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Physics Faculty Publications

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Articles 1411 - 1440 of 1942

Full-Text Articles in Physical Sciences and Mathematics

Hot Carbon Densities In The Exosphere Of Venus, Michael W. Liemohn, Jane L. Fox, Andrew F. Nagy, Xiaohua Fang Aug 2004

Hot Carbon Densities In The Exosphere Of Venus, Michael W. Liemohn, Jane L. Fox, Andrew F. Nagy, Xiaohua Fang

Physics Faculty Publications

The results of calculations of hot carbon densities in the exosphere of Venus are presented. The calculation is a two-step process. First a two-stream transport code is used to solve for the distribution function at the exobase, and then these results are used in a Liouville equation solution above the exobase. It is found that generally, photodissociation of carbon monoxide is the largest source of hot carbon atoms in the upper atmosphere of Venus, larger than dissociative recombination of CO+ and significantly larger than the creation of hot carbon through collisions with hot oxygen atoms. It is also found …

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L10 Ordered Fept:C Composite Films With (001) Texture, M. L. Yan, Renat F. Sabirianov, Y. F. Xu, X Z. Li, David J. Sellmyer Jul 2004

L10 Ordered Fept:C Composite Films With (001) Texture, M. L. Yan, Renat F. Sabirianov, Y. F. Xu, X Z. Li, David J. Sellmyer

Physics Faculty Publications

Highly textured (001) FePt:C nanocomposite thin films, deposited directly on thermally oxidized Si wafers, are obtained by multilayer deposition plus subsequent thermal annealing. Nanostructures, crystalline orientations, interactions, and magnetic properties are investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), magnetic force microscopy, and magnetic measurements. The formation of the ordered L10 phase is confirmed by XRD, and only visible (00 ) peaks indicate a high degree of the (001) texture. TEM observation reveals that FePt grains are embedded in the C matrix and appear to be well isolated.

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Simulations Of Ferroelectric Polymer Film Polarization: The Role Of Dipole Interactions, Chun-Gang Duan, Wai-Ning Mei, Jianjun Liu, John R. Hardy, Stephen Ducharme, Peter A. Dowben Jun 2004

Simulations Of Ferroelectric Polymer Film Polarization: The Role Of Dipole Interactions, Chun-Gang Duan, Wai-Ning Mei, Jianjun Liu, John R. Hardy, Stephen Ducharme, Peter A. Dowben

Physics Faculty Publications

We present a systematic study of the dipole alignment in the polyvinylidene fluoride (PVDF) films using first-principles total energy calculations. The ground state of a single layer film is a state with all the dipoles lying parallel to the film plane. This can also be explained by a dipole-dipole interaction model. The induced mirror charges on conducting substrates or substrates with a non-negligible dielectric response play an important role in aligning the polarization perpendicular to the film. From fitting the ab initio calculations, we obtain an effective monomer dipole moment of 4.7 x 10−30 C m. This corresponds to …

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Anomalous Capture And Emission From Internal Surfaces Of Semiconductor Voids: Nanopores In Sic, David C. Look, Z-Q. Fang, S. Soloviev, T. S. Sudarshan, J. J. Boeckl May 2004

Anomalous Capture And Emission From Internal Surfaces Of Semiconductor Voids: Nanopores In Sic, David C. Look, Z-Q. Fang, S. Soloviev, T. S. Sudarshan, J. J. Boeckl

Physics Faculty Publications

Deep level transient spectroscopy in nanoporous, n-type SiC reveals a new type of deep (˜0.8 eV) trap that can hold more than 100 electrons and that has anomalous capture and emission behavior. Here we quantitatively explain these effects with a new, general formalism that treats both emission and capture in the presence of dynamic energy barriers, resulting from the charging and discharging of states on the internal surfaces of voids, such as pores or nanopipes. The capture kinetics display a logarithmic time dependence over a certain filling range, as has often been observed in connection with dislocation-related trapping.

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Reduced Threshold Current Of A Quantum Dot Laser In A Short Period Superlattice Of Indirect-Band Gap, Greg Sun, Richard A. Soref, Jacob B. Khurgin Apr 2004

Reduced Threshold Current Of A Quantum Dot Laser In A Short Period Superlattice Of Indirect-Band Gap, Greg Sun, Richard A. Soref, Jacob B. Khurgin

Physics Faculty Publications

We propose the idea of making quantum dot lasers by embedding direct-band gap quantum dots in a short period superlattice whose band gap is indirect. This technique reduces the threshold current and its temperature dependence. We show that a higher characteristic-temperature T0 can be achieved in a quantum dot laser with indirect GaAs/AlAs superlattice barriers compared to that with direct GaAs barriers.

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Calculation Of The Radiation Trapping Force For Laser Tweezers By Use Of Generalized Lorenz-Mie Theory. Ii. On-Axis Trapping Force, James A. Lock Apr 2004

Calculation Of The Radiation Trapping Force For Laser Tweezers By Use Of Generalized Lorenz-Mie Theory. Ii. On-Axis Trapping Force, James A. Lock

Physics Faculty Publications

The efficiency of trapping an on-axis spherical particle by use of laser tweezers for a particle size from the Rayleigh limit to the ray optics limit is calculated from generalized Lorenz-Mie light-scattering theory and the localized version of a Gaussian beam that has been truncated and focused by a high-numericalaperture lens and that possesses spherical aberration as a result of its transmission through the wall of the sample cell. The results are compared with both the experimental trapping efficiency and the theoretical efficiency obtained from use of the localized version of a freely propagating focused Gaussian beam. The predicted trapping …

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Calculation Of The Radiation Trapping Force For Laser Tweezers By Use Of Generalized Lorenz-Mie Theory. I. Localized Model Description Of An On-Axis Tightly Focused Laser Beam With Spherical Aberration, James A. Lock Apr 2004

Calculation Of The Radiation Trapping Force For Laser Tweezers By Use Of Generalized Lorenz-Mie Theory. I. Localized Model Description Of An On-Axis Tightly Focused Laser Beam With Spherical Aberration, James A. Lock

Physics Faculty Publications

Calculation of the radiation trapping force in laser tweezers by use of generalized Lorenz-Mie theory requires knowledge of the shape coefficients of the incident laser beam. The localized version of these coefficients has been developed and justified only for a moderately focused Gaussian beam polarized in the x direction and traveling in the positive z direction. Here the localized model is extended to a beam tightly focused and truncated by a high-numerical-aperture lens, aberrated by its transmission through the wall of the sample cell, and incident upon a spherical particle whose center is on the beam axis. We also consider …

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Remote Hydrogen Plasma Doping Of Single Crystal Zno, Yuri M. Strzhemechny, Howard L. Mosbacker, David C. Look, Donald C. Reynolds, Cole W. Litton, Nelson Y. Garces, Nancy C. Giles, Larry E. Halliburton, Shigeru Niki, Leonard J. Brillson Apr 2004

Remote Hydrogen Plasma Doping Of Single Crystal Zno, Yuri M. Strzhemechny, Howard L. Mosbacker, David C. Look, Donald C. Reynolds, Cole W. Litton, Nelson Y. Garces, Nancy C. Giles, Larry E. Halliburton, Shigeru Niki, Leonard J. Brillson

Physics Faculty Publications

We demonstrate that remote plasma hydrogenation can increase electron concentrations in ZnO single crystals by more than an order of magnitude. We investigated the effects of this treatment on Hall concentration and mobility as well as on the bound exciton emission peak I4 for a variety of ZnO single crystals–bulk air annealed, Li doped, and epitaxially grown on sapphire. Hydrogen increases I4 intensity in conducting samples annealed at 500 and 600 °C and partially restores emission in the I4 range for Li-diffused ZnO. Hydrogenation increases carrier concentration significantly for the semi-insulating Li doped and epitaxial thin film …

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Reply To "Comment On 'Recombination Of Excitons Bound To Oxygen And Silicon Donors In Freestanding Gan' ", A. Wysmolek, K. P. Korona, R. Stepniewski, J. M. Baranowsky, J. Bloniarz, M. Potemski, R. L. Jones, David C. Look, J. Kuhl, Seong-Ju S. Park, S. K. Lee Apr 2004

Reply To "Comment On 'Recombination Of Excitons Bound To Oxygen And Silicon Donors In Freestanding Gan' ", A. Wysmolek, K. P. Korona, R. Stepniewski, J. M. Baranowsky, J. Bloniarz, M. Potemski, R. L. Jones, David C. Look, J. Kuhl, Seong-Ju S. Park, S. K. Lee

Physics Faculty Publications

In their Comment on our publication [Phys. Rev. B 66, 245317 (2002)], Freitas et al. criticize our identification of donor-bound exciton transitions and the analysis of two-electron satellite emission lines. We show that some arguments given in the Comment are in conflict with our time-resolved and magneto-optical data. We present a discussion of the intradonor transition energies and donor chemical shifts to avoid misunderstanding.

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Spectral Dependence Of Coherent Backscattering Of Light In A Narrow-Resonance Atomic System, D. V. Kupriyanov, I. M. Sokolov, N. V. Larionov, P. Kulatunga, C. I. Sukenik, S. Balik, M. D. Havey Mar 2004

Spectral Dependence Of Coherent Backscattering Of Light In A Narrow-Resonance Atomic System, D. V. Kupriyanov, I. M. Sokolov, N. V. Larionov, P. Kulatunga, C. I. Sukenik, S. Balik, M. D. Havey

Physics Faculty Publications

We report a combined theoretical and experimental study of the spectral and polarization dependence of near-resonant radiation coherently backscattered from an ultracold gas of 85Rb atoms. Measurements in a 6 MHz range about the 5s 2S1/25p 2P3/2, F=3F'=4 hyperfine transition are compared with simulations based on a realistic model of the experimental atomic density distribution. In the simulations, the influence of heating of the atoms in the vapor, magnetization of the vapor, finite spectral bandwidth, and other nonresonant hyperfine transitions are considered. Good agreement is found between the simulations and measurements.

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High-Quality, Melt-Grown Zno Single Crystals, D. C. Reynolds, C. W. Litton, David C. Look, J. E. Joelscher, B. Claflin, T. C. Collins, J. Nause, B. Nemeth Feb 2004

High-Quality, Melt-Grown Zno Single Crystals, D. C. Reynolds, C. W. Litton, David C. Look, J. E. Joelscher, B. Claflin, T. C. Collins, J. Nause, B. Nemeth

Physics Faculty Publications

High-quality, melt-grown ZnO crystals are reported. The reflection and emission spectra of the melt-grown samples are compared with the same spectra from high-quality, vapor-grown ZnO crystals. We isolate the reflection and emission spectra predominantly related to the intrinsic properties associated with the wurtzite structure of the crystals. The quality of the crystals is reflected in the spectral reproduction of the intrinsic properties of the crystals. Both the ground state and the n=2 state of the free excitons associated with the A, B, and C valence bands of the crystals are spectrally observed in reflection. Assuming a hydrogenic character for …

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Complete Angular Distribution Measurements Of Two-Body Deuteron Photodisintegration Between 0.5 And 3 Gev, H. Bagdasaryan, H. Bektasoglu, G. E. Dodge, T. A. Forest, C. E. Hyde-Wright, A. Klein, A. V. Klimenko, S. E. Kuhn, F. Sabatié, S. Stepanyan, L. B. Weinstein, J. Yun, Et Al., The Clas Collaboration Jan 2004

Complete Angular Distribution Measurements Of Two-Body Deuteron Photodisintegration Between 0.5 And 3 Gev, H. Bagdasaryan, H. Bektasoglu, G. E. Dodge, T. A. Forest, C. E. Hyde-Wright, A. Klein, A. V. Klimenko, S. E. Kuhn, F. Sabatié, S. Stepanyan, L. B. Weinstein, J. Yun, Et Al., The Clas Collaboration

Physics Faculty Publications

Nearly complete angular distributions of the two-body deuteron photodisintegration differential cross section have been measured using the CEBAF Large Acceptance Spectrometer detector and the tagged photon beam at the Thomas Jefferson National Accelerator Facility. The data cover photon energies between 0.5 and 3.0 GeV and center-of-mass proton scattering angles 10°–160°. The data show a persistent forward-backward angle asymmetry over the explored energy range, and are well described by the nonperturbative quark gluon string model.

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Experimental Determination Of The Evolution Of The Bjorken Integral At Low Q², A. Deur, P. Bosted, V. Burkert, G. Cates, J.P. Chen, Seonho Choi, D. Crabb, C.W. De Jager, R. De Vita, G.E. Dodge, R. Fatemi, T.A. Forest, F. Garibaldi, R. Gilman, E. W. Hughes, X. Jiang, W. Korsch, S. E. Kuhn, W. Melnitchouk, Z.-E. Meziani, R. Minehart, A.V. Skabelin, K. Slifer, M. Taiuti, J. Yun Jan 2004

Experimental Determination Of The Evolution Of The Bjorken Integral At Low Q², A. Deur, P. Bosted, V. Burkert, G. Cates, J.P. Chen, Seonho Choi, D. Crabb, C.W. De Jager, R. De Vita, G.E. Dodge, R. Fatemi, T.A. Forest, F. Garibaldi, R. Gilman, E. W. Hughes, X. Jiang, W. Korsch, S. E. Kuhn, W. Melnitchouk, Z.-E. Meziani, R. Minehart, A.V. Skabelin, K. Slifer, M. Taiuti, J. Yun

Physics Faculty Publications

We extract the Bjorken integral 𝚪1p-n in the range 0.17 < Q2 <1.10 GeV2 from inclusive scattering of polarized electrons by polarized protons, deuterons, and 3He, for the region in which the integral is dominated by nucleon resonances. These data bridge the domains of the hadronic and partonic descriptions of the nucleon. In combination with earlier measurements at higher Q2, we extract the nonsinglet twist-4 matrix element f2.

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Measurement Of The Electric Form Factor Of The Neutron At Q² = 0.5 And 1.0 Gev²/C², Jefferson Lab E93-026 Collaboration, G. Warren, F. Wesselmann, H. Zhu, A. Klimenko, S. E. Kuhn, L. Yuan, J. Yun, B. Zihlmann, Et Al. Jan 2004

Measurement Of The Electric Form Factor Of The Neutron At Q² = 0.5 And 1.0 Gev²/C², Jefferson Lab E93-026 Collaboration, G. Warren, F. Wesselmann, H. Zhu, A. Klimenko, S. E. Kuhn, L. Yuan, J. Yun, B. Zihlmann, Et Al.

Physics Faculty Publications

The electric form factor of the neutron was determined from measurements of the →d( →e, e'n)p reaction for quasielastic kinematics. Polarized electrons were scattered off a polarized deuterated ammonia (15ND3) target in which the deuteron polarization was perpendicular to the momentum transfer. The scattered electrons were detected in a magnetic spectrometer in coincidence with neutrons in a large solid angle detector. We find GnE =0.0526 ± 0.0033(stat) ± 0.0026(sys) and 0.0454 ± 0.0054 ± 0.0037 at Q2=0.5 and 1.0 (GeV/c)2, respectively.

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Unique Electron Polarimeter Analyzing Power Comparison And Precision Spin-Based Energy Measurement, J. M. Grames, C. K. Sinclair, J. Mitchell, E. Chudakov, H. Fenker, A. Freyberger, D. W. Higinbotham, M. Poelker, M. Steigerwald, M. Tiefenback, Vipuli Dharmawardane Jan 2004

Unique Electron Polarimeter Analyzing Power Comparison And Precision Spin-Based Energy Measurement, J. M. Grames, C. K. Sinclair, J. Mitchell, E. Chudakov, H. Fenker, A. Freyberger, D. W. Higinbotham, M. Poelker, M. Steigerwald, M. Tiefenback, Vipuli Dharmawardane

Physics Faculty Publications

Precision measurements of the relative analyzing powers of five electron beam polarimeters, based on Compton, Moller, and Mott scattering, have been performed using the CEBAF accelerator at the Thomas Jefferson National Accelerator Facility ( Jefferson Laboratory). A Wien filter in the 100 keV beam line of the injector was used to vary the electron spin orientation exiting the injector. High statistical precision measurements of the scattering asymmetry as a function of the spin orientation were made with each polarimeter. Since each polarimeter receives beam with the same magnitude of polarization, these asymmetry measurements permit a high statistical precision comparison of …

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Superionicity In Na3Po4: A Molecular Dynamics Simulation, Wei-Guo Yin, Jianjun Liu, Chun-Gang Duan, Wai-Ning Mei, Robert W. Smith, John R. Hardy Jan 2004

Superionicity In Na3Po4: A Molecular Dynamics Simulation, Wei-Guo Yin, Jianjun Liu, Chun-Gang Duan, Wai-Ning Mei, Robert W. Smith, John R. Hardy

Physics Faculty Publications

Fast ionic conduction in solid Na3PO4 is studied by use of molecular dynamics simulation based on the modified Lu-Hardy approach. We obtain reasonable agreement with experiment for the structural transition and diffusion of the sodium ions. All the sodium ions are found to contribute comparably to the high ionic conductivity. The results of the simulation are discussed in terms of the relative magnitude of the two proposed transport mechanisms: percolation and paddle-wheel. It appears to us that the percolation mechanism dominates the sodium diffusion.

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Large Dielectric Constant And Maxwell-Wagner Relaxation In Bi2/3cu3ti4o12, Jianjun Liu, Chun-Gang Duan, Wei-Guo Yin, Wai-Ning Mei, Robert W. Smith, John R. Hardy Jan 2004

Large Dielectric Constant And Maxwell-Wagner Relaxation In Bi2/3cu3ti4o12, Jianjun Liu, Chun-Gang Duan, Wei-Guo Yin, Wai-Ning Mei, Robert W. Smith, John R. Hardy

Physics Faculty Publications

We studied frequency and temperature dependences of impedance, electric modulus, and dielectric permittivity of Bi2/3Cu3Ti4O12 in the ranges of 10−1–106 Hz and −150–200 °C, respectively. We first observed two electrical responses in the impedance and modulus formalisms. Then we detected a Debye-like relaxation in the permittivity formalism. Most interestingly, we found that the large dielectric constant of Bi2/3Cu3Ti4O12 is independent of the temperature and frequency below 150°C. The results are interpreted in terms of a two-layer model with conducting grains partitioned from each other by poorly conducting grain boundaries. Using this model, we attributed the two electrical responses in impedance …

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Electronic Properties Of Nacdf3: A First-Principles Prediction, Chun-Gang Duan, Wai-Ning Mei, Jianjun Liu, Wei-Guo Yin, John R. Hardy, Robert W. Smith, M. J. Mehl, L. L. Boyer Jan 2004

Electronic Properties Of Nacdf3: A First-Principles Prediction, Chun-Gang Duan, Wai-Ning Mei, Jianjun Liu, Wei-Guo Yin, John R. Hardy, Robert W. Smith, M. J. Mehl, L. L. Boyer

Physics Faculty Publications

Based on first-principles total energy calculations, we predict that NaCdF3 could be formed in a ferroelectric crystal structure. Using a symmetry guided search with structure optimization, we found two ferroelectric structures, nearly degenerate in energy, competing for the ground state: a rhombohedral structure with space group R3c and an orthorhombic structure with space group Pna21. The energies of both structures are '60 meV lower than the sum of those of the constituents, NaF and CdF2, implying chemical stability.

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Age Differences In Central (Semantic) And Peripheral Processing: The Importance Of Considering Both Response Times And Errors, Philip A. Allen, Martin D. Murphy, Miron Kaufman, Karen E. Groth, Ana Begovic Jan 2004

Age Differences In Central (Semantic) And Peripheral Processing: The Importance Of Considering Both Response Times And Errors, Philip A. Allen, Martin D. Murphy, Miron Kaufman, Karen E. Groth, Ana Begovic

Physics Faculty Publications

In this project we examined the effect of adult age on visual word recognition by using combined reaction time (RT) and accuracy methods based on the Hick–Hyman law. This was necessary because separate Brinley analyses of RT and errors resulted in contradicting results. We report the results of a lexical decision task experiment (with 96 younger adults and 97 older adults). We transformed the error data into entropy and then predicted RT by using entropy values separately for exposure duration (thought to influence peripheral processes) and word frequency (thought to influence central processes). For exposure duration, the entropy–RT functions indicate …

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Variable-Temperature Scanning Optical And Force Microscope, Petru S. Fodor, H. Zhu, N. G. Patil, J. Levy Jan 2004

Variable-Temperature Scanning Optical And Force Microscope, Petru S. Fodor, H. Zhu, N. G. Patil, J. Levy

Physics Faculty Publications

The implementation of a scanning microscope capable of working in confocal, atomic force and apertureless near field configurations is presented. The microscope is designed to operate in the temperature range 4–300 K, using conventional helium flow cryostats. In atomic force microscope(AFM) mode, the distance between the sample and an etchedtungsten tip is controlled by a self-sensing piezoelectrictuning fork. The vertical position of both the AFM head and microscope objective can be accurately controlled using piezoelectric coarse approach motors. The scanning is performed using a compact XYZ stage, while the AFM and optical head are kept fixed, allowing scanning probe and …

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Inclusive Photoproduction Of Lepton Pairs In The Parton Model, A. Psaker Jan 2004

Inclusive Photoproduction Of Lepton Pairs In The Parton Model, A. Psaker

Physics Faculty Publications

In the framework of the QCD parton model, we study unpolarized scattering of high energy real photons from a proton target into lepton pairs and a system of hadrons. For a given parametrization of parton distributions in the proton, we calculate the cross section of this process and show the cancellation of the interference terms.

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Complete Measurement Of Three-Body Photodisintegration Of 3He For Photon Energies Between 0.35 And 1.55 Gev, H. Bagdasaryan, M. Bektasoglu, K. V. Dharmawardane, G. E. Dodge, T. A. Forest, G. Gavalian, N. Guler, C. E. Hyde-Wright, A. Klein, S. E. Kuhn, L. M. Qin, S. Stepanyan, L. B. Weinstein, J. Yun, Et Al., The Clas Collaboration Jan 2004

Complete Measurement Of Three-Body Photodisintegration Of 3He For Photon Energies Between 0.35 And 1.55 Gev, H. Bagdasaryan, M. Bektasoglu, K. V. Dharmawardane, G. E. Dodge, T. A. Forest, G. Gavalian, N. Guler, C. E. Hyde-Wright, A. Klein, S. E. Kuhn, L. M. Qin, S. Stepanyan, L. B. Weinstein, J. Yun, Et Al., The Clas Collaboration

Physics Faculty Publications

The three-body photodisintegration of 3He has been measured with the CLAS detector at Jefferson Lab, using tagged photons of energies between 0.35 GeV and 1.55 GeV. The large acceptance of the spectrometer allowed us for the first time to cover a wide momentum and angular range for the two outgoing protons. Three kinematic regions dominated by either two- or three-body contributions have been distinguished and analyzed. The measured cross sections have been compared with results of a theoretical model, which, in certain kinematic ranges, have been found to be in reasonable agreement with the data.

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Hyperon Photoproduction In The Nucleon Resonance Region, K. V. Dharmawardane, G. E. Dodge, C. E. Hyde-Wright, S. E. Kuhn, L. M. Qin, L. B. Weinstein, J. Yun, Et Al., Clas Collaboration Jan 2004

Hyperon Photoproduction In The Nucleon Resonance Region, K. V. Dharmawardane, G. E. Dodge, C. E. Hyde-Wright, S. E. Kuhn, L. M. Qin, L. B. Weinstein, J. Yun, Et Al., Clas Collaboration

Physics Faculty Publications

High-statistics cross sections and recoil polarizations for the reactions γ+p → K++ Λ and γ+p→K++ Σ0 have been measured at CLAS for center-of-mass energies between 1.6 and 2.3 GeV. In the K+Λ channel we confirm a resonance-like structure near W = 1.9 GeV at backward kaon angles. Our data show more complex s- and u- channel behavior than previously seen, since structure is also present at forward angles, but not at central angles. The position and width change with angle, indicating that more than one resonance is playing a role. Large positive Λ polarization at …

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Measurement Of Beam-Spin Asymmetries For Π⁺ Electroproduction Above The Baryon Resonance Region, K. V. Dharmawardane, G. E. Dodge, C. E. Hyde-Wright, S. E. Kuhn, L. M. Qin, F. Sabatié, L. B. Weinstein, J. Yun, Et Al., Clas Collaboration Jan 2004

Measurement Of Beam-Spin Asymmetries For Π⁺ Electroproduction Above The Baryon Resonance Region, K. V. Dharmawardane, G. E. Dodge, C. E. Hyde-Wright, S. E. Kuhn, L. M. Qin, F. Sabatié, L. B. Weinstein, J. Yun, Et Al., Clas Collaboration

Physics Faculty Publications

We report the first evidence for a nonzero beam-spin azimuthal asymmetry in the electroproduction of positive pions in the deep-inelastic kinematic region. Data for the reaction e→pe'π+X have been obtained using a polarized electron beam of 4.3 GeV with the CEBAF Large Acceptance Spectrometer at the Thomas Jefferson National Accelerator Facility. The amplitude of the sin ᵠ modulation increases with the momentum of the pion relative to the virtual photon, z. In the range z = 0.5-0.8 the average amplitude is 0.038 ± 0.005 ± 0.003 for a missing mass Mx > 1.1 GeV and 0.037 …

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Scattering Of Shock Waves In Qcd, Ian Balitsky Jan 2004

Scattering Of Shock Waves In Qcd, Ian Balitsky

Physics Faculty Publications

The cross section of heavy-ion collisions is represented as a double functional integral with the saddle point being the classical solution of the Yang-Mills equations with boundary conditions/sources in the form of two shock waves corresponding to the two colliding ions. I develop the expansion of this classical solution in powers of the commutator of the Wilson lines describing the colliding particles and calculate the first two terms of the expansion.

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Comparisons Of Electron Fluxes Measured In The Crustal Fields At Mars By The Mgs Magnetometer/Electron Reflectometer Instrument With A B Field-Dependent Transport Code, Michael W. Liemohn, David L. Mitchell, Andrew F. Nagy, Jane L. Fox, Tamara W. Reimer, Yingjuan J. Ma Dec 2003

Comparisons Of Electron Fluxes Measured In The Crustal Fields At Mars By The Mgs Magnetometer/Electron Reflectometer Instrument With A B Field-Dependent Transport Code, Michael W. Liemohn, David L. Mitchell, Andrew F. Nagy, Jane L. Fox, Tamara W. Reimer, Yingjuan J. Ma

Physics Faculty Publications

We compare Mars Global Surveyor (MGS) magnetometer/electron reflectometer data with results from a B field–dependent kinetic transport code for ‘‘superthermal’’ electrons. The photoelectrons created on crustal field loops, when they are on the dayside, allow for the exploration of the magnetic topology and the upper atmospheric density structure. A case study of a typical orbit of the MGS satellite through the strong crustal field region in the southern hemisphere of Mars is examined. The results indicate that the low solar wind dynamic pressure during the selected orbit allowed for the expansion of the crustal field line to relatively high altitudes. …

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Fabrication And Characterization Of N-Zno/P-Algan Heterojunction Light-Emitting Diodes On 6h-Sic Substrates, Ya I. Alivov, E. V. Kalinina, A. E. Cherenkov, David C. Look, B. M. Ataev, A. K. Omaev, M. V. Chukichev, D. M. Bagnall Dec 2003

Fabrication And Characterization Of N-Zno/P-Algan Heterojunction Light-Emitting Diodes On 6h-Sic Substrates, Ya I. Alivov, E. V. Kalinina, A. E. Cherenkov, David C. Look, B. M. Ataev, A. K. Omaev, M. V. Chukichev, D. M. Bagnall

Physics Faculty Publications

We report on the fabrication of n-ZnO/p-AlGaN heterojunction light-emitting diodes on 6H-SiC substrates. Hydride vapor phase epitaxy was used to grow p-type AlGaN, while chemical vapor deposition was used to produce the n-type ZnO layers. Diode-like, rectifying I-V characteristics, with threshold voltage ~3.2 V and low reverse leakage current ~10-7 A, are observed at room temperature. Intense ultraviolet emission with a peak wavelength near 389 nm is observed when the diode is forward biased; this emission is found to be stable at temperatures up to 500 K and shown to originate from recombination within the ZnO.

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Twin-Rainbow Metrology. I. Measurement Of The Thickness Of A Thin Liquid Film Draining Under Gravity, Charles L. Adler, James A. Lock, Ian P. Rafferty, Wayne Hickok Nov 2003

Twin-Rainbow Metrology. I. Measurement Of The Thickness Of A Thin Liquid Film Draining Under Gravity, Charles L. Adler, James A. Lock, Ian P. Rafferty, Wayne Hickok

Physics Faculty Publications

We describe twin-rainbow metrology, a new optical technique used to measure the thickness of thin films in a cylindrical geometry. We also present an application of the technique: measurement of the thickness of a Newtonian fluid draining under gravity. We compare these measurements with fluid mechanics models. (C) 2003 Optical Society of America.

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Mode Structure Of Diffusive Transport In Hydroxypropylcellulose:Water, George D.J. Phillies, Robert O. Connell, Paul Whitford, Kiril A. Streletzky Nov 2003

Mode Structure Of Diffusive Transport In Hydroxypropylcellulose:Water, George D.J. Phillies, Robert O. Connell, Paul Whitford, Kiril A. Streletzky

Physics Faculty Publications

A systematic analysis of the mode structure of diffusive relaxations in 1 MDa hydroxypropylcellulose(HPC):water is presented. New methods and data include (1) use of integral spectral moments to characterize nonexponential decays, (2) spectra of small probes in concentrated HPC solutions, (3) temperature dependence of the mode structure, and (4) comparison of optical probe spectra and spectra of probe-free polymer solutions. We find that (1) probe and polymer relaxations are in general not the same; (2) the apparent viscometric crossover near ct≈6 g/l is echoed by probe behavior; (3) our HPC solutions have a characteristic dynamic length, namely the 50 nm …

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Evidence Of The Zn Vacancy Acting As The Dominant Acceptor In N-Type Zno, F. Tuomisto, V. Ranki, K. Saarinen, David C. Look Nov 2003

Evidence Of The Zn Vacancy Acting As The Dominant Acceptor In N-Type Zno, F. Tuomisto, V. Ranki, K. Saarinen, David C. Look

Physics Faculty Publications

We have used positron annihilation spectroscopy to determine the nature and the concentrations of the open volume defects in as-grown and electron irradiated (Eel=2   MeV, fluence 6×1017   cm-2) ZnO samples. The Zn vacancies are identified at concentrations of [VZn]≃2×1015   cm-3 in the as-grown material and [VZn]≃2×1016   cm-3 in the irradiated ZnO. These concentrations are in very good agreement with the total acceptor density determined by temperature dependent Hall experiments. Thus, the Zn vacancies are dominant acceptors in both as-grown and irradiated ZnO.

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