Digital Commons Network^™

Ab Initio Studies Of The Phase Transitions In K2Seo4, H. M. Lu, John R. Hardy

John R. Hardy Papers

An ab initio model is developed for the potentials in ionic molecular solids in which the electron covalency within the molecular ions substantially affects the interionic interactions. By treating the intermolecular and intramolecular interactions on the basis of the true electron charge densities of the molecular ions, this new model leads to an accurate parameter-free description of the potentialenergy surfaces for such crystals. We performed first-principles static structural relaxation, supercell molecular-dynamics simulation, and lattice-dynamics studies for the room-temperature paraelectric phase and the lower-temperature ferroelectric superstructure of K₂SeO₄ and predicted with good accuracy the transition from the former …

Collisional Excitation Of Co By 2.3 Ev H Atoms, George C. Mcbane, Scott H. Kable, Paul L. Houston, George C. Schatz

Peer Reviewed Articles

Vibrational and rotational distributions of CO excited by collisions with 2.3 eV H atoms have been obtained by monitoring the products with vacuum ultraviolet (VUV) laser induced fluorescence. Translational-to-vibrational (T→V) transfer is dominated by the dynamics of collisions occurring in the two wells on the H+CO potential energy surface, one characterizing the HCO radical and the other characterizing COH. The measured vibrational distributions agree well with the results of trajectory calculations performed on the ab initio potential energy surface of Bowman, Bittman, and Harding (BBH). The measured rotational distributions show two significant differences from the calculated ones. First, for v …

Theoretical Description Of The Binary Peak In Clothed Ion-Atom Collisions, C. O. Reinhold, Ronald E. Olson

Physics Faculty Research & Creative Works

The impulse or binary encounter approximation for ion-atom collisions is extended to treat the non-Coulomb interaction between a clothed projectile ion and the target electrons. This model is shown to reproduce the unexplained enhancement of the zero-degree binary peak for partially stripped ions over that for Equi velocity fully stripped ions that has recently been observed experimentally in F^q++H₂, He collisions. Very good agreement is obtained between theory and experiment and, furthermore, this model is used to illuminate the underlying dynamics which leads to the observed enhancement. © 1990 IOP Publishing Ltd.

Angular Distribution Of Auger Electrons Emitted Through The Resonant Transfer And Excitation Process Following O⁵⁺+He Collisions, Malika Benhenni, Stephen M. Shafroth, J. K. Swenson, Michael Schulz, J. P. Giese, Harald Schone, Charles Randy Vane, Peter F. Dittner, Sheldon Datz

Physics Faculty Research & Creative Works

This Letter reports the first measurements of the angular distribution of Auger electrons emitted from the decay of the (1s2s2p²)³D O^4+** doubly excited state formed predominantly through resonant transfer and excitation (RTE) in collisions of 13-MeV O⁵⁺ projectiles with He. The (1s2s2p²)³D angular distribution is strongly peaked along the beam direction, in agreement with recent calculations of the RTE angle-dependent impulse approximation. Furthermore, interference effects between the RTE and the elastic target direct-ionization channels are observed.

Mossbauer Spectroscopy Of Fe2+ Binding To Apo And Holo Mammalian Ferritin, Richard B. Frankel, Gerald D. Watt, Georgia C. Papaefthymiou

Physics

The anaerobic binding of Fe²⁺ to apo and holo Mammalian ferritin has been studied in the pH range from 6.0 to 10.0. Mossbauer spectroscopy of samples in which the added Fe 2+ is enriched in Fe-57 shows that the Fe²⁺ ions bind to the ferritin core and exchange electrons with Fe³⁺ ions in the core.

Deep Level Characterization Studies In Gaas, Gordhan R. Barevadia

Electrical & Computer Engineering Theses & Dissertations

The goal of this research was to investigate deep levels in different types of GaAs, a material for high power optically controlled bulk semiconductor switches. For low resistivity semiconductors, such as silicon doped GaAs material (p =0.054 Ω cm), deep level transient spectroscopy (DLTS) was used to characterize deep levels. Three deep levels (EL6, EL3, and EL2) have been detected in this material. For high resistivity semiconductors (p > 10⁴ Ω cm), difficulty of electrical carrier injection and of making a junction does not permit the use of DLTS technique. Therefore, an experimental set-up of the photo-induced current transient spectroscopy …

Computer Simulation Study Of Conductivity In A 2-Dimensional Binary Fluid Mixture, Ras B. Pandey

Faculty Publications

A computer-simulation model is introduced to study the transport properties of a binary fluid mixture in which the constituents of one fluid (the tracer particles) carry charges in a linear charge-density gradient in the background charge of the second fluid. In the steady-state equilibrium, an effective conductivity σ_c(p,r) is estimated as a function of the carrier concentration p and the range of interactions r. The conductivity is observed to vary nonmonotonically with the concentration p, and it exhibits a maximum at a characteristic value p_c. The conductivity decreases when the …

Quantum-Mechanical Harmonic Chain Attached To Heat Baths I: Equilibrium Properties, Ulrich Zürcher, Peter Talkner

Physics Faculty Publications

Starting from quantum Langevin equations for operators we study thermal properties of a one-dimensional harmonic chain to whose ends independent heat baths are attached. In this paper, we mainly discuss the thermal equilibrium state that the chain eventually approaches if the heat baths are at equal temperatures. In the classical limit, this state is determined by the Gibbs ensemble of the free chain, whereas in the quantal case, this is only true if the strength of coupling between chain and heat baths is made infinitely small. We find that corrections for finite coupling strength are appreciable only in boundary layers …

High-Velocity Molecular Gas Associated With Cold Iras Sources, Bruce Wilking, James Blackwell, Lee Mundy

Physics Faculty Works

Maps are presented in the J = 2-1 transition of CO for five molecular outflows associated with deeply embedded far-infrared sources. All of the outflows display lobes of both red- and blue-shifted gas with full velocity extents ranging from 37 to 63 km/s. At least two of the outflows are bipolar but neither is well-collimated. High-velocity C-13O emission is detected in all sources. The data are used to estimate the optical depths, excitation temperatures, masses, momentum supply rates, and energy supply rates for the outflows. A comparison between the properties of IRAS-selected and optically selected molecular outflows is made. The …

Theory Of Light Scattering By A Nonequilibrium Binary Mixture, J.C. Nieuwoudt, B.M. Law

Faculty Publications

A binary mixture subject to a large temperature gradient is studied. Solutions of the evolution equations for the time-dependent fluctuation correlations are obtained using mode-coupling theory subject to the assumption that the mixture is not close to a critical point. From these results predictions for the light-scattering spectrum at the Rayleigh and Brillouin lines are made. The temperature gradient is shown to cause a large enhancement of the scattering amplitude at the Rayleigh line, whereas the effect at the Brillouin line is found to be small.

Analytic Solutions For Three-State Systems With Overlapping Pulses, C. E. Carroll, Foek T. Hioe

Physics Faculty/Staff Publications

Two classes of analytic solutions for three-state systems involving two overlapping laser pulses of different shapes, or of similar shapes but with their centers displaced, are presented. We find a remarkable connection between the order of arrival of the two overlapping pulses and the effectiveness of transfer from the ground state to the third state, and we find remarkable results for the maximum occupation probability of the intermediate state. The approach of these analytic solutions to the adiabatic-following process is also demonstrated.

Random-Field Blume-Capel Model: Mean-Field Theory, Miron Kaufman, M. Kanner

Physics Faculty Publications

The global phase diagram of the Blume-Capel model in a random field obeying the bimodal symmetric distribution is determined by using the mean-field method. The phase diagram includes an isolated ordered critical end point and two lines of tricritical points. A new phase emerges for strong enough random fields: the ferromagnetic-nonmagnetic phase. It is argued that such a phase occurs in three dimensions.

Anomalous Hall-Effect Results In Low-Temperature Molecular-Beam-Epitaxial Gaas - Hopping In A Dense El2-Like Band, David C. Look, D. C. Walters, M. O. Manasreh, J. R. Sizelove, C. E. Stutz, K. R. Evans

Physics Faculty Publications

Molecular-beam-epitaxial GaAs grown at very low temperatures (∼200 °C) exhibits anomalous Hall-effect properties. Here we show conclusively that the room-temperature conduction is due to activated (nearest-neighbor) hopping in a deep defect band of concentration 3×10¹⁹ cm^-3, and energy E_c-0.75 eV, along with conduction due to free carriers thermally excited from this band. At low measurement temperatures, variable-range hopping [σ∝exp(-T₀/T)^1/4] prevails. The conduction-band mobility can be well explained by neutral-deep-donor scattering in parallel with lattice scattering.

Double Excitation Of He By Fast Ions, J. P. Giese, Michael Schulz, J. K. Swenson, Harald Schone, Malika Benhenni, S. L. Varghese, Charles Randy Vane, Peter F. Dittner, Stephen M. Shafroth, Sheldon Datz

Physics Faculty Research & Creative Works

Autoionization of He atoms following double excitation by electrons, protons, C^Q+ (Q=4-6), and F^Q+ (Q=7-9) ions has been studied. The electron-emission yields from the doubly excited 2s²(¹S), 2s2p(¹P), and 2p²(¹P) states were measured at the reduced projectile energy of 1.5 MeV/nucleon for observation angles between 10°and 60°. The results indicate excitation to the 2s²(¹S) and 2p²(¹D) states increases as approximately Q³, while excitation to the 2s2p(¹P) state varies as approximately Q², where Q is …

Magnetic Polarity Fractions In Magnetotactic Bacterial Populations Near The Geomagnetic Equator, F. F. Torres De Araujo, F. A. Germano, L. L. Goncalves, M. A. Pires, Richard B. Frankel

Physics

The relative numbers of North-seeking and South-seeking polarity types in natural populations of magnetotactic bacteria were determined at sites on the coast of Brazil. These sites were South of the geomagnetic equator and had upward geomagnetic inclinations of 1–12°. For upward inclinations >6°, South-seeking cells predominated over North-seeking cells by more than a factor of 10. For upward inclinations

Radiative Kaon Capture On Deuterium And The Λn Scattering Lengths, William J. Fickinger, D. K. Robinson

Faculty Scholarship

The photon spectrum from K-d→Λnγ at rest has been measured for the first time. We obtained the branching ratio, in the end-point region, of (1.89±0.12±0.28)×10-3 where the first error is statistical and the second is systematic. We have found that the shape of the photon energy spectrum is consistent with the distribution calculated by Workman and Fearing with Λn scattering lengths and effective ranges predicted by the Nijmegen group.

A Simulation Of A Multi-Hop Communications Network Using A Kinematic Topology Generator And Static Sphere-Packing Power Control, Kevin Charles Davis

Masters Theses

No abstract provided.

Measurement Of Parity Violation In The Elastic Scattering Of Polarized Electrons From 12C, P. A. Souder, R. Holmes, D. - H. Kim, K. S. Kumar, M. E. Schulze, K. Isakovich, G. W. Dodson, K. W. Dow, M. Farkhondeh, S. Kowalski, M. S. Lubell, J. Bellanca, M. Goodman, S. Patch, Richard Wilson, G. D. Cates, S. Dhawan, Timothy J. Gay, V. W. Hughes, A. Magnon, R. Michaels, H. R. Schaefer

Timothy J. Gay Publications

We have measured the parity-violating electroweak asymmetry in the elastic scattering of polarized electrons from ¹²C nuclei. Our result is A_expt=0.60±0.14±0.02 ppm, where the first error is statistical and the second is systematic. With a beam polarization of 0.37, we compute the isoscalar vector hadronic coupling constant γ̃ to be 0.136±0.032±0.009. The standard model predicts γ̃ =0.155 at the tree level, in agreement with our data.

32nd Rocky Mountain Conference

Rocky Mountain Conference on Magnetic Resonance

Program and registration information for the 32nd 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 29 - August 3, 1990.

Chemical And Reconstruction Induced Surface Core-Level Shifts: H On Low-Index W Surfaces, D. Mark Riffe, G. K. Wertheim, P. H. Citrin

All Physics Faculty Publications

The H-induced shift of the surface-atom core-level binding energy in W(110) is shown to arise from two distinct effects, one chemical in nature and the other structural. The structural shift supports a recently proposed (1p×1) reconstruction that turns on at ∼0.5 monolayer coverage. These new findings are used to provide a self-consistent interpretation of previously reported shifts from H-covered W(111) and W(100) surfaces.

The Study Of Oxygen Transport Through Polycrystalline, Single Crystal And Alloyed Silver, Dongchuan Wu

Physics Theses & Dissertations

The permeation of oxygen through large grain polycrystalline silver, through the (110), (111) and (100) single crystals of silver and through Ag0.05Zr alloy have been studied over the temperature range of 400 - 800 °C. In addition, studies were also conducted using glow discharge dissociation of the supply side ( upstream ) molecular oxygen in order to examine whether normal dissociative adsorption is a limiting step in the overall transport process.

The permeability of oxygen through polycrystalline silver was found to be quite linear and quite repeatable. The diffusivity measurements were found to exhibit two distinct linear regions, one above …

Use Of A Generalized Set Of Variables In Fluid Flow Calculations, Pawel Chwalowski

Mechanical & Aerospace Engineering Theses & Dissertations

In fluid flow calculations, a set of generalized field variables is used to replace the more conventional choice of either the conserved variables, or the primitive variables. This generalized set of variables represents an infinite number of possible choices for the specific set of field variables. For algorithms of both the implicit and explicit type, the resulting effect of a change in field variables on a steady-state flow solution is in general relatively small. However, for implicit algorithms, a consistent linearization with respect to the new variables results in dramatic changes in the overall matrix conditioning of the linear systems …

Universal Scaling Of Nonlocal And Local Resistance Fluctuations In Small Wires, H. Haucke, S. Washburn, A. D. Benoit, C. P. Umbach, Richard A. Webb

Faculty Publications

Resistance fluctuations in small metal samples result from coherent transport of the carriers. The wave functions of the carriers extend into regions which are not accessible classically. We have directly measured the length dependence of the nonlocal magnetoresistance fluctuations in Sb and Au wires by studying regions of our samples separated from the classical current path by a distance L which varied from 3L_cphi down to 0.2L_cphi (where L_cphi is the phase coherence length for the carriers in the metal). These fluctuations decay exponentially with L/L_cphi. Measurements along the classical current paths scale more slowly …

Observation Of Ballistic Phonons In Silicon Crystals Induced By Α Particles, Betty A. Young, Blas Cabrera, Adrian T. Lee

Physics

We have observed the ballistic-phonon-focusing pattern along the [100] axis of a 1-mm-thick silicon crystal using α-particle bombardment as the phonon source. These experiments on phonon-mediated particle detection are performed in vacuum at about 400 mK and use titanium-superconducting-transition-edge phonon sensors on the crystal surfaces. The ballistic time of flight is confirmed in one experiment and the focusing patterns are spatially resolved in another. These data indicate that about 1/3 of the phonon energy striking the back face during the first μsec is ballistic.

Coupled-Channel Optical Calculation Of Electron-Hydrogen Scattering: The Distorted-Wave Optical Potential, Igor Bray, Don H. Madison, Ian E. Mccarthy

Physics Faculty Research & Creative Works

The coupled-channel optical method solves a set of coupled momentum-space integral equations for a finite set of reaction channels. The remaining channels, including the target continuum, are described by the polarization potential operator, which formally depends on the full three-body state vectors for these channels. The distorted-wave optical potential makes the distorted-wave Born approximation for these state vectors, using exact target states. No other approximation is made. Calculations and comparison with experiment are reported for total ionization cross sections and asymmetries, total excitation cross sections, entrance-channel phenomena, and the coupled 1s,2s,2p channels, at a range of energies.

Two-Photon Ionization Of The Ar Atom And Detachment Of The F- Ionv, Cheng Pan, Bo Gao, Anthony F. Starace

Anthony F. Starace Publications

Theoretical calculations of the two-photon ionization cross section of argon and of the two-photon detachment cross section of the negative fluorine ion are presented for the energy region from threshold to the single-photon ionization or detachment threshold. Detailed analyses are presented of the effects of various kinds of electron correlations, whose contributions to the two-photon transition amplitudes are evaluated using variationally stable procedures to sum implicitly over intermediate states. These variationally stable procedures enable us to give much more reliable predictions in the region of the first few intermediate-state resonances in argon than were provided by previous calculations of one …

An Analytic Representation Of The Radial Distribution Of Dose From Energetic Heavy Ions In Water, Si, Lif, Nai, And Sio2, Robert Katz, Kim Sum Loh, Luo Baling, Guo-Rong Huang

Robert Katz Publications

An earlier representation of the radial distribution of dose about the path of a heavy ion in liquid water is modified and extended to include silicon, lithium fluoride, sodium iodide, and silicon dioxide.

The Chemistry Of The Gadolinium-Nickel Interface, D. Lagraffe, Peter A. Dowben, M. Onellion

Peter Dowben Publications

Gadolinium overlayers on Ni(111) have been studied by angle resolved photoemission, angle resolved AES, LEED, and RHEEB. We have observed pronounced interdiffusion of nickel with the gadolinium overlayer at temperatures as low as 150 K. This is in marked contrast with gadolinium overlayers on Cu(108) where substantial interdiffusion is not observed until 360 K, but is consistent with studies of ytterbium on nickel. [A. Nilsson, B Eriksson, N. Martenssom, J. N. Andersen, and J. Onsgaard, Phys. Rev. B 38,10357, ( 1988) and I. Chorkendorff, K. Onsgaard, J. Schmidt-May and R. Nyholm, Surf. Sci. 160, 587, (1985) .] There is a …

Effect Of Second-Order Exchange In Electron-Hydrogen Scattering, Don H. Madison, Igor Bray, Ian E. Mccarthy

Physics Faculty Research & Creative Works

The electron-hydrogen scattering problem has been a nemesis to theoretical atomic physicists due to the fact that even the most sophisticated of theoretical calculations, both perturbative and nonperturbative, do not agree with experiment. The current opinion is that the perturbative approach cannot be used for this problem since recent second-order calculations are not in agreement with the experimental data and higher-order calculations are deemed impractical However, these second-order calculations neglected second-order exchange. We have now added exchange to the second-order calculation and have found that the primary source of disagreement between experiment and theory for intermediate energies is attributable not …

Ordering Of Metal Overlayers On Metal Substrates Studied Using Atom Beam Scattering, G. Vidali, C.W. Hutchings, Peter A. Dowben, M. Karimi, C. Moses, M. Foresti

Peter Dowben Publications

We will illustrate how atom beam scattering (ABS) can be used to study the growth and ordering of adsorption of Hg on Cu(001). At low coverage (less than 2% of a monolayer), we obtain that the scattering cross section of He with (adsorbed) Hg is about 50 Ų. We find that mercury forms two stable phases on Cu(001) in the temperature range between 200 and 330 K, a c (2 x 2) and a high density c (4 x 4) phase. From ABS diffraction data, we can deduce the corrugation of the surface electron charge density of the …