Digital Commons Network^™

Far-Ultraviolet Stellar Photometry: A Field In Monoceros, Edward G. Schmidt, George R. Carruthers

Edward Schmidt Publications

Far-ultraviolet photometry of stars in a field in Monoceros in the wavelength rang from 1230 Å to 1600 Å has been carried out using data from an electrographic Schmidt camera carried on a sounding rocket. Ultraviolet magnitudes were extracted for 602 objects in the field. Fifty-eight percent were tentatively identified with visible stars using the SIMBAD data base while another 25% are blends of objects too close together to separate with our resolution. Eleven of the uv objects coincide with parts of the star clusters NGC 2169, NGC 2244, and KGC 2264 in which individual stars cannot be resolved. As …

Canted Magnetic Moments At The Gd(0001) Surface, Dongqi Li, Jiandi Zhang, Peter A. Dowben, K. Garrison, P.D. Johnson, H. Tang, T.G. Walker, H. Hopster, J.C. Scott, D. Weller, D.P. Pappas

Peter Dowben Publications

With spin polarized electron spectroscopies, we have investigated ordered GD(0001) films deposited on W(110). The photoemission features of the gadolinium 5d surface state, the 4f levels, and the background exhibit considerable spin polarization along the same direction in the plane of the film, indicative of ferromagnetic coupling between the surface and the bulk. The 4f spin polarized photoemission data provides strong evidence that the surface 4f polarization differs from the bulk 4f polarization for Gd(0001). Our temperature dependent measurements with spin polarized secondary electron spectroscopy conclusively establishes that the surface of clean Gd(0001) possesses a perpendicular polarization component which persists …

Modification Of The Eikonal Relation For Chemical Waves To Include Fluid Flow, J. W. Wilder, D. A. Vasquez, Boyd F. Edwards

All Physics Faculty Publications

Propagating wave fronts resulting from autocatalytic chemical reactions have been the focus of much recent research. For the most part, the hydrodynamics resulting from such reactions has been neglected. In this work, a relation is derived for the normal speed of a propagating wave front as a function of the local curvature when fluid motion is allowed. This ‘‘eikonal’’ equation is a generalization of one which was derived in the absence of fluid flow. It is also shown that small variations in the fluid density due to the chemical reaction do not change the form of the relation.

Photoquenching And Thermal Recovery Of A Thermally Stimulated Current Peak In Semi-Insulating Gaas, Z-Q. Fang, David C. Look

Physics Faculty Publications

A prominent thermally stimulated current peak T₅ appearing in semi‐insulating GaAs is shown to photoquench under infrared illumination, and then thermally recover at a rate r=2.0×10⁸ exp(−0.26 eV/kT) s⁻¹, exactly the same as that observed for EL2, within experimental error. Two possible explanations exist: (1) T₅ and EL2 are microscopically very similar, probably each with an As_Ga core; or (2) T₅ is an electron trap that only appears to quench and recover with EL2 because EL2 controls the electron lifetime. Several other traps show similar quenching and recovery behavior.

A Neutron Diffraction And Mössbauer Effect Study Of The Magnetic Structure Of Y₂(Fe₁₋ₓmnₓ)₁₄B, Gaya Kanishka Marasinghe, Oran Allan Pringle, Gary J. Long, William Joseph James, William B. Yelon, Fernande Grandjean

Physics Faculty Research & Creative Works

The magnetic structures of a series of Y₂(Fe _1-xMn_x)₁₄B samples, with x equal to 0.03, 0.10, 0.25, and 0.37, have been studied by powder neutron diffraction and Mössbauer spectroscopy. Y₂(Fe_0.97Mn _0.03)₁₄B and Y₂(Fe_0.9Mn _0.1)₁₄B are ferromagnetic at both 295 and 85 K, Y ₂(Fe_0.63Mn_0.37)₁₄B is paramagnetic at both 295 and 85 K, whereas Y₂(Fe_0.75Mn _0.25)₁₄B is paramagnetic at 295 K and is partially ordered at …

120kev Ar8+-Li Collisions Studied By Near Uv And Visible Photon Spectroscopy, E. Jacquet, P. Boduch, M. Chantepie, M. Druetta, D. Hennecart, X. Husson, D. Lecler, Ronald E. Olson, J. Pascale, N. Stolterfoht, M. Wilson

Physics Faculty Research & Creative Works

A spectroscopic analysis of light emitted in the 200-600 nm wavelength range by Ar⁷⁺, Ar⁶⁺ and Ar⁵⁺ ions after charge exchange in 120keV Ar⁸⁺-Li collisions is performed. Transitions with Δn = 1 and Δn = 2 for n = 8, 9, 10 and 11 states of Ar8 following single electron capture are identified and the production cross sections for n = 8 and n = 9 are deduced from emission cross sections and compared with those calculated by the three-body classical trajectory Monte-Carlo method. Lines due to double capture process were observed and identified …

Cp-Odd Nucleon Potential, Vladimir Gudkov, Xiao-Gang He, Bruce H.J. Mckellar

Faculty Publications

The P-odd and CP-odd nucleon potential for different models of CP violation in the one-meson exchange approximation is studied. It is shown that the main contribution is due to the π-meson exhcange which leads to a simple one-parameter CP-odd nucleon potential.

Resonant Inhibition Of Multiphoton Ionization, J. Greg Story, D. I. Duncan, Thomas F. Gallagher

Physics Faculty Research & Creative Works

When exposed to intense light of ~580 nm, the ground state of K shifts up in energy, passing through two-photon resonances with Rydberg states and finally crossing the two-photon ionization limit. Using laser pulses of 0.5 to 13 ps duration, we have shown experimentally that ionization occurs for short pulses, but for long pulses the population is diverted into the Rydberg states where some population survives the peak intensity of the pulse, in excellent agreement with a dynamic Floquet model.

Two Dimensional Power Spectral Estimation Using Constrained Iterative Spectral Deconvolution, Jerome Leslie Coggins

LSU New Orleans Theses and Dissertations

Two-dimensional power spectral estimation is an important tool for seismic data analysis and other applications. Some datasets, however, have a limited number of points in one or both dimensions. In seismic applications, there are typically fewer points in the spatial domain as compared to the temporal domain. Conventional spectral estimation techniques suffer from poor resolution on short datasets due to inherent smoothing or bias.

Ramaswamy and loup developed a one-dimensional method for the estimation of power spectra for short datasets. Constrained Iterative Spectral Deconvolution (CISD) greatly improves the power spectral resolution using a straight-forward algorithm. In a comparison to other …

Evidence Of A Nondiffusive Transport In A Monodisperse Screened Coulomb System By A Molecular-Dynamics Simulation, Michael Wild, Ras B. Pandey

Faculty Publications

A molecular-dynamics simulation is carried out for particles (tracers) interacting with a screened Coulomb potential in three dimensions. A phase transition is observed from a liquid to an fcc solid on reducing the temperature at a fixed density, consistent with previous studies. In the liquid phase, the variation of the rms displacement R_tr of the charged particles with time seems to depend on the density and the temperature. In the short-time regime, the effective exponent k for the subdiffusive power-law behavior, i.e., R_tr∼t^k, decreases on increasing the density and lowering the temperature. A crossover from …

Investigation Of Spin-Orbit Effects In The Excitation Of Noble Gases By Spin-Polarized Electrons, J. E. Furst, W. M. K. P. Wijayaratna, D. H. Madison, Timothy J. Gay

Timothy J. Gay Publications

We have measured the integrated Stokes parameters of the light emitted following the impact excitation by polarized electrons of the np⁵ (n+1)p [5/2] ₃ states in Ne (n=2), Ar (n=3), Kr (n=4), Xe (n=5), and the np⁵ (n+1) p[5/2] ₂ state in Kr. The near-threshold linear-polarization fractions η1 were consistent with zero for all of the J=3 states measured, providing no evidence of Mott scattering. For J=2 excitation, η₁ shows the clear influence of the intermediately coupled nature of the state. …

Properties Of Rigid Foams For Application As Materials For Light Weight Structures In Space, Huichen Chi

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The mechanical and mesoscopic structural properties of rigid cellular foam made of polystyrene have been investigated. Basic properties (e.g., density, total and available porosity, permeability, surface area, isotropicity, and cell size and cell wall thickness distributions) were measured. In most cases, alternative methods were used to determine which methods were most appropriate for the type of samples we studied. Standard compression and deflection mechanical tests were performed. The stress-strain curves and related mechanical properties were found to agree with standard cellular structural models of open-cell foams.

We investigated the effects of small (~ < 5 atm) hydrostatic stress applied to foam samples for long periods of time (~one day). We observed large changes (up to a factor of three) in the stress-strain diagrams, Young's modulus, elastic collapse stress, ultimate strength, resilience, Poisson's ratio, permeability, penetration depth, and available porosity. Effects were most pronounced above 2 atm applied pressure differential, but were observed even for 1 atm loads. Short-term exposure to loads up to ten times as large did not cause comparable changes. These changes were interpreted as resulting from observed changes in the mesoscopic structure occurring near the surface using standard cellular structural models.

This work was originally motivated by applications …

Adjustable Levels Of Strong Turbulence In A Positive/Negative Ion Plasma, D. P. Sheehan, R. Mcwilliams, N. Rynn

Physics and Biophysics: Faculty Scholarship

Positive/negative ion plasmas, composed of Ba+, SF6−, and residual electrons, were observed to display characteristics of strong turbulence.Experiments on the UCI Q machine linked the presence of negative ions (and the depletion of electrons) with large density fluctuations (δn/n≂1), large‐amplitude, low‐frequency electrostatic noise (f≤20 kHz), and rapid transport of ions across magnetic field lines (D⊥≂104 cm2/sec). Ion velocity distributions were heated parallel to and cooled perpendicular to the confining magnetic field. The partial pressure of gaseous SF6 was shown to serve as a regulator of plasma turbulence. Turbulence levels could be smoothly varied from quiescent states (δn/n≂0.01) to strongly turbulent …

A Novel Technique For Studying The Shear Elastic Properties Of Weak Solids, Jason A. Payne '93

Honors Projects

We have developed a simple, inexpensive, and precise technique to measure the shear elastic modulus of weak solids using electromagnetic and optical tools. This technique can be easily adapted to measure the viscosity of a liquid also. A Helmholtz pair was used to produce a torque on a permanent magnet mounted on the smaller of two concentric cylinders, coupled by the material to be studied. The torque was controlled precisely and measured accurately in terms of the current flowing through the coils of the Helmholtz pair. An optical lever was employed to measure the angular displacement of the inner cylinder …

A Lattice Gas Approach To The Structure And Dynamics Of Electrorheological Fluids, Jie Chen '93

Honors Projects

Electrorheological fluids consist of a colloidal suspension of dielectric particles in a continuous fluid of smaller dielectric constant. Molecular dynamics simulations of these fluids in an applied electric field have recently been shown to produce percolated, columnar structures. No systematic attempt has been made so far to simultaneously include the effects of temperature and the viscous drag due to the continuous fluid. We propose a dipolar lattice gas model for electrorheological fluids and study the resulting structures and dynamics. We attempt to incorporate the effect of the viscosity of the continuous medium by a dynamic ansatz that determines the range …

Unusual Thermal Stability Of A Site-Ordered Mc60 Rocksalt Structure (M=K, Rb, Or Cs), Q. Zhu, O. Zhou, J. E. Fischer, Andrew R. Mcghie, W. R. Romanow, Robert M. Strongin, M. A. Cichy, Amos B. Smith Iii

Chemistry Faculty Publications and Presentations

X-ray diffraction and differential scanning calorimetry of M_xC₆₀, with x∼1 and M=K, Rb, or Cs, reveal an unusual T-dependent phase sequence. A low-symmetry ground state is found, while the high-T limit is an ordered rocksalt structure in which only the octahedral sites are occupied. The unusual high-T stability of this ordered phase is attributed to the entropy of molecular orientational disorder and/or thermal disorder of the alkali-metal ions within the octahedral sites. Unique to K_xC₆₀ with x≥1.4, we find at intermediate temperatures an fcc site-disordered lattice gas …

The Xy Model On A Dynamical Random Lattice, Simon Catterall, John B. Kogut, Ray L. Renken

Physics - All Scholarship

We study the XY model on a lattice with fluctuating connectivity. The expectation is that at an appropriate critical point such a system corresponds to a compactified boson coupled to 2d quantum gravity. Our simulations focus, in particular, on the important topological features of the system. The results lend strong support to the two phase structure predicted on the basis of analytical calculations. A careful finite size scaling analysis yields estimates for the critical exponents in the low temperature phase.

Three-Dimensional Quantum Gravity Coupled To Gauge Fields, Simon Catterall, Ray L. Renken, John B. Kogut

Physics - All Scholarship

We show how to simulate U(1) gauge fields coupled to three-dimensional quantum gravity and then examine the phase diagram of this system. Quenched mean field theory suggests that a transition separates confined and deconfined phases (for the gauge matter) in both the negative curvature phase and the positive curvature phase of the quantum gravity, but numerical simulations find no evidence for such transitions.

Metastability In Two Dimensions And The Effective Potential, Mark Alford, Marcelo Gleiser

Dartmouth Scholarship

We study analytically and numerically the decay of a metastable phase in (2+1)-dimensional classical scalar field theory coupled to a heat bath, which is equivalent to two-dimensional Euclidean quantum field theory at zero temperature. By a numerical simulation we obtain the nucleation barrier as a function of the parameters of the potential, and compare it to the theoretical prediction from the bounce (critical bubble) calculation. We find the nucleation barrier to be accurately predicted by theory using the bounce configuration obtained from the tree-level (“classical”) effective action. Within the range of parameters probed, we found that using the bounce derived …

Evidence Of Preferential Directions For Gravity Wave Propagation Due To Wind Filtering In The Middle Atmosphere, Michael J. Taylor, E. H. Ryan, T. F. Tuan, R. Edwards

All Physics Faculty Publications

All-sky TV images of wave structure in the near-infrared hydroxyl (OH) nightglow emission were recorded over a 3-month period during May, June, and July 1988 from a high-altitude site at the Mountain Research Station (40.0° N, 105.6° W, 3050 m), near Nederland, Colorado. Well-defined, coherent wave patterns associated with the passage of short period (<1 hour) gravity waves were observed on a total of 22 occasions. The wave motions exhibited similar spatial and temporal properties during each month but a distinct tendency for northward propagation (68% of the wave azimuths within ± 40.0° N), with some eastward motion in May and June, was observed throughout the campaign. Although it is theoretically well known that upward propagating gravity waves can be blocked at a critical layer produced by the interaction of the waves with the horizontal background wind, observational evidence of this phenomenon is rare. To investigate the possibility that the asymmetry in the wave propagation directions was caused by the critical layer, a model based on mean climatological background winds and numerical tidal wave modes valid for any mid-latitude site and time of the year was constructed to show the regions forbidden to upward gravity wave propagation from critical layer theory. These “blocking diagrams” which vary with height and time were constructed for the OH altitude (∼87 km) for the present paper. Comparison of the predicted (i.e., least restricted) and the observed directions of the wave motion show almost complete agreement. This suggests that middle atmospheric winds can play an important role in determining the flux and the azimuthal distribution of short-period waves reaching the upper atmosphere.

Contribution Of High-Order Rainbows To The Scattering Of A Gaussian Laser Beam By A Spherical Particle, James A. Lock

Physics Faculty Publications

I review the theory of the scattering of a Gaussian laser beam by a dielectric spherical particle and give the details for constructing a computer program to implement the theory. Computational results indicate that if the width of the laser beam is much less than the diameter of the particle and if the axis of the beam is incident near the edge of the particle, the fifth-, sixth-, and ninth-order rainbows should be evident in the far-field scattered intensity. I performed an experiment that yielded tentative evidence for the presence of the sixth-order rainbow.

The Effect Of Ionizing And Displacive Radiation On The Thermal Conductivity Of Alumina, D. P. White

Physics Faculty Publications

The effects of ionizing and displacive radiation on the thermal conductivity of alumina at high temperatures have been studied. The phonon scattering relaxation times for several scattering mechanisms have been used to determine the effect on the thermal conductivity. The scattering mechanisms considered are scattering by electrons excited into the conduction band, vacancies, aluminum precipitates, and voids. It is found that under irradiation conditions where the electrical conductivity and dielectric loss tangent are greatly increased there is not a significant decrease in the thermal conductivity due to phonon-electron scattering. The conditions under which the scattering due to vacancies, aluminum precipitates, …

Electrostatic Positioning Of Droplets In Turbulent Flows (Lstm 375/Te/93), Nihad E. Daidzic, Adrian Melling

Aviation Department Publications

Report LSTM 375/TE/93, Lehrstuhl fuer Stroemungsmechanik Universitaet Erlangen-Nuernberg Cauerstr. 4, 8520 Erlangen Germany.

Filtered Noise Can Mimic Low-Dimensional Chaotic Attractors, P. E. Rapp, Alfonso M. Albano, T. I. Schmah, L. A. Farwell

Physics Faculty Research and Scholarship

This contribution presents four results. First, calculations indicate that when examined by the Grassberger-Procaccia algorithm alone, filtered noise can mimic low-dimensional chaotic attractors. Given the ubiquity Of signal filtering in experimental investigations, this is potentially important. Second, a criterion is derived which provides an estimate of the minimum data accuracy needed to resolve the dimension of an attractor. Third, it is shown that a criterion derived by Eckmann and Ruelle [Physica D 56, 185 (1992)] to estimate the minimum number of data points required in a Grassberger-Procaccia calculation can be used to provide a further check on these dimension estimates. …

Residual-Ion Orientation After Autoionization, G. T. Xu, Xiao Wang, J. Greg Story, William E. Cooke

Physics Faculty Research & Creative Works

We have measured the relative population in the two m_j states of barium 6p_1/2 ions produced by the autoionization of (6p_3/2nd)_J=MJ=3 states by detecting the helicity of the emitted fluorescence. These populations can be related to the relative branching ratio into the 6p_1/2εd_5/2 and 6p_1/2εg_7/2 continuum channels. Rydberg states with n=16-23 have similar branching ratios, producing approximately six times as much 6p_1/2εd_5/2 population as 6p_1/2εg_7/2 population.

Multiplet Fine Structure In The Photoemission Of The Gadolinium And Terbium 5p Levels, B.T. Thole, X.D. Wang, B.N. Harmon, Dongqi Li, Peter A. Dowben

Peter Dowben Publications

Fine structure is observed in the photoemission of the gadolinium and terbium 5p levels. The 5p levels are split into multiplets due to spin-orbit splitting and to Coulomb and exchange interactions with the f shell. The calculated theoretical spectra are in good agreement with the experimental results.

Millikan Lecture 1992: Hypermedia And The Knowing Of Physics: Standing Upon The Shoulders Of Giants, Robert Fuller

Robert G. Fuller Publications

Hypermedia is defined and its roots briefly discussed. Models of knowing physics and of intrinsically motivating instruction are presented. Uses of hypermedia to increase the knowing of physics and the motivation of learners are proposed.

Monte Carlo Simulations Of Water-Ice Layers On A Model Silver Iodide Substrate: A Comparison With Bulk Ice Systems, James H. Taylor, Barbara N. Hale

Physics Faculty Research & Creative Works

Two water layers adsorbed on a model silver iodide basal face are simulated at nine temperatures from 150 to 425 K using Monte Carlo methods. The periodic unit cell of 96 internally rigid water molecules (interacting via the revised central-force potentials) couples to the rigid-substrate atoms via effective pair potentials with Lennard-Jones short-range and Coulomb long-range terms. The distribution of molecules perpendicular to the substrate exhibits layering, and individual layer structure factors, dipole moments, and "pseudodiffusion" coefficients are calculated. A complex temperature dependence with the two layers taking on different solidlike, quasiliquid, or liquid properties at the same T is …

New Magnets From Interstitial Intermetallics, J.M.D. Coey, Ralph Skomski

Ralph Skomski Publications

The outlook for improving the energy product of permanent magnets beyond the theoretical limit of 516 kJ/m³ for Nd₂Fe₁₄B is discussed. Most promising are nanostructured two-phase magnets consisting of an aligned hard-magnetic skeleton phase possessing exceptionally high uniaxial anisotropy and a soft-magnetic phase which assures a high magnetization. Brown’s paradox is discussed for inhomogeneous magnets, and micromagnetic calculations are used to predict energy products as high as 1090 kJ/m3 in suitable nanostructured Sm₂Fe₁₇N₃/Fe₆₅Co₃₅ composites, such as multilayers or disordered two-phase magnets with common c axis.

Non-Resonant Transfer And Excitation For S^13+ Projectiles Colliding With Neutral Gas Targets, Liang Duo

Masters Theses

Non-resonant Transfer and Excitation (NTE) by 20-70 Mev S,3+ projectiles in collisions with neutral gas targets of He, Ne and Ar is investigated. For NTE, positively charged projectiles undergo excitation and electron capture in a single collision in which the capture and excitation processes are independent events. The mechanisms involved in the NTE process are electron-nucleus interactions, and the combination of projectile excitation and capture is a two-step process. In this work, NTE cross sections, along with total K x-ray production cross sections and total single-electron capture and loss cross sections, were measured as a function of projectile energy. The …