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Articles 3421 - 3450 of 5700
Full-Text Articles in Engineering
Optimization Of A Multi-Echelon Repair System Via Generalized Pattern Search With Ranking And Selection: A Computational Study, Derek D. Tharaldson
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 …
A Risk Assessment Methodology For Divesting Military Capabilities To Allied Nations, Jason A. Gastelum
A Risk Assessment Methodology For Divesting Military Capabilities To Allied Nations, Jason A. Gastelum
Theses and Dissertations
The United States spent over $400 billion dollars on national defense in 2005. Even with support for the war on terrorism still strong, it is doubtful that the U.S. can sustain such a level of defense investment. One strategy to offset the increasing burden of defense spending is to divest the procurement and/or sustainment of individual defense capabilities to allied nations. The decision to divest any capability, however, introduces risk. This thesis presents a methodology to quantify the risk of the decision to divest a military capability to an allied nation, where risk is defined as the set of risk …
Strategic Airlift En Route Analysis To Support The Global War On Terrorism Using A Value Focused Thinking Approach, Marykathryn W. Tharaldson
Strategic Airlift En Route Analysis To Support The Global War On Terrorism Using A Value Focused Thinking Approach, Marykathryn W. Tharaldson
Theses and Dissertations
The Global War on Terrorism (GWOT) has yielded new challenges to the United States' strategic airlift infrastructure. The network of en-route airfields that serve as refueling and maintenance stops were designed primarily to service relatively static Cold War requirements. However, the GWOT has resulted in the need for an infrastructure that is responsive to a highly dynamic environment. This research uses a "value focused" methodology to identify en-route airfield locations that simultaneously maximize cargo throughput capability while possessing a high degree of adaptability to volatile cargo delivery requirements.
Review Of The Joint Capability Integration And Development System (Jcids) And The National Security Space Acquisition Process (Nssap), Joyce A. Gamache
Review Of The Joint Capability Integration And Development System (Jcids) And The National Security Space Acquisition Process (Nssap), Joyce A. Gamache
Theses and Dissertations
Space systems are a critical enabler of the net-centric operation warfare (NCOW) needed to achieve victory in the Global War on Terrorism (GWOT). The effective acquisition of affordable systems is vital to our National Security Strategy. Space systems play an important role throughout a wide spectrum of military and civil operations. Several challenging factors unique to space systems development are the high level of technological complexity, a broad joint user base, and the reliance on seamless interoperable systems to achieve superior capabilities for US warfighters. This research examines the interaction between the Joint Capabilities Integration and Development System (JCIDS) and …
Evaluation And Analysis Of Node Localization Power Cost In Ad-Hoc Wireless Sensor Networks With Mobility, Brian A. Sessler
Evaluation And Analysis Of Node Localization Power Cost In Ad-Hoc Wireless Sensor Networks With Mobility, Brian A. Sessler
Theses and Dissertations
One of the key concerns with location-aware Ad-hoc Wireless Sensor Networks (AWSNs) is how sensor nodes determine their position. The inherent power limitations of an AWSN along with the requirement for long network lifetimes makes achieving fast and power-efficient localization vital. This research examines the cost (in terms of power) of network irregularities on communications and localization in an AWSN. The number of data bits transmitted and received are significantly affected by varying levels of mobility, node degree, and network shape. The concurrent localization approach, used by the APS-Euclidean algorithm, has significantly more accurate position estimates with a higher percentage …
Determining The Resistivity Of Resistive Sheets Using Transmission Measurements, Milo W. Hyde Iv
Determining The Resistivity Of Resistive Sheets Using Transmission Measurements, Milo W. Hyde Iv
Theses and Dissertations
In September 2005, radar cross section (RCS) measurements were made of resistive sheets, or R-cards, wrapped around a polystyrene foam cylinder to compare with a newly developed theoretical RCS prediction technique. The resistivities of the R-cards were initially measured with a direct current (DC) four-point probe. When the RCS measurements were compared to the theoretical predictions, it became clear that DC resistivity alone is not sufficient to accurately predict the scattering from an R-card. This thesis presents alternating current (AC) methods for determining the resistivity of an R-card. Both freespace and waveguide techniques are presented. Experimental verification of the techniques …
Development Of A Wireless Model Incorporating Large-Scale Fading In A Rural, Urban And Suburban Environment, Roger A. Illari
Development Of A Wireless Model Incorporating Large-Scale Fading In A Rural, Urban And Suburban Environment, Roger A. Illari
Theses and Dissertations
The goal of this research is to develop a more realistic estimate of received signal strength level as calculated by OPNET. The goal is accomplished by replacing the existing free-space pathloss model used by OPNET with the Hata and COST-231 pathloss models. The calculated received signal strength using the new models behaves similarly to the measured values, with a 0.245 dB difference for 880 MHz and a 1.365 dB difference for 1922 MHz between the pathloss slopes. There is an 11.3 dBm difference between the initial starting signal strength from the calculated values and the measured values. An important aspect …
Comparison Of Computational Electromagnetic Codes For Prediction Of Low-Frequency Radar Cross Section, Paul C. Lash
Comparison Of Computational Electromagnetic Codes For Prediction Of Low-Frequency Radar Cross Section, Paul C. Lash
Theses and Dissertations
Radar cross section (RCS) prediction of full-scale aircraft is of interest to military planners for a variety of applications. Several computational electromagnetic codes for RCS prediction are available with differing features and capabilities. The goal of this research is to compare the capabilities of three computational electromagnetic codes for use in production of RCS signature assessments at low frequencies in terms of performance, accuracy, and features: Fast Illinois Solver Code (FISC), Code for Analysis of Radiators on Lossy Surfaces (CARLOS-3D), and Science Applications International Corporation Full-wave solver (SAF). The comparison is accomplished through analysis of predicted and measured RCS of …
Decision Directed And Constant Modulus Algorithms Derived And Evaluated For Multicarrier Systems, Nicholas L. Linnenkamp
Decision Directed And Constant Modulus Algorithms Derived And Evaluated For Multicarrier Systems, Nicholas L. Linnenkamp
Theses and Dissertations
The purpose of this research is to derive and examine blind adaptive algorithms for equalizing multicarrier (MC) communication systems. The author analyzes how they perform under varying environmental conditions and parametric variations, focusing on equalizers set in cascade with the channel. Two well-accepted and widely known cost functions, Decision Directed (DD) and Constant Modulus (CM), are applied to the MC signal structure, and gradient descent algorithms based on both DD and CM functions are derived, analyzed, and compared. Comparison of the new algorithms, Multi-Carrier Decision Directed (MCDD) and Multi-Carrier Constant Modulus (MCCM), focuses on detailing how each algorithm performs when …
Side-Looking Airborne Adaptive Operation In Hot Clutter, Timothy W. Lawson
Side-Looking Airborne Adaptive Operation In Hot Clutter, Timothy W. Lawson
Theses and Dissertations
This research effort examines side-looking airborne radar operation in hot clutter. In this context, hot clutter is an electronic counter-measure used to degrade airborne radar performance. Hot clutter occurs by illuminating the ground with an airborne jammer at some velocity, azimuth, elevation, and range from the airborne radar. This research uses a simplifying assumption where the bistatic hot clutter radar cross section (RCS) scattering statistics are identical to the monostatic clutter RCS scattering statistics. When the airborne jammer waveform scattered returns are perfectly coherent with the radar waveform, the radar cannot distinguish between the returns transmitted by the jammer and …
Wideband Signal Detection Using A Down-Converting Channelized Receiver, Willie H. Mims
Wideband Signal Detection Using A Down-Converting Channelized Receiver, Willie H. Mims
Theses and Dissertations
Ultra wideband (UWB) signals typically occupy a very large spectral bandwidth resulting from extremely short duration pulses. Direct sequence spread spectrum (DSSS) signals typically occupy a large spectral bandwidth resulting from spreading methods. Both signals can be difficult to detect without having prior knowledge of their structure and/or existence. This research develops and evaluates techniques for the non-cooperative (non-matched filter) detection of such signals. Impulse-like UWB and DSSS signals are received in an Additive White Gaussian Noise (AWGN) channel and are assessed using a bandpass filtered, down-converting (BPF-D/C) channelized receiver architecture. Modeling and simulation are conducted to characterize BPF-D/C channelized …
Performance Analysis Of A Cooperative Search Algorithm For Multiple Unmanned Aerial Vehicles Under Limited Communication Conditions, Kevin M. Morris
Performance Analysis Of A Cooperative Search Algorithm For Multiple Unmanned Aerial Vehicles Under Limited Communication Conditions, Kevin M. Morris
Theses and Dissertations
This research investigates the impacts of realistic wireless communications upon a group of unmanned aerial vehicles (UAVs) utilizing a distributed search algorithm. The UAVs are used to survey an area for mobile targets and they require communication to cooperatively locate the targets. The mobile targets do not continually radiate energy, which exacerbates the search effort; a UAV could fly directly over a target and not detect it. A simulation of cooperative UAVs is implemented using the OPNET Modeler network simulation tool. The search performance of a group of UAVs is observed when communication range, data rate, and the number of …
Active Optical Tracking With Spatial Light Modulators, Steven R. Mawhorter
Active Optical Tracking With Spatial Light Modulators, Steven R. Mawhorter
Theses and Dissertations
Two spatial light modulators are utilized for beam splitting, steering and tracking. Both linear and holographic phase screens are used in a demonstration of technology to allow real time tracking to communicate in a one-to-several type scenario. One SLM is used to apply a linear phase modulation to steer multiple beams onto a detector. The spots that are produced represent the targets as they move around the field of view of the central communication node. A Gerchberg-Saxton algorithm will subsequently use the detected spots as the desired pointing locations. Using this as input, the Gerchberg-Saxton algorithm yields a phase only …
A Platform For Antenna Optimization With Numerical Electromagnetics Code Incorporated With Genetic Algorithms, Timothy L. Pitzer
A Platform For Antenna Optimization With Numerical Electromagnetics Code Incorporated With Genetic Algorithms, Timothy L. Pitzer
Theses and Dissertations
This thesis investigation presents a unique incorporation of the Method of Moments (MoM) with a Genetic Algorithm (GA). A GA is used in accord with the Numerical Electromagnetics Code, Version 4 (NEC4) to create and optimize typical wire antenna designs, including single elements and arrays. Design parameters for the antenna are defined and encoded into a chromosome composed of a series of numbers. The cost function associated with the specific antenna of interest is what quantifies improvement and, eventually, optimization. This cost function is created and used by the GA to evaluate the performance of a population of antenna designs. …
Characterization Of The Field Emission Properties Of Carbon Nanotubes Formed On Silicon Carbide Substrates By Surface Decomposition, Michael C. Pochet
Characterization Of The Field Emission Properties Of Carbon Nanotubes Formed On Silicon Carbide Substrates By Surface Decomposition, Michael C. Pochet
Theses and Dissertations
Dense arrays of vertically aligned carbon nanotubes (CNTs) form on the surface of silicon carbide wafers during high temperature anneals under moderate vacuum conditions. The novelty of this growth method is that the CNTs form without the aid of a metal catalyst, allowing for potentially impurity-free CNTs to form. In this study, CNT films were grown by the surface decomposition of silicon carbide substrates. The associated field emission characteristics were investigated to determine if films grown using this method possessed advantages over films grown using metal-catalyzed methods. The associated turn-on and threshold voltages, maximum current density, and emission current stability …
An Airborne Radar Model For Non-Uniformly Spaced Antenna Arrays, Matthew V. Young
An Airborne Radar Model For Non-Uniformly Spaced Antenna Arrays, Matthew V. Young
Theses and Dissertations
This thesis presents an airborne radar model for non-uniformly spaced antenna arrays. Non-uniform arrays potentially possess advantages unobtainable by uniformly spaced arrays. An element position matrix is defined to accommodate arbitrary element locations. The new element position matrix affects the time/phase delay to each element, spatial frequencies, steering vectors, space-time snapshots, and covariance matrices. The joint domain localized and factored time-space-time adaptive processing algorithms are also updated so they are compatible with the new model. The non-uniformly spaced array radar model is verified with previous models presented by Jaffer, Ward, and Hale. The model for non-uniform arrays is used to …
Verification Of A Decision Level Fusion Algorithm Using A Proven Atr System And Measured Sar Data, James Douglas Thompson
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.
Development And Testing Of An Inflatable, Rigidizable Space Structure Experiment, Sarah K. Helms
Development And Testing Of An Inflatable, Rigidizable Space Structure Experiment, Sarah K. Helms
Theses and Dissertations
Many recent space technology concepts require large space structures such as solar arrays and large aperture antennas; however, tight constraints on payload mass and volume often preclude their launch. Employing inflatable, rigidizable structures can reduce mass and volume while providing sufficient packing flexibility and structural stiffness. AFIT has developed RIGEX to flight-test this type of structure. RIGEX will test the deployment and structural characteristics of three thermoplastic composite Sub-Tg tubes. Once launched on the Space Shuttle in 2007, the spaceflight results will be compared to lab data to validate on-orbit reliability and ground test methods. This paper documents three main …
Some Aspects Of The Mechanical Response Of Bmi 5250-4 Neat Resin At 191°C: Experiment And Modeling, John G. Balaconis
Some Aspects Of The Mechanical Response Of Bmi 5250-4 Neat Resin At 191°C: Experiment And Modeling, John G. Balaconis
Theses and Dissertations
The mechanical response of BMI 5250-4 neat resin at 191 degrees C was studied using both creep and recovery tests where several variables were allowed to change. In these tests, the effect of stress rate, prior history, and panel variability were all taken into account. During the creep test, the material showed both primary and secondary creep over 20 h. The recovery tests showed full recovery after it was subjected to 80% UTS. The higher stress rate caused a much greater response in both creep and recovery tests. The prior history was studied by allowing the specimens to go through …
An Epidemiological Approach To Terrorism, Kjirstin A. Bentson
An Epidemiological Approach To Terrorism, Kjirstin A. Bentson
Theses and Dissertations
There are many types of models for counterterrorism, explaining different problems that the military faces in the fight against terrorism. This thesis proposes that one of the fundamental assumptions underlying existing models of counterterrorism is that the struggle with terrorists can be understood as a war in the traditional sense of the term. We propose to rethink the struggle against terrorism as a fight against an infection. The epidemic of terrorist ideology within part of the world is a result, from this perspective, of the infectiousness of that ideology. Using the insights of the field of the epidemiology of ideas, …
Optimal Periodic Inspection Of A Stochastically Degrading System, Timothy B. Booher
Optimal Periodic Inspection Of A Stochastically Degrading System, Timothy B. Booher
Theses and Dissertations
This thesis develops and analyzes a procedure to determine the optimal inspection interval that maximizes the limiting average availability of a stochastically degrading component operating in a randomly evolving environment. The component is inspected periodically, and if the total observed cumulative degradation exceeds a fixed threshold value, the component is instantly replaced with a new, statistically identical component. Degradation is due to a combination of continuous wear caused by the component's random operating environment, as well as damage due to randomly occurring shocks of random magnitude. In order to compute an optimal inspection interval and corresponding limiting average availability, a …
A Minimum Effort Control Approach To Guided Munition Path Planning, Jeffrey M. Borkowski
A Minimum Effort Control Approach To Guided Munition Path Planning, Jeffrey M. Borkowski
Theses and Dissertations
An advance in the development of smart munitions entails autonomously modifying target selection during flight to maximize the value of the target being destroyed. Target identification and classification provides a basis for target value, which is used in conjunction with multi-target tracks to determine an optimal aim point for the munition. A unique guidance law can be constructed that exploits attribute and kinematic data from an onboard video sensor. This thesis develops an innovative path planning algorithm that provides an obstacle avoidance function while navigating the munition toward the highest value target. The foundation of this path planning method is …
Space-Time Adaptive Processing For Side-Looking Arrays With Platform Maneuver, John T. Buckreis
Space-Time Adaptive Processing For Side-Looking Arrays With Platform Maneuver, John T. Buckreis
Theses and Dissertations
This research effort develops a space-time adaptive processing (STAP) radar data model for the side-looking (SL) array with platform maneuver. A primary assumption of most STAP models is the absence of platform maneuver during the coherent processing interval (CPI). This research abandons the platform stationarity assumption, allowing platform pitch, roll, and yaw during the CPI. The model developed characterizes platform maneuver effects on the clutter spectrum, examines Matched Filter (MF) output Signal-to-Interference-plus-Noise-Ratio (SINR), and investigates maneuver impact on sample support homogeneity. The introduction of pitch marginally impacts MF SINR due to the lack of achieved azimuth resolution in this research, …
Multiframe Shift Estimation, Stephen A. Bruckart
Multiframe Shift Estimation, Stephen A. Bruckart
Theses and Dissertations
The purpose of this research was to develop a fundamental framework for a new approach to multiframe translational shift estimation in image processing. This thesis sought to create a new multiframe shift estimator, to theoretically prove and experimentally test key properties of it, and to quantify its performance according to several metrics. The new estimator was modeled successfully and was proven to be an unbiased estimator under certain common image noise conditions. Furthermore its performance was shown to be superior to the cross correlation shift estimator, a robust estimator widely used in similar image processing cases, according to several criteria. …
Using Value-Focused Thinking To Evaluate The Practicality Of Porous Pavement Parking Areas On Air Force Installations, Christopher D. Bulson
Using Value-Focused Thinking To Evaluate The Practicality Of Porous Pavement Parking Areas On Air Force Installations, Christopher D. Bulson
Theses and Dissertations
Natural runoff processes have been altered by urban development; impervious surfaces (rooftops, highways, parking areas) and their associated storm water systems channel runoff from a vast area into one concentrated outflow. This storm water runoff can cause erosion, flooding, landslides, and significant damage to aquatic ecosystems. Runoff from highways and parking areas has also been known to contain high levels of suspended solids, heavy metals and hydrocarbons. Porous pavements allow infiltration of water through typically impervious surfaces, reducing storm water volumes and acting as a pollutant filtration system. Since there is currently no methodology for Air Force decision-makers to compare …
A Study Of Near Field Data Transformed To The Far Field For A Canonical Pec Scatterer, E. Matthew Cady
A Study Of Near Field Data Transformed To The Far Field For A Canonical Pec Scatterer, E. Matthew Cady
Theses and Dissertations
The purpose of this research was to analyze the error associated with the Image Based Near Field to Far Field Transformation (IB NFFFT) for a canonical perfectly electrically conductive (PEC) scatterer. This research compares two groups of data: far field RCS predicted by the IB NFFFT and far field RCS predicted by X-Patch. The IB NFFFT requires a complete set of calibrated monostatic near field scattering data of the object. A detailed description is given of the configuration of the measurement facilities and procedures that were required to obtain the calibrated near field scattering data, as well as the process …
Computational Modeling Of The Dielectric Barrier Discharge (Dbd) Device For Aeronautical Applications, Christopher S. Charles
Computational Modeling Of The Dielectric Barrier Discharge (Dbd) Device For Aeronautical Applications, Christopher S. Charles
Theses and Dissertations
Dielectric Barrier Discharge (DBD) type devices, when used as plasma actuators, have shown significant promise for use in many aeronautical applications. Experimentally, DBD actuator devices have been shown to induce motion in initially still air, and to cause re-attachment of air flow over a wing surface at a high angle of attack. This thesis explores the numerical simulation of the DBD device in both a lD and 2D environment. Using well established fluid equation techniques, along with the appropriate approximations for the regime under which these devices will be operating, computational results for various conditions and geometries are explored. In …
Structural Health Monitoring Considering Internal Beam Damage, Jessica B. Chronister
Structural Health Monitoring Considering Internal Beam Damage, Jessica B. Chronister
Theses and Dissertations
The present study establishes a nondestructive method of damage detection and assessment in cantilever beams. The specimens used are twelve-inch aluminum 2024-T3 beams with machined notches of varying lengths and locations. Laser Doppler vibrometry is used to obtain the frequency response of vibrating beams. Experimental methods are developed to detect the presence, location and extent of damage by direct observation of the eigenvector in the third through eighth modes. Models in MATLAB and ABAQUS are used to predict and validate the observed data. With this experimental method developed, the validity of the method is tested for specimens that have been …
Characteristics Of Two-Dimensional Triangular And Three-Dimensional Face-Centered-Cubic Photonic Crystals, Jeffery D. Clark
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 …
Hazardous Material Cargo Frustration At Military Aerial Ports Of Embarkation, Niel E. Christensen
Hazardous Material Cargo Frustration At Military Aerial Ports Of Embarkation, Niel E. Christensen
Theses and Dissertations
Since military units often require critical hazardous materials in an expedited manner, identifying choke points within the supply chain is necessary to improve logistic support to front line forces. Hazardous materials are some of the most critical assets for the war fighter, as well as the most restrictive and often most time consuming for transportation. This research quantifies the extent that vendor and depot supplied cargo is being delayed at Aerial Ports of Embarkation. By looking at frustrated hazardous material at Charleston Air Force Base, South Carolina and Dover Air Force Base, Delaware, a case study methodology is used to …