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Theses and Dissertations

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Articles 9121 - 9150 of 11508

Full-Text Articles in Engineering

Development Of A Higher-Order Upwind Algorithm For Compressible Fluid Flow, Barry A. Croker Mar 2005

Development Of A Higher-Order Upwind Algorithm For Compressible Fluid Flow, Barry A. Croker

Theses and Dissertations

A global fourth-order solution method that incorporates compact differencing with Roe's approximate Riemann solver was investigated. This method was incorporated into a one-dimensional numerical simulation of the compressible Euler equations, and applied to a one-dimensional shock tube problem. The method was also extended to two dimensions, and applied to a two-dimensional shock tube problem and an advecting vortical structure problem on both rectilinear and curvilinear meshes. The results were compared to a third-order Roe scheme and a fourth-order compact difference scheme. An order of accuracy determination showed that it has an order of accuracy somewhere near fourth order, with absolute …

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A Study In Drag Reduction Of Close Formation Flight Accounting For Flight Control Trim Positions And Dissimilar Formations, Michael T. Morgan Mar 2005

A Study In Drag Reduction Of Close Formation Flight Accounting For Flight Control Trim Positions And Dissimilar Formations, Michael T. Morgan

Theses and Dissertations

This thesis further defines the position of greatest fuel savings benefit for the trail aircraft flying in a two-ship formation. The HASC95 vortex lattice code was used for the examination. Investigations of a similar formation of F-16 aircraft and a dissimilar formation of a lead KC-135 aircraft and a trail F-16 aircraft were conducted. The analyses determined the effects of varying airspeed on the optimal position. In addition, flight control surface deflections were taken into account during the analyses. Both investigations trimmed the aircraft in the yaw and roll axes to determine the optimal savings. The similar analysis was conducted …

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Full Capability Formation Flight Control, Ryan K. Osteroos Mar 2005

Full Capability Formation Flight Control, Ryan K. Osteroos

Theses and Dissertations

The subject of automatic formation flight control is of current interest to the development of Unmanned Aerial Vehicles (UAV). Previous control approaches have been refined in this work to allow more robust maneuvering and to include a fourth control parameter. The equations of motion for each aircraft as a point mass, expressed in a wind-axis coordinate system, are coupled into differential equations that model the two aircraft system dynamics. Control laws are developed that include proportional and integral action. Gains are determined based on formation performance. Lead maneuvers are simulated and the controller is gauged on its ability to maintain …

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Parachute Extraction Of A Generic Store From A C-130; A Cfd Proof Of Concept, Stephen C. Platt Mar 2005

Parachute Extraction Of A Generic Store From A C-130; A Cfd Proof Of Concept, Stephen C. Platt

Theses and Dissertations

This thesis encompasses a feasibility analysis of a parachute extracted generic precision guided munition from the cargo bay of a C-130 aircraft in flight. This analysis utilizes the USAF Beggar code and incorporates full physics effects as well as aerodynamic loading assuming an inviscid aircraft and viscous store for a time-accurate solution. Both an immediate and time varying application of the parachute force are utilized as well as two different ordnance body styles at zero and 5 degrees AOA with the store placed on centerline and offset in the cargo bay. The time accurate parachute model is based on empirical …

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An Investigation Of A Simplified Gouging Model, Gregory S. Rickerd Mar 2005

An Investigation Of A Simplified Gouging Model, Gregory S. Rickerd

Theses and Dissertations

Gouging is a type of structural failure that becomes important when two metals slide against each other at velocities in the range of 1.5 kilometers per second. A computer model has previously been used to model the development of gouging at the Holloman High Speed Test Track. This model has not been experimentally verified to be correct, due to the complexity of the model. This research develops a simplified model that can be experimentally verified. The computer program utilized in this research was studied to determine the most appropriate options to use in simulations. This was accomplished by modeling a …

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Controlling Sideslip Angle To Reduce The Radar Exposure Of A Tactical, Rotary Winged Uav, Jonathan D. Bulseco Mar 2005

Controlling Sideslip Angle To Reduce The Radar Exposure Of A Tactical, Rotary Winged Uav, Jonathan D. Bulseco

Theses and Dissertations

This work investigates another way of contributing to the radar minimization solution for air vehicles in a threat environment. While much research has been conducted on structural solutions to radar exposure minimization, not much work has been done in the area of using control to continuously assess and present the smallest radar cross section of an air vehicle to oncoming threat radar systems by changing the aircraft's orientation. This work looks at the application of sideslip/beta angle feedback control of an unmanned helicopter to minimize radar cross section exposure in a hostile radar environment. A new way of controlling aircraft …

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A Redesigned Tail Rotor For Improvement Of Ch-53e High-Altitude Performance, James A. Pritchard Mar 2005

A Redesigned Tail Rotor For Improvement Of Ch-53e High-Altitude Performance, James A. Pritchard

Theses and Dissertations

The Global War on Terror with specific emphasis on the recent military operation in Afghanistan has shown the invaluable contribution that heavy lift helicopters bring to the combatant commander. However, the flight range, altitudes and lift capability required to operate effectively in such an austere environment are pushing the limits of these helicopters. In an attempt to increase the operational capability of the CH-53E, this study will investigate methods for maximizing tail rotor effectiveness at high gross weights and high altitudes. This thesis records an analytical study designed to investigate the intricacies of tail rotor design and, by the computational …

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Attitude Model Of A Reaction Wheel/Fixed Thruster Based Satellite Using Telemetry Data, Jason E. Smith Mar 2005

Attitude Model Of A Reaction Wheel/Fixed Thruster Based Satellite Using Telemetry Data, Jason E. Smith

Theses and Dissertations

Attitude determination of satellites is normally the job of inertial instruments, such as gyroscopes, or through sensing instruments, such as star trackers or Global Positioning Satellites (GPS). Satellite health monitoring systems watch and determine if the satellite deviates from its normal operating attitude orientation. Knowing the orientation of a satellite is essential in being able to control it in order to complete the satellite's designated mission. While there are a multitude of ways to determine a satellite's orientation, very little research has been done on determining if the attitude of a satellite can be determined directly from telemetry data of …

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Effect Of Temperature And Steam Environment On Fatigue Behavior Of An Oxide-Oxide Continuous Fiber Ceramic Composite, Chalene A. Eber Mar 2005

Effect Of Temperature And Steam Environment On Fatigue Behavior Of An Oxide-Oxide Continuous Fiber Ceramic Composite, Chalene A. Eber

Theses and Dissertations

There is an ever-increasing need for materials that maintain high strength and fracture toughness at elevated temperatures and in complex environments. Advanced aerospace applications are motivating the development of composite materials that can meet demanding requirements. This research effort investigates mechanical behavior of an oxide-oxide continuous fiber ceramic composite (CFCC) consisting of a porous alumina matrix reinforced with mullite/alumina Nextel 720 fibers developed specifically for advanced aerospace applications. Tension-tension fatigue behavior of this CFCC was studied at 1200 and 1330 °C in laboratory air and 100% steam environments. Fatigue resistance and retained strength properties were determined. Effects of environmental degradation …

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Orbit Estimation Algorithms For A Microsatellite Rendezvous With A Non-Cooperative Target, John P. Heslin Mar 2005

Orbit Estimation Algorithms For A Microsatellite Rendezvous With A Non-Cooperative Target, John P. Heslin

Theses and Dissertations

This study investigated the minimum requirements to establish a satellite tracking system architecture for a microsatellite to rendezvous with a non-cooperative target satellite. A prototype optical tracking system was reviewed with emphasis on a proposed tactical employment that could be used by technologically unsophisticated state or non-state adversaries. With the tracking system architecture selected, simulated tracking data was processed with a Non-Linear Least Squares batch orbit estimation algorithm and a Bayes sequential orbit determination filter to update the target satellite's state vector.

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Noise Estimation In The Presence Of Bpsk Digital Burst Transmissions, Susan E. Bettison Mar 2005

Noise Estimation In The Presence Of Bpsk Digital Burst Transmissions, Susan E. Bettison

Theses and Dissertations

This research explores noise estimation techniques in an attempt to improve upon a previously developed digital burst transmission Binary Phase Shift Keyed (BPSK) demodulator. The demodulator success is dependent on the accuracy of the estimate of Power Spectral Density (PSD) of the unknown noise. Given a discrete time signal transformed into the frequency domain, the research seeks to determine if it is possible to effectively estimate the PSD of the unknown noise. The demodulator was developed using a new signal model for digital burst transmissions based on linear spectral subspace theory. Using this model and the redundancy properties of BPSK …

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Executable Architectures And Their Application To A Geographically Distributed Air Operations Center, Robert J. Beal, Jeremy P. Hendrix, Garth P. Mcmurray, William C. Stewart Mar 2005

Executable Architectures And Their Application To A Geographically Distributed Air Operations Center, Robert J. Beal, Jeremy P. Hendrix, Garth P. Mcmurray, William C. Stewart

Theses and Dissertations

Integrated Architectures and Network Centric Warfare represent two central concepts in the Department of Defense's (DoD) on-going transformation. The true power of integrated architectures is brought to bear when they are combined with simulation to move beyond a static representation and create an executable architecture. This architecture can then be used to experiment with system configurations and parameter values to guide employment decisions. The process of developing and utilizing an executable architecture will be employed to assess an Air Operations Center (AOC). This thesis applies and expands upon the methodology of Dr. Alexander Levis, former Chief Scientist of the Air …

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Thermal Characteristics Of Pitch Based Carbon Foam And Phase Change Materials, Kevin W. Wierschke Mar 2005

Thermal Characteristics Of Pitch Based Carbon Foam And Phase Change Materials, Kevin W. Wierschke

Theses and Dissertations

Phase-change thermal energy storage devices offer thermal control systems an option that allows a smaller heat sink to be used by absorbing the thermal energy quickly and storing it in the phase change to prevent failure of electronic components and then slowly releasing the heat to the heat sink. This paper experimentally determined the transient response of carbon foam with a phase-change material by measuring the response to a step temperature input to test samples. The transient response was recorded until steady state was reached. An analytic response was created and compared against the measured response. A simplified analytic prediction …

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Technical Feasibility Of Loitering Lighter-Than-Air-Near-Space Maneuvering Vehicles, Eric R. Moomey Mar 2005

Technical Feasibility Of Loitering Lighter-Than-Air-Near-Space Maneuvering Vehicles, Eric R. Moomey

Theses and Dissertations

The near-space region of earth's atmosphere above 20 kilometers altitude is greatly underutilized. Lighter-than-air maneuvering vehicles, or airships, using the principle of buoyancy can take advantage of this region to become potential platforms for precision navigation, environmental monitoring, communication relays, missile warning, surveillance, and weapon delivery. These vehicles purportedly provide persistent coverage over large areas of the earth's surface at substantially lower costs than orbiting satellites. This study investigated the technical requirements to loiter an operational payload within this high altitude region using a lighter-than-air maneuvering platform. A parametric analysis was conducted to identify the critical technologies needed to achieve …

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A Comparison Of Hazard Predication And Assessment Capability (Hpac) Software Dose-Rate Contour Plots To A Sample Of Local Fallout Data From Test Detonations In The Continental United States, 1945-1962, Richard W. Chancellor Mar 2005

A Comparison Of Hazard Predication And Assessment Capability (Hpac) Software Dose-Rate Contour Plots To A Sample Of Local Fallout Data From Test Detonations In The Continental United States, 1945-1962, Richard W. Chancellor

Theses and Dissertations

A comparison of Hazard Prediction and Assessment Capability (HPAC) software dose-rate contour plots to a sample of local nuclear fallout data from test detonations in the continental United States, 1945 - 1962, is performed. Fallout data from test detonations is obtained from "Compilation of Local Fallout Data from Test Detonations 1945- 1962 Extracted from DASA 1251, Volume I - Continental U.S. Tests." This report contains fallout plots and radiation contours for each test in the atmospheric nuclear test program conducted by the United States prior to 1963. These plots are compared with the plots resulting from Defense Threat Reduction Agency's …

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Surface Oxidation Study Of Uranium Dioxide Under Wet And Dry Conditions, Gary T. Brett Mar 2005

Surface Oxidation Study Of Uranium Dioxide Under Wet And Dry Conditions, Gary T. Brett

Theses and Dissertations

The surface oxidation of pressed uranium dioxide (UO2) powder under controlled environmental conditions and the oxidation and reduction of pressed uranium trioxide (UO3) powder are presented. This is a continuing research project in the investigation of the oxidation of UO2 powder using Photoluminescence (PL) Spectroscopy. UO2 particles exposed to the ambient atmosphere will oxidize into a number of chemical complexes (specifically hydrates, hydroxides, and carbonates). During certain of these oxidation processes, the uranium ion can lose two of its electrons and change from uranous (UIV+) to uranyl (UVI+). This research …

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Air Force Jp-8 Fuel Distribution System: A Statistical Analysis To Determine Where And When To Sample, Eric J. Heath Mar 2005

Air Force Jp-8 Fuel Distribution System: A Statistical Analysis To Determine Where And When To Sample, Eric J. Heath

Theses and Dissertations

The Air Force Petroleum Office at Wright-Patterson Air Force Base, Ohio collects JP-8 sampling data, but this data doesn't undergo analysis to determine the health of the base-level JP-8 fuel distribution system. Commanders possess no known confidence level when assessing base-level fuel health. Therefore, the objective of this research is to assess Air Force base-level fuel sampling data to determine the base-level sampling point that ensures a quality and healthy product at the aircraft. Also, this research seeks to identify how often correlation sampling should take place. Sample test pass rates are analyzed from three locations, receipt, storage, and vehicles/aircraft, …

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Minimizing Security Forces Response Times Through The Use Of Facility Location Methodologies, Michael C. Dawson Mar 2005

Minimizing Security Forces Response Times Through The Use Of Facility Location Methodologies, Michael C. Dawson

Theses and Dissertations

Since the events of September 11, 2001, security for the nation's Intercontinental Ballistic Missile force has become a prominent concern for personnel in the highest levels of government. This has resulted in many physical security upgrades and new methods to counter hostile activities. This research seeks to find the optimal placement for one layer of the security net protecting these crucial assets, the daily-deployed security forces Fire Teams. The problem of finding the optimal placement for these forces is modeled as a facility location problem. Three of the methods of locating facilities available in the literature are selected to solve …

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A Multiple-Case Analysis Of Lean Six Sigma Deployment And Implementation Strategies, Peter M. O'Rourke Mar 2005

A Multiple-Case Analysis Of Lean Six Sigma Deployment And Implementation Strategies, Peter M. O'Rourke

Theses and Dissertations

Lean and Six Sigma are recent developments in continuous improvement methodology that have been popularized by several high-profile companies. The success and complementary nature of these methodologies has led to their combination into a single methodology, commonly called Lean Six Sigma or Lean Sigma. Although there is considerable literature available and many consultants involved with Lean Six Sigma, very little published research addresses the practical experiences of companies that have implemented Lean Six Sigma. The research question for this research is: How and why are certain private sector implementations of Lean Six Sigma successful or unsuccessful? The investigative questions further …

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Analysis Of Online-Delaunay Navigation For Time Sensitive Targeting, David Chow Mar 2005

Analysis Of Online-Delaunay Navigation For Time Sensitive Targeting, David Chow

Theses and Dissertations

Given the drawbacks of leaving time-sensitive targeting (TST) strictly to humans, there is value to the investigation of alternative approaches to TST operations that employ autonomous systems. This paper accomplishes five things. First, it proposes a short-hop abbreviated routing paradigm (SHARP) - based on Delaunay triangulations (DT), ad-hoc communication, and autonomous control - for recognizing and engaging TSTs that, in theory, will improve upon persistence, the volume of influence, autonomy, range, and situational awareness. Second, it analyzes the minimum timeframe need by a strike (weapons enabled) aircraft to navigate to the location of a TST under SHARP. Third, it shows …

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Feasibility Study Of Variance Reduction In The Thunder Campaign-Level Model, Earl M. Bednar Mar 2005

Feasibility Study Of Variance Reduction In The Thunder Campaign-Level Model, Earl M. Bednar

Theses and Dissertations

As an Air Force Chief of Staff endorsed topic, Air Force Studies and Analyses Agency (AFSAA) requested an effective and efficient way to reduce the variance in analysis results from THUNDER. THUNDER is a large-scale discrete event simulation of campaign-level military operations and is used to examine issues involving the utility and effectiveness of air and space power in a theater-level, joint warfare context. Given the large number of stochastic components within THUNDER, results are produced with highly variable measures of effectiveness (MOEs), causing difficulties in evaluating alternative force structures, weapon systems, etc. This work responds to AFSAA's request by …

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Optimal Maintenance For Stochastically Degrading Satellite Constellations, Timothy J. Cook Mar 2005

Optimal Maintenance For Stochastically Degrading Satellite Constellations, Timothy J. Cook

Theses and Dissertations

This thesis develops a methodology to determine an optimal policy for maintaining a satellite constellation that degrades over time. Previous work has developed a methodology to compute an optimal replacement policy for a satellite constellation in which satellites were viewed as binary entities, either operational or failed. This research extends the previous models by developing an optimal maintenance policy for satellite constellations in which each satellite may operate in a finite number of degraded states. The constellation is assumed to consist of a finite number of satellites, each with a finite number of functions with distinct failure mechanisms. Assuming each …

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A Knowledge Matrix Modeling Of The Intelligence Cycle, Kevin J. Whaley Mar 2005

A Knowledge Matrix Modeling Of The Intelligence Cycle, Kevin J. Whaley

Theses and Dissertations

This effort models information flow through the United States Intelligence Community's Intelligence Cycle using a knowledge matrix methodology. The knowledge matrix methodology takes explicit data from multiple sources and fuses that data to measure a current level of knowledge about a target, or situation. Knowledge matrices are used to develop a measure of user-needs satisfaction. User-needs satisfaction compares requested levels of knowledge to a probability of collecting that knowledge within a designated timeframe. This effort expands the work done by Captain Carl Pawling in his March 2004 thesis, Modeling and Simulation of the Military Intelligence Process, by modeling intelligence as …

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On The Use Of Surrogate Functions For Mixed Variable Optimization Of Simulated Systems, John E. Dunlap Mar 2005

On The Use Of Surrogate Functions For Mixed Variable Optimization Of Simulated Systems, John E. Dunlap

Theses and Dissertations

This research considers the efficient numerical solution of linearly constrained mixed variable programming (MVP) problems, in which the objective function is a black-box stochastic simulation, function evaluations may be computationally expensive, and derivative information is typically not available. MVP problems are those with a mixture of continuous, integer, and categorical variables, the latter of which may take on values only from a predefined list and may even be non-numeric. Mixed Variable Generalized Pattern Search with Ranking and Selection (MGPS-RS) is the only existing, provably convergent algorithm that can be applied to this class of problems. Present in this algorithm is …

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Usable Design Of Civil Engineer Information Systems, Gunther Kastenholz Mar 2005

Usable Design Of Civil Engineer Information Systems, Gunther Kastenholz

Theses and Dissertations

This research used a case study methodology where one instrument used to collect data was a heuristic usability inspection method. Data was collected from a literature review of pertinent Civil Engineer information system design documents, and conclusions drawn about the existing level of specification of usability engineering principles. The heuristic usability inspection method was used to validate the conclusions drawn through inspection of an information system representative of other Civil Engineer information systems, the Automated Civil Engineer System Personnel Readiness module.

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Modeling And Analysis Of Clandestine Networks, Clinton R. Clark Mar 2005

Modeling And Analysis Of Clandestine Networks, Clinton R. Clark

Theses and Dissertations

Since Sept. 11, 2001, there has been great interest in the military and intelligence communities in using Social Network Analysis (SNA) to support the disruption and destruction of global terrorist networks. SNA results, however, tend to be descriptive and are limited due to the lack of advantageous properties of the relationship measures applied to the arcs in a social network. Further, SNA techniques generally focus on a single network context while real relationships are based in multiple contexts. This thesis develops a new proxy measure of pair-wise potential influence between members of a network, a Holistic Interpersonal Influence Measure (HIIM). …

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Estimating Performance Time For Air Force Military Construction Projects, Greg J. Hoffman Mar 2005

Estimating Performance Time For Air Force Military Construction Projects, Greg J. Hoffman

Theses and Dissertations

The prediction of construction time performance is a problem of interest to both researchers and construction industry practitioners. This research seeks to identify significant factors which may influence construction durations for Air Force Military Construction (MILCON) projects to establish a time prediction model. Data were collected for 856 MILCON projects completed between 1988 and 2004; this included both traditional facility and non-facility (e.g. airfield pavements, utilities) projects. These data were analyzed using Bromilow's time-cost (BTC) model (1969) as well as multiple linear regression. Neither model produced acceptable results for non-facility projects; however, the multiple linear regression model was found to …

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An Evaluation Of Contingency Construction Methods Using Value Focused Thinking, John E. Tyron Mar 2005

An Evaluation Of Contingency Construction Methods Using Value Focused Thinking, John E. Tyron

Theses and Dissertations

Rapid Engineering Deployable, Heavy Operational Repair Squadron, Engineer (RED HORSE) Squadrons are 400-person, self-contained, combat engineer units that provide deployable and flexible expert construction capability for the United States Air Force. To help meet Air Force mission requirements, RED HORSE units currently employ a variety of traditional and innovative construction methods. But their alternatives-focused decision analysis approach to method selection limits their decision to known alternatives and may not fully achieve all of their objectives. This research developed a generic value-focused thinking (VFT) decision analysis model to help RED HORSE evaluate and select contingency construction methods. Eight alternatives were generated …

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Decision Analysis Using Value-Focused Thinking To Select Renewable Alternative Fuels, Eric A. Queddeng Mar 2005

Decision Analysis Using Value-Focused Thinking To Select Renewable Alternative Fuels, Eric A. Queddeng

Theses and Dissertations

The United States relies on imported oil as a result of domestic petroleum consumption rates greatly exceeding production rates. Alternative fuels are a major force in the effort to reduce petroleum consumption in the transportation industry. The transportation industry also accounts for 1/3 of all greenhouse gas emissions and nearly half of all cancers attributed to outdoor sources of pollutants. The purpose of this research was to evaluate the economic and environmental feasibility of renewable alternative fuels and associated blends (ethanol, methanol, 100% biodiesel (B100), 20% biodiesel (B20) and e-diesel) compared to non-renewable alternative fuels (compressed natural gas and propane) …

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Information Technology Implementation And Sustainment Model: Data Collection Instrument, Walter K. Yazzie Mar 2005

Information Technology Implementation And Sustainment Model: Data Collection Instrument, Walter K. Yazzie

Theses and Dissertations

The goal of this research was to develop a data collection instrument for an existing information technology implementation and sustainment model. In 2003, a unique system dynamics model was developed at the Air Force Institute of Technology to predict the behavior of information technology implementation and sustainment (Fonnesbeck, 2003). However, no empirical data was used during the model development. In order to collect the needed empirical data, this research develops a data collection instrument for the model. The instrument was sent to 60 Air Force community planners who are currently implementing a geographical information system (Air Force GeoBase) into their …

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