Engineering Commons^™

Reliability Analysis Of Nanocrystal Embedded High-K Nonvolatile Memories, Chia-Han Yang

Doctoral Dissertations

The evolution of the MOSFET technology has been driven by the aggressive shrinkage of the device size to improve the device performance and to increase the circuit density. Currently, many research demonstrated that the continuous polycrystalline silicon film in the floating-gate dielectric could be replaced with nanocrystal (nc) embedded high-k thin film to minimize the charge loss due to the defective thin tunnel dielectric layer.

This research deals with both the statistical aspect of reliability and electrical aspect of reliability characterization as well. In this study, the Zr-doped HfO₂ (ZrHfO) high-k MOS capacitors, which separately contain the nanocrystalline zinc …

Extending Depth Of Field Via Multifocus Fusion, Harishwaran Hariharan

Doctoral Dissertations

In digital imaging systems, due to the nature of the optics involved, the depth of field is constricted in the field of view. Parts of the scene are in focus while others are defocused. Here, a framework of versatile data-driven application independent methods to extend the depth of field in digital imaging systems is presented. The principal contributions in this effort are the use of focal connectivity, the direct use of curvelets and features extracted by Empirical Mode Decomposition, namely Intrinsic Mode Images, for multifocus fusion. The input images are decomposed into focally connected components, peripheral and medial coefficients and …

Processing, Microstructures, And Properties Of Aluminide-Strengthened Ferritic Steels, Zhenke Teng

Doctoral Dissertations

NiAl-strengthened ferritic steel is a material of interest for steam turbine applications due to their promising creep resistance, high thermal conductivity, low cost and thermal expansion coefficient. However, there are two critical issues restricting their applications: low room temperature ductility and limited creep resistance at temperatures higher than 600°C. The reasons for these behaviors have not been fully understood, especially the processing-microstructure-property relationship has not been clearly identified.

The alloys were designed, fabricated, and processed, according to the required microstructures and properties. The matrix and precipitates can be thoroughly characterized by a combination of techniques, including atom probe tomography, neutron …

Computational And Experimental Study Of Structure-Property Relationships In Nial Precipitate-Strengthened Ferritic Superalloys, Shenyan Huang

Doctoral Dissertations

Ferritic superalloys strengthened by coherent ordered NiAl B2-type precipitates are promising candidates for ultra-supercritical steam-turbine applications, due to their superior resistance to creep, coarsening, oxidation, and steam corrosion as compared to Cr ferritic steels at high temperatures. Combined computational and experimental tools have been employed to investigate the interrelationships among the composition, microstructure, and mechanical behavior, and provide insight into deformation micromechanisms at elevated temperatures.

Self and impurity diffusivities in a body-centered-cubic (bcc) iron are calculated using first-principles methods. Calculated self and impurity diffusivities compare favorably with experimental measurements in both ferromagnetic and paramagnetic states of bcc Fe. The calculated …

Wide Baseline Stereo Image Rectification And Matching, Wei Hao

Doctoral Dissertations

Perception of depth information is central to three-dimensional (3D) vision problems. Stereopsis is an important passive vision technique for depth perception. Wide baseline stereo is a challenging problem that attracts much interest recently from both the theoretical and application perspectives. In this research we approach the problem of wide baseline stereo using the geometric and structural constraints within feature sets.

The major contribution of this dissertation is that we proposed and implemented a more efficient paradigm to handle the challenges introduced by perspective distortion in wide baseline stereo, compared to the state-of-the-art. To facilitate the paradigm, a new feature-matching algorithm …

Robust Multichannel Functional-Data-Analysis Methods For Data Recovery In Complex Systems, Jian Sun

Doctoral Dissertations

In recent years, Condition Monitoring (CM), which can be performed via several sensor channels, has been recognized as an effective paradigm for failure prevention of operational equipment or processes. However, the complexity caused by asynchronous data collection with different and/or time-varying sampling/transmission rates has long been a hindrance in the effective use of multichannel data in constructing empirical models. The problem becomes more challenging when sensor readings are incomplete. Traditional sensor data recovery techniques are often prohibited in asynchronous CM environments, not to mention sparse datasets. The proposed Functional Principal Component Analysis (FPCA) methodologies, e.g., nonparametric FPC model and semi-parametric …

Shear-Band Formation And Thermal Activation In Metallic Glasses, Lu Wang

Doctoral Dissertations

Metallic glasses (MGs) usually have high strength, high hardness and high elastic strain limit. However, the deformation mode and mechanism in metallic glasses are radically different from those in conventional crystalline materials with a long-range ordered structure. For crystalline materials, the intrinsic relationship between their mechanical properties and crystal structures has been well described by dislocation theory. In contrast, for amorphous materials, theories on the structures and controlling factors of localized shear-band formation are far from being complete.

In this thesis, shear-banding behavior of MGs under nanoindentation was first reviewed. The hardness of MGs was found to be independent on …

Micromechanical Studies Of Intergranular Strain And Lattice Misorientation Fields And Comparisons To Advanced Diffraction Measurements, Lili Zheng

Doctoral Dissertations

Inhomogeneous deformation fields arising from the grain-grain interactions in polycrystalline materials have been evaluated using a crystal plasticity finite element method and extensively compared to neutron diffraction measurements under fatigue crack growth conditions. The roles of intergranular deformation anisotropy, grain boundary damage, and non-common deformation mechanisms (such as twinning for hexagonal close packed crystals) are systematically evaluated. The lattice misorientation field can be used to determine the intragranular deformation behavior in polycrystals or to describe the deformation inhomogeneity due to dislocation plasticity in single crystals. The study of indentation-induced lattice misorientation fields in single crystals sheds lights on the understanding …

Nanoscale Metal Thin Film Dewetting Via Nanosecond Laser Melting: Understanding Instabilities And Materials Transport In Patterned Thin Films, Yueying Wu

Doctoral Dissertations

Nanoscale metal thin film dewetting via laser treatment is studied in this dissertation. The purpose is to understand: 1) the spatial and temporal nature of intrinsic instabilities; and 2) mass transportation involved in dewetting pattern evolution in metal thin films as well as in lithographically patterned nanostructures; and finally 3) to explore advanced control of metallic nanostructure fabrication via the confluence of top down nanolithography and pulsed laser induced dewetting. This study includes three sections. In first section, thin film Cu-Ni alloys ranging from 2-8nm were synthesized and laser irradiated. The evolution of the spinodal dewetting process is investigated as …

Design And Control Of High Power Density Motor Drive, Dong Jiang

Doctoral Dissertations

This dissertation aims at developing techniques to achieve high power density in motor drives under the performance requirements for transportation system. Four main factors influencing the power density are the main objects of the dissertation: devices, passive components, pulse width modulation (PWM) methods and motor control methods.

Firstly, the application of SiC devices could improve the power density of the motor drive. This dissertation developed a method of characterizing the SiC device performance in phase-leg with loss estimation, and claimed that with SiC Schottky Barrier Diode the advantage of SiC JFET could benefit the motor drive especially at high temperature. …

Wide-Area Situational Awareness Application Developments, Yanzhu Ye

Doctoral Dissertations

This dissertation expands the topics from the wide-area situational awareness application development, system architecture design, to power system disturbance analysis. All the works are grounded on the wide-area Frequency Monitoring Network (FNET). The FNET system takes GPS-synchronized wide-area measurements in a low-cost, easily deployable manner at 120V single-phase power outlet. These synchronized observations enables the monitoring of bulk power systems, and provides critical information for understanding power system disturbances and system operations.

Firstly, the work addresses the viability of angle measurement to serve different types of situational awareness applications, including the development of new angle-based event location estimation methods, the …

Modeling Chemical Degradation And Proton Transport In Perfluorosulfonic Acid Ionomers, Milan Kumar

Doctoral Dissertations

The ionomer-membrane interface in a membrane electrode assembly connects the catalyst and membrane and allows hydrated protons to move between the catalyst and membrane. The continuous operation of the polymer membrane electrolyte fuel cell at high temperature and/or in frequent freeze/thaw cycles leads to membrane degradation and delamination of the interface, which lower the proton conductivity. In this dissertation, we modeled the chemical degradation and proton conductivity of perfluorosulfonic acid (PFSA) ionomers by ab initio calculations and macroscopic modeling. All ab initio calculations were performed using Gaussian 03 suites of program by employing B3LYP/6-311++G** method/basis set. The macroscopic modeling involves …

Wide-Area Measurement Application And Power System Dynamics, Lang Chen

Doctoral Dissertations

Frequency monitoring network (FNET) is a GPS-synchronized distribution-level phasor measurement system. It is a powerful synchronized monitoring network for large-area power systems that provides significant information and data for power system situational awareness, real time and post-event analysis, and other important aspects of bulk systems. This work explored FNET measurements and utilized them for different applications and power system analysis.

An island system was built and validated with FNET measurements to study the stability of the OTEC integration. FNET measurements were also used to validate a large system model like the U.S. Eastern Interconnection. It tries to match the simulation …

Packaging Design Of Igbt Power Module Using Novel Switching Cells, Shengnan Li

Doctoral Dissertations

Parasitic inductance in power modules generates voltage spikes and current ringing during switching which cause extra stress in power electronic devices, increase electromagnetic interference (EMI), and degrade the performance of the power converter system. As newer power devices have faster switching speeds and higher power ratings, the effect of the parasitic inductance of the power module is more pronounced. This dissertation proposes a novel packaging method for power electronics modules based on the concepts of novel switching cells: P-cell and N-cell. It can reduce the stray inductance in the current commutation path in a phase-leg module and hence improve the …

Design Of Wireless Power Transfer And Data Telemetry System For Biomedical Applications, Ashraf Bin Islam

Doctoral Dissertations

With the advancement of biomedical instrumentation technologies sensor based remote healthcare monitoring system is gaining more attention day by day. In this system wearable and implantable sensors are placed outside or inside of the human body. Certain sensors are needed to be placed inside the human body to acquire the information on the vital physiological phenomena such as glucose, lactate, pH, oxygen, etc. These implantable sensors have associated circuits for sensor signal processing and data transmission. Powering the circuit is always a crucial design issue. Batteries cannot be used in implantable sensors which can come in contact with the blood …

Bioreactor System Designs For Lipase-Catalyzed Synthesis Of Saccharide- Fatty Acid Esters In Solvent-Free Media, Ran Ye

Doctoral Dissertations

As nontoxic biobased surfactants derived from plant oils and cellulose or starch, saccharide-fatty acid esters are widely used in cosmetics, food, and pharmaceutical industries due to their biocompatibility, biodegradability as well as antimicrobial activity. Generally, saccharide-fatty acid esters are synthesized chemically under high pressure, temperature and the presence of alkaline or acid catalysts leading to low-quality products (chemo-degradation of double bonds and oxygenated moieties) and large amounts of byproducts. In contrast, biocatalytic synthesis enhances sustainability: near-ambient pressure and temperature, the absence of toxic, acids and bases catalysts, and improved selectivity of products. For lipase-catalyzed synthesis under nearly anhydrous conditions, the …

Study Of Mechanical Behaviors And Structures Of Bulk Metallic Glasses With High-Energy Synchrotron X-Ray Diffraction, Feng Jiang

Doctoral Dissertations

This dissertation addresses two critical issues in the mechanical behaviors and structures of bulk-metallic glasses (BMGs): (1) the effect of composition, fabrication method, and pretreatment of plastic deformation on mechanical properties and structures of BMGs; (2) the mechanical response and structural evolution of BMGs in the elastic and plastic region.

(Cu₅₀Zr₅₀)₉₄Al₆ and (Cu₅₀Zr₅₀)₉₂Al₈ amorphous alloys were used to study the effect of composition on mechanical properties and structures of BMGs. The (Cu₅₀Zr₅₀)₉₄Al₆ alloy exhibits lower yield stress and Young’s …

Dynamics, Electromyography And Vibroarthrography As Non-Invasive Diagnostic Tools: Investigation Of The Patellofemoral Joint, Filip Leszko

Doctoral Dissertations

The knee joint plays an essential role in the human musculoskeletal system. It has evolved to withstand extreme loading conditions, while providing almost frictionless joint movement. However, its performance may be disrupted by disease, anatomical deformities, soft tissue imbalance or injury. Knee disorders are often puzzling, and accurate diagnosis may be challenging. Current evaluation approach is usually limited to a detailed interview with the patient, careful physical examination and radiographic imaging. The X-ray screening may reveal bone degeneration, but does not carry sufficient information of the soft tissue conditions. More advanced imaging tools such as MRI or CT are available, …

The Impact Of Change On System Of Systems Performance With An Application To Small And Medium Multihospital Systems, Karima Tayeb

Doctoral Dissertations

An entity that functions as a system of systems (SoS) is composed of multiple systems that individually provide various functions which collectively provide a holistic functional capability. It is complex in design and function and tends to become even more complex over time as it evolves and responds to both internal and external changes. These changes might be in the composition or in the interoperability among its system members. Since interoperability affects how well the members work as one system, managing it is critical to the performance of the SoS over its lifespan.

In support of this goal, this dissertation, …

Performance Controlled Power Optimization For Virtualized Internet Datacenters, Yefu Wang

Doctoral Dissertations

Modern data centers must provide performance assurance for complex system software such as web applications. In addition, the power consumption of data centers needs to be minimized to reduce operating costs and avoid system overheating. In recent years, more and more data centers start to adopt server virtualization strategies for resource sharing to reduce hardware and operating costs by consolidating applications previously running on multiple physical servers onto a single physical server. In this dissertation, several power efficient algorithms are proposed to effectively reduce server power consumption while achieving the required application-level performance for virtualized servers.

First, at the server …

Collaborative Solutions To Visual Sensor Networks, Mahmut Karakaya

Doctoral Dissertations

Visual sensor networks (VSNs) merge computer vision, image processing and wireless sensor network disciplines to solve problems in multi-camera applications in large surveillance areas. Although potentially powerful, VSNs also present unique challenges that could hinder their practical deployment because of the unique camera features including the extremely higher data rate, the directional sensing characteristics, and the existence of visual occlusions.

In this dissertation, we first present a collaborative approach for target localization in VSNs. Traditionally; the problem is solved by localizing targets at the intersections of the back-projected 2D cones of each target. However, the existence of visual occlusions among …

Dynamics Of Polymeric Solutions In Complex Kinematics Bulk And Free Surface Flows: Multiscale/Continuum Simulations And Experimental Studies, Arash Abedijaberi

Doctoral Dissertations

While rheological and microstructural complexities have posed tremendous challenges to researchers in developing first principles models and simulation techniques that can accurately and robustly predict the dynamical behaviour of polymeric flows, the past two decades have offered several significant advances towards accomplishing this goal. These accomplishments include: (1). Stable and accurate formulation of continuum-level viscoelastic constitutive models and their efficient implementation using operator splitting methods to explore steady and transient flows in complex geometries, (2). Prediction of rheology of polymer solutions and melts based on micromechanical models as well as highly parallel self-consistent multiscale simulations of non-homogeneous flows. The main …

Spatially-Dependent Reactor Kinetics And Supporting Physics Validation Studies At The High Flux Isotope Reactor, David Chandler

Doctoral Dissertations

The computational ability to accurately predict the dynamic behavior of a nuclear reactor core in response to reactivity-induced perturbations is an important subject in the field of reactor physics. Space-time and point kinetics methodologies were developed for the purpose of studying the transient-induced behavior of the Oak Ridge National Laboratory (ORNL) High Flux Isotope Reactor’s (HFIR) compact core. The space-time simulations employed the three-group neutron diffusion equations, which were solved via the COMSOL partial differential equation coefficient application mode. The point kinetics equations were solved with the PARET code and the COMSOL ordinary differential equation application mode. The basic nuclear …

Strong Spin Orbital Coupling Effect On Magnetic Field Response Generated By Intermolecular Excited States In Organic Semiconductors, Liang Yan

Doctoral Dissertations

It has been found that non-magnetic organic semiconductors can show some magnetic responses in low magnetic field (<100 >mT). When applying magnetic field, the electroluminescence, electrical current, photocurrent, and photoluminescence could change with magnetic field, which are called magnetic field effects.

Magnetic field effects are generated through spin-dependent process affected by the internal magnetic interaction. In nonmagnetic materials, hyperfine interaction has been supposed to dominantly affect the spin-dependent process recently. But the conclusion was made in weak spin-orbital coupling organic semiconductor. The hyperfine interaction might not be the main reason responsible for magnetic field effects in strong spin-orbital coupling materials. …

Discovery And Development Of Rare Earth Activated Binary Metal Halide Scintillators For Next Generation Radiation Detectors, Kan Yang

Doctoral Dissertations

This work focuses on discovery and development of novel binary halide scintillation materials for radiation detection applications. A complete laboratory for raw materials handling, ampoule preparation, material rapid synthesis screening, single crystal growth, sample cutting, polishing and packaging of hygroscopic halide scintillation materials has been established. Ce³⁺ and Eu²⁺ activated scintillators in three binary systems: Alkali Halide – Rare Earth Halide (AX–REX₃), Alkali Halide – Alkaline Earth Halide (AX–AEX₂) and Alkalin Earth Halide – Rare Earth Halide (AEX₂–REX₃) were systematically studied. Candidates for new scintillation materials in the three systems …

Behavior Of Externally Fiber-Reinforced Polymer Reinforced Shrinkage-Compensating Concrete Beams, Qi Cao

Doctoral Dissertations

The major cause of cracking in bridge decks, concrete pavements, as well as slabs on grade, is restrained shrinkage of the concrete. The resulting steel corrosion problem causes tremendous increase of maintenance and replacement cost. Shrinkage-compensating concrete (SHCC) and fiber-reinforced polymer (FRP) are explored to develop a hybrid slab system as one possible method of delaying the cracking and eliminating corrosion. To achieve the objective, a hybrid FRP reinforced SHCC structural system was developmed, and short-term and long-term behavior of this hybrid FRP-SHCC beams were investigated in this dissertation.

In the first-stage development, a series of “coffee can” tests were …

Development Of A Safeguards Monitoring System For Special Nuclear Facilities, James Joseph Henkel

Doctoral Dissertations

Two important issues related to nuclear materials safeguards are the continuous monitoring of nuclear processing facilities to verify that undeclared uranium is not processed or enriched and to verify that declared uranium is accounted for. The International Atomic Energy Agency (IAEA) is tasked with ensuring special nuclear facilities are operating as declared and that proper material safeguards have been followed. Traditional safeguards measures have relied on IAEA personnel inspecting each facility and verifying material with authenticated instrumentation.

In newer facilities most plant instrumentation data are collected electronically and stored in a central computer. Facilities collect this information for a variety …

Multi-Scale Modeling Of Polymeric Materials: An Atomistic And Coarse-Grained Molecular Dynamics Study, Qifei Wang

Doctoral Dissertations

Computational study of the structural, thermodynamic and transport properties of polymeric materials at equilibrium requires multi-scale modeling techniques due to processes occurring across a broad spectrum of time and length scales. Classical molecular-level simulation, such as Molecular Dynamics (MD), has proved very useful in the study of polymeric oligomers or short chains. However, there is a strong, nonlinear dependence of relaxation time with respect to chain length that requires the use of less computationally demanding techniques to describe the behavior of longer chains. As one of the mesoscale modeling techniques, Coarse-grained (CG) procedure has been developed recently to extend the …

Acoustic Emission And X-Ray Diffraction Techniques For The In Situ Study Of Electrochemical Energy Storage Materials, Kevin James Rhodes

Doctoral Dissertations

Current demands on lithium ion battery (LIB) technology include high capacity retention over a life time of many charge and discharge cycles. Maximizing battery longevity is still a major challenge partly due to electrode degradation as a function of repeated cycling. The intercalation of lithium ions into an active material causes the development of stress and strain in active electrode materials which can result in fracture and shifting that can in turn lead to capacity fade and eventual cell failure. The processes leading to active material degradation in cycling LIBs has been studied using a combination of acoustic emission (AE) …

Characterization And Modeling Of Toxic Fly Ash Constituents In The Environment, Zhenwei Zhu

Doctoral Dissertations

Coal fly ash is a by-product of coal combustion that has drawn renewed public scrutiny due to the negative environmental impacts from accidental release of this waste material from storage facilities. Historically, the leaching of toxic elements from coal fly ash into the environment has always been a major environmental concern. Despite extensive efforts into the characterization of coal fly ash, effective models for the fate and transport of toxic fly ash constituents have remained lacking, making it difficult to perform accurate environmental impact assessment for coal fly ash. To close this critical knowledge gap, the overall objective of this …