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Articles 34081 - 34110 of 36547

Full-Text Articles in Physical Sciences and Mathematics

Determination Of Dissociation Energies And Thermal Functions Of Hydrogen‐Bond Formation Using High Resolution Ftir Spectroscopy, B. A. Wofford, M. E. Eliades, Shannon Lieb, J. W. Bevan Jan 1987

Determination Of Dissociation Energies And Thermal Functions Of Hydrogen‐Bond Formation Using High Resolution Ftir Spectroscopy, B. A. Wofford, M. E. Eliades, Shannon Lieb, J. W. Bevan

Scholarship and Professional Work - LAS

A technique which employs high resolution Fourier transform infrared spectroscopy is demonstrated for evaluation of hydrogen bonddissociation energiesD 0 and D e . Results for HCN‐‐HF give a D 0=20.77(22) and D e =28.77(45) kJ/mol which are compared with previously determined values obtained from microwave absolute intensity measurements and a b i n i t i o molecular orbital calculations. Rovibrational band information available for HCN‐‐HF also permits evaluation of thermal functions of dimer formation in kJ/mol: ΔU ○ 298.2 =20.1(2), ΔH ○ 298.2 =22.6(2), ΔG ○ 298.2 =59.4(2), ΔS ○ 298.2 =−0.1235.

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On A Ferromagnetic With A Three‐Spin Interaction, Harry A. Brown Jan 1987

On A Ferromagnetic With A Three‐Spin Interaction, Harry A. Brown

Physics Faculty Research & Creative Works

No abstract provided.

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Electron Correlation Effects In Nonresonant Multiphoton Ionization Processes, Anthony F. Starace Jan 1987

Electron Correlation Effects In Nonresonant Multiphoton Ionization Processes, Anthony F. Starace

Anthony F. Starace Publications

The role of electron correlations in nonresonant multiphoton processes of atoms is presented. The evidence for the validity of a lowest order perturbation theory (LOPT) approach for the laser field in the case of nonresonant processes is sketched. The growing consensus for a LOPT interpretation of even the multiply-charged ion spectra obtained with high intensity lasers is reviewed. Finally, a review of those specific electron correlation processes within LOPT that are important for the quantitative prediction of two-photon ionization cross sections is presented and some of their effects on calculated generalized cross sections are exhibited.

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Sites And Diffusion Of Muons In Fcc Metal Hydride Systems, James Russell Kempton Jan 1987

Sites And Diffusion Of Muons In Fcc Metal Hydride Systems, James Russell Kempton

Dissertations, Theses, and Masters Projects

A positive muon can be considered an isotope of hydrogen due to similarities in spin and charge. For metal hydride systems, the muon enters the sample "as the last hydrogen added," and competes for the same sites as the hydrogen atoms. to observe the site competition and diffusion of both particles (muon and proton), several FCC metal hydrides, TiH{dollar}\sb{lcub}1.83{rcub}{dollar}, TiH{dollar}\sb{lcub}1.97{rcub}{dollar}, TiH{dollar}\sb{lcub}1.99{rcub}{dollar}, YH{dollar}\sb{lcub}1.77{rcub}{dollar}, YH{dollar}\sb2{dollar}, ZrH{dollar}\sb{lcub}1.94{rcub}{dollar}, and LaH{dollar}\sb{lcub}2.06{rcub}{dollar}, were studied using transverse-, zero-, and low longitudinal-field {dollar}\mu{dollar}SR. The low temperature region results indicate that the muon predominately occupies octahedral sites for the FCC metal hydrides in this study. The probability for a …

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The Effect Of Closed Classical Orbits On Quantum Spectra: Ionization Of Atoms In A Magnetic Field, Meng Li Du Jan 1987

The Effect Of Closed Classical Orbits On Quantum Spectra: Ionization Of Atoms In A Magnetic Field, Meng Li Du

Dissertations, Theses, and Masters Projects

A quantitative theory of oscillatory spectra for atoms in a magnetic field is developed. When an atom is placed in a magnetic field, and absorption spectrum into states close to the ionization threshold is measured, it is found that the absorption as a function of energy is a superposition of many sinusoidal oscillations. Such interesting and surprising phenomenon are fully explained and described by the theory.;The theory is based on three approximations: (1) Near the atomic nucleus, the diamagnetic field is negligible. (2) Far from the nucleus, the wave propagates semiclassically. (3) Waves returning to the nucleus are similar to …

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Renormalization Group Theory Technique And Subgrid Scale Closure For Fluid And Plasma Turbulence, Ye Zhou Jan 1987

Renormalization Group Theory Technique And Subgrid Scale Closure For Fluid And Plasma Turbulence, Ye Zhou

Dissertations, Theses, and Masters Projects

Renormalization group theory is applied to incompressible three-dimension Navier-Stokes turbulence so as to eliminate unresolvable small scales. The renormalized Navier-Stokes equation includes a triple nonlinearity with the eddy viscosity exhibiting a mild cusp behavior, in qualitative agreement with the test-field model results of Kraichnan. For the cusp behavior to arise, not only is the triple nonlinearity necessary but the effects of pressure must be incorporated in the triple term.;Renormalization group theory is also applied to a model Alfven wave turbulence equation. In particular, the effect of small unresolvable subgrid scales on the large scales is computed. It is found that …

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Catastrophes And Stable Caustics In Bound States Of Hamiltonian Systems, John B. Delos Jan 1987

Catastrophes And Stable Caustics In Bound States Of Hamiltonian Systems, John B. Delos

Arts & Sciences Articles

Caustics—envelopes of families of classical trajectories, or boundaries between classically allowed and forbidden regions—correspond to singular points of a phase‐space surface called a Lagrangian manifold. According to catastrophe theory, only a limited number of types of caustics are stable under general perturbations of the manifold. Most of the caustics that are found in calculations correspond to members of the canonical list of elementary catastrophes. However, there are some exceptions—examination of trajectories of typical Hamiltonian systems shows that stable structures exist which are not in accord with the stability theorem of catastrophe theory. These exceptional cases are discussed in this paper. …

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Anneal Induced Changes In Amorphous Semiconductor Multilayers, David D. Allred, Jesus González-Hernández, O. V. Nguyen Jan 1987

Anneal Induced Changes In Amorphous Semiconductor Multilayers, David D. Allred, Jesus González-Hernández, O. V. Nguyen

Faculty Publications

We have prepared, heat treated and characterized various amorphous semiconductor periodic multilayers and ultrathin films. These were prepared by several vapor deposition techniques at substrate temperatures ranging from 25°C to 300°C and possessed periodicities from 22 to 400Å. Films were subjected to isochronal thermal treatments at progressively higher temperatures. Two effects were observed: enhanced diffusion and retarded crystallization. Interdiffusion, at rates which are many orders of magnitude higher than those anticipated from crystalline data, was observed in a-Si/a-Ge multilayers. Crystallization of germanium, the more readily crystallized member of the couple, is retarded; the extent depends on the thickness of the …

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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.

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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 …

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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

A criterion for the onset of vortex breakdown over a wide range of the Reynolds number is proposed. Based upon previous experimental, theoretical, and numerical studies, as well as a new numerical study, an appropriately defined local Rossby number is used to delineate the region where breakdown occurs. Comparisons are made with previously suggested criticality parameters and the unique features of the proposed Rossby number parameter are shown. A number of previous theoretical studies concentrating on inviscid standing‐wave analyses for trailing wing‐tip vortices are reviewed and reinterpreted, along with the previous numerical and experimental studies, in terms of the Rossby …

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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 …

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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∑^+_g systems of ^7Li_2.

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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 most several …

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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.

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Photoconductivity Parameters In Lithium Niobate, Robert Gerson, J. F. Kirchhoff, L. E. Halliburton, D. A. Bryan Dec 1986

Photoconductivity Parameters In Lithium Niobate, Robert Gerson, J. F. Kirchhoff, L. E. Halliburton, D. A. Bryan

Physics Faculty Research & Creative Works

Measurements on a variety of doped (magnesium and/or iron) and undoped lithium niobate crystals in the oxidized state demonstrate an Arrhenius dependence of dark conductivity on reciprocal temperature between 460 and 590 K. All of the crystals had roughly the same conductivity and activation energy (1.21 eV) over the temperature range, implying that all have about the same free-carrier concentration and mobility. The enhanced photoconductivity of magnesium-doped lithium niobate is attributed to a greatly reduced trapping cross section of Fe3+ for electrons, the smaller cross section being due to a changed substitutional site for Fe3+. The Fe …

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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).

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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

Masters 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 to …

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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

Sy-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 …

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Calculation Of Electron Capture Cross Sections Of Collisions Of Be ²⁺ On H, A. E. Wetmore, H. R. Cole, Ronald E. Olson Dec 1986

Calculation Of Electron Capture Cross Sections Of Collisions Of Be ²⁺ On H, A. E. Wetmore, H. R. Cole, Ronald E. Olson

Physics Faculty Research & Creative Works

Using the perturbed stationary state method, including electron translation factors, the authors have calculated electron capture cross sections for the helium-like ions Be2+ and B3+ incident on ground-state atomic hydrogen. The molecular structure calculation employs pseudo-potentials to represent the inactive K-shell electrons on the incident ions. The calculated cross sections vary rapidly in the 107 cm s-1 velocity range (E approximately 1 keV amu-1). The calculations show preferential transfer to the Be+(2s) and the B2+(2p) product states. The calculations for B3++H are in good agreement with experimental measurements of Cradall et al …

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Double Electron Transitions In Collisions Between Multiply Charged Ions And Helium Atoms, Ronald E. Olson, A. E. Wetmore, M. L. Mckenzie Dec 1986

Double Electron Transitions In Collisions Between Multiply Charged Ions And Helium Atoms, Ronald E. Olson, A. E. Wetmore, M. L. Mckenzie

Physics Faculty Research & Creative Works

A semiclassical model for He is applied to the study of multiply charged ions colliding with He at intermediate energies. Single and double-electron capture and ionisation and capture-ionisation reactions are studied for incident-ion charge states q=+1 to +50 at 1 MeV amu-1. For charge states q>or approximately=+10, single electron capture is found to be dominated by a two-electron transition in which one electron is captured and the other is ionised.

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Negative Ion Drift Velocities In Mixtures Of Methane And Sulphur Hexafluoride, M. C. Cornell, Ian M. Littlewood Dec 1986

Negative Ion Drift Velocities In Mixtures Of Methane And Sulphur Hexafluoride, M. C. Cornell, Ian M. Littlewood

Physics Faculty Research & Creative Works

The velocities of negative ions drifting in mixtures of methane and Sulphur hexafluoride have been measured. Measurements were made as a function of gas composition, reduced electric field strength between 3 and 185 Td, and total gas pressure in the range 100-600 Torr at 300K. The data indicate that SF 6- (SF6) ions are the dominant ion in all of the gas mixtures studied. Extrapolation of the data using Blanc's Law was used to determine the velocity of Sulphur hexafluoride ions drifting in pure methane.

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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, we add a consideration of dispersive effects to our previous calculation of …

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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 …

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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 ions in …

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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 …

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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 …

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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.

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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.

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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.

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