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Physics Faculty Research & Creative Works

1992

Articles 1 - 11 of 11

Full-Text Articles in Physical Sciences and Mathematics

Calculation Of The Residual Resistivity And The Thermoelectric Power Of Sp Impurities In Silver, Thomas Vojta, Ingrid Mertig, Rudolf Zeller Dec 1992

Calculation Of The Residual Resistivity And The Thermoelectric Power Of Sp Impurities In Silver, Thomas Vojta, Ingrid Mertig, Rudolf Zeller

Physics Faculty Research & Creative Works

We present ab initio calculations for the residual resistivity and the thermopower of sp impurities in silver. The calculations are based on density-functional theory and the Korringa-Kohn-Rostoker Greens-function method. The linearized Boltzmann equation is solved by means of a Fermi-surface harmonic expansion to calculate the residual resistivity, taking into account the anisotropic electronic properties of the dilute alloy. The thermoelectric power was obtained from the energy dependence of the residual resistivity by means of Mott's formula. The results are in satisfying agreement with highly precise experimental results and confirm experimentally obtained deviations from a quadratic dependence on the valence ...


State-Selective Capture In Collisions Of Protons With Noble Gases, Michael Schulz, D. M. Blankenship, S. W. Bross, A. D. Gaus, Timothy Gay, W. T. Htwe, John T. Park, Jerry Peacher Oct 1992

State-Selective Capture In Collisions Of Protons With Noble Gases, Michael Schulz, D. M. Blankenship, S. W. Bross, A. D. Gaus, Timothy Gay, W. T. Htwe, John T. Park, Jerry Peacher

Physics Faculty Research & Creative Works

We have measured coincidences between neutral H atoms and Lyman-α photons for collisions between 50-keV protons and noble gases as a function of the projectile scattering angle. The coincidences are dominated by capture to the 2p state of the projectile. While the total cross sections depend strongly on the target, the shape of the angular distribution of the differential cross sections was found to depend only weakly on that parameter. The data indicate that electrons are captured predominantly from the outermost shell of the target atom for the collision systems studied here.


Absolute Triple Differential Cross Section For Ionization Of Helium Near Threshold, T. Rösel, Jochen Röder, Leslie S. Frost, Kurt Jung, Hendrik Ehrhardt, Stephenie J. Jones, Don H. Madison Sep 1992

Absolute Triple Differential Cross Section For Ionization Of Helium Near Threshold, T. Rösel, Jochen Röder, Leslie S. Frost, Kurt Jung, Hendrik Ehrhardt, Stephenie J. Jones, Don H. Madison

Physics Faculty Research & Creative Works

Absolute measurements with an accuracy of 22% and theoretical results in a distorted-wave Born approximation (DWBA) are reported for the triple-differential cross section for 26.6-eV electron-impact ionization of helium. An apparatus is used that allows all scattering angles to be independently varied for both coplanar and noncoplanar geometries. The measurements are compared with a DWBA calculation that includes exchange distortion in the calculation of the distorted waves, as well as with earlier calculations by Crothers [J. Phys. B 19, 463 (1986)] and Pan and Starace [Phys. Rev. Lett. 67, 185 (1991)]. Emphasis is placed on understanding the mechanisms for ...


Adiabatic Cooling Of Atoms By An Intense Standing Wave, Jian Chen, J. Greg Story, Jeffrey J. Tollett, Randall G. Hulet Aug 1992

Adiabatic Cooling Of Atoms By An Intense Standing Wave, Jian Chen, J. Greg Story, Jeffrey J. Tollett, Randall G. Hulet

Physics Faculty Research & Creative Works

Lithium atoms channeled in the nodes of an intense standing-wave radiation field are cooled to near the recoil limit by adibatically reducing the radiation intensity. The final momentum distribution has a narrow component with a root-mean-squared momentum of 2ħk in one dimension, where ħk is the momentum of a radiation-field photon. The data are compared with the results of a Monte Carlo simulation using a two-level atom model. This process may be useful for cooling and increasing the phase-space density of atoms confined in a magnetic trap.


Electron Production In Proton Collisions With Atoms And Molecules: Energy Distributions, M. Eugene Rudd, Yongki Kim, Don H. Madison, Timothy Gay Apr 1992

Electron Production In Proton Collisions With Atoms And Molecules: Energy Distributions, M. Eugene Rudd, Yongki Kim, Don H. Madison, Timothy Gay

Physics Faculty Research & Creative Works

All known data on the energy distribution of secondary electrons from collisions of protons with atoms and molecules have been reviewed and differential cross sections have been collected. The two experimental methods used to obtain the data are discussed and possible sources of error pointed out. Theoretical treatments are reviewed and several methods of checking the consistency of the data are discussed. Two semiempirical models have been chosen to represent the differential cross sections, and parameters for these models are given which fit the average of the experimental data, subject to known constraints. Recommended values of differential cross sections are ...


Angular-Differential Cross Sections For H(2p) Formation In Intermediate-Energy Proton-Helium Collisions, Denver G. Seely, S. W. Bross, A. D. Gaus, John Wm Edwards, David R. Schultz, Timothy Gay, John T. Park, Jerry Peacher Feb 1992

Angular-Differential Cross Sections For H(2p) Formation In Intermediate-Energy Proton-Helium Collisions, Denver G. Seely, S. W. Bross, A. D. Gaus, John Wm Edwards, David R. Schultz, Timothy Gay, John T. Park, Jerry Peacher

Physics Faculty Research & Creative Works

Angular-differential cross sections for charge transfer with simultaneous emission of a photon in collisions of protons with helium atoms have been measured. The incident proton energies were 25, 50, and 100 keV and the center-of-mass scattering angles were between 0 and 2.0 mrad. In the experiment, hydrogen atoms that scattered through an angle θ were detected in coincidence with photons emitted perpendicular to the scattering plane with a wavelength between 1140 and 1400 Å. Differential cross sections for capture into the 2p state of the hydrogen atom were determined from the variation in the coincidence signal with θ. The ...


Mössbauer And Neutron Diffraction Studies Of Y₂(Fe₁₋ₓMnₓ)₁₄B, Oran Allan Pringle, Gaya Kanishka Marasinghe, Gary J. Long, William Joseph James, William B. Yelon, Decai Xie, Fernande Grandjean Feb 1992

Mössbauer And Neutron Diffraction Studies Of Y₂(Fe₁₋ₓMnₓ)₁₄B, Oran Allan Pringle, Gaya Kanishka Marasinghe, Gary J. Long, William Joseph James, William B. Yelon, Decai Xie, Fernande Grandjean

Physics Faculty Research & Creative Works

We have used Mössbauer spectroscopy and neutron diffraction to study a series of Y2(Fe1-xMnx)1 4B samples in the composition range from x=0.0 to 0.4. Y 2(Fe0.6Mn0.4)14B is paramagnetic at both room temperature and 85 K. The iron quadrupole splitting in this paramagnetic compound allows us to place an upper limit on the quadrupole shift in the magnetic Y2(Fe1-xMnx) 14B alloys. Refinement of Y2(Fe 1-xMnx)14B neutron diffraction data have been used ...


Magnetic Properties Of A Novel Iron Carbide Film, Fe₇C₃X Formed In A Glow Discharge, Oran Allan Pringle, Gary J. Long, Fernande Grandjean, Jun L. Li, George C. Hadjipanayis, William Joseph James Jan 1992

Magnetic Properties Of A Novel Iron Carbide Film, Fe₇C₃X Formed In A Glow Discharge, Oran Allan Pringle, Gary J. Long, Fernande Grandjean, Jun L. Li, George C. Hadjipanayis, William Joseph James

Physics Faculty Research & Creative Works

No abstract provided.


Structural Studies Of Rare Earth-Iron Nitrides By Neutron Powder Diffraction, William B. Yelon, George C. Hadjipanayis Jan 1992

Structural Studies Of Rare Earth-Iron Nitrides By Neutron Powder Diffraction, William B. Yelon, George C. Hadjipanayis

Physics Faculty Research & Creative Works

No abstract provided.


Pressure And Temperature Effects On The Energy Of Formation For Silicon Clusters, Sung-Ho Suck Salk, Chen K. Lutrus, Donald E. Hagen, T. Oshiro, Steven M. Beck, Gary L. Loper Jan 1992

Pressure And Temperature Effects On The Energy Of Formation For Silicon Clusters, Sung-Ho Suck Salk, Chen K. Lutrus, Donald E. Hagen, T. Oshiro, Steven M. Beck, Gary L. Loper

Physics Faculty Research & Creative Works

At present most theoretical studies of atomic clusters are limited to their physical properties referred to 0 K. To the best of our knowledge, there exists no theoretical study of the simultaneous dependence of cluster formation and cluster-size distributions on both pressure and temperature. In the present work both pressure and temperature effects on the formation of silicon clusters are explored. A universal semiempirical formula is obtained to show a general trend in the variation of binding energy as a function of cluster size for both atomic and molecular clusters.


Monte Carlo Study Of A Simple Model Bulk-Ice-Ih System: P-T Melting Behavior At Constant Volume, K. Han, Barbara N. Hale Jan 1992

Monte Carlo Study Of A Simple Model Bulk-Ice-Ih System: P-T Melting Behavior At Constant Volume, K. Han, Barbara N. Hale

Physics Faculty Research & Creative Works

An NVT Metropolis Monte Carlo computer simulation is used to examine the P-T behavior of a constant-density model periodic ice-Ih sample near melting. The ice unit cell with density 0.904 g/cm3 consists of 192 rigid water molecules interacting via the revised central-force potentials (RSL2) of Stillinger and Rahman [J. Chem. Phys. 68, 666 (1978)] with a cutoff. Intramolecular parameters are determined from a minimization of the total potential energy of the ice-Ih structure at 0 K. In the P-T plot, emergence of the liquid-solid coexistence region is signaled by a change in sign of dP/dT (when ...