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Resolving A Conflict Between Coherence Theory And Classical Radiometry, Incoherent Planar Sources Are Lambertian, Dorothy M. Seitz

Honors Capstone Projects and Theses

No abstract provided.

Determination Of The Bulk Modulus Of A Lennard-Jones Solid, Spencer A. Van Roekel

Masters Theses

The quantum Monte Carlo method is used to determine the bulk modulus of a Lennard-Jones solid. The quantum Monte Carlo method is discussed in detail and is compared with other numerical methods used previously.

The zero pressure bulk modulus of a Lennard-Jones solid is computed at a number of different temperatures and compared with experimental data.

The Photonic Band Structure Of Dielectric Systems With A Frequency Dependent Dielectric Function, Jiezhou Liu

Masters Theses

The concepts of band theory for electrons can be employed to describe the behavior of electromagnetic waves propagaiting in periodic dielectric structures with a frequency independent dielectric function. These periodic structures can produce photonic band gaps in which the propagation of electromagnetic waves is strictly prohibited. The introduction of a frequency dependent dielectric function in such systems gives rise to strong changes of the photonic bands in the neighborhood of the frequency resonance of the dielectric function.

In my thesis, the photonic band structure of a dielectric system with a frequency dependent dielectric function which undergoes a dielectric resonance will …

An Experimental Apparatus For Studying Double Differential Scattering By Low-Energy Multiply Charged Ions From Atomic Targets, Meenatchi S. Gopinathan

Masters Theses

A new differential energy-gain spectrometer with a movable parallel-plate electrostatic energy analyzer has been constructed and tested for the study of double differential (in energy and angle) cross sections for state-selective electron capture processes in collisions of low-energy multiply charged ions with atomic gases. The ion beam is produced by extracting recoil ions from a primary interaction region where these ions are generated in collisions between a neutral target gas and a fast fluorine beam from the WMU tandem Van de Graaff accelerator. An einzel lens is used to focus the ion beam extracted from the recoil-ion source into a …

Absolute Photonic Band Gaps Of Zincblende, Ulrich Bass

Masters Theses

One concept of examining the propagation of an electromagnetic wave through a periodic structure is the dispersion curve which relates the frequency of the propagating wave to its wave vector. In some cases frequency ranges occur where no propagation is possible. These ranges are called absolute photonic band gaps as far as periodic dielectric structures are concerned.

In my thesis I am interested in the dispersion curve of a Zincblende type dielectric array. Zincblende is a diamond-like structure and it has been shown that diamond structures possess absolute photonic band gaps. In studying Zincblende we want to gain deeper insight …

Frame Selection Performance Limits For Statistical Image Reconstruction Of Adaptive Optics Compensated Images, Stephen D. Ford

Theses and Dissertations

The U.S. Air Force uses adaptive optics systems to collect images of extended objects beyond the atmosphere. These systems use wavefront sensors and deformable mirrors to compensate for atmospheric turbulence induced aberrations. Adaptive optics greatly enhance image quality; however, wavefront aberrations are not completely eliminated. Therefore, post-detection processing techniques are employed to further improve the compensated images. Typically, many short exposure images are collected, recentered to compensate for tilt, and then averaged to overcome randomness in the images and improve signal-to-noise ratio. Experience shows that some short exposure images in a data set are better than others. Frame selection exploits …

Flow Visualization Of A Turbulent Shear Flow Using An Optical Wavefront Sensor, Daniel W. Jewell

Theses and Dissertations

The research reported here investigated the use of a shearing interferometer (SI) wavefront sensor to determine the effects of shear-layer turbulence on an optical wavefront. A collimated helium-neon laser beam was propagated through a plane shear-layer produced by mixing helium and nitrogen at different velocities. Since the gases have different indices of refraction, the optical wavefront was distorted by different amounts by each gas. The SI measured the wavefront slope across the sampled area of the wavefront. The shear-layer was viewed from two orthogonal directions. This document contains shadow graphs, interference patterns imaged by each of the SI's six cameras, …

Laser Beam Propagation In Non-Kolmogorov Atmospheric Turbulence, Bruce E. Stribling

Theses and Dissertations

Several observations of atmospheric turbulence statistics have been reported which do not obey Kolmogorov's power spectral density model. These observations have prompted the study of optical propagation through turbulence described by non-classical power spectra. This thesis presents an analysis of optical propagation through turbulence which causes index of refraction fluctuations to have spatial power spectra that obey arbitrary power laws. The spherical and plane wave structure functions are derived using Mellin transform techniques and are applied to the field mutual coherence function (MCF) using the extended Huygens-Fresnel principle. The MCF is used to compute the Strehl ratio of a focused, …

Multispectral Detection Of Ground Targets In Highly Correlated Backgrounds, Jason E. Thomas

Theses and Dissertations

Multispectral detection methods attempt to discriminate targets in a dominant clutter background using multiple images of the same real-world scene taken in different narrow spectral bands in the infrared. Detection is possible due to the empirically observed phenomenon that the radiance of man-made objects, such as a tank or truck, often lies off the main spectral correlation axis of that of natural backgrounds. Radiometric measurements of several vehicles and a tree canopy background taken over three days in June. 1994 were used to examine the factors affecting multispectral detection. Results clearly showed that the processes which provide for higher spectral …

Measurement Of N2+ Mobility In He Via Fourier Transform Emission Spectroscopy, Patrick D. Kee

Theses and Dissertations

Recently, Hong and Miller used Fourier Transform Emission (FTE) spectroscopy to determine the N₂⁺ mobility in helium by relating the observed Doppler shift of the N₂⁺ (B-X) transition to the measured electric field in the discharge as determined by probes. In order to establish the technique in-house, this effort duplicated that experiment and investigated the sensitivity and utility of the method. Doppler shift measurements in this experiment disagreed significantly with those reported by Hong and Miller. Attempts to reduce the data (and thus determine the mobility) using a model developed by Hong and Miller were unsuccessful. …

Analysis Of Instability Growth And Collisionless Relaxation In Thermionic Converters Using 1-D Pic Simulations, Bret B. Kreh

Theses and Dissertations

This work investigates the role that the beam-plasma instability may play in a thermionic converter. The traditional assumption of collisionally dominated relaxation is questioned, and the beam-plasma instability is proposed as a possible dominant relaxation mechanism. Theory is developed to describe the beam-plasma instability in the cold-plasma approximation, and the theory is tested with two common Particle-in- Cell (PIC) simulation codes. The theory is first confirmed using an unbounded plasma PIC simulation employing periodic boundary conditions, ES1. The theoretically predicted growth rates are on the order of the plasma frequencies, and ESl simulations verity these predictions within the order of …

Feasibility Exploration Of Throughfold As A Predictor For Target Loading And Associated Error Bounds, Kris G. Rongone

Theses and Dissertations

Various applications of the Fredholm integral equation appear m different fields of study. An application of particular interest to the Air Force arises in determination of target loading from nuclear effects simulations. Current techniques first unfold the incident spectrum then determine target loading; resulting spectrum and loading are assumed exact. This study investigates the feasibility of a new method, through-fold, for directly determining defensible error bounds on target loading. Through-fold uses a priori information to define input data and represents target response with a linear combination of instrument responses plus a remainder to derive a quadratic expression for exact target …

Generation Of A Single-Lobe, Far-Field Intensity Pattern From A Laser Diode Array Using An Optical Delay Line, Thomas A. Summers

Theses and Dissertations

A simple and practical technique is demonstrated to generate a stable, single-lobe, far-field intensity pattern from a one-dimensional, antiphased, laser diode array with gain-guided elements. The two far-field lobes of the array are combined after introducing an optical delay line into the path of one of the lobes to make the lobes mutually incoherent. The incoherent superposition of intensities produces a near-diffraction-limited, single-lobe, far-field intensity pattern containing 84% of the power, exceeding any previous (known) phase control experiments. This technique compares favorably with more elaborate schemes advanced previously using integrated phase plates, etc. The method is directly applicable to one-dimensional …

Detecting Alpha Particles Through Scintillation In Porous Materials, Martin E. Keillor

Theses and Dissertations

This thesis presents the results of a preliminary study of parameters essential to the development of a scintillation flow-cell detector with improved characteristics over existing cells. Such a detector with better than 10% alpha energy resolution could provide in situ capability to detect and identify important alpha-emitting radionuclides in dilute aqueous solutions. Gel-silica is a potential candidate that may provide the needed improvement in resolution while maintaining 100% detection efficiency; however, gel-silica with useful light output is yet to be developed. As a step toward realizing the system described, the dependence of alpha detection efficiency and intrinsic energy resolution on …

Subthreshold Channel Leakage Current In Gaas Mesfet's, Wei Long

Theses

In this thesis, a physical model including the subthreshold conpensation properties is presented. The Poisson equation is solved analytically in one dimension for GaAs MESFET's with undoped substrates in the subthreshold region. The solution is then used to derive expressions for subthreshold drain current and subshreshold swing in MESFET's with undoped substrates. Very good agreement between experimental and analytical results is achieved.

Two key parameters (Nilo and Iso) that determine the subthreshold Characteristics have been analyzed as a function of residual acceptor concentration Na, deep level EL2 concentration Nt, channel doping concentration Nd and threshold voltage Vt. It is shown …

Mbe Growth Of Inxga1-Xas/Gaas/Si Heterostructure System, Jun Liu

Theses

In this work, we grew the In_xGa_1-xAs/GaAs/Si (GaAs as buffer layer) by MBE technique. The surface of the buffer layer became microscopically rough as the thickness of the buffer layer increased and the growth mode of GaAs on Si underwent a change from three-dimensional to two-dimensional during the initial growth stage as indicated on the Reflection High Energy Electron Diffraction (RHEED) screen. The Scattering Electron Microscopy (SEM) observation of the etched surface of GaAs on Si showed that the structure of the buffer layer tended to be poly-crystalline and it was possible that a predominant orientation …

Measurement Of The Hall Coefficient And Electron Mobility Using Van Der Pauw Type Hall Effect Measurements, Hong-Sheng Luo

Theses

Hall effect measurement in the electrical characterization of semiconductor materials is very important. We set up the Hall effect measurement system and examined the system with a standard sample. The experimental results show that this Hall measurement system worked as well as expected. We also used this system to study the GaAs/GaAs and InGaAs/GaAs which grown by MBE. Finally, we disscussed and consided some common problems of Hall measurement. Some useful formulas and plots are presented.

Dosimetry Of High-Energy Heavy-Ion Beams Using Energy-Dependent Green's Functions, Sang Yull Chun

Physics Theses & Dissertations

A theoretical description of the transport of high-charge and high-energy (HZE) ion bombardment of biological tissue is developed. The energy-dependent Green’s functions and particle fluxes are obtained for two boundary distributions - the monoenergetic and the Gaussian. Approximate energy-dependent Green’s functions for the collision terms are obtained for computational simplicity. As an application of the energy-dependent Green’s function method, dosimetric quantities, such as dose, dose-equivalent, and average quality factor, for 600A MeV⁵⁶Fe , 517A MeV ⁴⁰Ar, and 625A MeV ²⁰Ne ion beams incident on a water target are obtained and compared with the values obtained from …

Simulation Of Active Control Of Asymmetric Flows Around Slender Pointed Forebodies, Hazem Sharaf El-Din

Mechanical & Aerospace Engineering Theses & Dissertations

At high angles of attack, the flowfield over slender forebodies becomes asymmetric with substantial side force, which may exceed the available control capability. The unsteady compressible Navier-Stokes equations are used to investigate the effectiveness of different active control methods to alleviate and possibly eliminate the flow asymmetry and the subsequent side force. Although the research work focuses on active control methods, a passive control method has been investigated. The implicit, Roe flux-difference splitting, finite volume scheme is used for the numerical computations. Both locally-conical and three-dimensional solutions of the Navier-Stokes equations are obtained.

The asymmetric flow over five-degree semi-apex angle …

High Resolution Fourier Transform Spectroscopy Of The First Overtone Of The N-O Stretch In Nitrosyl Bromide, Todd E. Wiest

Theses and Dissertations

Infrared Fourier transform spectroscopy of the first overtone of the nitric oxide (NO) bond stretch in nitrosyl bromide (ONBr) has been performed at a resolution of 0.02cm^-1 to obtain the rotational parameters of the V₁ = 2 energy level. Roughly 1000 transitions have been observed for rotational levels up to J = 80 and K_a = 7. The calculation of the complete set of rotational energy levels of this asymmetric molecule requires the numerical diagonalization of four, tridiagonal matricies for each J. From a non-linear least squares fit of observed transitions with J ≤ 40 using an …

Experiment Using Infrared Spectroscopy To Study The Effect Of Soil Characteristics Upon The Rate Of Trichloroethylene Desorption, Benjamin T. Kindt

Theses and Dissertations

This research investigated the influence of soil characteristics on the desorption of trichloroethylene (TCE). TCE is one of the most common contaminants at Superfund sites. Unfortunately, extraction of TCE from contaminated soils has been hindered by its slow and poorly understood desorption from soil particles. The rate and progress of desorption of TCE from seven types of soil with varying particle diameters and elemental compositions was measured using optical absorption techniques. Fitting the data to the Langmuir Isotherm functional form predicted in the literature yielded parameters for the desorption rate and total amount desorption each soil type. These parameters were …

A Three Region Analysis Of A Bounded Plasma Using Particle In Cell And Fluid Techniques, Don F. Nichols

Theses and Dissertations

A detailed collisionless sheath theory and a three-region collisional model of a bounded plasma are presented, and the suitability of the collisional model for analysis of ignited mode thermionic converters is investigated. The sheath theory extends previous analyses to regimes in which the sheath potential and electron temperatures are comparable in magnitude. In all operating regimes typical of a ignited mode thermionic converter, the predicted sheaths extend several mean-free paths. The apparent collisionality of the sheaths prompted development of a collisional, three-region model of the converter plasma. By interfacing Particle-in-Cell regions for the sheaths and fluid regions for the bulk …

Use Of Infrared Spectrometry To Determine The Effect Of Temperature On The Description Rates Of Trichloroethylene From Plastic Clay 98b, Abdellatif Fares

Theses and Dissertations

This thesis investigated the influence of temperature on the desorption rated of trichloroethylene (TCE) from plastic clay. It was expected that an increase in temperature will cause an increase in both the desorption rates of TCE and in the desorbed quantity. Previous studies on other chemicals indicated a faster decrease in the remaining sorbed concentration with an increase in temperature. This research made use of the infrared optical absorption technique. IR spectroscopy was used to measure the concentration of the vapor TCE that desorbed from the soil. The soil was exposed to liquid TCE for 2 days then placed inside …

A Procedure For G-Matrix Calculation From A Momentum Space Potential, Zhaohui Gao Busche

Masters Theses

In this work a numerical procedure was found to calculate the G-matrix in momentum space with a momentum space potential. The integral equation for the G-matrix was solved by conversion to a matrix equation. Two numerical integral methods, three-point Simpson method and Gaussian integral method, were employed in this process to determine the more efficient method.

The resulting G-matrix in momentum space was Fourier transformed into coordinate space. This was compared with the results of the G-matrix calculated from coordinate space directly as well as the results from solving the Bethe-Goldstone equation. A 2% accuracy was achieved with both the …

The Optical Emission And Absorption Properties Of Silicon-Germanium Superlattice Structures Grown On Non-Conventional Silicon Substrate Orientation, Theodore L. Kreifels

Theses and Dissertations

Optical emission and absorption properties of Si_1-x Ge_x/Si superlattices grown on (100), (110), and (111) Si substrates were investigated to determine the optimal growth conditions for these structures to be used as infrared detectors. Fully-strained Si_1-x Ge_x/Si superlattices were grown by molecular beam epitaxy MBE and examined using low-temperature photoluminescence PL to identify no-phonon and phonon-replica interband transitions across the alloy bandgap. Phonon-resolved emission was most intense for undoped quantum wells grown at 710°C for all three silicon orientations. Room temperature absorption measurements were conducted on (100) and (110) Si_1-x Ge_x/Si …

Asymmetric Adsorbate And Substrate Interactions In Physisorbed Systems: N2 On Graphite And Dipolar Molecules On Ionic Substrates, Teresa Ellen Burns

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Asymmetries in physisorbed systems give rise to interesting phases and phase transitions in two-dimensional (2D) monolayer and multilayer systems. The effects of asymmetric adsorbate and substrate interactions in monolayers of dipolar molecules on ionic substrates and N₂ on graphite are studied.

In the case of dipolar molecules on ionic substrates, 2D dielectric phase transitions using a modified Blume-Emery-Griffiths (BEG) model are determined theoretically. A dipole adsorbed vertically above a metal ion lattice site, and pointing up (down), is assigned a spin S=+1 (S=-1). An empty lattice site is assigned a spin S=0. Analytic solutions for both ferroelectrically and antiferroelectrically …

Building Of A Thermoacoustic Refrigerator And Measuring The Basic Performance, Torsten Blumreiter

Dissertations and Theses

The application of thermoacoustic phenomena for cooling purposes has a comparatively short history. However, recent experiments have shown that thermoacoustic refrigeration can achieve practical significance for both every day cooling in households and cryocooling for scientific purposes due to its high reliability, environmental safety and functioning under extreme conditions.

We build a thermoacoustic refrigerator driven by a commercial loudspeaker. It was equipped with a vacuum pump and an entrance port for introducing different gases under different pressures as working fluids. It contained two thermocouples and a pressure transducer for quantitative measurements of the basic performance. The resonance frequency of the …

Interfacing A Computer To A Scanning Tunneling Microscope, Markus Jarasch

Dissertations and Theses

A program was written in 'C' to control the functions of an already existing Scanning Tunneling Microscope (STM). A DAS-1601 data acquisition card (from Keithley Data Acquisition) was installed together with its drivers for 'C' on a computer with a 486-DX motherboard. The computer was interfaced to the electronics of the STM. Images taken of HOPG (highly oriented pyrolitic graphite) were of a reasonable quality and showed atomic resolution.

Electrophoretic Studies Of Ion Adsorption To Sarcoplasmic Reticulum And Phosphatidylcholine Membranes, Andreas Schilling

Dissertations and Theses

In this study, electrophoretic mobilities of native and two types of trypsin digested sarcoplasmic reticulum vesicles have been determined by microelectrophoresis using a Doppler Electrophoretic Light Scattering Analyzer to investigate the influence of hydrodynamic drag, caused by the Ca2⁺, Mg2⁺ -ATPase protruding from the surface of native sarcoplasmic reticulum vesicles. After the prolonged digestion (protein:trypsin ratio of 20 for 3 hours at 25°C), the ATPase was cleaved and removed from the sarcoplasmic reticulum membrane as shown with SDS gel electrophoresis and an ATPase activity assay. Ionic strength and pH dependence of mobility showed a nearly pH independent …

Interactions Of Ruthenium Red With Phospholipid Vesicles, Dirk Voelker

Dissertations and Theses

We have studied the electrostatic and other interactions of the inorganic, hexavalent dye Ruthenium Red (RR) with phospholipid vesicles composed of phosphatidylcholine (PC) and phosphatidylserine (PS) or phosphatidylinositol (Pl) in various mixtures and concentrations. Experiments were based on spectrophotometric absorption measurements which compared RR concentrations in the presence and in the absence of liposomes at different dye concentrations. Multilamellar liposomes were obtained by handshaken preparations. Five freeze-and-thaw cycles of the lipid-RR suspension produced an ion equilibrium distribution at the membrane-water interface. Results are given in terms of the Gouy-Chapman-Stem adsorption theory with the linear partition coefficient and a newly introduced …