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Air Force Institute of Technology

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Articles 3691 - 3720 of 5699

Full-Text Articles in Engineering

An Experimental Design For Measuring In Situ Radiation Damage To A Piezoelectric Transducer, Michael R. Severson Mar 2004

An Experimental Design For Measuring In Situ Radiation Damage To A Piezoelectric Transducer, Michael R. Severson

Theses and Dissertations

An experiment was conducted investigating the use of an acoustic pulse waveguide to collect response measurements from three piezoelectric acoustic emission (AE) transducers while the transducers were exposed to an active nuclear reactor neutron flux ranging from 1 x 1011 to 2.4 x 1012 neutrons per sq cms. Material, mechanical, and radiation studies were performed to determine a practical design for the construction of the experiment. Discreet frequency pulses generated by an Arbitrary Waveform Generator were transmitted by an aluminum waveguide to the core of the Ohio State University Research Reactor (OSURR). Three AF transducers coupled to the …

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An Analysis Of The Potential For Using Over-The-Horizon Radar Systems For Space Surveillance, Matthew J. Colbert Mar 2004

An Analysis Of The Potential For Using Over-The-Horizon Radar Systems For Space Surveillance, Matthew J. Colbert

Theses and Dissertations

The Australian Defence Force is investigating the development of a space surveillance system. While several dedicated facilities for space surveillance are in operation around the world, Australia s Over-The-Horizon Radar (OTHR) network has some potential for this role. The OTHR operates in the HF band and is constrained by the propagation effects of the ionosphere. A spherically stratified ionospheric model and a model for a nominal OTHR antenna are developed that allow calculation of path propagation, power distribution, and clutter returns. A software-based radar receiver processing system is modeled to determine detection probabilities and the minimum detectable radar cross-section of …

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Deviation Of Time-Resolved Luminescence Dynamics In Mwir Semiconductor Materials From Carrier Recombination Theory Predictions, Peter M. Johnson Mar 2004

Deviation Of Time-Resolved Luminescence Dynamics In Mwir Semiconductor Materials From Carrier Recombination Theory Predictions, Peter M. Johnson

Theses and Dissertations

Time resolved luminescence spectroscopy was used to characterize luminescence decay curves for a bulk InAs sample and an InAsSb type-I quantum-well sample over the first 3ns following excitation. The luminescence decay curves were then converted to carrier densities and used to find recombination coefficients that provided the least-squared-error solution of the rate equation describing carrier recombination. Recombination coefficients describing Shockley Read-Hall (ASRH) radiative (Brad) and Auger (CAug) recombination were determined at two different temperatures and four excitation powers, then analyzed for consistency and physical significance. For all of the resulting least …

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Detonation Branching In A Pde With Liquid Hydrocarbon Fuel, Kristin L. Panzenhagen Mar 2004

Detonation Branching In A Pde With Liquid Hydrocarbon Fuel, Kristin L. Panzenhagen

Theses and Dissertations

A pulse detonation engine (PDE) capitalizes on the large mass flux and pressure rise associated with detonations to create thrust, which is proportional to PDE cycle frequency. This research showed that using a branched detonation as an ignition source, as opposed to standard spark ignition, deposits more energy into the thrust tube head. The increase in energy decreases ignition delay and detonation to deflagration transition (DDT) time. This allows a theoretical 85% cycle frequency increase that is accompanied by an 85% increase in thrust. The increase in energy also reduces the need for a DDT enhancement device, thereby increasing thrust …

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Multiple Access Interference Characterization For Direct-Sequence Spread-Spectrum Communications Using Chip Waveform Shaping, Matthew G. Glen Mar 2004

Multiple Access Interference Characterization For Direct-Sequence Spread-Spectrum Communications Using Chip Waveform Shaping, Matthew G. Glen

Theses and Dissertations

This research characterizes MAI effects on DS/SSMA system performance through simulation in Matlab , and explores the impact of multiple access code selection, chip waveform shaping, and multiple access code length on BER for both synchronous and asynchronous multiple access networks. In addition, the simulated DS/SSMA model permits rapid research into the effects of additional factors on BER. Prior to experimental testing, model validation is conducted through single user trials and by comparison with existing research for similar system designs. For synchronous and asynchronous networks, Gold coding improves BER by 7.5 and 4.0 dB, respectively, relative to aperiodic random spreading …

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An Analysis Of Electromagnetic Interference (Emi) Of Ultra Wideband(Uwb) And Ieee 802.11a Wireless Local Area Network (Wlan) Employing Orthogonal Frequency Division Multiplexing (Ofdm), Juan Lopez Jr. Mar 2004

An Analysis Of Electromagnetic Interference (Emi) Of Ultra Wideband(Uwb) And Ieee 802.11a Wireless Local Area Network (Wlan) Employing Orthogonal Frequency Division Multiplexing (Ofdm), Juan Lopez Jr.

Theses and Dissertations

Military communications require the rapid deployment of mobile, high-bandwidth systems. These systems must provide anytime, anywhere capabilities with minimal interference to existing military, private, and commercial communications. Ultra Wideband (UWB) technology is being advanced as the next generation radio technology and has the potential to revolutionize indoor wireless communications. The ability of UWB to mitigate multipath fading, provide high-throughput data rates (e.g., greater than 100 Mbps), provide excellent signal penetration (e.g., through walls), and low implementation costs makes it an ideal technology for a wide range of private and public sector applications. Preliminary UWB studies conducted by The Institute for …

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Ion Based Pressure Sensor For Pulse Detonation Engines, Jeffrey S. Zdenek Mar 2004

Ion Based Pressure Sensor For Pulse Detonation Engines, Jeffrey S. Zdenek

Theses and Dissertations

A high speed, durable, ion probe based pressure sensor is being investigated for use in pulse detonation engines. Traditional pressure sensors are ill suited for the high temperature and vibratory environment encountered in such engines. An alternative transient pressure sensing method is investigated for pressures behind a hydrocarbon flame. These flames generate ions that are quenched by collisions as a function of pressure. An experiment was devised to correlate the ion decay rate with the pressure using an ion probe well suited for the flow. A correlation has been established showing the ion decay rate is a function of pressure. …

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Discovering The Merit Of The Wavelet Transform For Object Classification, Matthew D. Eyster Mar 2004

Discovering The Merit Of The Wavelet Transform For Object Classification, Matthew D. Eyster

Theses and Dissertations

Vision is the primary sense by which most biological systems collect information about their environment. Computer vision is a branch of artificial intelligence concerned with endowing machines with the ability to understand images. Object recognition is a key part of machine vision with far reaching benefits ranging from target recognition, surveillance systems, to automation systems. Extraction of salient features from an image is one of the key steps in object recognition. Typically, geometric primitives are extracted from an image using local analysis. However, the wavelet transform provides a global approach with good locality. Additionally, the directional and multiresolution properties may …

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Interference Suppression In Multiple Access Communications Using M-Ary Phase Shift Keying Generated Via Spectral Encoding, Abel S. Nunez Mar 2004

Interference Suppression In Multiple Access Communications Using M-Ary Phase Shift Keying Generated Via Spectral Encoding, Abel S. Nunez

Theses and Dissertations

A conceptual transform domain communication system (TDCS) is shown capable of operating successfully using M-Ary phase shift keying (MPSK) data modulation in a multiple access environment. Using spectral encoding, the conceptual TDCS provides an effective means for mitigating interference affects while achieving multiple access communications. The use of transform domain processing with MPSK data modulation (TD-MPSK) provides higher spectral efficiency relative to other modulation techniques (antipodal signaling and cyclic shift keying) considered previously for TDCS applications. The proposed TD-MPSK technique uses spectral encoding for both data and multiple access phase modulations. Demodulation of the spectrally encoded TD-MPSK communication symbols is …

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Investigating The Optimal Management Strategy For A Healthcare Facility Maintenance Program, Daria J. Gaillard Mar 2004

Investigating The Optimal Management Strategy For A Healthcare Facility Maintenance Program, Daria J. Gaillard

Theses and Dissertations

Reacting to the need to transform and the increasing pressure to outsource all non-core activities, Air Force Material Command Surgeon General discontinued its previous use of full service contracts with original equipment manufacturers and adopted a relatively new maintenance outsourcing strategy: strategic partnering with an equipment management firm. The objective of this study is to create a decision-model for selecting the optimal management strategy for a healthcare organization's facility maintenance program. This study used personal interviews with facility management personnel from MAJCOMs to collect and analyze data. This study offers a re-conceptualized framework for viewing and understanding the various maintenance …

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Keys To Successful Implementation And Sustainment Of Managed Maintenance For Healthcare Facilities, Elizabeth A. Waggoner Mar 2004

Keys To Successful Implementation And Sustainment Of Managed Maintenance For Healthcare Facilities, Elizabeth A. Waggoner

Theses and Dissertations

Health care providers are faced with two critical issues in today's evolving marketplace: lowering operational costs and achieving more efficient, cost-effective methods to deliver high quality patient care. The rising costs of healthcare and decreasing budgets have placed additional strain on the United States Air Force Medical Service to aggressively lower its facilities' costs. With fewer funds and less personnel, the Air Force medical service is re-evaluating its current maintenance outsourcing implementation practices and reexamining how these strategies might be implemented and sustained more successfully. This research offers some of the foundational needs for designing, implementing and sustaining any type …

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Fretting Fatigue Behavior Of The Titanium Alloy Ti-6al-4v Under Seawater Conditions, Lewis C. Lietch Mar 2004

Fretting Fatigue Behavior Of The Titanium Alloy Ti-6al-4v Under Seawater Conditions, Lewis C. Lietch

Theses and Dissertations

The fretting fatigue behavior of Ti-6A1-4V was investigated in laboratory air and under a controlled environment consisting of synthetic seawater. Fretting fatigue tests were performed for both low and high cycle fatigue regimes. Finite element analysis was utilized to model and analyze the experimental data. The applied stress range and the Modified Shear Stress Range were evaluated as potential fatigue parameters. The results found from this study can be summarized as: (1) seawater had a deleterious effect on fretting fatigue life in the low cycle fatigue regime but improved life in the high cycle fatigue regime, (2) although the Q/P …

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Data Sorting And Orbit Determination Of Tethered Satellite Systems, Mark J. Faulstich Mar 2004

Data Sorting And Orbit Determination Of Tethered Satellite Systems, Mark J. Faulstich

Theses and Dissertations

Tethered satellite system end masses do not obey the normal laws of motion developed for determining their orbits. In addition, tethered satellite systems cause unique problems for satellite tracking because there are potentially two or more objects which may be tracked. This thesis provides insight into these issues by developing a method of sorting out observation data of tethered satellite systems into their appropriate end mass and providing an estimate on the center of mass orbit of the tethered satellite system. The method used to accomplish both of these tasks is optimization of an estimated simulated orbit. This orbit estimate …

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Flow Around An Object Projected From A Cavity Into A Supersonic Freestream, Scott T. Bjorge Mar 2004

Flow Around An Object Projected From A Cavity Into A Supersonic Freestream, Scott T. Bjorge

Theses and Dissertations

The pressure and flow field of a supersonic flow over a cavity, with and without a store, was the focus of this experiment. One cavity geometry (length to depth ratio 3.6) was studied; the freestream Mach number and the placement of the store relative to the cavity floor were varied. The pressure spectra on the cavity floor were markedly different between Mach numbers of 1.8 and 2.9. The Mach 1.8 case exhibited clear spectral peaks consistent with predictions by Rossiter, whereas the Mach 2.9 flow did not. With the store placed within the free shear layer, the pressure fluctuations on …

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Optical Characterization And Modeling Of Compositionally Matched Indium Arsenide-Antimonide Bulk And Multiple Quantum Well Semiconductors, Scott C. Phillips Mar 2004

Optical Characterization And Modeling Of Compositionally Matched Indium Arsenide-Antimonide Bulk And Multiple Quantum Well Semiconductors, Scott C. Phillips

Theses and Dissertations

Indium arsenide-antimonide (InAsSb) semiconductors have been determined to emit in the 3-5 micrometer range, the window of interest for countermeasures against infrared electro-optical threats. This experiment set out to cross the bulk to quantum well characterization barrier by optically characterizing two sets of compositionally matched type I quantum well and bulk well material samples. Absorption measurements determined the band gap energy of the bulk samples and the first allowed subband transition for the quantum wells. By collecting absorption spectra at different temperatures, the trend of the energy transitions was described by fitting a Varshni equation to them. The expected result …

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Characterization Of Ultra Wideband Multiple Access Performance Using Time Hopped-Biorthogonal Pulse Position Modulation, Donald J. Clabaugh Mar 2004

Characterization Of Ultra Wideband Multiple Access Performance Using Time Hopped-Biorthogonal Pulse Position Modulation, Donald J. Clabaugh

Theses and Dissertations

The FCC's release of its UWB First Report and Order in April 2002 spawned renewed interest in impulse signaling research. This work combines Time Hopped (TH) multiple access coding with 4-ary UWB Biorthogonal Pulse Position Modulation (TH-BPPM). Multiple access performance is evaluated in a multipath environment for both synchronous and asynchronous networks. Fast time hopping is implemented by replicating and hopping each TH-BPPM symbol NH times. Bit error expressions are derived for biorthogonal TH-BPPM signaling and results compared with previous orthogonal TH-PPM work. Without fast time hopping (NH = 1), the biorthogonal TH-BPPM technique provided gains equivalent to Gray-coded QPSK; …

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Systems-Level Feasibility Analysis Of A Microsatellite Rendezvous With Non-Cooperative Targets, Allen R. Toso Mar 2004

Systems-Level Feasibility Analysis Of A Microsatellite Rendezvous With Non-Cooperative Targets, Allen R. Toso

Theses and Dissertations

The feasibility of using a microsatellite to accomplish an orbital rendezvous with a noncooperative target was evaluated. This study focused on identifying and further exploring the technical challenges involved in achieving a noncooperative rendezvous. A system engineering analysis and review of past research quickly led to a concentration on the guidance, navigation, and control elements of the microsatellite operation. The integration of control and orbit determination algorithms was investigated. A simple yet robust solution could not be found to meet reasonable rendezvous criteria, using essentially off-the-shelf technology and algorithms. System feasibility has been assessed to have a low probability in …

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Image Super-Resolution Using Adaptive 2-D Gaussian Basis Function Interpolation, Terence D. Hunt Mar 2004

Image Super-Resolution Using Adaptive 2-D Gaussian Basis Function Interpolation, Terence D. Hunt

Theses and Dissertations

Digital image interpolation using Gaussian radial basis functions has been implemented by several investigators, and promising results have been obtained; however, determining the basis function variance has been problematic. Here, adaptive Gaussian basis functions fit the mean vector and covariance matrix of a non-radial Gaussian function to each pixel and its neighbors, which enables edges and other image characteristics to be more effectively represented. The interpolation is constrained to reproduce the original image mean gray level, and the mean basis function variance is determined using the expected image smoothness for the increased resolution. Test outputs from the resulting Adaptive Gaussian …

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Structural Design And Analysis Of A Rigidizable Space Shuttle Experiment, Raymond G. Holstein Iii Mar 2004

Structural Design And Analysis Of A Rigidizable Space Shuttle Experiment, Raymond G. Holstein Iii

Theses and Dissertations

AFIT is in the process of designing a Space Shuttle experiment designated as the Rigidized Inflatable Get-Away-Special Experiment (RIGEX) to study the effects of microgravity on the deployment of rigidizable composite structures. Once in space, the experiment will inflate and rigidize three composite structures and perform a vibration analysis on each by exciting the tubes using piezoelectric patches and collecting data via an accelerometer. This paper presents the structural and vibration analysis of the RIGEX assembly and inflatable composite tubes using ABAQUS Finite Element Analysis (FEA) software. Comparison of the analysis has been carried out with Eigenvalue/Eigenvector experimentation by means …

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Decision Analysis With Value Focused Thinking As A Methodology To Assess Air Force Officer Retention Alternatives, Sang-Ho Moon Mar 2004

Decision Analysis With Value Focused Thinking As A Methodology To Assess Air Force Officer Retention Alternatives, Sang-Ho Moon

Theses and Dissertations

Many countries realize the importance of the retention of qualified military personnel, and have tried to solve this problem using various methods. Nevertheless, the effects of those methods have not been determined or proven yet. The military retention problem is closely related to each individual's separation decision from the military. The characteristics of this decision are multi-objective and highly subjective. Accordingly, the effectiveness of various methods is heavily dependant on the value set of each individual. Decision Analysis (DA) using Value Focused Thinking (VFT) can be an excellent process to deal with this decision. Also, the data can reflect the …

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Special Nuclear Material Imaging Using A High Purity Germanium Double Sided Strip Detector, Clifford V. Sulham Mar 2004

Special Nuclear Material Imaging Using A High Purity Germanium Double Sided Strip Detector, Clifford V. Sulham

Theses and Dissertations

The purpose of this research is to investigate the feasibility of using a High Purity Germanium Double Sided Strip Detector (HPGeDSSD) to image Special Nuclear Material (SNM) for use in the field of nuclear nonproliferation. SNM shape can be determined by using a gamma ray imaging system that is capable of imaging either Pu-239 or U-235. The detector used for this research is a liquid-nitrogen cooled germanium detector with five charge collection strips on both faces. The strips on the two faces are orthogonal to each other, creating a five by five array of data collection pixels. When the detector …

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Controlling The Primary Mirror In A Space-Based Telescope Utilizing An Eigenstructure Assignment Technique, Kim Kyongsoo Mar 2004

Controlling The Primary Mirror In A Space-Based Telescope Utilizing An Eigenstructure Assignment Technique, Kim Kyongsoo

Theses and Dissertations

The feasibility of using a sparse array of mirrors in a satellite system is being evaluated. This study focused on the control laws necessary for achieving the minimization of the effect of vibration which happens at the primary mirror of the satellite, by using the eigenstructure assignment technique. White Gaussian noise was assumed as the external input. AFRL has developed a 79 state model with 9 control inputs and 9 outputs, 3 sparse array mirrors, and a base. To extend the theory, a simplified model with 2 mirrors and a base which has 12 states, 4 control inputs and 8 …

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Axisymmetric Optical Membrane Modeling Based On Experimental Results, Brian J. Lutz Mar 2004

Axisymmetric Optical Membrane Modeling Based On Experimental Results, Brian J. Lutz

Theses and Dissertations

The United States Air Force, Department of Defense and commercial industry have recognized the great value of near-earth space development, specifically in satellites for use in communications, ground and space surveillance and more active roles. However, resolution, or the primary optic’s diameter, has been a limitation, especially for ground surveillance. Deployable optics has been investigated to allow larger optics in space and membrane optics has received increasing attention recently. The membrane’s flexible nature requires some passive and possibly active control to reduce optical distortion caused by manufacturing, deployment, or other effects during use. Piezoelectric surface controllers are one option to …

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An Investigation Relating Longitudinal Pilot-Induced Oscillation Tendency Rating To Describing Function Predictions For Rate-Limited Actuators, Joel B. Witte Mar 2004

An Investigation Relating Longitudinal Pilot-Induced Oscillation Tendency Rating To Describing Function Predictions For Rate-Limited Actuators, Joel B. Witte

Theses and Dissertations

The purpose of this study was to investigate pilot-induced oscillations (PIO) and determine a method by which PIO tendency rating could be predicted. In particular, longitudinal PIO in the presence of rate-limited actuators were singled out for examination. Sinusoidal input/triangular output describing function techniques using Nichols charts were used. A new criterion dubbed Gap Criterion was calculated for PIO sensitivity. This criterion consists of the product of pilot gain necessary to cause PIO and the normalized maximum amplitude of the commanded actuator. These results were paired with simulator and flight test PIO tendency rating data. The PIO rating scale used …

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Optimization Process For Configuration Of Flexible Joined-Wing, Cody C. Rasmussen Mar 2004

Optimization Process For Configuration Of Flexible Joined-Wing, Cody C. Rasmussen

Theses and Dissertations

This study established a weight optimized configuration design of a joined-wing sensor-craft. The joined-wing aircraft concept fulfills a proposed long-endurance surveillance mission that contains an antenna structure embedded in the wing skin. The analysis was completed utilizing structural optimization, aerodynamic analyses, and response surface methodology. A sample of 62 joined-wing configurations were weight optimized. Each optimized structure was determined through a change of skin, spar, and rib thickness in the wing box by determining trimmed maneuver and gust conditions for critical flight mission points. Since the joined-wing concept has non-linear deformation characteristics, the structural optimization used both strain and buckling …

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Vibrometric Detection Of Beam Damage Due To Inclusions, Aaron J. Reifsnyder Mar 2004

Vibrometric Detection Of Beam Damage Due To Inclusions, Aaron J. Reifsnyder

Theses and Dissertations

The Air Force Institute of Technology, in conjunction with the Structural Health Monitoring branch of the Air Force Research Laboratory, is researching methods of determining effects of notch location and size on beam structures using modal frequency analysis. This thesis explores the ability to detect included notches of varying magnitudes and locations within the frequency domain of an isotropic cantilever beam. A series of experiments employing centerline-notched 2024 T3 and 2024 0 aluminum beams was used to determine whether natural frequency measurement in beam structures is a valid mechanism for damage detection. Each specimen was excited by a strain actuator …

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Experimental And Computational Analysis Of Modes In A Partially Constrained Plate, Robert M. Vandawaker Mar 2004

Experimental And Computational Analysis Of Modes In A Partially Constrained Plate, Robert M. Vandawaker

Theses and Dissertations

The field of structural health monitoring (SHM) attempts to reduce labor and cost by allowing technicians to monitor selected properties of an aircraft's structure to detect impending failure. This research examines methods to detect damage to a thermal protection system (TPS) tile using representative 2024-T3 aluminum plates. Plates are subjected to modal analysis in single and joined conditions in an attempt to provide the capability of sensing damage to a tile on the surface of a vehicle while the sensors remain on the superstructure of the airframe. Jointly, the development of a means to model the system using finite element …

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Optimization Of Heterogeneous Uav Communications Using The Multiobjective Quadratic Assignment Problem, Mark P. Kleeman Mar 2004

Optimization Of Heterogeneous Uav Communications Using The Multiobjective Quadratic Assignment Problem, Mark P. Kleeman

Theses and Dissertations

The Air Force has placed a high priority on developing new and innovative ways to use Unmanned Aerial Vehicles (UAVs). The Defense Advanced Research Projects Agency (DARPA) currently funds many projects that deal with the advancement of UAV research. The ultimate goal of the Air Force is to use UAVs in operations that are highly dangerous to pilots, mainly the suppression of enemy air defenses (SEAD). With this goal in mind, formation structuring of autonomous or semi-autonomous UAVs is of future importance. This particular research investigates the optimization of heterogeneous UAV multi-channel communications in formation. The problem maps to the …

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Geolocation Of An Audio Source In A Multipath Environment Using Time-Of-Arrival, Jeffrey A. Boggs Mar 2004

Geolocation Of An Audio Source In A Multipath Environment Using Time-Of-Arrival, Jeffrey A. Boggs

Theses and Dissertations

The Air Force and the Department of Defense (DoD) are continually searching for ways to protect U.S. forces, both stateside and abroad. One continuing threat, especially in the current world environment, is gunfire from an unseen sniper. Designated areas, such as a forward deployed base or motorcade route, need to be continuously monitored for sniper fire. Once detected, these gunmen need to be located in real time. One possible method for accomplishing this task is to geolocate the audio signals generated using time-of-arrival (TOA) algorithms. These algorithms rely on direct-path measurements for accuracy. Multipath environments therefore pose a problem when …

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Swarm Based Implementation Of A Virtual Distributed Database System In A Sensor Network, Wen C. Lee Mar 2004

Swarm Based Implementation Of A Virtual Distributed Database System In A Sensor Network, Wen C. Lee

Theses and Dissertations

The deployment of unmanned aerial vehicles (UAVs) in recent military operations has had success in carrying out surveillance and combat missions in sensitive areas. An area of intense research on UAVs has been on controlling a group of small-sized UAVs to carry out reconnaissance missions normally undertaken by large UAVs such as Predator or Global Hawk. A control strategy for coordinating the UAV movements of such a group of UAVs adopts the bio-inspired swarm model to produce autonomous group behavior. This research proposes establishing a distributed database system on a group of swarming UAVs, providing for data storage during a …

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