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2001

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Articles 1081 - 1110 of 1795

Full-Text Articles in Engineering

Modeling Pressurized Water Reactor Kinetics, William H. Harman Mar 2001

Modeling Pressurized Water Reactor Kinetics, William H. Harman

Theses and Dissertations

A computer model of a pressurized water reactor (PWR) was developed for use as a teaching tool in graduate level nuclear reactor courses. The development, based on the diffusion equation, includes the methodology for solving the steady state spatial dependence of the neutron power output in a homogeneous right circular cylinder unreflected PWR system. This includes a two dimensional one energy group model, a three dimensional one energy group model, and a three dimensional two energy group model. To solve the homogeneous diffusion equation, a method was developed to search for criticality of the reactor based on the geometry and …

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Analysis Of The Application Of A Triggered Isomer Heat Exchanger As A Replacement For The Combustion Chamber In An Off-The-Shelf Turbojet, Carl R. Hartsfield Mar 2001

Analysis Of The Application Of A Triggered Isomer Heat Exchanger As A Replacement For The Combustion Chamber In An Off-The-Shelf Turbojet, Carl R. Hartsfield

Theses and Dissertations

The objective of this research was to evaluate the feasibility of using the triggered decay of a radioactive isomer in a solid-state heat exchanger to power a gas turbine engine. Primary performance measures were stagnation temperature increase and stagnation pressure drop across the heat exchanger. Analysis was performed using commercial software, and explored three types of heat exchanger: concentric tubes, radial fins with constant spacing, and radial fins with constant thickness. All met or exceeded performance of the baseline J-57 turbojet engine at static sea level conditions. A single configuration of heat exchanger, using concentric tubes, was evaluated at typical …

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Influence Of Personality Type And Anonymity On Participation In A Group Support System, Robert E. Hartmann Mar 2001

Influence Of Personality Type And Anonymity On Participation In A Group Support System, Robert E. Hartmann

Theses and Dissertations

A group support system (GSS) uses a combination of networked personal computers, software that collects, manipulates, and aggregates member's individual input, and human facilitation to improve the group decision-making process. A GSS has been promoted as a means of improving the quantity and quality of ideas within a decision-making meeting. Research into GSS has focused on the benefits of providing anonymity to improve participation. Anonymity in a GSS meeting has been offered as a means to improve participation, which in turn improves decision quality. To date this has not been proven through research. In fact, there is conflicting evidence as …

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An Analysis Of The Acquisition Process For Simplified Acquisition Of Base Engineering Requirements (Saber) Contracts And Its Potential Impact On Contractor Performance, Brian J. Heaps Mar 2001

An Analysis Of The Acquisition Process For Simplified Acquisition Of Base Engineering Requirements (Saber) Contracts And Its Potential Impact On Contractor Performance, Brian J. Heaps

Theses and Dissertations

The Simplified Acquisition of Base Engineering Requirements (SABER) contract's main purpose is to expedite contract award of civil engineer requirements through the issuance of individual delivery orders. The contract contains a collection of detailed task specifications that include most types of real property maintenance, repair, and construction work. The Assistant Secretary of the Air Force for Acquisition's Operational Contracting Division (SAF/AQCO) identified a number of failed SABER contracts. The problem statement designed for this research effort was: There are a large number of SABER contractors that are failing during the performance period on their SABER contracts. SAF/AQCO is trying to …

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Development And Testing Of A Multiple Filter Approach For Precise Dgps Positioning And Carrier-Phase Ambiguity Resolution, Paul E. Henderson Mar 2001

Development And Testing Of A Multiple Filter Approach For Precise Dgps Positioning And Carrier-Phase Ambiguity Resolution, Paul E. Henderson

Theses and Dissertations

The most precise relative positioning obtained using differential GPS depends on accurately determining carrier-phase integer ambiguities. To achieve high precision, many current static and kinematic algorithms use a floating-point solution until enough information becomes available to fix the carrier-phase ambiguities accurately. A mew method is presented that uses a multiple model Kalman filter to resolve the carrier-phase integer ambiguities. This method starts with the floating-point results, yet smoothly and rapidly attains the precision of the correct fixed-integer solution, eliminating the need to decide when to switch from the floating to the fixed-integer solution. This method is based on a theoretically …

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Utility Of Experimental Design In Automatic Target Recognition Performance Evaluation, James M. Higdon Mar 2001

Utility Of Experimental Design In Automatic Target Recognition Performance Evaluation, James M. Higdon

Theses and Dissertations

This research investigates current practices in test and evaluation of classification algorithms, and recommends improvements. We scrutinize the evaluation of automatic target recognition algorithms and rationalize the potential for improvements in the accepted methodology. We propose improvements through the use of an experimental design approach to testing. We demonstrate the benefits of improvements by simulating algorithm performance data and using both methodologies to generate evaluation results. The simulated data is varied to test the sensitivity of the benefits to a broad set of outcomes. The opportunities for improvement are threefold. First, the current practice of 'one-at-a-time factor variation (only one …

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A Low Power Application-Specific Integrated Circuit (Asic) Implementation Of Wavelet Transform/Inverse Transform, Daniel N. Harvala Mar 2001

A Low Power Application-Specific Integrated Circuit (Asic) Implementation Of Wavelet Transform/Inverse Transform, Daniel N. Harvala

Theses and Dissertations

A unique ASIC was designed implementing the Haar Wavelet transform for image compression/decompression. ASIC operations include performing the Haar wavelet transform on a 512 by 512 square pixel image, preparing the image for transmission by quantizing and thresholding the transformed data, and performing the inverse Haar wavelet transform, returning the original image with only minor degradation. The ASIC is based on an existing four-chip FPGA implementation. Implementing the design using a dedicated ASIC enhances the speed, decreases chip count to a single die, and uses significantly less power compared to the FPGA implementation. A reduction of RAM accesses was realized …

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Modeling Biodegradation Of Chlorinated Groundwater Contaminants Under Iron-Reducing Conditions Of A Constructed Wetland: A System Dynamics Approach, Max E. Johnson Mar 2001

Modeling Biodegradation Of Chlorinated Groundwater Contaminants Under Iron-Reducing Conditions Of A Constructed Wetland: A System Dynamics Approach, Max E. Johnson

Theses and Dissertations

The purpose of this study is to determine and explore the fundamental processes associated with biodegradation of chlorinated ethenes in iron-reducing conditions of a constructed wetland and to evaluate the impacts of changing conditions (both natural and engineer-controlled) on the system. The modeler uses a system dynamics approach to construct a model that represents behavior in the iron-reducing environment. The model incorporates hematite, a form of oxidized iron (Fe3+), as the electron acceptor in microbial biodegradation in the system. Vinyl chloride, cis-dichloroethene, and trans-dichloroethene are known to anaerobically degrade to carbon dioxide in the presence of oxidized iron. …

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A System Dynamics Approach To Modeling Temperature Effects In Solid Waste, David A. Jokinen Mar 2001

A System Dynamics Approach To Modeling Temperature Effects In Solid Waste, David A. Jokinen

Theses and Dissertations

The amount of municipal solid waste discarded to landfills is continually increasing even with extensive recycling efforts. The need to understand the behavior of waste in landfills is increased due to the decreasing number of active landfills, communities' concern to the potential hazards associated with landfills, and companies or installations with landfills on-site need to understand landfill behavior comply with new legislation concerning design and detecting hazardous material movement of-site. This research is focused on increasing the understanding of landfill behavior by examining the effects of temperature in a landfill system. A system dynamics approach was used in this research …

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A Study Of Linear Vs. Nonlinear Control Techniques For The Reconfiguration Of Satellite Formations, David J. Irvin Jr. Mar 2001

A Study Of Linear Vs. Nonlinear Control Techniques For The Reconfiguration Of Satellite Formations, David J. Irvin Jr.

Theses and Dissertations

This thesis investigates several linear and nonlinear feedback control methods for satellite formation reconfigurations and compares them to a near optimal open loop, discrete-time, impulsive maneuver. The reconfigurations are done in terms of a set of relative parameters that define an orbit about the leader satellite (or center reference position if a leader satellite does not exist at the center of the formation). The purpose of the study is two-fold, to compare the control usage of continuous feedback control methods versus a discrete bum method and to determine if nonlinear control techniques offer significant improvement over more conventional linear control …

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Simulating Wet Deposition Of Radiocesium From The Chernobyl Accident, Aaron M. Kinser Mar 2001

Simulating Wet Deposition Of Radiocesium From The Chernobyl Accident, Aaron M. Kinser

Theses and Dissertations

In response to the Chernobyl nuclear power plant accident of 1986, a cesium-137 deposition dataset was assembled. Most of the airborne Chernobyl cesium was wet deposited, either via interception by falling raindrops or via absorption into cloud droplets destined to become raindrops. The Hybrid Single-Particle Lagrangian rated Transport (HYSPLIT) model, developed at Air Resources Laboratory, is used to simulate the transport and deposition of Chernobyl cesium-137. A cloud base parameterization modification is tested and appears to slightly improve the accuracy of one HYSPLIT simulation of daily Chernobyl cesium-137 deposition over the course of the accident at isolated European sites, and …

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Wavelet Domain Communication System (Wdcs): Design, Model, Simulation, And Analysis, Randall W. Klein Mar 2001

Wavelet Domain Communication System (Wdcs): Design, Model, Simulation, And Analysis, Randall W. Klein

Theses and Dissertations

A proposed wavelet domain communication system (WDCS) using transform domain processing is demonstrated as having enhanced interference avoidance capability under adverse environmental conditions. The WDCS system samples the environment and uses the wavelet transform, to determine interference presence and time/scale location. A digital communication waveform (basis function) is subsequently designed in the wavelet domain to specifically avoid regions containing interference. The WDCS basis function is data modulated prior to transmission. Assuming perfect synchronization, the receiver replicates a locally generated basis function for correlating with the received signal and demodulating the data. The proposed system is modeled and simulation results are …

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A Delphi Assessment Of The Digital Rosetta Stone Model, Don M. Kelley Mar 2001

A Delphi Assessment Of The Digital Rosetta Stone Model, Don M. Kelley

Theses and Dissertations

Information that is stored digitally can only be used if it can be retrieved and interpreted. if the methods to retrieve the information are lost, it may be difficult, if not impossible, to recreate them. The knowledge to interpret the bitstream is also at risk. The Digital Rosetta Stone (DRS) Model was developed as a framework for capturing and maintaining the methods necessary to retrieve and display digital information stored on obsolete media or using obsolete software. However, this conceptual model had not yet been assessed by the community of professionals for its practical efficacy. This thesis began the assessment …

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Requirements-Based Methodology For Determining Age Inventory Levels, James A. Mackenna Mar 2001

Requirements-Based Methodology For Determining Age Inventory Levels, James A. Mackenna

Theses and Dissertations

The purpose of this research was to illuminate crucial areas in analyzing AGE needs on an operational flightllne and assist in determination of AGE inventory levels. Further refinements could result in more objective and accurate assessments of actual flightline AGE needs and associated risks involved with reduction of AGE inventory levels. The research in this thesis consists of a discrete event simulation to determine desired AGE inventory level through an analysis of aircraft launches and wait time for AGE support by varying AGE (mean time between failure) MTBF and AGE inventory. Stochastic inputs for aircraft failures, AGE delivery times, and …

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Routing Of Time-Sensitive Data In Mobile Ad Hoc Networks, Necdet Kilic Mar 2001

Routing Of Time-Sensitive Data In Mobile Ad Hoc Networks, Necdet Kilic

Theses and Dissertations

This research focuses on routing of time-sensitive data in mobile ad hoc networks. Routing protocols that were developed for ad hoc networks have been reviewed. Ad Hoc On-demand Distance Vectoring (AODV) routing protocol, which is a prominent routing protocol among these protocols have been implemented in OPNET, a discrete-event simulation tool. Taking AODV as a point of departure, a routing protocol named Real Time Routing Protocol (RTRP) has been developed and also implemented in simulation environment. The performance of these routing protocols have been observed by simulating them in various experiments where the workload has been chosen to be time-sensitive …

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Lifecycle Energy And Air Emission Differences Between Electric And Internal Combustion Vehicles, David L. Mccleese Mar 2001

Lifecycle Energy And Air Emission Differences Between Electric And Internal Combustion Vehicles, David L. Mccleese

Theses and Dissertations

The U.S. Federal Government has encouraged shifting from internal combustion engine vehicles (ICEVs) to electric vehicles (EVs) with three objectives, reducing foreign oil dependence, greenhouse gas emissions, and criteria pollutant emissions. This thesis uses Monte Carlo simulation to predict lifecycle emissions and energy consumption differences per kilometer driven from replacing ICEVs with three EV options: lead acid, nickel cadmium (Ni-Cd), and nickel metal hydride (NiMH). All three EV options reduce U.S. foreign oil dependence by shifting to domestic coal. The probabilities that lifecycle energy consumption per km driven improve are lead acid 76%, Ni-Cd 64%, and NiMH 90%. The probabilities …

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Desktop Computer Programs For Preliminary Design Of Transonic Compressor Rotors, Brian C. Mcdonald Mar 2001

Desktop Computer Programs For Preliminary Design Of Transonic Compressor Rotors, Brian C. Mcdonald

Theses and Dissertations

A need exist for correlation-based desktop computer programs that predict the flow through transonic compressor rotors with nominal computational time and cost. Modified versions of two desktop computer programs, BOWSHOCK and TRANSROTOR, were used to perform a parametric study on a modem compressor rotor. BOWSHOCK calculates the exit flow properties of a supersonic streamtube through a user-defined compressor rotor. TRANSROTOR calculates flow properties at three stations in a user-defined compressor stage. Modifications to TRANSROTOR included the incorporation of a recently published rotor loss model. Baseline and modified TRANSROTOR versions were run with two modern transonic compressor blades. Results were compared …

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Wavelet-Based Audio Embedding & Audio/Video Compression, Michael J. Mendenhall Mar 2001

Wavelet-Based Audio Embedding & Audio/Video Compression, Michael J. Mendenhall

Theses and Dissertations

With the decline in military spending, the United States relies heavily on state side support. Communications has never been more important. High-quality audio and video capabilities are a must. Watermarking, traditionally used for copyright protection, is used in a new and exciting way. An efficient wavelet-based watermarking technique embeds audio information into a video signal. Several highly effective compression techniques are applied to compress the resulting audio/video signal in an embedded fashion. This wavelet-based compression algorithm incorporates bit plane coding, first difference coding, and Huffman coding. To demonstrate the potential of this audio embedding audio/video compression system, an audio signal …

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Chromate Content Bias As A Function Of Particle Size In Aircraft Primer Paint Overspray, David B. Novy Mar 2001

Chromate Content Bias As A Function Of Particle Size In Aircraft Primer Paint Overspray, David B. Novy

Theses and Dissertations

Spray painting operations using chromate-containing primer paints produce particles which may expose workers to strontium chromate. Chromate contains hexavalent chromium (Cr(VI)) which is a confirmed human carcinogen. It is suspected that the smaller particles contain disproportionately less Cr(VI) than larger particles. In order to determine if a bias in chromate content exists, paint particles were collected and separated based on particle size and the Cr(VI) concentration was determined. Aviation primer paint from the DeSoto and Deft companies was sprayed in a booth and seven-stage cascade impactors were used to separate particles.

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Air Vehicle Optimal Trajectories For Radar Exposure Minimization, Michael C. Novy Mar 2001

Air Vehicle Optimal Trajectories For Radar Exposure Minimization, Michael C. Novy

Theses and Dissertations

This study addresses the problem of analyzing the single vehicle path planning problem for radar exposure minimization. The calculus of Variations and optimal control are applied to formulate the cost function and numerical algorithms are used to solve for the optimal paths. Cost sensitivity to path length is analyzed for flight against one radar; a second radar is then included in the formulation and the optimal path for flight between the radars is found for cases of equal and unequal radar power. The costs of the optimal path, direct path, and Voronoi diagram-generated paths are compared. Results indicate low sensitivity …

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Pilot Mental Workload Calibration, Jeremy B. Noel Mar 2001

Pilot Mental Workload Calibration, Jeremy B. Noel

Theses and Dissertations

Predicting high pilot mental workload is important to the U.S. Air Force because lives and aircraft can be lost when errors are made during periods of mental overload and task saturation. Current research efforts use psychophysiological measures such as electroencephalography, cardiac, ocular, and respiration measures in an attempt to identify and predict mental workload levels. The primary focus of this effort is the development of a calibration scheme that allows a small subset of salient psychophysiological features developed using actual flight data for one pilot on a given day to accurately classify pilot mental workload for a separate pilot on …

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A Model To Predict Diffraction Attenuation Resulting From Signal Propagation Over Terrain In Low Earth Orbit Satellite Systems, Peter R. Pollock Mar 2001

A Model To Predict Diffraction Attenuation Resulting From Signal Propagation Over Terrain In Low Earth Orbit Satellite Systems, Peter R. Pollock

Theses and Dissertations

This study focused on multipath communication propagation impairments to the LEOSAT communications channel. Two terrain diffraction models, based on the geometric theory of diffraction (GTD), were developed and applied to the space-to-ground communications channel. These models were used to predict the impact of terrain on the performance of three LEOSAT communication systems with designs based on the Iridium, Globalstar and Orbcomm implementations. The study verified the feasibility of applying models based on the GTD rather than empirical or statistical models, to approximate the effect of propagating signals over terrain. Both models confirm that signal blockage and multipath propagation, due to …

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Estimating C-17 Operating And Support Costs: Development Of A System Dynamics Model, Christopher D. Purvis Mar 2001

Estimating C-17 Operating And Support Costs: Development Of A System Dynamics Model, Christopher D. Purvis

Theses and Dissertations

This research provides justification for experimenting with system dynamics (SD) for performing Operation and Support Cost estimates. For the C-17 Globemaster III cargo aircraft, these costs could exceed $64 billion dollars. Also, many of our weapon systems are beginning to reach the end of their effective life span, and discussions about the impact of aging, on aircraft, has become a hot topic in the literature. System Dynamics is a modeling methodology developed in 1958, but never used extensively for cost estimating. SD offers unique capabilities to the cost estimator, including the ability to model causal relationships. This capability offers the …

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Phugoid Damping Control, Nicolas J. Schindeler Mar 2001

Phugoid Damping Control, Nicolas J. Schindeler

Theses and Dissertations

A novel phugoid damping control design methodology is developed, based on the use of wind axes and a point-mass aircraft model. The state variables are air speed, flight path angle, and heading angle, the control variables are thrust setting, angle of attack, bank angle, and sideslip angle, and the command signals are airspeed, flight path angle, and heading angle or heading rate. All the variables and parameters are nondimensionalized. A multivariable set point controller is developed which consists of: (1) a trim calculation-based nonlinear feed-forward control computer; thus, given a commanded new trim state (air speed, flight path angle, and …

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Concept Exploration Of An Australian Indigenous Space Launch Capability, Anthony J. Rogers Mar 2001

Concept Exploration Of An Australian Indigenous Space Launch Capability, Anthony J. Rogers

Theses and Dissertations

This thesis explores the possibility of establishing an Australian indigenous space launch capability through developing and examining an Australian space launch program model. The model is based around launch site location, vehicle design, program duration, and the percentage Australian indigenous input into the program. The model was optimised in an effort maximise the benefits of such a capability, namely political prestige, security and in country technological base, while minimising the program's overall cost.

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A Model For Palladium Catalyzed Destruction Of Chlorinated Ethenes In Contaminated Groundwater, Christopher M. Stoppel Mar 2001

A Model For Palladium Catalyzed Destruction Of Chlorinated Ethenes In Contaminated Groundwater, Christopher M. Stoppel

Theses and Dissertations

Groundwater contamination by chlorinated ethenes is a widespread environmental problem. Conventional remediation technologies have shortcomings that have prompted further research into the development of novel treatment technologies. A palladium/ alumina catalyst in the presence of dissolved molecular hydrogen (referred to hereafter as a PD/H2 system) has been demonstrated to rapidly destroy chlorinated ethene contaminated groundwater. First-order kinetics have been used to model chlorinated ethene destruction in a PD/H2 reactor. However, catalyst deactivation and regeneration are important processes that also need to be modeled in order to better understand their effect on treatment efficiency. This study presents a model …

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Gss Technology As A Moderator Of Influence And Perceived Expertise, Kevin V. Thompson Mar 2001

Gss Technology As A Moderator Of Influence And Perceived Expertise, Kevin V. Thompson

Theses and Dissertations

Group Support System (355) research has found this content and process anonymity influence problem solving groups. However, previous studies report mixed results on how OSS technology changes social influence processes and recognition of expertise which affect group performance. This thesis explored content and process anonymity's affect on influence and perceived expertise using three treatments to derive possible explanations for the mixed results found in previous GSS research. The study developed a theoretical model of influence, perceived expertise, and performance. Using structural equation modeling the study tested the relationships between expertise and participation rates, and overall group performance. An experiment was …

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Decision Analysis Methodology To Evaluate Integrated Solid Waste Management Alternatives For A Remote Alaskan Air Station, Mark J. Shoviak Mar 2001

Decision Analysis Methodology To Evaluate Integrated Solid Waste Management Alternatives For A Remote Alaskan Air Station, Mark J. Shoviak

Theses and Dissertations

Eareckson Air Station (AS), a remote U.S. Air Force installation, faces the complex decision of selecting a new municipal solid waste (MSW) management strategy to replace its current non-compliant system. This research effort applies value-focused thinking and multiattribute preference theory to decision analysis techniques to produce a multiple-objective decision analysis model that captures all of the site's MSW goals, objectives, and concerns in order to facilitate the evaluation of MSW management strategies available. The model ranks 40 specific MSW management alternatives, which were developed in accordance with the decision-maker's assumptions and constraints, based on how well they meet Eareckson's overall …

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Relating Initial Budget To Program Growth With Rayleigh And Weibull Models, Eric J. Unger Mar 2001

Relating Initial Budget To Program Growth With Rayleigh And Weibull Models, Eric J. Unger

Theses and Dissertations

Previous research on completed defense R&D shows that contract expenditures can be fit well with a Rayleigh model. With fixed outlay rates, as prescribed by the OSD comptroller, the budget profile must have most of the funds in the early years to produce Rayleigh-distributed expenditures. R&D programs with more delayed funding profiles may also produce expenditures that a Rayleigh model fits through schedule slips and cost overruns. This research tests how well the initial funding profile produces Rayleigh-distributed expenditures that can be related to the program's final cost overrun and schedule slips. Based only on the initial budget profile, we …

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Multicast Algorithms For Mobile Satellite Communication Networks, Ryan W. Thomas Mar 2001

Multicast Algorithms For Mobile Satellite Communication Networks, Ryan W. Thomas

Theses and Dissertations

With the rise of mobile computing and an increasing need for ubiquitous high speed data connections, Internet-in-the-sky solutions are becoming increasingly viable. To reduce the network overhead of one-to-many transmissions, the multicast protocol has been devised. The implementation of multicast in these Low Earth Orbit (LEO) constellations is a critical component to achieving an omnipresent network environment. This research examines the system performance associated with two terrestrial-based multicast mobility solutions, Distance Vector Multicast Routing Protocol (DVMRP) with mobile IP and On Demand Multicast Routing Protocol (ODMRP). These protocols are implemented and simulated in a six plane, 66 satellite LEO constellation. …

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