Digital Commons Network^™

Solar Cycle Dependence Of Spacecraft Charging In Low Earth Orbit, T. B. Frooninckx, Jan Josef Sojka

All Physics Faculty Publications

Recent experimental evidence has shown that Defense Meteorological Satellite Program (DMSP) polar orbiting spacecraft at 840 km can develop electric potentials as severe as −1430 V while at high magnetic latitudes. To explore this charging region, an analysis of DMSP F6, F7, F8, and F9 satellite precipitating particle and ambient plasma measurements taken during periods of high, medium, and low solar flux is performed. One hundred eighty-four charging events ranging from −46 to −1430 V are identified, and an extreme solar cycle dependence is found as charging is most frequent and severe during solar minimum. Satellite measurements and time-dependent ionospheric …

Atomic Collision Processes Of Interest In Controlled Thermonuclear Fusion Research, Victor Dewitt Irby

Doctoral Dissertations

"This thesis examines several atomic collisional processes involved in controlled thermonuclear fusion. Specifically, experimental studies have been made on the state- selective single capture reaction

³He²⁺ + He —> ³He⁺(n) + He⁺(n'), (1)

on the double capture reaction

³He²⁺ + H e—> ³He + He²⁺ , (2)

and on the single ionization of atomic targets X

A^q+ + X —> A^q+ + X⁺ + e^- (3)

by charged projectiles A^q+. Reactions (1) and (2) have an importance in plasma energy balance and in …

On The Standing Wave Mode Of Giant Pulsations, K. Takahashi, N. Sato, J. Warnecke, H. Luhr, Harlan E. Spence, Y. Tonegawa

Physics & Astronomy

Both odd-mode and even-mode standing wave structures have been proposed for giant pulsations. Unless a conclusion is drawn on the field-aligned mode structure, little progress can be made in understanding the excitation mechanism of giant pulsations. In order to determine the standing wave mode, we have made a systematic survey of magnetic field data from the AMPTE CCE spacecraft and from ground stations located near the geomagnetic foot point of CCE. We selected time intervals when CCE was close to the magnetic equator and also magnetically close to Syowa and stations in Iceland, and when either transverse or compressional Pc …

Alloy Scattering In P-Type Alxga1-Xas, David C. Look, D. K. Lorance, J. R. Sizelove, C. E. Stutz, K. R. Evans, D. W. Whitson

Physics Faculty Publications

The hole mobility of Be‐doped ( ~ 2 × 10¹⁷ cm^-3) AlxGa1-xAs, for x=0–1, is analyzed both theoretically and experimentally. Alloy scattering is very important, and in fact reduces the hole mobility from 150 to less than 90 cm²/V s at x=0.5. The main parameter in the alloy scattering formulation, the alloy potential Eal, is found to be about 0.5 eV for p‐type AlxGa1-xAs.

Densities And Vibrational Distribution Of H3+ In The Jovian Auroral Ionosphere, Y. H. Kim, Jane L. Fox, H. S. Porter

Physics Faculty Publications

Observations of the H₃⁺ infrared emission at 2 and 4 μm have suggested that H₃⁺ is in local thermodynamic equilibrium (LTE) in the region of the Jovian ionosphere from which the emissions originate. We have tested this assumption by calculating the vibrational distribution of H₃⁺ over the altitude range of 350 to 1500 km above the methane cloud tops (1 to 4 × 10⁻³ μbar). We have constructed a model of the Jovian auroral ionosphere in which the neutral temperatures are enhanced over those of the mid-latitude ionosphere, as suggested by observations and …

Proteolytic Modification Of The Ca²-Release Mechanism Of Sarcoplasmic Reticulum In Skeletal Muscle, Ute Goerke

Dissertations and Theses

Calcium ions are important mediators in the mechanism of contraction and relaxation of muscle fibers. Depolarization of sarcolemma and transverse tubule causes an increase of myoplasmic ca2+ concentration which induces contraction of the myofibrils. In skeletal muscle fibers, the intracellular Ca²⁺ concentraton is regulated by an extensive membrane system, the sarcoplasmic reticulum (SR). Ca²⁺-release from SR is initiated by depolarization of the transverse tubule via a process referred to as excitation-contraction coupling. The Ca²⁺ - release channel located in the junctional SR plays an important role in this mechanism.

Characterization Of As-Prepared And Annealed W/C Multilayer Thin Films, David D. Allred, Qi Wang, Jesus González-Hernández, B. S. Chao, D. A. Pawlik

Faculty Publications

Tungsten/carbon (W/C) multilayer thin films were prepared by dc magnetron sputtering. All samples consisted of 30 layer pairs with a nominal d-spacing varying from 2.5 to 14 nm, the W layer thickness was kept at 2 nm in all samples. The W/C multilayers were subjected to isochronal anneals in a quartz tube furnace at the temperature range from 500 to 950 °C under a flow of high purity Ar gas. X-ray diffraction, Raman scattering, and Auger depth profile were used to characterize the structure of the as-prepared and annealed multilayer films. Both the W and C layers appear to be …

X-Ray Diode Using A Silicon Field Emission Photocathode, W. I. Karian, Larry V. Knight, David D. Allred, A. Reyes-Mena

Faculty Publications

We have produced arrays of 10,000 sharp p-type silicon points using an etch plus oxidation method. The points were used as electron emitters. No high vacuum cesiation or high temperature cleaning was needed to observe the electron emission. These are seen to be photosensitive sources of electrons at 200 K and 300 K. They were also used to produce AlKα x-rays. This constitutes the first use of etched, point arrays for generating electrons for x-ray sources.

Manufacturing Of Atomically Sharp Silicon Tips And Their Use As Photocathodes, W. I. Karian, Larry V. Knight, David D. Allred, A. Reyes-Mena

Faculty Publications

The discovery and understanding of the photoelectric effect led to the study of photoemissive materials fall into two major categories: classical photoemitters and negative-electron-affinity (NEA) materials. Classical photoemitters usually involve an alkali metal, a group-V element such as phosphorus, silver, and/or oxygen. An example is the Ag-O-Cs (S1) photoemitter. NEA photocathodes consist of a photoconductive single crystal semiconductor covered with a thin layer of cesium and oxygen. This layer lowers the work function of the photocathode. A dipole layer is formed at the surface, and band bending occurs. This lowers the effective work function. An example is the GaAs(CsO) photocathode …

Density Effect In Cu K-Shell Ionization By 5.1-Gev Electrons, W. E. Meyerhof, D. G. Jensen, D. M. Kawall, S. E. Kuhn, D. W. Spooner, Z. E. Meziani, D.. N. Faust

Physics Faculty Publications

We have made an absolute measurement of the Cu K-shell impact ionization cross section by 5.1-GeV electrons, which demonstrates directly a density effect predicted by Fermi in 1940. By determining the ratio of the K x-ray yield from a thin front and back layer of the target by a novel grazing emission method, we have verified the effect of transition radiation on the x-ray production, suggested by Sorensen and reported by Bak et al.

Energetic Protons And Deuterons Emitted Following Μ⁻ Capture By ³He Nuclei, W. J. Cummings, G. E. Dodge, S. S. Hanna, B. H. King, S. E. Kuhn, Y. M. Shin, R. Helmer, R. B. Schubank, N. R. Stevenson, U. Wienands, Y. K. Lee, G. R. Mason, B. E. King, K. S. Chung, J. M. Lee, D. P. Rosenzweig

Physics Faculty Publications

Spectra of energetic protons and deuterons emitted following negative muon capture from rest in ³He have been measured for the first time. Significant capture strength is observed at high energy transfers (mμ- E_v >60 MeV) for the two-body and three-body breakup channels, indicative of the importance of nucleon-nucleon correlations and meson exchange currents in the capture process. A simple plane wave impulse approximation calculation reproduces the proton spectrum reasonably well, but underpredicts the deuteron rate at the highest energies by a large factor.

Science On The Great Plains: The History Of Physics And Astronomy At The University Of Nebraska-Lincoln, M. Eugene Rudd

M. Eugene Rudd Publications

The year 1988 marked the 100th anniversary of the founding of the Department of Physics at the University of Nebraska. While the year passed without fanfare in the department, DuaneJaecks, one of the members of the faculty, suggested to the author that it would be a good time to write a history of what is now the Department of Physics and Astronomy. He not only provided the initial impetus for the project, but has also given it his continual help and encouragement. While the initial plan was to write only a brief, informal departmental history, the project, like Topsy, grew. …

Spatial Correlation Between Ch, Cn And The Diffuse Interstellar Band Carriers, J Krelowski, T P. Snow, C G. Seab, J Papaj

Physics Faculty Publications

Observations are presented of the diffuse interstellar bands at 5780 and 5797 A and of the ultraviolet lines of CH and CN in the light of six bright stars which lie behind isolated interstellar clouds. It is found that CN and CH are only present when the 5797 band is deeper than the 5780 one. Comparisons with satellite measurements of the UV extinction show that the shape of the extinction curve is linked to the same band ratio in these stars. The results support a previous suggestion that the various components of the absorption spectrum of an isolated cloud (the …

Unitary One Matrix Models: String Equation And Flows, Konstantinos N. Anagnostopoulos, Mark Bowick

Physics - All Scholarship

We review the Symmetric Unitary One Matrix Models. In particular we discuss the string equation in the operator formalism, the mKdV flows and the Virasoro Constraints. We focus on the -function formalism for the flows and we describe its connection to the (big cell of the) Sato Grassmannian Gr (0) via the Plucker embedding of Gr (0) into a fermionic Fock space. Then the space of solutions to the string equation is an explicitly computable subspace of Gr (0) \Theta Gr (0) which is invariant under the flows.

Translational Correlations In The Vortex Array At The Surface Of A Type-Ii Superconductor, M. Cristina Marchetti, David R. Nelson

Physics - All Scholarship

We discuss the statistical mechanics of magnetic flux lines in a finite-thickness slab of type-II superconductor. The long wavelength properties of a flux-line liquid in a slab geometry are described by a hydrodynamic free energy that incorporates the boundary conditions on the flux lines at the sample's surface as a surface contribution to the free energy. Bulk and surface weak disorder are modeled via Gaussian impurity potentials. This free energy is used to evaluate the two-dimensional structure factor of the flux-line tips at the sample surface. We find that surface interaction always dominates in determining the decay of translational correlations …

Empirical Relations Between Static And Dynamic Exponents For Ising Model Cluster Algorithms, Paul D. Coddington, Clive F. Baillie

Physics - All Scholarship

We have measured the autocorrelations for the Swendsen-Wang and the Wolff cluster update algorithms for the Ising model in 2, 3 and 4 dimensions. The data for the Wolff algorithm suggest that the autocorrelations are linearly related to the specific heat, in which case the dynamic critical exponent zW int,E = α/ν. For the Swendsen-Wang algorithm, scaling the autocorrelations by the average maximum cluster size gives either a constant or a logarithm, which implies that zSW int,E = β/ν for the Ising model.

Diffraction Of Light By A Focused Ultrasonic Wave, J. Huang, Joel Alan Nissen, Erik Bodegom

Physics Faculty Publications and Presentations

The measurement of the acoustic pressure of a planar ultrasonic wave by light diffraction is well established. The ability to do similar measurements in the case of spherical waves has been doubted. However, we show that the range of validity can be extended to the focal region of a spherical concave piezoelectric transducer. Light is passed through the focal plane of a spherical concave transducer and is diffracted as a result of the variation in the index of refraction. The peak pressure can be calculated from the diffraction intensity by making the following simplification. We assume that in the focal …

Principal Linear Polarization States Of An Optical System, R. M.A. Azzam

Electrical Engineering Faculty Publications

The constraint on the Jones matrix of an optical system such that there exist two linear polarization states at its input that are mapped onto two corresponding linear states at its output is derived. These principal linear polarization (PLP) states, which characterize a broad range of systems, are also found in terms of the Jones matrix elements. Special cases when the PLP states are orthogonal, collapse onto one state, or become infinite in number are indicated. For a deterministic or nondeterministic optical system described by a Mueller matrix, the existence of two PLP states places a constraint on only 3 …

Bounds On The Polymer-Length Distribution In Equilibrium Polymerization, Rolfe G. Petschek

Faculty Scholarship

We obtain upper bounds on the polymer-length distribution in a class of models for equilibrium polymerization. This rules out a recent claim for the existence of a collapsed phase in which a nonzero fraction of the monomers are in infinite polymer(s). We discuss the behavior of finite systems, in which a collapse of sorts does occur, and indicate how this collapse disappears in the thermodynamic limit.

Schroedinger Equation With Spherically Averaged Potentials, C. A. Hughes

Journal of the Arkansas Academy of Science

Using a method adapted from few—body hyperspherical techniques, an approach to the solution of the Schroedinger equation with nonspherical potentials is discussed. The method is to spherically average the potential over spherical angles and then solve the resulting set of coupled differential equations. A discussion of how this method is applied to the Stark effect is presented.

Development Of A Variable Wavelength Flame Infrared Emission Gas Chromatography Detector, Weiqun Zhang, M. Keith Hudson, Mokhtar Mofidi

Journal of the Arkansas Academy of Science

No abstract provided.

Comparison Of Two Models For Breakdown Waves, Debra Burris, Mostafa Hemmati

Journal of the Arkansas Academy of Science

In this paper, the two theories concerning the propagation of breakdown waves are compared. The two theories are as follows: 1. The photoionization theory, in which the driving force of the propagation is the electromagnetic radiation from the hot gas generated at the electrode with the greatest potential gradient. 2. The electron fluid dynamical theory, in which the driving force of the propagation is the partial pressure of the high temperature electron gas generated in the neighborhood of the pulsed electrode. Successes in explaining the experimental data will be compared.

Competition Between Superconductivity And A New 20 K Phase In -(Bedt-Ttf)2i3: Specific Heat Measurements, Nathanael A. Fortune, K. Murata, K. Ikeda, T. Takahashi

Physics: Faculty Publications

We present here direct calorimetric evidence for a new transition at T*=22.25 K in the metallic state of quasi-2D organic superconductor -(BEDT-TTF)2I3 at ambient pressure, as suggested by our previous measurement of the temperature-dependent Hall coefficient RH(T). The apparent reduction in the effective electronic density of states at T* quantitatively explains for the first time the suppression of Tc from the pressure-stabilized eehigh-Tcee value of 8 K to the ambient-pressure cooled eelow-Tcee value of 1.5 K.

Hydration Behavior Of Laser Dye Aerosols Of Mixed Composition Having High Critical Supersaturations, Max B. Trueblood, Donald E. Hagen, Darryl J. Alofs

Mechanical and Aerospace Engineering Faculty Research & Creative Works

This Study Concerns Aerosol Particles of Mixed Composition. the Particles Contain a Water Insoluble Core (Polystyrene Latex), Surrounded by a Water Soluble Shell (Various Fluorescent Dyes). a Collison Nebulizer and an Electrostatic Aerosol Classifier Are Used to Prepare the Aerosol; its Critical Supersaturation Spectrum is Measured with a Diffusion Cloud Chamber. Experiments Were Done using Four Different Dyes (Disodium Fluorescein, Sulforhodamine 640, Sulforhodamine B and Rhodamine 560 Chloride) with Five Different Polystyrene Latex Sphere Sizes. the Results Indicate that a Kohler-Type Behavior is Obeyed. This Technique of Putting a Soluble Coating Onto an Insoluble Core is Found to Be a …

Track Structure Model For Damage To Mammalian Cell Cultures During Solar Proton Events, Francis A. Cucinotta, J. W. Wilson, L. W. Townsend, J. L. Shinn, Robert Katz

Robert Katz Publications

Solar proton events (SPEs) occur infrequently and unpredictably, thus representing a potential hazard to interplanetary space missions. Biological damage from SPEs will be produced principally through secondary electron production in tissue, including important contributions due to delta rays from nuclear reaction products. We review methods for estimating the biological effectiveness of SPEs using a high energy proton model and the parametric cellular track model. Results of the model are presented for several of the historically largest flares using typical levels and body shielding.

Comment On Ncrp Report No. 104, "The Relative Biological Effectiveness Of Radiations Of Different Quality", Robert Katz

Robert Katz Publications

The validity of a linear extrapolation to lowest fluences of charged particles demands that the transit of a single charged particle through the target volume is capable of inducing the chain of events leading to an observable end-point. This is always the case for one-hit detectors. It is not always the case for biological cells and tissues (Katz and Hofmann 1982).
By way of example, Cole ct al. (1980) found that, on average, some 500 electrons pass into the nucleus of a CHO cell for inactivation. Similarly, Warters et al. (1977) found that some 500 tritium decays in the nucleus …

Temperature And Suction Effects On The Instability Of An Infinite Swept Attachment Line, D. G. Lasseigne, T. L. Jackson, F. Q. Hu

Mathematics & Statistics Faculty Publications

It is known that the incompressible, infinite swept attachment line flow is unstable to streamwise disturbances that originate in the boundary layer when the cross-flow exceeds a critical magnitude. Furthermore, a small degree of suction at the surface has a significant stabilizing influence while a small degree of blowing has a considerable destabilizing influence. This paper investigates the stabilizing and destabilizing effects of, respectively, cooling or heating the plate and the competing or enhancing effects of suction or blowing. A nonorthogonal flow with respect to the attachment line is also considered by adding a component of shear to the mean …

Monte Carlo Study Of A Simple Model Bulk-Ice-Ih System: P-T Melting Behavior At Constant Volume, K. Han, Barbara N. Hale

Physics Faculty Research & Creative Works

An NVT Metropolis Monte Carlo computer simulation is used to examine the P-T behavior of a constant-density model periodic ice-Ih sample near melting. The ice unit cell with density 0.904 g/cm³ consists of 192 rigid water molecules interacting via the revised central-force potentials (RSL2) of Stillinger and Rahman [J. Chem. Phys. 68, 666 (1978)] with a cutoff. Intramolecular parameters are determined from a minimization of the total potential energy of the ice-Ih structure at 0 K. In the P-T plot, emergence of the liquid-solid coexistence region is signaled by a change in sign of dP/dT (when expansion occurs upon …

Pressure And Temperature Effects On The Energy Of Formation For Silicon Clusters, Sung-Ho Suck Salk, Chen K. Lutrus, Donald E. Hagen, T. Oshiro, Steven M. Beck, Gary L. Loper

Physics Faculty Research & Creative Works

At present most theoretical studies of atomic clusters are limited to their physical properties referred to 0 K. To the best of our knowledge, there exists no theoretical study of the simultaneous dependence of cluster formation and cluster-size distributions on both pressure and temperature. In the present work both pressure and temperature effects on the formation of silicon clusters are explored. A universal semiempirical formula is obtained to show a general trend in the variation of binding energy as a function of cluster size for both atomic and molecular clusters.

Magnetic Properties Of A Novel Iron Carbide Film, Fe₇C₃X Formed In A Glow Discharge, Oran Allan Pringle, Gary J. Long, Fernande Grandjean, Jun L. Li, George C. Hadjipanayis, William Joseph James

Physics Faculty Research & Creative Works

No abstract provided.