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Physics Faculty Research & Creative Works

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Articles 1291 - 1320 of 1762

Full-Text Articles in Physical Sciences and Mathematics

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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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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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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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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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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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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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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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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Neutron-Diffraction And Mössbauer Effect Study Of The Preferential Silicon Site Occupation And Magnetic Structure Of Nd₂Fe₁₄₋ₓsiₓb, Gaya Kanishka Marasinghe, Oran Allan Pringle, Gary J. Long, William Joseph James, Dianne J. Xiao, J. L. Li, William B. Yelon, Fernande Grandjean Nov 1993

Neutron-Diffraction And Mössbauer Effect Study Of The Preferential Silicon Site Occupation And Magnetic Structure Of Nd₂Fe₁₄₋ₓsiₓb, Gaya Kanishka Marasinghe, Oran Allan Pringle, Gary J. Long, William Joseph James, Dianne J. Xiao, J. L. Li, William B. Yelon, Fernande Grandjean

Physics Faculty Research & Creative Works

A neutron-diffraction study of Nd2Fe14-xSixB has shown that silicon preferentially occupies the 4c site in the transition-metal sublattice in Nd2Fe14B. Silicon also exhibits a moderate preference for the 8j1 site, is almost excluded from the 16k2 site, and avoids the 16k1, 8j2, and 4e sites. The silicon site occupancy is correlated with a preference for a silicon atom to have rare-earth atoms in its coordination environment. The Mössbauer spectra of Nd2Fe14-xSixB have been fit with a model which …

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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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Large-Cell Renormalization-Group Approach To Long-Range Hopping On Energetically Disordered Lattices, B. D. Bookout, Paul Ernest Parris Nov 1993

Large-Cell Renormalization-Group Approach To Long-Range Hopping On Energetically Disordered Lattices, B. D. Bookout, Paul Ernest Parris

Physics Faculty Research & Creative Works

We describe an approach for computing the conductivity associated with long-range hopping on energetically disordered lattices. Using a numerically exact supercell procedure we compute the distribution ρL(γ) of block conductances γL associated with conducting cubes of edge length L that are randomly chosen from the disordered system of interest. This distribution of block conductances is then used in a self-consistent numerical calculation to obtain the renormalized bulk conductivity. The approach displays a surprisingly fast approach to the infinite-system limit, allowing finite-size effects to be minimized. In this paper we use this approach to study transport in a series of binary …

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Spatially Resolved Transitions To Autoionizing States, J. Greg Story, D. I. Duncan, Thomas F. Gallagher Nov 1993

Spatially Resolved Transitions To Autoionizing States, J. Greg Story, D. I. Duncan, Thomas F. Gallagher

Physics Faculty Research & Creative Works

We have observed transitions to autoionizing states in Mg using two short optical pulses. Mg atoms are initially prepared in a high lying Rydberg wave packet with the first ps laser. A second ps laser is then used to excite the inner electron, producing an autoionizing state. The dependence of the transition probability on the delay between the two lasers shows that when the second laser is tuned away from the ionic resonance, the inner electron can make a transition only when the Rydberg wave packet is near the core.

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Differential Cross Sections For Single And Double Ionization Of Helium By Protons And Antiprotons, L. Meng, Ronald E. Olson, R. Dömer, J. Ullrich, H. Schmidt-Bocking Oct 1993

Differential Cross Sections For Single And Double Ionization Of Helium By Protons And Antiprotons, L. Meng, Ronald E. Olson, R. Dömer, J. Ullrich, H. Schmidt-Bocking

Physics Faculty Research & Creative Works

Theoretical and experimental cross sections are presented for single and double ionization of He differential in the projectile scattering angle and the transverse energy of the outgoing recoil ion. A dynamical four-body classical trajectory Monte Carlo method that includes radial electron correlation is utilized to calculate total and differential cross sections for 300 and 500 keV protons and antiprotons in impact collisions with He. The azimuthal emission characteristics of electrons, recoil ion and projectile relative to each other are analyzed to provide detailed information on the dynamical differences between single and double ionization and between proton and antiproton impact. © …

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Energy-Projected Effective-Medium Theory Of Long-Range Hopping On Energetically Disordered Lattices, Paul Ernest Parris, B. D. Bookout Oct 1993

Energy-Projected Effective-Medium Theory Of Long-Range Hopping On Energetically Disordered Lattices, Paul Ernest Parris, B. D. Bookout

Physics Faculty Research & Creative Works

We introduce energy-projected equations of motion to treat the diffusive transport of charge carriers that undergo long-range (i.e., greater than nearest-neighbor) hopping among the sites of an energetically disordered lattice. This approach leads naturally to an energy-projected effective-medium theory for treating such systems. Exact expressions for the diffusion constant associated with the energy-projected effective medium theory are obtained. Using the formalism in conjunction with what is normally a rather poor approximation, i.e., the virtual-crystal approximation, we are able to obtain the exact diffusion constant for the long-range symmetric-random-well problem. Effective-medium calculations and numerical simulations are presented for nearest-neighbor and long-range …

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Quantal And Classical Correspondence Of Double Scattering, Jianyi Wang, Ronald E. Olson, Karoly Tokési Sep 1993

Quantal And Classical Correspondence Of Double Scattering, Jianyi Wang, Ronald E. Olson, Karoly Tokési

Physics Faculty Research & Creative Works

Electron emission from atom-atom collisions is analyzed within the framework, of both quantal and classical dynamics. We examine the effect of explicit electron-electron (e-e) interactions on the ejected electron spectra in hard collisions involving simultaneous excitation and ionization in the collision of two structured atoms. A double scattering sequence represented by a second order Bom approximation has been shown to give a dominant contribution over the single scattering to projectile ionization. A classical simulation confirms the double scattering process is analogous to the Thomas two-step capture mechanism. We find good agreement between quantal and classical calculations, showing the convergence of …

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Transition From Quantum To Quasi-Classical Behaviour Of The Binary Encounter Peak In Collisions Of 0.6 To 3.6 Mev Amu“¹ I23+ And Xe21+ With He And Ar, J. L. Shinpaughfg, W. Wolff, H. E. Wolff, U. Ramm, O. Jagutzki, H. Schmidt-Böcking, J. Wangt, Ronald E. Olson Sep 1993

Transition From Quantum To Quasi-Classical Behaviour Of The Binary Encounter Peak In Collisions Of 0.6 To 3.6 Mev Amu“¹ I23+ And Xe21+ With He And Ar, J. L. Shinpaughfg, W. Wolff, H. E. Wolff, U. Ramm, O. Jagutzki, H. Schmidt-Böcking, J. Wangt, Ronald E. Olson

Physics Faculty Research & Creative Works

Double differentia] cross sections are reported for the production of binary encounter electrons in collisions of 0.6 MeV amu-1 I23+ and 1.4, 2.4, and 3.6 MeV amu-1 Xe21+ projectiles incident on He and Ar targets. Electron energy spectra were measured between 0: and 45: in the case of the two lower projectile energies, and between 17.5° and 60- for the two higher projectile energies. The data are compared with quantum mechanical impulse approximation and classical trajectory Monte Carlo calculations. While the quantum model calculation predicts a rapid disappearance of diffraction effects in the binary encounter peak …

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Temperature And Supersaturation Dependent Nucleation Rates Of Heterogeneous Water By Molecular Cluster Model Calculation, Chen K. Lutrus, Donald E. Hagen, Sung-Ho Suck Salk Aug 1993

Temperature And Supersaturation Dependent Nucleation Rates Of Heterogeneous Water By Molecular Cluster Model Calculation, Chen K. Lutrus, Donald E. Hagen, Sung-Ho Suck Salk

Physics Faculty Research & Creative Works

A statistical mechanical method to evaluate the energy of formation of water clusters attached to a foreign particle surface is described, with the binding energy being evaluated on a molecular level, using semiempirical modified neglect of diatomic overlap (MNDO) theory. The model is applied to water nucleation on a silicon oxide surface. The binding energy contribution, which represents the energy of formation at T=0 K, is found to slightly (but not negligibly in the thermal sense) increase with the number of hydrogen bonds between the water cluster and the condensation nucleus whose surface is made of silicon oxide. An analytic …

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Connection Between Superelastic And Inelastic Electron-Atom Collisions Involving Polarized Collision Partners, Klaus Bartschat, Don H. Madison Jul 1993

Connection Between Superelastic And Inelastic Electron-Atom Collisions Involving Polarized Collision Partners, Klaus Bartschat, Don H. Madison

Physics Faculty Research & Creative Works

It is shown how the results of a recent experiment by Jiang, Zuo, Vuković, and Bederson [Phys. Rev. Lett. 68, 915 (1992)], who investigated low-energy electron scattering from laser-excited polarized sodium atoms in the initial (3p) 2P°3/2 (F=3, MF=3) state, can be related to the inelastic 3S→3P transition involving initially unpolarized electron and atom beams. Hence, this method can provide an independent check of the traditional electron-scattering experiment with unpolarized beams.

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Long-Range Random Walks On Energetically Disordered Lattices, B. D. Bookout, Paul Ernest Parris Jul 1993

Long-Range Random Walks On Energetically Disordered Lattices, B. D. Bookout, Paul Ernest Parris

Physics Faculty Research & Creative Works

Although the master equation describing long-range random walks on an energetically disordered lattice is governed by a nonsymmetric transition matrix W, it may be mapped through a similarity transform onto an imaginary-time Schrödinger equation governed by a Hermitian (Hamiltonian) operator H0 having a nondegenerate ground state. Under this mapping the diffusion constant D can be expressed in terms of the exact ground state energy of operators that are infinitesimally perturbed from H0.

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Three-Body Distorted-Wave Born Approximation For Electron-Atom Ionization, Stephenie J. Jones, Don H. Madison, Achim Franz, P. L. Altick Jul 1993

Three-Body Distorted-Wave Born Approximation For Electron-Atom Ionization, Stephenie J. Jones, Don H. Madison, Achim Franz, P. L. Altick

Physics Faculty Research & Creative Works

We report a theoretical calculation for electron-impact ionization of atoms that includes short-range electron-atom effects for wave functions that satisfy the exact asymptotic boundary conditions. Results of this theory, which we label as the three-body distorted-wave Born approximation, are compared with experiment and other theories for ionization of hydrogen and helium for incident-electron energies from 4 to 18 times the ionization energy.

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Temporal Effects In Multiphoton Ionization Of Lithium, J. Greg Story, Thomas F. Gallagher Jun 1993

Temporal Effects In Multiphoton Ionization Of Lithium, J. Greg Story, Thomas F. Gallagher

Physics Faculty Research & Creative Works

The temporal effects of multiphoton ionization are investigated using a two-color method which determines both the time and intensity at which the process occurs. We show that the total ionization efficiency depends strongly on the time at which an atom makes a transition to an excited state during an intense laser pulse. This result clearly shows that the ac-Stark-shifted bound-state resonances not only enhance the cross section for photoionization, but that the excited bound states provide temporary storage states for the atomic population during the photoionization process.

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A Neutron Diffraction And Mössbauer Effect Study Of The Magnetic Structure Of Y₂(Fe₁₋ₓmnₓ)₁₄B, Gaya Kanishka Marasinghe, Oran Allan Pringle, Gary J. Long, William Joseph James, William B. Yelon, Fernande Grandjean May 1993

A Neutron Diffraction And Mössbauer Effect Study Of The Magnetic Structure Of Y₂(Fe₁₋ₓmnₓ)₁₄B, Gaya Kanishka Marasinghe, Oran Allan Pringle, Gary J. Long, William Joseph James, William B. Yelon, Fernande Grandjean

Physics Faculty Research & Creative Works

The magnetic structures of a series of Y2(Fe 1-xMnx)14B samples, with x equal to 0.03, 0.10, 0.25, and 0.37, have been studied by powder neutron diffraction and Mössbauer spectroscopy. Y2(Fe0.97Mn 0.03)14B and Y2(Fe0.9Mn 0.1)14B are ferromagnetic at both 295 and 85 K, Y 2(Fe0.63Mn0.37)14B is paramagnetic at both 295 and 85 K, whereas Y2(Fe0.75Mn 0.25)14B is paramagnetic at 295 K and is partially ordered at …

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Resonant Inhibition Of Multiphoton Ionization, J. Greg Story, D. I. Duncan, Thomas F. Gallagher May 1993

Resonant Inhibition Of Multiphoton Ionization, 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. Using laser pulses of 0.5 to 13 ps duration, we have shown experimentally that ionization occurs for short pulses, but for long pulses the population is diverted into the Rydberg states where some population survives the peak intensity of the pulse, in excellent agreement with a dynamic Floquet model.

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120kev Ar8+-Li Collisions Studied By Near Uv And Visible Photon Spectroscopy, E. Jacquet, P. Boduch, M. Chantepie, M. Druetta, D. Hennecart, X. Husson, D. Lecler, Ronald E. Olson, J. Pascale, N. Stolterfoht, M. Wilson May 1993

120kev Ar8+-Li Collisions Studied By Near Uv And Visible Photon Spectroscopy, E. Jacquet, P. Boduch, M. Chantepie, M. Druetta, D. Hennecart, X. Husson, D. Lecler, Ronald E. Olson, J. Pascale, N. Stolterfoht, M. Wilson

Physics Faculty Research & Creative Works

A spectroscopic analysis of light emitted in the 200-600 nm wavelength range by Ar7+, Ar6+ and Ar5+ ions after charge exchange in 120keV Ar8+-Li collisions is performed. Transitions with Δn = 1 and Δn = 2 for n = 8, 9, 10 and 11 states of Ar8 following single electron capture are identified and the production cross sections for n = 8 and n = 9 are deduced from emission cross sections and compared with those calculated by the three-body classical trajectory Monte-Carlo method. Lines due to double capture process were observed and identified …

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Monte Carlo Simulations Of Water-Ice Layers On A Model Silver Iodide Substrate: A Comparison With Bulk Ice Systems, James H. Taylor, Barbara N. Hale Apr 1993

Monte Carlo Simulations Of Water-Ice Layers On A Model Silver Iodide Substrate: A Comparison With Bulk Ice Systems, James H. Taylor, Barbara N. Hale

Physics Faculty Research & Creative Works

Two water layers adsorbed on a model silver iodide basal face are simulated at nine temperatures from 150 to 425 K using Monte Carlo methods. The periodic unit cell of 96 internally rigid water molecules (interacting via the revised central-force potentials) couples to the rigid-substrate atoms via effective pair potentials with Lennard-Jones short-range and Coulomb long-range terms. The distribution of molecules perpendicular to the substrate exhibits layering, and individual layer structure factors, dipole moments, and "pseudodiffusion" coefficients are calculated. A complex temperature dependence with the two layers taking on different solidlike, quasiliquid, or liquid properties at the same T is …

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Residual-Ion Orientation After Autoionization, G. T. Xu, Xiao Wang, J. Greg Story, William E. Cooke Apr 1993

Residual-Ion Orientation After Autoionization, G. T. Xu, Xiao Wang, J. Greg Story, William E. Cooke

Physics Faculty Research & Creative Works

We have measured the relative population in the two mj states of barium 6p1/2 ions produced by the autoionization of (6p3/2nd)J=MJ=3 states by detecting the helicity of the emitted fluorescence. These populations can be related to the relative branching ratio into the 6p1/2εd5/2 and 6p1/2εg7/2 continuum channels. Rydberg states with n=16-23 have similar branching ratios, producing approximately six times as much 6p1/2εd5/2 population as 6p1/2εg7/2 population.

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Evolution Of Atomic Motion In An Intense Standing Wave, Jian Chen, J. Greg Story, Randall G. Hulet Mar 1993

Evolution Of Atomic Motion In An Intense Standing Wave, Jian Chen, J. Greg Story, Randall G. Hulet

Physics Faculty Research & Creative Works

We have investigated the effect of the dipole force and its fluctuation on the motion of Li atoms in an intense, one-dimensional, near-resonant standing light wave. The duration of the interaction of the atoms with the standing wave was varied from several tens of spontaneous-emission lifetimes to several hundreds. For a standing-wave frequency blue detuned from resonance, diffusive heating can dominate the time-averaged dissipative dipole force so that there is no steady-state momentum distribution. However, for sufficiently large blue detunings, the rate of diffusion is so slow that the resulting distribution approaches a quasisteady state. For red detunings, the diffusion …

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Trapping-To-Percolation Transition In The Hopping Diffusion Of Substitutionally Disordered Solids With A Binary Energy Distribution, Paul Ernest Parris, B. D. Bookout Jan 1993

Trapping-To-Percolation Transition In The Hopping Diffusion Of Substitutionally Disordered Solids With A Binary Energy Distribution, Paul Ernest Parris, B. D. Bookout

Physics Faculty Research & Creative Works

We consider charge carriers that undergo nearest-neighbor hopping among the sites of a binary random lattice, each site of which is associated with one of two possible energies E1 or E2. A general and recently observed feature of this problem not predicted by previous treatments of disordered hopping models is a crossover between trap-limited conduction and percolation. We introduce new energy-projected equations of motion whose solutions reveal the deep conductivity minimum associated with this phenomenon, and compare the results predicted to numerical simulations.

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