Engineering Commons^™

Hydrodynamic Wave Contributions To Combustion Instability In Rockets, Esam M. T. Abu-Irshaid

Doctoral Dissertations

Experimental measurements suggest that a new source of instability in rocket motors is due to hydrodynamic disturbances. These disturbances, if ignored, could impact our assessment of rocket motor performance. In this work, the corresponding problem of hydrodynamic instability is considered. A mathematical model for these disturbances is carried out by perturbing the continuity and momentum equations. A one dimensional model which represents the wave disturbances in time and space is implemented to quantify the amplification rate, in time or space, and the wave amplitude. The only available measurements of these disturbances arise in cold flow experiments that simulate the gas …

Studies Of The Mechanism Of Electron Beam Induced Deposition (Ebid), Young Ryong Choi

Doctoral Dissertations

The controlled deposition of metals resulting from the passage of an ion beam through an atmosphere of a suitable precursor gas is a well-established procedure for micro scale materials manipulation. While the ion beam technique is rapid and reliable it has the disadvantage that the beam itself can ablate and contaminate the target with Gallium or other materials, and the fact that ion optics are less widely accessible than electron optical columns. We have therefore been investigating the theory and practice of depositing metal using an electron beam and variety of precursor gases. The aim of this work is to …

A High Gain Multi-Stage Operational Amplifier Using Compound Transconductance Element, Chandra Sekhar Acharyulu Durisety

Doctoral Dissertations

The rapid increase in integrated circuit complexity attributed to the advancements in fabrication techniques combined with the increasing demand for consumer applications has created an immense demand for high performance analog systems. These analog systems include high-resolution (≥ 14-bit) and/or high-speed (≥ 1 GHz) ADCs, high- linearity filters and power management circuits. The fundamental limitations in these systems are tied to the constraints imposed by the basic design elements that tend to include amplifiers and reference generators (voltage/current). With continued technology scaling, innovative circuits and design techniques are necessary in achieving high performance analog/mixed-signal systems.

The goal of this research …

The Thermophysical Roll Of Nanoparticles In Nanofluidic Heat And Mass Transport, Chan Hee Chon

Doctoral Dissertations

Nanofluids are colloids that consist of a base fluid and nanometer sized metallic particles, which serve to improve the heat and mass transport characteristics of nanofluids over those of the base fluid. Many researchers, attracted to the highly enhanced thermal conductivity, have studied nanofluids, and yet have never been able to reveal the basic mechanisms of their characteristic improvements. This present work thus seeks to gain an understanding of the role of nanoparticles in nanofluidic heat and mass transport characteristics through three experimental measurements: 1) thermal conductivity measurement, 2) thermophoretic motion measurement, and 3) evaporation measurement.

Using thermal conductivity, thermophoresis, …

Efficient Image Processing In Resource-Constrained Visual Sensor Networks, Hongtao Du

Doctoral Dissertations

Visual sensor networks (VSNs) that employ content-rich 2-D images or image sequences as the basic media have been evolving rapidly in recent years. Besides the critical resource constraints that are already inherent in any micro-sensor networks, the development of VSNs also faces challenges from device design, image transmission, and onboard image processing, among which efficient onboard processing is the most difficult to tackle. The focus of this dis- sertation is to develop efficient image processing solutions from three aspects: to improve the time-consuming image processing algorithms using pipelined and parallel computing; to dis- tribute the computation more effectively through novel …

Development Of A Test Methodology For Determining The Efficacy Of One Atmosphere Uniform Glow Discharge Plasma Against Airborne Contaminants, Ronald Edward Domitrovic

Doctoral Dissertations

A method of analysis is developed for an atmospheric plasma reactor in a ducted air stream with the intent of enabling parametric analysis for the multi-variable problem. Industrial uses for atmospheric plasma are numerous and in this case, a particular type of plasma known as “One Atmosphere Uniform Glow Discharge Plasma” (OAUGDP™) was studied for its chemistry generation abilities and its microorganism efficacy properties. The system of an OAUGDP reactor positioned in an air duct of fully-developed turbulent flow is constructed of nineteen pertinent variables and dimensional analysis is applied according to the Buckingham Pi method, yielding fourteen dimensionless variable …

Thermal Stability Of Binary Cr-Cr3Si And Ternary Nial-Mo Eutectic Alloys, Aravind Gali

Doctoral Dissertations

The thermal stability of multiphase intermetallics at temperatures to 1400°C was investigated by studying two model eutectic systems: Cr-Cr₃Si having a lamellar microstructure and NiAl-Mo having a fibrous microstructure. In drop cast Cr-Cr₃Si, coarsening was found to be interface controlled. The coarsening rate could be significantly reduced by microalloying with Ce and Re, two elements which were chosen because they were expected to segregate to the Cr-Cr₃Si interfaces and decrease their energies. Similarly, directional solidification, which is also expected to lower the Cr- Cr₃Si interfacial energy, was found to dramatically decrease the …

Scheduling Algorithms For Scalable High-Performance Packet Switching Architectures, Xike Li

Doctoral Dissertations

Packet switching fabrics constitute a fundamental building block of all Internet routers. As a core technology, the switching engine is responsible for enabling multiple input (ingress) ports to be dynamically linked to output (egress) ports, thereby allowing packets to effectively traverse the router. Scheduling algorithms, which play a key role in switching fabrics, determine the dynamic configurations of the input-output matchings. The ever growing need for additional bandwidth and more sophisticated service provisioning in next- generation networks necessitates the introduction of scalable packet scheduling solutions that go beyond legacy schemes.

Switch architectures can be coarsely classified into two categories, in …

An Investigation Of The Deposition And Characterization Of Materials Formed By Electron Beam Induced Deposition, Wei Li

Doctoral Dissertations

This dissertation deals with EBID – Electron Beam Induced Deposition – a novel bottom up nanofabrication technique. Since EBID was first employed for nano-patterning, a number of empirical factors were investigated to control deposition process. Meanwhile a few theoretical models were proposed based on some fundamental assumptions. So far little work has been done to verify the validity of these assumptions. The main objective of my PhD study, therefore, was to answer whether these assumptions are valid so that unifying the empirical factors and theoretical models would be possible. Electrical resistivity of deposited materials was another interesting topic included in …

A Study Of The Relationship Between Indentation Creep And Uniaxial Creep, James Anthony Lamanna Jr.

Doctoral Dissertations

The purpose of this work is to further the scientific understanding of the relationship between indentation creep and uniaxial creep. The data for this study was obtained by conducting both indentation and uniaxial creep experiments on amorphous selenium. Experiments were designed to collect data over a wide range of creep rates. Specific temperatures were chosen to collect creep data above and below the glass transition temperature of 31°C. The indentation and uniaxial compression data was used to accomplish several objectives.

The first objective was to test the ability of the Oliver-Pharr stiffness equation to predict contact area. The current contact …

The Stability Analysis Of Linear Dynamical Systems With Time-Delays, Ajeet Ganesh Kamath

Doctoral Dissertations

Time-delay systems, which are also sometimes known as hereditary systems or systems with memory, aftereffects or time-lag, represent a class of infinite-dimensional systems, and are used to describe, among other types of systems, propagation and transport phenomena, population dynamics, economic systems, communication net- works and neural network models. A key method for the stability analysis of time- delay dynamical systems is the Lyapunov’s second method, applied to functional differential equations. Specifically, stability of a given linear time-delay dynamical system is typically shown using a Lyapunov-Krasovskii functional, which involves a quadratic part and an integral part. The quadratic part is usually …

Pseudoelasticity And Shape Memory Effect In Single Crystal Fe3Al, Saurabh Kabra

Doctoral Dissertations

Fe₃Al is an intermetallic compound which has shown some excellent engineering properties and has been widely studied for this reason. It also shows interesting mechanical phenomenon like yield stress anomaly and pseudoelasticity. Mechanical behavior and diffraction studies on the pseudoelastic aspect of Fe₃Al have been presented in this work.

Single crystalline, D0₃ ordered Fe₃Al is known to show pseudoelastic behavior at room temperature. Pseudoelastic behavior was seen in both tension and compression with a distinct tension-compression asymmetry. No strain hardening occurred under tension even at high applied strains as opposed to compression, …

Analysis And Control Of Nonnegative Systems, Jayanthy Ramakrishnan

Doctoral Dissertations

Nonnegative systems are dynamical systems with nonnegative states for random non- negative initial conditions. A subclass of nonnegative systems are compartmental systems characterized by conservation laws.Nonnegative and compartmental systems have widespread applications in biological systems, medical systems, thermodynamic systems, network systems, economic systems, etc.

In this dissertation we have investigated the applications of nonnegative systems in biological and network systems. The specific focus in biological systems has been in the area of pharmacokinetics and we have addressed the consensus problem in network systems. We have specifically focused on the time-delay present in compartmental systems and have investigated the behavior of …

Methylsilane Derived Sic Particle Coatings Produced By Fluid-Bed Chemical Vapor Deposition, James Henry Miller

Doctoral Dissertations

This report describes the research effort that was undertaken to develop and understand processing techniques for the deposition of both low and high density SiC coatings from a non-halide precursor, in support of the Generation IV Gas-Cooled Fast Reactor (GFR) fuel development program.

The research was conducted in two phases. In the first phase, the feasibility of producing both porous SiC coatings and dense SiC coatings on surrogate fuel particles by fluidized bed chemical vapor deposition (FBCVD) using gas mixtures of methylsilane and argon was demonstrated. In the second phase, a combined experimental and modeling effort was carried out in …

Effects Of Temperature And Grain Size On The Transformation And The Deformation Behaviors Of The Trip (Transformation Induced Plasticity) Steels, Kaixiang Tao

Doctoral Dissertations

Two types of TRIP steels, a commercial 304L stainless steel and an Fe-10%Cr-5%Ni-8%Mn steel, have been used to investigate the effects of temperature and grain size on the transformation and mechanical behaviors. 304L SS was used to investigate the effects of temperature ranging from 300K to 77K, while the Fe-10%Cr-5%Ni-8%Mn steel was used for the investigation of the effects of the grain size at 300K.

At 203K, the fcc grains of the 304L SS with {200} plane normal parallel to the loading direction are preferred for the fcc to bcc transformation and the {200} plane normals of the newly-formed bcc …

A Lifetime-Prediction Approach To Understanding Corrosion: The Corrosion-Fatigue And The Corrosion Behavior Of A Nickel-Based Superalloy And A Nanocrystalline Alloy, Rejanah Vernice Steward

Doctoral Dissertations

Lifetime-prediction models are useful for simulating a material’s in-service behavior or outcome. Perhaps the greatest advantage of these models is the ability to use the predicted results to help optimize engineering designs and reduce costs. The Hastelloy^® C-2000^® superalloy is a single-phase material and face-centered cubic in structure at all temperatures. The C-2000^® alloy is a commercially designed alloy manufactured to function in both reducing and oxidizing solutions. C-2000^® is used as a fabrication material for heat exchangers, piping for chemical refineries, and storage repositories. The corrosion properties of C-2000^® are excellent, and the ductility …

Ex-Situ Epitaxial Yba2Cu3O7-Δ Films: Precursor Conversion And Film Characterization, Yifei Zhang

Doctoral Dissertations

BaF₂-based precursors were deposited on various substrates by electron beam co- evaporation and trifluoroactates-involved metal organic deposition (TFA-MOD) for fabricating biaxially-textured YBa₂Cu₃O_7-δ (YBCO) films. A low-pressure processing system was established for the conversion of the precursors. High critical current densities near 4 MA/cm² (77 K, self field) were obtained for the first time through the ex-situ conversion under the total pressures as low as 10 mTorr. The viability of the low- pressure conversion may enable a large-scale, cost-effective batch production of YBCO- based high temperature superconductor (HTS) wires.

The effects of the …

A Kinetic Study Of Indentation Pop-Out In Si, Songqing Wen

Doctoral Dissertations

The kinetics of the phenomenon of pop-out during nanoindentation of silicon were studied by a variety of mechanical and structural characterization techniques. Pop- out is commonly viewed to result from the reversal of a unique pressure-induced, volume reducing phase transformation that occurs in silicon and germanium.

The mechanical characteristics were examined by standard nanoindentation methods using a number of triangular pyramidal indenters with centerline-to-face angles varying in the range 35°-85°. The load at which pop-out occurs was systematically measured as a function of indenter angle, loading/unloading rate, and maximum load. Nanoindentation tests were conducted both at a constant loading rate …

Studying The Fatigue Behavior Of Zr-Based Bulk-Metallic Glasses And Composites, Gongyao Wang

Doctoral Dissertations

As excellent candidates for structural materials, the mechanical behavior of bulk metallic glasses (BMGs) is being widely studied. Although their fatigue behavior is very important for engineering applications, there are few studies on their fatigue behavior. Moreover, the understanding of the fatigue behavior is pretty limited.

High-cycle fatigue experiments were conducted on notched Zr-based BMGs under tension-tension loading in air and vacuum at room temperature. A sparking phenomenon was found by infrared camera at the final fracture moment of Zr₅₀Al₁₀Cu₃₀Ni₁₀ in air. The fatigue-endurance limit (983 MPa) of Zr₅₀Cu₃₇Al …

Computer Modeling Of Tennessee Valley Authority’S Coal Based Power Plant At Kingston To Predict The Effluent To Emory River, Bratendu Bagchi

Doctoral Dissertations

In the wake of stringent environmental regulations, this research studies ash pond discharge to the river by Kingston Power plant. Currently 1296 MGD of fresh water from the Emory river via plant intake is used in condenser cooling. 40 MGD of ash sluice water containing ammonium compounds, mercury compounds, phosphates, Arsenic, Selenium, etc, is discharged to the plant intake via the ash pond for recycle back as sluice water into the plant. Ammonia slip from SCR unit is responsible for the ammonia and mercury comes from the coal. The research addresses the methodology to predict pollutants in the ash pond …

Severe Plastic Deformation Using Friction Stir Processing, And The Characterization Of Microstructure And Mechanical Behavior Using Neutron Diffraction, Wanchuck Woo

Doctoral Dissertations

Friction-stir welding (FSW) is a solid-state joining process, which utilizes a cylindrical rotating tool consisting of a concentric threaded tool pin and tool shoulder. The strong metallurgical bonding during the FSW is accomplished through: (1) the severe plastic deformation caused by the rotation of the tool pin that plunges into the material and travels along the joining line; and (2) the frictional heat generated mainly from the pressing tool shoulder. Recently, a number of variations of the FSW have been applied to modify the microstructure, for example, grain refinements and homogenization of precipitate particles, namely friction-stir processing (FSP). Applications of …

Surface Composition And Interaction Of Thermally Treated White Oak With White Sprits, Roy Douglas Wilcox

Doctoral Dissertations

The surface composition and energy of two thermally treated white oak stave sources and the acidic composition of their white spirit extracts were studied to determine whether composition of the maturing extract could be attributed to variability in surface composition due to degradation of lignin, cellulose, and extractives with thermal treatment and extraction. The sources were from the Ozarks and Appalachia. Surface composition was determined by X-Ray photoelectron spectroscopy (XPS). Surface energy was obtained from the wicking method of contact angle determination with probe liquids and application of the van Oss geometric mean equation. Acid-base properties and composition of the …

Investigation Of Ethanol Dehydration In A Microscale Pervaporation Process, Sudhir Ramprasad

Doctoral Dissertations

Challenges due to surface tension effects for vaporization in microchannels have restricted the implementation of conventional separation processes that involve liquid boiling in a micro-chemical system. However, membrane separations offer a feasible alternative for exploring the advantages of liquid phase separation in micro-chemical systems. The main objective of this research was to evaluate the process intensification effects in a microscale pervaporation process with experiments involving the separation of ethanol/water using a commercially available polymer dehydration membrane.

The microchannels in the microseparator were fabricated by the dry etch process at Louisiana Tech University. Microchannel depths of 20 to 120 μm, with …

Fluorescent Enzymatic Smart Tattoos Comprising Hybrid Silicate Microparticles, Metalloporphyrin Complexes, And Mass Transport-Limiting Nanofilms, Erich Wayne Stein

Doctoral Dissertations

Diabetics are often required to self-monitor blood glucose levels to effectively deliver prescribed therapies. However, the pain and bother associated with traditional finger-prick measurements often result in decreased patient compliance and therefore poor disease management, which could result in the early-onset of complications. Enzymatic "smart tattoos"—implantable luminescent particles that may be transdermally interrogated with light—are being pursued as minimally-invasive diabetic monitoring devices, with hopes of increasing diabetic compliance by reducing excessive pain and bother associated with finger-prick measurements. These devices typically comprise an oxygen-quenched luminescent dye and glucose oxidase (GOx), an enzyme that catalyzes the oxidation of β-D-glucose. Under glucose-limited …

Mechanical Properties Of Granular Materials Using Nanoindentation And Modeling With Distinct Element Method, Amal Kumar Dutta

Doctoral Dissertations

The mechanics of granular material is an important issue that governs many geotechnical engineering applications. Two types of particles having similar particle size, but different shape are used in this research to evaluate the role of particle morphology on the physical properties of its assemblage. Experimentation of 1-D compression behavior at constant axial strain rate under laterally confined conditions is performed for these two particulate materials and the behavior of the stress path is analyzed in relation to the initial material packing and physical characteristics of the granules.

The behavior of granular assemblages under imposed loading conditions are also evaluated …

Temperature Dependent Analytical Modeling, Simulation And Characterizations Of Hemts In Gallium Nitride Process, Hasina F. Huq

Doctoral Dissertations

Research is being conducted for a high-performance building block for high frequency and high temperature applications that combine lower costs with improved performance and manufacturability. Researchers have focused their attention on new semiconductor materials for use in device technology to address system improvements. Of the contenders, silicon carbide (SiC), gallium nitride (GaN), and diamond are emerging as the front-runners.

GaN-based electronic devices, AlGaN/GaN heterojunction field effect transistors (HFETs), are the leading candidates for achieving ultra-high frequency and high-power amplifiers. Recent advances in device and amplifier performance support this claim. GaN is comparable to the other prominent material options for high-performance …

Design Assessment Of Two-Wheeled Luggage Based On Mechanical Models And A Usability Test, Jun-Seok Lee

Doctoral Dissertations

The purpose of this study is to ergonomically assess two-wheeled luggage design based on mechanical models and a usability test.

Three mechanical models were developed for the pulling force estimation and important luggage design factor finding. Three pulling conditions with three motion stages were considered in the model. In addition, a set of pre-questionnaires and a set of post-questionnaires were prepared for the investigation of users’ preferences for each design factor.

From the mechanical models, the minimum pulling force was found at the tilted angle of 65.56° in static staus, at the tilted angle of 30° in the initial phase, …

Population (Amoa-Based) And Activity (Amoa-Mrna-Based) Assessment Of Ammonia Oxidizing Bacteria (Aob) During Activated Sludge Wastewater Treatment, Hsion-Wen Kuo

Doctoral Dissertations

The population size and physiological activity of ammonia-oxidizing bacteria (AOB) are two crucial rate-limiting parameters for the removal of ammonia from wastewater (Wagner et al., 1995). These two biological parameters may be affected by operational/environmental conditions (e.g., low pH, low temperature, low dissolved oxygen (DO), or short solids retention time (SRT)), and these impacts may subsequently influence ammonia removal performance in wastewater treatment systems (Okabe et al., 1996; Nogueira et al., 2002; Robinson et al., 2004; Zimmerman et al., 2004; Hallin et al., 2005). The impacts of changes in population dynamics and microbial activity of AOB on overall nitrification efficiency …

Modeling Of Terrain Impact Caused By Off-Road Vehicles, Qinghe Li

Doctoral Dissertations

Terrain impact models were developed for both wheeled vehicles and tracked vehicles based on the analysis of vehicle dynamics, soil mechanics, and geometric relationships between vehicle parameters and the disturbed width. The terrain impact models, including both disturbed width models and impact severity models, were developed separately for tracked vehicles and wheeled vehicles.

The disturbed width models of both vehicle types were primarily based on the geometric relationship between vehicle contact width and vehicle dynamic parameters. For both vehicle types, the impact severity was defined as the ratio between soil shear stress and soil shear strength. The impact severity model …

Thermodynamic Characterization Of Polymeric Materials Subjected To Non-Isothermal Flows: Experiment, Theory And Simulation, Tudor Constantin Ionescu

Doctoral Dissertations

Frictional or viscous heating phenomena are found in virtually every industrial operation dealing with processing of polymeric materials. This work is aimed at addressing some of the existing shortcomings in modeling non-isothermal polymer flowing processes. Specifically, existing theories suggest that when a polymer melt is subjected to deformation, its internal energy changes very little compared to its conformational entropy. This statement forms the definition of the Theory of Purely Entropic Elasticity (PEE) applied to polymer melts. Under the auspices of this theory, the temperature evolution equation for modeling the polymer melt under an applied deformation is greatly simplified. In this …