Open Access. Powered by Scholars. Published by Universities.®

Digital Commons Network™

Open Access. Powered by Scholars. Published by Universities.®

Physics

Institution
Keyword
Publication Year
Publication
Publication Type
File Type

Articles 31261 - 31290 of 34246

Full-Text Articles in Entire DC Network

Forbidden Lines Of Np^Q Ions. Ii. Line Intensities, J. P. Lynch, Menas Kafatos Jan 1991

Forbidden Lines Of Np^Q Ions. Ii. Line Intensities, J. P. Lynch, Menas Kafatos

Mathematics, Physics, and Computer Science Faculty Articles and Research

Ground state forbidden transitions of np^q ions of C, N, 0, Ne, Mg, Si, S, and Fe can provide important information on the state of cosmic ionized gases. Wavelengths of these lines are in the far- and near-UV visible and near- and far-IR regions of the spectrum. The line intensity ratios of particular transitions in q = 2, 4 ions can provide information on the temperature of the gas and in q = 3 ions information on the density of the gas. In the present work we have tabulated the line intensities of 95 transitions of these ions, which include …

Go to article

Structure And Optical Characterization Of Znxcd1-Xte Thin Films Prepared By The Close Spaced Vapor Transport Method, David D. Allred, Jesus González-Hernández, O. Zelaya, J. G. Mendoza-Alverez, E. López-Cruz, D. A. Pawlik Jan 1991

Structure And Optical Characterization Of Znxcd1-Xte Thin Films Prepared By The Close Spaced Vapor Transport Method, David D. Allred, Jesus González-Hernández, O. Zelaya, J. G. Mendoza-Alverez, E. López-Cruz, D. A. Pawlik

Faculty Publications

Zinc cadmium telluride (ZnxCd1-xTe) solid solution films with 0≤x≤0.12 were deposited by the close spaced vapor transport method and characterized using photoluminescence, x-ray diffraction, and scanning electron microscopy. The two former techniques indicate that films with high crystalline quality can be prepared with moderate substrate temperatures and low argon pressures. Under these conditions deposition rates of up to 1000 Å/s are achieved and Zn concentration in the film is the same as that of the source. The electron micrographs show grain sizes comparable to the film thickness.

Go to article

Relaxation Time Of The Order Parameter In A High-Temperature Superconductor, G.L. Eesley, J. Heremans, M.S. Meyer, G.L. Doll, Sy_Hwang Liou Dec 1990

Relaxation Time Of The Order Parameter In A High-Temperature Superconductor, G.L. Eesley, J. Heremans, M.S. Meyer, G.L. Doll, Sy_Hwang Liou

Sy-Hwang Liou Publications

We present femtosecond time-resolved measurements on the high-Tc superconductor Tl2Ba2Ca2Cu3O10. At temperatures below Tc, we observe a relaxation process which is distinct from the equilibration of hot carriers in the normal state. Our results demonstrate an increasing relaxation rate as the superconducting gap opens. This is consistent with the behavior of conventional metallic superconductors.

Go to article

Power Law Exponents For A Spreading Front And Growing Interface In An Irreversible Wetting, Evan Willett, Ras B. Pandey Dec 1990

Power Law Exponents For A Spreading Front And Growing Interface In An Irreversible Wetting, Evan Willett, Ras B. Pandey

Faculty Publications

Using computer simulations, the power-law behavior of the interface growth of a spreading fluid is studied in a two-dimensional lattice model. The interface width exponent ν and the dynamical exponent k for the evolution of the front are consistent with their dynamical scaling relation. The magnitude of these exponents seems to depend upon the nature of the substrate and the concentration of the carriers of the wetting fluid.

Go to article

Uniform Stationary-Phase Methods For Energy Spectra Resulting From Collisions In A Complex Potential: Penning And Associative Ionization Of He*(2³S)+He*(23s), Ronald James Bieniek, M. W. Muller, M. Movre Dec 1990

Uniform Stationary-Phase Methods For Energy Spectra Resulting From Collisions In A Complex Potential: Penning And Associative Ionization Of He*(2³S)+He*(23s), Ronald James Bieniek, M. W. Muller, M. Movre

Physics Faculty Research & Creative Works

Heavy-particle collisions involving strong electronic coupling can be conveniently described by using a complex (optical) potential in the entrance channel. Uniform JWKB stationary-phase techniques are used to evaluate T-matrix elements for transitions where an electron is ejected. The semi-analytic expressions for the resulting electron energy spectra are no more difficult to implement than corresponding ones for totally real potentials. Numerical results are reported for Penning and associative ionization from sub thermal He*(23S)+He*(23S) collisions. These are in excellent agreement with fully quantal, complex-potential computations. The stationary-phase expressions for T-matrix elements and differential cross sections are employed to elucidate the rapid and …

Go to article

Projectile- And Target-Charge Dependent Effects In Ionizing Collisions Of H ⁺ And He 2+ With He, Ne And Ar Atoms, Timothy James Gay, M. W. Gealy, M. E. Rudd Dec 1990

Projectile- And Target-Charge Dependent Effects In Ionizing Collisions Of H ⁺ And He 2+ With He, Ne And Ar Atoms, Timothy James Gay, M. W. Gealy, M. E. Rudd

Physics Faculty Research & Creative Works

The spectra of electrons emitted in collisions between H + and He 2+ projectiles and He, Ne and Ar targets at energies of 50 and 100 keV amu -1 have been studied. The data are in qualitative agreement with results of Irby el al., but are in disagreement with measurements of Bernardi et al. It is shown that the observed electron spectra have a dependence on both target-ion and projectile effective charge that can be understood qualitatively in terms of 'saddle-point' ionization. Several issues relevant to saddle-point ionization are discussed. © 1990 IOP Publishing Ltd.

Go to article

Laser Cvd And Plasma Cvd Of Cro2 Films And Cobalt Doped Cro2 Films Using Organometallic Precursors, Peter A. Dowben, Marshall Onellion Dec 1990

Laser Cvd And Plasma Cvd Of Cro2 Films And Cobalt Doped Cro2 Films Using Organometallic Precursors, Peter A. Dowben, Marshall Onellion

Peter Dowben Publications

Chromium dioxide is deposited as a ferromagnetic layer onto selected portions of a substrate or over the entire substrate. Chromium hexacarbonyl vapor is introduced into a vacuum deposition chamber at e.g. 10 milliTorr and oxygen is introduced at e.g. 15 to 100 milliTorr. A UV laser beam is focused onto the substrate to form the CrO2 layer photolytically. The CrO2 layer can also be deposited by RF plasma deposition. This technique can also be employed for depositing MoC2, WC2, Mo2φ3, MoO2 or WO2. Magnetic recording or memory devices are …

Go to article

The Relationship Of The Virtual Orbitals Of Self-Consistent-Field Theory To Temporary Negative Ions In Electron Scattering From Molecules, Donghai Chen, Gordon A. Gallup Dec 1990

The Relationship Of The Virtual Orbitals Of Self-Consistent-Field Theory To Temporary Negative Ions In Electron Scattering From Molecules, Donghai Chen, Gordon A. Gallup

Gordon Gallup Publications

The theory given here shows how certain of the virtual orbitals of self-consistent field (SCF) theory provide a natural ingredient for constructing basis functions to study the shape resonances associated with temporary molecular ions. We give specific calculations of resonant behavior in H2, N2, ethylene, cyclopropene, and cyclobutene. In addition, we show how the theory can rationalize the relationship between Koopmans' theorem values of the energy of a resonance and the experimental values. The Journal of Chemical Physics is copyrighted by The American Institute of Physics.

Go to article

Fresnel And Fraunhofer Diffraction: Development Of An Advanced Laboratory Experiment, Jeff Adams Dec 1990

Fresnel And Fraunhofer Diffraction: Development Of An Advanced Laboratory Experiment, Jeff Adams

Senior Theses and Projects

The purpose of this lab is to help the student become more familiar with, or get a better feel for what is actually occurring, when observing the effects of double slit diffraction patterns. In most sophomore labs dealing with double slit diffraction, the student simply determines the diffraction angle, and slit spacing, from marking the positions of the maxima on the screen. No attempt is made to measure the relative intensity of the interference pattern, and see how the experimental data compare with the theory of interference and diffraction. In an attempt to further clarify this phenomena, we will attempt …

Go to article

Device For Dispersal Of Micrometer- And Submicrometer-Sized Particles In Vaccum, D. P. Sheehan, M. Carillo, W. Heidbrink Dec 1990

Device For Dispersal Of Micrometer- And Submicrometer-Sized Particles In Vaccum, D. P. Sheehan, M. Carillo, W. Heidbrink

Physics and Biophysics: Faculty Scholarship

A simple, versatile device for dispersing micrometer‐ and submicrometer-sized particles in vacuum is described. The source allows control of particle size (0.5 μm≤l≤200 μm) and particle flux density up to roughly 107 cm−2 s−1. Several types of microparticles were successfully dispersed.

Go to article

Extension Of The Metal Light Pipe Infrared Spectroscopy Technique: Applications To Surface Adsorption And High Tc Superconductors, Torsten Will Dec 1990

Extension Of The Metal Light Pipe Infrared Spectroscopy Technique: Applications To Surface Adsorption And High Tc Superconductors, Torsten Will

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The development of an infrared instrument for the study of surface adsorption and high Tc superconductors is presented and its applicability is discussed. The use of and theoretical background for the metal light pipe multiple-reflection technique are discussed in comparison to other infrared devices. Measurements are carried out to determine its limitations with powdered substrates as well as its sensitivity limitation for thin films. The results of the two test measurements, adsorption of CO on MgO and investigation of the energy gap of high Tc superconductors, are presented. Comparisons of the spectra with the experimental and theoretical literature …

Go to article

Unpinning Of Gaas Surface Fermi Level By 200 Degrees C Molecular Beam Epitaxial Layer, David C. Look, C. E. Stutz, K. R. Evans Dec 1990

Unpinning Of Gaas Surface Fermi Level By 200 Degrees C Molecular Beam Epitaxial Layer, David C. Look, C. E. Stutz, K. R. Evans

Physics Faculty Publications

Previous attempts to passivate the n‐type (100)GaAs surface have significantly reduced only the surface recombination centers, but not the surface acceptors which pin the Fermi level. Here we show that a 100 Å molecular beam epitaxial layer grown at 200 °C reduces the effective surface potential energy − eϕs from 0.70 to 0.17 eV, nearly eliminates light sensitivity, and permits nonalloyed ohmic contacts. After a 10 min, 450 °C anneal, − eϕs increases only to 0.22 eV.

Go to article

Design Of A Linear Gaussian Control Law For An Adaptive Optics System, Mark Alan Von Bokern Dec 1990

Design Of A Linear Gaussian Control Law For An Adaptive Optics System, Mark Alan Von Bokern

Theses and Dissertations

This thesis considers the design of a linear quadratic Gaussian (LQG) controller for a ground-based adaptive-optics telescopes. The incoming aberrated image is reflected from a 97-element piezoelectric mirror, then measured with a Hartmann-type wavefront sensor. A Kalman filter processes the outputs of the wavefront sensor and obtains estimates of system states. A linear quadratic regulator processes these state estimates and determines an appropriate set of commands for the deformable mirror. Atmospheric distortion is modeled as a set of fourteen Zernike coefficients whose dynamic behavior is produced by excitation of a set of shaping filters by zero-mean Gaussian white noise. The …

Go to article

Computer Model Of An Injection Locked Pulsed Co2 Laser, Allen M. Susie Dec 1990

Computer Model Of An Injection Locked Pulsed Co2 Laser, Allen M. Susie

Theses and Dissertations

With the discovery of the laser there have been continual attempts to increase the 'spectral brightness' of a laser for applications such as signal processing and lidar. To this end techniques using either passive or active cavity elements have been developed to isolate a single longitudinal mode in both continuous and pulsed laser systems. Although passive elements have useful applications in continuous systems their use in pulsed systems is difficult to control. The injection of an external signal has proved very successful.

Go to article

A Compact Optical Associative Memory Using Dynamic Holographic Storage Media And Photorefractive Gain And Attenuation Elements, Thomas J. Burns Dec 1990

A Compact Optical Associative Memory Using Dynamic Holographic Storage Media And Photorefractive Gain And Attenuation Elements, Thomas J. Burns

Theses and Dissertations

This research effort implemented a compact optical associative memory architecture consisting of a Fabry-Perot Confocal Resonator (FPCR) optical processing environment, two dynamically reprogrammable Lithium Niobate volume holograms, and Barium Titanate gain and attenuation elements. The reduced physical dimensions of the compact optical processing environment make it more adaptable to military applications than previous associative memory designs. The FPCR employs Mangin mirrors designed to reduce spherical aberrations in off-axis rays. The orientation of the gain element's grating vector angle and the model used to predict the profile of the attenuation element were unique to this research effort. The object stored in …

Go to article

A Biologically-Inspired Neural Network Architecture For Image Processing, Laurence E. Lazofson Dec 1990

A Biologically-Inspired Neural Network Architecture For Image Processing, Laurence E. Lazofson

Theses and Dissertations

This thesis project included a literature survey of biological and artificial neural network research followed by development and testing of high- order and image recognition hierarchical neural network algorithms. Following training, performance testing of second-order and third-order networks yielded maximum accuracies comparable to those achieved by multilayer perceptron classifiers operating on test data sets. Several versions of an image classification algorithm were tested for learning performance using pixel data from forward-looking infrared (FLIR) images of tanks, trucks, target boards, and clutter. Employing the biologically-motivated Lambertization and contrast normalization of pixel windows, correlations with multiple Gabor function wavelets, and a 'phase …

Go to article

Model-Based 3-D Recognition System Using Gabor Features And Neural Networks, Phung D. Le Dec 1990

Model-Based 3-D Recognition System Using Gabor Features And Neural Networks, Phung D. Le

Theses and Dissertations

A different approach to pattern recognition was attempted using Gabor features, artificial neural nets, and an image generator. The Gabor features and artificial neural nets are sound biological-based, and the image generator provides complete access to any view of an object. This thesis tested the idea that their integration could form a robust 3-D recognition system. The results of the research showed that the Gabor features together with a neural net were used successfully in classifying objects regardless of their positions, out-of- plane rotations, and to a lesser extent in-plane rotations. The Gabor features were obtained by correlating the image …

Go to article

Optical Image Segmentation Using Wavelet Filtering Techniques, Christopher P. Veronin Dec 1990

Optical Image Segmentation Using Wavelet Filtering Techniques, Christopher P. Veronin

Theses and Dissertations

This research effort successfully implemented an automatic, optically based image segmentation scheme for locating potential targets in a cluttered FLIR image. Such a design is critical to achieve real-time segmentation and classification for machine vision applications. The segmentation scheme used in this research was based on texture discrimination and employs orientation specific, bandpass spatial filters as its main component. The orientation specific, bandpass spatial filters designed during this research include symmetrically located circular apertures implemented on heavy, black aluminum foil; cosine and sine Gabor filters implemented with detour-phase computer generated holography photoreduced onto glass slides; and symmetrically located circular apertures …

Go to article

Using Error Detection And Correction Coding For A Turbulent Atmospheric Optical Communications Link, Mark A. Cloutier Dec 1990

Using Error Detection And Correction Coding For A Turbulent Atmospheric Optical Communications Link, Mark A. Cloutier

Theses and Dissertations

Probability of bit error (Pb) performance for a turbulent, atmospheric, optical, communications link with convolutional error detection and correction coding was investigated. The codes investigated were all rate 1/2 codes with constraint lengths ranging from 3 to 7. It was assumed that the coded data stream was sufficiently interleaved so that the turbulent channel could be considered memoryless. A theoretical bound on Pb, given by Viterbi for a memoryless channel, was used to plot curves of Pb versus the signal intensity of last transmitter. These curves were plotted for three different levels of atmospheric turbulence and three …

Go to article

Nonlinear Interferometry: Optical Image Addition/Subtraction And Novelty Filters, Gordon T. Hengst Dec 1990

Nonlinear Interferometry: Optical Image Addition/Subtraction And Novelty Filters, Gordon T. Hengst

Theses and Dissertations

This thesis investigated the performance characteristics of a beam fanning novelty filter and designed a switchable optical image adder/subtractor. The filter spatial resolution, contrast ratio, onset time, and velocity response were measured for both z-cut and 45 deg. cut BaTiO3 crystals in the beam fanning configuration. Experimental results show that the special 45 deg. cut crystal produces the best overall beam fanning novelty filter. In addition, switchable optical image subtraction and addition were demonstrated for the first time using a modified Michelson interferometer configured with a phase-conjugating mirror and an adjustable length leg. The system demonstrated addition and subtraction with …

Go to article

An Optically Pumped Molecular Bromine Laser, Jon W. Morrison Dec 1990

An Optically Pumped Molecular Bromine Laser, Jon W. Morrison

Theses and Dissertations

An optically pumped molecular bromine laser was studied to investigate the quenching kinetics state of Br2. This included characterization of the pressure dependence of the laser output power. The approach was to excite molecular bromine in a sealed cell with a Nd:YAG pumped dye laser. Unresolved side fluorescence and amplified stimulated emission (ASE) spectra were recorded. ASE offered the advantage of a simpler optical system with no externally induced wavelength dependencies. Stimulated emission as a signal monitor offered greater resolution than side fluorescence spectra and facilitated spectroscopic assignment.

Go to article

Operating Characteristics Of Xenon Gas Discharges, Michael E. Ruark Dec 1990

Operating Characteristics Of Xenon Gas Discharges, Michael E. Ruark

Theses and Dissertations

The voltage-current and spectral line intensity-current characteristics were measured for four Xenon gas discharges. The four discharge configurations were made up of two tubes, each examined at pressures of 1 and 10 Torr. The first tube was a hot filament tube with a 1 cm radius, and the second a cold cathode type tube of radius .3 cm. Intensity dependence upon current was primarily linear in all cases with some important deviations. The hot filament tube at 10 Torr showed a large decrease in intensity between 4 and 6 mA in the 8409 angstrom line. This is thought to be …

Go to article

Energy Transfer In Singlet Oxygen And Bromine Monofluoride, Barrett F. Lowe Dec 1990

Energy Transfer In Singlet Oxygen And Bromine Monofluoride, Barrett F. Lowe

Theses and Dissertations

The interhalogen molecule, bromine monofluoride (BrF), is currently under study as a potential candidate for a visible chemical laser medium. Previous studies have shown a strong emission from BrF(B3π(O+)) in the presence of singlet oxygen. While singlet oxygen will pump BrF(X) to BrF(B), the exact mechanism is not known. Chemiluminescence observed from BrF(B) excited by oxygen in a gas flowtube was used to study the energy transfer mechanism. The objective of this research was fourfold. First, the pumping process was identified as a 3- Body Mechanism. Second, the observed vibrational distribution clearly showed the population of …

Go to article

Determination Of The Optical Properties Of Organic Thin Films By Spectroscopic Ellipsometry, Mark L. Sward Dec 1990

Determination Of The Optical Properties Of Organic Thin Films By Spectroscopic Ellipsometry, Mark L. Sward

Theses and Dissertations

This thesis demonstrated the feasibility of determining the optical properties of organic and polymer thin films through the use of Spectroscopic Ellipsometry (SE). Tan Psi and cos Delta data from 300-800 nanometers (NM) were taken with a Rudolph Research s2000 spectroscopic ellipsometer four samples: indium tin oxide (ITO) coated glass; five layer poly-benzyl-L glutamate (PBLG) organic film on ITO coated glass; eight layer PBLG film on ITO coated glass; and a thiophene polymer film on a microscope slide. The data sets were fit to a choice of four computer models based on a paper written by Dwight Berreman in 1972. …

Go to article

Fluorescent Lifetime Measurements Of Rare Earth Elements In Gallium Arsenide, Danny J. Topp Dec 1990

Fluorescent Lifetime Measurements Of Rare Earth Elements In Gallium Arsenide, Danny J. Topp

Theses and Dissertations

Lifetime measurements of the excited states of three GaAs semiconductors doped with the rare earth elements Erbium (ER), Praseodymium (Pr) , and Thulium (Tm) has been studied using a pulsed nitrogen laser and germanium detector. The measurements were made with an experimental set up with a system response time of 0.34 micro seconds. A 330 milliwatt nitrogen laser with a wavelength of 3370 angstrums was used to excite transitions of the rare earth elements.

Go to article

A Computer Model Of A Co2 Oscillator-Amplifier System, William F. Anderson Dec 1990

A Computer Model Of A Co2 Oscillator-Amplifier System, William F. Anderson

Theses and Dissertations

An existing CO2 laser amplifier simulation model developed for use on IBM-compatible personal computers has been improved through the redesign and addition of supplemental procedures from several models. The models and selected procedures which form the basis of the improved model are described. One procedure calculates the pumping rates of CO2 and N2 through calculation of the Boltzmann equation. Another procedure calculates the average vibrational temperatures of C2's vibrational modes. A third procedure replaces the Runge- Kutta integrator used in the original model with a faster, more accurate Adams- Bashforth-Moulton predictor-corrector integrator.

Go to article

Analysis Of Space Radiation Effects In Gallium Arsenide And Cadmium Selenide Semiconductor Samples Using Luminescence Spectroscopic Techniques, Brad Lee Shaffer Dec 1990

Analysis Of Space Radiation Effects In Gallium Arsenide And Cadmium Selenide Semiconductor Samples Using Luminescence Spectroscopic Techniques, Brad Lee Shaffer

Theses and Dissertations

Analysis of space radiation effects in gallium arsenide and cadmium selenide semiconductor samples using luminescence spectroscopic techniques. The M0006 semiconductor samples were placed into a 28.5 degree inclination, 480 km altitude, near-circular orbit aboard the Long Duration Exposure Facility satellite and exposed to direct space environment for a period of 11 months, and were shielded by 0.313 inches of aluminum for another 58 months. The samples were examined for changes using cathodoluminescence and photoluminescence in various wavelength regions from 0.5 to 1.8 microns. Samples were cooled to approximately 10 degrees Kelvin in a vacuum of 10-8.

Go to article

An Evolution Operator Solution For A Nonlinear Beam Equation, Carl E. Crockett Dec 1990

An Evolution Operator Solution For A Nonlinear Beam Equation, Carl E. Crockett

Theses and Dissertations

A nonlinear partial differential equation, motivated by the transverse vibration of a beam, is shown to have a unique solution. The existence theory, which is in the setting of semigroups and evolution operators, is a composite and synthesis of theorems of Kato. The formulation of the problem and the verification that the formulation leads to a solution are new. The introductory chapter provides background on the topic generally. Chapter 2 provides detailed formulations for the constant coefficient case. Chapter 3 describes nonautonomous cases. The general theorem is presented here. In Chapter 4, a more general case is considered. Namely, Kelvin …

Go to article

Characterization Of Barium Titanate As An Optical Amplifier, George A. Vogel Dec 1990

Characterization Of Barium Titanate As An Optical Amplifier, George A. Vogel

Theses and Dissertations

The introduction of two-beam coupling in photorefractive materials has resulted in an extensive amount of research into their use as optical processing/computing elements. This dissertation develops the theoretical equations for two-beam coupling in barium titanate as an optical amplifier. One of the factors which limits the optical gain in photorefractive crystals is the loss of pump beam power to the amplification of parasitic light (beam fanning). This parasitic light is produced by light scattered from the pump beam by imperfections on both the crystal face and within the crystal. Through the analysis of signal and noise amplification as functions of …

Go to article

Electron Emission From Both Target And Projectile In C⁺ + He Collisions, C. O. Reinhold, D. R. Schultz, Ronald E. Olson, L. H. Toburen, R. (Robert) D. Dubois Dec 1990

Electron Emission From Both Target And Projectile In C⁺ + He Collisions, C. O. Reinhold, D. R. Schultz, Ronald E. Olson, L. H. Toburen, R. (Robert) D. Dubois

Physics Faculty Research & Creative Works

The first classical trajectory Monte Carlo calculation of the electronic spectra arising from both target and projectile ionization is presented and compared with experimental measurements of the differential cross section for electrons emitted in C++He collisions. The theoretical treatment is based on an independent-electron model in which the interactions between the electrons are approximated by quantum model potentials. Good agreement is obtained between theory and experiment and structures appearing in the measurements can be explained in terms of the electron emission from either, or both, target and projectile. Further, the relative importance of the electron capture to the continuum and …

Go to article

First Prev Next Last