Open Access. Powered by Scholars. Published by Universities.®
- Discipline
-
- Nuclear (19)
- Optics (16)
- Engineering (7)
- Engineering Physics (5)
- Plasma and Beam Physics (4)
-
- Atmospheric Sciences (3)
- Atomic, Molecular and Optical Physics (3)
- Oceanography and Atmospheric Sciences and Meteorology (3)
- Aerospace Engineering (2)
- Biological and Chemical Physics (2)
- Electrical and Computer Engineering (2)
- Materials Science and Engineering (2)
- Navigation, Guidance, Control and Dynamics (2)
- Applied Mathematics (1)
- Computer Engineering (1)
- Computer Sciences (1)
- Digital Communications and Networking (1)
- Earth Sciences (1)
- Electronic Devices and Semiconductor Manufacturing (1)
- Geophysics and Seismology (1)
- Medicine and Health Sciences (1)
- Other Electrical and Computer Engineering (1)
- Other Engineering (1)
- Other Materials Science and Engineering (1)
- Polymer and Organic Materials (1)
- Public Affairs, Public Policy and Public Administration (1)
- Public Health (1)
- Social and Behavioral Sciences (1)
- Keyword
-
- #antcenter (4)
- Monte Carlo Method (3)
- Spectroscopy (3)
- Detection (2)
- Detector (2)
-
- Detectors (2)
- Doping (2)
- Dose Rate (2)
- Fallout (2)
- Gallium Nitrides (2)
- Hall Effect (2)
- Ionosphere (2)
- Nuclear (2)
- Optical Properties (2)
- Plumes (2)
- Spectrometers (2)
- Tracking (2)
- Absorption Spectra (1)
- Adaptive Optics (1)
- Adaptive Systems (1)
- Aerosols (1)
- Alkali Metal-Noble Gas Cross Section (1)
- Aluminum Gallium Nitrides (1)
- Annihilation Reactions (1)
- Anomalies (1)
- Anthrax (1)
- Atmosphere Models (1)
- Atmospheric Density (1)
- Atomic Layer Epitaxy (1)
- Atomic spectroscopy (1)
Articles 1 - 30 of 55
Full-Text Articles in Physics
Characterization And Discrimination Of Large Caliber Gun Blast And Flash Signatures, Bryan J. Steward
Characterization And Discrimination Of Large Caliber Gun Blast And Flash Signatures, Bryan J. Steward
Theses and Dissertations
Two hundred and one firings of three 152 mm howitzer munitions were observed to characterize firing signatures of a large caliber gun. Muzzle blast expansion was observed with high-speed (1600 Hz) optical imagery. The trajectory of the blast front was well approximated by a modified point-blast model described by constant rate of energy deposition. Visible and near-infrared (450 - 850 nm) spectra of secondary combustion were acquired at 0.75 nm spectral resolution and depict strong contaminant emissions including Li, Na, K, Cu, and Ca. The O2 (X-b) absorption band is evident in the blue wing of the potassium D lines …
Electroluminescence Studies On Longwavelength Indium Arsenide Quantum Dot Microcavities Grown On Gallium Arsenide, John C. Ramsey
Electroluminescence Studies On Longwavelength Indium Arsenide Quantum Dot Microcavities Grown On Gallium Arsenide, John C. Ramsey
Theses and Dissertations
A comprehensive study of the electroluminescence of four GaAs/AlGaAs microcavity devices with InAs/GaInAs quantum dot active regions emitting near 1.3 µm was conducted. The four molecular beam epitaxial grown samples with AlAs oxide aperture confinement layers were fabricated, characterized, and optically modeled. Optical power transmission of the samples was modeled using Matlab and compared with measured transmission data. Resonant cavity light emitting diodes (RCLEDs) and three vertical cavity surface emitting laser (VCSEL) samples were fabricated and electro-optically characterized over a range of injection currents and temperatures. Devices achieved continuous wave room temperature lasing at 1.28 µm with an output power …
Kinetics Of The Electrical Discharge Pumped Oxygen-Iodine Laser, Matthew A. Lange
Kinetics Of The Electrical Discharge Pumped Oxygen-Iodine Laser, Matthew A. Lange
Theses and Dissertations
A systematic study of microwave discharges at 2.45 GHz has been performed through the pressure range of sustainable electric discharges in pure oxygen flows of 2 to 10 Torr. A corresponding study of 13.56 MHz has also been performed at pressures of 2, 4, and 7 Torr. Optical emissions from O2(a 1Δ), O2(b 1Σ), and O-atoms have been measured from the center of a μ-wave discharge. Discharge residence times from 0.1 to 5 ms have been reported. The O2(b 1Σ) emissions, with a spectral resolution of 0.01 nm, have been used to measure the temperature of the gas, which typically …
Background-Oriented Schlieren Pattern Optimization, Jeffery E. Hartberger
Background-Oriented Schlieren Pattern Optimization, Jeffery E. Hartberger
Theses and Dissertations
This paper describes a test series to investigate background patterns used for the Background-Oriented Schlieren field density measurement technique. Several varying background patterns were substituted under similar fluid density conditions to visualize and isolate the effects of patterns in the background images. A qualitative comparison was completed of the flow visualization results of each background pattern to categorize background conditions that improved the flow visualization image. Changes in background patterns revealed significant changes in flow visualization. Pattern contrast, spacing and sizing all played large parts in the quality of the visual density gradient imaging during the test series.
Integrated Approach To Free Space Optical Communications In Strong Turbulence, Jason A. Tellez
Integrated Approach To Free Space Optical Communications In Strong Turbulence, Jason A. Tellez
Theses and Dissertations
The propagation of a free space optical communication signal through atmospheric turbulence experiences random fluctuations in intensity, including signal fades which negatively impact the communications link performance. This research develops an analytical probability density function (PDF) to model the best case scenario of using multiple independent beams to reduce the intensity fluctuations. The PDF was further developed to account for partially correlated beams, such as would be experienced by beams having finite separation. The PDF was validated with results obtained from digital simulations as well as lab experiments. The research showed that as the number of transmitted beams increases the …
Distributed Spacing Stochastic Feature Selection And Its Application To Textile Classification, Jeffrey D. Clark
Distributed Spacing Stochastic Feature Selection And Its Application To Textile Classification, Jeffrey D. Clark
Theses and Dissertations
Many situations require the need to quickly and accurately locate dismounted individuals in a variety of environments. In conjunction with other dismount detection techniques, being able to detect and classify clothing (textiles) provides a more comprehensive and complete dismount characterization capability. Because textile classification depends on distinguishing between different material types, hyperspectral data, which consists of several hundred spectral channels sampled from a continuous electromagnetic spectrum, is used as a data source. However, a hyperspectral image generates vast amounts of information and can be computationally intractable to analyze. A primary means to reduce the computational complexity is to use feature …
Effect Of Storm Enhanced Densities On Geo-Location Accuracy Over Conus, Lindon H. Steadman
Effect Of Storm Enhanced Densities On Geo-Location Accuracy Over Conus, Lindon H. Steadman
Theses and Dissertations
Storm enhanced densities (SEDs) are ionospheric plasma enhancements that disrupt radio communications in the near-Earth space environment, degrading the Global Positioning System (GPS) and other key technologies. Accurate GPS/total electron content (TEC) correction maps produced by ionosphere models can mitigate degradations from SEDs. An artificial SED was created and ingested via slant TEC measurements into the Global Assimilation of Ionospheric Measurements Gauss-Markov Kalman Filter Model to determine how many ground GPS receivers are needed to produce reliable GPS/TEC correction maps over the continental United States during geomagnetic storming. It was found that 110 well-positioned GPS receivers produced the best overall …
Modeling Self-Referencing Interferometers With Extended Beacons And Strong Turbulence, Daniel J. Wheeler
Modeling Self-Referencing Interferometers With Extended Beacons And Strong Turbulence, Daniel J. Wheeler
Theses and Dissertations
The overall purpose of this research was to better understand the performance of a self-referencing interferometer (SRI) when used with extended beacons in strong atmospheric turbulence. It was performed by assuming the extended beacon could be modeled as a Gaussian Schell-model beam, then analyzing the effect of propagating this beam through strong atmospheric turbulence. Since the operation of an SRI requires coupling this light into a single-mode optical fiber, analytic expressions of the mean and normalized variance of the coupling efficiency were derived. An improved noise model for the SRI was then developed that included all potential noise sources such …
The Effects Of Rare Earth Doping On Gallium Nitride Thin Films, Stephen R. Mchale
The Effects Of Rare Earth Doping On Gallium Nitride Thin Films, Stephen R. Mchale
Theses and Dissertations
The thermal neutron capture cross section of the rare earth (RE) metal isotope Gd-157 is the largest of all known natural elements, which distinguishes the material as a logical candidate for neutron detection. To address an incomplete understanding of rare earth doped Gallium Nitride (GaN) materials, investigations of the surface electronic structure and interface properties of GaN thin films doped with rare earths (Yb, Er, Gd) were undertaken. Lattice ion occupation, bonding, rare earth 4f occupation, and gold Schottky barrier formation were examined using synchrotron photoemission spectroscopy. Measured Debye temperatures indicate substitutional occupation of Ga sites by RE ions. The …
Source Normalization Constants For Ground Distributed Fallout Fields, Justin M. Smith
Source Normalization Constants For Ground Distributed Fallout Fields, Justin M. Smith
Theses and Dissertations
Five assumptions regarding a first order model developed to calculate dose rate at a detector above a fallout field are analyzed. The omission of scattering is relaxed by the method of successive scatters resulting in a build up factor of 1.1. The use of a single average photon energy to represent a fallout distribution is analyzed using the Oak Ridge National Laboratory Isotope Generator (ORIGEN) Fallout Analysis Tool. An average photon energy of 0.81MeV is calculated and shown to be an accurate approximation of the fallout field energy distribution. A Gaussian distribution is used to calculate the minimal impact of …
Non-Adiabatic Atomic Transitions: Computational Cross Section Calculations Of Alkali Metal-Noble Gas Collisions, Charlton D. Lewis Ii
Non-Adiabatic Atomic Transitions: Computational Cross Section Calculations Of Alkali Metal-Noble Gas Collisions, Charlton D. Lewis Ii
Theses and Dissertations
Diode Pumped Alkali Lasers operate by exciting a gaseous cell of alkali metal to its P3/2 excited energy state. A noble gas, present in the cell, collisionally de-excites the alkali metal to its P1/2 state. The alkali atoms then relax to their S1/2 ground state by emitting photons. The non-radiative de-excitation due to inert gas atoms represents an interesting juncture for DPALs operation. This process must be faster than the radiative relaxation back to the S1/2 state for lasing to occur. The rate of non-radiative de-excitation is related to the collisional cross section and the cross …
Estimating Anthropometric Marker Locations From 3-D Ladar Point Clouds, Matthew J. Maier
Estimating Anthropometric Marker Locations From 3-D Ladar Point Clouds, Matthew J. Maier
Theses and Dissertations
An area of interest for improving the identification portion of the system is in extracting anthropometric markers from a Laser Detection and Ranging (LADAR) point cloud. Analyzing anthropometrics markers is a common means of studying how a human moves and has been shown to provide good results in determining certain demographic information about the subject. This research examines a marker extraction method utilizing principal component analysis (PCA), self-organizing maps (SOM), alpha hulls, and basic anthropometric knowledge. The performance of the extraction algorithm is tested by performing gender classification with the calculated markers.
Optical Flow-Based Odometry For Underground Tunnel Exploration, Terra Kier
Optical Flow-Based Odometry For Underground Tunnel Exploration, Terra Kier
Theses and Dissertations
As military operations in degraded or GPS-denied environments continue to increase in frequency and importance, there is an increased necessity to be able to determine precision location within these environments. Furthermore, authorities are finding a record number of tunnels along the U.S.-Mexico border; therefore, underground tunnel characterization is becoming a high priority for U.S. Homeland Security as well. This thesis investigates the performance of a new image registration technique based on a two camera optical- flow configuration using phase correlation techniques. These techniques differ from other image based navigation methods but present a viable alternative increasing autonomy and answering the …
Context Aided Tracking With Adaptive Hyperspectral Imagery, Andrew C. Rice
Context Aided Tracking With Adaptive Hyperspectral Imagery, Andrew C. Rice
Theses and Dissertations
A methodology for the context-aided tracking of ground vehicles in remote airborne imagery is developed in which a background model is inferred from hyperspectral imagery. The materials comprising the background of a scene are remotely identified and lead to this model. Two model formation processes are developed: a manual method, and method that exploits an emerging adaptive, multiple-object-spectrometer instrument. A semi-automated background modeling approach is shown to arrive at a reasonable background model with minimal operator intervention. A novel, adaptive, and autonomous approach uses a new type of adaptive hyperspectral sensor, and converges to a 66% correct background model in …
Modeling Of Bacillus Spores: Inactivation And Outgrowth, Alexis X. Hurst
Modeling Of Bacillus Spores: Inactivation And Outgrowth, Alexis X. Hurst
Theses and Dissertations
This research models and analyzes the thermochemical damage produced in Bacillus spores by short, high-temperature exposures as well the repair process within damaged Bacillus spores. Thermochemical damage in spores is significantly due to reaction with water, hydrolysis reactions. Applying heat to the spore causes absorbed and chemically bound water molecules become mobile within the spore. These mobile water molecules react by hydrolysis reactions to degrade DNA and enzyme molecules in the spore. In order to survive the thermal inactivation, the spore must repair the damaged DNA during spore germination. The DNA repair process, as well as other germination functions, is …
Radial Distribution Of Absorption In A Cesium Heat Pipe With Axial Laser Heating, Charles D. Fox
Radial Distribution Of Absorption In A Cesium Heat Pipe With Axial Laser Heating, Charles D. Fox
Theses and Dissertations
Diode Pumped Alkali Lasers (DPAL) have been scaled to greater than 100 W and exhibit slope efficiencies exceeding 80%, offering application for tactical laser weapons. The hybrid DPAL system combines efficient diode pumping with the good beam quality and thermal characteristics of gas lasers. Thermal effects on alkali concentration have been observed to degrade performance, while low speed flowing systems are in development. However, spatial gradients in temperature and concentrations have not previously been observed. In the present work, a 0.8 W/cm2 pump laser at the D1 frequency heats the medium in a T=50-100 °C cesium heat pipe …
Broadband Pumping Effects On The Diode Pumped Alkali Laser, Paul Nathaniel Jones
Broadband Pumping Effects On The Diode Pumped Alkali Laser, Paul Nathaniel Jones
Theses and Dissertations
This research seeks to gain greater insight on the mechanics of The Diode Pumped Alkali Laser through analytic modeling techniques. This work is an extension to a previous model developed by Dr. Gordon Hager, and focuses on the addition of pump-beam bandwidth. Specifically, it seeks to determine the effect that broadband pumping has on laser performance. The model incorporates all the fundamental parameters within the laser system, including alkali concentrations, collision partner concentrations, pump bandwidth, length and temperature of gain medium, transmission, and reflectivity. Baseline operating conditions set Rubidium (Rb) concentrations ranging from 1012 - 1014 atoms/cm3 …
Improving The Efficiency Of Photon Collection By Compton Rescue, Alexander W. Stevenson
Improving The Efficiency Of Photon Collection By Compton Rescue, Alexander W. Stevenson
Theses and Dissertations
A method to improve the efficiency of photon collection in thin planar HPGe detectors was investigated. The method involved implementing a second HPGe detector to collect Compton scattered photons from the primary detector and incorporating coincident interactions in the two detectors that sum to the full energy event into the energy spectrum. This method is termed Compton rescue because the Compton scattered photons make a partial energy deposition in the primary detector and are added back to the spectrum after being detected by the second detector. This research has implications on improving the efficiency of positron annihilation spectroscopy (PAS) techniques …
Diffusion Of Rubidium Vapor Through Hollow-Core Fibers For Gas-Phase Fiber Lasers, Eric M. Guild
Diffusion Of Rubidium Vapor Through Hollow-Core Fibers For Gas-Phase Fiber Lasers, Eric M. Guild
Theses and Dissertations
This work examines the diffusion of rubidium through a small diameter tube alone and in the presence of noble gases. A fluid dynamics analysis is investigated to aid in choosing a method for transferring atomic rubidium vapor that is reliable and efficient. Solutions to the time dependant ordinary differential equation describing the experimental flow properties of the system reveal more precise outcomes than previously practiced routines. Resolved viscosities and Poiseuille flow theory velocity profile distributions are characterized for noble gas carriers of the rubidium vapor. Applying Reynolds Numbers to the flow experiments provides pressure differential boundaries that are employed in …
Passive Ranging Of Dynamic Rocket Plumes Using Infrared And Visible Oxygen Attenuation, Robert Anthony Vincent
Passive Ranging Of Dynamic Rocket Plumes Using Infrared And Visible Oxygen Attenuation, Robert Anthony Vincent
Theses and Dissertations
Atmospheric oxygen absorption bands in observed spectra of boost phase missiles can be used to accurately estimate range from sensor to target. This work compares two oxygen absorption bands in the near-infrared (NIR) and visible (Vis) spectrum, centered at 762nm and 690 nm, to passively determine range. Spectra were observed from static tests of both surface-to-air missile simulators at 405m range and a full-scale solid rocket motor at 900m range. The NIR O2 band provided range estimates accurate to within 3% for both tests, while the Vis O2 band had range errors of 77% and 15 %, respectively. …
A Statistical Approach To Fusing 2-D And 3-D Ladar Systems, Paul F. Dolce
A Statistical Approach To Fusing 2-D And 3-D Ladar Systems, Paul F. Dolce
Theses and Dissertations
LADAR (LAser Detection and Ranging) systems can be used to provide 2-D and 3-D images of scenes. Generally, 2-D images possess superior spatial resolution but without range data due to the density of their focal plane arrays. A 3-D LADAR system can produce range to target data at each pixel, but lacks the 2-D system's superior spatial resolution. The 3-D system is limited by its hardware, specifically its imaging array. Currently developers are investigating ways to change the pixel size in the 3-D LADAR imaging array, but the costs of this research is quite expensive and technically robust. It is …
Shack-Hartmann And Interferometric Hybrid Wavefront Sensor, Troy R. Ellis
Shack-Hartmann And Interferometric Hybrid Wavefront Sensor, Troy R. Ellis
Theses and Dissertations
This document reports results of wave-optics simulations used to test the performance of a hybrid wavefront sensor designed to combine the self-referencing interferometer and Shack-Hartmann wavefront sensors in an optimal way. Optimal hybrid-wavefront sensor design required a thorough analysis of the noise characteristics of each wavefront sensor to produce noise models that assist in the design of an optimal phase-estimation algorithm. Feasible architectures and algorithms for combining wavefront sensors were chosen, and the noise models of the individual wavefront sensors were combined to form a model for the noise-induced error of the resulting hybrid sensor. The hybrid wavefront sensor and …
A Multispectral Bidirectional Reflectance Distribution Function Study Of Human Skin For Improved Dismount Detection, Bradley M. Koch
A Multispectral Bidirectional Reflectance Distribution Function Study Of Human Skin For Improved Dismount Detection, Bradley M. Koch
Theses and Dissertations
In 2008, the Sensors Exploitation Research Group at the Air Force Institute of Technology began using spectral properties of skin for the detection and classification of humans. Since then a multispectral skin detection system was developed to exploit the optical properties of human skin at wavelengths in the visible and near infrared region of the electromagnetic spectrum. A rules-based detector, analyzing an image spectrally, currently bases its skin pixel selection criteria on a diffuse skin reflectance model. However, when observing skin in direct view of the sun, a glint of light off skin is common and indicates specularity. The areas …
Optical Metamaterial Design, Fabrication And Test, Jack P. Lombardi
Optical Metamaterial Design, Fabrication And Test, Jack P. Lombardi
Theses and Dissertations
Metamaterials, materials that make use of naturally occurring materials and designed structures to create materials with special properties not found in nature, are a fascinating new area of research, combining the fields of physics, microfabrication, and material science. This work will focus on the development of metamaterials operating in the visible and infrared which will be constructed and tested for basic optical properties. Possible applications for these materials will not be investigated. The this work will go into the fabrication and test of layered metal-dielectric structures, called layered metamaterials, as these structures hold potential for applications in advanced optical systems. …
Background And Source Term Identification In Active Neutron Interrogation Methods, David A. Anthony
Background And Source Term Identification In Active Neutron Interrogation Methods, David A. Anthony
Theses and Dissertations
The detection and tracking of special nuclear material (SNM) is vitally important in order to know where these materials are and prevent them from being used in a harmful manner. Active neutron interrogation is a sought after method for this since the resulting high energy gamma rays produced by inelastic scattering and neutron capture reactions can pass through denser shielding than natural decay gammas, and their energy spectra are unique to each isotope. Using Monte Carlo N Particle (MCNP) simulations, this research investigated the characterization of gamma ray sources created by active neutron interrogation. Ring detector and mesh tallies within …
Combined Effects Of Radio Frequency And Electron Radiation On Cmos Inverters, Kristofer R. Dahl
Combined Effects Of Radio Frequency And Electron Radiation On Cmos Inverters, Kristofer R. Dahl
Theses and Dissertations
This research examines the measurement methodology, and the results of, the combined effects of electron and radio frequency irradiation (500kHz) on a CMOS Hex Inverter, CD4069UB. There have been many studies in recent years on the effects of electron radiation and electromagnetic interference on integrated circuits, however the combined effects have not been measured. A major obstacle for in-situ electron irradiation experiments is the over current hazard that exists to measurement equipment that comes from taking real-time, in-situ measurements. To overcome this, a test circuit was designed and built to allow for real-time in-situ measurement of the output voltage, current …
Cathodoluminescence And Photoemission Of Doped Lithium Tetraborate, Christina L. Dugan
Cathodoluminescence And Photoemission Of Doped Lithium Tetraborate, Christina L. Dugan
Theses and Dissertations
Lithium tetraborate (Li2B4O7) crystals are being developed for possible use in solid state neutron detectors. The 6Li(n,α)3H and 10B(n,α)7Li reactions are the basis for neutron detection, and a Li2B4O7 crystal enriched with Mn should show improved efficiency for neutron detection. There is a lack of fundamental characterization information regarding this useful material, particularly with regard to its electronic configuration. Photoemission spectroscopy was used to determine the energy level structure of the Mn doped Li2B4O7 crystals. …
Changes To Electrical Conductivity In Irradiated Carbon Nanocomposites, Nickolas A. Duncan
Changes To Electrical Conductivity In Irradiated Carbon Nanocomposites, Nickolas A. Duncan
Theses and Dissertations
Carbon nanotubes (CNT) and carbon nanofibers (CNF) are two nanoparticles incorporated in a polymer to create a composite material. These composites are two potential lightweight materials for use as replacements for aluminum structures on satellite systems. Both composite materials have a low resistivity that is consistent with conductive materials. However, the CNT composite is substantially more conductive than the CNF composite. The CNT and CNF composites were irradiated with electrons and neutrons to fluence levels of and. No changes were observed in the resistivity of the CNF composites following neutron and electron irradiation. A 3.7% increase in resistivity was observed …
Ray Next Event Estimator Transport Of Primary And Secondary Gamma Rays, Whitman T. Dailey
Ray Next Event Estimator Transport Of Primary And Secondary Gamma Rays, Whitman T. Dailey
Theses and Dissertations
This thesis investigated the application of the ray next event estimation Monte Carlo method to the transport of primary and secondary gamma rays. The problem of interest was estimation of the free field flux at a distant point in a vacuum from a point source in the atmosphere. An existing Fortran code for neutron transport, Ray Next-Event Estimator v4.0, was adapted to perform photon transport computations including coherent scattering, incoherent scattering, photoelectric absorption, and pair production interactions. Production and transport of secondary gamma rays produced in bremsstrahlung, neutron inelastic scatter, and neutron absorption interactions was also implemented. A new version …
Radiation Effects On The Electrical Properties Of Hafnium Oxide Based Mos Capacitors, Jesse C. Foster
Radiation Effects On The Electrical Properties Of Hafnium Oxide Based Mos Capacitors, Jesse C. Foster
Theses and Dissertations
Hafnium oxide-based MOS capacitors were investigated to determine electrical property response to radiation environments. In situ capacitance versus voltage measurements were analyzed to identify voltage shifting as a result of changes to trapped charge with increasing dose of gamma, neutron, and ion radiation. In situ measurements required investigation and optimization of capacitor fabrication to include dicing, cleaning, metalization, packaging, and wire bonding. A top metal contact of 200 angstroms of titanium followed by 2800 angstroms of gold allowed for repeatable wire bonding and proper electrical response. Gamma and ion irradiations of atomic layer deposited hafnium oxide on silicon devices both …