Physics Commons^™

Seasonal Variations In Theequatorial Thermospheric Wind Measured At Arequipa, Peru, M. A. Biondi, J. W. Meriwether, Bela G. Fejer, S. A. Gonzalez

Bela G. Fejer

Studies have been carried out at Arequipa, Peru, of the seasonal variations in the thermospheric winds at moderate solar flux levels and low geomagnetic activity. Fabry-Perot interferometer measurements of the Doppler shifts in the 630.0 nm nightglow emission line from March to August 1983 and from April to October 1988 have yielded monthly-average meridional winds that are nearly zero (<50 m/s) and possibly fluctuating in direction through much of the night but develop a southward flow at 50–100 m/s in the early and the late night from May onward. The average zonal winds are eastward throughout the night, reaching peak velocities before local midnight and then decreasing. The peak velocities increase to a maximum around the June solstice. The winds are generally stronger in 1988 than in 1983, even though the solar EUV fluxes are comparable for both years. Comparison of the present results with earlier satellite measurements, as embodied in the Horizontal Wind Model of Hedin et al., reveals generally satisfactory agreement at the equinox and June solstice, except for the June 1988 period. Killeen et al.'s vector spherical harmonic form of the NCAR Thermospheric General Circulation Model, calculated for similar solar flux levels, yields meridional and zonal wind variations which exhibit the same temporal behaviors but generally smaller values than the present measurements. The present wind patterns are also compared with those measured during the same years at Arecibo, Puerto Rico; one finds oppositely directed meridional flows and similar, eastward zonal flows at the two locations, as expected from a consideration of solar EUV heating as the principal driving force.

Effect Of Size And Dimensionality On The Magnetic Moment Of Transition Metals, Feng Liu, S. N. Khanna, P. Jena

Physics Publications

The effect of size and dimensionality on the magnetic moments of Fe, Co, and Ni have been studied theoretically by confining the atoms to various structural forms such as chains, surfaces, and thin films. The size of these systems is controlled by limiting the number of atoms. A new first‐principles theory is developed that enables us to study the electron spin density of states and moments of atoms in clusters containing two to a few thousand atoms. The theory is based upon the elementary principles governing the tight binding and linear combination of atomic orbitals formulations. It contains no adjustable …

Instrument Matrix Of The Four-Detector Photopolarimeter: Physical Meaning Of Its Rows And Columns And Constraints On Its Elements, R. M.A. Azzam

Electrical Engineering Faculty Publications

The four-detector photopolarimeter (FDP) is an arrangement of four photodetectors for measuring the state of polarization of light. The output current vector I of the FDP is related to the input Stokes vector S by I = AS, where A is the instrument matrix. The rows of A can be viewed as projection operators that determine the output currents of the detectors. This leads to the recognition of four special totally polarized input states, each of which maximizes the output of one detector. The associated four orthogonal states produce minimum signals. Because each detector is absorptive and its output is …

Specific-Heat Study Of The Anomalous Quantum Limit Of (Tmtsf)2clo4, Nathanael A. Fortune, J. S. Brooks, M. J. Graf, G. Montambaux, L. Y. Chiang, Jos A.A.J. Perenboom, D. Althof

Physics: Faculty Publications

We report calorimetric measurements of the organic conductor (TMTSF)2ClO4 in the quantum limit. In addition to the field-induced spin-density-wave (FISDW) phases, we have measured the magnetic-field-dependent specific heat associated with the recently discovered reentrant phase. In terms of a semiempirical model, we find that the reentrant transition is second order, but that the electronic density of states is greatly reduced in the reentrant phase. We also observe a specific-heat signal corresponding to the anomalous fast oscillations which are known to coexist with the FISDW phases.

Theoretical Intensity-Dependent Response Of Nonlinear Periodic Structures, Paul A. Gohman, Gust Bambakidis, Robert J. Spry

Physics Faculty Publications

We have modeled the response of a nonlinear periodic structure by means of the Abelés 2×2 matrix method. Our structure differs from the usual rejection‐band filter designs, in that we have chosen the filter elements to be index matched in the absence of radiation, providing a rejection band that both grows and shifts as a function of incident intensity. The intensity output function of the model not only directly demonstrates optical bistability, but also limiting, switching, self‐pulsing, and chaos.

In Situ Hall-Effect System For Real-Time Electron-Irradiation Studies, B. S. Ziebro, David C. Look, Joseph W. Hemsky, J. Rice

Physics Faculty Publications

A unique system capable of taking in situ Hall‐effect measurements during electron irradiation has been developed. The key element is a small, powerful rare‐earth magnet. Measurements can be taken while the electron beam is on, resulting in a considerable time savings and eliminating problems associated with mounting and demounting the sample. High resolution electron concentration and mobility versus fluence data are quickly and easily obtained, making possible detailed defect production rate studies as functions of energy and flux.

Review Of Hall Effect And Magnetoresistance Measurements In Gaas Materials And Devices, David C. Look

Physics Faculty Publications

The use of magnetic fields in the electrical characterization of semiconductor materials is familiar to everyone in the form of Hall‐effect measurements. However, there is another magnetic‐field‐based phenomenon, magnetoresistance (MR), which is highly useful but not nearly so familiar to the majority of workers. One of the unique features of MR measurements is their applicability to common device structures, in particular, field‐effect transistors (FETs) and contact‐resistance patterns. We will show how channel mobility information can be extracted from the MR data in metal‐semiconductor FETs (MESFETs) and modulation‐doped heterostructure FETs (MODFETs), and also how the material under ohmic contacts can be …

Transition Probabilities And Franck-Condon Factors For The Second Negative Band System Of O2+, Jane L. Fox, Alexander Dalgarno

Physics Faculty Publications

Transition probabilities for the second negative band system of O₂⁺ are computed using the dipole transition moment presented by Wetmore et al. [1984]. Vibrational levels υ″ = 0 − 54 of the X²Π_g ground state and υ′ = 0 − 33 of the excited A²Π_u state are included. Franck-Condon factors for ionization-excitation of O₂ (X³Σ_g⁻; υ = 0 − 25) to O₂⁺(A²Π_u;υ′ = 0 − 33) are also presented.

A Signature Of Auroral Precipitation In The Nightside Ionosphere Of Venus, Jane L. Fox, H. A. Taylor Jr.

Physics Faculty Publications

We show here that the densities of mass-28 ions measured by the Pioneer Venus Orbiter ion mass spectrometer (OIMS) on the nightside of Venus are highly variable and show little correlation with the values of the O⁺ densities. We have determined the total production rates of mass-28 ions in the chemical equilibrium region and find that this production rate cannot be explained by known chemical production reactions. We propose that the “excess” production is due to precipitation of electrons into the nightside thermosphere.

Rotational Effects In The Continuous Vacuum-Ultraviolet Fluorescence Spectrum Of H2 Associated With Spontaneous Dissociation, H. Schmoranzer, T. Noll, E. Roueff, H. Abgrall, Ronald James Bieniek

Physics Faculty Research & Creative Works

The effects of rotational-vibrational interaction, and of rotational coupling between the B 2p u+1 and C 2p u1 electronic states, on the B X fluorescence continuum of H2 associated with spontaneous dissociation were investigated spectroscopically using monochromatized synchrotron radiation for selective excitation of rovibronic states. The rotational shifts and perturbations in the modulated continua intensities observed agree well with close-coupling and Jeffreys-Wentzel-Kromers-Brillouin (JWKB) calculations also performed and are explained in terms of nonadiabatic coupling effects and rainbow-interference structures. A straightforward experimental technique is described to detect mixed electronic states. © 1990 The American Physical Society.

On The Linearization Stability Of The Conformally (Anti-) Self-Dual Einstein Equations, Charles G. Torre

All Physics Faculty Publications

The Einstein equations with a cosmological constant, when restricted to Euclidean space‐times with anti‐self‐dual Weyl tensor, can be replaced by a quadratic condition on the curvature of an SU(2) (spin) connection. As has been shown elsewhere, when the cosmological constant is positive and the space‐time is compact, the moduli space of gauge‐inequivalent solutions to this equation is discrete, i.e., zero dimensional; when the cosmological constant is negative, the dimension of the moduli space is essentially controlled by the Atiyah–Singer index theorem provided the field equations are linearization stable. It is shown that linearization instability occurs whenever the unperturbed geometry possesses …

A Study Of The Hydration Properties Of Selected Laser Dye Aerosols Including Continuous-Flow Parallel Plate And Alternating-Gradient Thermal Diffusion Cloud Chamber Measurements In The High Supersaturation Regime, Donald E. Hagen, Max B. Trueblood, Darryl J. Alofs

Mechanical and Aerospace Engineering Faculty Research & Creative Works

The Hydration Behavior of Aerosols made Up of Various Fluorescent Dyes when Exposed to Water Saturation or Supersaturated Conditions Has Been Studied. Critical Supersaturation Spectra Are Reported. the Dyes Are Found to Behave as High Molecular Weight Ionic Compounds that Obey Kohler Theory. their Relevant Kohler Parameters Are Measured. This Study Makes Use of and Compares Results from the Isothermal Hazecontinuous-Flowand Alternating-Gradient Thermal Diffusion Cloud Chambers. the Ability of the Continuous-Flow Thermal Diffusion Chamber to Operate Correctly at High Supersaturations is Shown. © 1990 Elsevier Science Publishing Co., Inc.

Measurement Of Magnetic Fluctuations By O-X Mode Conversion, L. L. Vahala, G. Vahala, N. Bretz

Electrical & Computer Engineering Faculty Publications

The possibility of measuring magnetic fluctuations in a fusion plasma is considered by examining the O→X mode conversion. Under certain conditions and with good angular resolution, this mode conversion can be attributed to the presence of magnetic fluctuations even though the level of these fluctuations is much lower than that of density fluctuations. Some nonideal effects such as mode polarization mismatch at the plasma edge are also discussed.

Application Of The Results Of Carbon Pellet Modeling To The Problem Of Plasma Penetration, L. L. Vahala, A. G. El Cashlan, G. A. Gerdin, P. B. Parks

Electrical & Computer Engineering Faculty Publications

The assumptions of the evaporation model for low-Z pellets interacting with magnetic fusion plasmas developed by Parks are tested. These assumptions are that the vapor density profile in the region adjacent to the pellet surface falls off with radial distance as r^-α , where 5 <α<6, and that the ionization time for the transition between charge states ז_f (i.e., for r < ~3 sonic radii). The first assumption is tested by solving a two-parameter eigenvalue problem for the evaporation cloud in the region interior to the sonic radius; the results are found to be consistent with the low-Z evaporation model. The second assumption, that ז_zi «ז_f, is tested at the sonic radius using the results from atomic physics and the low-Z evaporation model. It is found that indeed ז_zi «ז_f for plasmas with parameters close to thermonuclear conditions (e.g. CIT), but not for those of smaller Tokamaks such as …

Influence Of Copper Doping On The Performance Of Optically Controlled Gaas Switches, St. T. Ko, V. K. Lakdawala, K. H. Schoenbach, M. S. Mazzola

Electrical & Computer Engineering Faculty Publications

The influence of the copper concentration in silicon-doped gallium arsenide on the photoionization and photoquenching of charge carriers was studied both experimentally and theoretically. The studies indicate that the compensation ratio (N_Cu/N_Si) is an important parameter for the GaAs:Si:Cu switch systems with regard to the turn-on and turn-off performance. The optimum copper concentration for the use of GaAs:Si:Cu as an optically controlled closing and opening switch is determined.

Oxidation-Reduction Behavior Of Undoped And Sr-Doped Lamno3: Defect Structure, Electrical Conductivity, And Thermoelectric Power, J. H. Kuo, Harlan U. Anderson, Don M. Sparlin

Materials Science and Engineering Faculty Research & Creative Works

Seebeck coefficient and electrical conductivity measurements were performed for undoped and Sr-doped LaMnO₃ as a function of temperature and oxygen partial pressure. The results of electrical conductivity showed typical p-type behavior. As reduction proceeded, the electrical conductivity of these LaMnO₃-based perovskites decreased with P 1 4O₂. The analysis of the electrical conductivity data was performed by extending the defect model from a previous thermogravimetric (TG) study. The measured Seebeck coefficients were found to be positive except for the most reducing conditions when the decomposition into multiple phases occurred. The Heikes formula was adopted to interpret …

Subshell Electron Capture In Collisions Of Fully Stripped Ions With He And H2 At Intermediate Energies, L. Meng, C. O. Reinhold, Ronald E. Olson

Physics Faculty Research & Creative Works

Classical phase-space models of the hydrogen molecule and helium are utilized to study shell and subshell electron-capture processes in collisions of fully stripped ions on charge states from 1 to 15 with H2 and He at intermediate impact energies (20200 keV/amu). Autoionization after double electron capture is approximated and is found to be an important channel for high projectile charges. The resulting (n,l) distributions for proton impact of He and H₂ as well as total capture cross sections are found to be in very good agreement with experimental data. l distributions for high projectile charges are also analyzed for …

A Theoretical And Experimental Study Of The Three-Ring Electrostatic Electron Lens, Thomas Anthony Sommer

Dissertations and Theses

A theoretical and experimental study of the three-ring electrostatic lens is presented. The lens consists of three isolated ring-shaped conductors, equally spaced along a common axis of symmetry. When appropriate potentials are applied to the conductors an electric field is produced near the axis which is capable of focusing a collimated beam of electrons. In the theoretical study the charge density method is used to find a closed-form solution for the field. This method approximates the field by replacing each ring with an infinitely thin hoop of uniform charge. The radial and axial equations of motion are then solved numerically, …

Optimization And Thermodynamic Performance Measures Of A Class Of Finite Time Thermodynamic Cycles, Joseph D. Walters

Dissertations and Theses

Modifications to the quasistatic Carnot cycle are developed in order to formulate improved theoretical bounds on the thermal efficiency of certain refrigeration cycles that produce finite cooling power. The modified refrigeration cycle is based on the idealized endoreversible finite time cycle. Two of the four cycle branches are reversible adiabats, and the other two are the high and low temperature branches along which finite heat fluxes couple the refrigeration cycle with external heat reservoirs.

This finite time model has been used to obtain the following results: First, the performance of a finite time Carnot refrigeration cycle (FTCRC) is examined. In …

Improved Resolution Of A 6m Torodial Grating Monochromator, G. K. Wertheim, J. E. Rowe, D. Mark Riffe, N. V. Smith

All Physics Faculty Publications

We report a modification of the AT&T Bell Laboratories 6m toroidal grating monochromator at the National Synchrotron Light Source at Brookhaven National Laboratory which provides greatly improved resolution at midrange without the use of a movable exit slit. This modification is based on detailed ray tracing calculation, using the precedures developed by Haber, Howells, and McKinney and Howells, modified to include the holographic correction terms to the focusing equations. To maintain the optimum resolution requires an exit slit assembly movable over a distance of ∼20 cm. However, we show that an additional fixed slit 16.8 cm closer to the grating …

Cross Section, Robert Katz

Robert Katz Publications

In radiobiology the term cross section is used in ways that depart from its original physical meaning. Some of these conceptual extensions represent significant distortions of the original concept. These distortions lead to the misinterpretation of experimental findings.

Near-100% Production Of The Excited Be+ 1s22p Ion From Decay Of Be 1s2S22p, C. Denise Caldwell, Mark G. Flemming, Manfred O. Krause, Peter Van Der Meulen, Cheng Pan, Anthony F. Starace

Anthony F. Starace Publications

In examining the decay of photon-produced Be 1s2s²np(¹P), n=2,3, we discovered that the vastly predominant decay mode is to the final excited ionic states Be⁺ 1s²np, rather than the ground state. For n=2, the 2p ion accounts for 95% of the total production, with Be⁺ 1s²3p the other main contributor. For n=3, 3p is predominant, again with a very small fraction of 2s. The result for n=2 occurs as a consequence of the similarity between the 2s and …

Self-Consistent Effective Binary Diffusion In Multicomponent Gas Mixtures, John D. Ramshaw

Physics Faculty Publications and Presentations

The correct treatment of diffusion in multicomponent gas mixtures requires solution of a linear system of equations for the diffusive mass fluxes relative to the mass-averaged velocity of the mixture. Effective binary diffusion approximations are often used to avoid solving this system. These approximations are generally internally inconsistent in the sense that the approximate diffusion fluxes do not properly sum to zero. The origin of this inconsistency is identified, and a general procedure for removing it is presented. This procedure applies equally to concentration, forced, pressure, and thermal diffusion, either separately or in combination. It is used to obtain a …

Enhanced Radiative Auger Emission From Lithiumlike S13+16, E. M. Bernstein, M. W. Clark, C. S. Oglesby, J. A. Tanis, W. G. Graham, Robert H. Mcfarland, T. J. Morgan, B. M. Johnson, K. W. Jones

Physics Faculty Research & Creative Works

The radiative Auger emission (RAE) from 0.946.25-MeV/u ₁₆S¹³⁺ (lithiumlike) projectiles excited in collisions with He target atoms has been measured. For these highly stripped ions the intensity of RAE photons relative to K x-ray emission is enhanced by about a factor of five compared with theoretical calculations and an earlier experimental measurement for S ions with few electron vacancies. The enhancement of RAE for S¹³⁺ is qualitatively similar to results reported previously for lithiumlike ₂₃V²⁰⁺; however, some differences between S and V are evident. © 1990 The American Physical Society.

Experimental And Theoretical Study Of The Electron Spectra In 66.7350-Kev/U C++He Collisions, L. H. Toburen, R. (Robert) D. Dubois, C. O. Reinhold, D. R. Schultz, Ronald E. Olson

Physics Faculty Research & Creative Works

Measurements of the differential and total cross sections for production of free electrons are reported for collisions of 66.7350-keV/u C+ ions with He. The experimental data are compared with theoretical calculations that include electron emission from both target and projectile using the classical-trajectory Monte Carlo method and the independent-electron approximation. Good agreement is observed between theory and experiment, and structures appearing in the electron spectra can be explained in terms of either, or both, target and projectile ionization. © 1990 The American Physical Society.

Binary Nucleation Of Ethanol And Water, John L. Schmitt, J. Whitten, G. W. Adams, R. A. Zalabsky

Physics Faculty Research & Creative Works

The authors have used a fast expansion cloud chamber to measure binary homogeneous nucleation rates in several ethanol-water mixtures as a function of temperature, ethanol and water activities and nucleation rate. Data (ethanol and water activities) are presented for a range in nucleation rate from 10 3 to 105 drops/cm3 s from 263 to 293 K for mixtures having mole ratios (ethanol/water) of 10, 4, 0.1, 0.01, and 0.001. A comparison of the extensive data set to other data in the literature shows good agreement. We find current theory, as expected, is unable to accurately predict the data at low …

On-Line Process Fiber Optic Refractometer For Measuring Edible Oil Hydrogenation, Charles F. Cole, Robert A. Sims, Alois (Al) J. Adams

Journal of the Arkansas Academy of Science

The process of edible oil partial hydrogenation has improved steadily over the past decades, but few on-line process instruments exist capable of measuring the extent of hydrogenation. This work describes the design of a prototype, on-line fiber optic refractometer for controlling and monitoring of oils. It uses an established correlation between the degree of hydrogenation of an edible oil and its refractive index (Rl). The refractometer cell uses a bare optical fiber in direct contact with processing oil. Equations are given describing the power transmission characteristics of an optical fiber as a function of its cladding Rl. Comparisons between calculated …

Perturbations Of Gravitational Instantons, Charles G. Torre

All Physics Faculty Publications

Ashtekar's spinorial formulation of general relativity is used to study perturbations of gravitational instantons corresponding to finite-action solutions of the Euclidean Einstein equations (with a nonzero cosmological constant) possessing an anti-self-dual Weyl curvature tensor. It is shown that, with an appropriate "on-shell" form of infinitesimal gauge transformations, the space of solutions to the linearized instanton equation can be described in terms of an elliptic complex; the cohomology of the complex defines gauge-inequivalent perturbations. Using this elliptic complex we prove that there are no nontrivial solutions to the linearized instanton equation on conformally anti-self-dual Einstein spaces with a positive cosmological constant. …

The Longitude Dependence Of The Dayside F Region Trough: A Detailed Model-Observation Comparison, Jan Josef Sojka, Robert W. Schunk, J. A. Whalen

All Physics Faculty Publications

The nighttime main F region trough extends into the sunlit afternoon sector. This trough feature exhibits both a strong magnetic activity dependence and a longitude (UT) dependence. Whalen (1987), using International Geophysical Year (IGY) ionosonde data, showed that both of these effects are readily extracted from ƒ_oF₂ observations. In this study we show that the longitude effect is the same as that contained in the Utah State University time-dependent ionospheric model. It arises from the offset of the geomagnetic axis from the geographic axis. The magnetic activity dependency is associated with the westward convection in the afternoon …

Winds In The Upper Mesosphere At Mid-Latitude: First Results Using An Imaging Fabry-Perot Interferometer, D Rees, A Aruliah, T J. Fuller-Rowell, Vincent B. Wickwar, R J. Sica

All Physics Faculty Publications

The first stage of a new midlatitude facility at the Hardware Ranch Observatory near Bear Lake (41.93°N, 111.42°W, 1970 M elevation), for studies of the aeronomy of the middle and upper atmosphere, was completed during early September 1989. An Imaging Fabry‐Perot interferometer (IFPI) (Rees et al., 1982; Rees et al., 1990), was commissioned with a special Imaging Photon Detector (IPD) (McWhirter et al., 1982), equipped with a Gallium Arsenide (GaAs) photocathode. Wind and temperature structure can be deduced from observations of the Doppler shift and Doppler broadening of airglow and auroral emissions from the mesosphere and thermosphere. The near infra‐red …