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Articles 34381 - 34410 of 36546

Full-Text Articles in Physical Sciences and Mathematics

Raman Studies Of Heavily Implanted, Dye-Laser-Annealed Gaas, H. D. Yao, A. Compaan, Edward Boyd Hale Jan 1985

Raman Studies Of Heavily Implanted, Dye-Laser-Annealed Gaas, H. D. Yao, A. Compaan, Edward Boyd Hale

Physics Faculty Research & Creative Works

Raman scattering is used to study the annealing behavior produced by 10 nsec, 565 nm dye laser pulses in high dose ion-implanted GaAs. Samples were prepared with Sn and Cd implantations of 2, 5, and 10 x 1015 cm2. The Raman spectra indicate that the threshold for epitaxial growth lies between 0.2 - 0.3 J cm2. Best carrier activation (∼ 2%), however, is achieved at ∼1.6 J cm2 for the Sn-implanted sample (n-type). For Cd implantation the electrical activation appears to be very high ({greater-than or approximate} 50%) for low pulse energies({less-than or approximate} 0.3 J cm2) but decreases for …

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Evidence For Uncorrelated Electron Capture And K-Shell Excitation In S13++He Collisions, J. A. Tanis, E. M. Bernstein, M. W. Clark, W. G. Graham, Robert H. Mcfarland, T. J. Morgan, B. M. Johnson, K. W. Jones, M. Meron Jan 1985

Evidence For Uncorrelated Electron Capture And K-Shell Excitation In S13++He Collisions, J. A. Tanis, E. M. Bernstein, M. W. Clark, W. G. Graham, Robert H. Mcfarland, T. J. Morgan, B. M. Johnson, K. W. Jones, M. Meron

Physics Faculty Research & Creative Works

Evidence is presented for a two-step process in ion-atom collisions in which two independent interactions occur in a single encounter. Measurements for 15200-MeVS13++He collisions indicate that uncorrelated projectile K-shell excitation and capture of a target electron occur in a single collision with one target atom. The results are in reasonable qualitative agreement with theoretical predictions of this two-step process. © 1985 The American Physical Society.

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Laser-Assisted Charge-Transfer Collisions: K++Na, Y. P. Hsu, M. Kimura, Ronald E. Olson Jan 1985

Laser-Assisted Charge-Transfer Collisions: K++Na, Y. P. Hsu, M. Kimura, Ronald E. Olson

Physics Faculty Research & Creative Works

A theory has been formulated to characterize charge-transfer collisions in the presence of an external laser field. The molecular-state-expansion method is used to describe the scattering process within the impact-parameter formalism. Electron translation factors are included in the molecular-state expansion so that the scattering wave function satisfies the correct boundary conditions. The theory is applied to the process K++NaK+Na+. In addition, we have made a detailed analysis of laser-assisted charge transfer for low-energy collisions. In this case, a Landau-Zener formula can be derived which shows that the cross section increases with decreasing incident energy. In general the laser coupling is …

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The Production Of Highly Unidirectional Lower-Hybrid Waves, R. Mcwilliams, M. Okubo, R. C. Platt, D. P. Sheehan Jan 1985

The Production Of Highly Unidirectional Lower-Hybrid Waves, R. Mcwilliams, M. Okubo, R. C. Platt, D. P. Sheehan

Physics and Biophysics: Faculty Scholarship

The development of a highly unidirectional lower-hybrid wave source would improve the electron current drive efficiency in tokamaks. Lower-hybrid waves launched from a phased wave array are shown to be reflected from a grid placed in a cold, low-density plasma. The antenna-grid combination results in highly unidirectional lower-hybrid waves.

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Computerized Scanning Auger Microprobe, T. J. Sommerer, Edward Boyd Hale Jan 1985

Computerized Scanning Auger Microprobe, T. J. Sommerer, Edward Boyd Hale

Physics Faculty Research & Creative Works

An Auger spectrometer has been automated using a microcomputer. Fundamental considerations in the design and choice of the computerized system are presented and should be of general interest. The spectrometer was a Physical Electronics Ind. model 545 scanning Auger microprobe. The microcomputer chosen was a Southwest Technical Products 6809 computer system. Hardware details are discussed with emphasis on the four computer-spectrometer interface boards. These boards are (1) Auger energy control board, which sets the Auger detection energy with its 16 bit digital-to-analog converter (DAC); (2) read Auger signal board, which reads the Auger signal intensity with its 12 bit analog-to-digital …

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Interaction Of Electric And Magnetic Charges: Addendum, I. Adawi Jan 1985

Interaction Of Electric And Magnetic Charges: Addendum, I. Adawi

Physics Faculty Research & Creative Works

The problem of a head-on collision between a spherically symmetric electric and magnetic charge is reconsidered. The assumption of the equality of the electric and magnetic forces made earlier is abandoned as it does not follow from the model. It is shown that the rotational angular momentum a charge acquires is determined by the amount of the angular momentum which the charge removes from the field by virtue of its extension. The interaction energy of each charge with the dipole it induces in the other charge is equal to the rotational energy of the charge itself. This results in simple …

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Electron Capture By Slow Alq+ Ions Colliding With Hydrogen, R. A. Phaneuf, M. Kimura, H. Sato, Ronald E. Olson Jan 1985

Electron Capture By Slow Alq+ Ions Colliding With Hydrogen, R. A. Phaneuf, M. Kimura, H. Sato, Ronald E. Olson

Physics Faculty Research & Creative Works

Total electron-capture cross sections have been measured for collisions of Alq+ (q=210) with H and H2 in the 20120-eV/amu energy range. The general trend of the cross sections for both H and H2 is an approximately linear increase with ionic charge state. The Al2++H and Al3++H systems were investigated theoretically using the molecular-orbital method with a pseudopotential to represent the Al3+ ion core. Coupled-channel calculations realize good agreement with experiment. An anomalously small cross section for Al2++H is attributed to the fact that of the 1 and 3 entrance channels, only the 1 …

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Low-Dimensional Chaotic Attractors For An Unstable, Inhomogeneously Broadened, Single-Mode Laser, Alfonso M. Albano, J. Abounadi, T. H. Chyba, C. E. Searle, S. Yong, R. S. Gioggia, N. B. Abraham Jan 1985

Low-Dimensional Chaotic Attractors For An Unstable, Inhomogeneously Broadened, Single-Mode Laser, Alfonso M. Albano, J. Abounadi, T. H. Chyba, C. E. Searle, S. Yong, R. S. Gioggia, N. B. Abraham

Physics Faculty Research and Scholarship

Quantitative characterization of the intensity pulsations from an inhomogeneously broadened laser confirm that observed irregular pulsing has its origins in deterministic chaos corresponding to motion on a strange attractor of low fractal dimensionality. The pointwise information dimension and the Grassberger-Procaccia K2 (estimators from below of the fractal dimensionality of the attractor and the Kolmogorov entropy, respectively) have been determined for digitized time series from parameter regions identified qualitatively by power spectra as representing periodic, period-doubled, quasi-periodic, and chaotic behavior. Some amount of chaos seems present for almost all operating conditions.

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Combined Translational-Rotational Jumps In Solid (Alpha)-Co And Co(,2), Shang-Bin Liu Jan 1985

Combined Translational-Rotational Jumps In Solid (Alpha)-Co And Co(,2), Shang-Bin Liu

Dissertations, Theses, and Masters Projects

Combined translational-rotational jumps in two orientationally ordered solids, (alpha)-CO and CO(,2), have been measured using C('13) NMR. In the Pa3 structure of these solids, a molecule which jumps to a neighboring (presumably vacant) site will reorient, due to the orientationally ordered structure.;The rates of translation and rotation have been measured independently by using different NMR techniques. The rotations were detected at high field (14.7 MHz) through the modulation of the chemical shift anisotropy; spin echoes and stimulated echoes were used. The translational jumps modulate the dipolar interactions and were studied at low fields (1.256 MHz) with line narrowing and Slichter-Ailion …

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Fourth Order Mass Splitting In The Bag Model, Timothy John Havens Jan 1985

Fourth Order Mass Splitting In The Bag Model, Timothy John Havens

Dissertations, Theses, and Masters Projects

The fourth order diagrams in the perturbative expansion of the hadron mass are calculated using the static spherical cavity approximation to the MIT bag model and Quantum Chromodynamics (QCD). Only terms with color matrix structure different than that of the second order diagrams are retained.;The fourth order mass splitting is found to be smaller than the second order splitting by a factor of three or more.

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First Principles Structure Calculations Using The General Potential Lapw Method, Su-Huai Wei Jan 1985

First Principles Structure Calculations Using The General Potential Lapw Method, Su-Huai Wei

Dissertations, Theses, and Masters Projects

We have developed a completely general first principles self-consistent full-potential linearized-augmented-plane-wave (LAPW) method program within the density functional formalism to calculate electronic band structure, total energy, pressure and other quantities. No symmetry assumptions are used for the crystal structure. Shape unrestricted charge densities and potentials are calculated inside muffin-tin (MT) spheres as well as in the interstitial regions. All contributions to the Hamiltonian matrix elements are completely taken into account. The core states are treated fully relativistically using the spherical part of the potential only. Scalar relativistic effects are included for the band-states, and spin-orbit coupling is included using a …

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Analysis Of Solar Collector Surface To Air Flow Thermal Transfer Using Solid State Sensors And Microcomputer Interfacing, Rudolph J. Eichenberger Jan 1985

Analysis Of Solar Collector Surface To Air Flow Thermal Transfer Using Solid State Sensors And Microcomputer Interfacing, Rudolph J. Eichenberger

Journal of the Arkansas Academy of Science

No abstract provided.

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Quantum Electrodynamics Based On Self-Energy: Lamb Shift And Spontaneous Emission Without Field Quantization, A. O. Barut, Jean F. Van Huele Jan 1985

Quantum Electrodynamics Based On Self-Energy: Lamb Shift And Spontaneous Emission Without Field Quantization, A. O. Barut, Jean F. Van Huele

Faculty Publications

The theory of radiative processes in quantum theory is formulated on the basis of self-energy, in analogy to classical radiation theory, and is explicitly carried out for the calculation of the Lamb shift and spontaneous emission.

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Gravitational Twins Revisited, Br Holstein Dec 1984

Gravitational Twins Revisited, Br Holstein

Barry R Holstein

No abstract provided.

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Possible Weak Interaction Experiments With Polarized He-3, Br Holstein Dec 1984

Possible Weak Interaction Experiments With Polarized He-3, Br Holstein

Barry R Holstein

No abstract provided.

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Forced Harmonic-Oscillator - A Path Integral Approach, Br Holstein Dec 1984

Forced Harmonic-Oscillator - A Path Integral Approach, Br Holstein

Barry R Holstein

The problem of the harmonic oscillator driven by an external force is explored using path integral techniques. The qualitative features of the solution are demonstrated.

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Semileptonic Hyperon Decay - A Problem For Chiral Perturbation-Theory, Jf Donoghue, Br Holstein Dec 1984

Semileptonic Hyperon Decay - A Problem For Chiral Perturbation-Theory, Jf Donoghue, Br Holstein

Barry R Holstein

We study the recently computed mk2lnm2k corrections to hyperton beta decay found in chiral perturbation theory. The inclusion of these effects is not compatible with the high precision hyperon data, yielding a fit much inferior to the standard assumption of SU(3) invariance. This incompatibility of data and theory is a problem for the application of chiral perturbation theory.

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Viscosity Measurements In Dilute Helium-3-Helium-4 Mixtures, George Schmiedeshoff Dec 1984

Viscosity Measurements In Dilute Helium-3-Helium-4 Mixtures, George Schmiedeshoff

George Schmiedeshoff

We have measured the viscosity of a dilute mixture of 3He in 4He at temperatures from 5 to 100 mK and in magnetic fields of 0.35, 2.01 and 8.76 T using a vibrating wire viscometer. Subject to our choice of calibration function, the data at 0.35 T is in good agreement with theory. Due to an interaction of our viscometer with the magnetic field the motion of the wire at 2.01 and 8.76 T is not understood; however, the 2.01 T data can be brought into agreement with the 0.35 T data by adjusting a geometrical constant. An increase in …

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Segregation Of Copper To The Surface Of Copper-Nickel Alloys, Peter A. Dowben Dec 1984

Segregation Of Copper To The Surface Of Copper-Nickel Alloys, Peter A. Dowben

Peter Dowben Publications

Copper segregation profiles at the surfaces of Cu17Ni83(111) and Cu17Ni83(100) have been calculated by a semiempirical procedure based upon previously published data. These profiles indicate that surface enrichment of copper is not limited only to the topmost layer but occurs for several layers away from the surface as well. A comparison of the calculated segregation profiles based upon the experimental results for the (100) and (111) surfaces of Cu17Ni83 do not agree with predictions based upon thermodynamic models of segregation.

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Lattice Dynamics Of Mixed Crystals Of Tise2, Roger D. Kirby, G.A. Freund, Jr. Dec 1984

Lattice Dynamics Of Mixed Crystals Of Tise2, Roger D. Kirby, G.A. Freund, Jr.

Roger Kirby Publications

We present the results of Raman scattering measurements on the mixed-crystal systems TiSe2-xSx, TiSe2-xTex, ZrxTi1-x Se2. At room temperature with the pure compounds all have crystal structures represented by the D3d(P3̃m1) space group with three atoms per unit cell. There are two Raman-active k=0 phonons, one of A1gˉ symmetry and one of Eg symmetry. In the TiSe2-xTex system, the A1gˉ and Egˉ phonon frequencies shift smoothly with concentration, and the shifts are well described by a simple virtual-crystal …

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A Model For Orientation Effects In Electron‐Transfer Reactions, Paul Siders, Robert J. Cave, R.A. Marcus Dec 1984

A Model For Orientation Effects In Electron‐Transfer Reactions, Paul Siders, Robert J. Cave, R.A. Marcus

All HMC Faculty Publications and Research

A method for solving the single‐particle Schrödinger equation with an oblate spheroidal potential of finite depth is presented. The wave functions are then used to calculate the matrix element TBA which appears in theories of nonadiabatic electron transfer. The results illustrate the effects of mutual orientation and separation of the two centers on TBA. Trends in these results are discussed in terms of geometrical and nodal structure effects. Analytical expressions related to TBA for states of spherical wells are presented and used to analyze the nodal structure effects for TBA for the spheroidal wells.

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(Super)Conformal Symmetry Breaking, Andrew Strominger, V. Parameswaran Nair Dec 1984

(Super)Conformal Symmetry Breaking, Andrew Strominger, V. Parameswaran Nair

Publications and Research

We argue that the only consistent way to break conformal invariance in a quantum theory of gravity is spontaneously in a finite locally conformal supersymmetric theory. This generically occurs whenever scalar fields are present. Covariant surface-integral expressions for the super-charge and four-momentum in terms of asymptotically constant spinor fields are derived. These are used to discuss stability and other aspects of the theory.

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Renormalization Of The Energy-Momentum Tensor And The Validity Of The Equivalence Principle At Finite Temperature, Jf Donoghue, Br Holstein, Rw Robinett Dec 1984

Renormalization Of The Energy-Momentum Tensor And The Validity Of The Equivalence Principle At Finite Temperature, Jf Donoghue, Br Holstein, Rw Robinett

Barry R Holstein

Using the techniques of finite-temperature field theory we renormalize the electromagnetic and gravitational couplings of an electron which is immersed in a heat bath with T

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Increased Optical Damage Resistance In Lithium Niobate, D. A. Bryan, Robert Gerson, H. E. Tomaschke Dec 1984

Increased Optical Damage Resistance In Lithium Niobate, D. A. Bryan, Robert Gerson, H. E. Tomaschke

Physics Faculty Research & Creative Works

We have confirmed greatly improved resistance to photorefractive damage in compositions of lithium niobate containing 4.5 at. % MgO or more. Holographic diffraction measurements of photorefraction demonstrated that the improved performance is due to a hundredfold increase in the photoconductivity, rather than a decrease in the Glass current. The diffraction efficiency shows an Arrhenius dependence on temperature, with an activation energy of 0.1 eV for the damage-resistant compositions, compared with 0.5 eV for undoped or low-magnesium compositions. The damage-resistant compositions are distinguished by a 2.83-μm absorption line instead of the usual 2.87-μm line due to the OH-stretch vibration.

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Yellow Giants In Young Clusters. Ii. A Comparison Of Observation With Theory, Edward G. Schmidt Dec 1984

Yellow Giants In Young Clusters. Ii. A Comparison Of Observation With Theory, Edward G. Schmidt

Edward Schmidt Publications

Luminosities and effective temperatures are calculated for 17 nonvariable yellow giants and supergiants and nine Cepheids which were previously identified as members of open clusters. These stars are identified as being in the helium core burning stage of evolution. A comparison with the predictions of pulsation theory does not show any disagreement. On the other hand, several comparisons with the theory of stellar evolution produce discrepancies which suggest that effects neglected in the calculations may play an important role in the evolution of these stars.

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A Study Of Integral Equations For Computing Radial Distribution Functions, Robert C. Scherzer Dec 1984

A Study Of Integral Equations For Computing Radial Distribution Functions, Robert C. Scherzer

Masters Theses

The use of integral equations to find radial distribution functions for computing thermodynamic properties is examined. The system considered is a simple classical fluid with interactions according to the Lennard-Jones (6-12) pair potential function. Two parametric integral equations (C and T) are studied in detail. Derivation of equation T and a power series solution are given. Computer solutions at several different temperatures, densities, and parameter values are obtained. Comparisons are made betv/een these results and results from integral equation N, PY, and HNC, and results from Monte Carlo, molecular dynamics, and power series methods. Equations C and N are found …

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Threshold Effect In Mg-Doped Lithium Niobate, K. L. Sweeney, L. E. Halliburton, D. A. Bryan, R. R. Rice, Robert Gerson, H. E. Tomaschke Dec 1984

Threshold Effect In Mg-Doped Lithium Niobate, K. L. Sweeney, L. E. Halliburton, D. A. Bryan, R. R. Rice, Robert Gerson, H. E. Tomaschke

Physics Faculty Research & Creative Works

Optical absorption spectra were obtained after reducing (i.e., vacuum annealing) a series of LiNbO3 crystals grown from melts having various Mg concentrations and Li/Nb ratios. A band peaking at 500 nm, and assigned to oxygen vacancies containing two electrons, was the only absorption present in one set of crystals following reduction. In contrast, two overlapping bands peaking near 1200 and 760 nm were present in the other set of crystals immediately after the reduction. The 1200-nm band is assigned to a previously unreported electron trap and the 760-nm band to oxygen vacancies containing only one electron. These data are interpreted …

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Microprocessor-Based Pressure Controller, E. Redd, John T. Park Dec 1984

Microprocessor-Based Pressure Controller, E. Redd, John T. Park

Physics Faculty Research & Creative Works

A device for automatic control of pressure in an ion-atom scattering experiment has been constructed. The system was modeled to achieve the minimum time for transition from one pressure to another. The pressure controller "learns" the system response and iterates the parameters used in "profiling" the valve voltage to reduce the transition time. The device has been used with two different scattering chambers and has worked well with both.

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Fast Method For Calculating The Self-Consistent Electronic Structure Of Random Alloys, Duane D. Johnson, F. J. Pinski, G. M. Stocks Nov 1984

Fast Method For Calculating The Self-Consistent Electronic Structure Of Random Alloys, Duane D. Johnson, F. J. Pinski, G. M. Stocks

Duane D. Johnson

We describe a computationally efficient method for performing self-consistent-field calculations of the electronic structure of random solid-solution alloys within the multiple-scattering coherent-potential-approximation formalism (KKR-CPA). We utilize a cluster method for solving the KKR-CPA equations and integrate along a contour in the complex-energy plane to reconstruct the single-site electronic densities.

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Model Calculations Of The Micrometer To Millimeter Intrinsic Absorption For Simple Ceramics, John R. Hardy, P. J. Edwardson, J. A. O'Gara Nov 1984

Model Calculations Of The Micrometer To Millimeter Intrinsic Absorption For Simple Ceramics, John R. Hardy, P. J. Edwardson, J. A. O'Gara

John R. Hardy Papers

A systematic study has been made of the strength of the intrinsic absorption, or loss, for millimeter to micrometer electromagnetic radiation propagating in simple ceramic materials. This study employed a number of model diatomic systems whose simplicity enabled the basic two-phonon decay process, responsible for this intrinsic loss, to be computed with precision, even at the lowest frequencies, on a dedicated microcomputer. It was found that, at least at low frequencies, the loss was a relatively structureless universal function of the atomic mass ratio, in general agreement with earlier results for real alkali halides. In particular, it was found that, …

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