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Articles 1 - 30 of 67
Full-Text Articles in Engineering Physics
Efficiency Quantification For Pulsed-Source Digital Holographic Wavefront Sensing, Steven A. Owens
Efficiency Quantification For Pulsed-Source Digital Holographic Wavefront Sensing, Steven A. Owens
Theses and Dissertations
The efficiencies of a digital holography (DH) system in the pulsed configuration and the off-axis image plane recording geometry are analyzed. First, the system efficiencies of an infrared-wavelength DH system in a homodyne-pulsed configuration are measured and compared to those of a visible-wavelength DH system in a homodyne-continuous-wave (CW) configuration. The total-system, excess-reference-noise, shot-noise-limit, and mixing efficiencies of the pulsed-source system were found to be consistent with those of the CW-source system. This indicated no new efficiencies were necessary to characterize pulsed-source systems when no temporal delay exists between the pulses. The consistency of efficiencies also showed infrared DH systems …
Full Pattern Analysis And Comparison Of The Center Fed And Offset Fed Cassegrain Antennas With Large Focal Length To Diameter Ratios For High Power Microwave Transmission, Derek W. Mantzke
Theses and Dissertations
High power microwaves (HPM) have been a topic of research since the Cold War era. This paper will present a comparison between two Cassegrain-type antennas: the axially, or center fed, and the offset fed. Specifically, the 10 GHz operating frequency will be investigated with large focal length to diameter () ratios. Beam patterns which encompass the entire radiation pattern will be included for data validation and optimization. The simulations will follow a design of experiments factorial model to ensure all possible combinations of prescribed parameters are included, including an analysis of variance (ANOVA) study to find parameter influence on the …
Nonlinear Solution Of The Time Eigenvalue Of A Fast Burst Reactor Using The Finite Volume Method, Stephen H. Baxter
Nonlinear Solution Of The Time Eigenvalue Of A Fast Burst Reactor Using The Finite Volume Method, Stephen H. Baxter
Theses and Dissertations
This effort models fast burst reactors using the one dimensional, one group neutron diffusion equation to solve for the time eigenvalue, a method for which an analytical solution exists against which the numerical results can be verified. An existing solution method is enhanced by the addition of a second order accurate finite volume discretization, which is then used to model two separate fast burst reactors. The results of these models are then compared to the results of previous work, the analytical solution, and existing experimental burst width data for each of the two reactors.
A Comparison Of Sporadic-E Occurrence Rates Using Ionosondes And Gps Radio Occultation Measurements, Rodney A. Carmona Jr.
A Comparison Of Sporadic-E Occurrence Rates Using Ionosondes And Gps Radio Occultation Measurements, Rodney A. Carmona Jr.
Theses and Dissertations
Sporadic-E (Es) occurrence rates from Global Position Satellite radio occultation (GPS-RO) measurements have shown to vary by nearly an order of magnitude between studies, motivating a comparison with ground-based measurements. In an attempt to find an accurate GPS-RO technique for detecting Es formation, occurrence rates derived using five previously developed GPS-RO techniques are compared to ionosonde measurements over an eight-year period from 2010-2017. GPS-RO measurements within 170 km of a ionosonde site are used to calculate Es occurrence rates and compared to the ground-truth ionosonde measurements. Each technique is compared individually for each ionosonde site and then combined to determine …
Topological Realizations Of Entangling Quantum Gates, Adrian D. Scheppe
Topological Realizations Of Entangling Quantum Gates, Adrian D. Scheppe
Theses and Dissertations
Topological systems are immune to decoherence and provide a hunting ground for qubits that are fault tolerant. The process of calculating linear operator representations of Majorana fermion exchanges or braids is well known and well documented; however, there is no documented intuition or algorithm which provides the opposite; braids from quantum gates. In this document, all possible linear representations of single, double, triple, and quadruple qubit gates are calculated to find several key patterns which provide crucial insight into the manifestation of qubit gates. A n x n gate will require n + 2 Majoranas with ½n + 1 trivial …
Spectroscopic Diagnostics For Supersonic Air Microwave Discharges, James E. Caplinger
Spectroscopic Diagnostics For Supersonic Air Microwave Discharges, James E. Caplinger
Theses and Dissertations
Optical Emission Spectroscopy (OES) is an increasingly relevant technique in plasma diagnostics due to its inherent non-invasive nature and simple application relative to other popular techniques. In this work, common OES techniques are combined with novel methods, developed here, in an effort to provide comprehensive OES techniques for stationary and supersonic air microwave discharges. To this end, a detailed collisional-radiative model for strong atomic oxygen lines has been developed and used to identify the importance of often overlooked mechanisms including cascade emission and metastable excitation. Using these results, a combined argon actinometry technique was developed which makes use of the …
Enhanced Brdf Modeling Using Directional Volume Scatter Terms, Michael W. Bishop
Enhanced Brdf Modeling Using Directional Volume Scatter Terms, Michael W. Bishop
Theses and Dissertations
Accurate Bidirectional Reflectance Distribution Function (BRDF) models provide critical scatter behavior for computer graphics and remote sensing performance. The popular microfacet class of BRDF models is geometric-based and computationally inexpensive compared to wave-optics models. Microfacet models commonly account for surface scatter and Lambertian volume scatter, but not directional volume scatter. This work proposes directional volume scatter modeling for enhanced performance over all observation regions. Five directional volume models are incorporated into the modified Cook-Torrance microfacet model. Additionally, a semi-empirical directional volume term is presented based on the Beckmann microfacet distribution and a modified Fresnel reflection term. High fidelity, low density …
Targeted Germanium Ion Irradiation Of Aluminum Gallium Nitride/Gallium Nitride High Electron Mobility Transistors, Melanie E. Mace
Targeted Germanium Ion Irradiation Of Aluminum Gallium Nitride/Gallium Nitride High Electron Mobility Transistors, Melanie E. Mace
Theses and Dissertations
Microscale beams of germanium ions were used to target different locations of aluminum galliumnitride/gallium nitride (AlGaN/GaN) high electron mobility transistors (HEMTs) to determine location dependent radiation effects. 1.7 MeV Ge ions were targeted at the gap between the gate and the drain to observe displacement damage effects while 47 MeV Ge ions were targeted at the gate to observe ionization damage effects. Electrical data was taken pre, during, and post irradiation. To separate transient from permanent degradation, the devices were characterized after a room temperature anneal for at least 30 days. Optical images were also analyzed pre and post irradiation. …
Effects Of Sinusoidal Phase Modulation On Signal-To-Noise Ratio In A Digital Holography System, Davin Mao
Effects Of Sinusoidal Phase Modulation On Signal-To-Noise Ratio In A Digital Holography System, Davin Mao
Theses and Dissertations
Digital holography (DH) has been demonstrated to be an effective tool for tactical applications which involve in low signal-to-noise ratios (SNR). In practice, DH uses a strong reference beam from a local oscillator (LO) to scale SNR, however since DH relies on the interference of a signal beam with a mutually coherent LO, the coherence properties of the master oscillator (MO) can degrade system SNR for long range engagements. In this thesis, a digital holography system in the off-axis image plane recording geometry was assembled and used to measure the effects of the coherence properties of the MO on SNR. …
Variations Of Heavy Ion Abundances Relative To Proton Abundances In Large Solar Energetic Particle Events, Joseph F. Round
Variations Of Heavy Ion Abundances Relative To Proton Abundances In Large Solar Energetic Particle Events, Joseph F. Round
Theses and Dissertations
Past studies of heavy ions (Z>2) in large (E>10 MeV/nuc) gradual solar energetic particle (SEP) events have focused on elemental abundances relative to those of a single element, such as Fe or O, and have often neglected ionized H (the primary element used for space weather purposes). This work analyzes SEP abundances in a group of 15 large gradual SEP events from 2000 to 2015 across the energy range of 13.5-50.7 MeV. Hourly flux averages of He, C, O, Mg and Fe from the Advanced Composition Explorer/Solar Isotope Spectrometer (ACE/SIS) are compared to two-hour averages of H flux …
Electrical Characterization Of Crystalline Uo2, Tho2 And U0.71Th0.29O2, Christina L. Dugan
Electrical Characterization Of Crystalline Uo2, Tho2 And U0.71Th0.29O2, Christina L. Dugan
Theses and Dissertations
Uranium dioxide (UO2), thorium dioxide (ThO2), and UxTh1-xO2 alloys are characterized for suitability in uranium-based neutron detectors. ThO2 was studied for an envisioned UO2/ThO2 heterojunction. A U0.71Th0.29O2 alloy was studied because of its resistance to oxidation and potential use in surface passivation. The U0.71Th0.29O2 effective Debye temperature of 217± 24 K was measured using temperature-dependent x-ray photoemission spectroscopy (XPS). The specific heat capacity for the U0.71Th0.29O2 alloy was calculated from the Debye …
Improving Detection Of Dim Targets: Optimization Of A Moment-Based Detection Algorithm, Shannon R. Young
Improving Detection Of Dim Targets: Optimization Of A Moment-Based Detection Algorithm, Shannon R. Young
Theses and Dissertations
Wide area motion imagery (WAMI) sensor technology is advancing rapidly. Increases in frame rates and detector array sizes have led to a dramatic increase in the volume of data that can be acquired. Without a corresponding increase in analytical manpower, much of these data remain underutilized. This creates a need for fast, automated, and robust methods for detecting dim, moving signals of interest. Current approaches fall into two categories: detect-before-track (DBT) and track-before-detect (TBD) methods. The DBT methods use thresholding to reduce the quantity of data to be processed, making real time implementation practical but at the cost of the …
Evaluation And Quantification Of Diffractive Plenoptic Camera Algorithm Performance, Jack A. Shepherd Iii
Evaluation And Quantification Of Diffractive Plenoptic Camera Algorithm Performance, Jack A. Shepherd Iii
Theses and Dissertations
A diffractive plenoptic camera is a novel approach to the traditional plenoptic camera which replaces the main optic with a Fresnel zone plate making the camera sensitive to wavelength instead of range. However, algorithms are necessary to reconstruct the image produced by plenoptic cameras. While many algorithms exist for traditional plenoptic cameras, their ability to create spectral images in a diffractive plenoptic camera is unknown. This paper evaluates digital refocusing, super resolution, and 3D deconvolution through a Richardson-Lucy algorithm as well as a new Gaussian smoothing algorithm. All of the algorithms worked well near the Fresnel zone plate design wavelength, …
A Comparison Of High Frequency Angle Of Arrival And Ionosonde Data During A Traveling Ionospheric Disturbance, Kalen L. Knippling
A Comparison Of High Frequency Angle Of Arrival And Ionosonde Data During A Traveling Ionospheric Disturbance, Kalen L. Knippling
Theses and Dissertations
High Frequency (HF) geolocation techniques are commonly used to track the source of uncooperative HF emitters. A traveling ionospheric disturbance (TID) makes geolocation particularly difficult due to large perturbations in the local ionospheric electron density profile. Angle of Arrival (AoA) and ionosonde virtual height measurements collected at White Sands Missile Range, New Mexico in January 2014, are analyzed during a medium scale traveling ionospheric disturbance. TID characteristics are extracted from the measurements, and a comparison between the data sets is per- formed to provide a measure of correlation as a function of distance and time between the ionosonde and AoA …
Two-Photon Excitation Of Cesium Alkali Metal Vapor 72D, 82D Kinetics And Spectroscopy, Ricardo C. Davila
Two-Photon Excitation Of Cesium Alkali Metal Vapor 72D, 82D Kinetics And Spectroscopy, Ricardo C. Davila
Theses and Dissertations
Pulsed excitation on the two-photon Cs 62S½ → 72D3/2,5/2 transition results in time-resolved fluorescence at 697 nm and 672 nm. The rates for fine structure mixing between the 72D3/2,5/2 states have been measured for helium and argon rare gas collision partners. The mixing rates are very fast, 1.26 ± 0.05 x 10-9 cm3/(atom sec) for He and 1.52 ± 0.05 x 10-10 cm3 /(atom sec) for Ar, driven by the small energy splitting and large radial distribution for the valence electron. …
Rbhe Potential Energy Surface Sensitivity Study, Ethan D. Thorp
Rbhe Potential Energy Surface Sensitivity Study, Ethan D. Thorp
Theses and Dissertations
This paper studies how alterations of features of RbHe potential energy surfaces (PES) for a diode pumped alkali laser (DPAL) system effect the collisional cross section. The Split-Operator method is used to propagate a wave function along these PES and because they are radially coupled, the wave function can be transmitted from the starting surface to other energy surfaces. This transmittance is encoded in the correlation function. The full Hamiltonian used for propagation consists of the electronic potential, the nuclear kinetic energy, and the Coriolis coupling. The correlation function is used to generate the Scattering Matrix elements. These elements describe …
Total Electron Count Variability And Stratospheric Ozone Effects On Solar Backscatter And Lwir Emissions, John S. Ross
Total Electron Count Variability And Stratospheric Ozone Effects On Solar Backscatter And Lwir Emissions, John S. Ross
Theses and Dissertations
The development of an accurate ionospheric Total Electron Content (TEC) model is of critical importance to High Frequency (HF) radio wave propagation. However, the TEC is highly variable and is continuously influenced by geomagnetic storms, extreme Ultraviolet (UV) radiation, diurnal variation, and planetary waves. The ability to capture this variability is essential to improve current TEC models. Analysis of the growing body of data involving ionospheric fluctuations and thermal tides has revealed persistent correlation between increases in stratospheric ozone and variability of the TEC. The spectral properties of ozone show that it is a greenhouse gas that alters longwave emissions …
Passively Estimating Index Of Refraction For Specular Reflectors Using Polarimetric Hyperspectral Imaging, Jacob A. Martin
Passively Estimating Index Of Refraction For Specular Reflectors Using Polarimetric Hyperspectral Imaging, Jacob A. Martin
Theses and Dissertations
As off-nadir viewing platforms becoming increasingly prevalent in remote sensing, material classification and ID techniques robust to changing viewing geometries must be developed. Traditionally, either reflectivity or emissivity are used for classification, but these quantities vary with viewing angle. Instead, estimating index of refraction may be advantageous as it is invariant with respect to viewing geometry. This work focuses on estimating index of refraction from LWIR (875-1250 wavenumbers) polarimetric hyperspectral radiance measurements.
Evaluation Of Hydrothermally Synthesized Uranium Dioxide For Novel Semiconductor Applications, Christopher M. Young
Evaluation Of Hydrothermally Synthesized Uranium Dioxide For Novel Semiconductor Applications, Christopher M. Young
Theses and Dissertations
Neutron radiation detection is an important part of the national strategy for nonproliferation efforts worldwide. Key to the success of these programs is detector material development which establishes the limits of efficiency, sensitivity, and power usage for a detector of practical use. This research focused upon the study of neutron detection using single crystal actinide compounds, specifically UO2, taking advantage of the successful hydrothermal synthesis of UO2 at the Air Force Research Laboratories. Initial indications are that this material may be of sufficient quality for semiconductor application.
Capturing Atmospheric Effects On 3-D Millimeter Wave Radar Propagation Patterns, Richard D. Cook
Capturing Atmospheric Effects On 3-D Millimeter Wave Radar Propagation Patterns, Richard D. Cook
Theses and Dissertations
The need to model millimeter wave (MMW) radar propagation is imperative to proper design of aeronautical, civil, and military systems. Traditional radar propagation modeling is done using a path transmittance with little to no input for weather and atmospheric conditions. As radar advances into the MMW regime, atmospheric effects, such as attenuation and refraction, become more pronounced than at traditional radar wavelengths. The DoD High Energy Laser Joint Technology Offices High Energy Laser End-to-End Operational Simulation (HELEEOS), in combination with the Laser Environmental Effects Definition and Reference (LEEDR) code, is a powerful tool for simulating laser propagation and effects tied …
Temperature Dependent Rubidium-Helium Line Shapes And Fine Structure Mixing Rates, Wooddy S. Miller
Temperature Dependent Rubidium-Helium Line Shapes And Fine Structure Mixing Rates, Wooddy S. Miller
Theses and Dissertations
Diode Pumped Alkali Lasers (DPALs) are a new type of laser that uses alkali metal vapor as a gain medium and a buffer gas to control the line shape and kinetics. While these systems were first demonstrated in 2003 [48] they have just recently been scaled to the kilowatt power levels in 2012 [18]. To achieve these powers, the design of the gain cell relied on a set of incomplete line shape and kinetic data. The current focus areas of DPAL research are the continued power scaling of the systems and basic science research into the rates involved within the …
Identifying The Experimental And Theoretical Effective Characteristics Of Nonaligned Anisotropic Metamaterials, Michael R. Benson
Identifying The Experimental And Theoretical Effective Characteristics Of Nonaligned Anisotropic Metamaterials, Michael R. Benson
Theses and Dissertations
Previous research into anisotropic materials has assumed certain properties in order to make the underlying mathematics tractable. One of the assumptions is the alignment of the optical axes with the laboratory frame of reference, such as split-ring resonators lying at on the material plane. This assumption does not hold true for many metamaterials, such as tilted nanorods. Techniques such as ellipsometry are needed to analyze the effective characteristics of these highly anisotropic structures. In this research, tilted nanorods are analyzed using generalized ellipsometry to extract the indices of the optical axes. The underlying physics of ellipsometry is then used to …
Scaling Of An Optically Pumped Mid-Infrared Rubidium Laser, Paul J. Moran
Scaling Of An Optically Pumped Mid-Infrared Rubidium Laser, Paul J. Moran
Theses and Dissertations
An optically pumped mid-infrared rubidium (Rb) pulsed laser has been demonstrated in a heat pipe along the 62P3/2 - 62S1/2 transition at 2.730 µm and the 62P1/2 - 62S1/2 transition at 2.790 µm. The bleached limit, slope efficiency, and maximum laser output energy of the mid-IR Rb laser have been shown to scale linearly with increasing Rb density, contrary to prior laser demonstrations. A maximum output energy of 5 nJ per pulse had previously been observed before a rollover occurred in the scaling of output energy with Rb …
Absorption Spectroscopy Of Rubidium In An Alkali Metal Dispenser Cell And Bleached Wave Analysis, James M. Rosenthal
Absorption Spectroscopy Of Rubidium In An Alkali Metal Dispenser Cell And Bleached Wave Analysis, James M. Rosenthal
Theses and Dissertations
An absorption spectrum of a rubidium alkali metal dispenser (AMD) cell was obtained in order to determine the system s suitability for use in a diode pumped alkali laser (DPAL) and use in high-temperature spectroscopic studies. The AMD produced a concentration of 3.65 0.16 1010 cm-3, which is in the ideal range for Beer s Law region absorption spectroscopy, but too low to make a high-power DPAL in a 10 cm cell with a poor Q resonator. Before AMDs can be used to determine pressure broadening and shifting coefficients, issues concerning contamination and producing rubidium vapor at pressure must be …
Potential Energy Curves And Associated Line Shape Of Alkali-Metal And Noble-Gas Interactions, Larry A. Blank
Potential Energy Curves And Associated Line Shape Of Alkali-Metal And Noble-Gas Interactions, Larry A. Blank
Theses and Dissertations
Recent interest in optically-pumped alkali laser systems has prompted this study into the binary interaction potentials between species of alkali-metal and rare-gas atoms and the effects of the collision of these species on the alkali-metal atom absorption spectrum. Special attention is placed on the relationship of the interaction potentials and the resulting line shape. The X2Σ+1/2, A2π1/2, A2π3/2, and B2Σ+1/2 potential energy curves and associated dipole matrix elements are computed for M+ Ng at the spin-orbit multi-reference configuration interaction level, where M = …
Finite Element Analysis Modeling Of Chemical Vapor Deposition Of Silicon Carbide, Brandon M. Allen
Finite Element Analysis Modeling Of Chemical Vapor Deposition Of Silicon Carbide, Brandon M. Allen
Theses and Dissertations
Fiber-reinforced silicon carbide (SiC) composite materials are important for many applications due to their high temperature strength, excellent thermal shock and impact resistance, high hardness, and good chemical stability. The microstructure and phase composition of SiC composites can be tailored by fiber surface modification, the process parameters, and/or fiber preform architecture. One process by which SiC composites can be produced is chemical vapor deposition (CVD). This thesis primarily focuses on mass transport by gas-phase flow and diffusion, chemical reaction in gas phase and on solid surfaces, and thin film formation on curved surfaces, which are fundamental to the CVD process. …
Development And Characterization Of A High Speed Mid-Ir Tunable Diode Laser Absorption Spectrometer For Co And Co2 Detection In Detonation Events, Stephen D. Wakefield
Development And Characterization Of A High Speed Mid-Ir Tunable Diode Laser Absorption Spectrometer For Co And Co2 Detection In Detonation Events, Stephen D. Wakefield
Theses and Dissertations
A tunable diode laser absorption spectroscopy system, capable of collecting data at a 10 kHz repetition rate near 4.5 microns. This system was made feasible in recent years due to the development of quantum cascade lasers active in the 4.5 microns region of the spectrum. Reaching into the mid-IR region of the electromagnetic spectrum allowed for an analysis of the fundamental absorption bands for both CO and CO2. The spectral absorption was measured for ethylene, methane, ethane, and propane across a variety of equivalence ratios, at various heights above a Hencken Burner surface. For each fuel, the concentration …
Iron-Doped Zinc Selenide: Spectroscopy And Laser Development, Jonathan W. Evans
Iron-Doped Zinc Selenide: Spectroscopy And Laser Development, Jonathan W. Evans
Theses and Dissertations
We examine the quantum mechanics of optically active ions in crystals. Insight is developed which qualitatively explains the shape of the optical absorption and emission spectra of Fe2+ ions in II-VI materials. In addition to a discussion of the relevant theory, this work explores experimental techniques for absorption spectroscopy, laser-induced fluorescence spectroscopy, and upper-state lifetime measurements in detail. The data collected from these experiments are interpreted in the context of the theories developed herein. The theory and data are used to develop a simple model of the temperature dependence of the upper-state lifetime of Fe2+ ions in ZnSe. …
Electrical Characterization Of Spherical Copper Oxide Memristive Array Sensors, James P. Orta
Electrical Characterization Of Spherical Copper Oxide Memristive Array Sensors, James P. Orta
Theses and Dissertations
A new System Protection (SP) technology is explored by using electrical and mechanical interference-sensing devices that are implemented with granular memristive material. The granular materials consist of oxide-coated copper spheres with radii of about 700 µm that are placed in contact to produce thin oxide junctions which exhibit memristive behavior. Processes for etching, which compared acetic acid and nitric acid etches, and thermal oxidation at 100°C are performed and compared to produce copper spheres with a copper oxide layer over the sphere surface. Oxidized copper spheres are tested as sensor arrays by loading into a capillary tube in an aligned …
Band Gap Transition Studies Of U:Tho2 Using Cathodoluminescence, Joshua D. Reding
Band Gap Transition Studies Of U:Tho2 Using Cathodoluminescence, Joshua D. Reding
Theses and Dissertations
The Department of Defense has expressed interest in thorium dioxide (ThO2) and uranium dioxide (UO2) as possible candidates for use as special nuclear material in designing neutron detectors. Both materials have large neutron interaction cross sections. Uranium dioxide is particularly attractive due to its semiconducting properties and a relatively small band gap of 2 eV. Both materials fluoresce under ionizing radiation making them candidates for scintillating detectors. Three Ux:Th1-xO2 (x= 0.00, 0.01, 0.22) hydrothermally grown single crystals were examined using cathodoluminescence to interrogate the changing electronic properties of ThO2 as it became an alloy. Both depth-resolved and temperature- dependent cathodoluminescence …