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2000

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Articles 31 - 60 of 520

Full-Text Articles in Physics

Angular Momentum Partitioning And Hexacontatetrapole Moments In Impulsively Excited Argon Ions, H. M. Al-Khateeb, B. G. Birdsey, Timothy J. Gay Nov 2000

Angular Momentum Partitioning And Hexacontatetrapole Moments In Impulsively Excited Argon Ions, H. M. Al-Khateeb, B. G. Birdsey, Timothy J. Gay

Timothy J. Gay Publications

We have studied polarized electron collisions with Ar in which the target is simultaneously ionized and excited to form Ar+(3p4(1D)4p) states. We measured the integrated Stokes parameters of the subsequent fluorescence emitted by the 2F7/2, 2F5/2, 2D5/2, and 2P3/2 states along the direction of electron polarization. The Rubin-Bederson hypothesis is shown to hold for the L and S multipoles of these states. The electric quadrupole and hexadecapole of the 1D core are derived. By recoupling these moments with …

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Universal Quantum Limits On Single-Channel Information, Entropy, And Heat Flow, Miles Blencowe, Vincenzo Vitelli Nov 2000

Universal Quantum Limits On Single-Channel Information, Entropy, And Heat Flow, Miles Blencowe, Vincenzo Vitelli

Dartmouth Scholarship

We show that the recently discovered universal upper bound on the thermal conductance of a single channel comprising particles obeying arbitrary fractional statistics is in fact a consequence of a more general universal upper bound, involving the averaged entropy and energy currents of a single channel connecting heat reservoirs with arbitrary temperatures and chemical potentials. The latter upper bound in turn leads, via Holevo's theorem, to a universal (i.e., statistics independent) upper bound on the optimum capacity for classical information transmission down a single, wideband quantum channel.

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Comparative Studies Of Dissociative Electron Attachment To Methyl Halides, R. S. Wilde, Gordon A. Gallup, Ilya I. Fabrikant Nov 2000

Comparative Studies Of Dissociative Electron Attachment To Methyl Halides, R. S. Wilde, Gordon A. Gallup, Ilya I. Fabrikant

Gordon Gallup Publications

The dissociative electron attachment cross sections for the methyl halides vary in an enormous range from the virtually unmeasurable 10−23 cm2 for CH3Cl at room temperature to 10−14 cm2 for CH3I. In this paper we supplement our previous studies by calculations of dissociative electron attachment to CH3Br and compare results for all methyl halides studied so far. The rate as a function of temperature for CH3Cl and CH3Br exhibits an exponential dependence on 1/T (Arrhenius law) with the activation energy lower for CH3Br. …

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Two-Dimensional Pendulum Experiments Using A Spark Generator, Rand S. Worland, Matthew J. Moelter Nov 2000

Two-Dimensional Pendulum Experiments Using A Spark Generator, Rand S. Worland, Matthew J. Moelter

Physics

Student understanding of the superposition of perpendicular harmonic oscillators can be enhanced using a spark generator to record position-versus-time data for smallamplitude pendulum motion in two dimensions. Our students have used this arrangement to analyze the motion of a spherical pendulum and a “Y-suspended” (Blackburn) pendulum that has two effective lengths.

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Report Of The Qcd Tools Working Group, R. K. Ellis, R. Field, S. Mrenna, Gregory R. Snow, C. Balazs, E. Boos, J. Campbell, R. Demina, J. Huston, C-Y. P. Ngan, A. Petrelli, I. Puljak, T. Sjostrand, J. Smith, D. Stuart, K. Sumorok Nov 2000

Report Of The Qcd Tools Working Group, R. K. Ellis, R. Field, S. Mrenna, Gregory R. Snow, C. Balazs, E. Boos, J. Campbell, R. Demina, J. Huston, C-Y. P. Ngan, A. Petrelli, I. Puljak, T. Sjostrand, J. Smith, D. Stuart, K. Sumorok

Gregory Snow Publications

We report on the activities of the “QCD Tools for heavy flavors and new physics searches” working group of the Run II Workshop on QCD and Weak Bosons. The contributions cover the topics of improved parton showering and comparisons of Monte Carlo programs and resummation calculations, recent developments in Pythia, the methodology of measuring backgrounds to new physics searches, variable flavor number schemes for heavy quark electro-production, the underlying event in hard scattering processes, and the Monte Carlo MCFM for NLO processes.

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Tabletop Accelerators Are Brighter And Faster, Phil Schewe, Ben Stein, Donald P. Umstadter Nov 2000

Tabletop Accelerators Are Brighter And Faster, Phil Schewe, Ben Stein, Donald P. Umstadter

Donald Umstadter Publications

At last week's APS plasma physics meeting, Donald Umstadter of the University of Michigan's Center for Ultrafast Optical Science (734-764-2284, dpu@umich.edu) reported on advances at his lab and elsewhere in tabletop laser accelerators, devices that use light to accelerate beams of electrons and protons to energies of a million volts in distances of only microns. This acceleration rate or "gradient" is up to a thousand times larger than in conventional accelerators because the tabletop laser light can now exert pressures of gigabars, the highest ever achieved, and approaching the pressure of light near the Sun. Not only that, but Umstadter's …

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Temperature-Induced Configurational Excitations For Predicting Thermodynamic And Mechanical Properties Of Alloys, Duane D. Johnson, Andrei V. Smirnov, J. B. Staunton, F. J. Pinski, W. A. Shelton Nov 2000

Temperature-Induced Configurational Excitations For Predicting Thermodynamic And Mechanical Properties Of Alloys, Duane D. Johnson, Andrei V. Smirnov, J. B. Staunton, F. J. Pinski, W. A. Shelton

Duane D. Johnson

We show that a structural energy difference, ΔE, must include explicit symmetry-breaking changes of the electronic structure due to temperature-induced configurational excitations, and why ΔE at T=0 K is not necessarily relevant to thermodynamic and mechanical modeling. In Ni3V, we calculate a tenfold decrease of ΔE between D022 and L12 structures from T=0 K to states of order relevant to experiment. ΔE calculated directly from states with short-range order (8 meV) or with low partial order (7–12 meV) agree with high-T experiment (10 meV).

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Binary Condensation In A Supersonic Nozzle, Barbara Ellen Wyslouzil, Christopher H. Heath, Janice L. Cheung, Gerald Wilemski Nov 2000

Binary Condensation In A Supersonic Nozzle, Barbara Ellen Wyslouzil, Christopher H. Heath, Janice L. Cheung, Gerald Wilemski

Physics Faculty Research & Creative Works

We present data from the first systematic studies of binary condensation in supersonic nozzles. The apparatus used to conduct the experiments is described in detail, and the important issues of stability and reproducibility of the experiments are discussed. Experiments were conducted with water, ethanol, propanol, and binary mixtures of these compounds. Onset was determined in the temperature range of 190-215 K, and for each mixture composition the pressures of the condensible species at an onset temperature of 207 K were determined. For the ideal ethanol-propanol mixtures, the onset pressures at constant temperature vary almost linearly between those of the pure …

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Combined Effects Of Screening And Band Gap Renormalization On The Energy Of Optical Transitions In Zno And Gan, D. C. Reynolds, David C. Look, B. Jogai Nov 2000

Combined Effects Of Screening And Band Gap Renormalization On The Energy Of Optical Transitions In Zno And Gan, D. C. Reynolds, David C. Look, B. Jogai

Physics Faculty Publications

The energy positions of the optical transitions in both GaN and ZnO were investigated when the samples were excited simultaneously with a HeCd laser and an Ar+ ion laser. The increased number of free electrons excited by the Ar+ ion laser will effectively screen both the free exciton and bound exciton transitions, resulting in a blueshift. The increased number of free electrons also produces many-body effects, which lead to a reduction of the band gap energy and thus a redshift. The resultant of screening and renormalization results in a redshift of the optical transitions in ZnO but a …

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New Limit On The D Coefficient In Polarized Neutron Decay, L. J. Lising, S. R. Hwang, J. M. Adams, T. J. Bowles, M. C. Browne, T. E. Chupp, K. P. Coulter, M. S. Dewey, S. J. Freedman, B. K. Fujikawa, A. Garcia, G. L. Greene, Gordon L. Jones, H. P. Mumm, J. S. Nico, J. M. Richardson, R. G. H. Robertson, T. D. Steiger, W. A. Teasdale, A. K. Thompson, E. G. Wasserman, F. E. Wietfeldt, R. C. Welsh, J. F. Wilkerson Nov 2000

New Limit On The D Coefficient In Polarized Neutron Decay, L. J. Lising, S. R. Hwang, J. M. Adams, T. J. Bowles, M. C. Browne, T. E. Chupp, K. P. Coulter, M. S. Dewey, S. J. Freedman, B. K. Fujikawa, A. Garcia, G. L. Greene, Gordon L. Jones, H. P. Mumm, J. S. Nico, J. M. Richardson, R. G. H. Robertson, T. D. Steiger, W. A. Teasdale, A. K. Thompson, E. G. Wasserman, F. E. Wietfeldt, R. C. Welsh, J. F. Wilkerson

Articles

We describe an experiment that has set new limits on the time reversal invariance violating D coefficient in neutron beta decay. The emiT experiment measured the angular correlation [J] . (p(e) x p(p)) using an octagonal symmetry that optimizes electron-proton coincidence rates. The result is D=[-0.6+/-1.2(stat)+/-0.5(syst)] x 10(-3). This improves constraints on the phase of g(A)/g(V) and limits contributions to T violation due to leptoquarks. This paper presents details of the experiment, data analysis, and the investigation of systematic effects.

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Holography, A Covariant C Function, And The Geometry Of The Renormalization Group, Vatche Sahakian Nov 2000

Holography, A Covariant C Function, And The Geometry Of The Renormalization Group, Vatche Sahakian

All HMC Faculty Publications and Research

We propose a covariant geometrical expression for the c function for theories which admit dual gravitational descriptions. We state a c theorem with respect to this quantity and prove it. We apply the expression to a class of geometries, from domain walls in gauged supergravities, to extremal and near extremal Dp-branes, and the AdS Schwarzschild black hole. In all cases, we find agreement with expectations.

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Transport Anomalies And Marginal Fermi-Liquid Effects At A Quantum Critical Point, Dietrich Belitz, Theodore R. Kirkpatrick, Rajesh S. Narayanan, Thomas Vojta Nov 2000

Transport Anomalies And Marginal Fermi-Liquid Effects At A Quantum Critical Point, Dietrich Belitz, Theodore R. Kirkpatrick, Rajesh S. Narayanan, Thomas Vojta

Physics Faculty Research & Creative Works

The conductivity and the tunneling density of states of disordered itinerant electrons in the vicinity of a ferromagnetic transition at low temperature are discussed. Critical fluctuations lead to nonanalytic frequency and temperature dependencies that are distinct from the usual long-time tail effects in a disordered Fermi liquid. The crossover between these two types of behavior is proposed as an experimental check of recent theories of the quantum ferromagnetic critical behavior. In addition, the quasiparticle properties at criticality are shown to be those of a marginal Fermi liquid.

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Shubnikov–De Haas Effect In The Superconducting State Of An Organic Superconductor, J. Wosnitza, S. Wanka, J. Hagel, R. Häussler, H. V. Löhneysen, J. A. Schlueter, U. Geiser, P. G. Nixon, Rolf Walter Winter, Gary L. Gard Nov 2000

Shubnikov–De Haas Effect In The Superconducting State Of An Organic Superconductor, J. Wosnitza, S. Wanka, J. Hagel, R. Häussler, H. V. Löhneysen, J. A. Schlueter, U. Geiser, P. G. Nixon, Rolf Walter Winter, Gary L. Gard

Chemistry Faculty Publications and Presentations

We report the observation of Shubnikov–de Haas (SdH) oscillations in the mixed state of the organic superconductor β″-(BEDT-TTF)₂SF₅CH₂CF₂SO₃ (Tc≈4.4K). At low temperatures the SdH oscillations persist clearly below the upper critical field Bc₂(0)≈3.6 T almost down to the field where the resistivity vanishes. Rather unusually, no additional damping of the SdH-signal amplitude — as well as of the de Haas–van Alphen amplitude — is observed in the superconducting state. This indicates that the damping in the vortex state of this quasi-two-dimensional superconductor is different in character to that observed for most three-dimensional materials.

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Paramagnetic Meissner Effect In Nb Disks, Petru S. Fodor, Lowell E. Wenger Nov 2000

Paramagnetic Meissner Effect In Nb Disks, Petru S. Fodor, Lowell E. Wenger

Physics Faculty Publications

Further details of the zero-field-cooled-magnetization and field-cooled-magnetization results on Nb disks exhibiting the paramagnetic Meissner effect (PME) are described. These studies indicate that two well-defined temperatures can be associated with features in the magnetization results. The higher characteristic temperature Tu is correlated with appearance of the paramagnetic moment and is strongly dependent upon the process used in forming the disk-shaped geometry of these Nb samples. The lower temperature Tp is associated with the “intrinsic coupling” of the interior Nb platelets. These latest results are shown to be consistent with the flux compression model for the appearance of the PME.

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Metallic Nanoscale Fibers From Stable Iodine-Doped Carbon Nanotubes, Peter C. Eklund, Leonid Grigorian, Keith A. Williams, Gamini U. Sumanasekera, Shaoli Fang Oct 2000

Metallic Nanoscale Fibers From Stable Iodine-Doped Carbon Nanotubes, Peter C. Eklund, Leonid Grigorian, Keith A. Williams, Gamini U. Sumanasekera, Shaoli Fang

Physics and Astronomy Faculty Patents

A method of doping involves soaking single-walled carbon nanotubes in molten iodine. Excess physisorbed iodine may then be removed by annealing.

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Control Of High-Harmonic Generation And Laser-Assisted X-Ray-Atom Scattering With Static Electric And Magnetic Fields, D. B. Milošević, Anthony F. Starace Oct 2000

Control Of High-Harmonic Generation And Laser-Assisted X-Ray-Atom Scattering With Static Electric And Magnetic Fields, D. B. Milošević, Anthony F. Starace

Anthony F. Starace Publications

We consider the use of strong static fields to control two related atomic processes: laser-assisted x-ray-atom scattering (XAS) and high-harmonic generation (HHG). We first analyze the laser field intensity dependence of the differential cross section (DCS) plateau structures for the laser-assisted XAS process in the presence of a static electric field as a function of the number of photons exchanged with the laser field. Besides the recently discovered (Milošević, D.B. and Starace, A.F., 1998, Phys. Rev. Lett., 81, 5097) extended plateau for absorbed photons, which indicates a substantial increase of the scattered x-ray energies, a new plateau, having many …

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Observational Constraints On The Internal Velocity Field Of Quasar Emission-Line Clouds, Mark Bottorff, Gary J. Ferland, Jack Baldwin, Kirk Korista Oct 2000

Observational Constraints On The Internal Velocity Field Of Quasar Emission-Line Clouds, Mark Bottorff, Gary J. Ferland, Jack Baldwin, Kirk Korista

Physics and Astronomy Faculty Publications

This paper addresses the question, what does the spectrum of a typical quasar reveal about the velocity structure within its broad emission line region clouds? Turbulent (i.e., nonthermal) broadening of spectral lines can be due to macroturbulence or microturbulence. Microturbulence affects line formation and the emitted spectrum and may be required to account for the observed smoothness of the line profiles. The velocity field is crucial since it addresses the fundamental nature of the individual clouds and the global structure of the active galactic nuclei (AGNs) environment. For example, stellar winds or magnetically confined blobs might be highly microturbulent, requiring …

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Direct Measurement Of The W Boson Width In Pp̅ Collisions At √S = 1.8 Tev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration Oct 2000

Direct Measurement Of The W Boson Width In Pp̅ Collisions At √S = 1.8 Tev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

This Letter describes a direct measurement of the W boson total decay width, Γ W, using the Collider Detector at Fermilab. The measurement uses an integrated luminosity of 90 pb-1, collected during the 1994–1995 run of the Fermilab Tevatron pp̅ collider. The width is determined by normalizing predicted signal and background distributions to 49 844 W→ eν candidates and 21 806 W→μν candidates in the transverse-mass region MT < 200 GeV and then fitting the predicted shape to the 438 electron events and 196 muon events in the high-MT region, 100<MT < 200 GeV. The result is G Γ W= 2.04 ± 0.11(stat) ± 0.09(syst) GeV.

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Inhomogeneous Nucleation In A Quark-Hadron Pphase Transition, P. Shukla, A. K. Mohanty, S. K. Gupta, Marcelo Gleiser Oct 2000

Inhomogeneous Nucleation In A Quark-Hadron Pphase Transition, P. Shukla, A. K. Mohanty, S. K. Gupta, Marcelo Gleiser

Dartmouth Scholarship

The effect of subcritical hadron bubbles on a first-order quark-hadron phase transition is studied. These subcritical hadron bubbles are created due to thermal fluctuations, and can introduce a finite amount of phase mixing (quark phase mixed with hadron phase) even at and above the critical temperature. For reasonable choices of surface tension and correlation length, as obtained from the lattice QCD calculations, we show that the amount of phase mixing at the critical temperature remains below the percolation threshold. Thus, as the system cools below the critical temperature, the transition proceeds through the nucleation of critical-size hadron bubbles from a …

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Measurement Of J/Ψ And Ψ(2s) Polarization In Pp̅ Collisions At √S = 1.8 Tev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration Oct 2000

Measurement Of J/Ψ And Ψ(2s) Polarization In Pp̅ Collisions At √S = 1.8 Tev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We have measured the polarization of J/ψ and ψ(2S) mesons produced in pp̅ collisions at √s= 1.8 TeV, using data collected at the Collider Detector at Fermilab during 1992–1995. The polarization of promptly produced J/ψ[ψ(2S)] mesons is isolated from those produced in B-hadron decay, and measured over the kinematic range 4 [5.5] < PT < 20 GeV/c and |y| < 0.6. For PT≥ 12 GeV/c we do not observe significant polarization in the prompt component.

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Nonadiabatic Heat-Capacity Measurements Using A Superconducting Quantum Interference Device Magnetometer, A.I. Kharkovski, Christian Binek, Wolfgang Kleeman Oct 2000

Nonadiabatic Heat-Capacity Measurements Using A Superconducting Quantum Interference Device Magnetometer, A.I. Kharkovski, Christian Binek, Wolfgang Kleeman

Christian Binek Publications

Nonadiabatic measurements of the heat capacity involving sample-inherent thermometry are proposed. The method is realized with superconducting quantum interference device magnetometry and applied to FeBr2 single crystals by using the magnetization for both thermometry and relaxation calorimetry. When heating with a step pulse of laser light, the magnetization relaxes on a characteristic time scale Ί = RC, where C is the heat capacity and R is the heat resistance between the sample and the bath. R is independently determined from the temperature dependence of the magnetic moment measured with and without stationary light irradiation. ©2000 American Institute of …

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Search For New Physics In Eμx Data At Dø Using Sleuth: A Quasi-Model-Independent Search Strategy For New Physics, B. Abbott, Gregory R. Snow, D0 Collaboration Oct 2000

Search For New Physics In Eμx Data At Dø Using Sleuth: A Quasi-Model-Independent Search Strategy For New Physics, B. Abbott, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

We present a quasi-model-independent search for the physics responsible for electroweak symmetry breaking. We define final states to be studied, and construct a rule that identifies a set of relevant variables for any particular final state. A new algorithm (“SLEUTH”) searches for regions of excess in those variables and quantifies the significance of any detected excess. After demonstrating the sensitivity of the method, we apply it to the semi-inclusive channel ℯμX collected in 108 pb-1 of pp̅ collisions at √s = 1.8 TeV at the DØ experiment during 1992–1996 at the Fermilab Tevatron. We find no evidence of …

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Nanostructured Fept:B2O3 Thin Films With Perpendicular Magnetic Anisotropy, C.P. Luo, Sy_Hwang Liou, L. Gao, Yi Liu, David J. Sellmyer Oct 2000

Nanostructured Fept:B2O3 Thin Films With Perpendicular Magnetic Anisotropy, C.P. Luo, Sy_Hwang Liou, L. Gao, Yi Liu, David J. Sellmyer

Sy-Hwang Liou Publications

FePt/B2O3 multilayers were deposited by magnetron sputtering onto 7059 glass substrates. By annealing the as-deposited films at 550 °C, nanostructured FePt:B2O3 films consisting of FePt grains with L10 structure, embedded in a glassy B2O3 matrix, were obtained. The c axes of the FePt grains can be made to align with the film normal direction, which results in a perpendicular anisotropy constant of 3.5×107 erg/cc. The films remain layered structures after annealing when the B2O3 layer thickness exceeds 16 Å. The nanostructure of the films was investigated by …

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Powre: Driven Nonequilibrium Systems With Quenched Disorder: A Renormalization-Group Study, Susan R. Mckay Oct 2000

Powre: Driven Nonequilibrium Systems With Quenched Disorder: A Renormalization-Group Study, Susan R. Mckay

University of Maine Office of Research Administration: Grant Reports

This theory project develops a position-space renormalization-group approach to study driven diffusive lattice gases; the theory will be modified and applied to interacting cases and systems with quenched randomness. Systems driven far from equilibrium are prevalent in nature and particularly challenging with respect to fundamental understanding and property prediction. The models to be studied in this project are simple prototypes related to a variety of complex systems such as biological populations, binary fluid flow through random media, and fast ionic conductors. This is a research enhancement grant made under the Professional Opportunities for Women in Research and Education (POWRE) program. …

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Superspin Glass Behaviour Of Interacting Ferromagnetic Nanoparticles In Discontinuous Magnetic Multilayers, Christian Binek Oct 2000

Superspin Glass Behaviour Of Interacting Ferromagnetic Nanoparticles In Discontinuous Magnetic Multilayers, Christian Binek

Christian Binek Publications

Discontinuous magnetic multilayers [Co80Fe20(t)/Al2O3(3nm)]10 with t = 0.9 and 1.0nm are studied by SQUID magnetometry and ac susceptibility. Owing to dipolar interaction the superparamagnetic cluster systems undergo collective glass-like freezing upon cooling. While both samples exhibit very similar glass temperatures Tg » 45 K and critical exponents zn » 10 and g » 1.4 as obtained from the temperature dependencies of the relaxation time, t, and the nonlinear susceptibility, c3, dynamical scaling reveals different critical exponents, b(0.9nm) »1.0 and b(1.0nm) » 0.6, respectively.

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Electron Beam And Optical Depth Profiling Of Quasibulk Gan, L. Chernyak, A. Osinsky, G. Nootz, A. Schulte, J. Jasinski, M. Benamara, Z. Liliental-Weber, David C. Look, Richard J. Molnar Oct 2000

Electron Beam And Optical Depth Profiling Of Quasibulk Gan, L. Chernyak, A. Osinsky, G. Nootz, A. Schulte, J. Jasinski, M. Benamara, Z. Liliental-Weber, David C. Look, Richard J. Molnar

Physics Faculty Publications

Electron beam and optical depth profiling of thick (5.5–64 μm) quasibulk n-type GaN samples, grown by hydride vapor-phase epitaxy, were carried out using electron beam induced current (EBIC), microphotoluminescence (PL), and transmission electron microscopy (TEM). The minority carrier diffusion length, L, was found to increase linearly from 0.25 μm, at a distance of about 5 μm from the GaN/sapphire interface, to 0.63 μm at the GaN surface, for a 36-μm-thick sample. The increase in L was accompanied by a corresponding increase in PL band-to-band radiative transition intensity as a function of distance from the GaN/sapphire interface. We attribute …

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Identification Of The Gamma(5) And Gamma(6) Free Excitons In Gan, D. C. Reynolds, David C. Look, B. Jogai, A. W. Saxler, Seong-Ju S. Park, J. Y. Hahn Oct 2000

Identification Of The Gamma(5) And Gamma(6) Free Excitons In Gan, D. C. Reynolds, David C. Look, B. Jogai, A. W. Saxler, Seong-Ju S. Park, J. Y. Hahn

Physics Faculty Publications

The Γ5 and Γ6 free excitons have been identified in GaN from emission measurements. Another emission peak is also observed which we believe to be the longitudinal free exciton. These measurements along with electrical measurements, which show the sample to have very high peak mobility, attest to the high quality of the sample.

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Sn/Ge(111) Surface Charge-Density-Wave Phase Transition, T. E. Kidd, T. Miller, M. Y. Chou, T.-C. Chiang Oct 2000

Sn/Ge(111) Surface Charge-Density-Wave Phase Transition, T. E. Kidd, T. Miller, M. Y. Chou, T.-C. Chiang

Faculty Publications

Angle-resolved photoemission has been utilized to study the surface electronic structure of 1/3 monolayer of Sn of Ge(111) in both the room-temperature (√3 × √3)R30° phase and the low-temprature (3 × 3) charge-density-wave phase. The results reveal a gap opening around the (3 × 3) Brillouin zone boundary, suggesting a Peierls-like transition despite the well-documented lack of Fermi nesting. A highly sensitive electronic response to doping by intrinsic surface defects is the cause for the unusual behaior, and a detailed calculation illustrates the origin of the (3 × 3) symmetry.

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Magnetic Properties Of Disordered Ni3C, Lanping Yue, R. Sabiryanov, E.M. Kirkpatrick, Diandra Leslie-Pelecky Oct 2000

Magnetic Properties Of Disordered Ni3C, Lanping Yue, R. Sabiryanov, E.M. Kirkpatrick, Diandra Leslie-Pelecky

Diandra Leslie-Pelecky Publications

The metastable Ni3C phase has been produced by mechanically alloying Ni and C. Ni3C particles of diameter 10 nm are produced after 90 h of mechanical alloying with no evidence of crystalline Ni in x ray or electron diffraction. Linear muffin-tin orbital band-structure calculations show that Ni3C is not expected to be ferromagnetic due to strong Ni-C hybridization in the ordered alloy; however, the introduction of even small amounts of disorder produces locally Ni-rich regions that can sustain magnetism. Mechanically alloyed Ni3C is ferromagnetic, with a room-temperature coercivity of 70 Oe and …

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The Phases Of 2d Ncos, Vatche Sahakian Oct 2000

The Phases Of 2d Ncos, Vatche Sahakian

All HMC Faculty Publications and Research

We study the phases of the (1+1)-dimensional Non-Commutative Open String theory on a circle. We find that the length scale of non-commutativity increases at strong coupling, the coupling in turn being dressed by a power of D-string charge. The system is stringy at around this length scale, with dynamics involving an interplay between the open and wrapped closed strings sectors. Above this energy scale and at strong coupling, and below it at weak coupling, the system acquires a less stringy character. The near horizon geometry of the configuration exhibits several intriguing features, such as a flip in the dilaton field …

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