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Articles 2641 - 2670 of 4180
Full-Text Articles in Engineering
Re, Os, Al And Mg Boron Rich Ceramic Compounds For Structural Application, Zhilin Xie
Re, Os, Al And Mg Boron Rich Ceramic Compounds For Structural Application, Zhilin Xie
Electronic Theses and Dissertations
Hard and ultra-incompressible materials are of great interest due to their important applications in industry. A common route to design hard materials is combining transition metals with light and small covalent elements. Light elements such as carbon, oxygen, nitrogen and boron have been considered as good candidates. This study includes the synthesis of ReB2, OsB2 and another higher boride AlMgB14. Most of the techniques used for ReB2 synthesis reported 1:2.5 Re to B ratio because of the loss of the B during high temperature synthesis. However, as a result of B excess, the amorphous boron, located along the grain boundaries …
Experimental Investigation Of Transonic Shock Oscillations On Naca 0018 At Incidence, Christopher Allen Farrell
Experimental Investigation Of Transonic Shock Oscillations On Naca 0018 At Incidence, Christopher Allen Farrell
Electronic Theses and Dissertations
A NACA 0018 airfoil model with a 3-inch chord was mounted into the trisonic wind tunnel at the National Center for Physical Acoustics at the University of Mississippi. Tunnel runs were conducted with the angle of incidence increasing from 0 degrees to 6 degrees at 1 degree increments, while the Mach number was held steady at 0.73. High-speed schlieren images were recorded at a sample rate of 4,000 Hz. A Matlab code was developed to display the spatial power spectral density distribution in the region of the shock. This code calculated the frequency spectrum at regular points along the range …
Artificial Impedance Surfaces And Wire Media For Absorption And Cloaking, Yashwanth Reddy Padooru
Artificial Impedance Surfaces And Wire Media For Absorption And Cloaking, Yashwanth Reddy Padooru
Electronic Theses and Dissertations
The main objective of this dissertation is to investigate the ability of utilizing artificial impedance surfaces and wire media for absorption and cloaking applications. The dissertation includes two parts which focus on the electromagnetic wave propagation in absorbers formed by stacked metasurfaces and structured wire media, and electromagnetic wave interaction with the cylindrical cloaking structures. In the first part, we propose a variety of physical systems that show multiband and wideband absorption properties in the microwave regime. For the multiband absorbers, we propose a simple analytical model to study the absorption properties. Further, using the same circuit model, the physical …
Accelerating The Performance Of A Novel Meshless Method Based On Collocation With Radial Basis Functions By Employing A Graphical Processing Unit As A Parallel Coprocessor, Derek Owusu-Banson
Accelerating The Performance Of A Novel Meshless Method Based On Collocation With Radial Basis Functions By Employing A Graphical Processing Unit As A Parallel Coprocessor, Derek Owusu-Banson
Electronic Theses and Dissertations
In recent times, a variety of industries, applications and numerical methods including the meshless method have enjoyed a great deal of success by utilizing the graphical processing unit (GPU) as a parallel coprocessor. These benefits often include performance improvement over the previous implementations. Furthermore, applications running on graphics processors enjoy superior performance per dollar and performance per watt than implementations built exclusively on traditional central processing technologies. The GPU was originally designed for graphics acceleration but the modern GPU, known as the General Purpose Graphical Processing Unit (GPGPU) can be used for scientific and engineering calculations. The GPGPU consists of …
Advanced Design Methodologies And Novel Applications Of Reflectarray Antennas, Payam Nayeri
Advanced Design Methodologies And Novel Applications Of Reflectarray Antennas, Payam Nayeri
Electronic Theses and Dissertations
Reflectarray antennas combine the numerous advantages of printed antenna arrays and reflector antennas and create a hybrid high-gain antenna with a low-profile, low-mass, and diversified radiation performance. Reflectarrays are now emerging as the new generation of high-gain antennas for long-distance communications. In this dissertation, some advanced concepts demonstrating novel features of reflectarray antennas are presented. • First, various approaches for radiation analysis of reflectarray antennas are described and implemented. Numerical results are then presented for a variety of systems and the advantages, limitations, and accuracy of these approaches are discussed and compared with each other. • A broadband technique by …
Implementation Of A Software Defined Spread Spectrum Communication System, Mir Ali
Implementation Of A Software Defined Spread Spectrum Communication System, Mir Ali
Electronic Theses and Dissertations
The goal of this thesis is to develop a framework to prototype a software defined direct sequence spread spectrum transceiver that can be used as a node in an ad hoc network. We introduce the concept of a software radio, the current state of art, and GNU Radio and its concepts. We discuss in detail the design and development methods of GNU Radio and develop a flowgraph in Python to demonstrate the method of development. We present a mathematical analysis of (DSSS) modulation and demodulation schemes along with the transmitter and receiver design. We use this design to develop an …
Determination Of Cutoff Frequencies Of Simple Waveguides Using Finite Difference Method, Sridhar Kolagani
Determination Of Cutoff Frequencies Of Simple Waveguides Using Finite Difference Method, Sridhar Kolagani
Electronic Theses and Dissertations
No abstract provided.
Room Temperature Ionic Liquid (Rtil) Membranes For Bio-Methane Dehumidification, Ryan Amos
Room Temperature Ionic Liquid (Rtil) Membranes For Bio-Methane Dehumidification, Ryan Amos
Electronic Theses and Dissertations
Renewable fuels are heavily researched due to the increasing price of and resulting pollution from fossil fuels. The production of useable energy from waste—animal, sewage, discarded food, landfill matter would be a valuable renewable fuel production method. Biogas is a renewable fuel that is produced by anaerobic digestion, composed mainly of methane, carbon dioxide and small percentages of hydrogen sulfide and water vapor. Before this biogas—predominately bio-methane—can be converted to fuel, it must be dehumidified to become useable. Typically membrane-based gas dehumidification uses hydrophilic polymer membrane materials, such as polydimethylsiloxane (PDMS) and cellulose acetate (CA). The main problems with polymer …
Inspection Of Earthen Embankment Dams Using Time Lapse Electrical Resistivity Tomography, Jared Stewart Case
Inspection Of Earthen Embankment Dams Using Time Lapse Electrical Resistivity Tomography, Jared Stewart Case
Electronic Theses and Dissertations
According to the National Inventory of Dams (NID), the number of dams across the United States is approximately 85,000. Many of these dams are more than 50 years old and need vast attention to ensure their safety. It is difficult to obtain a full assessment of the dam just by visual inspections alone. This is because many problems associated with dam failure occur internally, which makes it difficult to be observed by the dam inspectors. Examples of these flaws are piping and seepage (flow of water through or around dam walls). It is in this area where geophysical methods can …
Unequal Error Protection Raptor Codes, Hussein Fadhel
Unequal Error Protection Raptor Codes, Hussein Fadhel
Electronic Theses and Dissertations
We design Unequal Error Protection (UEP) Raptor codes with the UEP property provided by the precode part of Raptor codes which is usually a Low Density Parity Check (LDPC) code. Existing UEP Raptor codes apply the UEP property on the Luby transform (LT) code part of Raptor codes. This approach lowers the bit erasure rate (BER) of the more important bits (MIB) of the data decoded by the LT part of the decoder of Raptor code at the expense of degrading the BER performance of Less Important Bits (LIB), and hence the overall BER of the data passed from the …
Synthesis And Evaluation Of Naturally Occuring Halogenated Bipyrroles In A Relevant Marine Species, Fundulus Heteroclitus, Kimberly Sheree Foster
Synthesis And Evaluation Of Naturally Occuring Halogenated Bipyrroles In A Relevant Marine Species, Fundulus Heteroclitus, Kimberly Sheree Foster
Electronic Theses and Dissertations
Halogenated dimethyl-2-2'-bipyrroles (HDBPs) have recently been discovered in seabird eggs and have been shown to bioaccumulate in trophic organisms. HDBPs are suspected to be biogenic in nature, derived from evidence of marine natural products that are persistent in the environment and widespread in the Pacific and Atlantic Ocean. The HDBPs exhibit chlorinated and brominated substitution patterns that closely resemble anthropogenic pollutants like the polychlorinated biphenyls (PCBs), polybrominated biphenyls (PBBs), and polybrominated diphenyl ethers (PBDEs). Environmental health concerns exists regarding these naturally occurring HDBPs because several of these analogs were shown to induce the cytochrome P4501A (CYP1A) gene through activation of …
Using Eye Tracking And Attention Maps In Computer Science Education, Austin Pernell
Using Eye Tracking And Attention Maps In Computer Science Education, Austin Pernell
Electronic Theses and Dissertations
Eye tracking has been used for many different areas of study where a user's eye movements are considered the most important information available. Before eye tracking was possible, the only way that information could be obtained was to ask the user where they looked and what caught their attention. Now, with the rise of eye tracking cameras, this data can be captured, stored, and processed in a meaningful way. These cameras aren't perfectly accurate however and there is still some interpretation that must be applied to more accurately represent the true gaze path of the user. This paper establishes some …
A Comparative Study Of Segmented Tungsten Rod Penetration Into A Thick Steel Target Plate, Michael Bryant Presnell
A Comparative Study Of Segmented Tungsten Rod Penetration Into A Thick Steel Target Plate, Michael Bryant Presnell
Electronic Theses and Dissertations
This thesis presents results from computational simulations of tungsten alloy segmented rod projectiles (SRP) penetrating an RHA semi-infinite target plate at high velocities. Penetration experimental data show improved penetration efficiency by the segmented projectiles when compared to monolithic (single solid rod) projectiles. For SRP with an aspect ratio (L/D) = 1/8, a loss in penetration efficiency was seen upon successive segment impacts. A numerical simulation impacting tungsten heavy alloy against RHA 4340 steel was performed using the Lagrangian finite element code EPIC 2006. The impact configuration that was modeled consisted of eight successive collinear impacts of discs measured 2mm in …
Analysis Of Wavelet Based Alternatives For Ofdm, Tassniem Rashed
Analysis Of Wavelet Based Alternatives For Ofdm, Tassniem Rashed
Electronic Theses and Dissertations
The objective of this thesis is to analyze wavelet based alternatives for orthogonal frequency division multiplexing (OFDM) and find whether a better system performance is achieved when compared to the discrete Fourier transform (DFT)-based OFDM. We analyze DFT, discrete wavelet transform (DWT), and dual tree complex wavelet transform (DT-CWT) based systems in an additive white Gaussian noise (AWGN) channel. The analysis is verified by Monte Carlo simulation. The results in the thesis indicate that the bit error probability (BEP) performance is the same for all types of systems. This confirms some results presented in the literature but differs from others. …
Smart Nanocoated Structure For Energy Harvesting At Low Frequency Vibration, Sudhanshu Sharma
Smart Nanocoated Structure For Energy Harvesting At Low Frequency Vibration, Sudhanshu Sharma
Electronic Theses and Dissertations
Increasing demands of energy which is cleaner and has an unlimited supply has led development in the field of energy harvesting. Piezoelectric materials can be used as a means of transforming ambient vibrations into electrical energy that can be stored and used to power other devices. With the recent surge of micro scale devices, piezoelectric power generation can provide a convenient alternative to traditional power sources. In this research, a piezoelectric power generator composite prototype was developed to maximize the power output of the system. A lead zirconate titanate (PZT) composite structure was formed and mounted on a cantilever bar …
A Fractal Analysis Of The Detection Of Glucose Molecules On Biosensor Surfaces, Lokesh Taneja
A Fractal Analysis Of The Detection Of Glucose Molecules On Biosensor Surfaces, Lokesh Taneja
Electronic Theses and Dissertations
A fractal analysis for the binding and dissociation of glucose molecules to different biosensor surfaces is presented. The sensors contain immobilized glucose oxidase enzymes that have an affinity for the glucose molecules in solution. Data for different modified biosensors is modeled and analyzed, and a single, dual or triple-fractal analysis is applied where adequate. The binding and dissociation kinetics coefficient where applicable are calculated for each of models along with the fractal dimensions. When both binding and dissociation phases are present, the affinity, K of the receptor to the glucose molecule is calculated and its variation with the fractal dimension …
Finite Element Modeling Of Seismic Wave Propagation In Earthen Embankments, Binyam Tadese
Finite Element Modeling Of Seismic Wave Propagation In Earthen Embankments, Binyam Tadese
Electronic Theses and Dissertations
The detection of internal seepage zones in embankments (dams and levees) by geophysical seismic techniques such as seismic refraction is limited by a number of factors. Some factors are associated with inversion and smoothing problems during processing, while others are associated with the natural characteristics of embankments and seepage anomalies. In this research, changes in the seismic response associated with: embankment soil compositions and moisture, characteristics of the seepage zone, presence of water in the reservoir, and shape of embankment was studied via 2D and 3D finite element (FE) embankment models. Artificial reflections from external boundaries and numerical dispersion were …
Thermal And Photochemical Interaction Of Co2 With Biochar, Eneruvie Uyoyou Okinedo
Thermal And Photochemical Interaction Of Co2 With Biochar, Eneruvie Uyoyou Okinedo
Electronic Theses and Dissertations
With interest in the changes that may occur to the carbonaceous portion of biochar obtain through the pyrolysis of biomass, the simple interaction between CO2 and biochar with water or a mixture of water and ethanol as hydrogen donor resulted in three significant observations. These reactions were carried out thermally at 333K and photochemically by simulating energy from the with a xenon lamp. The photochemical reaction involving biochar, CO2 with water or a mixture of water and ethanol as hydrogen donor led to a decrease in oxygen content of the parent biochar material, as observed by an increase in the …
Bacterial And Sediment Transport In An Artificial Sand Bed Stream During Unsteady Flow, Mary Alexandra Mccaskill
Bacterial And Sediment Transport In An Artificial Sand Bed Stream During Unsteady Flow, Mary Alexandra Mccaskill
Electronic Theses and Dissertations
Storms cause a substantial increase in the fecal indicator bacteria (FIB) concentrations in stream water. Causes for this concentration increase include FIB-laden stormwater runoff and the release of bacteria from stream-bottom sediments. Studies were carried out to quantify this second cause of water quality impairment. Coliform bacteria are a group of FIB, indicate the presence of pathogenic microorganisms, and have been shown to be transported in streams far from their source areas, especially during storms. FIB transport is dependent on several factors including water velocity, size and transport rates of bed sediments, and the FIB concentration in bed sediment. The …
Distributed Space-Time Message Relaying For Uncoded/Coded Wireless Cooperative Communications, Peng Huo
Distributed Space-Time Message Relaying For Uncoded/Coded Wireless Cooperative Communications, Peng Huo
Electronic Theses and Dissertations
During wireless communications, nodes can overhear other transmissions through the wireless medium, suggested by the broadcast nature of plane wave propagation, and may help to provide extra observations of the source signals to the destination. Modern research in wireless communications pays more attention to these extra observations which were formerly neglected within networks. Cooperative communication processes this abundant information existing at the surrounding nodes and retransmits towards the destination in various forms to create spatial and/or coding diversity, thereby to obtain higher throughput and reliability. The aim of this work is to design cooperative communication systems with distributed space-time block …
Virtual Worlds And Conservational Channel Evolution And Pollutant Transport Systems (Concepts), Chenchutta Denaye Jackson
Virtual Worlds And Conservational Channel Evolution And Pollutant Transport Systems (Concepts), Chenchutta Denaye Jackson
Electronic Theses and Dissertations
Many models exist that predict channel morphology. Channel morphology is defined as the change in geometric parameters of a river. Channel morphology is affected by many factors. Some of these factors are caused either by man or by nature. To combat the adverse effects that man and nature may cause to a water system, scientists and engineers develop stream rehabilitation plans. Stream rehabilitation as defined by Shields et al., states that "restoration is the return from a degraded ecosystem back to a close approximation of its remaining natural potential" [Shields et al., 2003]. Engineers construct plans that will restore streams …
Homogenization Of Structured Metasurfaces And Uniaxial Wire Medium Metamaterials For Microwave Applications, Chandra Sekhar Reddy Kaipa
Homogenization Of Structured Metasurfaces And Uniaxial Wire Medium Metamaterials For Microwave Applications, Chandra Sekhar Reddy Kaipa
Electronic Theses and Dissertations
In recent years, the study of electromagnetic wave interaction with artificial media has been the subject of intense research interest due to their extraordinary properties such as negative refraction, partial focusing, enhanced transmission, and spatial filtering, among others. Artificial media are crystals of various periodic metallic inclusions with dimensions of the order of ?/10 - ?/4. When compared to natural materials, the inclusions are, thus, not as small in terms of the wavelength, even in the optical band. Therefore, one should expect the electrodynamics of these media to be inherently non-local, characterized by strong spatial dispersion effects. The dissertation includes …
Submillisecond-Response Blue Phase Liquid Crystals For Display Applications, Kuan Ming Chen
Submillisecond-Response Blue Phase Liquid Crystals For Display Applications, Kuan Ming Chen
Electronic Theses and Dissertations
With exploding growth of information exchanges between people, display has become indispensable in our daily lives. After decades of intensive research and development in materials and devices, and massive investment in manufacturing technologies, liquid crystal display (LCD) has overcome various obstacles and achieved the performance we need, such as wide viewing angle, high contrast ratio, and high resolution, etc. These excellent performances make LCD prevailed in every perspective. Recently, with the demands of energy conservation, a greener LCD with lower power consumption is desired. In order to achieve this goal, new energy-effective driving methods, such as field sequential color display, …
Image Degradation Due To Surface Scattering In The Presence Of Aberrations, Narak Choi
Image Degradation Due To Surface Scattering In The Presence Of Aberrations, Narak Choi
Electronic Theses and Dissertations
This dissertation focuses on the scattering phenomena by well-polished optical mirror surfaces. Specifically, predicting image degradation by surface scatter from rough mirror surfaces for a two-mirror telescope operating at extremely short wavelengths (9nm~30nm) is performed. To evaluate image quality, surface scatter is predicted from the surface metrology data and the point spread function in the presence of both surface scatter and aberrations is calculated. For predicting the scattering intensity distribution, both numerical and analytic methods are considered. Among the numerous analytic methods, the small perturbation method (classical Rayleigh-Rice surface scatter theory), the Kirchhoff approximation method (classical BeckmanKirchhoff surface scatter theory), …
Injection-Locked Semiconductor Lasers For Realization Of Novel Rf Photonics Components, Nazanin Hoghooghi
Injection-Locked Semiconductor Lasers For Realization Of Novel Rf Photonics Components, Nazanin Hoghooghi
Electronic Theses and Dissertations
This dissertation details the work has been done on a novel resonant cavity linear interferometric modulator and a direct phase detector with channel filtering capability using injection-locked semiconductor lasers for applications in RF photonics. First, examples of optical systems whose performance can be greatly enhanced by using a linear intensity modulator are presented and existing linearized modulator designs are reviewed. The novel linear interferometric optical intensity modulator based on an injection-locked laser as an arcsine phase modulator is introduced and followed by numerical simulations of the phase and amplitude response of an injection-locked semiconductor laser. The numerical model is then …
A Production And Cost Modeling Methodology Of 2nd Generation Biofuel In The United States, David A. Poole
A Production And Cost Modeling Methodology Of 2nd Generation Biofuel In The United States, David A. Poole
Electronic Theses and Dissertations
The use of biofuels in the United States has increased dramatically in the last few years. The largest source of feedstock for ethanol to date has been corn. However, corn is also a vitally important food crop and is used commonly as feed for cattle and other livestock. To prevent further diversion of an important food crop to production of ethanol, there is great interest in developing commercial-scale technologies to make ethanol from non-food crops, or other suitable plant material. This is commonly referred to as biomass. A review is made of lignocellulosic sources being considered as feedstocks to produce …
Thermal Stability Characteristics Of Fisher-Tropsch And Hydroprocessed Alternative Aviation Fuels In A Fixed Bed Reactor, Sergio Quintero
Thermal Stability Characteristics Of Fisher-Tropsch And Hydroprocessed Alternative Aviation Fuels In A Fixed Bed Reactor, Sergio Quintero
Electronic Theses and Dissertations
Growing prices, limited supply, and public concern about greenhouse gases associated with crude-derived jet fuels have led to development of renewable alternatives which must be compatible with the worldwide civilian and military aviation infrastructure, which were designed for operation with Jet-A/JP-8. Any alternative fuel should not have negative effects on the aircraft engines and fuel systems, especially from a thermal stability perspective, since any adverse effect of the physical properties, and chemical composition, including existence of trace elements, of those fuels may only be revealed after extensive operation, resulting in higher life-cycle maintenance and operation costs. This study considered four …
Efficient And Scalable Evaluation Of Continuous, Spatio-Temporal Queries In Mobile Computing Environments, Jonathan M. Cazalas
Efficient And Scalable Evaluation Of Continuous, Spatio-Temporal Queries In Mobile Computing Environments, Jonathan M. Cazalas
Electronic Theses and Dissertations
A variety of research exists for the processing of continuous queries in large, mobile environments. Each method tries, in its own way, to address the computational bottleneck of constantly processing so many queries. For this research, we present a two-pronged approach at addressing this problem. Firstly, we introduce an efficient and scalable system for monitoring traditional, continuous queries by leveraging the parallel processing capability of the Graphics Processing Unit. We examine a naive CPU-based solution for continuous range-monitoring queries, and we then extend this system using the GPU. Additionally, with mobile communication devices becoming commodity, location-based services will become ubiquitous. …
Applications Of Volume Holographic Elements In High Power Fiber Lasers, Apurva Jain
Applications Of Volume Holographic Elements In High Power Fiber Lasers, Apurva Jain
Electronic Theses and Dissertations
The main objective of this thesis is to explore the use of volume holographic elements recorded in photo-thermo-refractive (PTR) glass for power scaling of narrow linewidth diffraction-limited fiber lasers to harness high average power and high brightness beams. Single fiber lasers enable kW level output powers limited by optical damage, thermal effects and non-linear effects. Output powers can be further scaled using large mode area fibers, however, at the cost of beam quality and instabilities due to the presence of higher order modes. The mechanisms limiting the performance of narrow-linewidth large mode area fiber lasers are investigated and solutions using …
Multiobjective Design Optimization Of Gas Turbine Blade With Emphasis On Internal Cooling, Narasimha Nagaiah
Multiobjective Design Optimization Of Gas Turbine Blade With Emphasis On Internal Cooling, Narasimha Nagaiah
Electronic Theses and Dissertations
In the design of mechanical components, numerical simulations and experimental methods are commonly used for design creation (or modification) and design optimization. However, a major challenge of using simulation and experimental methods is that they are timeconsuming and often cost-prohibitive for the designer. In addition, the simultaneous interactions between aerodynamic, thermodynamic and mechanical integrity objectives for a particular component or set of components are difficult to accurately characterize, even with the existing simulation tools and experimental methods. The current research and practice of using numerical simulations and experimental methods do little to address the simultaneous “satisficing” of multiple and often …