UScholar Works
 
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301 - 325 of 924
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CreatorTitleDescriptionSubjectDate
301 Sokolsky, PierreEvidence for correlated changes in the spectrum and composition of cosmic rays at extremely high energiesThe Utah Fly's Eye detector has revealed a change in the cosmic ray composition which is correlated with structure in the all-particle energy spectrum. The data can be fitted by a simple model of a steep power law spectrum of heavy nuclei which is overtaken at high energies by a flatter spectrum of ...Energy spectrum; Extensive air showers1993-11
302 Wu, Yong-ShiMott transition in an anyon gasWe introduce and analyze a lattice model of anyons in a periodic potential and an external magnetic field, which exhibits a transition from a Mott insulator to a quantum Hall fluid. The transition is characterized by the anyon statistics a, which can vary between fermions, a = 0, and bosons, ct - 1...Anyon gas; Periodic potentials; Mott transition1993-11
303 Kieda, David B.; Gaisser, Thomas K.; Sokolsky, PierreEvidence for correlated changes in the spectrum and composition of cosmic rays at extremely high energiesThe Utah Fly's Eye detector has revealed a change in the cosmic ray composition which is correlated with structure in the all-particle energy spectrum. The data can be fitted by a simple model of a steep power law spectrum of heavy nuclei which is overtaken at high energies by a flatter spectrum o...Ultrahigh energy cosmic rays; Fly's Eye; Cosmic ray composition; Cosmic ray spectrum1993-11
304 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
305 Vardeny, Zeev ValentineMagneto-optical studies of photoexcitations in C61We have used a variety of cw optical and optically detected magnetic-resonance techniques to characterize long-lived photoexeitations in methanofullerene (C6 1) as a dispersion in polystyrene glass, at temperatures below 10 K. We identify triplet excitons with zero-field-splitting (ZFS) parameters...Photoexcitations; C61; Methanofullerene1993-12
306 Williams, Clayton C.; Stringfellow, Gerald B.Effect of substrate misorientation on ordering in Ga0.5In0.5POrdering produced in Gao.5Ino.5P epitaxial layers grown by OMVPE can be controlled by variations in the substrate misorientation as well as the growth temperature and the growth rate. The ordering produced at a growth temperature of 620°C and a relatively low growth rate of 0.5 /μm/hr is found to ...Ga0.5In0.5P; Epitaxial layers; Epitaxial growth; OMVPE1994
307 Ailion, David CharlesNMR in substitutionally disordered incommensurate (Rb1-xKx)2ZnCl4The impurity-concentration dependence of the 8 7Rb NMR line shapes and phason-induced spin-lattice relaxation rates has been studied over a wide temperature range in substitutional^ disordered incommensurate (Rb1_xKJ C)2ZnCl4 for x =0.00, 0.02, and 0.06. The results yield information on the impurity...NMR; Line shapes; Phasons; Spin-lattice; Phase fluctuations1994
308 Ailion, David CharlesThermal fluctuations and NMR spectra of incommensurate insulatorsThe effects of thermal order-parameter fluctuations on the NMR line shape of incommensurate systems are evaluated within the mean-field Landau theory and the results are compared with the 8 7Rb and 3 9K 1/2 -1/2 NMR spectra of Rb2ZnCl4 and K2Se04 just below the paraelectric-incommensurate transition...NMR spectra; Thermal fluctuations; Line shapes; Incommensurate insulators1994
309 Symko, Orest GeorgeFormation of AlCuFe quasicrystalline thin films by solid state diffusionWe show that thin films 3000 A in thickness of the icosahedral AlCuFe phase can be formed by solid state diffusion of sputtered Al, Cu, and Fe layers. As for bulk materials, we propose that the icosahedral phase grows by diffusion of the 0.1 in the A13Fe layer previously formed by interdiffusion of...AlCuFe; Quasicrystalline thin films; Solid state diffusion; Icosahedral phase1994
310 Vardeny, Zeev ValentineLeng et al. replyConwell, Rothberg, and Mizes (CRM) claim [1] that, as a result of chain length distribution and vibronic sidebands of electronic levels in PPV films, there is little correlation between increase of pump photon energy (Hw) and increase of electronic energy, and therefore data from excitation spectros...Chain length distribution; Vibronic sidebands; PPV films; Pump photon energy1994
311 Ailion, David Charles93Nb NMR in the imcommensurate and quasi-commensurate phases of barium sodium niobateNMR spectra have been measured for the quadrupole perturbed 1/2 -1/2 transition of 9 3Nb in barium sodium niobate (BSN) between 300 and 650 K. The spectra are inhomogeneously broadened in the incommensurate (/) phase between T7 = 580 K and r c = 540 K as well as in the quasicommensurate (QC) phase ...NMR; Spectra; Barium sodium niobate; Line shapes1994
312 Vardeny, Zeev ValentineOptical probes of excited states in poly (p-phenylenevinylene)We have studied electronic excited states in films of poly(p-phenylenevinylene) using picosecond transient and cw photomodulation, photoluminescence, and their excitation spectra, as well as electroabsorption spectroscopy. We have determined all the important energy levels of singlet excitons with...Poly (p-phenylenevinylene); Photoexcitation1994-01
313 Kieda, David B.Observation of the shadows of the moon and sun using 100 TeV cosmic raysThe Chicago Air Shower Array (CASA) is a large ground-based scintillation detector [1-4]. It is located at the Dugway Proving Ground is west central Utah, latitude 40°N and mean atmospheric depth 870 g / c m 2. A schematic aerial view of CASA is shown in Fig. 1. Each dot represents one scintil...Chicago Air Shower Array; Scintillation detectors; Ultrahigh energy cosmic rays1994-02
314 DeTar, CarletonNature of the thermal phase transition with Wilson quarksWe describe a series of simulations of high temperature QCD with two flavors of Wilson quarks aimed at clarifying the nature of the high temperature phase found in current simulations. Most of our work is with four time slices, although we include some runs with six and eight time slices for compar...Wilson quarks; Landau gauge; Polyakov loop; Phase transitions1994-04
315 Wu, Yong-ShiAlgebraic and geometric aspects of generalized quantum dynamicsWe briefly discuss some algebraic and geometric aspects of the generalized Poisson bracket and noncommutative phase space for generalized quantum dynamics, which are analogous to properties of the classical Poisson bracket and ordinary symplectic structure.Quantum dynamics; Jacobi identity1994-06
316 DeTar, CarletonBaryon density correlations in high temperature hadronic matterAs part of an ongoing effort to characterize the high temperature phase of QCD, in a numerical simulation using the staggered fermion scheme, we measure the quark baryon density in the vicinity of a fixed test quark at high temperature and compare it with similar measurements at low temperature and ...Baryon density; Staggered fermions; Quark plasma1994-06
317 Vardeny, Zeev ValentineHigh-pressure study of picosecond exciton dynamics in solid C60We have studied the singlet exciton decay by picosecond photoinduced absorption in films of Qo, under pressures up to 62 kbar. The picosecond decay of excitons excited in the absorption tail continues to be dominated by broad distributions of lifetimes at high pressure. These results suggest that th...Picosecond exciton dynamics; Solid C601994-08
318 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
319 Wu, Yong-ShiStatistical distribution for generalized ideal gas of fractional-statistics particlesWe derive the occupation-number distribution in a generalized ideal gas of particles obeying fractional statistics, including mutual statistics, by adopting a state-counting definition. When there is no mutual statistics, the statistical distribution interpolates between bosons and fermions, and re...Fractional statistics; Ideal gas1994-08
320 DeTar, CarletonQCD thermodynamics with Wilson quarks at large KWe extend our study of the high temperature transition with two flavors of Wilson quarks on 123 x 6 lattices to K = 0.19. We also perform spectrum calculations on 123 x 24 lattices at K = 0.19 to find the physical lattice spacing and quark mass. At this value of K the transition is remarkable in tha...Wilson quarks; Polyakov loop; Phase transitions1994-09
321 Symko, Orest GeorgeDoes the quasicrystal AlCuFe follow Ohm's law?We present the first measurements of the electrical I-V characteristics of AlCuFe quasicrystalline thin films processed by solid state interdiffusion of magnetron sputtered Al, Cu, and Fe layers. Despite the peculiar electronic properties of quasicrystals, our results show that those samples follow ...AlCuFe; Quasicrystal1994-10
322 Vardeny, Zeev ValentineTransient spectroscopy of excitons and polarons in C60 films from femtosecond to millisecondsWe have studied photoexcitations in C60 films using transient photomodulation and photoluminescence from 100 fs to 50 ms and absorption-detected magnetic resonance (ADMR). We show that singlet Frenkel excitons are the primary photoexcitations; their recombination kinetics in the picosecond time dom...Transient spectroscopy; C60 films; Femtoseconds; Milliseconds1994-11
323 Vardeny, Zeev ValentineExcitons in poly(para-phenylenevinylene)We show that one-electron band theory fails to describe optical absorption in PPV and the absorption spectrum can be described only within a Coulomb-correlated model. The lowest optical state is an exciton, whose binding energy is estimated theoretically to be 0.90 ± 0 . 1 5 e V Measurements of the...Poly(para-phenylenevinylene); PPV1994-11
324 Vardeny, Zeev ValentineSymmetric light emitting divices from poly(p-di ethynylene phenylene) (p-di phenylene vinylene) derivativesLight emitting devices were fabricated from 2,5-dialkoxy derivatives of poly(p-di ethynylene phenylene-p-di phenylene vinylene) (PDEPDPV) sandwiched between indium tin oxide (ITO) and Al. The current-voltage (Iel-V) curve, electroluminescence (EL) intensity-voltage (IEL-V) curve, and the EL spectra ...Poly(p-di ethynylene phenylene); PPV; Pi-conjugated polymers1995
325 Vardeny, Zeev ValentinePhotoresponse and electroresponse of polymers light emitting diodesWe have studied the photoresponse and electroresponse of light emitting diodes (LEDs ) made from a variety of soluble conducting polymers sandwiched between indium tin oxide (ITO) and metals including calcium, aluminum and copper. Under illumination all freshly prepared LEDs exhibit relatively large...Photoresponse; Electroresponse; Photovoltage; I-V curves1995
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