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Thesis (M.Sc.) - University of KwaZulu-Natal, Pietermaritzburg, 2009. / Full text also available online. Scroll down for electronic link.

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Hydraulic conductivity fields (K) and degradation rate constants (a) are commonly used in predicting the fate and transport of reactive contaminants. The natural heterogeneity in aquifer porous materials and its effect on hydrological parameters such as K and a has to be accounted for by using an appropriate stochastic approach. The spatial distribution of K and its correlation with a were examined. Random fields of K having prescribed mean, variance, and correlation lengths were generated using the HYDRO_GEN method. Transport simulations were conducted for an ensemble of two-dimensionally heterogeneous aquifers. Both positive and negative correlations of K and a were considered. The solute’s remaining mass in both the positive and negative correlation scenarios was found to be, on average, within a small range. Concentration profiles for a positive K-a correlation displayed a more uniform behavior of the contaminated plume, compared to a more variable spreading in the negatively correlated cases.

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Orientador: Eduardo Daruge Junior / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba / Made available in DSpace on 2018-08-13T01:11:45Z (GMT). No. of bitstreams: 1 Rocha_PatriciaBitencourtda_M.pdf: 2037554 bytes, checksum: 601f62bcd204dd8ef700a9c08ae77eb2 (MD5) Previous issue date: 2009 / Resumo: Um exame de DNA pode ser o único e essencial instrumento para o esclarecimento de um inquérito policial, pois qualquer material deixado no local da investigação, de onde os peritos consigam extrair DNA, pode ser a principal prova contra o autor do delito. A tecnologia atual permite a realização da genotipagem de DNA a partir de quantidades pequenas de amostras biológicas. Em casos de crimes, a evidência biológica encontrada, vestígio, pode ser confrontada com amostra do suspeito e o laudo pode ser utilizado como prova em um processo judicial. O sucesso da análise depende do estado do material analisado. O grau de deterioração, a forma de conservação e o tempo decorrido podem influenciar o resultado ou impedir a identificação. Em casos de carbonização de corpos, comuns em acidentes aéreos, automobilísticos e alguns homicídios os ossos carbonizados são o material humano de primeira escolha para a análise de DNA sendo, o material genético obtido pela coleta de amostras da região do corpo melhor preservada. O estudo do comportamento do material genético humano ainda é muito controverso no meio científico, já que existem poucos trabalhados na área sobre o tempo de exposição e o grau da temperatura de degradação do DNA. Neste trabalho foi proposto analisar o comportamento de material genético humano (DNA Nuclear) obtido de amostra biológica (tecido ósseo) submetido à exposição às temperaturas de 100ºC, 200ºC, 300ºC, 400ºC, 500ºC e 600ºC, por intervalo de tempo de 10, 20 e 30 minutos. Possibilitando através dos resultados a confecção de um protocolo confiável para extração de DNA de ossos carbonizados. O grupo de estudo foi constituído de 50 (cinqüenta) cadáveres não identificados. Com base nos resultados obtidos, conclui-se que o método investigativo através do DNA possui várias vantagens sobre outros meios de identificação, como por exemplo, sorologia tradicional, antropologia forense, impressão digital, tomadas radiográficas, entre outros. Quando a estrutura óssea foi submetida à temperatura de 100ºC à 300ºC pelo período de 30 minutos, foi possível proceder-se a identificação humana por meio da análise do exame de DNA. O nosso estudo avaliou a degradação do DNA tomando-se por base a quantidade de marcadores amplificados. Em um procedimento de análise normal do sistema comercial multiloci através da técnica da PCR esperávamos amplificar até 16 (dezesseis) marcadores genéticos. Obedecendo ao protocolo internacional preconizado pelo programa CODIS do FBI, para assegurar uma identificação humana, se faz necessária uma amplificação mínima de 13 marcadores. Nas amostras submetidas a temperaturas de 400 ºC constatamos a degradação de 90,62% do material, ou seja, das 16 amplificações esperadas e exigidas pelo programa CODIS, apenas encontrou-se um marcador, dado insuficiente para uma identificação humana. Assim como, o estudo mostrou em 100% das amostras submetidas à temperatura acima de 500ºC por um período acima de 10 minutos seria suficiente para a degradação completa do DNA Nuclear, demonstrando a temperatura máxima que um osso do corpo humano pode sofrer. / Abstract: An examination of DNA may be the unique and essential tool for the elucidation of a police investigation, since any material left at the site of research, where experts will extract DNA, may be the main evidence against the offender. The current technology allows the realization of the genotyping of DNA from small quantities of biological samples. In cases of crimes, the biological evidence found, trace, may be faced with sample of the suspect and the award may be used as evidence in legal proceedings. The success of the analysis depends on the state of he material analyzed. The degree of deterioration, how to conserve time and may influence the outcome or to prevent identification. In cases of carbonized bodies, common in air accidents, homicides and some automobiles burned bones are the human material of choice for the analysis of DNA is the genetic material obtained by collecting samples from the body better preserved. The study of the behavior of human genetic material is still very controversial in the scientific, since there are few worked in the area about the time of exposure and the degree of temperature of degradation of DNA. This work was proposed to analyze the behavior of human genetic material (DNA Nuclear) obtained in biological sample (bone) subjected to exposure to temperatures of 100ºC, 200°C, 300°C, 400°C, 500ºC and 600ºC, for the time interval of 10, 20 and 30 minutes. Allowing the results through the creation of a reliable protocol for extraction of DNA from bones burned. The study group consisted of 50 (fifty) unidentified bodies. Based on the results, it appears that the method investigated by DNA has several advantages over other means of identification, such as traditional serology, forensic anthropology, fingerprint, radiographic taken, among others. When the bone structure was subjected to a temperature of 100ºC to 300ºC for a period of 30 minutes could be extended to human identification through DNA analysis of the examination. Our study evaluated the degradation of DNA based on the amount of amplified markers. In an analysis of the normal trading system through the technique of multiloci PCR amplifying expected by 16 (sixteen) genetic markers. According to international protocol recommended by the FBI's CODIS program, to ensure a human identification, amplification is needed a minimum of 13 markers. Samples subjected to temperatures of 400 ° C found a degradation of 90.62% of the material, or amplification of the 16 expected and required by the CODIS program, there was only a marker, as insufficient to identify a human. As the study showed in 100% of the samples subjected to temperature above 500 º C for a period longer than 10 minutes would be sufficient to complete the degradation of nuclear DNA, showing the maximum temperature that a bone in the human body can suffer. / Mestrado / Odontologia Legal e Deontologia / Mestre em Biologia Buco-Dental

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Fuel cells are electrochemical devices being developed for a variety of consumer applications including homes and vehicles. Before customers will accept this technology fuel cells must demonstrate suitable durability and reliability. One of the most important parts of a fuel cell stack is the polymer electrolyte membrane (PEM). This layer is responsible for conducting protons from anode to cathode and acting as a gas barrier, while operating in a harsh electrochemical environment. In order to develop better and more durable membranes researchers must understand the linkage between the causes of degradation, such as specific material properties and operational conditions. One significant mode of degradation of the electrolyte membrane is through chemical degradation caused by the crossover of reactant gases leading to the formation of peroxide and ultimately radical species. These radicals are able to attack vulnerable groups in the polymer structure of the membrane. The result is membrane thinning, increased gas crossover, fluoride ion release, and voltage degradation. Considerable experimental work has been done to understand these mechanisms, although there has been no attempt to model the connection between the causes of degradation and the physical effects of degradation on the electrolyte membrane. Such a model can be used as a valuable tool when evaluating different degradation mechanisms, developing stronger materials, and enable estimation of the influence of fuel cell operation and system design on degradation. This work presents the development and application of a dynamic semi-mechanistic chemical degradation model for a reinforced membrane in a polymer electrolyte membrane fuel cell. The model was developed using single cell testing with Gore™ PRIMEA® series 5510 catalyst coated membranes under open circuit voltage (OCV) conditions. Such conditions are useful for accelerated testing since they are believed to enhance chemical degradation in membranes since reactant gas partial pressures are at their maximum. It was found that the electrolyte layer closer to the cathode catalyst preferentially degraded. Furthermore, cumulative fluoride release curves for the anode and cathode began to reach plateaus at similar times. The developed model proposes that as the cathode electrolyte layer is degraded, fluoride release slows due to a lack of reactants since the inert reinforcement layer creates a barrier between the cathode and anode electrolyte layers. It is also believed that all fluoride release originates at the degradation site at the cathode. By fitting key parameters, the fluoride release trends were simulated. The proposed model links material properties such as the membrane gas permeability, membrane thickness, and membrane reactivity, as well as operating parameters such as hydrogen partial pressure and relative humidity to fluoride release, thickness change, and crossover. Further investigation into degradation at OCV operation and different relative humidity conditions showed that initial hydrogen crossover measurements were a good indicator of degradation rate over long testing times. The proposed semi-mechanistic model was able to best model the results when using a second order dependence on the hydrogen crossover term. In all cases there was some discrepancy between the model and experimental data after long times. This was attributed to the onset and contribution of anode side degradation. The effect of drawing current on fluoride release was also investigated. Experimental results showed that with increasing current density the fluoride release rate decreased. Using the developed semi-mechanistic model it was proposed that a decrease in hydrogen crossover was primarily responsible for the reduction in chemical degradation of the membrane. A macro-homogeneous model of the anode catalyst layer was used to show that a reduction in hydrogen concentration through the catalyst layer when a current is drawn is a possible reason for the reduction in degradation. Finally the model was applied to three different dynamic drive cycles. The model was able to show that over different drive cycles, the fuel cell will experience different degradation rates. Thus the developed model can be used as a potential tool to evaluate degradation in systems.

Fuel cells are electrochemical devices being developed for a variety of consumer applications including homes and vehicles. Before customers will accept this technology fuel cells must demonstrate suitable durability and reliability. One of the most important parts of a fuel cell stack is the polymer electrolyte membrane (PEM). This layer is responsible for conducting protons from anode to cathode and acting as a gas barrier, while operating in a harsh electrochemical environment. In order to develop better and more durable membranes researchers must understand the linkage between the causes of degradation, such as specific material properties and operational conditions. One significant mode of degradation of the electrolyte membrane is through chemical degradation caused by the crossover of reactant gases leading to the formation of peroxide and ultimately radical species. These radicals are able to attack vulnerable groups in the polymer structure of the membrane. The result is membrane thinning, increased gas crossover, fluoride ion release, and voltage degradation. Considerable experimental work has been done to understand these mechanisms, although there has been no attempt to model the connection between the causes of degradation and the physical effects of degradation on the electrolyte membrane. Such a model can be used as a valuable tool when evaluating different degradation mechanisms, developing stronger materials, and enable estimation of the influence of fuel cell operation and system design on degradation. This work presents the development and application of a dynamic semi-mechanistic chemical degradation model for a reinforced membrane in a polymer electrolyte membrane fuel cell. The model was developed using single cell testing with Gore™ PRIMEA® series 5510 catalyst coated membranes under open circuit voltage (OCV) conditions. Such conditions are useful for accelerated testing since they are believed to enhance chemical degradation in membranes since reactant gas partial pressures are at their maximum. It was found that the electrolyte layer closer to the cathode catalyst preferentially degraded. Furthermore, cumulative fluoride release curves for the anode and cathode began to reach plateaus at similar times. The developed model proposes that as the cathode electrolyte layer is degraded, fluoride release slows due to a lack of reactants since the inert reinforcement layer creates a barrier between the cathode and anode electrolyte layers. It is also believed that all fluoride release originates at the degradation site at the cathode. By fitting key parameters, the fluoride release trends were simulated. The proposed model links material properties such as the membrane gas permeability, membrane thickness, and membrane reactivity, as well as operating parameters such as hydrogen partial pressure and relative humidity to fluoride release, thickness change, and crossover. Further investigation into degradation at OCV operation and different relative humidity conditions showed that initial hydrogen crossover measurements were a good indicator of degradation rate over long testing times. The proposed semi-mechanistic model was able to best model the results when using a second order dependence on the hydrogen crossover term. In all cases there was some discrepancy between the model and experimental data after long times. This was attributed to the onset and contribution of anode side degradation. The effect of drawing current on fluoride release was also investigated. Experimental results showed that with increasing current density the fluoride release rate decreased. Using the developed semi-mechanistic model it was proposed that a decrease in hydrogen crossover was primarily responsible for the reduction in chemical degradation of the membrane. A macro-homogeneous model of the anode catalyst layer was used to show that a reduction in hydrogen concentration through the catalyst layer when a current is drawn is a possible reason for the reduction in degradation. Finally the model was applied to three different dynamic drive cycles. The model was able to show that over different drive cycles, the fuel cell will experience different degradation rates. Thus the developed model can be used as a potential tool to evaluate degradation in systems.

Nitroxide-mediated Controlled Degradation of Polypropylene <br /> Controlled-rheology polypropylene resins (CRPP) have been produced industrially for years using reactive extrusion processes employing peroxides as free radical initiators. The molecular weight characteristics of CRPP materials can be tailor-made depending on the final application in a very efficient and economic manner. <br /><br /> A PP-based nitroxide (NOR) with the trade name Irgatec CR76 has been recently developed by CIBA Chemicals, as a source of radicals and it is currently being evaluated for the production of CRPP. NORs are well-known as powerful stabilizers to protect plastics from the negative influence of light and heat, and easy in handling during processing. Preliminary experimental results exhibit a qualitative difference between Irgatec CR76 and other commonly used peroxides. <br /><br /> The purpose of this research work is to evaluate this new material as a potential replacement of commonly used peroxides in the production of CRPP. CRPP will be produced by reactive processing using varying amounts of Irgatec CR76 and the rheological properties of the materials produced will be investigated. By comparing results with Irgatec CR76 to those from other typical initiators, the effectiveness of Irgatec CR76 as an initiator will also be assessed. <br /><br /> The results of this research will have an impact not only on the potential extension of uses of the specific PP-based NOR (Irgatec CR76), but also, more generally, on the wider application of additives during degradation of PP. Potentially new materials can be produced with enhanced heat and light protection along with the other benefits inherent to standard CRPP.