Physics Commons^™

Angle-Resolved Studies Of Inner Shell Excitations For Argon, Krypton And Xenon Using Third Generation Synchrotron Sources, Ahmad H. Farhat

Dissertations

This dissertation, which is in the area of atomic physics, concentrates on the study of the interaction between VUV-soft X-ray radiation and atoms in the gas phase. The main area of interest is the study of Auger decay in atoms utilizing the process known as the resonance Auger effect, where an inner shell electron is excited to an unfilled orbital followed by the ejection of an Auger electron. The measurements in this thesis were performed by using the high resolution Atomic, Molecular and Optical Physics undulator beam line, which utilizes a spherical grating monochromator at the Advanced Light Source at …

Electric Potential In The Classical Hall Effect: An Unusual Boundary-Value Problem, Matthew J. Moelter, James Evans, Greg Elliot, Martin Jackson

Physics

The classical Hall effect presents a surprisingly unusual and challenging problem in electrostatics, with boundary conditions that are not of Dirichlet, Neumann, or of mixed Dirichlet and Neumann type. These unusual boundary conditions create several difficulties not normally encountered in standard problems, and ultimately lead to expansion of the electric potential in a nonorthogonal basis set. We derive the boundary conditions for the potential in a rectangular geometry, construct a solution for the potential, and discuss the relation between this problem and problems of the standard mixed type. We also address a commonly encountered misconception about the current distribution.

Disorder-Induced Topological Defects In A D=2 Elastic Medium At Zero Temperature, Alan Middleton

Physics - All Scholarship

The density and correlations of topological defects are investigated numerically in a model of a d=2 elastic medium subject to a periodic quenched random potential. The computed density of defects decreases approximately exponentially with the defect core energy. Comparing the defect-free ground state with the ground state with defects, it is found that the difference is described by string-like excitations, bounded by defect pairs, which have a fractal dimension of 1.250(3). At zero temperature, the disorder-induced defects screen the interaction of introduced vortex pairs.

Cold Relativistic Wavebreaking, J.K. Kim, Donald P. Umstadter

Donald Umstadter Publications

The two-dimensional wave-breaking of relativistic plasma waves driven by a ultrashort high-power lasers, is described within a framework of cold 2-D fluid theory. It is shown that the transverse nonlinearity of the plasma wave results in temporally increasing transverse plasma oscillation in the wake of the laser pulse, inevitably inducing wave-breaking below the 1-D threshold. A condition for wavebreaking is obtained and evaluated. A preformed density channel is found to partially cancel the effect and increase the length of wakefield that survives before wavebreaking occurs.

40th Rocky Mountain Conference On Analytical Chemistry

Rocky Mountain Conference on Magnetic Resonance

Final program, abstracts, and information about the 40th annual meeting of the Rocky Mountain Conference on Analytical Chemistry, co-sponsored by the Colorado Section of the American Chemical Society and the Rocky Mountain Section of the Society for Applied Spectroscopy. Held in Denver, Colorado, July 25 - August 1, 1998.

Statistics Of Active Galactic Nuclei In Rich Clusters Revisited, M. Way, R. Flores, H. Quintana

Physics Faculty Works

Using the spectrophotometry of a large sample of galaxies in 19 Abell clusters, we have selected 42 candidate active galactic nuclei (AGNs) using the criteria used by Dressler and coworkers in their analysis of the statistics of 22 AGNs in 14 rich cluster fields, which are based on the equivalent width of [O II] 3727 Å, Hβ, and [O III] 5007 Å emission. We have then discriminated AGNs from H II region-like galaxies (hereafter H II galaxies) in the manner developed by Veilleux & Osterbrock using the additional information provided by Hα and [N II] 6583 Å or Hα and …

Spiral Morphology-Dependent Resonances In An Optical Fiber: Effects Of Fiber Tilt And Focused Gaussian Beam Illumination, Andrew W. Poon, Richard K. Chang, James A. Lock

Physics Faculty Publications

Spiral morphology-dependent resonances have been observed in a tilted optical fiber. The polarization-preserving and the cross-polarized elastic-scattering spectra for plane-wave illumination show that the wavelengths of the resonances are blueshifted quadratically as the fiber tilt angle increases. When a focused Gaussian beam illuminates the fiber at its edge, the resonances are blueshifted and broadened as the detector is offset from the scattering plane with the maximum scattering intensity. The blueshift with focused beam illumination is also a consequence of the spiral resonances. (C) 1998 Optical Society of America.

Observation Of B+→ΩK+ And Search For Related B Decays Modes, T. Bergfeld, Kenneth A. Bloom, Cleo Collaboration

Kenneth Bloom Publications

We have searched for two-body charmless decays of B mesons to purely hadronic exclusive final states including ω or φ mesons using data collected with the CLEO II detector. With this sample of 6.6 X 10⁶ B mesons we observe a signal for the ωK⁺ final state, and measure a branching fraction of Ɓ(B⁺→ωK⁺) = (1.5_-0.6^+0.7 ± 0.2) X 10^-5. We also observe some evidence for the φK* final state, and upper limits are given for 22 other decay modes. These results provide the opportunity …

Algebraic Shape Invariant Models, S Chaturvedi, Ranabir Dutt, Asim Gangopadhyaya, Prasanta K. Panigrahi, C. Rasinariu, Uday P. Sukhatme

Physics: Faculty Publications and Other Works

Motivated by the shape invariance condition in supersymmetric quantum mechanics, we develop an algebraic framework for shape invariant Hamiltonians with a general change of parameters. This approach involves nonlinear generalizations of Lie algebras. Our work extends previous results showing the equivalence of shape invariant potentials involving translational change of parameters with standard SO (2,1) potential algebra for Natanzon type potentials.

Effects Of Randomness And Spatially Dependent Relaxation On Sandpile Models, Isiaka O. Akanbi

Electronic Dissertations and Theses

Random deposition represents the simplest growth model. From a randomly chosen site over the surface, a particle falls vertically until it reaches the top of the interface, whereupon it sticks irreversibly. To include surface relaxation, we allow the deposited particle to diffuse along the surface up to a finite distance, stopping when it finds the position with the lowest height. As a result of the relaxation process, the final interface will be smooth, compared to the model without relaxation. In this research we investigate two types of randomness in the relaxation of sandpile models when the slop at some point …

Thermal Stability And Nanostructure Of Cocrpt Longitudinal Recording Media, Mingjun Yu, Mary F. Doerner, David J. Sellmyer

David Sellmyer Publications

We report a systematic study of activation volumes and their correlation with physical grain sizes and thermal stability in CoCrPt media fabricated by magnetron sputtering. Different underlayers and CoCrPt layer thicknesses were used to provide a range of lateral grain sizes, M_Iδ (product of remanence M_I and film thickness δ) values, and remanence coercivities. Two methods, namely the field-sweep-rate dependence of coercivity and measurements of magnetic viscosity and irreversible susceptibility, were used to determine the activation volumes and the results obtained from the two methods are in reasonable agreement. For CoCrPt layer thickness from 10 nm to …

Measurement Of The Photorefractive Grating Phase Shift In A Polymer By An Ac Phase-Modulation Technique, Martin M Liphardt, Stephen Ducharme

Stephen Ducharme Publications

The complex coupling constant of a photorefractive polymer was measured as a function of an applied electric field by use of a modified ac phase modulation technique. We determined that both a photorefractive index grating and a nonphotorefractive absorption grating were present. The electric field dependencies of the amplitude and the phase of the photorefractive gain coefficient were accurately described by standard photorefractive theory. The accuracy of the photorefractive phase shift as measured by this phase-modulation technique was ±1° near phase shifts of 90° and ±3° near phase shifts of 45°.

Chemical Synthesis Of Nanostructured Cobalt At Elevated Temperatures, Diandra Leslie-Pelecky, M. Bonder, T. Martin, E.M. Kirkpatrick, X.Q. Zhang, S.-H. Kim, Reuben D. Reike

Diandra Leslie-Pelecky Publications

Chemical synthesis is a versatile technique for fabricating novel nanostructured materials. In the Rieke process, a metal salt is reduced by an alkali in a hydrocarbon solvent to form small, highly reactive particles. Synthesis at an elevated temperature (200°C) increases the as-synthesized particle size and produces higher coercivities and remanence ratios than observed in similar syntheses at room temperature. The ratio of synthesis temperature to solvent boiling point appears to be an important parameter in both coercivity and oxidation resistance.

Low Energy Electron Gun Power Control Unit, Chad Fish, Jr Dennison

Senior Theses and Projects

Near-Earth orbiting spacecraft are subject to a variety of physical environmental elements. Of these, natural space plasma and solar radiation produce spacecraft charging. Spacecraft charging consists of surface (external) and deep (internal) dielectric charging.

Natural space plasma is composed of electrons and positively charged atoms called ions. The plasma is generated by energy from solar radiation and high energy particles emitted by geomagnetic storms. The electrons produce a negative current and the ions produce a positive current. Positive photoelectron currents produced by solar radiation of spacecraft surfaces also add to the electrical fluxesⁱ.

As spacecraft move through the …

Elementary Excitation Spectrum Of A Trapped Weakly Interacting Bose-Einstein Condensate, Mircea Marinescu, Anthony F. Starace

Anthony F. Starace Publications

An analytic expression is presented for the elementary excitation spectrum of the Bose-Einstein condensate of a trapped boson system in the weakly interacting, low-density limit. Explicit analytic formulas for the elementary excitation spectrum are obtained for harmonic-oscillator traps. These formulas provide information about the behavior of the elementary excitation levels as a function of the number of atoms and their interaction strength for a given trap geometry. They also provide a low-density benchmark for results of fully numerical calculations.

Final-State-Interaction Effects On One- And Two-Photon Detachment Of H- In The Presence Of A Static Electric Field, Min-Qi Bao, Ilya I. Fabrikant, Anthony F. Starace

Anthony F. Starace Publications

We present a detailed theoretical formulation of the problem of an electron moving in a static electric field, a laser field, and an atomic potential. Our formulation treats the electron-atom interaction in the zero-range potential approximation and employs both the quasienergy approach and an analytic expression for the Green’s function describing electron propagation in a combination of static and laser electric fields. Our formulation is applied to one- and two-photon detachment of H^- in a strong static electric field and takes into account all final-state interactions of the detached electron with the static and laser fields and with the …

Magnetoelectric Néel Anisotropies, Ralph Skomski

Ralph Skomski Publications

The applicability of Néel's pair model to metallic 3d surfaces and interfaces is explained in terms of the tight-binding moments theorem. The Néel model reproduces itinerant magnetism so long as the band structure is approximated by third-moment atomic-pair contributions. This establishes an atomic Néel description of interfaces and impurities. The Néel parameter g depends on the d-band filling and, to some extent, on the atomic structure.

Iron And Nickel Surface And Interface Anisotropies, Ralph Skomski, D. Sander, C. Schmidthals, Axel Enders, J. Kirschner

Ralph Skomski Publications

The anisotropy of fcc (111) Fe/Ni and Fe/Ni/Fe layers is investigated. The films exhibit an oscillating behavior of the preferential magnetization direction depending on whether the surface layer is Ni or Fe. Anisotropy fields are obtained from polar and perpendicular Kerr hysteresis loops and yield a comparatively small perpendicular Fe/Ni interface anisotropy of about 0.15 mJ/m2. The real-space origin of the interface anisotropy is the interlayer hybridization of the yz, zx, and z² orbitals.

Experimental Observation Of Correlated Magnetic Reconnection And Alfvénic Ion Jets, Thomas W. Kornack , '98, Peter K. Sollins , '98, Michael R. Brown

Physics & Astronomy Faculty Works

Correlations between magnetic reconnection and energetic ion flow events have been measured with merging force free spheromaks at the Swarthmore Spheromak Experiment. The reconnection layer is measured with a linear probe array and ion flow is directly measured with a retarding grid energy analyzer. Flow has been measured both in the plane of the reconnection layer and out of the plane. The most energetic events occur in the reconnection plane immediately after formation as the spheromaks dynamically merge. The outflow velocity is nearly Alfvenic. As the spheromaks form equilibria and decay, the flow is substantially reduced.

Proton Nmr Spectroscopy As A Probe Of Dinuclear Copper(Ii) Active Sites In Metalloproteins. Characterization Of The Hyperactive Copper(Ii)-Substituted Aminopeptidase From Aeromonas Proteolytica, Richard C. Holz, Brian Bennett, Guanjing Chen, Li-June Ming

Physics Faculty Research and Publications

Proton NMR spectra of the hyperactive Cu(II)-substituted aminopeptidase from Aeromonas proteolytica (AAP) were recorded in both H₂O and D₂O buffered solution at pH 6.7. Several remarkably sharp, well resolved hyperfine shifted ¹H NMR signals were observed in the 70 to −20 ppm chemical shift range. That hyperfine shifted signals were observed is due to spin-coupling of the two Cu(II) ions. Comparison of the spectra recorded in H₂O and D₂O buffered solutions indicated that the signals at 44.6, 43.3, and 17.7 ppm were solvent exchangeable. The two most strongly downfield shifted signals …

Dynamics Of Rydberg States Of Nitric Oxide Probed By Two-Color Resonant Four-Wave Mixing Spectroscopy, Elizabeth Mccormack, F. Di Teodoro, J. M. Grochocinski, S. T. Pratt

Physics Faculty Research and Scholarship

Two-color resonant four-wave mixing (TC-RFWM) spectroscopy has been used to probe highly excited v = 0 and v = 1 Rydberg states of nitric oxide. Transitions to n = 16-30, v = 0, Rydberg states, and the 8p, 9p, 7f, 8f, 8s, and 9s, v = 1 Rydberg states from the A (2)Sigma(+), v' = 0 and 1 states have been recorded. The decay rate of the 8p and 9p, v = 1 states has been extracted from the observed line profiles by using a recently developed model for the excitation of quasibound resonances in TC-RFWM spectroscopy. Transitions from the …

Nonlinear Field Dependence Of The Mobility Of A Charge Subjected To A Superposition Of Dichotomous Stochastic Potentials, A. M. Kenkre, Marek Kus, David H. Dunlap, Paul Ernest Parris

Physics Faculty Research & Creative Works

A general prescription is presented to address a large variety of forms of the nonlinear dependence of the static charge mobility on the applied electric field. The system consists of a classical charge subjected to an arbitrarily strong steady state electric field and to a stochastic potential consisting of a linear superposition of an unlimited number of dichotomous potentials in one-dimensional space. It is shown that the nonlinear mobility can be calculated for arbitrary forms of the density function of the individual dichotomous components of the stochastic potential. Specific cases of physical interest are analyzed. One of them provides a …

Next-To-Leading Order Qcd Corrections For The B⁰B⁰ Mixing With An Extended Higgs Sector, Jorg Org Urban, Frank Krauss, Ulrich D. Jentschura, Gerhard Soff

Physics Faculty Research & Creative Works

We present a calculation of the B⁰B⁰ mixing including next-to-leading order (NLO) QCD corrections within the Two-Higgs Doublet Model (2HDM). The QCD corrections at NLO are contained in the factor denoted by η₂ which modifies the result obtained at the lowest order of perturbation theory. In the Standard Model case, we confirm the results for η₂ obtained by Buras, Jamin and Weisz [Nucl. Phys, B 347 (1990) 491]. The factor η₂ is gauge and renormalization prescription invariant and it does not depend on the infrared behaviour of the theory, which constitutes an important test …

Magnetic And Magneto-Optic Study Of A Layered Co/Pt - Dysprosium-Iron-Garnet System, J.M. Meldrim, Roger D. Kirby, M.J. Devries, John A. Woollam, David J. Sellmyer

Department of Physics and Astronomy: Faculty Publications

Abstract-We have studied the effects of placing Co/Pt multilayers on dysprosium-iron-garnet doped with bismuth and aluminum. The garnet was deposited by RF-magnetron sputtering and crystallized by rapid thermal annealing. The Co/Pt multilayers were then deposited by DC-magnetron sputtering. The garnet thickness was held constant at lOOO Å while the ColPt multilayer had the form of [3 Å Co/9 Å Pt]_n with n ranging from 1 to 16. Coercivities of the samples ranged from about 300 to 2000 Oe. Kerr rotations were as high as 1.8° and ellipticities up to 2° depending upon the wavelength of light and the number …

Experimental Investigations Of Wavelength And Angular Errors In Holographic Gratings With Non-Bragg-Matched Read Beams, Monish Ranjan Chatterjee, Vivek Ray

Electrical and Computer Engineering Faculty Publications

Perfect Bragg matching is generally desirable for accurate optical interconnections with holographic gratings. In reality, however, gratings may be illuminated by READ beams with non-Bragg-matched angles, or wavelengths, or both. In such cases, the scattered beams are generally misdirected, and may suffer loss of efficiency and possibly more serious errors such as crosstalk noise or missed connections. A conventional wave-vector triad method of analyzing the scattered beam errors leads readily to near-Bragg estimates of the output angular misalignment. However, the READ wave-vector triads appear to indicate a possible wavelength shift in the output beam even with a Bragg-matched READ wavelength, …

Reactions Of Oxygen And Nitric Oxide In A Microhollow Electrode Discharge, Joseph L. Desormeaux Jr.

Electrical & Computer Engineering Theses & Dissertations

Microhollow electrode discharges have been developed and researched in the Physical Electronics Research Institute Laboratories. This discharge typically operates in direct current mode. Microhollow electrode discharges are non-thermal discharges that produce electrons with energies greater than 10 electron volts. Passing gas mixtures through non-equilibrium discharges invokes excitation or dissociation of gas molecules.

The scope of my research was to study the effect of the discharge on the chemistry of two gases, oxygen and nitric oxide in nitrogen mixture. Initial experiments were performed in an effort to produce ozone near atmospheric pressure. This seemed possible since the discharge has a high-energy …

Coupled Electrodynamic-Monte Carlo Simulations Of Nanoscale Gaas Terahertz Optical Mixers, Jiang Li

Electrical & Computer Engineering Theses & Dissertations

The concept of mixing or heterodyning has traditionally been used for microwaves and for radio frequency communications. However, the concept can easily be extended into the optical frequency regime. By doing so, the photomixing process can serve as a very versatile tool for both the generation of ultrahigh frequency (terahertz) and the detection of weak optical signals.

The aim of this thesis is to perform a theoretical study of the photomixing process inside GaAs devices as the non-linear elements. A coupled approach which combines the Monte Carlo simulation scheme for the carrier transport, with Maxwell's equation for the electrodynamics, has …

Low Saturation Intensities In Two-Photon Ultracold Collisions, C. I. Sukenik, D. Hoffman, S. Bali, T. Walker

Physics Faculty Publications

We have observed violet photon emission resulting from energy-pooling collisions between ultracold Rb atoms illuminated by two colors of near-resonant infrared laser light. We have used this emission as a probe of doubly excited state ultracold collision dynamics. We have observed the lowest saturation intensity for light-induced ultracold collisions seen to date which we identify as due to depletion of incoming ground state flux. We have also varied the detuning of the lasers which allows us to clearly identify the effect of spontaneous emission and optical shielding.

An Injection Modelocked Titanium-Sapphire Laser, James C. Hovater

Electrical & Computer Engineering Theses & Dissertations

I have investigated the possibility of using an injection modelocked Ti-sapphire laser as a illumination source for GaAs photocathodes. A commercial Ti-sapphire laser was modified to accept a seed pulse from a gain-switched diode laser. Modelocked operation was obtained through gain modulation within the Ti-sapphire crystal as a result of injection seeding with a modelocked pulse train from a gain-switched diode laser. The Ti-sapphire laser essentially becomes a pulse amplifier for the diode laser. Unlike conventional modelocked lasers, the pulse repetition rate of this laser can be discretely varied by setting the seed laser repetition rate equal to multiples of …

Electrical Characteristics And Parallel Operation Of Microhollow Cathode Discharges, Wenhui Shi

Electrical & Computer Engineering Theses & Dissertations

This thesis describes the electrical properties of microhollow cathode discharges with argon as filling gas. The appearance and current-voltage characteristics of microhollow cathode discharges have been recorded. Three kinds of discharge modes (predischarge, hollow cathode discharge and abnormal discharge) have been observed. The range of operation of the hollow cathode discharge has been found to be 0.5 < pD & 5 Torr cm in argon. By reducing the hole diameter to 100 pm, we were able to operate the discharge to atmospheric pressure in a dc mode. The possibility of dc parallel operation of microhollow cathode discharges was explored. Parallel operation could be obtained without individual ballast for discharges with a positive I-V slope greater than 10 V/mA over a voltage range of more than 5 % of the sustaining voltage. For parallel operation outside the range the ballasting is required. This model was explored by using a segmented anode model. The result of the simple calculation coincides well with the experiment result, where a semi-insulator silicon was used as distributed ballast.