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Theses and Dissertations

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Articles 6511 - 6540 of 8341

Full-Text Articles in Physical Sciences and Mathematics

Toward The Static Detection Of Deadlock In Java Software, Jose E. Fadul Mar 2006

Toward The Static Detection Of Deadlock In Java Software, Jose E. Fadul

Theses and Dissertations

Concurrency is the source of many real-world software reliability and security problems. Concurrency defects are difficult to detect because they defy conventional software testing techniques due to their non-local and non-deterministic nature. We focus on one important aspect of this problem: static detection of the possibility of deadlock - a situation in which two or more processes are prevented from continuing while each waits for resources to be freed by the continuation of the other. This thesis proposes a flow-insensitive interprocedural static analysis that detects the possibility that a program can deadlock at runtime. Our analysis proceeds in two steps. …

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Optimization Of A Multi-Echelon Repair System Via Generalized Pattern Search With Ranking And Selection: A Computational Study, Derek D. Tharaldson Mar 2006

Optimization Of A Multi-Echelon Repair System Via Generalized Pattern Search With Ranking And Selection: A Computational Study, Derek D. Tharaldson

Theses and Dissertations

With increasing developments in computer technology and available software, simulation is becoming a widely used tool to model, analyze, and improve a real world system or process. However, simulation in itself is not an optimization approach. Common optimization procedures require either an explicit mathematical formulation or numerous function evaluations at improving iterative points. Mathematical formulation is generally impossible for problems where simulation is relevant, which are characteristically the types of problems that arise in practical applications. Further complicating matters is the variability in the simulation response which can cause problems in iterative techniques using the simulation model as a function …

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Flashlight: A Dynamic Detector Of Shared State, Race Conditions, And Locking Models In Concurrent Java Programs, Scott C. Hale Mar 2006

Flashlight: A Dynamic Detector Of Shared State, Race Conditions, And Locking Models In Concurrent Java Programs, Scott C. Hale

Theses and Dissertations

Concurrent Java programs are difficult to understand and implement correctly. This difficultly leads to code faults that are the source of many real-world reliability and security problems. Many factors contribute to concurrency faults in Java code; for example, programmers may not understand Java language semantics or, when using a Java library or framework, may not understand that their resulting program is concurrent. This thesis describes a dynamic analysis tool, named FlashLight, that detects shared state and possible race conditions within a program. FlashLight illuminates the concurrency within a program for programmers who are wholly or partially "in the dark" about …

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Evolving Self-Organized Behavior For Homogeneous And Heterogeneous Uav Or Ucav Swarms, Ian C. Price Mar 2006

Evolving Self-Organized Behavior For Homogeneous And Heterogeneous Uav Or Ucav Swarms, Ian C. Price

Theses and Dissertations

This investigation uses a self-organization (SO) approach to enable cooperative search and destruction of retaliating targets with swarms of homogeneous and heterogeneous unmanned aerial vehicles (UAVs). To facilitate specific system design, a facilitating SO algebraic framework is created that emphasizes scalability, robustness, and flexibility. This framework is then used to implement a UAV behavior architecture relying upon rules governing formation and target interaction. Sets of applicable behaviors are created by weighted summation of the rules where different weights act as distinct behavior archetypes. Appropriate behavior archetypes are based upon sense information distilled from the environment and a simple perceptron mapping. …

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A Real-Time Wireless Sensor Media Access Control (Mac) Protocol, Barry W. Park Mar 2006

A Real-Time Wireless Sensor Media Access Control (Mac) Protocol, Barry W. Park

Theses and Dissertations

Wireless sensor networks are rapidly becoming a platform for applications such as battlefield monitoring, intelligence gathering, environmental monitoring, and emergency response. Inherent in these applications is a priority and urgency of the information or messages. This means the messages must be delivered in a timely manner for them to be useful. This research assigns a message priority level and provides high-priority messages quicker access to the channel. Using MICA2 sensors and a modified Media Access Control (MAC) layer, real-time message End-to-End (ETE) delay was reduced by 50 percent. Coupled with this decrease in delay, these same real-time messages also had …

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Application Of Fuzzy State Aggregation And Policy Hill Climbing To Multi-Agent Systems In Stochastic Environments, Dean C. Wardell Mar 2006

Application Of Fuzzy State Aggregation And Policy Hill Climbing To Multi-Agent Systems In Stochastic Environments, Dean C. Wardell

Theses and Dissertations

Reinforcement learning is one of the more attractive machine learning technologies, due to its unsupervised learning structure and ability to continually even as the operating environment changes. Applying this learning to multiple cooperative software agents (a multi-agent system) not only allows each individual agent to learn from its own experience, but also opens up the opportunity for the individual agents to learn from the other agents in the system, thus accelerating the rate of learning. This research presents the novel use of fuzzy state aggregation, as the means of function approximation, combined with the policy hill climbing methods of Win …

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Multi-Dimensional Wave Front Sensing Algorithms For Embedded Tracking And Adaptive Optics Applications, Christopher C. Wood Mar 2006

Multi-Dimensional Wave Front Sensing Algorithms For Embedded Tracking And Adaptive Optics Applications, Christopher C. Wood

Theses and Dissertations

Current tracking and adaptive optics techniques cannot compensate for fast-moving extended objects, which is important for ground-based telescopes providing space situational awareness. To fill this need, a vector-projection maximum-likelihood wave-front sensing algorithm development and testing follows for this application. A derivation and simplification of the Cramer-Rao Lower Bound for wavefront sensing using a laser guide star bounds the performance of these systems and guides implementation of a vastly optimized maximum-likelihood search algorithm. A complete analysis of the bias, mean square error, and variance of the algorithm demonstrates exceptional performance of the new sensor. A proof of concept implementation shows feasibility …

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A Comparison Of Main Rotor Smoothing Adjustments Using Linear And Neural Network Algorithms, Nathan A. Miller Mar 2006

A Comparison Of Main Rotor Smoothing Adjustments Using Linear And Neural Network Algorithms, Nathan A. Miller

Theses and Dissertations

Helicopter main rotor smoothing is a maintenance procedure that is routinely performed to minimize airframe vibrations induced by non-uniform mass and/or aerodynamic distributions in the main rotor system. This important task is both time consuming and expensive, so improvements to the process have long been sought. Traditionally, vibrations have been minimized by calculating adjustments based on an assumed linear relationship between adjustments and vibration response. In recent years, artificial neural networks have been trained to recognize non-linear mappings between adjustments and vibration response. This research was conducted in order observe the character of the adjustment mapping of the Vibration Management …

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An Estimation Theory Approach To Detection And Ranging Of Obscured Targets In 3-D Ladar Data, Charles R. Burris Mar 2006

An Estimation Theory Approach To Detection And Ranging Of Obscured Targets In 3-D Ladar Data, Charles R. Burris

Theses and Dissertations

The purpose of this research is to develop an algorithm to detect obscured images in 3-D LADAR data. The real data used for this research was gathered using a FLASH LADAR system under development at AFRL/SNJM. The system transmits light with a wavelength of 1.55 micrometers and produces 20 128 X 128 temporally resolved images from the return pulse separated by less than 2 nanoseconds in time. New algorithms for estimating the range to a target in 3-D FLASH LADAR data were developed. Results from processing real data are presented and compared to the traditional correlation receiver for extracting ranges …

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Bda Enhancement Methodology Using Situational Parameter Adjustments, Michael V. Carras Jr. Mar 2006

Bda Enhancement Methodology Using Situational Parameter Adjustments, Michael V. Carras Jr.

Theses and Dissertations

In the context of close ground combat, the perception of Battle Damage Assessment (BDA) is closely linked with a soldier’s engagement decisions and has significant effects on the battlefield. Perceived BDA is also one of the most complex and uncertain processes facing the soldier in live combat. As a result, the modeling and simulation community has yet to adequately model the perceived BDA process in combat models. This research effort examines the BDA process from a perception standpoint and proposes a methodology to collect the pertinent data and model this perception in the Army’s current force-on-force model, CASTFOREM. A subject …

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Characteristics Of Two-Dimensional Triangular And Three-Dimensional Face-Centered-Cubic Photonic Crystals, Jeffery D. Clark Mar 2006

Characteristics Of Two-Dimensional Triangular And Three-Dimensional Face-Centered-Cubic Photonic Crystals, Jeffery D. Clark

Theses and Dissertations

The fabrication of photonic crystals (PhC) with photonic band gaps (PBG) in the visible range is a difficult task due to the small structural feature sizes of the PhC. The particular type of PhC examined is a two-dimensional (2-D) triangular structure with a PBG designed for visible wavelengths with applications in visible integrated photonic systems. This work examines the processes involved and viability of fabricating 2-D triangular PhC's by a variety of techniques: focused ion beam, electron lithography and holographic photo-polymerization/lithography. The design of the PhC was based on a program created to display gap maps for triangular structures. The …

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Analysis Of Bacterial Population And Distribution In The Developing Strata Of A Constructed Wetland Used For Chlorinated Ethene Bioremediation, Milton J. Clausen Jr. Mar 2006

Analysis Of Bacterial Population And Distribution In The Developing Strata Of A Constructed Wetland Used For Chlorinated Ethene Bioremediation, Milton J. Clausen Jr.

Theses and Dissertations

Chlorinated hydrocarbons and their degradation products are among of the most common organic groundwater contaminates in the United States. These compounds attack the central nervous system in animals and can affect the photosynthesis of plants. These compounds are also resistant to degradation in the environment and, because of this, pose a risk to any ecosystem in which they are present. This study identified the dominant microbial species in a constructed treatment wetland at Wright-Patterson AFB, Dayton, Ohio using 16S rRNA gene sequence analysis. Samples were taken from three different depths and during each of the four seasons. These samples were …

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Passive Ranging Using Atmospheric Oxygen Absorption Spectra, Michael R. Hawks Mar 2006

Passive Ranging Using Atmospheric Oxygen Absorption Spectra, Michael R. Hawks

Theses and Dissertations

The depth of absorption bands in observed spectra of distant, bright sources can be used to estimate range to the source. A novel approach is presented and demonstrated using observations of the oxygen absorption band near 762 nm. Range is estimated by comparing observed values of band-average absorption against curves derived from either historical data or model predictions. Curves are based on fitting a random band model to the data, which reduces average range error by 67% compared to the Beer's Law model used in previous work. A new modification to existing band models for long, inhomogeneous paths is presented …

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Mitigating Distributed Denial Of Service Attacks In An Anonymous Routing Environment: Client Puzzles And Tor, Nicholas A. Fraser Mar 2006

Mitigating Distributed Denial Of Service Attacks In An Anonymous Routing Environment: Client Puzzles And Tor, Nicholas A. Fraser

Theses and Dissertations

Online intelligence operations use the Internet to gather information on the activities of U.S. adversaries. The security of these operations is paramount, and one way to avoid being linked to the Department of Defense (DoD) is to use anonymous communication systems. One such system, Tor, makes interactive TCP services anonymous. Tor uses the Transport Layer Security (TLS) protocol and is thus vulnerable to a distributed denial-of-service (DDoS) attack that can significantly delay data traversing the Tor network. This research uses client puzzles to mitigate TLS DDoS attacks. A novel puzzle protocol, the Memoryless Puzzle Protocol (MPP), is conceived, implemented, and …

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Polar Phase Screens: A Comparison With Other Methods Of Random Phase Screen Generation, Rebecca J. Eckert Mar 2006

Polar Phase Screens: A Comparison With Other Methods Of Random Phase Screen Generation, Rebecca J. Eckert

Theses and Dissertations

This research provides the first organized comparison of random phase screen generation methods, including logarithmic polar Fourier series, using structure functions. Random phase screens are essential elements of simulating light propagation through turbulent media. In order to be effective, they must accurately reflect theory and be practical to implement. This research explains and evaluates three methods of generating random phase screens: using a Fourier series upon a polar frequency grid with logarithmic spacing; using the fast Fourier transform, with its Cartesian frequency grid; and using Zernike polynomials. It provides a comparison of the Polar Fourier Series technique with the two …

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Doppler Aliasing Reduction In Wide-Angle Synthetic Aperture Radar Using Phase Modulated Random Stepped-Frequency Waveforms, Andrew W. Hyatt Mar 2006

Doppler Aliasing Reduction In Wide-Angle Synthetic Aperture Radar Using Phase Modulated Random Stepped-Frequency Waveforms, Andrew W. Hyatt

Theses and Dissertations

This research effort examines the theory, application and results of side-looking airborne radar operation in hot clutter. Hot clutter is an electronic counter-measure used to degrade the performance of airborne radar. Hot clutter occurs by illuminating the ground with an airborne jammer at some velocity, azimuth, elevation, and range from the airborne radar. When the received RCS scattered hot clutter waveform is perfectly coherent with the radar waveform, the radar believes the returns created by the hot clutter jammer resulted from the transmitting radar. Hot clutter degrades radar performance at locations in azimuth and Doppler. The effect of hot clutter …

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Verification Of A Decision Level Fusion Algorithm Using A Proven Atr System And Measured Sar Data, James Douglas Thompson Mar 2006

Verification Of A Decision Level Fusion Algorithm Using A Proven Atr System And Measured Sar Data, James Douglas Thompson

Theses and Dissertations

Decision level fusion (DLF) algorithms combine outputs of multiple single sensors to make one confident declaration of a target. This research compares performance results of a DLF algorithm using measured data and a proven ATR system with results from simulated data and a modeled ATR system. This comparison indicates that DLF offers significant performance improvements over single sensor looks. However, results based on simulated data and a modeled ATR are slightly optimistic and overestimate results from measured data and a proven ATR system by nearly 10% over all targets tested.

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Lqg/Ltr Tilt And Tip Control For The Starfire Optical Range 3.5-Meter Telescope's Adaptive Optics System, Neil D. Paris Mar 2006

Lqg/Ltr Tilt And Tip Control For The Starfire Optical Range 3.5-Meter Telescope's Adaptive Optics System, Neil D. Paris

Theses and Dissertations

The Air Force Research Laboratory has sponsored research on the tracking control loop portion of the adaptive optics system in the Starfire Optical Range 3.5-meter telescope at Kirtland Air Force Base. The control loop includes two steering mirrors (Coarse Steering Mirror and Fine Steering Mirror) used to remove wavefront tilt and tip phase distortion from light entering the telescope. The objective of this research is to design a single Linear Quadratic Gaussian controller to control both steering mirrors in order to eliminate wavefront tilt and tip distortions induced by the earth's atmosphere, and to evaluate the stability robustness and performance …

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A Monocular Vision Based Approach To Flocking, Brian Kirchner Mar 2006

A Monocular Vision Based Approach To Flocking, Brian Kirchner

Theses and Dissertations

Flocking is seen in nature as a means for self protection, more efficient foraging, and other search behaviors. Although much research has been done regarding the application of this principle to autonomous vehicles, the majority of the research has relied on GPS information, broadcast communication, an omniscient central controller, or some other form of "global" knowledge. This approach, while effective, has serious drawbacks, especially regarding stealth, reliability, and biological grounding. This research effort uses three Pioneer P2-AT8 robots to achieve flocking behavior without the use of global knowledge. The sensory inputs are limited to two cameras, offset such that the …

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Quantitative Object Reconstruction Using Abel Transform Tomography And Mixed Variable Optimization, Kevin R. O'Reilly Mar 2006

Quantitative Object Reconstruction Using Abel Transform Tomography And Mixed Variable Optimization, Kevin R. O'Reilly

Theses and Dissertations

Researchers at the Los Alamos National Laboratory (LANL) are interested in quantitatively reconstructing an object using Abel transform x-ray tomography. Specifically, they obtain a radiograph by x-raying an object and attempt to quantitatively determine the number and types of materials and the thicknesses of each material layer. Their current methodologies either fail to provide a quantitative description of the object or are generally too slow to be useful in practice. As an alternative, the problem is modeled here as a mixed variable programming (MVP) problem, in which some variables are nonnumeric and for which no derivative information is available. The …

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Characterization Of Detonation Phenomena Observed In High-Speed Visible Imagery, Trevor W. Warren Mar 2006

Characterization Of Detonation Phenomena Observed In High-Speed Visible Imagery, Trevor W. Warren

Theses and Dissertations

Measurements for radius, angular velocity, initial time of observation, and final time of observation were made for turbulent vortices around detonation fireballs. A proxy for vortex power, determined through unit analysis, was found to correlate well to initial (and final) time of observation with R2 equal to 0.8572. The linear trend on a log10-log10 plot was indicative of a rapid decrease (over 10-1 s) in power associated with the decay of the fireball. Predictions, based on turbulent spectral theory were made for root-mean-square velocity fluctuations and Reynolds numbers, both as functions of time. In addition, …

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A Climatological Study Of Equatorial Gps Data And The Effects On Ionospheric Scintillation, Katharine A. Wicker Mar 2006

A Climatological Study Of Equatorial Gps Data And The Effects On Ionospheric Scintillation, Katharine A. Wicker

Theses and Dissertations

Ionospheric scintillation is detrimental to radio signals, especially those from the global positioning system. Such scintillation is caused when a signal permeates the ionosphere through plasma bubbles. The signal’s phase and amplitude can be altered, and a receiver on the ground can lose lock on the GPS signal. Measured using a zero to one index known as S4, scintillation severity is based upon season, solar cycle, time of day, location and frequency. The most severe scintillation occurs at the equatorial anomaly, or fifteen degrees north and south of the equator. Seven years of data from fifteen different locations around the …

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An Adaptable Energy-Efficient Medium Access Control Protocol For Wireless Sensor Networks, Justin T. Kautz Mar 2006

An Adaptable Energy-Efficient Medium Access Control Protocol For Wireless Sensor Networks, Justin T. Kautz

Theses and Dissertations

Wireless networks have become ubiquitous recently and therefore their usefulness has also become more extensive. Wireless sensor networks (WSN) detect environmental information with sensors in remote settings. One problem facing WSNs is the inability to resupply power to these energy-constrained devices due to their remoteness. Therefore to extend a WSN's effectiveness, the lifetime of the network must be increased by making them as energy efficient as possible. An energy efficient medium access control (MAC) can boost a WSN's lifetime. This research creates a MAC protocol called Adaptive sensor Medium Access Control (AMAC) which is based on Sensor Medium Access Control …

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Detecting Potential Insider Threats Through Email Datamining, James S. Okolica Mar 2006

Detecting Potential Insider Threats Through Email Datamining, James S. Okolica

Theses and Dissertations

No abstract provided.

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Comparison Of Ray Tracing Through Ionospheric Models, Shayne C. Aune Mar 2006

Comparison Of Ray Tracing Through Ionospheric Models, Shayne C. Aune

Theses and Dissertations

A comparison of ray tracing predictions for transionospheric electromagnetic wave refraction and group delays through ionospheric models is presented. Impacted applications include over-the-horizon RADAR, high frequency communications, direction finding, and satellite communications. The ionospheric models used are version 2.1 of Utah State University's Global Assimilation of Ionospheric Measurements (USU GAIM) model and the 2001 version of the International Reference Ionosphere (IRI) model. In order to provide ray tracing results applicable to satellite communications for satellites at geosynchronous orbit (GEO), a third ionospheric model is used to extend the sub-2000-km USU GAIM and IRI ionospheric specifications to 36540 km in altitude. …

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Measurement, Characterization, And Source Apportionment Of The Major Chemical Components Of Fine Particulate Material, Including Semi-Volatile Species, Brett D. Grover Feb 2006

Measurement, Characterization, And Source Apportionment Of The Major Chemical Components Of Fine Particulate Material, Including Semi-Volatile Species, Brett D. Grover

Theses and Dissertations

The promulgation of revised standards for atmospheric fine particles (PM2.5) by the US EPA has sparked renewed interest in the ability to accurately measure and characterize suspended atmospheric particulate matter. Semi-volatile material (SVM), consisting of ammonium nitrate and semi-volatile organic material (SVOM), is not accurately measured by EPA accepted methods such as the Federal reference method (FRM) or Tapered Element Oscillating Microbalance (TEOM). However, SVM is often a major fraction of urban aerosols. Recent advances in atmospheric sampling instrumentation allowed for the semi-continuous characterization of urban PM2.5, including SVM. The Filter Dynamic Measurement System (FDMS) was shown to measure total …

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Using Augmented Virtuality To Improve Human-Robot Interactions, Curtis W. Nielsen Feb 2006

Using Augmented Virtuality To Improve Human-Robot Interactions, Curtis W. Nielsen

Theses and Dissertations

Mobile robots can be used in situations and environments that are distant from an operator. In order for an operator to control a robot effectively he or she requires an understanding of the environment and situation around the robot. Since the robot is at a remote distant from the operator and cannot be directly observed, the information necessary for an operator to develop an understanding or awareness of the robot's situation comes from the user interface. The usefulness of the interface depends on the manner in which the information from the remote environment is presented. Conventional interfaces for interacting with …

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Characterization, Functionalization And Applications Of Alkyl Monolayers On Silicon Surfaces, Guilin Jiang Feb 2006

Characterization, Functionalization And Applications Of Alkyl Monolayers On Silicon Surfaces, Guilin Jiang

Theses and Dissertations

Investigations were performed on the stability, mechanism of formation and an application of alkyl monolayers chemomechanically prepared on silicon surfaces. A new method of surface modification, laser-activation modification of surfaces (LAMS), and multivariate analyses of time-of-flight secondary ion mass spectrometry (ToF-SIMS) images of LAMS spots were also reported. X-ray photoelectron spectroscopy (XPS) and other data show that alkyl monolayers prepared by scribing silicon under 1-iodoalkanes and 1-alkenes were stable over extended periods of time to air, water, a boiling acid and Al Ka X-rays. The stability is attributed to direct Si-C bonding in the monolayers. The observation that the oxygen …

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Macroscopic Computational Model Of Dielectric Barrier Discharge Plasma Actuators, Timothy R. Klein Feb 2006

Macroscopic Computational Model Of Dielectric Barrier Discharge Plasma Actuators, Timothy R. Klein

Theses and Dissertations

Recent progress in the generation and sustainment of gas discharges at atmospheric pressure has energized research in the field of plasma-aerodynamics. Plasma actuators are promising devices that achieve flow control with no moving parts, do not alter the airfoil shape and place no parts in the flow. The operation of a plasma actuator is examined using a macroscopic (force and power addition) computational fluid dynamic model of a dielectric barrier discharge, DBD, in Fluent. A parametric approach is adopted to survey the range of requisite magnitudes of momentum and energy delivered to the flow field and to identify the effects …

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Correlating Factors Between Student Participation And Student Learning Via A Service Learning Project In Secondary Education: A Case Study, Shawn V. Jensen Jan 2006

Correlating Factors Between Student Participation And Student Learning Via A Service Learning Project In Secondary Education: A Case Study, Shawn V. Jensen

Theses and Dissertations

In this study a service-learning project was conducted with secondary students in a construction technology based course. Three research questions were considered; (1) does service learning projects help to engage student participation, (2) can students learn the course curriculum while participating in a service learning project, and (3) is there a correlation between student participation and student learning as it pertains to service learning projects? The data was collected through surveys, observations, interviews, and evaluations. The researcher concluded the following from the study; 92% of the students were actively participating in the two week service project, 76% of the students …

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