Engineering Commons^™

The Advancement Of Bacterial Cellulose As A Bone And Vascular Scaffolds, Ryan Lee Hammonds

Doctoral Dissertations

Bacterial cellulose (BC) is a natural hydrogel made of nanofibers. This material has been used in commercial products, including wound dressings. BC can be modified and optimized for improved performance in multiple applications. This work will focus on producing and characterizing resorbable cellulose, a composite for bone applications, and a composite for a synthetic venous valve leaflet.

BC can be produced and modified to perform as a degradable tissue scaffold. This is achieved by an oxidation procedure after the initial production and purification of native BC. A material characterization of oxidized BC was performed to identify the changes in properties …

A Viscous Flow Analog To Prandtl’S Optimized Lifting Line Theory Utilizing Rotating Biquadratic Bodies Of Revolution, Mark Nathaniel Callender

Doctoral Dissertations

Prandtl’s lifting line theory expanded the Kutta-Joukowski theorem to calculate the lift and induced drag of finite wings. The circulation distribution about a real wing was represented by a superposition of infinitesimal vortex filaments. From this theory, the optimum distribution of circulation was determined to be elliptical. A consequence of this theory led to the prediction that the elliptical chord distribution on a real fixed wing would provide the elliptical circulation distribution. The author applied the same line of reasoning to lift-producing rotating cylinders in order to determine the cylindrical geometry that would theoretically produce an elliptical circulation distribution. The …

Rural To Urban Intercity Transit User Characteristics Analysis, Demand Estimation And Network Design, Hongtai Yang

Doctoral Dissertations

Rural transit always plays a critical role in transporting rural residents, especially the ones who do not have a car, cannot drive, or choose not to drive. Intercity bus (ICB), deviated fixed route transit (DFRT) and demand responsive transit (DRT) are three major modes of rural public transportation. Although there are more DFRT and DRT service providers and services in the US, due to institutional issues, there are much more studies about ICB than DFRT and DRT. Meanwhile, state governments are struggling on how to improve the rural transit system with limited budget. This dissertation is aimed to fill the …

High Energy Synchrotron X-Ray Study Of Fatigue Damage In Amorphous And Polycrystalline Engineering Alloys, Chih-Pin Chuang

Doctoral Dissertations

The dissertation summarizes a series of studies on the fatigue damage of both amorphous and crystalline engineering alloys. The attention focuses on the utilization of synchrotron x-ray scattering related techniques for advanced material characterizations. In the first part of the research, critical issues regarding the mechanical response and structural evolution of Bulk-Metallic Glasses (BMGs) in the elastic region are addressed. The effects of cyclic-loading on the microstructures of an amorphous alloy are investigated, aiming to provide better mechanistic understandings of fatigue damage in BMGs. The second part of the research focuses on the characterization method based on two-dimensional X-ray diffraction …

Adsorption And Diffusion Of Gases In Nano-Porous Materials, Nethika Sahani Suraweera

Doctoral Dissertations

In this work, a systematic computational study directed toward developing a molecular-level understanding of gas adsorption and diffusion characteristics in nano-porous materials is presented. Two different types of porous adsorbents were studied, one crystalline and the other amorphous. Physisorption and diffusion of hydrogen in ten iso-reticular metal-organic frameworks (IRMOFs) were investigated. A set of nine adsorbents taken from a class of novel, amorphous nano-porous materials composed of spherosilicate building blocks and isolated metal sites was also studied, with attention paid to the adsorptive and diffusive behavior of hydrogen, methane, carbon dioxide and their binary mixtures. Both classes of materials were …

Analysis, Segmentation And Prediction Of Knee Cartilage Using Statistical Shape Models, Joseph Michael Johnson

Doctoral Dissertations

Osteoarthritis (OA) of the knee is one of the leading causes of chronic disability (along with the hip). Due to rising healthcare costs associated with OA, it is important to fully understand the disease and how it progresses in the knee. One symptom of knee OA is the degeneration of cartilage in the articulating knee. The cartilage pad plays a major role in painting the biomechanical picture of the knee. This work attempts to quantify the cartilage thickness of healthy male and female knees using statistical shape models (SSMs) for a deep knee bend activity. Additionally, novel cartilage segmentation from …

Understanding Mechanical And Fatigue Behavior Of A Wrought Magnesium Alloy Using In-Situ Neutron And Synchrotron X-Ray Diffraction, Wei Wu

Doctoral Dissertations

Magnesium (Mg) alloys have received great attentions in the past several decades, due to their unique properties of low density, high strength-to-weight ratio, and high specific stiffness. Previous work on fatigue behavior of Mg alloys typically relies on ex situ microstructural characterization and crack-growth monitoring with replica techniques. The primary challenge is thus the lack of an in situ, non-destructive measurement on microstructural length scales, which prevents us from linking the stress analyses (top-down point of view) to the failure mechanisms on inter- and intra-granular scales (bottom-up point of view). A unique opportunity that resolves many of these difficulties …

Chemical Vapor Deposition Of Heteroepitaxial Boron Phosphide Thin Films, John Daniel Brasfield

Doctoral Dissertations

Boron monophosphide (BP) is a group III-V compound semiconductor with a wide band gap of 2.3 eV. Its unique electrical properties make it a promising material for use as a room temperature thermal neutron detector and thermoelectric device in high temperature and radiation fields. A thin film of BP enriched in the boron-10 isotope can yield 2.8MeV of energy, which in solid-state BP can yield ∼0.5 million electron-hole pairs that would be detectable with minimal amplification in a device. The high carrier concentration, wide band gap, inertness and refractory nature make it an attractive material for use in the extreme …

Reconstruction Of Patient-Specific Bone Models From X-Ray Radiography, Hatem Amin Abdel Fattah El Dakhakhni

Doctoral Dissertations

The availability of a patient‐specific bone model has become an increasingly invaluable addition to orthopedic case evaluation and planning [1]. Utilized within a wide range of specialized visualization and analysis tools, such models provide unprecedented wealth of bone shape information previously unattainable using traditional radiographic imaging [2]. In this work, a novel bone reconstruction method from two or more x‐ray images is described. This method is superior to previous attempts in terms of accuracy and repeatability. The new technique accurately models the radiological scene in a way that eliminates the need for expensive multi‐planar radiographic imaging systems. It is also …

Development Of Si Device Based Power Converters For High Temperature Operation In Hev Applications, Zhuxian Xu

Doctoral Dissertations

In this dissertation, the feasibility of operating Si devices at 200 ˚C [degree Celsius] is investigated and the guidelines on the development of a high temperature Si converter for operating with 105 ˚C high temperature liquid coolant in hybrid electrical vehicle (HEV) applications are provided.

First, the characterization of a Si IGBT operating at 200 ˚C junction temperatures is presented. It is shown that the commercial 175 ˚C Si IGBT under test can be successfully switched at an elevated junction temperature of 200 ˚C with increased but acceptable losses.

Second, a comprehensive evaluation of Si IGBT ruggedness at high temperature …

Optimization Of Scintillator Based Radiation Portal Monitors, Matthew J. Urffer

Doctoral Dissertations

Alternative neutron detection technologies are needed to replace the current He- 3 based Radiation Portal Monitors (RPM) which are employed to detect special nuclear material that may be entering the United States illicitly. Replacement technologies must fulfill the following criteria established by the Department of Homeland Security (DHS): 1) a neutron detection efficiency, 2) a gamma insensitivity, and 3) the performance of the detector should not suffer in the presence of a strong gamma field. Polymeric films containing Li-6 ranging from 15 to 300 microns have the ability to fulfill these criteria if suitably utilized. For a typical detector material …

Synthesis, Basic Characterization, And Resonant Ultrasound Studies Of Novel Materials: Iron-Based Superconductors And Mo3sb7-Based Thermoelectrics, Lindsay Heatherly Vanbebber

Doctoral Dissertations

The elastic behavior of materials with unusual low-temperature behavior involving structural, magnetic, and superconducting transitions has been studied using Resonant Ultrasound Spectroscopy (RUS). Two classes of materials have been examined, namely, iron-based superconductors and thermoelectric materials. A series of BaFe2As2 materials as well as TlFe1.6Se2 comprise the former class, and a series of Mo3Sb7 materials is included in the latter.

The elastic behavior of BaFe2As2 reveals that a large softening is observed as the material approaches a tetragonal-to-orthorhombic structural transition accompanied by an antiferromagnetic ordering near 132K. This significant shear softening indicates that the structural transition is due to magnetically-driven …

Bond Performance Of High-Capacity Strands In High Strength Concrete, Xin Jiang

Doctoral Dissertations

18-mm-diameter (0.7-in.) strand has the ability to introduce almost twice the prestressing force of 13-mm-diameter (0.5-in.) strand and 135% of the prestressing force of 15-mm-diameter (0.6-in.) strand, which could result in a significant increase in the span capacity of the current AASHTO bulb tee girders without having to modify the sections or acquire new forms. To date, the information regarding the bond performance of 18-mm-diameter (0.7-in.) prestressing strand is very limited, preventing its application despite its attractive high-strength. Also, our understanding of the bond mechanism is incomplete and non-quantitative; a rational understanding of the bond mechanism would help predict the …

Membrane And Performance Study In Polymer Electrolyte Membrane Fuel Cells And Hydrogen Bromine Redox Flow Batteries, Yujia Bai

Doctoral Dissertations

This dissertation represents the consideration of the problems of polymer electrolyte membrane fuel cells (PEMFC) and hydrogen-bromine redox flow batteries (RFB). Due to the importance of water management in PEMFCs, all the experiments were strictly controlled at different water hydration conditions. Water uptake and densities were measured for Nafion^® and a series of 3M ionomer membranes. The thermodynamics of water and polymer was analyzed based on water uptake experiment and calorimetry. Furthermore, partial molar volumes (PMV) of water/membrane system was defined for the first time and used to analyze the interaction between water and polymers. Three states of water …

A Study About Aqueous Reversible Air Electrode- Catalyst, Electrolyte And Structure, Ming Qi

Doctoral Dissertations

Developing a better high energy density rechargeable battery has becoming critically important for several industries. For building such kind of battery, reversible air electrode has been widely accepted as one of the key components. One of the major challenges for reversible air electrode is finding a good bifunctional catalyst to greatly reduce the recharge overpotential and increase the system efficiency. To achieve this goal, a new air battery chemistry based on cobalt salen modified Au catalyst is proposed in this dissertation as a very promising solution. The unique catalytic activity of this catalyst is found to be a two electron …

Bedload Transport Sampling, Characterization And Modeling On A Southern Appalachian Ridge And Valley Stream, Patrick Lasater Mcmahon

Doctoral Dissertations

Estimates of bedload transport rates developed from existing transport models are notoriously inaccurate(Wilcock 2001). The gravel bed models addressed in this study include the Meyer-Peter and Muller; Parker, Klingeman, and McLean; and Wilcock two-fraction models. The question of whether or not these models predict bedload transport rates in a Southern Appalachian Ridge and Valley stream is complicated by the fact that these models have only been previously assessed in terms of their agreement with bedload transport rates measured in the Western regions of the U.S. Further, due to the strongly non-linear form of bedload transport models discrete errors and cumulative …

Shape Optimization Of Turbomachinery Blades Using An Adjoint Harmonic Balance Method, Huang Huang

Doctoral Dissertations

The high-dimensional harmonic balance (HDHB) method has recently become popular in the field of periodic unsteady flow prediction due to its accuracy and high efficiency. In the present dissertation research, two and three-dimensional parallelized computational fluid dynamic (CFD) codes based on the HDHB method are developed and validated for unsteady turbulent flows. It is found that the stability condition for an explicit solver is highly dependent on the reduced grid frequency, a non-dimensional parameter that depends on the grid size, characteristic wave speed, and the highest frequency retained in the harmonic balance solver. Furthermore, for certain moderately and highly nonlinear …

System Studies Of Fission-Fusion Hybrid Molten Salt Reactors, Robert D. Woolley

Doctoral Dissertations

This work proposes and evaluates a Fission-Fusion Hybrid Molten Salt Reactor (FFHMSR), combining two subsystems, a deuterium + tritium (DT) fusion reactor surrounded by a neutron-absorbing Fusion Blanket (FB) and a critical Molten Salt fission Reactor (MSR). The molten salt, which contains dissolved actinides, circulates at a high rate between them.

As envisioned the MSR exhibits the large Conversion Ratio of graphite moderated reactors having small fissile and large fertile inventories. DT fusion neutrons irradiating actinides in the molten salt release additional neutrons which increase isotope conversion and fission. Actinide fuel is continually added while fission products are continually removed …

Decoding The `Nature Encoded' Messages For Wireless Networked Control Systems, Shuping Gong

Doctoral Dissertations

Because of low installation and reconfiguration cost wireless communication has been widely applied in networked control system (NCS). NCS is a control system which uses multi-purpose shared network as communication medium to connect spatially distributed components of control system including sensors, actuator, and controller. The integration of wireless communication in NCS is challenging due to channel unreliability such as fading, shadowing, interference, mobility and receiver thermal noise leading to packet corruption, packet dropout and packet transmission delay. In this dissertation, the study is focused on the design of wireless receiver in order to exploit the redundancy in the system state, …

Monte Carlo And Depletion Reactor Analysis For High-Performance Computing Applications, Brenden Thomas Mervin

Doctoral Dissertations

This dissertation discusses the research and development for a coupled neutron trans- port/isotopic depletion capability for use in high-preformance computing applications. Accurate neutronics modeling and simulation for \real" reactor problems has been a long sought after goal in the computational community. A complementary \stretch goal" to this is the ability to perform full-core depletion analysis and spent fuel isotopic characterization. This dissertation thus presents the research and development of a coupled Monte Carlo transport/isotopic depletion implementation with the Exnihilo framework geared for high-performance computing architectures to enable neutronics analysis for full-core reactor problems.

An in-depth case study of the current …

Development Of A Monitoring Framework For The Detection Of Diversion Of Intermediate Products In A Generic Natural Uranium Conversion Plant, Jennifer L. Ladd-Lively

Doctoral Dissertations

The objective of this work is the development of an on-line monitoring and data analysis framework that could detect the diversion of intermediate products such as uranium dioxide, uranium tetrafluoride, and uranium hexafluoride in a natural uranium conversion plant (NUCP) using a multivariate statistical approach. This was an initial effort to determine the feasibility of this approach for safeguards applications. This study was limited to a 100 metric ton of uranium (MTU) per year NUCP using the wet solvent extraction method for the purification of uranium ore concentrate. A key component in the multivariate statistical methodology was the Principal Component …

Design And Development Of Seed Hydration Analyzing Device And Its Utilization In Studying Cereal And Legume Hydration, Vinay Kumar Mannam

Doctoral Dissertations

Cereals and legumes are important sources of vegetable-based human nutrition. Together they account for 48.6 % of protein and 8.7 % carbohydrate consumption around the world. During preparation, majority of these agricultural staples are re-hydrated to aid in their digestibility, palatability and the bio-availability of the nutrients.

Study of hydration kinetics of cereals and legumes is an important and valuable necessity for industry and academia to understand and gain insights into seed hydration characteristics. An automatic seed hydration analyzing system is developed as a solution for lack of instruments with broad capabilities to study variety of seed properties. The device …

Structure And Energetics Of Nanoparticles And Ionomer Films In Fuel Cell Catalyst Layers, Qianping He

Doctoral Dissertations

Improving the durability and utilization efficiency of the platinum-on-carbon (Pt/C) catalyst is of vital importance to the commercialization of the polymer electrolyte membrane fuel cell (PEMFC). This body of work provides molecular level insights to aid the fulfillment of this goal. Chapter 1 describes the use of molecular dynamics (MD) simulation in an effort to understand the Pt/C degradation issue from the nano-adhesion point of view. The roles of catalyst nanoparticle size, shape, Pt/C surface oxidation and the extent of ionomer film hydration are investigated to study their effects on nano-particle adhesion. It is found that the adhesion force strengthens …

Fundamental Studies Of Single Crystal Alpha Alumina Microstructures Produced By Irradiation With Zirconium Ions, Younes Sina

Doctoral Dissertations

This research has discovered the following new information:

a) The threshold fluence for amorphization of single crystal α-Al₂O₃ [alpha alumina] samples irradiated with 175 keV Zr⁺ [Zr+] ions at room temperature is 1.5×10¹⁶ [1.5E16] Zr/cm² [Zr+/cm2] which is a much lower fluence than the previously thought.

b) A buried amorphous layer sandwiched between two highly-damaged crystalline regions was observed in samples irradiated with 175 keV Zr⁺ to a fluence of 1.5×10¹⁶ Zr⁺/cm² and higher at room temperature.The amorphous region contains short range order similar to γ-Al₂O_{3 …}

Effects Of Data Resolution And Human Behavior On Large Scale Evacuation Simulations, Wei Lu

Doctoral Dissertations

Traffic Analysis Zones (TAZ) based macroscopic simulation studies are mostly applied in evacuation planning and operation areas. The large size in TAZ and aggregated information of macroscopic simulation underestimate the real evacuation performance. To take advantage of the high resolution demographic data LandScan USA (the zone size is much smaller than TAZ) and agent-based microscopic traffic simulation models, many new problems appeared and novel solutions are needed. A series of studies are conducted using LandScan USA Population Cells (LPC) data for evacuation assignments with different network configurations, travel demand models, and travelers’ compliance behavior.

First, a new Multiple-Source-Nearest-Destination Shortest Path …

Processing, Structure, And Properties Of Nanoparticle Reinforced Nonwoven Sandwich Composites, Josh Griffith Fogle

Doctoral Dissertations

Shockwaves produced from ballistic impacts and improvised explosive devices are capable of causing severe internal trauma to soldiers. Current antiballistic materials give adequate protection to soldiers from high velocity impacts, however they are insufficient at absorbing and dissipating shockwave energy generated by these impacts and explosive blasts. The goal of this research was to develop shockwave absorbing protective materials which can be used as liners in conjunction with current antiballistic materials by reinforcing thermoplastic polyurethane nonwovens with high modulus nanoparticles

To determine the appropriate TPU for the application, a series of TPUs of shore hardness ranging from 60D to 85A …

Bayesian Dictionary Learning For Single And Coupled Feature Spaces, Li He

Doctoral Dissertations

Over-complete bases offer the flexibility to represent much wider range of signals with more elementary basis atoms than signal dimension. The use of over-complete dictionaries for sparse representation has been a new trend recently and has increasingly become recognized as providing high performance for applications such as denoise, image super-resolution, inpaiting, compression, blind source separation and linear unmixing. This dissertation studies the dictionary learning for single or coupled feature spaces and its application in image restoration tasks. A Bayesian strategy using a beta process prior is applied to solve both problems.

Firstly, we illustrate how to generalize the existing beta …

Wide-Area Measurement And Applications In Power System Dynamic Modeling And Control, Yong Liu

Doctoral Dissertations

Synchrophasor has been becoming the foundational element of power grid wide-area measurement system (WAMS) since first developed in 1980s. By utilizing global positioning system (GPS) time synchronization technique, synchrophasors offer highly accurate time-synchronized phasor measurements that can provide system operators with real-time information of operation status.

Frequency disturbance recorders (FDRs) are installed on the distribution level to measure power system dynamics and considered as a type of single-phase synchrophasors. In this dissertation, a detailed procedure for the FDRs’ calibration is summarized and a preliminary test of their dynamic performance is carried out. Moreover, this dissertation investigates the impact of GPS …

All-Sic Three-Phase Converters For High Efficiency Applications, Fan Xu

Doctoral Dissertations

The dissertation aims to improve the efficiency of three-phase converters using SiC power devices.The methodology to design a high efficiency all-SiC three-phase converter is presented. Four aspects are included: SiC power device evaluation, power loop parasitics analysis, high efficiency current source rectifier, and paralleled current source rectifier system.

The SiC JFET and MOSFET are tested based on voltage source and current source structures respectively. The dissertation proposes a device switching test circuit based on current source topology to simulate current commutation processes. The circuit can evaluate the switching performance and calculate switching loss of a power device used in a …

A Tale Of Two Protein Switches: Engineering, Characterizing, And Understanding A Novel And A Natural Switch, James Vincent Price

Doctoral Dissertations

Throughout nature, many proteins provide a specific function in response to some input signal (e.g., phosyphorylation, pH, etc.), a process that is oftentimes described as switching a protein “on” or “off.” The advent of protein engineering has allowed for the creation and understanding of chimeric proteins for uses in a number of applications such as therapeutics, biosensors and energy production. Two proteins, hemagglutinin (HA) of fowl plague influenza virus and a chimeric protein comprising a fusion between the LFA-1 I domain and the EF3 and EF4 hands of calmodulin, have been investigated in this dissertation. Both of these proteins undergo …