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Theses and Dissertations

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Articles 10021 - 10050 of 11503

Full-Text Articles in Engineering

Value Of Increased Use Of Scheduled Maintenance On Aircraft Availability And Maintenance Cost Of The C-5, William T. Webb Sep 1998

Value Of Increased Use Of Scheduled Maintenance On Aircraft Availability And Maintenance Cost Of The C-5, William T. Webb

Theses and Dissertations

The C-5 consistently performs below its established mission capable rate of 75 percent. The purpose of this study was to investigate whether or not mission capable rates and maintenance costs can be improved by increased use of scheduled maintenance. Nine C-5 components were studied. Availability and cost were compared when scheduled replacement occurred at ten, twenty, and thirty percent before their respective mean time between failure and actual failure times. Actual failure times were not available so they were generated using simulation. The trade-off of using preventive maintenance is the decreased cost of sending fewer maintenance repair teams and increased …

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Feasibility Study On The Use Of The Internet For Traffic Of Unclassified Data, Alexandre L. Guerra, Luiz Gustavo F. P. Silva Sep 1998

Feasibility Study On The Use Of The Internet For Traffic Of Unclassified Data, Alexandre L. Guerra, Luiz Gustavo F. P. Silva

Theses and Dissertations

This research compares two possible networking methods for connecting all Brazilian Air Force Materiel Command units responsible for support and operation of Brazilian Air Force's weapons systems. The network includes the use of dedicated X.25 links, and the use of a virtual Private Network using the Internet (TCP/IP) as the medium of transmission. The Brazilian Air Force Materiel Command, responsible to support operating units over a very large sparse territory, lacks an efficient media of computer communications, which makes it difficult to control the supply chain channels of materiel present in each unit, depots, and warehouses. We studied the network …

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Monotonic And Fatigue Behavior Of 2-D Woven Ceramic Matrix Composite At Room And Elevated Temperatures (Blackglas/Nextel 312), Musa Al-Hussein Sep 1998

Monotonic And Fatigue Behavior Of 2-D Woven Ceramic Matrix Composite At Room And Elevated Temperatures (Blackglas/Nextel 312), Musa Al-Hussein

Theses and Dissertations

This study investigated the monotonic tension and compression and the tension-tension and tension-compression fatigue loading of Blackglas/Nextel 312 woven CMC at room temperature and at 760 degrees centigrade. Young's Modulus and strain variation were evaluated. S-N curves were obtained for room and elevated temperatures. The ultimate tensile stress was lower at the elevated temperature and it was higher in the compression test. Failure-strain was higher at the elevated temperature in both tension and compression tests. There was no significant change in Young's Modulus at the elevated temperature. Also, there was no difference in the number of cycles to failure at …

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Effects Of Shiftwork On Air Force Aircraft Maintenance Personnel, Craig A. Campbell Sep 1998

Effects Of Shiftwork On Air Force Aircraft Maintenance Personnel, Craig A. Campbell

Theses and Dissertations

This study examined the effects of converting a large aircraft maintenance squadron from 8-hour shifts to 12-hour shifts. The squadron studied converted its 24- hour maintenance work force from three 8-hour work shifts to two 12-hour work shifts incrementally, with one section converting to 12-hour shifts in January, 1996, and the remaining section converting in July, 1996. Both sections remained on 12-hour shifts until September, 1997, when both sections converted back to a three shift 8-hour operation. Health and well being, on- and off-duty accident rates, day shift vs. night shift accident rates, and the effects of stress and fatigue …

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Global Positioning System (Gps) Receiver Design For Multipaths Mitigation, El-Sayed Abdel-Salam Gadallah Aug 1998

Global Positioning System (Gps) Receiver Design For Multipaths Mitigation, El-Sayed Abdel-Salam Gadallah

Theses and Dissertations

Multipath effects are a source of error degrading the accuracy of DGPS signal processing. The statistical models of multipath are determined by user location and, in addition are time varying. There is no unified statistical model for the multipath signal. Therefore the solution of the multipath problem using statistical models is difficult. This research introduces a new estimator that can detect the presence of multipath, can determine the unknown number of multipath components and can estimate multipath parameters in the GPS receiver (time delay and attenuation coefficients). Furthermore the multipath signal parameters are estimated at any instant of observation. The …

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Representations, Approximations, And Algorithms For Mathematical Speech Processing, Laura R. Suzuki Jun 1998

Representations, Approximations, And Algorithms For Mathematical Speech Processing, Laura R. Suzuki

Theses and Dissertations

Representing speech signals such that specific characteristics of speech are included is essential in many Air Force and DoD signal processing applications. A mathematical construct called a frame is presented which captures the important time-varying characteristic of speech. Roughly speaking, frames generalize the idea of an orthogonal basis in a Hilbert space, Specific spaces applicable to speech are L2(R) and the Hardy spaces Hp(D) for p> 1 where D is the unit disk in the complex plane. Results are given for representations in the Hardy spaces involving Carleson's inequalities (and its extensions), …

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The T-27 "Tucano" Engine Pipeline Of The Brazilian Air Force: A Managerial Approach, Jorge Barros Santos Jun 1998

The T-27 "Tucano" Engine Pipeline Of The Brazilian Air Force: A Managerial Approach, Jorge Barros Santos

Theses and Dissertations

The T-27 is a Brazilian-made aircraft, manufactured by "Empresa Brasileira de Aeronautica - EMBRAER". The purpose of this study is to describe the processes that take place in the logistic pipeline of the T-27 Engine. With the objective of identifying any existent bottlenecks and suggests managerial approaches to improve the overall system performance.

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The Scheduling Process In A Depot From The Brazilian Air Force, Fabricio J. Saito Jun 1998

The Scheduling Process In A Depot From The Brazilian Air Force, Fabricio J. Saito

Theses and Dissertations

The Brazilian Air Force (BAF) in its logistic structure contains 5 Air Logistic Centers (depots). This thesis concentrates its analysis on one of the most important BAF depots located at Sao Paulo (PAMASP). This thesis explores the scheduling process currently used in PAMASP. This thesis adopted a managerial approach in a sense that it looked to take a big picture of the current process. The researcher performed field interviews with the goal of describing the process. During the visit to PAMASP, the researcher also gathered problems related to the process. The recommendations stated on this study were based on the …

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Wind Tunnel Testing For Drag Reduction Of An Aircraft Laser Turret, Christopher H. Snyder Jun 1998

Wind Tunnel Testing For Drag Reduction Of An Aircraft Laser Turret, Christopher H. Snyder

Theses and Dissertations

This study investigated the use of aft-mounted fairings and splitter plates to reduce the drag of a half-scale aircraft laser turret. Forces, moments, and pressure distributions were measured in the AFIT 1.5-m (5-ft) wind tunnel at Reynolds numbers between 3x105 and 9x105 based on the turret diameter. Oil traces indicated the nature of the flow near the surface of the unmodified turret and the surrounding area. Tufts placed on the turret, fairings, and splitter plates showed changes in separation regions when configurations were changed. The flow around the turret was characterized by dominant vortices shedding from the top …

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High Amplitude Tracking Control, Joseph W. Mcnamee Jun 1998

High Amplitude Tracking Control, Joseph W. Mcnamee

Theses and Dissertations

The problem of tracking control in the face of high amplitude dynamic reference signals, hard state and control constraints, and open-loop unstable plants is investigated. Saturation effects mitigation is a current research topic, and a large body of literature exists which addresses this problem. However, with a few notable exceptions, little work has been accomplished which is applicable to the problem of high amplitude dynamic reference signal tracking in the face of hard state and control constraints, and open-loop unstable plants. Moreover, methods that do address the stated problem generally limit the exogenous reference signal to statically admissible values to …

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Development And Packaging Of Microsystems Using Foundry Services, Jeffrey T. Butler Jun 1998

Development And Packaging Of Microsystems Using Foundry Services, Jeffrey T. Butler

Theses and Dissertations

Micro-electro-mechanical systems (MEMS) are a new and rapidly growing field of research. Several advances to the MEMS state of the art were achieved through design and characterization of novel devices. Empirical and theoretical model of polysilicon thermal actuators were developed to understand their behavior. The most extensive investigation of the Multi-User MEMS Processes (MUMPs) polysilicon resistivity was also performed. The first published value for the thermal coefficient of resistivity (TCR) of the MUMPs Poly 1 layer was determined as 1.25 x 10(exp -3)/K. The sheet resistance of the MUMPs polysilicon layers was found to be dependent on linewidth due to …

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Trigonometric Transforms For Image Reconstruction, Thomas M. Foltz Jun 1998

Trigonometric Transforms For Image Reconstruction, Thomas M. Foltz

Theses and Dissertations

This dissertation demonstrates how the symmetric convolution-multiplication property of discrete trigonometric transforms can be applied to traditional problems in image reconstruction with slightly better performance than Fourier techniques and increased savings in computational complexity for symmetric point spread functions. The fact that the discrete Fourier transform a circulant matrix provides an alternate way to derive the symmetric convolution-multiplication property for discrete trigonometric transforms. Derived in this manner, the symmetric convolution-multiplication property extends easily to multiple dimensions and generalizes to multidimensional asymmetric sequences. The symmetric convolution-multiplication property allows for linear filtering of degraded images via point-by-point multiplication in the transform domain …

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Singularity Avoidance Strategies For Satellite Mounted Manipulators Using Attitude Control, Nathan A. Titus Jun 1998

Singularity Avoidance Strategies For Satellite Mounted Manipulators Using Attitude Control, Nathan A. Titus

Theses and Dissertations

Control concepts for satellite mounted manipulators (SMM) are examined. The primary focus is on base actuated concepts, which eliminate singularity problems associated with free floating SMMs. A new form of the equations of motion for an n-link SMM is developed using a quasi coordinate form of Lagrange's Equation. Alternative free floating SMM designs are presented which eliminate dynamic singularities, but still experience difficulties due to the unactuated base. A new generic SMM controller is developed as a framework for various control concepts with and without base actuation. Momentum constrained Jacobians are shown to produce better SMM tracking than fixed base …

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Effects Of Clutter Height Distribution On Adaptive Clutter Erasure Performance, Kelce Steven Wilson Jun 1998

Effects Of Clutter Height Distribution On Adaptive Clutter Erasure Performance, Kelce Steven Wilson

Theses and Dissertations

A new real beam interferometric processing technique, called Adaptive Clutter Erasure (ACE), is investigated for applicability to ground clutter suppression in airborne radar systems. By analysis and simulation, the viability of the ACE concept as a next generation clutter suppression technique is demonstrated to achieve performance enhancements commensurate with currently implemented techniques. Research results indicate the ACE concept provides a reliably consistent 10dB Signal-to-Clutter Ratio (SCR) advantage over the APG-63, an operational radar system used for baseline comparison. ACE system concept development and performance predictions are conducted in conformity with the physical and operational design parameters of the APG-63, namely …

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Parallel Implementation Of An Artificial Neural Network Integrated Feature And Architecture Selection Algorithm, Craig W. Rizzo Mar 1998

Parallel Implementation Of An Artificial Neural Network Integrated Feature And Architecture Selection Algorithm, Craig W. Rizzo

Theses and Dissertations

The selection of salient features and an appropriate hidden layer architecture contributes significantly to the performance of a neural network. A number of metrics and methodologies exist for estimating these parameters. This research builds on recent efforts to integrate feature and architecture selection for the multilayer perceptron. In the first stage of work a current algorithm is developed in a parallel environment, significantly improving its efficiency and utility. In the second stage, improvements to the algorithm are proposed. With regards to feature selection, a common random number (CRN) addition is proposed. Two new methods of architecture selection are examined, to …

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The Application Of Statistical Sampling Techniques To The Operational Readiness Inspection, Troy L. Dixon, Timothy S. Madgett Mar 1998

The Application Of Statistical Sampling Techniques To The Operational Readiness Inspection, Troy L. Dixon, Timothy S. Madgett

Theses and Dissertations

A Blue Ribbon Commission report to the Air Force Chief of Staff in February 1997 makes several specific recommendations on the conduct of Operational Readiness Inspections. This thesis develops a solution to one of the recommendations of that report; utilize scientifically based sampling techniques to reduce the footprint of the inspection on an evaluated unit. Acceptance sampling, common in industry, is developed for use in the environment of the Operational Readiness Inspection. The time saved from this more efficient sampling practice reduces Inspector General time at an evaluation, decreases the footprint, and answers the specific recommendations of the Blue Ribbon …

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Using Simulation To Model Time Utilization Of Army Recruiters, James D. Cordeiro Jr., Mark A. Friend Mar 1998

Using Simulation To Model Time Utilization Of Army Recruiters, James D. Cordeiro Jr., Mark A. Friend

Theses and Dissertations

It is a well-known fact Army recruiters work very long hours in a demanding environment. In many cases, recruiting stations are geographically isolated from military bases, with recruiters often tolerating a high cost of living, crime, and other such adverse conditions that characterize the communities they work in. The job itself demands self-starting, motivated individuals with a wide range of skills, from street-savvy to salesmanship, in order to succeed. A number of factors in recent years have made military recruiting more difficult, which include scandals involving highly-placed soldiers and changes in attitudes towards military service among eligible men and women. …

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Modified Multiple Model Adaptive Estimation (M3Ae) For Simultaneous Parameter And State Estimation, Mikel M. Miller Mar 1998

Modified Multiple Model Adaptive Estimation (M3Ae) For Simultaneous Parameter And State Estimation, Mikel M. Miller

Theses and Dissertations

In many estimation problems, it is desired to estimate system states and parameters simultaneously. However, inherent to traditional estimation architectures of the past, the designer has had to make a trade-off decision between designs intended for accurate state estimation versus designs concerned with accurate parameter estimation. This research develops one solution to this trade-off decision by proposing a new architecture based on Kalman filtering (KF) and Multiple Model Adaptive Estimation (MMAE) techniques. This new architecture, the Modified-MMAE (M3AE), exploits the benefits of an MMAE designed for accurate parameter estimation, and yet performs at least as well in state …

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Calculating A Value For Dominant Battlespace Awareness, Eric A. Beene Mar 1998

Calculating A Value For Dominant Battlespace Awareness, Eric A. Beene

Theses and Dissertations

In times of ever-tightening military budgets, methodologies are required that can compare the contributions of various systems involved in the warfighting process. While many tools are in use that directly measure the effects of greater numbers of enhanced hardware, and even improved processes, no validated methodology exists to measure elements that contribute to Command, Control, Communications, and Computers (C4); Intelligence, Surveillance, and Reconnaissance (ISR); or to analytically compare these elements with more traditional hardware. This thesis develops a methodology for mathematically quantifying awareness in a military command and control (C2) environment. This methodology begins with the Observe-Orient-Decide-Act Loop to show …

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Sensitivity Analysis Of Brawler Pilot Skill Levels, Daniel C. Buschor Mar 1998

Sensitivity Analysis Of Brawler Pilot Skill Levels, Daniel C. Buschor

Theses and Dissertations

BRAWLER is a high resolution air to air combat simulation model used for engagement level analyses of few on few air combat. It uses a value driven decision logic to help simulate pilot behavior. In order to account for varied pilot skill levels, BRAWLER has defined three skill levels; Rookie, Pilot, and Ace. A Rookie can track up to three aircraft in its mental model, the Pilot, up to five aircraft, while an Ace has no limit. Further, each skill level varies the amount of time before a known aircraft, which has not been recently observed, is purged from the …

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An Airlift Hub-And-Spoke Location-Routing Model With Time Windows: Case Study Of The Conus-To-Korea Airlift Problem, David W. Cox Mar 1998

An Airlift Hub-And-Spoke Location-Routing Model With Time Windows: Case Study Of The Conus-To-Korea Airlift Problem, David W. Cox

Theses and Dissertations

Traditionally, the United States Air Force's Air Mobility Command (AMC) has used the concept of direct delivery to airlift cargo and passengers from a point of embarkation to a point of debarkation. This study develops an alternative hub-and-spoke combined location-routing integer linear programming prototype model, and uses this model to determine what advantages a hub-and-spoke system offers, and in which scenarios it is better-suited than the direct delivery method. Additionally, the analysis suggests that the C-17 may be better-suited, in certain airlift situations, for theater airlift versus strategic (direct delivery) airlift. The model features the following elements: time windows, cargo …

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Sensitivity Analysis Of The Thunder Combat Simulation Model To Command And Control Inputs Accomplished In A Parallel Environment, David A. Davies Mar 1998

Sensitivity Analysis Of The Thunder Combat Simulation Model To Command And Control Inputs Accomplished In A Parallel Environment, David A. Davies

Theses and Dissertations

This research had two objectives. The first was to develop a methodology to demonstrate the parallel processing capability provided by Air Force's Aeronautical System's Command (ASC) Major Shared Resource Center (MSRC) and apply that methodology to the SIMAF Proof of Concept project. Secondly, AFSAA/SAAB requested a sensitivity analysis of THUNDER to the modeled command and control (C2) inputs. The power of parallelization can not be overemphasized. The data collection phase of this thesis was accomplished at the MSRC using a script developed to automate the processing of an experimental design, providing the analyst with a launch and leave capability. On …

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A Life Cycle Cost Model For Innovative Remediation Technologies, Osman S. Dereli Mar 1998

A Life Cycle Cost Model For Innovative Remediation Technologies, Osman S. Dereli

Theses and Dissertations

LCC analysis is a powerful tool for investigating the costs of competing systems. This thesis investigates the cost scaling methods to improve the traditional LCC modeling techniques. The motivation for this research is finding a good estimate for the remediation technologies when the contaminant volume is not exactly known. This specific case lead researcher to investigating the methods of cost scaling and effects of inflation in the cost estimation. As a result of study a generic LCC model is developed. Methods for considering inflation and scaling are recommended and embodied into the model. The developed model is applied the specific …

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Anderson-Darling And Cramer-Von Mises Based Goodness-Of-Fit Tests For The Weibull Distribution With Known Shape Using Normalized Spacings, Eric W. Frisco Mar 1998

Anderson-Darling And Cramer-Von Mises Based Goodness-Of-Fit Tests For The Weibull Distribution With Known Shape Using Normalized Spacings, Eric W. Frisco

Theses and Dissertations

Two new goodness-of-fit tests are developed for the three-parameter Weibull distribution with known shape parameter. These procedures eliminate the need for estimating the unknown location and scale parameters prior to initiating the tests and are easily adapted for censored data. This is accomplished by employing the Anderson-Darling and Cramer-von Mises statistics based on the normalized spacings of the sample data. Critical values of the new tests are obtained for common significance levels by large Monte Carlo simulations for shapes 0.5(0.5)4.0 and sample sizes 5(5)40 with up to 40% censoring (Type II) from the left and/or right. An extensive Monte Carlo …

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An Operational Review Of Air Campaign Planning Automation, William R. Haas Mar 1998

An Operational Review Of Air Campaign Planning Automation, William R. Haas

Theses and Dissertations

The air campaign planning process is a complex and dynamic process. Operations research has been applied to this problem to shorten the planning cycle with mixed results. The Joint Force Air Component Commander Planning Tool was developed as an air campaign planning aid. It uses the Conventional Targeting and Effectiveness Model (CTEM) as the force analysis model for master air attack plan (MAAP) planning. This thesis reviews the limitations and assumptions of CTEM and CTEM in JPT from and operational perspective. A new approach to using models in air campaign planning, collaborative planning, is being developed for use with JPT. …

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Investigating Sorbent Geometry Response Surfaces From Sorption Rate Data, H. Michael Harrison Mar 1998

Investigating Sorbent Geometry Response Surfaces From Sorption Rate Data, H. Michael Harrison

Theses and Dissertations

Sorption and desorption of hydrophobic organic compounds (HOCs) into soil particles occurs at Air Force contamination sites. Long-term desorption extends clean up time, costing billions. Accurately modeling desorption will reduce costs and improve clean up designs. State of the art models depict soil as uniform spherical particles which lose the effect of longer sorption path lengths. An alternate approach, the multiple sites in series (MSS) model, describes the sorption capacity of a mixture of soil particle sizes and shapes using a composite particle defined by a two parameter statistical distribution. When the MSS model uses a general radial geometry function …

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An Evaluation Of Frequency Domain Ensemble Averaging To Improve Aircraft Stability Derivative Estimation, Lawrence M. Hoffman Mar 1998

An Evaluation Of Frequency Domain Ensemble Averaging To Improve Aircraft Stability Derivative Estimation, Lawrence M. Hoffman

Theses and Dissertations

This research evaluated a process to improve aircraft stability derivative estimation results. The Have Derivatives process used overlap ensemble averaging in the frequency domain to minimize noise on the original time domain signals. The process estimated average complex frequency response functions that were then transformed back into the time domain as a set of discrete pulse responses with far less noise than the original signals. These clean signals were used in a parameter estimation program to estimate better stability derivatives than were estimated with the original noisy signals. Both simulation and flight test data were used to study the effects …

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A New Sequential Goodness Of Fit Test For The Three-Parameter Weibull Distribution With Known Shape Based On Skewness And Kurtosis, Jonathan C. Clough Mar 1998

A New Sequential Goodness Of Fit Test For The Three-Parameter Weibull Distribution With Known Shape Based On Skewness And Kurtosis, Jonathan C. Clough

Theses and Dissertations

The Weibull distribution finds wide applicability across a broad spectrum of disciplines and is very prevalent in reliability theory. Consequently, numerous statistical tests have been developed to determine whether sample data can be adequately modeled with this distribution. Unfortunately, the majority of these goodness-of-fit tests involve a substantial degree of computational complexity. The study presented here develops and evaluates a new sequential goodness-of-fit test for the three-parameter Weibull distribution with a known shape that delivers power comparable to popular procedures while dramatically reducing computational requirements. The new procedure consists of two distinct tests, using only the sample skewness and sample …

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Real Time Detection Of Anomalous Satellite Behavior Has Ground Based Telescope Images, Geoffrey S. Maron Mar 1998

Real Time Detection Of Anomalous Satellite Behavior Has Ground Based Telescope Images, Geoffrey S. Maron

Theses and Dissertations

Air Force analysts are faced with the task of monitoring satellites with ground based telescopes. Images are collected and analyzed in a time consuming and subjective effort to detect any behavior that is anomalous. This research maximizes use of a priori information to create an automated, real time satellite behavior classification tool. Using modeling software and knowledge of a satellite's orbit, reference imagery is created for each measured image in a satellite pass. Features are extracted from the measured and reference image pairs that provide good overall Gaussian classification accuracy (85%), reduce the dimensionality of the problem (from 32,768 down …

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A Value Focused Thinking Approach To Academic Course Scheduling, Shane A. Knighton Mar 1998

A Value Focused Thinking Approach To Academic Course Scheduling, Shane A. Knighton

Theses and Dissertations

In 1997, the School of Engineering of the United States Air Force Institute of Technology began exploring ways of automating the academic course scheduling process. The administration desired an expedient approach for course scheduling which supports the institute's mission of "providing scientific and technological education" to officers from all branches of military service, as well as international military forces. The scheduling approach needed to be flexible, efficient, and represent the institute's values and principles. Decision Analysis (DA) and specifically, Value Focused Thinking (VFT), is used to decompose the complex problem of academic course scheduling and determine the factors that are …

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