Engineering Commons^™

Characterization Of Porous Media And Refractory Materials, Xin Chen

Doctoral Dissertations

Because of its unique advantages on energy savings and casting complex shaper, Lost Foam Casting (LFC) has been widely used as a replacement to the conventional techniques (sand and investment castings). In order to continuously improve the quality of the Lost Foam Casting process for reducing scrap rate and increasing energy savings, the US Department of Energy through its National Industrial Competitiveness through Energy, Environment, and Economics (NICEEE) program sponsored the present study to develop new characterization techniques for enhancing the understanding of the fundamental properties of the refractory materials used in The Lost Foam Casting process. In this study, …

An Adaptive Tool-Based Telerobot Control System, Ge Zhang

Doctoral Dissertations

Modern telerobotics concepts seek to improve the work efficiency and quality of remote operations. The unstructured nature of typical remote operational environments makes autonomous operation of telerobotic systems difficult to achieve. Thus, human operators must always remain in the control loop for safety reasons. Remote operations involve tooling interactions with task environment. These interactions can be strong enough to promote unstable operation sometimes leading to system failures. Interestingly, manipulator/tooling dynamic interactions have not been studied in detail. This dissertation introduces a human-machine cooperative telerobotic (HMCTR) system architecture that has the ability to incorporate tooling interaction control and other computer assistance …

Convergence And Robustness Issues In Computational Fluids, Xiaoqiang Zeng

Doctoral Dissertations

The present research develops two methods to improve the convergence and robustness of CFL algorithm, the triple time method and error- limited time step ramping method.

A general formulation of the triple time scheme is developed by introducing three pseudo time-marching steps to control three preconditionings for artificial dissipation, non-linear equation iteration convergence and linear equation iteration convergence separately. It is proven that the triple time method can be degenerated to the single time method and the multiple DDLGS iteration method at special cases.

Stability analysis is used to choose the optimum combination of three preconditionings from the steady preconditioning, …

High Accuracy Distributed Target Detection And Classification In Sensor Networks Based On Mobile Agent Framework, Xiaoling Wang

Doctoral Dissertations

High-accuracy distributed information exploitation plays an important role in sensor networks. This dissertation describes a mobile-agent-based framework for target detection and classification in sensor networks. Specifically, we tackle the challenging problems of multiple- target detection, high-fidelity target classification, and unknown-target identification.

In this dissertation, we present a progressive multiple-target detection approach to estimate the number of targets sequentially and implement it using a mobile-agent framework. To further improve the performance, we present a cluster-based distributed approach where the estimated results from different clusters are fused. Experimental results show that the distributed scheme with the Bayesian fusion method have better performance …

Synthesis And Ordering Of Nanostructures Using Laser Light, Yingfeng Guan

Doctoral Dissertations

This dissertation focuses on the formation of 1-D and 2-D nanoscale structures induced by the KrF excimer UV laser irradiation of silicon (λ=248 nm). Relatively low laser energy density (E_d<=1 J/cm²) is required to produce nanostructures. Alignment of 2-D nanoripple structures and nanoprotrusions has been realized by using Lloyd’s mirror configuration.

Laser-generated silicon microcone arrays were used as templates for the growth of nanocolumns. The formation mechanism of the microstructure is reviewed, and the origin and growth of nanocolumns are discussed. The formation mechanism of nanocolumns requires highly localized melting, which explains why they fail to form on …

A Study Of The Evolution Of Laser-Induced Periodic Surface Microstructures On Silicon And Electronic Transport In Composite Carbon Nanotube Networks, Stephen Jesse

Doctoral Dissertations

This dissertation addresses two main topics, the formation of micron-scale surface structures on single crystal silicon by irradiation with a KrF (248 nm) pulsed excimer laser source, and an investigation into electronic transport through composites of polymer (PMMA) and single-walled carbon nanotubes. It is shown that the spacing between laser-generated surface structures is determined primarily by the melt time and that the crystal orientation of the substrate can determine whether surface structures will form at all and also influence the shape of individual surface structures. During the melt/solidification cycle, the shape of liquid-vapor interface in modified by surface tension, and …

Fundamental Studies Of X-Ray And Secondary Electron Spectroscopy, Staya Prasad Mulapudi

Doctoral Dissertations

Microanalysis of submicron particles in the Scanning Electron Microscope (SEM) is only possible by using low incident electron beam energies due to smaller interaction volume and suppressed beam induced charging. Such low beam energies must use L- and M- lines rather than the familiar K-lines. The information about the fundamental parameters of X-ray emission and transport at low energies is limited, so the use of L- and M- lines is problematic. The rate of generation of X-rays from an element irradiated at some energy E depends on the product of the ionization cross-section (E) and the fluorescent yield . Unfortunately …

Modeling And Source Apportionment Of Primary And Secondary Pm2.5 In The Atmosphere, Prakash Doraiswamy

Doctoral Dissertations

Source apportionment of PM_2.5 is important to identify the source categories that are responsible for the concentrations observed at a particular receptor. Although receptor models have been used to do source apportionment, they do not fully take into account the chemical reactions (including photochemical reactions) involved in the formation of secondary fine particles. Secondary fine particles are formed from photochemical and other reactions involving precursor gases such as sulfur dioxide (SO₂), oxides of nitrogen (NO_x), ammonia (NH₃) and volatile organic compounds (VOC). The purpose of this research work was to model primary and …

Polymer-Based Wide-Angle Micro -Optic Lens System With Dynamically Variable Focal Length And Field Of View, Mangilal Agarwal

Doctoral Dissertations

A novel polymer-based integrated wide-angle dynamic micro-optical lens system that can provide variable focal length and field of view (FOV) with large numerical aperture is designed, fabricated, and tested for its optical characteristics.

Initial experiments were conducted using static glass lenses to test for configuration of lenses that could provide wide FOV. From these initial experiments, it was found that the higher FOV could be achieved with double concave (DCV) lenses compared to double convex (DCX) lenses of the same focal length. Further, it was observed that increasing the number of DCV lenses increases FOV. Thus, an integrated dynamic polymer …

Layer-By-Layer Self -Assembly For Enzyme And Dna Encapsulation And Delivery, Amish Patel

Doctoral Dissertations

Thin wall microcapsules were formed via Layer-by-Layer Self-Assembly of alternate adsorption of oppositely charged polyelectrolyte on microcores. After the core dissolution, empty polymeric shells with 20–25 nm thick walls were obtained. These microcapsules were loaded with Myoglobin, Hemoglobin and Glucose Oxidase by opening capsule pores at low pH and closing them at higher pH. The native structure of the enzyme was not affected due to different treatments. Biocompatible nanoshells were also prepared for encasing DNA. Using the same Layer-by-Layer Self-Assembly approach nanoparticle were constructed containing DNA as one of the layers. The nanoparticles of different architecture were used to deliver …

Biomimetic Synthesis Within Polyelectrolyte Microcapsules: Characterization Of Enzyme Catalyzed Polyphenols And Polypeptides, Rohit C. Ghan

Doctoral Dissertations

An enzyme-catalyzed synthesis of novel polymers within layer-by-layer (LbL) constructed polyelectrolyte microcapsules has been developed. This approach is based on the selective permeability of polyelectrolyte-capsule walls to monomer molecules. Conversely biocatalysts and forming polymeric chains cannot exit the micro-capsule interior because of their characteristic high molecular weight. Horseradish Peroxidase (HRP) was encapsulated into four bilayer PSS (poly-styrenesulfonate)/PAH (poly-allylamine hydrochloride) capsules with an average diameter of 5 μm using pH-driven pore opening. The polymerization of 4-(2-Aminoethyl) phenol hydrochloride (tyramine) catalyzed by HRP produces easily detectable fluorescent polymeric products after the addition of hydrogen peroxide to the system. It is known that …

Layer-By-Layer Nanoassembly Combined With Microfabrication Techniques For Microelectronics And Microelectromechanical Systems, Jingshi Shi

Doctoral Dissertations

The objective of this work is to investigate the combination of layer-by-layer self-assembly with microfabrication technology and its applications in microelectronics and MEMS.

One can assemble, on a standard silicon wafer, needed multilayers containing different nanoparticles and polymers and then apply various micromanufacturing techniques to form microdevices with nanostructured elements.

Alternate layer-by-layer self-assembly of linear polyions and colloidal silica at elevated temperatures have been firstly studied by QCM and SEM. LbL self-assembly and photolithography were combined to fabricate an indium resistor. The RTA method was employed in the fabrication. Hot-embossing technique as a reasonably fast and moderately expensive technique was …

Computational Approaches To The Design And Analysis Of Stability Of Polypeptide Multilayer Thin Films, Bin Zheng

Doctoral Dissertations

The focus of this research is the development of computational approaches to understanding the physical basis of layer-by-layer assembly (LBL), a key methodology of nanomanufacturing. The results provided detailed information on structure which cannot be obtained directly by experiments.

The model systems chosen for study are polypeptide chains. Reasons for this are that polypeptides are no less polyelectrolytes than the more usual polyions, and one can control the primary structure of a polypeptide on a residue-by-residue basis using modern synthetic methods. Moreover, as peptides constitute one of the four major classes of biological macromolecules, research in this direction is expected …

Investigation Of Fiber Splitting In Side-By-Side Bicomponent Meltblown Nonwoven Webs Through Post Treatment, Yanbo Liu

Doctoral Dissertations

Finer fibers are increasingly desirable in the nonwoven industry in many applications due to increased specific surface area, increased surface adsorption ability, and improved filtration efficiency. Splitting bicomponent (Bico) fibers to produce finer fibrous nonwoven webs has become one of the hot topics in nonwoven industries.

Investigation of Bico fiber splitting mechanism and hence finding proper ways to achieve fiber splitting in S/S Bico MB nonwoven webs are the key issues in this research. Based on the fiber splitting mechanism, incompatible polymer pairs were chosen and appropriate post-treating methods as well as the post-treating agents were selected to facilitate fiber …

Free Radical (Co)Polymeirzation Of Methyl Methacrylate And Styrene In Room Temperature Ionic Liquids, Hongwei Zhang

Doctoral Dissertations

Conventional free radical polymerizations were carried out in a variety of room temperature ionic liquids (RTILs). Generally, methyl methacrylate (MMA) and styrene (St) were used as typical monomers to compare the polymerization behavior both in RTILs and in common volatile organic compound solvents (VOCs). In most cases, it was observed that both yields and molecular weights are enhanced in the RTIL. While we believe the “diffusion-controlled termination” mechanism makes the termination of the radical propagating chains difficult due to the highly viscous nature of RTIL, other researchers have suggested that the rapid polymerization rates are due to the high polarity …

Crystallization Of Polyamide 66 Copolymers At High Supercoolings, Xiaoping Guan

Doctoral Dissertations

Crystallization kinetics and morphologies of a series of random copolymers of PA 66 (or Nylon 66) have been investigated at high supercoolings. Optical microscopy with rapid cooling apparatus was employed to observe spherulitic morphologies and measure growth rates. Final spherulitic morphologies of PA 66 and copolymers could be changed with increasing supercoolings from impinged spherulites to isolated spherulites with decreasing size until total amorphous.

Spherulite growth results indicated that the rates of crystallization of PA 66 copolymers were reduced with increasing content of comonomer, and crystallization was moved to lower temperatures. The melting temperature, crystallinity, crystal structure and lamellar thickness …

A Study Of Charging In The Presence Of A Gaseous Environment, Xiaohu Tang

Doctoral Dissertations

Charge accumulation in insulating or semiconducting samples due to electron beam irradiation is one of the key problems in electron microscopy. One of the most promising techniques for reducing the severity of such charging is to surround the sample with a low pressure atmosphere of a gas. The charging behavior of a number of materials, surrounded by a variety of gases, has been determined to identify the important factors which control charging under these conditions. The magnitude of the surface potential was deduced from an analysis of X-ray spectra from the surface. The relationship between surface charge, gas pressure, and …

Volatile Fatty Acids Effects On Nitrite Removal And Nitrate Formation During Activated Sludge Treatment, Merve Oguz

Doctoral Dissertations

Reaction sequences of nitrifying and denitrifying bacteria are widely used to eliminate nitrogenous compounds from wastewater. During nitrification, ammonia is oxidized to nitrite by autotrophic ammonia oxidizing bacteria and nitrite is further oxidized to nitrate by nitrite oxidizers. Subsequently, nitrate or nitrite is reduced by denitrifying bacteria to gaseous nitrogen compounds. It is common knowledge that nitrification is an aerobic process and denitrification an anaerobic process. However, recent research has shown that denitrification can occur under aerobic conditions in pure cultures. Volatile fatty acids (VFAs), produced during anaerobic treatment processes, can affect both nitrite oxidation and aerobic denitrification. VFAs were …

Process Property Studies Of Melt Blown Thermoplastic Polyurethane Polymers, Youn Eung Lee

Doctoral Dissertations

The primary goal of this research was to determine optimum processing conditions to produce commercially acceptable melt blown (MB) thermoplastic polyurethane (TPU) webs. The rheological/thermal properties of TPU pellets and the morphological/mechanical properties of MB TPU fibers and webs were characterized by Advanced Rheometric Expansion System (ARES), Differential Scanning Calorimetry (DSC), Fourier Transform Infrared Spectroscopy (FTIR) and etc.

The 6-inch MB line and the 20-inch wide Accurate Products MB pilot line at the Textiles and Nonwovens Development Center (TANDEC), The University of Tennessee, Knoxville, were utilized for this study. Preliminary MB studies were performed with Noveon ESTANE^® 58277 on …

Travel Characteristics Of Urban Freight Vehicles And Their Effects On Air Quality, Annie Protopapas

Doctoral Dissertations

This research study collected local commercial vehicle data in Knox County, Tennessee from the United States Postal Service and two companies engaged in package pickup and delivery. A second urban commercial vehicle dataset from a wider spectrum of companies in North Carolina was also obtained for comparative analysis. The two datasets are analyzed in a similar manner to develop and compare travel characteristics/parameters commonly used in transportation engineering, such as Daily VMT, Daily Number of Trips, Vehicle Speed, Trip Length, Trip Travel Time and Stop Duration. Statistical tests demonstrate the similarities between certain vehicle classes from the two datasets and …

Prediction Of Organic Droplet Behavior On A Solid Surface As Influenced By Aqueous Surfactant Solutions, Samuel Albert Morton Iii

Doctoral Dissertations

This dissertation presents a model capable of predicting equilibrium oil droplet contact angles on a solid surface immersed in surfactant solution, a thorough discussion of the effects of surfactant concentration and salt addition on contact angles, and an experimental investigation into the impact of voltage application to the solid surface on oil droplet shape in an aqueous/organic/solid system. The work contained in this dissertation resulted in five journal articles and numerous presentations.

The model applies current theories of surfactant self-assembly, the quasi-chemical approximation for solid surface adsorption, and various aqueous/organic/solid system properties to determine organic droplet contact angles. The computational …

Effect Of Microfissures On Corrosion Performance And Mechanical Properties Of Austenitic Stainless Steel Weld Metals, Yan Cui

Doctoral Dissertations

It is generally recognized that hot cracking or microfissuring is one of the main concerns in austenitic stainless steel welding. Microfissures formation can be attributed to the presence of liquid film along the grain boundaries near the bulk solidus temperature under a sufficient strain to rupture the liquid film. Microfissures can be controlled to a certain extent by attention to consumable composition, purity, and welding technique, but they cannot be uniquely eradiated in real weld application. The occurrence of the microfissures can be the cause of weld rejection and may induce property degradation of the weld metal. With the increase …

Development Of An Fpga-Based Hardware Evaluation System For Use With Ga-Designed Artificial Neural Networks, Dennis Duncan Earl

Doctoral Dissertations

The Hardware-Evolved Digital Artificial Neural Network (HEDANN) design platform is a circuit design platform built to evolve complex architecture ANN circuits using re-configurable hardware. By using genetic algorithms to evolve complex architecture ANN designs in field programmable gate arrays, this system is the first design system to evolve physical ANN circuits with unconstrained network architectures. With the HEDANN design system, the evolution of ANNs with recursive, non-layered, complex architectural connections is made possible. In addition, the HEDANN design system is capable of evolving device-independent circuit designs that can operate properly across a wide range of operating temperatures. This system is …

Inferential Modeling And Independent Component Analysis For Redundant Sensor Validation, Jun Ding

Doctoral Dissertations

The calibration of redundant safety critical sensors in nuclear power plants is a manual task that consumes valuable time and resources. Automated, data-driven techniques, to monitor the calibration of redundant sensors have been developed over the last two decades, but have not been fully implemented. Parity space methods such as the Instrumentation and Calibration Monitoring Program (ICMP) method developed by Electric Power Research Institute and other empirical based inferential modeling techniques have been developed but have not become viable options.

Existing solutions to the redundant sensor validation problem have several major flaws that restrict their applications. Parity space method, such …

A High -Order Finite Difference Method For Solving Bioheat Transfer Equations In Three-Dimensional Triple -Layered Skin Structure, Haofeng Yu

Doctoral Dissertations

Investigations on instantaneous skin burns are useful for an accurate assessment of burn-evaluation and for establishing thermal protections for various purposes. Meanwhile, hyperthermia with radiation is important in the treatment of cancer, and it is essential for developers and users of hyperthermia systems to predict, and interpret correctly the biomass thermal and vascular response to heating. In this dissertation, we employ the well-known Pennes' bioheat transfer equation to predict the degree of skin burn and the temperature distribution in hyperthermia cancer treatment.

A fourth-order compact finite difference scheme is developed to solve Pennes' bioheat transfer equation in a three-dimensional single …

Fabrication, Characterization, And Modeling Of Organic Capacitors, Schottky Diodes, And Field Effect Transistors, Mo Zhu

Doctoral Dissertations

The objectives of this project are to fabricate, characterize, and model organic microelectronic devices by traditional lithography techniques and Technology Computer Aided Design (TCAD).

Organic microelectronics is becoming a promising field due to its number of advantages in low-cost fabrication for large area substrates. There have been growing studies in organic electronics and optoelectronics. In this project, several organic microelectronic devices are studied with the aid of experimentation and numerical modeling.

Organic metal-insulator-metal (MIM) and metal-insulator-semiconductor (MIS) capacitors consisting of insulating polymer poly(4-vinylphenol) (PVP) have been fabricated by spin-coating, photo lithography, and reactive ion etching techniques. Based on the fabricated …

Generalized Multigroup Method, Ibrahim Khalil Attieh

Doctoral Dissertations

Treatment of energy in the solution of the transport equation has been dominated by the multigroup method (MG). The multigroup method has the advantages of being simple and mathematically robust. However, it suffers from two disadvantages. When the multigroup transport equation is solved to find the group flux coefficients, the assumed spectrum becomes discontinuous at the energy boundaries, and the assumed spectrum maintains its original shape within the group. These characteristics are in contradiction with actual spectrum behavior. These disadvantages reduce the accuracy of the multigroup method, requiring a greater number of energy groups to converge to a solution with …

Laser Induced Surface Modification Of Aluminium Alloys, Subhadarshi Nayak

Doctoral Dissertations

Purpose of this work is to improve surface related properties of aluminum alloys by employing a laser based technique. Two approaches were taken to achieve this goal. First approach involves a rapid solidification induced by laser without any deliberate change in chemical composition. In second approach, laser was used to deposit Fe₃0₄ on A319, producing an Fe₃0₄/Al reaction composite coating.

In-situ high-speed infrared thermographs captured during laser surface melting of A319 enabled estimation of maximum temperature, temperature gradient and cooling rate. In light of limited spatial and time resolutions of the infrared camera, …

Three-Dimensional Mechanical Behavior Of Kaolin Clay With Controlled Microfabric Using True Triaxial Testing, Amit Prashant

Doctoral Dissertations

Clays in their natural state are mostly anisotropic because of their modes of deposition. Many boundary value problems in geotechnical engineering involve soil elements that are subjected to stress paths with varying relative magnitudes and orientation of principal stresses. In clay, these soil elements may also have different orientations of its microfabric. It is a well-known fact that the variation in relative magnitudes and orientation of principal stresses and the microfabric of clay have significant effect on the stress-strain, pore pressure and shear strength behavior of clay. In order to study this behavior of clay from a normally consolidated to …

Structure And Properties Of Cotton-Based Biodegradable/Compostable Nonwovens, Haoming Rong

Doctoral Dissertations

Cotton-based biodegradable nonwoven products have been receiving increasing attention in recent years with the growing environmental awareness throughout the world. A majority of the cotton-based nonwoven products are processed by carding with the binder fibers, and then point-bonding using a thermal calender.

In this work, different biodegradable binder fibers were used to produce cotton-based nonwovens. The structure and the properties of the resulting fabrics were studied. The effect of bonding temperature and binder fiber content on the bond morphology was investigated. The fracture and failure mechanisms of the fabrics produced with different binder fiber content and at different bonding temperature …