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Air Force Institute of Technology

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Articles 5101 - 5130 of 5698

Full-Text Articles in Engineering

Excited Atomic Bromine Energy Transfer And Quenching Mechanisms, Ray O. Johnson Aug 1993

Excited Atomic Bromine Energy Transfer And Quenching Mechanisms, Ray O. Johnson

Theses and Dissertations

Pulsed and steady-state photolysis experiments have been conducted to determine the rate coefficients for collisional deactivation of the spin-orbit excited state of atomic bromine, Br(2p1/2). Pulsed lifetime studies for quenching by Br2 and CO2, established absolute rate coefficients at room temperature of kBr2 = 1.2 ± 0.1 x 10-12 and kCO2 = 1.5 ± 0.2 x 10-11 cm3/molecule-s. Steady-state photolysis methods were used to determine the quenching rates for the rare gases, N2, 02, H2, D2, NO, …

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Application Of Sequence Comparison Methods To Multisensor Data Fusion And Target Recognition, Edmund W. Libby Jul 1993

Application Of Sequence Comparison Methods To Multisensor Data Fusion And Target Recognition, Edmund W. Libby

Theses and Dissertations

This research addresses methods for exploiting the joint likelihood of observed kinematic and nonkinematic (sensor signature) physical events to improve dynamic object and target recognition. A principal direction is the application of dynamic programming sequence comparison techniques to condition matching of object signatures to known models according to observed kinematics. A second direction is the application of kinematic/aspect-angle Kalman filter trackers to condition kinematic tracking according to observed signatures. These conditioning processes dramatically reduce ambiguity in object recognition, and can be used together or separately to allow computation of a posterior probabilities of object class membership using Bayesian methods. Proposals …

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Comparison Of A Distributed Kalman Filter Versus A Centralized Kalman Filter With Fault Detection Considerations, Paul J. Lawrence Jr. Jul 1993

Comparison Of A Distributed Kalman Filter Versus A Centralized Kalman Filter With Fault Detection Considerations, Paul J. Lawrence Jr.

Theses and Dissertations

This project examined the results obtained by simulating an aircraft navigation system with a partial complement of a typical avionics sensor array. Two different techniques of estimation processes were utilized and compared: the conventional Kalman and the federated filter architectures. Areas of interest include error state estimation accuracy and overall performance, residual behavior under normal and induced sensor failure conditions, and potential for failure detection and isolation. Several simulations were accomplished for each filter design and the results were compared in order to verify the validity of the newly developed federated filter architecture. Comparison of the error state estimation accuracies …

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Linear Characteristic Spatial Quadrature For Discrete Ordinates Neutral Particle Transport On Arbitrary Triangles, Dennis J. Miller Jun 1993

Linear Characteristic Spatial Quadrature For Discrete Ordinates Neutral Particle Transport On Arbitrary Triangles, Dennis J. Miller

Theses and Dissertations

A new discrete ordinates spatial quadrature for arbitrary triangular cells is derived and compared to its rectangular cell linear characteristic counterpart. The triangular mesh is more flexible, allowing curved surfaces and off-axis angles to be approximated with many fewer spatial cells. The triangle method is consistently more accurate on example problems tested here. Arbitrary orientation and size of the triangles allow non-patterned meshes to be developed which appears to ameliorate numerical diffusion. The triangle linear characteristic quadrature converges at nearly the same rate as rectangular Linear characteristic on Lathrop's problem. Mesh sensitivity measurements show large variations in triangle vertex locations …

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A Comparison Of Computational And Experimental Data For A Subscale High Speed Propulsive Nozzle At Low Mach Numbers, Yonghee Hyun Jun 1993

A Comparison Of Computational And Experimental Data For A Subscale High Speed Propulsive Nozzle At Low Mach Numbers, Yonghee Hyun

Theses and Dissertations

This computational study of a hypersonic sub-scale nozzle/cowl configuration compares numerical solutions with experimental data for nozzle performance at off design conditions (subsonic through supersonic Mach numbers. A combination of Van Leer and Roe flux-splitting algorithms was used to solve the flow field. The explicit formulation assumed laminar planar flow and the perfect gas equation of state. A validation for the numerical algorithm was accomplished by comparing with experimental data for a variety of cases. Grid refinement, geometry, and operating conditions all influenced the comparison of the experimental and computational data. Generally, as the Mach number and nozzle pressure ratio …

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Experimental Investigation Of The Effects Of Blowing Ratio Parameter On Heat Transfer To A Film-Cooled Flat Plate, Marco R. Valencia Jun 1993

Experimental Investigation Of The Effects Of Blowing Ratio Parameter On Heat Transfer To A Film-Cooled Flat Plate, Marco R. Valencia

Theses and Dissertations

The effects of blowing ratio on film cooling effectiveness were investigated. Two round-nosed test plates were used. One made of aluminum and the second of corian (low thermal conductivity). Injection at 35 degrees in the downstream direction was studied. Helium was mixed with air to produce a density ratio (coolant to mainstream) of 1.6 and 2.0, while the blowing ratio varied from 0.3 to 2.2. Surface temperature was measured by thin film gages located up to a nondimensional downstream distance X/D of 30. Two injection regimes, weak and strong, were found. In the weak regime, film cooling reduced gage heat …

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Development Of An Air-To-Air Refueling Automatic Flight Control System Using Quantitative Feedback Theory, Dennis W. Trosen Jun 1993

Development Of An Air-To-Air Refueling Automatic Flight Control System Using Quantitative Feedback Theory, Dennis W. Trosen

Theses and Dissertations

Quantitative Feedback Theory and the improved method Quantitative Feedback Theory are enhanced to include the rejection of disturbance at the system output. The enhanced Quantitative Feedback Theory and improved method Quantitative Feedback Theory processes are applied to the design of an automatic flight control system to regulate position of the C-135B fuel receiving aircraft relative to the tanker during air-to-air refueling. A simple feedback control system is developed that will achieve stable position regulation. State-space aircraft models &re generated. An inner loop autopilot is designed to reduce the plant cutoff frequency and provide the system inputs for the Quantitative Feedback …

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Phased Array Antenna Analysis Using Hybrid Finite Element Methods, Daniel T. Mcgrath Jun 1993

Phased Array Antenna Analysis Using Hybrid Finite Element Methods, Daniel T. Mcgrath

Theses and Dissertations

This research in computational electromagnetics developed a new method for predicting the near-field mutual coupling effects in phased array antennas, using the finite element method (FEM) in combination with integral equations. Accurate feed modeling is accomplished by enforcing continuity between the FEM solution and an arbitrary number of wave guide models across a ground plane aperture. A periodic integral equation is imposed above the antenna's physical structure in order to enforce the radiation condition and to confine the analysis to an array unit cell. The electric field is expanded in terms of vector finite elements, and Galerkin's method is used …

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A Decision Criteria To Select An Associative-Memory Organization That Minimizes The Execution Time Of A Mix Of Associative-Search Operations, David W. Banton Jun 1993

A Decision Criteria To Select An Associative-Memory Organization That Minimizes The Execution Time Of A Mix Of Associative-Search Operations, David W. Banton

Theses and Dissertations

The dissertation develops a decision criteria to select an associative-memory organization that minimizes the execution time of a mix of associative-search operations and a decision criteria to estimate the layout dimensions of each organization for a specified memory size. The dissertation reclassifies Feng's associative-search operations into three hardware-influenced categories: bit-position independent (BPI), record-content independent (RCI); bit-position dependent (BPD), RCI; and BPD, record-content dependent (RCD). It develops a relationship between the categories and three associative-memory organizations: the CAM, the bit-serial word-parallel associative memory (BSWPAM) , and the extreme-search associative memory (ESAM). A version of the CAM, three versions of the BSWPAM, …

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Experimental And Analytical Analysis Of The Response Of A Smart Beam To Rate Feedback, Terance J. Hoffman Jun 1993

Experimental And Analytical Analysis Of The Response Of A Smart Beam To Rate Feedback, Terance J. Hoffman

Theses and Dissertations

A smart beam with embedded sensors and actuators was analyzed and tested. The smart beam studied was constructed from graphite and epoxy with piezoceramic actuators and NiTiNOL sensors embedded. It was mounted vertically and subjected to transverse dynamic loading at the free end. Analytic expressions for the open loop and closed loop response (using strain rate feedback control) of the beam (including internal damping) to external forcing were derived in detail. Experimental testing of the beam verified the accuracy of the predicted open loop response.

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Radome Depolarization Effects On Monopulse Receiver Tracking Performance, Michael A. Temple Jun 1993

Radome Depolarization Effects On Monopulse Receiver Tracking Performance, Michael A. Temple

Theses and Dissertations

Boresight Error (BSE), defined as the angular deviation between the true position and the apparent position of a target as indicated by a radar, is an important figure of merit for a tracking radar. A significant contributor to system BSE is the protective radome. This research effort employed a GO technique to investigate the effects of a radome on BSE, expanding previous ray- trace receive techniques to include: (1) a uniquely defined/developed mathematical description for each surface within arbitrary multi-layer tapered radomes, (2) an 'ideal' taper function concept for obtaining optimum BSE prediction performance, (3) a generalized technique for calculating …

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Luminescence Study Of Ion-Implanted And Mbe-Grown Er-Doped Gaas And AlXGa1-XAs, Jose E. Colon Mar 1993

Luminescence Study Of Ion-Implanted And Mbe-Grown Er-Doped Gaas And AlXGa1-XAs, Jose E. Colon

Theses and Dissertations

The excitation and de-excitation mechanisms of the 1.54 microns emissions, from ion implanted and MBE grown GaAs:Er and AlxGa1-xAs:Er, were studied through luminescence experiments. Experimental techniques included photoluminescence, time resolved photoluminescence, and selective excitation photoluminescence. The Er3+ emissions were studied as a function of Er concentration, aluminum mole friction, n- and p-type doping level, and annealing temperature. In addition oxygen co-doping studies were done in order to determine the role played by oxygen in the Er3+ luminescence.

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Self-Referenced Speckle Holography (Srsh) Image Reconstruction Performance, John R. Devey Mar 1993

Self-Referenced Speckle Holography (Srsh) Image Reconstruction Performance, John R. Devey

Theses and Dissertations

The Speckle Holography technique uses a series of short exposure images and associated wave front sensor measurements to reconstruct astronomical images. The reconstruction technique effectively boosts the amplitude of high spatial frequencies to allow for finer resolution of astronomical objects. A simulation package that calculates the optical transfer function (OTF) of a telescopic system was previously developed for the Phillips Laboratory. This software was modified slightly to provide the Speckle Holography system transfer function (STF) for a telescopic system under varying seeing conditions.

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Frequency Domain Speech Compression Using The Karhunen-Loeve Transform, Donald W. Dryley Mar 1993

Frequency Domain Speech Compression Using The Karhunen-Loeve Transform, Donald W. Dryley

Theses and Dissertations

The purpose of this study was test the influence of phase on the quality of speech reproduced by a speaker dependent compression system. The tests consisted of compressing frequency domain speech vectors using the Karhunen-Loeve Transform, with and without phase, then making subjective judgements as to the reproduced quality. Error Metrics were then tested for their suitability as predictors of reproduced quality. The compression software transformed each speech vector into a vector of complex Fourier coefficients (only half of the coefficients are needed as transform is hermitian). Phase was preserved by using the real frequency components to form one vector …

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Mitigation Of Shock Waves In A Cylindrical Tunnel By Foam, Grant W. Fondaw Mar 1993

Mitigation Of Shock Waves In A Cylindrical Tunnel By Foam, Grant W. Fondaw

Theses and Dissertations

This study investigated the effectiveness of foam linings in mitigating shock waves in tunnels. A polyurethane foam liner of varying density, crush strength and thickness was modeled inside a 1 meter radius tunnel and an explosion of 1.25 kg of plastic explosive was simulated. Using CTH, an Eulerian- Lagrangian hydrodynamics code from Sandia National Laboratories, the overpressures were computed and compared graphically to determine the effect of varying each foam parameter. The walls of the tunnel consisted of a perfectly reflecting boundary, and in some cases, a foam liner. Low density foam provided the most shock attenuation. with a 20 …

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Amplification Of Shock Overpressure By Reflection Within Concave Corners, John E. Loftis Mar 1993

Amplification Of Shock Overpressure By Reflection Within Concave Corners, John E. Loftis

Theses and Dissertations

In this study, CTH, a production hydrodynamics code developed and provided by Sandia National Laboratories. modeled the interaction of a shock wave with tall V-shaped buildings with various wall lengths and vertex angles. The purpose of this study was to determine the degree to which the length and vertex angle affect the peak overpressure at the vertex. CTH performed two- dimensional Eulerian-Lagrangian computations to obtain solutions of this problem. The models were cast in two-dimensional rectangular geometry on a horizontal plane because of the computational costs of three-dimensional calculations. This geometry simulates tall buildings exposed to a tall Mach stem …

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Identification Of Significant Outliers In Time Series Data, Keri L. Robinson Mar 1993

Identification Of Significant Outliers In Time Series Data, Keri L. Robinson

Theses and Dissertations

This thesis examines the feasibility of using least median of squares (LMS) procedure applied to a reweighted least squares (RLS) autoregression model to identify significant outliers in time series data. The time series were analyzed for data points that were outliers. In order to perform detailed analysis on an outlier. the analyst must be able to determine that an outlier data point is significantly different from normally distributed data. This thesis examines a new method for identifying these outliers. Data from the field were characterized and fit with time series models using an autoregressive reweighted least squares routine (ARRLS) derived …

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Cost Constrained Improvements To The Military Retirement System, Cynthia A. Brown Mar 1993

Cost Constrained Improvements To The Military Retirement System, Cynthia A. Brown

Theses and Dissertations

This research studies possible changes to the current military retirement system. The current military retirement system refers to the system provided under the Military Reform Act of 1986, A new system is proposed which would provide the retiree with four options. Option 1 would provide a pay annuity and medical benefits to the retiree (this is the current system). Option 2 would provide a pay lump sum in place of the, annuity and would offer medical benefits. Option 3 would offer the pay annuity but give a medical lump sum amount in place of the medical benefit. Finally, option 4 …

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Modified Anderson-Darling And Cramer-Von Mises Goodness-Of-Fit Tests For The Normal Distribution, David A. Gwinn Sr. Mar 1993

Modified Anderson-Darling And Cramer-Von Mises Goodness-Of-Fit Tests For The Normal Distribution, David A. Gwinn Sr.

Theses and Dissertations

New techniques for calculating goodness-of-fit statistics for normal distributions with parameters estimated from the sample are investigated. Samples are generated for a Normal(0,1) distribution. Critical values are calculated for five modifications to the Anderson-Darling statistic and five modifications to the Cramer-Von Mises statistic. An extensive power study is done to test the power of the new statistics versus the power of the unmodified statistics. Powers of six of the new statistics show minimal to no improvement, two of the new statistics show a marked decrease in power, and two of the new statistics show an overall increase in power over …

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Predicting The Productive Capacity Of Air Force Aerospace Ground Equipment Personnel Using Aptitude And Experience Measures, Robert S. Faneuff Mar 1993

Predicting The Productive Capacity Of Air Force Aerospace Ground Equipment Personnel Using Aptitude And Experience Measures, Robert S. Faneuff

Theses and Dissertations

This study investigated the effects of mechanical aptitude and job experience on the job performance of 204 Air Force Aerospace Group Equipment (AGE) mechanics. Job performance was expressed as productive capacity (PC), which is derived from estimated performance times on job tasks. PC measures were derived for 50 tasks typically performed by airmen in the specialty. Aptitude measures took the form of Mechanical percentile composite scores on the Armed Services Vocational Aptitude Battery (ASVAB). A second-order logistic model was used to regress PC on aptitude and experience at the task level and at the overall job, or aggregate, level. Model …

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Construction And Testing Of A Neutron And Gamma Spectrometry System Using Pulse Shape Discrimination With An Organic Scintillator, Robert S. Pope Mar 1993

Construction And Testing Of A Neutron And Gamma Spectrometry System Using Pulse Shape Discrimination With An Organic Scintillator, Robert S. Pope

Theses and Dissertations

The goal of this thesis was to construct and test a neutron detector to measure the energy spectrum of 1 to 14-MeV neutrons in the presence of gammas. A spectrometer based on the process of pulse shape discrimination (PSD) was constructed, in which the scintillator NE-213 was used. The primary neutron/ gamma sources used were 78-mCi and 4.7-Ci 239PuBe sources, while 4.7-µCi and 97.6-µCi 22Na gamma sources were used for energy calibration and additional testing of the detector. Proton recoil spectra and Compton electron spectra were unfolded with the neutron and gamma unfolding code FORIST to generate the …

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A Monte Carlo Study Of The Raw And Normal Varimax Rotation Criterion In Factor Analysis, Willam M. Ibinson Mar 1993

A Monte Carlo Study Of The Raw And Normal Varimax Rotation Criterion In Factor Analysis, Willam M. Ibinson

Theses and Dissertations

Factor analysis is a multivariate statistical procedure for analyzing and reducing large data sets. Many factor analysis schemes and techniques are available that lead to strikingly different results from the same data. This research effort used a Monte Carlo approach to investigate the properties of two rotation methods for simple structure, Kaiser's raw and normal varimax criterion. Data sets were developed from a set of contrived experimental factor patterns by multiplying each factor pattern by its transpose to create a covariance matrix. Data sets of multivariate normal deviates were in turn generated from each covariance matrix via the Choleski algorithm. …

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Enhancements To The Animated Tutor For Air Combat Simulation, David A. Legge Mar 1993

Enhancements To The Animated Tutor For Air Combat Simulation, David A. Legge

Theses and Dissertations

This study investigates the use of the Ada programming language in combat modeling. It takes an existing combat model, the Animated Tutor for Air Combat Simulation (ATACS), and re-writes it into Ada. The new model also includes enhancements to the original model. ATACS+, as it is now called, is used as a learning tool in combat modeling classes at the Air Force Institute of Technology. ATACS+ consists of a preprocessor and a model, complete with two and three-dimensional graphics and engagement status reports. Conclusion are made about Ada's suitability for combat modeling, some of the features of Ada which can …

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Analysis Of Topaz Ii And Space-R Space Nuclear Power Plants Using A Modified Thermionic Model, Otto D. Habedank Mar 1993

Analysis Of Topaz Ii And Space-R Space Nuclear Power Plants Using A Modified Thermionic Model, Otto D. Habedank

Theses and Dissertations

Models based on the TDS thermionic diode model were developed for TOPAZ II and SPACER nuclear power systems. Several parameter studies were conducted with the TOPAZ II model. These determined system performance and efficiency while varying the following: (1) Coolant flow inlet temperatures. (2) Rate of coolant temperature change. (3) Power profile of the core. (4) Cesium reservoir temperature. Analysis of results indicate the model accurately represented the TOPAZ II system, underestimating published data by 10%. Coolant flow studies indicate that raising coolant temperatures up to 100 K higher increases system power by up to 5%. Additional increases in temperature …

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A Comparison Of Variable Selection Criteria For Multiple Linear Regression: A Second Simulation Study, David P. Woollard Mar 1993

A Comparison Of Variable Selection Criteria For Multiple Linear Regression: A Second Simulation Study, David P. Woollard

Theses and Dissertations

This thesis implements a variable selection method proposed by Alan J. Miller, and makes an extension of Ross J. Hansen's 1988 thesis research by comparing the methods he examined: Minimum MSE, Minimum Sp, and Minimum Cp with Miller's method. Response Surface methodology is employed with two performance measures: the percentage of correct variables in a model and the Theoretical Mean Squared Error of Prediction (TMSEP). Each technique is applied on generated data with known multicollinearities, variances, random predictors, and sample sizes. Both performance measures are computed for models selected under each technique. A full factorial design using each performance measure …

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Scheduling Air Mobility Command's Channel Cargo Missions, Gregory S. Rau Mar 1993

Scheduling Air Mobility Command's Channel Cargo Missions, Gregory S. Rau

Theses and Dissertations

Through the use of a linear programming model, this research revised the initial schedule for AMC's channel cargo missions to eliminate any excess delay enroute by minimizing the cumulative, weighted time-in-system for all cargo, according to a given cargo flow. In fact, the revised schedule minimizes any assigned nonnegative weighting of the time-in-system, due to the properties of equivalent measures of performance. When combined with Step One of a proposed two-step process for revising AMC's channel mission schedule, this research can be used to improve the current schedule based on Step One's cargo flow. By carefully defining the notation and …

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Theater Airlifter Survivability On The Ground, Michael A. Silver Mar 1993

Theater Airlifter Survivability On The Ground, Michael A. Silver

Theses and Dissertations

Airlifter attrition can severely decrease the throughput of cargo during extended airlift operations. Much work has been done to enhance the tactical airlifter survivability in the air but little study has gone into airlifter survivability on the ground. This thesis develops a method to measure the threat to parked aircraft from ground weapons. Specific scenarios cover airlifter mobility on the ground, time to off-load cargo, short-field takeoff capability and attack by infantry weapons. A weapon is examined at each of several firing ranges to target. The threat to the aircraft is measured as the probability that the aircraft is hit. …

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The Use Of Simulation To Evaluate Strategic Aeromedical Evacuation Policy And Planning, Charles W. Wolfe Jr. Mar 1993

The Use Of Simulation To Evaluate Strategic Aeromedical Evacuation Policy And Planning, Charles W. Wolfe Jr.

Theses and Dissertations

Strategic aeromedical evacuation (AE) of casualties from the theater of operations to the CONUS during wartime is a complex operation that involves the integration of medical personnel and policies with airlift concepts and capabilities. Military analysts within the Air Mobility Command Analysis Group (AMC/XPY) have traditionally used deterministic linear programming techniques to estimate the number of aircraft the United States Air Force (USAF) requires for given contingency scenarios. However, this group has yet to develop a stochastic approach to validate their resource recommendations, and more importantly, to study the interrelationships between key factors comprising strategic aeromedical evacuation. As the possibility …

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A Modified Chi-Squared Goodness-Of-Fit Test For The Three-Parameter Gamma Distribution With Unknown Parameters, Thomas J. Sterle Mar 1993

A Modified Chi-Squared Goodness-Of-Fit Test For The Three-Parameter Gamma Distribution With Unknown Parameters, Thomas J. Sterle

Theses and Dissertations

A modified chi-squared goodness-of-fit test was created for the gamma distribution in the case where all three parameters must be estimated from the sample. Critical values are generated using a Monte Carlo simulation procedure with 5000 repetitions each. Random samples of 8 different sizes were drawn from gamma distributions with shape parameters 1, 1.5, 2., and 2.5. The shape, scale, and location parameters were then estimated from each sample, using an iterative technique combining the maximum likelihood and minimum distance methods, enabling, computation of the chi-squared statistics and critical values. The same process is used to generate random samples, parameter …

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Using Animation In The Validation Of Simulation Models, Michael L. Carpenter Mar 1993

Using Animation In The Validation Of Simulation Models, Michael L. Carpenter

Theses and Dissertations

This study examined three aspects of animation (movement, color, and detail of icons) to determine which one (or ones) best communicated the operation of a simulation model. The procedure was done in the context of using animation to establish a model's face validity. Movement, color, and detail of icons were looked at individually and in combination. The ability to communicate was measured both subjectively and objectively. The subjective measures were a selection of best and worst animation types where best and worst referred to how well an animation communicated, and a pairwise comparison of the animation types which resulted in …

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