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Air Force Institute of Technology

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Articles 3661 - 3690 of 5699

Full-Text Articles in Engineering

Optimization Of A Quantum Cascade Laser Operating In The Terahertz Frequency Range Using A Multiobjective Evolutionary Algorithm, Traci A. Keller Jun 2004

Optimization Of A Quantum Cascade Laser Operating In The Terahertz Frequency Range Using A Multiobjective Evolutionary Algorithm, Traci A. Keller

Theses and Dissertations

A quantum cascade (QC) laser is a specific type of semiconductor laser that operates through principles of quantum mechanics. In less than a decade QC lasers are already able to outperform previously designed double heterostructure semiconductor lasers. Because there is a genuine lack of compact and coherent devices which can operate in the far-infrared region the motivation exists for designing a terahertz QC laser. A device operating at this frequency is expected to be more efficient and cost effective than currently existing devices. It has potential applications in the fields of spectroscopy, astronomy, medicine and free-space communication as well as …

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Excited States Of Silicon Carbide Clusters By Time Dependent Density Functional Theory, John E. Boyd Jun 2004

Excited States Of Silicon Carbide Clusters By Time Dependent Density Functional Theory, John E. Boyd

Theses and Dissertations

Previous AFIT research with density functional theory (DFT) has shown itself to be accurate for small SimCn (m,n ≤ 5) clusters at a fraction of the cost of other quantum mechanical methods, but it is only a ground state theory. Time dependent density functional theory (TDDFT), however, is able to calculate excited states as well. Evaluating the accuracy of these methods with respect to the excited states of these clusters was the focus of this research, specifically with respect to the excitation energies, geometries, and vibrational frequencies. It is shown that for the excited states that can …

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Aerodynamic Analysis Of Lattice Grid Fins In Transonic Flow, Karl S. Orthner Jun 2004

Aerodynamic Analysis Of Lattice Grid Fins In Transonic Flow, Karl S. Orthner

Theses and Dissertations

Lattice grid fins have been studied for missile tail control for several years. A lattice grid fin can be described as an unconventional missile control surface comprised of an outer frame supported by an inner lattice grid of lifting surfaces. This unconventional fin design offers favorable lift characteristics at high angle of attack as well as almost zero hinge moments allowing the use of small and light actuators. In addition, they promise good storability for potential tube-launched and internal carriage dispenser-launched applications. The drawback for the lattice grid fins is the high drag and potentially poor radar cross section performance …

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Magnetogasdynamic Flow Acceleration In A Scramjet Nozzle, Brian H. Harrington Jun 2004

Magnetogasdynamic Flow Acceleration In A Scramjet Nozzle, Brian H. Harrington

Theses and Dissertations

The effect of magnetogasdynamic (MGD) interactions on flow acceleration and thrust in a scramjet accelerator/nozzle are examined numerically at a free-stream flight condition of Mach 8. The parameters of conductivity pattern and load factor are varied in both inviscid and viscous flow regimes with the intent of increasing axial force exerted on the flow through a scramjet accelerator. The numerical code solves the Navier-Stokes equations with additional source terms for the MGD forces and energy interactions. An accelerating Lorentz force is applied to the flow resulting from a constant magnetic field and an electric field produced by two continuous side …

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Detached Eddy Simulation Analysis Of Pak-B Low Pressure Turbine Blade, Kyle Malone Jun 2004

Detached Eddy Simulation Analysis Of Pak-B Low Pressure Turbine Blade, Kyle Malone

Theses and Dissertations

Two cases were computationally investigated using the detached eddy simulation (DES) turbulence model: an unmodified Pak-B blade and a Pak-B blade with a dimple located at 65% of axial chord. Both cases were created so that they simulated an infinite span with an infinite number of dimples. The cases were run for an inlet Reynolds number of 25,000. The computed results were used to resolve the location of separation and reattachment, visualize the streamlines for the dimpled case, build velocity magnitude contour and vector plots, and map the thickness of the boundary layer. The results were then compared to previous …

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Isomer Heat Exchanger Combustor Replacement For A Supersonic Ramjet Powered Vehicle, Jonathan C. Cox Jun 2004

Isomer Heat Exchanger Combustor Replacement For A Supersonic Ramjet Powered Vehicle, Jonathan C. Cox

Theses and Dissertations

This study investigated the possibility of utilizing a Triggered Isomer Heat Exchanger (TIHE) within a ramjet engine to power a supersonic Conventional Air Launched Cruise Missile (CALCM). A computational ramjet engine was created using engine analysis software. This model was then run through a simulated cruise missile mission using AEDsys, a mission analysis and engine performance software suite. The replacement of the combustor with a TIHE led to an impressive range increase for the supersonic cruise missile.

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Aeroelastic Analysis Of A Joined-Wing Sensorcraft, Jennifer J. Sitz Jun 2004

Aeroelastic Analysis Of A Joined-Wing Sensorcraft, Jennifer J. Sitz

Theses and Dissertations

This study performed an aeroelastic analysis of a joined-wing SensorCraft. The analysis was completed using an aluminum structural model that was splined to an aerodynamic panel model. The force and pressure distributions were examined for the four aerodynamic panels: aft wing, fore wing, joint, and outboard tip. Both distributions provide the expected results (elliptical distribution), with the exception of the fore wing. The fore wing appears to be affected by interference with the joint. The use of control surfaces for lift and roll was analyzed. Control surfaces were effective throughout most of the flight profile, but may not be usable …

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Target Recognition Using Late-Time Returns From Ultra-Wideband, Short-Pulse Radar, Kenneth J. Pascoe Jun 2004

Target Recognition Using Late-Time Returns From Ultra-Wideband, Short-Pulse Radar, Kenneth J. Pascoe

Theses and Dissertations

The goal of this research is to develop algorithms that recognize targets by exploiting properties in the late-time resonance induced by ultra-wide band radar signals. A new variant of the Matrix Pencil Method algorithm is developed that identifies complex resonant frequencies present in the scattered signal. Kalman filters are developed to represent the dynamics of the signals scattered from several target types. The Multiple Model Adaptive Estimation algorithm uses the Kalman filters to recognize targets. The target recognition algorithm is shown to be successful in the presence of noise. The performance of the new algorithms is compared to that of …

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Estimating Equatorial F-Region Daytime Vertical E X B Drift Velocities From Ground-Based Magnetometer Measurements In The Philippine Longitude Sector, Shauna M. Kinkela Jun 2004

Estimating Equatorial F-Region Daytime Vertical E X B Drift Velocities From Ground-Based Magnetometer Measurements In The Philippine Longitude Sector, Shauna M. Kinkela

Theses and Dissertations

Ionospheric disturbances can severely impact Department of Defense (DoD) systems, such as radar. satellite. and navigation technologies. Forecasting disturbances and describing the Earth's ionosphere, in turn, relies upon innovative computer-based models that gather input parameters from ground and space-borne observations and empirical models for ionospheric drivers. Equatorial E x B drift velocities are significant input parameters that go into many ionospheric models, because they help describe vertical plasma motions near the magnetic equator. Previous work by Anderson, et al 2002 has demonstrated the ability to derive Peruvian longitude sector, daytime vertical E x B drifts from ground-based magnetometer data. The …

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Comparative Study On The Use Of Coherent Radar-Derived Electric Fields Vs. Statistical Electric Fields For The Initialization Of A High-Latitude Ionospheric Model, Christopher M. Hogue Jun 2004

Comparative Study On The Use Of Coherent Radar-Derived Electric Fields Vs. Statistical Electric Fields For The Initialization Of A High-Latitude Ionospheric Model, Christopher M. Hogue

Theses and Dissertations

The structure and time development of the magnetosphere-ionosphere system have significant impacts on the Air Force and its mission. Specifically, an accurate knowledge of ionospheric plasma densities is important for the operation of many Air Force systems. This research analyzes plasma density structure development through comparing two distinct electric field models. The two models compared here are a commonly used statistical model created by Heppner and Maynard 1987, and a more recently developed model using real-time coherent radar measurements from the SuperDARN radar network. Ionospheric simulations were run using Utah State University s Time-Dependent Ionospheric Model (TDIM) with the two …

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Shock Tube Investigation Of Pressure And Ion Sensors Used In Pulse Detonation Engine Research, Robert J. Mcmillan Jun 2004

Shock Tube Investigation Of Pressure And Ion Sensors Used In Pulse Detonation Engine Research, Robert J. Mcmillan

Theses and Dissertations

Shock tubes utilize a difference in pressures between gases separated by a diaphragm to create a shock wave when the diaphragm ruptures. By using sensors of known spacing, the speed of the wave can be determined. The AFIT 2-inch shock tube was reassembled and tested to ensure proper and safe operation. A high-speed data acquisition system was configured to take data at 2 MS/s. This research showed that the Mach number of the shock waves produced in this shock tube fall within 7% of theoretical values at speeds under Mach 3 and within 9% at higher speeds. The peak velocity …

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Extending The Aircraft Availability Model To A Constrained Depot Environment Using Activity-Based Costing And The Theory Of Constraints, Gerardo H. Acosta Voegeli Jun 2004

Extending The Aircraft Availability Model To A Constrained Depot Environment Using Activity-Based Costing And The Theory Of Constraints, Gerardo H. Acosta Voegeli

Theses and Dissertations

The Aircraft Availability Model (AAM) assists managers in the selection of an optimal list of items to repair in order to attain the best aircraft availability rate. The model considers procurement or repair costs for the components as if the costs were unit variable as a price, instead of a repair cost representing a mix of both fixed and variable cost. This research used the AAM in conjunction with Activity Based-Costing (ABC) and The Theory of Constraints (TOC) methodologies to investigate the relationships between price, product mix, Aircraft Availability (AA) and total cost. This approach explicitly recognizes that the Air …

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Implementing Institute Of Electrical And Electronics Engineers (Ieee) 802.11 Standard Medium Access Control Protocol For Wireless Local Area Networks (Lans) On A Laboratory Hardware Prototype, Joshua D. Green Jun 2004

Implementing Institute Of Electrical And Electronics Engineers (Ieee) 802.11 Standard Medium Access Control Protocol For Wireless Local Area Networks (Lans) On A Laboratory Hardware Prototype, Joshua D. Green

Theses and Dissertations

Wireless Local Area Networks (LANs) are extremely convenient, flexible, and easy to deploy. All LANs in which multiple hosts must access the same medium use a Medium Access Control (MAC) protocol to coordinate channel access. The MAC is part of the Data Link Layer of the Open Systems Interconnection (OSI) Reference Model. One MAC protocol in extensive use today is the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard. Since IEEE 802.11 devices are so prevalent in today s world, many researcher are exploring modifications and enhancements to the protocol. There are several well developed analytical and simulation models …

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Utilizing Near-Field Measurements To Characterize Far-Field Radar Signatures, John R. Watkins Jun 2004

Utilizing Near-Field Measurements To Characterize Far-Field Radar Signatures, John R. Watkins

Theses and Dissertations

The increased need for stealth aircraft requires an on-site Far-Field (FF) Radar Cross-Section (RCS) measurement process. Conducting these measurements in on-site Near-Field (NF) monostatic facilities results in significant savings for manufacturers and acquisition programs. However, NF measurements are not directly extended to a FF RCS. Therefore, a large target Near-Field to Far-Field Transformation (NFFFT) is needed for RCS measurements. One approach requires an Inverse Synthetic Aperture Radar (ISAR) process to create accurate scattering maps. The focus of this work is the development of accurate NF scattering maps generated by a monostatic ISAR process. As a first look, the process is …

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An Assessment Of Modern Methods For Rotor Track And Balance, Michael J. Renzi Jun 2004

An Assessment Of Modern Methods For Rotor Track And Balance, Michael J. Renzi

Theses and Dissertations

One routine maintenance item facing the helicopter industry today is the issue of rotor track and balance (RT&B). While the task of reducing vibrations is often overlooked as simply an unimportant maintenance concern, what should not be overlooked is the extensive amount of time and money committed by maintenance to smoothing an aircraft. If there were a way to make the process of rotor track and balance more efficient it would be a huge boost to the helicopter industry in both time and money. The first steps towards research into new and improved methods is to evaluate what is currently …

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Cold Flow Testing Of A Modified Subscale Model Exhaust System For A Space Based Laser, David B. Jarrett Jun 2004

Cold Flow Testing Of A Modified Subscale Model Exhaust System For A Space Based Laser, David B. Jarrett

Theses and Dissertations

The aim of this research was a continued study of gas-dynamic phenomena that occurred in a set of stacked nozzles as reported by Captains Ian Bautista in 2003 and Scott Bergren in 2002. The arrangement of the stacked nozzles was a modified version of a 1/5th scale-model of one quadrant of the conceptual Space Based Laser Integrated Flight Experiment (SBL IFX) gas dynamic laser. Rather than cylindrical rings of nozzles, the stacked nozzles were flat and able to be rotated about a vector normal to the nozzle exits. This set of stacked flat nozzles was installed on a blow-down/vacuum wind …

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Fretting Fatigue Behavior Of Shot-Peened Titanium Alloy Tl-6al-4v Under Seawater Conditions, William Y. Allen Jun 2004

Fretting Fatigue Behavior Of Shot-Peened Titanium Alloy Tl-6al-4v Under Seawater Conditions, William Y. Allen

Theses and Dissertations

The fretting fatigue behavior of the shot-peened titanium alloy, Ti-6Al-4V, was investigated under a corrosive environment of synthetic seawater. Fretting fatigue tests were performed over a wide stress range to determine the effect of seawater at high and low cycle fatigue regimes. The results from this study showed: (1) seawater significantly reduces the fretting fatigue life of shot-peened Ti-6Al-4V at both high and low cycle fatigue relative to its counterpart in ambient laboratory conditions, (2) shot peening increases the fretting fatigue life of Ti-6Al-4V when tested under dry and seawater conditions relative to its counterpart of unpeened Ti-6Al-4V, (3) surface …

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A Study Of A Skirtless Hovercraft Design, Edward A. Kelleher May 2004

A Study Of A Skirtless Hovercraft Design, Edward A. Kelleher

Theses and Dissertations

Initial study into three possible skirtless hovercraft designs. The designs utilize Coanda nozzles and a Coanda wing surface to generate lift and create a pressure cushion below the craft. The pressure cushion is to be maintained by an air curtain created by flow spill from the Coanda wing surface. Three proposed skirtless hovercraft designs were analyzed via computational fluid dynamics to ascertain their lift generation capabilities. The three designs were adaptations from William Walter's hybricraft primer and his patent for a fan driven lift generation device. Each design featured Coanda nozzles, or nozzles that utilize the Coanda effect, to redirect …

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A Value Focused Thinking Model For The Development And Selection Of Electrical Energy Source Alternatives At Military Installations, Gregory T. Schanding Mar 2004

A Value Focused Thinking Model For The Development And Selection Of Electrical Energy Source Alternatives At Military Installations, Gregory T. Schanding

Theses and Dissertations

Electrical power on military installations is vital for mission accomplishment. Most installations obtain electrical power from a local commercial utility. Although commercial power service has a very low interruption rate, the threat of a sustained power outage resulting from a terrorist act or a natural disaster is of concern. The military should posture itself to prevent such power outages and prepare to mitigate the adverse effects associated with the loss of power. This thesis presents a Value Focused Thinking approach to the development of a decision analysis model to assist a decision maker at a military installation in the generation …

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The Predictive Validity Of The Afit Graduate Management Program Admission Requirements: A Reassessment And Extension, Sarah E. Woods Mar 2004

The Predictive Validity Of The Afit Graduate Management Program Admission Requirements: A Reassessment And Extension, Sarah E. Woods

Theses and Dissertations

This research is based on the Air Force and AFIT balancing mission requirements of personnel needed for duty and training airmen in advanced studies. Currently, over 50% of AFIT students do not meet AFIT entrance requirements. The purpose of this research was to examine criteria to determine its predictability of graduate success, as measured by graduate GPA, as well as determine whether performance is different for students who require criteria to be waived. Current AFIT eligibility criteria include undergraduate GPA, GRE test scores, or GMAT test scores. Other variables examined in this study include: GRE-Analytical test scores; rank/grade; prior enlistment; …

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Coplanar Air Launch With Gravity-Turn Launch Trajectories, David W. Callaway Mar 2004

Coplanar Air Launch With Gravity-Turn Launch Trajectories, David W. Callaway

Theses and Dissertations

The purpose of this study was to determine the feasibility of launching a vehicle based on the Boeing AirLaunch System in a coplanar, direct to rendezvous trajectory with gravity-turn. The focus of the research was to model the launch trajectory and determine the ability to reach different coplanar orbits. The launch trajectory was modeled using two-dimensional equations of motion and a boundary value problem was posed and solved for the gravity-turn trajectory. Trajectories were then created in an attempt to reach different altitudes through coasting and transfer orbits. Finally a specific orbital altitude was chosen and the trajectories were analyzed …

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Analytical Results For A Single-Unit System Subject To Markovian Wear And Shocks, Daniel E. Finkelstein Mar 2004

Analytical Results For A Single-Unit System Subject To Markovian Wear And Shocks, Daniel E. Finkelstein

Theses and Dissertations

This thesis develops and analyzers a mathematical model for the reliability measures of a single-unit system subject to continuous wear due to its operating environment and randomly occurring shocks that inflict a random amount of damage to the unit. Assuming a Markovian operating environment and shock arrival mechanism, Laplace-Stieltjes transform expressions are obtained for the failure time distribution and all of its moments. Moreover, an analytical expression is derived for the long-run availability of the single-unit system when it is subject to an inspect-and-replace maintenance policy. The analytical results are illustrated, and their results compared with those of Monte Carlo-simulated …

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Analysis And Forecasting Of U.S. Navy Operating And Support (O&S) Costs For Rotary Aircraft, Christopher J. Wilkes Mar 2004

Analysis And Forecasting Of U.S. Navy Operating And Support (O&S) Costs For Rotary Aircraft, Christopher J. Wilkes

Theses and Dissertations

This research explores forecasting techniques to estimate the Cost per Flying Hour (CPFH) for Navy rotary aircraft. Three separate forecasting techniques were evaluated to better predict the CPFH for better estimating and budgeting by the U.S. Navy. The process begins by empirically analyzing Operating & Support cost categories for each helicopter. Trends were examined in CPFH. For forecasting purposes, actual CPFH figures were compiled from 1997 to 2003 for the CH-46D, the CH-53D, the MH-53E, the SH-60F, the UH-1N, and the UH-3H helicopters. The forecasting techniques explored were the 3-year moving average, the single exponential smoothing method, and Holt's linear …

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Low Temperature Hall Measurements Of Neutron Irradiated Silicon Carbide, Angelo M. Bonavita Mar 2004

Low Temperature Hall Measurements Of Neutron Irradiated Silicon Carbide, Angelo M. Bonavita

Theses and Dissertations

The purpose of this research was to search for evidence of low temperature annealing from neutron irradiated 4H-silicon carbide. No features suggesting annealing were found below a temperature of 340K. Temperature dependant Hall effect measurements were taken over a range of 100K to 340K recording resistivity, carrier densities, and mobility. Resistivity was noted to increase with irradiations, and carrier densities appeared to decrease, while mobility appeared minimally affected by neutron irradiation. This suggests the creation of active acceptor defects decreasing carrier concentrations. N-type samples measured were 5mm x 5mm square with Nickel contacts, and irradiated to 1010 and 10 …

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Purchasing And Supply Chain Management Costing: An Air Transport Perspective Derived Through Commercial Air Cargo Firms, Kurt Ettrich Mar 2004

Purchasing And Supply Chain Management Costing: An Air Transport Perspective Derived Through Commercial Air Cargo Firms, Kurt Ettrich

Theses and Dissertations

The Air Force has struggled to completely understand the costs associated with its operations. The issue of understanding cost is complex, involving many perspectives, methods and techniques. When examined from a broad standpoint, total supply chain costs can include a firm's costs plus upstream and downstream costs. This perspective takes vendors, suppliers and end customers into consideration. From this broad standpoint, the Air Force does not know its total supply chain cost. Since the Air Force's supply chain is too broad to be a focus of this study, a smaller segment was chosen for a closer look. Specifically, air cargo …

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A Linear Subspace Approach To Burst Communication Signal Processing, Daniel E. Gisselquist Mar 2004

A Linear Subspace Approach To Burst Communication Signal Processing, Daniel E. Gisselquist

Theses and Dissertations

This dissertation focuses on the topic of burst signal communications in a high interference environment. It derives new signal processing algorithms from a mathematical linear subspace approach instead of the common stationary or cyclostationary approach. The research developed new algorithms that have well-known optimality criteria associated with them. The investigation demonstrated a unique class of multisensor filters having a lower mean square error than all other known filters, a maximum likelihood time difference of arrival estimator that outperformed previously optimal estimators, and a signal presence detector having a selectivity unparalleled in burst interference environments. It was further shown that these …

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Experimental Investigation Into The Aerodynamic Performance Of Both Rigid And Flexible Wing Structured Micro-Air-Vehicles, Anthony M. Deluca Mar 2004

Experimental Investigation Into The Aerodynamic Performance Of Both Rigid And Flexible Wing Structured Micro-Air-Vehicles, Anthony M. Deluca

Theses and Dissertations

The Air Force Research Lab, Munitions Directorate, Eglin Air Force Base, Florida has designed a man-portable carbon-fiber Micro-Air-Vehicle (MA V) used for on-the-spot surveillance by Special Operations Forces (SOF) for enemy reconnaissance as well as post-strike Battle Damage Assessment (BDA).The main goals of this experiment are: 1) characterize the flow quality of the new AFIT 3' x 3' wind tunnel and 2) determine the aerodynamic performance characteristics of the 24" span, 6" chord flexible and rigid wing MA V s. The turbulent intensity of the wind tunnel was approximately 2%. Both MA Vs had an average lift slope within 3.5% …

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Evaluating The Navigation Potential Of The National Television System Committee Broadcast Signal, Ryan J. Eggert Mar 2004

Evaluating The Navigation Potential Of The National Television System Committee Broadcast Signal, Ryan J. Eggert

Theses and Dissertations

The accuracy and worldwide availability of the Global Positioning System (GPS) make it the dominant system for navigation and precise positioning. Unfortunately, many situations arise in which GPS may not be adequate, e.g., urban navigation. This research evaluates the navigation potential of the National Television System Committee (NTSC) broadcast signal using a time-difference-of-arrival (TDOA) algorithm. TDOA measurements are made using NTSC broadcast signals collected from low and high multipath environments. These measurements are then used to evaluate the severity and dynamic effects of NTSC broadcast multipath signals. Three data reduction algorithms were developed--one that modifies the classical cross-correlation TDOA approach, …

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Simulating A Chromotomographic Sensor For Hyperspectral Imaging In The Infrared, Anthony J. Dearinger Mar 2004

Simulating A Chromotomographic Sensor For Hyperspectral Imaging In The Infrared, Anthony J. Dearinger

Theses and Dissertations

Hyperspectral imaging systems passively sense radiant electromagnetic energy from a remote scene to form a three dimension profile of the remote scene. The data contained in this profile describes real images of the remote scene for a certain number of spectral wavelength bands across a finite spectral range of electromagnetic radiation. Typical grating type hyperspectral imaging systems collect spectral electromagnetic radiation in the visible and near infrared spectral range, by incrementally scanning across the spatial extent of the remote scene. The legacy of low optical throughput because of the optical scanning techniques employed in these systems means adapting these systems …

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Monotonic, Creep-Rupture, And Fatigue Behavior Of Carbon Fiber Reinforced Silicon Carbide (C/Sic) At An Elevated Temperature, John M. Engesser Mar 2004

Monotonic, Creep-Rupture, And Fatigue Behavior Of Carbon Fiber Reinforced Silicon Carbide (C/Sic) At An Elevated Temperature, John M. Engesser

Theses and Dissertations

The main objective of this research effort was to examine the impact that cyclic loading frequency has on the life of a C/SiC composite at an elevated temperature of 550°C. Cyclic loading of C/SiC was investigated at frequencies of 375 Hz, 10 Hz, 1 Hz, and 0.1 Hz. Creep-Rupture tests and tests that were combinations of creep-rupture and fatigue were also accomplished. A monotonic tensile test was performed at 550°C and compared to a room temperature monotonic test. This study showed that an elevated temperature of 550°C has very little effect on the Ultimate Tensile Strength (UTS) of C/SiC. The …

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