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Articles 31141 - 31170 of 34115
Full-Text Articles in Entire DC Network
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
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 …
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
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.
Laser Cvd And Plasma Cvd Of Cro2 Films And Cobalt Doped Cro2 Films Using Organometallic Precursors, Peter A. Dowben, Marshall Onellion
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 …
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
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.
Fresnel And Fraunhofer Diffraction: Development Of An Advanced Laboratory Experiment, Jeff Adams
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 …
Unpinning Of Gaas Surface Fermi Level By 200 Degrees C Molecular Beam Epitaxial Layer, David C. Look, C. E. Stutz, K. R. Evans
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.
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
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 …
Tunable Lasers At 1080 Nm For Helium Optical Pumping, Laird D. Schearer, Padetha Tin
Tunable Lasers At 1080 Nm For Helium Optical Pumping, Laird D. Schearer, Padetha Tin
Physics Faculty Research & Creative Works
We describe the current status of tunable, cw, solid-state lasers in the infrared region of the spectrum which may be tuned to the helium resonance transition near 1083 nm. The principal use for these laser devices is the optical pumping of 3He and 4He atoms via the 23S1 metastable state. The tunable lasers we have examined include Nd3+-doped YAlO3, LaxNd1-xMgAl11O19 (x ∼0.15), Nd:LiNbO3, and Nd:silica glass fibers. Power outputs from these lasers range from a milliwatt to more than 1 W at …
A High Power, Tunable, Arc-Lamp Pumped Nd-Doped Lanthanum-Hexaluminate Laser, Padetha Tin, Laird D. Schearer
A High Power, Tunable, Arc-Lamp Pumped Nd-Doped Lanthanum-Hexaluminate Laser, Padetha Tin, Laird D. Schearer
Physics Faculty Research & Creative Works
An LNA (Nd-doped lanthanum-hex aluminate) crystal has been pumped with a cw, krypton arc lamp in a commercial Nd:YAG cavity. The cw output power greater than 6 W is obtained in a 28-cm long, plane mirror cavity. The free-running wavelength is near 1083 nm and has a width of about 0.8 nm. Inserting a 0.25 mm thick, uncoated solid etalon in the cavity permits the laser output to be continuously tuned from 1082 to 1084 nm by tilting the etalon. The laser bandwidth is reduced to below 0.016 nm. Over 3 W are obtained at the helium resonance transition. The …
Magnetism Of Rare-Earth–Transition-Metal Nanoscale Multilayers. Ii. Theoretical Analysis Of Magnetization And Perpendicular Magnetic Anisotropy, Z.S. Shan, David J. Sellmyer, Sitaram Jaswal, Y.J. Wang, J.X. Shen
Magnetism Of Rare-Earth–Transition-Metal Nanoscale Multilayers. Ii. Theoretical Analysis Of Magnetization And Perpendicular Magnetic Anisotropy, Z.S. Shan, David J. Sellmyer, Sitaram Jaswal, Y.J. Wang, J.X. Shen
David Sellmyer Publications
Systematic studies of rare-earth–transition-metal amorphous compositionally modulated films (CMF) permit the development of a detailed model for understanding the magnetization and perpendicular magnetic anisotropy and their distributions along the film normal. It is shown that the single-ion anisotropy of rare-earth ions with orbital angular momentum is the major contributor to the perpendicular anisotropy for this class of CMF. The calculated results agree well with the experimental data for Dy/Co and Tb/Fe CMF when the individual layer thicknesses are small enough (<10 Å); these films have structures which can be characterized as compositionally modulated amorphous alloys.
Magnetism Of Rare-Earth–Transition-Metal Nanoscale Multilayers. I. Experiments On Dy/Co, Dy/Fe, And Tb/Fe, Z.S. Shan, David J. Sellmyer
Magnetism Of Rare-Earth–Transition-Metal Nanoscale Multilayers. I. Experiments On Dy/Co, Dy/Fe, And Tb/Fe, Z.S. Shan, David J. Sellmyer
David Sellmyer Publications
Experimental investigations of magnetic and structural properties for rare-earth–transition-metal (RE-TM) compositionally modulated films (CMF) are presented in this paper. In particular, ARE/BTM including ARE=Dy and Tb and BTM=Fe, Co, and Ni, are studied. The layer thickness and temperature dependence of magnetic properties, which can be interpreted in terms of the antiferromagnetic coupling of RE and TM moments and their atomic distributions, are reported. These ARE/BTM CMF with nanoscale layer thicknesses exhibit perpendicular magnetic anisotropy (PMA) and the range of the layer thickness required for PMA is determined. The …
A Biologically-Inspired Neural Network Architecture For Image Processing, Laurence E. Lazofson
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 …
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 …
Characterization Of Barium Titanate As An Optical Amplifier, George A. Vogel
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 …
Model-Based 3-D Recognition System Using Gabor Features And Neural Networks, Phung D. Le
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 …
Device For Dispersal Of Micrometer- And Submicrometer-Sized Particles In Vaccum, D. P. Sheehan, M. Carillo, W. Heidbrink
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.
Single Transfer-Excitation Resonance Observed Via The Two-Photon Decay In He-Like Ge³⁰⁺, Paul H. Mokler, S. Reusch, A. Warczak, Zbigniew Stachura, T. Kambara, Alfred K. Muller, Reinhold S. Schuch, Michael Schulz
Single Transfer-Excitation Resonance Observed Via The Two-Photon Decay In He-Like Ge³⁰⁺, Paul H. Mokler, S. Reusch, A. Warczak, Zbigniew Stachura, T. Kambara, Alfred K. Muller, Reinhold S. Schuch, Michael Schulz
Physics Faculty Research & Creative Works
We measured the 2E1 decay of the 1s2s 1S0 →1s2 1S0 transition in He-like germanium for 12- to 19-MeV/u Ge31+ +H2 collisions. The resonant population of the 2s2p 1P1 state by transfer excitation was isolated due to its cascading to the 1s2s 1S0 state. The experimental cross sections compare well with calculations using dielectronic recombination rates. The method gives the unique possibility to populate selectively the 1S0 state in heavy He-like ions.
Fluorescent Lifetime Measurements Of Rare Earth Elements In Gallium Arsenide, Danny J. Topp
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.
Design Of A Linear Gaussian Control Law For An Adaptive Optics System, Mark Alan Von Bokern
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 …
Computer Model Of An Injection Locked Pulsed Co2 Laser, Allen M. Susie
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.
A Compact Optical Associative Memory Using Dynamic Holographic Storage Media And Photorefractive Gain And Attenuation Elements, Thomas J. Burns
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 …
Optical Image Segmentation Using Wavelet Filtering Techniques, Christopher P. Veronin
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 …
Using Error Detection And Correction Coding For A Turbulent Atmospheric Optical Communications Link, Mark A. Cloutier
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 …
Detection Of High Altitude Aircraft Wake Vortices Using Infrared Doppler Lidar: An Assessment, Michael J. Estes
Detection Of High Altitude Aircraft Wake Vortices Using Infrared Doppler Lidar: An Assessment, Michael J. Estes
Theses and Dissertations
This thesis investigated the feasibility of air-to-air detection of high altitude aircraft wake vortices at long ranges using infrared Doppler lidar. The purpose of this technique is to detect otherwise stealthy aircraft. Three laser wavelengths were analyzed: 1.064, 2.091, and 9.115 microns. Analysis revealed that the spectral width of the return signal from an aircraft wake presented a good signature for detection. Based on the analysis, a minimum signal-to-noise ratio of 0 db was established. Detection performance was then analyzed using signal-to-noise ratio calculations for backscatter by ambient atmospheric aerosols, jet engine exhaust soot particles, and condensation trail ice particles. …
Nonlinear Interferometry: Optical Image Addition/Subtraction And Novelty Filters, Gordon T. Hengst
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 …
Operating Characteristics Of Xenon Gas Discharges, Michael E. Ruark
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 …
Energy Transfer In Singlet Oxygen And Bromine Monofluoride, Barrett F. Lowe
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 …
An Optically Pumped Molecular Bromine Laser, Jon W. Morrison
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.
Determination Of The Optical Properties Of Organic Thin Films By Spectroscopic Ellipsometry, Mark L. Sward
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. …
A Computer Model Of A Co2 Oscillator-Amplifier System, William F. Anderson
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.