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Articles 6001 - 6030 of 11510
Full-Text Articles in Engineering
Solution Processed Cu(In,Ga)S2 Thin Film And Nanowire Photovoltaics, Johnthan Armstrong
Solution Processed Cu(In,Ga)S2 Thin Film And Nanowire Photovoltaics, Johnthan Armstrong
Theses and Dissertations
Solar energy conversion is a highly attractive process for clean and renewable power for the future. Cu(In,Ga)(Se,S)2/CdS/ZnO has proven itself to be a worthwhile photovoltaic combination achieving record efficiencies upwards of 20%. These record efficiencies have been obtained through vacuum-based approaches. However, the high cost of vacuum-based fabrication processes become a barrier to affordable solar cells as an energy source. As a result, solution-based approaches have become the focus of many studies which have achieved record efficiencies of 15%. These solution-based approaches have not matched up with the vacuum-based approaches. In this work, we investigate methods to improve the solution-based …
Myoelectric Prostheses: Novel Methodologies For Enhancing Usability And Control, Ghulam Rasool
Myoelectric Prostheses: Novel Methodologies For Enhancing Usability And Control, Ghulam Rasool
Theses and Dissertations
Control of powered prostheses using the information from leftover muscles in amputees is a challenging problem. I investigated the problem with a view to find clinically reliable and robust schemes that can interpret human intent and control a powered prosthesis in real-time. Recently, pattern classification systems have been suggested to map muscle activation patterns to the human intent (or the movement). However, due to the underlying generic structure, system-specific information cannot be exclusively incorporated into pattern classification algorithms. I have proposed two new methodologies in my research. The first one extended the pattern classification with a new feature set comprised …
Quantifying Individual Losses In A Direct Methanol Fuel Cell, Jennifer Rae Ruffing
Quantifying Individual Losses In A Direct Methanol Fuel Cell, Jennifer Rae Ruffing
Theses and Dissertations
The performance of a direct methanol fuel cell (DMFC) is complicated due to the complex interactions of kinetic and transport processes. As a result, changes in one aspect of the cell have consequences in other aspects, which are difficult to elucidate from the full-cell polarization (i.e. voltage vs. current) behavior that fuel cell researchers often use to characterize the performance of their systems. The objective of this work was to develop a strategy to use current and voltage relationships from anode half cells, cathode half-cells, and a hydrogen pump, coupled with methanol crossover data and a mathematical model, to quantify …
Quantitative Comparison Of Time-Frequency Decomposed Gait Emg Signals, L. Patrick Mitchell
Quantitative Comparison Of Time-Frequency Decomposed Gait Emg Signals, L. Patrick Mitchell
Theses and Dissertations
Falls in the senior population represent an immediate threat to both current and future generations’ quality of life. The results of falls can be disastrous, create a long road to recovery, and in many cases result in death. Hypertension represents a difficult-to-quantify condition which is known to contribute to gait and balance dysfunction. Accurate assessment of conditions such as these represents an area of primary investigative need. In order to meet this need, a new experimental setup is developed which combines time-frequency analysis with surface electromyography (sEMG) signals obtained during ambulation. 3-bit pressure data is acquired using a pressure-sensitive mat, …
Cost Avoidance Analysis Of Military Aircraft Components Utilizing Condition-Based Maintenance Practices, Erin Ballentine
Cost Avoidance Analysis Of Military Aircraft Components Utilizing Condition-Based Maintenance Practices, Erin Ballentine
Theses and Dissertations
This research involves two major case studies. Both look at the current maintenance practices done by the United States Army and propose a solution for improvement utilizing condition-based maintenance (CBM) practices. Each study details a cost avoidance that can be earned by implementing the solutions and the resulting benefits that can be experienced. Case Study I is a return on investment (ROI) that analyzes the benefits of the implementation of elastomeric wedges as vibration control on the Apache (AH-64D) aircraft. Analysis of the material and operational costs shows that the use of self-adhering elastomeric trailing edge wedges on the Apache …
Functionalized Graphitic Nanoreinforcement For Cement Composites, Nima Zohhadi
Functionalized Graphitic Nanoreinforcement For Cement Composites, Nima Zohhadi
Theses and Dissertations
Physical and mechanical properties of graphitic nanomaterials, in particular multiwalled carbon nanotubes (MWCNTs) and graphene nano-platelets (GNPs) make them promising candidates for nanoreinforcement of cement composites. The two key challenges associated with the incorporation of MWCNTs and GNPs are to attain uniform dispersion and interfacial bonding within the composite matrix. The effects of three main-stream dispersion techniques (namely, ultrasonication, acid-etching, and surfactant-coating) on the mechanical properties and microstructure of MWCNT- and GNP-cement composites were experimentally studied. Compressive strength tests and different characterization techniques including dynamic light scattering, Raman spectroscopy, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission …
Influence Of Defects In Epitaxial Graphene Towards Material Growth And Device Performances, Shamaita Shithi Shetu
Influence Of Defects In Epitaxial Graphene Towards Material Growth And Device Performances, Shamaita Shithi Shetu
Theses and Dissertations
Since its invention in 2004, Graphene, a two dimensional array of SP2 bonded carbon atoms has received significant interest by the scientific community due to its unique electrical, optical and mechanical properties. A promising route to the synthesis of large-area graphene, is epitaxial graphene formed by sublimation of silicon atoms from Silicon carbide at elevated temperatures (>1200oC). Although the electronic and mechanical properties of graphene with perfect atomic lattice are outstanding, the structural defects, which may appear during graphene growth, can influence the growth mechanism and material properties. However, deviations from perfection, i.e. introducing dopants in semiconductors often considered …
High Level Control Implementation For A Residential Smart Grid Power System, Hang Xu
High Level Control Implementation For A Residential Smart Grid Power System, Hang Xu
Theses and Dissertations
With the environment protection and energy usage efficiency promotion issues concerned more and more by governments and industries these days, smart grid technologies have been in rapid development. On this new technology stage, residential site power management system has become a star. This paper introduces the concept, development of two high level control methods for “Smart Green Power Node” (SGPN), solutions of demand side energy management system. One control algorithm is optimal model method which uses the predictive data of a battery model with electrical parameters and pricing methods, to keep scheduling the optimal control input on the receding time …
Application Of Various Adsorbents To Remove Micro-Pollutants In Aquatic System, Chanil Jung
Application Of Various Adsorbents To Remove Micro-Pollutants In Aquatic System, Chanil Jung
Theses and Dissertations
Untreated or insufficiently treated pharmaceuticals and endocrine disrupting compounds (EDCs) as well as heavy metals have influenced the ecosystem and their exposures in the water system have threatened human health; causing cancers and adverse health effect to immune system. While various water treatment techniques have been applied to solve this problem, adsorption has been considered as one of the most efficient and manageable water purification techniques. Advanced analysis methods for aqueous contaminants have improved comprehension, allowing proficiency about the fate of trace leveled emerging contaminants, thus allowed to reveal the adsorption mechanisms of each pollutant. This dissertation focuses on the …
Advanced Digital Signal Processing Based Redefined Power Quality Indices, And Their Applications To Wind Power, Md Moinul Islam
Advanced Digital Signal Processing Based Redefined Power Quality Indices, And Their Applications To Wind Power, Md Moinul Islam
Theses and Dissertations
This dissertation proposes a time-frequency distribution (TFD) based new method to redefine the power quality (PQ) indices for the assessment of PQ disturbances typically present in electric power systems. The redefined PQ indices are applied to various types of synthetic and real-world PQ disturbances in order to verify the efficacy and applicability of the proposed method. The case studies show that the proposed method provides actual results with respect to the existing TFD-based transient PQ indices, and provides much more accurate results than the traditional fast Fourier transform (FFT) based PQ indices under stationary and nonstationary PQ disturbances. In addition, …
High-Performance Meta-Genomic Gene Identification, Ibrahim Savran
High-Performance Meta-Genomic Gene Identification, Ibrahim Savran
Theses and Dissertations
Computational Genomics, or Computational Genetics, refers to the use of computational and statistical analysis for understanding the structure and the function of genetic material in organisms. The primary focus of research in computational genomics in the past three decades has been the understanding of genomes and their functional elements by analyzing biological sequence data. The high demand for low-cost sequencing has driven the development of highthroughput sequencing technologies, next-generation sequencing (NGS), that parallelize the sequencing process, producing thousands or millions of sequences concurrently. Moore’s Law is the observation that the number of transistors on integrated circuits doubles approximately every two …
Novel Biofabrication Technologies To Recapitulate In Vivo Geometries In Collagen Hydrogels, Veronica Rodriguez-Rivera
Novel Biofabrication Technologies To Recapitulate In Vivo Geometries In Collagen Hydrogels, Veronica Rodriguez-Rivera
Theses and Dissertations
Tissue engineering and regenerative medicine aims to restore form and function to tissues that have been lost or damaged due to disease, congenital defect, or trauma. Biomaterials suitable to restore these complex tissues need to provide a balance between chemical and mechanical properties, providing accurate cell-matrix interaction and induce in vivo behaviors such as proliferation, differentiation and migration. It also requires that physical and chemical cues be presented to the body in the proper temporal and spatial pattern. The extracellular matrix exerts forces that are transmitted through focal adhesion causing changes in the cell behavior. The hypothesis for this dissertation …
Low Reynolds Number Turbulence: Mechanisms And Applications, Wei Zhao
Low Reynolds Number Turbulence: Mechanisms And Applications, Wei Zhao
Theses and Dissertations
Turbulence, as one of "the most important unsolved classical problem in physics" (R. Feynman, 1932), has been investigated for more than 130 years. Conventionally, turbulence is believed to be a phenomenon of high Reynolds numbers (Re). However, we find that turbulence can also be achieved at low Re by proper external forcing, either in macroflows or in microflows. In macroflows, the characteristics of high Re turbulence can be achieved in confined flows, when the bulk flow Re is around 400, by external forcing at its optimal frequency (Wang 2003; Wang 2006). Interestingly, the optimal narrow band of frequency is fixed …
Surface Modification Of Nanoplatelets In Polymer Nanocomposites, Shailesh K. Shori
Surface Modification Of Nanoplatelets In Polymer Nanocomposites, Shailesh K. Shori
Theses and Dissertations
In polymer nanocomposites (PNCs), it is very important that the nanofiller (typically an inorganic) is well-dispersed in an organic polymer matrix. Optimal compatibility results in end-use products such as packaging materials with enhanced properties. In practice, however, this is challenging to achieve because “ideal” dispersions require the complete uniform separation, termed exfoliation, of the nanofiller within the matrix. As a result, different nanofillers including calcium niobate (CN) and montmorillonite (MMT) are first studied for their ability to exfoliate in aqueous suspensions by measuring the organic cation uptake. The cation exchange capacity, or CEC, determined that CN needs further work before …
Applications Of Advanced Imaging Methods: Macro-Scale Studies Of Woven Composites And Micro-Scale Measurements On Heated Ic Packages, Siming Guo
Theses and Dissertations
As a representative advanced imaging technique, the digital image correlation (DIC) method has been well established and widely used for deformation measurements in experimental mechanics. This methodology, both 2D and 3D, provides qualitative and quantitative information regarding the specimen’s non-uniform deformation response. Its full-field capabilities and non-contacting approach are especially advantageous when applied to heterogeneous material systems such as fiber-reinforced composites and integrated chip (IC) packages. To increase understanding of damage evolution in advanced composite material systems, a series of large deflection bending-compression experiments and model predictions have been performed for a woven glass-epoxy composite material system. Stereo digital image …
Practical Concurrency Support For Web Service Transactions, Emad Alsuwat
Practical Concurrency Support For Web Service Transactions, Emad Alsuwat
Theses and Dissertations
Traditional database concurrency control methods use locking, timestampordering, and optimistic-ordering to achieve DB consistency. However, these approaches are not suitable for long-running Web Service Compositions (WSCs) due to associated performance degradation. Our hypothesis asserts that, using transactional semantic and ordering information, the execution time of a WSC can be reduced, thus allowing the use of traditional database concurrency control methods while avoiding unacceptable performance degradation. Our solution is based on the following approaches: § We model a WSC as WS-BPEL specification, i.e., a partial order of WS transactions. § We allow some of the WS transactions in the WSC to …
Experimental And Theoretical Studies Of Native And Engineered Vascular Tissue Mechanics, Boran Zhou
Experimental And Theoretical Studies Of Native And Engineered Vascular Tissue Mechanics, Boran Zhou
Theses and Dissertations
Background: Implantation of vascular grafts provides a means to restore blood flow in compromised regions of the circulatory system, and thus is used to treat a wide range of cardiovascular diseases. Despite significant advancements in autologous grafting strategies as well as the engineering of synthetic alternatives, mechanical, structural, and compositional incongruities between the graft and the host artery remain as contributing factors to graft failure. The typical failure modality manifests as proximal anastomotic intimal hyperplasia, which places restrictions on the host vessel size currently treated with grafting strategies (> 5 mm internal diameter). In order to improve long-term clinical outcomes, …
Automated Scratchpad Mapping And Allocation For Embedded Processors, Yang Gao
Automated Scratchpad Mapping And Allocation For Embedded Processors, Yang Gao
Theses and Dissertations
Embedded system-on-chip processors such as the Texas Instruments C66 DSP and the IBM Cell provide the programmer with a software controlled on-chip memory to supplement a traditional but simple two-level cache. By decomposing data sets and their corresponding workload into small subsets that fit within this on-chip memory, the processor can potentially achieve equivalent or better performance, power efficiency, and area efficiency than with its sophisticated cache. However, program controlled on chip memory requires a shift in the responsibility for management and allocation from the hardware to the programmer. Specifically, this requires the explicit mapping of program arrays to specific …
Theoretical Investigation Of The Catalytic, Liquid-Phase Hydrodeoxygenation Of Organic Acids And Esters, Sina Behtash
Theoretical Investigation Of The Catalytic, Liquid-Phase Hydrodeoxygenation Of Organic Acids And Esters, Sina Behtash
Theses and Dissertations
With worldwide fossil fuel resources dwindling and greenhouse gas emissions rising, it is urgent to find renewable liquid fuel alternatives from e.g. biomass to meet the world’s growing energy demand. Lipid feedstocks and pyrolysis oils from woody biomass can be utilized for the production of second-generation biofuels via a catalytic hydrodeoxygenation (HDO) process. The conversion of fatty acids and esters plays an important role in the activity and selectivity of these processes. Understanding the HDO reaction mechanism of organic acids and esters on metal surfaces is a prerequisite for the rational design of new HDO catalysts specifically designed for upgrading …
Benefits Of Video Games In Multidisciplinary Scientific Research, Jeremiah Jeffrey Shepherd
Benefits Of Video Games In Multidisciplinary Scientific Research, Jeremiah Jeffrey Shepherd
Theses and Dissertations
In recent years, computer-based games have been shown to be effective both as a tool for conducting research in a variety of domains and for research on games itself. In this work, we show that implementing games that have a basis in theory and that are combined with the most recent gaming practices result in effective research tools. We demonstrate this via game implementations for three domains. The first implementation is based on new theories in speech pedagogy, and demonstrates the effectiveness of our approach. The second implementation shows that using a game that simulates therapeutic speech practices can aid …
Behavior Of Piezoelectric Wafer Active Sensor In Various Media, Tuncay Kamas
Behavior Of Piezoelectric Wafer Active Sensor In Various Media, Tuncay Kamas
Theses and Dissertations
The dissertation addresses structural health monitoring (SHM) techniques using ultrasonic waves generated by piezoelectric wafer active sensors (PWAS) with an emphasis on the development of theoretical models of standing harmonic waves and guided waves. The focal objective of the research is to extend the theoretical study of electro-mechanical coupled PWAS as a resonator/transducer that interacts with standing and traveling waves in various media through electro-mechanical impedance spectroscopy (EMIS) method and guided wave propagation. The analytical models are developed and the coupled field finite element analysis (CF-FEA) models are simulated and verified with experiments. The dissertation is divided into two parts …
Context-Sensitive Seismic Strengthening And Repair Of Substandard Confined Masonry, Rahim Ghorbani
Context-Sensitive Seismic Strengthening And Repair Of Substandard Confined Masonry, Rahim Ghorbani
Theses and Dissertations
Confined masonry (CM) is a construction system consisting of load-bearing masonry panels that are confined with cast-in-place reinforced concrete tie columns and beams. Due to satisfactory seismic performance, CM has become the predominant low-rise residential construction system in several areas around the world. However, in developing regions, the use of substandard materials, details and construction practices may result in inadequate performance as highlighted in the 2010 earthquakes in Haiti and Chile. In the aftermath of an earthquake, households are often reluctant to reoccupy their dwellings due to concerns about safety of structures. If feasible, preventive (pre-hazard) strengthening or structural repair …
Scheduling Of Container Handling Equipment In Marine Container Terminals, Narges Kaveshgar
Scheduling Of Container Handling Equipment In Marine Container Terminals, Narges Kaveshgar
Theses and Dissertations
To improve the competitiveness of marine container terminals, it is critical to minimize the makespan of a container vessel. The makespan is defined as the latest completion time among all handling tasks of the container vessel. Lower makespan (i.e. lower vessel turn time) can be achieved through better scheduling of the container handling equipment during vessel operations. The scheduling of terminal equipment is an operational problem, and a detailed schedule for each type of equipment operating in the terminal is necessary. Several studies have applied operations research techniques to optimize the processes of equipment in a terminal. This dissertation investigates …
Slow Wave Structures Integrated With Ferro-Magnetic And Ferro-Electric Thin Films For Smart Rf Applications, B M Farid Rahman
Slow Wave Structures Integrated With Ferro-Magnetic And Ferro-Electric Thin Films For Smart Rf Applications, B M Farid Rahman
Theses and Dissertations
Modern communications systems are following a common trend to increase the operational frequency, level of integration and number of frequency bands. Although 90-95% components in a cell phone are passives which take 80% of the total board area. High performance RF passive components play limited role and are desired towards this technological advancement. Slow wave structure is one of the most promising candidates to design compact RF and mm-Wave passive components. Slow wave structures are the specially designed transmission line realized by placing the alternate narrow and wide signal conductors in order to reduce the physical size of the components. …
Finite Element Analysis Simulations Of Micro And Nano-Electromechanical Sensors For Design Optimization, Nicholas Frank Deroller
Finite Element Analysis Simulations Of Micro And Nano-Electromechanical Sensors For Design Optimization, Nicholas Frank Deroller
Theses and Dissertations
Micro and Nano-electromechanical sensors (MEMS and NEMS) provide a means of actively sensing minute changes in the surrounding environment. Small changes in temperature, momentum, and strain may be sensed in passive modes while greater sensing possibilities exist in active modes. Theoretical femto-gram resolution mass detection and heated element sensing methods may be used while volatile organic compound (VOC) sensing may be achieved when combined with a functionalization layer or device heating. These devices offer a great reduction in cost and offer increased mobility by allowing a "lab-on-chip" solution for the prospective user while also greatly reducing the amount of energy …
Synthesis Of Au And Ag Catalysts With Controlled Sizes Of Metal Particles, Eleni A. Kyriakidou
Synthesis Of Au And Ag Catalysts With Controlled Sizes Of Metal Particles, Eleni A. Kyriakidou
Theses and Dissertations
The performance of supported metal catalysts largely depends on the structure and composition of the metal particles and the nature of the support. In order to achieve better control over these parameters, synthetic route based on the use of templating agents has been proposed. Among the different templating agents, poly(amidoamine) (PAMAM) dendrimers have attracted a lot of recent attention as nanoparticle stabilizers. In this thesis, Au/G4OH nanocomposites were synthesized in aqueous solutions and used as precursors for the preparation of SiO2-supported Au nanoparticles. Elemental analysis, UV-Vis, and STEM measurements were used to estimate the extent of the Au-dendrimer interactions and …
On The Development Of High Strain Rate Experiments For The Characterization Of Engineering Materials, Silas P. Mallon
On The Development Of High Strain Rate Experiments For The Characterization Of Engineering Materials, Silas P. Mallon
Theses and Dissertations
In order to predict the damage accumulation and failure processes associated with highly dynamic events such as blast loading, shock wave loading, and ballistic impact loading, a commensurate understanding of the fundamental constitutive and fracture behavior of materials subjected to such high rate loading conditions is necessary. In this effort, high strain rate experimental facilities consisting of a shock tube apparatus and a torsional split Hopkinson bar apparatus have been designed, constructed, and subsequently used to investigate the mechanical properties of an array of engineering materials subjected to a variety of dynamic loading conditions. Designs for the experimental equipment utilized …
Fabrication And Characterization Of Novel Electrodes For Solid Oxide Fuel Cell For Efficient Energy Conversion, Yu Chen
Theses and Dissertations
Solid oxide fuel cells (SOFCs) have been considered as one of the most promising technologies for future energy conversion since they can in principle be operated with fuels ranging from H2 to any hydrocarbon fuel. However, the system cost and coking (when using hydrocarbon as fuel) issues for the state-of-art electrode materials/designs often limit their further application. The objective of this Ph.D dissertation is aiming at overcoming these problems and accelerating SOFC commercialization. One approach to cost reduction is lowering the SOFC operating temperature to below 800 or even 600 oC, so that inexpensive materials can be used and quick …
Characterization Of Electrodeposited Copper Foil Surface Roughness For Accurate Conductor Power Loss Modeling, Michael B. Griesi
Characterization Of Electrodeposited Copper Foil Surface Roughness For Accurate Conductor Power Loss Modeling, Michael B. Griesi
Theses and Dissertations
As computer data rates have increased, designers observed that the standard models for estimating the impact of copper foil surface roughness on conductor loss are limited to a few GHz. The more recent snowball model (a “snowball” estimation of the Huray Model) has demonstrated improved conductor loss predictions up to 50 GHz by estimating the necessary parameters using reasonable assumptions about the geometric surface features of electrodeposited copper foil. Since then, the Huray Model has been incorporated into commercial electromagnetic field simulators. However, a standard method of characterizing the electrodeposited copper foil used in high-speed circuits to directly implement the …
Comprehensive Joint Time-Frequency Analysis Toward Condition Based Maintenance Regimes For Electrical And Mechanical Components, David Lee Coats
Comprehensive Joint Time-Frequency Analysis Toward Condition Based Maintenance Regimes For Electrical And Mechanical Components, David Lee Coats
Theses and Dissertations
Based upon a framework of time-frequency analysis, we outline condition based maintenance (CBM), or maintenance only upon evidence of need, for both electrical and mechanical systems. We apply novel time-frequency cross-correlation metrics to helicopter drivetrain systems and electrical cables as remaining useful life assessments by non-destructive and non-invasive tests. In both cases, these metrics for health assessment provide a basis for diagnostic and prognostic analysis of underlying systems and components by performing accelerated condition tests on actual mechanical and electrical systems. We present novel time-frequency domain vibration analysis of a gearbox failure in an AH-64 Apache drivetrain testbed and quantify …