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Improved Gaussian Beam-Scattering Algorithm, James A. Lock Jan 1995

Improved Gaussian Beam-Scattering Algorithm, James A. Lock

Physics Faculty Publications

The localized model of the beam-shape coefficients for Gaussian beam-scattering theory by a spherical particle provides a great simplification in the numerical implementation of the theory. We derive an alternative form for the localized coefficients that is more convenient for computer computations and that provides physical insight into the details of the scattering process. We construct a FORTRAN program for Gaussian beam scattering with the localized model and compare its computer run time on a personal computer with that of a traditional Mie scattering program and with three other published methods for computing Gaussian beam scattering. We show that the …

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Linear Transport Theory Of Magnetoconductance In Metallic Multilayers: A Real-Space Approach, Horacio E. Camblong Jan 1995

Linear Transport Theory Of Magnetoconductance In Metallic Multilayers: A Real-Space Approach, Horacio E. Camblong

Physics and Astronomy

The linear transport behavior of metallic multilayers is studied by using the real-space Kubo formula, for a model Hamiltonian consisting of zero-range spin-dependent impurity-scattering potentials. The resulting theory allows a direct comparison with the Boltzmann equation approach in the quasiclassical limit, which is expected to be a good approximation for most magnetic multilayers. Furthermore, the regimes for which quantum corrections might be needed are explicitly indicated. It is explicitly shown that: (i) periodicity is not required as a mechanism for giant magnetoresistance, and (ii) the two main geometries, current in the plane of the layers and perpendicular to the plane …

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The Origin Of N Iii Λ990 And C Iii Λ977 Emission In Agn Narrow-Line Region Gas, Jason W. Ferguson, Gary J. Ferland, A. K. Pradham Jan 1995

The Origin Of N Iii Λ990 And C Iii Λ977 Emission In Agn Narrow-Line Region Gas, Jason W. Ferguson, Gary J. Ferland, A. K. Pradham

Physics and Astronomy Faculty Publications

We discuss implications of Hopkins Ultraviolet Telescope (HUT) detections of C III λ977 and N III λ990 emission from the narrow-line region of the Seyfert 2 galaxy NGC 1068. In their discovery paper Kriss et al. showed that the unexpectedly great strength of these lines implies that the emitting gas must be shock-heated if the lines are collisionally excited. Here we investigate other processes which excite these lines in photoionization equilibrium. Recombination, mainly dielectronic, and continuum fluorescence are strong contributors to the line. The resulting intensities are sensitive to the velocity field of the emitting gas and require …

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State-Selected Ion-Molecule Reactions: Charge Transfer And Atomic Rearrangement Processes In Thermal Energy Collisions Of H2+ (X;V)+N2 And Of N2+ (X,A;V) + H2, Cornelis J. Uiterwaal, J. Van Eck, A. Niehaus Jan 1995

State-Selected Ion-Molecule Reactions: Charge Transfer And Atomic Rearrangement Processes In Thermal Energy Collisions Of H2+ (X;V)+N2 And Of N2+ (X,A;V) + H2, Cornelis J. Uiterwaal, J. Van Eck, A. Niehaus

C.J.G.J. Uiterwaal Publications

Using the photo-electron-product-ion-coincidence method (PEPICO) we have measured state-selective cross sections for the following processes: (A) N2+ (X,A;v)+ H2→N2H+ + H, (B) H2+ (X;v) + N2→N2H+ + H, (C) N2+ (X,A;v)+H2→H2+ + N2, and (D) H2+ (X;v)+N2→N2+ + H2 . The measurements were performed at thermal velocities (Ec.m. ≈ 40 meV).We have found that the charge transfer processes (C) and (D) …

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Implications Of Fumi’S Theorem For Auxiliary Particle Methods, S. E. Barnes Jan 1995

Implications Of Fumi’S Theorem For Auxiliary Particle Methods, S. E. Barnes

Physics Articles and Papers

Fumi’s theorem in conjunction with some general theorems associated with auxiliary particle methods dictates the functional form of the on-shell auxiliary particle self-energy Σ for a certain class of impurity scattering problems. An explicit calculation which confirms the result is described and the implications for various approaches to the Kondo effect discussed.

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Asymptotic Form Of The Penetration Probability Of The Quantum Harmonic Oscillator Into The Classically Forbidden Region, D. E. Atems Jan 1995

Asymptotic Form Of The Penetration Probability Of The Quantum Harmonic Oscillator Into The Classically Forbidden Region, D. E. Atems

Physics and Astronomy Faculty Research Publications

The penetration probability of the quantum harmonic oscillator into the classically forbidden region is examined in the limit of large quantum numbers using analytical methods. An expression is derived for the asymptotic form of the penetration probability, and is shown to be in good agreement with an earlier result obtained by numerical methods. The asymptotic form of the probability density in the region between the classical turning points is also presented and found to have a simple physical interpretation.

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Optical Measurements On The Bp Iii To Isotropic Phase Transition In Highly Chiral Liquid Crystals, Jonathan Brent Becker , '92, Peter J. Collings Jan 1995

Optical Measurements On The Bp Iii To Isotropic Phase Transition In Highly Chiral Liquid Crystals, Jonathan Brent Becker , '92, Peter J. Collings

Physics & Astronomy Faculty Works

Optical activity and light scattering measurements in the chiral-racemic system of 4-(2-methylbutyl) phenyl-4-hexyloxybenzoate (CE4) reveal a much larger decrease in the discontinuity at the third blue phase (BP III) to isotropic phase transition than reported previously using adiabatic scanning calorimetry on another compound. Whereas these new data show that the transition is still slightly discontinuous for the pure optical isomer of CE4, similar light scattering measurements on the pure optical isomer of 4″-(2- methylbutylphenyl)-4′-(2-methylbutyl)-4-biphenyl-carboxylate (CE2), which is more chiral than CE4, show no discontinuity at all.

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A Simple Technique To Measure Stress In Ultrathin Films During Growth, D. Sander, Axel Enders, J. Kirschner Jan 1995

A Simple Technique To Measure Stress In Ultrathin Films During Growth, D. Sander, Axel Enders, J. Kirschner

Axel Enders Publications

We demonstrate an easy implementation of the cantilever bending beam approach to measure stress during film growth in ultrahigh vacuum. Using a simple and compact optical deflection technique, film stress with sub-monolayer sensitivity can be detected. A stress measurement during FeSi, formation on Si(l11) is presented.

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Optical Measurements Of The Core Radius Of High-Δ Fibers With 1-Nm Resolution, Peter N. Saeta Jan 1995

Optical Measurements Of The Core Radius Of High-Δ Fibers With 1-Nm Resolution, Peter N. Saeta

All HMC Faculty Publications and Research

An optical technique for measuring the core radius of high-Δ optical fibers is described. Variations in the core radius of step-index fibers can be measured down to a scale of 1 nm.

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Demonstrating Hysteresis In Ferroelectric Materials, Deborah Schurr, Timothy Usher Jan 1995

Demonstrating Hysteresis In Ferroelectric Materials, Deborah Schurr, Timothy Usher

Physics Faculty Publications

No abstract provided.

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Introduction To Monte Carlo Methods, Sue Ellen Mccloskey, Wilfred J. Braithwaite Jan 1995

Introduction To Monte Carlo Methods, Sue Ellen Mccloskey, Wilfred J. Braithwaite

Journal of the Arkansas Academy of Science

Monte Carlo computer programming is becoming increasingly popular to those who use it, due to the ease with which complex problems may be formulated and solved. However, the growth of MC programming for small projects is inhibited by a frequent misconception of difficulty, inferred from the high level of complexity of problems solved in High Energy and Nuclear Physics using MC methods. In addition, few students of science and engineering are receiving exposure to the basic issues involved in the Monte Carlo process despite the ease with which MC can be used to solve classical physics problems, especially those problems …

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Comment On 'Simulation Of A Two-Dimensional Rayleigh-Bénard System Using The Direct Simulation Monte Carlo Method, Alejandro Garcia, F. Baras, M. Malek Mansour Jan 1995

Comment On 'Simulation Of A Two-Dimensional Rayleigh-Bénard System Using The Direct Simulation Monte Carlo Method, Alejandro Garcia, F. Baras, M. Malek Mansour

Faculty Publications

No abstract provided.

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Collection Of Athermal Phonons Into Doped Germanium Thermistors Using Quasiparticle Trapping, S. M. Grannan, Betty A. Young, Andrew E. Lange, S. Labov, Bernard Sadoulet, J. Emes, Eugene E. Haller Jan 1995

Collection Of Athermal Phonons Into Doped Germanium Thermistors Using Quasiparticle Trapping, S. M. Grannan, Betty A. Young, Andrew E. Lange, S. Labov, Bernard Sadoulet, J. Emes, Eugene E. Haller

Physics

We have developed a low‐temperature particle detector that uses a novel quasiparticle trapping mechanism to funnel athermal phonon energy from an 80 mg Ge absorber into a 1.6 mg doped Ge thermistor via a superconducting Al film. We report on pulse height spectra obtained at 320 mK by scanning a 241Am alpha source along the device, and show that up to 20% of the energy deposited in the Ge absorber by a 5.5 MeV alpha particle interaction can be collected into a thermistor via quasiparticle trapping. We show that this device is sensitive to the position of an alpha …

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Justifying A Search For A Unifying Theory Of Unconstitutional Conditions, Roberto L. Corrada Jan 1995

Justifying A Search For A Unifying Theory Of Unconstitutional Conditions, Roberto L. Corrada

Sturm College of Law: Faculty Scholarship

This essay explores why many scholars, including Frederick Schauer and Larry Alexander, feel that an attempt at unification of the doctrine of unconstitutional conditions is unworthy of scholarly attention. Although the subject of this particular essay is less ambitious than the many attempts that have been made to unify the doctrine of unconstitutional conditions, and indeed proposes no unifying theory itself, it nevertheless examines why attempts to explain the doctrine in a unified way might be valid even if no unification is ultimately possible. It also attempts to persuade that a unifying theory of the doctrine may be attainable, although …

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Parameterized Ionospheric Model: A Global Ionospheric Parameterization Based On First Principles Models, R. E. Daniell Jr., L. D. Brown, D. N. Anderson, M. W. Fox, P. H. Doherty, D. T. Decker, Jan Josef Sojka, Robert W. Schunk Jan 1995

Parameterized Ionospheric Model: A Global Ionospheric Parameterization Based On First Principles Models, R. E. Daniell Jr., L. D. Brown, D. N. Anderson, M. W. Fox, P. H. Doherty, D. T. Decker, Jan Josef Sojka, Robert W. Schunk

All Physics Faculty Publications

We describe a parameterized ionospheric model (PIM), a global model of theoretical ionospheric climatology based on diurnally reproducible runs of four physics based numerical models of the ionosphere. The four numerical models, taken together, cover the E and F layers for all latitudes, longitudes, and local times. PIM consists of a semianalytic representation of diurnally reproducible runs of these models for low, moderate, and high levels of both solar and geomagnetic activity and for June and December solstice and March equinox conditions. PIM produces output in several user selectable formats including global or regional latitude/longitude grids (in either geographic or …

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Radio-Frequency Superconducting Parametric Transducer For Gravitational-Wave Antennae, M. A. Fisher, Mark F. Bocko, Linda E. Marchese, Guizhen Zhang, Munawar Karim Jan 1995

Radio-Frequency Superconducting Parametric Transducer For Gravitational-Wave Antennae, M. A. Fisher, Mark F. Bocko, Linda E. Marchese, Guizhen Zhang, Munawar Karim

Physics Faculty/Staff Publications

We report on the design and testing of an ultrasensitive, electromechanical transducer for use on resonant mass gravitational wave antennae. The transducer is a superconducting, radio frequency resonant bridge circuit operating near 200 MHz. We have minimized several important sources of noise in this transducer system. The Johnson noise of the transducer circuit is reduced through using a superconducting niobium stripline circuit and low‐loss insulating materials. At a temperature of 4.2 K we have achieved unloaded electrical quality factors of 200 000. The bridge circuit is balanced by piezoelectric actuators which control the spacing between the proof mass and capacitive …

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Building A Continuous Wave Titanium Sapphire Laser, Sean Mcclain Jan 1995

Building A Continuous Wave Titanium Sapphire Laser, Sean Mcclain

Honors Theses, 1963-2015

In fulfilling the requirement of a senior thesis, I have constructed and optimized a continuous wave (cw) titanium sapphire laser, loosely based on the designs of other experimenters. A maximum output power of 500 mw at 23. nm was obtained after trying several cavity configurations. The beam characteristics, including wavelength, beam width, power and position stability were found to be sensitively dependent on the pump power, supplied by an argon ion laser.

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The Integral Quantum Hall Effect, John Jens Ryan Jan 1995

The Integral Quantum Hall Effect, John Jens Ryan

Honors Theses, 1963-2015

Temperature dependencies of the integer quantum Hall effect in an AlGaAs sample are reported. We obtained measurements at temperatures between 2.2 and 4.2 K, and magnetic fields up to 8 T. Shubnikov de Hass oscillations were also observed and analyzed. The relation between dp,/dB, the slopes between Hall plateaus, and temperature was also investigated and found to not fit the T-r~e lationship which others have experimentally found. Dependencies of the Hall plateaus on the magnetic field, Hall current, and the temperature are also investigated.

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Vibrational Dynamics And Structure Of Amorphous Carbon Modeled Using The Embedded Ring Approach, T. E. Doyle, John R. Dennison Jan 1995

Vibrational Dynamics And Structure Of Amorphous Carbon Modeled Using The Embedded Ring Approach, T. E. Doyle, John R. Dennison

All Physics Faculty Publications

The Raman spectrum of graphitic amorphous carbon (g-C) is modeled with simple classical methods, using rings as medium-range structural units. g-C provides a simple [nearly two dimensional (2D) with a single type of atom and one dominant bond type] prototypic example of a large class of continuous random network (CRN) solids where ring or cluster vibrations cannot be decoupled from the network in which they are embedded. We determined the in-plane vibrational modes of n=4, 5, 6, 7, and 8-membered symmetric, planar carbon rings using bond-stretching and bond-angle bending force constants; an additional force constant couples each ring node to …

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Mcplib: A Collection Of Nonlinear Mixed Complementarity Problems, Steven P. Dirkse, Michael C. Ferris Jan 1995

Mcplib: A Collection Of Nonlinear Mixed Complementarity Problems, Steven P. Dirkse, Michael C. Ferris

University Faculty Publications and Creative Works

The origins and some motivational details of a collection of nonlinear mixed complementarity problems are given. This collection serves two purposes. Firstly, it gives a uniform basis for testing currently available and new algorithms for mixed complementarity problems. Function and Jacobian evaluations for the resulting problems are provided via a GAMS interface, making thorough testing of algorithms on practical complementarity problems possible. Secondly, it gives examples of how to formulate many popular problem formats as mixed complementarity problems and how to describe the resulting problems in GAMS format. We demonstrate the ease and power of formulating practical models in the …

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Electrical Characterization Of The (La,Ca) (Cr,Co)O3 System, S. R. Sehlin, Harlan U. Anderson, Don M. Sparlin Jan 1995

Electrical Characterization Of The (La,Ca) (Cr,Co)O3 System, S. R. Sehlin, Harlan U. Anderson, Don M. Sparlin

Materials Science and Engineering Faculty Research & Creative Works

The results of electrical conductivity and thermopower measurements are presented for selected (La,Ca)(Cr,Co)O3 compositions. The La1 - xCaxCrO3 compounds are typical p-type small polaron conductors. The La1 - xCaxCrO3 compounds are found to be small polaron conductors at room temperature for x ≤ 0.20 with a higher electrical conductivity than the corresponding chromite's. The electrical conductivity at room temperature is lower for Co-rich compositions than for Cr-rich compositions for compositions containing 10 mol% and 20 mol% Ca. This fact is attributed to the trapping of p-type small polarons at energetically lower Cr sites, resulting in a broad room temperature conductivity …

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Some Remarks On Gravitational Analogs Of Magnetic Charge, Charles G. Torre Jan 1995

Some Remarks On Gravitational Analogs Of Magnetic Charge, Charles G. Torre

All Physics Faculty Publications

Existing mathematical results are applied to the problem of classifying closed p-forms which are locally constructed from Lorentzian metrics on an n-dimensional orientable manifold M(0

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What Is The Source Of Observed Annual Variations In Plasmaspheric Density?, S. M. Guiter, C. E. Rasmussen, T. I. Gombosi, Jan Josef Sojka, Robert W. Schunk Jan 1995

What Is The Source Of Observed Annual Variations In Plasmaspheric Density?, S. M. Guiter, C. E. Rasmussen, T. I. Gombosi, Jan Josef Sojka, Robert W. Schunk

All Physics Faculty Publications

Plasmaspheric densities have been observed previously to be higher in December than in June, with the ratio varying between 1.5 and 3.0 and with larger variations at lower L shells. In order to search for the cause of the observed annual variations, we have modeled plasmaspheric density, using a time-dependent hydrodynamic model. On an L = 2 field line with geomagnetic longitude equal to 300°, the modeled plasmaspheric densities were a factor of 1.5 times higher in December than in June. The modeled December to June density ratio was found to increase slightly with L shell, in contrast to observations; …

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A Correlative Comparison Of The Ring Current And Auroral Electrojets Using Geomagnetic Indices, W. B. Cade Iii, Jan Josef Sojka, Lie Zhu Jan 1995

A Correlative Comparison Of The Ring Current And Auroral Electrojets Using Geomagnetic Indices, W. B. Cade Iii, Jan Josef Sojka, Lie Zhu

All Physics Faculty Publications

From a study of the 21 largest geomagnetic storms during solar cycle 21, a strong correlation is established between the ring current index Dst and the time-weighted accumulation of the 1-hour auroral electrojet indices, AE and AL. The time-weighted accumulation corresponds to convolution of the auroral electrojet indices with an exponential weighting function with an e-folding time of 9.4 hours. The weighted indices AEw and ALw have correlation coefficients against Dst ranging between 0.8 and 0.95 for 20 of the 21 storms. Correlation over the entire solar cycle 21 database is also strong but not as …

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Natural Symmetries Of The Yang-Mills Equations, Charles G. Torre Jan 1995

Natural Symmetries Of The Yang-Mills Equations, Charles G. Torre

All Physics Faculty Publications

A natural generalized symmetry of the Yang–Mills equations is defined as an infinitesimal transformation of the Yang–Mills field, built in a local, gauge invariant, and Poincaré invariant fashion from the Yang–Mills field strength and its derivatives to any order, which maps solutions of the field equations to other solutions. On the jet bundle of Yang–Mills connections a spinorial coordinate system is introduced that is adapted to the solution subspace defined by the Yang–Mills equations. In terms of this coordinate system the complete classification of natural symmetries is carried out in a straightforward manner. It is found that all natural symmetries …

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Molecular Fluorescence Spectroscopy In The Vicinity Of A Microstructure, P.T. Leung, Thomas F. George Jan 1995

Molecular Fluorescence Spectroscopy In The Vicinity Of A Microstructure, P.T. Leung, Thomas F. George

Physics Faculty Publications and Presentations

A brief review is presented on fluorescence spectroscopy of molecules in the vicinity of a microstructure, which could be a surface structure, clustered ions/atoms, a colloidal particle in a solution, or a tip in certain molecular probes. This structure can be viewed as microscopic, mesoscopic or macroscopic, depending on the specific environment in which the molecule is located. An overview is given for selected experimental and theoretical aspects of this phenomenon, emphasizing some of the previous modeling work of the authors. Discussion of possible future attempts to explore the phenomenon in more detail is presented at the end.

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The Massive Multi - Flavor Schwinger Model, James E. Hetrick, Y. Hosotani, S. Iso Jan 1995

The Massive Multi - Flavor Schwinger Model, James E. Hetrick, Y. Hosotani, S. Iso

All Faculty Articles - School of Engineering and Computer Science

Non-perturbatively generated effective potentials play an extremely useful and often critical role in string and inflationary model building. These potentials are typically computed by methods that assume the system is in equilibrium. For systems out of equilibrium, like an inflaton rolling down its potential, there are corrections to the semi-classical evolution due to transient phenomena. We provide a new qualitative and quantitative understanding of non-perturbative effects in real time for a wide class of toy quantum mechanical models. We derive an effective Schrödinger equation that does not rely on any notion of equilibrium and captures the low-energy dynamics supposedly described …

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Femtosecond Laser-Produced Plasma X-Rays From Periodically Modulated Surface Targets, J. C. Gautheir, S. Bastiani, P. Audebert, J. P. Geindre, K. Neuman, Thomas D. Donnelly, M. Hoffer, R. W. Falcone, R. Shepherd, D. Price, B. White Jan 1995

Femtosecond Laser-Produced Plasma X-Rays From Periodically Modulated Surface Targets, J. C. Gautheir, S. Bastiani, P. Audebert, J. P. Geindre, K. Neuman, Thomas D. Donnelly, M. Hoffer, R. W. Falcone, R. Shepherd, D. Price, B. White

All HMC Faculty Publications and Research

We have studied theoretically and experimentally the x-ray production above 1 keV from femtosecond laser plasmas generated on periodically modulated surface targets. Laser energy coupling to plasma surface waves has been modeled using a numerical differential method. Almost total absorption of incident laser radiation is predicted for optimized interaction conditions. Silicon gratings have been irradiated by a 120fs Ti:sapphire laser at irradiances in excess of 1016 W/cm2. X-ray intensities above 1.5 keV (K-shell lines) have been measured as a function of the incidence angle. Results show a distinct x-ray emission maximum for the first order diffraction …

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A Consistent Boltzmann Algorithm, Alejandro Garcia, F. Alexander, B. Alder Jan 1995

A Consistent Boltzmann Algorithm, Alejandro Garcia, F. Alexander, B. Alder

Faculty Publications

The direct simulation Monte Carlo method for the Boltzmann equation is modified by an additional displacement in the advection process and an enhanced collision rate in order to obtain the exact hard sphere equation of state at all densities. This leads to consistent thermodynamic and transport properties in the low density (Boltzmann) regime. At higher densities transport properties are comparable to the predictions of the Enskog model. The algorithm is faster than molecular dynamics at low and moderate densities and readily run on a parallel architecture

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Monte-Carlo Simulation Of Bulk Hole Transport In Alxga1-Xas, In1-Xalxas, And Gaasxsb1-X, M. J. Martinez, David C. Look, J. R. Sizelove, F. L. Schuermeyer Jan 1995

Monte-Carlo Simulation Of Bulk Hole Transport In Alxga1-Xas, In1-Xalxas, And Gaasxsb1-X, M. J. Martinez, David C. Look, J. R. Sizelove, F. L. Schuermeyer

Physics Faculty Publications

We report a Monte Carlo study of hole transport in AlxGa1−xAs, In1−xAlxAs, and GaAsxSb1−x. The effects of alloy scattering are significant in all three cases, but mobilities are still high enough to be advantageous in particular device applications. We separately calculate the Hall r factors by a Boltzmann transport method and show that these factors are vitally important when attempting to compare Monte Carlo drift mobilities with experimental Hall data.

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