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Phenomenological Theory Of Cuprate Superconductivity, Mario Rabinowitz, T. Mcmullen Jan 1993

Phenomenological Theory Of Cuprate Superconductivity, Mario Rabinowitz, T. Mcmullen

Physics Publications

Reasonably good agreement with the superconducting transitiontemperatures of the cuprate high‐T c superconductors can be obtained on the basis of an approximate phenomenological theory. In this theory, two criteria are used to calculate the superconducting transitiontemperature. One is that the quantum wavelength is of the order of the electron‐pair spacing. The other is that a fraction of the normal carriers exist as Cooper pairs at T c . The resulting simple equation for T c contains only two parameters: the normal carrier density and effective mass. We calculate specific transition temperatures for 12 cuprate superconductors.

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Light-Scattering Technique For The Study Of Dynamic Thickness Fluctuations In Thin Liquid Films, Richard C. Haskell, Daniel C. Petersen, Mark W. Johnson Jan 1993

Light-Scattering Technique For The Study Of Dynamic Thickness Fluctuations In Thin Liquid Films, Richard C. Haskell, Daniel C. Petersen, Mark W. Johnson

All HMC Faculty Publications and Research

The authors describe a light-scattering technique capable of probing the dynamics of thickness fluctuations in lipid bilayers. The technique, which they call reflectance fluctuation spectroscopy (RFS), is keenly sensitive to light scattered from the squeeze modes of motion in a thin liquid film, and insensitive to light scattered from the bend modes. A laser beam is focused to a small spot on the film, and the power in the specularly reflected beam is recorded in real time. Thickness fluctuations associated with the squeeze modes of motion give rise to fluctuations in the power of the specularly reflected light. The frequency …

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Light-Scattering Technique For The Study Of Dynamic Thickness Fluctuations In Thin Liquid Films, Richard C. Haskell, Daniel C. Petersen, Mark W. Johnson Jan 1993

Light-Scattering Technique For The Study Of Dynamic Thickness Fluctuations In Thin Liquid Films, Richard C. Haskell, Daniel C. Petersen, Mark W. Johnson

All HMC Faculty Publications and Research

The authors describe a light-scattering technique capable of probing the dynamics of thickness fluctuations in lipid bilayers. The technique, which they call reflectance fluctuation spectroscopy (RFS), is keenly sensitive to light scattered from the squeeze modes of motion in a thin liquid film, and insensitive to light scattered from the bend modes. A laser beam is focused to a small spot on the film, and the power in the specularly reflected beam is recorded in real time. Thickness fluctuations associated with the squeeze modes of motion give rise to fluctuations in the power of the specularly reflected light. The frequency …

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Mass And Mixing-Angle Patterns In The Standard Model And Its Minimal Supersymmetric Extension, H. Arason, Diego Castano, E. J. Piard, P. Ramond Jan 1993

Mass And Mixing-Angle Patterns In The Standard Model And Its Minimal Supersymmetric Extension, H. Arason, Diego Castano, E. J. Piard, P. Ramond

Chemistry and Physics Faculty Articles

Using renormalization group techniques, we examine several interesting relations among masses and mixing angles of quarks and leptons in the standard model. We extend the analysis to the minimal supersymmetric extension to determine its effect on these mass relations. Remarkably supersymmetry allows for these relations to be satisfied at a single grand unified scale.

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Lamellar Ordering In Symmetric Diblock Copolymers, R. A. Sones, E. M. Terentjev, Rolfe G. Petschek Jan 1993

Lamellar Ordering In Symmetric Diblock Copolymers, R. A. Sones, E. M. Terentjev, Rolfe G. Petschek

Faculty Scholarship

We calculate the lamellar period L and interphase thickness a of an incompressible melt of symmetric diblock copolymers from the onset of phase segregation (weak segregation limit) to the limit where segregation is almost complete (strong segregation limit) by numerically solving a mean field lattice model, where the lattice spacing is taken small enough to approximate a continuum. Our results for L and a agree with previously derived theoretical formulas in both limits. Based on the first few terms of a Fourier series expansion of the density profile, we show analytically that L = 0.844R(χN)0.571 at the weak segregation limit, …

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A First-Principle Derivation Of The High Latitude Total Electron Content Distribution, D. J. Crain, Jan Josef Sojka, Robert W. Schunk, P. H. Doherty, J. A. Klobucher Jan 1993

A First-Principle Derivation Of The High Latitude Total Electron Content Distribution, D. J. Crain, Jan Josef Sojka, Robert W. Schunk, P. H. Doherty, J. A. Klobucher

All Physics Faculty Publications

Calculation of the high-latitude distribution of the vertical total electron content (TEC) is possible using a three-dimensional, time-dependent ionospheric model. Global and local comparisons may be made with observations of TEC. We compare the local diurnal variation of TEC calculated by the model with observations of TEC at Goose Bay, Labrador and Hamilton, Massachusetts. Data from the period of March 1–11, 1989, and monthly averaged data for solar maximum and solar minimum periods are examined. We extend the model to predict diurnal variations of TEC in the polar cap and compare these results with the observed TEC at Thule, Greenland, …

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A Time-Dependent Model Of Polar Cap Arcs, Lie Zhu, Jan Josef Sojka, Robert W. Schunk, D. J. Crain Jan 1993

A Time-Dependent Model Of Polar Cap Arcs, Lie Zhu, Jan Josef Sojka, Robert W. Schunk, D. J. Crain

All Physics Faculty Publications

A two-dimensional time-dependent model of polar cap arcs has been developed. The electrodynamics of the polar cap arcs are treated self-consistently in the frame of the coupled magnetosphere-ionosphere system. The focus of this paper is to introduce the physics and mathematical formulation of the model and describe the features of the spatial structure and temporal evolution of the polar cap arcs. The modeling results indicate that the time constant for the formation of the polar cap arcs is around 10 min. It is found that an initial single-arc precipitation pattern associated with a polar cap arc tends to split into …

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Fullerene Derivatives And Fullerene Superconductors, H. H. Wang, J. A. Schlueter, A. C. Cooper, J. L. Smart, M. E. Whitten, U. Geiser, K. D. Carlson, J. M. Williams, U. Welp, J. D. Dudek, M. A. Caleca Jan 1993

Fullerene Derivatives And Fullerene Superconductors, H. H. Wang, J. A. Schlueter, A. C. Cooper, J. L. Smart, M. E. Whitten, U. Geiser, K. D. Carlson, J. M. Williams, U. Welp, J. D. Dudek, M. A. Caleca

Faculty Publications - Department of Biological & Molecular Science

A series of 1:1 Cgo cycloaddition adducts, CgoA (A = anthracene, butadiene, cyclopentadiene, and methylcyclopentadiene), has been synthesized. The products are cleanly separated and characterized by use of TGA, iH-NMR, IR, and mass spectrometry. Among these adducts, Cgodaethylcyclopentadiene) showed the highest thermal stability and was doped with three equivalents of rubidium. The resulting Rb3C6o(MeCp) is a semiconductor but can be thermally converted to the superconducting Rb3C6O through a retro-Diels-Alder reaction. A one-step doping process to prepare Rb3Ceo crystals has been developed. The optimal doping condition occurs at ~300°C. High superconducting shielding fractions: between 60 and 90% and sharp transition widths …

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Recovery Of Quenched Hopping Conduction In Gaas-Layers Grown By Molecular-Beam Epitaxy At 200-Degrees-C, David C. Look, Z-Q. Fang, J. R. Sizelove Jan 1993

Recovery Of Quenched Hopping Conduction In Gaas-Layers Grown By Molecular-Beam Epitaxy At 200-Degrees-C, David C. Look, Z-Q. Fang, J. R. Sizelove

Physics Faculty Publications

The dark current at 82 K, in GaAs layers grown by molecular-beam epitaxy at 200 °C and annealed at 550 °C, is reduced by a factor 350 after 5 min of IR (hν<~1.12 eV) light illumination. As temperature is swept upward at 0.2 K/s, the current recovers rapidly near 130 K. A numerical analysis of the current recovery, based on hopping conduction, gives an excellent fit to the data for a thermal recovery rate r=3×108 exp(-0.26/kT), very close to the rate observed for EL2 (AsGa). This proves that the conduction below 300 K in this material is due to hopping between AsGa-related centers in their ground states. Variable-range hopping [exp-(T0/T)1/4] gives a slightly better fit to the data than nearest-neighbor hopping [exp(-ɛ3/kT)] in the range T=82-160 K, but the fitted recovery …

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The Production And Escape Of Nitrogen Atoms On Mars, Jane L. Fox Jan 1993

The Production And Escape Of Nitrogen Atoms On Mars, Jane L. Fox

Physics Faculty Publications

We have computed the production rates and densities of odd nitrogen species in the Martian atmosphere using updated rate coefficients and a revised ionosphere-thermosphere model. We find that the computed densities of NO are somewhat smaller than those measured by Viking 1, but reasonable agreement can be obtained by assuming that the rate coefficient for loss of odd nitrogen in the reaction of N with NO is smaller at temperatures that prevail in the lower Martian thermosphere (about 130–160 K) than the standard value, which applies to temperatures of 200–400 K. We have also modeled the escape fluxes of N …

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Ultraviolet Spectra Of Acetic Acid, Glycine, And Glyphosate, J. Scott Mcconnell, Rose M. Mcconnell, Lloyd R. Hossner Jan 1993

Ultraviolet Spectra Of Acetic Acid, Glycine, And Glyphosate, J. Scott Mcconnell, Rose M. Mcconnell, Lloyd R. Hossner

Journal of the Arkansas Academy of Science

The influence of pH on the ultraviolet spectra of 0.001, 0.005, and 0.010 M glyphosate, glycine, and acetic acid was investigated. Each dilution of each acid was adjusted to acidic, neutral, and basic pH values. Ultraviolet spectra were recorded from 300 to 200 nm for each acid-dilution-pH combination. The wavelength of maximum absorption (Lambdamax) of glyphosate and glycine was slightly higher in the high pH solutions than in the neutral and low pH solutions. The Lambdamax of acetic acid was apparently unaffected by changes in ph. Molar extinction coefficients (epsilon) at Lambdamax increased with pH for all three acids. Regression …

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New Asga Related Center In Gaas, David C. Look, Z-Q. Fang, J. R. Sizelove, C. E. Stutz Jan 1993

New Asga Related Center In Gaas, David C. Look, Z-Q. Fang, J. R. Sizelove, C. E. Stutz

Physics Faculty Publications

A new center related to AsGa has been found at relatively high concentrations (1017 cm-;3) in semi‐insulating (2×10;7 Ω cm) molecular beam epitaxial GaAs grown at 400 °C. Although the ir photoquenching and thermal recovery characteristics are nearly identical to those of ;EL2, the thermal activation energy is only 0.65±0.01 eV, much lower than the ;EL2 value of 0.75±0.01 eV. Other properties which are different include the electron‐capture barrier energy, hyperfine constant, and magnetic circular dichroism spectrum.

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Paschen's Law For A Hollow Cathode Discharge, H. Eichhorn, K. H. Schoenbach, T. Tessnow Jan 1993

Paschen's Law For A Hollow Cathode Discharge, H. Eichhorn, K. H. Schoenbach, T. Tessnow

Bioelectrics Publications

An expression for the breakdown voltage of a one‐dimensional hollow cathode discharge has been derived. The breakdown condition which corresponds to Paschen’s law contains, in addition to the first Townsend coefficient, and the secondary electron emission coefficient two parameters which characterize the reflecting action of the electric field and the lifetime of the electrons in the discharge. The breakdown voltage for a hollow cathode discharge in helium was calculated and compared to that of a glow discharge operating under similar conditions.

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Defect Structure Of Y1-Ycaymno3 And La1-Ycaymno3. I. Electrical Properties, J. W. Stevenson, M. M. Nasrallah, Harlan U. Anderson, Don M. Sparlin Jan 1993

Defect Structure Of Y1-Ycaymno3 And La1-Ycaymno3. I. Electrical Properties, J. W. Stevenson, M. M. Nasrallah, Harlan U. Anderson, Don M. Sparlin

Materials Science and Engineering Faculty Research & Creative Works

Electrical conductivity and the Seebeck coefficient of compositions in the system Y1-yCayMnO3 and La1-yCayMnO3 were studied to determine the mechanism of electrical transport and defect structure. Electrical conduction appeared to occur via a small polaron hopping mechanism for compositions with 0.30 ≤ y ≤ 0.80. The Seebeck coefficient data did not support the assumption that Mn is present in Cadoped Mn perovskites only in the +3 and +4 valence states. A new defect model was developed which includes the thermally excited disproportion of Mn3+ and Mn4+ pairs. The …

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The Development Of A Solar Radiation Extinction Correction For Satellite Data, Widad I. Mohamed Jan 1993

The Development Of A Solar Radiation Extinction Correction For Satellite Data, Widad I. Mohamed

Electronic Theses and Dissertations

The main objectives of this thesis are the following: 1) Remove the haze using water surfaces in Landsat satellite imagery of the visible and near-infrared regions for their properties of high absorption of solar radiation and weak reflection of it. The scattered solar radiation is most obvious in dark weakly reflecting regions such as water. The haze removal technique depends on subtraction of scattered light from picture elements within the satellite imagery. 2) Derive a formula and techniques for a given image to correct for extinction by transforming the observed intensity of the signal transmitted to the Landsat detector to …

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Dipole-Dipole Spin Relaxation In Solids. The Unrestricted Hopping Model And The Methyl Proton - Non-Methyl Proton Interaction, Christopher Palmer, Alfonso M. Albano, Peter A. Beckmann Jan 1993

Dipole-Dipole Spin Relaxation In Solids. The Unrestricted Hopping Model And The Methyl Proton - Non-Methyl Proton Interaction, Christopher Palmer, Alfonso M. Albano, Peter A. Beckmann

Physics Faculty Research and Scholarship

We report proton Zeeman relaxation rates R as a function of temperature T at 8.5 and 53 MHz in polycrystalline 1,9-dimethylphenanthrene (1,9-DMP) and l-trideuteriomethyl-9-methylphenanthrene (1, 9-DMP[1-d3]). The data are interpreted using a Davidson-Cole spectral density for intramolecular reorientation and the implications of this are discussed. R vs T−1data for 1,9-DMP[1-d3] are used to determine the parameters that characterize the reorientation of the 9-methyl group. By assuming that the parameters characterizing the dynamics of the 9-methyl group are the same in 1,9-DMP and 1,9-DMP[1-d3], we subtract out the R vs T−1 contribution of the 9-methyl group in 1,9-DMP to …

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Determination Of The Neutron Spin Structure Function, P. L. Anthony, R. G. Arnold, H. R. Band, H. Borel, P.E. Bosted, V. Breton, G. D. Cates, T. E. Chupp, F. S. Dietrich, J. Dunne, R. Erbacher, J. Fellbaum, H. Fonvielle, R. Gearhart, R. Holmes, E. W. Hughes, J. R. Johnson, D. Kawall, C. Keppel, S. E. Kuhn, R. M. Lombard-Nelsen, J. Marroncle, T. Maruyama, W. Meyer, Z. E. Meziani, H. Middleton, J. Morgenstern, N. R. Newbury, G. G. Petratos, R. Pitthan, R. Prepost, Y. Roblin, S. E. Rock, S. H. Rokni, G. Shapiro, T. Smith, P. A. Souder, M. Spengos, F. Staley, L. M. Stuart, Z. M. Szalata, Y. Terrien, A. K. Thompson, J. L. White, M. Woods, J. Xu, C. C. Young, G. Zapalac, E142 Collaboration Jan 1993

Determination Of The Neutron Spin Structure Function, P. L. Anthony, R. G. Arnold, H. R. Band, H. Borel, P.E. Bosted, V. Breton, G. D. Cates, T. E. Chupp, F. S. Dietrich, J. Dunne, R. Erbacher, J. Fellbaum, H. Fonvielle, R. Gearhart, R. Holmes, E. W. Hughes, J. R. Johnson, D. Kawall, C. Keppel, S. E. Kuhn, R. M. Lombard-Nelsen, J. Marroncle, T. Maruyama, W. Meyer, Z. E. Meziani, H. Middleton, J. Morgenstern, N. R. Newbury, G. G. Petratos, R. Pitthan, R. Prepost, Y. Roblin, S. E. Rock, S. H. Rokni, G. Shapiro, T. Smith, P. A. Souder, M. Spengos, F. Staley, L. M. Stuart, Z. M. Szalata, Y. Terrien, A. K. Thompson, J. L. White, M. Woods, J. Xu, C. C. Young, G. Zapalac, E142 Collaboration

Physics Faculty Publications

The spin structure function of the neutron g1n has been determined over the range 0.03 < x < 0.6 at an average Q2 of 2 (GeV/c)2 by measuring the asymmetry in deep inelastic scattering of polarized electrons from a polarized 3He target at energies between 19 and 26 GeV. The integral of the neutron spin structure function is found to be f-10 gn1(x)dx = -0.022 ± 0.011. Earlier reported proton results together with the Bjorken sum rule predict f-10 gn1(x)dx = -0.059 ± 0.019.

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On The System Of Diffuse Interstellar Bands At 5844 And 5850 Å, J Krelowski, Theodore P. Snow, J Papaj, C G. Seab, B Wszolek Jan 1993

On The System Of Diffuse Interstellar Bands At 5844 And 5850 Å, J Krelowski, Theodore P. Snow, J Papaj, C G. Seab, B Wszolek

Physics Faculty Publications

Two neighboring diffuse interstellar bands (DIBs) at 5844 and 5850 Å are shown to be of different origin. The presence or absence of the 5844 DIB is related to the ratio of the two prominent DIBs at 5780 and 5797 Å as well as to the nature of the ultraviolet extinction curve. The 5844 Å DIB is very sensitive to the extinction, being completely absent in cases where the far-UV extinction is low. This suggests that the carrier is destroyed by photons having energies above 11 or 12 eV. The 5850 Å DIB correlates very well with the well-studied DIB …

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Defect Structure Of Y1-Ycaymno3 And La1-Ycaymno3. Ii. Oxidation-Reduction Behavior, J. W. Stevenson, M. M. Nasrallah, Harlan U. Anderson, Don M. Sparlin Jan 1993

Defect Structure Of Y1-Ycaymno3 And La1-Ycaymno3. Ii. Oxidation-Reduction Behavior, J. W. Stevenson, M. M. Nasrallah, Harlan U. Anderson, Don M. Sparlin

Materials Science and Engineering Faculty Research & Creative Works

Electrical conductivity, Seebeck coefficient, and thermogravimetric behavior of compositions in the systems Y1-yCayMnO3 and Y1-yCayMnO3 were studied as functions of temperature and ambient oxygen activity in order to determine the mechanism of electrical transport and defect structure. Compositions in Y1-yCayMnO3 exhibited very slight oxygen activity-dependent behavior as the ambient oxygen activity was reduced. A defect model which includes the thermally excited disproportionation of Mn3+ into Mn2+ and Mn4+ pairs was applied to the oxygen-activity-dependent data for La0.80Ca0.20MnO3 …

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Hydrodynamic Theory Of Multicomponent Diffusion And Thermal Diffusion In Multitemperature Gas Mixtures, John D. Ramshaw Jan 1993

Hydrodynamic Theory Of Multicomponent Diffusion And Thermal Diffusion In Multitemperature Gas Mixtures, John D. Ramshaw

Physics Faculty Publications and Presentations

A phenomenological theory is developed for multicomponent diffusion, including thermal diffusion, in gas mixtures in which the components may have different temperatures. The theory is based on the hydrodynamic approach of Maxwell and Stefan, as extended and elaborated by Furry [1] and Williams [2]. The present development further extends these earlier treatments to multiple temperatures and multicomponent thermal diffusion. The resulting diffusion fluxes obey generalized Stefan-Maxwell relations which include the effects of ordinary, forced, pressure, and thermal diffusion. When thermal diffusion is neglected, these relations have the same form as the usual single-temperature ones, except that mole fractions are replaced …

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A Magnetic Suspension System With A Large Angular Range, Colin P. Britcher, Mehran Ghofrani Jan 1993

A Magnetic Suspension System With A Large Angular Range, Colin P. Britcher, Mehran Ghofrani

Mechanical & Aerospace Engineering Faculty Publications

In order to explore and develop technology required for the magnetic suspension of objects over large ranges of orientation, a small-scale laboratory system, the large-angle magnetic suspension test fixture (LAMSTF) has been constructed at NASA Langley Research Center. This apparatus falls into the category of large-gap, actively stabilized magnetic levitation systems. The hardware comprises five conventional electromagnets in a circular arrangement, each driven from a separate bipolar power amplifier. Electromagnet currents are commanded by a digital control system, implemented on a microcomputer, which in turn derives the position and attitude of the suspended element from an infrared optical system. The …

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Glow-Discharge Enhanced Permeation Of Oxygen Through Silver, D. Wu, R. A. Outlaw, Robert L. Ash Jan 1993

Glow-Discharge Enhanced Permeation Of Oxygen Through Silver, D. Wu, R. A. Outlaw, Robert L. Ash

Mechanical & Aerospace Engineering Faculty Publications

The permeation of oxygen through Ag0.05Zr over the temperature range of 300-650°C under glow-discharge conditions has been studied and compared to the permeation of thermally dissociated molecular oxygen. A low-energy dc glow-discharge in O2 has been employed which produced approximately 10% atoms. The permeation rate during the glow discharge was found to be much higher (a factor of ∼10) than without the glow discharge. The small fraction of oxygen atoms generated appears to dominate the permeation because of much higher solution probabilities. Below 500°C, the activation energy for the permeation with glow discharge was found to be 15.5 kcal/mol …

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A Numerical Study Of Wave Propagation In A Confined Mixing Layer By Eigenfunction Expansions, Fang Q. Hu Jan 1993

A Numerical Study Of Wave Propagation In A Confined Mixing Layer By Eigenfunction Expansions, Fang Q. Hu

Mathematics & Statistics Faculty Publications

It is well known that the growth rate of instability waves of a two-dimensional free shear layer is reduced greatly at supersonic convective Mach numbers. In previous works, it has been shown that new wave modes exist when the shear layers are bounded by a channel due to the coupling effect between the acoustic wave modes and the motion of the mixing layer. The present work studies the simultaneous propagation of multiple stability waves using numerical simulation. It is shown here that the coexistence of two wave modes in the flow field can lead to an oscillatory growth of disturbance …

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Induced Mach Wave-Flame Interactions In Laminar Supersonic Fuel Jets, F. Q. Hu, T. L. Jackson, D. G. Lasseigne, C. E. Grosch Jan 1993

Induced Mach Wave-Flame Interactions In Laminar Supersonic Fuel Jets, F. Q. Hu, T. L. Jackson, D. G. Lasseigne, C. E. Grosch

Mathematics & Statistics Faculty Publications

A model problem is proposed to investigate the steady response of a reacting, compressible laminar jet to Mach waves generated by wavy walls in a channel of finite width. The model consists of a two-dimensional jet of fuel emerging into a stream of oxidizer which are allowed to mix and react in the presence of the Mach waves. The governing equations are taken to be the steady parabolized Navier-Stokes equations which are solved numerically. The kinetics is assumed to be a one-step, irreversible reaction of the Arrhenius type. Two important questions on the Mach wave-flame interactions are discussed: (i) how …

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Monte Carlo Director Modeling And Display, Using The Cern Laboratory, Christine A. Byrd, Charles M. Byrd, Wilfred J. Braithwaite Jan 1993

Monte Carlo Director Modeling And Display, Using The Cern Laboratory, Christine A. Byrd, Charles M. Byrd, Wilfred J. Braithwaite

Journal of the Arkansas Academy of Science

Detectors for high energy nuclear physics experiments are being modeled using programs developed and maintained at CERN, the European Organization for Nuclear Research. These programs include data handling and display routines, as well as those using random-sampling Monte Carlo techniques to calculate energy depositions for high energy particles as they pass through the various parts of the detector system. The complete CERN library has been imported for use with our Workstation computers in a multiple user environment. The enormous CERN Monte Carlo program GEANT(French for GIANT) tracks the progress of a particle through a detector on a simulated event-by-event basis. …

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User-Interface Coding For The Cern/Geant Nuclear Physics Program, David L. Roetzel, Wilfred J. Braithwaite Jan 1993

User-Interface Coding For The Cern/Geant Nuclear Physics Program, David L. Roetzel, Wilfred J. Braithwaite

Journal of the Arkansas Academy of Science

Explanations will be given of the various user-written routines required by the Monte Carlo detector-modeling program GEANT, developed by CERN, the European Organization for Nuclear Research. User-written routines must be linked with the CERN library to accomplish the researcher's intentions. Examples will illustrate how GEANT passes information to subprograms needed to model events. Various data structures used by GEANT library calls and included in each user routine, are similarly illustrated. Both computational-speed and memory-size limitations need to be factored into the construction of a simulation model. This will constrain the calls used in the user-written routines. Examples are provided of …

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High-Energy Behavior Of The Double Photoionization Of Helium From 2 To 12 Kev, Jon C. Levin, Ivan A. Sellin, B. M. Johnson, Dennis W. Lindle, R. D. Miller, Y. Azuma, H. G. Berry, D.-H. Lee, N. Berrah Jan 1993

High-Energy Behavior Of The Double Photoionization Of Helium From 2 To 12 Kev, Jon C. Levin, Ivan A. Sellin, B. M. Johnson, Dennis W. Lindle, R. D. Miller, Y. Azuma, H. G. Berry, D.-H. Lee, N. Berrah

Chemistry and Biochemistry Faculty Research

We report the ratio of double-to-single photoionization of He at several photon energies from 2 to 12 keV. By time-of-Aight methods, we find a ratio consistent with an asymptote at 1.5%±0.2%, essentially reached by h v≈4 keV. Fair agreement is obtained with older shake calculations of Byron and Joachain [Phys. Rev. 164, 1 (1967)], of Aberg [Phys. Rev. A 2, 1726 (1970)], and with recent many-body perturbation theory (MBPT) of Ishihara, Hino, and McGuire [Phys. Rev. A 44, 6980 (1991)]. The result lies below earlier MPBT calculations by Amusia et al. [J. Phys. B 8 …

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Temporal Development Of Electric Field Structures In Photoconductive Gaas Switches, K. H. Schoenbach, J. S. Kenney, F.E. Peterkin, R. J. Allen Jan 1993

Temporal Development Of Electric Field Structures In Photoconductive Gaas Switches, K. H. Schoenbach, J. S. Kenney, F.E. Peterkin, R. J. Allen

Bioelectrics Publications

The temporal development of the electric field distribution in semi‐insulating GaAs photoconductive switches operated in the linear and lock‐on mode has been studied. The field structure was obtained by recording a change in the absorption pattern of the switch due to the Franz–Keldysh effect at a wavelength near the band edge of GaAs. In the linear mode, a high field layer develops at the cathode contact after laser activation. With increasing applied voltage, domainlike structures become visible in the anode region and the switch transits into the lock‐on state, a permanent filamentary electrical discharge. Calibration measurements show the field intensity …

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Electromagnetism, Yimin Wang, Clifton Keller Jan 1993

Electromagnetism, Yimin Wang, Clifton Keller

All Books

No abstract provided.

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Sign Correlations And The Mechanism For Parity Violation, Vladimir Gudkov Jan 1993

Sign Correlations And The Mechanism For Parity Violation, Vladimir Gudkov

Faculty Publications

The problem of possible sign correlations of P-odd effects due to parity mixing on the compound nuclear stage is discussed. For an unambiguous test of the conventional model of parity violation on the compound nuclear stage, it is not enough only to measure the sign correlation of P-odd effects on some resonances, but it is necessary also to know the neutron decay amplitudes for each resonance.

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