UScholar Works
 
Filters: Department: "Physics" Collection: "ir_uspace"
276 - 300 of 924
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CreatorTitleDescriptionSubjectDate
276 Vardeny, Zeev ValentineStudies of photoexcited states in polyacetylene and poly(parpahenylenevinylene) by absorption detected magnetic resonance: the case of neutral photoexcitationsPhotoexcited states in trans polyacetylene [f-(CH).x ] and in alkoxy derivatives of poly(paraphenylenevinylene) (PPV) have been studied by the technique of absorption detected magnetic resonance. In addition to the stable charged photoexcitations, which are charged solitons in f-(CH).x and bipolaro...Poly(parpahenylenevinylene); Photoexcitation1992-02
277 Wu, Yong-ShiMultisheet configuration space and fractional quantum statisticsWe show that if one uses a multisheet configuration space for a system of identical particles, then fractional quantum statistics in two dimensions can be geometrically characterized as a topological quantum number for going from one sheet to the next. Furthermore, the spectrum of such a g-sheet s...1992-05
278 Wu, Yong-ShiNonlinear Ŵ∞ current algebra in the SL(2,R)/U(1) coset modelWe show that in the world-sheet SL(2,R)/U(l) coset model there exists a hidden nonlinear W∞ current algebra, which incorporates all higher-spin (s≥ 2) currents including the energy-momentum tensor. Our proof is based on a free-field realization of Woo in terms of two scalars, as well as an ele...W-algebras; Coset model; World-sheet; String theory; Spacetime; Quantum currents1992-05
279 Vardeny, Zeev ValentinePhotoexcitation dynamics in polyacetylene probed by transient photoinduced resonant Raman scatteringWe have measured photoexcitation dynamics in the picosecond time domain in fully trans and partially isomerized (CH)X and (CD)X films with different cis/trans content ratios, using the technique of transient photoinduced resonant Raman scattering. Following the distinctively different decay kineti...Photoexcitation dynamics1992-05
280 DeTar, CarletonQCD thermodynamics with two flavors at Nt=6The first results of numerical simulations of quantum chromodynamics on the Intel iPSC/860 parallel processor are presented. We performed calculations with two flavors of Kogut-Susskind quarks at Nt = 6 with masses of 0.15T and 0.075T (0.025 and 0.0125 in lattice units) in order to locate the crosso...Kogut-Susskind quarks; Crossover temperature; Chiral symmetry; Polyakov loop; Phase transitions1992-05
281 Wu, Yong-ShiDiophantine equation for the three-dimensional quantum Hall effectWhen the Fermi level lies in a gap, the Hall conductivity of three-dimensional electrons in a periodic potential is expressed in a topologically invariant form with a set of three integers. If the magnetic fluxes through the three independent areas of the periodic lattice are rational numbers, one...Hall conductivity; Periodic potentials1992-06
282 DeTar, CarletonToward an effective chiral model of high-temperature QCDIn an effort to expose the mechanism for chiral-symmetry restoration in high-temperature QCD, we use numerical simulations of lattice QCD with staggered fermions to obtain information about possible effective chiral models. We propose the strategy of comparing expressions built from expectation val...Chiral model; Meson fields; Chiral symmetry; Phase transitions1992-06
283 Vardeny, Zeev ValentineEvolution of excitons and polarons in polythiophene from femtoseconds to millisecondsWe have studied the photoexcitation dynamics in electrochemically polymerized polythiophene thin films using transient photomodulation spectroscopy measured from 100 fs to 20 ms in the spectral range from 0.25 to 2.2 eV, and by the novel technique of absorption-detected magnetic resonance (ADMR). ...Femtoseconds; Milliseconds; Photoexcitation dynamics1992-07
284 Sokolsky, PierreSearch for compact sources of cosmic photons above 200 TeVFrom April 1988 to February 1990 we used a two-level array of scintillators to search in the cosmic radiation for compact sources of y rays above 200 TeV. Counters on the surface measured the size and direction of extensive air showers while counters buried 3 m below ground measured their muon conte...Extensive air showers; Cygnus X-3; Hercules X-1; Crab Nebula; Ultrahigh energies1992-10
285 Mattis, Daniel C.Thermal conductivity and thermodynamics of phonons for an exactly soluble model of disorderWe calculate the exact thermal conductivity and the heat capacity of an insulator for which the lattice dynamics are given by a phonon gas in the presence of frozen-in disorder, in the special case of the "backward-scattering'' model of impurity scattering.Thermal conductivity; Heat capacity; Insulators; Defects; Phonon gas; Backward-scattering model1992-10
286 Kieda, David B.; Sokolsky, PierreSearch for compact sources of cosmic photons above 200 TeVFrom April 1988 to February 1990 we used a two-level array of scintillators to search in the cosmic radiation for compact sources of y rays above 200 TeV. Counters on the surface measured the size and direction of extensive air showers while counters buried 3 m below ground measured their muon conte...Compact sources; Air showers1992-10
287 DeTar, CarletonQCD thermodynamics with two flavors of Wilson quarks at Nt=6We report on a study of hadron thermodynamics with two flavors of Wilson quarks on 123 X6 lattices. We have studied the crossover between the high- and low-temperature regimes for three values of the hopping parameter, K=0. 16, 0.17, and 0.18. At each of these values of K we have carried out spect...Wilson quarks; Staggered quarks; Chiral symmetry; Phase transitions1992-11
288 Wu, Yong-ShiTwo-loop analysis of non-Abelian Chern-Simons theoryPerturbative renormalization of a non-Abelian Chern-Simons gauge theory is examined. It is demonstrated by explicit calculation that, in the pure Chern-Simons theory, the & function for the coefficient of the Chern-Simons term vanishes to three-loop order. Both dimensional regularization and regula...Chern-Simons theory; Yang-Mills theory; Regularization1992-12
289 Williams, Clayton C.Mapping of mobile charges on insulator surfaces with the electrostatic force microscopeMigration of surface ions in lateral fields on insulator surfaces may modify the electrical characteristics of underlying semiconductor structures causing device instabilities. A high sensitivity electrostatic force microscope is used to image the movement and spatial distribution of surface ions on...Insulator surfaces; Surface ions; Electrostatic force microscope1993
290 Ailion, David Charles31P NMR spin-lattice relaxation: structural glass dynamics in Rb1-x(ND4)xD2PO4We performed 3 1P NMR measurements of the temperature-dependent spin-lattice relaxation time in several mixed single crystals of Rbi_x(ND4 ) xD2P04 [DRADP] having different ammonium concentration x (x =0.22, 0.44, 0.78) as well as in three pure single crystals (ND4)D2P04 [DADP], (NH4)H2P04 [ADP], an...NMR; Spin-lattice; Relaxation; Crystals; Glass; Spin-glass1993
291 Wu, Yong-ShiOn the Kadomtsev-Petviashvili hierarchy, Ŵ∞ algebra, and conformal SL(2,R)/U(1) model. II. The quantum caseThis article is devoted to constructing a quantum version of the famous Kadomtsev-Petviashvili (KP) hierarchy by deforming its second Hamiltonian structure, namely, the nonlinear W, algebra. This is achieved bx quantizing the conformal noncompact SL(2,R) k/ U(1) coset model, in which W, appears as ...Kadomtsev-Petviashvili hierarchy; Quantum charges; W-algebras1993
292 Vardeny, Zeev ValentinePhotoexcitations in polythiophene at high pressureWe report optical-absorption, photoluminescence (PL), and picosecond photoinduced absorption (PA) decay in films of poly-3-hexyl-thiophene at pressures up to 80 kbar. The spectral bands redshift nonlinearly with pressure and the PL intensity decreases markedly. Thermochromic transitions are complete...Photoexcitations1993-01
293 Vardeny, Zeev ValentineResonant Raman-scattering spectroscopy of polydiacetylene films at high pressureWe studied the electronic energies and phonon frequencies of polydiacetylene 4-BCMU thin films at high pressures up to 50 kbar using Raman scattering under preresonant and resonant conditions. Pressure-induced changes in the resonant Raman scattering (RRS) include (1) hardening of the most strongly...Resonant raman scattering spectroscopy; Polydiacetylene films; Pi-conjugated polymers1993-02
294 Kieda, David B.; Gaisser, Thomas K.; Sokolsky, PierreCosmic-ray composition around 10^18 eVWe use the depth of maximum distribution as measured by the stereo Fly's Eye detector to study the chemical composition of the primary cosmic radiation between 3x 1017 eV and 1019 eV. The analysis depends on the use of simulations to study the response of the detector as well as sensitivity to assum...Fly's Eye; Cosmic ray composition; Cosmic ray nuclei; Chemical composition1993-03
295 Symko, Orest GeorgeTunneling studies of mesoscopic all-NBN junctionsA scanning tunneling microscope (STM) was used to position a NbN tip near a NbN thin film sputtered on a Si substrate. Measurements at 4.2 K clearly show an energy gap of 5.0 mV. The Coulomb blockade of tunneling and the Coulomb staircase, formed by single-electron charging of the central electrod...All-NbN junctions; NbN1993-03
296 Sokolsky, PierreCosmic-ray composition around 10^18 eVWe use the depth of maximum distribution as measured by the stereo Fly's Eye detector to study the chemical composition of the primary cosmic radiation between 3 x 10^17 eV and 10^19 eV. The analysis depends on the use of simulations to study the response of the detector as well as sensitivity to as...Energy spectrum; Extensive air showers; Inelasticity; Hadronic interactions1993-03
297 Wu, Yong-ShiTransitions between the quantum Hall states and insulators induced by periodic potentialsTransitions between two quantum Hall states or between a quantum Hall state and a Mott insulator induced by periodic potentials are studied in the 1 /TV expansion. The transitions are found to be continuous in the large-TV limit and are described by a critical point that depends on a real parameter ...Periodic potentials; Insulators1993-03
298 Symko, Orest GeorgeLarge steps in long Josephson junctionsLarge constant voltage current-steps were observed in the IV-characteristics of long NbN-MgO-NbN Josephson junctions in the presence of external magnetic fields of a few Gauss. The steps are separated by a voltage AV corresponding roughly to 3 to 5 times the voltage spacing expected between adjacent...NbN-MgO-NbN; Long junctions; Current-steps; Voltage1993-03
299 DeTar, CarletonTunneling and the spectrum of the Potts modelThe three-dimensional, three-state Potts model is studied as a paradigm for high-temperature quantum chromodynamics. In a high-statistics numerical simulation using a Swendson-Wang algorithm, we study cubic lattices of dimension as larger as 643 and measure correlation functions on long lattices of ...Potts model; Tunneling; Transfer matrix; Phase transitions1993-05
300 Vardeny, Zeev ValentineTransient and steady-state photoconductivity of a solid C60 filmWe report the experimental results of the subnanosecond time-resolved transient photoconductivity (PC) of solid C60 film at various photon energies, and the spectral response of the steady-state PC in the energy range between 1.5 and 4.5 eV. The initial fast transient PC response decays exponenti...Transient photoconductivity; Steady-state photoconductivity; Solid C60 film1993-09
276 - 300 of 924