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Full-Text Articles in Physics

Computationally Modeling The Effects Of Surface Roughness On Soft X-Ray Multilayer Reflectors, Jedediah Edward Jensen Johnson Dec 2006

Computationally Modeling The Effects Of Surface Roughness On Soft X-Ray Multilayer Reflectors, Jedediah Edward Jensen Johnson

Theses and Dissertations

Electromagnetic scattering from a rough two dimensional homogeneous scatterer has been computationally modeled. The scatterer is intended to simulate reflection from a two interface multilayer. The rough scatterer was created from Gaussian random points centered about an ideal interface. The points were connected with a third order spline interpolant which accounts for correlation between neighboring surface atoms. The scalar electric field integral equation (EFIE) and magnetic field integral equation (MFIE) were solved using the Nystrom method to obtain the reflected intensity as a function of observation angle. Verification of the accuracy of the code was obtained by means of comparison …


A New Application Of The Channel Packet Method For Low Energy 1-D Elastic Scattering, Clint M. Zeringue Sep 2006

A New Application Of The Channel Packet Method For Low Energy 1-D Elastic Scattering, Clint M. Zeringue

Theses and Dissertations

An algorithm is presented which uses the channel packet method (CPM) to simulate low-energy, wave-packet propagation and compute S-matrix elements. A four-by-four matrix containing the momentum, expansion coefficients of the reactants and products is introduced to account for initial and final states having both positive and negative momentum. The approach does not consider scattering from one side or the other, rather it considers both incoming and outgoing wave packets from the left and right simultaneously. Therefore, during one simulation all four S-matrix elements, and elements, S+k,-K, S-k, +k, S+k, +k and S-k,-k are computed. …


Fast Scene Based Nonuniformity Correction With Minimal Temporal Latency, Christopher A. Rice Sep 2006

Fast Scene Based Nonuniformity Correction With Minimal Temporal Latency, Christopher A. Rice

Theses and Dissertations

The focus of this research was to derive a new algorithm for correction of gain nonuniformities in LIDAR focal plane arrays using as few frames as possible. Because of the current low production rate of LIDAR focal plane arrays there is a natural tendency for extreme nonuniformities to exist on a pixel by pixel basis as the manufacturing technique has not yet been perfected. Generally, nonuniformity correction techniques require a large number of frames and/or have obscure requirements on the translational shifts in the input image frames. This thesis presents a solution for finding multiplicative nonuniformities that exist in a …


Sound Absorption And Sound Power Measurements In Reverberation Chambers Using Energy Density Methods, David B. Nutter Aug 2006

Sound Absorption And Sound Power Measurements In Reverberation Chambers Using Energy Density Methods, David B. Nutter

Theses and Dissertations

Measurements in a reverberation chamber use spatially averaged squared pressure to calculate sound absorption, sound power, and other sound measurements. While a reverberation chamber provides an approximation of a diffuse sound field, variations in the measurements introduce uncertainty in measurement results. Room qualification procedures require a sufficient number of source-receiver locations to obtain suitable measurements. The total acoustic energy density provides greater spatial uniformity than squared pressure, which requires fewer source-receiver positions to produce similar or better accuracy in measurement results. This paper explores the possibility of using energy density in place of squared pressure, using methods outlined in current …


Feedback Applications In Active Noise Control For Small Axial Cooling Fans, Matthew J. Green Aug 2006

Feedback Applications In Active Noise Control For Small Axial Cooling Fans, Matthew J. Green

Theses and Dissertations

Feedback active noise control (ANC) has been applied as a means of attenuating broadband noise from a small axial cooling fan. Such fans are used to maintain thermal stability inside of computers, projectors, and other office equipment and home appliances. The type of low-level noise radiated from axial cooling fans has been classified as harmful to productivity and human well being. Previous research has successfully implemented feed-forward ANC, targeting specific narrow-band fan noise content related to the blade passage frequency (BPF) of the fan. The reference signal required for a feed-forward algorithm limits its ability to attenuate much of the …


Optimization Of Active Noise Control For Small Axial Cooling Fans, Brian B. Monson Jul 2006

Optimization Of Active Noise Control For Small Axial Cooling Fans, Brian B. Monson

Theses and Dissertations

Previous work has shown that active noise control is a feasible solution to attenuate tonal noise radiated by small axial cooling fans, such as those found in desktop computers. One such control system reduced noise levels of a baffled 80-mm fan in the free field with four small loudspeakers surrounding the fan. Due to industry specified spatial constraints, a smaller fan and speaker configuration was desirable. The smaller configuration maintains similar control performance, further facilitating practical implementation of the control system. The smaller control system employs a smaller fan running at a higher speed. Different loudspeaker configurations for control exist …


A Search For Low-Amplitude Variability Among Population I Main Sequence Stars, Michael Benjamin Rose Jul 2006

A Search For Low-Amplitude Variability Among Population I Main Sequence Stars, Michael Benjamin Rose

Theses and Dissertations

The detection of variable stars in open clusters is an essential component of testing stellar structure and evolution theories. The ability to detect low-amplitude variability among cluster members is directly related to the quality of the photometric results. Point Spread Function (PSF) fitting is the best method available for measuring accurate magnitudes within crowded fields of stars, while high-precision differential photometry is the preferred technique for removing the effects of atmospheric extinction and variable seeing. In the search for new variable stars among hundreds or thousands of stars, the Robust Median Statistic (RoMS) is proven more effective for finding low-amplitude …


Mechanisms Of The Wurtzite To Rock Salt Phase Transitions In Galium Nitride, Jesse Z. Gunter Jun 2006

Mechanisms Of The Wurtzite To Rock Salt Phase Transitions In Galium Nitride, Jesse Z. Gunter

Theses and Dissertations

We studied the wurtzite to rock salt phase transition in gallium nitride ( GaN ). Using the mapping algorithm of COMSUBS we found 435 possible mechanisms for this transition. We then used FIREBALL to do density functional theory calculations and found enthalpy barrier heights for the transition pathway. We used this to determine the mechanisms that are the most favorable for GaN. The most favorable mechanisms for GaN are those that break no bonds during the phase transition. The bond-preserving mechanisms involve bilayer sliding of (010) hexagonal plane in the plus or minus [100] hexagonal direction.


An Analysis Of Nonlinear Elastic Deformations For A Homogeneous Beam At Varying Tip Loads And Pitch Angles, Robert J. Mcgraw Jun 2006

An Analysis Of Nonlinear Elastic Deformations For A Homogeneous Beam At Varying Tip Loads And Pitch Angles, Robert J. Mcgraw

Theses and Dissertations

The Princeton beam experiments of 1975 were performed in hopes of producing viable data for beam nonlinear elastic deformation models in hopes of improving helicopter main beam designs. The recorded data, specifically for homogeneous beams of 7075 aluminum, have been referenced as a baseline for the past thirty years to validate numerous computer models and theories in an effort to build beams capable of withstanding aeroelastic, static, and dynamic loading. The purpose of this study is to improve upon the data recorded in 1975 using newer technologies including a laser distance meter, digital inclinometer, and three-dimensional traverse to test X-axis, …


Characterizing A Co-Flow Nozzle For Use In A Filtered Rayleigh Scattering System, David S. Miceli Jun 2006

Characterizing A Co-Flow Nozzle For Use In A Filtered Rayleigh Scattering System, David S. Miceli

Theses and Dissertations

Research was conducted on the flow field exiting a co-annular flow nozzle for use in filtered Rayleigh scattering flow visualizations. More specifically, the flow visualizations were of the flow field exiting a coflow nozzle and illuminated by a tunable, nominal 4.2 watt narrow line width Argon laser operating at 514.5nm. ND:YAG lasers are typically used in this application, but some of the properties of a tunable Argon laser make it an attractive alternative. Before generating flow visualizations, the coflow nozzle was characterized both experimentally and computationally. Due to a flow asymmetry in the outer annulus flow field, the nozzle was …


An Experimental Study Of A Pulsed Dc Plasma Flow Control Actuator, Jennifer D. Wall Jun 2006

An Experimental Study Of A Pulsed Dc Plasma Flow Control Actuator, Jennifer D. Wall

Theses and Dissertations

An experiment on the effects of a pulsed DC plasma actuator on a separated flow in a low speed wind tunnel was conducted. The actuator consisted of two asymmetric copper electrodes oriented normal to the flow separated by a dielectric barrier and mounted on a flat plate in the center of the tunnel. A contoured insert was constructed and used to create an adverse pressure gradient in the test section comparable to a Pak-B low pressure turbine blade distribution. Suction was applied from the upper wall to induce separation along the flat plate over the electrodes. The DC power supply …


Development And Comparison Of Highly Directional Loudspeakers, Gordon Robert Dix May 2006

Development And Comparison Of Highly Directional Loudspeakers, Gordon Robert Dix

Theses and Dissertations

Highly directive loudspeakers have long been important tools for sound system designers, experimental acousticians, and many other professionals in the audio industry. They allow sound engineers to more easily manipulate the radiation pattern of their loudspeakers to accommodate the purpose of the venue. Many commercially available products, while exhibiting good directivity at mid and high frequencies, generally lack control in the low frequency range. A new method for controlling the radiation pattern of a loudspeaker at low frequencies has been developed and modeled extensively. Prototypes have been built and tested in an anechoic chamber. Results from computer modeling and experimental …


Direct Observation Of Laser Filamentation In High-Order Harmonic Generation, John Charles Painter May 2006

Direct Observation Of Laser Filamentation In High-Order Harmonic Generation, John Charles Painter

Theses and Dissertations

We investigate the spatial evolution of an intense laser pulse as it generates high-order harmonics in a long gas cell, filled with 80 torr of helium. A thin foil separates the gas-filled region of the cell from a subsequent evacuated region. The exit plane of the gas cell can be scanned along the laser axis so that the evolution of the laser throughout the focus can be observed (full scanning range of 9 cm). We constructed an apparatus that images the laser radial energy profile as it exits the cell. The high harmonics, odd orders ranging from 45 to 91, …


Performance-Metric Driven Atmospheric Compensation For Robust Free-Space Laser Communication, Peter N. Crabtree Apr 2006

Performance-Metric Driven Atmospheric Compensation For Robust Free-Space Laser Communication, Peter N. Crabtree

Theses and Dissertations

The effect of turbulence on laser propagation is a significant challenge to current electro-optical systems. While atmospheric compensation techniques in space object imaging and high-energy laser weapons have been thoroughly investigated, optimizing these techniques for Laser Communication (LaserCom) has not been examined to the same degree. Average Strehl ratio is the typical design metric for current atmospheric compensation systems. However, fade probability is the relevant metric for LaserCom. This difference motivated the investigation into metric-driven atmospheric compensation. Metric-based tracking techniques for fade mitigation is the first major focus of this research. In a moderate range air-to-air scenario, focal plane spot …


Backward Amplification And Beam Cleanup Of A Raman Fiber Laser Oscillator Using A Multi-Mode Graded Index Fiber Amplifier, Jesse D. S. Morgan Iii Mar 2006

Backward Amplification And Beam Cleanup Of A Raman Fiber Laser Oscillator Using A Multi-Mode Graded Index Fiber Amplifier, Jesse D. S. Morgan Iii

Theses and Dissertations

This thesis tested a CW fiber-based Raman amplifier implemented in a backward pumped geometry. To create a seed for the amplifier, a CW Nd:YAG laser operating at 1.064µm was used to pump a 50µm multimode graded index fiber using fiber Bragg gratings to create a Raman Fiber Laser (RFL) Oscillator with a Stokes beam at 1.116µm. The Stokes beam was then used to seed two lengths, 5.3km and 2.5km, of 50µm multimode graded index fiber. The fiber amplifier was pumped by a second CW Nd:YAG laser in the backward geometry. Spectral data taken for both fibers indicated that the backward …


Assessing The Potential For Improved Scramjet Performance Through Application Of Electromagnetic Flow Control, Martin F. Lindsey Mar 2006

Assessing The Potential For Improved Scramjet Performance Through Application Of Electromagnetic Flow Control, Martin F. Lindsey

Theses and Dissertations

Hypersonic flight using scramjet propulsion bridges the gap between turbojets and rockets. Recent efforts focus on magnetogasdynamic (MGD) flow control to mitigate the problems of high thermomechanical loads and low efficiencies associated with scramjets. This research is the first flight-scale, three-dimensional computational analysis of a realistic scramjet to assess how MGD flow control improves scramjet performance. Developing a quasi-one dimensional design tool culminated in the first open source scramjet geometry. This geometry was tested with the Air Force Research Laboratory's electromagnetic computational code. To increase fidelity, an algorithm was developed to incorporate thermochemistry, resulting in the only open-source model of …


The Violation Of Bell's Inequality In A Deterministic But Nonlocal Model, Stephanie Allred Magleby Mar 2006

The Violation Of Bell's Inequality In A Deterministic But Nonlocal Model, Stephanie Allred Magleby

Theses and Dissertations

This thesis investigates the violation of Bell's Inequality through the use of nonlocal measurement schemes as encapsulated in a quasi-deterministic toy model. This toy model, called the Q Box, is reminiscent of Mermin's Box in that it describes a system that appears to be deterministic yet produces the statistics of a quantum type system. [1] The workings of the Q Box are detailed both as a thought experiment and as a computer simulation. Nonlocal measurement protocols similar to those which generate a violation of Bell's Inequality in the Q Box are also applied to Mermin's Box, with comparable results. [1] …


Development Of A Three-Dimensional Air Blast Propagation Model Based Upon The Weighted Average Flux Method, Stephen R. Mchale Mar 2006

Development Of A Three-Dimensional Air Blast Propagation Model Based Upon The Weighted Average Flux Method, Stephen R. Mchale

Theses and Dissertations

Accurate numerical modeling of complex, multi-dimensional shock propagation is needed for many Department of Defense applications. A three-dimensional code, based upon E.F. Toro's weighted average flux (WAF) method has been developed, tested, and validated. Code development begins with the introduction and application of all techniques in a single dimension. First-order accuracy is achieved via Godunov's scheme using an exact Riemann solver. Adaptive techniques, which employ approximate solutions, are implemented to improve computational efficiency. The WAF method produces second-order accurate solutions, but introduces spurious oscillations near shocks and contact discontinuities. Total variation diminishing (TVD) flux and weight limiting schemes are added …


Comparison Of Climatological Optical Turbulence Profiles To Standard, Statistical And Numerical Models Using Heleeos, Liesebet E. Gravley Mar 2006

Comparison Of Climatological Optical Turbulence Profiles To Standard, Statistical And Numerical Models Using Heleeos, Liesebet E. Gravley

Theses and Dissertations

Optical turbulence within earth’s atmosphere plays a significant role in electromagnetic radiation propagation from a high energy laser. The index of refraction structure constant, Cn2, characterizes turbulent spatial fluctuations due to temperature gradients. These changes in the index of refraction affect the intensity of the laser wave front on its intended target. It is important to characterize this parameter throughout the atmosphere, the boundary layer and above, for its applications regarding the Airborne Laser (ABL) and the Advanced Tactical Laser (ATL). There are several ways to obtain values of optical turbulence, including standard and statistical models, physically-based numerical models, and …


Efficient And Accurate Computation Of Elastic Cross Sections In The Single-Level Breit-Wigner Resonance Region, Edward L. Hobbs Mar 2006

Efficient And Accurate Computation Of Elastic Cross Sections In The Single-Level Breit-Wigner Resonance Region, Edward L. Hobbs

Theses and Dissertations

The use of piecewise cubic Hermite polynomials to approximate resonance region cross sections provides a means to accomplish the same task with increased accuracy and fewer points that require exact cross section calculation. Once the derivative of the cross section formula is derived and the interpolating cubic is appropriately shifted and scaled for numerical stability, use of the piecewise cubic Hermite polynomial is easily inserted into computer codes that depend on cross section calculation in the resonance energy region.


Radiometric Analysis Of Daytime Satellite Detection, Katherine B. Lilevjen Mar 2006

Radiometric Analysis Of Daytime Satellite Detection, Katherine B. Lilevjen

Theses and Dissertations

A radiometric model for daylight satellite detection is developed and used to evaluate the effects of various parameters on signal-to-noise ratio (SNR). Detection of reflected sunlight from a low-earth orbit, diffuse, planar satellite by a single-pixel infrared photovoltaic detector is considered. Noise considered includes photon noise from the background and signal, as well as thermal noise. Parameters considered include atmospheric conditions, optical parameters, and detector parameters. The Phillips Laboratory Expert-assisted User System, an atmospheric modeling tool that employs the MODTRAN and FASCODE transmission codes, is used to model wavelength-dependent atmospheric transmission and background radiance. The SNR is found to increase …


Type Ii Quantum Computing Algorithm For Computational Fluid Dynamics, James A. Scoville Mar 2006

Type Ii Quantum Computing Algorithm For Computational Fluid Dynamics, James A. Scoville

Theses and Dissertations

An algorithm is presented to simulate fluid dynamics on a three qubit type II quantum computer: a lattice of small quantum computers that communicate classical information. The algorithm presented is called a three qubit factorized quantum lattice gas algorithm. It is modeled after classical lattice gas algorithms which move virtual particles along an imaginary lattice and change the particles’ momentums using collision rules when they meet at a lattice node. Instead of moving particles, the quantum algorithm presented here moves probabilities, which interact via a unitary collision operator. Probabilities are determined using ensemble measurement and are moved with classical communications …


A Study Of Collapse Events In Ultraviolet Light Filaments Due To Transient Edge Effects, Paul L. Muller Mar 2006

A Study Of Collapse Events In Ultraviolet Light Filaments Due To Transient Edge Effects, Paul L. Muller

Theses and Dissertations

Intense, short light pulses can form filaments capable of propagating kilometers through the atmosphere. This is due to the nonlinear index of refraction of the atmosphere in response to the pulse's high intensity, which creates a self-focusing effect that further intensifies the pulse. This focusing is balanced by the formation of defocusing plasma by the pulse. A split-step propagation model was used to simulate the propagation of these pulses through the atmosphere and investigate the collapse of long ultraviolet pulses of 10-100 picoseconds in duration due to transient edge effects. The structures of individual collapse events in the pulse were …


Development Of A Multiple Beam Combiner Using Stimulated Raman Scattering In Multimode Fiber, Brian M. Flusche Mar 2006

Development Of A Multiple Beam Combiner Using Stimulated Raman Scattering In Multimode Fiber, Brian M. Flusche

Theses and Dissertations

Beam combination was demonstrated by splitting the beam from a diode pumped Q-switched Nd:YAG laser and pumping a multiple input, single output fiber squid. Beam cleanup of the resulting output beam using stimulated Raman scattering was then demonstrated in both 100 μm fiber (Stokes M2 = 1.86) and 200 μm fiber (Stokes M2 = 1.40). The performance of the 200 μm fiber was compared to that of the 100 μm fiber. Energy conversion efficiency into the Stokes beam was measured as a function of input energy and found to be limited by the attenuation characteristics of the fiber. …


Shockwave Interactions With Argon Glow Discharges, Nicholas S. Siefert Mar 2006

Shockwave Interactions With Argon Glow Discharges, Nicholas S. Siefert

Theses and Dissertations

The purpose of this research was study shock wave interactions with argon glow discharges. Specifically, this thesis sought to answer whether it is possible to compress nonequilibrium electrons at the shock wave. The results in the thesis found that both equilibrium and nonequilibrium electrons could be compressed at the shock front. The double layer at the shock front, normalized by electron temperature, matched the calculated values for the double layer within a factor or two in all cases. The results also demonstrate that excited metastable states can be compressed at the shock front, as well. The culmination of this effort …


Passive Multiple Beam Combination In Optical Fibers Via Stimulated Brillouin Scattering, Kirk C. Brown Mar 2006

Passive Multiple Beam Combination In Optical Fibers Via Stimulated Brillouin Scattering, Kirk C. Brown

Theses and Dissertations

Many active methods of scaling laser brightness have been demonstrated in recent years. The goal of this research was to demonstrate the feasibility of passively combining multiple laser beams using Stimulated Brillouin Scattering (SBS) in a long multimode optical fiber. This method of combination employed a “Gatling gun” fiber array that allowed several collimated beams to be focused by a lens into an optical fiber. The retroreflected Stokes beam is passed through the center of the beam combiner for analysis. In addition to experimental methodology and equipment used, the theoretical and historical background of SBS in optical fibers is provided. …


Singlet Delta Oxygen: A Quantitative Analysis Using Off-Axis Integrated-Cavity-Output-Spectroscopy (Icos), Jeffrey E. Gallagher Mar 2006

Singlet Delta Oxygen: A Quantitative Analysis Using Off-Axis Integrated-Cavity-Output-Spectroscopy (Icos), Jeffrey E. Gallagher

Theses and Dissertations

A new spectroscopic technique applicable to the detection of ultra-weak and for- bidden molecular transitions is presented. The method is based on off-axis integrated-cavity-output spectroscopy (ICOS). The primary goal for this research effort is to utilize the ICOS technique and demonstrate its ability to provide quantitative data of singlet delta oxygen. This thesis will focus on three areas of characterization to achieve this goal. First, the absolute line positions will be determined and compared to values derived from the most recent theory. Second, the integrated absorption cross-sections will be verified using Boltzmann analysis. Finally, pressure broadening coefficients will be determined …


Reproducibility Distinguishability And Correlation Of Fireball And Shockwave Dynamics In Explosive Munitions Detonations, Bryan J. Steward Mar 2006

Reproducibility Distinguishability And Correlation Of Fireball And Shockwave Dynamics In Explosive Munitions Detonations, Bryan J. Steward

Theses and Dissertations

The classification of battlespace detonations, specifically the determination of munitions type and size using temporal and spectral features of infrared emissions, is a particularly challenging problem. The intense infrared radiation produced by the detonation of high explosives is largely unstudied. Furthermore, the time-varying fireball imagery and spectra are driven by many factors including the type, size and age of the chemical explosive, method of detonation, interaction with the environment, and the casing used to enclose the explosive. To distinguish between conventional military munitions and improvised or enhanced explosives, the current study investigates fireball expansion dynamics using high speed, multi-band imagery. …


Prediction Of The Temporal Evolution Of Solar X-Ray Flares, Aaron J. Williams Mar 2006

Prediction Of The Temporal Evolution Of Solar X-Ray Flares, Aaron J. Williams

Theses and Dissertations

A solar flare is an explosive release of stored magnetic energy on the Sun. Much of this energy is converted into x-ray photons which escape into space. As a solar flare begins, the 1-8 Å x-ray photon flux at Earth’s orbit, as measured by the GOES satellite, rapidly increases. It quickly reaches a peak and slowly decays. A plot of this flux exhibits an approximate lognormal shape. A lognormal function becomes a normal, symmetric, function when the logarithm of the independent variable is taken. Once the peak flux is reached, this symmetry is used to make a prediction of the …


Spatially-Resolved Temperature Diagnostic For Supersonic Flow Using Cross-Beam Doppler-Limited Laser Saturation Spectroscopy, Grady T. Phillips Mar 2006

Spatially-Resolved Temperature Diagnostic For Supersonic Flow Using Cross-Beam Doppler-Limited Laser Saturation Spectroscopy, Grady T. Phillips

Theses and Dissertations

Optical techniques for measuring the temperature in three-dimensional supersonic reactive flows have typically depended on lineshape measurements using single-beam laser absorption spectroscopy. However, absorption over extended path lengths in flows with symmetric, turbulent eddies can lead to systematically high extracted temperatures due to Doppler shifts resulting from flow along the absorption path. To eliminate these problems, Cross-Beam Saturation Absorption Spectroscopy (CBSAS) and Cross-Beam Inter-Modulated Fluorescence (CBIMF) have been developed which utilize two crossed and nearly copropogating laser beams.to record the spectral signal of an I2 ro-vibrational line in a small three-dimensional volume using a tunable CW dye laser. Temperature …