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 (<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 -