UScholar Works
 
Filters: Department: "Physics" Collection: "ir_uspace"
251 - 275 of 924
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CreatorTitleDescriptionSubjectDate
251 Vardeny, Zeev ValentineExperimental determination of the charge/neutral branching ratio η in the photoexcitation of ∏-conjugated polymers by broadband ultrafast spectroscopyWe demonstrate a long-sought reliable method for determining the important branching ratio η between photogenerated charged polarons and neutral excitons in ∏-conjugated polymer films and solutions, using femtosecond transient photomodulation spectroscopy with broad spectral range from 0.14 to ...pi-conjugated polymers; Charge/neutral branching ratio; Photoexcitation; nu value; Broadband ultrafast spectroscopy2007-02
252 Boehme, ChristophExperimental discrimination of geminate and non-geminate recombination in a-Si:HA study of charge-carrier recombination in intrinsic hydrogenated amorphous silicon (a-Si:H) is presented using pulsed electrically and pulsed optically detected magnetic-resonance spectroscopies in order to measure the influence of spin-dependent recombination on photoluminescence (PL) and photoc...Geminate recombination2009-05
253 Lupton, John MarkExperimental evidence for exciton scaling effects in self-assembled molecular wiresResonant Rayleigh scattering from self-assembled one-dimensional molecular J-aggregate wires reveals a distinct dependence of the exciton energy on the width of lateral extension. For the J aggregates used in this study, strong in-line dipole coupling leads to a delocalization of the exciton wave fu...Exciton scaling effects; Molecular wires; J-aggregate wires; Quantum wires2004-12
254 Wu, Yong-ShiExplicit solutions of the Bethe ansatz equations for Bloch electrons in a magnetic fieldFor Bloch electrons in a magnetic field, explicit solutions are obtained at the center of the spectrum for the Bethe ansatz equations of Wiegmann and Zabrodin. When the magnetic flux per plaquette is 1/(Q with Q an odd integer, distribution of the roots of the Bethe ansatz equation is uniform except...Bloch electron; Magnetic flux1994-08
255 Mattis, Daniel C.Extinction of antiferromagnetism by holes in CuO2The introduction of a sufficient number of holes into antiferromagnetic planes of Cu02 in La-Cu-O and Y-Ba-Cu-O causes antiferromagnetism to disappear at a critical density xc, beyond which superconductivity occurs. We investigate two competing tendencies, which determine the dependence of xc on the...Antiferromagnets1991-08
256 DeTar, Carletonf B for various actions: approaching the continuum limit with dynamical fermionsWe present results for pseudoscalar decay constants of heavy-light mesons using both quenched and Nf = 2 dynamical fermion configurations. A variety of fermion actions is investigated: Wilson, nonperturbative clover, and fat-link clover. For heavy quarks the Fermilab formalism is applied. In the q...Decay constants; Wilson fermions2001-03
257 Vardeny, Zeev ValentineFabrication and properties of gallium metallic photonic crystalsGallium metallic photonic crystals with 100% filling factor have been fabricated via infiltration of liquid gallium into opals of 300-nm silica spheres using a novel high pressure-high temperature technique. The electrical resistance of the Ga-opal crystals was measured at temperatures from 10 to 2...2003-10
258 Boehme, ChristophFast nuclear spin hyperpolarization of phosphorus in siliconWe experimentally demonstrate a method for obtaining nuclear spin hyperpolarization, that is, polarization significantly in excess of that expected at thermal equilibrium. By exploiting a nonequilibrium Overhauser process, driven by white light irradiation, we obtain more than 68% negative nuclear p...Hyperpolarization; Spin coherence; Electrical readout2009-01
259 Wu, Yong-ShiFast tracking detector with fiber scintillators and a position sensitive photomultiplierWe have studied the properties of a tracking detector composed of 32 fiber scintillators coupled to a multianode photo-multiplier placed in a pion beam at TRIUMF. We measured the efficiency of the detector, as well as its tracking capabilities and double hit resolution.Fast tracking detector; Fiber scintillators; Position sensitive photomultiplier1989-02
260 DeTar, CarletonfB quenched and unquenchedResults for fβ, / fβs, /fD, /fDs , and their ratios are presented. High statistics quenched runs at β = 5.7, 5.85, 6.0, and 6.3, plus a run still in progress at β = 6.52 make possible a preliminary extrapolation to the continuum. The data allows good control of all systematic errors except for q...Decay constants; Wilson quarks1996-03
261 Vardeny, Zeev Valentine; Symko, Orest GeorgeFemtosecond dynamics of quasi-particles in YBa2Cu3O7-δ superconductor filmsWe have studied the transient electronic response of YBa2Cu307-δ epitaxialy grown H T c superconductor thin films in the femtosecond time domain, using transient photoinduced reflectivity (AR) with 60 fsec time resolution. For temperatures T>Tc only a bolometric signal was observed with ARrO. For ...Femtosecond dynamics; YBa2Cu3O7-8; Transient electronic response; Transient optical response1991-03
262 Symko, Orest George; Vardeny, Zeev ValentineFemtosecond dynamics of quasi-particles in YBa2Cu3O7-δ superconductor filmsWe have studied the transient electronic response of YBa2Cu30y . 5 epitaxialy grown HTC superconductor thin films in the femtosecond time domain, using transient photoinduced reflectivity (∆R) with 60 fsec time resolution. For temperatures T>TC only a bolometric signal was observed with ∆R>0. F...Femtosecond dynamics; Superconductor films; YBCO films1991-03
263 Vardeny, Zeev ValentineFemtosecond dynamics of the nonlinear optical response in polydiethynylsilaneWe have measured the femtosecond dynamics of the nonlinear optical response xc3' in polydiethynylsilane ( C4H2SiBu2)x, a novel class of r-conjugated polymers incorporating Si, using degenerate four-wave mixing and photoinduced absorption techniques. In resonance conditions at 620 nm we found x (3) ...Polydiethynylsilane; Femtosecond dynamics; Nonlinear optical response; Pi-conjugated polymers1991
264 Symko, Orest George; Vardeny, Zeev ValentineFemtosecond optical detection of quasiparticle dynamics in high-Tc YBa2Cu3O7- 8 superconducting thin filmsFemtosecond dynamics of photogenerated quasiparticles in YBa2Cu307-δ superconducting thin films shows at T ≤ Tc two main electronic processes: (i) quasiparticle avalanche production during hot-carrier thermalization, which takes about 300 fsec; (ii) recombination of quasiparticles to form Cooper ...Quasiparticle dynamics; High-Tc; Femtosecond dynamics; Photogenerated quasiparticles1990-11
265 Vardeny, Zeev Valentine; Symko, Orest GeorgeFemtosecond optical detection of quasiparticle dynamics in High-Tc YBa2Cu3O7-δ superconducting thin filmsFemtosecond dynamics of photogenerated quasiparticles in YBa2Cu307-δ superconducting thin films shows at r < Tc two main electronic processes: (i) quasiparticle avalanche production during hot-carrier thermalization, which takes about 300 fsec; (ii) recombination of quasiparticles to form Cooper pa...Femtosecond optical detection; HTc YBa2Cu3O7-81990-11
266 Mattis, Daniel C.Ferromagnetism and spin waves in the band theoryIntra-atomic exchange (Hund's rule mechanism) and Heisenberg nearest-neighbor exchange are examined for their role in the ferromagnetism of metals with degenerate bands. We examine the ground state, and find there is ferromagnetism once the largest eigenvalue j00 of the exchange matrix exceeds 1/2...Band theory; Hund's rule1963-12
267 Mattis, Daniel C.Few-body problem on a latticeThe author explores some of the inherent simplifications of "quantum lattice physics." He distinguishes between fermions and bosons and analyzes the n-body problem for each, with n = 1,2,3... typically a small number. With delta-function (zero-range) interactions, the three-body problem on a lattice...Quantum; Electrons; Spin1986
268 Vardeny, Zeev ValentineFilm morphology and photophysics of polyfluoreneWe have studied the interplay between photophysics and film morphology of poly(9,9-dioctyl)fluorene (PFO) using a variety of optical probes. Upon slowly warming a spin-cast PFO film from 80 to 300 K, a fraction of the sample is transformed into a different solid phase, the ß phase. Absorption and e...Polyfluorene; Photophysics; Film morphology2000-12
269 DeTar, CarletonFinite temperature lattice QCD with clover fermionsWe report on our simulation of finite temperature lattice QCD with two flavors of O(a) Symanzik-improved fermions and O(a2) Symanzik-improved glue. Our thermodynamic simulations were performed on an 83 × 4 lattice, and we have performed complementary zero temperature simulations on an 83 × 16 la...Wilson quarks; Clover fermions1997-02
270 DeTar, CarletonFinite temperature QCD: progress and outstanding problemsI review recent progress in numerical simulations of finite temperature quantum chromodynamics and discuss the status of some outstanding problems. Included is (1) a discussion of recent results determining the temperature of the "phase transition" in full QCD, (2) a scaling analysis of the Polyakov...Phase transitions; Staggered fermions; Wilson fermions; Polyakov loop; Deconfinement; Instanton1995-04
271 DeTar, CarletonFinite-size and quark mass effects on the QCD spectrum with two flavorsWe have carried out spectrum calculations with two flavors of dynamical Kogut-Susskind quarks on four lattice sizes from 83X24 to 163 X 24 at couplings that correspond to chiral symmetry restoration for a lattice with six time slices. We estimate that the linear spatial sizes of the lattices range f...Kogut-Susskind quarks; Hadron mass; Pion mass1993-11
272 DeTar, CarletonFirst determination of the strange and light quark masses from full lattice QCDWe compute the strange quark mass ms and the average of the u and d quark masses mˆ using full lattice QCD with three dynamical quarks combined with the experimental values for the rr and K masses. The simulations have degenerate u and d quarks with masses mu=md=mˆ αs low as ms/8, and two diffe...Staggered quarks; Quark-gluon plasma2004-08
273 Sokolsky, PierreFirst observation of the Greisen-Zatsepin-Kuzmin suppressionThe High Resolution Fly's Eye (HiRes) experiment has observed the Greisen-Zatsepin-Kuzmin suppression (called the GZK cutoff) with a statistical significance of five standard deviations. HiRes' measurement of the flux of ultrahigh energy cosmic rays shows a sharp suppression at an energy of 6 x 10^1...Extensive air showers; Suppression; Energy spectrum; Fluorescence; GZK cutoff2008-03
274 DeTar, CarletonFirst signs for string breaking in two-flavor QCDWe have been examining the phenomenon of string breaking in QCD with two flavors of dynamical staggered quarks. We construct a transfer matrix from a combination of "string" and "two-meson" channels. Preliminary results with low statistics show the expected signs of string breaking.String breaking; Wilson loop; Staggered quarks2000-04
275 Ailion, David CharlesFloating of the modulation wave and phase pinning in incommensurate Rb2ZnBr4Nuclear-magnetic-resonance measurements in incommensurate Rb2ZnBr4 show the existence of regions where the modulation wave is floating. The floating regions coexist with other regions where the modulation wave is static. Impurity phase pinning and a roughening of the modulation wave at higher temper...Floating; Incommensurate phase; Phason mode; Lattices1983
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