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An Evaluation Of A Taylor-Galerkin Algorithm For High Speed Inviscid Flows Using Quadrilateral And Triangular Elements, Kim S. Bey

Mechanical & Aerospace Engineering Theses & Dissertations

The Taylor-Galerkin finite element algorithm is used to obtain solutions to the two-dimensional compressible Euler equations. The mathematical formulation of the algorithm is presented for a typical scalar equation. The derivation results in element equations which are assembled over the entire solution domain to obtain the system of equations that are solved explicitly. The algorithm has the unique feature that the finite element matrices can be evaluated in closed form, avoiding expensive numerical integration. Aspects of vector programming strategies and mesh generation important to an effective analysis procedure are also described. Solutions to supersonic flow problems with exact solutions are …

Laser Pump And Probe Excited State Absorption Measurements, Shawpin Jong

Electrical & Computer Engineering Theses & Dissertations

A pump and probe technique was used to investigate triplet-triplet excited state absorption in solutions of the scintillators 2,5 diphenyloxazole (PPO) and 2,1 naphthyl,5 phenylzole (a-NPO) in several solvents.

KrF excimer radiation (248 nm) was used to pump the samples under investigation as well as a tunable dye laser which was used as the probe. Time-resolution was obtained by changing the optical path difference between the pump and probe beams.

Transient excited state absorption was measured in a wide spectral region between 330 nm and 600 nm, showing a peak at 400 nm for PPO solutions, and two …

Comment On "Role Of Long-Wavelength Degrees Of Freedom In The Rod-To-Coil Transition In Polymers", Rolfe G. Petschek

Faculty Scholarship

[No abstract available]

A Semiclassical Model For Orientation Effects In Electron Transfer Reactions, Robert J. Cave, Stephen J. Klippenstein, R.A. Marcus

All HMC Faculty Publications and Research

An approximate solution to the single‐particle Schrödinger equation with an oblate spheroidal potential well of finite depth is presented. The electronic matrix element H_BA for thermal electron transfer is calculated using these wave functions, and is compared with values of H_BA obtained using the exact solution of the same Schrödinger equation. The present method yields accurate results for H_BA, within the oblate spheroidal potential well model, and is useful for examining the orientational effects of the two centers on the rate of electron transfer.

Renormalization Group Equations In Broken Supersymmetric Theories Using Superspace Methods, Asim Gangopadhyaya, Darwin Chang

Physics: Faculty Publications and Other Works

We apply the superfield method with the spurion technique to derive the renormalization-group equations in broken supersymmetric theories. We point out some possible ambiguities in this procedure and show that it is in general necessary to express the supersymmetry-breaking terms in explicit D-type form. We also found that it is possible to construct broken supersymmetric theories where some of the symmetry-breaking parameters do not receive any infinite renormalization.

Photoelectron Angular Distributions For Atomic Chlorine, Siamak Shahabi , Anthony F. Starace

Anthony F. Starace Publications

Photoelectron angular distribution asymmetry parameters for photoionization to each of the three term levels of the Cl⁺ ion are calculated above the ¹S ionic threshold with use of the open-shell transition-matrix method. Comparison is made with frozen-core Hartree-Fock asymmetry parameters and with the multiconfiguration Hartree-Fock results of Fielder and Armstrong. The calculated asymmetry parameters are used to estimate partial-cross-section branching ratios at 584 Å from the relative experimental photoelec- tron intensity measurements of Kimura, Yamazaki, and Achiba.

Summary Abstract - Theoretical And Experimental Capacitance-Voltage Behavior Of Modulation-Doped Al(0.3)Ga(0.7)As/Gaas Heterojunctions, George B. Norris, David C. Look, W. Koop, J. Klem, H. Morkoç

Physics Faculty Publications

No abstract provided.

Magnetic Properties Of FeXCu100-X Solid Solutions, C.L. Chien, Sy_Hwang Liou, D. Kofalt, Wu Yu, T. Egami, Thomas J. Watson, T.R. Mcguire

Sy-Hwang Liou Publications

In the equilibrium states, the solid solubility between Fe and Cu is negligibly small. Using vapor deposition, however, we produced Fe_xCu_100-x solid solutions over the entire composition range. All the samples were crystalline: bcc structure at the Fe-rich side and fcc structure at the Cu-rich side. The transition from bcc to fcc occurred at around x=70, where the two phases were found to coexist. The fcc alloys exhibit a magnetic dilution leading to a magnetic percolation threshold at x_c≃18, rarely seen in binary Fe alloys. Below x_c, only spin-glass-like ordering is …

Carrier-Concentration–Induced Ferromagnetism In Pbsnmnte, T. Story, R. R. Galazka, Richard B. Frankel, P. A. Wolff

Physics

The influence of charge-carrier concentration on the magnetic properties of the semimagnetic semiconductor [(PbTe)_1-x(SnTe)_x]_1-y[MnTe] _y (x=0.72, y=0.03) is reported. Magnetization, magnetic susceptibility, and specific heat have been measured. For carrier concentrations below p=3 x 10²⁰ cm^-3 the alloy is paramagnetic. For p≥3 x 10²⁰ cm^-3 an abrupt transition to a ferromagnetic phase is observed at helium temperatures. The ferromagnetic transition temperature increases with increasing p. This is the first demonstration of the effect of carrier concentration on the magnetic properties of semimagnetic semiconductors.

Methyl And Tert-Butyl Reorientation And Distributions Of Activation Energies In Molecular Solids: A Nuclear Spin-Relaxation Study In 2,4- And 2,5-Di-Tert-Butylhydroxybenzene, Peter A. Beckmann, A. M. Cheung, E. E. Fisch, F. A. Fusco, R. E. Herzog, M. Narisimhan

Physics Faculty Research and Scholarship

We have measured proton Zeeman relaxation rates R in the 2,4- and 2,5-isomers of di tert-butylhydroxybenzene (DTHB) in the solid state. R was measured as a function of temperature T at proton Larmor frequencies of (j)/21T = 8.50,22.5, and 53.0 MHz. The Tranges were from 78 K to just below the melting points of 2,4- and 2,5-DTHB, 385 and 323 K, respectively. The 2,5- DTHB R vs T and (j) can be interpreted qualitatively in terms of three Bloembergen-PurcellPound (BPP) spectral densities, one for each of the three types of rotors in the molecule. The quantitative agreement is poor but …

Altering The Photorefractive Properties Of Batio3 By Reduction And Oxidation At 650 °C, Stephen Ducharme, Jack Feinberg

Stephen Ducharme Publications

The photorefractive Properties of a nominally pure single crystal of BaTiO3 were altered by treating the crystal at 650 °C in oxygen at different partial pressures. Treatment altered the effective density of photorefractive charge carriers in the crystal and couls convert an inactive crystal into an active one. Treatment at low oxygen pressure (reduction) decreased the temperature of the tetragonal-to-cubic phase transition of the crystal and also decreased the measured optical band gap, implying that oxygen vacancies had been introduced into the bulk crystal. These oxygen vacancies are associated with negative photorefractive charge sonors. Either hole transport or electron transport …

Angular And Energy Dependence Of Cross Sections For Ejection Of Electrons From Water Vapor, Ii: 15-150-Kev Proton Impact, M. A. Bolorizadeh, M. Eugene Rudd

M. Eugene Rudd Publications

Absolute values of cross sections for electron ejection by protons of 15-150 keV energy have been measured as a function of the angle and energy of the electrons. The range of angles was 10° to 160° and the electron energy range was 1-300 eV. The doubly differential cross sections were also integrated over energy or angle to obtain singly differential and total cross sections and also average ejected electron energies. Good agreement is obtained with Senger's DDCS-MT (doubly differential cross section-mixed treatment) theoretical treatment using the Salin factor.

Angular And Energy Dependence Of Cross Sections For Ejection Of Electrons From Water Vapor, Iii: 20- 150-Kev Neutral-Hydrogen Impact, M. A. Bolorizadeh, M. Eugene Rudd

M. Eugene Rudd Publications

Absolute values of cross sections for electron production in collisions of neutral hydrogen atoms of 20-150 keV energy with water vapor molecules have been measured as a function of the ejection energy and angle. The range of angles was 10° to 160° and the electron energy range was 1-300 eV. The doubly differential cross sections were integrated over angle and/or energy to obtain singly differential cross sections, total electron production cross sections, and average energies of ejection. The angular distribution of the electron loss peak was found to have some features in common with the cross section for elastic scattering …

Electric-Dipole Matrix-Element Formulas In Hyperspherical Coordinates With Applications To H- And He, Chang-Hwan Park, Anthony F. Starace, Jiang Tan, Chii-Dong Lin

Anthony F. Starace Publications

Theoretical formulas for the length, velocity, and acceleration forms of the electric-dipole matrix element within the adiabatic hyperspherical coordinate representation are presented. The length and acceleration formulas are used to calculate the photoionization cross section for He up to 1.0 a.u. above threshold and the photodetachment cross section for H^- up to 0.35 a.u. above threshold. Length- and acceleration-form results for the dipole oscillator strengths for the discrete He transitions, 1sns(¹S^e)→1smp(¹P⁰), where n=1, 2, and 3 and m=2, 3, and 4, are also presented. The accuracy of the length- and acceleration-form …

Plastic Deformation, Vacancy Diffusion, And Vacancy Delocalization In Bcc 3He, Matthew J. Moelter, M. B. Manning, C. Elbaum

Physics

The plastic deformation of bcc ³He crystals has been studied near the melting curve, in the temperature range 0.65 K ≤T≤.17 K, and for strain rates, ɛ˙, from 2x10^-6 to 2x10^-4 sec^-1. The resulting relations between strain rate and stress, at a given temperature, are accounted for in terms of dislocation climb and vacancy diffusion in the solid He. The temperature dependence of the strain rate at a given stress indicates that a nonclassical mechanism underlies the deformation process. The vacancy diffusion coefficient in bcc ³He, as a function of temperature, is deduced from …

Direct Observation Of Ensemble Averaging Of The Aharonov-Bohm Effect In Normal-Metal Loops, C. P. Umbach, C. Van Haesendonck, R. B. Laibowitz, S. Washburn, Richard A. Webb

Faculty Publications

Aharonov-Bohm magnetoconductance oscillations have been measured in series arrays of 1, 3, 10, and 30 submicron-diameter Ag loops. At constant temperature, the amplitude of the h/e oscillations is observed to decrease as the square root of number of loops, while the amplitude of h/2e conductance oscillations, measured in the same samples, is independent of the number of series loops. This is direct confirmation of the ensemble averaging properties of h/e oscillations in multiloop systems. The amplitude of the h/e oscillations is in good agreement with recent calculations.

Difference Spectra: Dominance Of Two-Body Cascades In Antiproton-Neutron Annihilations At Rest, R. Debbe, William J. Fickinger, D. K. Robinson

Faculty Scholarship

A novel method of analysis which eliminates the combinatorial background in searches for states produced in p¯n annihilations and in association with a recoil Ï€- is presented. The difference between Ï€- and Ï€+ spectra on p¯n annihilations is the spectrum of the recoiling Ï€- or difference spectrum. We applied this analysis to the exclusive channels p¯n→2Ï€-Ï€+, 2Ï€-Ï€+Ï€0, 3Ï€-2Ï€+. A new prominent state of mass and width ≃1480 and 100 MeV/c2 is present in the first and dominates the third channel. These three channels are interpreted in terms of two-body intermediate states only. The suppression or absence of ‘‘direct’’ annihilation is …

Evidence For A New State Produced In Antiproton Annihilations At Rest In Liquid Deuterium, R. Debbe, William J. Fickinger, R. Marino, D. K. Robinson

Faculty Scholarship

Inclusive charged-pion spectra from p¯d annihilations at rest have been measured in a high-statistics experiment in search of broad states. Analysis of these spectra reveals an enhancement of the π- spectrum at 315 MeV/c. This may be interpreted as a production of a new state of mass 1485 MeV/c2 and width at most 200 MeV/c2 recoiling against the π-. This quasi two-body final state accounts for a large fraction of the p¯n annihilations.

Theory Of In Situ Measurement Of Wave-Vector-Dependent Dynamic Susceptibility And Esr Spectroscopy Using The Ac Josephson Effect, S. E. Barnes, F. Mehran

Physics Articles and Papers

The elementary theory of in situ measurements of the wave-vector-dependent dynamic susceptibility χ(q,ω) in superconductor-insulator-superconductor (SIS) and superconductor–normal-metal–superconductor (SNS) Josephson junctions is presented in some detail. The theory for more complicated SISN and SINS junctions is also described. In addition, the theory of point-contact and superconducting quantum interference device geometries, relevant to the recent experiments of Baberschke, Bures, and Barnes is developed. Involved is a detailed application of the Maxwell and London equations along with the distributed Josephson effect. In a measurement of χ(q,ω), the frequency ω is determined by the relation 2eV₀=ħω where V₀ is the …

Derivation Of Exact Results For The Single-Ion Kondo Problem With The Use Of Diagrammatic Methods, S. E. Barnes

Physics Articles and Papers

It is shown that exact results for the single-impurity Kondo problem can be obtained by diagrammatic methods. The results for the susceptibility and specific heat agree with those obtained by Wilson’s numerical methods. In particular, the crossover W’=(π/e)^1/2 and Wilson R=2 ratios are reproduced exactly. Conduction-electron scattering from the impurity reaches the unitarity limit corresponding to a phase shift δ=π/2. Both this and the compensation of the impurity spin are also exact results. The methods described are relatively easily extended to the Anderson model and the corresponding lattice problems.

Untitled (Subject: Reverberation), Richard C. Heyser

Unpublished Writings

In this paper, Richard C. Heyser explains how sound reverberates and why he developed a time delay spectrometer (TDS) to measure sound.

Nonequilibrium Fluctuations Studied By A Rarefied Gas Simulation, Alejandro Garcia

Faculty Publications

A dilute gas under a constant heat flux is studied with use of a Monte Carlo simulation based on the Boltzmann equation. Results for several spatial correlation functions of equal-time fluctuations are reported and compared qualitatively with previous fluctuating hydrodynamics calculations for liquids.

Infrared Surface-Wave Interferometry On W(100), L. M. Hanssen, D. Mark Riffe, A. J. Sievers

All Physics Faculty Publications

An IR grating on a clean W(100) surface is shown to generate both homogeneous and inhomogeneous surface electromagnetic waves. An observed interference between these two components, which can be described in terms of a two-beam interferometer with variable arm amplitude and fixed optical path, is used to measure the plasma frequency accurately in the IR.

Problems With Deducing Ionospheric Plasma Convection Patterns, Jan Josef Sojka, Robert W. Schunk

All Physics Faculty Publications

It is well-known that convection electric fields have an important effect on the ionosphere-thermosphere system at high latitudes and that a quantitative understanding of their effect requires a knowledge of the plasma convection pattern. Consequently, convection electric fields have been measured by a variety of techniques, including satellite, rocket, and balloon-borne probes, optical tracking of ionized barium clouds, incoherent scatter observations of drifting F region plasma, and coherent scatter observations of drifting E region irregularities. Since all of these measurement techniques provide information on only a limited spatial region at any time, the construction of the overall convection pattern requires …

Crossover From Contact Propagation To Chemical Propagation In First-Passage Percolation, A. R. Kerstein, Boyd F. Edwards

All Physics Faculty Publications

On lattices whose bonds are assigned time delays from a bimodal distribution with modes at b and a≫b whose relative weights are p and 1-p, the dependence of the first-passage velocity v on p is investigated by means of scaling arguments and computations. As p increases, v exhibits a sharp rise near the percolation threshold due to a crossover from the contact-propagation regime, in which slow-bond crossings are rate limiting, to the chemical-propagation regime, in which the tortuosity of the shortest path through the fast-bond network is rate limiting. Previous analyses of criticality in the limit a/b→∞ are extended by …

A Theoretical Study Of The Production And Decay Of Localized Electron Density Enhancements In The Polar Ionosphere, Jan Josef Sojka, Robert W. Schunk

All Physics Faculty Publications

The origins, transport, and decay of large-scale (≳ 10 km) F region density irregularities were theoretically studied using a high-latitude time dependent ionospheric model. Such density irregularities (blobs) have been found both in the polar cap and the auroral zone. The model study, which focuses on blobs being produced by auroral precipitation, shows that the observed energy fluxes can readily account for the blob densities if a plasma flux tube is exposed to the precipitation for 5-10 min. Once the flux tube is transported away from the source, the F region density profile recovers its shape on a time scale …

Comparison Of Simultaneous Chatanika And Millstone Hill Observations With Ionospheric Model Predictions, C. E. Rasmussen, Robert W. Schunk, Jan Josef Sojka, Vincent B. Wickwar, O. De La Beaujardiere, J. Foster, J. Holt, D. S. Evans, E. Nielsen

All Physics Faculty Publications

As part of the MITHRAS program, the Chatanika and Millstone Hill incoherent-scatter radars made coordinated observations of the polar ionosphere on June 27 and 28, 1981. We compare these data with predictions made by a high-latitude ionospheric model. Qualitatively, the same features are evident in both the model and the radar data: fairly constant densities on the dayside with a mid-latitude trough forming poleward of 65 degrees around 1900 MLT (magnetic local time). This trough is seen to extend equatorward with increasing MLT, such that the minimum densities occurring in the trough appear just after midnight around 60 degrees dipole …

Theoretical Study Of The Electron Temperature In The High-Latitude Ionosphere For Solar Maximum And Winter Conditions, Robert W. Schunk, Jan Josef Sojka, M. D. Bowline

All Physics Faculty Publications

The electron temperature (T_e) variation in the high-latitude ionosphere at altitudes between 120 and 800 km has been modeled for solar maximum, winter solstice, and strong magnetic activity conditions. The calculated electron temperatures are consistent with the plasma densities and ion temperatures computed from a time-dependent ionospheric model. Heating rates for both solar EUV and auroral precipitation were included. In general, the predicted UT variation of the electron temperature that results from the displacement between the magnetic and geographic poles is only a few hundred degrees. However, in sunlit trough regions, T_e hot spots develop, and …

Formation Kinetics Of Thermal Donors In Silicon, J T. Borenstein, J W. Corbett, David Peak

All Physics Faculty Publications

The kinetics of thermal donor formation in Czochralski-silicon at ca. 450° C are explained by a simple model based on the work of Suezawa and Sumino which derives forward and reverse reaction rates for each electrically active species from the general features of the infrared electronic absorption spectra. The model, which is independent of the chemical nature of the thermal donor core, assumes that all thermal donors beyond the first donor species are chemically stable at the donor formation temperature, and approximates the reactions for species smaller than the first thermal donor as being in chemical equilibrium. The model is …

Effects Of Different Convection Models Upon The High-Latitude Ionosphere, C. E. Rasmussen, Robert W. Schunk, Jan Josef Sojka

All Physics Faculty Publications

It is well known that convection electric fields have an important effect on the ionosphere at high latitudes and that a quantitative understanding of their effect requires a knowledge of plasma convection over the entire high-latitude region. Two empirical models of plasma convection that have been proposed for use in studying the ionosphere are the Volland and Heelis models. Both of these models provide a similar description of two-celled ionospheric convection, but they differ in several ways, in particular, in the manner in which plasma flows over the central polar cap and near the polar cap boundary. In order to …