▼ The need for advanced thermal management materials is well recognized in the electronics and communication industries. An overall reduction in size of electronic components has lead to higher power dissipation and increased the necessity for innovative cooling designs. In response, material suppliers have developed and are continuing to develop, an increasing number of light weight thermal management materials. The new carbon foam is a low density and high thermal conductivity material which has the potential to radically improve heat transfer, thereby reducing size and weight of equipment while simultaneously increasing its efficiency and capabilities. However, carbon foam exhibits low strength and low heat capacity. The present work is intended to overcome these two main drawbacks using a combinatorial approach: (i) initially, copper coating was carried out to improve the thermo-mechanical properties of carbon foam. The thermal and mechanical properties of coated foam were measured using laser flash technique and compression test, respectively. An analytical model was developed to calculate the effective thermal conductivity. It was observed that the copper-coated carbon foam with 50% porosity can attain a thermal conductivity of 180 W/mK. The results from the analytical model were in a very good agreement with experimental results. The modulus increased from 4.5 MPa to 8.6 MPa and the plateau stress increased from 54 kPa to 171 kPa. The relationships between the measured properties and the copper weight ratio were determined. The above analyses demonstrated the significance of copper coating in tailoring carbon foam properties. (ii) Numerical and experimental studies were performed to analyze the phase change behavior of wax/foam composite encapsulated in metal casing. A two-energy equation model was solved using computational fluid dynamics software (CFD). Interfacial effects at the casing-composite junction and between the wax-foam surfaces and the capillary pressure within the foam matrix were investigated. These factors lowered the heat transfer rate considerably and the melting area was reduced by more than 23%. Two samples, coated and uncoated carbon foam, were infiltrated with PCM and subjected to a uniform heat load test in a vacuum. The coated foam showed excellent performance compared to the uncoated foam. (iii) Finally, the new engineered carbon foam was used as a heat sink and heat exchanger in a thermoelectric cooler for a cooling vest application. Using carbon foam as the core material for this application, the effective transfer of heat was significantly increased while reducing the size and weight of the heat exchanger. Advisors/Committee Members: Lafdi, Khalid.

▼ Agitation is a critical aspect of many processes, such as food production, mineral processing, and water treatment, with liquid-solid agitators representing a significant portion of all agitation installations. Improper mixing operation in liquid-solid agitators can result in negative financial and environmental issues. Over-mixing may damage solid particles and erode impeller blades as well as waste energy. On the other hand, under-mixing may allow solids to settle down on the base of the tank, which may cause solids to adhere to one another and bring about difficulties of solids removal from the vessel. The purpose of this work is to develop a design guideline that can be used to successfully predict the agitation speed required to suspend a solid mixture in just-suspended condition, in which no solid remains on the base of tank for longer than 1-2 seconds, based on a knowledge of agitation speeds required to suspend the individual components in the solids mixture. The primary design guideline investigated is summing the powers required to suspend the individual solids alone to predict the power required to suspend the solids mixture. The secondary design guideline that is investigated is that the speed required to suspend the solids mixture is equal to the speed required to suspend the more difficult to suspend solid alone. All binary solids mixtures can be categorized into three different groups in this work based on the magnitude of specific gravity of the solids in each system. It is found that speed predicted based on the sum of powers required to suspend the individual solids is normally higher than the actual speed at which a solids mixture is at the just-suspended condition in the case of low-density systems where the specific gravities of both solids are below 1.5 grams per cubic centimeter. In other cases, including mixed-density system, which is a solid with low density (below 1.5 grams per cubic centimeter) plus a solid with high density (above 2.4 grams per cubic centimeter), and high-density system in which both solids have densities above 2.4 grams per cubic centimeter, the prediction speed found by summing the powers required for suspension of each individual component in a solid mixture is approximately equal to that necessary to suspend solids mixture. However, a few systems diverge from these typical behaviors, possibly due to the unusual characteristics of one solid – olivine sand. Results from those solids mixtures involving olivine sand are not consistent with typical conclusion obtained from the sum of powers hypothesis. Adding olivine sand always reduces mixture suspension speed from the speed predicted by summing of powers estimation. A reasonable explanation of these atypical phenomena should be investigated in future studies. In addition, two systems that consisted of three different solids were tested and it was found that the speed based on summing the powers required for suspension of individual components provided a reasonable prediction of the suspension speed of those ternary systems. Advisors/Committee Members: Myers, Kevin.

▼ Interest in the development and application of functionally graded materials (FGM) has increased in recent years, leading to their limited use in a number of commercial and military products. More recently, interest in the use of FGMs in aircraft fuselage structures as integrated thermal protection systems has also begun to develop. However, our limited ability to predict the nucleation and fatigue propagation of cracks in these materials limits the application of FGMs to non fracture critical structures, reducing the potential benefits of their incorporation. A first step toward addressing this technology gap is to evaluate whether linear elastic fracture mechanics methods, appropriately modified to account for material non homogeneity, can be used to predict fatigue crack propagation in an arbitrarily graded metal/ceramic FGM. This dissertation documents new developments for characterization and modeling of fatigue crack propagation in FGMs. Unique precracking and characterization methods, and a Paris equation dependent upon stress intensity and material phase volume fraction and gradients are developed for FGMs. Hybrid numerical experiments are used to develop and verify a multivariable regression (MVR) method for identifying the effective crack tip coordinates and accurately recovering stress intensity from 2-D crack tip displacement field measurements in FGMs. Numerical and experimental results for Ti-TiB FGM specimens validate the MVR method for recovery of stress intensity in FGMs when allowing for the presence of manufacturing-induced residual stresses. Predicted fatigue crack propagation rates also compare favorably with experimental results, but are limited in accuracy by the effects of residual stresses. Residual stresses modify crack tip stress intensities and their effects are only accountable here by using the MVR recovered stress intensities. The results suggest that a Paris equation including material gradients as independent variables is viable. However, an accurate means of accounting for residual stresses in arbitrary FGM forms must be developed if linear elastic fracture mechanics methods are to be used effectively, otherwise excessive experimental characterization of fatigue crack propagation properties would be required. Advisors/Committee Members: Brockman, Robert A.

▼ Part 10 of MPEG-4 describes the Advanced Video Coding (AVC) method widely known as H.264. H.264 is the product of a collaborative effort known as the Joint Video Team(JVT). The final draft of the standard was completed in May of 2003, and since then H.264 has become one of the most commonly used formats for compression of high definition video [9]. The entire H.264/AVC encoder is inherently a sequential process, which typically lends itself to a software solution. Within the H.264 Standard, two entropy decoders are discussed. These two lossless encoding methods are known as Context Adaptive Variable Length Coding (CAVLC) and Context Adaptive Binary Arithmetic Coding (CABAC). CAVLC offers the most basic solution, while CABAC provides increased compression rates at a cost in algorithm complexity. For fast encoding of H.264 bit streams, three solutions are presented in this thesis. Two implementations of CAVLC are discussed, including a software and a hardware solution. Finally, a simple implementation of CABAC is proposed. Advisors/Committee Members: Balster, Eric.

▼ Carbon nanopearls (CNPs), also known as carbon spheres and nanospheres, are of interest to the nanoscience community due to their field emission and tribology capabilities. There have been numerous reports on the properties and potential applications of CNPs; however, there have been few studies on the behavior of the catalyst during synthesis. Carbon nanopearls are limited to being used as cold cathodes and lubricants for tribology if the nickel catalyst remains. This research focused on studying the behavior of the nickel catalyst during chemical vapor deposition of CNPs. Carbon nanopearls were grown at various growth times (10 sec, 30 sec, 60 sec, 90 sec, 120 sec and 300 sec) using two different nickel catalyst sizes (20 nm nickel nanoparticles and 100 nm nickel nanoparticles). Chemical analysis was conducted using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). This enabled observation of the chemical phases as growth time increased. Imaging of the CNPs samples was performed using transmission electron microscopy (TEM). Raman spectroscopy was performed to observe the defects and order in the graphitic structures as growth time varied. The melting temperature of the nickel nanoparticles was investigated experimentally by performing differential scanning calorimetry (DSC) on the nickel catalyst. Theoretically, the melting temperature was calculated using the Gibb-Thomson equation. The question “does the Ni catalyst evaporate during synthesis of carbon nanopearls” was addressed both theoretically and experimentally. Theoretically, the Kelvin effect was used to calculate the vapor pressure of the nickel nanoparticles. The vapor pressure of the nanoparticles was compared to the vapor pressure for bulk nickel, and this helped to determine if the nanoparticles were evaporating. Weight loss experiments were conducted and thermal gravimetric analysis (TGA) was performed on the nickel nanoparticles. These experiments were used to identify the temperature of evaporation. The results from this research showed that during the synthesis process, the Ni oxidized. XRD and XPS showed that the nickel oxide reduced as growth time increased, followed by the formation of a nickel carbide phase. Towards the longer growth times, the carbide decomposed leaving only nickel and graphite. TEM results revealed that the remaining nickel did not exist in the core of the carbon nanopearl, but that it was nickel that had segregated from the CNPs and agglomerated with other nickel particles. DSC identified the melting temperature of the 20 nm nickel nanoparticles to be lower than the bulk melting temperature of nickel. The Gibbs-Thomson effect was used as a guideline for determining the melting temperature of the nanoparticles. Oxidation of the nickel nanoparticles prevented determination of the evaporation temperature. Results from the Kelvin effect indicated that the Ni nanoparticles evaporate sooner than bulk nickel. However, due to XRD identifying Ni at the longer growth times, there was no evidence to conclude that the Ni had evaporated. Finally, a model for CNPs growth was presented based off the results in this research. Advisors/Committee Members: Murray, Paul T.

▼ On average, every day in the United States 32 people die in motor vehicle crashes involving alcohol-impaired drivers. This is equivalent to one death every 45 minutes. The objectives of this study were three-fold: (1) to identify counties in the state of Ohio with relative high alcohol-related traffic crash rates; (2) to develop a visual presentation of results by using Geographic Information System (GIS on the Ohio map of counties); (3) to recommend areas or locations needing elevated and targeted alcohol-related driving reinforcement and educational efforts. Ohio traffic crash, number of population, number of registered vehicles, number of licensed drivers and average daily vehicle miles of travel data at the county level for 2007-2010 were used to analyze the alcohol-related traffic crash rates in counties. The results indicate that the most urbanized counties of Franklin, Cuyahoga, Hamilton, Summit, Montgomery, Lucas and their surrounding counties which are highly populated and also with high traffic volumes are the locations where most of the alcohol related traffic crashes occurred. The interesting results, however, were obtained from analysis of the risk of alcohol-related traffic crashes when the population and other exposure metrics were factored in order to determine the relative risk rates, which enable us to compare the counties fairly. Population density, daily vehicle miles of travel, the number of licensed drivers and the number of registered vehicles enabled us to capture counties with high risk rates. Generally, rural southern counties in the Appalachian areas and in the eastern parts of the state are the ones that appeared on the top of the list in almost all risk rate methods used in this study. In the northeastern area, the county of Ashtabula was the only county in that area which was ranked among the most risk counties in almost all the risk traffic crash rates methods used in this study. Counties that were highly ranked include Carroll, Harrison, Guernsey, Perry, Belmont, and Muskingum counties in the eastern part of the state and counties in the southern part highly ranked include Vinton, Ross, Pike, Adams, and Lawrence. Advisors/Committee Members: Eustace, Dr.Deogratias.

▼ The objective of this research is to investigate the biocompatibility of carbon nanomaterial. It was found that the cytotoxicity of multiwalled carbon nanotubes (MWNTs) depend on their concentration, size, and surface chemical groups (e.g., -COOH). MWNTs and MWNT-COOH could accumulate in human lung macrophage cells (U937) to different degrees, and they did not produce overt cell toxicity within the concentration range of 5-50 µg/ml up to 24 h. However, there were morphological alterations at low doses of MWNT-COOH and significant reactive oxygen species (ROS) generation for MWNTs at higher doses, indicating a distinguished possible cellular stress response and DNA damage from both materials. In the second part of this study, reduced graphene oxide (rGO) was demonstrated to show the concentration-dependent and cell-specific cytotoxicity. Specifically, rGO was found to stimulate cell proliferation of human skin fibroblast cells at relatively low concentrations (< 5 µg/mL), but inhibit human skin fibroblast cells proliferation at high concentrations. rGO-induced concentration-dependent and cell-specific generation of ROS and activation of NF-κB transcription factors were also observed, indicating an oxidative stress mechanism. Furthermore, rGO was showed to be more biocompatibility to human skin fibroblast cells with respect to mouse embryonic fibroblast cells (NIH-3T3 cells). In the third part of this study, the soft lithography technique was used to build PDMS microfluidic devices for monitoring cells viability and performing dynamic study of the carbon nanomaterial biocompatibility. Compared to the traditional in vitro technique, this research opens up a new approach to biocompatibility evaluation of nanomaterials with a reduced usage of animal in toxicity study. By using the newly-developed microfluidic devices, the biocompatibility of MWNTs and rGO were investigated. It was found that both particles could enter into the circulation system in the microfluidic devices. Possible damage to bovine aortic endothelium cells (BAECs) caused by carbon nanomaterials was investigated. The interaction of MWNTs (1D) and rGO sheets (2D) with BAECs in both static (cell culture) and dynamic (microfluidic) environments indicated that both nanoparticles reduced the mitochondrial function and lipoprotein (LDL) uptake. These results were concentration and morphology depended. MWNTs showed a better biocompatibility than rGO in both static and dynamic environments, while the microfluidic tests exhibited better biocompatibilities than those in cell culture dishes for both nanoparticles. Advisors/Committee Members: Eylon, Daniel.