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Articles 1651 - 1680 of 1948

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Spectral Equivalence Of Bosons And Fermions In One-Dimensional Harmonic Potentials, Michael Crescimanno, Adam S. Landsberg Feb 2001

Spectral Equivalence Of Bosons And Fermions In One-Dimensional Harmonic Potentials, Michael Crescimanno, Adam S. Landsberg

WM Keck Science Faculty Papers

Recently, Schmidt and Schnack [Physica A 260, 479 (1998)], following earlier references, reiterate that the specific heat of N noninteracting bosons in a one-dimensional harmonic well equals that of N noninteracting fermions in the same potential. We show that this peculiar relationship between heat capacities results from a more dramatic equivalence between Bose and Fermi systems. Namely, we prove that the excitations of such Bose and Fermi systems are spectrally equivalent. Two complementary proofs of this equivalence are provided; one based on a combinatoric argument, the other from analysis of the underlying dynamical symmetry group.

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Dirac Theory Of Ring-Shaped Electron Distributions In Atoms, P Krekora, R E. Wagner, Q Su, Rainer Grobe Feb 2001

Dirac Theory Of Ring-Shaped Electron Distributions In Atoms, P Krekora, R E. Wagner, Q Su, Rainer Grobe

Faculty publications – Physics

The time-dependent Dirac equation is solved numerically on a space-time grid for an atom in a strong static magnetic field and a laser field. The resonantly induced relativistic motion of the atomic electron leads to a ringlike spatial probability density similar to the features that have been recently predicted [Wagner, Su, and Grobe, Phys. Rev. Lett. 84, 3282 (2000)] based on a phase-space method. We further demonstrate that spin-orbit coupling for a fast-moving electron in such an atom becomes significant and the time dependence of the spin can dephase even if initially aligned parallel to the direction of the static …

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Non-Adiabatic Features In Magnetotail Fast Flows: Orbit Tracing And Data Comparisons, Bryan Michael Boll Jan 2001

Non-Adiabatic Features In Magnetotail Fast Flows: Orbit Tracing And Data Comparisons, Bryan Michael Boll

Doctoral Dissertations

The purpose of this study is to investigate velocity space distribution functions in space plasmas. Orbit tracing methods are used to generate self-consistent models of several different magnetic and electric field configurations. Fast flows in the magnetotail are selected to be modeled using a relatively thin current sheet compared with quiet times. Four different electric fields are imposed, varying in characteristic thickness and magnitude. Using these four particle based models we were able to generate velocity distribution functions that show clear evidence of non-adiabatic features that depend on the electric field characteristic width. Several years of Geotail Comprehensive Plasma Instrumentation …

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Electroproduction Of The Λ(1520) Hyperon, M. Bektasoglu, G. E. Dodge, T. A. Forest, C. E. Hyde-Wright, S. E. Kuhn, R. A. Niyazov, L. B. Weinstein, Et Al., The Clas Collaboration Jan 2001

Electroproduction Of The Λ(1520) Hyperon, M. Bektasoglu, G. E. Dodge, T. A. Forest, C. E. Hyde-Wright, S. E. Kuhn, R. A. Niyazov, L. B. Weinstein, Et Al., The Clas Collaboration

Physics Faculty Publications

The reaction e→pe′K+Λ(1520) with Λ(1520)→p′K− was studied at electron beam energies of 4.05, 4.25, and 4.46 GeV, using the CLAS detector at the Thomas Jefferson National Accelerator Facility. The cos θK+, φK+, Q2, and W dependencies of Λ(1520) electroproduction are presented for the kinematic region 0.9 < Q2 < 2.4 GeV2 and 1.95 < W < 2.65 GeV. Also, the Q2 dependence of the Λ(1520) decay angular distribution is presented for the first time. The cosθK+ angular distributions suggest t-channel diagrams dominate the production process. Fits to the Λ(1520) t-channel helicity frame decay angular distributions indicate the m …

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The Ep → E'P Η Reaction At And Above The S₁₁ (1535) Baryon Resonance, R. Thompson, G. E. Dodge, C. E. Hyde-Wright, A. Klein, S. E. Kuhn, R. A. Niyazov, L. M. Qin, L. B. Weinstein, Et Al., The Clas Collaboration Jan 2001

The Ep → E'P Η Reaction At And Above The S₁₁ (1535) Baryon Resonance, R. Thompson, G. E. Dodge, C. E. Hyde-Wright, A. Klein, S. E. Kuhn, R. A. Niyazov, L. M. Qin, L. B. Weinstein, Et Al., The Clas Collaboration

Physics Faculty Publications

New cross sections for the reaction ep → ep η are reported for total center of mass energy W = 1.5-1.86 GeV and invariant momentum transfer Q2 = 0.25-1.5 (GeV/c)2. This large kinematic range allows extraction of important new information about response functions, photocouplings, and etaN coupling strengths of baryon resonances. Newly observed structure at W ~ 1.65 GeV is shown to come from interference between S and P waves and can be interpreted with known resonances. Improved values are derived for the photon coupling amplitude for the S11(1535) resonance.

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Photoemission And Photo-Absorption Studies Of Ultrathin Iron Films On Copper(100) Oxidized At Elevated Temperature., Reginaldt Hamilton Madjoe Jan 2001

Photoemission And Photo-Absorption Studies Of Ultrathin Iron Films On Copper(100) Oxidized At Elevated Temperature., Reginaldt Hamilton Madjoe

LSU Historical Dissertations and Theses

In this investigation, I have focused on understanding the structure and morphology of ultrathin iron oxide films and characterizing them by using LEED, photoemission (both angle-resolved and angle-integrated) and photoabsorption measurements. Fe films were deposited on a Cu(100) substrate at room temperature growing in a layer by layer fashion. The sample was then annealed to 810K in oxygen ambient. This oxidation process led to dramatic changes of the sample surface and electronic structure depending on initial Fe coverage. Half-metallic oxides such as CrO2 and Fe3O4 may provide opportunities for new magnetic devices since their single spin orientation at the Fermi …

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Shell Model Description Of Normal Parity Bands In Heavy Deformed Nuclei., Gabriela Popa Jan 2001

Shell Model Description Of Normal Parity Bands In Heavy Deformed Nuclei., Gabriela Popa

LSU Historical Dissertations and Theses

The low-energy spectra and electromagnetic transition strengths in 160,162,164Dy, 156,158,160Gd, and 168Er are described in the framework of the pseudo-SU(3) model. The Hamiltonian includes spherical single-particle energies, the Quadrupole-quadrupole interaction, and proton and neutron pairing terms with the strengths of these interaction fixed from systematics. The strengths of an additional four rotor-like terms that are included in the Hamiltonian, which do not mix SU(3) representations and induce only small changes in the spectra, were allowed to vary and a consistent set of these parameters was found. Proton and neutron degrees of freedom are considered explicitly by building the basis states …

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Center Vortices In Confinement., Viorel-Andrei Alexandru Jan 2001

Center Vortices In Confinement., Viorel-Andrei Alexandru

LSU Historical Dissertations and Theses

The confinement property of quarks is still one of the puzzles of today's physics. Although QCD is believed to accurately describe the interaction between quarks, due to the peculiar nature of the theory we are still unable to prove that it confines the quarks. Most analytical efforts in QCD are based on perturbative techniques which are useless in studying confinement. Lattice gauge theory enables us to get non-perturbative results. We use lattice techniques to investigate one of the proposed mechanisms of quark confinement, namely the center vortex idea. We first present a cursory introduction to lattice theory and the methods …

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Measurement Of Bottom Quark Production In Two -Photon Collisions., Sepehr Saremi Jan 2001

Measurement Of Bottom Quark Production In Two -Photon Collisions., Sepehr Saremi

LSU Historical Dissertations and Theses

The cross section for bottom quark production in two-photon collisions, sigma( e+e- → e+e- bb¯X), is measured for the first time. The measurement is performed with the L3 detector at the Large Electron Positron (LEP) collider at the European Center for Nuclear and Particle Physics (CERN). The data corresponds to 410 pb-1 taken at center-of-mass energies from 189 GeV to 202 GeV. Hadrons containing a bottom quark are identified by detecting electrons or muons from their semi-leptonic decays. The measured cross section is in excess of the Next to Leading Order QCD prediction by a factor of three.

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Indium Arsenide/Gallium Arsenide Quantum Dots And Nanomesas: Multimillion-Atom Molecular Dynamics Solutions On Parallel Architectures., Xiaotao Su Jan 2001

Indium Arsenide/Gallium Arsenide Quantum Dots And Nanomesas: Multimillion-Atom Molecular Dynamics Solutions On Parallel Architectures., Xiaotao Su

LSU Historical Dissertations and Theses

Multimillion-atom molecular dynamics (MD) simulations have been performed to study the flat InAs overlayers with self-limiting thickness on GaAs square nanomesas. The in-plane lattice constant of InAs layers parallel to the InAs/GaAs(001) interface starts to exceed the InAs bulk value at 12th monolayer (ML) and the hydrostatic stresses in InAs layers become tensile above ∼12 th ML. As a result, it is not favorable to have InAs overlayers thicker than 12 ML. This may explain the experimental findings of the growth of flat InAs overlayers with self-limiting thickness of ∼11 ML on GaAs nanomesas. We have also examined the lateral …

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De Haas-Van Alphen Effect Measurements On Cerium-Lanthanum-M-Indium (M = Cobalt, Rhodium, Iridium) Alloys., Umit Alver Jan 2001

De Haas-Van Alphen Effect Measurements On Cerium-Lanthanum-M-Indium (M = Cobalt, Rhodium, Iridium) Alloys., Umit Alver

LSU Historical Dissertations and Theses

The de Haas van Alphen (dHvA) effect, which measures the oscillatory component of the magnetization, in several CexLa1-x MIn5 (M = Rh, Co, Ir) alloys for 0 ≤ x ≤ 1 has been studied in detail using torque, pulse field and field modulation techniques. The frequencies, associated extremal cross sectional areas of the Fermi surface and effective masses of each sample throughout each of the series are reported. The energy band calculations of CeRhIn5, CeCoIn5 and CeIrIn5 assume that the 4f electrons in Ce are completely delocalized and these electrons make a significant contribution to the topology of the Fermi …

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Electrons In Image States Near Roughened Metal Surfaces, Brian K. Clark, Brian W. Gregory, Jean M. Standard Dec 2000

Electrons In Image States Near Roughened Metal Surfaces, Brian K. Clark, Brian W. Gregory, Jean M. Standard

Faculty Publications – Chemistry

Electrons near roughened Ag and Au surfaces with chemisorbed dielectric overlayers of alkanethiol or alkaneselenol self-assembled monolayers are shown to move within the sulfur or selenium head-group layer on the metal terraces. The electrons exist in image states with respect to Ag or Au step edges. There is no substantial image force between the electrons and the terraces.

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Coupled Nonlinear Dynamical Systems, Hongyan Sun Dec 2000

Coupled Nonlinear Dynamical Systems, Hongyan Sun

Graduate Theses, Dissertations, and Problem Reports (ETD)

In this dissertation, we study coupled nonlinear dynamical systems that exhibit new types of complex behavior. We numerically and analytically examine a variety of dynamical models, ranging from systems of ordinary differential equations (ODE) with novel elements of feedback to systems of partial differential equations (PDE) that model chemical pattern formation. Chaos, dynamical uncertainty, synchronization, and spatiotemporal pattern formation constitute the primary topics of the dissertation. Following the introduction in Chapter 1, we study chaos and dynamical uncertainty in Chapter 2 with coupled Lorenz systems and demonstrate the existence of extreme complexity in high-dimensional ODE systems. In Chapter 3, we …

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Kinetic Energy Release In Electron-Induced Decay Reactions Of Molecular Ions: C3h8+ And C3h7+, S. Matt, Olof E. Echt, A. Stamatovic, T. D. Mark Jul 2000

Kinetic Energy Release In Electron-Induced Decay Reactions Of Molecular Ions: C3h8+ And C3h7+, S. Matt, Olof E. Echt, A. Stamatovic, T. D. Mark

Physics & Astronomy

We have measured the kinetic energy release (KER) distributions for electron-induced dissociation of mass-selected molecular parent and fragment ions of propane. They are compared with distributions determined for spontaneous (metastable) dissociation. The average KER for induced dissociation of C3H8+ into C3H7+ is 13.2 +/- 1.2 meV, about 42% larger than for the spontaneous reaction. This large difference is attributed to the dramatically reduced time at which the induced reaction can be sampled. In contrast, the KER for dissociation of C3H7+ into C3H5+, which is characterized by a large reverse activation energy, is hardly affected by the experimental time scale. (C) …

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Low Temperature Anomaly In Mesoscopic Kondo Wires, P. Mohanty, Richard A. Webb May 2000

Low Temperature Anomaly In Mesoscopic Kondo Wires, P. Mohanty, Richard A. Webb

Faculty Publications

We report the observation of an anomalous magnetoresistance in extremely dilute quasi-one-dimensional AuFe wires at low temperatures, along with a hysteretic background at low fields. The Kondo resistivity does not show the unitarity limit down to the lowest temperature, implying uncompensated spin states. We suggest that the anomalous magnetoresistance may be understood as the interference correction from the accumulation of geometric phase in the conduction electron wave function around the localized impurity spin.

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An Investigation Of Small-Scale Relationships Between Optical And Hf Radar Aurora, Veronika Besser Apr 2000

An Investigation Of Small-Scale Relationships Between Optical And Hf Radar Aurora, Veronika Besser

Theses (Unassigned)

An investigation is undertaken of the relationship between visual aurora and the occurrence of radar-detectable irregularities in the nightside ionosphere. Understanding how auroral signatures appear in HF radar backscatter could combine the advantages of detailed information about auroral fluxes in optical measurements with extended coverage of HF radars. Auroral particle precipitation ionizes the ionosphere and creates localized plasma density enhancements. Irregularities with various smaller sizes are generated from larger density structures through instability-induced cascading. HF waves are coherently scattered by decameter structures within the ionospheric plasma. Hence aurorally induced irregularities can be seen by the radar in the form of …

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Electromagnetic Scattering By Spheroidal Particles: Applications To The Atmosphere, Hans Arthur Eide Apr 2000

Electromagnetic Scattering By Spheroidal Particles: Applications To The Atmosphere, Hans Arthur Eide

Theses (Unassigned)

An efficient and reliable method is presented for computing the expansion coefficients in the eigenfunction series representing the prolate and oblate spheroidal functions. While the traditional method is based on recurrence relations, infinite continued fractions, and a variational procedure, the new method is based on reformulating the computational task as an eigenvalue problem. In contrast with the traditional method, the new method requires no initial estimates of the eigenvalues, and the computations can be performed using readily available computer library routines. The new method is shown to produce accurate expansion coefficients for the spheroidal functions required to study scattering by …

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Optical Spectroscopic Observations Of Sprites, Blue Jets, And Elves: Inferred Microphysical Processes And Their Macrophysical Implications, Matthew James Heavner Apr 2000

Optical Spectroscopic Observations Of Sprites, Blue Jets, And Elves: Inferred Microphysical Processes And Their Macrophysical Implications, Matthew James Heavner

Theses (Unassigned)

During the past decade, several new upper atmospheric phenomena associated with thunderstorms have been discovered. The four main types of optical emissions are now called sprites, blue jets, lves, and halos. Sprites are primarily red and appear between 40--95 km altitude and last between 1--100 ms. The dominant sprite emission is the molecular nitrogen first positive band, a relatively low energy emission also observed in the red lower borders of aurorae. The total optical energy output of a bright sprite is on the order of 50 kJ. Based on spectral observations, the total vibrational and electronic energy deposited in molecular …

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Cloud And Surface Properties And The Solar Radiation Budget Derived From Satellite Data Over The Arctic Ocean: Comparisons With Surface Measurements And In Situ Aircraft Data, Xiaozhen Xiong Apr 2000

Cloud And Surface Properties And The Solar Radiation Budget Derived From Satellite Data Over The Arctic Ocean: Comparisons With Surface Measurements And In Situ Aircraft Data, Xiaozhen Xiong

Theses (Unassigned)

Use of satellite data to study the surface and cloud properties and the solar radiation budget (SRB) is very important for improving our understanding of cloud and sea-ice albedo feedback in the Arctic. Based on an accurate and comprehensive Radiative Transfer Model (RTM), algorithms were developed for using the National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) data for the discrimination of cloud from snow/ice surfaces, retrieval of snow surface properties and surface albedo, and retrieval of cloud optical depth (tau) and effective droplet size ( re). Through the improved estimation of solar reflectance in AVHRR …

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Small Spatial And Fast Temporal Ionosphere -Magnetosphere Coupling Processes, Hua Zhu Apr 2000

Small Spatial And Fast Temporal Ionosphere -Magnetosphere Coupling Processes, Hua Zhu

Theses (Unassigned)

I have developed a two-dimensional, three-fluid model (electrons, ions and neutrals) to simulate small-scale magnetosphere-ionosphere coupling processes. The code includes ionization and recombination processes, the Hall term in Ohm's law, and various heat sources in the energy equations. The electro-dynamic response and the evolution of the collision frequencies are treated self-consistently in a height resolved ionosphere. The model allows for the propagation of Alfven waves. The simulation is particularly suited for fast temporal variations and small spatial scale ionospheric structures associated with filamentary aurora and ionospheric heating experiments (e.g. HAARP). I have investigated the evolution of field-aligned currents in the …

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Classical Versus Quantum Dynamics For A Driven Relativistic Oscillator, Rainer Grobe, Qichang Su, P J. Peverly, R E. Wagner Mar 2000

Classical Versus Quantum Dynamics For A Driven Relativistic Oscillator, Rainer Grobe, Qichang Su, P J. Peverly, R E. Wagner

Faculty publications – Physics

We compare the time evolution of the quantum-mechanical spatial probability density obtained by solving the time-dependent Dirac equation with its classical counterpart obtained from the relativistic Liouville equation for the phase-space density in a regime in which the dynamics is essentially relativistic. For a resonantly driven one-dimensional harmonic oscillator, the simplest nontrivial model system to perform this comparison, we find that, despite the nonlinearity induced by relativity, the classical ensemble description matches the quantum evolution remarkably well.

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Quantum Stochastic Dilation Of Completely Positive Semigroups And Flows., Debashish Goswami Dr. Feb 2000

Quantum Stochastic Dilation Of Completely Positive Semigroups And Flows., Debashish Goswami Dr.

Doctoral Theses

The central theme of the present thesia is quantum stochastic dilation af semigroupe of completely panitive mapa on operator algebran. It is the sim of all mathemati- cal, or even all scientific theorics, to understand a given class of objects through a tanonical and simpler subclass of it. For example, abstract C"-algebras are studied through their conerete realisation as elgebra of operators, contractions on a Hilbert space by unitaries. Hilbert modules by the factorissble ones, to mention anly a few. In most af these caes, a general object of the relavant class is sociated with a canonical candidate of the …

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Disorder-Induced Desynchronization In A 2x2 Circular Josephson Junction Array, Adam S. Landsberg Feb 2000

Disorder-Induced Desynchronization In A 2x2 Circular Josephson Junction Array, Adam S. Landsberg

WM Keck Science Faculty Papers

Analytical results are presented which characterize the behavior of a dc-biased, two-dimensional circular array of overdamped Josephson junctions subject to increasing levels of disorder. It is shown that high levels of disorder can abruptly destroy the synchronous functioning of the array. We identify the transition boundary between synchronized and desynchronized behavior, along with the mechanism responsible for the loss of frequency locking. Comparisons with recent results for arrays with rectangular lattice geometries are described.

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Placement Of Bright S88b Objects On A Hertzprung-Russel Diagram Using Visible Light Measurements, Geoffrey A. Bonvallet Jan 2000

Placement Of Bright S88b Objects On A Hertzprung-Russel Diagram Using Visible Light Measurements, Geoffrey A. Bonvallet

Physics Senior Independent Study Theses

Thesis digitized from Physics Department I.S. Archive.

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Renormalons As Dilation Modes In The Functional Space, A. Babansky, I. Balitsky Jan 2000

Renormalons As Dilation Modes In The Functional Space, A. Babansky, I. Balitsky

Physics Faculty Publications

There are two possible sources of the factorial large-order behavior of a typical perturbative series. First, the number of different Feynman diagrams may be large; second, there may be abnormally large diagrams known as renormalons. It is well known that the large combinatorial number of diagrams is described by instanton-type solutions of the classical equations. We demonstrate that, from the functional-integral viewpoint, the renormalons do not correspond to a particular configuration but manifest themselves as dilatation modes in the functional space.

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Magnetic Measurements Of Rare Earth Hexaborides., Alem Abraha Teklu Jan 2000

Magnetic Measurements Of Rare Earth Hexaborides., Alem Abraha Teklu

LSU Historical Dissertations and Theses

The de Haas van Alphen (dHvA) effect is used, using the field modulation method, to study the orientation dependence of the extremal cross-sectional areas of the Fermi surface (FS) and effective masses of CexLa 1--xB6 alloys for x between 0 and 0.05. Previous measurements on these samples, using the pulsed field method, up to x = 1 showed that the FS was spin polarized at very low Ce concentration, at x = 0.05, indicating a spin polarity-dependent scattering mechanism. Moreover, the effective mass was enhanced by the increase of Ce concentration. This was the motivation for the present work which …

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Atomic And Electronic Properties Of Neutral And Cationic Metallic Clusters., Andrew Marc Kolchin Jan 2000

Atomic And Electronic Properties Of Neutral And Cationic Metallic Clusters., Andrew Marc Kolchin

LSU Historical Dissertations and Theses

We find optimal atomic and electronic structures for neutral and singly, positively charged clusters of beryllium and beryllium-lithium (of the form BeLik) using density functional theory in the local spin density approximation. Ions are moved with a steepest descent method, and the electronic wave functions optimized using a fictitious dynamics with simulated annealing, as conceived by Car and Parrinello. Shell-like orbitals, filling angular momentum states in the order: 1s 2p 2s 1d, are obtained for the beryllium clusters. The same ordering is found for the BeLik clusters which indicates a departure from the ordering found in pure alkali clusters by …

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A Solar Comparison, Larry Weinstein Jan 2000

A Solar Comparison, Larry Weinstein

Physics Faculty Publications

[First paragraph] Gilbert Ward [Phys.Teach 38, 333 (Sept. 2000)] states, "You emit more than 7000 times as much heat per unit mass as the Sun does." This difference was pointed out to me much more graphically by Brian Quinn many years ago as, "If the sun were made out of gerbils, the Earth would be incinerated."

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Deeply Virtual Compton Scattering At Small X, Ian Balitsky, Elena Kuchina Jan 2000

Deeply Virtual Compton Scattering At Small X, Ian Balitsky, Elena Kuchina

Physics Faculty Publications

We calculate the cross section of deeply virtual Compton scattering at large energies and intermediate momentum transfers.

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Long-Lived Localized Field Configurations In Small Lattices: Application To Oscillons, M. Gleiser, A. Sornborger Aug 1999

Long-Lived Localized Field Configurations In Small Lattices: Application To Oscillons, M. Gleiser, A. Sornborger

Dartmouth Scholarship

Long-lived localized field configurations such as breathers, oscillons, or more complex objects naturally arise in the context of a wide range of nonlinear models in different numbers of spatial dimensions. We present a numerical method, which we call the adiabatic damping method, designed to study such configurations in small lattices. Using three-dimensional oscillons in φ4 models as an example, we show that the method accurately (to one part in 105 or better) reproduces results obtained with static or dynamically expanding lattices, dramatically cutting down in integration time. We further present results for two-dimensional oscillons, whose lifetimes would be prohibitively …

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