UScholar Works
 
Filters: Department: "Physics" Collection: "ir_uspace"
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CreatorTitleDescriptionSubjectDate
126 Wu, Yong-ShiQuantum phase transition in a multicomponent Bose-Einstein condensate in optical latticesWe present a general lattice model for a multicomponent atomic Bose-Einstein system in an optical lattice. Using the model, we analytically study the quantum phase transition between the Mott insulator and a superfluid. A mean-field theory is developed from the Mott-insulator ground state. When the...Quantum phase transitions; Optical lattices; Bose-Einstein condensation; Boson-Hubbard model; Superfluids2003-01
127 Symko, Orest GeorgeTemperature dependence of the order parameter in a dilute AgMn spin glassThe magnetization of a dilute AgMn spin glass containing 150 ppm Mn has been measured over the temperature range from 20 mK to 2 K in an applied field of 0.9 Oe, using a SQUID magnetometer. A comparison of the measured magnetization with numerical calculations of the magnetization based on the Mean ...AgMn spin glass; Mean random field; MRF; Temperature dependence; Order parameter; RKKY interactions1982
128 Vardeny, Zeev ValentineMagnetic field effects in ∏-conjugated polymer-fullerene blends: evidence for multiple componentsWe studied magnetoconductance (MC) and magnetoelectroluminescence (MEL) in organic diodes from blends of ∏-conjugated polymers and fullerenes at various concentrations, c. The MC response is composed of several components that depend on the applied bias voltage and c. A dominant positive low-field...pi-conjugated polymers; Fullerene blends; Magnetic field effects; Magnetoconductance; Magnetoelectroluminescence; MC; MEL; Organic magnetoresistance; OMAR; Organic diodes2008-12
129 Vardeny, Zeev ValentinePhotoexcitation dynamics in regioregular and regiorandom polythiophene filmsUsing a variety of optical probes techniques we studied the photoexcitation dynamics in thin films of poly-3-hexyl thiophene with regioregular order that forms lamellae structures with increased interchain interaction, as well as regiorandom order that keeps a chainlike morphology. In regiorandom fi...Photoexcitation dynamics; Regio-regular; Regio-random; Polythiophene films2001-11
130 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
131 Williams, Clayton C.High-resolution photothermal laser probeAn advance in photothermal imaging is described. A photothermal laser probe is presented that operates at a frequency of 1 GHz. At this frequency the spacial resolution is limited only by the optical spot size of the probe beam. The photothermal sensitivity of the probe is 1.2 X 10-4 degrees Celsiu...Laser probes1985
132 Vardeny, Zeev ValentineRandom lasing in human tissuesA random collection of scatterers in a gain medium can produce coherent laser emission lines dubbed "random lasing." We show that biological tissues, including human tissues, can support coherent random lasing when infiltrated with a concentrated laser dye solution. To extract a typical random reson...Random lasing; Gain medium; Human tissues; Malignant tissues2004
133 Wu, Yong-ShiQuiver matrix mechanics for IIB string theory (II): generic dual tori, fractional matrix membrane and SL(2, Z) dualityWith the deconstruction technique, the geometric information of a torus can be encoded in a sequence of orbifolds. By studying the Matrix Theory on these orbifolds as quiver mechanics, we present a formulation that (de)constructs the torus of generic shape on which Matrix Theory is "compactified". T...2005-02
134 Symko, Orest GeorgeSpin-glass transition of a dilute Ag-Mn alloy in a magnetic fieldThe spin-glass state in a magnetic field is studied in a very dilute Ag-Mn sample containing 150 ppm of Mn. The field-cooled magnetization of this system is investigated over temperatures ranging from 4 down to 0.01 K in magnetic fields from 932 to 1 Oe. Scaling is observed in the nonlinear suscepti...Spin-glass transition; Spin-glass state; Ag-Mn alloy; Silver-manganese alloy1986-01
135 DeTar, CarletonLattice calculation of 1-+ hybrid mesons with improved Kogut-Susskind fermionsWe report on a lattice determination of the mass of the exotic 1-+ hybrid meson using an improved Kogut-Susskind action. Results from both quenched and dynamical quark simulations are presented. We also compare with earlier results using Wilson quarks at heavier quark masses. The results on lattice...Staggered quarks; Kogut-Susskind fermions2003-10
136 Vardeny, Zeev ValentineLaser action in polydialkylfluorene films: influence of low-temperature thermal treatmentWe have used a variety of optical probes to investigate the changes occurring upon low-temperature thermal treatment to the emissive properties of dialkyl substituted polyfluorene thin films. We found that the low-temperature-driven morphological changes involving aggregates formation, which are ob...Laser action; Polydialkylfluorene films; pi-conjugated polymers; Thermal treatment1999
137 Dawson, KyleRadiation tolerance of fully-depleted P-channel CCDs designed for the SNAP satelliteThick, fully depleted p-channel charge-coupled devices (CCDs) have been developed at the Lawrence Berkeley National Laboratory (LBNL). These CCDs have several advantages over conventional thin, n-channel CCDs, including enhanced quantum efficiency and reduced fringing at near-infrared wavelengths an...P-Channel CCDs; SNAP satellite; Space-based telescopes2008-06
138 Gondolo, PaoloAGAPEROS: searching for microlensing in the LMC with the pixel method. I. Data treatment and pixel light curves productionRecent surveys monitoring millions of light curves of resolved stars in the LMC have discovered several microlensing events. Unresolved stars could however signi _x000C_cantly contribute to the microlensing rate towards the LMC. Monitoring pixels, as opposed to individual stars, should be able to ...Data analysis techniques; Halo; Galaxies; Gravitational lensing; Pixel method; Large Magellanic Cloud; LMC1999
139 Gerton, JordanDipolar relaxation collisions in magnetically trapped 7LiWe report the measurement of the rate constant for dipolar relaxation from the (F=2, mF=2) hyperfine state of 7Li. The atoms are confined in a permanent magnet trap at a field of 10^3 G. The measured value of (1.05±0.10)X10^-14 cm3/s agrees well with theory. Additionally, we determine an upper bo...1999-02
140 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
141 Vardeny, Zeev Valentine; Symko, Orest GeorgeQuasiparticle relaxation in high-Tc superconductorRecent measurements by Eesley et al. [1] of transient reflectivity in superconducting Tl2Ba2Ca2Cu30io were interpreted as evidence for order-parameter relaxation in the vicinity of Tc, which was analyzed in terms of BCS weak coupling for ?(r)/?(0). In this Comment we question this interpretation ...Quasiparticle relaxation1991
142 Gondolo, PaoloStellar orbit constraints on neutralino annihilation at the galactic centerDark matter annihilation has been proposed to explain the TeV gamma rays observed from the Galactic Center. We study constraints on this hypothesis coming from the mass profile around the Galactic Center measured by observing stellar dynamics. We show that for several proposed WIMP candidates, the...Neutralinos; Annihilation2006-09
143 Vardeny, Zeev ValentineUltrafast spectroscopy of excitons in single-walled carbon nanotubesWe studied the femtosecond dynamics of photoexcitations in films containing semiconducting and metallic single-walled carbon nanotubes (SWNTs), using various pump-probe wavelengths and intensities.We found that confined excitons and charge carriers with subpicosecond dynamics dominate the ultrafas...Ultrafast spectroscopy; Excitons; Single-walled carbon nanotubes; SWNT2004-01
144 Gondolo, PaoloDetectability of the Sgr dwarf leading tidal stream with Auger, EUSO, or OWLWe point out that if heavy metastable particles composing the dark matter of our galaxy are responsible for the ultrahigh energy cosmic rays (UHECR) then the leading tidal stream of the Sagittarius dwarf galaxy could be detected through UHECR. The signal would be an anisotropy in the UHECR flux sma...Sagittarius dwarf galaxy; Sgr stream; anisotropy2004-07
145 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
146 DeTar, CarletonEquation of state for two flavor QCD at Nt=6We calculate the two flavor equation of state for QCD on lattices with lattice spacing a=(6T)21 and find that cutoff effects are substantially reduced compared to an earlier study using a=(4T)21. However, it is likely that significant cutoff effects remain. We fit the lattice data to expected forms ...Phase transitions; Quark-gluon plasma; Dynamical quarks1997-06
147 Symko, Orest GeorgeBackground signals in SQUID magnetometersSince a SQUID magnetometer is an extremely sensitive device capable of detecting minute magnetic flux changes in a sample, it will also detect unwanted signals from materials near the magnetometer. The presence of temperature dependent "background signals" limits the accuracy of measurements of ...SQUID magnetometer; Background signals1974
148 Symko, Orest GeorgeSpin-glass behavior in dilute magnetic alloys with hcp structureA simple physical model is presented for calculating the magnetization of dilute magnetic systems with hep hosts which incorporates elements of both crystal-field theory and the molecular-field theory of spin-glasses. To permit the computation of the Ruderman-Kittel-Kasuya-Yosida contribution, the i...Spin-glass behavior; HCP structure; HCP alloys; Dilute magnetic systems; Molecular-field theory; MgMn; ZnMn1982-05
149 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
150 Mattis, Daniel C.Phonons and phase transitions of heliumWe find a new collective shear-wave-like mode above Tλ, merging with the longitudinal acoustic mode at a higher critical temperature. The speed of the new sound wave is predicted to vanish near Tλ as s ∞ (T -Tλ)½ .1973-06
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