donor polymers are very similar to each other, the current generated from the various junctions differed drastically. In addition to the absorption spectrum, JSC depends on the fraction of photogenerated excitons reaching the D-A interface, the dissociation efficiency of these excitons into free carriers and the transport efficiency of the resulting free carriers. To understand and identify the causes for the observed trend in JSC we turn to analyzing the absorption, phase separation, driving force for exciton dissociation into free charge carriers and carrier mobilities. In order to determine the percentage of excitons that can reach and dissociate at the donor/acceptor interface, the photoluminescence quenching efficiencies (PLQE) are measured by directly comparing the PL intensity of the polymer donor, acceptor and BHJ films under the same excitation wavelength, geometry and equipment parameters. The trend in PL quenching efficiency correlates well with the observed trend in JSC (shown in Figure 2c). A poor PL quenching might be due to either large domains or energy level mismatch, which inhibits charge transfer. Resonant Soft X-ray Scattering (RSoXS) is used to obtain the phase separation characteristics of the polymer blends. This technique is essential in this case because the contrast of the scattering signal of hard X-ray is too weak from the all-polymer blends.30-33 A resonant photon energy of 283 eV is used to enhance the contrast of the polymer:polymer blends. To confirm the RSoXS scattering is originating from the polymer:polymer phase separation, a non-resonant energy 270 eV that is less sensitive to polymer:polymer contrast but more sensitive to mass-thickness variations is also utilized. The stronger and more pronounced scattering peak at 283 eV indicates that the RSoXS measures polymer:polymer phase separation at that energy (Figure S8). The scattering profiles at 283 eV are displayed in Figure 2d and represent the distribution function of spatial frequency, s = q/2π, of the samples. The median of the distribution smedian corresponds to the characteristic median length scale, ξ, of the corresponding phase distribution in real space with ξ = 1/smedian. The ξ is 260 nm for PiI-tT/P(TP), 100 nm for PiI-2F/P(TP), 50 nm for PiI-BDT/P(TP) and 54 nm for PiI-2T/P(TP), respectively. The trend in the characteristic median length scale correlates well with the PL quenching efficiency as well as the JSC, i.e. a smaller domain size was found to give a higher JSC and a higher PLQE. The dissociation of excitons into free charge carriers involves electron transfer that forms the charge transfer (CT) state, in which the electron resides on the acceptor molecule while the hole remains on the donor molecule. When such a CT state is lower in energy than the neat donor or acceptor exciton, it is characterized by weak absorption and emission at energies below the optical gap of the neat materials. Sensitive EQE measurements in the sub-gap region of most studied organic solar cell BHJs therefore reveal CT absorption.34 The driving force for charge transfer, defined by the difference between the lowest optical gaps of the neat material and the CT state optical gap, can be deduced from such measurements.34, 35 For our all-polymer BHJs, highly sensitive EQE measurements did not reveal any distinct sub-gap CT absorption band (Figure S3a-d). On the other hand, when using regioregular poly(3-hexylthiophene) (P3HT) with a shallower LUMO as the donor material blended with P(TP), a CT band in the P3HT gap region was clearly visible (See Figure S3e). This indicates that the absence of a sub-gap CT band for the isoindigo polymers under investigation here is due to their deeper LUMO level as compared to P3HT. The smaller LUMO-LUMO offset between the donor and acceptor resulted in a lower driving force for charge transfer and subsequently CT state formation. Similarly, the electroluminescence spectra of the blends showed only emission spectra resembling that of the neat donor polymer, with no CT band observed (Figure S3). This again confirms that the CT state in these BHJs is very high in energy, close to the energy of the excitons in the neat material. In some cases (Figure S3a) the peak positions of EL and EQE of the blends were even blue shifted as compared to the pure material. This is probably due to a decrease in aggregation of the isoindigo polymer upon blending. The employments of both EQE and EL spectra enable the accurate determination of the optical gaps of the neat donor polymers and blends. Based on the above values, the VOC of the devices correlates well with the deduced optical gap of the blend (VOC =Eg-0.6 V). The absence of a subgap CT absorption or emission band correlation indicate that for all the blends studied in this work, the energy loss due to electron transfer is minimized, hence maximizing the VOC. It is remarkable that despite the lack of a large driving force for electron transfer, a decent charge generation (6.5 mA cm−2) is still possible in these materials. Similar observations have been reported before for other isoindigo polymer:PCBM BHJs.36, 37 The mobilities measured from space-charge limited current (SCLC) are listed in Table S3. The hole mobilities in the blend films are all around 2 × 10−4 cm2 V−1 s−1, while the acceptor polymer P(TP) has a lower electron mobility of 2 × 10−5 cm2 V−1 s−1. The hole mobilities of the donors do not correlate well to the JSC, indicating that the charge transport efficiency of the devices may be limited by the low electron mobility of the acceptor polymer. The absorption (A(E)) of the blend films was in the similar range, indicating that the differences of the JSC were not originated from the absorption difference either (Figure S4). The above characterizations suggest that phase separation domain size is the most significant factor that gives rise to the dramatically different device performance. Therefore, we proceed to modify the best polymer donor polymer by attaching a small percentage of PS side chains to demonstrate a new route to control phase separation behavior in all-polymer blends (Scheme S1).22 With such polymer side-chain modification, we expected to reduce the domain size in the blend film by reducing the strong tendency for self-aggregation in the D-A donor polymer. In fact, the average PCE of the PiI-2T-PS5/P(TP), in which 5 mol% of the repeating units in PiI-2T are attached with PS side chains, reached 4.2%, with a JSC as high as 8.8 mA cm−2, and a VOC of 1.04 V. The highest measured PCE was up to 4.4%, and JSC­ was as high as 9.0 mA cm−2. From RSoXS data in Figure 3c, the median domain size (30 nm) of these devices was indeed 45% smaller than that formed by the PiI-2T/P(TP) blend (54 nm). To test the applicability of the PS-side-chain modification approach to other donor polymers, the same modification on the worst performing donor polymer PiI-tT is performed. After being modified by 5 mol% of PS side-chain, the PCE of PiI-tT-PS5/P(TP) increased to 2.75% from 1.67%, with a JSC as high as 5.92 mA cm−2, and a VOC of 0.99 V(Shown in Figure S5). The phase separation length scale of the blend film, measured by RSoXS, was reduced from 260 nm to 50 nm by attaching 5% PS side chains in the donor polymer. In this case (Figure S5), the PLQE increased from 66% to 76% after the attachment of PS side-chain, confirming again a reduction of the domain length scale and a more efficient exciton dissociation. Different device fabrication conditions are utilized to optimize the device performance. Annealing temperatures from 80 to 140 °C are applied to the active films prior to the thermal evaporation of the electrodes. Similar J–V curves are obtained indicating that phase separations of the polymers blends were stable under different thermal annealing conditions (Figure S7). The PCEs of devices are not very sensitive to the donor/acceptor blend ratios from 5/4 to 4/5. These robust fabrication features are highly desirable for future large scale production. In conclusion, a side-chain engineering approach using polystyrene enables manipulation of phase separation domain size and enhances all-polymer solar cell performance to reach PCE as high as 4.4%. A JSC as high as 9.0 mA cm−2 is obtained with a donor-acceptor pair despite of a low LUMO-LUMO energy offset of less than 0.1 eV. The phase separation domain length scale correlates well with the JSC and is found to be highly sensitive to the aromatic co-monomer molecular structures used in the crystalline donor polymers. With the PS polymer side-chain engineering, the phase separation domain length scale decreased by more than 45%. The PCE and JSC of the devices increased accordingly by more than 20%. This work demonstrates that a better understanding of tuning polymer phase separation domain size provides an important path towards high performance all-polymer solar cells. The use of polymer side-chain engineering provides an effective molecular engineering approach that may be combined with additional processing parameter control to further elevate the performance of all-polymer solar cells. General Method: All the polymers were synthesized according to previously reported procedures.15, 22, 24 All the polymers were purified via preparation SEC at room temperature with chloroform as solvent. The molecular weight and PDI of all polymers were measured by high temperature GPC with 1,2,4-trichlorobenzene as the solvent and polystyrenes as the calibration standards at 160 °C. 2D-GIXD images were collected in reflection mode with a planar area detector in a He atmosphere at beamline 11–3 of the Stanford Synchrotron Radiation Lightsource. The sample−detector distance was nominally set to 400 mm, and the incidence angle was 0.12°; the X-ray wavelength was 0.9758 Å. Slits were set to 150 and 50 μm in the horizontal and vertical directions, respectively. R-SoXS measurements were performed at beamline 11.0.1.2 at the Advanced Light Source.38 The sample films used for R-SoXS were spin-cast on sodium polysulfonate covered glass as substrate. To carry out R-SoXS experiment in transmission, the film is floated off in deionized water and picked up with a 1.5 mm by 1.5 mm silicon nitride window. The film is then dried in air before being transferred into the vacuum chamber for R-SoXS. Photoemission spectroscopy of occupied and unoccupied states of the system was performed using a VG ESCA Lab system equipped with both UPS and IPES. The spectrometer chamber of the UHV system had a base pressure of 8 × 10−11 Torr. Occupied states (or valence band) spectra were obtained by UPS using the unfiltered He I line (21.2 eV) of a discharge lamp with the samples biased at -5.0 V to avoid the influence of the detector work function and to observe the true low-energy secondary cutoff. The typical instrumental resolution for UPS measurements ranges from 0.03 to 0.1 eV with photon energy dispersion of less than 20 meV. Unoccupied states (or conduction bands) were measured by IPES using a custom-made spectrometer composed of a commercial Kimball Physics ELG-2 electron gun and a bandpass photon detector prepared according to an existing design. IPES was done in the isochromat mode using a photon detector centered at a fixed energy of 9.8 eV. The combined resolution (electron + photon) of the IPES spectrometer was determined to be 0.6 eV from the width of the Fermi edge measured on a clean polycrystalline Au film. The UPS and IPES energy scales were aligned by measuring the position of the Fermi level on a freshly evaporated Au film. The position of the vacuum level, Evac, was measured for each surface using the onset of the secondary cutoff in the UPS spectra. All the measurements were done at room temperature. Absorption spectra were recorded on a Cary 6000i Spectrometer. The PL spectra were obtained from a Horiba Jobin-Yvon FluoroMax-4 Luminescence Spectrometer. Solar Cell Fabrication and Testing: Glass substrates coated with patterned indium-doped tin oxide (ITO) with a sheet resistance of 13 Ω/◻ was purchased from Xin Yan Technology Lt. Before device fabrication, the ITO/glass substrates were subjected to a series of wet-cleaning processes in an ultrasonic bath sequentially in acetone, detergent, deionized water and isopropanol. After dried in the vacuum oven at 80 °C for 10 mins and followed by a 20-min UV-Ozone treatment, ZnO sol-gel was spun-coated onto the ITO surface at a speed of 4000 rpm for 18 s.39 The ZnO was baked at 200 °C for 0.5 h in air to formed a 30 nm thick film. The polymers were dissolved into 1,2-dichlorobenzene with stirring over night at 100 °C. The concentration was 10 mg/mL for PiI-2T, PiI-2T-PS5 and PiI-2F, and 20 mg/mL for PiI-BDT, PiI-tT and P(TP), respectively. The blend solutions were freshly made prior spin-coating and kept at 50 °C. All the active layers were spun-coated at 700 rpm for 25 s in the glove box. The wet films were put into a covered Petri dish and allowed to dry at room temperature overnight. The dried films were subsequently annealed in the glove box at 100 °C for 5 mins before they were transferred to a vacuum evaporator for electrode deposition. The thickness of the active layer was 100 nm for PiI-2T/P(TP) and PiI-2F/P(TP), 93 nm for PiI-2T-PS5/P(TP), 120 nm for PiI-BDT/P(TP), 180 nm for PiI-tT/P(TP), measured by a Dektak surface profiler. A MoO3 layer (15 nm) followed by a Ag layer (70 nm) were thermally deposited at a pressure of 6 × 10−6 Torr. The device active area is 4.0 mm2. All the devices were tested inside a nitrogen glove box with less than 40 ppm O2 and 4 ppm H2O. The PCE was tested under AM 1.5G illumination with an intensity of 100 mW cm−2 (Newport Solar Simulator 94021A) calibrated by a Newport certified silicon photo diode covered with KG5 filter with active area as 0.0663 cm2, comparable to our device area of 0.04 cm2.40 The J–V curves were recorded with a Keithley 2400 semiconductor analyzer. The IPCE and double-pass absorption were measurements under monochromic illumination and the calibration of the incident light intensity was performed with a calibrated silicon photodiode. The double-pass absorptions measurements were carried out in an integrating sphere and the parasitic absorptions of the electrode materials calculated by transfer matrix were deducted. For the sensitive EQE measurements, the current from the devices was measured as a function of photon energy using a lock-in amplifier (Stanford Instruments SR 830). For IQE calculation, the parasitic absorptions were calculated by transfer matrix optical modelling.41 Electroluminescence spectra were measured using a spectrograph (Acton Research SpectraPro 500i) equipped with a silicon CCD (charge-coupled device) array detector (Hamamatsu). The spectra were corrected for the instrument response. Acknowledge support from the Office of Naval Research (N00014-14-1-0142), KAUST Center for Advanced Molecular Photovoltaics at Stanford and the Stanford Global Climate and Energy Program, NSF DMR-1303742 and the National Natural Science Foundation of China (Projects 21174004 and 21222403). Soft X-ray characterization and analysis by NCSU supported by the U.S. Department of Energy, Office of Science, Basic Energy Science, Division of Materials Science and Engineering under Contract DE-FG02–98ER45737. Soft X-ray data was acquired at beamlines 11.0.1.2 at the Advanced Light Source, which is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02–05CH11231. We thank Professor Michael D. McGehee, Dr. George F. Burkhard and Dr. Eric T. Hoke for their help in discussion of the recombination mechanism. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article. DA - 2014/6/11/ PY - 2014/6/11/ DO - 10.1002/adma.201306242 VL - 26 IS - 22 SP - 3767-3772 SN - 1521-4095 ER - TY - JOUR TI - Essential ingredients in core-collapse supernovae AU - Hix, W. R. AU - Lentz, E. J. AU - Endeve, E. AU - Baird, M. AU - Chertkow, M. A. AU - Harris, J. A. AU - Messer, O. E. B. AU - Mezzacappa, A. AU - Bruenn, S. AU - Blondin, J. AU - al., T2 - AIP ADVANCES AB - Carrying 1044 joules of kinetic energy and a rich mix of newly synthesized atomic nuclei, core-collapse supernovae are the preeminent foundries of the nuclear species which make up our solar system and ourselves. Signaling the inevitable death of a massive star, and the birth of a neutron star or black hole, core-collapse supernovae combine physics over a wide range in spatial scales, from kilometer-sized hydrodynamic motions (eventually growing to gigameter scale) down to femtometer-scale nuclear reactions. We will discuss our emerging understanding of the convectively-unstable, neutrino-driven explosion mechanism, based on increasingly realistic neutrino radiation hydrodynamic simulations that include progressively better nuclear and particle physics. Multi-dimensional models with spectral neutrino transport from several research groups, which slowly develop successful explosions for a range of progenitors, have recently motivated changes in our understanding of the neutrino reheating mechanism. In a similar fashion, improvements in nuclear physics, most notably explorations of weak interactions on nuclei and the nuclear equation of state, continue to refine our understanding of the births of neutron stars and the supernovae that result. Recent progress on both the macroscopic and microscopic effects that affect core-collapse supernovae are discussed. DA - 2014/4// PY - 2014/4// DO - 10.1063/1.4870009 VL - 4 IS - 4 SP - SN - 2158-3226 ER - TY - JOUR TI - Dual-fission chamber and neutron beam characterization for fission product yield measurements using monoenergetic neutrons AU - Bhatia, C. AU - Fallin, B. AU - Gooden, M.E. AU - Howell, C.R. AU - Kelley, J.H. AU - Tornow, W. AU - Arnold, C.W. AU - Bond, E.M. AU - Bredeweg, T.A. AU - Fowler, M.M. AU - Moody, W.A. AU - Rundberg, R.S. AU - Rusev, G. AU - Vieira, D.J. AU - Wilhelmy, J.B. AU - Becker, J.A. AU - Macri, R. AU - Ryan, C. AU - Sheets, S.A. AU - Stoyer, M.A. AU - Tonchev, A.P. T2 - Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment AB - A program has been initiated to measure the energy dependence of selected high-yield fission products used in the analysis of nuclear test data. We present out initial work of neutron activation using a dual-fission chamber with quasi-monoenergetic neutrons and gamma-counting method. Quasi-monoenergetic neutrons of energies from 0.5 to 15 MeV using the TUNL 10 MV FM tandem to provide high-precision and self-consistent measurements of fission product yields (FPY). The final FPY results will be coupled with theoretical analysis to provide a more fundamental understanding of the fission process. To accomplish this goal, we have developed and tested a set of dual-fission ionization chambers to provide an accurate determination of the number of fissions occurring in a thick target located in the middle plane of the chamber assembly. Details of the fission chamber and its performance are presented along with neutron beam production and characterization. Also presented are studies on the background issues associated with room-return and off-energy neutron production. We show that the off-energy neutron contribution can be significant, but correctable, while room-return neutron background levels contribute less than <1% to the fission signal. DA - 2014/9// PY - 2014/9// DO - 10.1016/J.NIMA.2014.03.022 VL - 757 SP - 7-19 J2 - Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment LA - en OP - SN - 0168-9002 UR - http://dx.doi.org/10.1016/J.NIMA.2014.03.022 DB - Crossref KW - Fission product yields KW - Dual-fission chamber KW - Neutron production KW - Beam characterization ER - TY - JOUR TI - Cross section and.gamma-ray spectra for U-238(n,gamma) measured with the DANCE detector array at the Los Alamos Neutron Science Center AU - Ullmann, J. L. AU - Kawano, T. AU - Bredeweg, T. A. AU - Couture, A. AU - Haight, R. C. AU - Jandel, M. AU - O'Donnell, J. M. AU - Rundberg, R. S. AU - Vieira, D. J. AU - Wilhelmy, J. B. AU - Becker, J. A. AU - Chyzh, A. AU - Wu, C. Y. AU - Baramsai, B. AU - Mitchell, G. E. AU - Krticka, M. T2 - PHYSICAL REVIEW C AB - Background: Accurate knowledge of the $^{238}\mathrm{U}$($n$,$\ensuremath{\gamma}$) cross section is important for developing theoretical nuclear reaction models and for applications. However, capture cross sections are difficult to calculate accurately and often must be measured.Purpose: We seek to confirm previous measurements and test cross-section calculations with an emphasis on the unresolved resonance region from 1 to 500 keV.Method: Cross sections were measured from 10 eV to 500 keV using the DANCE detector array at the LANSCE spallation neutron source. The measurements used a thin target, 48 mg/cm${}^{2}$ of depleted uranium. Gamma cascade spectra were also measured to provide an additional constraint on calculations. The data are compared to cross-section calculations using the code CoH${}_{3}$ and cascade spectra calculations made using the code dicebox.Results: This new cross-section measurement confirms the previous data. The measured gamma-ray spectra suggest the need for additional low-lying dipole strength in the radiative strength function. New Hauser-Feshbach calculations including this strength accurately predict the capture cross section without renormalization.Conclusions: The present cross-section data confirm previous measurements. Including additional low-lying dipole strength in the radiative strength function may lead to more accurate cross-section calculations in nuclei where $\ensuremath{\langle}{\ensuremath{\Gamma}}_{\ensuremath{\gamma}}\ensuremath{\rangle}$ has not been measured. DA - 2014/3/10/ PY - 2014/3/10/ DO - 10.1103/physrevc.89.034603 VL - 89 IS - 3 SP - SN - 1089-490X ER - TY - JOUR TI - Cancer/Testis Antigen PAGE4, a Regulator of c-Jun Transactivation, Is Phosphorylated by Homeodomain-Interacting Protein Kinase 1, a Component of the Stress-Response Pathway AU - Mooney, Steven M. AU - Qiu, Ruoyi AU - Kim, John J. AU - Sacho, Elizabeth J. AU - Rajagopalan, Krithika AU - Johng, Dorhyun AU - Shiraishi, Takumi AU - Kulkarni, Prakash AU - Weninger, Keith R. T2 - BIOCHEMISTRY AB - Prostate-associated gene 4 (PAGE4) is a cancer/testis antigen that is typically restricted to the testicular germ cells but is aberrantly expressed in cancer. Furthermore, PAGE4 is developmentally regulated with dynamic expression patterns in the developing prostate and is also a stress-response protein that is upregulated in response to cellular stress. PAGE4 interacts with c-Jun, which is activated by the stress-response kinase JNK1, and plays an important role in the development and pathology of the prostate gland. Here, we have identified homeodomain-interacting protein kinase 1 (HIPK1), also a component of the stress-response pathway, as a kinase that phosphorylates PAGE4 at T51. We show that phosphorylation of PAGE4 is critical for its transcriptional activity since mutating this T residue abolishes its ability to potentiate c-Jun transactivation. In vitro single molecule FRET indicates phosphorylation results in compaction of (still) intrinsically disordered PAGE4. Interestingly, however, while our previous observations indicated that the wild-type nonphosphorylated PAGE4 protein interacted with c-Jun [Rajagopalan , K. et al. ( 2014 ) Biochim, Biophys. Acta 1842 , 154 -163], here we show that phosphorylation of PAGE4 weakens its interaction with c-Jun in vitro. These data suggest that phosphorylation induces conformational changes in natively disordered PAGE4 resulting in its decreased affinity for c-Jun to promote interaction of c-Jun with another, unidentified, partner. Alternatively, phosphorylated PAGE4 may induce transcription of a novel partner, which then potentiates c-Jun transactivation. Regardless, the present results clearly implicate PAGE4 as a component of the stress-response pathway and uncover a novel link between components of this pathway and prostatic development and disease. DA - 2014/3/18/ PY - 2014/3/18/ DO - 10.1021/bi500013w VL - 53 IS - 10 SP - 1670-1679 SN - 0006-2960 ER - TY - JOUR TI - Calculation of geometric phases in electric dipole searches with trapped spin-1/2 particles based on direct solution of the Schrodinger equation AU - Steyerl, A. AU - Kaufman, C. AU - Mueller, G. AU - Malik, S. S. AU - Desai, A. M. AU - Golub, R. T2 - PHYSICAL REVIEW A AB - Pendlebury $\mathit{et}\phantom{\rule{0.28em}{0ex}}\mathit{al}.$ [Phys. Rev. A 70, 032102 (2004)] were the first to investigate the role of geometric phases in searches for an electric dipole moment (EDM) of elementary particles based on Ramsey-separated oscillatory field magnetic resonance with trapped ultracold neutrons and comagnetometer atoms. Their work was based on the Bloch equation and later work using the density matrix corroborated the results and extended the scope to describe the dynamics of spins in general fields and in bounded geometries. We solve the Schr\"odinger equation directly for cylindrical trap geometry and obtain a full description of EDM-relevant spin behavior in general fields, including the short-time transients and vertical spin oscillation in the entire range of particle velocities. We apply this method to general macroscopic fields and to the field of a microscopic magnetic dipole. DA - 2014/5/22/ PY - 2014/5/22/ DO - 10.1103/physreva.89.052129 VL - 89 IS - 5 SP - SN - 1094-1622 ER - TY - JOUR TI - Ab Initio Calculation of the Spectrum and Structure of O-16 AU - Epelbaum, Evgeny AU - Krebs, Hermann AU - Laehde, Timo A. AU - Lee, Dean AU - Meissner, Ulf-G. AU - Rupak, Gautam T2 - PHYSICAL REVIEW LETTERS AB - We present ab initio lattice calculations of the low-energy even-parity states of $^{16}$O using chiral nuclear effective field theory. We find good agreement with the empirical energy spectrum, and with the electromagnetic properties and transition rates. For the ground state, we find that the nucleons are arranged in a tetrahedral configuration of alpha clusters. For the first excited spin-0 state, we find that the predominant structure is a square configuration of alpha clusters, with rotational excitations that include the first spin-2 state. DA - 2014/3/12/ PY - 2014/3/12/ DO - 10.1103/physrevlett.112.102501 VL - 112 IS - 10 SP - SN - 1079-7114 ER - TY - JOUR TI - A Study of Compton Form Factors in Scalar QED AU - Bakker, Bernard L. G. AU - Ji, Chueng-Ryong T2 - FEW-BODY SYSTEMS DA - 2014/6// PY - 2014/6// DO - 10.1007/s00601-014-0820-8 VL - 55 IS - 5-7 SP - 395-400 SN - 1432-5411 ER - TY - JOUR TI - A CR-HYDRO-NEI MODEL OF THE STRUCTURE AND BROADBAND EMISSION FROM TYCHO'S SUPERNOVA REMNANT AU - Slane, P. AU - Lee, S. -H. AU - Ellison, D. C. AU - Patnaude, D. J. AU - Hughes, J. P. AU - Eriksen, K. A. AU - Castro, D. AU - Nagataki, S. T2 - ASTROPHYSICAL JOURNAL AB - Tycho's supernova remnant (SNR) is well-established as a source of particle acceleration to very high energies. Constraints from numerous studies indicate that the observed γ-ray emission results primarily from hadronic processes, providing direct evidence of highly relativistic ions that have been accelerated by the SNR. Here we present an investigation of the dynamical and spectral evolution of Tycho's SNR by carrying out hydrodynamical simulations that include diffusive shock acceleration of particles in the amplified magnetic field at the forward shock of the SNR. Our simulations provide a consistent view of the shock positions, the nonthermal emission, the thermal X-ray emission from the forward shock, and the brightness profiles of the radio and X-ray emission. We compare these with the observed properties of Tycho to determine the density of the ambient material, the particle acceleration efficiency and maximum energy, the accelerated electron-to-proton ratio, and the properties of the shocked gas downstream of the expanding SNR shell. We find that evolution of a typical Type Ia supernova in a low ambient density (n0 ∼ 0.3 cm−3), with an upstream magnetic field of ∼5 μG, and with ∼16% of the SNR kinetic energy being converted into relativistic electrons and ions through diffusive shock acceleration, reproduces the observed properties of Tycho. Under such a scenario, the bulk of observed γ-ray emission at high energies is produced by π0-decay resulting from the collisions of energetic hadrons, while inverse-Compton emission is significant at lower energies, comprising roughly half of the flux between 1 and 10 GeV. DA - 2014/3/1/ PY - 2014/3/1/ DO - 10.1088/0004-637x/783/1/33 VL - 783 IS - 1 SP - SN - 1538-4357 KW - acceleration of particles KW - cosmic rays KW - ISM: individual objects (Tycho's SNR) KW - ISM: supernova remnants KW - shock waves ER - TY - JOUR TI - Uniform WKB, multi-instantons, and resurgent trans-series AU - Dunne, Gerald V. AU - Uensal, Mithat T2 - PHYSICAL REVIEW D AB - We illustrate the physical significance and mathematical origin of resurgent trans-series expansions for energy eigenvalues in quantum mechanical problems with degenerate harmonic minima, by using the uniform WKB approach. We provide evidence that the perturbative expansion, combined with a global eigenvalue condition, contains all information needed to generate all orders of the nonperturbative multi-instanton expansion. This provides a dramatic realization of the concept of resurgence, whose structure is naturally encoded in the resurgence triangle. We explain the relation between the uniform WKB approach, multi-instantons, and resurgence theory. The essential idea applies to any perturbative expansion, and so is also relevant for quantum field theories with degenerate minima which can be continuously connected to quantum mechanical systems. DA - 2014/5/12/ PY - 2014/5/12/ DO - 10.1103/physrevd.89.105009 VL - 89 IS - 10 SP - SN - 1550-2368 ER - TY - JOUR TI - The MAJORANA DEMONSTRATOR Neutrinoless Double-Beta Decay Experiment AU - Abgrall, N. AU - Aguayo, E. AU - Avignone, F. T., III AU - Barabash, A.S. AU - Bertrand, F.E. AU - Boswell, M. AU - Brudanin, V. AU - Busch, M. AU - Caldwell, A.S. AU - Chan, Y.-D. AU - Christofferson, C.D. AU - Combs, D.C. AU - Detwiler, J.A. AU - Doe, P.J. AU - Efremenko, Yu. AU - Egorov, V. AU - Ejiri, H. AU - Elliott, S.R. AU - Esterline, J. AU - Fast, J.E. AU - Finnerty, P. AU - Fraenkle, F.M. AU - Galindo-Uribarri, A. AU - Giovanetti, G.K. AU - Goett, J. AU - Green, M.P. AU - Gruszko, J. AU - Guiseppe, V.E. AU - Gusev, K. AU - Hallin, A.L. AU - Hazama, R. AU - Hegai, A. AU - Henning, R. AU - Hoppe, E.W. AU - Howard, S. AU - Howe, M. AU - Keeter, K.J. AU - Kidd, M.F. AU - Knecht, A. AU - Kochetov, O. AU - Konovalov, S.I. AU - Kouzes, R.T. AU - LaFerriere, B.D. AU - Leon, J. AU - Leviner, L.E. AU - Loach, J.C. AU - Luke, P.N. AU - MacMullin, S. AU - Martin, R.D. AU - Mertens, S. AU - Mizouni, L. AU - Nomachi, M. AU - Orrell, J.L. AU - O'Shaughnessy, C. AU - Overman, N.R. AU - Phillips, D. AU - Poon, A.W.P. AU - Pushkin, K. AU - Radford, D.C. AU - Rielage, K. AU - Robertson, R.G.H. AU - Ronquest, M.C. AU - Schubert, A.G. AU - Shanks, B. AU - Shima, T. AU - Shirchenko, M. AU - Snavely, K.J. AU - Snyder, N. AU - Steele, D. AU - Strain, J. AU - Suriano, A.M. AU - Thompson, J. AU - Timkin, V. AU - Tornow, W. AU - Varner, R.L. AU - Vasilyev, S. AU - Vetter, K. AU - Vorren, K. AU - White, B.R. AU - Wilkerson, J.F. AU - Williams, T. AU - Xu, W. AU - Yakushev, E. AU - Young, A.R. AU - Yu, C.-H. AU - Yumatov, V. T2 - Advances in High Energy Physics AB - The M ajorana D emonstrator will search for the neutrinoless double-beta(ββ0ν)decay of the isotopeGe with a mixed array of enriched and natural germanium detectors. The observation of this rare decay would indicate that the neutrino is its own antiparticle, demonstrate that lepton number is not conserved, and provide information on the absolute mass scale of the neutrino. The D emonstrator is being assembled at the 4850-foot level of the Sanford Underground Research Facility in Lead, South Dakota. The array will be situated in a low-background environment and surrounded by passive and active shielding. Here we describe the science goals of the D emonstrator and the details of its design. DA - 2014/// PY - 2014/// DO - 10.1155/2014/365432 VL - 2014 SP - 365432 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84895105114&partnerID=MN8TOARS ER - TY - JOUR TI - Semiconductor Solar Superabsorbers AU - Yu, Yiling AU - Huang, Lujun AU - Cao, Linyou T2 - SCIENTIFIC REPORTS AB - Understanding the maximal enhancement of solar absorption in semiconductor materials by light trapping promises the development of affordable solar cells. However, the conventional Lambertian limit is only valid for idealized material systems with weak absorption and cannot hold for the typical semiconductor materials used in solar cells due to the substantial absorption of these materials. Herein we theoretically demonstrate the maximal solar absorption enhancement for semiconductor materials and elucidate the general design principle for light trapping structures to approach the theoretical maximum. By following the principles, we design a practical light trapping structure that can enable an ultrathin layer of semiconductor materials, for instance, 10 nm thick a-Si, absorb > 90% sunlight above the bandgap. The design has active materials with one order of magnitude less volume than any of the existing solar light trapping designs in literature. This work points towards the development of ultimate solar light trapping techniques. DA - 2014/2/17/ PY - 2014/2/17/ DO - 10.1038/srep04107 VL - 4 SP - SN - 2045-2322 ER - TY - JOUR TI - Self-healing dynamics of surfactant coatings on thin viscous films AU - Strickland, Stephen L. AU - Hin, Matthew AU - Sayanagi, M. Richard AU - Gaebler, Cameron AU - Daniels, Karen E. AU - Levy, Rachel T2 - PHYSICS OF FLUIDS AB - We investigate the dynamics of an insoluble surfactant on the surface of a thin viscous fluid spreading inward to fill a surfactant-free region. During the initial stages of surfactant self-healing, Marangoni forces drive an axisymmetric ridge inward to coalesce into a growing central distension; this is unlike outward-spreading, in which the ridge decays. In later dynamics, the distension slowly decays and the surfactant concentration equilibrates. We present results from experiments in which we simultaneously measure the surfactant concentration (using fluorescently-tagged lipids) and the fluid height profile (via laser profilometry). We compare the results to simulations of a mathematical model using parameters from our experiments. For surfactant concentrations close to but below the critical monolayer concentration, we observe agreement between the height profiles in the numerical simulations and the experiment, but disagreement in the surfactant distribution. In experiments at lower concentrations, the surfactant spreading and formation of a Marangoni ridge are no longer present, and a persistent lipid-free region remains. This observation, which is not captured by the simulations, has undesirable implications for applications where uniform coverage is advantageous. Finally, we probe the generality of the effect, and find that distensions of similar size are produced independent of initial fluid thickness, size of initial clean region, and surfactant type. DA - 2014/4// PY - 2014/4// DO - 10.1063/1.4872020 VL - 26 IS - 4 SP - SN - 1089-7666 ER - TY - JOUR TI - SPITZER IRS OBSERVATIONS OF THE XA REGION IN THE CYGNUS LOOP SUPERNOVA REMNANT AU - Sankrit, Ravi AU - Raymond, John C. AU - Bautista, Manuel AU - Gaetz, Terrance J. AU - Williams, Brian J. AU - Blair, William P. AU - Borkowski, Kazimierz J. AU - Long, Knox S. T2 - ASTROPHYSICAL JOURNAL AB - We report on spectra of two positions in the XA region of the Cygnus Loop supernova remnant obtained with the InfraRed Spectrograph on the Spitzer Space Telescope. The spectra span the 10-35 micron wavelength range, which contains a number of collisionally excited forbidden lines. These data are supplemented by optical spectra obtained at the Whipple Observatory and an archival UV spectrum from the International Ultraviolet Explorer. Coverage from the UV through the IR provides tests of shock wave models and tight constraints on model parameters. Only lines from high ionization species are detected in the spectrum of a filament on the edge of the remnant. The filament traces a 180 km/s shock that has just begun to cool, and the oxygen to neon abundance ratio lies in the normal range found for Galactic H II regions. Lines from both high and low ionization species are detected in the spectrum of the cusp of a shock-cloud interaction, which lies within the remnant boundary. The spectrum of the cusp region is matched by a shock of about 150 km/s that has cooled and begun to recombine. The post-shock region has a swept-up column density of about 1.3E18 cm^-2, and the gas has reached a temperature of 7000 to 8000 K. The spectrum of the Cusp indicates that roughly half of the refractory silicon and iron atoms have been liberated from the grains. Dust emission is not detected at either position. DA - 2014/5/20/ PY - 2014/5/20/ DO - 10.1088/0004-637x/787/1/3 VL - 787 IS - 1 SP - SN - 1538-4357 KW - infrared: ISM KW - ISM: abundances KW - ISM: individual objects (Cygnus Loop) KW - ISM: supernova remnants ER - TY - JOUR TI - Rapid kinetics of iron responsive element (IRE) RNA/iron regulatory protein 1 and IRE-RNA/eIF4F complexes respond differently to metal ions AU - Khan, Mateen A. AU - Ma, Jia AU - Walden, William E. AU - Merrick, William C. AU - Theil, Elizabeth C. AU - Goss, Dixie J. T2 - NUCLEIC ACIDS RESEARCH AB - Metal ion binding was previously shown to destabilize IRE-RNA/IRP1 equilibria and enhanced IRE-RNA/eIF4F equilibria. In order to understand the relative importance of kinetics and stability, we now report rapid rates of protein/RNA complex assembly and dissociation for two IRE-RNAs with IRP1, and quantitatively different metal ion response kinetics that coincide with the different iron responses in vivo. kon, for FRT IRE-RNA binding to IRP1 was eight times faster than ACO2 IRE-RNA. Mn2+ decreased kon and increased koff for IRP1 binding to both FRT and ACO2 IRE-RNA, with a larger effect for FRT IRE-RNA. In order to further understand IRE-mRNA regulation in terms of kinetics and stability, eIF4F kinetics with FRT IRE-RNA were determined. kon for eIF4F binding to FRT IRE-RNA in the absence of metal ions was 5-times slower than the IRP1 binding to FRT IRE-RNA. Mn2+ increased the association rate for eIF4F binding to FRT IRE-RNA, so that at 50 µM Mn2+ eIF4F bound more than 3-times faster than IRP1. IRP1/IRE-RNA complex has a much shorter life-time than the eIF4F/IRE-RNA complex, which suggests that both rate of assembly and stability of the complexes are important, and that allows this regulatory system to respond rapidly to change in cellular iron. DA - 2014/// PY - 2014/// DO - 10.1093/nar/gku248 VL - 42 IS - 10 SP - 6567-6577 SN - 1362-4962 ER - TY - JOUR TI - Quantification of Nano- and Mesoscale Phase Separation and Relation to Donor and Acceptor Quantum Efficiency, J(SC), and FF in Polymer:Fullerene Solar Cells AU - Ma, Wei AU - Tumbleston, John R. AU - Ye, Long AU - Wang, Cheng AU - Hou, Jianhui AU - Ade, Harald T2 - ADVANCED MATERIALS AB - Two characteristic length scales are revealed and quantified in a complex hierarchical polymer–fullerene blend by combining different X-ray scattering techniques. Anti-correlated composition variations between meso- and nanoscale separation are observed and impacted by the solvent mixture. Due to competition between the impact of the two length scales, the relation to device performance is complex and an ideal morphology is yet to be delineated. DA - 2014/7/2/ PY - 2014/7/2/ DO - 10.1002/adma.201400216 VL - 26 IS - 25 SP - 4234-4241 SN - 1521-4095 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84903724646&partnerID=MN8TOARS ER - TY - JOUR TI - MAGNETIC FIELD AMPLIFICATION IN NONLINEAR DIFFUSIVE SHOCK ACCELERATION INCLUDING RESONANT AND NON-RESONANT COSMIC-RAY DRIVEN INSTABILITIES AU - Bykov, Andrei M. AU - Ellison, Donald C. AU - Osipov, Sergei M. AU - Vladimirov, Andrey E. T2 - ASTROPHYSICAL JOURNAL AB - We present a nonlinear Monte Carlo model of efficient diffusive shock acceleration (DSA) where the magnetic turbulence responsible for particle diffusion is calculated self-consistently from the resonant cosmic-ray (CR) streaming instability, together with non-resonant short- and long-wavelength CR-current-driven instabilities. We include the backpressure from CRs interacting with the strongly amplified magnetic turbulence which decelerates and heats the super-alfvenic flow in the extended shock precursor. Uniquely, in our plane-parallel, steady-state, multi-scale model, the full range of particles, from thermal (~eV) injected at the viscous subshock, to the escape of the highest energy CRs (~PeV) from the shock precursor, are calculated consistently with the shock structure, precursor heating, magnetic field amplification (MFA), and scattering center drift relative to the background plasma. In addition, we show how the cascade of turbulence to shorter wavelengths influences the total shock compression, the downstream proton temperature, the magnetic fluctuation spectra, and accelerated particle spectra. A parameter survey is included where we vary shock parameters, the mode of magnetic turbulence generation, and turbulence cascading. From our survey results, we obtain scaling relations for the maximum particle momentum and amplified magnetic field as functions of shock speed, ambient density, and shock size. DA - 2014/7/10/ PY - 2014/7/10/ DO - 10.1088/0004-637x/789/2/137 VL - 789 IS - 2 SP - SN - 1538-4357 KW - acceleration of particles KW - cosmic rays KW - ISM: supernova remnants KW - magnetohydrodynamics (MHD) KW - shock waves KW - turbulence ER - TY - JOUR TI - Influence of Fluorination and Molecular Weight on the Morphology and Performance of PTB7:PC71BM Solar Cells AU - He, Xiaoxi AU - Mukherjee, Subhrangsu AU - Watkins, Scott AU - Chen, Ming AU - Qin, Tianshi AU - Thomsen, Lars AU - Ade, Harald AU - McNeill, Christopher R. T2 - JOURNAL OF PHYSICAL CHEMISTRY C AB - The device performance and microstructure of a series of PTB7-based polymers with varied molecular weight and degree of fluorination are investigated. Although the energy level of the highest occupied molecular orbital is found to increase with degree of fluorination, a strong relative molecular weight dependence of device performance dominates any underlying fluorination-dependent trend on overall performance. Microstructural investigation using a combination of X-ray techniques reveals a striking effect of polymer molecular characteristics on film morphology, with the size of PC71BM domains systematically decreasing with increasing polymer molecular weight. Furthermore, the relative purity of the mixed PTB7:PC71BM domain is found to systematically decrease with increasing molecular weight. When domain sizes with and without the use of the solvent additive diiodooctane (DIO) are compared, the effectiveness of DIO in reducing PC71BM domain sizes is also found to be strongly dependent on the molecular weight of the polymer. It is found that molecular weights of at least 150 kg mol–1 are required for DIO to be effective in reducing the PC71BM domain size in order to produce high short-circuit current densities. Finally, it is shown that relatively high device efficiencies can be achieved with low degrees of fluorination; an efficiency of 4.6% is achieved for a degree of fluorination of only 5.3%. DA - 2014/5/15/ PY - 2014/5/15/ DO - 10.1021/jp501222w VL - 118 IS - 19 SP - 9918-9929 SN - 1932-7447 ER - TY - JOUR TI - Anomalous Minimum in the Shear Viscosity of a Fermi Gas AU - Elliott, E. AU - Joseph, J. A. AU - Thomas, J. E. T2 - PHYSICAL REVIEW LETTERS AB - We measure the static shear viscosity $\eta$ in a two-component Fermi gas near a broad collisional (Feshbach) resonance, as a function of interaction strength and energy. We find that $\eta$ has both a quadratic and a linear dependence on the interaction strength $1/({k_{FI}a})$, where $a$ is the s-wave scattering length and $k_{FI}$ is the Fermi wave vector for an ideal gas at the trap center. For energies above the superfluid transition, the minimum in $\eta$ as a function of interaction strength is significantly shifted toward the BEC side of resonance, to $1/(k_{FI}a)\simeq 0.25$. DA - 2014/7/10/ PY - 2014/7/10/ DO - 10.1103/physrevlett.113.020406 VL - 113 IS - 2 SP - SN - 1079-7114 ER - TY - JOUR TI - Ultrasound Molecular Imaging of Secreted Frizzled Related Protein-2 Expression in Murine Angiosarcoma AU - Tsuruta, James K. AU - Klauber-DeMore, Nancy AU - Streeter, Jason AU - Samples, Jennifer AU - Patterson, Cam AU - Mumper, Russell J. AU - Ketelsen, David AU - Dayton, Paul T2 - PLOS ONE AB - Angiosarcoma is a biologically aggressive vascular malignancy with a high metastatic potential. In the era of targeted medicine, knowledge of specific molecular tumor characteristics has become more important. Molecular imaging using targeted ultrasound contrast agents can monitor tumor progression non-invasively. Secreted frizzled related protein 2 (SFRP2) is a tumor endothelial marker expressed in angiosarcoma. We hypothesize that SFRP2-directed imaging could be a novel approach to imaging the tumor vasculature. To develop an SFRP2 contrast agent, SFRP2 polyclonal antibody was biotinylated and incubated with streptavidin-coated microbubbles. SVR angiosarcoma cells were injected into nude mice, and when tumors were established the mice were injected intravenously with the SFRP2 -targeted contrast agent, or a control streptavidin-coated contrast agent. SFRP2 -targeted contrast agent detected tumor vasculature with significantly more signal intensity than control contrast agent: the normalized fold-change was 1.6 ± 0.27 (n = 13, p = 0.0032). The kidney was largely devoid of echogenicity with no significant difference between the control contrast agent and the SFRP2-targeted contrast agent demonstrating that the SFRP2-targeted contrast agent was specific to tumor vessels. Plotting average pixel intensity obtained from SFRP2-targeted contrast agent against tumor volume showed that the average pixel intensity increased as tumor volume increased. In conclusion, molecularly-targeted imaging of SFRP2 visualizes angiosarcoma vessels, but not normal vessels, and intensity increases with tumor size. Molecular imaging of SFRP2 expression may provide a rapid, non-invasive method to monitor tumor regression during therapy for angiosarcoma and other SFRP2 expressing cancers, and contribute to our understanding of the biology of SFRP2 during tumor development and progression. DA - 2014/1/29/ PY - 2014/1/29/ DO - 10.1371/journal.pone.0086642 VL - 9 IS - 1 SP - SN - 1932-6203 ER - TY - JOUR TI - Supersonic Flow Patterns from Electrothermal Plasma Source for Simulated Ablation and Aerosol Expansion Following a Fusion Disruption AU - Majumdar, Rudrodip AU - Gilligan, John G. AU - Winfrey, A. Leigh AU - Bourham, Mohamed A. T2 - JOURNAL OF FUSION ENERGY DA - 2014/2// PY - 2014/2// DO - 10.1007/s10894-013-9635-8 VL - 33 IS - 1 SP - 25-31 SN - 1572-9591 KW - Fusion disruption KW - Electrothermal plasma KW - Supersonic patterns ER - TY - JOUR TI - Nuclear chromodynamics: Novel nuclear phenomena predicted by QCD AU - Bakker, Bernard L. G. AU - Ji, Chueng-Ryong T2 - PROGRESS IN PARTICLE AND NUCLEAR PHYSICS AB - With the acceptance of QCD as the fundamental theory of strong interactions, one of the basic problems in the analysis of nuclear phenomena became how to consistently account for the effects of the underlying quark/gluon structure of nucleons and nuclei. Besides providing more detailed understanding of conventional nuclear physics, QCD may also point to novel phenomena accessible by new or upgraded nuclear experimental facilities. We review several interesting applications of QCD to nuclear physics. DA - 2014/1// PY - 2014/1// DO - 10.1016/j.ppnp.2013.10.001 VL - 74 SP - 1-34 SN - 1873-2224 KW - Nuclear physics KW - Quantum chromodynamics KW - Quark models ER - TY - JOUR TI - Communication: Fixed-node errors in quantum Monte Carlo: Interplay of electron density and node nonlinearities AU - Rasch, Kevin M. AU - Hu, Shuming AU - Mitas, Lubos T2 - The Journal of Chemical Physics AB - We elucidate the origin of large differences (two-fold or more) in the fixed-node errors between the first- vs second-row systems for single-configuration trial wave functions in quantum Monte Carlo calculations. This significant difference in the valence fixed-node biases is studied across a set of atoms, molecules, and also Si, C solid crystals. We show that the key features which affect the fixed-node errors are the differences in electron density and the degree of node nonlinearity. The findings reveal how the accuracy of the quantum Monte Carlo varies across a variety of systems, provide new perspectives on the origins of the fixed-node biases in calculations of molecular and condensed systems, and carry implications for pseudopotential constructions for heavy elements. DA - 2014/1/28/ PY - 2014/1/28/ DO - 10.1063/1.4862496 VL - 140 IS - 4 SP - 041102 J2 - The Journal of Chemical Physics LA - en OP - SN - 0021-9606 1089-7690 UR - http://dx.doi.org/10.1063/1.4862496 DB - Crossref ER - TY - JOUR TI - The gp41(659-671) HIV-1 Antibody Epitope: A Structurally Challenging Small Peptide AU - Zhang, Yuan AU - Sagui, Celeste T2 - JOURNAL OF PHYSICAL CHEMISTRY B AB - We report on extensive molecular dynamics (MD) simulations of the tridecapeptide corresponding to residues 659-671 of the envelope glycoprotein gp41 of HIV-1, which spans the 2F5 monoclonal antibody epitope ELDKWA. Previously, X-ray crystallography, nuclear magnetic resonance, and circular dichroism experiments have yielded conflicting conformational information, but there is a growing consensus that the monomeric peptide in aqueous solution is disordered. Here, we use the latest, state-of-the-art AMBER force fields to describe the complex conformational landscape of gp41(659-671). We have analyzed the conformational ensembles of the peptide in solution both without applied restraints and under successive tensile restraints. In contrast to previous MD simulations, our results are consistent with the bulk of the experimental findings. The amount of helical population is important in aqueous solution, but this structure forms part of a flexible conformational ensemble with a rugged free energy landscape with shallow minima. Under uniaxial tension, the disordered peptide first becomes fully helical before melting into turns, loops, and 310-helices. The conformational ensemble includes epitope conformations close to an NMR solution structure (PDB ID 1LCX ) as well as epitope conformations close to a very different, extended crystal structure (PDB ID 1TJH ). DA - 2014/1/9/ PY - 2014/1/9/ DO - 10.1021/jp409355r VL - 118 IS - 1 SP - 69-80 SN - 1520-5207 ER - TY - JOUR TI - The Stress-response protein prostate-associated gene 4, interacts with c-Jun and potentiates its transactivation AU - Rajagopalan, K. AU - Qiu, R. Y. AU - Mooney, S. M. AU - Rao, S. AU - Shiraishi, T. AU - Sacho, E. AU - Huang, H. Y. AU - Shapiro, E. AU - keith AU - Kulkarni, P. AU - al. T2 - BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR BASIS OF DISEASE AB - The Cancer/Testis Antigen (CTA), Prostate-associated Gene 4 (PAGE4), is a stress-response protein that is upregulated in prostate cancer (PCa) especially in precursor lesions that result from inflammatory stress. In cells under stress, translocation of PAGE4 to mitochondria increases while production of reactive oxygen species decreases. Furthermore, PAGE4 is also upregulated in human fetal prostate, underscoring its potential role in development. However, the proteins that interact with PAGE4 and the mechanisms underlying its pleiotropic functions in prostatic development and disease remain unknown. Here, we identified c-Jun as a PAGE4 interacting partner. We show that both PAGE4 and c-Jun are overexpressed in the human fetal prostate; and in cell-based assays, PAGE4 robustly potentiates c-Jun transactivation. Single-molecule Förster resonance energy transfer experiments indicate that upon binding to c-Jun, PAGE4 undergoes conformational changes. However, no interaction is observed in presence of BSA or unilamellar vesicles containing the mitochondrial inner membrane diphosphatidylglycerol lipid marker cardiolipin. Together, our data indicate that PAGE4 specifically interacts with c-Jun and that, conformational dynamics may account for its observed pleiotropic functions. To our knowledge, this is the first report demonstrating crosstalk between a CTA and a proto-oncogene. Disrupting PAGE4/c-Jun interactions using small molecules may represent a novel therapeutic strategy for PCa. DA - 2014/2// PY - 2014/2// DO - 10.1016/j.bbadis.2013.11.014 VL - 1842 IS - 2 SP - 154-163 SN - 0006-3002 KW - PAGE4 KW - Cancer/Testis Antigen KW - c-Jun KW - smFRET KW - Prostate cancer KW - Intrinsically disordered protein ER - TY - JOUR TI - Surface-plasmon mediated photoluminescence from Ag-coated ZnO/MgO core-shell nanowires AU - Mayo, Daniel C. AU - Marvinney, Claire E. AU - Bililign, Ephraim S. AU - McBride, James R. AU - Mu, Richard R. AU - Haglund, Richard F., Jr. T2 - THIN SOLID FILMS AB - Plasmon–exciton coupling mechanisms were studied in ZnO/MgO core–shell nanowires by comparing nanowires with and without a silver-nanoparticle coating. By varying the thickness of the MgO layer, it was possible to examine the distance-dependent plasmonic effects and elucidate the mechanisms responsible for enhancing the band-edge photoluminescence. The core–shell nanowires exhibited optical cavity effects as a function of MgO thickness that dramatically enhanced the band-edge photoluminescence yields in the ultraviolet. Decorating the core–shell nanowires with Ag nanoparticles resulted in a two-fold plasmonic enhancement of the band-edge emission compared to the resonant cavity effects alone. In this case, an additional differential enhancement of the band-edge emission is observed for the first higher-order mode compared to the lowest-order mode. The visible luminescence is not significantly enhanced and does not follow the trend of enhanced photoluminescence observed for the band-edge decay. DA - 2014/2/28/ PY - 2014/2/28/ DO - 10.1016/j.tsf.2013.11.131 VL - 553 SP - 132-137 SN - 0040-6090 KW - ZnO excitons KW - Ag plasmons KW - Plasmon-exciton coupling KW - Resonant optical cavity KW - Core-shell nanowire KW - Photoluminescence ER - TY - JOUR TI - Spectroscopic Studies of Single and Double Variants of M Ferritin: Lack of Conversion of a Biferrous Substrate Site into a Cofactor Site for O-2 Activation AU - Kwak, Yeonju AU - Schwartz, Jennifer K. AU - Haldar, Suranjana AU - Behera, Rabindra K. AU - Tosha, Takehiko AU - Theil, Elizabeth C. AU - Solomon, Edward I. T2 - BIOCHEMISTRY AB - Ferritin has a binuclear non-heme iron active site that functions to oxidize iron as a substrate for formation of an iron mineral core. Other enzymes of this class have tightly bound diiron cofactor sites that activate O2 to react with substrate. Ferritin has an active site ligand set with 1-His/4-carboxylate/1-Gln rather than the 2-His/4-carboxylate set of the cofactor site. This ligand variation has been thought to make a major contribution to this biferrous substrate rather than cofactor site reactivity. However, the Q137E/D140H double variant of M ferritin, has a ligand set that is equivalent to most of the diiron cofactor sites, yet did not rapidly react with O2 or generate the peroxy intermediate observed in the cofactor sites. Therefore, in this study, a combined spectroscopic methodology of circular dichroism (CD)/magnetic CD (MCD)/variable temperature, variable field (VTVH) MCD has been applied to evaluate the factors required for the rapid O2 activation observed in cofactor sites. This methodology defines the coordination environment of each iron and the bridging ligation of the biferrous active sites in the double and corresponding single variants of frog M ferritin. Based on spectral changes, the D140H single variant has the new His ligand binding, and the Q137E variant has the new carboxylate forming a μ-1,3 bridge. The spectra for the Q137E/D140H double variant, which has the cofactor ligand set, however, reflects a site that is more coordinately saturated than the cofactor sites in other enzymes including ribonucleotide reductase, indicating the presence of additional water ligation. Correlation of this double variant and the cofactor sites to their O2 reactivities indicates that electrostatic and steric changes in the active site and, in particular, the hydrophobic nature of a cofactor site associated with its second sphere protein environment, make important contributions to the activation of O2 by the binuclear non-heme iron enzymes. DA - 2014/1/28/ PY - 2014/1/28/ DO - 10.1021/bi4013726 VL - 53 IS - 3 SP - 473-482 SN - 0006-2960 ER - TY - JOUR TI - SN 2010jl: OPTICAL TO HARD X-RAY OBSERVATIONS REVEAL AN EXPLOSION EMBEDDED IN A TEN SOLAR MASS COCOON AU - Ofek, Eran O. AU - Zoglauer, Andreas AU - Boggs, Steven E. AU - Barriere, Nicolas M. AU - Reynolds, Stephen P. AU - Fryer, Chris L. AU - Harrison, Fiona A. AU - Cenko, S. Bradley AU - Kulkarni, Shrinivas R. AU - Gal-Yam, Avishay AU - Arcavi, Iair AU - Bellm, Eric AU - Bloom, Joshua S. AU - Christensen, Finn AU - Craig, William W. AU - Even, Wesley AU - Filippenko, Alexei V. AU - Grefenstette, Brian AU - Hailey, Charles J. AU - Laher, Russ AU - Madsen, Kristin AU - Nakar, Ehud AU - Nugent, Peter E. AU - Stern, Daniel AU - Sullivan, Mark AU - Surace, Jason AU - Zhang, William W. T2 - ASTROPHYSICAL JOURNAL AB - (Abridged) Some supernovae (SNe) may be powered by the interaction of the SN ejecta with a large amount of circumstellar matter (CSM). Here we outline a method to measure the mass of the optically thick CSM around such SNe. We present observations of SN2010jl, including the first detection of a SN using NuSTAR. The total radiated luminosity of SN2010jl is extreme, at least 9e50 erg. By modeling the visible-light data, we robustly show that the mass of the circumstellar material within ~1e16 cm of the progenitor was in excess of 10 solar masses, likely ejected tens of years prior to the SN explosion. Our modeling suggests that the shock velocity during shock breakout was ~6000 km/s, decelerating to ~2600 km/s about two years after maximum light. Our late-time NuSTAR+XMM spectra of the SN presumably provide the first direct measurement of SN shock velocity two years after the SN maximum light -- measured to be in the range of 2000 to 4500 km/s if the ions and electrons are in equilibrium, and >~2000 km/s if they are not in equilibrium. This measurement is in agreement with the shock velocity predicted by our modeling of the optical data. We also show that the mean radial density distribution of the CSM roughly follows an r^-2 law. A possible explanation for the massive CSM with a wind-like profile is that they are the result of multiple pulsational pair instability events prior to the SN explosion, separated from each other by years. DA - 2014/1/20/ PY - 2014/1/20/ DO - 10.1088/0004-637x/781/1/42 VL - 781 IS - 1 SP - SN - 1538-4357 KW - stars: mass-loss KW - supernovae: general KW - supernovae: individual (SN 2010jl) ER - TY - JOUR TI - Many-Body Effects in Valleytronics: Direct Measurement of Valley Lifetimes in Single-Layer MoS2 AU - Mai, Cong AU - Barrette, Andrew AU - Yu, Yifei AU - Semenov, Yuriy G. AU - Kim, Ki Wook AU - Cao, Linyou AU - Gundogdu, Kenan T2 - NANO LETTERS AB - Single layer MoS2 is an ideal material for the emerging field of "valleytronics" in which charge carrier momentum can be finely controlled by optical excitation. This system is also known to exhibit strong many-body interactions as observed by tightly bound excitons and trions. Here we report direct measurements of valley relaxation dynamics in single layer MoS2, by using ultrafast transient absorption spectroscopy. Our results show that strong Coulomb interactions significantly impact valley population dynamics. Initial excitation by circularly polarized light creates electron-hole pairs within the K-valley. These excitons coherently couple to dark intervalley excitonic states, which facilitate fast electron valley depolarization. Hole valley relaxation is delayed up to about 10 ps due to nondegeneracy of the valence band spin states. Intervalley biexciton formation reveals the hole valley relaxation dynamics. We observe that biexcitons form with more than an order of magnitude larger binding energy compared to conventional semiconductors. These measurements provide significant insight into valley specific processes in 2D semiconductors. Hence they could be used to suggest routes to design semiconducting materials that enable control of valley polarization. DA - 2014/1// PY - 2014/1// DO - 10.1021/nl403742j VL - 14 IS - 1 SP - 202-206 SN - 1530-6992 KW - MoS2 KW - valley relaxation KW - transient absorption KW - many-body interactions KW - transition metal dichalcogenides KW - two-dimensional materials ER - TY - JOUR TI - Investigating rare events with nonequilibrium work measurements. II. Transition and reaction rates (vol 140, 034115, 2014) AU - Moradi, Mahmoud AU - Sagui, Celeste AU - Roland, Christopher T2 - JOURNAL OF CHEMICAL PHYSICS AB - First Page DA - 2014/2/14/ PY - 2014/2/14/ DO - 10.1063/1.4865582 VL - 140 IS - 6 SP - SN - 1089-7690 ER - TY - JOUR TI - Investigating rare events with nonequilibrium work measurements. I. Nonequilibrium transition path probabilities (vol 140, 034114, 2014) AU - Moradi, Mahmoud AU - Sagui, Celeste AU - Roland, Christopher T2 - JOURNAL OF CHEMICAL PHYSICS AB - First Page DA - 2014/2/14/ PY - 2014/2/14/ DO - 10.1063/1.4865580 VL - 140 IS - 6 SP - SN - 1089-7690 ER - TY - JOUR TI - Dynamics of dysprosium silicide nanostructures on Si(001) and (111) surfaces AU - Zeman, M. C. AU - Nemanich, R. J. AU - Sunda-Meya, A. T2 - Journal of Materials Science DA - 2014/// PY - 2014/// VL - 49 IS - 4 SP - 1812-1823 ER - TY - JOUR TI - Density dependence of fixed-node errors in diffusion quantum Monte Carlo: Triplet pair correlations AU - Kulahlioglu, Adem H. AU - Rasch, Kevin AU - Hu, Shuming AU - Mitas, Lubos T2 - CHEMICAL PHYSICS LETTERS AB - Abstract We analyze trial wave function fixed-node errors for a three-electron fully spin-polarized atomic systems with varying atomic number Z . The fully spin-polarized state 4 S ( 1 s 2 s 3 s ) is the lowest quadruplet with S -symmetry and even parity and it is nearly-degenerate with the 4 S ( 1 s 2 p 3 p ) state. We find significant fixed-node errors proportional to Z at the Hartree–Fock level while the two-configuration wave function leads to nearly exact energies. This broadly agrees with our analogous study on Be-like atoms so that the dependence of fixed-node errors on density appears to be similar in both spin-polarized and unpolarized atomic systems. DA - 2014/1/20/ PY - 2014/1/20/ DO - 10.1016/j.cplett.2013.11.033 VL - 591 SP - 170-174 SN - 1873-4448 ER - TY - JOUR TI - Classical Electrostatics for Biomolecular Simulations AU - Cisneros, G. Andres AU - Karttunen, Mikko AU - Ren, Pengyu AU - Sagui, Celeste T2 - CHEMICAL REVIEWS AB - ADVERTISEMENT RETURN TO ISSUEPREVReviewNEXTADDITION / CORRECTIONThis article has been corrected. View the notice.Classical Electrostatics for Biomolecular SimulationsG. Andrés Cisneros†, Mikko Karttunen‡, Pengyu Ren§, and Celeste Sagui*∥View Author Information† Department of Chemistry, Wayne State University, Detroit, Michigan 48202, United States‡ Department of Chemistry and Waterloo Institute for Nanotechnology, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, Canada N2L 3G1§ Department of Biomedical Engineering, BME 5.202M, The University of Texas at Austin, 1 University Station, C0800, Austin, Texas 78712-1062, United States∥ Department of Physics, North Carolina State University, Raleigh, North Carolina 27695, United States *E-mail: [email protected]Cite this: Chem. Rev. 2014, 114, 1, 779–814Publication Date (Web):August 27, 2013Publication History Received20 November 2012Published online27 August 2013Published inissue 8 January 2014https://doi.org/10.1021/cr300461dCopyright © 2013 American Chemical SocietyRequest reuse permissionsArticle Views5976Altmetric-Citations211LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (6 MB) Get e-AlertscloseSUBJECTS:Chemical calculations,Electrical properties,Electrostatics,Molecular mechanics,Polarization Get e-Alerts DA - 2014/1/8/ PY - 2014/1/8/ DO - 10.1021/cr300461d VL - 114 IS - 1 SP - 779-814 SN - 1520-6890 ER - TY - JOUR TI - Characterization of large area, thick, and segmented silicon detectors for neutron beta decay experiments AU - Salas-Bacci, A. AU - McGaughey, P.L. AU - Baeßler, S. AU - Broussard, L. AU - Makela, M.F. AU - Mirabal, J. AU - Pattie, R.W. AU - Počanić, D. AU - Sjue, S.K.L. AU - Penttila, S.I. AU - Wilburn, W.S. AU - Young, A.R. AU - Zeck, B.A. AU - Wang, Z. T2 - Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment AB - The “Nab” and “UCNB” collaborations have proposed to measure the correlation parameters in neutron β-decay at Oak Ridge and Los Alamos National Laboratory, using a novel detector design. Two large area, thick, hexagonal-segmented silicon detectors containing 127 pixels per detector will be used to detect the proton and electron from neutron decay. Both silicon detectors are connected by magnetic field lines of a few Tesla field strength, and set on an electrostatic potential, such that protons can be accelerated up to 30 keV in order to be detected. Characteristics of the detector response to low energy conversion electrons and protons from 15 keV to 35 keV, including the evaluation of the dead layer thickness and other contributions to the pulse height defect for proton detection are presented for Si detectors of 0.5 mm and 1 mm of thickness. DA - 2014/1// PY - 2014/1// DO - 10.1016/J.NIMA.2013.09.059 VL - 735 SP - 408–415 SN - 0168-9002 UR - http://dx.doi.org/10.1016/J.NIMA.2013.09.059 KW - Neutron beta decay KW - Silicon detector KW - Pulse height defect KW - Nuclear defect KW - Dead layer ER - TY - JOUR TI - A segmented, enriched N-type germanium detector for neutrinoless double beta-decay experiments AU - Leviner, L.E. AU - Aalseth, C.E. AU - Ahmed, M.W. AU - Avignone, F.T., III AU - Back, H.O. AU - Barabash, A.S. AU - Boswell, M. AU - De Braeckeleer, L. AU - Brudanin, V.B. AU - Chan, Y.-D. AU - Egorov, V.G. AU - Elliott, S.R. AU - Gehman, V.M. AU - Hossbach, T.W. AU - Kephart, J.D. AU - Kidd, M.F. AU - Konovalov, S.I. AU - Lesko, K.T. AU - Li, Jingyi AU - Mei, D.-M. AU - Mikhailov, S. AU - Miley, H. AU - Radford, D.C. AU - Reeves, J. AU - Sandukovsky, V.G. AU - Umatov, V.I. AU - Underwood, T.A. AU - Tornow, W. AU - Wu, Y.K. AU - Young, A.R. T2 - Nuclear Instruments & Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors, and Associated Equipment AB - We present data characterizing the performance of the first segmented, N-type Ge detector, isotopically enriched to 85% $^{76}$Ge. This detector, based on the Ortec PT6x2 design and referred to as SEGA (Segmented, Enriched Germanium Assembly), was developed as a possible prototype for neutrinoless double beta-decay measurements by the {\sc Majorana} collaboration. We present some of the general characteristics (including bias potential, efficiency, leakage current, and integral cross-talk) for this detector in its temporary cryostat. We also present an analysis of the resolution of the detector, and demonstrate that for all but two segments there is at least one channel that reaches the {\sc Majorana} resolution goal below 4 keV FWHM at 2039 keV, and all channels are below 4.5 keV FWHM. DA - 2014/1/21/ PY - 2014/1/21/ DO - 10.1016/J.NIMA.2013.08.081 VL - 735 SP - 66–77 J2 - Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment LA - en OP - SN - 0168-9002 UR - http://dx.doi.org/10.1016/J.NIMA.2013.08.081 DB - Crossref KW - Double beta decay KW - Segmented KW - Germanium KW - Detector KW - Majorana KW - Neutrinoless ER - TY - JOUR TI - A HIGH-RESOLUTION X-RAY AND OPTICAL STUDY OF SN 1006: ASYMMETRIC EXPANSION AND SMALL-SCALE STRUCTURE IN A TYPE IA SUPERNOVA REMNANT AU - Winkler, P. Frank AU - Williams, Brian J. AU - Reynolds, Stephen P. AU - Petre, Robert AU - Long, Knox S. AU - Katsuda, Satoru AU - Hwang, Una T2 - ASTROPHYSICAL JOURNAL AB - We introduce a deep (670 ks) X-ray survey of the SN1006 remnant from Chandra, plus a deep H-alpha image from the 4m telescope at CTIO. Comparison with Chandra images from 2003 gives the first measurement of X-ray proper motions around the entire rim. We find that the expansion velocity varies significantly with azimuth: the highest velocity of ~7400 km/s (almost 2.5 times that in the NW) is found along the SE rim, where both kinematics and spectra indicate that most of the X-rays stem from undecelerated ejecta. Asymmetries in the distribution of ejecta are seen on a variety of spatial scales. Si-rich ejecta are especially prominent in the SE quadrant, while O and Mg are more uniformly distributed, indicating large-scale asymmetries arising from the explosion itself. Ne emission is strongest in a sharp filament just behind the primary shock along the NW rim, where the preshock density is highest. Here the Ne is likely interstellar, while Ne within the shell may include a contribution from ejecta. Within the interior of the projected shell we find a few isolated "bullets" of what appear to be supernova ejecta that are immediately preceded by bowshocks seen in H-alpha--features we interpret as ejecta knots that have reached relatively dense regions of the surrounding ISM. Recent 3-dimensional hydrodynamic models for SN Ia display small-scale features that resemble the ones seen in X-rays in SN1006; an origin in the explosion itself or from subsequent instabilities both remain viable options. We have expanded the search for precursor X-ray emission ahead of a synchrotron-dominated shock front. Profiles along both NE and SW rims require that a precursor be thinner than about 3 arcsec and fainter than about 5% of the post-shock peak. These limits suggest that the magnetic field is amplified by a factor of 7 or more in a narrow precursor region, promoting diffusive particle acceleration. DA - 2014/2/1/ PY - 2014/2/1/ DO - 10.1088/0004-637x/781/2/65 VL - 781 IS - 2 SP - SN - 1538-4357 KW - ISM: individual objects (SN 1006) KW - ISM: kinematics and dynamics KW - ISM: supernova remnants KW - supernovae: individual (SN 1006) KW - X-rays: individual (SN1006) KW - X-rays: ISM ER - TY - JOUR TI - Observation of Conformal Symmetry Breaking and Scale Invariance in Expanding Fermi Gases AU - Elliott, E. AU - Joseph, J. A. AU - Thomas, J. E. T2 - PHYSICAL REVIEW LETTERS AB - We precisely test scale invariance and examine local thermal equilibrium in the hydrodynamic expansion of a Fermi gas of atoms as a function of interaction strength. After release from an anisotropic optical trap, we observe that a resonantly interacting gas obeys scale-invariant hydrodynamics, where the mean square cloud size $⟨{\mathbf{r}}^{2}⟩=⟨{x}^{2}+{y}^{2}+{z}^{2}⟩$ expands ballistically (like a noninteracting gas) and the energy-averaged bulk viscosity is consistent with zero, $0.00(0.04)\mathrm{\ensuremath{\hbar}}n$, with $n$ the density. In contrast, the aspect ratios of the cloud exhibit anisotropic ``elliptic'' flow with an energy-dependent shear viscosity. Tuning away from resonance, we observe conformal symmetry breaking, where $⟨{\mathbf{r}}^{2}⟩$ deviates from ballistic flow. DA - 2014/1/29/ PY - 2014/1/29/ DO - 10.1103/physrevlett.112.040405 VL - 112 IS - 4 SP - SN - 1079-7114 ER - TY - JOUR TI - Nuclear Deformation and Neutron Excess as Competing Effects for Dipole Strength in the Pygmy Region AU - Massarczyk, R. AU - Schwengner, R. AU - Donau, F. AU - Frauendorf, S. AU - Anders, M. AU - Bemmerer, D. AU - Beyer, R. AU - Bhatia, C. AU - Birgersson, E. AU - Butterling, M. AU - Elekes, Z. AU - Ferrari, A. AU - Gooden, M. E. AU - Hannaske, R. AU - Junghans, A. R. AU - Kempe, M. AU - Kelley, J. H. AU - Kogler, T. T2 - Physical Review Letters DA - 2014/// PY - 2014/// VL - 112 IS - 7 ER - TY - JOUR TI - Leaky mode engineering: A general design principle for dielectric optical antenna solar absorbers AU - Yu, Yiling AU - Cao, Linyou T2 - OPTICS COMMUNICATIONS AB - We present a general principle for the rational design of dielectric optical antennas with optimal solar absorption enhancement: leaky mode engineering. This builds upon our previous study that demonstrates the solar absorption of a material with a given volume only dependent on the density and the radiative loss of leaky modes of the material. Here we systematically examine the correlation among the modal properties (density and radiative loss) of leaky modes, physical features, and solar absorption of dielectric antenna structures. Our analysis clearly points out the general guidelines for the design of dielectric optical antennas with optimal solar absorption enhancement: (a) using 0D structures; (b) the shape does not matter much; (c) heterostructuring with non-absorbing materials is a promising strategy; and (d) the design of a large-scale nanostructure array can use the solar absorption of single nanostructures as a reasonable reference. DA - 2014/3/1/ PY - 2014/3/1/ DO - 10.1016/j.optcom.2013.10.051 VL - 314 SP - 79-85 SN - 1873-0310 KW - Leaky mode KW - Optical antenna KW - Solar absorber KW - Solar cell KW - Semiconductor ER - TY - JOUR TI - Finite volume effects in low-energy neutron-deuteron scattering AU - Rokash, A. AU - Epelbaum, E. AU - Krebs, H. AU - Lee, D. AU - Meissner, U. G. T2 - Journal of Physics. G, Nuclear and Particle Physics DA - 2014/// PY - 2014/// VL - 41 IS - 1 ER - TY - JOUR TI - Asymmetries in core-collapse supernovae from maps of radioactive Ti-44 in Cassiopeia A AU - Grefenstette, B. W. AU - Harrison, F. A. AU - Boggs, S. E. AU - Reynolds, S. P. AU - Fryer, C. L. AU - Madsen, K. K. AU - Wik, D. R. AU - Zoglauer, A. AU - Ellinger, C. I. AU - Alexander, D. M. AU - An, H. AU - Barret, D. AU - Christensen, F. E. AU - Craig, W. W. AU - Forster, K. AU - Giommi, P. AU - Hailey, C. J. AU - Hornstrup, A. AU - Kaspi, V. M. AU - Kitaguchi, T. AU - Koglin, J. E. AU - Mao, P. H. AU - Miyasaka, H. AU - Mori, K. AU - Perri, M. AU - Pivovaroff, M. J. AU - Puccetti, S. AU - Rana, V. AU - Stern, D. AU - Westergaard, N. J. AU - Zhang, W. W. T2 - NATURE AB - Asymmetry is required by most numerical simulations of stellar core-collapse explosions, but the form it takes differs significantly among models. The spatial distribution of radioactive 44Ti, synthesized in an exploding star near the boundary between material falling back onto the collapsing core and that ejected into the surrounding medium, directly probes the explosion asymmetries. CassiopeiaA is a young, nearby, core-collapse remnant from which 44Ti emission has previously been detected but not imaged. Asymmetries in the explosion have been indirectly inferred from a high ratio of observed 44Ti emission to estimated 56Ni emission, from optical light echoes, and from jet-like features seen in the X-ray and optical ejecta. Here we report spatial maps and spectral properties of the 44Ti in Cassiopeia A. This may explain the unexpected lack of correlation between the 44Ti and iron X-ray emission, the latter being visible only in shock-heated material. The observed spatial distribution rules out symmetric explosions even with a high level of convective mixing, as well as highly asymmetric bipolar explosions resulting from a fast-rotating progenitor. Instead, these observations provide strong evidence for the development of low-mode convective instabilities in core-collapse supernovae. DA - 2014/2/20/ PY - 2014/2/20/ DO - 10.1038/nature12997 VL - 506 IS - 7488 SP - 339-+ SN - 1476-4687 ER - TY - JOUR TI - Toward Single-Crystal Hybrid-Carbon Electronics: Impact of Graphene Substrate Defect Density on Copper Phthalocyanine Film Growth AU - McAfee, Terry AU - Gann, Eliot AU - Guan, Tianshuai AU - Stuart, Sean C. AU - Rowe, Jack AU - Dougherty, Daniel B. AU - Ade, Harald T2 - CRYSTAL GROWTH & DESIGN AB - Graphene has long been recognized as a potential replacement for indium tin oxide as a transparent conducting substrate that may not only be cheaper to manufacture but also may provide mechanical flexibility and templating for preferential organic film growth. Here, we report the discovery that the thin film growth mode and crystal structure of copper phthalocyanine (CuPc), a prototype organic semiconductor, is extremely sensitive to even atomic-scale defects (e.g., steps) on the graphene surface and that high quality films can be grown with a well-defined crystal orientation that should be favorable for optimized solar cell applications. The initial growth involves flat-lying copper phthalocyanine molecules in a triclinic brickstone crystal with (012̅) orientation. Thicker films on pristine graphite, as well as thin films on lower quality graphene, show an orientational transition to the flat-lying (112̅)-oriented brickstone, which nucleates near film defects and grows in more compact 3D islands. The thickness dependent transition between these two flat-lying crystal orientations is sensitive to substrate defect density since this determines the extent to which initial island elongation along the substrate can alleviate strain in the film. The sensitivity of copper phthalocyanine film morphology demonstrates the extreme importance of graphene substrate quality to controlling organic film growth. The high crystallinity and optimal molecular orientation achieved here implies a new driving force for high performance organic optoelectronics based on substrate-controlled crystal engineering. DA - 2014/9// PY - 2014/9// DO - 10.1021/cg500504u VL - 14 IS - 9 SP - 4394-4401 SN - 1528-7505 ER - TY - JOUR TI - NONUNIFORM EXPANSION OF THE YOUNGEST GALACTIC SUPERNOVA REMNANT G1.9+0.3 AU - Carlton, A. K. AU - Borkowski, K. J. AU - Reynolds, Stephen AU - Hwang, U. AU - Petre, R. AU - Green, D. A. AU - Krishnamurthy, K. AU - Willett, R. T2 - ASTROPHYSICAL JOURNAL LETTERS AB - We report measurements of X-ray expansion of the youngest Galactic supernova remnant, G1.9+0.3, using Chandra observations in 2007, 2009, and 2011. The measured rates strongly deviate from uniform expansion, decreasing radially by about 60% along the X-ray bright SE-NW axis from 0.84% +/- 0.06% per yr to 0.52% +/- 0.03% per yr. This corresponds to undecelerated ages of 120-190 yr, confirming the young age of G1.9+0.3, and implying a significant deceleration of the blast wave. The synchrotron-dominated X-ray emission brightens at a rate of 1.9% +/- 0.4% per yr. We identify bright outer and inner rims with the blast wave and reverse shock, respectively. Sharp density gradients in either ejecta or ambient medium are required to produce the sudden deceleration of the reverse shock or the blast wave implied by the large spread in expansion ages. The blast wave could have been decelerated recently by an encounter with a modest density discontinuity in the ambient medium, such as found at a wind termination shock, requiring strong mass loss in the progenitor. Alternatively, the reverse shock might have encountered an order-of-magnitude density discontinuity within the ejecta, such as found in pulsating delayed-detonation Type Ia models. We demonstrate that the blast wave is much more decelerated than the reverse shock in these models for remnants at ages similar to G1.9+0.3. Similar effects may also be produced by dense shells possibly associated with high-velocity features in Type Ia spectra. Accounting for the asymmetry of G1.9+0.3 will require more realistic 3D Type Ia models. DA - 2014/8/1/ PY - 2014/8/1/ DO - 10.1088/2041-8205/790/2/l18 VL - 790 IS - 2 SP - SN - 2041-8213 UR - https://doi.org/10.1088/2041-8205/790/2/L18 KW - ISM: individual objects (G1.9+0.3) KW - ISM: supernova remnants KW - X-rays: ISM ER -