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Articles 7801 - 7830 of 11510

Full-Text Articles in Engineering

Cavity Coupled Aeroramp Injector Combustion Study, Dell T. Olmstead Jun 2009

Cavity Coupled Aeroramp Injector Combustion Study, Dell T. Olmstead

Theses and Dissertations

The difficulties with fueling of supersonic combustion ramjet engines with hydrocarbon based fuels presents many challenges that are currently being tackled by the Air Force Research Lab Propulsion Directorate Aerospace Propulsion Division. As the scramjet engine designs are scaled up, the need for a better solution to supersonic mixing has led to the development of many different styles of fuel injection. An aerodynamic ramp injector has been shown to have a quantitative improvement over a physical ramp while still achieving desirable mixing characteristics. The objectives for this research was quantifying the performance and operability implications of replacing four 15 degree …

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Aeroelastic Optimization Of Sounding Rocket Fins, Joseph R. Simmons Iii Jun 2009

Aeroelastic Optimization Of Sounding Rocket Fins, Joseph R. Simmons Iii

Theses and Dissertations

This research effort develops a multidisciplinary design tool to optimize sounding rocket fin geometries that minimize the mass of the fins while maintaining aerodynamic performance. This research grew out of a design problem experienced by the US Air Force Academy's Falcon LAUNCH program. The Falcon LAUNCH program is a senior design capstone project during which Air Force Academy cadets design, build and fly a sounding rocket over the course of an academic year. In the Spring of 2007, the Falcon LAUNCH V vehicle experienced a catastrophic failure when three of its four fins sheared off due to flutter. When the …

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Performance And Operability Of A Dual Cavity Flame Holder In A Supersonic Combustor, Mackenzie J. Collatz Jun 2009

Performance And Operability Of A Dual Cavity Flame Holder In A Supersonic Combustor, Mackenzie J. Collatz

Theses and Dissertations

The current generation of hydrocarbon fueled scramjet combustors typically requires a flame holding device to facilitate flame ignition and stable combustion. The amount of time available for fuel injection, fuel-air mixing, and combustion is very short, on the order of 1 millisecond. This short dwell time, along with the relatively long ignition delay times of hydrocarbon fuels, makes the flow path and flame holder design extremely important. This study investigates the performance and operability of using a symmetric dual cavity flame holder flow path to stabilize and enhance supersonic combustion. Testing of this flow path configuration, as well as a …

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An Efficient And Effective Implementation Of The Trust System For Power Grid Compartmentalization, Juan M. Carlos Gonzalez Jun 2009

An Efficient And Effective Implementation Of The Trust System For Power Grid Compartmentalization, Juan M. Carlos Gonzalez

Theses and Dissertations

As utility companies develop and incorporate new technologies, such as moving to utility Internet technology based architecture and standard; it is crucial that we do so with history in mind. We know that traditional utility protection and control systems were not designed with security in their top priorities. This presents a danger in an environment where near real-time responses are required to ensure safe operations. As a consequence, system security becomes a burden to the system rather than necessary protection. Unfortunately, technology implementation is not the only concern. The number of utility privately-owned companies has multiplied as the market has …

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Investigation Of Additives For Use In Electroless Plating Solutions For Fabrication Of Nanowires, Elliott J. Bird Jun 2009

Investigation Of Additives For Use In Electroless Plating Solutions For Fabrication Of Nanowires, Elliott J. Bird

Theses and Dissertations

This study focused on improvement of electroless plating methods by use of particular bath additives. The techniques developed here can enable us to plate very thin layers selectively on a nonconductive substrate and thus create metallized features on a nanoscale. Through the development of such bottom-up techniques this work contributes a key technology to achieving self-assembled nanocircuits. The use of additives in an electroless plating environment can modify the barriers to nucleation (or seeding) and growth. Two additives, namely 3-mercapto-1-propanesulfonic Acid (MPS) and 1,3-propanedisulfonic acid (PDS), notably increased the selectivity of electroless metallization on chemically modified surfaces, which can be …

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Automated All-Quadrilateral Mesh Adaptation Through Refinement And Coarsening, Bret D. Anderson Jun 2009

Automated All-Quadrilateral Mesh Adaptation Through Refinement And Coarsening, Bret D. Anderson

Theses and Dissertations

This thesis presents a new approach to conformal all-quadrilateral mesh adaptation. In finite element modeling applications, it is often desirable to modify the node density of the mesh; increasing the density in some parts of the mesh to provide more accurate results, while decreasing the density in other parts to reduce computation time. The desired node density is typically determined by a sizing function based on either the geometry of the model or the results of a finite element solution. Although there are numerous mesh adaptation methods currently in use, including initial adaptive mesh generation, node redistribution, and adaptive mesh …

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Growth, Characterization And Applications Of Multifunctional Ferroelectric Thin Films, Bo Xiao Jun 2009

Growth, Characterization And Applications Of Multifunctional Ferroelectric Thin Films, Bo Xiao

Theses and Dissertations

Ferroelectric materials have been extensively studied theoretically and experimentally for many decades. Their ferroelectric, piezoelectric, pyroelectric, dielectric and electro-optical properties offer great promise in various applications such as non-volatile random access memory devices, non linear optics, motion and thermal sensors, and tunable microwave devices. Advanced applications for high dielectric constant insulators and nonvolatile memories in semiconductor industry have led to a meteoric rise of interest in the ferroelectrics recently. As most studied and technically important ferroelectric materials, lead zirconate titanate (PZT) and barium strontium titanate (BST) are widely investigated to understand their properties for potential device applications. Using radio frequency …

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System Identification Of An On Orbit Spacecraft's Antenna Dynamics, Christopher M. Sylvester Jun 2009

System Identification Of An On Orbit Spacecraft's Antenna Dynamics, Christopher M. Sylvester

Theses and Dissertations

As a result of previous efforts [Pachter, Barba, 2007] a tight control loop was designed to meet performance specifications while minimizing the feedback control system’s gains of a spacecraft mounted flexible antenna. Emphasis is now shifted to on orbit system identification of the antenna dynamics in order to increase nominal plant knowledge, estimate plant uncertainty bounds, as well as determine the disturbance band. Non-parametric system identification is undertaken. Knowledge of the plant dynamics along with the corresponding uncertainty bounds will provide for the design of a control system which meets the specifications (tracking and disturbance rejection) while at the same …

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Structural Optimization Of Joined-Wing Beam Model With Bend-Twist Coupling Using Equivalent Static Loads, Nicholas S. Green May 2009

Structural Optimization Of Joined-Wing Beam Model With Bend-Twist Coupling Using Equivalent Static Loads, Nicholas S. Green

Theses and Dissertations

This study is based on the merger of two separate theories to further the efficiency with which joined-wing structural models are designed. The first theory is Geometrically Exact Beam Theory (GEBT). GEBT is a small strain beam theory which is capable of accurately capturing the geometric bend-twist coupling in beam elements that are experiencing large global deformations. This is crucial to the joined-wing problem as it is geometrically nonlinear. The second theory concerns Equivalent Static Loads (ESL). These ESL consist of a load vector that produces the same nodal displacements and rotations as those computed from a pure nonlinear analysis. …

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An Internal Representation For Adaptive Online Parallelization, Koy D. Rehme May 2009

An Internal Representation For Adaptive Online Parallelization, Koy D. Rehme

Theses and Dissertations

Future computer processors may have tens or hundreds of cores, increasing the need for efficient parallel programming models. The nature of multicore processors will present applications with the challenge of diversity: a variety of operating environments, architectures, and data will be available and the compiler will have no foreknowledge of the environment until run time. Adaptive Online Parallelization (ADOPAR) is a unifying framework that attempts to overcome diver sity by separating discovery and packaging of parallelism. Scheduling for execution may then occur at run time when diversity may best be resolved. This work presents a compact representation of parallelism based …

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Integrated Actuation And Energy Harvesting In Prestressed Piezoelectric Synthetic Jets, Poorna Mane May 2009

Integrated Actuation And Energy Harvesting In Prestressed Piezoelectric Synthetic Jets, Poorna Mane

Theses and Dissertations

With the looming energy crisis compounded by the global economic downturn there is an urgent need to increase energy efficiency and to discover new energy sources. An approach to solve this problem is to improve the efficiency of aerodynamic vehicles by using active flow control tools such as synthetic jet actuators. These devices are able to reduce fuel consumption and streamlined vehicle design by reducing drag and weight, and increasing maneuverability. Hence, the main goal of this dissertation is to study factors that affect the efficiency of synthetic jets by incorporating energy harvesting into actuator design using prestressed piezoelectric composites. …

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Frequency Response Of The Skin On The Head And Neck During Production Of Selected Speech Sounds, Jacob B. Munger May 2009

Frequency Response Of The Skin On The Head And Neck During Production Of Selected Speech Sounds, Jacob B. Munger

Theses and Dissertations

Vibration within the vocal tract during speech is transmitted through body tissue to the skin surface and can be used to transmit speech. Achieving quality speech signals using skin vibration is desirable but problematic, primarily due to the different sources of sound during speech. The objective of this study was to characterize the frequency content of speech signals at various locations on the head and neck. Signals were recorded using accelerometers attached to 15 locations on the heads and necks of 14 males and 10 females as well as a microphone to record audible speech. The subjects produced several isolated …

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Fabrication And Device Applications Of Self Assembled Nanostructures, Bhargava Ram Kanchibotla V May 2009

Fabrication And Device Applications Of Self Assembled Nanostructures, Bhargava Ram Kanchibotla V

Theses and Dissertations

The spin dynamics of electrons in inorganic and organic semiconducting nanostructures has become an area of interest in recent years. The controlled manipulation of an electron’s spin, and in particular its phase, is the primary requirement for applications in quantum information processing. The phase decoheres in a time known as the transverse relaxation time or T2 time. We have carried out a measurement of the ensemble-averaged transverse spin relaxation time (T2*) in bulk and few molecules of the organic semiconductor tris-(8-hydroxyquinolinolato aluminum) or Alq3. The Alq3 system exhibits two characteristic T2* times: the longer of which is temperature independent and …

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Multiscale Modeling Of Airway Inflammation Induced By Mechanical Ventilation, Kittisak Koombua May 2009

Multiscale Modeling Of Airway Inflammation Induced By Mechanical Ventilation, Kittisak Koombua

Theses and Dissertations

Mechanical ventilation (MV) is a system that partially or fully assists patients whose respiratory system fails to achieve a gas exchange function. However, MV can cause a ventilator-associated lung injury (VALI) or even contribute to a multiple organ dysfunction syndrome (MODS) in acute respiratory distress syndrome (ARDS) patients. Despite advances in today technologies, mortality rates for ARDS patient are still high. A better understanding of the interactions between airflow from mechanical ventilator and the airway could provide useful information used to develop a better strategy to ventilate patients. The mechanisms, which mechanical ventilation induces airway inflammation, are complex processes and …

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Economic Development Criteria And Project Prioritization, Jason Scott Mcgee May 2009

Economic Development Criteria And Project Prioritization, Jason Scott Mcgee

Theses and Dissertations

To provide a more in-depth analysis of potential roadway projects, the Utah Department of Transportation (UDOT) desired a method of evaluating projects according to their economic potential without using potentially costly computer models or excessive data collection. Brigham Young University (BYU) was retained to research and recommend criteria for the economic development criteria in the project-prioritization process. A literature review was first undertaken to better understand the transportation-economic development relationship. Using the literature review, combined with the information from the Economic Development Corporation of Utah, the Governor's Office of Planning and Budget, the Governor's Office of Economic Development, and a …

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Influence Of Structural Flexibility On Flapping Wing Propulsion, Aaron M. Mcclung Apr 2009

Influence Of Structural Flexibility On Flapping Wing Propulsion, Aaron M. Mcclung

Theses and Dissertations

The inelastic deformation behavior of PMR-15 neat resin, a high-temperature thermoset polymer, was investigated at 288 degrees C. The experimental program was designed to explore the influence of strain rate on tensile loading, unloading, and strain recovery behaviors. In addition, the effect of the prior strain rate on the relaxation response of the material, as well as on the creep behavior following strain controlled loading were examined. The experimental data were modeled with the Viscoplasticity Based on Overstress (VBO) theory. A systematic procedure for determining model parameters was developed and the model was employed to predict the response of the …

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Understanding Performance--Limiting Mechanisms In Li-Ion Batteries For High-Rate Applications, Indrajeet Vilasrao Thorat Apr 2009

Understanding Performance--Limiting Mechanisms In Li-Ion Batteries For High-Rate Applications, Indrajeet Vilasrao Thorat

Theses and Dissertations

This work presents novel modeling and experimental techniques that provide insight into liquid-phase mass transport and electron transfer processes in lithium-ion batteries. These included liquid-phase ionic mass transport (conduction and diffusion), lithium diffuion in the solid phase and electronic transport in the solid phase. Fundamental understanding of these processes is necessary to efficiently design and optimize lithium-ion batteries for different applications. To understand the effect of electrode structure on the electronic resistance of the cathode, we tested power performance of cathodes with combinations of three different carbon conductivity additives: vapor-grown carbon fibers (CF), carbon black (CB) and graphite (GR). With …

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Real-Time Optical Flow Sensor Design And Its Application On Obstacle Detection, Zhaoyi Wei Apr 2009

Real-Time Optical Flow Sensor Design And Its Application On Obstacle Detection, Zhaoyi Wei

Theses and Dissertations

Motion is one of the most important features describing an image sequence. Motion estimation has been widely applied in structure from motion, vision-based navigation and many other fields. However, real-time motion estimation remains a challenge because of its high computational expense. The traditional CPU-based scheme cannot satisfy the power, size and computation requirements in many applications. With the availability of new parallel architectures such as FPGAs and GPUs, applying these new technologies to computer vision tasks such as motion estimation has been an active research field in recent years. In this dissertation, FPGAs have been applied to real-time motion estimation …

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A Parallel Molecular Dynamics Program For Simulation Of Water In Ion Channels, Laxmi Mullapudi Apr 2009

A Parallel Molecular Dynamics Program For Simulation Of Water In Ion Channels, Laxmi Mullapudi

Theses and Dissertations

With a modest beginning from developing a model of dynamics of hard liquid spheres (Alder et al., 1957), molecular dynamics (MD) simulations have come to a point where complex biomolecules can be simulated with precision close to reality (Noskov et al., 2007). In this context, a parallel molecular dynamics program for simulation of ion channels associated with cellular membranes has been developed. The parallel MD code developed is simple, efficient, and easily coupled to other codes such as the hybrid molecular dynamics/ brownian dynamics (MD/BD) code developed for the study of protein interactions (Ying et al., 2005). The Atom Decomposition …

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Structural And Functional Considerations In The Design Of Collagen-Based Electrospun Scaffolds, Chantal Ayres Apr 2009

Structural And Functional Considerations In The Design Of Collagen-Based Electrospun Scaffolds, Chantal Ayres

Theses and Dissertations

Electrospinning can be used to selectively process a variety of natural and synthetic polymers into highly porous scaffolds composed of nano-to-micron diameter fibers. This process shows great potential as a gateway to the development of physiologically relevant tissue engineering scaffolds. In this study we examine the structural and functional considerations regarding electrospun scaffolds for dermal template applications using novel quantification techniques. In order to characterize scaffold structure, a technique utilizing the fast Fourier transform was developed to systematically quantify fiber alignment and evaluate how different electrospinning parameters impact the structure and material properties of an electrospun scaffold. Gelatin was suspended …

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Cad-Centric Dynamic Workflow Generation, Travis L. Kenworthy Apr 2009

Cad-Centric Dynamic Workflow Generation, Travis L. Kenworthy

Theses and Dissertations

CAD systems are important design tools that enable the designer to conceptualize, visualize, analyze, and manufacture a design (Shahin 2008). Although high-end CAD systems provide several built-in design applications, the users of CAD often select various custom or proprietary non-CAD analyses that constrain, optimize, or evaluate their designs. An efficient method is needed to perform trade studies from within the CAD environment. Methods have been developed to meet the challenges associated with this need. The methods have been implemented in a program, called the Process Integrator, which resides in a CAD system and allows the user to perform trade studies …

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A Numerical Model Of The Friction Stir Plunge, Stanford Wayne Mcbride Apr 2009

A Numerical Model Of The Friction Stir Plunge, Stanford Wayne Mcbride

Theses and Dissertations

A Lagrangian finite-element model of the plunge phase of the friction stir welding process was developed to better understand the plunge. The effects of both modeling and experimental parameters were explored. Experimental friction stir plunges were made in AA 7075-T6 at a plunge rate of 0.724 mm/s with spindle speeds ranging from 400 to 800 rpm. Comparable plunges were modeled in Forge2005. Various simulation parameters were explored to assess the effect on temperature prediction. These included the heat transfer coefficient between the tool and workpiece (from 0 to 2000 W/m-K), mesh size (node counts from 1,200 to 8,000), and material …

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Botulinum Toxin For Non-Surgical Lateral Release In Subjects With Patellofemoral Pain, Laura Maple Apr 2009

Botulinum Toxin For Non-Surgical Lateral Release In Subjects With Patellofemoral Pain, Laura Maple

Theses and Dissertations

Previous studies for treating Patellofemoral Pain Syndrome (PFPS) are controversial regarding the effectiveness in alleviating anterior knee pain (AKP). The muscular imbalance between the vastus medialis oblique/vastus lateralis (VMO/VL) may be the underlying mechanical issue causing PFPS. It is hypothesized that Botox can decrease the force production capability of the lateral musculature mechanically similar to surgery. Strengthening the VMO while using Botox treatment can alleviating the muscular imbalance that occurs with subjects with PFPS. A double blind study, having all participants blinded and uninformed of the injection contents, was implemented to test this hypothesis testing three female subjects. Four knees …

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Characterizing Component Hiding Using Ancestral Entropy, Jason A. Williams Mar 2009

Characterizing Component Hiding Using Ancestral Entropy, Jason A. Williams

Theses and Dissertations

In this research, the problem of software protection and the attributes that define that protection is considered. Specifically, how to protect programs defined as structural combinational logic gates. Obfuscation is one technique for protecting such circuits and involves replacing an original circuit with a functionally equivalent variant that has some definable hiding property. The difficulty of reverse engineering versus identifying and recovering the original components or sub-circuits within an original circuit is compared. With a polymorphic circuit engine that produces semantically equivalent variations of standard benchmark circuits the level of component hiding across variants with different physical configurations is determined …

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Removing Redundant Logic Pathways In Polymorphic Circuits, Hanseok Kim Mar 2009

Removing Redundant Logic Pathways In Polymorphic Circuits, Hanseok Kim

Theses and Dissertations

Evaluating the quality of software and circuit obfuscators is a research goal of great interest. However, there exists little research about evaluation of obfuscation effectiveness through analyzing and investigating redundancies found in the obfuscated variants. In this research, we consider programs represented as structural combinational circuits and then analyze obfuscated variants of those circuits through a tool that produces functionally equivalent variants based on subcircuit selection and replacement. We then consider how Boolean logic and reduction affects the size and levelization of circuit variants, giving us a concrete metric by which to consider obfuscation effectiveness. To accomplish these goals, we …

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Determining The Orbit Locations Of Turkish Airborne Early Warning And Control Aircraft Over The Turkish Air Space, Nebi Sarikaya Mar 2009

Determining The Orbit Locations Of Turkish Airborne Early Warning And Control Aircraft Over The Turkish Air Space, Nebi Sarikaya

Theses and Dissertations

The technology improvement affects the military needs of individual countries. The new doctrine of defense for many countries emphasizes detecting threats as far away as you can from your homeland. Today, the military uses both ground RADAR and Airborne Early Warning and Control (AEW&C) Aircraft. AEW&C aircraft has become vital to detect low altitude threats that a ground RADAR cannot detect because of obstacles on the earth. Turkey has ordered four AEW&C aircraft for her air defense system because of the lack of complete coverage by ground RADAR. This research provides optimal orbit locations that can be updated according to …

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Frequency Diversity For Improving Synthetic Aperture Radar Imaging, Jawad L. Farooq Mar 2009

Frequency Diversity For Improving Synthetic Aperture Radar Imaging, Jawad L. Farooq

Theses and Dissertations

In this work, a novel theoretical framework is presented for using recent advances in frequency diversity arrays (FDAs). Unlike a conventional array, the FDA simultaneously transmits a unique frequency from each element in the array. As a result, special time and space properties of the radiation pattern are exploited to improve cross-range resolution. The idealized FDA radiation pattern is compared with and validated against a full-wave electromagnetic solver, and it is shown that the conventional array is a special case of the FDA. A new signal model, based on the FDA, is used to simulate SAR imagery of ideal point …

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Evaluation Of Full-Depth Reclamation On Strength And Durability Of Pavement Base Layers, Benjamin Earl Griggs Mar 2009

Evaluation Of Full-Depth Reclamation On Strength And Durability Of Pavement Base Layers, Benjamin Earl Griggs

Theses and Dissertations

The purpose of this research was to determine the effect of full-depth reclamation (FDR) on the strength and durability of aggregate base layers in a coordinated approach involving both field and laboratory testing. Field comparisons between the pre-reclamation neat base and post-reclamation blended base were supplemented with laboratory experiments conducted to determine the effects of reclaimed asphalt pavement (RAP) content, compaction effort, and heating on the strength and durability of roadways reconstructed using FDR with a portable asphalt recycling machine (PARM). Also, the effect of reclamation on the spatial uniformity of the pavement structures was explored by comparing variability in …

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Methodology For Value-Driven Enterprise Architecture Development Goals: Application To Dodaf Framework, Justin W. Osgood Mar 2009

Methodology For Value-Driven Enterprise Architecture Development Goals: Application To Dodaf Framework, Justin W. Osgood

Theses and Dissertations

The Department of Defense Architectural Framework (DoDAF) describes 29 distinct views but offers limited guidance on view selection to meet system needs. This research extends the Value-Driven Enterprise Architecture Score (VDEA-Score) from a descriptive, evaluation protocol toward a prescriptive one by evaluating each DoDAF view and its contribution to the overall objective of the completed architecture. This extension of VDEA is referred to as VDEA-Development Goals (VDEA-DG). The program manager or other decision-makers may use this insight to justify the allocation of resources to the development of specific architecture views considered to provide maximum value. This research provides insight into …

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Application Of Time-Frequency Representation To Non-Stationary Radar Cross Section, John D. Mcshane Mar 2009

Application Of Time-Frequency Representation To Non-Stationary Radar Cross Section, John D. Mcshane

Theses and Dissertations

Radar Cross Section (RCS) imaging of a non-wide sense stationary signal poses significant problems in identifying scattering centers in the post processed radar- generated image. A non-wide sense stationary RCS is typically encountered when moving parts on the target impress a phase shift into the backscatter signal that is uncorrelated to the previous return pulse. When the Fourier transform of the phase shifted complex signal is taken, range and cross range information on scattering centers are misplaced. Time Frequency Representations (TFR) must be used to help locate these scattering centers so they can be properly treated to reduce the target’s …

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