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Title: PREVENTION OF ENVIRONMENTALLY INDUCED DEGRADATION IN CARBON/EPOXY COMPOSITE MATERIAL VIA IMPLEMENTATION OF A POLYMER BASED COATING SYSTEM.
Creator: Tipton, Bradford, Sohn, Yongho, University of Central Florida
Abstract / Description: As the use of fiber reinforced plastics increases in such industries as aerospace, wind energy, and sporting goods, factors effecting long-term durability, such as environmental exposure, are of increasing interest. The primary objectives of this study were to examine the effects of extensive environmental exposure (specifically UV radiation and moisture) on carbon/epoxy composite laminate structures and to determine the relative effectiveness of polymer-based coatings at mitigating...
Show moreAs the use of fiber reinforced plastics increases in such industries as aerospace, wind energy, and sporting goods, factors effecting long-term durability, such as environmental exposure, are of increasing interest. The primary objectives of this study were to examine the effects of extensive environmental exposure (specifically UV radiation and moisture) on carbon/epoxy composite laminate structures and to determine the relative effectiveness of polymer-based coatings at mitigating degradation incurred due to such exposure. Carbon/epoxy composite specimens, both coated and uncoated, were subjected to accelerated weathering in which prolonged outdoor exposure was simulated by controlling the radiation wavelength (in the UV region), temperature, and humidity. Mechanical test data obtained for the uncoated specimens indicated a reduction in strength of approximately 6% after an environmental exposure duration of 750 hours. Test data revealed that no further degradation occurred with increased exposure duration. This reduction resulted from the erosion of the epoxy matrix in additional to the formation of matrix microcracks. The protective coatings evaluated were all epoxy based and included two different surfacing films applied during initial cure of the carbon/epoxy composite laminate and a chromate containing epoxy based paint primer applied after the cure was complete. Although the chromate primer performed well initially, degradation of the underlying substrate was detected with extended exposure durations. In contrast, the surfacing films provided superior protection against environmentally induced degradation. Although similar degradation attributes were identified in the surfacing film as observed in the uncoated composite, it is likely that this degradation was either confined within the surfacing film layer or only penetrated the very near surface of the carbon/epoxy substrate, as it did not result in a substantial reduction in mechanical strength.
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Date Issued: 2008
Identifier: CFE0002406, ucf:47731
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002406

Title: The Colonial Legacy of Environmental Degradation in Nigeria's Niger River Delta.
Creator: England, Joseph, Walker, Ezekiel, Lyons, Amelia, Sacher, John, University of Central Florida
Abstract / Description: Nigeria's petroleum industry is the lynchpin of its economy. While oil has been the source of immense wealth for the nation, that wealth has come at a cost. Nigeria's main oil-producing region of the Niger River Delta has experienced tremendous environmental degradation as a result of decades of oil exploration and production. Although there have been numerous historical works on Nigeria's oil industry, there have been no in-depth analyses of the historical roots of environmental degradation...
Show moreNigeria's petroleum industry is the lynchpin of its economy. While oil has been the source of immense wealth for the nation, that wealth has come at a cost. Nigeria's main oil-producing region of the Niger River Delta has experienced tremendous environmental degradation as a result of decades of oil exploration and production. Although there have been numerous historical works on Nigeria's oil industry, there have been no in-depth analyses of the historical roots of environmental degradation over the full range of time from the colonial period to the present. This thesis contends that the environmental degradation of Nigeria's oil producing region of the Niger Delta is the direct result of the persistent non-implementation of regulatory policies by post-independence Nigerian governments working in collusion with oil multinationals. Additionally, the environmental neglect of Nigeria's primary oil-producing region is directly traceable back to the time of colonial rule. Vital to this argument is the view that the British colonial state created the economic institutions which promoted Nigerian economic dependency after independence was achieved in 1960. The weakness of Nigeria's post-colonial dependent system is exposed presently through the continued neglect of regulatory policies by successive post-colonial Nigerian governments.
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Date Issued: 2012
Identifier: CFE0004534, ucf:49251
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004534

Title: DEVELOPMENT OF REDUCTIVE METAL SYSTEMS FOR THE DEGRADATION OF ENERGETIC COMPOUNDS (TATP, TNT, AND RDX).
Creator: Albo, Rebecca, Geiger, Cherie, University of Central Florida
Abstract / Description: Triacetone triperoxide (TATP), a cyclic peroxide explosive, is frequently used by terrorists and amateur chemists due to the ease of synthesis and the availability of reagents. TATP is extremely sensitive to shock, heat, and friction thus a safe and rapid method for treating TATP is needed. The major objective of this dissertation was to develop in situ methodologies that could safely degrade TATP in various field situations using reductive metal systems. The reductive metal systems tested...
Show moreTriacetone triperoxide (TATP), a cyclic peroxide explosive, is frequently used by terrorists and amateur chemists due to the ease of synthesis and the availability of reagents. TATP is extremely sensitive to shock, heat, and friction thus a safe and rapid method for treating TATP is needed. The major objective of this dissertation was to develop in situ methodologies that could safely degrade TATP in various field situations using reductive metal systems. The reductive metal systems tested included zero-valent iron, activated magnesium systems, and magnesium bimetals, such as Mg/Pd. TATP degradation rates with the different reactive systems were calculated to test their effectiveness. The major product for the TATP decomposition was determined as acetone, and a carbon material balance was calculated to determine each reactive system's conversion efficiency. The mechanism of TATP degradation using these reactive metal/bimetal particles was also explored including reaction pathway, intermediates, and activation energies. In addition to investigating the use of zero-valent metals to degrade TATP, studies were also conducted on the use of certain metal and semimetal ionic species. Antimony (III) ions in antimony (III) chloride were found to have the greatest effect on TATP concentration. The Sb3+ was theorized to instantaneously cleave the ring structure of the TATP molecule forming a Sb3+ complex; thus Sb3+systems could be used to successfully treat TATP. In order to treat TATP in the field, the metal and bimetal reactive particles were combined with an application technology, liquid membrane systems, to form emulsified zero-valent metal (EZVM) systems. EZVM systems containing the reactive metal/bimetal particles were made from an organic outer layer, water, and a nonionic surfactant. The EZVM systems were observed to absorb and dissolve the TATP into the emulsion droplets where TATP degradation then occurred. EZVM systems would be ideal for degrading dry TATP residues that might be found on a carpet, door entrance, steel, concrete, plastics, etc. Other studies focused on the use of microscale mechanically alloyed bimetals, particularly Mg/Pd, Fe/Pd, and Fe/Ni, as alternative remediation methods for the catalytic reduction of 2, 4, 6-trinitrotoluene (TNT), and 1, 3, 5-trimethylene-2, 4, 6-trinitramine (RDX). All the bimetals tested were shown to reduce TNT and RDX contamination in water samples, with varying reactivities under ambient reaction conditions. These metal systems could be combined with EZVM or paste treatment systems (bimetallic treatment systems (BTS)) for the in situ treatment of these environmental contaminants.
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Date Issued: 2010
Identifier: CFE0003332, ucf:48476
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003332

Title: HIGH VOLTAGE BIAS TESTING AND DEGRADATION ANALYSIS OF PHOTOVOLTAIC MODULES.
Creator: Hadagali, Vinaykumar, Dhere, Neelkanth, University of Central Florida
Abstract / Description: This thesis mainly focuses on two important aspects of the photovoltaic modules. The first aspect addressed the high voltage bias testing and data and degradation analysis of high voltage biased thin film photovoltaic modules. The second aspect addressed the issues of reliability and durability of crystalline silicon module. Grid-connected photovoltaic systems must withstand high voltage bias in addition to harsh environmental conditions such as intermittent solar irradiance, high humidity,...
Show moreThis thesis mainly focuses on two important aspects of the photovoltaic modules. The first aspect addressed the high voltage bias testing and data and degradation analysis of high voltage biased thin film photovoltaic modules. The second aspect addressed the issues of reliability and durability of crystalline silicon module. Grid-connected photovoltaic systems must withstand high voltage bias in addition to harsh environmental conditions such as intermittent solar irradiance, high humidity, heat and wind. a-Si:H thin-film photovoltaic modules with earlier generation SnO2:F transparent conducting oxide (TCO) on the front glass installed on the FSEC High Voltage Test Bed were monitored since December 2001. The data was collected on a daily basis and analyzed. The leakage currents for some chosen time period were calculated and compared with the measured values. Current-voltage characteristic measurements were carried out to check any reduction in the power. Samples were cored and extracted for analysis from one of the -600 V biased modules. Leakage currents in high-voltage-biased laminates specially prepared with improved SnO2:F TCO are being monitored in the hot and humid climate in Florida. Negatively-biased modules showed clear signs of delamination. The leakage currents in high-voltage biased photovoltaic modules are functions of both temperature and relative humidity. Photovoltaic module leakage conductance was found to be thermally stimulated with a characteristic activation energy that depends on relative humidity. The adhesional strength was lost completely in the damaged area. Leakage current values from support to ground in new, unframed laminates fabricated with improved SnO2:F TCO layer were ~100 times lower under the high voltage bias in hot and humid environment. Information on the failure of field deployed modules must be complemented with why and how the modules fail while considering the issues of reliability and durability of crystalline silicon module. At present, all the failure modes have not been identified and failure mechanisms have not been understood. Experience has shown that as the materials and processes are changed, reliability issues that apparently had been resolved resurface. A multicrystalline silicon photovoltaic module that was manufactured by a non-US company and that had shown >50% performance loss in field-deployment of <2 years in hot and dry climate were studied for degradation analysis in comparison with a mc-Si module that was manufactured by the same company and that performed well after 10 years of field-deployment in hot and humid climate.. I-V measurements were carried out to analyze the reduction in photovoltaic parameters. Solder bond strength in mc-Si photovoltaic modules were measured to understand early degradation of performance. Samples were cored and extracted for further analysis. Adhesional strength between the busline metallization and the silicon cell in a newer generation mc-Si photovoltaic module was found to be considerably lower than that in the earlier vintage module. These results can be useful for early detection and diagnosis of field reliability issues and could assist in establishing correlation between long-term field data and observations and accelerated environmental stress testing. It is suggested that more detailed study should be undertaken using unencapsulated strings of crystalline silicon modules so as to avoid complication due to encapsulant creeping beneath the ribbons.
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Date Issued: 2005
Identifier: CFE0000798, ucf:46563
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000798

Title: A PRELIMINARY STUDY FOR ESTIMATING POSTMORTEM INTERVAL OF FABRIC DEGRADATION IN CENTRAL FLORIDA.
Creator: Humbert, Lorraine, Schultz, John, University of Central Florida
Abstract / Description: Forensic anthropologists rely on forensic evidence to estimate the postmortem interval of a decedent. This may include the study of the degree of deterioration of the human body, the life stage of insects, and the degradation of associated material evidence. Material evidence comes in many forms, and certain taphonomic processes will affect the material and must be considered when making inferences about a PMI. These include variables such as the characteristics of the soil, microorganisms,...
Show moreForensic anthropologists rely on forensic evidence to estimate the postmortem interval of a decedent. This may include the study of the degree of deterioration of the human body, the life stage of insects, and the degradation of associated material evidence. Material evidence comes in many forms, and certain taphonomic processes will affect the material and must be considered when making inferences about a PMI. These include variables such as the characteristics of the soil, microorganisms, and the presence of a decaying organic material. Previous research has undertaken studies in how fabric degrades over time; however, there is no standard methodology in use. The purpose of this research project is to establish a comprehensive scoring system and description standard after analyzing the degradation of four different fabric types. This will be useful for future studies in need of a standard methodology. In addition, the methods used in this project can be applied to actual forensic cases. After retrieval, the fabric type with the highest degradation was the cotton with about 1/3 of all cotton fabric swatches demonstrating more than 50% total degradation. For all fabric types, swatches that were positioned flat tended to degrade more than those that were positioned crumpled. Cotton fabric swatches degraded more in Trench 1 and Trench 2 than the Ground Surface, however, all other fabric types demonstrated slightly more degradation on the Ground Surface than the other two Areas. Soil moisture fluctuated the most on the Ground Surface while Trench 1 and Trench 2 were able to retain more water in the soil. Overall, cotton was the only fabric type to degrade significantly enough to show how it degrades over time, while the other fabric types have longer degradation intervals that must be studied further.
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Date Issued: 2013
Identifier: CFH0004515, ucf:45220
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH0004515

Title: Expression of Trichoderma reesei (&)#223;-Mannanase in Tobacco Chloroplasts and its Utilization in Lignocellulosic Woody Biomass Hydrolysis.
Creator: Agrawal, Pankaj, Daniell, Henry, Kolattukudy, Pappachan, Self, William, University of Central Florida
Abstract / Description: Lignocellulosic ethanol offers a promising alternative to conventional fossil fuels. One among the major limitations in the lignocellulosic biomass hydrolysis is unavailability of efficient and environmentally biomass degrading technologies. Plant-based production of these enzymes on large scale offers a cost effective solution. Cellulases, hemicellulases including mannanases and other accessory enzymes are required for conversion of lignocellulosic biomass into fermentable sugars. ?...
Show moreLignocellulosic ethanol offers a promising alternative to conventional fossil fuels. One among the major limitations in the lignocellulosic biomass hydrolysis is unavailability of efficient and environmentally biomass degrading technologies. Plant-based production of these enzymes on large scale offers a cost effective solution. Cellulases, hemicellulases including mannanases and other accessory enzymes are required for conversion of lignocellulosic biomass into fermentable sugars. ?-mannanase catalyzes endo-hydrolysis of the mannan backbone, a major constituent of woody biomass. In this study, man1 gene encoding ?-mannanase was isolated from Trichoderma reesei and expressed via the chloroplast genome. PCR and Southern hybridization analysis confirmed the site-specific transgene integration into the tobacco chloroplast genomes and homoplasmy. Transplastomic plants were fertile and set viable seeds. Germination of seeds showed inheritance of transgenes into the progeny without Mendelian segregation. Expression of the endo-?-mannanase gene for the first time in plants facilitated its characterization for use in enhanced lignocellulosic biomass hydrolysis. Gel diffusion assay for endo-?-mannanase showed the zone of clearance confirming functionality of chloroplast-derived mannanase. Endo-?-mannanase expression levels reached up to 25 units per gram of leaf (fresh weight). Chloroplast-derived mannanase had higher temperature stability (40 (&)deg;C to 70 (&)deg;C) and wider pH optima (pH 3.0 to 7.0) than E.coli enzyme extracts. Plant crude extracts showed 6-7 fold higher enzyme activity than E.coli extracts due to the formation of disulfide bonds in chloroplasts, thereby facilitating their direct utilization in enzyme cocktails without any purification. Chloroplast-derived mannanase when added to the enzyme cocktail containing a combination of different enzymes yielded 20% more glucose equivalents from pinewood than the cocktail without mannanase. Our results demonstrate that chloroplast-derived mannanase is an important component of enzymatic cocktail for woody biomass hydrolysis and should provide a cost-effective solution for its diverse applications in the paper, oil, pharmaceutical, coffee and detergent industries.
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Date Issued: 2011
Identifier: CFE0004467, ucf:49309
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004467

Title: Quantitative Assessment of the effects of Microbial Degradation of a Simple Hydrocarbon Mixture.
Creator: Kindell, Jessica, Sigman, Michael, Bridge, Candice, Campiglia, Andres, University of Central Florida
Abstract / Description: Ignitable liquids consist of either a single organic compound or a complex organic mixture. In regards to fire debris analysis, the analyst is responsible for determining if an ignitable liquid residue is present. However, when extracted from soil-containing fire debris evidence, chemical degradation from microorganisms is observed to result in the loss of compounds based on chemical structure. It can also happen when the evidence container is stored at room temperature before analysis. This...
Show moreIgnitable liquids consist of either a single organic compound or a complex organic mixture. In regards to fire debris analysis, the analyst is responsible for determining if an ignitable liquid residue is present. However, when extracted from soil-containing fire debris evidence, chemical degradation from microorganisms is observed to result in the loss of compounds based on chemical structure. It can also happen when the evidence container is stored at room temperature before analysis. This can present a challenge to the fire debris analyst when identifying and classifying the ignitable liquid residue based on the criteria established by standard test methods. The purpose of this research was to observe the microbial degradation of fourteen compounds, at room temperature over a period of time, for possible by-product formation that could coincide with compounds normally present in an ignitable liquid. Additionally, a quantitative assessment was performed to observe and record the loss rate of compounds in a representative simple mixture. Finally, the loss rate from the simple mixture was compared to commercially available ignitable liquids. Degradation studies were conducted to observe the microbial degradation of a representative compounds (individually and in a simple mixture, both weathered and unweathered) and seven ignitable liquids of different ASTM E1618 classifications. Potting soil was spiked with 20 (&)#181;L of a liquid/compound and was allowed to stand at room temperature for a period of time. The simple mixture was evaporated to 50% and 90% using a steady nitrogen gas flow to compare the degradation process to the unweathered mixture. All samples were extracted and analyzed using passive-headspace concentration and gas chromatography-mass spectrometry.The formation of by-products was not observed when degrading the compounds from the simple mixture individually as seen in other research. The simple mixture, unweathered and 50% weathered, resulted in rapid degradation of their oxygenated compounds. The straight-chained alkanes and toluene were observed to be more susceptible to microbial attack than the highly-substituted aromatics and the branched and cyclic alkanes. The 90% weathered mixture followed the same degradation trend as the unweathered and 50% weathered samples, although it only contained two compounds. The loss rates/half-lives for each simple mixture sample (unweathered, 50% weathered, and 90% weathered) were determined to be approximately 3.5, 3.5, and 0.84 days. The unweathered and 50% weathered sample half-lives were similar due to containing compounds with similar susceptibility to degradation, while the 90% weathered sample contained one compound that was more highly susceptible to degradation. When comparing the 3.5 day half-life to the seven different ASTM class liquids, the isoparaffinic product and the naphthenic-paraffinic product had similar rates of degradation while aromatic solvent and normal alkane classes had the shortest half-lives. When observing the degradation of the gasoline, medium petroleum distillate and the miscellaneous, the constituent compounds were seen to exhibit a range of degradation rates that corresponded to half-lives less than and greater than 3.5 days.
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Date Issued: 2015
Identifier: CFE0005966, ucf:50817
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005966

Title: The Behavior of Cerium Oxide Nanoparticles in Polymer Electrolyte Membranes in Ex-Situ and In-Situ Fuel Cell Durability Tests.
Creator: Pearman, Benjamin, Hampton, Michael, Blair, Richard, Clausen, Christian, Seal, Sudipta, Campiglia, Andres, Yestrebsky, Cherie, Mohajeri, Nahid, University of Central Florida
Abstract / Description: Fuel cells are known for their high efficiency and have the potential to become a major technology for producing clean energy, especially when the fuel, e.g. hydrogen, is produced from renewable energy sources such as wind or solar. Currently, the two main obstacles to wide-spread commercialization are their high cost and the short operational lifetime of certain components.Polymer electrolyte membrane (PEM) fuel cells have been a focus of attention in recent years, due to their use of...
Show moreFuel cells are known for their high efficiency and have the potential to become a major technology for producing clean energy, especially when the fuel, e.g. hydrogen, is produced from renewable energy sources such as wind or solar. Currently, the two main obstacles to wide-spread commercialization are their high cost and the short operational lifetime of certain components.Polymer electrolyte membrane (PEM) fuel cells have been a focus of attention in recent years, due to their use of hydrogen as a fuel, their comparatively low operating temperature and flexibility for use in both stationary and portable (automotive) applications.Perfluorosulfonic acid membranes are the leading ionomers for use in PEM hydrogen fuel cells. They combine essential qualities, such as high mechanical and thermal stability, with high proton conductivity. However, they are expensive and currently show insufficient chemical stability towards radicals formed during fuel cell operation, resulting in degradation that leads to premature failure. The incorporation of durability improving additives into perfluorosulfonic acid membranes is discussed in this work.Cerium oxide (ceria) is a well-known radical scavenger that has been used in the biological and medical field. It is able to quench radicals by facilely switching between its Ce(III) and Ce(IV) oxidation states.In this work, cerium oxide nanoparticles were added to perfluorosulfonic acid membranes and subjected to ex-situ and in-situ accelerated durability tests.The two ceria formulations, an in-house synthesized and commercially available material, were found to consist of crystalline particles of 2 (-) 5 nm and 20 (-) 150 nm size, respectively, that did not change size or shape when incorporated into the membranes.At higher temperature and relative humidity in gas flowing conditions, ceria in membranes is found to be reduced to its ionic form by virtue of the acidic environment. In ex-situ Fenton testing, the inclusion of ceria into membranes reduced the emission of fluoride, a strong indicator of degradation, by an order of magnitude with both liquid and gaseous hydrogen peroxide. In open-circuit voltage (OCV) hold fuel cell testing, ceria improved durability, as measured by several parameters such as OCV decay rate, fluoride emission and cell performance, over several hundred hours and influenced the formation of the platinum band typically found after durability testing.
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Date Issued: 2012
Identifier: CFE0004789, ucf:49731
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004789

Title: MECHANISMS OF LIFETIME IMPROVEMENT IN THERMAL BARRIER COATINGS WITH HF AND/OR Y MODIFICATION OF CMSX-4 SUPERALLOY SUBSTRATES.
Creator: Liu, Jing, Sohn, Yong ho, University of Central Florida
Abstract / Description: In modern turbine engines for propulsion and energy generation, thermal barrier coating (TBCs) protect hot-section blades and vanes, and play a critical role in enhancing reliability, durability and operation efficiency. In this study, thermal cyclic lifetime and microstructural degradation of electron beam physical vapor deposited (EB-PVD) Yttria Stabilized Zirconia (YSZ) with (Ni,Pt)Al bond coat and Hf- and/or Y- modified CMSX-4 superalloy substrates were examined. Thermal cyclic lifetime...
Show moreIn modern turbine engines for propulsion and energy generation, thermal barrier coating (TBCs) protect hot-section blades and vanes, and play a critical role in enhancing reliability, durability and operation efficiency. In this study, thermal cyclic lifetime and microstructural degradation of electron beam physical vapor deposited (EB-PVD) Yttria Stabilized Zirconia (YSZ) with (Ni,Pt)Al bond coat and Hf- and/or Y- modified CMSX-4 superalloy substrates were examined. Thermal cyclic lifetime of TBCs was measured using a furnace thermal cycle test that consisted of 10-minute heat-up, 50-minute dwell at 1135C, and 10-minute forced-air-quench. TBC lifetime was observed to improve from 600 cycles to over 3200 cycles with appropriated Hf- and/or Y alloying of CMSX-4 superalloys. This significant improvement in TBC lifetime is the highest reported lifetime in literature with similar testing parameters. Beneficial role of reactive element (RE) on the durability of TBCS were systematically investigated in this study. Photostimulated luminescence spectroscopy (PL) was employed to non-destructively measure the residual stress within the TGO scale as a function of thermal cycling. Extensive microstructural analysis with emphasis on the YSZ/TGO interface, TGO scale, TGO/bond coat interface was carried out by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and scanning electron microscopy (STEM) as a funcion of thermal cycling including after the spallation failure. Focused ion beam in-situ lift-out (FIB-INLO) technique was employed to prepare site-specific TEM specimens. X-ray diffraction (XRD) and secondary ion mass spectroscopy (SIMS) were also employed for phase identification and interfacial chemical analysis. While undulation of TGO/bond coat interface (e.g., rumpling and ratcheting) was observed to be the main mechanism of degradation for the TBCs on baseline CMSX-4, the same interface remained relatively flat (e.g., suppressed rumpling and ratcheting) for durable TBCs on Hf- and/or Y-modified CMSX-4. The fracture paths changed from the YSZ/TGO interface to the TGO/bond coat interface when rumpling was suppressed. The geometrical incompatibility between the undulated TGO and EB-PVD YSZ lead to the failure at the YSZ/TGO interface for TBCs with baseline CMSX-4. The magnitude of copressive residual stress within the TGO scale measured by PL gradually decreased as a function of thermal cycling for TBCs with baseline CMSX-4 superalloy substrates. This gradual decrease corrsponds well to the undulation of the TGO scale that may lead to relaxation of the compressive residual stress within the TGO scale. For TBCs with Hf- and/or Y-modified CMSX-4 superalloy substrates, the magnitude of compressive residual stress within the TGO scale remained relatively constant throughout the thermal cycling, although PL corresponding to the stress-relief caused by localized cracks at the TGO/bond coat interface and within the TGO scale was observed frequently starting 50% of lifetime. A slightly smaller parabolic growth constant and grain size of the TGO scale was observed for TBCs with Hf- and/or Y- modified CMSX-4. Small monoclinic HfO2 precipitates were observed to decorate grain boundaries and the triple pointes within the alpha-Al2O3 scale for TBCs with Hf- and/or Y-modified CMSX-4 substrates. Segregation of Hf/Hf4+ at the TGO/bond coat interfaces was also observed for TBCs with Hf- and/or Y-modified CMSX-4 superalloys substrates. Adherent and pore-free YSZ/TGO interface was observed for TBCs with Hf- and/or Y-modified CMSX-4, while a significant amount of decohesion at the YSZ/TGO interface was observed for TBCs with baseline CMSX-4. The beta-NiAl(B2) phase in the (Ni,Pt)Al bond coat was observed to partially transform into gama prime-Ni3Al (L12) phase due to depletion of Al in the bond coat during oxidation. More importantly, the remaining beta-NiAl phase transformed into L10 martensitic phase upon cooling even though there was no significant difference in these phase transformations for all TBCs. Results from these microstructural observations are documented to elucidate mechanisms that suppress the rumpling of the TGO/bond coat interface, which is responsible for superior performance of EB-PVD TBCs with (Ni,Pt)Al bond coat and Hf- and/or Y-modified CMXS-4 superalloy.
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Date Issued: 2007
Identifier: CFE0001872, ucf:47382
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001872

Title: Assessing the Impact of Radionuclides Released into the Floridan Aquifer by a Massive Sinkhole on Local Municipal Water Supplies.
Creator: Arenas Daza, Maria, Duranceau, Steven, Sadmani, A H M Anwar, Wang, Dingbao, University of Central Florida
Abstract / Description: In late August 2016, a sinkhole spanning 45 feet (13.7 meters) in diameter opened at a phosphate fertilizer facility (Mosaic Company) near Mulberry, Florida, leaking an estimated 215 million gallons (813,000 cubic meters) of radionuclide-contaminated water 300 feet into the Floridan aquifer. An investigation to determine possible impacts to the environment and local community drinking water supplies was implemented that focused on two 1.5 million gallon per day (MGD) Tampa Bay Water (TBW)...
Show moreIn late August 2016, a sinkhole spanning 45 feet (13.7 meters) in diameter opened at a phosphate fertilizer facility (Mosaic Company) near Mulberry, Florida, leaking an estimated 215 million gallons (813,000 cubic meters) of radionuclide-contaminated water 300 feet into the Floridan aquifer. An investigation to determine possible impacts to the environment and local community drinking water supplies was implemented that focused on two 1.5 million gallon per day (MGD) Tampa Bay Water (TBW) production wells and two Polk County Utilities (PCU) water treatment facilities. Water samples collected between June 2017 and January 2018 at the TBW and PCU sites were found to contain radionuclides below regulated levels. To evaluate the effectiveness of membrane treatment should the TBW and PCU drinking water wells be affected by the spill in the future, bench-scale, flat-sheet reverse osmosis (RO) and nanofiltration (NF) membrane process testing was performed using TBW and PCU wellfield sample aliquots. NF and RO were shown to be capable of removing at minimum of 86 and 92 percent, respectively, of the barium content that had been spiked into groundwater testing aliquots. Based on testing results, a conceptual opinion of probable capital cost for a membrane process ranged from $1.7 and $3.5 million for a 0.25 MGD and 2.0 MGD design capacity, respectively. Process operation and maintenance costs ranged between $0.99/Kgal and $0.26/Kgal for a 0.25 MGD and 2.0 MGD design capacity, respectively. The amortized total cost based on a 20-year period and 8 percent interest rate ranged between $1.88/Kgal for a 0.25 MGD and $0.49/Kgal for a 2.0 MGD design capacity plant. An estimate of unavailable water value due to a long-term well shut-down was approximated as $0.64/Kgal.
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Date Issued: 2018
Identifier: CFE0006970, ucf:52911
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006970

Title: GaN Power Devices: Discerning Application-Specific Challenges and Limitations in HEMTs.
Creator: Binder, Andrew, Yuan, Jiann-Shiun, Sundaram, Kalpathy, Roy, Tania, Kapoor, Vikram, Chow, Lee, University of Central Florida
Abstract / Description: GaN power devices are typically used in the 600 V market, for high efficiency, high power-density systems. For these devices, the lateral optimization of gate-to-drain, gate, and gate-to-source lengths, as well as gate field-plate length are critical for optimizing breakdown voltage and performance. This work presents a systematic study of lateral scaling optimization for high voltage devices to minimize figure of merit and maximize breakdown voltage. In addition, this optimization is...
Show moreGaN power devices are typically used in the 600 V market, for high efficiency, high power-density systems. For these devices, the lateral optimization of gate-to-drain, gate, and gate-to-source lengths, as well as gate field-plate length are critical for optimizing breakdown voltage and performance. This work presents a systematic study of lateral scaling optimization for high voltage devices to minimize figure of merit and maximize breakdown voltage. In addition, this optimization is extended for low voltage devices ((<) 100 V), presenting results to optimize both lateral features and vertical features. For low voltage design, simulation work suggests that breakdown is more reliant on punch-through as the primary breakdown mechanism rather than on vertical leakage current as is the case with high-voltage devices. A fabrication process flow has been developed for fabricating Schottky-gate, and MIS-HEMT structures at UCF in the CREOL cleanroom. The fabricated devices were designed to validate the simulation work for low voltage GaN devices. The UCF fabrication process is done with a four layer mask, and consists of mesa isolation, ohmic recess etch, an optional gate insulator layer, ohmic metallization, and gate metallization. Following this work, the fabrication process was transferred to the National Nano Device Laboratories (NDL) in Hsinchu, Taiwan, to take advantage of the more advanced facilities there. Following fabrication, a study has been performed on defect induced performance degradation, leading to the observation of a new phenomenon: trap induced negative differential conductance (NDC). Typically NDC is caused by self-heating, however by implementing a substrate bias test in conjunction with pulsed I-V testing, the NDC seen in our fabricated devices has been confirmed to be from buffer traps that are a result of poor channel carrier confinement during the dc operating condition.
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Date Issued: 2019
Identifier: CFE0007885, ucf:52786
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007885

Title: Use of an Activated Magnesium/cosolvent System for the Desorption and Degradation of Polycyclic Aromatic Hydrocarbons and Their Oxygenated Derivatives in Contaminated Soils.
Creator: Elie, Marc, Yestrebsky, Cherie, Clausen, Christian, Elsheimer, Seth, Campiglia, Andres, Randall, Andrew, University of Central Florida
Abstract / Description: The contamination of soils, with polycyclic aromatic hydrocarbons (PAHs), remains a widespread environmental concern. In the past two decades, many physical, chemical and biological methods have been developed and evaluated for the degradation of PAHs. However, due to their low aqueous solubility, high sorption affinity, hydrophobicity and recalcitrance, the environmental remediation of PAHs in soil continues to be economically challenging. In addition to PAH contamination, the presence of...
Show moreThe contamination of soils, with polycyclic aromatic hydrocarbons (PAHs), remains a widespread environmental concern. In the past two decades, many physical, chemical and biological methods have been developed and evaluated for the degradation of PAHs. However, due to their low aqueous solubility, high sorption affinity, hydrophobicity and recalcitrance, the environmental remediation of PAHs in soil continues to be economically challenging. In addition to PAH contamination, the presence of oxygenated derivatives of PAHs (OPAHs), in soils, has increasingly become a concern due to their greater toxic properties compared to parent PAH compounds. To date, no investigations on OPAH-remediation methods have been presented in the literature. The use of zero-valent metals (ZVMs) has been reported for several halogenated contaminants in solution systems, but the effectiveness of ZVM to degrade sorbed PAHs and OPAHs has been rarely addressed. This present research focuses on the development of a combined technique for the feasible desorption and degradation of PAHs and OPAHs in soils. PAH and OPAH degradation efficiency, using activated magnesium (Mg) metal combined with an ethanol-ethyl lactate cosolvent (1:1 ratio), was initially examined in soil-free systems. This metal/cosolvent system demonstrated adequate degradation (above 80%) for high-molecular-weight (HMW) PAHs, which were subsequently converted into hydroaromatic compounds; while OPAHs were degraded and converted into hydroxylated or hydrogenated derivatives. Further soil-free studies revealed that the degradation rate was affected by the surface or reactive sites of the metal and that optimum degradation efficiency were obtained with Mg ball milled with graphite (Mg/C).In a bench-scale feasibility test, the efficacy of this system was assessed on a soil spiked with a mixture of three HMW PAHs compounds and three OPAHs compounds with amounts ranging from 0.033 mmol to 0.060 mmol. The experimental results show that 2 mL of an ethanol-ethyl lactate solvent mixture resulted in 58% to 85% extraction efficiency for the selected contaminants in 1 g of spiked soil, followed by 64 - 87% degradation efficiency of the extracted contaminants with 4.11 mmol of the activated metal. This activated-Mg/cosolvent system can be considered as a promising alternative method for ex situ remediation of PAH and OPAH-contaminated soils.
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Date Issued: 2012
Identifier: CFE0004533, ucf:49259
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004533

Title: Modeling of Thermal Properties of Fiber Glass Polyester Resin Composite Under Thermal Degradation Condition.
Creator: Tsoi, Marvin, Chen, Ruey-Hung, Gou, Jihua, Ilie, Marcel, University of Central Florida
Abstract / Description: Composites, though used in a variety of applications from chairs and office supplies to structures of U.S. Navy ships and aircrafts, are not all designed to hold up to extreme heat flux and high temperature. Fiber-reinforced polymeric composites (FRPC) have been proven to provide the much needed physical and mechanical properties under fire exposure. FRPC notable features are its combination of high specific tensile strength, low weight, along with good corrosion and fatigue resistance....
Show moreComposites, though used in a variety of applications from chairs and office supplies to structures of U.S. Navy ships and aircrafts, are not all designed to hold up to extreme heat flux and high temperature. Fiber-reinforced polymeric composites (FRPC) have been proven to provide the much needed physical and mechanical properties under fire exposure. FRPC notable features are its combination of high specific tensile strength, low weight, along with good corrosion and fatigue resistance. However FRPC are susceptible to thermal degradation and decomposition, which yields flammable gas, and are thus highly combustible. This property restricts polymeric material usage.This study developed a numerical model that simulated the degradation rate and temperature profiles of a fiber-reinforced polyester resin composite exposed to a constant heat flux and hydrocarbon fire in a cone calorimeter. A numerical model is an essential tool because it gives the composite designer the ability to predict results in a time and cost efficient manner. The goal of this thesis is to develop a numerical model to simulate a zonal-layer polyester resin and fiber-glass mat composite and then validate the model with experimental results from a cone calorimeter. By inputting the thermal properties of the layered composite of alternating polymer and polymer-infused glass fiber mat layers, the numerical model is one step closer to representing the experimental data from the cone calorimeter test. The final results are achieved through adding a simulated heat flux from the pilot ignition of the degraded gas of the polyester resin. The results can be coupled into a mechanical model, which may be separately constructed for future study on the mechanical strength of composites under fire conditions.
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Date Issued: 2011
Identifier: CFE0004171, ucf:49076
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004171

Title: experimental and numerical investigations on bond durability of cfrp strengthened concrete members subjected to environmental exposure.
Creator: Al-Jelawy, Haider, Mackie, Kevin, Gou, Jihua, Chopra, Manoj, University of Central Florida
Abstract / Description: Fiber reinforced polymer (FRP) composites have become an attractive alternative to conventional methods for external-strengthening of civil infrastructure, particularly as applied to flexural strengthening of reinforced concrete (RC) members. However, durability of the bond between FRP composite and concrete has shown degradation under some aggressive environments. Although numerous studies have been conducted on concrete members strengthened with FRP composites, most of those studies have...
Show moreFiber reinforced polymer (FRP) composites have become an attractive alternative to conventional methods for external-strengthening of civil infrastructure, particularly as applied to flexural strengthening of reinforced concrete (RC) members. However, durability of the bond between FRP composite and concrete has shown degradation under some aggressive environments. Although numerous studies have been conducted on concrete members strengthened with FRP composites, most of those studies have focused on the degradation of FRP material itself, relatively few on bond behavior under repeated mechanical and environmental loading.This thesis investigates bond durability under accelerated environmental conditioning of two FRP systems commonly employed in civil infrastructure strengthening: epoxy and polyurethane systems. Five environments were considered under three different conditioning durations (3 months, 6 months, and 1 year). For each conditioning environment and duration (including controls), the following were laboratory tested: concrete cylinders, FRP tensile coupons, and FRP-strengthened concrete flexural members. Numerical investigations were performed using MSC MARC finite element software package to support the outcomes of durability experimental tests. Precise numerical studies need an accurate model for the bond between FRP and concrete, a linear brittle model is proposed in this work that is calibrated based on nonlinear regression of existing experimental lap shear data.Results of tensile tests on FRP coupons indicate that both epoxy and polyurethane FRP systems do not degrade significantly under environmental exposure. However, flexural tests on the FRP strengthened concrete beams indicate that bond between FRP and concrete shows significant degradation, especially for aqueous exposure. Moreover, a protective coating suppresses the measured degradation. Also, experimental load-displacement curves for control beams show excellent agreement with numerical load-displacement curves obtained using the proposed bond model. Finally, a bond-slip model is predicted for concrete leachate conditioned beams by matching load-displacement curves for those beams with numerical load-displacement curves.
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Date Issued: 2013
Identifier: CFE0004971, ucf:49589
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004971

Title: Fire Retardant Polymer Nanocomposites: Materials Design and Thermal Degradation Modeling.
Creator: Zhuge, Jinfeng, Gou, Jihua, Chen, Ruey-Hung, Kapat, Jayanta, Zhai, Lei, University of Central Florida
Abstract / Description: Compared to conventional materials, polymer matrix composites (PMCs) have a number of attractive properties, including light weight, easiness of installation, potential to lower system-level cost, high overall durability, and less susceptibility to environmental deterioration. However, PMCs are vulnerable to fire such that they degrade, decompose, and sometimes yield toxic gases at high temperature. The degradation and decomposition of composites lead to loss in mass, resulting in loss in...
Show moreCompared to conventional materials, polymer matrix composites (PMCs) have a number of attractive properties, including light weight, easiness of installation, potential to lower system-level cost, high overall durability, and less susceptibility to environmental deterioration. However, PMCs are vulnerable to fire such that they degrade, decompose, and sometimes yield toxic gases at high temperature. The degradation and decomposition of composites lead to loss in mass, resulting in loss in mechanical strength.This research aims to improve the structural integrity of the PMCs under fire conditions by designing and optimizing a fire retardant nanopaper coating, and to fundamentally understand the thermal response and post-fire mechanical behavior the PMCs through numerical modeling. Specifically, a novel paper-making process that combined carbon nanofiber, nanoclay, exfoliated graphite nanoplatelet, and ammonium polyphosphate into a self-standing nanopaper was developed. The nanopaper was then coated onto the surface of the PMCs to improve the fire retardant performance of the material. The morphology, thermal stability, flammability, and post-fire flexural modulus of the nanopaper coated-PMCs were characterized. The fire retardant mechanism of the nanopaper coating was studied.Upon successfully improving the structure integrity of the PMCs by the nanopaper coatings, a thermal degradation model that captured the decomposition reaction of the polymer matrix with a second kind boundary condition (constant heat flux) was solved using Finite Element (FE) method. The weak form of the model was constructed by the weighted residual method. The model quantified the thermal and post-fire flexural responses of the composites subject to continuously applied heat fluxes. A temperature dependent post-fire residual modulus was assigned to each element in the FE domain. The bulk residual modulus was computed by assembling the modulus of each element. Based on the FE model, a refined Finite Difference (FD) model was developed to predict the fire response of the PMCs coated with the nanopapers. The FD model adopted the same post-fire mechanical evaluation method. However, unlike the FE model, the flow of the decomposed gas, and permeability and porosity of the composites were taken into account in the refined FD model. The numerical analysis indicated that the thickness and porosity of the composites had a profound impact on the thermal response of the composites.The research funding from the Office of Naval Research (ONR) and Federal Aviation Administration Center of Excellence for Commercial Space Transportation (FAA COE AST) is acknowledged.
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Date Issued: 2012
Identifier: CFE0004263, ucf:49534
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004263

Title: FUNDAMENTAL STUDY OF MECHANICAL AND CHEMICAL DEGRADATION MECHANISMS OF PEM FUEL CELL MEMBRANES.
Creator: Yoon, Wonseok, Huang, Xinyu, University of Central Florida
Abstract / Description: One of the important factors determining the lifetime of polymer electrolyte membrane fuel cells (PEMFCs) is membrane degradation and failure. The lack of effective mitigation methods is largely due to the currently very limited understanding of the underlying mechanisms for mechanical and chemical degradations of fuel cell membranes. In order to understand degradation of membranes in fuel cells, two different experimental approaches were developed; one is fuel cell testing under open circuit...
Show moreOne of the important factors determining the lifetime of polymer electrolyte membrane fuel cells (PEMFCs) is membrane degradation and failure. The lack of effective mitigation methods is largely due to the currently very limited understanding of the underlying mechanisms for mechanical and chemical degradations of fuel cell membranes. In order to understand degradation of membranes in fuel cells, two different experimental approaches were developed; one is fuel cell testing under open circuit voltage (OCV) with bi-layer configuration of the membrane electrode assemblies (MEAs) and the other is a modified gas phase FentonÃ‚Â's test. Accelerated degradation tests for polymer electrolyte membrane (PEM) fuel cells are frequently conducted under open circuit voltage (OCV) conditions at low relative humidity (RH) and high temperature. With the bi-layer MEA technique, it was found that membrane degradation is highly localized across thickness direction of the membrane and qualitatively correlated with location of platinum (Pt) band through mechanical testing, Infrared (IR) spectroscopy, fluoride emission, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS) measurement. One of the critical experimental observations is that mechanical behavior of membranes subjected to degradation via FentonÃ‚Â's reaction exhibit completely different behavior with that of membranes from the OCV testing. This result led us to believe that other critical factors such as mechanical stress may affect on membrane degradation and therefore, a modified gas phase FentonÃ‚Â's test setup was developed to test the hypothesis. Interestingly, the results showed that mechanical stress directly accelerates the degradation rate of ionomer membranes, implying that the rate constant for the degradation reaction is a function of mechanical stress in addition to commonly known factors such as temperature and humidity. Membrane degradation induced by mechanical stress necessitates the prediction of the stress distribution in the membrane under various conditions. One of research focuses was on the developing micromechanism-inspired continuum model for ionomer membranes. The model is the basis for stress analysis, and is based on a hyperelastic model with reptation-inspired viscous flow rule and multiplicative decomposition of viscoelastic and plastic deformation gradient. Finally, evaluation of the membrane degradation requires a fuel cell model since the degradation occurs under fuel cell operating conditions. The fuel cell model included structural mechanics models and multiphysics models which represents other phenomena such as gas and water transport, charge conservation, electrochemical reactions, and energy conservation. The combined model was developed to investigate the compression effect on fuel cell performance and membrane stress distribution.
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Date Issued: 2010
Identifier: CFE0003006, ucf:48359
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003006

Title: Investigation of a Novel Magnesium and Acidified Ethanol System for the Degradation of Persistent Organic Pollutants.
Creator: Maloney, Phillip, Yestrebsky, Cherie, Clausen, Christian, Elsheimer, Seth, Frazer, Andrew, Quinn, Jacqueline, University of Central Florida
Abstract / Description: For centuries chemists have sought to improve humankind's quality of life and address many of society's most pressing needs through the development of chemical processes and synthesis of new compounds, often with phenomenal results. Unfortunately, there also are many examples where these chemicals have had unintended, detrimental consequences that are not apparent until years or decades after their initial use. There are numerous halogenated molecules in this category that are globally...
Show moreFor centuries chemists have sought to improve humankind's quality of life and address many of society's most pressing needs through the development of chemical processes and synthesis of new compounds, often with phenomenal results. Unfortunately, there also are many examples where these chemicals have had unintended, detrimental consequences that are not apparent until years or decades after their initial use. There are numerous halogenated molecules in this category that are globally dispersed, resistant to natural degradation processes, bioaccumulative, and toxic to living organisms. Chemicals such as these are classified as persistent organic pollutants (POPs), and due to their negative environmental and health effects, they require safe, effective, and inexpensive means of remediation.This research focuses on the development and optimization of a reaction matrix capable of reductively dehalogenating several POPs. Initial experiments determined that powdered magnesium and 1% V/V acetic acid in absolute ethanol was the most effective system for degrading polychlorinated biphenyl (PCB), an extraordinarily recalcitrant environmental contaminant. Further studies showed that this matrix also was capable of degrading polychlorinated dibenzo-p-dioxins (PCDDs), polybrominated diphenyl ethers (PBDEs), and four organochlorine pesticides (OCPs); dieldrin, heptachlor, heptachlor epoxide, and chlordane. During this phase of testing, field samples contaminated with chlordane were washed with ethanol and this ethanol/chlordane solution was degraded using the same reaction matrix, thereby demonstrating this technology's potential for (")real-world(") remediation projects. Finally, a set of experiments designed to provide some insight into the mechanism of dechlorination seems to indicate that two distinct processes are necessary for degradation to occur. First, the passivated outer layer of the magnesium must be removed in order to expose the zero-valent magnesium core. Next, an electron is transferred from the magnesium to the target molecule, causing the cleavage of the halide bond and the subsequent abstraction of either a hydrogen or proton from a solvent molecule. It is anticipated that an understanding of these fundamental chemical processes will allow this system to be tailored to a wide range of complex environmental media.
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Date Issued: 2013
Identifier: CFE0005109, ucf:50723
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005109

Title: Intrinsic Factors Affecting Decomposition Changes in Archaeological Head Hair from Kellis 2 Cemetery, Dakhleh Oasis, Egypt.
Creator: Cole, Kathleen, Dupras, Tosha, Williams, Lana, Groff, Amanda, University of Central Florida
Abstract / Description: Post-mortem hair root degradation, and associated characteristics such as post-mortem root banding, brush-like ends, and hard keratin points, has remained a little understood phenomenon in the forensics discipline since its discovery in the 1800's. At present, the underlying causes of these characteristics are still unknown. In addition, there is no standardization for preparing samples for forensic or archaeological analysis. In this study, 1200 hairs from a total of 51 individuals (males, n...
Show morePost-mortem hair root degradation, and associated characteristics such as post-mortem root banding, brush-like ends, and hard keratin points, has remained a little understood phenomenon in the forensics discipline since its discovery in the 1800's. At present, the underlying causes of these characteristics are still unknown. In addition, there is no standardization for preparing samples for forensic or archaeological analysis. In this study, 1200 hairs from a total of 51 individuals (males, n = 22; females, n = 29) ranging in age from 16 to 60+ and interred at the Kellis 2 cemetery in the Dakhleh Oasis, Egypt are examined microscopically for evidence of post-mortem hair root degradation. These remains date from ~50AD to ~450AD, and all were naturally mummified. The purposes of this thesis are two-fold; 1) to determine the efficacy of two preparation methods, and 2) to examine the intrinsic and extrinsic variables in each hair in order to ascertain the factors that affect the degradation of the human hair root after death. The preparation methods include a dry sample, where the hair is directly removed from the scalp tissue using tweezers, and a wet sample, where a 1cm portion of the scalp was first rehydrated using dimethyl sulfoxide (DMSO) for 48 hours before the hairs were extracted. Results indicate that when working with naturally mummified remains the wet method provides for easier acquisition of the sample and less chance of breakage before the hair is mounted for observation. This, therefore, provides a larger sample size for analysis.Each hair was observed using polarizing microscopy to determine whether postmortem root degradation was present, the growth stage of the hair, color, pigment density and distribution, pigment aggregate size and shape, medulla continuity and opacity, cuticle scale profile and thickness, inner cuticle margin, and the presence of ovoid bodies. Significant correlations were found between the incidence of postmortem root degradation and the growth stage, hair color, cuticle thickness, cuticle scale profile, and individual's age. The remaining variables did not show any significant correlations.
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Date Issued: 2017
Identifier: CFE0006577, ucf:51342
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006577

Title: ESTABLISHING DEGRADATION RATES AND SERVICE LIFETIME OF PHOTOVOLTAIC SYSTEMS.
Creator: Leyte-Vidal, Albert, Hickman, James, University of Central Florida
Abstract / Description: As fossil fuel sources continue to diminish, oil prices continue to increase, and global warming and CO2 emissions keep impacting the environment, it has been necessary to shift energy consumption and generation to a different path. Solar energy has proven to be one of the most promising sources of renewable energy because it is environmentally friendly, available anywhere in the world, and cost competitive. For photovoltaic (PV) system engineers, designing a PV system is not an easy task....
Show moreAs fossil fuel sources continue to diminish, oil prices continue to increase, and global warming and CO2 emissions keep impacting the environment, it has been necessary to shift energy consumption and generation to a different path. Solar energy has proven to be one of the most promising sources of renewable energy because it is environmentally friendly, available anywhere in the world, and cost competitive. For photovoltaic (PV) system engineers, designing a PV system is not an easy task. Research demonstrates that different PV technologies behave differently under certain conditions; therefore energy production varies not only with capacity of the system but also with the type of module. For years, researchers have also studied how these different technologies perform for long periods of time, when exposed out in the field. In this study, data collected by the Florida Solar Energy Center for periods of over four years was analyzed using two techniques, widely accepted by researchers and industry, to evaluate the long‐term performance of five systems. The performance ratio analysis normalizes system capacity and enables the comparison of performance between multiple systems. In PVUSA Regression analysis, regression coefficients are calculated which correspond to the effect of irradiance, wind speed, and ambient temperature, and these coefficients are then used to calculate power at a predetermined set of conditions. This study allows manufacturers to address the difficulties found on system lifetime when their modules are installed out on the field. Also allows for the further development and improvement of the different PV technologies already commercially available.
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Date Issued: 2010
Identifier: CFE0003326, ucf:48483
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003326

Title: APPLICATION OF ABSORPTIVE TREATMENTS ON TRAFFIC NOISE BARRIERS IN FLORIDA.
Creator: Chua, Chin Boon, Wayson, Roger, University of Central Florida
Abstract / Description: In this thesis, the parallel barrier analysis feature in the Federal Highway Administration Traffic Noise Model (FHWA TNM), which is based on RAYVERB was used to explore the effects of multiple reflections due to single and parallel barriers and the use of absorptive treatment. Database was developed from the data collected from previous research efforts was used to generate a best fit equation model that can be used as a predetermining tool to determine the magnitude of parallel barrier...
Show moreIn this thesis, the parallel barrier analysis feature in the Federal Highway Administration Traffic Noise Model (FHWA TNM), which is based on RAYVERB was used to explore the effects of multiple reflections due to single and parallel barriers and the use of absorptive treatment. Database was developed from the data collected from previous research efforts was used to generate a best fit equation model that can be used as a predetermining tool to determine the magnitude of parallel barrier insertion loss. The best fit equation model was then used to test against measured/model result and TNM prediction results for its validity. Absorptive materials were also studied such that 3 top of them were selected and recommended for Florida highway barrier use. It was found that the top three absorptive treatments for use on Florida highway barriers have been determined to be cementitous material, metal wool and glass fiber. These materials can be used to reduce the sound reflections for single and parallel barriers. The developed best fit equation model from this research is Deg = -2.17NRC - CW0.42 + 1.97eln(BH) + RH0.29 + DBB0.27; the prediction results give moderately high R2 value of 0.55 if compared to the results from database. Prediction results from best fit equation model was also found to be consistent with the results from the measure/modeled results, providing further proof of the validity of the model. However, if compared results from equation model, TNM and measured/model (measured and model compared results using ANSI method), TNM was shown to provide higher insertion loss degradation. It was found that the most effective placement of absorptive material was the pattern which covers the barrier from the bottom up; it was also found that only about 60% from the bottom of the barrier area requires covering with high NRC absorptive treatment (NRC greater than 0.8) without sacrificing insertion loss. Also, if the barrier area near the top includes an easily obtainable NRC value of 0.4, only 40% to 50% of the bottom barrier needs absorptive treatment with a higher, more expensive NRC rating. These findings can substantially reduce the cost of conventional absorptive barrier which have full coverage of high NRC absorptive treatment. This research has begun important improvements in noise barrier design, additional work can be continued to further verify all the findings in this thesis such that easier and better equation model can be developed to calculate insertion loss degradation and cheaper absorptive barrier with less absorptive material usage can be built.
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Date Issued: 2004
Identifier: CFE0000008, ucf:46127
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000008

degradation (5)	+ -
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composite (2)	+ -

concrete (2)	+ -
304 stainless steel (1)	+ -
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Accelerated durability (1)	+ -
Adaptable Computer Architecture (1)	+ -
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Application Vulnerability Characterization (1)	+ -
Bias Temperature Instability (BTI) (1)	+ -
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CDO environment (1)	+ -
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Colonialism (1)	+ -
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Compiler Optimizations (1)	+ -
Contaminated Soils (1)	+ -
Continuum Damage Mechanics (1)	+ -
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