UScholar Works
 
Filters: Department: "Physics" Collection: "ir_uspace"
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CreatorTitleDescriptionSubjectDate
1 Vardeny, Zeev Valentine; Gellermann, WernerAmplified resonant Raman scattering in conducting polymer thin filmsUsing picosecond pulsed laser excitation, we investigate the optical emission characteristics of poly(2,5-dioctyloxy-p-phenylenevinylene), (DOO-PPV), thin films at high excitation intensities (~1-90 MW/cm2). We observe the presence of amplified resonance Raman scattering in the emission spectra of c...Amplified resonant Raman scattering; High excitation intensities; pi-conjugated polymers1998
2 Vardeny, Zeev ValentineCylindrical micolasers and light emitting devices from conducting polymersSubstantially improved, photopumped polymer lasers are demonstrated using microrings and microdisks of various diameters D ranging from 5 to 200 mm. Various cavity-dependent laser modes were observed, which for D,10 mm were dominated by a single longitudinal mode with linewidth of less than 1 Å. Th...Cylindrical micolasers; OLED; Photopumped polymer lasers; Microrings; Microdisks; Microlasers1998
3 Vardeny, Zeev ValentineDouble-modulation electro-optic sampling for pump-and-probe ultrafast correlation measurementsWe describe a novel electro-optic double-modulation (DM) sampling technique for ultrafast transient spectroscopy, which is characterized by a superior signal-to-noise ratio compared to that of a regular single-modulation technique. DM is achieved by a combined effect of a radio-frequency modulation,...Double-modulation; Electro-optic sampling; Ultrafast transient spectroscopy; Pump; Probe1998
4 Gondolo, PaoloEvidence for "sterile neutrino" dark matter?I show that it may be possible to explain the present evidence for a gamma-ray emission from the galactic halo as due to halo WIMP annihilations. Not only the intensity and spatial pattern of the halo emission can be matched but also the relic density of the candidate WIMP can be in the cosmologica...Sterile neutrino; WIMP; Weakly interacting massive particles; Annihilations; Z boson; Higgs sector1998
5 Vardeny, Zeev Valentine; Taylor, P. CraigExcitation energy dependence of photoinduced absorption in intrinsic a-Si:HWe have studied subgap absorption of intrinsic a-Si:H induced by below- and above-gap photoexcitation. We find very similar photoinduced subgap absorption spectra when excited with 2.4 eV or 1.2 eV light. Both spectra exhibit a power-law dependence on laser intensity ?T ~ 1a, where a is 0.5 and 0.7...Intrinsic a-Si:H; Subgap absorption; Photoinduced absorption; Gap photoexcitation; Photomodulation; Electronic states1998
6 Sokolsky, PierreHighest-energy cosmic raysWhat in the cosmos can possibly be accelerating protons to 1020 electron volts and beyond? And how can they preserve such extreme energies while plowing through the cosmic microwave background on their way to us?Energy spectrum; GZK cutoff; Atmospheric fluorescence1998
7 Gerton, JordanPhase-contrast imaging of atomic superfluid state in degenerate gas of 6Li atomsThe recent experimental realizations of Bose-Einstein condensation in trapped ultracold atomic gases composed of bosonic alkali atoms has generated a broad interest in studying different properties of these degenerate atomic Bose systems. Although the degenerate atomic gas composed of fermionic atom...1998
8 Vardeny, Zeev ValentinePlastic microring lasers on fibers and wiresPhotopumped, pulsed, narrow line laser emission is demonstrated using cylindrical microcavities formed by p-conjugated polymer thin films wrapped around thin glass optical fibers and metal wires with various diameters D. A variety of cavity-dependent resonant laser mode structures were observed, whi...Microring lasers; pi-conjugated polymers; pi-conjugated polymer thin films; Microcavities1998
9 Saam, BrianProtection circuitry for high-power diode laser arraysA comprehensive protection scheme is presented for use with high-power (;500 W dc input! diode laser arrays. The circuitry requires no separate power, using instead the voltage from the laser's power supply. Overcurrent and overvoltage silicon controlled rectifier crowbars are the primary protection...Protection circuitry; High-power diode laser arrays1998
10 Williams, Clayton C.Two step dopant diffusion study performed in two dimensions by scanning capacitance microscopy and TSUPREM IVWe report the results of a two-step two- dimensional (2D) diffusion study by scanning capacitance microscopy (SCM) and 2D SUPREM IV process simulation. A quantitative 2D dopant profile of a gate-like structure is measured with the SCM on a cross-sectioned polished silicon wafer. The gate-like struct...Scanning capacitance microscopy; SCM; Doping1998
11 Mattis, Daniel C.Uses of quantum field theory in diffusion-limited reactionsThe techniques of quantum field theory on a lattice are used to examine the diffusion and reaction processes of particles in a solid, such as vacancies or interstitials, or chemical species of all kinds which move by discrete random hopping processes and react in a prescribed way when they are in pr...Recombination; Dynamics; Equation1998
12 Wu, Yong-ShiBrane creation in M(atrix) theoryWe discuss, in the context of M(atrix) theory, the creation of a membrane suspended between two longitudinal five-branes when they cross each other. It is shown that the membrane creation is closely related to the degrees of freedom in the off-diagonal blocks which are related via dualities to the ...1998-02
13 DeTar, CarletonContinuum limit of lattice QCD with staggered quarks in the quenched approximation: a critical role for the chiral extrapolationWe calculate the light quark spectrum of lattice QCD in the quenched approximation using staggered quarks. We take the light quark mass, infinite volume, continuum limit. With nonlinear chiral extrapolations, we find that the nucleon to p mass ratio is mN/mp =­ 1.254 + 0.018 + 0.028, where the err...Staggered quarks; Chiral extrapolations1998-10
14 Vardeny, Zeev ValentineCooperative and stimulated emission in poly(p-phenylene-vinylene) thin films and solutionsWe discuss cooperative and stimulated emissions and separate their respective contributions to the emission spectral narrowing in thin films and solutions of poly(p-phenylene-vinylene) derivatives. Whereas cooperative radiation is favored in films with poor optical confinement, directional stimula...pi-conjugated polymers; PPV; Spectral narrowing1998-04
15 DeTar, CarletonCritical behavior at the chiral phase transitionIt is generally expected that two-flavor QCD undergoes a high temperature chiral symmetry restoring phase transition at zero quark mass, with O(4) critical behavior[1]. Verifying this expectation is important for understanding the phenomenology of the transition and for facilitating an extrapolation...Phase transitions; Staggered fermions1998-04
16 DeTar, CarletonHeavy-light decay constants - MILC results with the Wilson actionWe present the current status of our ongoing calculations of pseudoscalar meson decay constants for mesons that contain one light and one heavy quark (fB, fBs , fD, fDs ). We are currently generating new gauge configurations that include dynamical quarks and calculating the decay constants. In add...Decay constants; Wilson action; Kogut-Susskind quarks; Staggered quarks; Chiral extrapolation1998-01
17 Gondolo, PaoloIndirect detection of dark matter in km-size neutrino telescopesNeutrino telescopes of kilometer size are currently being planned. They will be two or three orders of magnitude bigger than presently operating detectors, but they will have a much higher muon energy threshold. We discuss the trade-off between area and energy threshold for indirect detection of neu...Neutrino telescopes; Energy threshold; Neutralino annihilations; Supersymmetric models1998-11
18 DeTar, CarletonLight hadron spectrum - MILC results with the Kogut-Susskind and Wilson actions*We present the current status of our ongoing calculations of the light hadron spectrum with both Kogut-Susskind (KS) and Wilson quarks in the valence or quenched approximation. We discuss KS quarks first and find that the chiral extrapolation is potentially the biggest source of systematic error. F...Staggered quarks; Hadron spectrum; Kogut-Susskind quarks; Wilson quarks; Chiral extrapolation1998-01
19 DeTar, CarletonLight quark spectrum with improved gauge and fermion actionsWe report on a study of the light quark spectrum using an improved gauge action and both Kogut-Susskind and Naik quark actions. We have studied six different lattice spacings, corresponding to plaquette couplings ranging from 6.8 to 7.9, with five to six quark masses per coupling. We compare the t...Quark spectrum; Kogut-Susskind quarks; Naik quarks1998-04
20 Gondolo, PaoloLimits on R-parity violation from cosmic ray antiprotonsWe constrain the hadronic R-parity violating couplings in extensions to the minimal supersymmetric standard model. These interactions violate baryon and lepton number, and allow the lightest superpartner (LSP) to decay into standard model particles. The observed flux of cosmic ray antiprotons plac...R-parity; Supersymmetric models1998-06
21 Gondolo, PaoloNeutralino decay rates with explicit R-parity violationWe compute the neutralino decay rate in the minimal supersymmetric standard model with the addition of explicit R-parity violation. We include the complete squark and slepton mixing matrices, previously neglected, and we improve and correct published formulas. These decays are relevant to accelerat...Neutralinos; R-parity; Decay rates; Sfermions1998-03
22 Wu, Yong-ShiNoncommutative gauge theories in matrix theoryWe present a general framework for matrix theory compactified on a quotient space Rn/G, with G a discrete group of Euclidean motions in R". The general solution to the quotient conditions gives a gauge theory on a noncommutative space. We characterize the resulting noncommutative gauge theory in t...Matrix theory; Noncommutative space1998-09
23 Wu, Yong-ShiP-p′ strings in M(atrix) theoryWe study the off-diagonal blocks in the M(atrix) model that are supposed to correspond to open strings stretched between a Dp-brane and a Dp′-brane. It is shown that the spectrum, including the quantum numbers, of the zero modes in the off-diagonal blocks can be determined from the index theorem a...1998-08
24 DeTar, CarletonQuenched hadron spectroscopy with improved staggered quark actionWe investigate light hadron spectroscopy with an improved quenched staggered quark action. We compare the results obtained with an improved gauge plus an improved quark action, an improved gauge plus standard quark action, and the standard gauge plus standard quark action. Most of the improvement ...Staggered quarks; Chiral symmetry; Flavor symmetry1998-07
25 Wu, Yong-ShiSchrödinger-like equation for a nonrelativistic electron in a photon field of arbitrary intensityThe Schrödinger equation with minimal coupling for a nonrelativistic electron interacting with a single-mode photon field is not satisfied by the nonrelativistic limit of the exact solutions to the corresponding Dirac equation. A Schrödinger-like equation valid for arbitrary photon intensity is d...Photon field; Nonrelativistic electron1998-07
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