Physical Sciences and Mathematics Commons^™

Forbidden Lines Of Np^Q Ions. Ii. Line Intensities, J. P. Lynch, Menas Kafatos

Mathematics, Physics, and Computer Science Faculty Articles and Research

Ground state forbidden transitions of np^q ions of C, N, 0, Ne, Mg, Si, S, and Fe can provide important information on the state of cosmic ionized gases. Wavelengths of these lines are in the far- and near-UV visible and near- and far-IR regions of the spectrum. The line intensity ratios of particular transitions in q = 2, 4 ions can provide information on the temperature of the gas and in q = 3 ions information on the density of the gas. In the present work we have tabulated the line intensities of 95 transitions of these ions, which include …

The (First) Three B’S Of The Skyrme Model, Alec Schramm

Alec J Schramm

No abstract provided.

Higgs Boson Production In Peripheral Heavy-Ion Collisions: Coherent Double-Pomeron Exchange, Alec Schramm, Berndt Muller

Alec J Schramm

Higgs boson production by coherent double-pomeron exchange in peripheral nuclear collisions at energies of several TeV per nucleon is calculated. It is shown that a trigger on quasi-elastic nuclear collisions strongly suppresses the cross section. The analogous two-photon process is predicted to dominate for collisions of heavy nuclei.

Digital-Image-Based Study Of Circular Holes In An Elastic Matrix, Anthony Day, K. Snyder, E. Garboczi, M. Thorpe

Anthony Roy Day

No abstract provided.

Solving Ill-Posed Problems With Artificial Neural Networks, Arun D. Kulkarni

Arun Kulkarni

Universal Conductivity Curve For A Plane Containing Random Holes., E. J. Garboczi, M. F. Thorpe, M. S. Devries, Anthony Roy Day

Anthony Roy Day

This paper examines the general percolation problem of cutting randomly centered insulating holes in a two-dimensional conducting sheet, and explores how the electrical conductivity sigma decreases with the remaining area fraction. This problem has been studied in the past for circular, square, and needlelike holes, using both computer simulations and analog experiments. In this paper, we extend these studies by examining cases where the insulating hole is of arbitrary shape, using digital-image-based numerical techniques in conjunction with the Y- [nabla] algorithm. We find that, within computational uncertainty, the scaled percolation threshold, xc=nc=5.9±0.4, is a universal quantity for all the cases …

Relaxation Time Of The Order Parameter In A High-Temperature Superconductor, G.L. Eesley, J. Heremans, M.S. Meyer, G.L. Doll, Sy_Hwang Liou

Sy-Hwang Liou Publications

We present femtosecond time-resolved measurements on the high-T_c superconductor Tl₂Ba₂Ca₂Cu₃O₁₀. At temperatures below T_c, we observe a relaxation process which is distinct from the equilibration of hot carriers in the normal state. Our results demonstrate an increasing relaxation rate as the superconducting gap opens. This is consistent with the behavior of conventional metallic superconductors.

Power Law Exponents For A Spreading Front And Growing Interface In An Irreversible Wetting, Evan Willett, Ras B. Pandey

Faculty Publications

Using computer simulations, the power-law behavior of the interface growth of a spreading fluid is studied in a two-dimensional lattice model. The interface width exponent ν and the dynamical exponent k for the evolution of the front are consistent with their dynamical scaling relation. The magnitude of these exponents seems to depend upon the nature of the substrate and the concentration of the carriers of the wetting fluid.

Projectile- And Target-Charge Dependent Effects In Ionizing Collisions Of H ⁺ And He 2+ With He, Ne And Ar Atoms, Timothy James Gay, M. W. Gealy, M. E. Rudd

Physics Faculty Research & Creative Works

The spectra of electrons emitted in collisions between H + and He 2+ projectiles and He, Ne and Ar targets at energies of 50 and 100 keV amu -1 have been studied. The data are in qualitative agreement with results of Irby el al., but are in disagreement with measurements of Bernardi et al. It is shown that the observed electron spectra have a dependence on both target-ion and projectile effective charge that can be understood qualitatively in terms of 'saddle-point' ionization. Several issues relevant to saddle-point ionization are discussed. © 1990 IOP Publishing Ltd.

Uniform Stationary-Phase Methods For Energy Spectra Resulting From Collisions In A Complex Potential: Penning And Associative Ionization Of He*(2³S)+He*(23s), Ronald James Bieniek, M. W. Muller, M. Movre

Physics Faculty Research & Creative Works

Heavy-particle collisions involving strong electronic coupling can be conveniently described by using a complex (optical) potential in the entrance channel. Uniform JWKB stationary-phase techniques are used to evaluate T-matrix elements for transitions where an electron is ejected. The semi-analytic expressions for the resulting electron energy spectra are no more difficult to implement than corresponding ones for totally real potentials. Numerical results are reported for Penning and associative ionization from sub thermal He*(23S)+He*(23S) collisions. These are in excellent agreement with fully quantal, complex-potential computations. The stationary-phase expressions for T-matrix elements and differential cross sections are employed to elucidate the rapid and …

Laser Cvd And Plasma Cvd Of Cro2 Films And Cobalt Doped Cro2 Films Using Organometallic Precursors, Peter A. Dowben, Marshall Onellion

Peter Dowben Publications

Chromium dioxide is deposited as a ferromagnetic layer onto selected portions of a substrate or over the entire substrate. Chromium hexacarbonyl vapor is introduced into a vacuum deposition chamber at e.g. 10 milliTorr and oxygen is introduced at e.g. 15 to 100 milliTorr. A UV laser beam is focused onto the substrate to form the CrO₂ layer photolytically. The CrO₂ layer can also be deposited by RF plasma deposition. This technique can also be employed for depositing MoC₂, WC₂, Mo_2φ3, MoO₂ or WO₂. Magnetic recording or memory devices are …

The Relationship Of The Virtual Orbitals Of Self-Consistent-Field Theory To Temporary Negative Ions In Electron Scattering From Molecules, Donghai Chen, Gordon A. Gallup

Gordon Gallup Publications

The theory given here shows how certain of the virtual orbitals of self-consistent field (SCF) theory provide a natural ingredient for constructing basis functions to study the shape resonances associated with temporary molecular ions. We give specific calculations of resonant behavior in H₂, N₂, ethylene, cyclopropene, and cyclobutene. In addition, we show how the theory can rationalize the relationship between Koopmans' theorem values of the energy of a resonance and the experimental values. The Journal of Chemical Physics is copyrighted by The American Institute of Physics.

Magnetism Of Rare-Earth–Transition-Metal Nanoscale Multilayers. Ii. Theoretical Analysis Of Magnetization And Perpendicular Magnetic Anisotropy, Z.S. Shan, David J. Sellmyer, Sitaram Jaswal, Y.J. Wang, J.X. Shen

David Sellmyer Publications

Systematic studies of rare-earth–transition-metal amorphous compositionally modulated films (CMF) permit the development of a detailed model for understanding the magnetization and perpendicular magnetic anisotropy and their distributions along the film normal. It is shown that the single-ion anisotropy of rare-earth ions with orbital angular momentum is the major contributor to the perpendicular anisotropy for this class of CMF. The calculated results agree well with the experimental data for Dy/Co and Tb/Fe CMF when the individual layer thicknesses are small enough (<10 Å); these films have structures which can be characterized as compositionally modulated amorphous alloys.

Magnetism Of Rare-Earth–Transition-Metal Nanoscale Multilayers. I. Experiments On Dy/Co, Dy/Fe, And Tb/Fe, Z.S. Shan, David J. Sellmyer

David Sellmyer Publications

Experimental investigations of magnetic and structural properties for rare-earth–transition-metal (RE-TM) compositionally modulated films (CMF) are presented in this paper. In particular, A^RE/B^TM including A^RE=Dy and Tb and B^TM=Fe, Co, and Ni, are studied. The layer thickness and temperature dependence of magnetic properties, which can be interpreted in terms of the antiferromagnetic coupling of RE and TM moments and their atomic distributions, are reported. These A^RE/B^TM CMF with nanoscale layer thicknesses exhibit perpendicular magnetic anisotropy (PMA) and the range of the layer thickness required for PMA is determined. The …

Elastic Magnetic Electron Scattering From 'Ca, H Baghaei, A Cichocki, J B. Flanz, M Frodyma, Y Han, R S. Hicks, R A. Miskimen, Gerald Alvin Peterson, S H. Rokni

Gerald Alvin Peterson

The elastic magnetic form factor of 41Ca has been determined by 180° electron scattering in the momentum-transfer range 0.9–2.0 fm-1. An analysis of the data indicates that the amplitudes of the M3 and M5 multipoles are quenched by factors of 0.57±0.16 and 0.68±0.07 relative to the simple shell model. In contrast, the magnitude of the M7 form factor is in good accord with this model. Calculations that include multiparticle-multihole configurations in the 1f7/2 and 1d3/2 subshells, first-order core polarization to higher excited orbitals, and meson exchange currents give reasonable agreement with the data for all multipoles. The rms radius of …

Unpinning Of Gaas Surface Fermi Level By 200 Degrees C Molecular Beam Epitaxial Layer, David C. Look, C. E. Stutz, K. R. Evans

Physics Faculty Publications

Previous attempts to passivate the n‐type (100)GaAs surface have significantly reduced only the surface recombination centers, but not the surface acceptors which pin the Fermi level. Here we show that a 100 Å molecular beam epitaxial layer grown at 200 °C reduces the effective surface potential energy − eϕ_s from 0.70 to 0.17 eV, nearly eliminates light sensitivity, and permits nonalloyed ohmic contacts. After a 10 min, 450 °C anneal, − eϕ_s increases only to 0.22 eV.

Tunable Lasers At 1080 Nm For Helium Optical Pumping, Laird D. Schearer, Padetha Tin

Physics Faculty Research & Creative Works

We describe the current status of tunable, cw, solid-state lasers in the infrared region of the spectrum which may be tuned to the helium resonance transition near 1083 nm. The principal use for these laser devices is the optical pumping of ³He and ⁴He atoms via the 2³S₁ metastable state. The tunable lasers we have examined include Nd³⁺-doped YAlO₃, La_xNd_1-xMgAl₁₁O₁₉ (x ∼0.15), Nd:LiNbO₃, and Nd:silica glass fibers. Power outputs from these lasers range from a milliwatt to more than 1 W at …

A High Power, Tunable, Arc-Lamp Pumped Nd-Doped Lanthanum-Hexaluminate Laser, Padetha Tin, Laird D. Schearer

Physics Faculty Research & Creative Works

An LNA (Nd-doped lanthanum-hex aluminate) crystal has been pumped with a cw, krypton arc lamp in a commercial Nd:YAG cavity. The cw output power greater than 6 W is obtained in a 28-cm long, plane mirror cavity. The free-running wavelength is near 1083 nm and has a width of about 0.8 nm. Inserting a 0.25 mm thick, uncoated solid etalon in the cavity permits the laser output to be continuously tuned from 1082 to 1084 nm by tilting the etalon. The laser bandwidth is reduced to below 0.016 nm. Over 3 W are obtained at the helium resonance transition. The …

Single Transfer-Excitation Resonance Observed Via The Two-Photon Decay In He-Like Ge³⁰⁺, Paul H. Mokler, S. Reusch, A. Warczak, Zbigniew Stachura, T. Kambara, Alfred K. Muller, Reinhold S. Schuch, Michael Schulz

Physics Faculty Research & Creative Works

We measured the 2E1 decay of the 1s2s ¹S₀ →1s^{2 1}S₀ transition in He-like germanium for 12- to 19-MeV/u Ge³¹⁺ +H₂ collisions. The resonant population of the 2s2p ¹P₁ state by transfer excitation was isolated due to its cascading to the 1s2s ¹S₀ state. The experimental cross sections compare well with calculations using dielectronic recombination rates. The method gives the unique possibility to populate selectively the ¹S₀ state in heavy He-like ions.

Extension Of The Metal Light Pipe Infrared Spectroscopy Technique: Applications To Surface Adsorption And High Tc Superconductors, Torsten Will

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The development of an infrared instrument for the study of surface adsorption and high T_c superconductors is presented and its applicability is discussed. The use of and theoretical background for the metal light pipe multiple-reflection technique are discussed in comparison to other infrared devices. Measurements are carried out to determine its limitations with powdered substrates as well as its sensitivity limitation for thin films. The results of the two test measurements, adsorption of CO on MgO and investigation of the energy gap of high T_c superconductors, are presented. Comparisons of the spectra with the experimental and theoretical literature …

Fresnel And Fraunhofer Diffraction: Development Of An Advanced Laboratory Experiment, Jeff Adams

Senior Theses and Projects

The purpose of this lab is to help the student become more familiar with, or get a better feel for what is actually occurring, when observing the effects of double slit diffraction patterns. In most sophomore labs dealing with double slit diffraction, the student simply determines the diffraction angle, and slit spacing, from marking the positions of the maxima on the screen. No attempt is made to measure the relative intensity of the interference pattern, and see how the experimental data compare with the theory of interference and diffraction. In an attempt to further clarify this phenomena, we will attempt …

Electron Emission From Both Target And Projectile In C⁺ + He Collisions, C. O. Reinhold, D. R. Schultz, Ronald E. Olson, L. H. Toburen, R. (Robert) D. Dubois

Physics Faculty Research & Creative Works

The first classical trajectory Monte Carlo calculation of the electronic spectra arising from both target and projectile ionization is presented and compared with experimental measurements of the differential cross section for electrons emitted in C++He collisions. The theoretical treatment is based on an independent-electron model in which the interactions between the electrons are approximated by quantum model potentials. Good agreement is obtained between theory and experiment and structures appearing in the measurements can be explained in terms of the electron emission from either, or both, target and projectile. Further, the relative importance of the electron capture to the continuum and …

Device For Dispersal Of Micrometer- And Submicrometer-Sized Particles In Vaccum, D. P. Sheehan, M. Carillo, W. Heidbrink

Physics and Biophysics: Faculty Scholarship

A simple, versatile device for dispersing micrometer‐ and submicrometer-sized particles in vacuum is described. The source allows control of particle size (0.5 μm≤l≤200 μm) and particle flux density up to roughly 107 cm−2 s−1. Several types of microparticles were successfully dispersed.

Higgs-Boson Production In Peripheral Heavy-Ion Collisions: Electromagnetic Production, Alec Schramm, Burndt Muller

Alec J Schramm

Higgs-boson production via fusion of two virtual photons in nuclear collisions at energies of several TeV per nucleon is calculated. It is shown that although a trigger on quasielastic nuclear collisions suppresses the Higgs-boson production cross section, this mechanism could still provide a method for producing and detecting intermediate-mass Higgs bosons (MZ≲MH≲2MW).

United States Patent: Metaginsulator Composites Having Improved Properties And Method For Their Preparation, Chia-Ling Chien, Gang Xiao, Sy-Hwang Liou

Sy-Hwang Liou Publications

Improved cermets having superior properties comprising a ferromagnetic metal and an insulator. By controlling process conditions, cermets having high magnetization and high coercivity as well as chemical stability, wear resistance and corrosion resistance are prepared. The cermets of this invention find particular utility as high density recording media.

Anomalous Dimensions Of Anisotropic Gauge Theory Operators, David G. Robertson, Frank Wilczek

Physics Faculty Scholarship

The anomalous dimensions of the anisotropic dimension four operators in SU(N) gauge theory coupled to fermions are calculated to lowest order. The possibility of comparison with numerical simulations is pointed out.

Effects Of Magnetic Field And Temperature On The Critical Current Hysteresis In Tl-Ca-Ba-Cu-O Thin Films, Hung-Lun Chang, Jenh-Yih Juang, Sy_Hwang Liou, Tzeng-Ming Uen, Yih-Shun Gou

Sy-Hwang Liou Publications

The behavior of the critical current density of Tl-Ca-Ba-Cu-O superconducting thin films in a cycling magnetic field was investigated. The hysteresis of the transport J_c manifested similar features to those found in polycrystalline Y-Ba-Cu-O and granular Nb, Al thin films in zero-field cooling. However, a novel result of the transport J_c in field-cooled samples has been observed. The results were attributed to the presence of a saturated trapped magnetic flux in the weaklink network. The effects of temperature on both the trapped flux and the transport J_c suggest the existence of various states of the trapped flux …

Coincident Charge State Production In F⁶⁺+Ne Collisions, D. R. Schultz, Ronald E. Olson, C. O. Reinhold

Physics Faculty Research & Creative Works

Total cross sections are presented for the production of various stages of multiple ionization of the target in coincidence with the final projectile charge state for collisions of F⁶⁺ with Ne at 10 and 15 MeV. In particular, the current measurements are compared with the results of a classical trajectory Monte Carlo method in which electrons are included explicitly on both target and projectile (nCTMC) and with those based on the conventional independent electron model (IEM). It is shown by the good agreement with experiment that the nCTMC model simultaneously represents well the ionization, charge transfer and excitation channels …

Average Reaction Cross Sections For 74- To 112-Mev Α Particles On 127I And 133Cs, R. E. Warner, H. W. Wilschut, W. F. Rulla, Gary Felder

Physics: Faculty Publications

The average reaction cross section for 74- to 112-MeV α particles on 127I and 133Cs was measured by a new method using a magnetic spectrograph and a CsI scintillation detector. The result, σR=2220±50 mb, is in good agreement with optical model calculations and finite-range microscopic calculations. Zero-range microscopic calculations underpredict σR by about 10%, while strong absorption theories overpredict σR by large amounts.

Radiative Transfer In Astronomical Masers. I. The Linear Maser, Moshe Elitzur

Physics and Astronomy Faculty Publications

This is the first in a series of three papers presenting a comprehensive, unified approach for radiative transfer in astronomical maser sources. This paper provides the general formalism and presents the detailed analytic solution of the linear maser, including the case of a source illuminated by background radiation.