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Spin-Resolved (E,2e) Coincidences For Heavy Rare-Gas Targets, Stephenie J. Jones, Don H. Madison, G. Friedrich Hanne

Physics Faculty Research & Creative Works

It has been well established that the Coulomb force alone can produce spin-dependent effects for electron-impact excitation of heavy rare-gas atoms if the incident electrons are spin polarized and the final J state of the atom is resolved. This effect has become known as the fine-structure effect. Here we demonstrate that the same type of effect may be expected for electron-impact ionization.

High Energy Coupled Nucleon Tranpsort In One Dimension, Stanley L. Lamkin

Physics Theses & Dissertations

The problem of energetic nucleon transport through extended bulk matter is considered in the context of the 'straight ahead' approximation. The applicable form of the Boltzmann transport equation is derived and solved in one dimension. The production term for secondary generation nucleons due to nuclear fragmentation includes 'coupling' of the flux to other types of nucleon projectiles. A physically motivated perturbation series approach is developed to enhance solution convergence. The Boltzmann operator is inverted and the flux is computed using a numerical marching scheme. The secondary production integrals are optimized for second order accuracy using a set of analytical benchmarks. …

Optimal Active And Passive Control Design For A Slewing Piezoelectric Laminate Beam, Travis V. Dubois

Mechanical & Aerospace Engineering Theses & Dissertations

This thesis presents the development and experimental verification of a distributed parameter model for a slewing beam system with piezoelectric actuators and sensors. Also presented is the development of an optimal active control synergism which employs IMSC, (Independent Modal Space Control) and an optimally designed, viscoelastic damping treatment. The beam is pinned at the proximal end and patches of thin piezoelectric laminates are attached to its surface. Formulation is general enough to allow the patches to be located anywhere on the beam's surface. A viscoelastic material with a constraining layer covers the rest of the beam. The differential equation of …

A Direct Numerical Simulation Of Vortex Breakdown Induced Tail Buffet, Steven James Massey

Mechanical & Aerospace Engineering Theses & Dissertations

A simulation of tail buffet is presented for a delta wing-vertical tail configuration. Flow conditions are chosen such that the wing primary-vortex cores experience vortex breakdown and the resulting turbulent wake flow impinges on the vertical tail. The dimensions and material properties of the vertical tail are chosen such that the deflections are large enough to insure interaction with the flow, and the natural frequencies are high enough to facilitate a practical computational solution. This multidisciplinary problem is solved sequentially for the fiuid flow, the elastic deformations and the grid displacements. The fluid flow is simulated by time accurately solving …

Unsteady Flow Simulations About Moving Boundary Configurations Using Dynamic Domain Decomposition Techniques, Guan-Wei Yen

Mechanical & Aerospace Engineering Theses & Dissertations

A computational method is developed to solve the coupled governing equations of an unsteady flowfield and those of rigid-body dynamics in six degrees-of-freedom (6-DOF). This method is capable of simulating the unsteady flowfields around multiple component configurations with at least one of the components in relative motion with respect to the others. Two of the important phenomena that such analyses can help us to understand are the unsteady aerodynamic interference and the boundary-induced component of such a flowfield. By hybridizing two dynamic domain decomposition techniques, the grid generation task is simplified, the computer memory requirement is reduced, and the governing …

Derivative Absorption Spectroscopy With Tunable Laser Diodes, Andrew D. Jackson

Electrical & Computer Engineering Theses & Dissertations

Derivative Absorption Spectroscopy using tunable diode lasers provides a non­ intrusive, sensitive, and convenient method for monitoring gaseous characteristics such as concentration, temperature, and flow velocity. In addition, the specie type can be identified, and if the equation of state is known, pressure may be deduced.

This technique was used on molecular oxygen, in which the rovibronic transitions of the A-band ( b ¹ ∑_g ⁺ ← X ³ ∑g ^- ; v^II = O, v^I = O) were probed. Phase sensitive detection with a lock-in amplifier provides the flexibility to examine lineshape derivatives; several such derivative …

Flow Simulations About Steady-Complex And Unsteady Moving Configurations Using Structured-Overlapped And Unstructured Grids, James Charles Newman Iii

Mechanical & Aerospace Engineering Theses & Dissertations

The limiting factor in simulating flows past realistic configurations of interest has been the discretization of the physical domain on which the governing equations of fluid flow may be solved. In an attempt to circumvent this problem, many Computational Fluid Dynamic (CFD) methodologies that are based on different grid generation and domain decomposition techniques have been developed. However, due to the costs involved and expertise required, very few comparative studies between these methods have been performed. In the present work, the two CFD methodologies which show the most promise for treating complex three-dimensional configurations as well as unsteady moving boundary …

Slowing Of 85Rb Atoms With Isotropic Light, Herman Batelaan, S. Padua, D. H. Yang, C. Xie, R. Gupta, Harold Metcalf

Department of Physics and Astronomy: Faculty Publications

We have demonstrated the slowing of a rubidium atomic beam by isotropic monochromatic light. The results agree with a model calculation, thus allowing its use for designing a practical isotropic light slower. The large hyperfine splittings of rubidium lead to natural multifrequency slowing, which is also included in our model.

Vanishing Freedericksz Transition Threshold Voltage In A Chiral Nematic Liquid Crystal, Karl A. Crandall, Michael R. Fisch, Rolfe G. Petschek, Charles Rosenblatt

Faculty Scholarship

A negative dielectric anisotropy cholesteric liquid crystal, oriented homeotropically in a wedged capacitance cell, was subjected to an applied electric field. The Freedericksz transition threshold voltage was found to depend on the local thickness of the sample, and was found to vanish at a thickness of order 3/2 P, where P is the pitch of the cholesteric in the bulk. The results are consistent with a continuum elastic theory. A discussion of the technological ramifications is presented.

Absence Of Size Dependence Of The Kondo Resistivity, V. Chandrasekhar, P. Santhanam, N. A. Penebre, Richard A. Webb, H. Vloeberghs, C. Van Haesendonck, Y. Bruynseraede

Faculty Publications

We have measured the low temperature resistivity of AuFe wires in the dilute magnetic impurity limit as a function of wire width, temperature, and magnetic field. When the width dependence of the electron-electron interaction contribution to the resistivity is taken into account, the temperature dependence of the remaining Kondo contribution to the resistivity of all samples with the same impurity concentration is identical. Similar behavior is observed for the magnetic field dependent resistivity. Thus, the Kondo contribution to the resistivity is independent of width down to 38 nm, much smaller than the Kondo length ξ_K=ħv_F/k_{B …}

Solar Spectroscopy Using 50 Meters Of Fiber Optic Cable And Ccd Camera, Christopher P. Smith

Opportunities for Undergraduate Research Experience Program (OURE)

Measurements of the variation of the Can K line profile using very modest equipment is discussed. The equipment used included a Spex 0.75 meter spectrometer, a Santa Barbara Instrument Group 16 bit ST-6 Charge Coupled Device (CCD) camera, fiber optic cable, and a 10-inch Cassegrain telescope. Observations were made in both regions of little or no solar activity as well as in regions of high solar activity (sunspots). A roughly 8% increase in Ca II K emission was observed over a sunspot. The combination of the unique observing apparatus and the intensity resolution of the CCD camera was essential for …

Feasibility Of Using Ultrasonic Cavitation To Produce Silica Sol, Gary L. Vines

Honors Capstone Projects and Theses

No abstract provided.

On The Absence Of An Exponential Bound In Four Dimensional Simplicial Gravity, Simon Catterall, John B. Kogut, R. Renken

Physics - All Scholarship

We have studied a model which has been proposed as a regularisation for four dimensional quantum gravity. The partition function is constructed by performing a weighted sum over all triangulations of the four sphere. Using numerical simulation we find that the number of such triangulations containing V simplices grows faster than exponentially with V. This property ensures that the model has no thermodynamic limit.

Surface Core-Level Shifts Of Ta(110) And W(110) Vs. Alkali-Atom Coverage: Implications For Thealkali-Substrate Interaction, A. B. Andrews, D. Mark Riffe, G. K. Wertheim

All Physics Faculty Publications

The change in the average surface-atom core-level shift (SCS) produced by submonolayer coverages of alkali adsorbates is quite small for both Ta(110) and W(110), less than 45 meV in magnitude. The small change of the measured SCS’s as a function of coverage decisively supports the covalent-bonding picture of alkali adsorption proposed by Ishida and Terakura.

Unoccupied Surface Electronic Structure Of Gd(0001), Dongqi Li, Peter A. Dowben, J.E. Ortega, F.J. Himpsel

Peter Dowben Publications

The unoccupied surface electronic structure of Gd(0001) was investigated with high-resolution inverse-photoemission spectroscopy. An empty surface state near E_F is observed at Γ¯. Two other surface-sensitive features are also revealed at 1.2 and 3.1 eV above the Fermi level. Hydrogen adsorption on Gd surfaces was used to distinguish the surface-sensitive features from the bulk features. The unoccupied bulk-band critical points are determined to be Γ_3^- at 1.9 eV and A₁ at 0.8 eV.

Coherence Parameters For Electron Capture In H⁺ + He Collisions, C. J. Lundy, Ronald E. Olson, D. R. Schultzi, J. P. Pascale

Physics Faculty Research & Creative Works

The classical trajectory Monte Carlo method is used to calculate coherence parameters for electron capture to H(n = 2, 3 and 4) in 30 to 250 keV H+ + He collisions. The parameters evaluated are the x- and z-components of the dipole moment (D) and the z-component of the perihelion velocity of the captured electron (L x A). The calculated integral values are found to be in reasonable agreement with available experimental results. Components of the dipole moment and (L x A) were also evaluated as a function of projectile scattering angle. Here, rapid variations of the parameters are observed …

Scaling Of Voltage-Current Characteristics Of Thin-Film Y-Ba-Cu-0 At Low Magnetic Fields, Brandon R. Brown

Physics and Astronomy

We have measured voltage-current characteristics for YBa2Cu3O7 thin films in magnetic fields from 5 T to ambient, including some in the millitesla range. In all cases, the resistivity-current density isotherms can be separated into two classes: those which exhibit upward curbature, and have constant resistivity at low currents, and those which exhibit downward curvature at all currents. These two classes of isotherms are separated by a field-dependent temperture Tg. For each field, the isotherms scale in a manner consistent with a three dimensional vortex-liquid to vortex-glass phase transition. The region that can be scaled is several kelving at 5 T …

Exchange Coupling And Energy Product In Random Two- Phase Aligned Magnets, Ralph Skomski, J.M.D. Coey

Ralph Skomski Publications

Size effects in two-phase Boolean magnets composed of an aligned hard phase and a soft phase with high magnetization are investigated. In 'over-critical' magnets, where the size of the soft regions is larger than the Blochwall width δ_h of the hard phase, the energy product is reduced compared to the corresponding 'undercritical' magnets with small soft regions, where theoretical energy products as high as 1 M J / m³ have been predicted. Nevertheless, the theoretical energy product only gradually drops with increasing size of the soft regions, and it may still exceed the theoretical energy product 516 kJ/m …

Magnetoresistance In Nanostructured Co-Ag Prepared By Mechanical- Alloying, J.M.D. Coey, A.J. Fagan, Ralph Skomski, J. Gregg, K. Ounadjela, S.M. Thompson

Ralph Skomski Publications

Fine cobalt and silver powders have been ball-milled to yield a granular solid of composition Co₃₀Ag₇₀ in the form of coarse powder. The material is an intimate mixture of grains of fcc CO in a silver matrix. The cobalt is in the single-domain size range, and the samples exhibit coercivity (0.07 T at 296 K) and unusual thermomagnetic effects, including field-induced unidirectional anisotropy. There is a large, isotropic negative magnetoresistance, which exceeds 10 % at 4.2 K.

Magnetoresistance In Nanostructured Co-Ag Prepared By Mechanical- Alloying, J.M.D. Coey, A.J. Fagan, Ralph Skomski, J. Gregg, K. Ounadjela, S.M. Thompson

Ralph Skomski Publications

Fine cobalt and silver powders have been ball-milled to yield a granular solid of composition Co₃₀Ag₇₀ in the form of coarse powder. The material is an intimate mixture of grains of fcc CO in a silver matrix. The cobalt is in the single-domain size range, and the samples exhibit coercivity (0.07 T at 296 K) and unusual thermomagnetic effects, including field-induced unidirectional anisotropy. There is a large, isotropic negative magnetoresistance, which exceeds 10 95 at 4.2 K.

Rank Conditioned Rank Selection Filters For Signal Restoration, Russell C. Hardie, Kenneth E. Barner

Electrical and Computer Engineering Faculty Publications

A class of nonlinear filters called rank conditioned rank selection (RCRS) filters is developed and analyzed in this paper. The RCRS filters are developed within the general framework of rank selection(RS) filters, which are filters constrained to output an order statistic from the observation set. Many previously proposed rank order based filters can be formulated as RS filters. The only difference between such filters is in the information used in deciding which order statistic to output. The information used by RCRS filters is the ranks of selected input samples, hence the name rank conditioned rank selection filters. The number of …

Correlated Two-Electron Wave Functions Of Any Symmetry, Christopher Bottcher, David R. Schultz, Don H. Madison

Physics Faculty Research & Creative Works

Using a procedure originally due to Hylleraas, a convenient expansion in coupled spherical harmonics which terminates in a very small number of terms is applied to the treatment of fully correlated two-electron wave functions of any symmetry (total angular momentum, parity, and spin). Coupled equations satisfied by these wave functions are derived which are well adapted to computation and which we discretize on a numerical lattice utilizing the basis-spline collocation method. Use of this method which relies on very flexible basis functions is intended to facilitate subsequently the consideration of time-dependent rearrangments such as autoionization, photoionization, and electron-impact excitation and …

Feasibility Analysis For Predicting A Kinetic Kill Zone For Aircraft Homing Missile Defense, Mark E. Ennis

Theses and Dissertations

An extended Kalman filter is used to predict a kinetic kill zone for use in aircraft self defense versus homing missiles. The analysis is limited to an in-the-plane analysis and focuses on finding the model parameters which have the largest impact on the predicted kill zone. No attempt is made to optimize the design of the filter model itself. The analysis computes the kill zone relative to an assumed aircraft trajectory using strictly filter computed statistics. No Monte-Carlo simulations are used throughout the thesis. The filter assumed to be on the evading aircraft, uses an onboard laser radar (ladar) to …

Generalized Coulomb Gap In The Spherical Version Of A Lattice Model Of Disordered And Correlated Localized Particles, Thomas Vojta, Michael Schreiber

Physics Faculty Research & Creative Works

We study the spherical version of a model of localized particles in a random potential which are subject to a power-law interaction U_ij ~ r_ij^-σ. In the case of a repulsive interaction with σ = 1 the model is identical to the spherical version of the Coulomb-glass model of disordered localized electrons. The use of continuous variables instead of discrete occupation numbers of the sites renders the model exactly solvable. Analytic results are obtained for the free energy and for the single-particle density of states (DOS) as an example for single-particle properties. The zero-temperature DOS shows …

Non-Equilibrium Gas-Phase Nitrogenation, S. Brennan, Ralph Skomski, J.M.D. Coey

Ralph Skomski Publications

Non-equilibrium nitrogenation of transition-metal rich rare-earth intermetallics can be used to increase the nitrogen content beyond its equilibrium concentration. For example, nitrogenation of Sm₂Fe₁₇ using ammonia yields volume expansions up to 8.3 vol %, which correspond to a composition Sm₂Fe₁₇N_x with x = 4. This effect is related to catalytic action at the metal surface where ammonia is decomposed into nitrogen and hydrogen, with nitrogen absorption on a site where it is weakly bound, as an intermediate step. For overloaded Sm₂Fe₁₇N_x with x>3 the net reaction …

A Measurement Of B(D+S → Φl+Ν) B(D+S → Φπ+), Cleo Collaboration, F. Butler, Manoj Thulasidas

Research Collection School Of Computing and Information Systems

Using the CLEO II detector at CESR, we have measured the ratio of branching fractions B(D → φlν) B(D → φπ) = 0.54 ± 0.05 ± 0.04. We use this measurement to obtain a model dependent estimate of B(D → φπ). © 1994.

A Mössbauer Effect Study Of The Microscopic Magnetic Properties Of Th₂Fe₁₇ And Its Nitride, Th₂Fe₁₇N₂.₆, Gary J. Long, Oran Allan Pringle, Fernande Grandjean, T. H. Jacobs, K. H. Buschow

Chemistry Faculty Research & Creative Works

The Mössbauer spectra of Th₂Fe₁₇ and Th₂Fe₁₇N_2.6 have been measured at various temperatures between 85 and 295 K and analyzed with a model that is based on the Wigner-Seitz cell environment of each iron site, the orientation of the magnetization, and the magnetic moments as determined from either neutron-diffraction measurements or band-structure calculations. Upon nitrogenation of Th₂Fe₁₇, the 85 K weighted average isomer shift increases from 0.037 to 0.156 mm/s and further the isomer shifts of the four crystallographically distinct sites increase in agreement with the increase observed …

Nonlinear Plasma Waves Resonantly Driven By Optimized Laser Pulse Trains, Donald Umstadter, Eric Esarey, J. Kim

Donald Umstadter Publications

A method for generating large-amplitude plasma waves, which utilizes an optimized train of independently adjustable, intense laser pulses, is discussed and analyzed. Both the pulse widths and interpulse spacings are optimally determined such that resonance is maintained and the plasma wave amplitude is maximized. By mitigating the effects of both phase and resonant detuning, and by reducing laser-plasma instabilities, the use of appropriately tailored multiple laser pulses is a highly advantageous technique for accelerating electrons. Practical methods of producing the required pulse trains are suggested.

Domainlike Antiferromagnetic Correlations Of Paramagnetic Fecl2: A Field-Induced Griffiths Phase?, Christian Binek, Wolfgang Kleemann

Christian Binek Publications

Domainlike antiferromagnetic correlations are detected by SQUID measurements of the low-frequency susceptibility in the metamagnet FeCl₂ when exposed to an axial magnetic field H at temperatures T_c (H)≤T≤T_N. A distinct change of curvature of χ’’ vs T appearing at T_N is explained in terms of fluctuating distributions of demagnetizing fields and, hence, transition temperatures. The field-induced dynamic domain phase—an analog of the Griffiths phase predicted for a ferromagnet with dilution x within T_c(x)≤T≤T_c(0)—is confirmed by elastic light scattering experiments.

On The Theory Of Astronomical Masers In Three Dimensions, Moshe Elitzur

Physics and Astronomy Faculty Publications

In the standard theory of three-dimensional astronomical masers, the radiation field is described as if the source were comprised of a collection of linear masers. To leading order, the standard theory is shown to provide the correct description of three-dimensional masers and its results remain intact, but only within a frequency core whose half-width is χ_sΔν_D, where Δν_D is the Doppler width and χ_s is a dimensionless parameter. For any given geometry, χ_s is ~1θ_sat, where θ_sat is the beaming angle of a maser with that geometry that has …