Digital Commons Network^™

Birefringence Measurements Of The Uniaxial-Stress Dependence Of The Incommensurate Phase Transition In K2Seo4, D. P. Billesbach, F. G. Ullman, John R. Hardy

John R. Hardy Papers

The uniaxial-stress dependence of the incommensurate-phase-transition temperature (at 130 K) in K₂SeO₄ was measured along all three crystal axes by observation of the anomalies in the birefringence caused by the structure change. The results for the c-axis-stress dependence (- 17.0±0.2 K/kbar) agree with previous studies of other workers. This experiment has also provided the first direct measurements of the a-axis- and b-axis-stress dependences (+ 3.1 ±0.2 K/kbar and +7.7± 0.2 K/kbar, respectively). Also, a value of -6.2±0.3 K/kbar was calculated from these data for the dependence of the transition temperature on hydrostatic pressure. This …

Emerging Technologies For Verification Of Arms Control Treaties, David W. Hafemeister

Physics

Progress in the technical means of monitoring to verify compliance to arms control treaties is discussed in the following areas: Real-time surveillance with charge-coupled devices in the visible and infrared; image enhancement with digital 1 image processing and with adaptive optics; imaging with radars based on satellites and on the ground; seismic monitoring with high frequency discrimination and with unattended in-country seismic stations; and nuclear weapons test monitoring with the global positioning satellite system.

Magnetoresistance Method To Determine Gaas And Alxga1-Xas Mobilities In Alxga1-Xas/Gaas Modulation-Doped Field-Effect Transistor Structures, David C. Look, George B. Norris, W. Kopp, T. Henderson, H. Morkoç

Physics Faculty Publications

Charge carrier mobilities are conveniently measured in simple, homostructure field-effect transistors (FET's) by means of the geometric magnetoresistance (GMR) technique. Heterostructure FET's, however, are more complicated because of multiple conducting regions, as well as multiple conducting bands within a given region. We apply a multilayer GMR mobility model to a frequently used heterostructure FET design, namely, the Al_0.3Ga_0.7As conduction band. In the particular MODFET structure studied here, the lowest GaAs subband mobility ranges from 5.7X10³ cm²/Vs at threshold to 6.9X10³ cm²/Vs at saturation while Al_0.3Ga_0.7As mobility …

Theoretical And Experimental Capacitance-Voltage Behavior Of Al0.3ga0.7as Gaas Modulation-Doped Heterojunctions - Relation Of Conduction-Band Discontinuity To Donor Energy, George B. Norris, David C. Look, W. Kopp, J. Klem, H. Morkoç

Physics Faculty Publications

For the first time, we show that the capacitance-voltage behavior of modulation-doped heterojunctions may be accurately described by a first-principles theory that includes selfconsistent quantum two-dimensional (2-D) electron subbands in the GaAs, numerical solution of Poisson's equation for band bending and space charge in the (Al,Ga) As, and series resistance in the 2-D channel and heterointerface. The excellent agreement found between the theory and measurements on selected high-quality Al_0.3Ga_0.7 As/GaAs heterojunctions allows accurate determination of the maximum 2-D carrier concentration. From this, we find a strong relationship between the conduction-band discontinuity and donor binding energy, giving offsets. …

Low Temperature Tunneling Dynamics In Condensed Media, Paul Ernest Parris, Robert J. Silbey

Physics Faculty Research & Creative Works

There has been considerable interest recently in the low temperature dynamics of condensed phase tunneling phenomena. In this paper we consider the interplay between quasiparticle transport and vibrational relaxation; the former taking place via tunneling in a double well potential, and the latter occurring due to interactions of the tunneling system with a harmonic bath. Taking the system-bath interactions to be linear in the bath coordinates, and explicitly allowing for a vibrationally excited well, we present a unified treatment of the weak and strong coupling regimes and obtain reduced equations of motion for the tunneling particle position operator. Solutions are …

A Study Of Integral Equations For Computing Radial Distribution Functions, Zainuriah Hassan

Masters Theses

Integral equation T (a two parameter equation of the Ornstein-Zernike form) is studied for computing the radial distribution functions of simple classical fluids interacting pairwise according to the Lennard-Jones 6-12 potential function. Numerical calculations are done on a computer for the system in the gas and liquid phases. At a high temperature, equation T results are found to agree very well with equation C when the parameters are chosen in a similar way. At a temperature slightly above the critical temperature, results from other sources over a wide density range. In equation T, by varying two of the parameters, the …

Thindown In Radiobiology, Robert Katz, D. E. Dunn, G. L. Sinclair

Robert Katz Publications

A new expression for the radial dose distribution, tested against available data, and yielding good agreement with enzyme and virus cross sections, is used to calculate cellular inactivation cross sections from track theory models and parameters. We use a cellular model and radiosensitivity parameters, fitted to HILAC data 15 years ago, to represent mammalian cells irradiated at the UNILAC. The observed branching with Z and the decline in cellular action cross sections with an increase in ion LET are attributed to thindown; that is, to the limits imposed by the maximum radial penetration of delta rays. Target size and structure …

Cross Sections For Ionization Of Gases By 10-2000-Kev He+ Ions And For Electron Capture And Loss By 5-350-Kev He+ Ions, M. Eugene Rudd, T. V. Goff, A. Itoh, R. D. Dubois

M. Eugene Rudd Publications

Cross sections for production of positive and negative charge for 10-2000-keV He⁺ ions on He, Ne, Ar, Kr, H₂, N₂, CO, O₂, CH₄, and CO₂ were measured by the transverse-field method. Electron-capture and -loss cross sections for 5-350-keV He⁺ ions on the same targets were measured by the method of beam deflection of various charge states after passing through a known length of target gas. Secondary-emission detectors were used to detect neutral, singly charged, and doubly charged beam components. The equation σ₊- σ_- = σ_{10 …}

27th Rocky Mountain Conference

Rocky Mountain Conference on Magnetic Resonance

Program and abstracts from the 27th annual meeting of the Rocky Mountain Conference, co-sponsored by the Rocky Mountain Section of the Society for Applied Spectroscopy and the Rocky Mountain Chromatography Discussion Group. Held in Denver, Colorado, July 14-18, 1985.

Incident Beam Polarization For Laser Doppler Velocimetry Employing A Sapphire Cylindrical Window, James A. Lock, Harold J. Schock

Physics Faculty Publications

For laser Doppler velocimetry studies employing sapphire windows as optical access ports, the birefringency of sapphire produces an extra beam intersection volume which serves to effectively smear the acquired velocity flow field data. It is shown that for a cylindrical window geometry, the extra beam intersection volume may be eliminated with minimal decrease in the fringe visibility of the remaining intersection volume by suitably orienting the polarizations of the initial laser beams. For horizontally incident beams, these polarizations were measured at three intersection locations within the cylinder. It was found that the measured polarization angles agreed with the theoretical predictions.

A Generalized Molien Function For Field Theoretical Hamiltonians, Jeffrey W. Felix, Dorian M. Hatch

Faculty Publications

A generating function, or Molien function, the coefficients of which give the number of independent polynomial invariants in G, has been useful in the Landau and renormalization group theories of phase transitions. Here a generalized Molien function for a field theoretical Hamiltonian (with short-range interactions) of the most general form invariant in a group G is derived. This form is useful for more general renormalization group calculations. Its Taylor series is calculated to low order for the FGamma-2 representation of the space group R[3 bar]c and also for the l=1 (faithful) representation of SO(3).

Angle-Resolved Photoemission From Bromine Chemisorbed On Ni(100), Peter A. Dowben, Y. Sakisaka, T.N. Rhodin

Peter Dowben Publications

Molecular bromine dissociatively adsorbs to form a chemisorbed overlayer on Ni(100). The bromine induced 4p_x,y and 4p_z orbitals have been identified at Γ̅ with binding energies of 6.6 ± 0.2 eV and 5.3 ± 0.2 eV below the Fermi energy, respectively. The relative ionization cross-section variations of the two bromine levels 4p_x and 4p_z are observed to differ with changing photon energy.

Semiflexible Self-Avoiding Polymers: Low-Temperature Expansions For Models, Rolfe G. Petschek

Faculty Scholarship

Two models for dense, overlapping systems of semiflexible self-avoiding chain polymers in two dimensions are discussed. A method is presented for obtaining their equilibrium thermodynamic properties as an expansion around the low-temperature (stiff-polymer) limit. The first two nontrivial terms in this expansion are given.

Minimal Norm Constrained Interpolation, Larry Dean Irvine

Mathematics & Statistics Theses & Dissertations

In computational fluid dynamics and in CAD/CAM a physical boundary, usually known only discreetly (say, from a set of measurements), must often be approximated. An acceptable approximation must, of course, preserve the salient features of the data (convexity, concavity, etc.) In this dissertation we compute a smooth interpolant which is locally convex where the data are locally convex and is locally concave where the data are locally concave.

Such an interpolant is found by posing and solving a minimization problem. The solution is a piecewise cubic polynomial. We actually solve this problem indirectly by using the Peano kernel theorem to …

Mossbauer Study Of Gadolinium Iron Garnet, Jun Li

Physics Theses & Dissertations

The Mossbauer spectroscopic study of Gadolinium Iron Garnet R₃Fe5^O12 (GdIG) has been performed over the temperature range of 7K to 715K. Both high temperature and low temperature properties of GdIG have been studied. The magnetization is along (111) direction over this temperature range. The internal magnetic fields at Fe⁵⁷ sites in GdIG gave two values for the octahedral(a), site which differ by 4-6 KOe and one value for the tetrahedral (d), site at each temperature. Measurements of the total isomer shift in the spectra show that the shift of the center of the spectra consists …

Observation Of H/E Aharonov-Bohm Oscillations In Normal-Metal Rings, Richard A. Webb, S. Washburn, C. P. Umbach, R. B. Laibowitz

Faculty Publications

Magnetoresistance oscillations periodic with respect to the flux h/e have been observed in submicron-diameter Au rings, along with weaker h/2e oscillations. The h/e oscillations persist to very large magnetic fields. The background structure in the magnetoresistance was not symmetric about zero field. The temperature dependence of both the amplitude of the oscillations and the background are consistent with the recent theory by Stone.

Effects Of Dissipation And Temperature On Macroscopic Quantum Tunneling, S. Washburn, Richard A. Webb, R. F. Voss, S. M. Faris

Faculty Publications

Measurements of the tunneling rate Γ out of the zero-voltage state for several Nb edge junctions with differing shunt capacitances are described. At zero temperature, increasing the shunt capacitance lowers Γ in agreement with dissipative calculations of the macroscopic-quantum-tunneling rate. As temperature increases, ln[Γ(T)/Γ(0)]∝T² as recently predicted.

Copper Electrodeposition In A Magnetic Field, Hiroshi Takeo

Dissertations and Theses

The effect of a magnetic field on copper electrodeposition was investigated. Copper was electrodeposited onto square copper cathodes 1 sq cm in area from an aqueous solution (0.5 M CuSO₄, 0.5 M H₂SO₄. A glass cell was placed between the pole pieces of an electromagnet, and the magnetic fields applied were in the range from 0 to 12.5 kG. The current density was in the range from 80 mA/sq cm to 880 mA/sq cm. In each of the experiments, cell current, cell voltage, and cell temperature were monitored with a microcomputer. The weight …

Crystalline And Amorphous Feti And Fe2Ti, C.L. Chien, Sy_Hwang Liou

Sy-Hwang Liou Publications

Amorphous FeTi, Fe₂Ti, and their crystalline counterparts are compared by measurements of x-ray diffraction, conductivity, and ⁵⁷Fe Mössbauer spectroscopy. In FeTi one has the unique opportunity to compare a cubic crystal with its amorphous analog. X-ray diffraction and hyperfine interactions indicate no clear correlation between the crystalline and the amorphous states. The electrical conductivity exhibits distinctive behavior for the two states.

First-Principles Study Of Structural Instabilities In Halide-Based Perovskites: Competition Between Ferroelectricity And Ferroelasticity, J. W. Flocken, R. A. Guenther, John R. Hardy, L. L. Boyer

John R. Hardy Papers

We have made a systematic theoretical survey of the competition between ferroelastic and ferroelectric instabilities in the family of halide-based perovskites of formula ABX₃, where A is an alkali-metal ion, B is a Be, Mg, or Ca ion, and X is a halide ion. Initially we surveyed the whole series of such compounds, making a theoretical lattice-dynamical study using first-principles interionic potentials composed of a long-range pure Coulomb interaction between the spherically symmetric free ions, and a short-range component calculated by the Gordon-Kim approach from the overlapping free-ion charge densities. We then proceeded to examine in more detail …

First-Principles Study Of Structural Instabilities In Halide-Based Perovskites: Competition Between Ferroelectricity And Ferroelasticity, John W. Flocken, R. A. Guenther, John R. Hardy, L. L. Boyer

Physics Faculty Publications

We have made a systematic theoretical survey of the competition between ferroelastic and ferroelectric instabilities in the family of halide-based perovskites of formula ABX3, where A is an alkali-metal ion, B is a Be, Mg, or Ca ion, and X is a halide ion. Initially we surveyed the whole series of such compounds, making a theoretical lattice-dynamical study using first-principles interionic potentials composed of a long-range pure Coulomb interaction between the spherically symmetric free ions, and a short-range component calculated by the Gordon-Kim approach from the overlapping free-ion charge densities. We then proceeded to examine in more detail three compounds, …

Reduction Of Mammalian Ferritin, G. D. Watt, Richard B. Frankel, G. C. Papaefthymiou

Physics

Mammalian ferritin from horse spleen undergoes an electrochemical or chemical reduction reaction in which each iron atom present is reduced by one electron (2300 electrons per ferritin molecule containing 2300 Fe³⁺ ions). Midpoint potentials of -190 mV, -310 mV, and -416 mV were determined at pH 7.0, 8.0, and 9.0. This variation of potential with pH indicates that ≈ 2 H⁺ are transferred to the core for each Fe³⁺ reduced to Fe²⁺. Mössbauer measurements of partially reduced ferritin give spectra that consist of a ferric quadrupole doublet with a superposed ferrous quadrupole doublet. The relative …

Relativistic Plasma-Wave Excitation By Collinear Optical Mixing, C.E. Clayton, C. Joshi, C. Darrow, Donald P. Umstadter

Donald Umstadter Publications

The relativistic plasma wave excited when the frequency difference between two copropagating CO₂ laser beams equals the plasma frequency is detected for the first time. The plasma-wave frequency, wave number, spatial extent, and saturation time are directly measured by use of 7-mrad, collective, ruby Thomson scattering and the forward-scattered ir spectrum. The wave amplitude ñ/n₀ is inferred to be (1-3)% which gives a longitudinal electric field of 0.3 to 1 GV/m at a laser intensity of 1.7×10¹³ W/cm², in reasonable agreement with theory.

Kl−Ks Mass Difference And Supersymmetric Left-Right-Symmetric Theories, Asim Gangopadhyaya

Physics: Faculty Publications and Other Works

The supersymmetric contributions to the K_L−K_S mass difference makes the previously obtained bounds on the right-handed scale (M_R>1.6 TeV) much weaker. This raises the interesting possibility that the left-right model could be tested as an alternative to SU_L(2)⊗U(1) at low energies. Also we find that to demand that the supersymmetric contribution to the K_L−K_S mass difference be less than 3.5×10⁻¹⁵ GeV requires that scalar-quark masses be more than 400 GeV.

Experimental Study Of Spin-Exchange Effects In Elastic And Ionizing Collisions Of Polarized Electrons With Polarized Hydrogen Atoms, G. D. Fletcher, M. J. Alguard, Timothy J. Gay, V. W. Hughes, P.F. Wainwright, M. S. Lubell, W. Raith

Timothy J. Gay Publications

Using crossed beams of polarized electrons and polarized hydrogen atoms we have investigated the effect of spin exchange on 90° elastic scattering from 4.4 to 30.3 eV and impact ionization from 14.1 to 197.0 eV. Our results suggest that the range of validity of various theoretical approximation methods is more restricted than had been assumed previously.

Measuring R And D Productivity, Richard A. Pappas, Donald S. Remer

All HMC Faculty Publications and Research

Measuring the productivity of an R&D organization is extremely tricky. Productivity is usually defined as a ratio of an output, like number of cars produced on an assembly line, to an input, like the wages paid the workers. While R&D may have a measurable input, the output is often intangible and difficult to quantify. This is further complicated because the return from an R&D department may not be realized for one or two decades,which means the time lag is much higher than in factory measurements. Furthermore, many researchers believe that this kind of measurement may be counterproductive,since the mere act …

Applications Of A Direct Fast Field/Reflectivity Method To Wave Propagation Modeling In Underwater Acoustic And Solid Earth Seismic Environments, Gerard Joseph Tango

LSU New Orleans Theses and Dissertations

A new method is discussed for exact rapid computation of the depth-dependent Green's function occuring in full integral solutions to the acoustic and elastic Helmholtz wave equation, allowing calculations of underwater acoustic propagation loss and full wavefield synthetic seismograms, in range-independent plane stratified media.

Analysis Of A Rocket-Borne Resonant Scatter System For Measurement Of Atomic Oxygen, Neil B. Myers

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

A computer model has been developed at Utah State University for interpreting the results of a rocket-borne resonant scatter measurement system using 1304 A radiation. Atomic oxygen densities are obtained from 65 to 140 km from three rocket flights. The resolution of the system is < 0.1 km, and considerable structure has been observed. The variety of shapes exhibited by the three profiles suggest a dynamic nature to atomic oxygen density profiles in the lower ionosphere. Maximum densities between 2.6 x 10¹¹ and 1.2 x 10¹² cm^-3 were observed at altitudes between 92 and 95 km.

Feasibility Studies Of Conversion Electron Mossbauer Spectroscopy (Cems) Of Iron-Doped Inp, Edward Agyekum

Physics Theses & Dissertations

An electron detector for conversion electron Mossbauer spectroscopy (CEMS) has been designed and built. Tests have been performed to study the effects on the electron detector resolution with respect to high anode voltage, He/CH₄ gas flow rate, and counting rate. These parameters have been optimized to detect the 7.3 keV conversion electrons emitted following resonant absorption of the 14.4 keV source gamma-rays associated with the Mossbauer effect using ⁵⁷Fe nuclei. CEMS spectra have been obtained using standard ⁵⁷Fe enriched and natural iron samples. CEMS spectra and Mossbauer transmission spectra have also been obtained for iron-compensated InP (InP:Fe) …

Beyond The Rigid-Ion Approximation With Spherically Symmetric Ions, L. L. Boyer, M. J. Mehl, J. L. Feldman, John R. Hardy, C. Y. Fong

Physics Faculty Publications

Ab initio calculations show that a spherically symmetric charge relaxation of ions in a crystal, in response to the long-range electrostatic potential, is important for understanding the splitting between longitudinal- and transverse-optic-mode frequencies, and the violation of the Cauchy relations among elastic constants.