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Physics Faculty Research & Creative Works

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Articles 1321 - 1350 of 1959

Full-Text Articles in Physical Sciences and Mathematics

Transport Anomalies And Marginal Fermi-Liquid Effects At A Quantum Critical Point, Dietrich Belitz, Theodore R. Kirkpatrick, Rajesh S. Narayanan, Thomas Vojta Nov 2000

Transport Anomalies And Marginal Fermi-Liquid Effects At A Quantum Critical Point, Dietrich Belitz, Theodore R. Kirkpatrick, Rajesh S. Narayanan, Thomas Vojta

Physics Faculty Research & Creative Works

The conductivity and the tunneling density of states of disordered itinerant electrons in the vicinity of a ferromagnetic transition at low temperature are discussed. Critical fluctuations lead to nonanalytic frequency and temperature dependencies that are distinct from the usual long-time tail effects in a disordered Fermi liquid. The crossover between these two types of behavior is proposed as an experimental check of recent theories of the quantum ferromagnetic critical behavior. In addition, the quasiparticle properties at criticality are shown to be those of a marginal Fermi liquid.

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Binary Condensation In A Supersonic Nozzle, Barbara Ellen Wyslouzil, Christopher H. Heath, Janice L. Cheung, Gerald Wilemski Nov 2000

Binary Condensation In A Supersonic Nozzle, Barbara Ellen Wyslouzil, Christopher H. Heath, Janice L. Cheung, Gerald Wilemski

Physics Faculty Research & Creative Works

We present data from the first systematic studies of binary condensation in supersonic nozzles. The apparatus used to conduct the experiments is described in detail, and the important issues of stability and reproducibility of the experiments are discussed. Experiments were conducted with water, ethanol, propanol, and binary mixtures of these compounds. Onset was determined in the temperature range of 190-215 K, and for each mixture composition the pressures of the condensible species at an onset temperature of 207 K were determined. For the ideal ethanol-propanol mixtures, the onset pressures at constant temperature vary almost linearly between those of the pure …

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Resummation Of Nonalternating Divergent Perturbative Expansions, Ulrich D. Jentschura Oct 2000

Resummation Of Nonalternating Divergent Perturbative Expansions, Ulrich D. Jentschura

Physics Faculty Research & Creative Works

A method for the resummation of a nonalternating divergent perturbation series is described. The procedure constitutes a generalization of the Borel-Padã method. Of crucial importance is a special integration contour in the complex plane. Nonperturbative imaginary contributions can be inferred from the purely real perturbative coefficients. A connection is drawn from the quantum field theoretic problem of resummation to divergent perturbative expansions in other areas of physics.

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Ionization Of Hydrogen Atoms By Fast Electrons, Sindu P. Jones, Don H. Madison Oct 2000

Ionization Of Hydrogen Atoms By Fast Electrons, Sindu P. Jones, Don H. Madison

Physics Faculty Research & Creative Works

We study ionization of atomic hydrogen by fast electrons using asymptotically correct two-center wave functions to describe the scattering system both initially and finally. For the final state, we employ the well-known product wave function of Redmond, which treats all three two-body Coulomb interactions exactly, albeit independently. This "3C" wave function is the leading term of the exact scattering wave function, regardless of how slow the three particles are, if any two particles have large relative separation [Y.E. Kim and A.L. Zubarev, Phys. Rev. A 56, 521 (1997)]. Here we extend the analysis of Qiu et al. [Phys. Rev. A …

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Resummation Of Qed Perturbation Series By Sequence Transformations And The Prediction Of Perturbative Coefficients, Ulrich D. Jentschura, Jens Becher, Ernst Joachim Weniger, Gerhard Soff Sep 2000

Resummation Of Qed Perturbation Series By Sequence Transformations And The Prediction Of Perturbative Coefficients, Ulrich D. Jentschura, Jens Becher, Ernst Joachim Weniger, Gerhard Soff

Physics Faculty Research & Creative Works

We propose a method for the resummation of divergent perturbative expansions in quantum electrodynamics and related field theories. The method is based on a nonlinear sequence transformation and uses as input data only the numerical values of a finite number of perturbative coefficients. The results obtained in this way are for alternating series superior to those obtained using Padé approximants. The nonlinear sequence transformation fulfills an accuracy-through-order relation and can be used to predict perturbative coefficients. In many cases, these predictions are closer to available analytic results than predictions obtained using the Padé method.

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Concept Of Local Polaritons And Optical Properties Of Mixed Polar Crystals, Lev I. Deych, Alexey Yamilov, Alexander A. Lisyansky Sep 2000

Concept Of Local Polaritons And Optical Properties Of Mixed Polar Crystals, Lev I. Deych, Alexey Yamilov, Alexander A. Lisyansky

Physics Faculty Research & Creative Works

The concept of local polaritons is used to describe the optical properties of mixed crystals in the frequency region of their restrahlen band. It is shown that this concept allows for a physically transparent explanation of the presence of weak features in the spectra of so-called one-mode crystals and for one-two mode behavior. The previous models Were able to explain these features only with the use of many fitting parameters. We show that under certain Conditions new impurity-induced polariton modes may arise within the restrahlen of the host crystals, and study their dispersion laws and density of states. Particularly, we …

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Short-Pulse Laser-Induced Stabilization Of Autoionizing States, Heider N. Ereifej, J. Greg Story Sep 2000

Short-Pulse Laser-Induced Stabilization Of Autoionizing States, Heider N. Ereifej, J. Greg Story

Physics Faculty Research & Creative Works

Atoms in doubly excited states above the first ionization limit can decay via autoionization in which an electron is emitted leaving an ion, or by photoemission which leaves the atom in a singly excited state. In this paper, it is demonstrated that interaction between the atoms and a laser pulse that is short compared to the autoionization lifetime can lead to large enhancement of the photoemission process by stimulating the atoms to emit a photon. Since the resultant singly excited atoms do not autoionize, this process can be viewed as an enhancement of the stabilization of the doubly excited atoms …

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Observation Of Stratospheric Ozone Depletion Associated With Delta Ii Rocket Emissions, Martin N. Ross, Darin W. Toohey, W. T. Rawlins, E. C. Richard, K. K. Kelly, A. F. Tuck, M. H. Proffitt, Donald E. Hagen, Alfred R. Hopkins, Philip D. Whitefield, J. R. Benbrook, W. R. Sheldon Aug 2000

Observation Of Stratospheric Ozone Depletion Associated With Delta Ii Rocket Emissions, Martin N. Ross, Darin W. Toohey, W. T. Rawlins, E. C. Richard, K. K. Kelly, A. F. Tuck, M. H. Proffitt, Donald E. Hagen, Alfred R. Hopkins, Philip D. Whitefield, J. R. Benbrook, W. R. Sheldon

Physics Faculty Research & Creative Works

Ozone, chlorine monoxide, methane, and submicron particulate concentrations were measured in the stratospheric plume wake of a Delta II rocket powered by a combination of solid (NH4ClO4/Al) and liquid (LOX/kerosene) propulsion systems. We apply a simple kinetics model describing the main features of gas-phase chlorine reactions in solid propellant exhaust plumes to derive the abundance of total reactive chlorine in the plume and estimate the associated cumulative ozone loss. Measured ozone loss during two plume encounters (12 and 39 minutes after launch) exceeded the estimate by about a factor of about two. Insofar as only the …

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Final Quantum Nf State Analysis For Multiply Charged Ion-Circular Rydberg Target Collisions, K. R. Cornelius, Ronald E. Olson Jul 2000

Final Quantum Nf State Analysis For Multiply Charged Ion-Circular Rydberg Target Collisions, K. R. Cornelius, Ronald E. Olson

Physics Faculty Research & Creative Works

The classical trajectory Monte Carlo method has been used to simulate fully stripped ion-circular Rydberg atom collisions. We report that the mechanisms that govern the capture process for ions colliding with aligned Rydberg targets, namely direct and indirect velocity matching, alternate as to which is dominant. Previous experimental and theoretical results for singly charged ion-Rydberg atom collisions demonstrate that direct capture processes dominate at intermediate collision speeds. We have found that for highly charged ion-Rydberg atom collisions electron capture via indirect velocity matching is dominant at intermediate collision speeds and contributes up to 90% of the total capture cross-section.

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Direct Measurement Of Oscillations Between Degenerate Two-Electron Bound-State Configurations In A Rapidly Autoionizing System, Heider N. Ereifej, J. Greg Story Jul 2000

Direct Measurement Of Oscillations Between Degenerate Two-Electron Bound-State Configurations In A Rapidly Autoionizing System, Heider N. Ereifej, J. Greg Story

Physics Faculty Research & Creative Works

In this paper we report a direct observation of the oscillation between bound-state configurations in a rapidly autoionizing system. Calcium atoms were excited to a pure 4p3/2nd two-electron configuration using a 500-fsec laser pulse. The initial 4p3/2nd doubly excited state is energy degenerate with the 4p1/2n'd states and several continuum channels. Because of the short-pulse excitation, the initial state of the atom is not an energy eigenstate, but a nonstationary wave packet. As a result, oscillations between the two bound configurations were produced. These oscillations were measured by scanning the timing of a second …

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Neutral Beam Stopping And Emission In Fusion Plasmas. I: Deuterium Beams, H. Anderson, M. G. Von Hellermann, R. Hoekstra, L. D. Horton, A. C. Howman, R. W.T. Konig, R. Martin, Ronald E. Olson, H. P. Summers Jul 2000

Neutral Beam Stopping And Emission In Fusion Plasmas. I: Deuterium Beams, H. Anderson, M. G. Von Hellermann, R. Hoekstra, L. D. Horton, A. C. Howman, R. W.T. Konig, R. Martin, Ronald E. Olson, H. P. Summers

Physics Faculty Research & Creative Works

The charge transfer reaction of neutral deuterium beams with impurities enables one of the principle quantitative diagnostic measurements of the hot core fusion plasma; that is, charge exchange spectroscopy. The complementary measurement of beam emission spectroscopy has been fruitful in motional Stark wavelength shift and fluctuation studies, but less so in using absolute measured intensities. In the last two years we have achieved substantial improvement in the quantitative analysis and agreement between the observed and modelled beam emission at the JET Joint Undertaking. This has depended on improved spectral fitting of the overlayed Dα motional Stark multiplet, self-consistent beam emission …

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State-Selective Cross Section Scalings For Electron Capture Collisions, K. R. Cornelius, K. Wojtkowski, Ronald E. Olson Jun 2000

State-Selective Cross Section Scalings For Electron Capture Collisions, K. R. Cornelius, K. Wojtkowski, Ronald E. Olson

Physics Faculty Research & Creative Works

The classical-trajectory Monte Carlo method is used to calculate total and final nf state-selective electron capture cross sections for various fully stripped ions, ranging from He2+ to Ne10+, incident on H(ni = 1-4) and Li(2s and 2p) targets over the collision energies of 1-100 keV u-1. Theoretical derivations of two scaling laws for state-selective electron capture cross sections as a function of collision energy, initial and final bound electron states and projectile charge are presented. The new scaling rules reduce the state-selective capture cross sections to very distinct universal curves. Curve fits …

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Single Ionization Of Ne By Intense Laser Fields, C. R. Feeler, Ronald E. Olson Jun 2000

Single Ionization Of Ne By Intense Laser Fields, C. R. Feeler, Ronald E. Olson

Physics Faculty Research & Creative Works

A three-dimensional classical Monte Carlo method has been used to examine the final state electron dynamics after single ionization of neon in an electric field generated by a short-pulse high-intensity laser. Linearly and circularly polarized fields were studied. Intensities ranging from 3 x 1014 to 3 x 1015 W cm-2 were used with a wavelength of 800 nm and a full-width at half-maximum of 30 fs. At these values, the Keldysh parameter is less than one, making the classical approximation valid. A potential determined by Hartree-Fock calculations has been used to model the Ne atom. A kinematically complete picture …

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Annealed Disorder, Rare Regions, And Local Moments: A Novel Mechanism For Metal-Insulator Transitions, Dietrich Belitz, Theodore R. Kirkpatrick, Thomas Vojta May 2000

Annealed Disorder, Rare Regions, And Local Moments: A Novel Mechanism For Metal-Insulator Transitions, Dietrich Belitz, Theodore R. Kirkpatrick, Thomas Vojta

Physics Faculty Research & Creative Works

It is shown that, for noninteracting electron systems, annealed magnetic disorder leads to a new mechanism, and a new universality class, for a metal-insulator transition. The transition is driven by a vanishing of the thermodynamic density susceptibility rather than by localization effects. The critical behavior in d = 2 + ∈ dimensions is determined, and the underlying physics is discussed. It is further argued that annealed magnetic disorder, in addition to underlying quenched disorder, describes local magnetic moments in electronic systems.

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Genuine Saddle Point And Nucleation Potential For Binary Systems, Jinsong Li, Igor L. Maksimov, Gerald Wilemski May 2000

Genuine Saddle Point And Nucleation Potential For Binary Systems, Jinsong Li, Igor L. Maksimov, Gerald Wilemski

Physics Faculty Research & Creative Works

A generalized nucleation potential is constructed for binary systems. The potential consists of the reversible work of cluster formation plus additional terms arising from various kinetic effects. We show that the major nucleation flux passes through the saddle point (termed the genuine saddle point) of this generalized nucleation potential. The generalized nucleation potential reduces to the kinetic potential of a unary system when one component vanishes. The genuine saddle point concept provides a convenient way to identify systems and conditions for which the ridge crossing phenomenon occurs. Our theory agrees approximately with exact numerical results.

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Photoelectron Diffraction Determination Of The Structure Of Ultrathin Vanadium Films On Cu(001), George Daniel Waddill, D. P. Moore, Osman Ozturk Mar 2000

Photoelectron Diffraction Determination Of The Structure Of Ultrathin Vanadium Films On Cu(001), George Daniel Waddill, D. P. Moore, Osman Ozturk

Physics Faculty Research & Creative Works

X-ray photoelectron diffraction (XPD) and low-energy electron diffraction (LEED) have been used to study the structural properties of V thin films on Cu(001). For room-temperature growth, submonolayer coverages result in (1x1) LEED patterns that evolve to exhibit very diffuse (2x1) structure at approximately 1 monolayer coverage. We do not observe any V forward-focusing enhancements for V films that exhibit either the (1x1) or (2x1) structure, suggesting that these structures are limited to the first 1-2 vanadium layers. At coverages above 1 monolayer, the V films display complex LEED patterns characteristic of four bcc(110) domains. This structure persists to V coverages …

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Quantum Gravity Corrections To The Schwarzschild Mass, Marco Cavaglia, Carlo Ungarelli Feb 2000

Quantum Gravity Corrections To The Schwarzschild Mass, Marco Cavaglia, Carlo Ungarelli

Physics Faculty Research & Creative Works

Vacuum spherically symmetric Einstein gravity in (N≥4) dimensions can be cast in a two-dimensional conformal nonlinear sigma model form by first integrating on the (N - 2)-dimensional (hyper)sphere and then performing a canonical transformation. The conformal sigma model is described by two fields which are related to the Arnowitt-Deser-Misner (ADM) mass and to the radius of the (N - 2)-dimensional (hyper)sphere, respectively. By quantizing perturbatively the theory we estimate the quantum corrections to the ADM mass of a black hole.

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Observations Of Particulates Within The North Atlantic Flight Corridor: Polinat 2, September-October 1997, J. D. Paladino, Donald E. Hagen, Philip D. Whitefield, Alfred Raymond Hopkins, Otmar Schmid, M. R. Wilson, Hans Schlager, Peter Schulte Feb 2000

Observations Of Particulates Within The North Atlantic Flight Corridor: Polinat 2, September-October 1997, J. D. Paladino, Donald E. Hagen, Philip D. Whitefield, Alfred Raymond Hopkins, Otmar Schmid, M. R. Wilson, Hans Schlager, Peter Schulte

Physics Faculty Research & Creative Works

This paper discusses particulate concentration and size distribution data gathered using the University of Missouri-Rolla Mobile Aerosol Sampling System (UMR-MASS), and used to investigate the southern extent of the eastern end of the North Atlantic Flight Corridor (NAFC) during project Pollution From Aircraft Emissions in the North Atlantic Flight Corridor/Subsonic Assessment (SASS) Ozone and Nitrogen Oxide Experiment (POLINAT 2/SONEX) from September 19 to October 23, 1997. The analysis presented in this paper focuses on "the corridor effect," or enhancement of pollutants by jet aircraft combustion events. To investigate the phenomena, both vertical and horizontal profiles of the corridor, and regions …

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Excitation Of Ar 3p⁵4s-3p⁵4p Transitions By Electron Impact, Colette M. Maloney, Jerry Peacher, Klaus Bartschat, Don H. Madison Feb 2000

Excitation Of Ar 3p⁵4s-3p⁵4p Transitions By Electron Impact, Colette M. Maloney, Jerry Peacher, Klaus Bartschat, Don H. Madison

Physics Faculty Research & Creative Works

Electron-impact excitation of argon from the 3p54s (J=0,2) metastable states to the 3p54p (J=0,1,2,3) manifold has been investigated in the semirelativistic first-order distorted-wave and plane-wave Born approximations. The results are compared with recent experimental data of Boffard et al. [Phys. Rev. A 59, 2749 (1999)] and R-matrix predictions by Bartschat and Zeman [Phys. Rev. A 59, R2552 (1999)]. In cases for which perturbative approaches are expected to be valid, the plane-wave Born approximation is found to be sufficiently accurate and thus allows for an efficient calculation of results over a wide range of collision energies.

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Correlated Three-Electron Continuum States In Triple Ionization By Fast Heavy-Ion Impact, Michael Schulz, Robert Moshammer, Wayne M. Schmitt, Holger Kollmus, Rido Mann, Siegbert Hagmann, Ronald E. Olson, Joachim Hermann Ullrich Feb 2000

Correlated Three-Electron Continuum States In Triple Ionization By Fast Heavy-Ion Impact, Michael Schulz, Robert Moshammer, Wayne M. Schmitt, Holger Kollmus, Rido Mann, Siegbert Hagmann, Ronald E. Olson, Joachim Hermann Ullrich

Physics Faculty Research & Creative Works

We have performed a kinematically complete experiment for triple ionization in atomic collisions. Data were obtained for 3.6-MeV/amu Au53+ impact on Ne. A specific Dalitz representation was developed allowing one to plot in a single spectrum the energy of all three ionized electrons and, simultaneously, obtain information on their emission angles with respect to the projectile direction. The data show distinct fragmentation patterns favoring very asymmetric energy partitionings with one fast and two slow electrons. They are compared to various Classical Trajectory Monte Carlo (CTMC) models. The experimental results are well described only if the electron-electron interaction is included …

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Crystal And Magnetic Structures Of Lani₅₋ₓmnₓ, Chiu-Ying Tai, G. K. Marasinghe, Oran Allan Pringle, William Joseph James, Muguo Chen, William B. Yelon, I. Dubenko, Naushad Ali, Ph. I'Héritier Jan 2000

Crystal And Magnetic Structures Of Lani₅₋ₓmnₓ, Chiu-Ying Tai, G. K. Marasinghe, Oran Allan Pringle, William Joseph James, Muguo Chen, William B. Yelon, I. Dubenko, Naushad Ali, Ph. I'Héritier

Physics Faculty Research & Creative Works

The crystallographic and magnetic properties of LaN5-xMnx with x = 1, 1.5, and 2, have been investigated using x-ray and neutron diffraction, vibrating sample magnetometer and superconducting quantum interference device measurements. All the samples crystallize in the hexagonal CaCu5-type (P6/mmm) structure. Manganese atoms preferentially occupy the 3 g site in the LaNi5 structure. The bulk magnetization of the LaNi5-xMnx powder samples decreases rapidly as nickel is replaced by manganese. A ferrimagnetic model is applied to describe the magnetic structure of the LaNi5-xMnx samples for x = 1.5 and …

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The Effects Of Substituting Iron For Manganese In Smmn₆Ge₆: Magnetic And Crystallographic Properties, J. Han, William B. Yelon, Naushad Ali, I. Dubenko, G. K. Marasinghe, Ph. I'Héritier, William Joseph James Jan 2000

The Effects Of Substituting Iron For Manganese In Smmn₆Ge₆: Magnetic And Crystallographic Properties, J. Han, William B. Yelon, Naushad Ali, I. Dubenko, G. K. Marasinghe, Ph. I'Héritier, William Joseph James

Physics Faculty Research & Creative Works

No abstract provided.

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X-Ray Emission Following Low-Energy Charge Exchange Collisions Of Highly Charged Ions, P. Beiersdorfer, Ronald E. Olson, G. V. Brown, H. Chen, C. L. Harris, P. A. Neill, L. Schweikhard, S. B. Utter, K. Widmann Jan 2000

X-Ray Emission Following Low-Energy Charge Exchange Collisions Of Highly Charged Ions, P. Beiersdorfer, Ronald E. Olson, G. V. Brown, H. Chen, C. L. Harris, P. A. Neill, L. Schweikhard, S. B. Utter, K. Widmann

Physics Faculty Research & Creative Works

K-shell x-ray emission following low-energy charge exchange collisions (≤11 eV/amu) has been measured for ten bare and hydrogenic ions up to U91+. The data resolve capture into angular momentum states with ℓ=1 and provide a stringent test of theory. The assumption of Stark mixing of angular momentum states is inappropriate at such energies. Results from detailed calculations give a better description of the data, but significant discrepancies are noted. The measurements show that the hardness ratio of charge-exchange induced K-shell x-ray emission represents a diagnostic of the dynamics of ion-atom interactions in situations where the energy is below …

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Neutron Scattering From Aerosols: Intraparticle Structure Factor, Guinier Analysis Of Particle Speed, And Crossed Beam Kinematics, Gerald Wilemski Jan 2000

Neutron Scattering From Aerosols: Intraparticle Structure Factor, Guinier Analysis Of Particle Speed, And Crossed Beam Kinematics, Gerald Wilemski

Physics Faculty Research & Creative Works

A theoretical formalism for neutron scattering from systems of particles is applied to liquid nanodroplet aerosols. A term arising from intraparticle, intermolecular correlations is identified. The kinematical theory of two body scattering is recast into a form convenient for interpreting the results of experiments with crossed beams of neutrons and aerosol particles. Based on a theoretical analysis of the scattered intensity in the Guinier region, a method for determining the particle velocity directly from the experimental data is outlined. The method is not restricted by assumptions about particle shape, composition, uniformity, or size distribution.

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Electron Correlations Observed Through Intensity Interferometry, Michael Schulz, Robert Moshammer, Wayne M. Schmitt, Holger Kollmus, Bernold Feuerstein, Rido Mann, Siegbert Hagmann, Joachim Hermann Ullrich Jan 2000

Electron Correlations Observed Through Intensity Interferometry, Michael Schulz, Robert Moshammer, Wayne M. Schmitt, Holger Kollmus, Bernold Feuerstein, Rido Mann, Siegbert Hagmann, Joachim Hermann Ullrich

Physics Faculty Research & Creative Works

Intensity interferometry was applied to study electron correlations in doubly ionizing ion-atom collisions. In this method, the probability to find two electrons emitted in the same double ionization event with a certain momentum difference is compared to the corresponding probability for two uncorrelated electrons from two independent events. The ratio of both probabilities, the so-called correlation function, is found to sensitively reveal electron correlation effects, but it is rather insensitive to the collision dynamics.

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Initial State Dependence Of Low-Energy Electron Emission In Fast Ion Atom Collisions, Robert Moshammer, Pablo Daniel Fainstein, Michael Schulz, Wayne M. Schmitt, Holger Kollmus, Rido Mann, Siegbert Hagmann, Joachim Hermann Ullrich Dec 1999

Initial State Dependence Of Low-Energy Electron Emission In Fast Ion Atom Collisions, Robert Moshammer, Pablo Daniel Fainstein, Michael Schulz, Wayne M. Schmitt, Holger Kollmus, Rido Mann, Siegbert Hagmann, Joachim Hermann Ullrich

Physics Faculty Research & Creative Works

Single and multiple ionization of neon and argon atoms by 3.6 MeV/u Au53+ impact has been explored in kinematically complete experiments. Doubly differential cross sections for low-energy electron emission have been obtained for a defined charge state of the recoiling target ion and the receding projectile. Observed target specific structures in the electron continuum are attributable to the nodal structure of the initial bound state momentum distribution. The experimental data are in excellent accord with continuum-distorted-wave eikonal-initial-state single ionization calculations if multiple ionization is considered appropriately.

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Laser-Induced Stabilization Of Autoionizing States, Heider N. Ereifej, J. Greg Story Nov 1999

Laser-Induced Stabilization Of Autoionizing States, Heider N. Ereifej, J. Greg Story

Physics Faculty Research & Creative Works

Stabilization of autoionizing states of barium by laser-induced, stimulated emission of light is demonstrated. Relative to purely flourescent stabilization, the data clearly show an enhancement of the stabilization process for laser pulses short compared to the flourescent lifetime of the autoionizing states. Shakeup spectra in which the principal quantum number of both electrons changes during the stimulated emission process are also clearly demonstrated.

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Differential Projectile Energy Loss In Multiply Ionizing Collisions, M. Schulz, R. Moshammer, W. Schmitt, H. Kollmus, R. Mann, S. Hagmann, Ronald E. Olson, J. Ullrich Oct 1999

Differential Projectile Energy Loss In Multiply Ionizing Collisions, M. Schulz, R. Moshammer, W. Schmitt, H. Kollmus, R. Mann, S. Hagmann, Ronald E. Olson, J. Ullrich

Physics Faculty Research & Creative Works

The momentum vectors of the recoil ion and up to three electrons were measured in coincidence with the projectiles which did not change charge state for 3.6 MeV amu-1 Au53+ → Ne collisions. New techniques were applied to obtain differential energy-loss spectra for multiple-target ionization as a function of the recoil-ion charge state. A resolution unprecedented for this energy regime was achieved. The data are in good agreement with a classical trajectory Monte Carlo calculation. Our studies represent a first step for a method of modelling stopping powers on a microscopic level and are relevant for plasma applications.

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Critical Behavior Of Disordered Quantum Magnets: The Relevance Of Rare Regions, Rajesh S. Narayanan, Thomas Vojta, Dietrich Belitz, Theodore R. Kirkpatrick Oct 1999

Critical Behavior Of Disordered Quantum Magnets: The Relevance Of Rare Regions, Rajesh S. Narayanan, Thomas Vojta, Dietrich Belitz, Theodore R. Kirkpatrick

Physics Faculty Research & Creative Works

The effects of quenched disorder on the critical properties of itinerant quantum antiferromagnets and ferromagnets are considered. Particular attention is paid to locally ordered spatial regions that are formed in the presence of quenched disorder even when the bulk system is still in the paramagnetic phase. These rare regions or local moments are reflected in the existence of spatially inhomogeneous saddle points of the Landau-Ginzburg-Wilson functional. We derive an effective theory that takes into account small fluctuations around all of these saddle points. The resulting free energy functional contains a new term in addition to those obtained within the conventional …

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Doppler Shift Anisotropy In Small Angle Neutron Scattering, Barbara Ellen Wyslouzil, Gerald Wilemski, Janice L. Cheung, Reinhard Strey, John G. Barker Oct 1999

Doppler Shift Anisotropy In Small Angle Neutron Scattering, Barbara Ellen Wyslouzil, Gerald Wilemski, Janice L. Cheung, Reinhard Strey, John G. Barker

Physics Faculty Research & Creative Works

The two-dimensional patterns in our small angle neutron scattering (SANS) experiments from rapidly moving aerosols are anisotropic. To test the kinematic theory of two-body scattering that describes the anisotropy, we conducted SANS experiments using a constant source of D2O aerosol with droplets moving at ~440 m/s, and varied the neutron velocity from 267 to 800 m/s. The theoretically predicted anisotropy of the laboratory scattering intensities agrees well with the experimental results. Based on an analysis of the scattering intensity in the Guinier region, we also determined the particle velocity. The results are in very good agreement with independent …

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