Digital Commons Network^™

A Plasma Focus Interrupting Switch, Gregory Francis Knapp

Electrical & Computer Engineering Theses & Dissertations

The feasibility of using a dense plasma focus (DPF) as a current interrupting device has been investigated. Specifically, a 34-kJ, Mather-type DPF was modified to accept a third electrode so that a discharge could be created between this electrode and the center electrode of the DPF by a 10-kJ inductive energy storage circuit. It was anticipated that the accelerating mechanisms of the DPF pinch, which are known to cause a rapid reduction in the DPF current, would interrupt the 1-kA to 10-kA secondary discharge current thus forcing the secondary current through an external load and hence result in power amplification. …

The Development Of A Microprocessor Controlled Linearly Actuated Valve Assembly, Raymond H. Wall

Mechanical & Aerospace Engineering Theses & Dissertations

The development of a proportional fluid control valve/assembly is presented. This electro-mechanical system is needed for space applications to replace the current proportional flow controllers that use bulky hydraulic or pneumatic actuation systems. The flow is controlled by a microprocessor system that monitors the control parameters of upstream pressure and requested volumetric flow rate. The microprocessor achieves the ·proper valve stem displacement by means of a digital linear actuator. A linear displacement sensor is used to measure the valve stem position. 'Ibis displacement is monitored by the microprocessor system as a feedback signal to close the control loop. With an …

Homogeneous Nucleation Rate For Water, Donald E. Hagen, James L. Kassner

Physics Faculty Research & Creative Works

Homogeneous nucleation rate data for water extending over an exceptionally large domain of rate (J), supersaturation ratio (S), and temperature (T) was recently published. Because it spans a large J-S-T surface, this data constitutes a good test of nucleation theory. Here classical nucleation theory is used to analyze this data. By adjusting only the sticking coefficient, we are able to obtain a good fit between theory and experiment. It was necessary to include an increase in the water molecular density associated with the finite water compressibility.

Weak Localization Of Two-Dimensional Conduction Holes, S. Washburn, Richard A. Webb, E. E. Mendez, L. L. Chang, L. Esaki

Faculty Publications

We report transport measurements which we interpret as weak localization of two-dimensional conduction holes in a GaSb-InAs-GaSb quantum-well structure. This system is unique in that it has parallel conduction channels containing both holes and electrons. The longitudinal resistance of the sample was measured for temperatures between 0.006 and 25 K; the magnetoresistance was measured in a perpendicular magnetic field. Weak localization of the holes was indicated by negative magnetoresistance and by a large logarithmic correction to the conductivity.

Magnetic Hardening In Rapidly Quenched Fe-Pr And Fe-Nd Alloys, David J. Sellmyer, A. Ahmed, G. Muench, George C. Hadjipanayis

David Sellmyer Publications

We report studies of high-field magnetization and thermomagnetic effects in rapidly quenched and heat treated alloys based on Fe-Pr and Fe-Nd. Coercivities up to ~40 kOe and large energy products result from the precipitation of a finely dispersed crystalline phase. Studies of varying the alloy composition and heat treatment are reported. Journal of Applied Physics is copyrighted by The American Institute of Physics.

Spin-Glass-Like Freezing In Disordered Mnpd3 And Crpd3 Alloys, M.H. Rashid, David J. Sellmyer

David Sellmyer Publications

We report studies of dc and ac susceptibility and high-field magnetization on disordered samples of MnPd₃ and CrPd₃. Both samples undergo spin-glass-like transitions, as is evident from susceptibility peaks at 45 and 37 K, respectively. The effective paramagnetic moments deduced from Curie–Weiss fits of the susceptibility in the paramagnetic region are 0.38µ_B/Mn and 0.4µ_B/Cr. Both materials show saturation effects at high applied fields and a flat χ(T) below the spin-freezing temperature in the field-cooled state. The data are discussed in terms of a cluster-glass model with local antiferromagnetic interactions. Journal of …

Mössbauer Study Of Sputtered Fe-Ti Alloys With Wide Composition Range, Sy_Hwang Liou, C.L. Chien

Sy-Hwang Liou Publications

Fe_xTi_100-x alloys over a wide composition range has been made by high-rate sputtering and studied by ⁵⁷Fe Mössbauer spectroscopy. Samples with 30 ≤ x ≤ 80 are amorphous whereas samples with x ≥ 85 are metastable crystalline bcc alloys. Large differences in magnetic properties (e.g., T_c) and hyperfine interactions (Heff, isomer shift) are found between the amorphous and bcc alloys. Comparison of FeTi and Fe₂Ti in amorphous and crystalline states show that the short-range order in the amorphous state has no resemblence to that of the crystalline compounds.

Relativistic Invariance And Zitterbewegung, James A. Lock

Physics Faculty Publications

We examine the question of what it is about the structure of relativistic quantum mechanics that causes the nonintuitive phenomenon of the Zitterbewegung of particle position to exist. Further, we examine various assumptions concerning the measurement process which are implicit in the observation of Zitterbewegung.

Precipitation Of Fe3O4 In Magnetotactic Bacteria, Richard B. Frankel, Richard P. Blakemore

Physics

The magnetotactic bacterium A. magnetotacticum contains ferrous ions, a low density hydrous ferric oxide, a high density hydrous ferric oxide (ferrihydrite) and Fe₃O₄, which is precipitated by partial reduction of the ferrihydrite precursor.

Elastic Differential Cross Sections For Small-Angle Scattering Of 25-, 40-, And 60-Kev Protons By Atomic Hydrogen, Eduard P. Rille, Jerry Peacher, E. Redd, Thomas J. Kvale, Denver G. Seely, D. M. Blankenship, Ronald E. Olson, John T. Park

Physics Faculty Research & Creative Works

Elastic angular differential cross sections for small-angle scattering of protons by atomic hydrogen have been measured. The technique utilized unambigously distinguishes the elastically and inelastically scattered ions. The cross sections fall monotonically by 3 orders of magnitude in the angular range from 0.5 to 3.0 mrad, in the center-of-mass system. The experimental data obtained are in very good agreement with a multistate calculation and in fair agreement with both our Glauber-approximation and classical-trajectory Monte Carlo results.

Coexistence And Spinodal Curves In Directionally Bonded Liquids Using The Four-Cluster Approximation, Erik Bodegom, Paul H. Meijer

Physics Faculty Publications and Presentations

We derive the phase diagrams and spinodals of binary liquid systems with anisotropic interactions, such as hydrogen-bonded molecules. The work is based on the four-particle cluster variation method, using a different potential for different contact points. It is shown that the introduction of a cluster larger than previously used by Barker and Fock, leads to a considerable improvement in the shape of the phase diagram and avoids some of the difficulties encountered in their calculation. Phase diagrams are displayed for various choices of the parameters: the number of contact points, the interaction potential, and the order of the approximation.

H- And He In A Uniform Magnetic Field: Ground-State Wave Functions, Energies, And Binding Energies For Fields Below 109 G, Chang-Hwan Park, Anthony F. Starace

Anthony F. Starace Publications

Wave functions, energies, and binding energies for the lowest singlet states of H- and He in uniform magnetic fields B<10⁹ G are calculated using an adiabatic approximation in hyperspherical coordinates. In computing the angular part of the wave functions, a coupled expansion in one-electron oblate spheroidal angle functions is used. In addition to contracting the two-electron wave function radially, the magnetic field is found to distort the angular part of the wave function mainly by reducing the ss¹S character of the state and replacing it with an sd ¹D character. Results for energies and binding energies …

Esr And Magnetization Of The Spin-Glass Cumn At Low Concentrations, F. R. Hoekstra, G. J. Nieuwenhuys, K. Baberschke, S. E. Barnes

Physics Articles and Papers

We have determined the resonance frequency ω versus resonant field H diagram for CuMn with Mn concentrations 2, 3.5, and 5 at.%, both when H⃗ is parallel and antiparallel to the cooling field H⃗_c. From the parallel measurements we find anisotropy energy density constants K that are in agreement with K values determined from transverse susceptibility and torque measurements. However, the K values determined from the remanence reversal of dc magnetization are smaller by a factor of approximately 2. We suggest that this is caused by a breakdown of rigid-body spin rotations. By combining the parallel data with …

Esr In Situ With A Josephson Tunnel Junction, K. Baberschke, K. D. Bures, S. E. Barnes

Physics Articles and Papers

The in situ electron-spin resonance of a voltage-biased NbAuNb Josephson junction is reported. The Au barrier is doped with Gd or ¹⁶⁷Er ions. Sharp resonances appear in the I-V curves at frequencies equivalent to the crystal-field splitting of AuGd (1.0 and 1.7 GHz) and to the hyperfine splitting of Au¹⁶⁷Er (2.87 GHz). The principle of this new type of ESR-Josephson-junction spectrometer, as well as its application, is discussed.

Esr Relaxation In Spin Glasses, S. E. Barnes

Physics Articles and Papers

The Bloch-Hasegawa theory for the ESR of magnetic alloys is adapted and extended to spin glasses in the paramagnetic regime, that is, for temperatures T>T_G, the cusp temperature. Negative residual widths, reduced thermal broadening, and a possible critical divergence of the residual width are all explained in terms of minor extensions of the standard theory.

Scaling Approach To Spin-Glass Phenomena, S. E. Barnes, A. P. Malozemoff, B. Barbara

Physics Articles and Papers

The scaling model of spin-glass phenomena is extended to consider both longitudinal and transverse order parameters q₁ and q_t. The lowest-order coupling in the free energy goes as q_l²q_t². The field (h) dependence of the reduced temperature t for transverse freezing is found to be t∼h^4/δ where δ is the conventional nonlinear susceptibility field exponent (χ∼h^2/δ). While the transverse correlation length diverges at t=0, the longitudinal correlation length remains finite.

Velocity Measurements Of Humans By Computers, J. B. Rafert, R. C. Nicklin

Faculty Publications

Distance and time, two fundamental quantities, are discussed early in most introductory physics courses. By dividing a change in distance by time to get velocity, and by dividing a change in velocity by time to get acceleration, two more important quantities result. With these the real world of automobiles and jet planes and applications of Newton's second law is available for interpretation from an analytical point of view. In order to get students thinking reliably about these important ideas it seems important to have direct measurements of distance and time over short enough intervals to talk sensibly about "instantaneous" velocities.

Nuclear-Spin-Relaxation Study Of Internal Motion In Two Organic Molecular Solids, Alfonso M. Albano, Peter A. Beckmann, M. E. Carrington, E. E. Fisch, F. A. Fusco, A. E. O'Neill, Mary E. Scott

Physics Faculty Research and Scholarship

We investigate proton spin-lattice relaxation in two powdered organic molecular solids with reorienting methyl (CH3) and tert-butyl [C(CH3)3] groups: 3,5-di-tert-butylphenol (DTBP) and 1,3,5-tri-tert-butylbenzene (TTBZ). The temperature and Larmor frequency dependence of the relaxation rate is considerably more complicated than would be expected on the basis of random reorientations of the CH3 and C(CH3)3 groups. The spectral densities describing the relaxation are broader, and show more structure, than those customarily used to interpret relaxation data. Assuming that the spectral densities may be expressed as linear superpositions of Lorentzians, we are able to obtain a single, nonexponential correlation function which leads to …

Mithras: A Brief Description, O De La Beaujardiere, Vincent B. Wickwar, M J. Baron, J Holt, R M. Wand, W L. Oliver, P Bauer, M Blanc, C Senior, D Alcayde, G Caudal, J Foster, E Nielsen, R Heelis

All Physics Faculty Publications

Between May 1981 and June 1982 an intensive campaign of 33 coordinated observations was carried out using the three incoherent-scatter radars capable of probing the auroral zone. During this period the groups operating the Dynamic Explorer satellites and the STARE radar made special efforts to acquire data coincident with the radar observations. The objective of these MITHRAS experiments and subsequent analysis is to further our understanding of the interactions of the magnetosphere, the ionosphere, and the thermosphere, with special emphasis on local time/universal time variations. Three experimental modes with different time resolution and spatial coverage were used to examine different …

Nighttime Thermospheric Winds Over Sondre Stromfjord, Greenland, J W. Meriwether Jr., P Shih, T L. Killeen, Vincent B. Wickwar, R G. Roble

All Physics Faculty Publications

Observations of nighttime thermospheric neutral winds made at Sondre Stromfjord, Greenland, with optical and radar instrumentation, showed an occasional abatement in the equatorward meridional wind at a magnetic local time corresponding to the nighttime division between the evening and morning convection cells. This abatement appeared primarily in the poleward observations. In contrast, however, the characteristic midnight “surge” was usually seen in the equatorward set of observations. The apparent acceleration of about 250 m/s or greater within 4.6° latitude we attribute, in part, to a merging of neutral jet streams generated by polar cap ion drag adjacent to the auroral zone …

The Polar Ionosphere: Editorial, Vincent B. Wickwar, J W. Meriwether Jr.

All Physics Faculty Publications

Editorial

On The Reversal From “Sunward” To “Antisunward” Plasma Convection In The Dayside High Latitude Ionosphere, T S. Jorgensen, E Friis-Christensen, Vincent B. Wickwar, J D. Kelly, C R. Clauer, P M. Banks

All Physics Faculty Publications

Preliminary observations of dayside high latitude ionospheric plasma convection with the Sondrestrom incoherent‐scatter radar indicate that plasma can be observed to enter the polar cap region through rotational reversals at most local times between dawn and dusk and not just in a narrow region around noon. Assuming that rotational reversals are signatures of a solar wind‐magnetosphere interaction which drives magnetospheric convection, the observations indicate that this interaction occurs over a longitudinally wide area of the dayside magnetosphere. The observations also show that the distribution of F‐region plasma in the polar cap is dependent on ionization sources anywhere between dawn and …

Probability Densities And The Random Variable Transformation Theorem, John D. Ramshaw

Physics Faculty Publications and Presentations

D. T. Gillespie has recently derived and discussed a random variable transformation (RVT) theorem relating the joint probability densities of functionally dependent sets of random variables.....

It is hoped that the present discussion will help to disseminate this basic relation among a wider circle of nonspecialists.

Very High Electron Temperatures In The Daytime F-Region At Sondrestrom, W Kofman, Vincent B. Wickwar

All Physics Faculty Publications

Sondrestrom observations show that a characteristic F‐region signature of the interaction between the magnetosphere and ionosphere is a narrow band of elevated electron temperatures. Its location is associated with the ion convection reversal in the morning and evening convection cells. Typically, near 500 km altitude, the temperature is 3500 to 4000 K. However, on 24 April 1983, a geomagnetically very active day with Kp values of 6‐ during the period of interest, the electron temperature reached 6000 K in the afternoon convection reversal. The ion velocities were between 1 and 2 km/s on both sides of the reversal. There was …

Ionospheric Currents And F-Region Plasma Boundaries Near The Dayside Cusp, S Vennerstrom, E Friis-Christensen, T S. Jorgensen, C. E. Rasmussen, C R. Clauer, Vincent B. Wickwar

All Physics Faculty Publications

Observational evidence of the location of a dayside high‐latitude ionospheric current (DPY current) with respect to the different regimes of the high‐latitude magnetosphere is obtained by analyzing data from the magnetometer chain along the west coast of Greenland in conjunction with simultaneous measurements from the newly established incoherent‐scatter radar facility at Sondre Stromfjord. The latitudinal location of the DPY current is compared with the location of the maximum F‐region electron temperature and with the location of the plasma convection reversal from sunward to antisunward. The maximum in the F‐region electron temperature roughly coincides with the velocity reversal boundary, while the …

The Meridional Thermospheric Neutral Wind Measured By Radar And Optical Techniques In The Auroral Region, Vincent B. Wickwar, J W. Meriwether Jr., P B. Hays, A F. Nagy

All Physics Faculty Publications

Radar observations of ion velocities in the magnetic zenith over Chatanika, Alaska, were used to determine the geomagnetic meridional component of the thermospheric neutral wind. Corrections for molecular diffusion and molecular ion contamination of the pure O⁺ composition assumed for the ionosphere were included in the analysis. Comparison of the averaged diurnal variation of the meridional wind showed good agreement between the two measurement techniques. Good agreement was also found for several cases of simultaneous observations. The evidence suggested that differences were caused by gravity waves. The 7 years of radar meridional wind results were examined with respect to …

Initial Millstone Hill, Sondrestrom, And Hilat Observations Of Thermospheric Temperatures And Frictional Heating, W L. Oliver, J C. Foster, J M. Holt, G B. Loriot, Vincent B. Wickwar, J D. Kelly, O De La Beaujardiere, P F. Bythrow, D I. Meng, F J. Rich, R E. Huffman

All Physics Faculty Publications

Elevation scan observations made by the Millstone Hill and Sondrestrom incoherent scatter radars are combined to provide extended latitudinal coverage of thermospheric measurements. Maps of the latitudinal and temporal structure of the exospheric temperature are presented for two 24‐hour periods over the latitude range 45 to 72 degrees north. On the magnetically quiet June day the Millstone and Sondrestrom data formed a consistent picture of thermospheric structure. On the disturbed July day the two radars observed very different behavior, with Millstone Hill observing strong, long‐lived ion frictional heating events but Sondrestrom observing more quiescent behavior. Comparison with HILAT satellite data …

Pitch Angle Properties Of Magnetospheric Thermal Protons And Satellite Sheath Interference In Their Observation, Jan Josef Sojka, G. L. Wrenn, J.F. E. Johnson

All Physics Faculty Publications

Cold proton observations from the geosynchronous GEOS 2 satellite are presented to show the pitch angle distribution of the refilling cold ion population found beyond the plasmapause. This refilling cold ion population flows into the depleted equatorial regions of the flux tubes from the topside ionosphere. This refilling is observed both day and night. The ions have energies between 0.5 and 3 eV. These energy characteristics are consistent with other recent observations. Although the observed angular distribution of these ions is highly complex, when allowance is made for the satellite sheath several conclusions can be made concerning the ion pitch …

Plasma Characteristics Of Polar Cap F-Layer Arcs, H C. Carlson Jr., Vincent B. Wickwar, E J. Weber, J Buchau, J G. Moore, W Whiting

All Physics Faculty Publications

First results are reported of a comprehensive campaign to measure ionospheric structure and dynamics of nighttime polar cap F‐layer or F‐region arcs. Airborne optical and digital ionosonde data were collected simultaneously with ground based incoherent scatter radar data, continuously over many hours in time and 500 to 1000 km in space. Polar cap F‐region sub‐visual auroral arcs, which are commonly observed during quiet magnetic conditions, are found to represent boundaries (or shears) in the polar cap plasma circulation pattern. F‐region electron concentration enhancements are found in these features and can be of significance to polar thermospheric circulation, composition, and thermal …

Observations Of Interplanetary Magnetic Field And Of Ionospheric Plasma Convection In The Vicinity Of The Dayside Polar Cleft, C R. Clauer, P M. Banks, A Q. Smith, T S. Jorgensen, E Friis-Christensen, S Vennerstrom, Vincent B. Wickwar

All Physics Faculty Publications

Dayside ionospheric convection at high latitudes has been examined during a series of experiments using the Sondrestrom radar together with ancillary observations of the interplanetary magnetic field (IMF) by the IMP‐8 spacecraft. The radar experiments obtained a latitude coverage of 67.6° Λ to 81.30° Λ and a temporal resolution of between 14 to 25 minutes. A total of 17 rotations through the dayside cleft region during April, June and July, 1983 have been examined. The observations show two convection cells with sunward flow at lower latitudes and antisunward flow at higher latitudes. The flow commonly rotates through a 180° angle …