O aumento dos níveis plasmáticos de glicocorticoides com concomitante diminuição de níveis plasmáticos de andrógenos em resposta a estressores é comumente observado em diversos vertebrados. Adicionalmente, os glicocorticoides, bem como os andrógenos, exercem importantes efeitos imunomodulatórios. Populações naturais de anfíbios respondem a agentes estressores de maneiras variadas, incluindo aumento dos níveis plasmáticos de corticosterona (principal glicocorticoide em anfíbios - CORT), alterações na resposta imune e a diminuição dos níveis plasmáticos de testosterona (T). Utilizando o cativeiro como um agente estressor para populações naturais de anfíbios, investigamos os efeitos da manutenção em cativeiro sobre os níveis plasmáticos de CORT e T, resposta imune (capacidade bactericida do plasma - CBP e fagocitose de células peritoneais) e condição corpórea de indivíduos machos de Rhinella schneideri e R. icterica, a partir de indivíduos coletados em populações naturais e mantidos em cativeiro por 60 e 90 dias, respectivamente. Machos adultos foram amostrados em campo, para coleta de dados basais, transportados e mantidos em cativeiro, onde amostras foram coletadas após 7, 30, 60 e 90 dias. Inicialmente, foi realizada a padronização da metodologia do ensaio de fagocitose das células peritoneais em sapos. Nossos resultados demonstraram que a o ensaio de fagocitose e a análise por citometria de fluxo por imagem resultam em um método confiável e preciso para a análise de atividade fagocítica de células peritoneais de sapos. Em resposta ao cativeiro, ambas as espécies (R. schneideri e R. icterica) apresentaram aumento dos níveis plasmáticos de CORT, diminuição dos níveis plasmáticos de T e resposta imune (CBP e fagocitose), indicando uma condição de estresse crônico. Indivíduos da espécie R. schneideri apresentaram uma acentuada perda da condição corpórea em resposta ao cativeiro, enquanto os indivíduos da espécie R. icterica mantiveram a condição corpórea ao longo do tempo em cativeiro. A CBP esteve positivamente correlacionada com a CORT plasmática quando não houve variação da condição corpórea (R. icterica), enquanto que em R. schneideri, os indivíduos que perderam massa ao longo do tempo apresentaram níveis elevados de CORT plasmática e menores valores de CBP. Adicionalmente, os níveis plasmáticos de T estavam positivamente correlacionados com a fagocitose em ambas as espécies estudadas. Estes resultados indicam que a manutenção em cativeiro pode ser considerada um estressor crônico para sapos, uma vez que promove o aumento de CORT e diminuição de T e resposta imune nestes animais. De maneira associada, a variação da resposta imune em resposta à manutenção em cativeiro depende do parâmetro avaliado e tempo de resposta (dias em cativeiro). Nossos resultados ainda sugerem que a imunomodulação nas condições de cativeiro em sapos pode estar associada às variações de CORT e T plasmática, dependendo de sinalização da condição corpórea do animal / Increased plasma glucocorticoid levels with concomitant decrease in plasma androgen levels in response to stressors are commonly observed in several vertebrates. In addition, glucocorticoids, as well as androgens, plays important immunomodulatory effects. Natural populations of amphibians respond to stressors in different ways, including increased corticosterone (main glucocorticoid in amphibians - CORT) plasma levels, changes in immune responses, and decreased plasma testosterone (T) levels. Given that captivity is a stressor for amphibian natural populations, we investigated the effects of captivity maintenance on plasma CORT and T levels, immune response (plasma bacterial killing ability - BKA and phagocytosis of peritoneal cells) and body condition of male individuals of Rhinella schneideri and R. icterica, from individuals collected in natural populations and kept in captivity for 60 and 90 days, respectively. Adult males were sampled in the field for baseline measurements, transported and kept in captivity, where samples were collected after 7, 30, 60 and 90 days. Initially, we standardized the phagocytosis of peritoneal cells assay for toads. Our results demonstrated that the phagocytosis assay and the imaging flow cytometry analysis result in a reliable and accurate method for the analysis of phagocytic activity of peritoneal cells of toads. In response to captivity, both species (R. schneideri and R. icterica) showed increased plasma CORT, decreased plasma T levels and immune response (BKA and phagocytosis), indicating a chronic stress condition. Individuals of R. schneideri showed accentuated body condition loss in response to captivity, while individuals of R. icterica displayed sustained body condition over time in captivity. BKA was positively correlated with plasma CORT when there was no change in body condition (R. icterica), whereas in R. schneideri, individuals showing the highest body mass loss over time, also presented the highest CORT levels and the lowest BKA values. Additionally, plasma T levels were positively correlated with phagocytosis in both studied species. These results indicate that captivity maintenance can be considered a chronic stressor for toads, promoting increased CORT and decreased T and immune response in these animals. Moreover, the variation in immunity in response to captivity maintenance depends on the evaluated parameter and time (days in captivity). Our results further suggest that immunomodulation in captivity conditions in toads may be associated with changes in plasma CORT and T, depending on the individual\'s body condition. Keywords: Stress, corticosterone, testosterone, immune response, body condition

abstract: Hydraulic fracturing is an effective technique used in well stimulation to increase petroleum well production. A combination of multi-stage hydraulic fracturing and horizontal drilling has led to the recent boom in shale gas production which has changed the energy landscape of North America. During the fracking process, highly pressurized mixture of water and proppants (sand and chemicals) is injected into to a crack, which fractures the surrounding rock structure and proppants help in keeping the fracture open. Over a longer period, however, these fractures tend to close due to the difference between the compressive stress exerted by the reservoir on the fracture and the fluid pressure inside the fracture. During production, fluid pressure inside the fracture is reduced further which can accelerate the closure of a fracture. In this thesis, we study the stress distribution around a hydraulic fracture caused by fluid production. It is shown that fluid flow can induce a very high hoop stress near the fracture tip. As the pressure gradient increases stress concentration increases. If a fracture is very thin, the flow induced stress along the fracture decreases, but the stress concentration at the fracture tip increases and become unbounded for an infinitely thin fracture. The result from the present study can be used for studying the fracture closure problem, and ultimately this in turn can lead to the development of better proppants so that prolific well production can be sustained for a long period of time. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2014

Indiana University-Purdue University Indianapolis (IUPUI) / Reduction of the polymerization shrinkage stress inherent of dimethacrylate-based resin composites has been a work in progress since the phenomenon was first described by Dr. Rafael L. Bowen in 1967. Contemporary efforts to modify the composites or the curing protocols for polymerization have proven a challenging task with controversial results. Influenced by existing mathematical models relating exposure, curing time and depth of cure of resin composites, a novel method for the reduction of polymerization shrinkage stress is proposed. By polymerizing through a single aperture mask, a dental light curing unit is transformed from a planar light source to a point light source, and a fully cured, three-dimensional “bullet” shaped curing front is predicted for the cured resin below. So long as the edges of the bullet do not touch the cavity walls or floor, the shrinkage stress of the bullet is not transferred. Follow-up with an unmasked curing unit then fully polymerizes the restoration. By reducing the volume of uncured composite in contact with the cavity walls and floor, shrinkage stress of the restoration is also reduced. The objective of the present study was to demonstrate this curing phenomenon with a model resin composite using masks with aperture diameters of 0.5, 0.4, and 0.25 mm and curing times of 10, 20, 30, and 40 seconds. The resulting curing front was evaluated quantitatively and qualitatively. From this, mathematical models of the curing front were derived. Selected combinations of aperture mask and curing time were then investigated to evaluate the influence of this phenomenon on the degree of conversion, Knoop hardness, and polymerization shrinkage stress of the same model resin composite. Group differences were analyzed using a one-way ANOVA at 5% significance.