Digital Commons Network^™

Optimal Design And Freeform Extrusion Fabrication Of Functionally Gradient Smart Parts, Amir Ghazanfari

Doctoral Dissertations

"An extrusion-based additive manufacturing process, called the Ceramic On-Demand Extrusion (CODE) process, for producing three-dimensional ceramic components with near theoretical density was developed. In this process, an aqueous paste of ceramic particles with a very low binder content (<1 vol%) is extruded through a moving nozzle at room temperature. After a layer is deposited, it is surrounded by oil (to a level just below the top surface of most recent layer) to preclude non-uniform evaporation from the sides. Infrared radiation is then used to partially, and uniformly, dry the just-deposited layer so that the yield stress of the paste increases and the part maintains its shape. The same procedure is repeated for every layer until part fabrication is completed. Sample parts made of alumina and fully stabilized zirconia were produced using this process and their mechanical properties including density, strength, Young's modulus, Weibull modulus, toughness, and hardness were examined. Microstructural evaluation was also performed to measure the grain size, and critical flaw sizes were obtained. The results indicate that the proposed method enables fabrication of geometrically complex parts with superior mechanical properties. Furthermore, several methods were developed to increase the productivity of the CODE process and enable manufacturing of functionally graded materials with an optimum distribution of material composition. As an application of the CODE process, advanced ceramic components with embedded sapphire optical fiber sensors were fabricated and properties of parts and sensors were evaluated using standard test methods"--Abstract, page iv.

Receiver Function Imaging Of Mantle Transition Zone Discontinuities Beneath Alaska, Haider Hassan Faraj Dahm

Doctoral Dissertations

"Subduction of tectonic plates is one of the most important tectonic processes, yet many aspects of subduction zone geodynamics remain unsolved and poorly understood, such as the depth extent of the subducted slab and its geometry. The Alaska subduction zone, which is associated with the subduction of the Pacific Plate beneath the North America plate, has a complex tectonic setting and carries a series of subduction episodes, and represents an excellent target to study such plate tectonic processes. Previous seismological studies in Alaska have proposed different depth estimations and geometry for the subducted slab. The Mantle transition zone discontinuities of …

Gamma Spectroscopy By Artificial Neural Network Coupled With Mcnp, Huseyin Sahiner

Doctoral Dissertations

"While neutron activation analysis is widely used in many areas, sensitivity of the analysis depends on how the analysis is conducted. Even though the sensitivity of the techniques carries error, compared to chemical analysis, its range is in parts per million or sometimes billion. Due to this sensitivity, the use of neutron activation analysis becomes important when analyzing bio-samples. Artificial neural network is an attractive technique for complex systems. Although there are neural network applications on spectral analysis, training by simulated data to analyze experimental data has not been made. This study offers an improvement on spectral analysis and optimization …

Reliability Prediction In Early Design Stages, Yao Cheng

Doctoral Dissertations

"In the past, reliability is usually quantified with sufficient information available. This is not only time-consuming and cost-expensive, but also too late for occurred failures and losses. For solving this problem, the objective of this dissertation is to predict product reliability in early design stages with limited information. The current research of early reliability prediction is far from mature. Inspired by methodologies for the detail design stage, this research uses statistics-based and physics-based methodologies by providing general models with quantitative results, which could help design for reliability and decision making during the early design stage. New methodologies which accommodate component …

Studies On Neutron Diffraction And X-Ray Radiography For Material Inspection, Fahima Fahmida Islam

Doctoral Dissertations

"Among the different probes to study the structures of the bio and structural materials, X-ray and neutron are widely used because of their distinctive usefulness in investigating different structures. X-ray radiography and neutron diffraction are two widely known non-destructive techniques for material inspection. Here we demonstrate the design of neutron diffractometer with low power source and analyze the digital image produced by the X-ray radiography instead of neutron diffraction because of the availability of the data. Neutron diffraction is a powerful tool for understanding the behavior of crystal structures and phase behaviors of materials. While neutron diffraction capabilities continue to …

Durability Behavior Of Fiber Reinforced Polymer And Steel Reinforced Polymer For Infrastructure Applications, Wei Wang

Doctoral Dissertations

"Crack development in reinforced concrete (RC) structures is common in elements such as bridge decks. However, these cracks can impose significant problems over time, because they allow chlorides from deicing chemicals to infiltrate concrete which will then corrode steel bars as RC structures are exposed to harsh weather. In the last decade, composite reinforcement systems are internally or externally applied to concrete structures instead of traditional steel reinforcing bars, or to strengthen concrete elements in flexure and shear. However, studies regarding the long-term durability performance of composite reinforcement systems is limited. Therefore, in order to popularize the application of these …

Experimental Study Of Natural Convection Heat Transfer And Gaseous Dynamics From Dual-Channel Circulation Loop, Ibrahim Ahmed Said Abdallah

Doctoral Dissertations

"This research focuses on establishing a range of scaled separate and integral effects experiments for studying thermal-hydraulic behavior occurring within a component or region of the prismatic very high-temperature reactor (VHTR) such as plenum-to-plenum heat transfer and gaseous dynamics during natural circulation. Natural circulation of the coolant is the leading capability for VHTR to transport the decay heat from the core to the reactor vessel during accident scenarios. To address this need, a scaled-down facility is designed and developed with only two channels with upper and lower plena. The emphasis is placed on high-resolution and high-fidelity experimental data for local …

Development Of Active Microwave Thermography For Structural Health Monitoring, Ali Foudazi

Doctoral Dissertations

"Active Microwave Thermography (AMT) is an integrated nondestructive testing and evaluation (NDT&E) method that incorporates aspects of microwave NDT and thermography techniques. AMT uses a microwave excitation to generate heat and the surface thermal profile of the material or structure under test is subsequently measured using a thermal camera (or IR camera). Utilizing a microwave heat excitation provides advantages over traditional thermal excitations (heat lamps, etc.) including the potential for non-contact, selective and focused heating. During an AMT inspection, two heating mechanisms are possible, referred to as dielectric and induction heating. Dielectric heating occurs as a result of the interaction …

Theoretical Calculations For Electron Impact Ionization Of Atoms And Molecules, Sadek Mohamed Fituri Amami

Doctoral Dissertations

"In the last twenty years, significant progress has been made for the theoretical treatment of electron impact ionization (e,2e) of atoms and molecules and, for some cases, very nice agreement between experiment and theory has been achieved. In particular, excellent agreement between theory and experiment and theory has been achieved for ionization of hydrogen and helium. However, agreement between experiment and theory is not nearly as good for ionization of larger atoms and molecules. In the first part of this dissertation, different theoretical approaches will be employed to study the triply differential cross section (TDCS) for low and intermediate energy …

Advanced Control Architectures For Grid Connected And Standalone Converter Systems, Subhajyoti Mukherjee

Doctoral Dissertations

"This dissertation proposes new control algorithms dedicated towards improving the reliability, computational burden and stability in grid-connected and stand-alone based power electronic converter systems applicable for ac microgrids.

Two voltage sensorless control architectures, one for stand-alone applications and the other for grid-connected application are established in this thesis. The output voltage of a standalone single-phase inverter is controlled directly by controlling the output filter capacitor current without using a dedicated output voltage sensor. A method to estimate the output filter capacitance is also presented. For the grid connected converter, a novel closed loop estimation is presented to estimate the grid …

Optimization Of Solvent Suppression Sequences For Nmr Analysis Of Aqueous Solutions, Annalise Rose Pfaff

Doctoral Dissertations

"When the use of deuterated solvents is precluded in the NMR analysis of biomolecules in their natural environment, pre-saturation solvent suppression pulse sequences are frequently employed to avoid interference from the overbearing solvent signal. However, these sequences generally require extensive re-adjustment of NMR parameters between samples. For this reason, the EXCEPT (EXponentially Converging Eradication Pulse Train) solvent suppression sequence was developed, which exhibits a tolerance of over an order of magnitude in sample T₁ variation. EXCEPT uses an innovative version of "inversion-recovery nulling" with frequency-selective, low-power adiabatic pulses and exponentially decreasing interpulse delays that effectively reduce solvent net magnetization by …

Characterizing Long-Term Groundwater Conditions And Lithology For The Design Of Large-Scale Borehole Heat Exchangers, David Charles Smith

Doctoral Dissertations

"Construction of large scale ground coupled heat pump (GCHP) systems that operate with hundreds or even thousands of boreholes for the borehole heat exchangers (BHE) has increased in recent years with many coming on line in the past 10 years. Many large institutions are constructing these systems because of their ability to store energy in the subsurface for indoor cooling during the warm summer months and extract that energy for heating during the cool winter months.

Despite the increase in GCHP system systems constructed, there have been few long term studies on how these large systems interact with the subsurface. …

Real-Time Diesel Particulate Matter Monitoring In Underground Mine Atmospheres, Association With The Standard Method And Related Challenges, Muhammad Usman Khan

Doctoral Dissertations

"Diesel-powered equipment is a significant component of underground mining operations. Miners' exposure to diesel exhaust is harmful. The standard Diesel Particulate Matter (DPM) monitoring method (NIOSH 5040 method) has limitations that preclude rapid DPM estimation and detailed understanding of DPM variations over time. However, real-time DPM monitors do not inherit these limitations. Biodiesel is often used as a substitute for regular petroleum-diesel because of its ability to emit less DPM. However, accuracy of available real-time DPM monitors has not been determined in mines using 70% to 99% (high-percent) biodiesel. The present research addresses this need by rigorous testing of a …

Impact Of Vertical Internals On The Hydrodynamics And Heat Transfer Coefficient In A Gas-Solid Fluidized Bed, Haidar Moafaq Taofeeq

Doctoral Dissertations

"This research studied the impact of the dense vertical immersed heat exchanging tubes on the gas and solids hydrodynamic characteristics, flow regime, pressure drop, and heat transfer in a 0.14 m inside diameter gas-solid fluidized bed column of. Two sizes of vertical internal tube bundles (0.0127 and 0.0254 m) of circular arrangement have been implemented to represent the heat exchange tubes covering 25% of the column cross-sectional area. The experimental work was achieved at different operating conditions and various solids particle types that differ in average particle size, solids density, particles shape, and particles sphericity. The experimental measurements were performed …

Design And Performance Of Cost-Effective Ultra High Performance Concrete For Bridge Deck Overlays, Mahdi Valipour

Doctoral Dissertations

"The main objective of this research is to develop a cost-effective ultra-high performance concrete (UHPC) for bonded bridge deck overlays. The high durability and mechanical properties of such repair material can offer shorter traffic closures and prolong the service life of the pavement. The UHPC was optimized using supplementary cementitious materials (SCMs), proper combinations of sands, and adequate selection of fiber types and contents. Packing density studies included paste, sand, and fiber combinations. The robustness of optimized UHPC mixtures to variations of mixing and curing temperatures was examined. The efficiency of various shrinkage mitigation approaches in reducing autogenous and drying …

Characterization And Numerical Simulation Of The Microstructural And Micromechanical Viscoelastic Behavior Of Oil Sands Using The Discrete Element Method, Eric Kofi Gbadam

Doctoral Dissertations

"Oil sands are naturally geologic formations of predominantly quartz sand grains whose void spaces are filled with bitumen, water, and dissolved gases. The electric rope shovel is the primary equipment used for excavating the Athabasca oil sand formations. The equipment's static and dynamic loads are transferred to the formation during excavation and propel. These loads cause ground instability leading to sinkage or rutting, crawler wear, and fracture failures. These problems result in unplanned downtimes, production losses, and high maintenance costs. In order to address these problems, there is a need to develop valid models that capture the behavior and performance …

The Maculoprotective Effect Of A Thiol Antioxidant In Retinal Degeneration Models, Hsiu-Jen Wang

Doctoral Dissertations

"Age-related macular degeneration (AMD) is a leading cause of irreversible blindness among adults, age 60 and older, in developed countries. While oxidative stress is implicated in the pathogenesis of AMD, clinical studies have shown that dietary antioxidants can delay progression of AMD. Currently, there is no FDA-approved treatment for AMD. Therefore, we hypothesized that N-acetylcysteine amide (NACA), a thiol antioxidant, would protect retinal pigment epithelium and impede the progression of retinal degeneration. The goal of this work was to evaluate the efficacy of NACA in preventing retinal pigment epithelial cell and photoreceptor death in AMD models. To achieve this, we …

Numerical And Experimental Study Of New Designs Of All-Vanadium Redox Flow Batteries For Performance Improvement, Mohammed Abdulkhabeer Ali Al-Yasiri

Doctoral Dissertations

"Energy storage is envisioned as a key part of a renewable energy solution incorporated in a grid that overcomes two critical limits of renewable energy: intermittency and uncertainty. Among various technologies, a vanadium redox flow battery (VRFB) offers a promise because of its unique features such as long cycle life, separation of energy and power ratings, and capability of a deep discharge. The remaining challenges, however, include the limited application due to low energy density and complicated geometries. The complex geometry makes it difficult to optimize the performance and can cause a serious concern about leakage of the liquid. The …

Experimental And Computational Investigation Of Multi-Principal Element Alloys, Mohsen Beyramali Kivy

Doctoral Dissertations

"Multi-principal element (MPE) alloys, unlike traditional alloys, consist of five or more principal elements with near equi-atomic compositions creating a large new compositional space for exploring new alloy possibilities. However, designing MPE alloys with the desired phases, microstructures and properties is challenging task, and there is a demand for basic research for a better understanding of structure-processing-property relations in these alloys.

In this Ph.D. research, different computational models and experiments were integrated to study phase formations, and mechanical properties of different MPE alloys. Density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations were used to determine crystal structures, …

Long-Period Fiber Grating Corrosion Sensors For Life-Cycle Monitoring And Assessment Of Reinforced Concrete Structures, Yizheng Chen

Doctoral Dissertations

"This study aims to: (1) explore, develop, calibrate and validate Fe-C coated, long period fiber grating (LPFG) sensors for short-term mass loss measurement of the Fe-C coating; (2) develop, calibrate, and validate steel tube-encapsulated, fiber optic probes and LPFG sensors for long-term mass loss detection of the steel tube; (3) correlate the corrosion process of packaging metal materials with that of steel bars in direct contact with the packaged probe or sensor except for a thin insulation tape; and (4) apply both types of corrosion sensors into reinforced concrete (RC) structures for reinforcing bar corrosion monitoring and structural condition assessment. …

Zero-Dimensional Spaces And Their Inverse Limits, Sahika Sahan

Doctoral Dissertations

"In this dissertation we investigate zero-dimensional compact metric spaces and their inverse limits. We construct an uncountable family of zero-dimensional compact metric spaces homeomorphic to their Cartesian squares. It is known that the inverse limit on [0,1] with an upper semi-continuous function with a connected graph has either one or infinitely many points. We show that this result cannot be generalized to the inverse limits on simple triods or simple closed curves. In addition to that, we introduce a class of zero-dimensional spaces that can be obtained as the inverse limits of arcs. We complete by answering a problem by …

Manufacturing Of Advanced Continuous Fiber Reinforced Composites For High Temperature Applications, James Robert Nicholas

Doctoral Dissertations

"New resin systems have enabled composites to be considered as attractive alternatives in structural applications that require material to be stronger, lighter and/or more resilient to environmental effects. The current work is on the development of processes to produce continuous fiber reinforced materials from two state of the art resin systems. Two processes were developed to produce continuous fiber reinforced ceramic materials from a preceramic polymer. The first was a vacuum forming process developed using the out-of-autoclave polymer composite manufacturing technique in conjunction with the polymer infiltration and pyrolysis process to produce ceramic composite material of zirconium diboride-silicon carbide reinforced …

Drinking Water Disinfection By-Products Detection, Formation And The Precursors Removal Study, Runmiao Xue

Doctoral Dissertations

"Haloacetic acids (HAAs) and trihalomethanes (THMs) are two groups of commonly found disinfection by-products (DBPs). Iodinated THMs and HAAs were observed after disinfection of water containing high level of iodide and are proved to be more toxic than their corresponding chlorinated and brominated species. In the presented dissertation, a novel rapid and sensitive high performance ion chromatography-tandem mass spectrometry (HPIC-MS/MS) method has been developed for simultaneous analysis of all these HAAs, bromate, bromide, iodide, and iodate, seventeen compounds in total, without any tedious sample preparation. Besides an efficient analytical method for the detection of DBPs, seeking for a green disinfectant …

Imaging A Fly Ash Landfill Using Non-Invasive Technologies (Ert And Masw), Atiat Shaban Qasim Alsaaideh

Doctoral Dissertations

"Electrical resistivity tomography (ERT) data were acquired across a segment of an existing fly ash landfill in southwestern Missouri. The objective was to map potential karst features and identify probable groundwater seepage through and beneath the landfill.

Variations in the moisture content were mapped below and above the two liners (clay and synthetic) systems, the soil and bedrock. Seepage pathways were mapped through the fly ash and the underlying soil and rock. No visual evidence was found on any of the 3D ERT profiles of the presence of either pre-existing air-filled voids or pre-existing or newly infilled clay-filled voids. There …

T-Closed Sets, Multivalued Inverse Limits, And Hereditarily Irreducible Maps, Hussam Abobaker

Doctoral Dissertations

"This dissertation consists of three subjects: T-closed sets, inverse limits with multivalued functions, and hereditarily irreducible maps.

For a subset A of a continuum X define T(A) = X \ {x ∈ X : there exists a subcontinuum K of X such that x ∈ int_xX(K) ⊂ K ⊂ X \ A}. This function was defined by F. Burton Jones and extensively investigated in the book [20] by Sergio Macias. A subset A of a continuum X is called T-closed set if T(A) = A. A characterization of T-closed set is given using generalized …

Discrete Ordinates Ct Organ Dose Simulator (Doctors), Edward T. Norris

Doctoral Dissertations

"Computed tomography (CT) has become pervasive in medical diagnostics as improved imaging techniques and processing algorithms provide higher quality information to doctors. However, the exponentially increasing usage of CT has raised concerns regarding long term low-dose radiological risks.

Currently, the dose to patients is computed using Monte Carlo methods and experimental tests. In other areas of radiation transport, deterministic codes have been shown to be much faster than Monte Carlo codes.

Currently, no deterministic methodology exists to automatically generate a spatially distributed dose profile from a CT voxel phantom. This work proposes a new code, Discrete Ordinate CT Organ Dose …

Advanced Analytical Strategies To Determine Biomedical Parameters For Medical Diagnostics, Drug Delivery, And Therapy, Sisi Chen

Doctoral Dissertations

"Biomedical parameters are critical for diseases prognosis, diagnosis and therapy. Many research groups have dedicated their studies to develop analytical instrumentation and apply analytical methods to determine biomedical parameters that have the potential to help with disease control and increase public health. This dissertation focuses on three major aspects of analytical strategies development and applications: 1) detection of pH changes caused by nanotoxicity (induced by TiO₂ nanoparticles) using newly developed micro-pH sensor, 2) quantification of renal cell carcinoma (RCC) biomarkers by high-performance liquid chromatography - tandem mass spectrometry (HPLC-MS/MS), and 3) nuclear magnetic resonance (NMR) studies of porous wall …

Designing High Performance Overall Water Splitting Electrocatalysts From Non-Precious Metal Selenides, Abdurazag T. Swesi

Doctoral Dissertations

“The energy production has been depending mostly on fossil fuel which will be depleted someday in the near future. Aspects such as the loss of energy resources and destruction of the environment have motivated researchers for pursuing transition away from fossil fuels to renewable solar-fuels. Therefore, in order to meet the continuous increasing demand for energy, the hydrogen, with the largest energy density stored in it, can then efficiently be used in fuel cells without concern of contaminants. Water splitting reaction to generate H₂ and O₂ is one promising method of converting solar energy into fuels. The major …

Data Analysis And Application Guidelines Of Particle Gel Treatments, Yue Qiu

Doctoral Dissertations

“Water production is a severe worldwide issue in mature oilfields, which results in shortening the economic life of oil and gas wells. Particle gel have been widely applied in mature oilfields to improve reservoir sweep efficiency and control water production. To date, more than 10,000 injection wells were successfully treated by particle gels. However, considerable uncertainty still exists regarding to where and how particle gel treatments can be best applied.

The main objective of this study is to provide application guidelines and prediction model for particle gel treatments through data analysis. In this study, four particle gel treatment datasets have …

A New Reinforcement Learning Algorithm With Fixed Exploration For Semi-Markov Decision Processes, Angelo Michael Encapera

Masters Theses

"Artificial intelligence or machine learning techniques are currently being widely applied for solving problems within the field of data analytics. This work presents and demonstrates the use of a new machine learning algorithm for solving semi-Markov decision processes (SMDPs). SMDPs are encountered in the domain of Reinforcement Learning to solve control problems in discrete-event systems. The new algorithm developed here is called iSMART, an acronym for imaging Semi-Markov Average Reward Technique. The algorithm uses a constant exploration rate, unlike its precursor R-SMART, which required exploration decay. The major difference between R-SMART and iSMART is that the latter uses, in addition …