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Articles 9631 - 9660 of 11503

Full-Text Articles in Engineering

Ambiguity Function Analysis And Direct-Path Signal Filtering Of The Digital Audio Broadcast (Dab) Waveform For Passive Coherent Location (Pcl), Abdulkadir Guner Mar 2002

Ambiguity Function Analysis And Direct-Path Signal Filtering Of The Digital Audio Broadcast (Dab) Waveform For Passive Coherent Location (Pcl), Abdulkadir Guner

Theses and Dissertations

This research presents an ambiguity function analysis of the digital audio broadcast (DAB) waveform and one signal detection approach based on signal space projection techniques that effectively filters the direct-path signal from the receiver target channel. Currently, most Passive Coherent Location (PCL) research efforts are focused and based on frequency modulated (FM) radio broadcasts and analog television (TV) waveforms. One active area of PCL research includes the search for new waveforms of opportunity that can be exploited for PCL applications. As considered for this research, one possible waveform of opportunity is the European digital radio standard DAB. For this research, …

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A Study Of Satellite Navigation, Dilution Of Precision, And Positioning Techniques For Use On And Around The Moon, John H. Macnicol Mar 2002

A Study Of Satellite Navigation, Dilution Of Precision, And Positioning Techniques For Use On And Around The Moon, John H. Macnicol

Theses and Dissertations

The National Aeronautics and Space Agency is examining several approaches to meet navigational requirements for spacecraft in lunar orbit, in transit to or from the moon, and for personnel on the lunar surface requiring an accurate, real-time, on-board navigation capability. This work addresses one possible solution to the navigation problem in the vicinity of the moon using a lunar satellite navigation system. Dilution of precision is the figure of merit used to determine if a candidate lunar satellite navigation system can meet accuracy specifications based on a given satellite constellation and the measurement types used. Ten satellite constellations, using two …

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Ins Aiding By Tracking An Unknown Ground Object, Mursy Polat Mar 2002

Ins Aiding By Tracking An Unknown Ground Object, Mursy Polat

Theses and Dissertations

The reduction of the navigation error in an inertial navigation system by optically tracking a ground object is investigated. Multiple observations of the ground object are used. The location of the ground object is assumed unknown. A careful analysis of the measurement situation at hand reveals that by optically tracking an unknown ground object using passive, bearings-only measurements, the aircraft's angle of attack and sideslip angle can be measured. Thus, two new independent measurement equations featuring the aircraft's angular navigation variables are obtained. Hence, by optically tracking over time an unknown ground object, inertial navigation system aiding is in fact …

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An Analysis Of Mutually Dispersive Brown Symbols For Non-Linear Ambiguity Suppression, Matthew J. Papaphotis Mar 2002

An Analysis Of Mutually Dispersive Brown Symbols For Non-Linear Ambiguity Suppression, Matthew J. Papaphotis

Theses and Dissertations

This thesis significantly advances research towards the implementation of optimal Non-linear Ambiguity Suppression (NLS) waveforms by analyzing the Brown theorem. The Brown theorem is reintroduced with the use of simplified linear algebraic notation. A methodology for Brown symbol design and digitization is provided, and the concept of dispersive gain is introduced. Numerical methods are utilized to design, synthesize, and analyze Brown symbol performance. The theoretical performance in compression and dispersion of Brown symbols is demonstrated and is shown to exhibit significant improvement compared to discrete codes. As a result of this research a process is derived for the design of …

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Translation And Rotation Invariant Multiscale Image Registration, Jennifer L. Manfra Mar 2002

Translation And Rotation Invariant Multiscale Image Registration, Jennifer L. Manfra

Theses and Dissertations

The most recent research involved registering images in the presence of translations and rotations using one iteration of the redundant discrete wavelet transform. We extend this work by creating a new multiscale transform to register two images with translation or rotation differences, independent of scale differences between the images. Our two-dimensional multiscale transform uses an innovative combination of lowpass filtering and the continuous wavelet transform to mimic the two-dimensional redundant discrete wavelet transform. This allows us to obtain multiple subbands at various scales while maintaining the desirable properties of the redundant discrete wavelet transform. Whereas the discrete wavelet transform produces …

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Using The Gps To Collect Trajectory Data For Ejection Seat Design, Validation, And Testing, Brian R. Tredway Mar 2002

Using The Gps To Collect Trajectory Data For Ejection Seat Design, Validation, And Testing, Brian R. Tredway

Theses and Dissertations

The dynamic characteristics of an aircraft ejection seat are a crucial concern when evaluating aircraft ejection systems and their ability to separate aircrew members safely from disabled aircraft. Every ejection seat model undergoes real-time dynamic tests to determine potential injury to aircrew members during ejection. Ejection seat tests are conducted at high-speed test tracks. The test track facilities provide the required telemetry and high-speed photography to monitor and validate the aircraft escape system performance. Ejection seat test and evaluation requires very accurate position and velocity determination during each test run to determine the relative positions between the aircraft, ejection seat, …

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Development And Characterization Of An Emergency Communications System Using Near Vertical Incident Skywave Antennas, Richard A. Allnutt Mar 2002

Development And Characterization Of An Emergency Communications System Using Near Vertical Incident Skywave Antennas, Richard A. Allnutt

Theses and Dissertations

The NVIS system characterized in this work was designed to eliminate skip propagation by optimizing the design for contiguous coverage. The NVIS technique involves use of transmission and receiving antennas that create nearly vertical propagation and continuous coverage from the transmitter to a distance of 200 miles. Man portable, very low power transceivers (5 watts maximum) and horizontal dipole antennas five feet above the ground are used in an NVIS communication system for this work. The system is designed for the purpose of supporting communication with emergency workers in areas where other communication is difficult. Digital and analog effectiveness are …

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Estimating The Operating And Support Cost Difference Among Tuaf C-130, C-130b And Usaf C-130j Aircraft, Kubilay Kosucu Mar 2002

Estimating The Operating And Support Cost Difference Among Tuaf C-130, C-130b And Usaf C-130j Aircraft, Kubilay Kosucu

Theses and Dissertations

In an era of decreasing defense budgets in Korea, the Korean Air Force Transportation Department has suffered from an insufficient vehicles procurement budget, resulting in fewer vehicles of increasing age, as well as decreasing military morale. For these reasons, the Korean Air Force Transportation Department needs a breakthrough to retain the transportation ability to support the field of operation in an effective and economic way. However, the Korea Air Force Transportation Department has only one method for procuring general-purpose vehicles, which is purchasing. Thus, the comparative analysis of leasing versus buying vehicle study started from the recognition of this situation …

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Use Of Critical Chain Scheduling To Increase Aircraft Availability, Daniel D. Mattioda Mar 2002

Use Of Critical Chain Scheduling To Increase Aircraft Availability, Daniel D. Mattioda

Theses and Dissertations

This study addresses the operation and support cost differences between the TUAF C-130E & C-130B, and the USAF C-130J aircraft. The TUAF C-130s have been being used for more than 30 years and changing world situations give armed forces different roles, and Turkey participates in all peacekeeping missions that are assigned by NATO (North Atlantic Treaty Organization) and the United Nations. While performing these roles, the importance of air mobility and the importance of reliability became widely appreciated. Moreover, the coming retiring age of the existing C-130s in the TUAF forced the TUAF to look for ways to improve its …

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An Evaluation Of The Hazard Prediction And Assessment Capability (Hpac) Software's Ability To Model The Chornobyl Accident, Dirk E. Plante Mar 2002

An Evaluation Of The Hazard Prediction And Assessment Capability (Hpac) Software's Ability To Model The Chornobyl Accident, Dirk E. Plante

Theses and Dissertations

A parameter study was conducted for a space nuclear reactor radiation shield. The focus of this research was to explore alternatives to current radiation shield designs to reduce the mass while maintaining the same shielding performance. MCNP4C was used to determine the parameters necessary to build an optimum shield. A design known as the split scatter shield offered some potential for reductions in shield mass. In theory, less material is required for this type of shield, which uses thin shield sections to scatter radiation away from the dose plane. The parameters for this shield design are the shield geometry, number …

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A Multiple Ant Colony Metaheuristic For The Air Refueling Tanker Assignment Problem, Ronjon Annaballi Mar 2002

A Multiple Ant Colony Metaheuristic For The Air Refueling Tanker Assignment Problem, Ronjon Annaballi

Theses and Dissertations

The performance of the Nuclear Facility (NFAC) incident module in modeling a nuclear reactor accident is evaluated. Fallout predictions are compared with air concentration measurements of I-131 in Europe over a five-day period. Two categories of source term specifications are used: NFAC-generated source terms based on plant conditions and accident severity, and user-defined source terms based on specifying the release of I-131. The Atmospheric Transport Model Evaluation Study report source term provided the needed detailed release information. The Air Force Combat Climatology Center provided weather data covering Europe during the release's 11-day duration. For the NFAC-generated source terms as few …

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An Examination Of Latency And Degradation Issues In Unmanned Combat Aerial Vehicle Environments, Shane A. Dougherty Mar 2002

An Examination Of Latency And Degradation Issues In Unmanned Combat Aerial Vehicle Environments, Shane A. Dougherty

Theses and Dissertations

Since the multidimensional knapsack problems are NP-hard problems, the exact solutions of knapsack problems often need excessive computing time and storage space. Thus, heuristic approaches are more practical for multidimensional knapsack problems as problems get large. This thesis presents the results of an empirical study of the performance of heuristic solution procedures based on the coefficients correlation structures and constraint slackness settings. In this thesis, the three representative greedy heuristics, Toyoda, Senju and Toyoda, and Loulou and Michaelides methods, are studied. The purpose of this thesis is to explore which heuristic of the three representative greedy heuristics perform best under …

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Investigation Of Cooperative Behavior In Autonomous Wide Search Munitions, Robert E. Dunkel Iii Mar 2002

Investigation Of Cooperative Behavior In Autonomous Wide Search Munitions, Robert E. Dunkel Iii

Theses and Dissertations

The purpose of this research is to investigate the effectiveness of wide-area search munitions in various scenarios using different cooperative behavior algorithms. The general scenario involves multiple autonomous munitions searching for an unknown number of targets of different priority in unknown locations. Three cooperative behavior algorithms are used in each scenario: no cooperation, cooperative attack only, and cooperative classification and attack. In the cooperative cases, the munitions allocate tasks on-line as a group, using linear programming techniques to determine the optimum allocation. Each munition provides inputs to the task allocation routine in the form of probabilities of successfully being able …

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Analysis Of Air Force Contingency Contracting Training Needs, Peter S. Lasch Mar 2002

Analysis Of Air Force Contingency Contracting Training Needs, Peter S. Lasch

Theses and Dissertations

This research examines the Air Force training needs of contingency contracting officers (CCOs). The study utilized the deductive approach to research. A survey instrument captured the data for the study. The survey captured input from CCOs with deployment experience and each of the Air Force components and MAJCOMs. Series 1 of the survey polls CCOs with deployment experience to determine the training CCOs require based on their personal experiences. Series 2 surveys the component and MAJCOM level supervisors to determine their perception of the training that should be required for CCOs. Comparing the two series will identify any differences in …

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Performance Evaluation Of Hyperbolic Position Location Technique In Cellular Wireless Networks, Hakan Senturk Mar 2002

Performance Evaluation Of Hyperbolic Position Location Technique In Cellular Wireless Networks, Hakan Senturk

Theses and Dissertations

This study addresses the wireless geolocation problem that has been an attractive subject for the last few years after Federal Communications Commission (FCC) mandate for wireless service providers to locate emergency 911 users with a high degree of accuracy -within a radius of 125 meters, 67 percent of the time by October 2001. There are a number of different geolocation technologies that have been proposed. These include, Assisted GPS (A-GPS), network-based technologies such as Enhanced Observed Time Difference (E-OTD), Time Difference of Arrival (TDOA), Angle of Arrival (AOA), and Cell of Origin (COO). This research focuses on network based techniques, …

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Performance Tradeoff Study Of A Gps-Aided Ins For A Rocket Trajectory, Muhittin Istanbulluoglu Mar 2002

Performance Tradeoff Study Of A Gps-Aided Ins For A Rocket Trajectory, Muhittin Istanbulluoglu

Theses and Dissertations

The Turkish Air Force (TuAF) has started a project to launch a satellite using only Turkish resources. Primary motivation behind this research is to assist TuAF's project by keeping up with these innovations in the navigational arena. The basic challenge in navigation system design is to decide which navigation system (or systems) and implementation techniques will be used, depending on accuracy requirements. The two primary navigation systems that will be integrated in this research are the Inertial Navigation System (INS), and the Global Positioning System (GPS). The Kalman filter algorithm is used to integrate INS and GPS. The rocket (Atlas …

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Measurements Of Neutron Induced Surface And Bulk Defects In 4h Silicon Carbide, Kent T. Jones Mar 2002

Measurements Of Neutron Induced Surface And Bulk Defects In 4h Silicon Carbide, Kent T. Jones

Theses and Dissertations

Epitaxial n-type 4H-silicon carbide (SiC) is irradiated with 2 MeV protons to evaluate the dislocation damage effects on the optical and electrical characteristics of the material. The optical properties of the material are investigated using temperature-dependant photoluminescence (PL) and the effects of proton irradiation on the electrical properties are evaluated using current-voltage measurements and constant-voltage deep level transient spectroscopy (CV-DLTS). Subsequent high-temperature thermal annealing and recovery of the irradiated material is investigated over the temperature range of 900-1500°C. Proton-induced irradiation damage is apparent in the 4H-SiC material, affecting both the optical and electrical characteristics of the devices. The radiative behavior …

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Computational Aerodynamic Analysis Of The Flow Field About A Hypervelocity Test Sled, Andrew J. Lofthouse Mar 2002

Computational Aerodynamic Analysis Of The Flow Field About A Hypervelocity Test Sled, Andrew J. Lofthouse

Theses and Dissertations

The flow field about the nose section of a hypervelocity test sled is computed using computational fluid dynamics. The numerical model of the test sled corresponds to the Nike O/U narrow gage sled used in the upgrade program at the High Speed Test Track facility, Holloman Air Force Base, New Mexico. The high temperatures and pressures resulting from the aerodynamic heating and loading affect the sled structure and the performance of the vehicle. The sled transitions from an air environment to a helium environment at a speed of approximately 3,300 feet per second (Mach 3 in air, Mach 1.02 in …

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Alternative Pulse Detonation Engine Ignition System Investigation Through Detonation Splitting, August J. Rolling Mar 2002

Alternative Pulse Detonation Engine Ignition System Investigation Through Detonation Splitting, August J. Rolling

Theses and Dissertations

A Pulse Detonation Engine (PDE) combusts fuel air mixtures through a form of combustion: detonation. Recent PDE research has focused on designing working subsystems. This investigation continued this trend by examining ignition system alternatives. Existing designs required spark plugs in each separate thrust tube to ignite premixed reactants. A single thrust tube could require the spark plug to fire hundreds of times per second for long durations. The goal was to minimize hardware and increase reliability by limiting the number of ignition sources. This research used a continuously propagating detonation wave as both a thrust mechanism and an ignition system …

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Suppression Of Pilot-Induced Oscillation (Pio), Donald A. Johnson Mar 2002

Suppression Of Pilot-Induced Oscillation (Pio), Donald A. Johnson

Theses and Dissertations

Closed loop instability caused by excess phase lag induced by actuator rate limiting has been suspected in many pilot-induced oscillations (PIOs) and oscillatory departures from controlled flight. As part of the joint AFIT/TPS program, a longitudinal pilot command notch filter activated by a real-time oscillation verifier (ROVER) algorithm was developed to eliminate the PIO source for any developing, severe PIO. Closed loop computer simulations were conducted to prepare for the flight test. The HAVE ROVER flight test project was flown using the NF-16D Variable Stability In-flight Simulator Test Aircraft (VISTA). A programmable heads-up display (HUD) was used to generate a …

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The Combined Effects Of Freestream Turbulence, Pressure Gradients, And Surface Roughness On Turbine Aerodynamics, Christine P. Ellering Mar 2002

The Combined Effects Of Freestream Turbulence, Pressure Gradients, And Surface Roughness On Turbine Aerodynamics, Christine P. Ellering

Theses and Dissertations

This work used scaled facsimiles of real turbine blade surfaces to characterize correlations between turbine blade roughness, freestream turbulence, pressure gradients and skin friction (Cf). Addition of roughness caused Cf to increase: up to 300% for the roughest surface. Addition of freestream turbulence resulted in 125% increase for the same surface. The combined effects showed increases up to 380%. Although decreasing roughness, freestream turbulence, and Reynolds number resulted in less dramatic results, it was concluded that the Cf increases due to combined effects were consistently higher than their corresponding sum of the parts. The combined effects of roughness and pressure …

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Examination Of Contact Width On Fretting Fatigue, Russell S. Magaziner Mar 2002

Examination Of Contact Width On Fretting Fatigue, Russell S. Magaziner

Theses and Dissertations

The primary goal of this study was to find the effects on the fretting fatigue life when systematically holding the fretting fatigue variables, peak contact pressure, maximum/minimum nominal bulk stress, and the ratio of shear traction to pressure force constant while varying the contact semi-width through changes in pad radius and normal load. Experimental tests were performed on a test setup capable of independent pad displacement. Analytical and finite element simulations of the different experimental tests were performed. The local mechanistic parameters were inspected. Five different critical plane based fatigue predictive parameters lacked effectiveness in predicting changes in life with …

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Periodic Methods For Controlling A Satellite In Formation, Erin Y. Carraher Mar 2002

Periodic Methods For Controlling A Satellite In Formation, Erin Y. Carraher

Theses and Dissertations

Precise position determination and control is necessary to accomplish proposed satellite formation flying missions of ground movement target indication and synthetic aperture radar. This thesis combines the estimation and control techniques of past AFIT theses with various time-varying and time-invariant LQG control methods. Linear time-invariant control is ideal for on-board satellite estimation and control applications, freeing-up the satellite's limited computational capacity. Using a dynamics frame transformation from the nodal frame to an orbital frame, a higher fidelity, time-periodic model produced nearly identical results for either time-varying or time-invariant control for many scenarios. Scenarios included initial perturbations in the radial, in-track, …

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Beyond A-76: How To Achieve The Goals Without The Pain, Kurt A. Chelf Mar 2002

Beyond A-76: How To Achieve The Goals Without The Pain, Kurt A. Chelf

Theses and Dissertations

The Department of Defense has determined that Outsourcing and Privatization is key to reducing operating costs and subsequently providing the fiscal dollars necessary to modernize the U.S. Armed Forces. In an effort to achieve this goal, the DoD has mandated that the Air Force study at least 5% of its manning positions for possible conversion to contract. This mandate effects over 200,000 positions throughout the department. Office of Management and Budget (OMB) Circular, Number A-76, Performance Of Commercial Activities dictates the process used to study the appropriateness of these conversions. This thesis explores the usefulness and applicability of this process, …

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Task Load And Automation Use In An Uncertain Environment, Mark A. Daly Mar 2002

Task Load And Automation Use In An Uncertain Environment, Mark A. Daly

Theses and Dissertations

The purpose of this research was to investigate the effects that user task load level has on the relationship between an individual's trust in and subsequent use of a system's automation. Automation research has demonstrated a positive correlation between an individual's trust in and subsequent use of the automation. Military decision-makers trust and use information system automation to make many tactical judgments and decisions. In situations of information uncertainty (information warfare environments), decision-makers must remain aware of information reliability issues and temperate their use of system automation if necessary. An individual's task load may have an effect on his use …

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An Analysis Of The Knowledge And Skill Levels Required To Effectively Support Analytical Cost Decisions In Source Selections, Anthony L. Smith Mar 2002

An Analysis Of The Knowledge And Skill Levels Required To Effectively Support Analytical Cost Decisions In Source Selections, Anthony L. Smith

Theses and Dissertations

We analyze these three factors (education, experience, and training) in an effort to identify the knowledge and skills necessary for cost analysts to possess to be effective members of cost panel evaluation teams during source selections. This research effort assesses whether the cost panel members and senior Air Force acquisition military and civilian personnel associate the levels of education, experience, and training as being key factors in fulfilling cost analysts duties while supporting the selection of a source in the government procurement process. To accomplish this objective, a literature review, personal interviews, and questionnaires were utilized. Descriptive statistics and hypothesis …

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A Collaborative Visualization Framework Using Jini™ Technology, Chad M. Harris Mar 2002

A Collaborative Visualization Framework Using Jini™ Technology, Chad M. Harris

Theses and Dissertations

It is difficult to achieve mutual understanding of complex information between individuals that are separated geographically. Two well-known techniques commonly used to deal with this difficultly are collaboration and information visualization. This thesis develops a generic flexible framework that supports both collaboration and information visualization. It introduces the Collaborative Visualization Environment (COVE) framework, which simplifies the development of real-time synchronous multi-user applications by decoupling the elements of collaboration from the application. This allows developers to focus on building applications and leave the difficulties of collaboration (i.e., concurrency controls, user awareness, session management, etc.) to the framework. The framework uses an …

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Smart Structures For Control Of Optical Surfaces, D. Michael Sobers Jr. Mar 2002

Smart Structures For Control Of Optical Surfaces, D. Michael Sobers Jr.

Theses and Dissertations

The development of lightweight, large-aperture optics is of vital importance to the Department of Defense and the US Air Force for advancing remote sensing applications and improving current capabilities. Synthetic polymer optics offer weight and flexibility advantages over current generation glass mirrors, but require active control to maintain tight surface figure tolerances. This research explores the feasibility of using imbedded piezoelectric materials to control optical surfaces. Membrane-based and stiff piezo-controlled mirrors were constructed to develop and validate control techniques. Test results verified that surface control on the order of tens of wavelengths is possible using these systems.

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Evaluating Air Force Civil Engineer's Current Automated Information Systems, Edward P. Phillips Mar 2002

Evaluating Air Force Civil Engineer's Current Automated Information Systems, Edward P. Phillips

Theses and Dissertations

Almost every organization has some form of information system where data is captured and stored for later use. The Air Force civil engineering organization is no exception and is in the process of transitioning from the Interim Work Information Management System (WIMS) to the Automated Civil Engineer System (ACES). This research focused on users perceptions of both database and data importance to determine if significant differences existed between various user sub-groups. The research also attempted to identify the most frequently reported problems regarding system usage. The methods of analysis of variance and content analysis were used to answer the research …

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An Analysis Of Horizontal Flow Treatment Well Applicability For The Treatment Of Chlorinated Solvent Contaminated Groundwater At United States Forces Korea Installations, Michael R. Staples Mar 2002

An Analysis Of Horizontal Flow Treatment Well Applicability For The Treatment Of Chlorinated Solvent Contaminated Groundwater At United States Forces Korea Installations, Michael R. Staples

Theses and Dissertations

Past research has shown that there is a rising public concern with environmental issues in the Republic of Korea (ROK). As Korean government and public interest in the environment grow, there is likely to be increased pressure to remediate environmental contamination at United States Department of Defense (DoD) installations in Korea. Impacting DoD's ability to remediate contaminated sites overseas is the fact that limited environmental funds must compete with high priority mission requirements. Thus, particularly at overseas bases, there is an urgent need for inexpensive and effective groundwater remediation technologies. Horizontal Flow Treatment Well (HFTW) systems have been demonstrated in …

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