Physical Sciences and Mathematics Commons^™

Post-Prior Symmetrical First-Order T Matrix For Charge Transfer, Jack C. Straton, M. D. Girardeau

Physics Faculty Publications and Presentations

The Fock-Tani Hamiltonian is found for systems containing two protons and one electron. It is shown that a post-prior symmetrical T-matrix element for a⁺ + (b⁺ c^-)→(a⁺ c^-)+b⁺ may be found from that of the simpler proton-proton-electron system if a and b are treated as isospin projections of a single type of nucleon. The Coulomb-exchange contribution to the inelastic (isospin flip) scattering of this system gives a first-order T matrix that is completely symmetrical with respect to post and prior interactions and orthogonalizations, a symmetry of the exact …

One-Dimensional Quantum Transport In The Presence Of Traps, Paul Ernest Parris

Physics Faculty Research & Creative Works

A study is made of the survival probability P(t) for a quantum particle moving coherently on an ordered one-dimensional chain containing randomly placed irreversible traps in concentration q. We consider two separate models of the trapping process, focusing on the long-time limit of each. In the first model, intended to describe substitutional traps, the trapping impurities act as disruptive absorbing barriers which prevent further motion along the chain. For this model it is shown that -ln[P(t)]1/4t^1/4. The second model is intended to describe interstitial trapping impurities which do not disrupt the transport. It is argued for this case …

Full Optical Potential For The Electron-Hydrogen Entrance Channel, Igor Bray, Don H. Madison, Ian E. Mccarthy

Physics Faculty Research & Creative Works

Differential and total elastic and total reaction cross sections are calculated for electron-hydrogen scattering at 30, 100, and 400 eV using an ab initio optical potential that treats bound and continuum nonelastic channels in the distorted-wave Born approximation. Multichannel and partial wave expansions are carried out to numerical convergence. Convergence criteria and quadratures for the continuum-energy integration are chosen for 1% overall accuracy. Results are compared with experiment and less detailed calculations.

Calculation Of Dielectric Susceptibility For Complex Ionic Systems: Application To A Predicted Superlattice, J. L. Feldman, L. L. Boyer, P. J. Edwardson

John R. Hardy Papers

The Gordon-Kim theory of interionic interactions between closed-shell ions, which has had considerable success for existing alkali halide systems, has been applied to the determination of the structure, phonon dispersion, and room-temperature dielectric properties of a proposed superlattice, RbF(NaC1)₂, of alkali halides. The dielectric properties of such a hypothetical material can have an unusually strong low-frequency dependence because of the presence of Brillouin-zonefolded "infrared”-active modes. In evaluating the standard expressions for the dielectric properties, in the rigid-ion approximation, we make use of standard cubic and quartic anharmonic terms in addition to the instantaneous-phonon cubic anharmonic term, which is …

Thermochemistry Of The Gadolinium-Copper Interface, D. Lagraffe, Peter A. Dowben, M. Onellion

Peter Dowben Publications

We have characterized the thermochemistry of the gadolinium-copper interface using valence-band photoemission. We find that the copper substrate binds strongly with the gadolinium overlayer, based upon valence-band binding-energy shifts that occur with increasing gadolinium coverages on Cu(100). The net potential for copper at the interface is 3.82 eV/atom which is some 0.51 eV/atom greater than the heat of sublimation for copper. The strong bonds formed between copper and gadolinium provide a thermochemical driving force for copper gadolinium-alloy formation. We observed a surface-to-bulk core-level shift for gadolinium of 0.3–0.4 eV. We also observed a Cu 3d binding-energy increase of 0.73 …

The Chromosphere Of Beta Cassiopeiae, Terry J. Teays, Edward G. Schmidt, Massimo Fracassini, Laura E. Pasinetti Fracassini

Edward Schmidt Publications

We have carried out high-resolution, long-wavelength IUE observations and ground-based photometry of the δ Scuti star β Cas. The ground-based observations were used together with previous results of Antonello et al. to ensure that the IUE observations were correctly phased relative to the photometric variation. Fluxes for the emission core of the Mg _II k λ2796 line were obtained from the ultraviolet spectra over several cycles in 1986 and 1987. We found that there is an increase in the emission during part of the cycle but it occurs near minimum light in contrast to another δ Scuti star, ρ Pup, …

The Response Of The Alanine Detector After Charged-Particle And Neutron Irradiations, M. P. R. Waligorski, G. Danialy, Robert Katz

Robert Katz Publications

Radiosensitivity parameters of track structure theory, representing alanine as a one-hit detector, have been fitted for this free-radical amino-acid system on the basis of the available experimental data on the relative effectiveness of alanine after charged particle and neutron irradiations. The experimental data set can be reproduced by theoretical calculations, roughly to within experimental accuracy. A charged-particle “equivalent radiation” is introduced which can mimic the response of alanine to neutron irradiations. Implications of the results of model calculations for alanine on the shape of the radial distribution of δ-ray dose postulated by track theory, are discussed.

Exact Time-Dependent Evolution Of Electron Velocity Distribution Functions In A Gas Using The Boltzmann Equation, P J. Drallos, J M. Wadehra

Physics and Astronomy Faculty Research Publications

A numerical technique, starting from the Boltzmann equation, for obtaining the time-dependent behavior of the electron-velocity distribution function in a gas is presented. A unique feature of this technique is that, unlike previously used procedures, it does not make use of any expansion of the distribution function. This allows the full anisotropy of the distribution function to be included in the solution. Furthermore, the problem associated with multiterm-expansion techniques of choosing a sufficient number of terms for convergence is completely avoided. The distribution function obtained by the present method is exact and, in principle, contains all of the expansion terms …

Analytical Determination Of The Complex Dielectric Function Of An Absorbing Medium From Two Angles Of Incidence Of Minimum Parallel Reflectance, R. M.A. Azzam

Electrical Engineering Faculty Publications

The real and imaginary parts of the complex dielectric function (or complex refractive index) of an opaque substrate or a thick film can be determined from two pseudo-Brewster angles measured in two transparent incidence media of different refractive indices. This two-angle method is simple in that it involves no photometric or polarimetric analysis and in that the solution for the optical properties in terms of the measured angles is explicit, analytical, and direct (i.e. noniterative). The two-angle method is demonstrated for an opaque TiN film on a Cleartran ZnS substrate as a specific example. The effect of angle-of-incidence errors on …

Absorption At Radio Frequencies In Superconducting Y1Ba2Cu3OY, Stephen Ducharme, R. Durny, J. Hautala, D.J. Zheng, P.C. Taylor, O.G. Symko, S. Kulkarni

Stephen Ducharme Publications

The large magnetic-field-dependent ac absorption in superconducting Y₁Ba₂Cu₃O_y ceramics and powders decreases slowly with increasing frequency in the range 2–16 MHz. The magnetic-field-dependent ac absorption is observed below T_c in superconducting Y₁Ba₂Cu₃O_y ceramics, powders and twinned crystals and in (La,Sr)₂ CuO₂ and BaPb_0.75 Bi_0.25 CuO₃ powders and appears to contain distinct contributions from trapped flux and/or intragrain tunnel junctions and from ordinary superconductor surface impedance. The contribution from trapped flux and/or intragrain tunnel junctions is important in dc magnetic fields …

Resonant Dielectronic And Direct Excitation In Crystal Channels, Sheldon Datz, Charles Randy Vane, Peter F. Dittner, J. P. Giese, J. C. Gomez Del Campo, N. L. Jones, Herbert F. Krause, Philip D. Miller, Michael Schulz, Harald Schone, Thomas M. Rosseel

Physics Faculty Research & Creative Works

We have observed dielectronic and direct excitation of H-like S¹⁵⁺ and Ca¹⁹⁺ and He-like Ti²⁰⁺ ions in silicon channels caused by collision with weakly bound target electrons which behave as a free-electron gas. As in vacuo, relaxation of the doubly excited states can occur radiatively leading to ions of decreased charge, but in a crystal channel collisional effects can cause double ionization. The effects are seen in both the x-ray yields and charge-state fractions, and, in the case of Ti²⁰⁺, in charge-state x-ray coincidences.

Conformal Transformations In Quantum Mechanics, Alec Schramm, Alfons Stahlhofen

Alec J Schramm

We discuss the occurrence of orientation- or area-preserving diffeomorphism groups in quantum mechanics. We show that the generators of these groups are contained in the generators of the symmetry group of a central potential, as is demonstrated by the example of the Coulomb problem. Our approach is based on the recently introduced concept of a factor space of scattering states.

Finite Temperature Effects In Na3+ And Na3: A Path Integral Monte Carlo Study, Randall W. Hall

Randall W. Hall

31st Rocky Mountain Conference

Rocky Mountain Conference on Magnetic Resonance

Program and registration information for the 31st annual meeting of the Rocky Mountain Conference, co-sponsored by the Rocky Mountain Section of the Society for Applied Spectroscopy and the Rocky Mountain Chromatography Discussion Group. Held in Denver, Colorado, July 30 - August 4, 1989.

Magnetic Ordering Of Thin Gd Overlayers, D. Lagraffe, Peter A. Dowben, M. Onellion

Peter Dowben Publications

1–6-monolayer-thick films of Gd have been studied with use of synchrotron-radiation photoemission. A method is described that utilizes the linear light polarization to obtain information about the overlayer magnetization. The method is complementary to electron-spin-polarization techniques. The thinner Gd overlayers exhibit a local magnetization component along the surface normal that decreases for thicker overlayers. The Gd films exhibit a 5d exchange splitting that changes from approximately 1.1 to 0.6 eV as the overlayer thickness increases.

Mixed-Crystal Lattice Dynamics Of HfXTi1-XSe2, Vanvilai Katkanant, Roger D. Kirby

Department of Physics and Astronomy: Faculty Publications

The first-order Raman spectra of the mixed-crystal layered compound Hf_xTi_1-xSe₂ have been studied over the whole range of concentrations 0≤x≤1. Both pure compounds, TiSe₂ and HfSe₂, have the CdI₂ structure and so have two Raman-active phonons of A_1g phonon is at about 205 cm ^-1. As x is decreased from 1.0, a new Raman peak, of A_1g symmetry, appears near 180 cm ^-1. As x is decreased further, this peak shifts smoothly upwards in frequency, until it finally merges (by x=0.05) with the pure TiSe₂ A …

A Comparison Of Magnetite Particles Produced Anaerobically By Magnetotactic And Dissimilatory Iron‐Reducing Bacteria, Bruce M. Moskowitz, Richard B. Frankel, Dennis A. Bazylinski, Holger W. Jannasch, Derek R. Lovley

Physics

We compare the magnetic properties of fine‐grained magnetite produced by two newly isolated anaerobic bacteria, a magnetotactic bacterium (MV‐1) and a dissimilatory iron‐reducing bacterium (GS‐15). Although room‐temperature magnetic properties are generally different between the two microorganisms, MV‐1 and GS‐15 magnetites can be most easily distinguished by the temperature variation of saturation remanence obtained at liquid helium temperatures. Magnetite produced by MV‐1 displays a sharp discontinuity in intensity at 100 K related to the Verwey transition. Magnetite produced by GS‐15 displays a gradual decrease in intensity with temperature due to the progressive unblocking of magnetization. The differing behavior is due exclusively …

Uniformity Of 3-In, Semi-Insulating, Vertical-Gradient-Freeze Gaas Wafers, David C. Look, D. C. Walters, M. G. Mier, J. S. Sewell, J. S. Sizelove, A. Akselrad, J. E. Clemans

Physics Faculty Publications

We have evaluated the uniformity in [EL2], dislocation (or etch‐pit) density (EPD), resistivity, mobility, and carrier concentration for 3‐in., semi‐insulating GaAs wafers grown by the vertical‐gradient‐freeze (VGF) technique. Although slight W or U patterns were observed in [EL2] and EPD along the 〈110〉 directions, for the first time, nevertheless the overall uniformity was excellent, and comparable to that in the best In‐doped and whole‐boule‐annealed ingots grown by the liquid‐encapsulated Czochralski (LEC) technique. Based on results from implant‐activation studies on LEC wafers, it is estimated that the measured nonuniformities in EPD and [EL2] for the VGF wafers would contribute only about …

Topological Gauge Theory And Twistors, V. Parameswaran Nair, Jeremy Schiff

Publications and Research

By use of harmonic superfields, Witten’s topological gauge theory is written as a field theory on a supertwistor space. Further, using the realisation of complex compactified Minkowski space as a quadric in CP⁵, we show that the theory has a simple formulation in terms of analytic superfields on super-CP⁵ × CP³ .

Chemical Vapor Deposition Of Boron And Boron Nitride From Decaborane(L4) A), Yoon Gi Kim, Peter A. Dowben, J.T. Spencer, G.O. Ramseyer

Peter Dowben Publications

We have investigated photoassisted, plasma enhanced chemical vapor deposition and pyrolytic deposition of boron from decaborane (B₁₀H₁₄) and boron nitride from decaborane combined with nitrogen or ammonia. The use of decaborane for depositing boron and boron nitride thin films is seen as a viable alternative to diborane or boron halides.

Nuclear Fragmentation Energy And Momentum Transfer Distributions In Relativistic Heavy-Ion Collisions, Ferdous Khan

Physics Theses & Dissertations

An optical model description of energy and momentum transfer in relativistic heavy-ion collisions, based upon composite particle multiple scattering theory, is presented. Transverse and longitudinal momentum transfers to the projectile are shown to arise from the real and absorptive part of the optical potential, respectively. Comparisons of fragment momentum distribution observables with experiments are made and trends outlined based on our knowledge of the underlying nucleon-nucleon interaction. Corrections to the above calculations are discussed. Finally, use of the model as a tool for estimating collision impact parameters is indicated.

Single And Double-Electron Removal From H− In Energetic Collisions With Multiply-Charged Argon Ions, F. Melchert, W. Debus, M. Liehr, Ronald E. Olson, E. Salzborn

Physics Faculty Research & Creative Works

Absolute cross-sections have been measured and compared to CTMC-calculations for single and double-electron removal from H− in collisions with Ar^q+ ions (q ≤ 8) at E_c.m. = 50 keV. The single-electron removal cross-sections are found to scale with q^1.3, and for the H⁻ + Ar⁴⁺ system, this cross-section is found to have a weak energy dependence from 3 keV to 100 keV. A major implication of our measurements is that plasma neutralizers based on multiply charged ions for high-efficiency conversion of intense H⁻ beams into H⁰ gain little in expected reduced …

Thermally Activated Methyl And T-Butyl Group Reorientation In Solids, Peter A. Beckmann

Physics Faculty Research and Scholarship

We reinterpret proton spin-lattice relaxation measurements in solid 1,4-di-t-butylbenzene (1,4-DTB) [P. A. Beckmann, F. A. Fusco, and A. E. O'Neill, J. Magn. Reson. 59 63 (1984)] in light of a recent study of solid 1,3-DTB [P. A. Beckmann, A. I. Hill, E. B. Kohler, and H. Yu, Phys. Rev. B 38 11098 (1988))]. We investigate the relationship between the spectral density that characterizes the intramolecular reorientation of the t-butyl groups and their constituent methyl groups in DTB, and the t-butyl group environment which dictates the symmetry of the local electrostatic potential. For both isomers, if one assumes a sixfold potential, …

U(1) Chern-Simons Theory And C=1 Conformal Blocks, Michiel Bos, V. Parameswaran Nair

Publications and Research

The quantization of the U ( 1 ) Chern-Simons action in three dimensions is carried out in a coherent state representation. The wave functionals obtained are generating functionals for the current correlator blocks of two-dimensional c= 1 rational conformal field theories, explicitly realizing a connection found by Witten.

Nife Invar Alloys: Theoretical Insights Into The Underlying Mechanisms Responsible For Their Physical Properties, Duane D. Johnson, F. J. Pinski, J. B. Staunton, B. L. Gyorffy, G. M. Stocks

Duane D. Johnson

What are the "driving forces" responsible for various physical properties of alloys? What causes alloy systems to order chemically and/or magnetically? To answer these questions, we have been using a quantum mechanical (QM) method to calculate cohesive energies, magnetic properties, and thermodynamic phase instability of alloys. This scheme directly incorporates the inherent disorder of the high-temperature solid solution and in this sense goes beyond traditional "band theory." Although approximations have been made at various steps in the thermodynamical averaging, and in the QM treatment of the electrons, adjustable parameters have not been used. Recently, for FCC NiFe (INVAR) alloys, we …

Lossless Propagation Of Optical Pulses Through N-Level Systems With Gell-Mann Symmetry, Foek T. Hioe

Physics Faculty/Staff Publications

Propagation of optical pulses through atomic media consisting of atoms with N transition levels and possessing the so-called Gell-Mann symmetry is studied. An analytic solution of the appropriate Maxwell-Bloch equations having the form of simultaneous different wavelength optical solutions is presented. The special case of N = 3 was known previously.

Fundamental Magnetic Studies Of Iron-Rare-Earth-Metalloid Alloys Grant Numbers: De-Fgo2-86er45262, David J. Sellmyer

David Sellmyer Publications

This research is focused on the synthesis of new iron-rare-earth magnetic phases which may have significant technological properties. An important aim is to investigate new methods for producing these materials such as melt spinning and sputtering plus specific heat treatments. Studies are made of the relationship between microstructure and properties such as coercivity, spontaneous magnetization, and anisotropy (magnitude and direction) in bulk and thin film samples. Our goal is to understand these relatively complex materials on the basis of fundamental electronic structure, theory is of itinerant magnetism and localized 4f electronic states, and the microstructural effects which control the extrinsic …

Orientation Of Hydrogen 2P After Tilted-Foil Excitation, C. J. Liu, Timothy J. Gay, K. P. Schuler

Timothy J. Gay Publications

The circular polarization of Lyman-α photons resulting from beam-tilted-foil excited H(2p) was measured at energies between 9 and 20 keV with foil tilt angles up to 60°. Various interaction models are used to fit the data, and their physical significance is discussed.

An Improved Correction Algorithm For Number Density Measurements Made With The Forward-Scattering Spectrometer Probe, James A. Lock, Edward A. Hovenac

Physics Faculty Publications

A correction factor to the number density measured by the Forward Scattering Spectrometer Probe (FSSP) which compensates for dead time and coincidence errors was determined by calculating the probabilities of and the average number of particles in the six possible types of dead time and coincidence events. These probabilities and averages were calculated by means of a probabilistic model based on Poisson statistics. A Monte Carlo computer simulation of the FSSP operation was also carried out and the number density correction factor was compared with the Monte Carlo data. For an actual number density of 2000/cm³, it was …

A Correction Algorithm For Particle-Size Distribution Measurements Made With The Forward-Scattering Spectrometer Probe, James A. Lock, Edward A. Hovenac

Physics Faculty Publications

Multiparticle coincidence events in the scattering volume of the forward-scattering spectrometer probe (FSSP) cause the instrument to bias the measurement of the particle size distribution of atmospheric aerosols toward large diameters. We employ a probabilistic model based on Poisson statistics to determine the average diameter and rms width of the actual size distribution as functions of the average diameter and rms width of the measured distribution. We compare our predictions to a Monte Carlo simulation of the FSSP operation