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Articles 1771 - 1800 of 1948

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Interacting Rydberg Channels In Diatomic Molecules., Ning Yi Du Jan 1989

Interacting Rydberg Channels In Diatomic Molecules., Ning Yi Du

LSU Historical Dissertations and Theses

A new model for a class of heteronuclear diatomic molecules is presented. This model readily combines multichannel quantum defect theory (MQDT) with a nonperturbative Fermi-type analysis. Applications to a series of alkali-He dimers, such as CsHe, have shown that this very simple model can give results (e.g. Born-Oppenheimer potential curves) very close to those from more elaborated methods (e.g. $\ell$-dependent pseudopotential method). Applications to heteronuclear rare gas dimers, such as ArXe, give the first detailed interpretation and classification of some of the observed spectra, which are too complicated to be studied by conventional molecular methods. Another MQDT application is also …

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Experimental Study Of Nonlinear Conductance In Small Metallic Samples, Richard A. Webb, S. Washburn, C. P. Umbach May 1988

Experimental Study Of Nonlinear Conductance In Small Metallic Samples, Richard A. Webb, S. Washburn, C. P. Umbach

Faculty Publications

We have directly observed current-dependent, nonlinear contributions to the conductance fluctuations of phase-coherent metallic wires and loops. The fluctuations in the current-voltage curves are reproducible, asymmetric about I=0, and in qualitative agreement with theoretical predictions. In ac measurements, the nonlinear terms also generate large harmonic signals of the conductance fluctuations whose dependence on the drive current can be understood qualitatively. The spectra of harmonics from loops and wires have different dependences on the voltage across the sample.

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Normal-Metal Aharonov-Bohm Effect In The Presence Of A Transverse Electric Field, S. Washburn, H. Schmid, D. Kern, Richard A. Webb Oct 1987

Normal-Metal Aharonov-Bohm Effect In The Presence Of A Transverse Electric Field, S. Washburn, H. Schmid, D. Kern, Richard A. Webb

Faculty Publications

The effects of transverse electric fields on the conductance fluctuations in an Sb loop have been studied. We show that the electric field can be used to tune the position (or phase) of Aharonov-Bohm oscillations as well as to alter the aperiodic conductance fluctuation patterns. We disucss two mechanisms which might cause the observed dependence of the fluctuation pattern on transverse electric field. The first is the electrostatic Aharonov-Bohm effect, and the second is the spatial shifting of the electron trajectories by the electric field.

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Length-Independent Voltage Fluctuations In Small Devices, A. Benoit, C. P. Umbach, R. B. Laibowitz, Richard A. Webb Jun 1987

Length-Independent Voltage Fluctuations In Small Devices, A. Benoit, C. P. Umbach, R. B. Laibowitz, Richard A. Webb

Faculty Publications

Conductance fluctuations in one-dimensional lines of length L shorter than the phase-coherence length Lφ are not universal but diverge as L-2. Using the Onsager relations and voltage additivity, we show that the voltage fluctuations are independent of the distance between voltage probes. The antisymmetric (Hall-type) contribution to the voltage fluctuations is constant for all values of L. Measurements of the voltage fluctuations and correlation function between different regions in Au and Sb lines confirm these results.

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Electron Transport And Optical Emissions In The Aurora, Dirk Lummerzheim Apr 1987

Electron Transport And Optical Emissions In The Aurora, Dirk Lummerzheim

Physics

A one-dimensional, steady state auroral model is developed based on a linear electron transport calculation. A set of cross sections for electron neutral collisions describing elastic scattering, energy loss, and photon emission is compiled and used in conjunction with a discrete ordinate transport code. Calculated electron intensities are compared with in situ rocket measurements. Auroral optical emissions that result from direct electron impact on neutrals are calculated for synthetic and observed electron spectra. A systematic dependence of the brightness of auroral features on energy flux, characteristic energy, and atmospheric composition is found and parameterized. A method for interpreting the brightness …

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Preregularization And Anomalies, Md Abul Chowdhury Jan 1987

Preregularization And Anomalies, Md Abul Chowdhury

Digitized Theses

'Pre-regularization', a symmetry preserving technique for handling divergent Feynman integrals, is described. We apply this technique to gauge theories and to supersymmetric theories. Using pre-regularization, the supercurrent anomaly, the higher dimensional chiral anomaly and the second order radiative corrections to the VVA triangle graph are computed. These involve using surface terms that arise due to the shift of integration variable in more than logarithmic divergent integrals, in order to ensure that symmetries of the theory not broken. In all cases, the usual results of perturbation theory are recovered without having to introduce an explicit regulating parameter into the initial action.

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Asymmetry In The Magnetoconductance Of Metal Wires And Loops, A. D. Benoit, S. Washburn, C. P. Umbach, R. B. Laibowitz, Richard A. Webb Oct 1986

Asymmetry In The Magnetoconductance Of Metal Wires And Loops, A. D. Benoit, S. Washburn, C. P. Umbach, R. B. Laibowitz, Richard A. Webb

Faculty Publications

Universal conductance fluctuations in wires and Aharonov-Bohm oscillations in loops are not symmetric about H=0. The observation of asymmetry in the periodic oscillations is possible when the phase-coherence length of the wave function is comparable to the separation of the voltage probes. In both cases, four-probe measurements yield resistances which depend on lead configuration. The asymmetries appear like Hall voltages, and are consistent with Onsager's relations.

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Observation Of Resonant Tunneling In Silicon Inversion Layers, A. B. Fowler, G. L. Timp, J. J. Wainer, Richard A. Webb Jul 1986

Observation Of Resonant Tunneling In Silicon Inversion Layers, A. B. Fowler, G. L. Timp, J. J. Wainer, Richard A. Webb

Faculty Publications

Measurements of the temperature and carrier-density dependence of the strongly localized conductance of short silicon inversion layers are reported. At the lowest temperatures we observe well-isolated, large conductance peaks whose width and temperature dependence are only consistent with resonant tunneling and are inconsistent with Mott hopping. Several new features are observed which we believe may be the result of Coulomb interactions.

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Interaction Effects Among Two-Dimensional Electrons And Holes, S. Washburn, Richard A. Webb, E. E. Mendez, L. L. Chang, L. Esaki Jun 1986

Interaction Effects Among Two-Dimensional Electrons And Holes, S. Washburn, Richard A. Webb, E. E. Mendez, L. L. Chang, L. Esaki

Faculty Publications

We report large logarithmic corrections to the conductivity of two-dimensional electrons and holes in GaSb-InAs-GaSb double heterostructures. From ∼ 40 mK to 1 K, the conductivity increased with the logarithm of the temperature but with a slope as much as 30 times larger than estimated from the theories of weak localization and carrier interaction. The discrepancy apparently results from electron-hole interactions not included in the theory.

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Solar- Terrestrial Physics: A Space Age Birth, R. W. Schunk May 1986

Solar- Terrestrial Physics: A Space Age Birth, R. W. Schunk

Faculty Honor Lectures

Solar- Terrestrial Physics, in its broadest sense, is concerned with the transport of energy, particles, and fields from the sun to the earth and their consequent effect on the terrestrial environment. Most of the solar energy eventually deposited in our atmosphere, at a rate of approximately a trillion megawatts, arrives in the form of visible light. The study of how this energy affects our environment falls within the purview of meteorology, a discipline that has experienced an independent development and that has sufficiently different problems from solar-terrestrial physics that it can be regarded as a separate but neighboring discipline. In …

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Numerical Study Of The Atmospheric Radiative Transfer Process With Application To The Arctic Energy Balance, Si-Chee Tsay Apr 1986

Numerical Study Of The Atmospheric Radiative Transfer Process With Application To The Arctic Energy Balance, Si-Chee Tsay

Theses (Unassigned)

A high-order discrete-ordinate approximation is utilized to solve the radiative transfer equation for both solar and terrestrial spectra. The solutions have been compared with other methods and found to be reliable and efficient. These solutions have been used to construct a complete and comprehensive radiation model for the arctic atmosphere. The bulk radiative properties (e.g. fluxes and heating/cooling rates) as well as the angular distribution of intensity can be computed as functions of wavelength at various levels in vertically inhomogeneous atmospheres. The radiation model treats Rayleigh scattering, gaseous absorption/emission, scattering and absorption/emission by cloud droplets and haze particles. Snow conditions …

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Direct Observation Of Ensemble Averaging Of The Aharonov-Bohm Effect In Normal-Metal Loops, C. P. Umbach, C. Van Haesendonck, R. B. Laibowitz, S. Washburn, Richard A. Webb Jan 1986

Direct Observation Of Ensemble Averaging Of The Aharonov-Bohm Effect In Normal-Metal Loops, C. P. Umbach, C. Van Haesendonck, R. B. Laibowitz, S. Washburn, Richard A. Webb

Faculty Publications

Aharonov-Bohm magnetoconductance oscillations have been measured in series arrays of 1, 3, 10, and 30 submicron-diameter Ag loops. At constant temperature, the amplitude of the h/e oscillations is observed to decrease as the square root of number of loops, while the amplitude of h/2e conductance oscillations, measured in the same samples, is independent of the number of series loops. This is direct confirmation of the ensemble averaging properties of h/e oscillations in multiloop systems. The amplitude of the h/e oscillations is in good agreement with recent calculations.

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Wooster Magazine: Winter 1986, Peter Havholm Jan 1986

Wooster Magazine: Winter 1986, Peter Havholm

Wooster Magazine: 1981-1990

This edition of the Wooster Magazine was published in the winter of 1986. The first article of the magazine, "Inside Taylor Hall," explores the physics and mathematics departments at the College of Wooster. Taylor Hall and the departments housed within it are the main focus of this edition. The next section debates the usefulness and necessity of personal computers. Later articles discuss computer games, alumni careers in physics and math, the renovations done to Taylor Hall, and the role of machines in teaching. The Class Notes begin on page 46 and detail notes from classes all the way back …

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The Fricative Sound Source Spectrum Derived From A Vocal Tract Analog., Lawrence Edward Zagar Jan 1986

The Fricative Sound Source Spectrum Derived From A Vocal Tract Analog., Lawrence Edward Zagar

LSU Historical Dissertations and Theses

The applications of speech synthesis for computer voice response and speech analysis present the need for highly intelligible and natural synthesized speech. In order to improve the synthesis of fricative and related sounds, the use of simple models for the source spectrum of fricative sounds is investigated. The investigation is based on the use of a vocal tract analog and experimental measurements. Measurements of the sound pressure spectra of fricative consonants are made. Simple sound pressure measurements and measurements based on the technique for measuring intensity are utilized. The fricatives studied are /f/, /th/, /s/, /sh/, and /h/. Fricative sound …

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Temperature Dependence Of The Normal-Metal Aharonov-Bohm Effect, S. Washburn, C. P. Umbach, R. B. Laibowitz, Richard A. Webb Oct 1985

Temperature Dependence Of The Normal-Metal Aharonov-Bohm Effect, S. Washburn, C. P. Umbach, R. B. Laibowitz, Richard A. Webb

Faculty Publications

The amplitude of h/e periodic oscillations in the magnetoresistance of very small normal-metal (Au) rings, as well as the harmonic h/2e, have been studied as a function of temperature. The amplitudes depend on the temperature T roughly as T-1/2, as expected from the averaging of conduction channels in the absence of inelastic scattering, but may not be entirely consistent with this model. At the lowest T, the size of the fluctuations in the conductance is about ΔG∼e2/h, as predicted recently.

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Observation Of H/E Aharonov-Bohm Oscillations In Normal-Metal Rings, Richard A. Webb, S. Washburn, C. P. Umbach, R. B. Laibowitz Jun 1985

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.

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Effects Of Dissipation And Temperature On Macroscopic Quantum Tunneling, S. Washburn, Richard A. Webb, R. F. Voss, S. M. Faris Jun 1985

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.

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Katabatic Winds In Adelie Land, Antarctica (Snow, Automatic Weather Stations, Pressure Gradient, Coreless Winter), Yuji Kodama Apr 1985

Katabatic Winds In Adelie Land, Antarctica (Snow, Automatic Weather Stations, Pressure Gradient, Coreless Winter), Yuji Kodama

Theses (Unassigned)

Data from Automatic Weather Stations (AWS) on Adelie Land, Antarctica, were analysed. The findings are: (1) The high directional constancy of surface winds, which has been explained by the inversion strength and topography of the slope, was found at the slope stations even in summer when the inversion is weak or destroyed. An analysis of data and model simulations of diurnal variations of katabatic winds in summer show that synoptic geostrophic winds and eddy viscosity also effect the constancy of the wind direction in summer. (2) Wind directional constancies at the slope stations in winter, when the inversion is expected …

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Origin Of The Peaked Structure In The Conductance Of One-Dimensional Silicon Accumulation Layers, Richard A. Webb, A. Hartstein, J. J. Wainer, A. B. Fowler Apr 1985

Origin Of The Peaked Structure In The Conductance Of One-Dimensional Silicon Accumulation Layers, Richard A. Webb, A. Hartstein, J. J. Wainer, A. B. Fowler

Faculty Publications

We have made extensive studies of the temperature, gate voltage, and electric field dependences of the conductance peaks in small silicon inversion layers in order to distinguish between resonant-tunneling models and a hopping model. We find that many of the peaks are consistent only with a hopping model, whereas some could be consistent with an early resonant-tunneling model. None of our structure is consistent with resonant tunneling if the recent formulation of Stone and Lee is correct.

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New Shubnikov-De Haas Effects In A Two-Dimensional Electron-Hole System, S. Washburn, Richard A. Webb, E. E. Mendez, L. L. Chang, L. Esaki Jan 1985

New Shubnikov-De Haas Effects In A Two-Dimensional Electron-Hole System, S. Washburn, Richard A. Webb, E. E. Mendez, L. L. Chang, L. Esaki

Faculty Publications

We report the temperature dependence of the Shubnikov–de Haas oscillations from a two-dimensional electron-hole system in GaSb-InAs-GaSb quantum wells at very low temperatures. The samples are double heterostructures containing separate electron and hole layers. The oscillations arising from the electron layer behave regularly with temperature. Additional oscillations, characterized by strong temperature dependence, and relatively large peak widths are believed to arise from the presence of hole layers.

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I. Toward The Quantum Limit In Gravitational Wave Detectors. Ii. Several Theoretical Problems In Condensed Matter Physics., Bu-Xin Xu Jan 1985

I. Toward The Quantum Limit In Gravitational Wave Detectors. Ii. Several Theoretical Problems In Condensed Matter Physics., Bu-Xin Xu

LSU Historical Dissertations and Theses

Part I. We analyze a gravity wave detector consisting of a Weber type resonant antenna, an inductive transducer and a dc SQUID coupling system. We derive the complete set of equations of motion for the system and discuss their implications and solutions in detail. The results obtained are applied to the LSU gravity wave detector, and the optimum system parameters are calculated. We show that it is possible to approach quantum limited sensitivity for the detector if these optimum system parameters and matching conditions are properly satisfied. In the final chapter we present our preliminary experimental results. We have built …

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Absence Of Minimum Metallic Conductivity In Gd(3-X)Vxs4 At Very Low Temperature And Evidence For A Coulomb Gap, S. Washburn, Richard A. Webb, S. Von Molnar, F. Holtzberg Nov 1984

Absence Of Minimum Metallic Conductivity In Gd(3-X)Vxs4 At Very Low Temperature And Evidence For A Coulomb Gap, S. Washburn, Richard A. Webb, S. Von Molnar, F. Holtzberg

Faculty Publications

Gd(3-x)vxS4 provides a convenient analog of a compensated semiconductor in which, for x≃0.3, the mobility edge can be tuned smoothly through the Fermi energy by the application of a magnetic field. The results of a search for a minimum metallic conductivity demonstrate that, down to T=6 mK, the metal-insulator transition is smooth. In the insulating regime, the temperature dependence of the conductivity was more consistent with the theory of mutual interactions than with the theory of pure localization.

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Magnetoresistance Of Small, Quasi-One-Dimensional, Normal-Metal Rings And Lines, C. P. Umbach, S. Washburn, R. B. Laibowitz, Richard A. Webb Oct 1984

Magnetoresistance Of Small, Quasi-One-Dimensional, Normal-Metal Rings And Lines, C. P. Umbach, S. Washburn, R. B. Laibowitz, Richard A. Webb

Faculty Publications

The magnetoresistance of sub-0.4-μm-diam Au and Au60Pd40 rings was measured in a perpendicular magnetic field at temperatures as low as 5 mK in search of simple, periodic resistance oscillations that would be evidence of flux quantization in normal-metal rings. However, instead of simple oscillations, a very complex structure developed in the magnetoresistance at low temperatures. Fourier analysis of all the data did not reveal convincing evidence for flux quantization in the rings. Complex structure similar to that observed in the rings was also found in the magnetoresistance of short, narrow, Au and Au60Pd …

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Auroral Zone Thermospheric Dynamics Using Fabry-Perot Interferometric Measurements Of The Neutral Oxygen 15867k Emission (Solar Maximum, Electrojets, Temperature), Robert Joseph Sica Apr 1984

Auroral Zone Thermospheric Dynamics Using Fabry-Perot Interferometric Measurements Of The Neutral Oxygen 15867k Emission (Solar Maximum, Electrojets, Temperature), Robert Joseph Sica

Theses (Unassigned)

Forty-four nights of thermospheric neutral wind and temperature measurements were obtained from College, Alaska (65(DEGREES) invariant latitude) during solar maximum using a ground-based Fabry-Perot interferometer. When averaged by increasing geomagnetic activity, the wind exhibits two main features. First, the general flow pattern, poleward and westward in the evening, changing to southward and eastward in the morning, persists with increasing activity. The flow velocity increases and the change in direction occurs earlier in magnetic local time as the geomagnetic activity increases. Second, as the activity increases, the meridional wind pattern shifts equatorward with the auroral oval. Consequently, the low geomagnetic activity …

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Weak Localization Of Two-Dimensional Conduction Holes, S. Washburn, Richard A. Webb, E. E. Mendez, L. L. Chang, L. Esaki Mar 1984

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.

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Solutions To The Two-Dimensional Aesthetic Field Equations, Murali Ramanathan Jan 1984

Solutions To The Two-Dimensional Aesthetic Field Equations, Murali Ramanathan

Theses and Dissertations

No abstract provided.

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Magnetic Field Behavior Of A Josephson-Junction Array: Two-Dimensional Flux Transport On A Periodic Substrate, Richard A. Webb, Richard F. Voss, G. Grinstein, P. M. Horn Aug 1983

Magnetic Field Behavior Of A Josephson-Junction Array: Two-Dimensional Flux Transport On A Periodic Substrate, Richard A. Webb, Richard F. Voss, G. Grinstein, P. M. Horn

Faculty Publications

This Letter reports measurements down to 3 mK of the magnetic field dependence of the resistance and critical current of a weakly coupled periodic array of Josephson junctions. Below 700 mK the resistance is an oscillatory function of field. The temperature dependence of the resistance for integral numbers of flux quanta per cell suggests the existence of a Kosterlitz-Thouless transition involving the unbinding of defects in the flux lattice.

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Conserving Numerical Methods For X = F(X), Donald Greenspan Jul 1983

Conserving Numerical Methods For X = F(X), Donald Greenspan

Mathematics Technical Papers - Archive

Physics is characterized by conservation laws and by symmetry [1]. Unfortunately, the application of numerical methodology in approximating solutions of initial value problems usually does not preserve either of these invariants. In this sense, the use of a computer destroys the physics of a dynamical model. We will show here how to conserve total energy when solving the nonlinear initial value problem [see pdf for notation] on a computer. Moreover, the energy conserved will be exactly that of (1.1), not a new "energy" which is defined by the numerical method (see, e.g., Langdon [5]). Two distinctly different methods will be …

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Electric Conductivities, Currents And Energy Dissipation In The Polar Ionosphere, Byung-Ho Ahn Apr 1983

Electric Conductivities, Currents And Energy Dissipation In The Polar Ionosphere, Byung-Ho Ahn

Theses (Unassigned)

During the International Magnetospheric Study (IMS), magnetic records from the six IMS meridian chain stations were obtained on March 17, 18 and 19, 1978. The data set is one of the most comprehensive ever obtained. Furthermore, several advanced computer codes calculating ionospheric current distributions based on the ground magnetic data were recently introduced. Combining the data set and the computer code developed by Kamide et al. (1981), it is attempted to re-examine the longstanding uncertainties in the current distributions and the energy dissipation rates in the polar ionosphere during substorms. For this purpose, a conductivity model which can reflect substorm …

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Electronic Structure Of Iron., Diola Bagayoko Jan 1983

Electronic Structure Of Iron., Diola Bagayoko

LSU Historical Dissertations and Theses

A survey of previous theoretical and experimental works on iron in some Bravais lattices and at various temperature and pressures shows this 3d transition metal to exhibit a wealth of allotropic transformations and to possess, along with some of its alloys, peculiar magnetic properties in the face centered cubic (FCC) phase. We present an ab-initio self-consistent spin polarized band structure study of this metal in the body (BCC) and face centered cubic lattices at absolute zero and at various atomic volumes. Our calculations employed gaussian basis functions in a LCAO scheme and used the RSK local density potential. In contrast …

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