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Geostatistical Analysis Of Hydraulic Conductivity In Heterogeneous Aquifers, Craig S. Biondo Dec 1995

Geostatistical Analysis Of Hydraulic Conductivity In Heterogeneous Aquifers, Craig S. Biondo

Theses and Dissertations

Observations of the spatial variability of hydraulic conductivity of the heterogeneous alluvial aquifer at Columbus Air Force Base in Mississippi are analyzed using parametric geostatistical approaches. Field studies have revealed that the heterogeneity of the aquifer hydraulic conductivity field controls the movement and dispersion of groundwater solutes. Therefore, a means of quantifying spatial variability is essential for the application of flow and solute transport models to practical problems. Application of these models requires a large number of hydraulic conductivity measurements. Geostatistical analysis and kriging estimation procedures assist in providing these large numbers of values when sampling designs have provided sparse …


Thermo-Mechanical Fatigue Behavior Of Cross-Ply Ceramic Matrix Composite Under Tension-Tension Loading, Dana G. Allen Dec 1995

Thermo-Mechanical Fatigue Behavior Of Cross-Ply Ceramic Matrix Composite Under Tension-Tension Loading, Dana G. Allen

Theses and Dissertations

The purpose of this study was to investigate the combined effect of cyclic temperature and loading on the fatigue life of a ceramic matrix composite with a cross ply lay-up. The material used in this study was a potassium borosilicate glass (BSG) doped magnesium aluminosilicate (MAS) cordierite matrix reinforced with Nicalon (silicon carbide, SiC) fibers in a [0/90]4s lay-up. Thermomechanical fatigue (TMF) tests were performed with a period of 180 seconds/cycle, or 0.00556 Hz, and a triangular wave-form. The temperature was cycled between 566°C and l093°C, and the stress levels varied between 60 MPa and 145 MPa. All tests …


Stress/Strain Ratio Effects On Fatigue Response Of A Scs-6/Ti-15-3 Metal Matrix Composite At Elevated Temperature, Sean C. Jackson Dec 1995

Stress/Strain Ratio Effects On Fatigue Response Of A Scs-6/Ti-15-3 Metal Matrix Composite At Elevated Temperature, Sean C. Jackson

Theses and Dissertations

This study investigated the fatigue life and damage mechanisms of a [0]8, SCS-6/Ti-15-3, metal matrix composite at 427°C for three different stress/strain ratios, R = -1, 0 and 0.5. Fatigue life and damage mechanism comparisons were made for the varying R ratios and between the load and strain control modes. Fatigue life comparisons show that on a maximum stress/strain basis as R is increased fatigue life increases while on a stress/strain range basis as R increases fatigue life decreases. Similar damage mechanisms were found between the R = -1 and R = 0 tests conducted at the same …


Numerical Simulation Of Supersonic Turbulent Boundary Layer Flow Under The Influence Of Mild Pressure Gradients, Eric T. Fick Dec 1995

Numerical Simulation Of Supersonic Turbulent Boundary Layer Flow Under The Influence Of Mild Pressure Gradients, Eric T. Fick

Theses and Dissertations

Mach 2.9 boundary layer flow (Re/m ≈ 1.75x107) under the influence of mild pressure gradients is studied numerically. Baldwin-Lomax and k - ω turbulence models are incorporated into a cell centered finite volume flow solver and the results are compared with hot wire anemometry and Laser Doppler Velocimetry (LDV) measurements obtained for the same geometries in the AFIT Mach 2.9 wind tunnel. Agreement between the present simulations obtained with the k - ω turbulence model and experimental velocity profiles is excellent in all test sections. Nondimensional turbulent shear stress predictions closely match experimental data in the …


Compressible Turbulence Measurement In The Mixing Layer Of An Adiabatic Normal Slot Injection Into Supersonic Flow, Christopher D. Whitcomb Dec 1995

Compressible Turbulence Measurement In The Mixing Layer Of An Adiabatic Normal Slot Injection Into Supersonic Flow, Christopher D. Whitcomb

Theses and Dissertations

In this study mean flow and compressible turbulence measurements were taken at a station x = 72W downstream of the injection, where W is the injector throat width, of an adiabatic 2-D Mach 1.6 normal slot injection into a Mach 2.9 flow. Data were collected using a conventional Pitot probe, a cone-static probe, and multiple overheat cross-wire anemometry. In addition, schlieren and shadowgraph flow visualization was used to investigate the flow structure at both the injection point and at the downstream data collection point. From these measurements, mass flux component turbulence intensities of 8% to 10% were seen. The total …


Sub-Optimal Control Of Rigid Spacecraft Reorientation Using Three Momentum Wheels, Gregory W. Schultz Dec 1995

Sub-Optimal Control Of Rigid Spacecraft Reorientation Using Three Momentum Wheels, Gregory W. Schultz

Theses and Dissertations

This thesis addresses sub-optimal employment of 3 momentum wheels for large angle reorientation of rigid spacecraft with minimal induced spacecraft motion during maneuvers. In addition to development of general theory for 3 wheel vehicles, simulation results for a vehicle using momentum wheels for secondary attitude control (GPS Block IIR) are compared to results for a vehicle using them for primary attitude control (the Hubble Space Telescope), to demonstrate practical applications and limitations. While the control laws were developed assuming no external perturbing torques on the vehicle, reorientation scenarios were run both in a torque free environment as well as an …


Electrical Characterization Of 4h-And 6h-Silicon Carbide Schottky Diodes, Jeffrey C. Wiemeri Dec 1995

Electrical Characterization Of 4h-And 6h-Silicon Carbide Schottky Diodes, Jeffrey C. Wiemeri

Theses and Dissertations

The electrical properties of silicon carbide (SiC) make it an excellent candidate for use in high temperature/high power devices due to its wide bandgap, high breakdown field, high electron mobility, etc. In this work two Schottky diodes of platinum (Pt) on n-type carbon faced 4H-SiC and three Schottky diodes of nickel (Ni) on n-type silicon faced 6H-SiC were electrically characterized. The diodes exhibited good performance up to 698 K for both the forward and reverse (up to -100v) bias voltages. The barrier heights measured by I-V-T tests were found to be 0.32 and 0.61 eV for the Pt/4H-SiC samples, but …


Evaluating The Feasibility Of Sequential Indicator Simulation In Reproducing Spatial Connectivity In A Heterogeneous Transmissivity Field, D. Duane Kenyon Dec 1995

Evaluating The Feasibility Of Sequential Indicator Simulation In Reproducing Spatial Connectivity In A Heterogeneous Transmissivity Field, D. Duane Kenyon

Theses and Dissertations

A Non-Parametric estimation technique was used to simulate realizations of a heterogeneous transmissivity field based upon sampled values from three different sampling scenarios. These realizations were compared to output from a parametric estimation technique with respect to truth as defined by an exhaustive data set of 6,000 transmissivity values. Estimated transmissivity fields were then used as input into a flow model from which fields of heads and specific discharges were obtained and compared. Given the financial limitations imposed upon the number and quality of samples reasonably available, Sequential Indicator Simulation, a non-parametric technique, was shown to be of considerable value …


Validation Testing A Contaminant Transport And Natural Attenuation Simulation Model Using Field Data, Steven J. Flier Dec 1995

Validation Testing A Contaminant Transport And Natural Attenuation Simulation Model Using Field Data, Steven J. Flier

Theses and Dissertations

This research extends the work begun by Enyeart (1994) which evaluated the process of intrinsic bioremediation, and which developed a model for predicting the velocity of an aerobic degradation front, as it traverses the length of a JP-4 contaminant plume. It is assumed this aerobic front will traverse the contaminant plume as dissolved oxygen is carried by the ground water through the sorption-retarded contaminant. The ultimate purpose of Enyeart's model is to use it to develop field guidance for assessing the feasibility of intrinsic bioremediation to restore petroleum-contaminated soils. After simulating intrinsic bioremediation many times with a spreadsheet model, results …


In Situ Warming And Soil Venting To Enhance The Biodegradation Of Jp-4 In Cold Climates: A Critical Study And Analysis, Ricky D. Cox Dec 1995

In Situ Warming And Soil Venting To Enhance The Biodegradation Of Jp-4 In Cold Climates: A Critical Study And Analysis, Ricky D. Cox

Theses and Dissertations

Numerous bioremediation projects have proven effective in accelerating contaminant biodegradation by injecting oxygen into the vadose zone with a technique called bioventing. In cold climates, bioremediation is limited to the summer when soil temperatures are sufficient to support microbial growth. Laboratory studies directly correlate increased biodegradation rates with temperature. By raising soil temperatures, in situ jet fuel remediation can be accelerated which was shown by a bioventing project conducted in 1991 at Eielson AFB, Alaska, where three soil warming techniques were used. Two methods actively warmed the soil - warm water circulation and heat tape; the other passively warmed the …


A Differential Gps Aided Ins For Aircraft Landings, Ryan L. Britton Dec 1995

A Differential Gps Aided Ins For Aircraft Landings, Ryan L. Britton

Theses and Dissertations

The Department of Defense (DOD) and the commercial airline industry are in the process of replacing the instrument landing system (ILS) for aircraft precision approach landings. The use of differential Global Positioning System (DGPS) is thought to be a viable replacement for ILS precision approaches. This thesis explores the integration of an INS, DGPS, Barometric Altimeter, Pseudolite, and Radar Altimeter for a tanker type and a single engine aircraft precision approach. These devices are integrated using an extended Kalman filter (EKF). For the tanker type aircraft federal Aviation Administration (FAA) requirements for a Category I and a Category II precision …


Maximum Likelihood Estimation Of Wave Front Slopes Using A Hartmann-Type Sensor, Scott A. Sallberg Dec 1995

Maximum Likelihood Estimation Of Wave Front Slopes Using A Hartmann-Type Sensor, Scott A. Sallberg

Theses and Dissertations

Current methods for estimating the wave front slope at the pupil of a telescope equipped with a Hartmann-type wave front sensor (H-WFS) are based on a simple centroid calculation of the intensity distributions (spots) recorded in each subaperture of the H-WFS. The centroid method does not include any knowledge concerning correlation properties of the slopes over the subapertures or the amount of light collected by the telescope and diverted to the H-WFS for wave front reconstruction purposes. This thesis devises a maximum likelihood (ML) estimation of the spot centroids by incorporating statistical knowledge of the spot shifts. The light level …


Computer Aided Detection Of Microcalcifications Utilizing Texture Analysis, Ronald C. Dauk Dec 1995

Computer Aided Detection Of Microcalcifications Utilizing Texture Analysis, Ronald C. Dauk

Theses and Dissertations

A comparative study of texture measures for the classification of breast tissue is presented. The texture features investigated include Angular Second Moments, Power Spectrum Analysis and a novel feature, Laws Energy Ratios. The texture study was accomplished as part of the development of a Model Based Vision (MBV) system for the automatic detection of microcalcifications. An overview of the Microcalcification Detection System is presented, which applies image differencing techniques, feature selection methods, and neural networks for locating microcalcification clusters in mammograms. The Power Spectrum Analysis feature set had the best overall performance with an 83% Probability of Detection and an …


Design And Analysis Of A Navigation System Using The Federated Filter, Stephen J. Delory Dec 1995

Design And Analysis Of A Navigation System Using The Federated Filter, Stephen J. Delory

Theses and Dissertations

The purpose of this paper was to design and analyse a federated filter design, to be used for retrofit of an Embedded GPS/INS (EGI) navigation unit into an existing Kalman filter-based air navigation system. A design was selected and simulations were conducted in the Distributed Kalman Filter Simulation software (DKFSIM). As well, a centralized Kalman filter design was simulated under identical conditions for comparison purposes. The federated filter was shown to be a feasible design, with accuracy in position and velocity very close to centralized Kalman filter values. The federated filter design also showed some attractive fault detection and isolation …


Three Dimensional Localization Of Lesions From Digitized Mammograms, Amy L. Magnus Dec 1995

Three Dimensional Localization Of Lesions From Digitized Mammograms, Amy L. Magnus

Theses and Dissertations

This thesis describes new algorithms to localize regions-of-interests (ROIs) three dimensionally from a pair of digitized mammograms. This work is intended to add a layer of sophistication to computer aided diagnosis by putting to use the fixed and measurable parameters of mammographic imaging. The fixed parameters are the source to film orientation and the podium-image distance. Measurable parameters are the rotation angle of the x-ray tube from the horizontal and the compression depth (the distance from compression paddle to contact podium distance) at the time of imaging. As an additional benefit, three dimensional localization algorithms alleviate the confusion radiologists may …


Application Of Mixed-Norm Optimal Control To A Multi-Objective Active Suspension Problem, John B. Allison Dec 1995

Application Of Mixed-Norm Optimal Control To A Multi-Objective Active Suspension Problem, John B. Allison

Theses and Dissertations

Mixed norm optimal control synthesis is used to solve a multiobjective suspension problem. The objective is to develop a controller for an active suspension system onboard a tractor semitrailer vehicle. The problem is first approached by using H2 and H∞ optimization. It is shown that by combining both techniques into one mixed norm optimization method, it is possible to exploit the strengths of each norm to provide superior performance. Two H2/H∞ designs were completed. One design concentrated on optimal performance at one design condition. The second design concentrated on providing the best performance possible at a medium …


A Case Study Of The Environmental Impacts Of The Beddown Of The C-17 Globemaster Iii At Charleston Afb, Richard H. Houghton Jr. Dec 1995

A Case Study Of The Environmental Impacts Of The Beddown Of The C-17 Globemaster Iii At Charleston Afb, Richard H. Houghton Jr.

Theses and Dissertations

Unites States Air Force acquisition environmental planning has changed significantly since the passage of the National Environmental Policy Act in 1969. This research examined the role of environmental planning in weapon system acquisition. It focused on environmental planning performed for the C-17 Globemaster III prior to its beddown at Charleston Air Force Base. The case study of the C- 17 beddown included interviews, archival record reviews, and direct observations at the base. Evidence was collected to determine what environmental impacts occurred during the beddown. An environmental postaudit compared actual impacts with those predicted in environmental planning documentation. Impacts were analyzed …


Detection Of Clustered Microcalcifications Using Wavelets, Donald A. Mccandless Dec 1995

Detection Of Clustered Microcalcifications Using Wavelets, Donald A. Mccandless

Theses and Dissertations

An automated method for detecting microcalcification clusters is presented. The algorithm begins with a digitized mammogram and outputs the center coordinates of regions of interest (ROIs) that contain microcalcification clusters. The method presented uses a 12-tap Least Asymmetric Daubechies (LAD12) wavelet in a tree structured filter bank to increase the signal to noise level of microcalcifications. The signal to noise level gain achieved by the filtering allows subsequent thresholding to eliminate on average 90% of the image from further consideration without eliminating actual microcalcifications 95% of the time. A novel approach to isolating individual calcifications from background tissue through non-stationary …


Computer-Aided Diagnosis Of Mammographic Masses, William E. Polakowski Dec 1995

Computer-Aided Diagnosis Of Mammographic Masses, William E. Polakowski

Theses and Dissertations

A new Model-Based Vision algorithm was developed to find possibly cancerous regions of interest (ROIs) in digitized mammograms and to correctly identify the malignant masses. This work has shown a sensitivity of 92 percent for locating malignant ROIs. The database contained 272 images (12 bit, 1OO microns) with 36 malignant and 53 benign mass images. Of the 53 biopsied benign cases, 74 percent were correctly classified. The Focus of Attention (segmentation) Module algorithm used a physiologically motivated Difference of Gaussians (DoG) filter to highlight mass-like regions in the mammogram. The Index Module labeled the regions by their hypothesized class: large …


Validation Of The Articulated Total Body Model Data Set Describing The Large Advanced Dynamic Anthropomorphic Manikin, Joel J. Hagan Dec 1995

Validation Of The Articulated Total Body Model Data Set Describing The Large Advanced Dynamic Anthropomorphic Manikin, Joel J. Hagan

Theses and Dissertations

Recent cut-backs in Department of Defense spending have presented a need to augment full-scale ejection seat testing with computer simulation. To this end, the U.S. Air Force's Armstrong Laboratory has developed a data set describing the Advanced Dynamic Anthropomorphic Manikin (ADAM) for use in conjunction with the Articulated Total Body (ATB) model for the purpose of simulating the dynamics of the ADAM during sled track ejections. The purpose of this thesis is to validate the ADAM data set by graphically comparing ADAM joint angular displacements calculated by the ATB model with those measured during ejection seat sled track tests. The …


Experimental Investigation Of A Supersonic Turbulent Boundary Layer With Adverse Pressure Gradient, Chad S. Hale Dec 1995

Experimental Investigation Of A Supersonic Turbulent Boundary Layer With Adverse Pressure Gradient, Chad S. Hale

Theses and Dissertations

Laser Doppler Velocimetry (LDV) measurements were made to quantify the effect of adverse pressure gradient on the compressible turbulent flow structure in a Mach 2.9 boundary layer (Re/m= 1.75 x 107). Measurements included profiles of 2-D mean velocities, turbulence intensities, Reynolds shear stresses, intermittency, flatness and skewness. In addition, mean strain rates were also measured. The boundary layer measurements were acquired for both flat plate and compression ramp models. LDV measurements were made at two locations on the compression ramp model at 68 cm and 71 cm downstream of the nozzle throat. At these locations, Β …


Prediction Of An Axial Compressor Stage Characteristic From A One-Point Measurement, Shahnaz M. Punjani Dec 1995

Prediction Of An Axial Compressor Stage Characteristic From A One-Point Measurement, Shahnaz M. Punjani

Theses and Dissertations

This study focuses on predicting axial compressor stage characteristics using a single performance point comprised of mass flow, temperature and pressure rise coefficients obtained in experimental testing and a generic stage temperature characteristic. A new temperature characteristic is generated using a mapping technique where changes in stage blade angles are iterated from assumptions of free vortex flow and constant increment of flow turning angle with increased flow incidence. If additional data corresponding to the new curve are available, the characteristic is adjusted using non-linear least squares estimation, Essentially, the modified mapped curve results from a re-estimated change in the stator …


Numerical Study Of A Transpiration Cooled Rocket Nozzle, Jay A. Landis Dec 1995

Numerical Study Of A Transpiration Cooled Rocket Nozzle, Jay A. Landis

Theses and Dissertations

This study proved that transpiration cooling provides a better cooling scheme than regenerative cooling for long operating duration, liquid-fueled rocket engine nozzles. This proof was made on the basis of maximum wall temperature. This study compared transpiration cooling to regenerative cooling in the throat region of the Space Shuttle Main Engine Main Combustion Chamber. The study also analyzed the effects of porosity, solid thermal conductivity, and porous sphere size on a porous wall made of packed spheres. The transpiration cooled nozzle operated 35% cooler than a regeneratively cooled nozzle, but the temperature gradient at the hot gas surface was 72 …


The Role Of Frame Selection And Bispectrum Phase Reconstruction For Speckle Imaging Through Atmospheric Turbulence, Elizabeth A. Harpold Dec 1995

The Role Of Frame Selection And Bispectrum Phase Reconstruction For Speckle Imaging Through Atmospheric Turbulence, Elizabeth A. Harpold

Theses and Dissertations

Frame selection using quality sharpness metrics have been shown in previous AFIT theses, to be effective in improving the final product of images obtained using adaptive optics. This thesis extends this idea to noncompensated speckle image data. Speckle image reconstruction is simulated with and without frame selection. Speckle images require the processing of hundreds of data frames. Frame selection is a method of reducing the amount of data required to reconstruct the image. A collection of short exposure image data frames of a single object are sorted based on sharpness metrics. Only the highest quality frames are retained and processed …


Photoluminescence And Electroluminescence Of Erbium And Neodymium Implanted Semiconductors, James R. Hunter Dec 1995

Photoluminescence And Electroluminescence Of Erbium And Neodymium Implanted Semiconductors, James R. Hunter

Theses and Dissertations

Low temperature photoluminescence (PL) and electroluminescence (EL) measurements were used to study the excitation of erbium- and neodymium-implanted GaAs and AlxGa1-xAs (x=0. 1, 0.3) pn-junctions. The rare-earth (RE) emissions were investigated as a function of ion dose, aluminum mole fraction, laser excitation power, and applied forward bias voltage for the implanted samples. Low temperature PL was also measured from Er doped silicon grown by the metalorganic chemical vapor-phase deposition (MOCVD) method using various growth parameters.. The MOCVD-grown Si samples were studied as a function of metalorganic source temperature, silane (SiH4) flow, growth time, and …


Analysis And Interpretation Of Ion Data Associated With Neutral Gas Releases In The Earth's Ionosphere, Timothy M. Shadid Dec 1995

Analysis And Interpretation Of Ion Data Associated With Neutral Gas Releases In The Earth's Ionosphere, Timothy M. Shadid

Theses and Dissertations

Barium and strontium release experiments were conducted throughout 1991 from the Combined Release and Radiation Effects Satellite (CRRES) to study both natural and man-made disturbances in the earth's ionosphere. A mass spectrometer on the spacecraft counted the Ba and Sr ions as the cloud expanded. In this study, data from the G-1 (in sunlight) and G-11b (in darkness) releases were modeled to understand the source of the ion signals. The model reproduced the Ba+ sun data well assuming photoionization (τ = 28 s) was the primary ionization mechanism. However, it was not able to account for the remaining ion …


How Location And An Action Standard On A Risk Ladder Affect Perceived Risk, Lonny P. Baker Dec 1995

How Location And An Action Standard On A Risk Ladder Affect Perceived Risk, Lonny P. Baker

Theses and Dissertations

Efforts to explain risk magnitudes often rely on a risk ladder in which exposure levels and associated risk estimates are arranged with low levels at the bottom of the ladder and high levels at the top. An experiment was conducted to test the hypotheses that perceived threat varies with the location of a subject's assigned level on the risk ladder, and that perceived threat varies with the presence of an action standard on the risk ladder. Air Force Institute of Technology Professional Continuing Education students were asked to assume a particular level of a hypothetical hazard in their residences, to …


Comparison Of Gravel Substrate Vs Soil Substrate For The Construction Of An Experimental Fen, Carolyn S. Langley Dec 1995

Comparison Of Gravel Substrate Vs Soil Substrate For The Construction Of An Experimental Fen, Carolyn S. Langley

Theses and Dissertations

Under the Clean Water Act Section 404 of 1972 and 33 CFR 320-330 and 40 CFR 230 moderate the destruction of wetlands by the Air Force to make way for other uses. To obtain a permit for a design or construction project which affects a wetland, the Air Force must agree to create new wetlands, or replace lost wetland acreage through wetland creation or restoration. The Air Force is interested in building 'successful' wetlands as inexpensively as possible. It has been common practice to use hydric soil, which often had to be hauled in, as the substrate at the restored …


A System Dynamics Approach To Modelling The Degradation Of Biochemical Oxygen Demand In A Constructed Wetland Receiving Stormwater Runoff, Leslie A. Mudgett Dec 1995

A System Dynamics Approach To Modelling The Degradation Of Biochemical Oxygen Demand In A Constructed Wetland Receiving Stormwater Runoff, Leslie A. Mudgett

Theses and Dissertations

The objective of this research was to develop a tool to aid the Air Force Environmental Manager in the identification of the design parameters of a constructed wetland system that may be optimized to provide a desired biochemical oxygen demand (BOD) removal efficiency during the treatment of Air Force stormwater runoff. The objective is achieved through the development and use of a system dynamics model which simulates the hydrological functions of a constructed wetland as well as the processes within the wetland responsible for degradation of BOD. Based on literature review, the primary mechanism responsible for the degradation of BOD …


A Methodology To Assess Post-Launch Efforts To Counter Mobile Tactical Ballistic Missile Launchers, Wayne H. Hayes Dec 1995

A Methodology To Assess Post-Launch Efforts To Counter Mobile Tactical Ballistic Missile Launchers, Wayne H. Hayes

Theses and Dissertations

The Department of Defense has a requirement to quantify the force enhancement effects from various configurations of an envisioned multilayered Theater Missile Defense (TMD) system. TMD research accomplished to date has focused primarily on the pre-launch and in-flight tactical ballistic missile (TBM) operational phases while ignoring the post-launch phase during which mobile transporter-erector-launchers (TELs) are vulnerable to attack. No methodology currently exists to measure the effectiveness of various post-launch counter-TEL system configurations or their potential contribution to the overall TMD mission. This research uses the decision analysis technique of influence diagrams to model the post-launch counter-TEL process using notional variable …