UScholar Works
 
Filters: Department: "Physics" Collection: "ir_uspace"
201 - 225 of 924
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CreatorTitleDescriptionSubjectDate
201 Vardeny, Zeev Valentine; Ehrenfreund, Eitan A.Photoexcitation spectroscopy of polythiopheneRadiative recombination in polythiophene is studied by cw photoluminescence and photoinduced absorption spectroscopies and by photoluminescence-detected magnetic resonance. The fast-recombination centers are assigned to intrachain excitons in defect-free chains, while the slow recombination is due t...Radiative recombination; Photoexcitation spectroscopy1987-02
202 Vardeny, Zeev ValentineSteady-state photomodulation spectroscopy of α-Si:H/α-SiNx:H multilayer structuresThe steady-state photomodulation (PM) spectrum and its temperature dependence were studied in α-Si:H/α-SiNx:H multilayer structures (MLS). We found that the photocarrier properties in MLS with Si sublayer thickness ds < 20 A are dominated by band-tail broadening resulting from increase in disorder...Steady-state photomodulation spectroscopy; Photocarrier properties; Amorphous silicon1987-05
203 DeTar, CarletonPhenomenological lattice model of the high-temperature phase transition in quantum chromodynamicsWe propose a simple phenomenological lattice model for the high-temperature phase transition in a quark-gluon plasma, in which the elementary dynamical variables are Wilson lines and SU(iV) chiral spins. A mean-field analysis of the model shows a second-order chiral phase transition for N=2 and a fi...Quark plasma; Gluon plasma; Chiral symmetry; Phase transitions1987-06
204 Vardeny, Zeev Valentine; Ehrenfreund, Eitan A.Amplitude and phase modes in trans-polyacetylene: resonant Raman scattering and induced infrared activityThe resonant Raman scattering (RRS) from the three Ag modes of trans-polyacetylene and the charged-induced ir modes are analyzed with use of the amplitude- and phase-mode theories. It is shown that the observed phonon frequencies and the relative intensities of all modes obtained at various laser ex...Induced infrared activity; Ag modes; Amplitude modes; Phase modes; Trans-polyacetylene1987-07
205 DeTar, CarletonHadronic spectrum of the quark plasmaWe have carried out a numerical simulation in SU(3) lattice gauge theory with four flavors of low-mass staggered fermions at zero baryon-number density in the vicinity of the high-temperature phase transition on 6x 103 and 6x 102x20 lattices. Static screening masses (static susceptibilities) were m...Hadronic matter; Quark plasma; Chiral symmetry; Phase transitions1987-07
206 Mattis, Daniel C.Implications of infrared instability in a two-dimensional electron gasWe consider the tight-binding energy band in sq lattices and determine that in the half-filled case there exists an infrared instability in addition to the 2kF (nesting)-type instability. In view of the pseudo-two-dimensional band structure of La2-xBaxCu04 recently proposed by Jorgensen et al. and b...Fermi surface; Bosonization1987-07
207 Symko, Orest GeorgeMicrowave absorption in the superconducting and normal phases of Y-Ba-Cu-OMicrowave absorption in a dc magnetic field up to 12 kG, attributed to nonequilibrium contributions to the ac susceptibility, appears at Tc as the sample is cooled. ESR measurements of YBa-Cu-O show that Cu2+ exists only in the fraction of the sample which is not superconducting in a distorted octa...Microwave absorption; Superconducting phase; YBCO; High Tc1987-08
208 Vardeny, Zeev ValentinePicosecond optical time-of-flight studies of carrier transport in α-Si:H/α-SiNx:H multilayersWe report time-of-flight experiments in the time range from 0.2 psec to 1.8 nsec in 0-Si:H-a-SiNx:H multilayer structures using a purely optical technique. The transport mechanism of photoexcited carriers is shown to be dispersive and its characteristic parameters are determined in the temperature r...Time-of-flight; Amorphous silicon; Carrier transport; Photoexcited carriers1987-09
209 Mattis, Daniel C.Electron-phonon interaction in two dimensions: the case for strong coupling in high-Tc superconductorsA particular model interaction between electrons and acoustic phonons is found to cause electrons to become weakly "self-trapped" for an arbitrary filling factor in d=2, but not in d=1 nor, for different reasons, in d>3. To the extent that electron kinetic energy is reduced in d=2, the electronic in...Strong coupling1987-09
210 DeTar, CarletonMeasuring the hadronic spectrum of the quark plasmaIn an effort to characterize the large-scale structure and composition of the Q C D plasma at zero baryon-number density in the vicinity of the high-temperature phase transition, we have carried out a numerical simulation in SU(3) lattice gauge theory with four flavors of low-mass staggered fermions...Quark plasma; Gluon plasma; Hadronic matter; Deconfinement; Chiral symmetry; Phase transitions1987-11
211 Mattis, Daniel C.Mattis and Pan replyAfter several independent calculations failed to confirm our published1 numbers on the ground-state energy of the s = 1/2 antiferromagnet in two dimensions, we checked our computer programs and found some deplorable errors introduced in proceeding from one dimension to two.Ground-state energy; Antiferromagnets; Long-range order1988
212 Vardeny, Zeev Valentine; Ehrenfreund, Eitan A.Optically detected magnetic resonance study of recombination mechanisms in polythiopheneFrom detailed optically detected magnetic resonance measurements in polythiophene, we show that the g=2.003 signal is luminescence enhancing, and that the signal comes from a broad photoluminescence band peaking near 1.65 eV. This band is tentatively assigned to the radiative recombination of polaro...Recombination mechanisms1988
213 Ailion, David Charles; Morris, Alan H.Quantitative assessment of pulmonary edema by nuclear magnetic resonance methodsConsiderable progress has been made in the application of nuclear magnetic resonance (NMR) imaging and nonimaging techniques to the quantitative assessment of pulmonary edema. NMR measurements offer the advantages of being noninvasive, relatively rapid, and easily repeatable. In addition, NMR imagin...Quantitative assessment1988
214 Ailion, David CharlesNMR lineshapes and order parameter determination in proton pseudo-spin glassesThe quadrupole-perturbed NMR line shape has been evaluated in the local approximation for an arbitrary static random-field distribution coexisting with Gaussian time-fluctuating random fields. The special case of a spin-glass-type static local random-field distribution is treated also. The results ...NMR; Nuclear magnetic resonance; Line shape; Random fields; Proton pseudo-spin-glasses1988
215 Williams, Clayton C.Noise reduction technique for scanning tunneling microscopyNoise stemming from mechanical vibration, electronic noise, or low frequency (l / f power spectrum) inherent in the tunneling process, often limits the resolution, speed, or range of application of scanning tunneling microscopy (STM). We demonstrate a technique for minimizing the effect of these noi...Noise reduction; Dithering; Graphite1988
216 Williams, Clayton C.Measurement of in-plane magnetization by force microscopyWe present data which show that the magnetic force microscope is capable of detecting the component of the magnetic field parallel to the surface of a sample under study. Images of bits in a Co-alloy thin-film disk and of laser-written bits in a TbFe film were taken with a magnetized tip tilted at ...Co-alloy disc; Magnetization1988
217 Gondolo, PaoloGroups of galaxies in the local supercluster: some hypotheses on the evolutionary stageWe present a method capable of determining the evolutionary stage of bound, isolated systems of galaxies. In particular, we apply it to a sample of groups, belonging to the Local Supercluster, taken from the Geller and Huchra's (1983) catalogue. We find that most of them are still in the phase of c...Evolution of galaxy clusters1988
218 DeTar, CarletonSignals for hadronic modes in the quark plasmaWe give a new argument for the occurrence of hadronic modes in the high-temperature quark plasma, present a crude phenomenological model of the plasma, and discuss possible experimental signatures for the low-lying modes.Quark plasma; Hadronic matter; Phase transitions1988-01
219 DeTar, CarletonPseudodeconfinement and dynamical confinement in the quark plasmaWe elaborate upon phenomenological models of high-temperature hadronic matter at zero baryon density. We discuss the choice of a practical set of "fundamental" degrees of freedom, indicate their relationship to dynamically confined plasma modes, and suggest in what way they may account for the phase...Quark plasma; Gluon plasma; Hadronic matter; Deconfinement; Glueballs; Mesons; Phase transitions1988-04
220 Wu, Yong-ShiChiral bosonization and local Lorentz-invariant actions for chiral bosonsWe formulate a geometrical theory of self-dual scalar fields in two dimensions with a local Lorentz-invariant action. Path-integral quantization is used to derive chiral bosonization by demonstrating equivalence of correlation functions of currents and energy-momentum tensors in our theory with thos...Bosonization; String theory; Weyl fermions1988-06
221 Vardeny, Zeev ValentineTransient-photomodulation-spectroscopy studies of carrier thermalization and recombination in α-Si:HThe transient response of mid-gap absorption in a-Si:H to pulsed optical excitation is studied as a function of time (300 ns to 30 ms) and sample temperature (10-220 K) with use of probe wavelengths ranging from 0.75 to 5.5 fim. A numerical inversion process applied to the data gives the distributio...Amorphous silicon; a-Si:H; Transient-photomodulation-spectroscopy; Carrier thermalization; Carrier recombination; Pulsed optical excitation1988-07
222 Mattis, Daniel C.Ground-state energy of Heisenberg antiferromagnet for spins s=1/2 and s=1 in d=1 and 2 dimensionsA simple real-space renormalization method yields the ground-state energy of the Heisenberg antiferromagnet. We find the ground-state energy per spin for s=1/2 (-0.4438 in ID , -0.6723 in 2D ) and s = 1 (-1.388 in ID and -1.907 in 2D) to three-figure accuracy, using properties of relatively small o...Ground-state energy; Heisenberg antiferromagnet; Long-range order1988-07
223 Mattis, Daniel C.Statistical mechanics of CuO2 plane in the presence of localized holesBoth La2Cu04 and YBa2Cu306 are antiferromagnetic insulators, becoming less so as holes are introduced on individual oxygen bonds. We evaluate the free energy of a single Cu02 plane in the Ising representation. Beyond a critical concentration xo=0.29289 holes per O1O2 cell, antiferromagnetism is repl...Localized holes1988-10
224 Wu, Yong-ShiObservable effects of the quantum adiabatic phase for noncyclic evolutionIt is pointed out that, contrary to naive expectation, the gauge structure or Berry connection recently found in slowly varying quantum systems gives rise to observable effects even for noncyclic evolutions corresponding to open paths in parameter space. We propose to test such effects in muon spin ...Adiabatic phases; Noncyclic evolution; Eigenstates1988-12
225 Symko, Orest GeorgeAbsorption at radio frequencies in superconducting Y1Ba2Cu3OyThe large magnetic-field-dependent ac absorption in superconducting Y1Ba2Cu3Oy ceramics and powders decreases slowly with increasing frequency in the range 2-16 MHz. The magnetic-field-dependent ac absorption is observed below Tc in superconducting Y1Ba2Cu3Oy ceramics, powders and twinned crystals ...Copper-octahedral oxygen perovskites; Superconducting Y1Ba 2Cu3Oy; ac absorption1989
201 - 225 of 924