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Theses and Dissertations

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A Statistical Analysis Of Space Structure Mode Localization, Amy M. Cox Mar 1999

A Statistical Analysis Of Space Structure Mode Localization, Amy M. Cox

Theses and Dissertations

Cyclic structures, such as antenna arrays, multi-bay trusses, and compressor blades, are significantly impacted by slight changes to system periodicity. Manufacturing errors of 5% or less can result in drastic changes to a structure's modal behavior. This change in modal behavior is significant, since it may result in the focusing of modal energy to individual substructures of the system. Poor modal identification can result in poorly designed control systems, resulting in shape control and pointing issues for space antennae. Additionally, modal energy localization may damage individual system components due to unanticipated levels of cyclic loading, leading to high cycle fatigue.

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Toward Development Of An Integrated Aerospace Power Doctrine, Toby G. Doran Mar 1999

Toward Development Of An Integrated Aerospace Power Doctrine, Toby G. Doran

Theses and Dissertations

This thesis discusses the state of the Air Force, decision making factors in the making of military doctrine, the definition of doctrine, Air Force doctrines today, new ways to develop doctrine, including models and hypothesis-research-analysis loops, space doctrine, control of space, space superiority and a call for aerospace power doctrine.

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A Nonlinear Pre-Filter To Prevent Departure And/Or Pilot-Induced Oscillations (Pio) Due To Actuator Rate Limiting, Michael J. Chapa Mar 1999

A Nonlinear Pre-Filter To Prevent Departure And/Or Pilot-Induced Oscillations (Pio) Due To Actuator Rate Limiting, Michael J. Chapa

Theses and Dissertations

Closed loop instability caused by excess phase lag induced by actuator rate limiting has been suspected in many aircraft departures from controlled flight and pilot-induced oscillations (PIO). As part of the joint Air Force Institute of Technology Test Pilot School (AFITITPS) program, a nonlinear rate limiter pre-filter (RLPF) was developed to minimize the phase lag induced by rate limiting. RLFF performance was evaluated inside the feedback path, but primary emphasis was on the pilot command path. Closed loop computer and motion-based flight simulation were conducted to prepare for the flight test. The HAVE FILTER flight test project was flown using …

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Simsat: A Satellite System Simulator And Experimental Test Bed For Air Force Research, James E. Colebank, R. Dan Jones, Randall D. Pollak, Donald M. Mannebach, George R. Nagy Mar 1999

Simsat: A Satellite System Simulator And Experimental Test Bed For Air Force Research, James E. Colebank, R. Dan Jones, Randall D. Pollak, Donald M. Mannebach, George R. Nagy

Theses and Dissertations

SIMSAT (the SIMulation SATellite) is an AFIT-sponsored program to develop a laboratory-based physical satellite simulator. SIMSAT supports experimentation in areas of attitude control, precision pointing, and vibration suppression. SIMSAT development began with the purchase of a three-axis gas bearing which simulates a torque-free space environment. SIMSAT subsystems provide power, attitude control, telemetry, and structural support to experimental payloads. Project challenges included integration of attitude control software/hardware, high-output power storage devices, remote communications, high-frequency data collection, structural design, and computer display outputs.

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Space Launch Operations And The Lean Aerospace Initiative, Troy L. Endicott Mar 1999

Space Launch Operations And The Lean Aerospace Initiative, Troy L. Endicott

Theses and Dissertations

This study analyzes current expendable launch procedures and identifies truly lean, value-added steps in launch operation enterprises as they relate to the Lean Aerospace Initiative (LAI). LAI and the concepts of lean thinning are discussed and followed by a review of current and future launch system requirements and their opportunities for lean practices. The study also discusses in detail current Delta II expendable launch processing operations and presents results in a case study that show how lean principles have helped the Delta II launch team drastically reduce on-pad time, restructure its testing philosophy, and streamline its operations flow. Many of …

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Effects Of Pressure Gradients On Turbulent Boundary Layer Flow Over A Flat Plate With Riblets, Franklin L. Dement Jr. Mar 1999

Effects Of Pressure Gradients On Turbulent Boundary Layer Flow Over A Flat Plate With Riblets, Franklin L. Dement Jr.

Theses and Dissertations

The Air Force Institute of Technology Boundary Layer Research Facility test section was modified to create controlled non-zero streamwise pressure gradients. The capability of the modified facility to reproduce theoretical laminar boundary layer velocity profiles and to create a self-preserving flow with an adverse streamwise pressure gradient was verified with three-dimensional laser Doppler anemometry. The effects of streamwise adverse and favorable pressure gradients on turbulent boundary layer flow characteristics (velocity profiles, turbulence and skin friction) and vortex formation over a flat plate with riblets at low speed (U = 5 mIs) were studied. Normal and spanwise velocity profiles for both …

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Anti-Ballistic Missile Laser Predictive Avoidance Of Satellites: Theory And Software For Real-Time Processing And Deconfliction Of Satellite Ephemerides With A Moving Platform Laser, David J. Vloedman Mar 1999

Anti-Ballistic Missile Laser Predictive Avoidance Of Satellites: Theory And Software For Real-Time Processing And Deconfliction Of Satellite Ephemerides With A Moving Platform Laser, David J. Vloedman

Theses and Dissertations

The Anti-Ballistic missile Laser (ABL) Project is committed to defense against attack from enemy-launched Theater Ballistic Missiles using an airborne laser platform to disable an enemy missile in the boost phase of launch. Wielding a laser of this power and scope requires that no collateral damage be caused by laser energy which may escape from the theater of engagement. The most likely track of such a laser would pose a significant threat to space-based assets. The Predictive Avoidance algorithm is designed to predict the path of a given laser firing sequence, and perform real-time forecasting of, and deconfliction with, the …

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Characterization Of The Double Scatter Spectrum In Multiplexed Compton Scatter Tomography, David W. Gerts Mar 1999

Characterization Of The Double Scatter Spectrum In Multiplexed Compton Scatter Tomography, David W. Gerts

Theses and Dissertations

The Multiplexed Compton Scatter Tomograph (MCST) uses single back-scattered photons to image electron density in aluminum. A source of error in this imaging technique is the presence of multiple scatters. This thesis studies the double scatter spectrum as an approximation of the multiple scatter spectrum. A deterministic code called Monte Carlo Double Scatter (MOCADS) was developed to investigate the double scatter spectrum. The code includes calculations of the Rayleigh scatter, Compton scatter, Doppler broadening effects of the spectrum, and polarization effects following the Compton scatter. The Doppler broadening portion of the code was validated by a deterministic code called Scatgram. …

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Use Of Diffuse Reflectance Spectroscopy To Determine Desorption Coefficients Of Trichioroethylene From Powdered Soils, Jay H. Foil Mar 1999

Use Of Diffuse Reflectance Spectroscopy To Determine Desorption Coefficients Of Trichioroethylene From Powdered Soils, Jay H. Foil

Theses and Dissertations

This laboratory thesis investigated the applicability of reflectance spectroscopy as a tool to measure desorption rates by directly observing the change in trichloroethylene bound to surface sites. Diffuse reflectance spectroscopy holds the promise of being a faster technique with minimal sample preparation time. Reflectance spectroscopy's dependence on the surface of the sample is its greatest advantage, as well as its greatest disadvantage. Both high and low resolution scans were made of different soil samples contaminated by trichloroethylene. After the technique of spectral subtraction was used, potential TCE signals were observed from the dolomitic limestone sample. Unfortunately, due to the low …

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Electrical Characterization Of Ion-Implanted 4h-Silicon Carbide, Christian P. Morath Mar 1999

Electrical Characterization Of Ion-Implanted 4h-Silicon Carbide, Christian P. Morath

Theses and Dissertations

Electrical characterization has been performed on ion-implanted p-type 4H-SiC to assess the activation efficiency and implantation-related damage recrystallization with the intention of developing an implantation/annealing scheme. Low doped (Na - Nd = 5x1015cm3 epitaxial p-type layers grown by MOCVD were implanted with Al or B at doses ranging from 1x1013 to 1x1014/cm2 at room temperature or 500°C. The electrical technique of Temperature Dependent Hall Effect (TDHE) indicated that Al and B act as shallow acceptors 4H-SiC with ionization energies of ~252 and ~285 meV, respectively. The highest activation efficiency for Al and B …

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Inelastic Scattering Matrix Elements For The Collision B (2P1/2) + H2(J) → B (2P3/2) + H2(J'), Thomas A. Niday Mar 1999

Inelastic Scattering Matrix Elements For The Collision B (2P1/2) + H2(J) → B (2P3/2) + H2(J'), Thomas A. Niday

Theses and Dissertations

Initial efforts to characterize the scattering dynamics of B + H2 focus on computing scattering matrix elements for the fine structure transition B (2P1/2) --> B (2P3/2) in collisions with H2, allowing for rotational excitation. Using a new application of the time dependent Channel Packet Method (CPM), reactant and product wave packets are prepared in the asymptotic limit on the B (2P1/2) and B (2P3/2) surfaces. They are propagated using the split operator method together wit a unitary transformation between the …

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Band Structure Anisotropy In Semiconductor Quantum Wells, Steven J. Novotny Mar 1999

Band Structure Anisotropy In Semiconductor Quantum Wells, Steven J. Novotny

Theses and Dissertations

The focus of this research is an investigation of energy band anisotropy in simple quantum well structures. This anisotropy results from the asymmetry of the periodic potential within the crystal lattice. For sufficiently high doping levels, band structure anisotropy is expected to play an important role in the evaluation of the electronic and optical properties of the quantum well structures. The analysis uses a model based on a 6x6 Luttinger-Kohn k.p approach for bulk material valence band structure together with the Envelope Function Approximation. The model is used to analyze Si/SiGe, AlGaAs/GaAs, and GaAs/InGaAs quantum wells for the 001 and …

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Validation Of The Gallagher Protonospheric Model, Kelly M. Law Mar 1999

Validation Of The Gallagher Protonospheric Model, Kelly M. Law

Theses and Dissertations

Ionospheric models are used in many systems throughout the Department of Defense: for example, they are useful in correcting range errors in radio signals. However, correction models don't incorporate the protonosphere, the torus-shaped plasma volume above the ionosphere. The Gallagher Protonospheric Model, recently incorporated into the Parameterized Ionospheric Model 1.7 (PIM 1.7), was validated against protonospheric total electron content (PTEC) measurements made by the GPS system. Gallagher model calculations of slant PTEC for Pittsburgh ground station looking south with a raypath at an elevation of 26 degrees were compared against GPS PTEC measurements for the same configuration derived from the …

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Laser Beam Combining And Cleanup Via Stimulated Brillouin Scattering In Multi-Mode Optical Fibers, Blake C. Rodgers Mar 1999

Laser Beam Combining And Cleanup Via Stimulated Brillouin Scattering In Multi-Mode Optical Fibers, Blake C. Rodgers

Theses and Dissertations

The main objective of this thesis was to demonstrate the feasibility of combining and cleaning up multiple laser beams via Stimulated Brillouin Scattering (SBS) in a multi-mode optical fiber. Beam combining via SBS in an optical fiber is of interest because of the low SBS threshold power in an optical fiber allowing low power diode laser beams to be combined into one high power beam. SBS theory and some of the important historical results are described briefly. The experimental results clearly indicate that SBS in multi-mode optical fiber can indeed combine laser beams and clean up the beams at the …

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An Investigation Into The Noninvasive Assessment Of Bone Density Using Multiplexed Compton Scattered Tomography, Marc J. Sands Mar 1999

An Investigation Into The Noninvasive Assessment Of Bone Density Using Multiplexed Compton Scattered Tomography, Marc J. Sands

Theses and Dissertations

The purpose of this research is to investigate the application of a Compton scatter imaging technique to measure bone density. A demonstration Multiplexed Compton Scatter Tomograph (MCST) was assembled to demonstrate the feasibility of detecting osteoporosis by modifying a system originally designed to detect hidden corrosion in aluminum aircraft wings. Measurements were performed on an aluminum phantom representing a wrist bone containing varying densities in the center and varying thickness of the cortical shell. The densities in the center are comparable to normal trabecular bone, sixty-percent of normal trabecular bone and a void. The MCST images of the phantom were …

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A Continuous Wave Atomic Bromine Laser Produced By Photolysis Of Iodine Monobromide, Brian A. Smith Mar 1999

A Continuous Wave Atomic Bromine Laser Produced By Photolysis Of Iodine Monobromide, Brian A. Smith

Theses and Dissertations

An apparatus to generate continuous wave (CW) lasing at 2.714 µm by Br(2P1/2) atoms produced from photodissociation of IBr was designed, constructed and tested. A frequency doubled Nd:YAG laser firing 8 ns, 850 mJ pulses at 532 nm was used to photodissociate static IBr vapor inside a flow nozzle. The CaF2 windows on either side of the nozzle proved to have a damage threshold below the threshold for lasing. Pulsed lasing in static mode was not observed. Therefore, CW lasing in flow mode, using an Ar+ laser at 488 nm, could not be investigated.

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Numerical Solutions To The Two Dimensional Boltzmann Equation, Christopher G. Smithtro Mar 1999

Numerical Solutions To The Two Dimensional Boltzmann Equation, Christopher G. Smithtro

Theses and Dissertations

A strict kinetic, two-dimensional model of the electron kinetics within a glow discharge positive column is developed. The problem is solved in cylindrical geometry using the standard two-term Legendre expansion of the electron velocity distribution function. The model establishes a steady state solution, such that the net ionization rate is exactly balanced by the wall loss. In addition to a thorough analytic development, we present the numerical techniques used to solve the resulting elliptic partial differential equation, including an efficient method to treat sparse banded matrices. The model is validated against published results, local and nonlocal kinetic approximations, and a …

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Space Charge Structure Of A Glow Discharge In The Presence Of A Longitudinal Inhomogeneity, Frank A. Tersigni Mar 1999

Space Charge Structure Of A Glow Discharge In The Presence Of A Longitudinal Inhomogeneity, Frank A. Tersigni

Theses and Dissertations

A survey of space charge structures arising due to inhomogeneities in glow discharges was conducted. Space charge structures associated with tube geometries, the cathode sheath, striations, and shockwaves were examined. Space charge effects on the Electron Energy Distribution Function (EEDF) were explored for a geometric inhomogeneity using an approximate nonlocal solution to the one dimensional Boltzmann equation after Godyak. The approximate solution partially captured qualitative aspects of space charge effects on the EEDF. Simplification of collisional effects and adaptation of an approximate electric field restricted quantitative comparisons with experimental data. It is recommended that any future analysis of space charge …

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Double Layer Effects On Shock Wave Propagation, Shannon L. Walker Mar 1999

Double Layer Effects On Shock Wave Propagation, Shannon L. Walker

Theses and Dissertations

An analysis and assessment of two mechanisms in plasma shock interactions was conducted under conditions typically encountered in a weakly ionized glow discharge. The mechanisms of a spatially-dependent electron temperature and additional electron impact ionization at the shock front were examined for effects on shock structure and propagation. These mechanisms were incorporated into an existing one-dimensional, time-dependent, fluid dynamics code that uses the Riemami problem as a basis and numerically solves the Euler equations for two fluids: the neutral gas and the charged component. The spatial variation in electron temperature was modeled as a shock-centered rise in temperature. Additional ionization …

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Optimization Of A Multilayer Photothermal Sensor For Infrared Spectroscopy, Janine O.J. Wiggins Mar 1999

Optimization Of A Multilayer Photothermal Sensor For Infrared Spectroscopy, Janine O.J. Wiggins

Theses and Dissertations

Tri-layer thermal diffusion modeling was applied to the optimization of a multi-layer reed sensor for use in a photothermal infrared detector. The multi-layer reed sensor deflects in response to increased temperature. Deflection, of angstroms or larger, is measured using an atomic force microscope. A newly developed thermal diffusion model for three layer reeds was combined with an existing two-layer cantilever model, in order to explore the effects of length, operating frequency, and layer thickness on signal to noise ratio. Model behavior is presented, and compared to laboratory results.

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A Trade-Off Analysis For Quality Of Service In Real-Time Voice Over Ip, Tuncel Altunbasak Mar 1999

A Trade-Off Analysis For Quality Of Service In Real-Time Voice Over Ip, Tuncel Altunbasak

Theses and Dissertations

During the past several years, there has been a significant increase in interest in the use of packetized audio over packet-switched networks due to economic and technical feasibility. However, distribution of real-time voice traffic is basically different from traditional reliable data transfer since continuous voice is sensitive to end-to-end delays and variations of delays. The distribution of continuous voice across a packet-switched network requires consideration of encoding schemas, end-to-end network delays, delay variations, and packet loss, all of which significantly affect the playback quality at the receiving side. There is a trade-off among these factors that affects the quality of …

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Performance Analysis Of Tcp Enhancements In Satellite Data Networks, Ren H. Broyles Mar 1999

Performance Analysis Of Tcp Enhancements In Satellite Data Networks, Ren H. Broyles

Theses and Dissertations

This research examines two proposed enhancements to the well-known Transport Control Protocol (TCP) in the presence of noisy communication links. The Multiple Pipes protocol is an application-level adaptation of the standard TCP protocol, where several TCP links cooperate to transfer data. The Space Communication Protocol Standard - Transport Protocol (SCPS-TP) modifies TCP to optimize performance in a satellite environment. While SCPS-TP has inherent advantages that allow it to deliver data more rapidly than Multiple Pipes, the protocol, when optimized for operation in a high-error environment, is not compatible with legacy TCP systems, and requires changes to the TCP specification. This …

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A Performance Analysis Of Dynamic Routing Algorithms In An Iridium-Like Low Earth Orbit Satellite System, Stephen R. Pratt Mar 1999

A Performance Analysis Of Dynamic Routing Algorithms In An Iridium-Like Low Earth Orbit Satellite System, Stephen R. Pratt

Theses and Dissertations

This research presents a first of its kind comparative analysis of the Extended Bellman-Ford and Darting algorithms, using the Iridium low earth orbit (LEO) satellite system configuration for the simulation environment. The algorithms are compared to one another via discrete-event computer simulation and evaluated based on their ability to route real-time voice communications under low, medium, and high network loading conditions. The algorithms' ability to meet real-time voice constraints is evaluated with a full and degraded satellite constellation using an algorithmic satellite removal method. The investigation results indicate that both algorithms are suitable for use in a LEO environment and …

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Maintenance Resources Evaluation Technique, Jorge Guarnieri Mar 1999

Maintenance Resources Evaluation Technique, Jorge Guarnieri

Theses and Dissertations

The Argentine Air Force (AAF) has undertaken the task of reviewing its logistics doctrine with the aim of supporting its mission on the basis of better-designed resource structures. The adequate sizing of logistics support is essential to obtain the desired military capability, while optimizing resource use. A decision support tool tailored to the AAF environment is needed to size that logistics support. This research developed a mathematical logistics model to evaluate the mean number of aircraft that can be restored in a given time interval between consecutive sorties, for a given maintenance resources mix and base physical geometry. This maintenance …

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Acquisition Logistics Guidelines For Improving The Argentine Air Force Weapon System Acquisition Process, Guillermo A. Piuzzi Mar 1999

Acquisition Logistics Guidelines For Improving The Argentine Air Force Weapon System Acquisition Process, Guillermo A. Piuzzi

Theses and Dissertations

Increasing costs, complexity and demanded endurance have been typical characteristics of new weapon systems during the last decades. Meanwhile, severe contraction of defense budgets makes cost effective and well-planned acquisition crucial to ensure weapon system whole life supportability. This qualitative research explores the role of acquisition logistics in the endeavor of purchasing effective, efficient, and supportable systems in four countries, namely the United States, Australia, Spain, and Portugal. Through a multiple case study, a set of concepts is extracted and adapted to be proposed as the basis of a prospective Argentine Air Force weapon system acquisition process review. Suggested improvements …

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A Java Based Human Computer Interface For A Uav Decision Support Tool Using Conformal Mapping, Randy A. Flood Mar 1999

A Java Based Human Computer Interface For A Uav Decision Support Tool Using Conformal Mapping, Randy A. Flood

Theses and Dissertations

This paper describes the development of the Human Computer Interface (HCI) for a Decision Support System for routing Unmanned Aerial Vehicles (UAVs). This problem is a multi-vehicle routing problem with time-windows. Because of the unique nature of UAVs, a tool is needed to support dynamic re-routing. We solve the problem in two ways. First, we create a UAV Decision Support Tool (UAV DST) that uses a set of Java software objects to display maps and convert between latitude-longitude coordinates and x-y coordinates. Secondly, this library provides the ability for the user to dynamically reoptimize large UAV routing problems through a …

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Protein Structure Prediction Using Parallel Linkage Investigating Genetic Algorithms, Karl R. Deerman Mar 1999

Protein Structure Prediction Using Parallel Linkage Investigating Genetic Algorithms, Karl R. Deerman

Theses and Dissertations

AFIT has had a long-standing interest in solving the protein structure prediction (PSP) problem. The PSP problem is an intractable problem that if "solved" can lead to revolutionary new techniques for everything from the development of new medicines to optical computer switches. The challenge is to find a reliable and consistent method of predicting the 3-dimensional structure of a protein given its defining sequence of amino acids. PSP is primarily concerned with predicting the tertiary protein structure without regards to how the protein came to this folded state. The tertiary structure determines the protein's functionality.

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Strategies For Steganalysis Of Bitmap Graphics Files, Christopher J. Fogle Mar 1999

Strategies For Steganalysis Of Bitmap Graphics Files, Christopher J. Fogle

Theses and Dissertations

Steganography is the art and science of communicating through covert channels. The goal of steganography is to hide the fact that a message is even being transmitted. In the context of today's digital world, this ancient practice is enjoying resurgence due to the plethora of hiding places made possible by modern information media. Of particular concern is the use of graphics image files to conceal both legitimate and criminal communications.

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Parallel Data Mining With The Message Passing Interface Standard On Clusters Of Personal Computers, Lonnie P. Hammack Mar 1999

Parallel Data Mining With The Message Passing Interface Standard On Clusters Of Personal Computers, Lonnie P. Hammack

Theses and Dissertations

Piles of personal computers (PoPCs) have begun to challenge the performance of the traditional Massively Parallel Processors (MPPs) and the less traditional networks of workstations (NOWs) as platforms for parallel computing. Large clusters of PCs have reached and at times exceeded the performance of modern MPPs at a fraction of the cost. Built with commodity components, these clusters can be constructed for about half the cost of a comparable NOW. The primary competing operating systems (OIS) in use on PoPCs are Linux and Windows NT. This thesis investigation compares the performance of an NT cluster with that of a Linux …

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Methodology For Application Design Using Information Dissemination And Active Database Technologies, Robert H. Hartz Mar 1999

Methodology For Application Design Using Information Dissemination And Active Database Technologies, Robert H. Hartz

Theses and Dissertations

In dynamic data environments, the large volume of transactions requires flexible control structures to effectively balance the flow of information between producers and consumers. Information dissemination-based systems, using both data push and pull delivery mechanisms, provide a possible scalable solution for data-intensive applications. In this research, a methodology is proposed to capture information dissemination design features in the form of active database rules to effectively control dynamic data applications. As part of this design methodology, information distribution properties are analyzed, data dissemination mechanisms are transformed into an active rule framework, and the desired reactive behavior is achieved through rule customization. …

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