Open Access. Powered by Scholars. Published by Universities.®

Engineering Commons™

Open Access. Powered by Scholars. Published by Universities.®

Theses and Dissertations

Discipline
Institution
Keyword
Publication Year

Articles 8851 - 8880 of 11510

Full-Text Articles in Engineering

A Study Of Near Field Data Transformed To The Far Field For A Canonical Pec Scatterer, E. Matthew Cady Mar 2006

A Study Of Near Field Data Transformed To The Far Field For A Canonical Pec Scatterer, E. Matthew Cady

Theses and Dissertations

The purpose of this research was to analyze the error associated with the Image Based Near Field to Far Field Transformation (IB NFFFT) for a canonical perfectly electrically conductive (PEC) scatterer. This research compares two groups of data: far field RCS predicted by the IB NFFFT and far field RCS predicted by X-Patch. The IB NFFFT requires a complete set of calibrated monostatic near field scattering data of the object. A detailed description is given of the configuration of the measurement facilities and procedures that were required to obtain the calibrated near field scattering data, as well as the process …

Go to article

Computational Modeling Of The Dielectric Barrier Discharge (Dbd) Device For Aeronautical Applications, Christopher S. Charles Mar 2006

Computational Modeling Of The Dielectric Barrier Discharge (Dbd) Device For Aeronautical Applications, Christopher S. Charles

Theses and Dissertations

Dielectric Barrier Discharge (DBD) type devices, when used as plasma actuators, have shown significant promise for use in many aeronautical applications. Experimentally, DBD actuator devices have been shown to induce motion in initially still air, and to cause re-attachment of air flow over a wing surface at a high angle of attack. This thesis explores the numerical simulation of the DBD device in both a lD and 2D environment. Using well established fluid equation techniques, along with the appropriate approximations for the regime under which these devices will be operating, computational results for various conditions and geometries are explored. In …

Go to article

Structural Health Monitoring Considering Internal Beam Damage, Jessica B. Chronister Mar 2006

Structural Health Monitoring Considering Internal Beam Damage, Jessica B. Chronister

Theses and Dissertations

The present study establishes a nondestructive method of damage detection and assessment in cantilever beams. The specimens used are twelve-inch aluminum 2024-T3 beams with machined notches of varying lengths and locations. Laser Doppler vibrometry is used to obtain the frequency response of vibrating beams. Experimental methods are developed to detect the presence, location and extent of damage by direct observation of the eigenvector in the third through eighth modes. Models in MATLAB and ABAQUS are used to predict and validate the observed data. With this experimental method developed, the validity of the method is tested for specimens that have been …

Go to article

Characteristics Of Two-Dimensional Triangular And Three-Dimensional Face-Centered-Cubic Photonic Crystals, Jeffery D. Clark Mar 2006

Characteristics Of Two-Dimensional Triangular And Three-Dimensional Face-Centered-Cubic Photonic Crystals, Jeffery D. Clark

Theses and Dissertations

The fabrication of photonic crystals (PhC) with photonic band gaps (PBG) in the visible range is a difficult task due to the small structural feature sizes of the PhC. The particular type of PhC examined is a two-dimensional (2-D) triangular structure with a PBG designed for visible wavelengths with applications in visible integrated photonic systems. This work examines the processes involved and viability of fabricating 2-D triangular PhC's by a variety of techniques: focused ion beam, electron lithography and holographic photo-polymerization/lithography. The design of the PhC was based on a program created to display gap maps for triangular structures. The …

Go to article

Hazardous Material Cargo Frustration At Military Aerial Ports Of Embarkation, Niel E. Christensen Mar 2006

Hazardous Material Cargo Frustration At Military Aerial Ports Of Embarkation, Niel E. Christensen

Theses and Dissertations

Since military units often require critical hazardous materials in an expedited manner, identifying choke points within the supply chain is necessary to improve logistic support to front line forces. Hazardous materials are some of the most critical assets for the war fighter, as well as the most restrictive and often most time consuming for transportation. This research quantifies the extent that vendor and depot supplied cargo is being delayed at Aerial Ports of Embarkation. By looking at frustrated hazardous material at Charleston Air Force Base, South Carolina and Dover Air Force Base, Delaware, a case study methodology is used to …

Go to article

Development Of In-Plane Surface Deformation Sensing For Thin Film Pvdf Actuated Membrane Mirrors, John J. Cornelius Mar 2006

Development Of In-Plane Surface Deformation Sensing For Thin Film Pvdf Actuated Membrane Mirrors, John J. Cornelius

Theses and Dissertations

This study investigated the feasibility of surface deformation sensing of a membrane mirror using only embedded PVDF sensors. Results were compared to measured deformations using a scanning laser vibrometer. The frequency response function (FRF) was measured based on recorded voltages of a single-layer 7-sensor mirror actuated externally from the embedded PVDF actuators. Additionally, a two-layer, 7-sensor, 7-actuator membrane mirror was constructed for use, with one layer acting as the sensing layer and the other acting as the actuation layer. The measured FRF for this mirror was compared to previous results. Finally a single-layer 61-sensor PVDF mirror was constructed to experimentally …

Go to article

Exploiting Semi-Directional Transceivers For Localization In Communication Systems, Andrew S. Crockford Mar 2006

Exploiting Semi-Directional Transceivers For Localization In Communication Systems, Andrew S. Crockford

Theses and Dissertations

Localization is the process of determining relative, as well as absolute, positions of communicating devices. Traditionally, the process is conducted using range or directional estimates. In contrast, this research uses weak information to form relatively tight bounds on possible locations of communicating devices. Under certain conditions, achieved location estimation results are strong. However, these results are highly sensitive to the operating conditions of the proposed networks. More significant results were obtained from specialized cases and that the application yields somewhat limited information for a general randomized network topology. Feasible localization results were found to be attainable but not necessarily practical …

Go to article

Implementing Reliability-Centered Maintenance Analysis In A Revised Preventive Maintenance Program For The F-15, Michael H. Martin Mar 2006

Implementing Reliability-Centered Maintenance Analysis In A Revised Preventive Maintenance Program For The F-15, Michael H. Martin

Theses and Dissertations

Reliability-centered maintenance is an approach to analyzing how and when equipment fails in order to maintain a desired level of performance or functionality. It employs the use of failure modes, effects and criticality analysis to rank order potential failures, and combines this rank order with the use of a prescribed decision logic process to determine what preventive maintenance tasks should be performed and when. Reliability-centered maintenance analysis has been used by the United States Navy, the United States Coast Guard, and commercial airlines to develop and update preventive maintenance programs for their aircraft for many years. While the United States …

Go to article

Algebra Of Tankers, Margaret M. Romero Mar 2006

Algebra Of Tankers, Margaret M. Romero

Theses and Dissertations

The Air Force's aerial refueling tanker aircraft provide essential support for deployment and employment of combat and combat support aircraft, by extending their endurance and enhancing fighting efficiency. As the lead command for air refuelers, Air Mobility Command (AMC) must frequently examine the capability of current and proposed tanker fleets to meet mission requirements due to limited tanker resources. Analysts in AMC primarily use the Combined Mating and Ranging Plans System to provide actual tanker/receiver aircraft schedules and flight plans that take into account numerous system constraints. However, this tool can take weeks to run. Even recently developed quick look …

Go to article

Improving Intercontinental Ballistic Missile Maintenance Scheduling Through The Use Of Location Analysis Methodologies, Dale L. Overholts Ii Mar 2006

Improving Intercontinental Ballistic Missile Maintenance Scheduling Through The Use Of Location Analysis Methodologies, Dale L. Overholts Ii

Theses and Dissertations

The events of September 11, 2001 have led to increased security requirements for all ICBM-related activities. Missile maintenance managers must explore new scheduling techniques to sustain weapon system readiness levels in light of published security enhancements. The problem of improving missile maintenance scheduling is modeled as a two-stage heuristic that utilizes the maximal covering location problem methodology. Maintenance activities are categorized and weighted according to published priority designation and mission impact. The model’s first stage seeks to select two security umbrellas that maximize the weighted sum of maintenance activities. Stage two seeks to determine a maintenance schedule comprised of launch …

Go to article

Formation Flight Control For Aerial Refueling, Steven M. Ross Mar 2006

Formation Flight Control For Aerial Refueling, Steven M. Ross

Theses and Dissertations

A controller is designed for an aircraft to autonomously fly formation during aerial refueling. Requirements for a refueling autopilot are stated. A six-degree-of-freedom model is developed for an F-16 lead aircraft and a Learjet LJ-25 wing aircraft. Bare airframe stability of both aircraft is investigated, and stability augmentation is performed. A Matlab Simulink® simulation is built to reproduce the sensor inputs that will be available to the wing aircraft in flight, including disturbances. Control frames are investigated to determine the optimum presentation of the error vector for control during the task of air refueling. Control laws are developed from the …

Go to article

Creep-Rupture And Fatigue Behaviors Of Notched Oxide/Oxide Ceramic Matrix Composite At Elevated Temperature, Mark A. Sullivan Mar 2006

Creep-Rupture And Fatigue Behaviors Of Notched Oxide/Oxide Ceramic Matrix Composite At Elevated Temperature, Mark A. Sullivan

Theses and Dissertations

Oxide/oxide composites are being considered for use in high temperature aerospace applications where their inherent resistance to oxidation provides for better long life properties at high temperature than most other ceramic matrix composites (CMCs). One promising oxide/oxide CMC is Nextel 720/A (N720/A) which uses an 8-harness satin weave (8HSW) of Nextel 720 fibers embedded in a porous alumina matrix. Possible aerospace applications for N720/A will likely require inserting holes into the material for mounting and cooling purposes. The notch characteristics must be understood to ensure designs using the material are sufficient for the desired application. This research effort examined the …

Go to article

Variation Analysis Of Involute Spline Tooth Contact, Brian J. De Caires Feb 2006

Variation Analysis Of Involute Spline Tooth Contact, Brian J. De Caires

Theses and Dissertations

The purpose of this thesis is to provide an in-depth understanding of tooth engagement in splined couplings based on variations in clearances between mating teeth. It is standard practice to assume that 25-50% of the total spline teeth in a coupling are engaged due to variations from manufacture. Based on the assumed number of teeth engaged, the load capability of a splined coupling is determined. However, due to the variations in tooth geometry from manufacuture, the number of teeth actually engaged is dependent on the applied load and the tooth errors. The variations result in sequential tooth engagement with increasing …

Go to article

A Plastic-Based Thick-Film Li-Ion Microbattery For Autonomous Microsensors, Qian Lin Feb 2006

A Plastic-Based Thick-Film Li-Ion Microbattery For Autonomous Microsensors, Qian Lin

Theses and Dissertations

This dissertation describes the development of a high-power, plastic-based, thick-film lithium-ion microbattery for use in a hybrid micropower system for autonomous microsensors. A composite porous electrode structure and a liquid state electrolyte were implemented in the microbatteries to achieve the high power capability and energy density. The use of single-walled carbon nanotubes (SWNTs) was found to significantly reduce the measured resistance of the cathodes that use LiAl0.14Mn1.86O4 as active materials, increase active material accessibility, and improve the cycling and power performance without the need of compression. Optimized uncompressed macro cathodes were capable of delivering power densities greater than 50 mW/cm2, …

Go to article

Macroscopic Computational Model Of Dielectric Barrier Discharge Plasma Actuators, Timothy R. Klein Feb 2006

Macroscopic Computational Model Of Dielectric Barrier Discharge Plasma Actuators, Timothy R. Klein

Theses and Dissertations

Recent progress in the generation and sustainment of gas discharges at atmospheric pressure has energized research in the field of plasma-aerodynamics. Plasma actuators are promising devices that achieve flow control with no moving parts, do not alter the airfoil shape and place no parts in the flow. The operation of a plasma actuator is examined using a macroscopic (force and power addition) computational fluid dynamic model of a dielectric barrier discharge, DBD, in Fluent. A parametric approach is adopted to survey the range of requisite magnitudes of momentum and energy delivered to the flow field and to identify the effects …

Go to article

Experimental Study On Two-Dimensional Propagating Edge Flames: Cold Flow Modeling And Flame Spread Rate Measurements, Marcos Villa-Gonzalez Jan 2006

Experimental Study On Two-Dimensional Propagating Edge Flames: Cold Flow Modeling And Flame Spread Rate Measurements, Marcos Villa-Gonzalez

Theses and Dissertations

This thesis presents the results of an experimental study on two-dimensional, planar propagating edge flames. The results were generated using a new apparatus in which a thin stream of gaseous fuel is injected into a low-speed laminar wind tunnel thereby forming a flammable layer along the centerline. The fuel injector consists of aluminum airfoil with a thin slot in its trailing edge, from which fuel is injected. After the initial stratified fuel/air layer is developed, a flame is ignited near the tunnel outlet, and the flame spreads against the incoming air, toward the fuel source. Experiments were conducted with methane …

Go to article

Settling-Time Improvements In Positioning Machines Subject To Nonlinear Friction Using Adaptive Impulse Control, Tim Hakala Jan 2006

Settling-Time Improvements In Positioning Machines Subject To Nonlinear Friction Using Adaptive Impulse Control, Tim Hakala

Theses and Dissertations

A new method of adaptive impulse control is developed to precisely and quickly control the position of machine components subject to friction. Friction dominates the forces affecting fine positioning dynamics. Friction can depend on payload, velocity, step size, path, initial position, temperature, and other variables. Control problems such as steady-state error and limit cycles often arise when applying conventional control techniques to the position control problem. Studies in the last few decades have shown that impulsive control can produce repeatable displacements as small as ten nanometers without limit cycles or steady-state error in machines subject to dry sliding friction. These …

Go to article

Remote Terrain Navigation For Unmanned Air Vehicles, Stephen R. Griffiths Jan 2006

Remote Terrain Navigation For Unmanned Air Vehicles, Stephen R. Griffiths

Theses and Dissertations

There are many applications for which small unmanned aerial vehicles (SUAVs) are well suited, including surveillance, reconnaissance, search and rescue, convoy support, and short-range low-altitude perimeter patrol missions. As technologies for microcontrollers and small sensors have improved, so have the capabilities of SUAVs. These improvements in SUAV performance increase the possibility for hazardous missions through mountainous and urban terrain in the successful completion of many of these missions. The focus of this research was on remote terrain navigation and the issues faced when dealing with limited onboard processing and limited payload and power capabilities. Additional challenges associated with canyon and …

Go to article

Fuel-Nox Formation During Low-Grade Fuel Combustion In A Swirling-Flow Burner, Chunyang Wu Jan 2006

Fuel-Nox Formation During Low-Grade Fuel Combustion In A Swirling-Flow Burner, Chunyang Wu

Theses and Dissertations

Insufficient knowledge of fireside behavior in the near-burner region during biomass combustion is one of major factors preventing widespread use of this renewable fuel in pulverized coal power plants. The current research is aimed to investigate the impact of biomass cofiring on NO formation in the near-burner region through interpretation of computational fluid dynamics (CFD) predictions and data collected from a series of biomass tests in a pilot-scale (0.2 MW), swirling flow burner. Two-dimensional gas species mole fraction data were collected with state-of-theart instruments from nine experiments, composing one herbaceous biomass (straw), one woody biomass (sawdust), a low sulfur sub-bituminous …

Go to article

Correlating Factors Between Student Participation And Student Learning Via A Service Learning Project In Secondary Education: A Case Study, Shawn V. Jensen Jan 2006

Correlating Factors Between Student Participation And Student Learning Via A Service Learning Project In Secondary Education: A Case Study, Shawn V. Jensen

Theses and Dissertations

In this study a service-learning project was conducted with secondary students in a construction technology based course. Three research questions were considered; (1) does service learning projects help to engage student participation, (2) can students learn the course curriculum while participating in a service learning project, and (3) is there a correlation between student participation and student learning as it pertains to service learning projects? The data was collected through surveys, observations, interviews, and evaluations. The researcher concluded the following from the study; 92% of the students were actively participating in the two week service project, 76% of the students …

Go to article

A Framework For An Implantable Wireless Pressure And Volume Sensor Focusing On The Diagnosis And Treatment Of Shunt Failure In Hydrocephalus Patients, Donald Monte Wichern Jan 2006

A Framework For An Implantable Wireless Pressure And Volume Sensor Focusing On The Diagnosis And Treatment Of Shunt Failure In Hydrocephalus Patients, Donald Monte Wichern

Theses and Dissertations

The framework for a permanently implantable wireless compliance sensor was developed and validated using laboratory experiments. The proposed sensor would measure the intracranial pressure and fluid volume in the brain and return this information to a monitoring device. The designed sensor received power remotely from the monitoring device negating the need for an implanted power source. Impedance measurement estimation techniques were suggested, studied and applied to the compliance sensing system. A new impedance measurement technique, accounting for multiple variability in the domain, was developed. An extensive simulation environment was designed and used to develop the laboratory experiments and hardware. The …

Go to article

Development Of A Software Application To Extract The Features Of Normal Respiratory Sounds From The Lungs And The Trachea, Ranjani Sabarinathan Jan 2006

Development Of A Software Application To Extract The Features Of Normal Respiratory Sounds From The Lungs And The Trachea, Ranjani Sabarinathan

Theses and Dissertations

Auscultation has been widely regarded as one of the most important noninvasive diagnostic tools for clinical diagnosis of the respiratory tract. The purpose of this thesis was to develop a software application capable of extracting the key features of respiratory sound signals from the lungs and trachea of healthy persons. The efficacy of the program was evaluated by the verification of the important features of the sound signals from the left and right lungs and the trachea such as 1) right and left lung symmetry and 2) dissimilarity between the trachea and both lungs. The program was developed in LabView …

Go to article

Determination Of The Mechanical Properties Of Electrospun Gelatin Based On Polymer Concentration And Fiber Alignment, Leander Taylor Iii Jan 2006

Determination Of The Mechanical Properties Of Electrospun Gelatin Based On Polymer Concentration And Fiber Alignment, Leander Taylor Iii

Theses and Dissertations

The process of electrospinning has given the field of tissue engineering insight into many aspects of tissue engineered scaffolds, including how factors such as fiber diameter and porosity are affected by polymer concentration. However, the affects of fiber alignment upon the material properties of electrospun scaffolds remains unclear. The purpose of this study is to determine how the material properties of electrospun gelatin scaffolds are affected by changes in fiber alignment and starting gelatin concentration. Gelatin scaffolds, with starting concentrations of 80, 100, and 130mg/m1, were electrospun onto a target mandrel rotating at various speeds. Samples of each scaffold were …

Go to article

Scaffold Permeability As A Means To Determine Fiber Diameter And Pore Size Of Electrospun Fibrinogen, Scott Allen Sell Jan 2006

Scaffold Permeability As A Means To Determine Fiber Diameter And Pore Size Of Electrospun Fibrinogen, Scott Allen Sell

Theses and Dissertations

The purpose of this study was to construct a flowmeter that could accurately measure the hydraulic permeability of electrospun fibrinogen scaffolds, providing insight into the transport properties of electrospun scaffolds while making the measurement of their topographical features (fiber and pore size) more accurate. Three different concentrations of fibrinogen were used (100, 120, and 150mg/ml) to create scaffolds with three different fiber diameters and pore sizes. The fiber diameters and pore sizes of the electrospun scaffolds were analyzed through scanning electron microscopy and image analysis software. The permeability of each scaffold was measured and used to calculate permeability-based fiber diameters …

Go to article

The Effect Of Stationary Uv Excitation On The Optical Behavior Of Electrochemically Self-Assembled Semiconductor Nanowires, Rajesh A. Katkar Jan 2006

The Effect Of Stationary Uv Excitation On The Optical Behavior Of Electrochemically Self-Assembled Semiconductor Nanowires, Rajesh A. Katkar

Theses and Dissertations

In this work, we investigate the optical response of the semiconductor quantum wire array when excited by stationary UV light. The array is synthesized by selectively electro-depositing the semiconductor material in electrochemically self-assembled porous alumina templates. Our studies are based on the optical behavioral changes in CdS, ZnO, ZnSe and CdSe quantum wires of 50-, 25- and 10-nm diameters. We use a set of generalized Bloch equations to solve the interband polarization function of the semiconductors derived within the Hartree-Fock approximation, and theoretically model the UV excitation effect on the quantum wires. The solutions which consider the effects of screening, …

Go to article

Accelerating Whole-Cell Biocatalysis By Enhancing Outer Membrane Permeability, Ye Ni Jan 2006

Accelerating Whole-Cell Biocatalysis By Enhancing Outer Membrane Permeability, Ye Ni

Theses and Dissertations

Whole-cell biocatalysts are preferred in many biocatalysis applications. However, cell envelope often represents a formidable permeability barrier. As a result, reactions catalyzed by whole-cells are reportedly orders of magnitude slower than those of by their free enzyme counterparts. The present research addresses this critical issue by using membrane engineering approaches. Two E. coli strains with genetically altered outer membrane structures were used in the study, a lipopolysaccarides (LPS) mutant SM101 and a Braun's lipoprotein mutant E609L. The effects of outer membrane mutation on the permeability of substrates differing substantially in size and hydrophobicity were investigated by combining the mutant cells …

Go to article

Evaluation Of Prototype Cell Delivery Catheters Using Agarose Gel And Cell Culture Experiments, Sagar Panse Jan 2006

Evaluation Of Prototype Cell Delivery Catheters Using Agarose Gel And Cell Culture Experiments, Sagar Panse

Theses and Dissertations

Neurodegenerative diseases and brain tumors affect millions of patients worldwide and are associated with significant morbidity and mortality. The blood brain barrier constitutes a major obstacle to delivery of therapeutic agents administered systemically for treating these disorders. Intracranial drug delivery provides a novel way of bypassing the blood brain barrier and achieving high concentration of therapeutic agents in the brain while avoiding systemic side effects. However damage to tissues during insertion of catheters, release of air in the brain and consequent backtracking of dye are some disadvantages with this mode of treatment. We evaluated prototype cell delivery catheters (each with …

Go to article

A Computational Study Of Axial Compressor Rotor Casing Treatments And Stator Land Seals, Charles C. Cates Jan 2006

A Computational Study Of Axial Compressor Rotor Casing Treatments And Stator Land Seals, Charles C. Cates

Theses and Dissertations

As fuel prices soar ever higher, aircraft manufacturers and their airline customers demand that the next generation of engines used on their aircraft push the limits of efficiency and capability. This study consists of a computational examination of two currently accepted methods of axial compressor performance improvement in terms of surge margin and efficiency, rotor casing treatments and stator land seals.ADPAC and Fluent CFD solvers were used in the analysis of circumferential groove casing treatments and two types of stator seals, one typical of a front stage stator and one typical of a rear stage stator. The computational solutions and …

Go to article

Hmg-Coa Reductase Inhibitors Act Synergistically With Ucn-01 Through Ras Inhibition, Payal Khanna Jan 2006

Hmg-Coa Reductase Inhibitors Act Synergistically With Ucn-01 Through Ras Inhibition, Payal Khanna

Theses and Dissertations

The primary objective of this study is to elucidate the mechanism by which the reagent UCN-01 induces apoptosis when administered to leukemia cells along with HmG-CoA reductase inhibitors, mainly the statins. In this study, we demonstrated that exposure of leukemia cell lines to lovastatin (20 uM, 18 hours) and UCN-01 (100 nM, 18 hours) resulted in mitochondria dysfunction, procaspase 3 and 9 cleavage, and PAW degradation along with marked cytochrome C release and apoptosis. Although similar molecular mechanisms have not yet been confirmed in other cancers, our hypothesis holds that enhanced apoptotic effects of UCN-01 are due in part to …

Go to article

Green Organic Solar Cells From A Water Soluble Polymer And Nancrystalline Tio2, Qiquan Qiao Jan 2006

Green Organic Solar Cells From A Water Soluble Polymer And Nancrystalline Tio2, Qiquan Qiao

Theses and Dissertations

The cost of the present generation of inorganic silicon solar cells is very high and further breakthroughs in cost and efficiency using traditional materials are becoming less and less likely after over 50 years of development. Next generation organic solar cells offer a solution to the limitations of silicon through the vision of low-cost, liquid-based, large area fabrication technology based on polymer and nanomaterials at room temperature. However, most polymers used in solar cells are dissolved in organic solvents such as xylene, toluene, chloroform, and chlorobenzene. Such solvents are harmful to people and environments, leading to higher costs due to …

Go to article

First Prev Next Last