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1986

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Articles 1 - 30 of 177

Full-Text Articles in Physics

Positronium Formation From Li And Na Atoms By Use Of Pseudopotential, Sultana N. Nahar, J M. Wadehra Dec 1986

Positronium Formation From Li And Na Atoms By Use Of Pseudopotential, Sultana N. Nahar, J M. Wadehra

Physics and Astronomy Faculty Research Publications

The differential and total cross sections for the formation of positronium in its ground state from Li and Na atoms by the impact of intermediate-energy positrons are calculated in the first Born and distorted-wave Born approximations. Hellmann-type pseudopotentials are used to represent the alkali-metal ion cores. The difference in the use of pseudopotentials and the static potential for the core representation for evaluating various rearrangement cross sections is discussed.


Thermal And Structural Stability Of Cosputtered Amorphous TaXCu1-X Alloy Thin Films On Gaas, J.E. Oh, John A. Woollam, K.D. Aylesworth, David J. Sellmyer, J.J. Pouch Dec 1986

Thermal And Structural Stability Of Cosputtered Amorphous TaXCu1-X Alloy Thin Films On Gaas, J.E. Oh, John A. Woollam, K.D. Aylesworth, David J. Sellmyer, J.J. Pouch

David Sellmyer Publications

The thermal and chemical stabilities of amorphous-metal diffusion barrier films are of importance in high-temperature semiconductor device applications. The reaction characteristics of the barrier constituents with the surrounding elements as well as the crystallization temperature determine the thermal stability of an amorphous-alloy diffusion barrier. We report that suitable thin films of Ta-Cu have been prepared over a wide range of compositions, by cosputter deposition onto GaAs and fused-quartz substrates. The amorphous nature and crystallization behavior of the films have been monitored by x-ray diffraction and van der Pauw resistivity measurements. Films were found to be amorphous over the range of ...


A Criterion For Vortex Breakdown, R. E. Spall, T. B. Gatski, C. E. Grosch Dec 1986

A Criterion For Vortex Breakdown, R. E. Spall, T. B. Gatski, C. E. Grosch

CCPO Publications

Spall, R.E., Gatski, T.B., & Grosch, C.E. (1987). A criterion for vortex breakdown. Physics of Fluids, 30(11), 3434-3440. doi: 10.1063/1.866475


Polarizing Beam Splitters For Infrared And Millimeter Waves Using Single-Layer-Coated Dielectric Slab Or Unbacked Films, R. M.A. Azzam Dec 1986

Polarizing Beam Splitters For Infrared And Millimeter Waves Using Single-Layer-Coated Dielectric Slab Or Unbacked Films, R. M.A. Azzam

Electrical Engineering Faculty Publications

No abstract provided.


Exact Evaluation And Recursion Relations Of Two-Center Harmonic Oscillator Matrix Elements, P. J. Drallos, J. M. Wadehra Dec 1986

Exact Evaluation And Recursion Relations Of Two-Center Harmonic Oscillator Matrix Elements, P. J. Drallos, J. M. Wadehra

Physics and Astronomy Faculty Research Publications

Using vibrational wave functions of two relatively displaced harmonic oscillators of arbitrary frequencies, Franck–Condon overlap integrals and matrix elements of x^l, exp(−2cx), and exp(−cx^2) (x is the internuclear separation) are obtained. Useful three‐term, four‐term, and five‐term recursion relations among these matrix elements are derived. It is shown that all of the relevant matrix elements can be obtained from a mere knowledge of the lowest two Franck–Condon overlap integrals. Results are illustrated by computation of Franck–Condon factors for the A ^1∑^+_u –X ^1∑^+_g and the B ^1Π_u –X ^1 ...


The Moments Formulation For Determining Eigenvalues Of Physically Important Systems, Robert Morton Williams Dec 1986

The Moments Formulation For Determining Eigenvalues Of Physically Important Systems, Robert Morton Williams

ETD Collection for AUC Robert W. Woodruff Library

A fundamentally new method for determininc’ eigenvalues of linear differential operators is presented. The method involves the application of moments analysis and offers a fast and precise numerical alqorithm for eigenvalue computation, particularly in the strong and intermediate coupling reqimes. The most remarkable feature of this approach is that it provides exponentially converging lower and upper bounds to the eigenvalues. The effectiveness of this method is demonstrated by applyinq it to three important problems: the simple harmonic oscillator potential problem, the quantum potential x2 + ƛ2 / 1 + gx2(studied by Lai and Lin in 1982), and the simplified ...


Errata: First-Principles Theoretical Explanation Of Incommensurate Behavior In Rb2Znc4, V. Katanant, P.J. Edwardson, John Hardy, L. L. Boyer Dec 1986

Errata: First-Principles Theoretical Explanation Of Incommensurate Behavior In Rb2Znc4, V. Katanant, P.J. Edwardson, John Hardy, L. L. Boyer

John R. Hardy Papers

Figures 2(a) and 2(b) of this paper have been inadvertently interchanged; thus, the caption for Fig. 2(a) relates to Fig. 2(b) and the caption for Fig. 2(b) relates to Fig. 2(a).


Magnetic Relaxation In Fe-(Sio2) Granular Films, Gang Xiao, Sy_Hwang Liou, A. Levy, J.N. Taylor, C. L. Chien Dec 1986

Magnetic Relaxation In Fe-(Sio2) Granular Films, Gang Xiao, Sy_Hwang Liou, A. Levy, J.N. Taylor, C. L. Chien

Si-Hwang Liou Publications

Magnetic relaxation of granular Fe-(SiO2) solids with low metal-volume fraction has been studied by employing dc SQUID (superconducting quantum interference device) magnetometry and Mössbauer spectroscopy with the characteristic measuring time differing by nine orders of magnitude. The blocking temperatures (TB), extrapolated to zero external field as measured by the two techniques maintain a constant ratio of 0.35 independent of samples. Arrhenius law was found adequate in describing the relaxation process, with a well-defined relaxation-time constant of τ0≃10-13 sec. A cusp in the susceptibility is observed at TB, below which irreversible difference between ...


Photorefraction In Batio3, Stephen Ducharme Dec 1986

Photorefraction In Batio3, Stephen Ducharme

Stephen Ducharme Publications

This thesis summarizes the results of experimental investigations of the photorefractive properties of melt-grown BaTiO3 single crystals. Three basic photorefractive material properties are studied: (1) the effective density of photorefractive charges, (2) the photoconductivity of the photorefractive charges, and (3) the relative contributions of electron and hole photoconduction. Volume holographic measurement techniques are used: two-beam energy coupling, four-wave mixing, and erasure of volume holograms. The photorefractive properties were altered experimentally by chemically reducing or oxidizing a BaTiO3 crystal. I have extended the “hopping conduction” model of photorefractive transport to include simultaneous electron and hole photoconduction. The extension of ...


Auroral E-Region Plasma Waves Andelevated Electron Temperatures, Bela G. Fejer, J. Providakes, D. T. Farley, W. E. Swartz Dec 1986

Auroral E-Region Plasma Waves Andelevated Electron Temperatures, Bela G. Fejer, J. Providakes, D. T. Farley, W. E. Swartz

Bela G. Fejer

We have observed 3-m auroral E region plasma waves with a high-resolution 50-MHz radar interferometer at Ithaca. During postmidnight periods of very strong magnetic activity at Ottawa (L = 3.5), the backscattered power and Doppler spectra vary rapidly with time and range and may have both mean Doppler shifts and half power widths in excess of 200 Hz (600 m/s). In addition, when the radar and magnetometer data imply that the current is approximately parallel to the radar line of sight, sharp spectral peaks corresponding to phase velocities approaching 1 km/s sometimes appear suddenly. These persist for at ...


Pressure Dependence Of The Nematic-To-Isotropic Transition In The Lyotropic Liquid Crystal Cesium Perfluoro-Octanoate, Michael R. Fisch, Satyendra Kumar, J. D. Litster Dec 1986

Pressure Dependence Of The Nematic-To-Isotropic Transition In The Lyotropic Liquid Crystal Cesium Perfluoro-Octanoate, Michael R. Fisch, Satyendra Kumar, J. D. Litster

Physics Publications

We report light-scattering measurements under pressures up to 1000 bars of nematic short-range order in the isotropic phase of the lyotropic liquid-crystal system cesium perfluoro-octanoate and water. The nematic-to-isotropic transition temperature is a nonlinear function of pressure which changes strongly with concentration and dTNI/dp is from 10 to 100 times smaller than in typical thermotropic nematics. We also find the bare correlation length in the isotropic phase to be 12.5 ± 2 Å.


Determination Of Phenomenological Optical Model Parameters For Neutrons On 208Pb From 4 To 150 Mev, Randy L. Schutt Dec 1986

Determination Of Phenomenological Optical Model Parameters For Neutrons On 208Pb From 4 To 150 Mev, Randy L. Schutt

Master's Theses

Phenomenological o p tic a l model parameters for neutrons incident on 208Pb have been determined for neutron energies from 4 to 150 MeV using the code SNOOPY-8. Neutron total cross sections from 4 to 150 MeV and angular distributions for elastic scattering from 13.5 to 40.0 MeV were utilized. Analyses of total and differential cross sections were performed at a number of energies to determine energy dependent expressions for the real strengths of the central potential, imaginary surface potential, and imaginary volume potential. These energy dependent expressions for V, Wd, and WS were found ...


Weak Decays Of The H-Dibaryon, Jf Donoghue, E Golowich, Br Holstein Nov 1986

Weak Decays Of The H-Dibaryon, Jf Donoghue, E Golowich, Br Holstein

Barry R Holstein

We calculate decay rates and branching fractions for the postulated S=-2 H dibaryon, both for the expected ΔS=1 channels (nΛ,nΣ0,pΣ-) and for the possible ΔS=2 mode (nn). For ΔS=1 decays we find the S waves are dominated by ΔI=(3/2) transitions due to the Pauli principle, which forces the six-quark final state to be in a SU(3) 27-plet. If observed, this would be the first breakdown of the ΔI=1/2 rule. The lifetime is long, of order 10-8 sec, which should be considered in planning experiments. In the ΔS=2 case ...


The Radial Distribution Of Dose Around The Path Of A Heavy Ion In Liquid Water, M. P. R. Waligorski, R. N. Hamm, Robert Katz Nov 1986

The Radial Distribution Of Dose Around The Path Of A Heavy Ion In Liquid Water, M. P. R. Waligorski, R. N. Hamm, Robert Katz

Robert Katz Publications

Monte Carlo calculations of the radial distribution of dose in liquid water, incorporating energy deposition due to primary excitations and ionizations, have been performed for protons of energy 1, 10, 20, 50, and 100 MeV. By combining these results with earlier semi-empirical formulae used in track structure theory calculations, a corrected analytic formulation has been developed which on radial integration closely reproduces the value of stopping power for protons in the energy range 0.1–1000 MeV. After including a β-dependent ‘effective charge’ formula, this corrected formulation is tested against all published measurements of radial distribution of dose from energetic ...


The Fricke Dosimeter As A 1-Hit Detector, Robert Katz, G. L. Sinclair, M. P. R. Waligorski Nov 1986

The Fricke Dosimeter As A 1-Hit Detector, Robert Katz, G. L. Sinclair, M. P. R. Waligorski

Robert Katz Publications

A fit to the experimental data for the response of the Fricke dosimeter to energetic heavy ions is obtained using a calculation of the relative effectiveness of a 1-hit detector, from track theory. We use 2 fitted parameters, the target size, a0, which may be thought to represent a “diffusion length,” and E0, the dose of gamma-rays at which there is an average of one hit per target (the D-37 dose), and a new algorithm for the average radial distribution of dose in liquid water from the passing ion. The G value for ions is then given as ...


Beyond The Rigid-Ion Approximation With Spherically Symmetric Ions, L. L. Boyer, M. J. Mehl, J. L. Feldman, John R. Hardy, J. W. Flocken, C. Y. Fong Nov 1986

Beyond The Rigid-Ion Approximation With Spherically Symmetric Ions, L. L. Boyer, M. J. Mehl, J. L. Feldman, John R. Hardy, J. W. Flocken, C. Y. Fong

John R. Hardy Papers

In our recent Letter we introduced an ab initio model for spherically symmetric charge relaxation of ions in a crystal, called potential-induced breathing (PIB), and demonstrated its importance in the calculation of elastic constants. We also investigated the splitting of the longitudinal optic (LO) and transverse optic (TO) mode frequencies, which results from the macroscopic field associated with longitudinal modes. In the discussion immediately before and after Eq. (5) we argued, incorrectly, that the only contributions to the LO-TO splitting from PIB were from terms involving Sk, the derivative of the self-energy of the kth ion with respect ...


Thin-Film Beam Splitter That Reflects Light As A Half-Wave Retarder And Transmits It Without Change Of Polarization: Application To A Michelson Interferometer, R. M.A. Azzam Nov 1986

Thin-Film Beam Splitter That Reflects Light As A Half-Wave Retarder And Transmits It Without Change Of Polarization: Application To A Michelson Interferometer, R. M.A. Azzam

Electrical Engineering Faculty Publications

The refractive index n1 of a transparent layer of quarter-wave optical thickness coating a transparent substrate of refractive index n2 can be chosen to produce half-wave retardation (HWR) in reflection and no change of polarization in refraction at any angle of incidence ø. The function n1(ø, n2), and the associated polarization-independent reflectance of the film-substrate system R(ø, n2) are determined. Such a coated surface can be used as a beam splitter with excellent characteristics (e.g., split fractions that do not depend on source polarization, a split beam whose polarization is identical to ...


Two-Step Stabilization Of Autoionizing States, J. Greg Story, Linn D. Van Woerkom, William E. Cooke Nov 1986

Two-Step Stabilization Of Autoionizing States, J. Greg Story, Linn D. Van Woerkom, William E. Cooke

Physics Faculty Research & Creative Works

A two-step process using internal conversion and fluorescence to stabilize the 6P3/211d autoionizing state of barium has been observed. The internal conversion produces very highly excited autoionizing Rydberg states, which then emit fluorescence to produce singly excited, bound states. Inclusion of this process should bring calculations closer to agreement with recent measurements of dielectronic recombination.


Equilibrium Properties Of Short Field-Reversed Configurations, Ross L. Spencer, M. Tuszewski Nov 1986

Equilibrium Properties Of Short Field-Reversed Configurations, Ross L. Spencer, M. Tuszewski

Faculty Publications

Some features of short field-reversed configuration (FRC) equilibria relevant to transport and stability are studied numerically and analytically. It is shown that magnetic field curvature effects significantly increase the FRC magnetization for plasma elongations epsilon is less than or equal to 4.


Experimental Test Of Higher-Order Electron-Capture Processes In Collisions Of Fast Protons With Atomic Hydrogen, Hans G. Vogt, Reinhold S. Schuch, Edson L B Justiniano, Michael Schulz, W. Schwab Nov 1986

Experimental Test Of Higher-Order Electron-Capture Processes In Collisions Of Fast Protons With Atomic Hydrogen, Hans G. Vogt, Reinhold S. Schuch, Edson L B Justiniano, Michael Schulz, W. Schwab

Physics Faculty Research & Creative Works

We present measurements of the angular distribution of fast hydrogen atoms formed by electron capture of 2.8- and 5.0-MeV protons in atomic hydrogen. In the angular region of the Thomas peak (0.47 mrad) the experimental results obtained with this pure three-body collision system are in reasonable agreement with a strong-potential Born calculation and the impulse approximation, but not with other higher-order theories.


First-Principles Theoretical Explanation Of Incommensurate Behavior In Rbznc4, V. Katkanant, P. J. Edwardson, John R. Hardy, L. L. Boyer Oct 1986

First-Principles Theoretical Explanation Of Incommensurate Behavior In Rbznc4, V. Katkanant, P. J. Edwardson, John R. Hardy, L. L. Boyer

John R. Hardy Papers

We have carried out an ab initio theoretical study of the potential energy and molecular dynamics of Rb2ZnCl4. These calculations demonstrate that the incommensurate transition in this compound is caused by the relaxation of imperfect-hexagonal spirals of highly unstable ZnCl42- ions. This leads to angstrom-size displacements with essentially zero energy change. We argue that such "latent" (or imperfect) symmetry could be the general cause of incommensurate transitions in insulators.


Asymmetry In The Magnetoconductance Of Metal Wires And Loops, A. D. Benoit, S. Washburn, C. P. Umbach, R. B. Laibowitz, Richard A. Webb Oct 1986

Asymmetry In The Magnetoconductance Of Metal Wires And Loops, A. D. Benoit, S. Washburn, C. P. Umbach, R. B. Laibowitz, Richard A. Webb

Faculty Publications

Universal conductance fluctuations in wires and Aharonov-Bohm oscillations in loops are not symmetric about H=0. The observation of asymmetry in the periodic oscillations is possible when the phase-coherence length of the wave function is comparable to the separation of the voltage probes. In both cases, four-probe measurements yield resistances which depend on lead configuration. The asymmetries appear like Hall voltages, and are consistent with Onsager's relations.


Lung Cancer Risk At Low Doses Of Α Particles, Werner Hofmann, Robert Katz, Zhang Chunxiang Oct 1986

Lung Cancer Risk At Low Doses Of Α Particles, Werner Hofmann, Robert Katz, Zhang Chunxiang

Robert Katz Publications

A survey of inhabitant exposures arising from the inhalation of 222Rn and 220Rn progeny, and lung cancer mortality has been carried out in two adjacent areas in Guangdong Province, People’s Republic of China, designated as the “high background” and the “control” area. Annual exposure rates are 0.38 working level months (WLM) per year in the high background, and 0.16 WLM/yr in the control area. In 14 yr of continuous study, from 1970 to 1983, age-adjusted mortality rates were found to be 2.7 per 105 living persons of all ages in the high ...


Selection Rules For Vibrational Energy Loss By Resonant Electron Impact In Polyatomic Molecules, Gordon A. Gallup Oct 1986

Selection Rules For Vibrational Energy Loss By Resonant Electron Impact In Polyatomic Molecules, Gordon A. Gallup

Gordon Gallup Publications

Approximate expressions for inelastic elements of the S matrix are given in terms of integrals over vibrational functions and R-matrix electron states. The magnitude and symmetry of these integrals determine the vibrations that are excited by various resonances, and the present analysis successfully predicts the spectra measured for benzene, ethylene, and formaldehyde. The recently observed s-wave component in the rotational excitation of N2 is also explained by the treatment. The theory shows how vibrational excitation can give information about the symmetries of resonant electronic states. This can be particularly useful when angular distribution measurements are unavailable.


Semiconducting/Semi-Insulating Reversibility In Bulk Gaas, David C. Look, Phil W. Yu, W. M. Theis, W. Ford, G. Mathur, J. R. Sizelove, D. H. Lee, S. S. Li Oct 1986

Semiconducting/Semi-Insulating Reversibility In Bulk Gaas, David C. Look, Phil W. Yu, W. M. Theis, W. Ford, G. Mathur, J. R. Sizelove, D. H. Lee, S. S. Li

Physics Faculty Publications

Bulk, liquid‐encapsulated Czochralski GaAs may be reversibly changed from semiconducting (ρ∼1 Ω cm) to semi‐insulating (ρ∼107 Ω cm) by slow or fast cooling, respectively, following a 5 h, 950 °C soak in an evacuated quartz ampoule. This effect has been studied by temperature‐dependent Hall‐effect, photoluminescence, infrared absorption, mass spectroscopy, and deep level transient spectroscopy measurements. Except for boron, the samples are very pure, with carbon and silicon concentrations less than 3×1014 cm3. Donor and acceptor concentrations, on the other hand, are in the mid 1015 cm3 ...


Semiconducting/Semi-Insulating Reversibility In Bulk Gaas, David C. Look, Phil W. Yu, W. M. Theis, W. Ford, G. Mathur, J. R. Sizelove, D. H. Lee, S. S. Li Oct 1986

Semiconducting/Semi-Insulating Reversibility In Bulk Gaas, David C. Look, Phil W. Yu, W. M. Theis, W. Ford, G. Mathur, J. R. Sizelove, D. H. Lee, S. S. Li

Physics Faculty Publications

Bulk, liquid-encapsulated Czochralski GaAs may be reversibly changed from semiconducting (ρ~1 Ω cm) to semi-insulating (ρ~107 Ω cm) by slow or fast cooling, respectively, following a 5 h, 950°C soak in an evacuated quartz ampoule. This effect has been studied by temperature-dependent Han-effect, photoluminescence, infrared absorption, mass spectroscopy, and deep level transient spectroscopy measurements. Except for boron, the samples are very pure, with carbon and silicon concentrations less than 3 X 1014 cm-3. Donor and acceptor concentrations, on the other hand, are in the mid 1015 cm-3 range, which means that the ...


Multicritical Points In An Ising Random-Field Model, Miron Kaufman, Philip E. Klunzinger, A. Khurana Oct 1986

Multicritical Points In An Ising Random-Field Model, Miron Kaufman, Philip E. Klunzinger, A. Khurana

Physics Faculty Publications

The phase diagram of the mean-field Ising model in a random field obeying a symmetric three-peak distribution is determined. This distribution is relevant to diluted antiferromagnets in a uniform magnetic field. The phase diagram includes a fourth-order point, tricritical points, ordered critical points, critical end points, and a double critical end point. An ordered phase persists for arbitrarily large random fields at low temperatures.


Effects Of Second Sound On Acoustic Trasmission At The Solid-Liquid 4He Interface, Matthew J. Moelter, M. B. Manning, C. Elbaum Oct 1986

Effects Of Second Sound On Acoustic Trasmission At The Solid-Liquid 4He Interface, Matthew J. Moelter, M. B. Manning, C. Elbaum

Physics

We have calculated the reflection and transmission coefficients of acoustic waves propagating across a solid-liquid interface of 4He, using an extension of the treatment of Castaing and Nozières in which we include pressure changes associated with second sound. These calculations account well for the experimental results obtained over the temperature range 0.83 K≤ T ≤1.46 K and provide an alternative explanation to the one we offered previously for the lack of agreement between experiment and the theory of Castaing and Nozières.


Modular Forms And The Cosmological Constant, G Moore, J Harris, Philip C. Nelson, I Singer Oct 1986

Modular Forms And The Cosmological Constant, G Moore, J Harris, Philip C. Nelson, I Singer

Department of Physics Papers

The vacuum amplitude of the heterotic string in a flat background vanishes for the first twenty orders of string perturbation theory. The proof relies on the algebraic geometry of modular forms.


Experimental Fine-Structure Branching Ratios For Na-Rare-Gas Optical Collisions, Mark D. Havey, F. T. Delahanty, Linda L. Vahala, Gary E. Copeland Oct 1986

Experimental Fine-Structure Branching Ratios For Na-Rare-Gas Optical Collisions, Mark D. Havey, F. T. Delahanty, Linda L. Vahala, Gary E. Copeland

Electrical & Computer Engineering Faculty Publications

Experimental ratios for branching into the fine-structure levels of the Na 3p multiplet, as a consequence of an optical collision with He, Ne, Ar, Kr, or Xe, are reported. The process studied is Na(3s2S1/2)+R+nhNNa(3p2Pj)+R+(n-1)hN, where R represents a rare-gas atom and where the laser frequency N is tuned in the wings of the Na resonance transitions. The branching ratios are defined as I(D1)/I(D2) where I(D1) and I(D2) are measured intensities of the atomic Na D1 and D2 lines. The ratios are ...