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1991

Physics

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Articles 31 - 60 of 234

Full-Text Articles in Physical Sciences and Mathematics

Internal Caustic Structure Of Illuminated Liquid Droplets, James A. Lock, Edward A. Hovenac Oct 1991

Internal Caustic Structure Of Illuminated Liquid Droplets, James A. Lock, Edward A. Hovenac

Physics Faculty Publications

The internal electric field of an illuminated liquid droplet is studied in detail with the use of both wave theory and ray theory. The internal field attains its maximum values on the caustics within the droplet. Ray theory is used to determine the equations of these caustics and the density of rays on them. The Debye-series expansion of the interior-field Mie amplitudes is used to calculate the wave-theory version of these caustics. The physical interpretation of the sources of stimulated Raman scattering and fluorescence emission within a liquid droplet is then given.

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First-Principles Study Of Phase Stability In Cu-Zn Substitutional Alloys, P. E. A. Turchi, M. Sluiter, F. J. Pinski, Duane D. Johnson, D. M. Nicholson, G. M. Stocks, J. B. Staunton Sep 1991

First-Principles Study Of Phase Stability In Cu-Zn Substitutional Alloys, P. E. A. Turchi, M. Sluiter, F. J. Pinski, Duane D. Johnson, D. M. Nicholson, G. M. Stocks, J. B. Staunton

Duane D. Johnson

A parameter-free approach to phase stability in Cu-Zn substitutional alloys is shown to describe order-disorder phenomena and structural transformations with remarkable accuracy. The method is based on a multiple-scattering description of the electronic structure properties of the random alloy. Configurational order is treated within the generalized perturbation method and the concentration-functional theory. Thermodynamical properties of α and β brasses are derived from the cluster variation method. This advanced scheme is of general validity and is expected to yield similarly accurate results for other Hume-Rothery alloys.

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Auxiliary Field In Conformal Gauge Theory, James Thomas Wheeler Sep 1991

Auxiliary Field In Conformal Gauge Theory, James Thomas Wheeler

All Physics Faculty Publications

When the full conformal algebra is gauged there arises a gauge field for inverse translations in addition to the usual translational gauge field. By considering every scale-invariant action constructible from the curvatures of the conformal group and the metric, we show that when the gauge field of the usual translations is identified as the vierbein, the gauge field of inverse translations may always be eliminated by its own field equation. After this elimination, every torsion-free, scale-invariant action reduces to a linear combination of the square of the conformal curvature tensor Cαβμν and the square of the Weyl field strength …

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Track Physics Model Of Radiation Effects, Robert Katz Sep 1991

Track Physics Model Of Radiation Effects, Robert Katz

Robert Katz Publications

Radiation effects induced by heavy ions in many materials with diverse end points are well described by the conceptual structure and equations of track physics, first developed for heavy ion tracks in nuclear emulsions. The model describes scintillators, biological cell inactivation and mutation, radiation chemistry, latent tracks in insulators, the response of resists to heavy ions, and other systems. A detector is taken to be composed of small targets whose response to ionizing radiation is principally to secondary electrons. The response is calibrated through determination of the probability of target (in)activation as a function of the absorbed dose of γ …

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Paper Or Plastic?, Matthew J. Moelter Sep 1991

Paper Or Plastic?, Matthew J. Moelter

Physics

Letter to the Editor.

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Equatorial Thermospheric Wind Changes During The Solar Cycle: Measurements At Arequipa,Peru From 1983 To 1990, M. A. Biondi, J. W. Meriwether, Bela G. Fejer, S. A. Gonzalesz, D. C. Hallenbeck Sep 1991

Equatorial Thermospheric Wind Changes During The Solar Cycle: Measurements At Arequipa,Peru From 1983 To 1990, M. A. Biondi, J. W. Meriwether, Bela G. Fejer, S. A. Gonzalesz, D. C. Hallenbeck

Bela G. Fejer

Fabry-Perot interferometer measurements of Doppler shifts in the nightglow 630-nm emission line have been used to determine near-equatorial thermospheric wind velocities at Arequipa, Peru, over ∼2/3 of a solar cycle. Monthly-average nocturnal variations in the meridional and zonal wind components were calculated from the nightly data to remove short term (day-to-day) variability, facilitating display of seasonal changes in the wind patterns, as well as any additional changes introduced by the progression of the solar cycle. The measured seasonal variations in the wind patterns are more pronounced than the solar cycle variations and are more readily understandable in terms of the …

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On Compensation And Conductivity Models For Molecular-Beam-Epitaxial Gaas Grown At Low-Temperature, David C. Look Sep 1991

On Compensation And Conductivity Models For Molecular-Beam-Epitaxial Gaas Grown At Low-Temperature, David C. Look

Physics Faculty Publications

Molecular‐beam‐epitaxial GaAs grown at 200 °C has an extremely high (≳1019 cm−3) concentration of AsGa defects and, after an anneal at 550–600 °C, a high concentration of As precipitates. The relative roles of the AsGa defects and As precipitates in compensation and conductivity is controversial. Here criteria are developed to distinguish between two existing models.

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Can An Economic Approach Solve The High-Level Nuclear Waste Problem, Herbert Inhaber Sep 1991

Can An Economic Approach Solve The High-Level Nuclear Waste Problem, Herbert Inhaber

RISK: Health, Safety & Environment (1990-2002)

Building on the work of Professors O'Hare and Kunreuther, Dr. Inhaber proposes and argues for a non-coercive siting strategy that he calls a "reverse Dutch auction."

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Mie Theory Model Of The Corona, James A. Lock, Leiming Yang Aug 1991

Mie Theory Model Of The Corona, James A. Lock, Leiming Yang

Physics Faculty Publications

We performed a calculation of the corona colors that employed Mie theory to obtain the scattered light intensity. The scattered intensity was integrated over the visible spectrum for a number of different cloud droplet size distributions. The results were converted to chromaticity coordinates, convolved with the angular size of the sun, and plotted on the 1931 CIE chromaticity diagram. The results were compared to observations of multiple-ring coronas. It was found that, when using Mie theory to estimate cloud droplet sizes, water droplets with diameters in the 7-mu-m less-than-or-similar-to D less-than-or-similar-to 15-mu-m range produced the 13 multiple-ring coronas that were …

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Light And Color In The Open Air: Introduction By The Feature Editor, James A. Lock, Craig F. Bohren Aug 1991

Light And Color In The Open Air: Introduction By The Feature Editor, James A. Lock, Craig F. Bohren

Physics Faculty Publications

No abstract provided.

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Binary Peak Enhancement And Structure In Partially Stripped Ion-Atom Collisions, D. R. Schultz, Ronald E. Olson Aug 1991

Binary Peak Enhancement And Structure In Partially Stripped Ion-Atom Collisions, D. R. Schultz, Ronald E. Olson

Physics Faculty Research & Creative Works

Recent experiments have found both an unexpected enhancement and structure of the binary peak in the spectrum of electrons ejected in partially stripped ion-atom collisions. Utilizing the theoretical approach which has been used to elucidate the origin of this behavior, a survey of their manifestation is presented over a broad range of nuclear and ionic charges (C, F, Fe, I and U ions) and impact energies (0.1 to 100 MeV u-1). For forward binary electron emission it is shown that the greatest enhancement occurs for the lowest projectile ion charge states (highly screened nuclei). The magnitude of the enhancement maximizes …

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An Experimental Investigation Of The Finite Time Efficiency Of A Peltier Refrigeration Device, Thomas Schneider Aug 1991

An Experimental Investigation Of The Finite Time Efficiency Of A Peltier Refrigeration Device, Thomas Schneider

Dissertations and Theses

Since the need of energy conservation has become more and more urgent in the past decades, there has been an increased interest in the study and development of more efficient energy conversion systems. One of the fields that have arisen from that endeavor is a branch of physics called Finite Time Thermodynamics (FIT). It may be said that FIT was initiated through the famous paper by Curzon and Ahlborn (1975) that established new bounds on the efficiency of a finite time Carnot heat engine. Before, the traditional treatments gave a fundamental upper limit on the efficiency of any heat engine. …

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Differential And Total Cross Sections For Ionization Of Helium And Hydrogen By Electrons, M. Eugene Rudd Aug 1991

Differential And Total Cross Sections For Ionization Of Helium And Hydrogen By Electrons, M. Eugene Rudd

M. Eugene Rudd Publications

A comprehensive semiempirical model for singly and doubly differential and total ionization cross sections for electron production by electron impact is presented. The model is discussed in relation to several theoretically required constraints. Available experimental data for hydrogen and helium targets are examined, and recommended values of the data are given for all ranges of primary and secondary energies and angles of ejection.

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Average Vertical And Zonal F-Region Plasma Drifts Over Jicamarca, Bela G. Fejer, E. R. De Paula, S. Gonzalez, R. F. Woodman Aug 1991

Average Vertical And Zonal F-Region Plasma Drifts Over Jicamarca, Bela G. Fejer, E. R. De Paula, S. Gonzalez, R. F. Woodman

Bela G. Fejer

The seasonal averages of the equatorial F region vertical and zonal plasma drifts are determined using extensive incoherent scatter radar observations from Jicamarca during 1968–1988. The late afternoon and nighttime vertical and zonal drifts are strongly dependent on the 10.7-cm solar flux. We show that the evening prereversal enhancement of vertical drifts increases linearly with solar flux during equinox but tends to saturate for large fluxes during southern hemisphere winter. We examine in detail, for the first time, the seasonal variation of the zonal plasma drifts and their dependence on solar flux and magnetic activity. The seasonal effects on the …

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Anisotropy Of Polarized X-Ray Emission From Molecules, S. H. Southworth, Dennis W. Lindle, R. Mayer, P. L. Cowan Aug 1991

Anisotropy Of Polarized X-Ray Emission From Molecules, S. H. Southworth, Dennis W. Lindle, R. Mayer, P. L. Cowan

Chemistry and Biochemistry Faculty Research

Strongly anisotropic, polarized Cl K-V x-ray emission from gas-phase CF3Cl has been observed following resonant excitation with a linearly polarized x-ray beam. Distinctively different angular distributions are observed for x-ray emission involving molecular orbitals of different symmetries. A classical model of the x-ray absorption-emission process accurately describes the observed radiation patterns.

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Measurement Of The Ratio Of Double-To-Single Photoionization Of Helium At 2.8 Kev Using Synchrotron Radiation, Jon C. Levin, Dennis W. Lindle, N. Keller, R. D. Miller, Y. Azuma, N. Berrah Mansour, H. G. Berry, Ivan A. Sellin Aug 1991

Measurement Of The Ratio Of Double-To-Single Photoionization Of Helium At 2.8 Kev Using Synchrotron Radiation, Jon C. Levin, Dennis W. Lindle, N. Keller, R. D. Miller, Y. Azuma, N. Berrah Mansour, H. G. Berry, Ivan A. Sellin

Chemistry and Biochemistry Faculty Research

We report the first measurement of the ratio of double-to-single photoionization of helium well above the double-ionization threshold. Using a time-of-flight technique, we find He++/He+=1.6±0.3% at hν=2.8 keV. This value lies between calculations by Amusia (2.3%) and by Samson, who predicts 1.2% by analogy with electron-impact ionization cross sections of singly charged ions. Good agreement is obtained with older shake calculations of Byron and Joachain, and of Åberg, who predict 1.7%.

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Inhibited Spontaneous Emission By Photonic Band Gaps In A Square Lattice Of Periodic Dielectric Medium, Abdullah Al-Ghamdi Aug 1991

Inhibited Spontaneous Emission By Photonic Band Gaps In A Square Lattice Of Periodic Dielectric Medium, Abdullah Al-Ghamdi

Masters Theses

The concepts of band theory for electrons can be employed to describe the behavior of electromagnetic waves propagating in two-dimensional, periodic dielectric structures. These two-dimensional, periodic structures can produce photonic band gaps in which the spontaneous emission by atoms embedded in the structure is prohibited and as a result the performance of many semiconductor devices can be enhanced. The calculations are based on finding the eigenvalues of the algebraic equation for the frequencies of electromagnetic waves moving in a square lattice composed of square dielectric rods with different dielectric constants.

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Eta Photoproduction Via 2H(Γη)2H*, Yan Zhang Aug 1991

Eta Photoproduction Via 2H(Γη)2H*, Yan Zhang

Masters Theses

The reaction H(γη)2H* is studied using the impulse approximation. A recent fit to the H(γη)2H* elementary amplitude is employed in the calculation. The n-p final state is described by Reid's soft core potentials. The calculation shows very different cross sections for the final isospin 0 and isospin 1 break-up channels. The S11 resonance is demonstrated to dominate the eta cross sections in the 740 MeV photon laboratory energy region. Fermi motion in the deuteron does not significantly spread the effect of the S11 . All these results demonstrate that the reaction H(γη) …

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Ultrafast Electronic Disordering During Femtosecond Laser Melting Of Gaas, Peter N. Saeta, J.-K. Wang, Y. Siegal, N. Bloembergen, E. Mazur Aug 1991

Ultrafast Electronic Disordering During Femtosecond Laser Melting Of Gaas, Peter N. Saeta, J.-K. Wang, Y. Siegal, N. Bloembergen, E. Mazur

All HMC Faculty Publications and Research

We have observed an ultrarapid electronic phase transformation to a centrosymmetric electronic state during laser excitation of GaAs with intense femtosecond pulses. Reflection second-harmonic intensity from the upper 90 atomic layers vanishes within 100 fs; reflectivity rises within 0.5 ps to a steady value characteristic of a metallic molten phase, long before phonon emission can heat the lattice to the melting temperature.

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Laboratory Simulations Of Suprauroral Mechanisms Leading To Perpendicular Ion Heating And Conic Formation, D. P. Sheehan, R. Koslover, R. Mcwilliams Aug 1991

Laboratory Simulations Of Suprauroral Mechanisms Leading To Perpendicular Ion Heating And Conic Formation, D. P. Sheehan, R. Koslover, R. Mcwilliams

Physics and Biophysics: Faculty Scholarship

Laboratory experiments are presented simulating aspects of perpendicular ion heating and conic formation that are observed or hypothesized to occur in the terrestrial ionosphere and magnetosphere. Previous laboratory observations of ion conics in the presence of the current‐driven electrostatic ion cyclotron wave are reviewed. Field‐aligned ion beams, accompanied by beam‐generated electrostatic ion cyclotron modes, resulted in perpendicular energization of beam ions and also the heating of background plasma ions. Antenna‐launched broadband and narrow‐band lower hybrid waves produced considerable perpendicular ion heating and non‐Maxwellian “tail” formation. Laboratory results are discussed in light of in situ measurements by the S3‐3 satellite and …

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A Track Physics Model Of Radiation Action, Robert Katz Aug 1991

A Track Physics Model Of Radiation Action, Robert Katz

Robert Katz Publications

A model of radiation action by energetic heavy ions, inspired by a study of particle tracks in electron sensitive emulsion, has been successfully applied to many radiation effects in condensed matter, yielding quantitative descriptions and occasional predictions. Radiation effects are attributed primarily to secondary electrons. Each detector is imagined to be a collection of targets whose radiosensitivity is represented parametrically. We avoid a mechanistic description of detector response so as to retain the global character of the model. Attention is focused on the structure of particle tracks, on the radial deposition of dose about an ion’s path by “δ-rays,” and …

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Frequency Shifts Of Molecules At Rough Metal Surfaces, M. H. Hider, P.T. Leung Aug 1991

Frequency Shifts Of Molecules At Rough Metal Surfaces, M. H. Hider, P.T. Leung

Physics Faculty Publications and Presentations

The frequency shifts for dipolar transitions of molecules at rough metallic surfaces are studied in a phenomenological model following the approach of the authors' previous work [Phys. Rev. B 36, 4664 (1987)], with the surface roughness modeled by a shallow grating profile in most cases. The main findings here are as follows: (1) such surface-induced shifts are indeed observable for molecular frequencies away from the surface-plasmon resonance frequency of the metal; (2) the presence of surface roughness can either enhance or suppress the flat-surface-induced shifts, leading to extra morphology-dependent resonances originated from the radiative coupling between the molecular emission and …

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X-Ray Emission From Slow Highly Charged Ar Ions Interacting With A Ge Surface, Michael Schulz, C. Lewis Cocke, Siegbert Hagmann, Martin P. Stockli, Horst Schmidt-Bocking Aug 1991

X-Ray Emission From Slow Highly Charged Ar Ions Interacting With A Ge Surface, Michael Schulz, C. Lewis Cocke, Siegbert Hagmann, Martin P. Stockli, Horst Schmidt-Bocking

Physics Faculty Research & Creative Works

We have measured K x-ray spectra and yields from Ar17+ ions slowly approaching a single-crystal Ge surface. The yields were measured as a function of the projectile velocity component perpendicular to the surface. From the data a characteristic time of approximately 1 psec was extracted for the in-flight filling above the surface of the Ar K vacancy.

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Electronic And Magnetic Structures Of The Rare-Earth Compounds R2Fe17NΞ, Sitaram Jaswal, W.B. Yelon, George C. Hadjipanayis, Y.Z. Wang, David J. Sellmyer Jul 1991

Electronic And Magnetic Structures Of The Rare-Earth Compounds R2Fe17NΞ, Sitaram Jaswal, W.B. Yelon, George C. Hadjipanayis, Y.Z. Wang, David J. Sellmyer

David Sellmyer Publications

Structural and magnetic properties of the rare-earth compounds R2Fe17Nξ have been studied with neutron-diffraction measurements and self-consistent spin-polarized electronic-structure calculations. The diffraction results indicate for the Nd compound that N goes into two sites in two or more phases of varying fractional N occupations. For the Y compound N occupies only one site. Electronic-structure calculations for Y2Fe17 and Y2Fe17N3 give excellent results for site-dependent Fe moments, and, with spin-fluctuation theory, explain the large change in the Curie temperature on nitrogenation.

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33rd Rocky Mountain Conference On Applied Spectroscopy Jul 1991

33rd Rocky Mountain Conference On Applied Spectroscopy

Rocky Mountain Conference on Magnetic Resonance

Program and registration information for the 33rd annual meeting of the Rocky Mountain Conference on Applied Spectroscopy, sponsored by the Rocky Mountain Section of the Society for Applied Spectroscopy. Held in Denver, Colorado, July 28 - August 1, 1991.

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Solid State Proton Spin Relaxation In Ethylbenzenes: Methyl Reorientation Barriers And Molecular Structure, Peter A. Beckmann, Laura Happersett, Antonia V. Herzog, William M. Tong Jul 1991

Solid State Proton Spin Relaxation In Ethylbenzenes: Methyl Reorientation Barriers And Molecular Structure, Peter A. Beckmann, Laura Happersett, Antonia V. Herzog, William M. Tong

Physics Faculty Research and Scholarship

We have investigated the dynamics of the ethyl groups and their constituent methyl groups in polycrystalline ethylbenzene (EB), 1,2-diethylbenzene (1,2-DEB), 1,3-DEB, and 1,4-DEB using the solid state proton spin relaxation (SSPSR) technique. The temperature and Larmor frequency dependence of the Zeeman spin-lattice relaxation rate is reported and interpreted in terms of the molecular dynamics. We determine that only the methyl groups are reorienting on the nuclear magnetic resonance time scale. The observed barrier of about 12 kJ/mol for methyl group reorientation in the solid samples of EB, 1,2-DEB, and 1,3-DEB is consistent with that of the isolated molecule, implying that …

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Three-Point Correlations In Driven Diffusive Systems With Ising Symmetry, Beate Schmittmann, R. K. P. Zia Jul 1991

Three-Point Correlations In Driven Diffusive Systems With Ising Symmetry, Beate Schmittmann, R. K. P. Zia

Beate Schmittmann

For equilibrium systems with Ising symmetry, the three-point correlation function is always zero above criticality. When a lattice-gas version of this system is driven to a nonequilibrium steady state, this correlation becomes nontrivial. Its dominant large-scale behavior is found to be a consequence of both the manifest breaking of Ising symmetry by the driving force and the more subtle violation of the fluctuation-dissipation theorem.

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Construction Of A Quasiconserved Quantity In The Henon-Heiles Problem Using A Single Set Of Variables, Paul Finkler, C. Edward Jones, Glenn A. Sowell Jul 1991

Construction Of A Quasiconserved Quantity In The Henon-Heiles Problem Using A Single Set Of Variables, Paul Finkler, C. Edward Jones, Glenn A. Sowell

Paul Finkler Papers

The problem of finding the coefficients of a simple series expansion for a quasiconserved quantity K for the Henon-Heiles Hamiltonian H using a single set of variables is solved. In the past, this type of approach has been problematic because the solution to the equations determining the coefficients in the expansion is not unique. As a result, the existence of a consistent expression for K to all orders had not previously been established. We show how to deal with this arbitrariness in the expansion coefficients for K in a consistent way. Due to this arbitrariness, we find a class of …

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Target Dependence Of Angular Distributions For Near-Threshold (E,2E) Processes, Cheng Pan, Anthony F. Starace Jul 1991

Target Dependence Of Angular Distributions For Near-Threshold (E,2E) Processes, Cheng Pan, Anthony F. Starace

Anthony F. Starace Publications

Distorted-wave calculations of the triply differential cross sections for electron-impact ionization of H and He targets are presented for final-state electrons sharing 4-eV excess energy and leaving in opposite directions. The experimentally observed target dependence of the angular distributions is shown to stem essentially from short-range effects on the s-wave phase shifts of both incident and final-state continuum electrons.

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Enhanced Vibrational Broadening Of Core-Level Photoemission From The Surface Of Na(110), D. Mark Riffe, G. K. Wertheim, P. H. Citrin Jul 1991

Enhanced Vibrational Broadening Of Core-Level Photoemission From The Surface Of Na(110), D. Mark Riffe, G. K. Wertheim, P. H. Citrin

All Physics Faculty Publications

High-resolution temperature-dependent photoemission data from Na 2p core levels reveal substantially larger phonon broadening in the first atomic layer of Na(110) than in the bulk. We show that the enhanced width is due primarily to the excitation of relatively soft phonon modes perpendicular to the surface. Soft surface-phonon modes also account for previously reported but uninterpreted broadening of transition-metal surface-atom core levels.

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