Digital Commons Network^™

Dynamic Mechanisms Of He Single Ionization By Fast Proton Impact, A. Gensmantel, J. Ullrich, R. Dörner, Ronald E. Olson, K. Ullmann, E. Forberich, S. Lencinas, H. Schmidt-Böcking

Physics Faculty Research & Creative Works

Triple-differential ionization cross sections 3 pdcphipdprec, the momentum distributions of singly charged recoil ions transverse to the beam direction as a function of the projectile polar (p), and azimuthal (cphip) scattering angle were measured in order to elucidate the dynamics of 3-MeV H+ on He single ionization. For projectile polar deflections 0.2 p1 mrad and azimuthal scattering angles 0°cphip360°, the kinematic regimes where two-body interactions dominate the three-body momentum exchange of the single-ionization reaction were separated experimentally. © 1992 The American Physical Society.

Plasma As A High-Charge-State Projectile Stripping Medium, G. D. Alton, R. A. Sparrow, Ronald E. Olson

Physics Faculty Research & Creative Works

The classical trajectory Monte Carlo model has been used to computationally study the charge-state distributions that result from interactions between a high-energy, multielectron projectile and neutral and fully ionized targets. These studies are designed to determine the properties of a plasma for producing highly stripped ions as a possible alternative to gas and foil strippers that are commonly used to enhance the charge states of energetic ion beams. The results of these studies clearly show that a low-atomic-number, highly ionized plasma can yield higher charge states than a neutral target of the same density. The effect is principally attributable to …

Differential Cross Sections For State-Selective Electron Capture In 25100-Kev Proton-Helium Collisions, D. R. Schultz, C. O. Reinhold, Ronald E. Olson, D. G. Seely

Physics Faculty Research & Creative Works

Cross sections differential in the scattering angle of the projectile are presented for electron capture summed over all states and to the 2s, 2p, 3s, 3p, 4s, and 4p states of hydrogen in 25-, 50-, and 100-keV proton-helium collisions. The classical-trajectory Monte Carlo (CTMC) technique was employed for these calculations as well as to compute total cross sections as a function of impact energy. The latter are compared with experiment to display the behavior of the integral state-selective cross sections in this energy regime. Detailed comparison is also made between the calculated angular differential cross sections and the experimental measurements …

Classical Calculation Of High-Energy Electron Capture In 5-Mev Proton-Hydrogen Collisions, D. R. Schultz, C. O. Reinhold, Ronald E. Olson

Physics Faculty Research & Creative Works

The existence of the classical Thomas peak in the angular distribution of projectiles undergoing capture in collisions of 5-MeV protons with atomic hydrogen is explored using the three-body, three-dimensional classical-trajectory Monte Carlo technique. A method that selects only that portion of the initial phase space which yields capture at this energy was developed to make the calculation tractable due to the extremely small cross section. The spectrum obtained displays only a small shoulder near the angle predicted by Thomas on the basis of successive classical binary collisions and the total (integral) cross section is overestimated by a factor of 26 …

Real And Virtual Images Using A Classroom Hologram, Dale W. Olson

Faculty Work

No abstract provided.

Nonlinear Dynamics In Oscillating Waterfalls, Michael Schumann

Dissertations and Theses

The concern of this thesis was to investigate the nonlinear dynamics inherent in oscillating waterfalls.

An Attempt To Observe Mott Scattering Optically, J. E. Furst, Timothy J. Gay, W. M. K. P. Wijayaratna, K. Bartschat, H. Geesmann, M. A. Khakoo, D. H. Madison

Timothy J. Gay Publications

We report an attempt to make an optical observation of Matt scattering, involving the first studies of inelastic collisions between polarized electrons and a heavy noble gas. Polarization fractions of light emitted by the 5p⁵6p[5/7],(³D₃) state of Xe following impact excitation in an axial collision geometry were measured as a funclion of the incident electron energy, and compared with distorted-wave Bom calculations. The theoretical and experimental results agree qualitatively in the energy range where cascade contributions to the photon signal are small. We failed to measure non-zero values of the linear polarization fraction η …

Phase Transitions In K2Zncl4, H. M. Lu, John R. Hardy

John R. Hardy Papers

It is shown that the potential-energy surface in K₂ZnCl₄ contains a double-well structure, very similar to some of the other A₂BX₄ compounds (e.g., K₂SeO₄, Rb₂ZnCl₄), except that the double well is much deeper and broader, giving rise to a highly disordered high-temperature phase as observed experimentally. A lattice-dynamics study of the Pna2₁ structure shows an instability with the wave vector q=0.5b^*+(0.5±δ)c^*, providing an explanation to the incommensurate phase transition reported recently.

Simulations Of Phase Transitions In Rb2Zncl4, H. M. Lu, John R. Hardy

John R. Hardy Papers

Structural relaxations, molecular-dynamics simulations, and lattice-dynamics calculations were performed to study the phase transitions in Rb₂ZnCl₄, using intermolecular and intramolecular potentials generated from ab initio quantum-chemistry calculations for the whole molecular ion ZnCl₄ ^2-. Compared with an earlier treatment of the system by a polarizable-ion model, the present approach emphasizes the static effect of the electron covalency within the molecular ions that affects strongly both the intermolecular and intramolecular interactions. The calculations gave a close agreement with experiment on the static structures of the Pnam and the Pna2₁ phases and the transition …

Lattice- And Molecular-Dynamics Studies Of Phase Transitions In Csliso4, V. Katkanant

John R. Hardy Papers

We report results of a simulation of the phase transitions in CsLiSO₄. These are based on our previously developed method for calculating parameter-free potential-energy surface for ionic molecular crystals. Our lattice-dynamical and molecular-dynamics studies show that the roomtemperature (Pnam) phase is unstable and transforms to the observed low-temperature (P112₁/n) phase over approximately 200–280 K. The unstable modes of the Pnam phase have maximum instability at the zone center, which indicates a possible phase transformation without a cell multiplication. The rotational ordering of tetrahedral SOM₄ ^2- was found to be …

Track Structure Model Of Cell Damage In Space Flight, Robert Katz, Francis A. Cucinotta, John W. Wilson, Judy L. Shinn, Duc M. Ngo

Robert Katz Publications

Cell damage by high linear energy transfer (LET) radiations has been described by a phenomenological model (track theory) for more than 20 years. With track theory, molecules of biological significance (dry enzymes and viruses) act as one-hit detectors. Recent additions to tire class of one-hit detectors arc Escherichia coil B, and single- and double-strand breaks in SV-40 virus in EO buffer, where indirect effects predominate. The response of cells (survival, transformation, and chromosome aberration) to these radiations is typically described by a four-parameter model whose numerical values are determined from the equations of the theory being fit to experimental …

Effect Of Magnetic And Density Fluctuations On The Propagation Of Lower Hybrid Waves In Tokamaks, George Vahala, Linda L. Vahala, Paul T. Bonoli

Electrical & Computer Engineering Faculty Publications

Lower hybrid waves have been used extensively for plasma heating, current drive, and ramp-up as well as sawteeth stabilization, The wave kinetic equation for lower hybrid wave propagation is extended to include the effects of both magnetic and density fluctuations. This integral equation is then solved by Monte Carlo procedures for a toroidal plasma. It is shown that even for magnetic/density fluctuation levels on the order of 10^-4, there are significant magnetic fluctuation effects on the wave power deposition into the plasma. This effect is quite pronounced if the magnetic fluctuation spectrum is peaked within the plasma. For …

Second-Order Parametrized-Post-Newtonian Lagrangian, Matthew J. Benacquista

Physics & Astronomy Faculty Publications

A many-body Lagrangian to second post-Newtonian order using an extension of the parametrized-post-Newtonian (PPN) formalism is introduced and the properties of new parameters are explored. A parametrized gauge transformation is developed to permit comparison with theories of gravity in a variety of different coordinate systems. A procedure to impose Lorentz invariance on a general second-order post-Newtonian Lagrangian is developed. The Lagrangian is then constrained to possess Lorentz invariance and a "Lorentz-invariant" gauge is introduced. The constrained Lagrangian is found to be described by ten new second-order PPN parameters. When the Lagrangian is further constrained to describe theories of gravity for …

Adsorption Of Halogenated Phenolate Ions To Egg-Phosphatidylcholine Vesicles, Andreas Blochel

Dissertations and Theses

In this study, parameters for the adsorption of several halogenated phenolate ions to egg-phosphatidylcholine vesicles have been determined by microelectrophoresis.

The Application Of Liquid Junctions For Characterization Of Semiconductor Materials, Wu-Mian Shen

Dissertations, Theses, and Capstone Projects

In this study, liquid junctions were used to characterize silicon and silicon subjected to various reactive ion etching (RIE); surface optimization of CuInSe{dollar}\sb2{dollar}; and photo-modification of InSe. Impedance spectroscopy and modulation spectroscopies such as electrolyte electroreflectance (EER), photoreflectance (PR), and photoreflectance in the presence of electrolyte (EPR) were the major methodologies that were used for investigating the dielectric properties of the semiconductors and their interface with the ambients. It was shown that the above experimental techniques provide information about the flat-band potential, doping density, Fermi level pinning, the density and distribution of surface states, energy gap and broadening parameter related …

Charge-State Equilibrium And Nonequilibrium Modeling Of The Carbon-Pellet Plasma Interaction, A. G. Elcashlan, G. A. Gerdin, L. L. Vahala, P. B. Parks

Electrical & Computer Engineering Faculty Publications

Self-consistent equilibrium and nonequilibrium charge-state models are formulated for the spherical expansion of low-Z pellet vapor as an inviscid perfect gas of constant ratio of specific heats being heated volumetrically by the incident electrons of a thermonuclear plasma. The two models are found to be in agreement in the region where the ratio of the ionization length ζ_j to pellet radius r_p is less than unity, but a single parameter, such as the magnitude of this ratio on the sonic surface, is insufficient to determine whether an equilibrium model will be valid for all regions of the ablatant …

Effect Of Fluctuations On Lower Hybrid Power Deposition And Hard X-Ray Detection, George Vahala, Linda L. Vahala, Paul T. Bonoli

Electrical & Computer Engineering Faculty Publications

The hard X-ray intensity radial profiles from lower hybrid current drive experiments are interpreted as being correlated with fluctuations in the bulk plasma. This view seems to be dictated by comparing the hard X-ray data for various n_║ with the Monte Carlo solutions of the lower hybrid wave energy deposition on plasma electrons. Information on internal magnetic fluctuations may, under certain conditions, be unfolded from a n_║ scan of the hard X-ray profiles.

Self-Consistent Determination Of Low-Za Pellet Ablation And Pellet Penetration, Linda L. Vahala, Glenn Gerdin, A. G. El Cashlan, Paul Parks

Electrical & Computer Engineering Faculty Publications

The ablation dynamics of LiT pellets are solved self-consistently over a modest range of parameters using a surface dissociation model. The self-consistently determined parameters are then used to modify the standard low-Z pellet penetration codes. Since LiT pellets have certain advantages over carbon [in particular, Li conditioning of the walls and T for refueling a D-T reaction], the penetration of LiT into fusion plasmas is considered.

Electromagnetic Wave Scattering From Magnetic Fluctuations In Tokamaks, L. L. Vahala, G. Vahala, N. Bretz

Electrical & Computer Engineering Faculty Publications

Cross sections are calculated for electromagnetic wave scattering and mode transformation from magnetic and density fluctuations in a homogeneous plasma. For the special case of scattering perpendicular to the magnetic field, density fluctuations scatter ordinary to ordinary and extraordinary to extraordinary modes-but cannot transform these modes. On the other hand, magnetic fluctuations perpendicular to the field can transform modes but cannot scatter on a single branch. For incident frequencies on the order of the electron plasma frequency or gyrofrequency, the cross sections for scattering and transformation due to field and density fluctuations have a similar value. Estimates are given for …

Collisional Redistribution Of Polarized Radiation For Sr-Ar(He) Systems: A Numerical Comparison Of The Semiclassical Decoupiing/Locking Model To Exact Results, Ronald James Bieniek, Paul S. Julienne, Rank Rebentrost

Physics Faculty Research & Creative Works

Abstract Semiclassical formulations of collisional redistribution of polarized radiation are presented at several levels of approximation, from full classical path coupled equations to the backing/decoupling model. These are numerically tested against the results of a quantum mechanical coupled-channels formalism, by the comparison of polarization curves in both spectral wings of the Srf1 So-1 Pi) transition, with Ar and He as collisional perturbers. It is found that the locking/decoupling model can often produce good agreement with exact results if the effects due to trajectories and multiple Condon points are treated properly. Significant discrepancies due to the Condon approximation used ty the …

Magnetic Response Of A Single, Isolated Gold Loop, V. Chandrasekhar, Richard A. Webb, M. J. Brady, M. B. Ketchen, W. J. Gallagher, A. Kleinsasser

Faculty Publications

Measurements have been made of the low-temperature magnetic response of single, isolated, micron-size Au loops. The magnetic response is found to contain a component which oscillates with the applied magnetic flux with a fundamental period of Φ₀=h/e. The amplitude of the oscillatory component corresponds to a persistent current of ≃(0.3–2.0)ev_F/L, 1 to 2 orders of magnitude larger than predicted by current theories.

Surface-Induced Polarization At A Chiral-Nematice Substrate Interface, Sanjay Tripathi, Min-Hua Lu, Eugene M. Terentjev, Rolfe G. Petschek, Charles Rosenblatt

Faculty Scholarship

A novel linear electro-optic effect is observed in a surface-stabilized chiral nematic cell above the Fréedericksz transition threshold field. The slow dynamic response indicates that this effect arises from the interfacial region which elastically couples to the bulk, rather than directly from the bulk. Moreover, evidence suggests that the primary effect is a spontaneous electric polarization very near the interface. Other possible contributions to this effect are discussed.

Surface Structure Of √3x√3r 30 Cl/Ni(111) Determined Using Low-Temperature Angle-Resolved-Photoemission Extended Fine Structure, Li-Qiong Wang, Z. Hussain, Z. Q. Huang, A. E. Schach Von Wittenau, Dennis W. Lindle, D. A. Shirley

Chemistry and Biochemistry Faculty Research

A surface structural study of the √3 × √3 R30° Cl/Ni(111) adsorbate system was made using low-temperature angle-resolved photoemission extended fine structure. The experiments were performed along two emission directions, [111] and [110], and at two temperatures, 120 and 300 K. The multiple-scattering spherical-wave analysis determined that the Cl atom adsorbs in the fcc threefold hollow site, 1.837(8) Å above the first nickel layer, with a Cl-Ni bond length of 2.332(6) Å, and an approximate 5% contraction between the first and the second nickel layers (the errors in parentheses are statistical standard deviations only).

Electron-Energy And –Angular Distributions In The Double Photoionization Of Helium, R. Wehlitz, Franz Heiser, Oliver Hemmers, B. Langer, A. Menzel, U. Becker

Environmental Studies Faculty Publications

Photoelectron spectra of helium have been measured at different angles and at various energies above the double-ionization threshold up to 120 eV to investigate the behavior of the energy and angular distributions, of shake-off electrons. Both energy and angular distributions clearly show a U-shaped profile which turns to a flat curve near threshold pointing to a uniform intensity distribution over the kinetic energy for all angles in this excitation energy regime. Our results for the angular-distribution asymmetry parameter indicate qualitative agreement with theoretical predictions but fail to provide them quantitatively.

Resonant Electron Transfer And K-Shell Excitation Of Lithiumlike Projectiles In Collisions With Molecular Hydrogen, M. Anwar Kamal

Masters Theses

An experimental investigation of resonant transfer and excitation (RTE) for collisions of Mg⁹⁺ (lithiumlike) projectile ions with a molecular hydrogen gas target has been made. The experimental cross sections for projectile K-shell x rays coincident with electron capture in the energy of 33- to 60-MeV are found to be in good agreement with theoretical RTE calculations. The present results confirm the agreement between experiment and theory which has been reported for RTE involving K-shell excitation for projectiles with atomic numbers between 9 and 92 incident on H₂ and He targets.

Cross sections for total K-shell x-ray production and …

Lqg Control Of A Deformable Mirror Adaptive Optics System With Time- Delayed Measurements, David J. Anderson

Theses and Dissertations

This thesis proposes a linear quadratic Gaussian (LQG) control law for a ground-based deformable mirror adaptive optics system. The incoming image wavefront is distorted, primarily in phase, due to the turbulent effects of the earth's atmosphere. The adaptive optics system attempts to compensate for the distortion with a deformable mirror. A Hartman wavefront sensor measures the degree of distortion in the image wavefront. The measurements are input to a Kalman filter which estimates the system states. The state estimates are processed by a linear quadratic regulator which generates the appropriate control voltages to apply to the deformable mirror actuators. The …

A Rigorous Uniform Diffraction Analysis Of The Electromagnetic Scattering From Impedance Edges And Junctions, Joseph C. Fortney

Theses and Dissertations

This paper investigates the scattering from impedance strips and impedance-loaded conducting strips. The impedance strips are analyzed using Senior's impedance half plane formulation. Once the primary diffraction from the impedance half plane is presented, it is used to develop multiple diffraction mechanisms on an impedance strip. The scattering from impedance-loaded strips are analyzed using Maliuzhinets' impedance wedge formulation. The primary diffraction mechanism from an impedance wedge is used to develop the multiple diffractions on an impedance double wedge. The multiple diffractions on both types of strips are developed using the Extended Spectral Ray Method. Sample calculations are made for impedance …

Design And Testing Of A Lightweight, Planar Microwave Lens, Paul M. Proudfoot

Theses and Dissertations

This thesis documents the design, fabrication, and testing of a lightweight, planar microwave lens. The lens consists of two planar arrays of lightweight printed circuit antennas interconnected by microstrip lines whose length varies as a function of position on the lens. Microwave energy is coupled from one face of the lens to the other by means of a slot etched in the ground plane. At 8.0 GHz the lens is ten wavelengths across, is less than 1/8 inch thick, and weighs less than 4 pounds. The lens can scan a beam over a ± 30 degree region in both the …

Design Of A Fiber Optic Image Transmission Link, Justin D. Redd

Theses and Dissertations

An original design is presented for a fiber optic based digital image transmission link operating at a serial bit rate of 250 Mbits/Second. The link is designed as an integral part of an airborne infrared imaging system with particular emphasis on avoiding problems associated with aircraft electromagnetic interference (EMI). Unique features include simplicity (single PC board transmitter and receiver), low power, low cost (under $3,000), and use of the latest off-the-shelf components (including the Gazelle GA9011/GA9012 HOT ROD chip set). Theoretical modeling is used to predict a bit error rate of better than 10^-15, while actual measurements include …

Sensing Refractive Turbulence Profiles Using Wave Front Slope Measurements From Two Reference Sources, Michael D. Rejack

Theses and Dissertations

This thesis examines a remote sensing technique for measuring the atmospheric structure constant as a function of altitude by performing spatial correlation or wavefront sensor measurements. Two point sources are used to irradiate two wavefront sensors in the aperture plane of an optical system. The geometric relationship between the sources and the sensors gives rise to crossed optical paths. At the point where the paths cross, the correlation value of the turbulence contributions will be at a peak. The correlation is shown to be mathematically related to the structure constant in terms of an integral of the structure constant multiplied …