TY - CONF TI - Europium, Samarium, and Neodymium Isotopic Fractions in Metal-Poor Stars AU - Roederer, I.U. AU - Lawler, J.E. AU - Sneden, C. AU - Cowan, J.J. AU - Sobeck, J. AU - Pilachowski, C.A. T2 - Frank N. Bash Symposium 2007 A2 - Frebel, A. T3 - Astronomical Society of the Pacific conference series C2 - 2008/// C3 - New horizons in astronomy : Frank N. Bash Symposium 2007 : proceedings of a workshop held at the University of Texas, Austin, Texas, USA, 14-16 October 2007 CY - University of Texas, Austin, Texas DA - 2008/// PY - 2007/10/14/ SP - 263 ER - TY - JOUR TI - The Hobby‐Eberly Telescope Chemical Abundances of Stars in the Halo (CASH) Project. I. The Lithium‐,s‐, andr‐enhanced Metal‐poor Giant HKII 17435−00532 AU - Roederer, Ian U. AU - Frebel, Anna AU - Shetrone, Matthew D. AU - Allende Prieto, Carlos AU - Rhee, Jaehyon AU - Gallino, Roberto AU - Bisterzo, Sara AU - Sneden, Christopher AU - Beers, Timothy C. AU - Cowan, John J. T2 - The Astrophysical Journal AB - We present the first detailed abundance analysis of the metal-poor giant HKII 17435–00532. This star was observed as part of the University of Texas long-term project Chemical Abundances of Stars in the Halo (CASH). A spectrum was obtained with the High Resolution Spectrograph (HRS) on the Hobby-Eberly Telescope with a resolving power of R ∼ 15,000. Our analysis reveals that this star may be located on the red giant branch, red horizontal branch, or early asymptotic giant branch. We find that this metal-poor ([Fe/H] = − 2.2) star has an unusually high lithium abundance [log ε (Li) = + 2.1], mild carbon ([C/Fe] = + 0.7) and sodium ([Na/Fe] = + 0.6) enhancement, as well as enhancement of both s-process ([Ba/Fe] = + 0.8) and r-process ([Eu/Fe] = + 0.5) material. The high Li abundance can be explained by self-enrichment through extra mixing that connects the convective envelope with the outer regions of the H-burning shell. If so, HKII 17435–00532 is the most metal-poor star in which this short-lived phase of Li enrichment has been observed. The Na and n-capture enrichment can be explained by mass transfer from a companion that passed through the thermally pulsing AGB phase of evolution with only a small initial enrichment of r-process material present in the birth cloud. Despite the current nondetection of radial velocity variations (over ~180 days), it is possible that HKII 17435–00532 is in a long-period or highly inclined binary system, similar to other stars with similar n-capture enrichment patterns. DA - 2008/6// PY - 2008/6// DO - 10.1086/587794 VL - 679 IS - 2 SP - 1549-1565 J2 - ApJ LA - en OP - SN - 0004-637X 1538-4357 UR - http://dx.doi.org/10.1086/587794 DB - Crossref ER - TY - CONF TI - The Lithium-, r- and s-Enhanced Metal-Poor Giant HK-II 17435-00532 AU - Roederer, Ian U. AU - Frebel, Anna AU - Shetrone, Matthew AU - Prieto, Carlos Allende AU - Rhee, Jaehyon AU - Gallino, Roberto AU - Bisterzo, Sara AU - Sneden, Christopher AU - Beers, Timothy C. AU - Cowan, John J. AU - Guandalini, Roald AU - Palmerini, Sara AU - Busso, Maurizio T2 - IXTH TORINO WORKSHOP ON EVOLUTION AND NUCLEOSYNTHESIS IN AGB STARS AND THE IIND PERUGIA WORKSHOP ON NUCLEAR ASTROPHYSICS AB - We present the first detailed abundance analysis of the metal‐poor giant HK‐II 17435‐00532. This star was observed as part of the University of Texas Long‐Term Chemical Abundances of Stars in the Halo (CASH) Project. A spectrum was obtained with the High Resolution Spectrograph (HRS) on the Hobby‐Eberly Telescope with a resolving power of R∼15000. Our analysis reveals that this star may be located on the red giant branch, red horizontal branch, or early asymptotic giant branch. We find that this metal‐poor ([Fe/H] = −2.2) star has an unusually high lithium abundance (logε(Li) = +2.1), mild carbon ([C/Fe] = +0.7) and sodium ([Na/Fe] = +0.6) enhancement, as well as enhancement of both s‐process ([Ba/Fe] = +0.8) and r‐process ([Eu/Fe] = +0.5) material. The high Li abundance can be explained by self‐enrichment through extra mixing mechanisms that connect the convective envelope with the outer regions of the H‐burning shell. If so, HK‐II 17435‐00532 is the most metal‐poor starin which this short‐lived phase of Li enrichment has been observed. The r‐ and s‐process material was not produced in this star but was either present in the gas from which HK‐II 17435‐00532 formed or was transferred to it from a more massive binary companion. Despite the current non‐detection of radial velocity variations (over a time span of ∼180 days), it is possible that HK‐II 17435‐00532 is in a long‐period binary system, similar to other stars with both r and s enrichment. C2 - 2008/// C3 - AIP Conference Proceedings DA - 2008/// DO - 10.1063/1.2916960 PB - AIP UR - http://dx.doi.org/10.1063/1.2916960 ER - TY - ER - TY - ER - TY - JOUR TI - Europium, Samarium, and Neodymium Isotopic Fractions in Metal‐Poor Stars AU - Roederer, Ian U. AU - Lawler, James E. AU - Sneden, Christopher AU - Cowan, John J. AU - Sobeck, Jennifer S. AU - Pilachowski, Catherine A. T2 - The Astrophysical Journal AB - We have derived isotopic fractions of europium, samarium, and neodymium in two metal-poor giants with differing neutron-capture nucleosynthetic histories. These isotopic fractions were measured from new high-resolution (R ∼ 120,000), high signal-to-noise ratio (S/N ~ 160-1000) spectra obtained with the 2d-coudé spectrograph of McDonald Observatory's 2.7 m Smith telescope. Synthetic spectra were generated using recent high-precision laboratory measurements of hyperfine and isotopic subcomponents of several transitions of these elements and matched quantitatively to the observed spectra. We interpret our isotopic fractions by the nucleosynthesis predictions of the stellar model, which reproduces s-process nucleosynthesis from the physical conditions expected in low-mass, thermally pulsing stars on the AGB, and the classical method, which approximates s-process nucleosynthesis by a steady neutron flux impinging on Fe-peak seed nuclei. Our Eu isotopic fraction in HD 175305 is consistent with an r-process origin by the classical method and is consistent with either an r- or an s-process origin by the stellar model. Our Sm isotopic fraction in HD 175305 suggests a predominantly r-process origin, and our Sm isotopic fraction in HD 196944 is consistent with an s-process origin. The Nd isotopic fractions, while consistent with either r-process or s-process origins, have very little ability to distinguish between any physical values for the isotopic fraction in either star. This study for the first time extends the n-capture origin of multiple rare earths in metal-poor stars from elemental abundances to the isotopic level, strengthening the r-process interpretation for HD 175305 and the s-process interpretation for HD 196944. DA - 2008/3// PY - 2008/3// DO - 10.1086/526452 VL - 675 IS - 1 SP - 723-745 J2 - ApJ LA - en OP - SN - 0004-637X 1538-4357 UR - http://dx.doi.org/10.1086/526452 DB - Crossref ER - TY - JOUR TI - CHEMICAL INHOMOGENEITIES IN THE MILKY WAY STELLAR HALO AU - Roederer, Ian U. T2 - The Astronomical Journal AB - We have compiled a sample of 699 stars from the recent literature with detailed chemical abundance information (spanning −4.2≲ [Fe/H] ≲+0.3), and we compute their space velocities and Galactic orbital parameters. We identify members of the inner and outer stellar halo populations in our sample based only on their kinematic properties and then compare the abundance ratios of these populations as a function of [Fe/H]. In the metallicity range where the two populations overlap (−2.5≲ [Fe/H] ≲−1.5), the mean [Mg/Fe] of the outer halo is lower than the inner halo by −0.1 dex. For [Ni/Fe] and [Ba/Fe], the star-to-star abundance scatter of the inner halo is consistently smaller than in the outer halo. The [Na/Fe], [Y/Fe], [Ca/Fe], and [Ti/Fe] ratios of both populations show similar means and levels of scatter. Our inner halo population is chemically homogeneous, suggesting that a significant fraction of the Milky Way stellar halo originated from a well-mixed interstellar medium. In contrast, our outer halo population is chemically diverse, suggesting that another significant fraction of the Milky Way stellar halo formed in remote regions where chemical enrichment was dominated by local supernova events. We find no abundance trends with maximum radial distance from the Galactic center or maximum vertical distance from the Galactic disk. We also find no common kinematic signature for groups of metal-poor stars with peculiar abundance patters, such as the α-poor stars or stars showing unique neutron-capture enrichment patterns. Several stars and dwarf spheroidal systems with unique abundance patterns spend the majority of their time in the distant regions of the Milky Way stellar halo, suggesting that the true outer halo of the Galaxy may have little resemblance to the local stellar halo. DA - 2008/12/15/ PY - 2008/12/15/ DO - 10.1088/0004-6256/137/1/272 VL - 137 IS - 1 SP - 272-295 J2 - The Astronomical Journal OP - SN - 0004-6256 1538-3881 UR - http://dx.doi.org/10.1088/0004-6256/137/1/272 DB - Crossref ER - TY - CONF TI - RF MEMS behavior, surface roughness and asperity contact AU - Rezvanian, O. AU - Zikry, M.A. AU - Brown, C. AU - Krim, J. C2 - 2008/// C3 - Materials Research Society Symposium Proceedings DA - 2008/// VL - 1052 SP - 135-140 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-45849129829&partnerID=MN8TOARS ER - TY - SOUND TI - Improved Experimental Limits for Neutron-Antineutron Oscillations AU - Young, A.R. DA - 2008/2// PY - 2008/2// ER - TY - JOUR TI - A New Precision Measurement of the Lifetime of 19Ne AU - Broussard, L. AU - Pattie, R.W. AU - Back, H. AU - Young, A.R. AU - Dammalapati, U. AU - De, S. AU - Dendeooven, P. AU - Dermois, O. AU - Huisman, L. AU - Jungmann, K. AU - Mol, A. AU - Onderwater, C.G. AU - Rogachevskiy, A. AU - Sohani, M. AU - Traykov, E. AU - Willmann, L. AU - Wilschut, H. T2 - Bulletin of the American Physical Society DA - 2008/// PY - 2008/// VL - 53 IS - 5 SP - 61 ER - TY - SOUND TI - Personal and Biased Summary and Outlook AU - Young, A.R. DA - 2008/5// PY - 2008/5// ER - TY - SOUND TI - Development of an Ultracold Neutron Source at the PULSTAR Reactor AU - Young, A.R. DA - 2008/5// PY - 2008/5// ER - TY - SOUND TI - The UCNA Experiment: First Results for a Measurement of the Beta-Asymmetry with Ultracold Neutrons AU - Young, A.R. DA - 2008/4// PY - 2008/4// ER - TY - SOUND TI - Neutrinoless Double Beta-decay: the Majorana Project AU - Young, A.R. DA - 2008/4// PY - 2008/4// ER - TY - CONF TI - The UCNA Experiment: Progress Towards a Measurement of the Beta-Asymmetry with Ultracold Neutrons AU - Young, A.R. T2 - NP08 Symposium A2 - Young, A.R. C2 - 2008/3// C3 - NP08 Symposium CY - Mito, Japan DA - 2008/3// PY - 2008/3// ER - TY - JOUR TI - Erratum: Cold Neutron Energy Dependent Production of Ultracold Neutrons in Solid Deuterium [Phys. Rev. Lett.99, 262502 (2007)] AU - Atchison, F. AU - Blau, B. AU - Bodek, K. AU - van den Brandt, B. AU - Bryś, T. AU - Daum, M. AU - Fierlinger, P. AU - Frei, A. AU - Geltenbort, P. AU - Hautle, P. AU - Henneck, R. AU - Heule, S. AU - Holley, A. AU - Kasprzak, M. AU - Kirch, K. AU - Knecht, A. AU - Konter, J. A. AU - Kuźniak, M. AU - Liu, C.-Y. AU - Morris, C. L. AU - Pichlmaier, A. AU - Plonka, C. AU - Pokotilovski, Y. AU - Saunders, A. AU - Shin, Y. AU - Tortorella, D. AU - Wohlmuther, M. AU - Young, A. R. AU - Zejma, J. AU - Zsigmond, G. T2 - Physical Review Letters AB - Received 29 September 2008DOI:https://doi.org/10.1103/PhysRevLett.101.189902©2008 American Physical Society DA - 2008/10/27/ PY - 2008/10/27/ DO - 10.1103/PhysRevLett.101.189902 VL - 101 IS - 18 J2 - Phys. Rev. Lett. LA - en OP - SN - 0031-9007 1079-7114 UR - http://dx.doi.org/10.1103/PhysRevLett.101.189902 DB - Crossref ER - TY - JOUR TI - Efficient processing of TFO-directed psoralen DNA interstrand crosslinks by the UvrABC nuclease AU - Christensen, Laura A AU - Wang, Hong AU - Van Houten, Bennett AU - Vasquez, Karen M T2 - Nucleic acids research DA - 2008/// PY - 2008/// VL - 36 IS - 22 SP - 7136-7145 ER - TY - JOUR TI - Functional Characterization and Atomic Force Microscopy of a DNA Repair Protein Conjugated to a Quantum Dot AU - Wang, Hong AU - Tessmer, Ingrid AU - Croteau, Deborah L. AU - Erie, Dorothy A. AU - Van Houten, Bennett T2 - Nano Letters AB - Quantum dots (QDs) possess highly desirable optical properties that make them ideal fluorescent labels for studying the dynamic behavior of proteins. However, a lack of characterization methods for reliably determining protein−quantum dot conjugate stoichiometry and functionality has impeded their widespread use in single-molecule studies. We used atomic force microscopic (AFM) imaging to demonstrate the 1:1 formation of UvrB−QD conjugates based on an antibody-sandwich method. We show that an agarose gel-based electrophoresis mobility shift assay and AFM can be used to evaluate the DNA binding function of UvrB−QD conjugates. Importantly, we demonstrate that quantum dots can serve as a molecular marker to unambiguously identify the presence of a labeled protein in AFM images. DA - 2008/6// PY - 2008/6// DO - 10.1021/nl080316l VL - 8 IS - 6 SP - 1631-1637 J2 - Nano Lett. LA - en OP - SN - 1530-6984 1530-6992 UR - http://dx.doi.org/10.1021/nl080316l DB - Crossref ER - TY - JOUR TI - Is a Gas of Strongly Interacting Atomic Fermions a Nearly Perfect Fluid? AU - Turlapov, A. AU - Kinast, J. AU - Clancy, B. AU - Luo, Le AU - Joseph, J. AU - Thomas, J. E. T2 - Journal of Low Temperature Physics AB - We use all-optical methods to produce a highly-degenerate Fermi gas of spin-1/2 6Li atoms. A magnetic field tunes the gas near a collisional (Feshbach) resonance, producing strong interactions between spin-up and spin-down atoms. We have measured properties of a breathing mode over a wide range of temperatures. As the temperature is increased from below the superfluid transition to above, the frequency of the mode is always close to the hydrodynamic value, while the damping rate increases. A complete explanation of both the frequency and the damping rate in the normal collisional regime has not been achieved. Our measurements of the damping rate as a function of the energy of the gas are used to estimate an upper bound on the viscosity. Using our new measurements of the entropy of the gas, we estimate the ratio of the shear viscosity to the entropy density and compare the result with a recent string theory conjecture for the minimum viscosity of a perfect quantum fluid. DA - 2008/// PY - 2008/// DO - 10.1007/s10909-007-9589-1 VL - 150 IS - 3-4 SP - 567–576 SN - 0022-2291 1573-7357 UR - http://dx.doi.org/10.1007/s10909-007-9589-1 KW - Fermi gas KW - superfluidity KW - quantum viscosity KW - strong interactions ER - TY - JOUR TI - Primordial black holes in the Dark Ages: Observational prospects for future 21cm surveys DA - 2008/5/11/ PY - 2008/5/11/ ER - TY - JOUR TI - In the zone AU - Mack, K.J. T2 - American Scientist DA - 2008/// PY - 2008/// VL - 96 IS - 2 SP - 108-109 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-40749119768&partnerID=MN8TOARS ER - TY - JOUR TI - Effect of primordial black holes on the cosmic microwave background and coslogical parameter estimates AU - Ricotti, M. AU - Ostriker, J.P. AU - Mack, K.J. T2 - Astrophysical Journal AB - We investigate the effect of nonevaporating primordial black holes (PBHs) on the ionization and thermal history of the universe. X-rays emitted by gas accretion onto PBHs modify the cosmic recombination history, producing measurable effects on the spectrum and anisotropies of the cosmic microwave background (CMB). Using the third-year WMAP data and COBE FIRAS data we improve existing upper limits on the abundance of PBHs with masses >0.1 M☉ by several orders of magnitude. The new upper limits still allow PBHs to be important for the origin of supermassive black holes and ultraluminous X-ray sources. Fitting WMAP3 data with cosmological models that do not allow for nonstandard recombination histories, as produced by PBHs or other early energy sources, may lead to an underestimate of the best-fit values of the amplitude of linear density fluctuations (σ8) and the scalar spectral index (ns). Cosmological parameter estimates are affected because models with PBHs allow for larger values of the Thomson scattering optical depth, whose correlation with other parameters may not be correctly taken into account when PBHs are ignored. Values of τe ∼ 0.2, ns ∼ 1, and σ8 ∼ 0.9 are allowed at 95% CF. This result may relieve recent tension between WMAP3 data and clusters data on the value of σ8. PBHs may increase the primordial molecular hydrogen abundance by up to 2 orders of magnitude, this promoting cooling and star formation. The suppression of galaxy formation due to X-ray heating is negligible for models consistent with the CMB data. Thus, the formation rate of the first galaxies and stars would be enhanced by a population of PBHs. DA - 2008/// PY - 2008/// DO - 10.1086/587831 VL - 680 IS - 2 SP - 829-845 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-46249091829&partnerID=MN8TOARS KW - black hole physics KW - cosmic microwave background KW - cosmology : observations KW - cosmology : theory KW - cosmological parameters KW - early universe ER - TY - JOUR TI - X-ray Microscopy of Soft Matter AU - Ade, H T2 - Microscopy and Microanalysis AB - Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008 DA - 2008/8// PY - 2008/8// DO - 10.1017/S1431927608084092 VL - 14 IS - S2 SP - 58-59 J2 - Microsc Microanal LA - en OP - SN - 1431-9276 1435-8115 UR - http://dx.doi.org/10.1017/S1431927608084092 DB - Crossref ER - TY - CONF TI - Hydrodynamic view in the NICA energy range AU - Toneev, V. AU - Skokov, V. C2 - 2008/9// C3 - 13th International Conference on Selected Problems of Modern Theoretical Physics (SPMTP 08): Dedicated to the 100th Anniversary of the Birth of D.I. Blokhintsev (1908-1979) DA - 2008/9// UR - http://inspirehep.net/record/796594 ER - TY - JOUR TI - Molecular self-assembly guided by surface reconstruction: CH3SH monolayer on the Au(111) surface AU - Maksymovych, Peter AU - Dougherty, Daniel B. T2 - Surface Science AB - Self-assembly of methanethiol (CH3SH) on Au(1 1 1) was studied using scanning tunneling microscopy at T < 150 K when the S–H bond is intact. The CH3SH monolayer assumes a commensurate structure with a 6202 unit-cell. Only one of three possible azimuthal domains of the monolayer was observed with domain walls pinned at the rotational boundaries of the herringbone reconstruction. From a real-time observation of monolayer formation at T = 60 K we propose a phenomenological model for the growth of preferential domains, which is based on the interplay between molecular detachment from domain boundaries and anisotropic mass transport on the Au(1 1 1) surface due to its herringbone reconstruction. DA - 2008/6// PY - 2008/6// DO - 10.1016/j.susc.2008.03.047 VL - 602 IS - 12 SP - 2017-2024 J2 - Surface Science LA - en OP - SN - 0039-6028 UR - http://dx.doi.org/10.1016/j.susc.2008.03.047 DB - Crossref KW - self-assembly KW - methanethiol KW - CH(3)SH KW - gold KW - scanning tunneling microscopy KW - real-time KW - surface diffusion ER - TY - JOUR TI - Variable Temperature Scanning Tunneling Microscopy of Pentacene Monolayer and Bilayer Phases on Ag(111) AU - Dougherty, D. B. AU - Jin, W. AU - Cullen, W. G. AU - Reutt-Robey, J. E. AU - Robey, S. W. T2 - The Journal of Physical Chemistry C AB - Pentacene deposited onto a Ag(111) surface at 300 K is studied using scanning tunneling microscopy at temperatures of 300 and 50 K, providing structural insight into its unusual growth habit. At room temperature, an unexpectedly high pentacene coverage is needed to nucleate ordered pentacene islands, which appear surrounded by a disordered pentacene phase. These room temperature pentacene nuclei are revealed as bilayer structures from their coverage-dependent size evolution and molecularly resolved images of domain boundaries, recorded at 50 K. At this reduced temperature, two different monolayer phases with long-range order and commensurate with the Ag(111) surface lattice further emerge. These two monolayer phases exhibit comparable (0.7 vs 0.8 molecule/nm2) packing densities, but distinct intermolecular registration and alignment with respect to the silver sublattice. DA - 2008/11/24/ PY - 2008/11/24/ DO - 10.1021/jp804682v VL - 112 IS - 51 SP - 20334-20339 J2 - J. Phys. Chem. C LA - en OP - SN - 1932-7447 1932-7455 UR - http://dx.doi.org/10.1021/jp804682v DB - Crossref ER - TY - JOUR TI - The Relation Between Open-Circuit Voltage and the Onset of Photocurrent Generation by Charge-Transfer Absorption in Polymer : Fullerene Bulk Heterojunction Solar Cells AU - Vandewal, Koen AU - Gadisa, Abay AU - Oosterbaan, Wibren D. AU - Bertho, Sabine AU - Banishoeib, Fateme AU - Van Severen, Ineke AU - Lutsen, Laurence AU - Cleij, Thomas J. AU - Vanderzande, Dirk AU - Manca, Jean V. T2 - Advanced Functional Materials AB - Abstract Photocurrent generation by charge‐transfer (CT) absorption is detected in a range of conjugated polymer–[6,6]‐phenyl C 61 butyric acid methyl ester (PCBM) based solar cells. The low intensity CT absorption bands are observed using a highly sensitive measurement of the external quantum efficiency ( EQE ) spectrum by means of Fourier‐transform photocurrent spectroscopy (FTPS). The presence of these CT bands implies the formation of weak ground‐state charge‐transfer complexes in the studied polymer–fullerene blends. The effective band gap ( E g ) of the material blends used in these photovoltaic devices is determined from the energetic onset of the photocurrent generated by CT absorption. It is shown that for all devices, under various preparation conditions, the open‐circuit voltage ( V oc ) scales linearly with E g . The redshift of the CT band upon thermal annealing of regioregular poly(3‐hexylthiophene):PCBM and thermal aging of poly(phenylenevinylene)(PPV):PCBM photovoltaic devices correlates with the observed drop in open‐circuit voltage of high‐temperature treated versus untreated devices. Increasing the weight fraction of PCBM also results in a redshift of E g , proportional with the observed changes in V oc for different PPV:PCBM ratios. As E g corresponds with the effective bandgap of the material blends, a measurement of the EQE spectrum by FTPS allows us to measure this energy directly on photovoltaic devices, and makes it a valuable technique in the study of organic bulk heterojunction solar cells. DA - 2008/7/9/ PY - 2008/7/9/ DO - 10.1002/adfm.200800056 VL - 18 IS - 14 SP - 2064-2070 J2 - Adv. Funct. Mater. LA - en OP - SN - 1616-301X UR - http://dx.doi.org/10.1002/adfm.200800056 DB - Crossref ER - TY - JOUR TI - Ground-state charge-transfer complex formation in hybrid poly(3-hexyl thiophene):titanium dioxide solar cells AU - Haeldermans, I. AU - Vandewal, K. AU - Oosterbaan, W. D. AU - Gadisa, A. AU - D’Haen, J. AU - Van Bael, M. K. AU - Manca, J. V. AU - Mullens, J. T2 - Applied Physics Letters AB - The existence of a ground-state charge-transfer (CT) complex in a conjugated polymer:metal oxide nanoparticle bulk heterojunction photovoltaic cell is demonstrated by Fourier-transform photocurrent spectroscopy (FTPS). The CT complex between poly(3-hexylthiophene) (P3HT) and titanium dioxide (TiO2) is characterized by a weak additional photocurrent band (onset 1eV) in the FTPS spectra, situated below the conjugated polymer bandgap of 2eV. The presence of CT interaction between P3HT and TiO2 in relation to frontier orbital alignment is discussed, as well as the contribution of a sub-bandgap interfacial CT state to the electron transfer process in P3HT:TiO2 solar cells. DA - 2008/12// PY - 2008/12// DO - 10.1063/1.3041633 VL - 93 IS - 22 SP - 223302 J2 - Appl. Phys. Lett. LA - en OP - SN - 0003-6951 1077-3118 UR - http://dx.doi.org/10.1063/1.3041633 DB - Crossref KW - charge exchange KW - conducting polymers KW - Fourier transform spectra KW - organic-inorganic hybrid materials KW - photoconductivity KW - photovoltaic cells KW - solar cells KW - titanium compounds ER - TY - RPRT TI - The SCALE-UP Project: A Student-Centered, Active Learning Environment for Undergraduate Programs AU - Beichner, R. A3 - National Academy of Sciences DA - 2008/9// PY - 2008/9// M3 - white paper PB - National Academy of Sciences ER - TY - JOUR TI - Scaling up education reform AU - Gaffney, J. AU - Richards, E. AU - Kustusch, M.B. AU - Ding, L. AU - Beichner, R. T2 - Journal of College Science Teaching DA - 2008/5// PY - 2008/5// VL - 37 IS - 5 SP - 18-23 ER - TY - JOUR TI - Multidimensional, multiphysics simulations of core—collapse supernovae AU - Messer, O E B AU - Bruenn, S W AU - Blondin, J M AU - Hix, W R AU - Mezzacappa, A T2 - Journal of Physics: Conference Series AB - CHIMERA is a multi-dimensional radiation hydrodynamics code designed to study core-collapse supernovae. The code is made up of three essentially independent parts: a hydrodynamics module, a nuclear burning module, and a neutrino transport solver combined within an operator-split approach. We review the code's architecture and some recently improved implementations used in the code. We also briefly discuss preliminary results obtained with the code in three spatial dimensions. DA - 2008/8// PY - 2008/8// DO - 10.1088/1742-6596/125/1/012010 VL - 125 SP - 012010 ER - TY - JOUR TI - Structure and magnetic properties of the self-assembled Co52Pt48 nanowire arrays AU - Gao, Jian-Hua AU - Sun, Da-Li AU - Zhang, Xiang-Qun AU - Zhan, Qing-Feng AU - He, Wei AU - Sun, Young AU - Cheng, Zhao-Hua T2 - Applied Physics Letters AB - Co 52 Pt 48 nanowire arrays with diameter of about 10nm have been fabricated by electrodeposition into the anodic aluminum oxide templates. The as-deposited nanowire arrays exhibit fcc structure with [110]-preferred texture along the wire axes. The nanowire arrays present both large magnetocrystalline anisotropy along the [111] direction and strong shape anisotropy along the wire axis, resulting in high coercive fields parallel and perpendicular to the wire axes, respectively. From experimental results and micromagnetic simulation, the coercive field variation as a function of the angles evidenced that the [111] magnetocrystalline anisotropy plays important role besides shape magnetic anisotropy. DA - 2008/3/10/ PY - 2008/3/10/ DO - 10.1063/1.2894199 VL - 92 IS - 10 SP - 102501 J2 - Appl. Phys. Lett. LA - en OP - SN - 0003-6951 1077-3118 UR - http://dx.doi.org/10.1063/1.2894199 DB - Crossref ER - TY - JOUR TI - Investigation of heteroepitaxy on nanoscopically roughened (001)Si by real-time spectroscopic polarimetry AU - Liu, X. AU - Kim, I.-K. AU - Aspnes, D. E. T2 - physica status solidi (c) AB - We use a real-time spectroscopic polarimeter integrated with an organometallic chemical vapor deposition system to investigate growth of GaP on Si, and particularly nanoscopically roughened (nr-)Si. We find nanoroughening is necessary to increase the density of nucleation sites and decrease reactant mobility and thereby grow continuous films instead of widely spaced islands. The nrSi surfaces are more highly reactive to the trimethylgallium precursor than III-V growth surfaces, leading to the appearance of metallic Ga if standard growth conditions are used in the initial phase of heteroepitaxy. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) DA - 2008/5// PY - 2008/5// DO - 10.1002/pssc.200777896 VL - 5 IS - 5 SP - 1312-1315 J2 - phys. stat. sol. (c) LA - en OP - SN - 1610-1634 1610-1642 UR - http://dx.doi.org/10.1002/pssc.200777896 DB - Crossref ER - TY - JOUR TI - Systematic study of trace radioactive impurities in candidate construction materials for EXO-200 T2 - Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment AB - The Enriched Xenon Observatory (EXO) will search for double beta decays of 136Xe. We report the results of a systematic study of trace concentrations of radioactive impurities in a wide range of raw materials and finished parts considered for use in the construction of EXO-200, the first stage of the EXO experimental program. Analysis techniques employed, and described here, include direct gamma counting, alpha counting, neutron activation analysis, and high-sensitivity mass spectrometry. DA - 2008/// PY - 2008/// DO - 10.1016/j.nima.2008.03.001 VL - 591 IS - 3 SP - 490-509 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-45449103854&partnerID=MN8TOARS KW - radiopurity KW - trace analysis KW - neutron activation analysis KW - mass spectrometry KW - mass spectroscopy KW - germanium counting KW - alpha counting KW - low background KW - double beta decay KW - EXO KW - EXO-200 ER - TY - JOUR TI - A microfabricated sensor for thin dielectric layers AU - Fierlinger, P. AU - DeVoe, R. AU - Flatt, B. AU - Gratta, G. AU - Green, M. AU - Kolkowitz, S. AU - Leport, F. AU - Montero Diez, M. AU - Neilson, R. AU - O’Sullivan, K. AU - Pocar, A. AU - Wodin, J. T2 - Review of Scientific Instruments AB - We describe a sensor for the measurement of thin dielectric layers capable of operation in a variety of environments. The sensor is obtained by microfabricating a capacitor with interleaved aluminum fingers, exposed to the dielectric to be measured. In particular, the device can measure thin layers of solid frozen from a liquid or gaseous medium. Sensitivity to single atomic layers is achievable in many configurations and, by utilizing fast, high sensitivity capacitance readout in a feedback system onto environmental parameters; coatings of few layers can be dynamically maintained. We discuss the design, readout, and calibration of several versions of the device optimized in different ways. We specifically dwell on the case in which atomically thin solid xenon layers are grown and stabilized, in cryogenic conditions, from a liquid xenon bath. DA - 2008/// PY - 2008/// DO - 10.1063/1.2906402 VL - 79 IS - 4 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-42949108273&partnerID=MN8TOARS ER - TY - JOUR TI - Statistics of low-frequency fluctuations in stochastic processes with the 1/f α spectrum AU - Koverda, V.P. AU - Skokov, V.N. T2 - Doklady Physics DA - 2008/// PY - 2008/// DO - 10.1134/S1028335808060049 VL - 53 IS - 6 SP - 301-304 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-46649105474&partnerID=MN8TOARS ER - TY - JOUR TI - Effects of end group functionalization and level alignment on electron transport in molecular devices AU - Kim, Gunn AU - Wang, Shuchun AU - Lu, Wenchang AU - Buongiorno Nardelli, Marco AU - Bernholc, J. T2 - The Journal of Chemical Physics AB - The effect of metal-molecule coupling on electron transport is examined in the prototypical case of alkane chains sandwiched between gold contacts and bridged by either amine or thiol groups. The results show that end group functionalization plays a crucial role in controlling electron transport, and that the symmetries and spatial extent of orbitals near the Fermi level control the conductivity rather than the strength of the bonding. For amine/Au and thiol/Au junctions, a crossover in conductivity with increasing bias is predicted. DA - 2008/1/14/ PY - 2008/1/14/ DO - 10.1063/1.2822180 VL - 128 IS - 2 SP - 024708 J2 - The Journal of Chemical Physics LA - en OP - SN - 0021-9606 1089-7690 UR - http://dx.doi.org/10.1063/1.2822180 DB - Crossref ER - TY - CONF TI - Nucleosynthesis in Outflows from Kerr Black Hole Accretion Disks AU - Surman, R. AU - McLaughlin, G. C. AU - Sabbatino, N. AU - Hix, W. R. T2 - FIRST STARS III: First Stars II Conference AB - Observational evidence suggests long‐duration, collapsar‐type gamma‐ray bursts (GRBs) may have been more common in the early universe. These events are thought to be powered by accretion disks around black holes (AD‐BHs). While GRBs require AD‐BHs, not all AD‐BHs will power bursts and therefore their formation will be more common than GRBs themselves. Outflows from AD‐BHs may therefore be important contributors to the nuclear abundances in the oldest stars, particularly for rare species or those not uniformly observed. Here we consider the nucleosynthesis in this environment starting with relativistic disk models of Kerr black holes and following the element synthesis in a parameterized outflow. We present nucleosynthesis results from a range of AD‐BH models. C2 - 2008/// C3 - DA - 2008/// DO - 10.1063/1.2905566 PB - American Institute of Physics UR - http://dx.doi.org/10.1063/1.2905566 DB - Crossref ER - TY - JOUR TI - Temporal spike pattern learning AU - Talathi, S.S. AU - Abarbanel, H.D.I. AU - Ditto, W.L. T2 - Physical Review E - Statistical, Nonlinear, and Soft Matter Physics AB - Sensory systems pass information about an animal's environment to higher nervous system units through sequences of action potentials. When these action potentials have essentially equivalent wave forms, all information is contained in the interspike intervals (ISIs) of the spike sequence. How do neural circuits recognize and read these ISI sequences? We address this issue of temporal sequence learning by a neuronal system utilizing spike timing dependent plasticity (STDP). We present a general architecture of neural circuitry that can perform the task of ISI recognition. The essential ingredients of this neural circuit, which we refer to as "interspike interval recognition unit" (IRU) are (i) a spike selection unit, the function of which is to selectively distribute input spikes to downstream IRU circuitry; (ii) a time-delay unit that can be tuned by STDP; and (iii) a detection unit, which is the output of the IRU and a spike from which indicates successful ISI recognition by the IRU. We present two distinct configurations for the time-delay circuit within the IRU using excitatory and inhibitory synapses, respectively, to produce a delayed output spike at time t_{0}+tau(R) in response to the input spike received at time t_{0} . R is the tunable parameter of the time-delay circuit that controls the timing of the delayed output spike. We discuss the forms of STDP rules for excitatory and inhibitory synapses, respectively, that allow for modulation of R for the IRU to perform its task of ISI recognition. We then present two specific implementations for the IRU circuitry, derived from the general architecture that can both learn the ISIs of a training sequence and then recognize the same ISI sequence when it is presented on subsequent occasions. DA - 2008/// PY - 2008/// DO - 10.1103/PhysRevE.78.031918 VL - 78 IS - 3 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-53449087688&partnerID=MN8TOARS ER - TY - JOUR TI - Spike timing dependent plasticity promotes synchrony of inhibitory networks in the presence of heterogeneity AU - Talathi, S.S. AU - Hwang, D.-U. AU - Ditto, W.L. T2 - Journal of Computational Neuroscience AB - Recently spike timing dependent plasticity was observed in inhibitory synapse in the layer II of entorhinal cortex. The rule provides an interesting zero in the region of $\Delta t=t_{post}-t_{pre}=0$ and in addition the dynamic range of the rule lie in gamma frequency band. We propose a robust mechanism based on this observed synaptic plasticity rule for inhibitory synapses for two mutually coupled interneurons to phase lock in synchrony in the presence of intrisic heterogeneity in firing. We study the stability of the phase locked solution by defining a map for spike times dependent on the phase response curve for the coupled neurons. Finally we present results on robustness of synchronization in the presence of noise. DA - 2008/// PY - 2008/// DO - 10.1007/s10827-008-0077-7 VL - 25 IS - 2 SP - 262-281 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-51349162681&partnerID=MN8TOARS KW - inhibitory synapses KW - spike timing dependent plasticity KW - synchronization KW - networks KW - heterogeneity ER - TY - JOUR TI - Non-parametric early seizure detection in an animal model of temporal lobe epilepsy AU - Talathi, S.S. AU - Hwang, D.-U. AU - Spano, M.L. AU - Simonotto, J. AU - Furman, M.D. AU - Myers, S.M. AU - Winters, J.T. AU - Ditto, W.L. AU - Carney, P.R. T2 - Journal of Neural Engineering AB - The performance of five non-parametric, univariate seizure detection schemes (embedding delay, Hurst scale, wavelet scale, nonlinear autocorrelation and variance energy) were evaluated as a function of the sampling rate of EEG recordings, the electrode types used for EEG acquisition, and the spatial location of the EEG electrodes in order to determine the applicability of the measures in real-time closed-loop seizure intervention. The criteria chosen for evaluating the performance were high statistical robustness (as determined through the sensitivity and the specificity of a given measure in detecting a seizure) and the lag in seizure detection with respect to the seizure onset time (as determined by visual inspection of the EEG signal by a trained epileptologist). An optimality index was designed to evaluate the overall performance of each measure. For the EEG data recorded with microwire electrode array at a sampling rate of 12 kHz, the wavelet scale measure exhibited better overall performance in terms of its ability to detect a seizure with high optimality index value and high statistics in terms of sensitivity and specificity. DA - 2008/// PY - 2008/// DO - 10.1088/1741-2560/5/1/009 VL - 5 IS - 1 SP - 85-98 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-40549088889&partnerID=MN8TOARS KW - 1 ER - TY - JOUR TI - Exploiting nonlinear dynamics to store and process information AU - Miliotis, A. AU - Sinha, S. AU - Ditto, W.L. T2 - International Journal of Bifurcation and Chaos AB - By applying nonlinear dynamics to the dense storage of information, we demonstrate how a single nonlinear dynamical element can store M items, where M is variable and can be large. This provides the capability for naturally storing data in different bases or in different alphabets and can be used to implement multilevel logic. Further we show how this method of storing information can serve as a preprocessing tool for (exact or inexact) pattern matching searches. Since our scheme involves just a single procedural step, it is naturally set up for parallel implementation and can be realized with hardware currently employed for chaos-based computing architectures. DA - 2008/// PY - 2008/// DO - 10.1142/S0218127408021166 VL - 18 IS - 5 SP - 1551-1559 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-47749092109&partnerID=MN8TOARS KW - chaos computing KW - data storage KW - information processing KW - encoding KW - search KW - threshold control ER - TY - BOOK TI - Effective and Anatomical Connectivity in a Rat Model of Spontaneous Limbic Seizure AU - Carney, P.R. AU - Cadotte, A. AU - Demarse, T.B. AU - Vemuri, B. AU - Mareci, T.H. AU - Ditto, W. AB - Chapter 4 Effective and Anatomical Connectivity in a Rat Model of Spontaneous Limbic Seizure Paul R. Carney, Paul R. Carney University of Florida, McKnight Brain Institute, Departments of Pediatrics, Neurology, Neuroscience and Biomedical Engineering, P.O. Box 100296, Gainesville, FL 32610-0296, USASearch for more papers by this authorAlex Cadotte, Alex Cadotte University of Florida, McKnight Brain Institute, Department of Pediatrics and Biomedical Engineering, P.O. Box 100296, Gainesville, FL 32610-0296, USASearch for more papers by this authorThomas B. Demarse, Thomas B. Demarse University of Florida, Department of Biomedical Engineering, 147 Biomedical Engineering Bldg, Gainesville, FL 32611-6131, USASearch for more papers by this authorBaba Vemuri, Baba Vemuri University of Florida, Department of Computer and Information Science and Engineering, P.O. Box 116120, Gainesville, FL 32611-6131, USASearch for more papers by this authorThomas H. Mareci, Thomas H. Mareci University of Florida, McKnight Brain Institute, Department of Biochemistry and Molecular Biology, P.O.Box 100245, Gainesville, FL 32610-0245, USASearch for more papers by this authorWilliam Ditto, William Ditto University of Florida, Department of Biomedical Engineering, 147 Biomedical Engineering Bldg, Gainesville, FL 32611-6131, USASearch for more papers by this author Paul R. Carney, Paul R. Carney University of Florida, McKnight Brain Institute, Departments of Pediatrics, Neurology, Neuroscience and Biomedical Engineering, P.O. Box 100296, Gainesville, FL 32610-0296, USASearch for more papers by this authorAlex Cadotte, Alex Cadotte University of Florida, McKnight Brain Institute, Department of Pediatrics and Biomedical Engineering, P.O. Box 100296, Gainesville, FL 32610-0296, USASearch for more papers by this authorThomas B. Demarse, Thomas B. Demarse University of Florida, Department of Biomedical Engineering, 147 Biomedical Engineering Bldg, Gainesville, FL 32611-6131, USASearch for more papers by this authorBaba Vemuri, Baba Vemuri University of Florida, Department of Computer and Information Science and Engineering, P.O. Box 116120, Gainesville, FL 32611-6131, USASearch for more papers by this authorThomas H. Mareci, Thomas H. Mareci University of Florida, McKnight Brain Institute, Department of Biochemistry and Molecular Biology, P.O.Box 100245, Gainesville, FL 32610-0245, USASearch for more papers by this authorWilliam Ditto, William Ditto University of Florida, Department of Biomedical Engineering, 147 Biomedical Engineering Bldg, Gainesville, FL 32611-6131, USASearch for more papers by this author Book Editor(s):Dr. Björn Schelter, Dr. Björn Schelter University of Freiburg, Bernstein Center for Computational Neuroscience, Hansastr. 9a, 79104 Freiburg, Germany Freiburg Center for Data Analysis and Modeling, Eckerstr. 1, 79104 Freiburg, GermanySearch for more papers by this authorDr. Jens Timmer, Dr. Jens Timmer University of Freiburg, Bernstein Center for Computational Neuroscience, Hansastr. 9a, 79104 Freiburg, Germany Freiburg Center for Data Analysis and Modeling, Eckerstr. 1, 79104 Freiburg, GermanySearch for more papers by this authorDr. Andreas Schulze-Bonhage, Dr. Andreas Schulze-Bonhage University of Freiburg, Bernstein Center for Computational Neuroscience, Hansastr. 9a, 79104 Freiburg, Germany University Hospital of Freiburg, Epilepsy Center, Breisacher Str. 64, 79106 Freiburg, GermanySearch for more papers by this author First published: 20 August 2008 https://doi.org/10.1002/9783527625192.ch4 AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Summary This chapter contains sections titled: Introduction Granger Causality Structural Visualization with Magnetic Resonance Acknowledgments References Seizure Prediction in Epilepsy: From Basic Mechanisms to Clinical Applications RelatedInformation DA - 2008/// PY - 2008/// DO - 10.1002/9783527625192.ch4 SE - 45-59 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84889476603&partnerID=MN8TOARS ER - TY - JOUR TI - Chaos computing: Ideas and implementations AU - Ditto, W.L. AU - Murali, K. AU - Sinha, S. T2 - Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences AB - We review the concept of the 'chaos computing' paradigm, which exploits the controlled richness of nonlinear dynamics to obtain flexible reconfigurable hardware. We demonstrate the idea with specific schemes and verify the schemes through proof-of-principle experiments. DA - 2008/// PY - 2008/// DO - 10.1098/rsta.2007.2116 VL - 366 IS - 1865 SP - 653-664 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-38149114147&partnerID=MN8TOARS KW - chaos KW - computation KW - logic gates ER - TY - CHAP TI - Theoretical Approach to Polarization Effects in Semiconductors AU - Boguslawski, Piotr AU - Bernholc, J. T2 - Polarization Effects in Semiconductors PY - 2008/// DO - 10.1007/978-0-387-68319-5_1 SP - 2-25 OP - PB - Springer US SN - 9780387368313 9780387683195 UR - http://dx.doi.org/10.1007/978-0-387-68319-5_1 DB - Crossref ER - TY - CONF TI - Multiscale Simulations of High Performance Capacitors and Nanoelectronic Devices AU - Bernholc, J. AU - Jiang, J. AU - Ranjan, V. AU - Yu, L. AU - Nardelli, M. Buongiorno AU - Lu, W. T2 - 2008 DoD HPCMP Users Group Conference AB - Recent advances in theoretical methods combined with the advent of massively-parallel supercomputers allow one to reliably simulate the properties of complex materials and device structures from .first principles. We describe applications in two general areas: (i) novel polymer composites for ultrahigh density capacitors, necessary for pulsed power applications, such as electric discharges, power conditioning, and dense electronic circuitry, and (ii) electronic properties of graphene nanoribbons, which are candidate materials for ultraspeed electronics and spintronics. Polypropylene is an excellent capacitor dielectric that, however, has already reached its energy density limit. We investigate polypropylene-alumina nanocomposites and show that the dielectric permittivity of the composite can be significantly enhanced. For sufficiently dispersed alumina, the composite should still exhibit the excellent stability and high breakdown .field of pure polypropylene. We have also investigated Poly-Vinylidene Fluoride (PVDF)-based copolymers and show that in addition to co-polymer of VDF-chlorotrifluoroethylene [P(VDFCTFE)], P(VDF-TeFE) can also be a high energy density material, provided an appropriate TeFE concentration and dispersion is achieved. We present a composition range where its energy density would be similar to that of P(VDF-CTFE). For graphene nanoribbons, we report the results of extensive ab initio investigations of the properties of edge states, .nding that the edge-related peaks in the local density of states depend on spin polarization, and that defects at zigzag edges and/or higher-index edges can switch o. The polarization, leading to a non-magnetic ribbon. Our results explain differences between disparate scanning tunneling spectroscopy experiments as due to spin-polarized and unpolarized edges, respectively. C2 - 2008/// C3 - 2008 DoD HPCMP Users Group Conference DA - 2008/// DO - 10.1109/dod.hpcmp.ugc.2008.78 PB - IEEE SN - 9780769535159 9781424433230 UR - http://dx.doi.org/10.1109/dod.hpcmp.ugc.2008.78 DB - Crossref ER - TY - CONF TI - Supernovae in Galactic evolution: direct and indirect metallicity effects AU - Fröhlich, C. AU - Hirschi, R. AU - Liebendörfer, M. AU - Thielemann, F. -K. AU - Martínez Pinedo, G. AU - Bravo, E. C2 - 2008/// C3 - The Metal-Rich Universe DA - 2008/// ER - TY - CONF TI - Iron-60 Injection in the Protosolar Nebula: How Early and How Well Mixed? AU - Dauphas, N. AU - Cook, D. L. AU - Sacarabany, A. AU - Frohlich, C. AU - Davis, A. M. AU - Wadhwa, M. AU - Pourmand, A. AU - Rauscher, T. AU - Gallino, R. C2 - 2008/3// C3 - Lunar and Planetary Science Conference DA - 2008/3// ER - TY - CONF TI - Nucleosynthesis Yields from the Explosion of Massive Stars AU - Frohlich, Carla AU - Fischer, T. AU - Liebendoerfer, M. AU - Thielemann, F. -K. AU - Truran, J. W. C2 - 2008/4// C3 - APS April Meeting Abstracts DA - 2008/4// ER - TY - CONF TI - Detailed Nucleosynthesis Yields from the Explosion of Massive Stars AU - Fröhlich, Carla AU - Fischer, T. AU - Liebendörfer, M. AU - Thielemann, F. -K. AU - Truran, J. W. AB - Abstract Despite the complexity and uncertainties of core collapse supernova simulations there is a need to provide correct nucleosynthesis abundances for the progressing field of galactic evolution and observations of low metallicity stars. Especially the innermost ejecta are directly affected by the explosion mechanism, i.e. most strongly the yields of Fe-group nuclei for which an induced piston or thermal bomb treatment will not provide the correct yields because the effect of neutrino interactions is not included. Recent observations of metal-poor halo stars support the suggested existence of a lighter element primary process (LEPP) which operates very early in the galaxy and is independent of the r-process. We present a candidate for the LEPP, the so-called ν p -process. C2 - 2008/6// C3 - Massive Stars as Cosmic Engines DA - 2008/6// DO - 10.1017/S1743921308020759 ER - TY - JOUR TI - 60Fe in the cosmic blender AU - Dauphas, N. AU - Cook, D. L. AU - Sacarabany, A. AU - Fröhlich, C. AU - Davis, A. M. AU - Wadhwa, M. AU - Pourmand, A. AU - Rauscher, T. AU - Gallino, R. T2 - Geochimica et Cosmochimica Acta Supplement DA - 2008/7// PY - 2008/7// ER - TY - JOUR TI - Nuclear physics with spherically symmetric supernova models AB - In recent years, Boltzmann neutrino transport led to a new and reliable generation of spherically symmetric models of stellar core-collapse and postbounce evolution. After the failure to prove the principles of the supernova explosion mechanism, these sophisticated models continue to illuminate the close interaction between high-density matter under extreme conditions and the transport of leptons and energy, in general, relativistically curved spacetime. We emphasize that very different input physics is likely to be relevant for the different evolutionary phases, e.g. nuclear structure for weak rates in collapse, the equation of state of bulk nuclear matter during bounce, multidimensional plasma dynamics in the postbounce evolution and neutrino cross sections in the explosive nucleosynthesis. We illustrate the complexity of the dynamics using preliminary 3D MHD high-resolution simulations based on parametrized deleptonization. With established spherically symmetric models we show that typical features of the different phases are reflected in the predicted neutrino signal and that a consistent neutrino flux leads to electron fractions larger than 0.5 in neutrino-driven supernova ejecta. DA - 2008/1/1/ PY - 2008/1/1/ DO - 10.1088/0954-3899/35/1/014056 UR - http://dx.doi.org/10.1088/0954-3899/35/1/014056 ER - TY - JOUR TI - Nuclear physics in core-collapse supernovae AB - Core-collapse and the launch of a supernova explosion form a very short episode of few seconds in the evolution of a massive star, during which an enormous gravitational energy of several times 1053 erg is transformed into observable neutrino-, kinetic-, and electromagnetic radiation energy. We emphasize the wide range of matter conditions that prevail in a supernova event and sort the conditions into distinct regimes in the density and entropy phase diagram to briefly discuss their different impact on the neutrino signal, gravitational wave emission, and ejecta. DA - 2008/10// PY - 2008/10// DO - 10.1016/j.newar.2008.05.006 UR - http://dx.doi.org/10.1016/j.newar.2008.05.006 KW - Supernova KW - Neutron star KW - Neutrino transport KW - Gravitational wave ER - TY - JOUR TI - Mass measurements in the vicinity of ther p-process and theν p-process paths with the Penning trap facilities JYFLTRAP and SHIPTRAP AB - The masses of very neutron-deficient nuclides close to the astrophysical $\mathit{r} \mathit{p}$- and $\ensuremath{\nu} p$-process paths have been determined with the Penning trap facilities JYFLTRAP at JYFL/Jyv\"askyl\"a and SHIPTRAP at GSI/Darmstadt. Isotopes from yttrium ($Z=39$) to palladium ($Z=46$) have been produced in heavy-ion fusion-evaporation reactions. In total, 21 nuclides were studied, and almost half of the mass values were experimentally determined for the first time: $^{88}\mathrm{Tc}$, $^{90\ensuremath{-}92}\mathrm{Ru}$, $^{92\ensuremath{-}94}\mathrm{Rh}$, and $^{94,95}\mathrm{Pd}$. For the $^{95}\mathrm{Pd}$${}^{m}$, ($21/{2}^{+}$) high-spin state, a first direct mass determination was performed. Relative mass uncertainties of typically $\ensuremath{\delta}m/m=5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$ were obtained. The impact of the new mass values has been studied in $\ensuremath{\nu} p$-process nucleosynthesis calculations. The resulting reaction flow and the final abundances are compared with those obtained with the data of the Atomic Mass Evaluation 2003. DA - 2008/11/12/ PY - 2008/11/12/ DO - 10.1103/physrevc.78.054310 UR - http://dx.doi.org/10.1103/physrevc.78.054310 ER - TY - JOUR TI - Iron 60 Evidence for Early Injection and Efficient Mixing of Stellar Debris in the Protosolar Nebula AB - Among extinct radioactivities present in meteorites,60Fe (t1/2 = 1.49 Myr) plays a key role as a high-resolution chronometer, a heat source in planetesimals, and a fingerprint of the astrophysical setting of solar system formation. A critical issue with 60Fe is that it could have been heterogeneously distributed in the protoplanetary disk, calling into question the efficiency of mixing in the solar nebula or the timing of 60Fe injection relative to planetesimal formation. If this were the case, one would expect meteorites that did not incorporate 60Fe (either because of late injection or incomplete mixing) to show 60Ni deficits (from lack of 60Fe decay) and collateral effects on other neutron-rich isotopes of Fe and Ni (coproduced with 60Fe in core-collapse supernovae and AGB stars). Here, we show that measured iron meteorites and chondrites have Fe and Ni isotopic compositions identical to Earth. This demonstrates that 60Fe must have been injected into the protosolar nebula and mixed to less than 10% heterogeneity before formation of planetary bodies. DA - 2008/10/10/ PY - 2008/10/10/ DO - 10.1086/589959 UR - http://dx.doi.org/10.1086/589959 KW - methods : analytical KW - nuclear reactions, nucleosynthesis, abundances KW - solar system : formation KW - supernovae : general ER - TY - JOUR TI - Effective Field Theory and Finite Density Systems AU - Furnstahl, Richard J. AU - Rupak, Gautam AU - Schäfer, Thomas T2 - Ann.Rev.Nucl.Part.Sci. AB - This review gives an overview of effective field theory (EFT) as applied at finite density, with a focus on nuclear many-body systems. Uniform systems with short-range interactions illustrate the ingredients and virtues of many-body EFT; we also survey the varied frontiers of EFT for finite nuclei and nuclear matter. DA - 2008/1// PY - 2008/1// DO - 10.1146/annurev.nucl.58.110707.171142 VL - 58 SP - 1-25 UR - http://inspirehep.net/record/776820 KW - nuclear matter KW - many-body physics KW - chiral symmetry ER - TY - CONF TI - Performance of adaptive coded modulation enabled by long-range fading prediction with data-aided noise reduction AU - Jia, Tao AU - Duel-Hallen, A. AU - Hallen, H. AB - Performance of uncoded adaptive modulation (UAM) and adaptive coded modulation (ACM) enabled by the long-range prediction (LRP) that utilizes data-aided noise reduction (DANR) is investigated for rapidly varying mobile radio channels. Due to improved prediction accuracy and low pilot rate, the DANR-aided LRP outperforms previously proposed prediction methods that rely on oversampled pilots to achieve noise reduction (NR). While ACM is more sensitive to prediction errors than UAM, utilization of DANR substantially increases its spectral efficiency (SE) relative to previously proposed methods. The set of SNR values and prediction ranges where positive coding gain is achieved by ACM enabled by DANR-aided LRP is determined. It is also demonstrated that adaptive modulation (AM) aided by LRP has better performance for the realistic physical model than for the Jakes model in the practical SNR range. C2 - 2008/// C3 - MILCOM 2008 - 2008 IEEE Military Communications Conference CY - Piscataway, NJ, USA DA - 2008/// DO - 10.1109/MILCOM.2008.4753263 SP - 7 pp. - UR - http://dx.doi.org/10.1109/MILCOM.2008.4753263 ER - TY - CONF TI - Improved long-range prediction with data-aided noise reduction for adaptive modulation systems AU - Jia, Tao AU - Duel-Hallen, Alexandra AU - Hallen, Hans AB - A novel data-aided noise reduction (DANR) method is proposed to enhance the accuracy of long-range prediction (LRP) for wireless fading channels, thereby improving the spectral efficiency (SE) of adaptive modulation (AM) system enabled by the LRP. This method includes an adaptive pilot transmission mechanism, robust noise reduction and decision-directed channel estimation. An improved practical AM scheme is used to test the proposed DANR method. Since this method maintains low pilot rates, it results in higher SE than previously proposed noise reduction (NR) techniques, which rely on oversampled pilots. These conclusions are confirmed for practical prediction ranges using the standard Jakes model and our realistic physical model. C2 - 2008/// C3 - CISS 2008, The 42nd Annual Conference on Information Sciences and Systems CY - Princeton, NJ, United states DA - 2008/// DO - 10.1109/CISS.2008.4558694 SP - 1161 - 1166 UR - http://dx.doi.org/10.1109/CISS.2008.4558694 ER - TY - CONF TI - Resonance Raman measurements utilizing a deep UV source AU - Willitsford, A. AU - Chadwick, C.T. AU - Hallen, H. AU - Philbrick, C.R. AB - Raman scattering techniques have long been used as unique identifiers for spectral fingerprints of chemical and biological species. Raman lidar has been utilized on a routine basis to remotely measure several constituents in the atmosphere. While Raman scattering is very reliable in uniquely identifying molecules, it suffers from very small scattering cross sections that diminish its usefulness at increased ranges and decreased concentrations of the species of interest. By utilizing a resonance Raman technique, where the laser excitation is tuned near an electronic absorption band, it is possible to increase the Raman scattering cross section. An optical parametric oscillator (OPO) with a UV tuning range of ~220 nm - 355 nm has been utilized to explore the wavelength dependence of Raman scattering for diamond, water, benzene, and toluene. Resonance enhancements of the Raman spectra have been studied. C2 - 2008/4// C3 - Proc. SPIE - Int. Soc. Opt. Eng. DA - 2008/4// DO - 10.1117/12.778253 VL - 6950 SP - 69500 - 1 UR - http://dx.doi.org/10.1117/12.778253 KW - resonance Raman KW - tunable ultraviolet laser KW - benzene KW - toluene KW - diamond KW - resonance scatter ER - TY - BOOK TI - The relation between open-circuit voltage and the onset of photocurrent generation by charge-transfer absorption in polymer: Fullerene bulk heterojunction solar cells AU - VANDEWAL, Koen AU - GADISA DINKU, Abay AU - OOSTERBAAN, Wibren AU - BERTHO, Sabine AU - BANISHOEIB, Fateme AU - VAN SEVEREN, Ineke AU - LUTSEN, Laurence AU - CLEIJ, Thomas AU - VANDERZANDE, Dirk AU - MANCA, Jean DA - 2008/// PY - 2008/// UR - http://hdl.handle.net/1942/8450 ER - TY - BOOK TI - Ground-state charge-transfer complex formation in hybrid poly(3-hexyl thiophene):titanium dioxide solar cells AU - HAELDERMANS, Ilse AU - VANDEWAL, Koen AU - OOSTERBAAN, Wibren AU - GADISA DINKU, Abay AU - Jan D'HAEN, AU - VAN BAEL, Marlies AU - MANCA, Jean AU - MULLENS, Jules DA - 2008/// PY - 2008/// UR - http://hdl.handle.net/1942/9087 ER - TY - BOOK TI - Effect of temperature on the morphological and photovoltaic stability of bulk heterojunction polymer: fullerene solar cells AU - BERTHO, Sabine AU - Janssen, Griet AU - CLEIJ, Thomas AU - CONINGS, Bert AU - MOONS, Wouter AU - GADISA DINKU, Abay AU - Jan D'HAEN, AU - Goovaerts, E. AU - LUTSEN, Laurence AU - MANCA, Jean AU - VANDERZANDE, Dirk DA - 2008/// PY - 2008/// UR - http://hdl.handle.net/1942/8330 ER - TY - JOUR TI - Strain and composition mapping of epitaxial nanostructures AU - Cionca, CN AU - Riposan, A AU - Kumah, DP AU - Husseini, NS AU - Walko, DA AU - Yacoby, Y AU - Millunchick, JM AU - Clarke, R T2 - Applied Physics Letters AB - We have used surface x-ray diffraction and a direct method of phase reconstruction to obtain subangström resolution maps of an ion-beam milled In0.27Ga0.73As∕GaAs(001) thin film exhibiting three-dimensional (3D) epitaxial nanostructures. The 3D electron density was calculated based on the diffraction pattern along the Bragg rods measured with synchrotron radiation, from which the chemical composition, strain profile, and average nanostructure shape were extracted. The film maintained a wetting layer exhibiting a sharp strain gradient, which extended into the substrate. Atop the wetting layer, the ion-beam milled islands possessed an apical shape and were depleted in indium. DA - 2008/// PY - 2008/// DO - 10.1063/1.2908214 VL - 92 IS - 15 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-42349115693&partnerID=MN8TOARS ER - TY - JOUR TI - Structure determination of monolayer-by-monolayer grown La1-xSrxMnO3 thin films and the onset of magnetoresistance T2 - Physical Review B AB - Surface x-ray diffraction was used to determine the atomic structures of ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{MnO}}_{3}$ thin films, grown monolayer by monolayer on ${\mathrm{SrTiO}}_{3}$ by pulsed laser deposition. Structures for one-, two-, three-, four-, six-, and nine-monolayer-thick films were solved using the Coherent Bragg rod analysis phase-retrieval method and subsequent structural refinement. Four important results were found. First, the out-of-plane lattice constant is elongated across the substrate-film interface. Second, the transition from substrate to film is not abrupt, but proceeds gradually over approximately three unit cells. Third, Sr segregates towards the topmost monolayer of the film: we determined a Sr-segregation enthalpy of $\ensuremath{-}15\phantom{\rule{0.3em}{0ex}}\mathrm{kJ}∕\mathrm{mol}$ from the occupation parameters. Finally, the electronic bandwidth $W$ was used to explain the onset of magnetoresistance for films of nine or more monolayers thickness. Resistivity measurements of the nine monolayer-thick film confirm magnetoresistance and the presence of a dead layer with mostly insulating properties. DA - 2008/// PY - 2008/// DO - 10.1103/PhysRevB.77.085401 VL - 77 IS - 8 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-38849209039&partnerID=MN8TOARS ER - TY - JOUR TI - Resonant coherent Bragg rod analysis of strained epitaxial heterostructures T2 - Applied Physics Letters AB - The resonant response of the complex x-ray scattering factor has been used in conjunction with the coherent Bragg rod analysis phase-retrieval algorithm to determine the composition and strain profiles of ultrathin layers of GaAs grown on InGaAs buffers. The buffer layers are nominally latticed matched with the InP substrate and the subsequent GaAs growth is compared at two different temperatures: 480 and 520°C. We show that electron density maps extracted from Bragg rod scans measured close to the Ga and As K-edges can be used to deconvolute roughness and intermixing. It is found that indium incorporation and roughening lead to a significant reduction of the strain in this system. DA - 2008/// PY - 2008/// DO - 10.1063/1.2975835 VL - 93 IS - 8 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-51349103419&partnerID=MN8TOARS ER - TY - JOUR TI - Mapping single-crystal dendritic microstructure and defects in nickel-base superalloys with synchrotron radiation AU - Husseini, NS AU - Kumah, DP AU - Yi, JZ AU - Torbet, CJ AU - Arms, DA AU - Dufresne, EM AU - Pollock, TM AU - Jones, JW AU - Clarke, R T2 - Acta Materialia AB - Solidification of single-crystal nickel-base superalloys introduces large-scale segregation of constituent elements and defects such as dislocations and mosaicity. By exploiting the energy tunability and interference capabilities of high-brilliance X-ray radiation, key structural features of the dendritic single crystals were mapped over large areas. Interference and diffraction of synchrotron X-rays revealed significant misorientations between individual dendrites in the as-solidified state. For the first time this mosaic structure was quantified for an array of dendrites and correlated with the density of “grown-in” dislocations whose density ranged from 107 to 108 cm−2. Absorption contrast permitted simultaneous mapping of the distribution of refractory metal additives (e.g. rhenium and tungsten), which segregated preferentially to the dendrite cores with a linear composition gradient toward the interdendritic regions. The results demonstrate that synchrotron X-ray imaging is promising for in situ studies of single-crystal structure and defects in nickel-base superalloys. DA - 2008/// PY - 2008/// DO - 10.1016/j.actamat.2008.05.041 VL - 56 IS - 17 SP - 4715-4723 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-51449107913&partnerID=MN8TOARS KW - Superalloy KW - X-ray radiography KW - Microstructure KW - Dislocations KW - Lattice defects ER - TY - JOUR TI - In situ imaging of high cycle fatigue crack growth in single crystal nickel-base superalloys by synchrotron X-radiation AU - Liu, L AU - Husseini, NS AU - Torbet, CJ AU - Kumah, DP AU - Clarke, R AU - Pollock, TM AU - Jones, JW T2 - Journal of Engineering Materials and Technology-Transactions of the Asme AB - A novel X-ray synchrotron radiation approach is described for real-time imaging of the initiation and growth of fatigue cracks during ultrasonic fatigue (f=20kHz). We report here on new insights on single crystal nickel-base superalloys gained with this approach. A portable ultrasonic fatigue instrument has been designed that can be installed at a high-brilliance X-ray beamline. With a load line and fatigue specimen configuration, this instrument produces stable fatigue crack propagation for specimens as thin as 150μm. The in situ cyclic loading/imaging system has been used initially to image real-time crystallographic fatigue and crack growth under positive mean axial stress in the turbine blade alloy CMSX-4. DA - 2008/// PY - 2008/// DO - 10.1115/1.2840966 VL - 130 IS - 2 SP - 0210081-0210086 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-47149111212&partnerID=MN8TOARS ER - TY - JOUR TI - Matching of experimental and statistical-model thermonuclear reaction rates at high temperatures AU - Newton, J. R. AU - Longland, R. AU - Iliadis, C. T2 - Physical Review C AB - We address the problem of extrapolating experimental thermonuclear reaction rates toward high stellar temperatures ($T>1$ GK) by using statistical model (Hauser-Feshbach) results. Reliable reaction rates at such temperatures are required for studies of advanced stellar burning stages, supernovae, and x-ray bursts. Generally accepted methods are based on the concept of a Gamow peak. We follow recent ideas that emphasized the fundamental shortcomings of the Gamow peak concept for narrow resonances at high stellar temperatures. Our new method defines the effective thermonuclear energy range (ETER) by using the 8th, 50th, and 92nd percentiles of the cumulative distribution of fractional resonant reaction rate contributions. This definition is unambiguous and has a straightforward probability interpretation. The ETER is used to define a temperature at which Hauser-Feshbach rates can be matched to experimental rates. This matching temperature is usually much higher compared to previous estimates that employed the Gamow peak concept. We suggest that an increased matching temperature provides more reliable extrapolated reaction rates since Hauser-Feshbach results are more trustwhorthy the higher the temperature. Our ideas are applied to 21 ($p,\ensuremath{\gamma}$), ($p,\ensuremath{\alpha}$), and ($\ensuremath{\alpha},\ensuremath{\gamma}$) reactions on $A=20\ensuremath{-}40$ target nuclei. For many of the cases studied here, our extrapolated reaction rates at high temperatures differ significantly from those obtained using the Gamow peak concept. DA - 2008/8// PY - 2008/8// DO - 10.1103/physrevc.78.025805 VL - 78 IS - 2 ER - TY - JOUR TI - Single molecule correlation spectroscopy in continuous flow mixers with zero-mode waveguides AU - Liao, D. AU - Galajda, P. AU - Riehn, R. AU - Ilic, R. AU - Puchalla, J.L. AU - Yu, H.G. AU - Craighead, H.G. AU - Austin, R.H. T2 - Optics Express AB - Zero-Mode Waveguides were first introduced for Fluorescence Correlation Spectroscopy at micromolar dye concentrations. We show that combining zero-mode waveguides with fluorescence correlation spectroscopy in a continuous flow mixer avoids the compression of the FCS signal due to fluid transport at channel velocities up to approximately 17 mm/s. We derive an analytic scaling relationship [equation: see text] converting this flow velocity insensitivity to improved kinetic rate certainty in time-resolved mixing experiments. Thus zero-mode waveguides make FCS suitable for direct kinetics measurements in rapid continuous flow. DA - 2008/// PY - 2008/// DO - 10.1364/OE.16.010077 VL - 16 IS - 14 SP - 10077-10090 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-47249143308&partnerID=MN8TOARS ER - TY - JOUR TI - Invited Article: Development of high-field superconducting Ioffe magnetic traps AU - Yang, L. AU - Brome, C. R. AU - Butterworth, J. S. AU - Dzhosyuk, S. N. AU - Mattoni, C. E. H. AU - McKinsey, D. N. AU - Michniak, R. A. AU - Doyle, J. M. AU - Golub, R. AU - Korobkina, E. AU - O’Shaughnessy, C. M. AU - Palmquist, G. R. AU - Seo, P.-N. AU - Huffman, P. R. AU - Coakley, K. J. AU - Mumm, H. P. AU - Thompson, A. K. AU - Yang, G. L. AU - Lamoreaux, S. K. T2 - Review of Scientific Instruments AB - We describe the design, construction, and performance of three generations of superconducting Ioffe magnetic traps. The first two are low current traps, built from four racetrack shaped quadrupole coils and two solenoid assemblies. Coils are wet wound with multifilament NbTi superconducting wires embedded in epoxy matrices. The magnet bore diameters are 51 and 105 mm with identical trap depths of 1.0 T at their operating currents and at 4.2 K. A third trap uses a high current accelerator-type quadrupole magnet and two low current solenoids. This trap has a bore diameter of 140 mm and tested trap depth of 2.8 T. Both low current traps show signs of excessive training. The high current hybrid trap, on the other hand, exhibits good training behavior and is amenable to quench protection. DA - 2008/3// PY - 2008/3// DO - 10.1063/1.2897133 VL - 79 IS - 3 SP - 031301 J2 - Review of Scientific Instruments LA - en OP - SN - 0034-6748 1089-7623 UR - http://dx.doi.org/10.1063/1.2897133 DB - Crossref ER - TY - JOUR TI - Self-propelled particle model for cell-sorting phenomena AU - Belmonte, Julio M. AU - Thomas, Gilberto L. AU - Brunnet, Leonardo G. AU - Almeida, Rita M. C. AU - Chate, Hugues T2 - Physical Review Letters AB - A self-propelled particle model is introduced to study cell sorting occurring in some living organisms. This allows us to evaluate the influence of intrinsic cell motility separately from differential adhesion with fluctuations, a mechanism previously shown to be sufficient to explain a variety of cell rearrangement processes. We find that the tendency of cells to actively follow their neighbors greatly reduces segregation time scales. A finite-size analysis of the sorting process reveals clear algebraic growth laws as in physical phase-ordering processes, albeit with unusual scaling exponents. DA - 2008/// PY - 2008/// DO - 10.1103/PhysRevLett.100.248702 VL - 100 IS - 24 ER - TY - JOUR TI - Transverse and longitudinal momentum spectra of fermions produced in strong SU(2) fields AU - Skokov, Vladimir V. AU - Levai, Peter T2 - Physical Review D - Particles, Fields, Gravitation and Cosmology AB - We study the transverse and longitudinal momentum spectra of fermions produced in a strong, time-dependent non-Abelian SU(2) field. Different time-dependent field strengths are introduced. The momentum spectra are calculated for the produced fermion pairs in a kinetic model. The obtained spectra are similar to the Abelian case, and they display exponential or polynomial behavior at high ${p}_{T}$, depending on the given time dependence. We investigated different color initial conditions and discuss the recognized scaling properties for both Abelian and SU(2) cases. DA - 2008/// PY - 2008/// DO - 10.1103/PhysRevD.78.054004 VL - 78 IS - 5 SP - 054004 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-51849107398&partnerID=MN8TOARS ER - TY - JOUR TI - Physics of Particles and Nuclei: Preface AU - Blaschke, D. AU - Skokov, V. AU - Wambach, J. T2 - Physics of Particles and Nuclei DA - 2008/// PY - 2008/// DO - 10.1134/S1063779608070010 VL - 39 IS - 7 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-56749173935&partnerID=MN8TOARS ER - TY - CONF TI - Probing molecular-level organizational structure and electronic decoupling of tartaric acid domains supported on Ag(111) AU - Santagata, N. M. AU - Lakhani, A. M. AU - DeWitt, D. J. AU - Luo, P. AU - Pearl, T. P. C2 - 2008/// C3 - Proceedings of the 17th international vacuum congress/13th international conference on surface science/international conference on nanoscience and technology DA - 2008/// VL - 100 ER - TY - JOUR TI - Abelian-Higgs phase of SU(2) QCD and glueball energy AU - Jia, D. J. T2 - Chinese Physics. C DA - 2008/// PY - 2008/// VL - 32 IS - 7 SP - 509-514 ER - TY - JOUR TI - Recent Progress in Application of Light-Front Dynamics to Hadron Physics AU - Ji, Chueng Ryong T2 - JOURNAL OF THE KOREAN PHYSICAL SOCIETY DA - 2008/12// PY - 2008/12// DO - 10.3938/jkps.53.3714 VL - 53 IS - 6 SP - 3714-3718 SN - 0374-4884 KW - Light-front Dynamics KW - Hadron physics ER - TY - JOUR TI - Percolation in nanocomposites with complex geometries: Experimental and Monte Carlo simulation studies AU - Stevens, D. R. AU - Downen, L. N. AU - Clarke, L. I. T2 - PHYSICAL REVIEW B AB - The development of nanocomposites (a matrix, often polymeric, enhanced by a particle with a nanometer-sized dimension) has expanded dramatically in recent years with a particular focus on materials with complex microstructure and nanostructure. Such composites rely on formation of a connected network of particles throughout the sample volume in order to enhance the polymer's mechanical and electrical properties. From a fundamental perspective, this network formation will be governed by a percolation process within the constrained geometry of the particular microstructure. In this paper, the percolation process within a particular complex nanostructure, namely, a mat of electrospun nanofibers with fiber size of $\ensuremath{\approx}100\text{ }\text{nm}$ and high porosity, is studied via continuum Monte Carlo simulations, where the sample geometry (fiber and particle sizes, orientation, and sample porosity) is matched to the mats utilized in our previous experimental work. A good agreement between experimental and computational results is observed. Simulations of spherical dopant in uniform samples, with zero, one, or two sample dimensions similar in size to the particle, were completed to explore the effects of confinement, in particular within a single fiber. These results were compared and contrasted with those from porous fibrous mats to determine the influence of porosity on the critical volume fraction. The results indicate that percolation in fibrous mats occurs via pathways that include sections of many fibers rather than being contained within single fibers which span the sample. The detailed dependence of critical volume fraction on porosity and the sensitivity to fiber number and width is discussed. DA - 2008/12// PY - 2008/12// DO - 10.1103/physrevb.78.235425 VL - 78 IS - 23 SP - SN - 2469-9969 KW - electrical conductivity KW - Monte Carlo methods KW - nanocomposites KW - nanoporous materials KW - particle size KW - percolation KW - polymer fibres KW - porosity ER - TY - JOUR TI - Experimental study of the low-lying structure of Zr-94 with the (n, n ' gamma) reaction AU - Elhami, E. AU - Orce, J. N. AU - Scheck, M. AU - Mukhopadhyay, S. AU - Choudry, S. N. AU - McEllistrem, M. T. AU - Yates, S. W. AU - Angell, C. AU - Boswell, M. AU - Fallin, B. AU - Howell, C. R. AU - Hutcheson, A. AU - Karwowski, H. J. AU - Kelley, J. H. AU - Parpottas, Y. AU - Tonchev, A. P. AU - Tornow, W. T2 - PHYSICAL REVIEW C AB - The low-lying structure of ${}_{40}^{94}\mathrm{Zr}$ was studied with the ($n,{n}^{'}\ensuremath{\gamma}$) reaction, and a level scheme was established based on excitation function and $\ensuremath{\gamma}\ensuremath{\gamma}$ coincidence measurements. Branching ratios, multipole mixing ratios, and spin assignments were determined from angular distribution measurements. Lifetimes of levels up to 3.4 MeV were measured by the Doppler-shift attenuation method, and for many transitions the reduced transition probabilities were determined. In addition to the anomalous ${2}_{2}^{+}$ state, which has a larger $B(E2;{2}_{2}^{+}\ensuremath{\rightarrow}{0}_{1}^{+})$ value than the $B(E2;{2}_{1}^{+}\ensuremath{\rightarrow}{0}_{1}^{+})$, the experimental results revealed interesting and unusual properties of the low-lying states in $^{94}\mathrm{Zr}$. In a simple interpretation, the excited states are classified in two distinct categories, i.e., those populating the ${2}_{2}^{+}$ state and those decaying to the ${2}_{1}^{+}$ state. DA - 2008/12// PY - 2008/12// DO - 10.1103/physrevc.78.064303 VL - 78 IS - 6 SP - SN - 1089-490X ER - TY - JOUR TI - Edge States and Optical Transition Energies in Carbon Nanoribbons AU - Jiang, J. AU - Lu, W. AU - Bernholc, J. T2 - Physical Review Letters AB - The edge states and optical transition energies in carbon nanoribbons are investigated with density-functional calculations. While the ground state of zigzag ribbons is spin polarized, defects at the edges destroy spin polarization and lead to a nonmagnetic ground state. Scanning tunneling spectroscopy will thus show different features depending on edge quality. Optical transition energies in nanoribbons Eii are strongly affected by the edges and confinement, which introduce a term inversely proportional to their width. After removing that term, the scaling of Eii is quantitatively similar to that in carbon nanotubes. DA - 2008/12/9/ PY - 2008/12/9/ DO - 10.1103/physrevlett.101.246803 VL - 101 IS - 24 SP - J2 - Phys. Rev. Lett. LA - en OP - SN - 0031-9007 1079-7114 UR - http://dx.doi.org/10.1103/PhysRevLett.101.246803 DB - Crossref ER - TY - JOUR TI - Cryogenic Performance of RF MEMS Switch Contacts AU - Brown, Chris AU - Morris, Arthur S., III AU - Kingon, Angus I. AU - Krim, Jacqueline T2 - JOURNAL OF MICROELECTROMECHANICAL SYSTEMS AB - A series of experiments was performed to characterize RF microelectromechanical system switch performance under variable environmental conditions and cryogenic temperatures. Data were recorded in helium and nitrogen environments to lower stiction failure rates as well as to circumvent switch bouncing arising from low pressure at cryogenic temperatures. Contact resistance values were observed to be lower at cryogenic temperatures but still two orders of magnitude higher than the values predicted for the constriction resistance of gold asperity contacts, consistent with the presence of adsorbed films on the contacts. An asperity-heating model was applied, from which it was deduced that contact voltages can selectively disassociate adsorbed films from the contact surface while not softening the gold asperity contacts. The results are consistent with the reduced mobility of the adsorbed surface films at cryogenic temperatures. DA - 2008/12// PY - 2008/12// DO - 10.1109/JMEMS.2008.2005328 VL - 17 IS - 6 SP - 1460-1467 SN - 1941-0158 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-57449110516&partnerID=MN8TOARS KW - Contact resistance KW - electrical contacts KW - microelectromechanical systems (MEMS) KW - RF MEMS KW - switches ER - TY - JOUR TI - Viscous damping of r-mode oscillations in compact stars with quark matter AU - Jaikumar, P. AU - Rupak, G. AU - Steiner, A. W. T2 - Physical Review. D, Particles, Fields, Gravitation, and Cosmology DA - 2008/// PY - 2008/// VL - 78 IS - 12 ER - TY - JOUR TI - DOTS, CLUMPS, AND FILAMENTS: THE INTERMITTENT IMAGES OF SYNCHROTRON EMISSION IN RANDOM MAGNETIC FIELDS OF YOUNG SUPERNOVA REMNANTS AU - Bykov, Andrei M. AU - Uvarov, Yury A. AU - Ellison, Donald C. T2 - ASTROPHYSICAL JOURNAL LETTERS AB - Non-thermal X-ray emission in some supernova remnants originates from synchrotron radiation of ultra-relativistic particles in turbulent magnetic fields. We address the effect of a random magnetic field on synchrotron emission images and spectra. A random magnetic field is simulated to construct synchrotron emission maps of a source with a steady distribution of ultra-relativistic electrons. Non-steady localized structures (dots, clumps and filaments), in which the magnetic field reaches exceptionally high values, typically arise in the random field sample. These magnetic field concentrations dominate the synchrotron emission (integrated along the line of sight) from the highest energy electrons in the cut-off regime of the distribution, resulting in an evolving, intermittent, clumpy appearance. The simulated structures resemble those observed in X-ray images of some young supernova remnants. The lifetime of X-ray clumps can be short enough to be consistent with that observed even in the case of a steady particle distribution. The efficiency of synchrotron radiation from the cut-off regime in the electron spectrum is strongly enhanced in a turbulent field compared to emission from a uniform field of the same magnitude. DA - 2008/12/20/ PY - 2008/12/20/ DO - 10.1086/595868 VL - 689 IS - 2 SP - L133-L136 SN - 2041-8213 KW - acceleration of particles KW - radiation mechanisms: nonthermal KW - supernova remnants KW - turbulence KW - X-rays: ISM ER - TY - JOUR TI - Color superconductivity in dense quark matter AU - Alford, Mark G. AU - Schmitt, Andreas AU - Rajagopal, Krishna AU - Schaefer, Thomas T2 - REVIEWS OF MODERN PHYSICS AB - Matter at high density and low temperature is expected to be a color superconductor, which is a degenerate Fermi gas of quarks with a condensate of Cooper pairs near the Fermi surface that induces color Meissner effects. At the highest densities, where the QCD coupling is weak, rigorous calculations are possible, and the ground state is a particularly symmetric state, the color-flavor locked (CFL) phase. The CFL phase is a superfluid, an electromagnetic insulator, and breaks chiral symmetry. The effective theory of the low-energy excitations in the CFL phase is known and can be used, even at more moderate densities, to describe its physical properties. At lower densities the CFL phase may be disfavored by stresses that seek to separate the Fermi surfaces of the different flavors, and comparison with the competing alternative phases, which may break translation and/or rotation invariance, is done using phenomenological models. We review the calculations that underlie these results and then discuss transport properties of several color-superconducting phases and their consequences for signatures of color superconductivity in neutron stars. DA - 2008/// PY - 2008/// DO - 10.1103/revmodphys.80.1455 VL - 80 IS - 4 SP - 1455-1515 SN - 1539-0756 UR - http://inspirehep.net/record/762418 KW - BCS theory KW - chiral symmetries KW - fermion systems KW - flavour model KW - ground states KW - neutron stars KW - nuclear superfluid model KW - quantum chromodynamics KW - quark matter KW - quarks KW - spontaneous symmetry breaking KW - stellar internal processes ER - TY - JOUR TI - Abnormal domain switching in Pb(Zr,Ti)O-3 thin film capacitors AU - Wu, A. Y. AU - Vilarinho, P. M. AU - Wu, D. AU - Gruverman, A. T2 - Applied Physics Letters DA - 2008/// PY - 2008/// VL - 93 IS - 26 ER - TY - JOUR TI - Suppression of Ge-O and Ge-N bonding at Ge-HfO2 and Ge-TiO2 interfaces by deposition onto plasma-nitrided passivated Ge substrates AU - Lee, S. AU - Long, J. P. AU - Lucovsky, G. AU - Luening, J. T2 - THIN SOLID FILMS AB - A study of changes in nano-scale morphology of thin films of nano-crystalline transition metal (TM) elemental oxides, HfO2 and TiO2, on plasma-nitrided Ge(100) substrates, and Si(100) substrates with ultra-thin (∼ 0.8 nm) plasma-nitrided Si suboxide, SiOx, x < 2, or SiON interfacial layers is presented. Near edge X-ray absorption spectroscopy (NEXAS) has been used to determine nano-scale morphology of these films by Jahn–Teller distortion removal of band-edge d-state degeneracies. These results identify a new and novel application for NEXAS based on the resonant character of the respective O K1 and N K1 edge absorptions. Their X-ray energy difference of > 150 eV is critical for this approach. DA - 2008/11/3/ PY - 2008/11/3/ DO - 10.1016/j.tsf.2008.08.099 VL - 517 IS - 1 SP - 155-158 SN - 0040-6090 KW - Ge/dielectric interfaces KW - Remote plasma nitridation of Ge KW - Band edge defects KW - Remote plasma deposition KW - Thermal annealing ER - TY - JOUR TI - Study of GEM-like detectors with resistive electrodes for RICH applications AU - Agocs, A. G. AU - Di Mauro, A. AU - Ben David, A. AU - Clark, B. AU - Martinengo, P. AU - Nappi, E. AU - Peskov, V. T2 - NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT AB - We have developed prototypes of GEM-like detectors with resistive electrodes to be used as RICH photodetectors equipped with CsI photocathodes. The main advantages of these detectors are their intrinsic spark-protection and possibility to operate at high gain (∼105) in many gases including poorly quenched ones, allowing for the adoption of windowless configurations in which the radiator gas is also used in the chamber. Results of systematic studies of the resistive GEMs combined with CsI photocathodes are presented: their quantum efficiency, rate characteristics, long-term stability, etc. On the basis of the obtained results, we believe that the new detector will be a promising candidate for upgrading the ALICE RICH detector. DA - 2008/9/21/ PY - 2008/9/21/ DO - 10.1016/j.nima.2008.07.031 VL - 595 IS - 1 SP - 128-130 SN - 1872-9576 KW - RICH KW - VHMPID KW - CsI photocathodes KW - GEM KW - Resistive GEM ER - TY - JOUR TI - Quantum Monte Carlo calculations of structural properties of FeO under pressure AU - Kolorenc, J. AU - Mitas, L. T2 - Physical Review Letters DA - 2008/// PY - 2008/// VL - 101 IS - 18 ER - TY - CONF TI - Finite difference formulation to calculate the induced current density profile inside the retina by a microcoil array AU - Srinivas, S. AU - George, J. S. AU - Lazzi, G. C2 - 2008/// C3 - 2008 IEEE International Symposium on Antennas and Propagation and USNC/URSI National Radio Science Meeting DA - 2008/// SP - 3074-3077 PB - [Piscataway, NJ]: IEEE SN - 978-1-4244-2041-4 ER - TY - JOUR TI - EJECTA, DUST, AND SYNCHROTRON RADIATION IN SNR B0540-69.3: A MORE CRAB-LIKE REMNANT THAN THE CRAB AU - Williams, Brian J. AU - Borkowski, Kazimierz J. AU - Reynolds, Stephen P. AU - Raymond, John C. AU - Long, Knox S. AU - Morse, Jon AU - Blair, William P. AU - Ghavamian, Parviz AU - Sankrit, Ravi AU - Hendrick, Sean P. AU - Smith, R. Chris AU - Points, Sean AU - Winkler, P. Frank T2 - ASTROPHYSICAL JOURNAL AB - We present near- and mid-infrared observations of the pulsar-wind nebula (PWN) SNR B0540–69.3 and its associated supernova remnant made with the Spitzer Space Telescope. We report detections of the PWN with all four IRAC bands, the 24 μm band of MIPS, and the Infrared Spectrograph (IRS). We find no evidence of IR emission from the X-ray/radio shell surrounding the PWN resulting from the forward shock of the supernova blast wave. The flux of the PWN itself is dominated by synchrotron emission at shorter (IRAC) wavelengths, with a warm dust component longward of 20 μm. We show that this dust continuum can be explained by a small amount [~(1–3) × 10−3 M☉] of dust at a temperature of ~50-65 K, heated by the shock wave generated by the PWN being driven into the inner edge of the ejecta. This is evidently dust synthesized in the supernova. We also report the detection of several lines in the spectrum of the PWN and present kinematic information about the PWN as determined from these lines. Kinematics are consistent with previous optical studies of this object. Line strengths are also broadly consistent with what one expects from optical line strengths. We find that lines arise from slow (~20 km s−1) shocks driven into oxygen-rich clumps in the shell swept up by an iron-nickel bubble, which have a density contrast of ~100-200 relative to the bulk of the ejecta, and that faster shocks (~250 km s−1) in the hydrogen envelope are required to heat dust grains to observed temperatures. We infer from estimates of heavy-element ejecta abundances that the progenitor star was likely in the range of 20-25 M☉. DA - 2008/11/10/ PY - 2008/11/10/ DO - 10.1086/592139 VL - 687 IS - 2 SP - 1054-1069 SN - 1538-4357 KW - dust, extinction KW - Magellanic Clouds KW - pulsars: individual (SNR 0540-69.3) KW - supernova remnants ER - TY - JOUR TI - Chemical bonding and graded interfacial transition regions at transition metal, Hf(Zr),/high-k gate dielectric, Hf(Zr)O(2), interfaces AU - Lucovsky, G. AU - Whitten, J. L. T2 - THIN SOLID FILMS AB - One of the most significant and challenging process integration issues for high-k dielectrics is the replacement of poly-Si gates in CMOS devices with either dual metal gates, or a single mid-band gap metal. The issue is the stability of the metal gate/high-k gate dielectric interface with respect to post-deposition thermal processing. Ab initio quantum chemistry calculations address this issue, and two questions have been resolved, providing results that are consistent with the experiment. The interface between a metal gate electrode and a high gate electrode and oxide dielectric cannot be atomically abrupt after post-deposition thermal processing. Instead there must be a chemically-graded interfacial transition region that mitigates some of the benefits of replacing dual poly-Si gates by metals, except for gate-last processing. However, electrical stress and heating during device operation will be significant driving force atomic motion, and the formation of an interfacial transition region. DA - 2008/11/3/ PY - 2008/11/3/ DO - 10.1016/j.tsf.2008.08.034 VL - 517 IS - 1 SP - 343-345 SN - 0040-6090 KW - High-k dielectrics KW - Hf(Zr)O(2) KW - Transition metal KW - Chemical bonding KW - Graded interfacial regions KW - O-atom vacancies KW - Discrete band edge ER - TY - JOUR TI - Bulk defects in nano-crystalline and in non-crystalline HfO2-based thin film dielectrics AU - Lee, S. AU - Seo, H. AU - Lucovsky, G. AU - Fleming, L. B. AU - Ulrich, M. D. AU - Luening, J. T2 - THIN SOLID FILMS AB - Defect states in the form of band edge electron and hole traps in HfO2 nano-crystalline films are qualitatively different in two different length scale regimes. For grain sizes > 3–4 nm, they are discrete band edge states associated with O-atom vacancies pinned and clustered at grain boundaries, whereas in as-deposited films, and films with a physical thickness of ~ 2 nm, they are band-tail defects with a density reduced by more than an order of magnitude. Defect states in non-crystalline high Si3N4 content Hf Si oxynitride alloys are qualitatively different than those in the either regime of nano-crystallinity, but instead are similar to those in SiO2, with densities < 1011 cm− 2 contrasted with defects densities in excess of 1011 cm− 2 in films with nano-grains ~ 2 nm, and extending to > 1012 cm− 2 in films with nano-grains > 3–4 nm. DA - 2008/11/3/ PY - 2008/11/3/ DO - 10.1016/j.tsf.2008.08.098 VL - 517 IS - 1 SP - 437-440 SN - 0040-6090 KW - Thin film high-k dielectrics KW - Non-crystalline transition metal oxides KW - Nano-crystalline transition metal oxides KW - Bulk defects KW - Intrinsic bonding defects KW - Divacancies ER - TY - JOUR TI - Force chains in seismogenic faults visualized with photoelastic granular shear experiments AU - Daniels, Karen E. AU - Hayman, Nicholas W. T2 - JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH AB - Natural faults have many characteristics in common with granular systems, including granular fault rocks, shear localization, and stick‐slip dynamics. We present experimental results which provide insight into granular behavior in natural faults. The experiments allow us to directly image force chains within a deforming granular media through the use of photoelastic particles. The experimental apparatus consists of a spring‐pulled slider block which deforms the photoelastic granular aggregate at a constant velocity. Particles that carry more of the load appear brighter when viewed through crossed polarizers, making the internal stresses optically accessible. The resulting pattern is a branched, anisotropic force chain network inclined to the shear zone boundaries. Under both constant volume and dilational boundary conditions, deformation occurs predominantly through stick‐slip displacements and corresponding force drops. The particle motion and force chain changes associated with the deformation can either be localized to the central slip zone or span the system. The sizes of the experimental slip events are observed to have power law (Gutenberg‐Richter‐like) distributions; the minimum dimensions of events and the behavior of force chains suggest that a particle scale controls the lower limits of the power law distributions. For large drops in pulling force with slip, the shape of the size distributions is strongly affected by the choice of boundary condition, while for small to moderate drops the probability distributions are approximately independent of boundary condition. These size‐dependent variations in stick‐slip behavior are associated with different spatial patterns: on average, small events typically correspond to localized force chain or particle rearrangements, whereas large events correspond to system‐spanning changes. Such force chain behavior may be responsible for similar size‐dependent behaviors of natural faults. DA - 2008/11/26/ PY - 2008/11/26/ DO - 10.1029/2008jb005781 VL - 113 IS - B11 SP - SN - 2169-9356 ER - TY - JOUR TI - Dynamics within Alkylsiloxane Self-Assembled Monolayers Studied by Sensitive Dielectric Spectroscopy AU - Scott, Mary C. AU - Stevens, Derrick R. AU - Bochinski, Jason R. AU - Clarke, Laura I. T2 - ACS NANO AB - Self-assembled monolayers are a ubiquitous laboratory tool and have been the subject of many experimental investigations which have primarily focused on static properties of full coverage monolayers, with the maximum density and ordering possible. In this work, dynamics within low density, planar siloxane self-assembled monolayers are studied utilizing highly sensitive dielectric spectroscopy. Dilute, disordered films were intentionally fabricated in order to study the widest range of possible motions. At low coverage, an interacting relaxation is observed, which has similar dynamics to polyethylene-like glass transitions observed in phase-segregated side-chain polymers, despite the rigidity of the substrate and the constraint of ethyl groups in relatively short chains. As density is increased, a second local relaxation, previously observed in three-dimensional SAMs and associated with rotation within a small segment of the alkyl chain, is also observed. DA - 2008/11// PY - 2008/11// DO - 10.1021/nn800543j VL - 2 IS - 11 SP - 2392-2400 SN - 1936-0851 KW - monolayer KW - rotational dynamics KW - siloxane KW - dielectric spectroscopy ER - TY - JOUR TI - Thickness inhomogenities in the organometallic chemical vapor deposition of GaP AU - Liu, X. AU - Aspnes, D. E. T2 - APPLIED PHYSICS LETTERS AB - We analyze exponential lateral-thickness variations observed in the growth of GaP on (001) GaAs, thermally generated SiO2, (001) Si, and nanoscopically roughened Si surfaces by organometallic chemical vapor deposition, using as a reference the polycrystalline GaP deposited on the Mo susceptor surrounding the 2in. wafers. We find these variations to be due to differences in the chemical reactivities of the various surfaces toward the generation of a precursor, probably a H–P=Ga–CH3 dimer adduct, by heterogeneous catalysis followed by desorption and diffusion through the gas phase. DA - 2008/11/17/ PY - 2008/11/17/ DO - 10.1063/1.3029742 VL - 93 IS - 20 SP - SN - 0003-6951 KW - catalysis KW - desorption KW - diffusion KW - gallium compounds KW - III-V semiconductors KW - MOCVD KW - semiconductor growth KW - semiconductor thin films ER - TY - JOUR TI - Thermodynamic properties of Fe-56,Fe-57 AU - Algin, E. AU - Agvaanluvsan, U. AU - Guttormsen, M. AU - Larsen, A. C. AU - Mitchell, G. E. AU - Rekstad, J. AU - Schiller, A. AU - Siem, S. AU - Voinov, A. T2 - PHYSICAL REVIEW C AB - Nuclear level densities for $^{56,57}\mathrm{Fe}$ have been extracted from the primary $\ensuremath{\gamma}$-ray spectra using (${}^{3}\mathrm{He}, {}^{3}{\mathrm{He}}^{'}\ensuremath{\gamma}$) and (${}^{3}\mathrm{He}, \ensuremath{\alpha}\ensuremath{\gamma}$) reactions. Nuclear thermodynamic properties for $^{56}\mathrm{Fe}$ and $^{57}\mathrm{Fe}$ are investigated using the experimental level densities. These properties include entropy, Helmholtz free energy, caloric curves, chemical potential, and heat capacity. In particular, the breaking of Cooper pairs and single-quasiparticle entropy are discussed and shown to be important concepts for describing nuclear level density. Microscopic model calculations are performed for level densities of $^{56,57}\mathrm{Fe}$. The experimental and calculated level densities are compared. The average number of broken Cooper pairs and the parity distribution are extracted as a function of excitation energy for $^{56,57}\mathrm{Fe}$ from the model calculations. DA - 2008/11// PY - 2008/11// DO - 10.1103/physrevc.78.054321 VL - 78 IS - 5 SP - SN - 1089-490X ER - TY - JOUR TI - The short GRB 070707 afterglow and its very faint host galaxy AU - Piranomonte, S. AU - D'Avanzo, P. AU - Covino, S. AU - Antonelli, L. A. AU - Beardmore, A. P. AU - Campana, S. AU - Chincarini, G. AU - D'Elia, V. AU - Della Valle, M. AU - Fiore, F. AU - Fugazza, D. AU - Guetta, D. AU - Guidorzi, C. AU - Israel, G. L. AU - Lazzati, D. AU - Malesani, D. AU - Parsons, A. M. AU - al, et T2 - Astronomy and Astrophysics (Berlin, Germany : West) DA - 2008/// PY - 2008/// VL - 491 IS - 1 SP - 183-188 ER - TY - JOUR TI - The Sackler Colloquium on promises and perils in nanotechnology for medicine AU - Austin, Robert H. AU - Lim, Shuang-fang T2 - PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA AB - The Sackler Colloquium entitled “Nanomaterials in Biology and Medicine: Promises and Perils” was held on April 10–11, 2007. We have been able to assemble a representative sampling of 17 of the invited talks ranging over the topics presented. Any new technology carries with it both a promise of transforming the way we do things and the possibility that there are unforeseen consequences. The papers collected here represent a cross-section of these issues. As an example, we present our own work on nano-upconversion phosphors as an example of this new class of nanomaterials with potential use in medicine and biology. DA - 2008/11/11/ PY - 2008/11/11/ DO - 10.1073/pnas.0709499105 VL - 105 IS - 45 SP - 17217-17221 SN - 0027-8424 KW - nanomaterials KW - upconversion ER - TY - JOUR TI - TURBULENCE DISSIPATION AND PARTICLE INJECTION IN NONLINEAR DIFFUSIVE SHOCK ACCELERATION WITH MAGNETIC FIELD AMPLIFICATION AU - Vladimirov, Andrey E. AU - Bykov, Andrei M. AU - Ellison, Donald C. T2 - ASTROPHYSICAL JOURNAL AB - The highly amplified magnetic fields suggested by observations of some supernova remnant shells are most likely an intrinsic part of efficient particle acceleration by shocks. This strong turbulence, which may result from cosmic-ray-driven instabilities, both resonant and nonresonant, in the shock precursor, is certain to play a critical role in self-consistent, nonlinear models of strong, cosmic-ray-modified shocks. Here we present a Monte Carlo model of nonlinear diffusive shock acceleration (DSA) accounting for magnetic field amplification through resonant instabilities induced by accelerated particles, and including the effects of dissipation of turbulence upstream of a shock and the subsequent precursor plasma heating. Feedback effects between the plasma heating due to turbulence dissipation and particle injection are strong, adding to the nonlinear nature of efficient DSA. Describing the turbulence damping in a parameterized way, we reach two important results: first, for conditions typical of supernova remnant shocks, even a small amount of dissipated turbulence energy (~10%) is sufficient to significantly heat the precursor plasma; and second, the heating upstream of the shock leads to an increase in the injection of thermal particles at the subshock by a factor of several. In our results, the response of the nonlinear shock structure to the boost in particle injection prevented the efficiency of particle acceleration and magnetic field amplification from increasing. We argue, however, that more advanced (possibly nonresonant) models of turbulence generation and dissipation may lead to a scenario in which particle injection boost due to turbulence dissipation results in more efficient acceleration and even stronger amplified magnetic fields than without the dissipation. DA - 2008/12/1/ PY - 2008/12/1/ DO - 10.1086/592240 VL - 688 IS - 2 SP - 1084-1101 SN - 1538-4357 KW - acceleration of particles KW - cosmic rays KW - magnetic fields KW - shock waves KW - supernova remnants KW - turbulence ER - TY - JOUR TI - Suppression of defect states in HfSiON gate dielectric films on n-type Ge(100) substrates AU - Chung, K. B. AU - Seo, H. AU - Long, J. P. AU - Lucovsky, G. T2 - APPLIED PHYSICS LETTERS AB - Defect states in HfO2 and HfSiON films deposited on Ge(100) substrates were studied by spectroscopic ellipsometry (SE) and x-ray absorption spectroscopy (XAS). In addition, structural and compositional changes in these films were examined via medium energy ion scattering (MEIS). SE and XAS experiments revealed two distinct band edge defect states, located at 1.7±0.1eV and at 2.7±0.1 below the conduction band edges of these films. The number of defect states in HfO2 increased noticeably following postdeposition annealing (PDA), whereas in HfSiON, it showed only small increases following the same treatment. MEIS measurements showed that Ge diffusion into HfO2 films was enhanced significantly by PDA as well; however, this effect was less pronounced in the HfSiON films. The suppression of defect state enhancement in HfSiON films was correlated with lower levels of Ge diffusion and increased structural stability with respect to HfO2. DA - 2008/11/3/ PY - 2008/11/3/ DO - 10.1063/1.3005422 VL - 93 IS - 18 SP - SN - 0003-6951 KW - annealing KW - conduction bands KW - defect states KW - diffusion KW - ellipsometry KW - germanium KW - hafnium compounds KW - high-k dielectric thin films KW - ion-surface impact KW - X-ray absorption spectra ER - TY - JOUR TI - Structural determination of large molecules through the reassembly of optimized fragments AU - Lee, Jung-Goo AU - Lee, Yoon Sup AU - Roland, Christopher T2 - JOURNAL OF MOLECULAR GRAPHICS & MODELLING AB - The accurate determination of the optimized structures of large molecules is, computationally quite expensive. As an alternate to the conventional approaches to structural optimization, we have explored the accuracy and speed-up obtained when variants of the fragmentation optimization and recombination method (FORM) are used. Specifically, the method was applied to eight prototypical molecules -n-decane, hexa-alanine, a long conjugate hydrocarbon molecule, a large polar conjugated molecule, large (5,5) armchair single-walled carbon nanotubes, a salen-aluminum complex and a multiply H-bonded system (two conformers of vancomycin aglycon with Di-N-acetyl-l-Lys-d-Ala-d-Ala - without optimizing the structure of the whole molecules. We find that FORM can predict the structure of these molecules with an acceptable accuracy, all at a computational cost that is 2-11 times less than conventional quantum mechanical methods at the Hartree-Fock (HF), density functional theory (DFT) and MP2 level of accuracy. FORM may therefore represent a viable approach for the fast structural predictions of large molecules. DA - 2008/10// PY - 2008/10// DO - 10.1016/j.jmgm.2008.06.004 VL - 27 IS - 3 SP - 364-375 SN - 1873-4243 KW - Divide and conquer KW - Geometry optimization KW - Ab initio KW - FORM ER - TY - JOUR TI - PolLux: A new facility for soft x-ray spectromicroscopy at the Swiss Light Source AU - Raabe, J. AU - Tzvetkov, G. AU - Flechsig, U. AU - Boege, M. AU - Jaggi, A. AU - Sarafimov, B. AU - Vernooij, M. G. C. AU - Huthwelker, T. AU - Ade, H. AU - Kilcoyne, D. AU - Tyliszczak, T. AU - Fink, R. H. AU - Quitmann, C. T2 - REVIEW OF SCIENTIFIC INSTRUMENTS AB - We report on the successful installation and operation of a scanning transmission x-ray microspectroscope (STXM) at the PolLux facility at the Swiss Light Source. This integration of an advanced STXM with improved sample handling capabilities and a novel beamline provides unique capabilities. PolLux uses linearly or circularly polarized x-rays from a bending magnet with an extended photon energy range (200–1400 eV). It is therefore well suited to determine a sample’s quantitative chemical composition, molecular orientation, or thickness of organic as well as condensed matter materials. The local magnetic state of magnetic thin films is accessible through fast helicity switching by steering the electron beam off axis through the bending magnet. Ex vacuo girder movers allow fast and highly reproducible (&lt;1 μm) alignment of the instrument with respect to the photon beam. The present spatial resolution is ∼20 nm, limited by the zone plates utilized. The instrument has the stability and positional resolution to operate with much higher resolution optics as it becomes available. In addition to characterization experiments, we present several typical examples from materials research and environmental science to exemplify the capabilities. DA - 2008/11// PY - 2008/11// DO - 10.1063/1.3021472 VL - 79 IS - 11 SP - SN - 1089-7623 KW - image resolution KW - light sources KW - X-ray apparatus KW - X-ray microscopy KW - X-ray optics KW - X-ray spectroscopy KW - zone plates ER - TY - JOUR TI - Interfacial reaction of atomic-layer-deposited HfO2 film as a function of the surface state of an n-GaAs (100) substrate AU - Kim, C. Y. AU - Cho, S. W. AU - Cho, M. -H. AU - Chung, K. B. AU - An, C. -H. AU - Kim, H. AU - Lee, H. J. AU - Ko, D. -H. T2 - APPLIED PHYSICS LETTERS AB - The characteristics of interfacial reactions and the valence band offset of HfO2 films grown on GaAs by atomic layer deposition were investigated by combining high-resolution x-ray photoelectron spectroscopy and high-resolution electron transmission microscopy. The interfacial characteristics are significantly dependent on the surface state of the GaAs substrate. Polycrystalline HfO2 film on a clean GaAs surface was changed to a well-ordered crystalline film as the annealing temperature increased, and a clean interface with no interfacial layer formed at temperatures above 600°C. The valence band offset of the film grown on the oxidized GaAs surface gradually increased with the stoichiometric change in the interfacial layer. DA - 2008/11/10/ PY - 2008/11/10/ DO - 10.1063/1.2996261 VL - 93 IS - 19 SP - SN - 1077-3118 KW - annealing KW - atomic layer deposition KW - gallium arsenide KW - hafnium compounds KW - stoichiometry KW - thin films KW - transmission electron microscopy KW - valence bands KW - X-ray photoelectron spectra ER - TY - JOUR TI - Effective field theory and finite-density systems AU - Furnstahl, R. J. AU - Rupak, G. AU - Schafer, T. T2 - Annual Review of Nuclear and Particle Science DA - 2008/// PY - 2008/// VL - 58 SP - 1-25 ER - TY - JOUR TI - Coulomb excitation of radioactive Na-21 and its stable mirror Ne-21 AU - Schumaker, M. A. AU - Cline, D. AU - Hackman, G. AU - Morton, A. C. AU - Pearson, C. J. AU - Svensson, C. E. AU - Wu, C. Y. AU - Andreyev, A. AU - Austin, R. A. E. AU - Ball, G. C. AU - Bandyopadhyay, D. AU - Becker, J. A. AU - Boston, A. J. AU - Boston, H. C. AU - Buchmann, L. T2 - Physical Review. C, Nuclear Physics DA - 2008/// PY - 2008/// VL - 78 IS - 4 ER - TY - JOUR TI - Analysis of interface layers by spectroscopic ellipsometry AU - Kim, T. J. AU - Yoon, J. J. AU - Kim, Y. D. AU - Aspnes, D. E. AU - Klein, M. V. AU - Ko, D. -S. AU - Kim, Y. -W. AU - Elarde, V. C. AU - Coleman, J. J. T2 - APPLIED SURFACE SCIENCE AB - Abstract We investigate the relative validity of the Bruggeman effective-medium approximation and several alloy models to describe interfaces in the analysis of spectroscopic ellipsometric data of laminar samples, using data obtained on an Al x Ga 1− x As multilayer sample fabricated specifically for this purpose. The investigation highlights the types of errors that result from the use of inappropriate models. Optimum results are obtained with the alloy model where the graded-composition regions are approximated with multilayer stacks. DA - 2008/11/30/ PY - 2008/11/30/ DO - 10.1016/j.apsusc.2008.07.005 VL - 255 IS - 3 SP - 640-642 SN - 1873-5584 KW - AlGaAs KW - Ellipsometry KW - Multilayer ER - TY - JOUR TI - Evolution of the nanomorphology of photovoltaic polyfluorene blends: sub-100 nm resolution with x-ray spectromicroscopy AU - McNeill, C. R. AU - Watts, B. AU - Swaraj, S. AU - Ade, H. AU - Thomsen, L. AU - Belcher, W. AU - Dastoor, P. C. T2 - NANOTECHNOLOGY AB - We investigate the influence of annealing on the morphology of intimately mixed blends of the conjugated polymers poly(9,9'-dioctylfluorene-co-bis-N,N'-(4-butylphenyl)-bis-N,N'-phenyl-1,4-phenylene-diamine) (PFB) and poly(9,9'-dioctylfluorene-co-benzothiadiazole) (F8BT) with scanning transmission x-ray microscopy (STXM). Through the use of a zone plate with theoretical Rayleigh resolution of 30 nm, we are able to resolve sub-100 nm bulk structure in these films. Surprisingly, for unannealed films spin-coated from chloroform we observe features with an average diameter of 85 nm. The high degree of photoluminescence quenching in these as-spun films (>95%) implies that there is significant intermixing within the 85 nm structures, indicating that a hierarchy of phase separation exists even on the length scale of less than 100 nm. With annealing up to 160 °C, close to the T(g) of the components, there is little change in the feature sizes observed by STXM, although an increase in variation of the composition is observed. With annealing above 160 °C the imaged features begin to evolve in size, increasing to 225 nm in extent, alongside large changes in composition with annealing to 200 °C. Comparing the evolution of morphology imaged by STXM with the change in photoluminescence quenching with annealing, we propose that phase separation first evolves via the evolution of relatively pure phases on the length scale of a few to tens of nanometres within the larger 85 nm structures. Once the length scale of compositional fluctuations exceeds 85 nm (for anneal temperatures above 160 °C) the hierarchy of phase separation is lost and the subsequent morphological evolution is readily imaged by STXM. Applying the results of an exciton diffusion and quenching model, we find good agreement between the size of the domains measured by STXM (above 180 °C) and the results of the model for an exciton diffusion length of 15 nm. The growth in domain size and towards purer structures has also been observed with resonant soft x-ray scattering. DA - 2008/10/22/ PY - 2008/10/22/ DO - 10.1088/0957-4484/19/42/424015 VL - 19 IS - 42 SP - SN - 1361-6528 ER - TY - JOUR TI - Three-dimensional model of broadband emission from supernova remnants undergoing nonlinear diffusive shock acceleration AU - Lee, Shiu-Hang AU - Kamae, Tuneyoshi AU - Ellison, Donald C. T2 - ASTROPHYSICAL JOURNAL AB - We present a three-dimensional model of supernova remnants (SNRs) in which the hydrodynamical evolution of the remnant is modeled consistently with nonlinear diffusive shock acceleration occurring at the outer blast wave. The model includes particle escape and diffusion outside of the forward shock and particle interactions with arbitrary distributions of external ambient material, such as molecular clouds. We include synchrotron emission and cooling, bremsstrahlung radiation, neutral pion production, and inverse Compton (IC) and Coulomb energy loss. Broadband spectra have been calculated for typical parameters, including dense regions of gas external to a 1000 yr old SNR. In this paper, we describe the details of our model, but do not attempt a detailed fit to any specific remnant. We also do not include magnetic field amplification (MFA), even though this effect may be important in some young remnants. Our aim is to develop a flexible platform that can be generalized to include effects such as MFA, and that can be easily adapted to various SNR environments, including Type Ia SNRs, which explode in a constant-density medium, and Type II SNRs, which explode in a presupernova wind. When applied to a specific SNR, our model will predict cosmic-ray spectra and multiwavelength morphology in projected images for instruments with varying spatial and spectral resolutions. We show examples of these spectra and images and emphasize the importance of measurements in the hard X-ray, GeV, and TeV gamma-ray bands for investigating key ingredients in the acceleration mechanism, and for deducing whether or not TeV emission is produced by IC from electrons or pion decay from protons. DA - 2008/10/10/ PY - 2008/10/10/ DO - 10.1086/591308 VL - 686 IS - 1 SP - 325-336 SN - 1538-4357 KW - acceleration of particles KW - cosmic rays KW - gamma rays : observations KW - supernova remnants KW - X-rays : general ER - TY - JOUR TI - Organic thermometry for chondritic parent bodies AU - Cody, G. D. AU - Alexander, C. M. O'D. AU - Yabuta, H. AU - Kilcoyne, A. L. D. AU - Araki, T. AU - Ade, H. AU - Dera, R. AU - Fogel, M. AU - Militzer, B. AU - Mysen, B. O. T2 - EARTH AND PLANETARY SCIENCE LETTERS AB - Abstract A unique spectroscopic feature has been identified in a study of twenty-five different samples of meteoritic insoluble organic matter (IOM) spanning multiple chemical classes, groups, and petrologic types, using carbon X-ray Absorption Near Edge Structure (XANES) spectroscopy. The intensity of this feature, a 1s − σ⁎ exciton, appears to provide a precise measure of parent body metamorphism. The intensity of this exciton is also shown to correlate well with a large negative paramagnetic shift observed through solid state 13C NMR. Experiments reveal that upon heating primitive IOM is transformed into material that is indistinguishable from that in thermally processed chondrites, including the development of the 1s − σ⁎ exciton. A thermo-kinetic expression is derived from the experimental data that allows the intensity of the 1s − σ⁎ exciton to be used to estimated the effective temperature integrated over time. A good correlation is observed between the intensity of the 1s − σ⁎ exciton and previously published microRaman spectral data. These data provide a self-consistent organic derived temperature scale for the purpose of calibrating Raman based thermometric expressions. DA - 2008/7/30/ PY - 2008/7/30/ DO - 10.1016/j.epsl.2008.05.008 VL - 272 IS - 1-2 SP - 446-455 SN - 0012-821X KW - chondrite KW - parent bodies KW - insoluble organic matter KW - thermal metamorphism KW - C-XANES KW - NMR KW - Raman ER - TY - JOUR TI - Onset of ferrielectricity and the hidden nature of nanoscale polarization in ferroelectric thin films AU - Nunez, M. AU - Nardelli, M. B. T2 - Physical Review Letters DA - 2008/// PY - 2008/// VL - 101 IS - 10 ER - TY - JOUR TI - Fabrication and characterization of electrospun chitosan nanofibers formed via templating with polyethylene oxide AU - Ojha, Satyajeet S. AU - Stevens, Derrick R. AU - Hoffman, Torissa J. AU - Stano, Kelly AU - Klossner, Rebecca AU - Scott, Mary C. AU - Krause, Wendy AU - Clarke, Laura I. AU - Gorga, Russell E. T2 - BIOMACROMOLECULES AB - Chitosan is an abundantly common, naturally occurring, polysaccharide biopolymer. Its biocompatible, biodegradable, and antimicrobial properties have led to significant research toward biological applications such as drug delivery, artificial tissue scaffolds for functional tissue engineering, and wound-healing dressings. For applications such as tissue scaffolding, formation of highly porous mats of nanometer-sized fibers, such as those fabricated via electrospinning, may be quite important. Previously, strong acidic solvents and blending with synthetic polymers have been used to achieve electrospun nanofibers containing chitosan. As an alternative approach, in this work, polyethylene oxide (PEO) has been used as a template to fabricate chitosan nanofibers by electrospinning in a core-sheath geometry, with the PEO sheath serving as a template for the chitosan core. Solutions of 3 wt % chitosan (in acetic acid) and 4 wt % PEO (in water) were found to have matching rheological properties that enabled efficient core-sheath fiber formation. After removing the PEO sheath by washing with deionized water, chitosan nanofibers were obtained. Electron microscopy confirmed nanofibers of ∼250 nm diameter with a clear core-sheath geometry before sheath removal, and chitosan nanofibers of ∼100 nm diameter after washing. The resultant fibers were characterized with IR spectroscopy and X-ray diffraction, and the mechanical and electrical properties were evaluated. DA - 2008/9// PY - 2008/9// DO - 10.1021/bm800551q VL - 9 IS - 9 SP - 2523-2529 SN - 1526-4602 ER - TY - JOUR TI - Elimination of GeO2 and Ge3N4 interfacial transition regions and defects at n-type Ge interfaces: A pathway for formation of n-MOS devices on Ge substrates AU - Lucovsky, G. AU - Lee, S. AU - Long, J. P. AU - Seo, H. AU - Luning, J. T2 - Applied Surface Science AB - The contribution from relatively low-K SiON interfacial transition regions (ITRs) between Si and transition metal (TM) gate dielectrics places a significant limitation on equivalent oxide thickness (EOT) scaling for Si complementary metal-oxide-semiconductor (CMOS) devices. This limitation is equally significant and limiting for Ge CMOS devices. Low-K Ge-based ITRs in Ge devices have also been shown to limit performance and reliability, particular for n-MOS field effect transistors. This article identifies the source of significant electron trapping at interfaces between n-Ge or inverted p-Ge, and Ge oxide, nitride and oxynitride ITRs. This is shown to be an interfacial band alignment issue in which native Ge ITRs have conduction band offset energies smaller than those of TM dielectrics, and trap electrons for negative Ge substrate bias. This article also describes a novel remote plasma processing approach for effectively eliminating any significant native Ge ITRs and using a plasma-processing/annealing process sequence for bonding TM gate dielectrics directly to the Ge substrate surface. DA - 2008/// PY - 2008/// DO - 10.1016/j.apsusc.2008.03.157 VL - 254 IS - 23 SP - 7933-7937 ER - TY - JOUR TI - Vortex ferroelectric domains AU - Gruverman, A. AU - Wu, D. AU - Fan, H. J. AU - Vrejoiu, I. AU - Alexe, M. AU - Harrison, R. J. AU - Scott, J. F. T2 - Journal of Physics. Condensed Matter DA - 2008/// PY - 2008/// VL - 20 IS - 34 ER - TY - JOUR TI - The potential and challenges of nanopore sequencing AU - Branton, Daniel AU - Deamer, David W. AU - Marziali, Andre AU - Bayley, Hagan AU - Benner, Steven A. AU - Butler, Thomas AU - Di Ventra, Massimiliano AU - Garaj, Slaven AU - Hibbs, Andrew AU - Huang, Xiaohua AU - Jovanovich, Stevan B. AU - Krstic, Predrag S. AU - Lindsay, Stuart AU - Ling, Xinsheng Sean AU - Mastrangelo, Carlos H. AU - Meller, Amit AU - Oliver, John S. AU - Pershin, Yuriy V. AU - Ramsey, J. Michael AU - Riehn, Robert AU - Soni, Gautam V. AU - Tabard-Cossa, Vincent AU - Wanunu, Meni AU - Wiggin, Matthew AU - Schloss, Jeffery A. T2 - NATURE BIOTECHNOLOGY AB - A nanopore-based device provides single-molecule detection and analytical capabilities that are achieved by electrophoretically driving molecules in solution through a nano-scale pore. The nanopore provides a highly confined space within which single nucleic acid polymers can be analyzed at high throughput by one of a variety of means, and the perfect processivity that can be enforced in a narrow pore ensures that the native order of the nucleobases in a polynucleotide is reflected in the sequence of signals that is detected. Kilobase length polymers (single-stranded genomic DNA or RNA) or small molecules (e.g., nucleosides) can be identified and characterized without amplification or labeling, a unique analytical capability that makes inexpensive, rapid DNA sequencing a possibility. Further research and development to overcome current challenges to nanopore identification of each successive nucleotide in a DNA strand offers the prospect of 'third generation' instruments that will sequence a diploid mammalian genome for approximately $1,000 in approximately 24 h. DA - 2008/10// PY - 2008/10// DO - 10.1038/nbt.1495 VL - 26 IS - 10 SP - 1146-1153 SN - 1546-1696 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-53649108801&partnerID=MN8TOARS ER - TY - JOUR TI - Supernova remnants at high energy AU - Reynolds, Stephen P. T2 - ANNUAL REVIEW OF ASTRONOMY AND ASTROPHYSICS AB - Many shell supernova remnants are now known to radiate synchrotron X-rays. Several objects have also been detected in TeV gamma rays. Nonthermal X-rays and gamma rays can be produced in shell remnants by extremely energetic ions and electrons due to decay of π 0 mesons produced in inelastic collisions between ions and thermal gas, or by electron synchrotron, bremsstrahlung, or inverse-Compton radiation. Thus observations at X-ray and gamma-ray wavelengths constrain the process of particle acceleration to high energies in the shock waves of supernova remnants. This review examines the relevant characteristics of Type Ia and core-collapse supernovae, the dynamics of their evolution through the Sedov blast-wave phase, the basic physics of diffusive shock acceleration, and the physics of the relevant radiative processes. It also reviews the current status of observations of shell remnants from X-rays to TeV gamma rays, and summarizes what we can learn about particle acceleration. DA - 2008/// PY - 2008/// DO - 10.1146/annurev.astro.46.060407.145237 VL - 46 SP - 89-126 SN - 0066-4146 KW - cosmic rays KW - gamma-ray sources KW - shock acceleration KW - X-ray sources ER - TY - JOUR TI - Nanodomain faceting in ferroelectrics AU - Scott, J. F. AU - Gruverman, A. AU - Wu, D. AU - Vrejoiu, I. AU - Alexe, M. T2 - Journal of Physics. Condensed Matter DA - 2008/// PY - 2008/// VL - 20 IS - 42 ER - TY - JOUR TI - Ground state energy at unitarity AU - Lee, Dean T2 - PHYSICAL REVIEW C AB - We consider two-component fermions on the lattice in the unitarity limit. This is an idealized limit of attractive fermions where the range of the interaction is zero and the scattering length is infinite. Using Euclidean time projection, we compute the ground state energy using four computationally different but physically identical auxiliary-field methods. The best performance is obtained using a bounded continuous auxiliary field and a nonlocal updating algorithm called the hybrid Monte Carlo. With this method, we calculate results for 10 and 14 fermions at lattice volumes ${4}^{3},{5}^{3},{6}^{3},{7}^{3},{8}^{3}$ and extrapolate to the continuum limit. For 10 fermions in a periodic cube, the ground state energy is $0.292(12)$ times the ground state energy for noninteracting fermions. For 14 fermions, the ratio is $0.329(5)$. DA - 2008/8// PY - 2008/8// DO - 10.1103/physrevc.78.024001 VL - 78 IS - 2 SP - SN - 1089-490X ER - TY - JOUR TI - Deformation of rotational structures in Kr-73 and Rb-74: Probing the additivity principle at triaxial shapes AU - Johnston-Theasby, F. AU - Afanasjev, A. V. AU - Andreoiu, C. AU - Austin, R. A. E. AU - Carpenter, M. P. AU - Dashdorj, D. AU - Freeman, S. J. AU - Garrett, P. E. AU - Greene, J. AU - Gorgen, A. AU - Jenkins, D. G. AU - Joshi, P. AU - Macchiavelli, A. O. AU - Moore, F. AU - Mukherjee, G. AU - Reviol, W. T2 - Physical Review. C, Nuclear Physics DA - 2008/// PY - 2008/// VL - 78 IS - 3 ER - TY - JOUR TI - BSSN in spherical symmetry AU - Brown, J. David T2 - CLASSICAL AND QUANTUM GRAVITY AB - The BSSN (Baumgarte–Shapiro–Shibata–Nakamura) formulation of the Einstein evolution equations is written in spherical symmetry. These equations can be used to address a number of technical and conceptual issues in numerical relativity in the context of a single Schwarzschild black hole. One of the benefits of spherical symmetry is that the numerical grid points can be tracked on a Kruskal–Szekeres diagram. Boundary conditions suitable for puncture evolution of a Schwarzschild black hole are presented. Several results are shown for puncture evolution using a fourth-order finite difference implementation of the equations. DA - 2008/10/21/ PY - 2008/10/21/ DO - 10.1088/0264-9381/25/20/205004 VL - 25 IS - 20 SP - SN - 1361-6382 UR - http://inspirehep.net/record/751519 ER - TY - JOUR TI - Tribological degradation of fluorocarbon coated silicon microdevice surfaces in normal and sliding contact AU - Hook, D. Adam AU - Timpe, Shannon J. AU - Dugger, Michael T. AU - Krim, Jacqueline T2 - Journal of Applied Physics AB - Reported here is a study of the tribological degradation of the contact interface of a fluorocarbon monolayer-coated polycrystalline silicon microdevice. A surface micromachined silicon tribometer is employed to track changes in the adhesion and friction properties during repetitive normal and sliding contacts. Evidence for tribological degradation commences immediately for parallel sliding contact motion, and is slightly delayed in the case of repetitive impact loading normal to the surface. The observed changes in interfacial behavior indicate dramatic changes in the chemical (i.e., surface energy) and physical (i.e., roughness, real contact area, etc.) nature of the contacting surfaces. Results from microscale sliding and impact experiments are interpreted in the light of the primary physical and chemical degradation mechanisms of monolayer-coated silicon microdevices. DA - 2008/8// PY - 2008/8// DO - 10.1063/1.2960567 VL - 104 IS - 3 SP - 034303 J2 - Journal of Applied Physics LA - en OP - SN - 0021-8979 1089-7550 UR - http://dx.doi.org/10.1063/1.2960567 DB - Crossref ER - TY - JOUR TI - Single molecule measurements with photoelectron emission microscopy AU - Kong, Xianhua AU - Rowe, J. E. AU - Nemanich, R. J. T2 - JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B AB - In this research, variable wavelength photoelectron emission microscopy (PEEM) with tunable UV light from the Duke University free electron laser is applied to image single fibrinogen molecules adsorbed onto n-type silicon surfaces. High resolution PEEM images (∼10nm) are obtained with photon energies from 4to6eV. Wavelength-dependent image sequences are analyzed to determine the photoionization spectrum and the photoelectron emission threshold of individual molecules. The experimental data are fitted using temperature dependent Fowler law, square-root law, and cube-root law. The details of the theoretical models are discussed. The square-root and cube-root fittings reveal the ionization threshold of 5.0eV for fibrinogen adsorbed onto n-type silicon, while temperature dependent Fowler law shows a threshold of 4.9eV. The accuracy of the measurements is calculated to be ±0.2eV. The authors conclude that no significant difference is observed from the three theoretical fitting approaches. DA - 2008/7// PY - 2008/7// DO - 10.1116/1.2932094 VL - 26 IS - 4 SP - 1461-1465 SN - 2166-2746 ER - TY - JOUR TI - The effect of lane-change maneuvers on a simplified car-following theory AU - Wang, Chao AU - Coifman, Benjamin T2 - IEEE TRANSACTIONS ON INTELLIGENT TRANSPORTATION SYSTEMS AB - This paper investigates the linearity of empirically observed spacing-speed relations for various drivers in the context of car-following theory and how lane-change maneuvers perturb the relation. It is shown that the impacts of lane-change maneuvers are not balanced, and the response time to an exiting vehicle is much longer than the response time to an entering vehicle. This accommodation imbalance will propagate upstream, and as discussed herein, it appears to be a source of speed and flow fluctuations (or oscillations) within a queue. This paper is motivated by Newell's simplified car-following theory, namely, that during congested periods, the trajectory of a given vehicle is essentially identical to the preceding vehicle's trajectory, except for a translation in space and time. One of the basic assumptions in Newell's presentation is that spacing and speed are linearly related. While other researchers have found macroscopic evidence supporting Newell's theory, they have also found that it fails in the presence of frequent lane-change maneuvers. This paper takes a microscopic approach, employing vehicle trajectory data. This paper provides support for Newell's assumed linear relation between spacing and speed over a large range of speeds when vehicles are not impacted by lane-change maneuvers. It also offers a possible explanation for the degraded performance of Newell's theory in the presence of heavy lane-change maneuvers. Although the focus is on Newell's simplified car-following theory, the empirical results of this paper have similar implications for many other car-following theories as well. DA - 2008/9// PY - 2008/9// DO - 10.1109/TITS.2008.928265 VL - 9 IS - 3 SP - 523-535 SN - 1558-0016 KW - car following KW - lane-change maneuvers KW - road transportation KW - traffic flow theory ER - TY - JOUR TI - Organizational structure and electronic decoupling of surface bound chiral domains and biomolecules AU - Santagata, Nancy M. AU - Luo, Pengshun AU - Lakhani, Amit M. AU - DeWitt, Darryl J. AU - Day, B. Scott AU - Norton, Michael L. AU - Pearl, Thomas P. T2 - IEEE SENSORS JOURNAL AB - For the development of reagentless biological and chemical species detection at the single molecule level using external fields, including terahertz radiation, it is paramount to study model systems that uncover how intermolecular and molecule-surface interactions dictate monolayer ordering and electronic properties. This paper addresses two types of molecule-surface interactions and two distinct molecular systems, both of which impact our fundamental understanding of confined molecular domains and single molecule detection. We will first discuss the ordering and electronic characteristics of a chiral molecule, tartaric acid , weakly bound to an achiral metal surface, Ag(111), as studied with low temperature scanning tunneling microscopy (STM). This particular molecule-surface system contains many key elements, including hydrogen bonding interactions and stereochemical features, that would be common to other functional detection schemes. This paper will also treat the characterization of isolated, thiolated DNA molecules chemically bound to Au(111) terraces. Ambient STM and atomic force microscopy (AFM) measurements of both short and long DNA structures in both single and double strand configurations will be discussed with particular attention paid to imaging mechanisms involved. These results are particularly relevant to systems involving biomolecules anchored to inert metal surfaces, such as those used in external field-based assays. DA - 2008/// PY - 2008/// DO - 10.1109/JSEN.2008.923187 VL - 8 IS - 5-6 SP - 758-766 SN - 1558-1748 KW - biomolecules KW - metals KW - microscopy KW - monolayer KW - surfaces ER - TY - JOUR TI - Nanosensors for defense and security AU - Woolard, Dwight L. AU - Trew, Robert J. AU - Polla, Dennis L. AU - Stroscio, Michael A. AU - Varshney, Usha AU - Jensen, Janet AU - Jensen, James O. AU - Lugli, Paolo O. AU - Aono, Masakazu T2 - IEEE SENSORS JOURNAL AB - The 59 articles in this special issue focus on nanosensors for defense and security. DA - 2008/// PY - 2008/// DO - 10.1109/jsen.2008.924436 VL - 8 IS - 5-6 SP - 641-646 SN - 1530-437X ER - TY - JOUR TI - Doping-Dependent Negative Differential Resistance in Hybrid Organic/Inorganic Si−Porphyrin−Si Junctions AU - Ribeiro, Filipe J. AU - Lu, Wenchang AU - Bernholc, Jerzy T2 - ACS Nano AB - Quantum transport properties of porphyrin-bridged p−n junctions with Si leads are investigated by ab initio calculations. It is shown that this system exhibits strong negative differential resistance (NDR) peaks, whose magnitude and position can be controlled by the doping levels of the leads and by changing the central transition metal atom of the porphyrin. These results are explained by bias-induced on−off switching of resonant tunneling channels associated with specific molecular orbitals. The predicted behavior is general and should be observable for other organic molecules bridging doped semiconducting leads. DA - 2008/7/11/ PY - 2008/7/11/ DO - 10.1021/nn800252b VL - 2 IS - 8 SP - 1517-1522 J2 - ACS Nano LA - en OP - SN - 1936-0851 1936-086X UR - http://dx.doi.org/10.1021/nn800252b DB - Crossref KW - porphyrin KW - quantum transport KW - negative differential resistance KW - silicon KW - doping ER - TY - JOUR TI - Reversible chemical phase separation in on-state of art ReWritable (RW) Ge2Sb2Te5 optical phase change memories AU - Lucovsky, Gerald AU - Phillips, James C. T2 - JOURNAL OF NON-CRYSTALLINE SOLIDS AB - Abstract Ge 2 Sb 2 Te 5 is one of the chalcogenide alloy materials of choice for ReWritable (RW) optical discs that are currently in manufacturing; however, there are many issues relating to the physics and chemistry underpinning the switching mechanism that have as yet to be resolved. This is paper identifies important relationships between the chemical bonding in the non-crystalline phase of Ge 2 Sb 2 Te 5 , and in the face-centered-cubic (FCC) nano-crystalline alloy phase that account for the markedly different optical and electrical properties that are enabling for memory applications. The non-crystalline material is characterized as an intermediate phase (IP) with minimal (i) bond-strain and (ii) extended macroscopic-strain, and includes a precursor bonding arrangement crucial to optical and electronic RW memories. The FCC phase has nano-crystallites trapped in a metastable diphasic composite that is stabilized by the inclusion of non-crystalline GeTe x ( x  ∼ 5) nano-clusters pinned at grain boundaries. DA - 2008/5/1/ PY - 2008/5/1/ DO - 10.1016/j.jnoncrysol.2007.09.059 VL - 354 IS - 19-25 SP - 2753-2756 SN - 0022-3093 KW - amorphous semiconductors KW - crystallization KW - synchrotron radiation KW - chalcogenides KW - laser-matter interactions KW - microcrystallinity KW - percolation KW - nano-clusters KW - nano-crystals KW - optical properties KW - reflectivity KW - defects KW - medium-range order KW - short-range order KW - glass transition ER - TY - JOUR TI - Relaxation of spin polarized He-3 in mixtures of He-3 and He-4 below the He-4 lambda point AU - Ye, Q. AU - Dutta, D. AU - Gao, H. AU - Kramer, K. AU - Qian, X. AU - Zong, X. AU - Hannelius, L. AU - McKeown, R. D. AU - Heyburn, B. AU - Singer, S. AU - Golub, R. AU - Korobkina, E. T2 - PHYSICAL REVIEW A AB - We report a first study of the depolarization behavior of spin polarized $^{3}\text{H}\text{e}$ in a mixture of $^{3}\text{H}\text{e-}^{4}\text{H}\text{e}$ at a temperature below the $^{4}\text{H}\text{e}$ $\ensuremath{\lambda}$ point in a deuterated tetraphenyl butadiene-doped deuterated polystyrene (dTPB-dPS) coated acrylic cell. In our experiment the measured $^{3}\text{H}\text{e}$ relaxation time is due to the convolution of the $^{3}\text{H}\text{e}$ longitudinal relaxation time, ${T}_{1}$, and the diffusion time constant of $^{3}\text{H}\text{e}$ in superfluid $^{4}\text{H}\text{e}$ since depolarization takes place on the walls. We have obtained a $^{3}\text{H}\text{e}$ relaxation time of $\ensuremath{\sim}3000\text{ }\text{s}$ at a temperature around 1.9 K. We have shown that it is possible to achieve values of wall depolarization probability on the order of $(1--2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$ for polarized $^{3}\text{H}\text{e}$ in the superfluid $^{4}\text{H}\text{e}$ from a dTPB-dPS coated acrylic surface. DA - 2008/5// PY - 2008/5// DO - 10.1103/physreva.77.053408 VL - 77 IS - 5 SP - SN - 1094-1622 ER - TY - JOUR TI - Quantitative organic and light-element analysis of comet 81P/Wild 2 particles using C-, N-, and O-mu-XANES AU - Cody, George D. AU - Ade, Harald AU - Alexander, Conel M. O'D. AU - Araki, Tohru AU - Butterworth, Anna AU - Fleckenstein, Holger AU - Flynn, George AU - Gilles, Mary K. AU - Jacobsen, Chris AU - Kilcoyne, A. L. D. AU - Messenger, Keiko AU - Sandford, Scott A. AU - Tyliszczak, Tolek AU - Westphal, Andrew J. AU - Wirick, Susan AU - Yabuta, Hikaru T2 - METEORITICS & PLANETARY SCIENCE AB - Abstract— Synchrotron‐based soft X‐ray micro‐analysis was performed on particles extracted from the Stardust aerogel collector in order to obtain detailed organic functional group information on any organic solids captured as part of the Principal Examination suite of analyses for samples from comet 81P/Wild 2. It is observed that cometary organic carbon captured in aerogel is present in a number of different manifestations and often intimately associated with silicates. Carbon X‐ray absorption near edge structure (XANES) spectra reveal considerable chemical complexity in all of the organic particles studied so far. Universally, the comet 81P/Wild 2 organic particles contain low concentrations of aromatic and/or olefinic carbon relative to aliphatic and heteroatom‐containing functional groups, e.g., amide, carboxyl, and alcohol/ethers. N‐XANES confirms the presence and assignments of these functional groups. In general, the XANES data record considerable chemical complexity across the range of organic samples currently analyzed. The atomic ratios, N/C and O/C, derived from XANES data reveal a wide range in heteroatom content; in all cases these elemental ratios are higher than that of primitive meteoritic organic matter. The wide range in chemistry, both in elemental abundances and specific organic functional groups, suggests that the comet 81P/Wild 2 organic solids may have multiple origins. DA - 2008/// PY - 2008/// DO - 10.1111/j.1945-5100.2008.tb00627.x VL - 43 IS - 1-2 SP - 353-365 SN - 1945-5100 ER - TY - JOUR TI - Length scale discontinuities between non-crystalline and nano-crystalline thin films: Chemical bonding self-organization, broken constraints and reductions of macroscopic strain AU - Lucovsky, G. AU - Phillips, J. C. T2 - Journal of Non-crystalline Solids DA - 2008/// PY - 2008/// DO - 10.1016/j.jnoncryso1.2007.09.044 VL - 354 IS - 19-25 SP - 2702-2705 ER - TY - JOUR TI - Electrostatics in biomolecular simulations: Where are we now and where are we heading? AU - Karttunen, Mikko AU - Rottler, Joerg AU - Vattulainen, Ilpo AU - Sagui, Celeste T2 - COMPUTATIONAL MODELING OF MEMBRANE BILAYERS AB - In this review, we discuss current methods and developments in the treatment of electrostatic interactions in biomolecular and soft matter simulations. We review the current ‘work horses’, namely, Ewald summation based methods such the Particle-Mesh Ewald, and others, and also newer real-space methods such as multigrid methods, and local algorithms for Coulomb's law. We also pay attention to boundary conditions. Although periodic boundary conditions are used most commonly, it is often desirable to have systems that are confined or have boundaries. Finally, we briefly describe some current and available software for the computation of electrostatics in biomolecular and soft matter simulations. DA - 2008/// PY - 2008/// DO - 10.1016/s1063-5823(08)00002-1 VL - 60 SP - 49-89 SN - 1063-5823 ER - TY - JOUR TI - Electrical conductivity and Meyer-Neldel rule: The role of localized states in hydrogenated amorphous silicon AU - Abtew, T. A. AU - Zhang, MingLiang AU - Pan, Yue AU - Drabold, D. A. T2 - JOURNAL OF NON-CRYSTALLINE SOLIDS AB - The Meyer–Neldel rule (MNR) has been observed in recent calculations of the electrical conductivity of hydrogenated amorphous silicon. To elucidate the origin of this effect, we have performed comparative studies on crystalline Si and non-hydrogenated a-Si. We find that the MNR is not present in the crystal, and is present in a-Si. This suggests that the existence of localized states and the energy dependence of the electron-lattice coupling for these states is an essential feature of the MNR for amorphous phases of silicon. DA - 2008/5/1/ PY - 2008/5/1/ DO - 10.1016/j.jnoncrysol.2007.09.103 VL - 354 IS - 19-25 SP - 2909-2913 SN - 1873-4812 KW - silicon KW - conductivity ER - TY - JOUR TI - Defect scaling in non-crystalline floppy/under-constrained and rigid/over-constrained thin films: Applications to a-Se, a-Si, and a-Si(H) AU - Lucovsky, Gerald AU - Kasap, Safa O. AU - Phillips, James C. T2 - JOURNAL OF NON-CRYSTALLINE SOLIDS AB - Bond constraint theory provides insights into glass and intermediate phase formation in covalently-bonded non-crystalline networks. Metrics are the average number of bonds/atom, Nav, and average number of bending and stretching constraints per atom, Cav. Cav is a linear function of Nav:Cav = 2.5Nav − 3, with ideal, low defect density glasses and thin films having values of Nav and Cav equal to 2.4, and 3.0, respectively. In over-constrained films, it has been argued and demonstrated experimentally, that the density of intrinsic defects is proportional to Nav − 2.4. In this paper we demonstrate that this scaling relationship, with the same empirical constants applies to floppy or under-constrained films with the example being a-Se where Nav has been determined from EXAFS studies and is ∼2.2. In addition we demonstrate that the density of defects in as deposited a-Si with a 6% density deficit, and broken bonding constraints, can be treated in the same way as spacing–filling over-constrained networks. DA - 2008/5/1/ PY - 2008/5/1/ DO - 10.1016/j.jnoncrysol.2007.09.048 VL - 354 IS - 19-25 SP - 2724-2727 SN - 1873-4812 KW - amorphous semiconductors KW - silicon KW - thin film transistors KW - nanocrystals KW - synchrotron radiation KW - UPS/XPS KW - glass transition KW - oxynitride glasses KW - chalcogenides KW - defects KW - nano-clusters KW - silica KW - medium-range order KW - short-range order ER - TY - JOUR TI - Bond constraint theory studies of chalcogenide phase change memories AU - Paesler, M. A. AU - Baker, D. A. AU - Lucovsky, G. T2 - Journal of Non-crystalline Solids DA - 2008/// PY - 2008/// DO - 10.1016/j.jnoncryso1.2007.09.045 VL - 354 IS - 19-25 SP - 2706-2710 ER - TY - JOUR TI - Thermal annealing effects on the atomic layer deposited LaAlO3 thin films on Si substrate AU - Eom, Dail AU - Hwang, Cheol Seong AU - Kim, Hyeong Joon AU - Cho, Mann-Ho AU - Chung, K. B. T2 - ELECTROCHEMICAL AND SOLID STATE LETTERS AB - The changes in film structure of amorphous atomic layer deposited thin films after thermal annealing were examined by medium-energy ion-scattering measurements and angle-resolved X-ray photoelectron spectroscopy. Thermal annealing induces Si-rich LaSiO and Al-deficient layers on a few monolayers of . Al atoms do not participate in silicate formation during annealing. Instead, they migrate toward the film surface, which induces nonhomogeneity in the films along the vertical direction. The concentrations of Al and La on the film surface increase and decrease, respectively, as a result of Si diffusion from the substrate and silicate formation. DA - 2008/// PY - 2008/// DO - 10.1149/1.2916437 VL - 11 IS - 7 SP - G33-G36 SN - 1944-8775 ER - TY - JOUR TI - Structure of submonolayer oleic acid coverages on inorganic aerosol particles: evidence of island formation AU - Garland, Eva R. AU - Rosen, Elias P. AU - Clarke, Laura I. AU - Baer, Tomas T2 - PHYSICAL CHEMISTRY CHEMICAL PHYSICS AB - A series of submonolayer deposition studies of oleic acid on both hydrophobic and hydrophilic surfaces has shown that oleic acid self-associates into islands rather than uniformly covering the surfaces. The studies were performed by vapor deposition on 1.6 μm diameter polystyrene aerosol particles as well as on polystyrene and silica surfaces. The surfaces were investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), ellipsometry and contact-angle goniometry. After timescales of minutes to hours of vapor deposition at 70 °C, the oleic acid arranged itself in the form of islands with diameters of about 100 nm. Many of the islands are 25–30 Å high, suggesting that the oleic acid sits vertically on the surface. The surface structure of oleic acid on particles is expected to impact on several atmospherically relevant properties such as the reactivity of the oleic acid and the hygroscopicity of the particles. DA - 2008/// PY - 2008/// DO - 10.1039/b718013f VL - 10 IS - 21 SP - 3156-3161 SN - 1463-9084 ER - TY - JOUR TI - Precipitation and delamination of crystalline graphite bubbles from molten iron, nickel and cobalt by splat cooling AU - Winder, S. M. AU - Bender, J. W. T2 - Carbon AB - Nearly ideal graphite crystals have been precipitated from molten transition metals for several decades. Curved crystals of graphite have recently been synthesized by precipitation of dissolved carbon from millimeter-scale drops of molten iron, nickel and cobalt, under high vacuum. The surface of a small molten metal drop provides a convenient template for curved graphite crystal growth. When graphite-encapsulated molten metal is splat-cooled in situ, free-standing crystalline graphite membranes spontaneously form. Some of these graphite membranes are spherical bubbles with diameter exceeding 100 μm and thickness on the order of 10 nm. We propose that the curved membranes are inverted replicas of pits in the parent metal. Splat-cooled samples are characterized by SEM, AFM and Raman spectroscopy. Gradually cooled samples are characterized by XRD. DA - 2008/// PY - 2008/// DO - 10.1016/j.carbon.2008.02.023 VL - 46 IS - 6 SP - 940-948 ER - TY - JOUR TI - Model dielectric functions for AlxGa1-xAs alloys of arbitrary compositions AU - Jung, Y. W. AU - Kim, T. J. AU - Yoon, J. J. AU - Kim, Y. D. AU - Aspnes, D. E. T2 - JOURNAL OF APPLIED PHYSICS AB - Many optical models have been used to construct analytic composition-dependent dielectric functions of AlxGa1−xAs alloys. However, these models incorporate various unphysical assumptions to improve their fits to data. Here, we provide the parameters needed to calculate dielectric functions of AlxGa1−xAs for 1.5≤E≤6.0 eV and 0≤x≤1 by means of the parametric model of Johs et al. [Thin Solid Films 313–314, 137 (1998)], which eliminates these problems. A representative example concerning interface analysis is discussed, where it is necessary to construct a dielectric function of an alloy of essentially arbitrary composition. DA - 2008/7/1/ PY - 2008/7/1/ DO - 10.1063/1.2952536 VL - 104 IS - 1 SP - SN - 1089-7550 ER - TY - JOUR TI - Meson and tetra-quark mixing AU - Wang, Ping AU - Cotanch, Stephen R. AU - General, Ignacio J. T2 - EUROPEAN PHYSICAL JOURNAL C AB - The mixing between qq̄ meson and qq̄qq̄ tetra-quark states is examined within an effective QCD Coulomb gauge Hamiltonian model. Mixing matrix elements of the Hamiltonian are computed and then diagonalized yielding an improved prediction for the low-lying JPC=0±+,1– isoscalar spectra. Mixing effects were found significant for the scalar hadrons but not for the 1– states, which is consistent with the ideal mixing of vector mesons. A perturbative assessment of the exact QCD kernel is also reported. DA - 2008/6// PY - 2008/6// DO - 10.1140/epjc/s10052-008-0605-7 VL - 55 IS - 3 SP - 409-415 SN - 1434-6044 ER - TY - JOUR TI - Dependence of plasmon polaritons on the thickness of indium tin oxide thin films AU - Rhodes, C. AU - Cerruti, M. AU - Efremenko, A. AU - Losego, M. AU - Aspnes, D. E. AU - Maria, J.-P. AU - Franzen, S. T2 - Journal of Applied Physics AB - The evolution of polariton features with increasing thickness in p-polarized (TM) reflectance spectra of indium tin oxide (ITO) thin films deposited on BK7 glass reveals the nature of plasmons in conducting thin films without interference from band-to-band transitions or the tendency of very thin films to form islands, both of which are complicating factors with the noble metals Au and Ag. Although the dependence on energy, film thickness, and angle of incidence is complex, these features are accurately described by the three-phase (substrate/overlayer/ambient) Fresnel model using only the Drude free-electron representation for the dielectric function of the ITO film. For film thicknesses less than 80nm the relevant excitation is a one-dimensional screened-bulk plasmon (SBP) that corresponds to charge transfer across the entire film. The associated SBP polariton (SBPP) occurs at the energy of the SBP and is relatively independent of the angle of incidence. For film thicknesses greater than 120nm, the relevant excitation is the surface plasmons (SP). The associated surface plasmon polariton (SPP) exhibits the usual strong dependence of energy on the angle of incidence. For larger thicknesses this structure gradually weakens, in agreement with theory. No other collective excitations are observed. The optimum thicknesses for the SPP in ITO is 160nm, whereas the SBPP is observed only when the film thickness is less than 70nm. The SBPP exhibits many of the features that make the SPP attractive for both science and technology, but has not been observed previously. Our results show that ITO films, in particular, and conducting-metal-oxide films in general provide new opportunities for investigating plasmons in conductors and obtaining new insights into plasmons, plasmon polaritons, and related optical phenomena. DA - 2008/5// PY - 2008/5// DO - 10.1063/1.2908862 VL - 103 IS - 9 SP - 093108 J2 - Journal of Applied Physics LA - en OP - SN - 0021-8979 1089-7550 UR - http://dx.doi.org/10.1063/1.2908862 DB - Crossref ER - TY - JOUR TI - Change in the interfacial reaction of Hf-silicate film as a function of thickness and stoichiometry AU - Cho, M. -H. AU - Kim, C. Y. AU - Moon, K. AU - Chung, K. B. AU - Yim, C. J. AU - Ko, D. -H. AU - Sohn, H. C. AU - Jeon, Hyeongtag T2 - JOURNAL OF CHEMICAL PHYSICS AB - Medium energy ion scattering and high-resolution transmission electron microscopy are used to investigate the depth of the interfacial reaction of Hf-silicate film. The interfacial reaction is critically affected by the film thickness and the mole fraction of HfO(2) in silicate film. The interfacial compressive strain generated at the surface of the Si substrate is dependent on the film thickness during the postannealing process in film with a thickness of approximately 4 nm. Finally, the phase separation phenomenon demonstrates critically different behaviors at different film thicknesses and stoichiometries because the diffusion of Si from interface to surface is dependent on these factors. Moreover, the oxidation by oxygen impurity in the inert ambient causes SiO(2) top formation. DA - 2008/7/21/ PY - 2008/7/21/ DO - 10.1063/1.2955461 VL - 129 IS - 3 SP - SN - 0021-9606 ER - TY - JOUR TI - Catalytic role of carbons in methane decomposition for CO- and CO(2)-free hydrogen generation AU - Huang, Liping AU - Santiso, Erik E. AU - Nardelli, Marco Buongiorno AU - Gubbins, Keith E. T2 - JOURNAL OF CHEMICAL PHYSICS AB - Decomposition of methane is an environmentally attractive approach to CO- and CO(2)-free hydrogen production. Using first principles calculations at the density functional theory level, our studies demonstrate that the defective carbons can be used as catalysts for methane decomposition, without the need for other catalysts, such as transition metals or oxides, and the catalytic sites can be regenerated by the deposition of carbon decomposed from methane, to make the hydrogen production a continuous process. Additionally, since no other gases are produced in the process, the cost of CO(2) sequestration and hydrogen purification from CO contamination will be dramatically reduced. DA - 2008/6/7/ PY - 2008/6/7/ DO - 10.1063/1.2931456 VL - 128 IS - 21 SP - SN - 0021-9606 ER - TY - JOUR TI - r-process nucleosynthesis in hot accretion disk flows from black hole-neutron star mergers AU - Surman, R. AU - McLaughlin, G. C. AU - Ruffert, M. AU - Janka, H. T. AU - Hix, W. R. T2 - Astrophysical Journal Letters AB - We consider hot accretion disk outflows from black hole - neutron star mergers in the context of the nucleosynthesis they produce. We begin with a three dimensional numerical model of a black hole - neutron star merger and calculate the neutrino and antineutrino fluxes emitted from the resulting accretion disk. We then follow the element synthesis in material outflowing the disk along parameterized trajectories. We find that at least a weak r-process is produced, and in some cases a main r-process as well. The neutron-rich conditions required for this production of r-process nuclei stem directly from the interactions of the neutrinos emitted by the disk with the free neutrons and protons in the outflow. DA - 2008/// PY - 2008/// DO - 10.1086/589507 VL - 679 IS - 2 SP - L117-120 ER - TY - JOUR TI - Untangling supernova-neutrino oscillations with beta-beam data AU - Jachowicz, N. AU - McLaughlin, G. C. AU - Volpe, C. T2 - PHYSICAL REVIEW C AB - Recently, we suggested that low-energy \ensuremath{\beta}-beam neutrinos can be very useful for the study of supernova-neutrino interactions. In this article, we examine the use of a such experiment for the analysis of a supernova-neutrino signal. Because supernova neutrinos are oscillating, it is very likely that the terrestrial spectrum of supernova neutrinos of a given flavor will not be the same as the energy distribution with which these neutrinos were first emitted. We demonstrate the efficacy of the proposed method for untangling multiple neutrino spectra. This is an essential feature of any model aiming at gaining information about the supernova mechanism, probing proto-neutron star physics, and understanding supernova nucleosynthesis, such as the neutrino process and the r-process. We also consider the efficacy of different experimental approaches including measurements at multiple beam energies and detector configurations. DA - 2008/5// PY - 2008/5// DO - 10.1103/physrevc.77.055501 VL - 77 IS - 5 SP - SN - 1089-490X ER - TY - JOUR TI - Two-step gamma cascades following thermal neutron capture in Mo-95 AU - Krticka, M. AU - Becvar, F. AU - Tomandl, I. AU - Rusev, G. AU - Agvaanluvsan, U. AU - Mitchell, G. E. T2 - PHYSICAL REVIEW C AB - A strong enhancement of the photon strength function at low \ensuremath{\gamma}-ray energies was recently reported for several Mo isotopes. To study this enhancement further we have measured the spectra of two-step \ensuremath{\gamma} cascades following thermal neutron capture in $^{95}\mathrm{Mo}$. These spectra were compared with simulations of the \ensuremath{\gamma} decay of $^{96}\mathrm{Mo}$ performed with the aid of the dicebox algorithm. Simulations with a large number of model combinations of photon strength functions for $E1,M1,$ and $E2$ radiation are not consistent with the strong enhancement observed in the $^{96}\mathrm{Mo}$($^{3}\mathrm{He}$,$^{3}\mathrm{He}$${}^{'}\ensuremath{\gamma}$)$^{96}\mathrm{Mo}$ and $^{97}\mathrm{Mo}$($^{3}\mathrm{He}$,$\ensuremath{\alpha}\ensuremath{\gamma})$$^{96}\mathrm{Mo}$ reactions. Predictions based on a combination of $E1,M1,$ and $E2$ photon strength functions with no enhancement of the photon strength functions at low \ensuremath{\gamma}-ray energies are in good agreement with the two-step \ensuremath{\gamma} cascade data. DA - 2008/5// PY - 2008/5// DO - 10.1103/physrevc.77.054319 VL - 77 IS - 5 SP - SN - 1089-490X ER - TY - JOUR TI - Thermal neutron capture cross sections of the palladium isotopes AU - Krticka, M. AU - Firestone, R. B. AU - McNabb, D. P. AU - Sleaford, B. AU - Agvaanluvsan, U. AU - Belgya, T. AU - Revay, Z. S. T2 - PHYSICAL REVIEW C AB - Precise thermal neutron capture \ensuremath{\gamma}-ray cross sections ${\ensuremath{\sigma}}_{\ensuremath{\gamma}}$ were measured for all elements with $Z=1\text{\ensuremath{-}}83,90$, and 92, except for He and Pm, at the Budapest Reactor. These data were evaluated with additional information from the literature to generate the Evaluated Gamma-ray Activation File (EGAF). Isotopic radiative neutron cross sections can be deduced from the total transition cross section feeding the ground state, ${\ensuremath{\sigma}}_{0}=\ensuremath{\Sigma}{\ensuremath{\sigma}}_{\ensuremath{\gamma}}(\mathrm{GS})$ if the decay scheme is complete. The EGAF file contains partial \ensuremath{\gamma}-ray cross sections for all stable palladium isotopes. None of these decay schemes are complete, although in each case transitions de-exciting low-lying levels are known. We have performed Monte Carlo simulations of the palladium thermal neutron capture decay schemes using the computer code DICEBOX. The simulated populations of low low-lying levels are normalized to the measured ${\ensuremath{\sigma}}_{\ensuremath{\gamma}}$ values from EGAF and the total radiative neutron cross section ${\ensuremath{\sigma}}_{0}$ is obtained. The ${\ensuremath{\sigma}}_{0}$ values derived for the palladium isotopes agree well with previous measurements and were in several cases more precise. Complementary use of \ensuremath{\gamma}-ray cross-section data and Monte Carlo calculations has proven effective in determining both the palladium total radiative cross sections and new nuclear structure information. DA - 2008/5// PY - 2008/5// DO - 10.1103/physrevc.77.054615 VL - 77 IS - 5 SP - SN - 1089-490X ER - TY - JOUR TI - The youngest Galactic supernova remnant: G1.9+0.3 AU - Reynolds, Stephen P. AU - Borkowski, Kazimierz J. AU - Green, David A. AU - Hwang, Una AU - Harrus, Ilana AU - Petre, Robert T2 - ASTROPHYSICAL JOURNAL LETTERS AB - Our 50 ks Chandra observation of the small radio supernova remnant (SNR) G1.9+0.3 shows a complete shell structure with strong bilateral symmetry, about 100'' in diameter. The radio morphology is also shell-like, but only about 84'' in diameter, based on observations made in 1985. We attribute the size difference to expansion between 1985 and our Chandra observations of 2007. Expansion is confirmed in comparing radio images from 1985 and 2008. We deduce that G1.9+0.3 is of order 100 years old—the youngest supernova remnant in the Galaxy. Based on a very high absorbing column density of 5.5 × 1022 cm−2, we place G1.9+0.3 near the Galactic center, at a distance of about 8.5 kpc, where the mean remnant radius would be about 2 pc, and the required expansion speed about 14,000 km s−1. The X-ray spectrum is featureless and well described by the exponentially cut off synchrotron model srcut. With the radio flux at 1 GHz fixed at 0.9 Jy, we find a spectral index of 0.65 and a rolloff frequency of 1.4 × 1018 Hz. The implied characteristic rolloff electron energy of about 94(B/10 μ G)−1/2 TeV is the highest ever reported for a shell supernova remnant. It can easily be reached by standard diffusive shock acceleration, given the very high shock velocities; it can be well described by either age-limited or synchrotron-loss-limited acceleration. Not only is G1.9+0.3 the youngest known Galactic remnant, it is also only the fourth Galactic X-ray-synchrotron-dominated shell supernova remnant. DA - 2008/6/10/ PY - 2008/6/10/ DO - 10.1086/589570 VL - 680 IS - 1 SP - L41-L44 KW - acceleration of particles KW - ISM : individual (G1.9+0.3) KW - supernova remnants KW - supernovae : general KW - X-rays : ISM ER - TY - JOUR TI - The nearly aligned rotating-monoplate compensator AU - Asar, M. AU - Aspnes, D. E. T2 - PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE AB - Abstract A rotating‐compensator polarimeter with a misaligned monoplate compensator generates first, third, and fifth harmonics as well as the zeroth (dc), second, and fourth harmonics that provide information about the sample. We outline a general procedure for calculating the detected intensity with mis‐ aligned components, then provide some results where multiple internal reflections in the component are ignored. The analysis involves several orders of tensors, and a quartic secular equation instead of the usual quadratic of a quadratic. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) DA - 2008/4// PY - 2008/4// DO - 10.1002/pssa.200777871 VL - 205 IS - 4 SP - 739-742 SN - 1862-6300 ER - TY - JOUR TI - The anisotropic bond model of nonlinear optics AU - Adles, E. J. AU - Aspnes, D. E. T2 - physica status solidi (a) AB - Abstract The anisotropic‐bond model (ABM) of nonlinear optics (NLO) provides a simple means of calculating NLO properties of materials by factoring the problem into four parts: first, determination of the local field at a bond‐charge site; second, solution of the anharmonic force equation of the bond charge; third, calculation of the radiation from the charge; and fourth, superposition of the radiation from all charges. Because this factorization is impossible in linear optics, this is one of the few cases where a nonlinear problem is simpler than its linear equivalent. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) DA - 2008/4// PY - 2008/4// DO - 10.1002/pssa.200777846 VL - 205 IS - 4 SP - 728-731 J2 - phys. stat. sol. (a) LA - en OP - SN - 1862-6300 1862-6319 UR - http://dx.doi.org/10.1002/pssa.200777846 DB - Crossref ER - TY - JOUR TI - Temperature dependence of single-asperity diamond-diamond friction elucidated using AFM and MD Simulations AU - Brukman, Matthew J. AU - Gao, Guangtu AU - Nemanich, Robert J. AU - Harrison, Judith A. T2 - JOURNAL OF PHYSICAL CHEMISTRY C AB - Complementary experimental (atomic force microscopy) and theoretical (molecular dynamics) techniques were used to investigate friction between diamond−diamond junctions as a function of temperature. The simulation and experimental conditions were designed to correspond as closely as possible. In the atomic force microscopy (AFM) experiments, two microcrystalline-diamond (μCD) AFM tips of differing contact radii were used to examine the friction of diamond (111) and (001) single crystals from 24 to 225 K in an ultrahigh vacuum. At all temperatures, the experimentally determined dependence of friction on load was consistent with the occurrence of single-asperity interfacial friction, where friction is proportional to contact area. In addition, the behavior of the contact was fit well by the Derjaguin−Muller−Toporov continuum model. Friction measurements within a given series were highly repeatable; however, as is typical with AFM measurements, there was some variation in measurements taken from different regions of the sample and with different tips. Interfacial shear strength, or the intrinsic resistance to sliding, decreased slightly with increasing temperature for both surfaces. To shed additional insight into the AFM results, MD simulations were performed with the diamond single crystals of the same orientation. The calculations also show that the average friction force decreased slightly as the temperature increased for both diamond surfaces and for all sliding directions. Both AFM and MD results agree with the numerical analysis of friction as a function of temperature published by Sang et al. (Sang, Y.; Dube, M.; Grant, M. Phys. Rev. Lett. 2001, 87, 174301). DA - 2008/6/26/ PY - 2008/6/26/ DO - 10.1021/jp711959e VL - 112 IS - 25 SP - 9358-9369 SN - 1932-7455 ER - TY - JOUR TI - Search for intrinsic collective excitations in Sm-152 AU - Kulp, W. D. AU - Wood, J. L. AU - Garrett, P. E. AU - Wu, C. Y. AU - Cline, D. AU - Allmond, J. M. AU - Bandyopadhyay, D. AU - Dashdorj, D. AU - Choudry, S. N. AU - Hayes, A. B. AU - Hua, H. AU - Mynk, M. G. AU - McEllistrem, M. T. AU - McKay, C. J. AU - Orce, J. N. AU - Teng, R. AU - Yates, S. W. T2 - Physical Review. C, Nuclear Physics DA - 2008/// PY - 2008/// VL - 77 IS - 6 ER - TY - JOUR TI - Run-in behavior of nanocrystalline diamond coatings studied by in situ tribometry AU - Chromik, Richard. R. AU - Winfrey, A. Leigh AU - Luening, Jan AU - Nemanich, Robert J. AU - Wahl, Kathryn J. T2 - WEAR AB - The friction performance of nanocrystalline diamond coatings was evaluated using in situ tribometry with sapphire counterfaces. Coatings were grown by microwave plasma assisted chemical vapor deposition in an Ar–H–CH4 plasma, with H ranging from 0 to 36%. In situ examination of the sliding contact, combined with ex situ analysis of the sapphire counterface revealed that the velocity accommodation mode was interfacial sliding of a carbonaceous transfer film versus the coating wear track. For most tests, the contact diameter increased during the first 50 sliding cycles and then remained constant. The in situ measure of the contact diameter was found to correlate confidently to ex situ measurements of counterface wear. The performance of the diamond coatings, characterized by quick run-in to low friction was best when a small but detectable graphite peak was present in the X-ray diffraction (XRD) profile. The relative intensity of the XRD graphite peak was also found to directly correlate with the peak position of the C1s → π* transition as measured by near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Increasing the relative amount of graphite-bonded sp2 carbon in the NCD films decreased run-in cycles to low friction. DA - 2008/7/31/ PY - 2008/7/31/ DO - 10.1016/j.wear.2007.11.023 VL - 265 IS - 3-4 SP - 477-489 SN - 1873-2577 KW - diamond KW - friction KW - nanocrystalline diamond KW - in situ tribometry KW - wear KW - NEXAFS ER - TY - JOUR TI - Recent developments and applications of the real-space multigrid method AU - Bernholc, J AU - Hodak, Miroslav AU - Lu, Wenchang T2 - Journal of Physics: Condensed Matter AB - The salient features of the real-space multigrid method and its recent applications are described. This method is suitable for very large scale, massively parallel calculations of atomic and electronic structure, as well as quantum molecular dynamics. Its nearly O(N) implementation provides a compact, variationally optimized basis that is also very useful for fully O(N) calculations of quantum transport. Recently, we also developed a hybrid method for simulating biomolecules in solution, in which most of the solvent is inexpensively treated using an approximate density-functional method, while the biomolecule and its first solvation shells are described at the full Kohn–Sham level. Our calculations show excellent parallel efficiency and scaling on massively parallel supercomputers. DA - 2008/6/24/ PY - 2008/6/24/ DO - 10.1088/0953-8984/20/29/294205 VL - 20 IS - 29 SP - 294205 J2 - J. Phys.: Condens. Matter OP - SN - 0953-8984 1361-648X UR - http://dx.doi.org/10.1088/0953-8984/20/29/294205 DB - Crossref ER - TY - JOUR TI - Photoinduced dissociation of water and transport of hydrogen between silver clusters AU - Zhang, Yu AU - Whitten, Jerry L. T2 - JOURNAL OF PHYSICAL CHEMISTRY A AB - Theoretical electronic structure calculations are reported for the dissociation of water adsorbed on a 31-atom silver cluster, Ag31, and subsequent transfer of a H to a second Ag31 cluster leaving OH on the first cluster. Both ground and excited electronic state processes are considered for two choices of Ag cluster separation, 6.35 and 7.94 A, on the basis of preliminary calculations for a range of separation distances. The excited electronic state of interest is formed by photoemission of an electron from one Ag cluster and transient attachment of the photoemitted electron to the adsorbed water molecule. A very large energy barrier is found for the ground-state process (3.53 eV at a cluster separation of 6.35 A), while the barrier in the excited state is small (0.38 eV at a cluster separation of 6.35 A). In the excited state, partial occupancy of an OH antibonding orbital facilitates OH stretch and concomitant movement of the negatively charged OH toward the electron-hole in the metal cluster. The excited-state pathway for dissociation of water and transfer of H begins with the formation of an excited electronic state at 3.59-3.82 eV. Stretch of the OH bond occurs with little change in energy (0.38-0.54 eV up to a stretch of 1.96 A). In this region of OH stretch the molecule must return to the ground-state potential energy surface to fully dissociate and to transfer H to the other Ag cluster. Geometry optimizations are carried out using a simplex algorithm and a semigrid method. These methods allow the total energy to be calculated directly using configuration interaction theory. DA - 2008/7/17/ PY - 2008/7/17/ DO - 10.1021/jp800528j VL - 112 IS - 28 SP - 6358-6363 SN - 1089-5639 ER - TY - JOUR TI - Measurement of the Am-241(n, 2n) reaction cross section from 7.6 MeV to 14.5 MeV AU - Tonchev, A. P. AU - Angell, C. T. AU - Boswell, M. AU - Crowell, A. S. AU - Fallin, B. AU - Hammond, S. AU - Howell, C. R. AU - Hutcheson, A. AU - Karwowski, H. J. AU - Kelley, J. H. AU - Pedroni, R. S. AU - Tornow, W. AU - Becker, J. A. AU - Dashdorj, D. AU - Kenneally, J. AU - Macri, R. A. AU - Stoyer, M. A. AU - al, T2 - Physical Review. C, Nuclear Physics DA - 2008/// PY - 2008/// VL - 77 IS - 5 ER - TY - JOUR TI - Interface phase and tuning of polarization in metal-ferroelectric junctions: A theoretical study AU - Nunez, M. AU - Nardelli, M. B. T2 - Applied Physics Letters DA - 2008/// PY - 2008/// VL - 92 IS - 25 ER - TY - JOUR TI - Gas adsorption on a C-60 monolayer AU - Trasca, R. A. AU - Cole, M. W. AU - Coffey, T. AU - Krim, J. T2 - PHYSICAL REVIEW E AB - The adsorption geometry of various gases on top of a ${\text{C}}_{60}$ monolayer is investigated. The potential energy experienced by an adsorbate atom in the vicinity of a ${\text{C}}_{60}$ molecule consists of Lennard-Jones interactions integrated over the spherical surface of the molecule. The adsorption potential exhibits strongly attractive sites which lead to a commensurate phase. The next adsorption sites are assumed on the basis of the symmetries of the triangular ${\text{C}}_{60}$ array. The competition between different adsorption phases is solved by energy minimization. The onset pressure of each phase is computed and compared with experimental data for Kr on top of a ${\text{C}}_{60}$ monolayer. DA - 2008/4// PY - 2008/4// DO - 10.1103/physreve.77.041603 VL - 77 IS - 4 SP - SN - 1550-2376 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-42449113449&partnerID=MN8TOARS ER - TY - JOUR TI - Euclidean correlation functions in a holographic model of QCD AU - Schäfer, Thomas T2 - Phys.Rev.D AB - We compute Euclidean coordinate space correlation functions in a holographic model of QCD. We concentrate, in particular, on channels that are related to the $U(1{)}_{A}$ problem, the flavor-singlet axial vector, pseudoscalar meson, and pseudoscalar glueball (topological charge) correlator. We find that even a very simple holographic model defined on a slice of five-dimensional anti-de Sitter space provides a qualitatively correct description of QCD correlation functions. We study the role of anomaly terms, and show that both Euclidean positivity and low energy theorems based on the axial anomaly relation are correctly implemented. We compare the results with expectations from an instanton model of the QCD vacuum. DA - 2008/11// PY - 2008/11// DO - 10.1103/PhysRevD.77.126010 VL - 77 IS - 12 SP - 126010 UR - http://inspirehep.net/record/766482 ER - TY - JOUR TI - Equivalence of dipole correction and Coulomb cutoff techniques in supercell calculations AU - Yu, Liping AU - Ranjan, V. AU - Lu, W. AU - Bernholc, J. AU - Nardelli, M. Buongiorno T2 - PHYSICAL REVIEW B AB - In ab initio calculations of surfaces or nonperiodic systems, one frequently relies on the supercell approximation, where the periodic replicas of the system are separated by enough empty space to avoid spurious interactions between the successive images. However, a vacuum separation is not sufficient to screen the dipolar interaction that appears in asymmetrically charged or polar systems. The dipole correction and Coulomb cutoff methods are often used to eliminate such interactions between the periodic replicas. In this work, these methods are compared under the same conditions in the framework of plane-wave based density-functional theory. The dipole correction method is shown to be equivalent to the rigorous Coulomb cutoff formalism in the calculations of total energy, force, charge density, and self-consistent potential. We demonstrate that the band structures obtained by these methods coincide for the localized bound states and that the corrections have essentially no influence on the occupied energy bands, only substantially affecting the unoccupied bands. By comparing the results of the two methods, the localized bound states of interest can be easily distinguished from the highly delocalized unoccupied states using a relatively small supercell. This comparison offers substantial savings in the computational time when ascertaining convergence with supercell size. The accuracy of the dipole correction method is also confirmed by comparing the results for a model ferroelectric ${\text{BaTiO}}_{3}$ slab with a Berry-phase calculation of polarization for the bulk system. DA - 2008/6// PY - 2008/6// DO - 10.1103/physrevb.77.245102 VL - 77 IS - 24 SP - SN - 1098-0121 ER - TY - JOUR TI - Dielectric properties of InAsP alloy thin films and evaluation of direct- and reciprocal-space methods of determining critical-point parameters AU - Choi, S. G. AU - Aspnes, D. E. AU - Stoute, N. A. AU - Kim, Y. D. AU - Kim, H. J. AU - Chang, Y. -C. AU - Palmstrom, C. J. T2 - PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE AB - Abstract Spectroscopic ellipsometry is used to determine pseudodielectric function spectra 〈 ε 〉 = 〈 ε 1 〈 + i 〈 ε 2 〈 of InAs x P 1– x al‐loy thin films from 1.5 to 6.0 eV at room temperature. The structures for the E 1 , E 1 + Δ 1 , E ′ 0 , E 2 , and E ′ 2 critical points (CPs) were observed in the data. We compare direct‐ and reciprocal‐space methods of extracting CP energies E g . The direct‐space values show less uncertainty, a result of how the two procedures use available information. Energies obtained are compared with the results of theoretical calculations using the linear augmented Slater‐type orbital (LASTO) method. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) DA - 2008/4// PY - 2008/4// DO - 10.1002/pssa.200777848 VL - 205 IS - 4 SP - 884-887 SN - 1862-6300 ER - TY - JOUR TI - Conformal symmetry and pion form factor: Space- and timelike region AU - Choi, Ho-Meoyng AU - Ji, Chueng-Ryong T2 - PHYSICAL REVIEW D AB - We extend a recent analysis of the pion electromagnetic form factor constrained by the conformal symmetry to explore the timelike region. We show explicitly that the timelike form factor obtained by the analytic continuation of the spacelike form factor correctly satisfies the dispersion relation. Our results indicate that the quark spin and dynamical mass effects are crucial to yield the realistic features of the vector meson dominance phenomena. DA - 2008/6// PY - 2008/6// DO - 10.1103/physrevd.77.113004 VL - 77 IS - 11 SP - SN - 1550-2368 ER - TY - JOUR TI - The role of creep in the time-dependent resistance of Ohmic gold contacts in radio frequency microelectromechanical system devices AU - Rezvanian, O. AU - Brown, C. AU - Zikry, M. A. AU - Kingon, A. I. AU - Krim, J. AU - Irving, D. L. AU - Brenner, D. W. T2 - Journal of Applied Physics AB - It is shown that measured and calculated time-dependent electrical resistances of closed gold Ohmic switches in radio frequency microelectromechanical system (rf-MEMS) devices are well described by a power law that can be derived from a single asperity creep model. The analysis reveals that the exponent and prefactor in the power law arise, respectively, from the coefficient relating creep rate to applied stress and the initial surface roughness. The analysis also shows that resistance plateaus are not, in fact, limiting resistances but rather result from the small coefficient in the power law. The model predicts that it will take a longer time for the contact resistance to attain a power law relation with each successive closing of the switch due to asperity blunting. Analysis of the first few seconds of the measured resistance for three successive openings and closings of one of the MEMS devices supports this prediction. This work thus provides guidance toward the rational design of Ohmic contacts with enhanced reliabilities by better defining variables that can be controlled through material selection, interface processing, and switch operation. DA - 2008/7/15/ PY - 2008/7/15/ DO - 10.1063/1.2953072 VL - 104 IS - 2 SP - 024513 J2 - Journal of Applied Physics LA - en OP - SN - 0021-8979 1089-7550 UR - http://dx.doi.org/10.1063/1.2953072 DB - Crossref ER - TY - JOUR TI - Effects of reoxidation on band alignment in N-incorporated SiON films as a function of sequential thermal annealing in NO and NH3 AU - Lee, W. J. AU - Cho, M. -H. AU - Chung, K. B. AU - Lee, Y. S. AU - Kim, D. C. AU - Choi, S. Y. AU - Chung, U. I. AU - Moon, J. T. T2 - APPLIED PHYSICS LETTERS AB - The effects of reoxidation on the band structure of N-incorporated SiON films were investigated as a function of thermal treatment in NO and NH3. Reoxidation-associated changes in band gap and valence band offset of the N-incorporated SiON films prepared by sequential thermal annealing in both NO and NH3 were less than those observed for the nitrided film prepared by thermal annealing in only NH3. The differences in band-alignment characteristics of the nitrided films that resulted from use of different nitridation methods were strongly related to the depth distribution of N and the chemical states of N bonded to Si. DA - 2008/7/7/ PY - 2008/7/7/ DO - 10.1063/1.2955835 VL - 93 IS - 1 SP - SN - 1077-3118 ER - TY - JOUR TI - Titanium Interlayer Mediated Epitaxy of CoSi2 on Si1-xGex AU - Burnette, James E. AU - Kiesel, Sharon AU - Sayers, Dale E. AU - Nemanich, Robert J. T2 - THIN SOLID FILMS AB - Abstract Titanium Interlayer Mediated Epitaxy (TIME) has been shown to promote the formation of epitaxial CoSi2 on Si (100). Similarities between Si and Si1−xGex alloys have motivated a study of whether the TIME process could be successful in forming epitaxial CoSi2 on Si1−xGex. Titanium layers of varying thickness were deposited as interlayers between a Co layer and c-Si/Si0.8Ge0.2 grown epitaxially onto Si (100) to investigate their role in the formation of epitaxial CoSi2 on Si1−xGex alloys. The effect of Ti interlayer thickness on the orientation of CoSi2 to the Si1−xGex substrate, and the conditions under which a polycrystalline CoSi2 film has been formed have been studied. It was found that Ti was beneficial in promoting epitaxy to the substrate in all cases. The experimental results indicate that with a Ti interlayer thickness of ∼ 50 A, the formation of epitaxial CoSi2 adjacent to the substrate was achieved, and pinhole formation was minimized. It was also observed that for increased interlayer thickness, Ti reacted with Si to form a titanium silicide. DA - 2008/2/29/ PY - 2008/2/29/ DO - 10.1016/j.tsf.2007.08.045 VL - 516 IS - 8 SP - 1809-1817 SN - 0040-6090 KW - CoSi2 KW - Si1-xGex KW - epitaxy KW - Ti interlayer KW - TIME process KW - XANES KW - XRD KW - pinhole formation ER - TY - JOUR TI - The symmetric heavy-light ansatz AU - Lee, D. T2 - EUROPEAN PHYSICAL JOURNAL A AB - The symmetric heavy-light ansatz is a method for finding the ground state of any dilute unpolarized system of attractive two-component fermions. Operationally it can be viewed as a generalization of the Kohn-Sham equations in density functional theory applied to N -body density correlations. While the original Hamiltonian has an exact Z2 symmetry, the heavy-light ansatz breaks this symmetry by skewing the mass ratio of the two components. In the limit where one component is infinitely heavy, the many-body problem can be solved in terms of single-particle orbitals. The original Z2 symmetry is recovered by enforcing Z2 symmetry as a constraint on N -body density correlations for the two components. For the 1D, 2D, and 3D attractive Hubbard models the method is in very good agreement with exact Lanczos calculations for few-body systems at arbitrary coupling. For the 3D attractive Hubbard model there is very good agreement with lattice Monte Carlo results for many-body systems in the limit of infinite scattering length. DA - 2008/2// PY - 2008/2// DO - 10.1140/epja/i2008-10537-2 VL - 35 IS - 2 SP - 171-187 SN - 1434-601X ER - TY - JOUR TI - Suppression of Ge-O and Ge-N bonding at Ge-HfO2 and Ge-TiO2 interfaces by deposition onto plasma-nitrided passivated Ge substrates: Integration issues Ge gate stacks into advanced devices AU - Lee, S. AU - Long, J. P. AU - Lucovsky, G. AU - Whitten, J. L. AU - Seo, H. AU - Luning, J. T2 - MICROELECTRONICS RELIABILITY AB - A study of changes in nano-scale morphology of thin films of nano-crystalline transition metal (TM) elemental oxides, HfO2 and TiO2, on plasma-nitrided Ge(1 0 0) substrates, and Si(1 0 0) substrates with ultra-thin (∼0.8 nm) plasma-nitrided Si suboxide, SiOx, x < 2, or SiON interfacial layers is presented. Near edge X-ray absorption spectroscopy (NEXAS) has been used to determine nano-scale morphology of these films by Jahn-Teller distortion removal of band edge d-state degeneracies. These results identify a new and novel application for NEXAS based on the resonant character of the respective O K1 and N K1 edge absorptions. This paper also includes a brief discussion of the integration issues for the introduction of this Ge breakthrough into advanced semiconductor circuits and systems. This includes a comparison of nano-crystalline and non-crystalline dielectrics, as well as issues relative to metal gates. DA - 2008/3// PY - 2008/3// DO - 10.1016/j.microrel.2007.07.068 VL - 48 IS - 3 SP - 364-369 SN - 0026-2714 ER - TY - JOUR TI - Statistical copolymers of 2-(trimethylsilyloxy)ethyl methacrylate and methyl methacrylate synthesized by ATRP AU - Ritz, Pavel AU - Latalova, Petra AU - Kriz, Jaroslav AU - Genzer, Jan AU - Vlcek, Petr T2 - JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY AB - Abstract No Abtract. DA - 2008/3/1/ PY - 2008/3/1/ DO - 10.1002/pola.22436 VL - 46 IS - 5 SP - 1919-1923 SN - 1099-0518 KW - atom transfer radical polymerization (ATRP) KW - copolymerization KW - functionalization of polymers KW - gradient copolymers KW - monomer KW - reactivity ratios ER - TY - JOUR TI - Reliable adaptive modulation and interference mitigation for mobile radio slow frequency hopping channels AU - Lei, Ming AU - Due-Hallen, Alexandra AU - Hallen, Hans T2 - IEEE TRANSACTIONS ON COMMUNICATIONS AB - The long range fading prediction algorithm for Slow Frequency Hopping (SFH) systems is proposed and demonstrated to enable combined adaptive modulation and adaptive frequency diversity to mitigate the effects of fading and partial-band interference. Significant performance gains are demonstrated relative to non-adaptive methods in realistic mobile radio SFH channels where the total bandwidth does not exceed approximately 15 times the coherence bandwidth. DA - 2008/3// PY - 2008/3// DO - 10.1109/TCOMM.2008.040662 VL - 56 IS - 3 SP - 352-355 SN - 1558-0857 UR - http://dx.doi.org/10.1109/TCOMM.2008.040662 KW - slow frequency hopping KW - channel state information KW - long range prediction KW - adaptive transmission KW - partial-band interference KW - diversity ER - TY - JOUR TI - Puncture Evolution of Schwarzschild Black Holes AU - Brown, J.David T2 - Phys.Rev.D AB - The moving puncture method is analyzed for a single, nonspinning black hole. It is shown that the puncture region is not resolved by current numerical codes. As a result, the geometry near the puncture appears to evolve to an infinitely long cylinder of finite areal radius. The puncture itself actually remains at spacelike infinity throughout the evolution. In the limit of infinite resolution the data never become stationary. However, at any reasonable finite resolution the grid points closest to the puncture are rapidly drawn into the black hole interior by the $\ensuremath{\Gamma}$-driver shift condition. The data can then evolve to a stationary state. These results suggest that the moving puncture technique should be viewed as a type of ``natural excision.'' DA - 2008/// PY - 2008/// DO - 10.1103/PhysRevD.77.044018 VL - 77 IS - 4 SP - 044018 UR - http://inspirehep.net/record/750274 ER - TY - JOUR TI - Persistent current of correlated electrons in mesoscopic ring with impurity AU - Krcmar, R. AU - Gendiar, A. AU - Mosko, M. AU - Nemeth, R. AU - Vagner, P. AU - Mitas, L. T2 - PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES AB - The persistent current of correlated electrons in a continuous one-dimensional ring with a single scatterer is calculated by solving the many-body Schrodinger equation for several tens of electrons interacting via the electron–electron (e–e) interaction of finite range. The problem is solved by the configuration-interaction (CI) and diffusion Monte Carlo (DMC) methods. The CI and DMC results are in good agreement. In both cases, the persistent current I as a function of the ring length L exhibits the asymptotic dependence I∝L-1-α typical of the Luttinger liquid, where the power α depends only on the e–e interaction. The numerical values of α agree with the known formula of the renormalization-group theory. DA - 2008/3// PY - 2008/3// DO - 10.1016/j.physe.2007.09.074 VL - 40 IS - 5 SP - 1507-1509 SN - 1873-1759 KW - one-dimensional transport KW - mesoscopic ring KW - persistent current KW - electron-electron interaction ER - TY - JOUR TI - Oscillation effects and time variation of the supernova neutrino signal AU - Kneller, James P. AU - McLaughlin, Gail C. AU - Brockman, Justin T2 - PHYSICAL REVIEW D AB - The neutrinos detected from the next galactic core-collapse supernova will contain valuable information on the internal dynamics of the explosion. One mechanism leading to a temporal evolution of the neutrino signal is the variation of the induced neutrino flavor mixing driven by changes in the density profile. With one and two-dimensional hydrodynamical simulations we identify the behavior and properties of prominent features of the explosion. Using these results we demonstrate the time variation of the neutrino crossing probabilities due to changes in the Mikheyev-Smirnov-Wolfenstein (MSW) neutrino transformations as the star explodes by using the $S$-matrix---Monte Carlo---approach to neutrino propagation. After adopting spectra for the neutrinos emitted from the proto-neutron star we calculate for a galactic supernova the evolution of the positron spectra within a water Cerenkov detector and find that this signal allows us to probe of a number of explosion features. DA - 2008/2// PY - 2008/2// DO - 10.1103/physrevd.77.045023 VL - 77 IS - 4 SP - SN - 1550-2368 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-41049093044&partnerID=MN8TOARS ER - TY - JOUR TI - Low-spin lifetime measurements in Kr-74 AU - Valiente-Dobon, J. J. AU - Svensson, C. E. AU - Afanasjev, A. V. AU - Ragnarsson, I. AU - Andreoiu, C. AU - Appelbe, D. E. AU - Austin, R. A. E. AU - Ball, G. C. AU - Cameron, J. A. AU - Carpenter, M. P. AU - Clark, R. M. AU - Cromaz, M. AU - Dashdorj, D. AU - Fallon, P. AU - Freeman, S. J. AU - Garrett, P. E. AU - al., T2 - Physical Review. C, Nuclear Physics DA - 2008/// PY - 2008/// VL - 77 IS - 2 ER - TY - JOUR TI - Isomerization kinetics of small hydrocarbons in confinement AU - Santiso, Erik E. AU - Nardelli, Marco Buongiorno AU - Gubbins, Keith E. T2 - ADSORPTION-JOURNAL OF THE INTERNATIONAL ADSORPTION SOCIETY DA - 2008/6// PY - 2008/6// DO - 10.1007/s10450-007-9075-8 VL - 14 IS - 2-3 SP - 181-188 SN - 1572-8757 KW - chemical reactions KW - confinement KW - carbon KW - density functional theory KW - variational transition state theory ER - TY - JOUR TI - Invited article: Development of high-field superconducting Ioffe magnetic traps AU - Yang, L. AU - Brome, C. R. AU - Butterworth, J. S. AU - Dzhosyuk, S. N. AU - Mattoni, C. E. H. AU - McKinsey, D. N. AU - Michniak, R. A. AU - Doyle, J. M. AU - Golub, R. AU - Korobkina, E. AU - O'Shaughnessy, C. M. AU - Palmquist, G. R. AU - Seo, P. N. AU - Huffman, P. R. AU - Coakley, K. J. AU - Mumm, H. P. AU - al., T2 - Review of Scientific Instruments DA - 2008/// PY - 2008/// VL - 79 IS - 3 ER - TY - PAT TI - Gallium nitride material transistors and methods associated with the same AU - Nagy, W. H. AU - Borges, R. M. AU - Brown, J. D. AU - Chaudhari, A. D. AU - Cook, J. W. AU - Hanson, A. W. AU - Johnson, J. W. AU - Linthicum, K. J. AU - Piner, E. L. AU - Rajagopal, P. AU - Roberts, J. C. AU - Singhal, S. AU - Therrien, R. J. AU - Vescan, A. C2 - 2008/// DA - 2008/// PY - 2008/// ER - TY - JOUR TI - Computational physics in the introductory calculus-based course AU - Chabay, Ruth AU - Sherwood, Bruce T2 - AMERICAN JOURNAL OF PHYSICS AB - The integration of computation into the introductory calculus-based physics course can potentially provide significant support for the development of conceptual understanding. Computation can support three-dimensional visualizations of abstract quantities, offer opportunities to construct symbolic rather than numeric solutions to problems, and provide experience with the use of vectors as coordinate-free entities. Computation can also allow students to explore models in a way not possible using the analytical tools available to first-year students. We describe how we have incorporated computer programming into an introductory calculus-based course taken by science and engineering students. DA - 2008/// PY - 2008/// DO - 10.1119/1.2835054 VL - 76 IS - 4-5 SP - 307-313 SN - 0002-9505 ER - TY - JOUR TI - Characterization of electrical and mechanical properties for coaxial nanofibers with poly(ethylene oxide) (PEO) core and multiwalled carbon nanotube/PEO sheath AU - Ojha, Satyajeet S. AU - Stevens, Derrick R. AU - Stano, Kelly AU - Hoffman, Torissa AU - Clarke, Laura I. AU - Gorga, Russell E. T2 - MACROMOLECULES AB - The present work focuses on the electrical and mechanical characterization of nanocomposite fibers having core−sheath (or bicomponent) morphologies. Owing to their unique mechanical and electrical properties, multiwalled carbon nanotubes (MWNTs) have been utilized in the nanocomposite construction. Submicron diameter nanofibers (200–300 nm) with core−sheath morphology were fabricated from a polymer/MWNT solution and collected in random mats. By constraining the MWNTs to the sheath, significant increases in the mechanical properties were observed at lower MWNT concentrations when compared to mats made from single-layer fibers. The electrical properties of the core−sheath mats showed similar gains, having a critical weight percent more than 10 times lower than that of the single-layer mats. DA - 2008/4/8/ PY - 2008/4/8/ DO - 10.1021/ma702634a VL - 41 IS - 7 SP - 2509-2513 SN - 1520-5835 ER - TY - JOUR TI - The infrared detection of the pulsar wind nebula in the galactic supernova remnant 3C 58 AU - Slane, P. AU - Helfand, D. J. AU - Reynolds, S. P. AU - Gaensler, B. M. AU - Lemiere, A. AU - Wang, Z. T2 - ASTROPHYSICAL JOURNAL LETTERS AB - We present infrared observations of 3C 58 with the Spitzer Space Telescope and the Canada-France-Hawaii Telescope. Using the IRAC camera, we have imaged the entire source, which results in clear detections of the nebula at 3.6 and 4.5 μm. The derived flux values are consistent with extrapolation of the X-ray spectrum to the infrared band, demonstrating that any cooling break in the synchrotron spectrum must occur near the soft X-ray band. We also detect the torus surrounding PSR J0205+6449, the 65 ms pulsar that powers 3C 58. The torus spectrum requires a break between the infrared and X-ray bands, and perhaps multiple breaks. This complex spectrum, which is an imprint of the particles injected into the nebula, has considerable consequences for the evolution of the broadband spectrum of 3C 58. We illustrate these effects and discuss the impact of these observations on the modeling of broadband spectra of pulsar wind nebulae. DA - 2008/3/20/ PY - 2008/3/20/ DO - 10.1086/587031 VL - 676 IS - 1 SP - L33-L36 SN - 2041-8205 KW - ISM : individual (3C 58) KW - pulsars : general KW - pulsars : individual (PSR J0205+6449) KW - supernova remnants ER - TY - JOUR TI - Piezoresponse force microscopy studies of switching behavior of ferroelectric capacitors on a 100-ns time scale AU - Gruverman, A. AU - Wu, D. AU - Scott, J. F. T2 - Physical Review Letters DA - 2008/// PY - 2008/// VL - 1 IS - 9 ER - TY - JOUR TI - NEXAFS microscopy and resonant scattering: Composition and orientation probed in real and reciprocal space AU - Ade, Harald AU - Hitchcock, Adam P. T2 - POLYMER AB - Near Edge X-ray Absorption Fine Structure (NEXAFS) spectromicroscopy, resonant scattering and resonant reflectivity are specialized, synchrotron radiation based, soft X-ray characterization tools that provide moiety-specific contrast and either real-space imaging at ∼30 nm spatial resolution, or scattering signals which can be inverted to provide chemically sensitive information at an even higher spatial resolution (<5 nm). These X-ray techniques complement other real and reciprocal space characterization tools such as various microscopies and conventional electron, X-ray and neutron scattering. We provide an overview of these synchrotron based tools, describe their present state-of-the-art and discuss a number of applications to exemplify their unique aspects. DA - 2008/2/4/ PY - 2008/2/4/ DO - 10.1016/j.polymer.2007.10.030 VL - 49 IS - 3 SP - 643-675 SN - 1873-2291 KW - X-ray microscopy KW - NEXAFS KW - resonant scattering KW - polymers KW - chemical mapping ER - TY - JOUR TI - Magnetic field amplification and rapid time variations in SNR RX J1713.7-3946 AU - Ellison, Donald C. AU - Vladimirov, Andrey T2 - ASTROPHYSICAL JOURNAL LETTERS AB - Evidence is accumulating suggesting that collisionless shocks in supernova remnants (SNRs) can amplify the interstellar magnetic field to hundreds of microgauss or even milligauss levels, as recently claimed for SNR RX J1713.7–3946. If these fields exist, they are almost certainly created by magnetic field amplification (MFA) associated with the efficient production of cosmic rays by diffusive shock acceleration (DSA) and their existence strengthens the case for SNRs being the primary source of Galactic cosmic-ray ions to the "knee" and beyond. However, the high magnetic field values in SNRs are obtained exclusively from the interpretation of observations of radiation from relativistic electrons, and if MFA via nonlinear DSA produces these fields, the magnetic field that determines the maximum ion energy will be substantially less than the field that determines the maximum electron energy. We use results of a steady-state Monte Carlo simulation to show how nonlinear effects from efficient cosmic-ray production and MFA reduce the maximum energy of protons relative to what would be expected from test-particle acceleration. DA - 2008/1/20/ PY - 2008/1/20/ DO - 10.1086/527359 VL - 673 IS - 1 SP - L47-L50 SN - 2041-8213 KW - acceleration of particles KW - cosmic rays KW - magnetic fields KW - shock waves supernova KW - remnants KW - turbulence ER - TY - JOUR TI - Levitation compensation method for dynamic electrostatic comb-drive actuators AU - Timpe, S. J. AU - Hook, D. A. AU - Dugger, M. T. AU - Komvopoulos, K. T2 - SENSORS AND ACTUATORS A-PHYSICAL AB - An analytical method was developed for maintaining a constant levitation height during dynamic operation of reciprocating comb-drive actuators. The dependence of the translational position and the levitation height on the applied voltage was used to design waveforms that maintain a given translational motion without altering the levitation height. An experimental protocol was established for determining the necessary geometric factors of a particular comb-drive design, which were then used to generate constant-velocity levitation waveforms. The analytical model was tested experimentally by examining the levitation and translation positions of a surface micromachine under both compensated and uncompensated signals. A significant reduction in the range of levitation was obtained over the entire amplitude of the oscillatory motion, while the translational motion remained relatively unchanged. Design and fabrication effects on the compensated levitation height of an oscillating surface micromachine are discussed in the context of analytical and experimental results. DA - 2008/5/16/ PY - 2008/5/16/ DO - 10.1016/j.sna.2007.11.025 VL - 143 IS - 2 SP - 383-389 SN - 0924-4247 KW - comb-drive actuators KW - levitation KW - motion control method KW - oscillation ER - TY - JOUR TI - Application of the anisotropic bond model to second-harmonic generation from amorphous media AU - Adles, E. J. AU - Aspnes, D. E. T2 - PHYSICAL REVIEW B AB - As a step toward analyzing second-harmonic generation (SHG) from crystalline Si nanospheres in glass, we develop an anisotropic bond model (ABM) that expresses SHG in terms of physically meaningful parameters and provide a detailed understanding of the basic physics of SHG on the atomic scale. Nonlinear-optical (NLO) responses are calculated classically via the four fundamental steps of optics: evaluate the local field at a given bond site, solve the force equation for the acceleration of the charge, calculate the resulting radiation, then superpose the radiation from all charges. Because the emerging NLO signals are orders of magnitude weaker and occur at wavelengths different from that of the pump beam, these steps are independent. Paradoxically, the treatment of NLO is therefore simpler than that of linear optics (LO), where these calculations must be done self-consistently. The ABM goes beyond previous bond models by including the complete set of underlying contributions: retardation (RD), spatial-dispersion (SD), and magnetic (MG) effects, in addition to the anharmonic restoring force acting on the bond charge. Transverse as well as longitudinal motion is also considered. We apply the ABM to obtain analytic expressions for SHG from amorphous materials under Gaussian-beam excitation. These materials represent an interesting test case not only because they are ubiquitous but also because the anharmonic-force contribution that dominates the SHG response of crystalline materials and ordered interfaces vanishes by symmetry. The remaining contributions, and hence the SHG signals, are entirely functions of the LO response and beam geometry, so the only new information available is the anisotropy of the LO response at the bond level. The RD, SD, and MG contributions are all of the same order of magnitude, so none can be ignored. Diffraction is important in determining not only the pattern of the emerging beam but also the phases and amplitudes of the different terms. The plane-wave expansion that gives rise to electric quadrupole magnetic dipole effects in LO appears here as retardation. Using the paraxial-ray approximation, we reduce the results to the isotropic case in two limits, that where the linear restoring force dominates (glasses) and that where it is absent (metals). Both forward- and backscattering geometries are discussed. Estimated signal strengths and conversion efficiencies for fused silica appear to be in general agreement with data where available. Predictions that allow additional critical tests of these results are made. DA - 2008/4// PY - 2008/4// DO - 10.1103/physrevb.77.165102 VL - 77 IS - 16 SP - SN - 1098-0121 ER - TY - JOUR TI - Overlayer effects in the critical-point analysis of ellipsometric spectra: Application to InxGa1-xAs alloys AU - Ghong, T. H. AU - Kim, T. J. AU - Jung, Y. W. AU - Kim, Y. D. AU - Aspnes, D. E. T2 - JOURNAL OF APPLIED PHYSICS AB - We investigate the effect of incomplete removal of semiconductor overlayers on critical-point (CP) parameters determined from the analysis of ellipsometric spectra. An approximate analytic expression shows that CP energies and broadening parameters should be relatively unaffected for isolated CPs if the dielectric response of the overlayer varies slowly with energy. The results are confirmed by model calculations for InAs, which show that the energies of the E1 and E1+Δ1 CP structures that are commonly used for compositional analysis of semiconductor alloys are relatively unaffected. We also analyze overlayer-removal data for a series of InxGa1−xAs alloy samples. Consistent with the above, the amplitudes and phases are affected significantly for all CPs, while the energies of the well-separated E1 and E1+Δ1 transitions are relatively invariant. The results show that accurate values of composition can be obtained from the analysis of the E1 and E1+Δ1 CP structures, even if complete removal of overlayers is not achieved. DA - 2008/4/1/ PY - 2008/4/1/ DO - 10.1063/1.2902502 VL - 103 IS - 7 SP - SN - 1089-7550 ER - TY - JOUR TI - Optical properties of InxAl1-xAs alloy films AU - Yoon, J. J. AU - Ghong, T. H. AU - Byun, J. S. AU - Kim, Y. D. AU - Aspnes, D. E. AU - Kim, H. J. AU - Chang, Y. C. AU - Song, J. D. T2 - APPLIED PHYSICS LETTERS AB - Pseudodielectric functions ⟨ε⟩ of InxAl1−xAs ternary alloy films were determined from 1.5to6.0eV by spectroscopic ellipsometry. We minimized overlayer effects by performing wet-chemical etching to more accurately determine intrinsic bulk dielectric responses. Energies of the E1, E1+Δ1, E0′, E2, E2+Δ2 and E2′ critical points (CPs) were identified by band structure calculations of the linear augmented Slater-type orbital method. These calculations also showed a crossing of the E0′ and E2 CP structures with increasing In composition and a new saddle point in the AlAs band structure. DA - 2008/4/14/ PY - 2008/4/14/ DO - 10.1063/1.2909546 VL - 92 IS - 15 SP - SN - 1077-3118 ER - TY - JOUR TI - Electrical and photoelectrical characterization of undoped and S-doped nanocrystalline diamond films AU - Kulkarni, P. AU - Porter, L. M. AU - Koeck, F. A. M. AU - Tang, Y. -J. AU - Nemanich, R. J. T2 - JOURNAL OF APPLIED PHYSICS AB - Nanocrystalline diamond (NCD) films are being intensively researched for a variety of potential applications, such as optical windows, electrochemical electrodes, and electron emitting surfaces for field emission displays. In this study Zr, Ti, Cu, and Pt on intrinsic and lightly sulfur-doped (n-type) NCD films were electrically and photoelectrically characterized. Intrinsic and sulfur-doped NCD films were synthesized on 1in. diameter quartz and silicon substrates by microwave plasma assisted chemical vapor deposition. All metals showed linear (Ohmic) current-voltage characteristics in the as-deposited state. The Schottky barrier heights (ΦB) at the metal-film interface were investigated using x-ray and ultraviolet photoelectron spectroscopies. The undoped NCD films exhibited a negative electron affinity and a band gap of 5.0±0.4eV. The ΦB were calculated based on this band gap measurement and the consistent indication from Hall measurements that the films are n-type. The ΦB values were calculated from shifts in the core-level (C1s) peaks immediately obtained before and after in situ, successive metal depositions. The ΦB values for Zr, Ti, and Pt on undoped films were calculated to be 3.3, 3.2, and 3.7eV, respectively. The S-doped films also showed increasing ΦB with metal work functions: 3.0, 3.1, and 3.4eV for Zr, Ti, and Pt, respectively. In general accordance with the barrier height trends, the specific contact resistivity (ρc) values increased with the metal work functions for both undoped and S-doped films. For the undoped films ρc increased from 3×10−5Ωcm2 for Zr to 6.4×10−3Ωcm2 for Pt. The ρc values for the S-doped films were approximately two orders of magnitude lower than those for the undoped films: 3.5×10−7–4.5×10−5Ωcm2 for Zr and Pt, respectively. The Hall-effect measurements indicated that the average sheet resistivity and carrier concentration values were 0.16 and 3.5×1018cm−3 for the undoped films and 0.15Ωcm and 4.9×1019cm−3 for the S-doped films. DA - 2008/4/15/ PY - 2008/4/15/ DO - 10.1063/1.2908884 VL - 103 IS - 8 SP - SN - 1089-7550 ER - TY - JOUR TI - Dilute neutron matter on the lattice at next-to-leading order in chiral effective field theory AU - Borasoy, B. AU - Epelbaum, E. AU - Krebs, H. AU - Lee, D. AU - Meissner, U. -G. T2 - EUROPEAN PHYSICAL JOURNAL A AB - We discuss lattice simulations of the ground state of dilute neutron matter at next-to-leading order in chiral effective field theory. In a previous paper the coefficients of the next-to-leading-order lattice action were determined by matching nucleon-nucleon scattering data for momenta up to the pion mass. Here the same lattice action is used to simulate the ground state of up to 12 neutrons in a periodic cube using Monte Carlo simulations. We explore the density range from 2% to 8% of normal nuclear density and analyze the ground-state energy as an expansion about the unitarity limit with corrections due to finite scattering length, effective range, and P -wave interactions. DA - 2008/3// PY - 2008/3// DO - 10.1140/epja/i2008-10545-2 VL - 35 IS - 3 SP - 357-367 SN - 1434-601X ER - TY - JOUR TI - Chiral effective field theory on the lattice at next-to-leading order AU - Borasoy, B. AU - Epelbaum, E. AU - Krebs, H. AU - Lee, D. AU - Meissner, U.-G. T2 - EUROPEAN PHYSICAL JOURNAL A AB - We study nucleon-nucleon scattering on the lattice at next-to-leading order in chiral effective field theory. We determine phase shifts and mixing angles from the properties of two-nucleon standing waves induced by a hard spherical wall in the center-of-mass frame. At fixed lattice spacing we test model independence of the low-energy effective theory by computing next-to-leading-order corrections for two different leading-order lattice actions. The first leading-order action includes instantaneous one-pion exchange and same-site contact interactions. The second leading-order action includes instantaneous one-pion exchange and Gaussian-smeared interactions. We find that in each case the results at next-to-leading order are accurate up to corrections expected at higher order. DA - 2008/3// PY - 2008/3// DO - 10.1140/epja/i2008-10544-3 VL - 35 IS - 3 SP - 343-355 SN - 1434-6001 ER - TY - PAT TI - Normal incidence rotating compensator ellipsometer AU - Aspnes, D. E. C2 - 2008/// DA - 2008/// PY - 2008/// ER - TY - JOUR TI - Competition and bistability of ordered undulations and undulation chaos in inclined layer convection AU - Daniels, Karen E. AU - Brausch, Oliver AU - Pesch, Werner AU - Bodenschatz, Eberhard T2 - JOURNAL OF FLUID MECHANICS AB - Experimental and theoretical investigations of undulation patterns in high-pressure inclined layer gas convection at a Prandtl number near unity are reported. Particular focus is given to the competition between the spatiotemporal chaotic state of undulation chaos and stationary patterns of ordered undulations. In experiments, a competition and bistability between the two states is observed, with ordered undulations most prevalent at higher Rayleigh number. The spectral pattern entropy, spatial correlation lengths and defect statistics are used to characterize the competing states. The experiments are complemented by a theoretical analysis of the Oberbeck–Boussinesq equations. The stability region of the ordered undulations as a function of their wave vectors and the Rayleigh number is obtained with Galerkin techniques. In addition, direct numerical simulations are used to investigate the spatiotemporal dynamics. In the simulations, both ordered undulations and undulation chaos were observed dependent on initial conditions. Experiment and theory are found to agree well. DA - 2008/2/25/ PY - 2008/2/25/ DO - 10.1017/S0022112007009615 VL - 597 SP - 261-282 SN - 1469-7645 ER - TY - JOUR TI - Adaptively biased molecular dynamics for free energy calculations AU - Babin, V. AU - Roland, C. AU - Sagui, C. T2 - Journal of Chemical Physics AB - We present an adaptively biased molecular dynamics (ABMD) method for the computation of the free energy surface of a reaction coordinate using nonequilibrium dynamics. The ABMD method belongs to the general category of umbrella sampling methods with an evolving biasing potential and is inspired by the metadynamics method. The ABMD method has several useful features, including a small number of control parameters and an O(t) numerical cost with molecular dynamics time t. The ABMD method naturally allows for extensions based on multiple walkers and replica exchange, where different replicas can have different temperatures and/or collective variables. This is beneficial not only in terms of the speed and accuracy of a calculation, but also in terms of the amount of useful information that may be obtained from a given simulation. The workings of the ABMD method are illustrated via a study of the folding of the Ace-GGPGGG-Nme peptide in a gaseous and solvated environment. DA - 2008/// PY - 2008/// DO - 10.1063/1.2844595 VL - 128 IS - 13 ER - TY - JOUR TI - Pfaffian pairing and backflow wavefunctions for electronic structure quantum Monte Carlo methods AU - Bajdich, M. AU - Mitas, L. AU - Wagner, L. K. AU - Schmidt, K. E. T2 - PHYSICAL REVIEW B AB - We investigate pfaffian trial wavefunctions with singlet and triplet pair orbitals by quantum Monte Carlo methods. We present mathematical identities and the key algebraic properties necessary for efficient evaluation of pfaffians. Following upon our previous study [Bajdich et al., Phys. Rev. Lett. 96, 130201 (2006)], we explore the possibilities of expanding the wavefunction in linear combinations of pfaffians. We observe that molecular systems require much larger expansions than atomic systems and linear combinations of a few pfaffians lead to rather small gains in correlation energy. We also test the wavefunction based on fully antisymmetrized product of independent pair orbitals. Despite its seemingly large variational potential, we do not observe additional gains in correlation energy. We find that pfaffians lead to substantial improvements in fermion nodes when compared to Hartree-Fock wavefunctions and exhibit the minimal number of two nodal domains in agreement with recent results on fermion nodes topology. We analyze the nodal structure differences of Hartree-Fock, pfaffian, and essentially exact large-scale configuration interaction wavefunctions. Finally, we combine the recently proposed form of backflow correlations [Drummond et al., J. Phys. Chem. 124, 22401 (2006); Rios et al., Phys. Rev. E. 74, 066701 (2006)] with both determinantal and pfaffian based wavefunctions. DA - 2008/3// PY - 2008/3// DO - 10.1103/physrevb.77.115112 VL - 77 IS - 11 SP - SN - 1098-0121 ER - TY - JOUR TI - Fission cycling in a supernova r process AU - Beun, J. AU - McLaughlin, G. C. AU - Surman, R. AU - Hix, W. R. T2 - PHYSICAL REVIEW C AB - Recent halo star abundance observations exhibit an important feature of consequence to the $r$ process: the presence of a main $r$ process between the second and third peaks that is consistent among halo stars. We explore fission cycling and steady \ensuremath{\beta} flow as the driving mechanisms behind this feature. The presence of fission cycling during the $r$ process can account for nucleosynthesis yields between the second and third peaks, whereas the presence of steady \ensuremath{\beta} flow can account for consistent $r$-process patterns, robust under small variations in astrophysical conditions. We employ the neutrino-driven wind of the core-collapse supernova to examine fission cycling and steady \ensuremath{\beta} flow in the $r$ process. As the traditional neutrino-driven wind model does not produce the required very neutron-rich conditions for these mechanisms, we examine changes to the neutrino physics necessary for fission cycling to occur in the neutrino-driven wind environment, and we explore under what conditions steady \ensuremath{\beta} flow is obtained. DA - 2008/3// PY - 2008/3// DO - 10.1103/physrevc.77.035804 VL - 77 IS - 3 SP - SN - 1089-490X ER - TY - JOUR TI - A simple method for determining linear polarization and energy calibration of focused soft X-ray beams AU - Watts, B. AU - Ade, H. T2 - JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA AB - Although critical to quantitative linear dichroism studies of molecular orientation, the degree of linear polarization of focused soft X-ray beams delivered by X-ray microscopes has not been previously measured. Here, we present a scaled-down version of a recently developed technique in which the π∗ near edge X-ray absorption fine structure (NEXAFS) resonance of highly oriented pyrolytic graphite (HOPG) is used to probe the electric field intensity in each direction and hence deduce the degree of linear polarization of the incident X-ray beam. Applying this technique to the soft X-ray microscope at beamline 5.3.2 of the Advanced Light Source in Berkeley, CA, yielded a measured value of 79±11%, for the first Stokes parameter of 0.79±0.11 or as a Stöhr P factor of 0. 89±0.06. It is expected that the error margin could be significantly reduced via the use of an in-vacuum rotation actuator. We have also calibrated the energy of the graphite exciton to be 291.65±0.025 eV, improving the utility of graphite as an energy calibration standard for NEXAFS and allowing the convenience of both energy calibration and polarization determination with a single inexpensive sample. DA - 2008/2// PY - 2008/2// DO - 10.1016/j.elspec.2007.08.008 VL - 162 IS - 2 SP - 49-55 SN - 1873-2526 KW - NEXAFS KW - linear dichroism KW - polarization KW - soft X-ray KW - graphite KW - HOPG KW - carbon KW - synchrotron radiation KW - X-ray microscopy KW - photon energy calibration ER - TY - JOUR TI - Synthesis of carboxylic acid monolayers by ozonolysis of 10-undecenyltrichlorosilane SAMs AU - Hallen, Mark A. AU - Hallen, Hans D. T2 - JOURNAL OF PHYSICAL CHEMISTRY C AB - A high-yield method has been developed for the production of carboxyl-terminated alkylsiloxane monolayers on silicon using the ozonolysis and hydrolysis of 10-undecenyltrichlorosilane self-assembled monolayers (SAMs). Contact angles with water, a common measure of hydrophilicity and thus an effective measure of carboxyl termination, were brought to 0° on receding and approximately 16° on advancing, compared to 98° and 105° respectively before ozonation. Ellipsometry showed the presence of a full monolayer, 1 nm thick before ozonation, that decreases by about 0.2 nm during ozone treatment, largely due to the removal of a carbon atom in the process. This removed material coalesces as nanoparticles, observed with atomic force microscopy (AFM) imaging. The process has a surprisingly narrow ozone dose window, with excess ozonation resulting in complete layer removal. The carboxylate moieties allow further chemical modification of the surface in addition to the hydrophilic surface that can be produced by exposing the silicon dioxide substrate. DA - 2008/2/14/ PY - 2008/2/14/ DO - 10.1021/jp709664r VL - 112 IS - 6 SP - 2086-2090 SN - 1932-7455 UR - http://dx.doi.org/10.1021/jp709664r ER - TY - JOUR TI - Surface chemical analysis of plasma-deposited copolymer films prepared from feed gas mixtures of ethylene or styrene with allylamine AU - Swaraj, Sufal AU - Oran, Urnut AU - Lippitz, Andreas AU - Unger, Wolfgang E. S. T2 - PLASMA PROCESSES AND POLYMERS AB - Abstract Plasma deposited ethylene/allylamine and styrene/allylamine copolymer films were prepared and analyzed using XPS, NEXAFS and ToF‐SIMS. The relative partial flow rate of the each monomer was used as the variable deposition parameter, while the other deposition parameters were kept constant at optimized values for the retention of functional groups. The effect of the variation in the relative partial flow rates of co‐monomers on various chemical aspects of the films like unsaturation, nitrogen retention and branching was investigated revealing several non‐linear correlations. This observation is taken as an indication for chemical copolymerization processes during film deposition. An attempt is made to compare these non‐linear correlations with approaches which have been developed for classic radical copolymerization processes. The aging behavior of these plasma copolymer films was also studied; the results indicated a stabilization against oxidation in comparison to the aging of allylamine plasma homopolymers. magnified image DA - 2008/1/10/ PY - 2008/1/10/ DO - 10.1002/ppap.200700106 VL - 5 IS - 1 SP - 92-104 SN - 1612-8869 KW - ethylene-allylamine copolymer KW - ESCA KW - NEXAFS KW - plasma polymerization KW - styrene-allylamine copolymer KW - surface characterization KW - TOF-SIMS KW - XPS ER - TY - JOUR TI - Stimulated emission and lasing from an Al0.13Ga0.87N∕GaN double heterostructure grown on a silicon substrate AU - Al-Ajmi, F. S. AU - Kolbas, R. M. AU - Roberts, J. C. AU - Rajagopal, P. AU - Cook, J. W., Jr. AU - Piner, E. L. AU - Linthicum, K. J. T2 - Applied Physics Letters AB - Stimulated emission and laser action with well developed longitudinal optical modes from an Al0.13Ga0.87N∕GaN double heterostructure with a 25nm GaN active layer grown on a silicon substrate by metal-organic chemical vapor deposition is demonstrated. Lasing was observed from cleaved platelets at room temperature with well resolved Fabry-Pérot modes at a wavelength as short as 368nm at room temperature. A clear threshold was observed in the plot of the emission intensity versus the pumping power at both 77K and room temperature. The effective index of refraction during laser operation was measured to be 2.65. DA - 2008/1/14/ PY - 2008/1/14/ DO - 10.1063/1.2819614 VL - 92 IS - 2 SP - 021118 J2 - Appl. Phys. Lett. LA - en OP - SN - 0003-6951 1077-3118 UR - http://dx.doi.org/10.1063/1.2819614 DB - Crossref ER - TY - JOUR TI - A remarkable shape-catalytic effect of confinement on the rotational isomerization of small hydrocarbons AU - Santiso, Erik E. AU - Nardelli, Marco Buongiorno AU - Gubbins, Keith E. T2 - JOURNAL OF CHEMICAL PHYSICS AB - As part of an effort to understand the effect of confinement by porous carbons on chemical reactions, we have carried out density functional theory calculations on the rotational isomerization of three four-membered hydrocarbons: n-butane, 1-butene, and 1,3-butadiene. Our results show that the interactions with the carbon walls cause a dramatic change on the potential energy surface for pore sizes comparable to the molecular dimensions. The porous material enhances or hinders reactions depending on how similar is the shape of the transition state to the shape of the confining material. The structure of the stable states and their equilibrium distributions are also drastically modified by confinement. Our results are consistent with a doubly exponential behavior of the reaction rates as a function of pore size, illustrating how the shape of a catalytic support can dramatically change the efficiency of a catalyst. DA - 2008/1/21/ PY - 2008/1/21/ DO - 10.1063/1.2819238 VL - 128 IS - 3 SP - SN - 1089-7690 ER - TY - JOUR TI - The role of neutrinos in r-process nucleosynthesis in supernovae and gamma-ray bursts AU - Surman, R. AU - Beun, J. AU - McLaughlin, G. C. AU - Kane, S. AU - Hix, W. R. T2 - JOURNAL OF PHYSICS G-NUCLEAR AND PARTICLE PHYSICS AB - The exact astrophysical site of the r-process is uncertain, but the likely candidates—supernovae and compact merger events—are environments with high neutrino fluxes. Here we examine the role of neutrinos in r-process nucleosynthesis under two separate scenarios. In the first, we consider the consequences of a reduction in the electron neutrino flux in a core-collapse supernova environment. We show that such a reduction results in a vigorous r-process with a robust abundance signature due to fission cycling. In the second, we examine the production of r-process nuclei in the outflows from a black hole accretion disk as thought to accompany a merger-type gamma-ray burst (GRB). We use a parameterized outflow model and find the neutrino fluxes emitted from the GRB accretion disk facilitate the synthesis of light r-process nuclei over a broad region of the parameter space explored. DA - 2008/1// PY - 2008/1// DO - 10.1088/0954-3899/35/1/014059 VL - 35 IS - 1 SP - SN - 1361-6471 ER - TY - JOUR TI - Low energy electron-excited nanoscale luminescence spectroscopy studies of intrinsic defects in HfO2 and SiO2-HfO2-SiO2-Si stacks AU - Strzhemechny, Y. M. AU - Bataiev, M. AU - Tumakha, S. P. AU - Goss, S. H. AU - Hinkle, C. L. AU - Fulton, C. C. AU - Lucovsky, G. AU - Brillson, L. J. T2 - Journal of Vacuum Science & Technology. B, Microelectronics and Nanometer Structures DA - 2008/// PY - 2008/// VL - 26 IS - 1 SP - 232-243 ER - TY - JOUR TI - Fluctuations, correlations and transitions in granular materials: statistical mechanics for a non-conventional system AU - Behringer, R. P. AU - Daniels, Karen E. AU - Majmudar, Trushant S. AU - Sperl, Matthias T2 - PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES AB - In this work, we first review some general properties of dense granular materials. We are particularly concerned with a statistical description of these materials, and it is in this light that we briefly describe results from four representative studies. These are: experiment 1: determining local force statistics, vector forces, force distributions and correlations for static granular systems; experiment 2: characterizing the jamming transition, for a static two-dimensional system; experiment 3: characterizing plastic failure in dense granular materials; and experiment 4: a dynamical transition where the material 'freezes' in the presence of apparent heating for a sheared and shaken system. DA - 2008/2/28/ PY - 2008/2/28/ DO - 10.1098/rsta.2007.2106 VL - 366 IS - 1865 SP - 493-504 SN - 1471-2962 KW - granular materials KW - jamming KW - disordered solids ER - TY - JOUR TI - Excitonic states and resonance Raman Spectroscopy of single-wall carbon nanotubes AU - Saito, R. AU - Fantini, C. AU - Jiang, J. T2 - Carbon nanotubes DA - 2008/// PY - 2008/// VL - 111 SP - 251-286 ER - TY - JOUR TI - Effects of end group functionalization and level alignment on electron transport in molecular devices AU - Kim, G. AU - Wang, S. C. AU - Lu, W. C. AU - Nardelli, M. B. AU - Bernholc, J. T2 - Journal of Chemical Physics DA - 2008/// PY - 2008/// VL - 128 IS - 2 ER - TY - JOUR TI - Bond constraint theory and the quest for the glass computer AU - Agarwal, S. C. AU - Paesler, M. A. AU - Baker, D. A. AU - Taylor, P. C. AU - Lucovsky, G. AU - Edwards, A. T2 - PRAMANA-JOURNAL OF PHYSICS DA - 2008/2// PY - 2008/2// DO - 10.1007/s12043-008-0043-y VL - 70 IS - 2 SP - 245-254 SN - 0973-7111 KW - switching KW - chalcogenide glass KW - bond constraint theory ER - TY - JOUR TI - Liquid crystal deposition on poled, single crystalline lithium niobate AU - Bharath, S. C. AU - Pimputkar, K. R. AU - Pronschinske, A. M. AU - Pearl, T. P. T2 - APPLIED SURFACE SCIENCE AB - For the purpose of elucidating the mechanisms for molecular organization at poled ferroelectric surfaces, single crystalline lithium niobate (LN), ‘Z-cut’ along the (0 0 0 1) plane, has been prepared and characterized and subsequently exposed to liquid crystal molecules. As a model system we chose to study the anchoring of 4-n-octyl-4′-cyanobiphenyl (8CB) to LN. Liquid crystalline films are of interest because of their useful electronic and optical properties as well as chemical sensing attributes. Low-energy electron diffraction (LEED), atomic force microscopy (AFM), surface contact angle measurements (CA), and X-ray photoelectron spectroscopy (XPS) were used to characterize the surface of lithium niobate as well as the nature of 8CB films grown on the surface. Atomically flat LN surfaces were prepared as a support for monolayer thick, 8CB molecular domains. 8CB liquid crystal molecules were deposited by an ambient vaporization technique and the films were analyzed using XPS and CA. Understanding electrostatic anchoring mechanisms and thin film organization for this molecule on uniformly poled surfaces allows for a fuller appreciation of how molecular deposition of other polarizable molecules on periodically poled and patterned poled lithium niobate surfaces would occur. DA - 2008/1/30/ PY - 2008/1/30/ DO - 10.1016/j.apsusc.2007.08.040 VL - 254 IS - 7 SP - 2048-2053 SN - 1873-5584 KW - lithium niobate KW - ferroelectric KW - surface KW - liquid crystal KW - monolayer ER - TY - JOUR TI - Kinetics of Ga and In desorption from (7x7)Si(111) and (3x3)6H-SiC(0001) surfaces AU - King, S. W. AU - Davis, R. F. AU - Nemanich, R. J. T2 - SURFACE SCIENCE AB - The desorption characteristics of Ga and In on (7 × 7) Si(1 1 1) and (3 × 3) 6H-SiC(0 0 0 1) surfaces have been determined using temperature programmed desorption. Two peaks were observed for desorption of a 1.5 ± 0.25 monolayer of Ga from the latter surface. The peak at Tmax = 670 °C exhibited zeroth order kinetics; the activation energy and pre-exponential were determined to be 2.6 ± 0.1 eV and 6 × 1027 ± 0.5 atom/cm2 s, respectively. The peak at Tmax = 535 °C exhibited first order desorption kinetics with an activation energy and pre-exponential of 6.2 ± 0.3 eV and 7 × 1021 ± 2 s−1, respectively. In contrast, only zeroth order kinetics and a lower activation energy of 2.0 ± 0.1 eV were determined for desorption of a 1.5 ± 0.25 monolayer of Ga from (7 × 7) Si(1 1 1). The values of these results in tandem with those of related studies of desorption from Si and SiC surfaces indicate that the low and high temperature Ga peaks from SiC are due to desorption from either a wetting layer or adatom sites and from Ga islands, respectively. The difference in desorption activation energies for Ga on Si(1 1 1) and on 6H-SiC(0 0 0 1) surfaces is attributed to differences in lattice matching of Ga to these surfaces. By contrast, only multilayer desorption was observed for 4 ± 1 monolayer of In on SiC(0 0 0 1). The zeroth order desorption activation energy and pre-exponential were 2.4 ± 0.1 eV and 6 × 1027±0.5 atom/cm2 s; they are consistent with the heat of sublimation (2.45–2.5 eV) for liquid In. DA - 2008/1/15/ PY - 2008/1/15/ DO - 10.1016/j.susc.2007.10.034 VL - 602 IS - 2 SP - 405-415 SN - 1879-2758 KW - silicon carbide KW - gallium KW - indium KW - temperature programmed desorption KW - kinetics ER - TY - JOUR TI - Hybrid ab initio Kohn-Sham density functional theory/frozen-density orbital-free density functional theory simulation method suitable for biological systems AU - Hodak, Miroslav AU - Lu, Wenchang AU - Bernholc, J. T2 - The Journal of Chemical Physics AB - A hybrid computational method intended for simulations of biomolecules in solution is described. The ab initio Kohn-Sham (KS) density functional theory (DFT) method is used to describe the chemically active part of the system and its first solvation shells, while a frozen-density orbital-free (FDOF) DFT method is used to treat the rest of the solvent. The molecules in the FDOF method have fixed internal structures and frozen electron densities. The hybrid method provides a seamless description of the boundary between the subsystems and allows for the flow of molecules across the boundary. Tests on a liquid water system show that the total energy is conserved well during molecular dynamics and that the effect of the solvent environment on the KS subsystem is well described. An initial application to copper ion binding to the prion protein is also presented. DA - 2008/1/7/ PY - 2008/1/7/ DO - 10.1063/1.2814165 VL - 128 IS - 1 SP - 014101 SN - 0021-9606 1089-7690 UR - http://dx.doi.org/10.1063/1.2814165 ER - TY - JOUR TI - Amino acid adsorption on the Si(100) surface: The case of glycine AU - Luo, Xuan AU - Qian, Gefei AU - Sagui, Celeste AU - Roland, Christopher T2 - JOURNAL OF PHYSICAL CHEMISTRY C AB - Using first principles total energy methods, we have investigated the adsorption of glycinethe simplest amino acidon the Si(100)- c(4 × 2)surface, with a focus on the associated energetics, charge transfer, electronic properties, and structural characteristics. We find that glycine adsorbs primarily on the “down” atoms of a Si dimer, with adsorption of the amino group being slightly favored over the absorption of the carboxylic acid group. Glycine on Si(100) may also involve the removal of a H atom from the chemical group most directly absorbed. In addition, there is evidence for a [2 + 2] cycloaddition reaction when both “CO” atoms absorb, as well as the more drastic breakup of the glycine molecule and the formation of a ketenimine molecule under high-energy conditions. DA - 2008/2/21/ PY - 2008/2/21/ DO - 10.1021/jp0775193 VL - 112 IS - 7 SP - 2640-2648 SN - 1932-7455 ER - TY - JOUR TI - Accessory proteins stabilize the acceptor complex for synaptobrevin, the 1 : 1 syntaxin/SNAP-25 complex AU - Weninger, Keith AU - Bowen, Mark E. AU - Choi, Ucheor B. AU - Chu, Steven AU - Brunger, Axel T. T2 - STRUCTURE AB - Syntaxin/SNAP-25 interactions precede assembly of the ternary SNARE complex that is essential for neurotransmitter release. This binary complex has been difficult to characterize by bulk methods because of the prevalence of a 2:1 dead-end species. Here, using single-molecule fluorescence, we find the structure of the 1:1 syntaxin/SNAP-25 binary complex is variable, with states changing on the second timescale. One state corresponds to a parallel three-helix bundle, whereas other states show one of the SNAP-25 SNARE domains dissociated. Adding synaptobrevin suppresses the dissociated helix states. Remarkably, upon addition of complexin, Munc13, Munc18, or synaptotagmin, a similar effect is observed. Thus, the 1:1 binary complex is a dynamic acceptor for synaptobrevin binding, and accessory proteins stabilize this acceptor. In the cellular environment the binary complex is actively maintained in a configuration where it can rapidly interact with synaptobrevin, so formation is not likely a limiting step for neurotransmitter release. DA - 2008/2// PY - 2008/2// DO - 10.1016/j.str.2007.12.010 VL - 16 IS - 2 SP - 308-320 SN - 1878-4186 ER -