Digital Commons Network^™

Graphite Aerogels And The Formation Mechanism Of Unusual Micron-Sized Rod And Helical Structures, Clarissa Ann Wisner

Doctoral Dissertations

"Pyrolysis at 800 ºC under argon has shown that polyimide (PI), polyacrylonitrile (PAN), polydicyclopentadiene (DCPD) and polybenzoxazine (PBO) aerogels are all viable alternatives to traditional resorcinol-formaldehyde (RF) aerogels as precursors to amorphous carbon aerogels. Subsequent high temperature pyrolysis at 2300 ºC of such carbon aerogels under helium has shown that amorphous carbon from PI and PBO yields the highest degree of graphitization, whereas from RF aerogels yields the lowest.

Those two types of graphite aerogels include also a high concentration of micron-size columnar and helical (screw-like) structures, whose formation is favored by macroporosity and high nitrogen retention in the 800 …

Investigation Of Fluids Flow Behavior In Nano-Scale Channels By Using Optic Imaging System, Qihua Wu

Doctoral Dissertations

"Tight gas and shale gas reservoirs are characterized to have small pores with diameters in nanometer (nm) range. The physics of fluid flow in nanopores is poorly understood. Knowing the fluid flow behavior in the nano-range channels is of major importance for stimulation design, gas production optimization and calculations of the relative permeability of gas in tight shale gas systems. In this work, a lab-on-chip approach for direct visualization of the fluid flow behavior in nano-scale channels was developed using an advanced epi-fluorescence microscopy method combined with a nano-fluidic chip. The nanofluidic chips with different dimensions were designed and fabricated. …

Preformed Particle Gel Transport Through Fractures, Hao Zhang

Doctoral Dissertations

"Polymer gel treatment is one of the most cost-effective methods to control water production in mature oil fields. The main objective of gel treatments is to reduce water or gas flow through high-permeability channels or fractures without damaging productive zones. Preformed particle gels (PPGs) have been applied for conformance control because they can overcome some potential drawbacks inherent in an in-situ gelation system.

In this study, lab experiments were performed to quantify PPG propagation through fractures and fracture-like channels by using screen models and open fracture models. The main findings in these experiments can guide the selection of best particle …

Seismic Anisotropy And Mantle Flow Beneath Africa And Arabia, Ahmed Abdalla Elsheikh

Doctoral Dissertations

"In spite of numerous studies, the mechanisms for the rifting, uplifting, and volcanism on the African plate remain enigmatic. The most popular hypotheses proposed for explaining these tectonic phenomena involve edge-driven small-scale mantle convection and the thermal or dynamic effects of one or more mantle plumes. In this study we use continental scale shear-wave splitting (SWS) measurements to provide additional constraints on the various models of rifting, uplifting, and volcanism of the Cameroon Volcanic Line (CVL) and the Arabian plate. The splitting of P-to-S converted phases at the core-mantle boundary on the receiver side (XKS including PKS, SKKS, and SKS) …

Sparse Nonlinear Optimization For Signal Processing And Communications, Zengli Yang

Doctoral Dissertations

"This dissertation proposes three classes of new sparse nonlinear optimization algorithms for network echo cancellation (NEC), 3-D synthetic aperture radar (SAR) image reconstruction, and adaptive turbo equalization in multiple-input multiple-output (MIMO) underwater acoustic (UWA) communications, respectively.

For NEC, the proposed two proportionate affine projection sign algorithms (APSAs) utilize the sparse nature of the network impulse response (NIR). Benefiting from the characteristics of l₁-norm optimization, affine projection, and proportionate matrix, the new algorithms are more robust to impulsive interferences and colored input than the conventional adaptive algorithms.

For 3-D SAR image reconstruction, the proposed two compressed sensing (CS) approaches exploit the …

Maximum Crosstalk Estimation And Modeling Of Electromagnetic Radiation From Pcb/High-Density Connector Interfaces, Matthew Scott Halligan

Doctoral Dissertations

"This dissertation explores two topics pertinent to electromagnetic compatibility research: maximum crosstalk estimation in weakly coupled transmission lines and modeling of electromagnetic radiation resulting from printed circuit board/high-density connector interfaces. Despite an ample supply of literature devoted to the study of crosstalk, little research has been performed to formulate maximum crosstalk estimates when signal lines are electrically long. Paper one illustrates a new maximum crosstalk estimate that is based on a mathematically rigorous, integral formulation, where the transmission lines can be lossy and in an inhomogeneous media. Paper two provides a thorough comparison and analysis of the newly derived maximum …

Cross-Layer Schemes For Performance Optimization In Wireless Networks, Quanmin Ye

Doctoral Dissertations

"Wireless networks are undergoing rapid progress and inspiring numerous applications. As the application of wireless networks becomes broader, they are expected to not only provide ubiquitous connectivity, but also support end users with certain service guarantees.

End-to-end delay is an important Quality of Service (QoS) metric in multihop wireless networks. This dissertation addresses how to minimize end-to-end delay through joint optimization of network layer routing and link layer scheduling. Two cross-layer schemes, a loosely coupled cross-layer scheme and a tightly coupled cross-layer scheme, are proposed. The two cross-layer schemes involve interference modeling in multihop wireless networks with omnidirectional antenna. In …

Synthesis And Properties Of Transition-Metal Arsenide Nanostructures: From Superparamagnetism To Superconductivity, Prachi Desai

Doctoral Dissertations

"This dissertation study focuses on developing new protocols for synthesis of nanostructured transition-metal pnictides including superconducting LiFeAs and studying their structure- property relationship. Nanostructured materials are known to differ in properties compared to their bulk counterparts owing to enhanced surface area and increased packing efficiency in devices. Synthetic chemistry skills and nanofabrication techniques like wet chemistry, electrodeposition, solvothermal, hydrothermal and lithography, are extremely useful for creating nanostructures of these functional materials. This is a challenging task simply because maintaining the phase composition same as that of the bulk material along with achieving nanostructures (nanoparticles, nanowires, nanopillars etc.) simultaneously is not …

Manufacturing Of Vegetable Oils-Based Epoxy And Composites For Structural Applications, Rongpeng Wang

Doctoral Dissertations

"Epoxidized vegetable oil (EVO) is one of the largest industrial applications of vegetable oils (VOs) and is widely used as a plasticizer and as a synthetic intermediate for polyol or unsaturated polyester. However, the utility of EVO as monomer for high performance epoxy thermoset polymer is limited by its reactivity and by the resulting physical properties. Herein, VO-based epoxy monomers, i.e., glycidyl esters of epoxidized fatty acids derived from soybean oil (EGS) or linseed oil (EGL), have been synthesized and were benchmarked against commercial available diglycidyl ether of bisphenol A (DGEBA) and also epoxidized soybean oil (ESO) controls. EGS and …

Energy Efficient And Latency Aware Adaptive Compression In Wireless Sensor Networks, Thomas Mark Daniel Szalapski

Doctoral Dissertations

"Wireless sensor networks are composed of a few to several thousand sensors deployed over an area or on specific objects to sense data and report that data back to a sink either directly or through a series of hops across other sensor nodes. There are many applications for wireless sensor networks including environment monitoring, wildlife tracking, security, structural heath monitoring, troop tracking, and many others. The sensors communicate wirelessly and are typically very small in size and powered by batteries. Wireless sensor networks are thus often constrained in bandwidth, processor speed, and power. Also, many wireless sensor network applications have …

Functionally Graded Ti6sl4v And Inconel 625 By Laser Metal Deposition, Syamala Rani Pulugurtha

Doctoral Dissertations

"The objective of the current work was to fabricate a crack-free functionally graded Ti6Al4V and Inconel 625 thin wall structure by Laser Metal Deposition (LMD). One potential application for the current material system is the ability to fabricate a functionally graded alloy that can be used in a space heat exchanger. The two alloys, Inconel 625 and Ti6Al4V are currently used for aerospace applications. They were chosen as candidates for grading because functionally grading those combines the properties of high strength/weight ratio of Ti6Al4V and high temperature oxidation resistance of Inconel 625 into one multifunctional material for the end application. …

Local Liquid Velocity Measurement Of Trickle Bed Reactor Using Digitial Industrial X-Ray Radiography, Khairul Anuar Mohd Salleh

Doctoral Dissertations

"Trickle Bed Reactors (TBRs) are fixed beds of particles in which both liquid and gas flow concurrently downward. They are widely used to produce not only fuels but also lubrication products. The measurement and the knowledge of local liquid velocities (VLL) in TBRs is less which is essential for advancing the understanding of its hydrodynamics and for validation computational fluid dynamics (CFD). Therefore, this work focused on developing a new, non-invasive, statistically reliable technique that can be used to measure local liquid velocity (V_LL) in two-dimensions (2-D). This is performed by combining Digital Industrial X-ray Radiography (DIR) and …

Modeling And Estimation Of Crosstalk Across A Channel With Multiple, Non-Parallel Coupling And Crossings Of Multiple Aggressors In Practical Pcbs, Arun Reddy Chada

Doctoral Dissertations

"In Section 1, the focus is on alleviating the modeling challenges by breaking the overall geometry into small, unique sections and using either a Full-Wave or fast equivalent per-unit-length (Eq. PUL) resistance, inductance, conductance, capacitance (RLGC) method or a partial element equivalent circuit (PEEC) for the broadside coupled traces that cross at an angle. The simulation challenge is resolved by seamlessly integrating the models into a statistical simulation tool that is able to quantify the eye opening at BERs that would help electrical designers in locating crosstalk sensitive regions in the high speed backplane channel designs.

Section 2 investigates the …

Privacy And Trustworthiness Management In Moving Object Environments, Sashi Gurung

Doctoral Dissertations

"The use of location-based services (LBS) (e.g., Intel's Thing Finder) is expanding. Besides the traditional centralized location-based services, distributed ones are also emerging due to the development of Vehicular Ad-hoc Networks (VANETs), a dynamic network which allows vehicles to communicate with one another. Due to the nature of the need of tracking users' locations, LBS have raised increasing concerns on users' location privacy. Although many research has been carried out for users to submit their locations anonymously, the collected anonymous location data may still be mapped to individuals when the adversary has related background knowledge.

To improve location privacy, in …

Dissolution Behavior Of Phosphate Glasses, Li Na Ma

Doctoral Dissertations

"The solubility of phosphate glasses in aqueous solutions can be tailored through compositional control to obtain a wide range of ion release rates required for a variety of applications. The principal objective of this dissertation is to advance the understanding of the dissolution behavior of phosphate glasses in aqueous environments.

Two families of glasses, sodium-iron phosphate (NFP) glasses and sodium-calcium phosphate (NCP) glasses, were evaluated. The dissolution behavior depends on the phosphate anions that constitute the glass structure and the associated metal (Me) cations. The phosphate glass structure, defined by the distribution and average size of phosphate anions and depending …

A Contingency Base Camp Framework Using Model Based Systems Engineering And Adaptive Agents, Dustin Scott Nottage

Doctoral Dissertations

"This research investigates the use of adaptive agents and hybridization of those agents to improve resource allocation in dynamic systems and environments. These agents are applied to contingency bases in an object oriented approach utilizing Model-based Systems Engineering (MBSE) processes and tools to accomplish these goals. Contingency bases provide the tools and resources for the military to perform missions effectively. There has been increasing interest in improving the sustainability and resilience of the camps, as inefficiencies in resource usage increases. The increase in resource usage leads to additional operational costs and added danger to military personnel guarding supply caravans.

The …

Probabilistic Engineering Analysis And Design Under Time-Dependent Uncertainty, Zhen Hu

Doctoral Dissertations

"Time-dependent uncertainties, such as time-variant stochastic loadings and random deterioration of material properties, are inherent in engineering applications. Not considering these uncertainties in the design process may result in catastrophic failures after the designed products are put into operation. Although significant progress has been made in probabilistic engineering design, quantifying and mitigating the effects of time-dependent uncertainty is still challenging. This dissertation aims to help build high reliability into products under time-dependent uncertainty by addressing two research issues. The first one is to efficiently and accurately predict the time-dependent reliability while the second one is to effectively design the time-dependent …

Modeling And Optimization Of Energy Storage System For Microgrid, Xin Qiu

Doctoral Dissertations

"The vanadium redox flow battery (VRB) is well suited for the applications of microgrid and renewable energy. This thesis will have a practical analysis of the battery itself and its application in microgrid systems. The first paper analyzes the VRB use in a microgrid system.

The first part of the paper develops a reduced order circuit model of the VRB and analyzes its experimental performance efficiency during deployment. The statistical methods and neural network approximation are used to estimate the system parameters. The second part of the paper addresses the implementation issues of the VRB application in a photovoltaic-based microgrid …

Energy Aware And Privacy Preserving Protocols For Ad Hoc Networks With Applications To Disaster Management, Mayank Raj

Doctoral Dissertations

"Disasters can have a serious impact on the functioning of communities and societies. Disaster management aims at providing efficient utilization of resources during pre-disaster (e.g. preparedness and prevention) and post-disaster (e.g. recovery and relief) scenarios to reduce the impact of disasters. Wireless sensors have been extensively used for early detection and prevention of disasters. However, the sensor's operating environment may not always be congenial to these applications. Attackers can observe the traffic flow in the network to determine the location of the sensors and exploit it. For example, in intrusion detection systems, the information can be used to identify coverage …

Investigation Of Projectile Coherence Effects In Fully Differential Studies Of 75 Kev Proton - H₂ Collisions, Sachin Sharma

Doctoral Dissertations

"Fully differential cross sections (FDCS) have been measured for single ionization of H₂ by 75 keV proton impact with varying transverse coherence length of the projectiles. As reported in recent years, the scattering angle dependence of the doubly differential cross sections (DDCS) are significantly affected by the projectile coherence properties. The interference structures were observed for the coherent beam, however were absent for an incoherent beam. Interestingly, the FDCS measurements for fixed momentum transfer do not suggest significant differences between the coherent and incoherent cross sections. However, for the FDCS with fixed recoil-ion momentum, clear differences between the two …

Thermal-Fluid Modeling Of The Missouri S&T Reactor, Susan Maria Sipaun

Doctoral Dissertations

"Thermal-fluid modeling of the Missouri University of Science and Technology Reactor (MSTR) was carried out using a computational fluid dynamics code (CFD), STAR-CCM+. First, a three-dimensional parallel-plate model was developed, and the cosine-shaped heat flux was applied to the MSTR core. Simulation results for fluid flow under natural convection condition show coolant temperature and velocity as a function of core power. A characteristic equation for the parallel-plate model was obtained based on Forchheimer's flow equation. The inertial resistance tensor and viscous resistance tensor were found to be 281005 kg/m^4 and 7121.6 kg/m^3 respectively. The MSTR core was then defined as …

Part I: In-Situ Fluorometric Quantification Of Microalgal Neutral Lipids Part Ii: Thermal Degradation Behavior Of Investment Casting Polymer Patterns, Hongfang Zhao

Doctoral Dissertations

"Research described in this dissertation covers two topics. Part-I is focused on in-situ determination of neutral lipid content of microalgae using a lipophilic fluorescent dye. The traditional Nile red stain-based method for detecting microalgal intracellular lipids is limited due to varying composition and thickness of rigid cell walls. In this study, the addition of dilute acid and heating of solution, were found to greatly enhance staining efficiency of Nile red for microalgal species evaluated. Oil-in-water (O/W) microemulsion stabilized by a non-ionic surfactant was employed as a pseudo-standard that mimics lipid-bearing microalgal cells suspended in water. The average neutral lipid contents …

Semiconductor Nanocrystals For Novel Optical Applications, Jong-Sik Moon

Doctoral Dissertations

“Inspired by the promise of enhanced spectral response, photorefractive polymeric composites photosensitized with semiconductor nanocrystals have emerged as an important class of materials. Here, we report on the photosensitization of photorefractive polymeric composites at visible wavelengths through the inclusion of narrow band-gap semiconductor nanocrystals composed of PbS. Through this approach, internal diffraction efficiencies in excess of 82%, two-beam-coupling gain coefficients in excess of 211 cm^-1, and response times 34 ms have been observed, representing some of the best figures-of-merit reported on this class of materials. In addition to providing efficient photosensitization, however, extensive studies of these hybrid composites …

Advanced Active Rectifiers For Electric Vehicle Battery Charging, Darren Lee Paschedag

Doctoral Dissertations

"In a big picture sense, the work presented in this dissertation is in the area of fully electric or plug-in hybrid electric vehicles. Both of these vehicle types require an external power source to fully charge their large amount of energy storage. For most consumers this means plugging their vehicle into the utility which necessitates battery charging circuitry. More specifically, this dissertation focuses on the power factor correction (PFC) circuit which makes up one part of a typical battery charging system. The circuits presented here are not dependent on battery chemistry, so they can be utilized with all popular chemistries …

Modeling And Simulation Of Continuous Fiber-Reinforced Ceramic Composites, Venkata Bheemreddy

Doctoral Dissertations

"Finite element modeling framework based on cohesive damage modeling, constitutive material behavior using user-material subroutines, and extended finite element method (XFEM), are developed for studying the failure behavior of continuous fiber-reinforced ceramic matrix composites (CFCCs) by the example of a silicon carbide matrix reinforced with silicon carbide fiber (SiC/SiCf) composite. This work deals with developing comprehensive numerical models for three problems: (1) fiber/matrix interface debonding and fiber pull-out, (2) mechanical behavior of a CFCC using a representative volume element (RVE) approach, and (3) microstructure image-based modeling of a CFCC using object oriented finite element analysis (OOF). Load versus displacement behavior …

Bioactive Glass/Polymer Composites For Bone And Nerve Repair And Regeneration, Ali Mohammadkhah

Doctoral Dissertations

"Bioactive glasses have several attractive properties in hard and soft tissue repair but their brittleness limited their use, as scaffolding materials, for applications in load- bearing hard tissue repair. At the same time, because of their bioactive properties, they are being studied more often for soft tissue repair. In the present work, a new glass/polymer composite scaffold was developed for the repair of load-bearing bones with high flexural strength and without brittle behavior. The new composites have 2.5 times higher flexural strength and ~100 times higher work of fracture (without catastrophic failure) compared to a similar bare glass scaffold.

Also …

Electric-Drive Vehicle Emulation Using Advanced Test Bench, Poria Fajri

Doctoral Dissertations

"Vehicle electrification is considered to be the most promising approach toward addressing the concerns on climate change, sustainability, and rapid depletion of fossil fuel resources. As a result electric-drive vehicle (EDV) technology is becoming the subject of many research studies, from academia and research laboratories to automotive industries and their suppliers. However, a crucial step toward the success of EDV implementation is developing test platforms that closely emulate the behavior of these vehicles.

In this dissertation, a new approach for emulating an EDV system on a motor/dynamometer test bench is investigated. Two different methods of emulation are discussed which are …

Automated Classification Of Malignant Melanoma Based On Detection Of Atypical Pigment Network In Dermoscopy Images Of Skin Lesions, Nabin K. Mishra

Doctoral Dissertations

“Melanoma causes more deaths than any other form of skin cancer. Early melanoma detection is important to prevent progression to a more deadly stage. Automated computer-based identification of melanoma from dermoscopic images of skin lesions is the most efficient method in early diagnosis. An automated melanoma identification system must include multiple steps, involving lesion segmentation, feature extraction, feature combination and classification. In this research, a classifier-based approach for automatically selecting a lesion border mask for segmentation of dermoscopic skin lesion images is presented. A logistic regression based model selects a single lesion border mask from multiple border masks generated by …

Degradable Nanocomposite Preformed Particle Gel For Chemical Enhanced Oil Recovery Applications, Paul Tongwa

Doctoral Dissertations

”This work presents two new materials that can be potentially used in conformance control to increase ultimate oil recovery from mature oilfields.

The first product is a degradable nanocomposite preformed particle gel for enhanced in-depth mobility control. Three different types of degradable nanocomposite preformed particle gels were synthesized. These three nanocomposite hydrogels were made using Laponite XLG, Calcium Montmorillonite, and Sodium Montmorillonite nanomaterials. It was observed that after degradation, Laponite XLG nanocomposite hydrogels had the highest post-degradation viscosity (4437 cp), followed by sodium nanocomposite hydrogels (129 cp), and lastly calcium nanocomposite hydrogels (75.5 cp). Thus, degradable Laponite XLG nanocomposite hydrogels …

Multiple Security Domain Nondeducibility In Cyber-Physical Systems, Gerry W. Howser

Doctoral Dissertations

"Cyber-physical Systems (CPS) present special problems for security. This dissertation examines the cyber security problem, the physical security problem, the security problems presented when cyber systems and physical systems are intertwined, and problems presented by the fact that CPS leak information simply by being observed. The issues presented by applying traditional cyber security to CPS are explored and some of the shortcomings of these models are noted. Specific models of a "drive-by-wire'' automobile connected to a road side assistance network, a "Stuxnet type'' attack, the smart grid, and others are presented in detail.

The lack of good tools for CPS …