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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
321

A participação de diferentes sistemas neuromodulatórios no hipocampo, núcleo basolateral da amígdala e córtex pré-frontal ventromedial na extinção de memórias aversivas

Fiorenza, Natália Gindri January 2012 (has links)
A extinção é uma forma de aprendizado inibitório que se origina na omissão do reforço ou estímulo incondicionado, inibindo a evocação de uma resposta ou comportamento aprendido anteriormente. Muitas formas de aprendizado são moduladas por receptores β- noradrenérgicos, D1-dopaminérgicos e H2-histaminérgicos no córtex pré-frontal ventromedial (vmPFC), no complexo basolateral da amígdala (BLA) e no hipocampo dorsal (DH). Assim, o objetivo do presente trabalho foi investigar a modulação da extinção de memória aversiva nestas três regiões cerebrais. Para isso, utilizamos ratos machos Wistar, que foram submetidos ao paradigma de esquiva inibitória (EI) ou condicionamento contextual ao medo (CCM). As diferentes drogas utilizadas foram infundidas através das cânulas guias implantadas estereotaxicamente no DH, BLA ou vmPFC imediatamente após a sessão de extinção e seus efeitos sobre a extinção foram avaliados em uma sessão de teste realizada 24 h depois. A DSerina (50 μg/lado), modulador positivo do receptor NMDA, e o SKF9188 (12.5 μg/lado), inibidor da enzima histamina metil-transferase, melhoraram a consolidação da memória de extinção nas tarefas de EI e CCM. Entretanto, o AP5 (5 μg/lado), antagonista do receptor glutamatérgico NMDA, e a ranitidina (17.5 μg/lado), antagonista do receptor histaminérgico H2, prejudicaram a extinção em ambos os paradigmas, indicando que os receptores glutamatérgicos do tipo NMDA estão envolvidos na consolidação dos dois paradigmas utilizados, e que os receptores histaminérgicos H2 modulam a extinção nas três estruturas estudadas. A noradrenalina (1 μg/lado), o antagonista β-adrenoreceptor, timolol (1 μg/lado), o agonista dos receptores D1, SKF38393 (12.5 μg/lado) e o antagonista dos receptores D1, SCH23390 (1.5 μg/lado) também afetam a extinção nas duas tarefas, porém, seus efeitos são variados dependendo da tarefa e do local da infusão, sugerindo que a modulação da extinção pelos receptores β- e D1 é mais complexa. Nossos resultados mostram que as três estruturas são ativadas durante o processo de extinção da memória e que os sistemas neuromodulatórios atuam de formas distintas nessas tarefas. / Extinction consists of the learned inhibition of retrieval of previously acquired memory. Many forms of learning are modulated by β-noradrenergic, D1-dopaminergic and H2-histaminergic receptors on ventromedial prefrontal cortex (vmPFC), basolateral amygdala (BLA) and dorsal hippocampus. Therefore, the aim of this work was investigated the modulation of aversive memory extinction in these brain structures. Male Wistar rats were submitted to inhibitory avoidance paradigm (EI) or contextual fear conditioning (CCM). The drugs were infused through cannulae implanted into the DH, BLA or vmPFC immediately after the extinction session and their effects were evaluated 24 h later. D-serine (50 μg/side), a NMDA receptor stimulant, and SKF9188 (12.5 μg/side), a histamine methyl-transferase inhibitor, enhanced the consolidation of the extinction memory in EI and CCM tasks. However, AP5 (5 μg/side), a NMDA-antagonist, and ranitidine (17.5 μg/side), a H2- histaminergic antagonist, impaired the extinction of both tasks, indicated that NMDA receptors are involved in the consolidation of extinction of both tasks, and histamine H2 receptors modulate that process in all areas studied. Noradrenaline (1 μg/side), timolol 1 μg/side), a β-adrenergic antagonist, SKF38393 (12.5 μg/side) and SCH23390 (1.5 μg/side), D1 agonist and antagonist receptor, respectively, also affected the extinction, but their effects varied with the task and with the site of infusion, suggesting that extinction modulation by β- and D1 is more complex. In conclusion, the three structures investigated are activated in the aversive memory extinction and the neuromodulatory systems act of different forms in these structures.
322

Can Species Distribution Models Predict Colonizations and Extinctions?

Venne, Simon 23 November 2018 (has links)
Aim MaxEnt, a very popular species distribution modelling technique, has been used extensively to relate species’ geographic distributions to environmental variables and to predict changes in species’ distributions in response to environmental change. Here, we test its predictive ability through time (rather than through space, as is commonly done) by modeling colonizations and extinctions. Location Continental U.S. and southern Canada. Time period 1979-2009 Major taxa studied Twenty-one species of passerine birds. Methods We used MaxEnt to relate species’ geographic distributions to the variation in environmental conditions across North America. We then modelled site-specific colonizations and extinctions between 1979 and 2009 as functions of MaxEnt-estimated previous habitat suitability and inter- annual change in habitat suitability and neighborhood occupancy. We evaluated whether the effects were in the expected direction, we partitioned model’s explained deviance, and we compared colonization and extinction model’s accuracy to MaxEnt’s AUC. Results IV Colonization and extinction probabilities both varied as functions of previous habitat suitability, change in habitat suitability, and neighborhood occupancy, in the expected direction. Change in habitat suitability explained very little deviance compared to other predictors. Neighborhood occupancy accounted for more explained deviance in colonization models than in extinction models. MaxEnt AUC correlates with extinction models’ predictive ability, but not with that of colonization models. Main conclusions MaxEnt appears to sometime capture a real effect of the environment on species’ distributions since a statistical effect of habitat suitability is detected through both time and space. However, change in habitat suitability (which is much smaller through time than through space) is a poor predictor of change in occupancy. Over short time scales, proximity of sites occupied by conspecifics predicts changes in occupancy just as well as MaxEnt. The ability of MaxEnt models to predict spatial variation in occupancy (as measured by AUC) gives little indication of transferability through time. Thus, the predictive value of species distribution models may be overestimated when evaluated through space only. Future prediction of species’ responses to climate change should make a distinction between colonization and extinction, recognizing that the two processes are not equally well predicted by SDMs.
323

Estudo experimental da produção de fuligem em chamas laminares

Soares, Diego January 2016 (has links)
Sérios problemas ambientais têm origem em processos de combustão incompletos. Entre os produtos indesejados está a fuligem, considerada como um dos principais fatores da mudança climática observada nos último anos. Desta forma, ferramentas para diagnóstico da emissão de material particulado se fazem necessárias. Com o advento do laser, o desenvolvimento de técnicas óticas não intrusivas teve início. Dentre elas, destaca-se a técnica denominada incandescência induzida por laser (laser induced incandescence – LII), a qual pode gerar resultados resolvidos no espaço para a fração volumétrica de fuligem. Neste contexto, este trabalho apresenta um estudo experimental sobre a produção de fuligem em duas situações: na primeira, foram estudadas chamas laminares pré-misturadas de etileno e ar aplicando-se a técnica LII. Os resultados foram calibrados a partir da fração volumétrica de fuligem média empregando a técnica de extinção de luz, obtendo-se, então, resultados quantitativos espacialmente resolvidos da fração volumétrica de fuligem. A utilização de diferentes gases no escoamento anular também foi avaliada. A segunda situação abordada envolve o estudo de chamas laminares não pré-misturadas utilizando o gás natural como combustível. O impacto da diluição de inertes em diferentes proporções sobre a fração volumétrica de fuligem em diversas alturas da chama foi estudado por meio da técnica LII. Os resultados obtidos foram comparados à outros resultados presentes na literatura e servirão como validação de futuros modelos de formação de fuligem. / Serious environmental problems are assigned to incomplete combustion processes. Among the unwanted products, soot can be related as an important factor of climate changes observed in the last years. Thus, particulate material emissions diagnostic tools are necessary. Due the laser advent, the development of non-intrusive optical techniques was possible. One of the most importante technique is the laser induced incandescence, LII, which can generate spatially and temporally resolved results of soot volume fraction. In this context, an experimental study regarding the soot production was developed in two different situations: in the first one, premixed laminar flames of ethylene and air were investigated by applying the LII technique. The results were calibrated through the average of soot volume fraction results obtained by the light extinction technique. Therefore, it was possible to obtain quantitative results of spatially resolved soot volume fraction. Different gases employment at the annular flow were also evaluated. The second situation studied involves the analysis of natural gas laminar non-premixed flames. The impact of different inert gas dilution ratio on the soot volume fraction at different heights of the flame was evaluated by the LII technique. The results were compared to other authors and will serve as validation for future soot formation models.
324

Cargos em extinção : as marcas das mudanças do e no trabalho na universidade

Sarmento, Thaís Ferrugem January 2016 (has links)
O atual processo de reestruturação produtiva trouxe profundas transformações na gestão e na organização do trabalho no contexto das universidades públicas no Brasil, repercutindo na saúde de seus servidores. A extinção de cargos no âmbito do serviço público federal, preconizada no Plano Diretor da Reforma do Estado nos anos 1990 e implementada pela Lei nº 9.632 de 1998, atinge o conjunto do funcionalismo, incidindo nas universidades públicas federais. Assim, esta pesquisa objetiva dar visibilidade aos efeitos das transformações ocorridas nas universidades públicas federais na saúde e no trabalho dos servidores ocupantes de cargos em processo de extinção. Trata-se de um estudo qualitativo, desenvolvido na Universidade Federal do Rio Grande do Sul (UFRGS), o qual contou com a realização de entrevistas semiestruturadas com nove servidores ativos ocupantes de cargos em processo de extinção, um representante do setor de gestão de pessoas e um representante sindical. As entrevistas, depois de transcritas, foram submetidas à análise de conteúdo temática e divididas considerando-se as seguintes categorias: mercado de trabalho; condições de trabalho; saberes do trabalho; relações do e no trabalho; relações entre trabalho e outras dimensões da vida; cargo e atividades desempenhadas. Os servidores descrevem as dificuldades de inserção no mercado de trabalho como a principal justificativa para ingresso e permanência na universidade. A escolaridade acima da exigida pelo cargo e o amplo conhecimento institucional adquirido ao longo dos anos de trabalho, aliados à falta de servidores em algumas áreas, contribuem para que suas atividades se modifiquem ao longo dos anos. Tal contexto permite a estes servidores suprir lacunas institucionais, tornando o desvio de função uma das principais características desses cargos. Práticas de gestão com caráter fortemente culpabilizante e individualizante levam ao ocultamento dos processos institucionais que constituem a realidade de trabalho desses servidores. O enfrentamento das dificuldades se dá predominantemente por meio de estratégias individuais, as quais, conjuntamente com as frágeis estratégias coletivas sustentadas nas relações de troca e ajuda mútua, têm efeitos meramente paliativos, sendo incapazes de modificar a condição em que os servidores se encontram. Conclui-se que o trabalho destes servidores é composto por um conjunto de elementos heterogêneos e contraditórios, no seio do qual lhes restam poucas e limitadas alternativas, sendo as estratégias individuais por eles empregadas incapazes de solucionar as dificuldades enfrentadas. O sofrimento social emerge como principal efeito das mudanças da universidade na saúde dos servidores ocupantes de cargos em extinção. / The current productive reorganization process has brought significant changes in management and organization of work in the context of public universities in Brazil, which has influenced the health of their public servants. The extinction of positions in Brazil’s national public service, as advocated in the Directive Plan of the State Reform in the 1990s and implemented by Law n. 9.632, from 1998, affects the entire public workers category, including the ones who work in national public universities. Therefore, this research aims to give visibility to the effects of changes occurred in the national public universities considering health and work of public servants who have a job position which is becoming extinct. The study was developed at Federal University of Rio Grande do Sul (UFRGS) and included semi-structured interviews with nine active public servants who have a job position which is becoming extinct, a representative of the people management department and a union labor representative. The interviews, after transcribed, underwent thematic content analysis and were divided considering the following categories: labor market; working conditions; knowledge about the job; relationships of and in work; relationships between work and other aspects of life; job and activities performed. Public servants describe the difficulties to enter the labor market as the main reason to start and stay working in the university. Their education, higher than required by the position, and the broad institutional knowledge acquired over the years of work, along with the lack of public servants in some areas, contribute for a change on their activities over the years. This context allows these public servants to fill institutional gaps, which makes the change in the work performed be one of the main characteristics of these positions. Strong guilt-inducing and individualizing management practices lead to hiding institutional processes which are a working reality to these servants. The difficulties are faced predominantly through individual strategies, which, along with the fragile collective strategies sustained in the exchanging relationships and mutual support, have only palliative effects, being unable to change the condition in which the servants are. These servers’ jobs are composed by a set of heterogeneous and contradictory elements and, thus, there are few and limited alternatives left, and the individual strategies used by them are unable to solve the difficulties faced. Social suffering emerges as the main effect of the changes of the university on the health of public servants who have a job position which is becoming extinct.
325

Cargos em extinção : as marcas das mudanças do e no trabalho na universidade

Sarmento, Thaís Ferrugem January 2016 (has links)
O atual processo de reestruturação produtiva trouxe profundas transformações na gestão e na organização do trabalho no contexto das universidades públicas no Brasil, repercutindo na saúde de seus servidores. A extinção de cargos no âmbito do serviço público federal, preconizada no Plano Diretor da Reforma do Estado nos anos 1990 e implementada pela Lei nº 9.632 de 1998, atinge o conjunto do funcionalismo, incidindo nas universidades públicas federais. Assim, esta pesquisa objetiva dar visibilidade aos efeitos das transformações ocorridas nas universidades públicas federais na saúde e no trabalho dos servidores ocupantes de cargos em processo de extinção. Trata-se de um estudo qualitativo, desenvolvido na Universidade Federal do Rio Grande do Sul (UFRGS), o qual contou com a realização de entrevistas semiestruturadas com nove servidores ativos ocupantes de cargos em processo de extinção, um representante do setor de gestão de pessoas e um representante sindical. As entrevistas, depois de transcritas, foram submetidas à análise de conteúdo temática e divididas considerando-se as seguintes categorias: mercado de trabalho; condições de trabalho; saberes do trabalho; relações do e no trabalho; relações entre trabalho e outras dimensões da vida; cargo e atividades desempenhadas. Os servidores descrevem as dificuldades de inserção no mercado de trabalho como a principal justificativa para ingresso e permanência na universidade. A escolaridade acima da exigida pelo cargo e o amplo conhecimento institucional adquirido ao longo dos anos de trabalho, aliados à falta de servidores em algumas áreas, contribuem para que suas atividades se modifiquem ao longo dos anos. Tal contexto permite a estes servidores suprir lacunas institucionais, tornando o desvio de função uma das principais características desses cargos. Práticas de gestão com caráter fortemente culpabilizante e individualizante levam ao ocultamento dos processos institucionais que constituem a realidade de trabalho desses servidores. O enfrentamento das dificuldades se dá predominantemente por meio de estratégias individuais, as quais, conjuntamente com as frágeis estratégias coletivas sustentadas nas relações de troca e ajuda mútua, têm efeitos meramente paliativos, sendo incapazes de modificar a condição em que os servidores se encontram. Conclui-se que o trabalho destes servidores é composto por um conjunto de elementos heterogêneos e contraditórios, no seio do qual lhes restam poucas e limitadas alternativas, sendo as estratégias individuais por eles empregadas incapazes de solucionar as dificuldades enfrentadas. O sofrimento social emerge como principal efeito das mudanças da universidade na saúde dos servidores ocupantes de cargos em extinção. / The current productive reorganization process has brought significant changes in management and organization of work in the context of public universities in Brazil, which has influenced the health of their public servants. The extinction of positions in Brazil’s national public service, as advocated in the Directive Plan of the State Reform in the 1990s and implemented by Law n. 9.632, from 1998, affects the entire public workers category, including the ones who work in national public universities. Therefore, this research aims to give visibility to the effects of changes occurred in the national public universities considering health and work of public servants who have a job position which is becoming extinct. The study was developed at Federal University of Rio Grande do Sul (UFRGS) and included semi-structured interviews with nine active public servants who have a job position which is becoming extinct, a representative of the people management department and a union labor representative. The interviews, after transcribed, underwent thematic content analysis and were divided considering the following categories: labor market; working conditions; knowledge about the job; relationships of and in work; relationships between work and other aspects of life; job and activities performed. Public servants describe the difficulties to enter the labor market as the main reason to start and stay working in the university. Their education, higher than required by the position, and the broad institutional knowledge acquired over the years of work, along with the lack of public servants in some areas, contribute for a change on their activities over the years. This context allows these public servants to fill institutional gaps, which makes the change in the work performed be one of the main characteristics of these positions. Strong guilt-inducing and individualizing management practices lead to hiding institutional processes which are a working reality to these servants. The difficulties are faced predominantly through individual strategies, which, along with the fragile collective strategies sustained in the exchanging relationships and mutual support, have only palliative effects, being unable to change the condition in which the servants are. These servers’ jobs are composed by a set of heterogeneous and contradictory elements and, thus, there are few and limited alternatives left, and the individual strategies used by them are unable to solve the difficulties faced. Social suffering emerges as the main effect of the changes of the university on the health of public servants who have a job position which is becoming extinct.
326

A participação de diferentes sistemas neuromodulatórios no hipocampo, núcleo basolateral da amígdala e córtex pré-frontal ventromedial na extinção de memórias aversivas

Fiorenza, Natália Gindri January 2012 (has links)
A extinção é uma forma de aprendizado inibitório que se origina na omissão do reforço ou estímulo incondicionado, inibindo a evocação de uma resposta ou comportamento aprendido anteriormente. Muitas formas de aprendizado são moduladas por receptores β- noradrenérgicos, D1-dopaminérgicos e H2-histaminérgicos no córtex pré-frontal ventromedial (vmPFC), no complexo basolateral da amígdala (BLA) e no hipocampo dorsal (DH). Assim, o objetivo do presente trabalho foi investigar a modulação da extinção de memória aversiva nestas três regiões cerebrais. Para isso, utilizamos ratos machos Wistar, que foram submetidos ao paradigma de esquiva inibitória (EI) ou condicionamento contextual ao medo (CCM). As diferentes drogas utilizadas foram infundidas através das cânulas guias implantadas estereotaxicamente no DH, BLA ou vmPFC imediatamente após a sessão de extinção e seus efeitos sobre a extinção foram avaliados em uma sessão de teste realizada 24 h depois. A DSerina (50 μg/lado), modulador positivo do receptor NMDA, e o SKF9188 (12.5 μg/lado), inibidor da enzima histamina metil-transferase, melhoraram a consolidação da memória de extinção nas tarefas de EI e CCM. Entretanto, o AP5 (5 μg/lado), antagonista do receptor glutamatérgico NMDA, e a ranitidina (17.5 μg/lado), antagonista do receptor histaminérgico H2, prejudicaram a extinção em ambos os paradigmas, indicando que os receptores glutamatérgicos do tipo NMDA estão envolvidos na consolidação dos dois paradigmas utilizados, e que os receptores histaminérgicos H2 modulam a extinção nas três estruturas estudadas. A noradrenalina (1 μg/lado), o antagonista β-adrenoreceptor, timolol (1 μg/lado), o agonista dos receptores D1, SKF38393 (12.5 μg/lado) e o antagonista dos receptores D1, SCH23390 (1.5 μg/lado) também afetam a extinção nas duas tarefas, porém, seus efeitos são variados dependendo da tarefa e do local da infusão, sugerindo que a modulação da extinção pelos receptores β- e D1 é mais complexa. Nossos resultados mostram que as três estruturas são ativadas durante o processo de extinção da memória e que os sistemas neuromodulatórios atuam de formas distintas nessas tarefas. / Extinction consists of the learned inhibition of retrieval of previously acquired memory. Many forms of learning are modulated by β-noradrenergic, D1-dopaminergic and H2-histaminergic receptors on ventromedial prefrontal cortex (vmPFC), basolateral amygdala (BLA) and dorsal hippocampus. Therefore, the aim of this work was investigated the modulation of aversive memory extinction in these brain structures. Male Wistar rats were submitted to inhibitory avoidance paradigm (EI) or contextual fear conditioning (CCM). The drugs were infused through cannulae implanted into the DH, BLA or vmPFC immediately after the extinction session and their effects were evaluated 24 h later. D-serine (50 μg/side), a NMDA receptor stimulant, and SKF9188 (12.5 μg/side), a histamine methyl-transferase inhibitor, enhanced the consolidation of the extinction memory in EI and CCM tasks. However, AP5 (5 μg/side), a NMDA-antagonist, and ranitidine (17.5 μg/side), a H2- histaminergic antagonist, impaired the extinction of both tasks, indicated that NMDA receptors are involved in the consolidation of extinction of both tasks, and histamine H2 receptors modulate that process in all areas studied. Noradrenaline (1 μg/side), timolol 1 μg/side), a β-adrenergic antagonist, SKF38393 (12.5 μg/side) and SCH23390 (1.5 μg/side), D1 agonist and antagonist receptor, respectively, also affected the extinction, but their effects varied with the task and with the site of infusion, suggesting that extinction modulation by β- and D1 is more complex. In conclusion, the three structures investigated are activated in the aversive memory extinction and the neuromodulatory systems act of different forms in these structures.
327

Estudo experimental da produção de fuligem em chamas laminares

Soares, Diego January 2016 (has links)
Sérios problemas ambientais têm origem em processos de combustão incompletos. Entre os produtos indesejados está a fuligem, considerada como um dos principais fatores da mudança climática observada nos último anos. Desta forma, ferramentas para diagnóstico da emissão de material particulado se fazem necessárias. Com o advento do laser, o desenvolvimento de técnicas óticas não intrusivas teve início. Dentre elas, destaca-se a técnica denominada incandescência induzida por laser (laser induced incandescence – LII), a qual pode gerar resultados resolvidos no espaço para a fração volumétrica de fuligem. Neste contexto, este trabalho apresenta um estudo experimental sobre a produção de fuligem em duas situações: na primeira, foram estudadas chamas laminares pré-misturadas de etileno e ar aplicando-se a técnica LII. Os resultados foram calibrados a partir da fração volumétrica de fuligem média empregando a técnica de extinção de luz, obtendo-se, então, resultados quantitativos espacialmente resolvidos da fração volumétrica de fuligem. A utilização de diferentes gases no escoamento anular também foi avaliada. A segunda situação abordada envolve o estudo de chamas laminares não pré-misturadas utilizando o gás natural como combustível. O impacto da diluição de inertes em diferentes proporções sobre a fração volumétrica de fuligem em diversas alturas da chama foi estudado por meio da técnica LII. Os resultados obtidos foram comparados à outros resultados presentes na literatura e servirão como validação de futuros modelos de formação de fuligem. / Serious environmental problems are assigned to incomplete combustion processes. Among the unwanted products, soot can be related as an important factor of climate changes observed in the last years. Thus, particulate material emissions diagnostic tools are necessary. Due the laser advent, the development of non-intrusive optical techniques was possible. One of the most importante technique is the laser induced incandescence, LII, which can generate spatially and temporally resolved results of soot volume fraction. In this context, an experimental study regarding the soot production was developed in two different situations: in the first one, premixed laminar flames of ethylene and air were investigated by applying the LII technique. The results were calibrated through the average of soot volume fraction results obtained by the light extinction technique. Therefore, it was possible to obtain quantitative results of spatially resolved soot volume fraction. Different gases employment at the annular flow were also evaluated. The second situation studied involves the analysis of natural gas laminar non-premixed flames. The impact of different inert gas dilution ratio on the soot volume fraction at different heights of the flame was evaluated by the LII technique. The results were compared to other authors and will serve as validation for future soot formation models.
328

Uranium Isotope Variations Across Key Evolutionary Intervals in Geological History

January 2018 (has links)
abstract: There is a growing body of evidence that the evolving redox structure of the oceans has been an important influence on the evolutionary trajectory of animals. However, current understanding of connections between marine redox conditions and marine extinctions and recoveries is hampered by limited detailed knowledge of the timing, duration, and extent of marine redox changes. The recent development of U isotopes (δ238U) in carbonates as a global ocean redox proxy has provided new insight into this problem. Reliable application and interpretation of the δ238U paleoproxy in geological records requires a thorough understanding of the reliability of δ238U recorded by bulk carbonate sediments. In this dissertation, I evaluate the robustness of δ238U paleoproxy by examining δ238U variations in marine carbonates across Permian-Triassic boundary (PTB) sections from different paleogeographic locations. Close agreement of δ238U profiles from coeval carbonate sections thousands of kilometers apart, in different ocean basins, and with different diagenetic histories, strongly suggests that bulk carbonate sediments can reliably preserve primary marine δ238U signals, validating the carbonate U-isotope proxy for global-ocean redox analysis. To improve understanding of the role of marine redox in shaping the evolutionary trajectory of animals, high-resolution δ238U records were generated across several key evolutionary periods, including the Ediacaran-to-Early Cambrian Explosion of complex life (635-541 Ma) and the delayed Early Triassic Earth system recovery from the PTB extinction (252-246 Ma). Based on U isotope variations in the Ediacaran-to-the Early Cambrian ocean, the initial diversification of the Ediacara biota immediately postdates an episode of pervasive ocean oxygenation across the Shuram event. The subsequent decline and extinction of the Ediacara biota is coincident with an episode of extensive anoxic conditions during the latest Ediacaran Period. These findings suggest that global marine redox changes drove the rise and fall of the Ediacara biota. Based on U isotope variations, the Early Triassic ocean was characterized by multiple episodes of extensive marine anoxia. By comparing the high-resolution δ238U record with the sub-stage ammonoid extinction rate curve, it appears that multiple oscillations in marine anoxia modulated the recovery of marine ecosystems following the latest Permian mass extinction. / Dissertation/Thesis / Doctoral Dissertation Geological Sciences 2018
329

The Late Pleistocene Southern Fuego-Patagonian Archaeological Sites: New Findings, New Problems / Los sitios arqueológicos del Pleistoceno Final de Fuego-Patagonia austral: nuevos hallazgos, nuevos problemas

Prieto, Alfredo, Labarca, Rafael 10 April 2018 (has links)
The Fuego-Patagonian Late Pleistocene archaeological sites are scarce; we have only a handful of them for understanding a periodof time that extends for about 1000 years. These deposits coincide with a period of substantial environmental changes that contributed to the extinction of megafauna in the region, as in the rest of the Americas. All sites registered are located in caves and rock shelters. Attempts to find new sites in other contexts of the region have not yet yielded the expected results. However, thanksto recent work done by paleobiologists seeking to obtain increasingly detailed records of climate change and its causes, we are ableto propose new research directions. / Los sitios arqueológicos finipleistocénicos de Fuego-Patagonia austral son bastante escasos. Se cuenta con apenas cinco de ellos para comprender un período que se extiende por cerca de 1000 años. Estos yacimientos coinciden con una etapa de cambios ambientales muy marcados y asisten a la extinción de la megafauna en la región, al igual que en el resto del continente americano. Todos ellos se ubican en cuevas y aleros rocosos. Los intentos por hallar nuevos emplazamientos en otros contextos del área no han dado los frutos esperados aún. Sin embargo, se analizan otras posibilidades de búsqueda a la luz de los resultados de los trabajos recientes de los paleobiólogos comprometidos en obtener registros cada vez más acuciosos del cambio climático y sus causas.
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Mathematical Modeling of Intraguild Predation and its Dynamics in Ecology

January 2012 (has links)
abstract: A functioning food web is the basis of a functioning community and ecosystem. Thus, it is important to understand the dynamics that control species behaviors and interactions. Alterations to the fundamental dynamics can prove detrimental to the future success of our environment. Research and analysis focus on the global dynamics involved in intraguild predation (IGP), a three species subsystem involving both competition and predation. A mathematical model is derived using differential equations based on pre-existing models to accurately predict species behavior. Analyses provide sufficient conditions for species persistence and extinction that can be used to explain global dynamics. Dynamics are compared for two separate models, one involving a specialist predator and the second involving a generalist predator, where systems involving a specialist predator are prone to unstable dynamics. Analyses have implications in biological conservation tactics including various methods of prevention and preservation. Simulations are used to compare dynamics between models involving continuous time and those involving discrete time. Furthermore, we derive a semi-discrete model that utilizes both continuous and discrete time series dynamics. Simulations imply that Holling's Type III functional response controls the potential for three species persistence. Complicated dynamics govern the IGP subsystem involving the white-footed mouse, gypsy moth, and oak, and they ultimately cause the synchronized defoliation of forests across the Northeastern United States. Acorn mast seasons occur every 4-5 years, and they occur simultaneously across a vast geographic region due to universal cues. Research confirms that synchronization can be transferred across trophic levels to explain how this IGP system ultimately leads to gypsy moth outbreaks. Geographically referenced data is used to track and slow the spread of gypsy moths further into the United States. Geographic Information Systems (GIS) are used to create visual, readily accessible, displays of trap records, defoliation frequency, and susceptible forest stands. Mathematical models can be used to explain both changes in population densities and geographic movement. Analyses utilizing GIS softwares offer a different, but promising, way of approaching the vast topic of conservation biology. Simulations and maps are produced that can predict the effects of conservation efforts. / Dissertation/Thesis / M.S. Applied Biological Sciences 2012

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