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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
51

DEVELOPMENT OF A MECHANICAL CAVOPULMONARY ASSIST DEVICE FOR THE FAILING FONTAN PATIENTS

Kapadia, Jugal 12 October 2009 (has links)
The long term objective of this research is to develop a collapsible, percutaneously inserted, axial flow blood pump to improve blood flow in the cavopulmonary circulation. Through this research, the experimental evaluation of five blood pump prototypes and hemolysis testing of one blood pump prototype were performed. All prototypes demonstrated acceptable hydraulic performance. A comparison of the experimental results with numerical predictions demonstrated a 10-20% deviation, an acceptable range per industry standard. Hemolysis testing of a four bladed adult blood pump showed plasma free hemoglobin level of 20.04 mg/dL and maximum NIH (normalized index of hemolysis) level was 0.017 g/100L. This thesis project serves as a solid foundation from which to continue development of this suited intravascular axial flow blood pump. Successful completion of this research will lead to a novel percutaneously inserted axial flow pump for infants and adult patients with a failing Fontan physiology.
52

DESIGN AND DEVELOPMENT OF A PVDF SENSOR TO MONITOR INTRACRANIAL PRESSURE (ICP)

VIJAYWARGI, VIVEK 04 November 2009 (has links)
Monitoring ICP non-invasively is a challenge. A novel method to measure ICP using actuators and sensors has been proposed where the skull is vibrated at high frequencies and the receiving signal is measured at the surface eyelid. A design of experiments approach is used to develop the sensor part of the ICP monitoring device so that gain can be maximized using factors such as area, thickness, electrode, and applied pressure. Statistical analysis showed that thickness has the biggest effect on overall gain. Numerical analysis confirmed these results. In addition, sensor packaging is optimized to minimize dampening of the signal and ensure durability, reliability, and repeatability of the measurements. Optimized parameters are then incorporated into a design, the ICP glasses that allow ease of application and consistency of the measurements. The sensitivity of the sensor was measured to be 0.211mV/V.
53

Optical Characterization of Wide Bandgap Detector-Grade Semiconductors

Elshazly, Ezzat 02 July 2010 (has links)
Wide bandgap semiconductors are being widely investigated because they have the potential to satisfy the stringent material requirements of high resolution, room temperature gamma-ray spectrometers. In particular, Cadmium Zinc Telluride (Cd1-xZnxTe, x~0.1) and Thallium Bromide (TlBr), due to their combination of high resistivity, high atomic number and good electron mobility, have became very promising candidates for use in X- and gamma-ray detectors operating at room temperature. In this study, carrier trapping times were measured in CZT and TlBr as a function of temperature and material quality. Carrier lifetimes and tellurium inclusion densities were measured in detector-grade Cadmium Zinc Telluride (CZT) crystals grown by the High Pressure Bridgman method and Modified Bridgman method. Excess carriers were produced in the material using a pulsed YAG laser with a 1064nm wavelength and 7ns pulse width. Infrared microscopy was used to measure the tellurium defect densities in CZT crystals. The electronic decay was optically measured at room temperature. Spatial mapping of lifetimes and defect densities in CZT was performed to determine the relationship between defect density and electronic decay. A significant and strong correlation was found between the volume fraction of tellurium inclusions and the carrier trapping time. Carrier trapping times and tellurium inclusions were measured in CZT in the temperature range from 300K to 110K and the results were analyzed using a theoretical trapping model. Spatial mapping of carrier trapping times and defect densities in CZT was performed to determine the relationship between defect density and electronic decay. While a strong correlation between trapping time and defect density of tellurium inclusions was observed, there was no significant change in the trap energy. Carrier trapping times were measured in detector grade thallium bromide (TlBr) and compared with the results for cadmium zinc telluride (CZT) in a temperature range from 300K to 110K. The experimental data was analyzed using a trapping model. In CZT, because the majority carrier concentration is close to the intrinsic carrier concentration, the trapping time increases exponentially as the temperature decreases below about 160K. While, in TlBr, the majority carrier concentration is many orders of magnitude greater than the intrinsic carrier concentration and the trapping time followed a temperature dependence over the range of temperatures studied. The results of the model suggest that a moderately deep compensation center, located approximately 200 meV from the middle of the bandgap, could be used to significantly increase the room temperature trapping time in TlBr. The results of this model demonstrate that the room temperature trapping time in TlBr can, in principle, approach 0.1ms through the introduction of a moderately deep compensation level but without decreasing the overall trap concentration. This strategy is not possible in CZT, because the band gap is too small to use a moderately deep compensation level while still maintaining high material resistivity. Carrier trapping times were measured in three polycrystalline TlBr samples produced by melting commercial TlBr beads in a sealed quartz ampoule for two hours at three different temperatures near the melting point. The trapping time decreased with increasing melting temperature, presumably due to the thermal generation of a trap state.
54

Characterization of Sapphire: for Its Material Properties at High Temperatures

Unknown Date (has links)
There are numerous needs for sensing, one of which is in pressure sensing for high temperature application such as combustion related process and embedded in aircraft wings for reusable space vehicles. Currently, silicon based MEMS technology is used for pressure sensing. However, due to material properties the sensors have a limited range of approximately 600°C which is capable of being pushed towards 1000°C with active cooling. This can introduce reliability issues when you add more parts and high flow rates to remove large amounts of heat. To overcome this challenge, sapphire is investigated for optical based pressure transducers at temperatures approaching 1400°C. Due to its hardness and chemical inertness, traditional cutting and etching methods used in MEMS technology are not applicable. A method that is being investigated as a possible alternative is laser machining using a picosecond laser. In this research, we study the material property changes that occur from laser machining and quantify the changes with the experimental results obtained by testing sapphire at high-temperature with a standard 4-point bending set-up. Keywords: Sapphire, Bayesian analysis, thermomechanics, alumina / A Thesis submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Master of Science. / Fall Semester 2015. / November 9, 2015. / Anisotropy, Laser ablation / Includes bibliographical references. / William S. Oates, Professor Directing Thesis; Rajan Kumar, Committee Member; Eric Hellstrom, Committee Member.
55

Stretchlon Film Enhanced Fabriaction of Nanocomposites with the Resin Infusion Between Double Flexible Tooling

Unknown Date (has links)
Recent studies have shown that the incorporation of carbon nanotubes (CNT) in to carbon fiber composite parts significantly increase mechanical as well as thermal properties. Polymer nanocomposites are polymer matrix composites that consist of reinforcements that have at least one dimension in the nanometer range. The polymer nanocomposite fabricated parts achieve greater mechanical, thermal, electrical and other properties with a low CNT reinforcement volume fraction. Nanocomposites achieve improved properties because of the higher properties of the nano-reinforcement and the high ratio of surface area to volume (aspect ratio) that provides greater interfacial interaction with the matrix. The fabrication of nanocomposites is primarily by the liquid composite molding (LCM) processes that can be complex process with many challenges. These challenges include poor CNT dispersion, poor bonding between resin and CNT, and blocking or filtration during the infusion process. The Resin Infusion between Double Flexible Tooling (RIDFT) however offers some advantages over the other LCM processes. The preservation and extended use of the mold can result in higher productivity and profit. In addition, a significantly lower pressure that translates to lower equipment cost, will be required to drive the high viscosity CNT-rich resin through the two-dimensional flow in a RIDFT process compared to the three-dimensional flow in the RTM. The RIDFT process may also be used for out-of-autoclave fabrication of composites from pre-pregs. The RIDFT process however has a number of fabrication issues militating against its wide use. These include long production cycle time due to the bottle neck associated with the setup time for cleaning the silicone sheet and the high cost of replacement of the flexible silicone membranes of the RIDFT machine. The introduction of Stretchlon Bagging 800 film may reduce the time that is expended on cleaning the silicone sheets and at the same time reduce the damage that is made to the silicone membranes. The goal of this thesis is to evaluate the performance of the Stretchlon bagging technique with the RIDFT process with the aim of significantly reducing the production cycle time as well as the production cost of composites and nanocomposites without adversely affecting the mechanical properties of the fabricated parts. The results show that the use of the Stretchlon bagging film resulted in reduction in the production cycle time of GFRP and CNT_GFRP parts of 32% and 42% respectively. It also resulted in production set-up (mold preparation) cost reduction for GFRP and CNT-GFRP parts of 49% and 72% respectively. It resulted in increased durability and service life of the silicon mold thereby helping to reduce the production cost. In addition, the use of the Stretchlon bagging film did not adversely affect the mechanical properties of the fabricated GFRP and CNT-GFRP parts. It resulted in an increase of 31.94% and 12.62% in the mean UTS of the GFRP and CNT-GFRP respectively. The Stretchlon film however resulted in reduction in the flexural properties of the fabricated GFRP and CNT-GFRP parts by 30.12% and 18.69% respectively. The use of the Stretchlon bagging film enhanced the in-plane properties of the fabricated parts by helping to increase the fiber volume fraction. The lower resin contents in the parts fabricated with the Stretchlon film may have had an adverse effect in the interlaminar properties resulting in lower flexural strengths. Furthermore, thermal analysis confirmed that there was no change in the glass transition (Tg) temperature of the fabricated parts. Parts fabricated with the Stretchlon bagging film also exhibited better surface finish than those fabricated without using the Stretchlon bagging film. In addition, a new design for the RIDFT with higher pressure capability for better quality parts (higher fiber volume fraction and lower void content) fabrication has been made. The new design also incorporates infrared lamp system for expedited curing of the composite parts in order to reduce the cycle time. Further work is however needed to optimize the RIDFT-Stretchlon film fabrication process for nanocomposites. A more detailed microscopy study needs to be performed to gain better insights into the reasons for the enhanced fiber volume content and in-plane properties achieved with the use of the Stretchlon film. In addition, the study needs to be repeated with functionalized CNTs to study the effects of functionalized CNTs on the fabricated parts, the silicon mold and the Stretchlon film. There is also the need to fabricate the new RIDFT design and optimize its performance for nanocomposite fabrication. / A Thesis submitted to the Department of Industrial & Manufacturing Engineering in partial fulfillment of the Master of Science. / Fall Semester 2015. / October 6, 2015. / Includes bibliographical references. / Okenwa Okoli, Professor Directing Thesis; Zhiyong (Richard) Liang, Committee Member; Tarik Dickens, Committee Member; David Olawale, Committee Member.
56

Development of Carbon Nanotube/Carbon Fiber Multiscale Reinforcement Composites

Unknown Date (has links)
High performance composites are currently being used in the marine, automotive, aerospace and defense industries. These industries demand materials with properties that are similar or better than conventional metals at a fraction of the weight. The development of nanoparticle reinforced composites is presently one of the most explored areas in materials science and engineering. The exceptional properties of nanoparticles have made them a focus of widespread research. By combining nanoparticles with traditional reinforcement materials, multiscale composites can be produced with superior properties to that of regular composites. This research focuses on the development of multiscale reinforcement composites, through the use of carbon nanotubes (CNTs), IM7 and T800 carbon fibers and SC-79 epoxy resin. Vacuum assisted resin transfer molding and hand lay-up/ vacuum bagging processes were evaluated for the manufacturing of multiscale composites. Results from this research showed that the use of carbon nanotubes can increase the tensile strength by up to 27% and toughness by up to 38%, with the addition of 2.5wt% multiwall carbon nanotubes (MWNTs). However there were no significant changes in the flexural properties with the addition of carbon nanotubes. Analysis of the fracture surfaces, using scanning electron microscopy showed that there was good dispersion of the carbon nanotubes through out the matrix material. The good dispersion of tubes aided in toughening the SC-79 epoxy resin. This toughening effect was evident though the change in crack propagation patterns on the fracture surface. There was also evidence of the nanotubes bridging cracks and holding resin particles together, which also lead to increased fracture toughness / A Thesis submitted to the Department of Industrial Engineering in partial fulfillment of the Requirements for the degree of Master of Science. / Degree Awarded: Fall Semester, 2005. / Date of Defense: October 31, 2005. / Multiscale, SC-79 Epoxy Resin, T800, IM7, Carbon Nanotubes, Composite / Includes bibliographical references. / Richard Liang, Professor Co-Directing Thesis; Okenwa Okoli, Professor Co-Directing Thesis; James Sands, Outside Committee Member; Reginald Parker, Committee Member; Ben Wang, Committee Member.
57

Kinetic Modeling of Mithochondral ATP Production: Sensitivity Analysis and Development of Overall Rate Law

Unknown Date (has links)
The objectives of this work are to determine the extent to which intracellular metabolite diffusion limits aerobic metabolism and hence dictates cellular dimensions and metabolic organization. The particular focus is on the reaction and diffusion of metabolites that link mitochondria and cellular ATPases, which include ATP, ADP, Pi, arginine phosphate (AP), and arginine in fish and crab muscle as model systems that provide insight into burst swimming muscles. The current work also incorporates oxygen and myoglobin diffusion and reaction and their coupling to the mitochondria. In the first step of model development, an analytical equation for the ATP flux from the mitochondrial inter membrane space was developed from detailed mitochondrial models reported in the literature. This function provides ATP flux from the mitochondria in terms of ADP, Pi, and oxygen concentrations, and it is incorporated within one and two dimensional models of muscle cells. Sensitivity analysis of the mitochondrial model is used to determine the key parameters that affect the kinetics of ATP formation. The second step involves incorporating this analytical function as a boundary condition in a transient spatially dependent diffusion-reaction model of the muscle cell. The full system of partial differential equations are solved with finite element methods and are used to assess the relative effects of diffusion and reaction on overall ATP utilization. / Thesis submitted to the Department of Chemical and Biomedical Engineering in partial fulfillment of the requirements for the degree of Master of Science. / Degree Awarded: Spring Semester, 2007. / Date of Defense: April 20, 2007. / Mitochondria, ATP / Includes bibliographical references. / Bruce R. Locke, Professor Directing Thesis; Teng Ma, Committee Member; Samuel Grant, Committee Member.
58

Low-Cost Concentrating Solar Collector for Steam Generation

Unknown Date (has links)
Concentrating solar power (CSP) is a unique renewable energy technology. CSP systems have the ability to provide electricity, refrigeration and water purification in one unit. This technology will be extremely helpful in improving the quality of life for many people around the world who lack the energy needed to live a healthy life. An economic parabolic dish concentrating system was built at the Sustainable Energy Science and Engineering Center (SESEC) at Florida State University in Tallahassee, Florida. The goal of the project was to provide 6.67 kW of thermal energy. This is the amount of energy required to produce 1 kW of electricity with a conventional micro steam turbine. The system had a price goal of $1000 per kW and must be simple enough to be maintained by non-technical personnel. A 14 m^2 fiberglass parabolic concentrator was made at SESEC to ensure simplicity of production and operation. The concentrator was coated with a highly reflective polymer film. The cavity type receiver was filled with sodium nitrate to act as a heat storage and transfer medium. The collection efficiency of the cavity was estimated at 70%. The gross thermal conversion efficiency of the system was 39%, which represented a 333% improvement over the first concentrator assembled at SESEC. At peak insolation 5.46 kW of thermal energy was produced. The material cost for the system was $3,052. / A Thesis submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Master of Science. / Degree Awarded: Spring Semester, 2009. / Date of Defense: March 26, 2009. / Solar Thermal Collector, Aborber, Tilt Angle, Receiver Cavity Optimization / Includes bibliographical references. / Anjaneyulu Krothapalli, Professor Directing Thesis; Brenton Greska, Committee Member; Juan Carlos Ord´o˜nez, Committee Member; William S. Oates, Committee Member.
59

Surface Flow Measurements of Supersonic Impinging Microjets.

Unknown Date (has links)
Impinging supersonic microjets have been studied experimentally where both surface pressure and shear stress measurements and flow-field visualizations have been obtained. Microjets with diameters of 400 and 1000 microns have been investigated, operating at pressure ratios of 3, 5, and 8 and impinging plate distances of 2 to 8 diameters. The primary work concentrates on the application of oil-film interferometry to the flowfield in order to determine the surface shear stress. The results of this study indicate that high shear stress levels exist over a significant region around the impingement point and that the shear stress gradients are very high. For example, at a pressure ratio of 8, shear stress value at 2 and 11 nozzle diameters from the impingement point was found to be 300 Pa and 50 Pa, respectively. The shear stress distributions were compared with surface pressure distributions and to the limited computational results available for impinging jets. Although, a direct comparison is impossible due to lack of such data in literature, the trends observed in the present study appear to agree with those of larger supersonic impinging jets. The measurements indicate that oil-film interferometry provides repeatable, and reliable shear stress data in this complex flowfield - dominated by regions of high shear and large pressure gradients – which may not be amenable to other methods. The study also suggests some improvements, which can be implemented to further improve its reliability. / A Thesis submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Master of Science. / Degree Awarded: Fall Semester, 2003. / Date of Defense: July 9, 2003. / Jets, Surface Flow, Supersonic / Includes bibliographical references. / Farrukh S. Alvi, Professor Directing Thesis; Chiang Shih, Committee Member; George Buzyna, Committee Member; Jonathan Naughton, Outside Committee Member.
60

Resilience of Residential Structures: Analysis and Mitigation Strategies for Hurricane Wind Loads

Unknown Date (has links)
TBD / A Thesis submitted to the Department of Civil and Environmental Engineering in partial fulfillment of the requirements for the degree of Master of Science. / Spring Semester 2018. / April 17, 2018. / Includes bibliographical references. / Yassir AbdelRazig, Professor Directing Thesis; Michelle Roddenberry, Committee Member; Lisa Spainhour, Committee Member; Raphael Kampmann, Committee Member.

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