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Physics Faculty Research & Creative Works

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Articles 1471 - 1500 of 1959

Full-Text Articles in Physical Sciences and Mathematics

Comment On "Critical Behavior Of The Coulomb Glass", Thomas Vojta, Michael Schreiber Nov 1994

Comment On "Critical Behavior Of The Coulomb Glass", Thomas Vojta, Michael Schreiber

Physics Faculty Research & Creative Works

No abstract provided.

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Neutron Diffraction And Mössbauer Effect Study Of Several Nd₂Fe₁₇₋ₓalₓ Solid Solutions, William B. Yelon, H. Xie, Gary J. Long, Oran Allan Pringle, Fernande Grandjean, K. H. J. Buschow Nov 1994

Neutron Diffraction And Mössbauer Effect Study Of Several Nd₂Fe₁₇₋ₓalₓ Solid Solutions, William B. Yelon, H. Xie, Gary J. Long, Oran Allan Pringle, Fernande Grandjean, K. H. J. Buschow

Physics Faculty Research & Creative Works

Aluminum-substituted Nd2Fe17-xAlx solid solutions with x=2.30, 4.44, 6.13, 8.00, and 9.40 have been studied by neutron diffraction and Mössbauer spectroscopy. A Rietveld analysis of the neutron scattering indicates that the aluminum atoms have a high initial affinity for the 18h site, show a high affinity for the 6c site at high aluminum concentrations, and are absent from the 9d site at all aluminum concentrations. The Mössbauer spectra show a maximum in both the maximum and weighted average hyperfine field for x≅2. This indicates that the lattice expansion which occurs with aluminum substitution is sufficient, at …

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Quantum Electromagnetic Wormholes And Geometrical Description Of The Electric Charge, Marco Cavaglia Oct 1994

Quantum Electromagnetic Wormholes And Geometrical Description Of The Electric Charge, Marco Cavaglia

Physics Faculty Research & Creative Works

I present and discuss a class of solutions of the Wheeler-DeWitt equation describing wormholes generated by coupling of gravity to the electromagnetic field for Kantowski-Sachs and Bianchi type-I spacetimes. Since the electronic charge can be viewed as electric lines of force trapped in a finite region of spacetime, these solutions can be interpreted as the quantum corresponding to the Einstein-Rosen-Misner-Wheeler electromagnetic geon.

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Neutron-Diffraction And Mössbauer Effect Study Of The Tb₂Fe₁₇₋ₓalₓ Solid Solutions, Gaya Kanishka Marasinghe, Sanjay R. Mishra, Oran Allan Pringle, Gary J. Long, Zhong Bo Hu, William B. Yelon, Fernande Grandjean, D. P. Middleton, K. H. J. Buschow Sep 1994

Neutron-Diffraction And Mössbauer Effect Study Of The Tb₂Fe₁₇₋ₓalₓ Solid Solutions, Gaya Kanishka Marasinghe, Sanjay R. Mishra, Oran Allan Pringle, Gary J. Long, Zhong Bo Hu, William B. Yelon, Fernande Grandjean, D. P. Middleton, K. H. J. Buschow

Physics Faculty Research & Creative Works

The magnetic properties of a series of Tb2Fe17-xAlx solid solutions, with nominal x compositions of 0, 2, 3, 4, 5, 6, 7, and 8, have been studied by neutron diffraction and Mössbauer spectroscopy. Neutron-diffraction data indicate that the compounds all crystallize with the Th2Zn17 structure and that the aluminum atoms are excluded from the 9d site and show a distinct preference for the 6c site only for an aluminum content greater than 6. The unit-cell volume increases by approximately 1% per aluminum atom substituted in the formula unit. The magnetic moment per …

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Differential Double Excitation Cross Sections In Proton-Helium Collisions Studied By Energy-Loss Spectroscopy, W. T. Htwe, Tibor Vajnai, M. Barnhart, A. D. Gaus, Michael Schulz Sep 1994

Differential Double Excitation Cross Sections In Proton-Helium Collisions Studied By Energy-Loss Spectroscopy, W. T. Htwe, Tibor Vajnai, M. Barnhart, A. D. Gaus, Michael Schulz

Physics Faculty Research & Creative Works

We have measured ion energy-loss spectra for 150 keV proton-helium collisions as a function of the projectile scattering angle. From the data we obtained double excitation cross sections differential in the proton scattering angle as well as the ratios of both double excitation and single ionization to single excitation. In these ratios pronounced peak structures are observed at about 0.7 mrad. Two alternative interpretations of these peak structures are offered: They may be due to binary collisions between the projectile and the target electrons, or they could be a manifestation of an interference between different transition amplitudes leading to the …

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He²⁺-He Collisions: One-Electron Capture And Target-Ion Excitation, H. O. Folkerts, F. W. Bliek, L. Meng, Ronald E. Olson, R. Morgenstern, M. V. Von Hellermann, H. P. Summers, R. Hoekstra Aug 1994

He²⁺-He Collisions: One-Electron Capture And Target-Ion Excitation, H. O. Folkerts, F. W. Bliek, L. Meng, Ronald E. Olson, R. Morgenstern, M. V. Von Hellermann, H. P. Summers, R. Hoekstra

Physics Faculty Research & Creative Works

By means of photon emission spectroscopy the authors have studied state selective one-electron capture and target-ion excitation in collisions of He2+ with He. The collision energy has been varied from 1 to 75 keV amu-1. Four-body classical trajectory Monte Carlo calculations have been performed in the energy range of 50-300 keV amu-1. In the energy range where experiment and theory overlap there is in general fair agreement, although the l-distributions within a principal quantum shell exhibit differences. At energies below 50 keV amu-1 the experiments confirm the results of atomic orbital calculations, presented in an accompanying paper by Fritsch (1994). …

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Neutron-Diffraction Study Of Γ-Fe At High Pressure, Oran Allan Pringle, Rafael Calvo, R. E. Parra Aug 1994

Neutron-Diffraction Study Of Γ-Fe At High Pressure, Oran Allan Pringle, Rafael Calvo, R. E. Parra

Physics Faculty Research & Creative Works

Face-centered-cubic iron (γ-Fe) coherently precipitated in a single crystal of Cu has been studied by neutron diffraction at high pressures up to 0.9 GPa and in the temperature range from about 5 to 110 K. It undergoes antiferromagnetic ordering at 67±2 K at ambient pressure. The ordering temperature TN monotonically decreases with increasing pressure following a relation TN(K)=67-12.8p - 11.1p2 - 6.17p3, where p is in units of GPa. The change of TN in γ-Fe is discussed in terms of the volume change caused by pressurization or by alloying.

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Landau-Zener Treatment Of Intensity-Tuned Multiphoton Resonances Of Potassium, J. Greg Story, D. I. Duncan, Thomas F. Gallagher Aug 1994

Landau-Zener Treatment Of Intensity-Tuned Multiphoton Resonances Of Potassium, J. Greg Story, D. I. Duncan, Thomas F. Gallagher

Physics Faculty Research & Creative Works

When exposed to intense light of ~580 nm, the ground state of K shifts up in energy, passing through two photon resonances with Rydberg states, and finally crossing the two-photon ionization limit. We have used laser pulses of varying duration to study the nature of the population transfer from the ground state to the excited state due to the intensity-tuned resonances encountered during the rising edge of the pulse. A dynamic Floquet approach in which the resonances are treated as avoided crossings of the Floquet energy levels is used to model the population transfer and gives excellent agreement with the …

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Effect Of Carrier Gas Pressure On Condensation In A Supersonic Nozzle, Barbara Ellen Wyslouzil, Gerald Wilemski, M. G. Beals, Michael B. Frish Aug 1994

Effect Of Carrier Gas Pressure On Condensation In A Supersonic Nozzle, Barbara Ellen Wyslouzil, Gerald Wilemski, M. G. Beals, Michael B. Frish

Physics Faculty Research & Creative Works

Supersonic nozzle experiments were performed with a fixed water or ethanol vapor pressure and varying amounts of nitrogen to test the hypothesis that carrier gas pressure affects the onset of condensation. Such an effect might occur if nonisothermal nucleation were important under conditions of excess carrier gas in the atmospheric pressure range, as has been suggested by Ford and Clement [J. Phys. A 22, 4007 (1989)]. Although a small increase was observed in the condensation onset temperature as the stagnation pressure was reduced from 3 to 0.5 atm, these changes cannot be attributed to any nonisothermal effects. The pulsed nozzle …

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Differential Transfer Ionization Cross Sections For 50175-Kev Proton-Helium Collisions, S. W. Bross, S. M. Bonham, A. D. Gaus, Jerry Peacher, Tibor Vajnai, Michael Schulz, Horst Schmidt-Bocking Jul 1994

Differential Transfer Ionization Cross Sections For 50175-Kev Proton-Helium Collisions, S. W. Bross, S. M. Bonham, A. D. Gaus, Jerry Peacher, Tibor Vajnai, Michael Schulz, Horst Schmidt-Bocking

Physics Faculty Research & Creative Works

We have measured coincidences between neutralized projectiles and He recoil ions for 50175-keV proton-helium collisions. From the data we obtained transfer ionization (TI) cross sections differential in the projectile scattering angle. Laboratory scattering angles range from 0 to 2.0 mrad. The experimental method allowed separation of the postcollision charge states of the target atoms. The ratio of the cross sections for TI to the sum of TI and single capture, F, is presented as a function of projectile scattering angle. Comparison is made to previous measurements of this ratio where data is available. The differential cross sections are compared to …

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Critical Correlations And Susceptibilities In The Random-Field Spherical Model, Thomas Vojta, Michael Schreiber Jul 1994

Critical Correlations And Susceptibilities In The Random-Field Spherical Model, Thomas Vojta, Michael Schreiber

Physics Faculty Research & Creative Works

We investigate the behavior of the correlation function and the susceptibility of the random-field spherical model at the critical point. In particular we calculate the critical exponents η and η- describing the divergences of the susceptibility and its disconnected part, respectively. In the case of short-range interactions we obtain η=η-=0. For power-law interactions Uij~rij-σ we find η=1/2η-=D+2-σ (for D<σ

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A Magnetic, Neutron Diffraction, And Mössbauer Spectral Study Of Nd₂Fe₁₅Ga₂ And The Tb₂Fe₁₇₋ₓgaₓ Solid Solutions, Zhong Bo Hu, William B. Yelon, Sanjay R. Mishra, Gary J. Long, Oran Allan Pringle, D. P. Middleton, K. H. J. Buschow, Fernande Grandjean Jul 1994

A Magnetic, Neutron Diffraction, And Mössbauer Spectral Study Of Nd₂Fe₁₅Ga₂ And The Tb₂Fe₁₇₋ₓgaₓ Solid Solutions, Zhong Bo Hu, William B. Yelon, Sanjay R. Mishra, Gary J. Long, Oran Allan Pringle, D. P. Middleton, K. H. J. Buschow, Fernande Grandjean

Physics Faculty Research & Creative Works

An x-ray diffraction study of the substitution of gallium in Tb 2Fe17 to form the Tb2Fe17-xGax solid solutions indicates that the compounds adopt the rhombohedral Th2Zn17 structure. The unit cell volume and the a-axis lattice parameter increase linearly with increasing gallium content. The c-axis lattice parameter increases linearly from x=0 to 6 and then decreases between x=7 and 8. Magnetic studies show the Curie temperature increases by ~150° above that of Tb2Fe17 to reach a maximum between x=3 and 4, and then decreases with further increases in …

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Projectile And Electron Spectra Resulting From Positron-Argon Collisions, R. A. Sparrow, Ronald E. Olson Jun 1994

Projectile And Electron Spectra Resulting From Positron-Argon Collisions, R. A. Sparrow, Ronald E. Olson

Physics Faculty Research & Creative Works

A three-body classical trajectory Monte-Carlo calculation is used to evaluate the differential cross sections for the ejected electron, as well as the projectile scattering for 50, 100 and 150 eV e++Ar0 electron removal collisions. In the ionized eleciron spectra both the electron capture to the continuum (ecc) and binary peak structures are observed. The theoretical ecc peak is diffuse and shifted to lower energies than expected from simple arguments. The calculated double differential cross sections for electron ejection have been compared to experiment, When the experimental apparatus function of Moxom et al is used to convolute the theoretical spectra, good …

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State-Selective Electron Capture In He²⁺-H2 Collisions, L. Meng, Ronald E. Olson, H. O. Folkerts, R. Hoekstra Jun 1994

State-Selective Electron Capture In He²⁺-H2 Collisions, L. Meng, Ronald E. Olson, H. O. Folkerts, R. Hoekstra

Physics Faculty Research & Creative Works

A classical phase-space model of the hydrogen molecule which includes both electrons and nuclear centers is utilized to study state selective electron capture for collisions with alpha particles at intermediate impact energies (30-200 keV amu‑1), The calculations are performed within the framework of the classical trajectory Monte Carlo method. The direct one-electron transfer process and the transfer ionization reaction which becomes increasingly important at the higher impact energies are directly included in the cross section determinations. Photon emission spectroscopy experiments were conducted to obtain line emission cross sections for capture to the He+(np) states, n = 2-5, for energies from …

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Anisotropic Wormhole: Tunneling In Time And Space, Marco Cavaglia, Vittorio De Alfaro, Fernado De Felice Jun 1994

Anisotropic Wormhole: Tunneling In Time And Space, Marco Cavaglia, Vittorio De Alfaro, Fernado De Felice

Physics Faculty Research & Creative Works

We discuss the structure of a gravitational Euclidean instanton obtained through coupling of gravity to electromagnetism. This Euclidean solution can be interpreted as a tunneling to a hyperbolic space (baby universe) or alternatively as a static wormhole that joins two asymptotically flat spaces of a Reissner-Nordström type solution.

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Channel Closing In Multiphoton Ionization Of Mg, J. Greg Story, D. I. Duncan, Thomas F. Gallagher May 1994

Channel Closing In Multiphoton Ionization Of Mg, J. Greg Story, D. I. Duncan, Thomas F. Gallagher

Physics Faculty Research & Creative Works

Experimental data are presented showing the channel closing of four-photon ionization of Mg. It is shown that, for circularly polarized light, the ionization versus intensity spectra exhibit sharp breaks from the normal I4 intensity dependence at the critical intensity where the channel closing occurs. Above the critical intensity, the population of Rydberg states which survives the laser pulse is observed. The residual Rydberg population is found to be greatly reduced for linearly polarized light due to the relatively large probability of ionization of the low-angular-momentum Rydberg states. The data are in good agreement with a model which includes averaging …

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Spin-Resolved (E,2e) Coincidences For Heavy Rare-Gas Targets, Stephenie J. Jones, Don H. Madison, G. Friedrich Hanne Apr 1994

Spin-Resolved (E,2e) Coincidences For Heavy Rare-Gas Targets, Stephenie J. Jones, Don H. Madison, G. Friedrich Hanne

Physics Faculty Research & Creative Works

It has been well established that the Coulomb force alone can produce spin-dependent effects for electron-impact excitation of heavy rare-gas atoms if the incident electrons are spin polarized and the final J state of the atom is resolved. This effect has become known as the fine-structure effect. Here we demonstrate that the same type of effect may be expected for electron-impact ionization.

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Coherence Parameters For Electron Capture In H⁺ + He Collisions, C. J. Lundy, Ronald E. Olson, D. R. Schultzi, J. P. Pascale Mar 1994

Coherence Parameters For Electron Capture In H⁺ + He Collisions, C. J. Lundy, Ronald E. Olson, D. R. Schultzi, J. P. Pascale

Physics Faculty Research & Creative Works

The classical trajectory Monte Carlo method is used to calculate coherence parameters for electron capture to H(n = 2, 3 and 4) in 30 to 250 keV H+ + He collisions. The parameters evaluated are the x- and z-components of the dipole moment (D) and the z-component of the perihelion velocity of the captured electron (L x A). The calculated integral values are found to be in reasonable agreement with available experimental results. Components of the dipole moment and (L x A) were also evaluated as a function of projectile scattering angle. Here, rapid variations of the parameters are observed …

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Generalized Coulomb Gap In The Spherical Version Of A Lattice Model Of Disordered And Correlated Localized Particles, Thomas Vojta, Michael Schreiber Mar 1994

Generalized Coulomb Gap In The Spherical Version Of A Lattice Model Of Disordered And Correlated Localized Particles, Thomas Vojta, Michael Schreiber

Physics Faculty Research & Creative Works

We study the spherical version of a model of localized particles in a random potential which are subject to a power-law interaction Uij ~ rij-σ. In the case of a repulsive interaction with σ = 1 the model is identical to the spherical version of the Coulomb-glass model of disordered localized electrons. The use of continuous variables instead of discrete occupation numbers of the sites renders the model exactly solvable. Analytic results are obtained for the free energy and for the single-particle density of states (DOS) as an example for single-particle properties. The zero-temperature DOS shows …

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Correlated Two-Electron Wave Functions Of Any Symmetry, Christopher Bottcher, David R. Schultz, Don H. Madison Mar 1994

Correlated Two-Electron Wave Functions Of Any Symmetry, Christopher Bottcher, David R. Schultz, Don H. Madison

Physics Faculty Research & Creative Works

Using a procedure originally due to Hylleraas, a convenient expansion in coupled spherical harmonics which terminates in a very small number of terms is applied to the treatment of fully correlated two-electron wave functions of any symmetry (total angular momentum, parity, and spin). Coupled equations satisfied by these wave functions are derived which are well adapted to computation and which we discretize on a numerical lattice utilizing the basis-spline collocation method. Use of this method which relies on very flexible basis functions is intended to facilitate subsequently the consideration of time-dependent rearrangments such as autoionization, photoionization, and electron-impact excitation and …

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The Spatial Evolution Of Particles Diffusing In The Presence Of Randomly Placed Traps, David H. Dunlap, Randall A. Laviolette, Paul Ernest Parris Feb 1994

The Spatial Evolution Of Particles Diffusing In The Presence Of Randomly Placed Traps, David H. Dunlap, Randall A. Laviolette, Paul Ernest Parris

Physics Faculty Research & Creative Works

The evolution of a particle undergoing a continuous-time random walk in the presence of randomly placed imperfectly absorbing traps is studied. At long times, the spatial probability distribution becomes strongly localized in a sequence of trap-free regions. The subsequent intermittent transfer of the survival probability from small trap-free regions to larger trap-free regions is described as a time-directed variable range hopping among localized eigenstates in the Lifshitz tail. An asymptotic expression for the configurational average of the spatial distribution of surviving particles is obtained based on this description. The distribution is an exponential function of distance which expands superdiffusively, with …

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Differential Cross Sections For The Production Of Highly Charged Recoil Ions In 10 Mev F⁸⁺ → Ne Collisions, S. Lencinas, J. Ullrich, R. Domer, Ronald E. Olson, W. Wolff, H. Wolf, L. Spielberger, S. Hagmann, M. Horbatsch, C. L. Cocke, H. Schmidt-Bocking Jan 1994

Differential Cross Sections For The Production Of Highly Charged Recoil Ions In 10 Mev F⁸⁺ → Ne Collisions, S. Lencinas, J. Ullrich, R. Domer, Ronald E. Olson, W. Wolff, H. Wolf, L. Spielberger, S. Hagmann, M. Horbatsch, C. L. Cocke, H. Schmidt-Bocking

Physics Faculty Research & Creative Works

Using recoil-ion momentum spectroscopy (rims), we have measured differential cross sections for the production of highly charged Ne ions in collisions with 10 MeV Fs+ as a function of the recoil-ion transverse momentum and charge state. In addition, the outgoing projectiles were charge-state analyzed and detected in coincidence with the Ne recoil-ions. Thus, different reaction channels like direct ionization, single- and double-electron capture by the projectile could be separated. The recoil-ion transverse momentum p£ was determined with an accuracy comparable to a projectile scattering angle resolution of 2.5 x 10"5 rad. The experimental data are compared to results of classical …

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Low-Energy Electrons And Their Dynamical Correlation With Recoil Ions For Single Ionization Of Helium By Fast, Heavy-Ion Impact, R. Moshammer, J. Ullrich, M. Unverzagt, W. Schmidt, P. Jardin, Ronald E. Olson, R. Mann, R. Dörner, V. Mergel, U. Buck, H. Schmidt-Böcking Jan 1994

Low-Energy Electrons And Their Dynamical Correlation With Recoil Ions For Single Ionization Of Helium By Fast, Heavy-Ion Impact, R. Moshammer, J. Ullrich, M. Unverzagt, W. Schmidt, P. Jardin, Ronald E. Olson, R. Mann, R. Dörner, V. Mergel, U. Buck, H. Schmidt-Böcking

Physics Faculty Research & Creative Works

Helium single ionization by 3.6 me V/u Ni24+ impact was explored in a kinematically complete experiment by combining a high-resolution recoil-ion momentum spectrometer with a novel 4 low-energy electron analyzer. More than 90% of the "soft electrons" (Ee50 eV) are ejected in the forward direction in agreement with classical-trajectory Monte Carlo predictions. The electron longitudinal momentum is not balanced by the longitudinal momentum change of the projectile but mainly by the backwards recoiling He1+ ion. Energy losses of the 0.2 GeV projectiles as small as EPEP=3.4x10-7 are observable. © 1994 The American Physical Society.

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Superelastic And Inelastic He2++He State-Selective Electron Capture, V. D. Irby, Timothy James Gay, John T. Park, S. W. Bross, A. D. Gaus Jan 1994

Superelastic And Inelastic He2++He State-Selective Electron Capture, V. D. Irby, Timothy James Gay, John T. Park, S. W. Bross, A. D. Gaus

Physics Faculty Research & Creative Works

Experimental studies have been made of super elastic and inelastic collision processes involved in the state-selective single-electron capture reaction He2+3+He (1 1S)3He+(n)+He+(n), where n and n are the final principal quantum-number states of the collision products. Total cross sections have been measured at projectile energies of 15, 30, and 45 keV/u, by examining the energy loss-gain of the fast He+3 product ions, for the super elastic n=n=1 channel, and for the sum of the inelastic n=2, n=1 and n=1, n=2 states. Measurements are also presented for Ne and Ar targets. © 1994 The American Physical Society.

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Anisotropy Effects In Electron Capture By O6+ From Aligned Na*(3p), S. Schippers, A. R. Schlatmann, W. P. Wiersema, R. Hoekstra, R. Morgenstern, Ronald E. Olson, J. Pascale Jan 1994

Anisotropy Effects In Electron Capture By O6+ From Aligned Na*(3p), S. Schippers, A. R. Schlatmann, W. P. Wiersema, R. Hoekstra, R. Morgenstern, Ronald E. Olson, J. Pascale

Physics Faculty Research & Creative Works

We report results of one electron capture by highly charged ions colliding with laser excited aligned Na*(3p). The O vi(10→8) photon emission cross section after electron capture by the O6+ projectile is measured in the collision energy range 2-8 keV/amu. Effects of the Na*(3p) orbital alignment on the) O vi(10→8) emission are observed and found to be "reversed" as compared to the He2+→Na*(3p) collision system. Classical trajectory Monte Carlo calculations agree with the measured data and indicate that capture to states with n>10, contributing to the O vi(10→8) emission via cascades, plays a crucial role in the alignment cross …

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Clean Ultrahigh Vacuum System With Single-Structure Diffusion Pumps, Timothy J. Gay, M. C. Fritts, E. R. Mell, M. T. Sieger Jan 1994

Clean Ultrahigh Vacuum System With Single-Structure Diffusion Pumps, Timothy J. Gay, M. C. Fritts, E. R. Mell, M. T. Sieger

Physics Faculty Research & Creative Works

A practical example of the use of single-structure diffusion pumping groups in an experiment requiring hydrocarbon-free, ultrahigh vacuum is presented. With the use of proper vacuum procedures and careful foreline design and operation, but with no exotic hardware or liquid nitrogen, we have demonstrated that such a pump could provide vacuum that was "clean," i.e., which had no residual pump-oil contamination to a partial pressure below 10 -8 mbar. Their use is thus compatible, at least in peripheral vacuum chambers, with standard "UHV-surface science" processes. We discuss our vacuum system in detail, and present a review of the literature on …

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Electron-Electron Interaction In Projectile Ionization Investigated By High Resolution Recoil Ion Momentum Spectroscopy, R. Dörner, V. Mergel, R. Ali, U. Buck, C. L. Cocke, K. Froschauer, O. Jagutzki, S. Lencinas, W. E. Meyerhof, S. Nüttgens, Ronald E. Olson, H. Schmidt-Böcking, L. Spielberger, K. Tökesi, J. Ullrich Jan 1994

Electron-Electron Interaction In Projectile Ionization Investigated By High Resolution Recoil Ion Momentum Spectroscopy, R. Dörner, V. Mergel, R. Ali, U. Buck, C. L. Cocke, K. Froschauer, O. Jagutzki, S. Lencinas, W. E. Meyerhof, S. Nüttgens, Ronald E. Olson, H. Schmidt-Böcking, L. Spielberger, K. Tökesi, J. Ullrich

Physics Faculty Research & Creative Works

Contributions of the electron-electron and the nuclear-electron interactions to projectile electron loss in He+ on helium collisions have been clearly separated kinematically for the first time by measuring the longitudinal and transverse momenta of the recoiling target ion with precision of better than ±0.15 a.u. The longitudinal and transverse momentum distributions are in general agreement with two-center n-body classical trajectory Monte Carlo calculations. © 1994 The American Physical Society.

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Neutron-Diffraction And Mössbauer-Effect Studies Of Pr₂(Fe₁₋ₓmnₓ)₁₄B, Oran Allan Pringle, Jie Fu, Gary J. Long, William Joseph James, Decai Xie, William B. Yelon, Fernande Grandjean Dec 1993

Neutron-Diffraction And Mössbauer-Effect Studies Of Pr₂(Fe₁₋ₓmnₓ)₁₄B, Oran Allan Pringle, Jie Fu, Gary J. Long, William Joseph James, Decai Xie, William B. Yelon, Fernande Grandjean

Physics Faculty Research & Creative Works

A neutron-diffraction investigation of a series of Pr2(Fe 1-xMnx)14B samples, with x values of 0.00, 0.11, 0.22, 0.30, and 0.35, reveals a preference for the manganese to occupy the 8j2 transition-metal site,the transition-metal site with the largest Wigner-Seitz cell volume. Similar site occupancies have been reported previously for Er2(Fe1-xMnx) 14B and Y2(Fe1-xMnx) 14B. An analysis of the 295-K Mössbauer spectrum of Pr2(Fe0.89Mn0.11)14B indicates that the internal hyperfine fields on the …

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High-Voltage Variable Resistor For Ion Energy Spectroscopy, Timothy James Gay, V. D. Irby, S. P. Yallaly Dec 1993

High-Voltage Variable Resistor For Ion Energy Spectroscopy, Timothy James Gay, V. D. Irby, S. P. Yallaly

Physics Faculty Research & Creative Works

A high-voltage variable resistor was designed, built, and implemented to modify an ion-energy spectrometer for the study of ion-atom collisions in which the projectiles change charge. The resistor is remotely switchable from 0 to 2050 MΩ and has a voltage rating of 200 kV. The design criteria and the electrical and mechanical details of the apparatus are discussed. The design and construction of an ancillary device, comprising two precision resistive-divider voltmeters, are also discussed.

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Simulation Of Bulk Silicon Crystals And Si(111) Surfaces With Application To A Study Of Fluorine Coverage Of The Surfaces, Chen K. Lutrus, T. Oshiro, Donald E. Hagen, Sung-Ho Suck Salk Nov 1993

Simulation Of Bulk Silicon Crystals And Si(111) Surfaces With Application To A Study Of Fluorine Coverage Of The Surfaces, Chen K. Lutrus, T. Oshiro, Donald E. Hagen, Sung-Ho Suck Salk

Physics Faculty Research & Creative Works

Computational efficiency for the simulation of bulk crystals and surfaces is highly desirable. In an effort to study semiconductor crystals, we present a self-consistent treatment for the simulation of silicon crystals and surfaces based on the combination of a siligen model and a semiempirical Hamiltonian method. An artificial atom called siligen is introduced for the application of the semiempirical method to finite-size silicon clusters. The calculated average bond energies for the saturated silicon clusters are between 2.045 and 2.568 eV, compared to the measured value of 2.31 eV. A simulated bulk silicon surface using siligens is introduced in order to …

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