Dissertations / Theses on the topic 'Environmental stress'
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Lou, Yuqian. "Environmental stress adaptation and stress protection in Listeria monocytogenes /." The Ohio State University, 1997. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487943341529077.
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Reginato, Luis Gabriel Marques. "Algoritmos ABC em Environmental Stress Screening." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/45/45133/tde-30082015-142622/.
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É comum, em problemas de inferência bayesiana, deparar-se com uma distribuição a priori para o parâmetro de interesse, theta, que seja intratável analítica ou computacionalmente. Como a priori é uma escolha do pesquisador, tal situação ocorre por conta da intratabilidade da função de verossimilhança. Por meio de algoritmos ABC, é possível simular-se uma amostra da distribuição a posteriori, sem a utilização da verossimilhança. Neste trabalho, aplica-se o ABC no contexto de Environmental Stress Screening - ESS. ESS é um procedimento de estresse, em um processo de produção industrial, que visa evitar que peças de qualidade inferior sejam utilizadas no produto final. A partir de uma abordagem bayesiana do ESS, depara-se com uma verossimilhança (e, consequentemente, uma posteriori) intratável para o vetor de parâmetros de interesse. Utiliza-se, então, o ABC para obtenção de uma amostra da posteriori e calcula-se o tempo ótimo de duração de um futuro procedimento de estresse a partir da simulação feita. É também proposta uma generalização do problema de ESS para a situação em que existem k tipos de peças no processo de produção. Quantifica-se o problema e, novamente, aplica-se um algoritmo ABC para a obtenção de uma simulação da posteriori, bem como calcula-se o tempo ótimo de duração de um futuro teste de estresse.In Bayesian inference problems, it is common to obtain a posterior distribution for the parameter of interest, theta, which is analytically or computationally intractable. Since the priori is chosen by the researcher, this situation arises from the intractability of the likelihood function. Through ABC algorithms it is possible to simulate a sample from the posterior distribution, without the analytical use of the likelihood function. In this work ABC is applied in the context of Environmental Stress Screening - ESS. ESS is a stress procedure, in an industrial production process, which aims to avoid low quality parts to be used in the final product. Under a Bayesian approach to ESS, an intractable likelihood (consequently, a posterior) is obtained for the paramater of interest. ABC is used to simulate a sample from the posterior and the optimal duration for a next stress procedure is calculated afterwards. A generalization of the ESS is also proposed considering that there are k types of parts in the production process. Again, ABC is used to simulate a sample from the posterior, and it is calculated the optimal duration for a next stress procedure.
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Runeson, Roma. "Personality, Stress, and Indoor Environmental Symptomatology." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-5899.
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Björkman, Tony. "Redesign of environmental stress screening software." Thesis, Uppsala universitet, Signaler och System, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-228161.
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In this thesis a industrial test process used during the manufacturing of pressure sensors has beenexamined. The examination is aimed to find areas of improvements related to the software that isused in the process. This test process separates faulty components, in this case circuit boards, beforethey are assembled into a finished product. The separation is made by letting a software applicationmonitor how the functionality of the circuit boards is affected during stress by high temperature andvibration. How the process is performed from a operator viewpoint was examined in the productionplant and suggestions from the operators collected. A preliminary design specification ,that wassupplied at the beginning of the thesis, was completed with the information that was gathered. Thekey improvements to the software were that the evaluation of test results should be automatic andthe software solution should be more scalable in terms of the amount of circuit boards that it canmonitor. The completed specification has been implemented in LabVIEW as a prototype applicationthat contains the key improvements of increased scalability and automatic evaluation of results.
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Fox, Marc A. "Adaptation of Rhizobium to environmental stress." Thesis, University of Reading, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.427836.
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Eccott, A. R. "Environmental stress cracking resistance of phenolic compounds." Thesis, Swansea University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636763.
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The environmental stress cracking (ESC) behaviour of a series of phenolics toughened with varying proportions of thermoplastic (0-35%), has been studied. Since these materials have been designed for applications in 'under-the-bonnet' automotive components, testing took place in serveral 'in-service' environments and in some of the constituent chemicals as well as in air. Initial screening of the materials using three point bend testing highlighted the most hostile environments for further study. Tensile testing of samples in air and in methanol and immersion of samples in various environments provided a further insight concerning the diffusion effects likely to be encountered. Creep tests were conducted in selected environments at 23oC, as well as at increased temperatures to provide more realistic 'under-the-bonnet' situations. The observed increase in creep rate in most hostile environments was related to crack initiation and growth. Within the range of added thermoplastic studied, two scales of morphology were seen to occur. In addition to a small scale morphology, only observed using TEM, there exists a large scale ribbon-like morphology. This was studied using light microscopy as well as SEM, on samples etched with permanganate and it was shown using X-ray microanalysis that the ribbons visible were thermoplastic rich regions. A good correlation was obtained between the amount of ribbon-like areas and the thermoplastic content of the sample. Samples, apparently prepared under identical conditions, vary slightly in colour. Further investigation revealed that these colour differences could be correlated with a variation in large scale morphology as well as considerable property differences. TEM, SEM and light microscopy were performed to relate the ESC behaviour with the material morphology. TEM investigations concerning the small scale morphology effect upon crack growth were inconclusive. However, from viewing etched samples subject to ESC via bend tests in methanol, using SEM and light microscopy, it was evident that the large scale morphology was responsible for deflecting microcracks.
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Hecht, Vivian (Vivian Chaya). "Biophysical responses of lymphocytes to environmental stress." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/103693.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Biological Engineering, 2016.Cataloged from PDF version of thesis. "February 2016."
Includes bibliographical references (pages 139-151).
Cellular biophysical properties both reflect and influence cell state. These parameters represent the consequences of the interactions of multiple molecular events, and thus may reveal information otherwise obscured when measuring individual pathways in isolation. Previous work has demonstrated how precise measurements of certain of these properties, such as mass, volume, density and deformability using a suspended microchannel resonator (SMR) can help characterize cellular behavior and physiological role. Here, we expand upon this previous work to demonstrate the necessity of measuring multiple parameters simultaneously to fully determine cellular responses to environmental perturbations, and describe a situation in which changes to density and size promote survival under conditions of limited nutrient availability. We first investigate the relationship between cell density, volume, buoyant mass, and passage time through a narrow constriction under a variety of environmental stresses. Osmotic stress significantly affects density and volume, as previously shown. In contrast to density and volume, the effect of an osmotic challenge on passage time is relatively small. Deformability, determined by comparing passage times for cells with similar volume, exhibits a strong dependence on osmolarity, indicating that passage time alone does not always provide a meaningful proxy for deformability. Finally, we find that protein synthesis inhibition, cell cycle arrest, protein kinase inhibition, and cytoskeletal disruption result in unexpected relationships between deformability, density, and volume. Taken together, our results suggest that measuring multiple biophysical parameters can detect unique characteristics that more specifically reflect cellular behaviors. We next examine how cellular biophysical changes occurring immediately after growth factor depletion in lymphocytes promote adaptation to reduced nutrient uptake. We describe an acute biophysical response to growth factor withdrawal, characterized by a simultaneous decrease in cell volume and increase in cell density prior to autophagy initiation, observed in both FL5.12 cells depleted of IL-3 and primary CD8+ T cells depleted of IL-2 and differentiating towards memory cells. The response reduces cell surface area to minimize energy expenditure while conserving biomass, suggesting that the biophysical properties of cells can be regulated to promote survival under conditions of nutrient stress.
by Vivian Hecht.
Ph. D.
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Harvie, Duncan Robert. "Environmental stress and virulence in Bacillus cereus." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615619.
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Barrington, Christopher. "Epigenetic responses to environmental stress in plants." Thesis, University of Warwick, 2013. http://wrap.warwick.ac.uk/59638/.
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Environmental signals can directly influence gene expression through epigenetic mechanisms, causing phenotypic changes that can be transmitted to progeny. In plants, this is in part achieved by short interfering RNA (siRNA) which guide covalent modification of DNA, such as cytosine methylation, to specific targets including repetitive sequences and transposable elements. Environmental stress also leads to genome-wide DNA hypomethylation, misregulation of transposable elements and ultimately ‘genomic shock’. Although most stress-induced epigenetic modifications are not thought to be heritable, there is increasing evidence for the inheritance of novel environmentally-induced epigenetic states or ‘environmental epialleles’. The formation of environmental epialleles represents an important source of variation and a powerful driving force of adaptive evolution but the precise mechanism remains unclear. The aim of this thesis is to identify environmental epialleles through computational methods. Analysis of Illumina sequencing data from environmentally stressed maize plants sampled during stress and after a recovery period has so far revealed that a significant proportion of the maize genome is misregulated at both the genetic and epigenetic level. These findings indicate that plants continue to respond after exposure to stress and that this response is likely mediated by at least one epigenetic mechanism, including siRNA-directed DNA modifications.
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Pauw, Marina. "Chitin synthesis in response to environmental stress." Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/86435.
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Thesis (MSc)--Stellenbosch University, 2014.ENGLISH ABSTRACT: Previous studies have indicated that fermentation with yeast strains whose cell walls contain higher chitin levels may lead to reduced wine haze formation. In order to adjust cell wall chitin levels, more information on the regulation of chitin synthesis in wine-relevant yeast is required. Yeast cells are known to increase chitin levels when subjected to certain environmental changes such as an increase in temperature. The main aim of this project was to investigate chitin accumulation and synthesis in wine yeast strains when exposed to environmental change. This was achieved by subjecting the strains to various environmental conditions and comparing chitin levels. The information gained may aid future selection and/or manipulation of yeast strains for the production of higher chitin levels. Three Saccharomyces cerevisiae strains and two Saccharomyces paradoxus strains were subjected to conditions that had been linked to a change in chitin synthesis in past studies in laboratory yeast strains. Of the conditions used in this study, the addition of calcium to a rich media led to the highest cell wall chitin levels. The data also show that chitin synthesis is largely strain dependant. Two conditions which resulted in increased chitin deposition were chosen for gene expression analyses, using strains with strongly diverging average chitin levels. Results showed that an increase in chitin levels correlates with an increase in expression of GFA1, the gene encoding for the first enzyme of the chitin synthesis pathway. Overall, this study provides novel insights into chitin synthesis in Saccharomyces cerevisiae wine yeast strains as well as Saccharomyces paradoxus strains, with possible future implications on haze prevention studies.
AFRIKAANSE OPSOMMING: Vorige studies het aangetoon dat fermentasie met gisrasse waarvan die selwande hoë chitienvlakke bevat, kan lei tot verminderde wynwaasvorming. Om selwandchitienvlakke aan te pas, word daar meer inligting rakende die regulering van chitienvlakke in wyn gisrasse verlang. Dit is bekend dat gisselle chitienvlakke verhoog wanneer die selle onderwerp word aan sekere veranderinge in die omgewing soos ’n verhoging in temperatuur. Die hoofdoel van hierdie projek was om die chitienopbou en -sintese in wyngisrasse te ondersoek waar gis blootgestel word aan omgewingsveranderinge. Dit is bereik deur die selle aan verskeie omgewingstoestande bloot te stel en chitienvlakke met mekaar te vergelyk. Die inligting hieruit verkry kan toekomstige gisraskeuses asook die manipulering van gisrasse met die oog op hoër vlakke van chitienproduksie vergemaklik. Drie Saccharomyces cerevisiae rasse en twee Saccharomyces paradoxus rasse is onderwerp aan toestande wat in vorige studies gekoppel is aan ’n verandering in chitienvorming in laboratorium-gisrasse. Van die toestande toegepas in hierdie studie, het die toevoeging van kalsium tot ’n nutrientryke medium gelei tot die hoogste chitienvlakke in selwande. Die data toon ook aan dat chitiensintese hoofsaaklik rasverwant is. Twee toestande wat gelei het tot verhoogde chitienafsetting is gekies vir geen-uitdrukkingsanalise, terwyl rasse gebruik is met gemiddelde chitienvlakke wat wyd uiteenlopend is. Die resultate het getoon dat ’n verhoging in chitienvlakke ooreenstem met ’n verhoging in die uitdrukkingsvlakke van GFA1, die geen wat kodeer vir die eerste ensiem in die chitiensintesebaan. Oor die algemeen verskaf hierdie studie nuwe insigte oor chitiensintese in Saccharomyces cerevisiae wyngisrasse en Saccharomyces paradoxus rasse en verskaf dit belangrike inligting vir moontlike toekomstige studies oor waasvoorkoming.
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Loureiro, Cláudia Sofia Brites. "Ecological interactions in populations facing environmental stress." Doctoral thesis, Universidade de Aveiro, 2012. http://hdl.handle.net/10773/10537.
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Moutoramento em BiologiaO zooplâncton, particularmente os cladóceros, são organismos de água doce importantes na regulação da produção primária dos ecossistemas de água doce. No entanto, também podem adaptar-se a condições salobras. Tendo em conta as previsões no âmbito das alterações climáticas, a intrusão salina pode ocorrer a par com a subida de temperatura. As populações de água doce podem ficar vulneráveis aos efeitos interativos da salinidade e da temperatura, de acordo com os seus limites de tolerância e capacidade de adaptação ao stress ambiental. Assim, a presente tese analisou as interações resultantes das alterações destes agentes de stress em populações de cladóceros de água doce. Primeiro, comparou-se a halotolerância de diferentes genótipos de Simocephalus vetulus provenientes de populações de água doce e de água salobra de modo a avaliar a existência de uma componente genética de resistência à salinidade. A sensibilidade aguda dos genótipos variou na mesma gama de concentrações; todavia, todos os genótipos da população salobra, exceto um, foram mais tolerantes do que os de água doce, em termos de tempo à imobilização. Contudo, não foi possível estabelecer uma relação entre a performance reprodutiva em condições salobras e o contexto ambiental de origem destes genótipos. Mais, estes ensaios mostraram que as populações de água doce têm potencial para tolerar incrementos de salinidade. Como tal, pode-se concluir que a seleção a que os genótipos estão sujeitos no seu local de origem foi mais fraca do que o esperado. Segundo, investigou-se a capacidade de aclimatação de Daphnia galeata à salinidade e temperatura, de modo a avaliar a halotolerância de Daphnia a duas temperaturas num cenário de aclimatação multigeracional. O objetivo foi compreender se a pré-adaptação ao stress ambiental (20ºC e 25ºC versus 0 g/L e 1 g/L de NaCl) influenciou posteriormente as respostas a estes agentes de stress. Verificou-se uma tendência para um aumento de sensibilidade ao NaCl, a temperaturas mais elevadas. No entanto, este efeito foi anulado após nove gerações, mas apenas quando os organismos foram aclimatados aos dois agentes de stress em simultâneo (salinidade e temperatura elevada). Terceiro, demonstrou-se experimentalmente que a salinidade interferiu com a competição interespecífica, alterando a composição das comunidades zooplanctónicas. Este conjunto de evidências permitiu-nos refletir nos múltiplos impactos de agentes de stress, particularmente os relacionados com as previsões de alterações climáticas. Em paralelo aos estudos de natureza experimental, e numa perspetiva de Educação para o Desenvolvimento Sustentável (EDS), importa também promover o desenvolvimento de competências necessárias à compreensão de mudanças ambientais globais (e.g., o impacto da salinidade e da temperatura) para implementar estratégias de mitigação e adaptação. Neste contexto, foi realizada uma atividade com estudantes do ensino secundário, que se tornou uma boa oportunidade para a sua aprendizagem e aquisição de competências de interpretação de dados experimentais, assim como de sensibilização para as questões ambientais.
Zooplankton, namely cladocerans, are important regulators of primary production in freshwater ecosystems. However, these filter-feeders can also be found in brackish waters and can therefore adapt to this stressful condition. Bearing in mind climate change predictions, saline intrusion can occur in coastal freshwater systems, accompanied by increasing temperatures. Freshwater populations can thus become vulnerable to the interactive effect of salinity and temperature, framed within their tolerance limits and adaptation ability to environmental stress. Taking this into consideration, the present thesis aimed at addressing the complex interactions resulting from the challenge of these environmental stressors on freshwater cladoceran populations. First, the halotolerance of different Simocephalus vetulus genotypes from two freshwater and one brackish population (salinity 2.3) was explored. The goal was to determine whether there was a genetic component of salinity resistance. Clone acute sensitivity was comparable among populations. However, all brackish clones, except one, were more halotolerant than freshwater genotypes, in terms of survival time. Life history assays, carried out with extreme genotypes (from previous experiment) revealed no relationship between fitness and the original environmental context of genotypes. Also, these experiments showed that freshwater populations do have the potential to tolerate salinity increases. As such, we can conclude that the local selective pressure caused by salinity was weaker than expected. Second, the acclimation ability of Daphnia galeata to salinity and temperature was investigated in this study, by evaluating Daphnia’s sensitivity to salinity, at two different temperatures, along a multigenerational acclimation scenario. The objective was to understand whether pre-adaptation to environmental stress (20ºC and 25ºC versus 0 g/L and 1 g/L of added NaCl) influenced the response to the latter exposure to these stressors. A tendency towards the increase of sensitivity to NaCl was observed, at higher temperature. However, this temperature-dependent effect was nullified after nine generations, but only when animals had been acclimated to both stressors (salinity and higher temperature). Third, we experimentally demonstrated that salinity interfered with inter-specific competition, altering the community composition of zooplankton communities. This body of evidence allowed us to reflect on the impacts of multiple stressors, particularly those related to climate change predictions. In parallel with experimental studies, within the framework of Education for Sustainable Development, it is also important to promote the development of the necessary competences towards the comprehension of global environmental change (e.g. the impact of salinity and temperature), in order to implement adequate mitigation and adaptation strategies. Hence, an activity with secondary school students was conducted, providing a good opportunity towards learning and competence acquisition in the interpretation of experimental data, as well as increasing awareness towards environmental issues.
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Cuco, Ana Patrícia Domingues. "Host-parasite interactions in environmental stress scenarios." Doctoral thesis, Universidade de Aveiro, 2017. http://hdl.handle.net/10773/22246.
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Doutoramento em BiologiaThe overarching objective of this thesis was to explore ecologically relevant scenarios of contamination by agrochemical fungicides, in particular their interaction with disease (a ubiquitous and relevant natural stressor), using a host (Daphnia spp.) × parasite (Metschnikowia bicuspidata) system as an experimental model. Because parasites act as modulators of population dynamics and genetic diversity, interaction scenarios between disease and anthropogenic factors (namely pollution) are important to clarify. For this work, copper sulphate and tebuconazole were selected as chemical stressors, given their widespread use as fungicides and frequent detection in aquatic systems. This thesis presents a sequential series of research steps that were undertaken to assess the hazards posed by these chemicals under multi-stressor (i.e., realistic) scenarios. First, we assessed the toxicity of copper sulphate and tebuconazole in two host (Daphnia) clones, considering their joint effects with increasing temperatures. This allowed simulating two important agents of environmental change. Temperature was the most influencing factor on Daphnia fitness, although both copper and tebuconazole reduced the fecundity and survival of Daphnia. A temperature-dependent pattern was found for both fungicides, although this was highly context-dependent. Second, we investigated the reciprocal effects of these pollutants and parasite challenge, using the Daphnia-M. bicuspidata experimental system. The toxicants decreased Daphnia fitness, whilst the parasite strongly reduced host survival. Whilst copper sulphate and parasite effects were mostly independent, tebuconazole suppressed the M. bicuspidata infection at an environmentally relevant range of concentrations (> 6.25 μg l-1). Third, these contrasting outcomes were assessed at two distinct temperatures, because temperature is an important modulator of both toxicity and hostparasite relationships. Indeed, we observed that temperature increased parasite virulence and acted as a modulator of existent interactions between pollution and disease (in the case of tebuconazole). Based on these evidences, we directed our focus to the observed anti-parasitic effect of tebuconazole, which we hypothesize that is more widespread than reported. In a fourth step, we evaluated the influence of different exposure scenarios to tebuconazole (timing × concentration) on the Daphnia-M. bicuspidata experimental system. Infection data revealed an “all-or-nothing” effect, with tebuconazole suppressing infection within a narrow range of tebuconazole concentrations (3.65–13.5 μg l-1). We were able to confirm that tebuconazole inhibited sporulation of M. bicuspidata, and possibly also the vegetative growth of the yeast cells. Finally, we determined if M. bicuspidata could adapt to this anthropogenic selective pressure, by experimentally promoting the rapid evolution of M. bicuspidata lineages to tebuconazole. Infectivity, spore load and survival time of the infected hosts revealed that evolved parasite lineages performed worse than naive lineages, although this could be easily reversed after removal of the stressor. This demonstrates that there were transient costs of prolonged exposure to tebuconazole and that the microparasitic yeast M. bicuspidata did not reveal potential for rapid evolution to the fungicide. Altogether, our findings support the idea that long term exposure to tebuconazole is hazardous to non-target fungi at environmentally realistic concentrations, putatively affecting numerous microparasites and decomposers, as well as the processes were they intervene (disease and decomposition). Copper sulphate, on the other hand, revealed a less contextdependent toxicity pattern, without interacting with parasitism in this case. Our findings with tebuconazole demonstrate negative ecological effects of antifungal agents (which include agrochemicals and pharmaceuticals, many sharing mode of action), which may have so far been overlooked.
O objetivo fundamental desta tese centrou-se na exploração de cenários ecologicamente relevantes de contaminação por fungicidas, e em particular a sua interação com a doença (um factor de stress natural e omnipresente), usando para isso um modelo experimental composto por um hospedeiro (Daphnia spp.) e um parasita (Metschnikowia bicuspidata). Tendo em conta o papel importante dos parasitas como moduladores da diversidade genética e dinâmica das populações, torna-se importante clarificar cenários de interação entre doença e factores antropogénicos (nomeadamente a poluição). Neste trabalho, selecionou-se o sulfato de cobre e o tebuconazole como fatores de stress químico, devido ao seu amplo uso como fungicidas e frequente deteção em sistemas aquáticos. Esta tese apresenta-se como uma sequência de etapas de investigação, realizadas com o intuito de avaliar os perigos apresentados por estes agentes químicos em cenários de stress múltiplo (i.e. mais próximos da realidade). Primeiro, a toxicidade de sulfato de cobre e tebuconazole foi determinada em dois hospedeiros (dois genótipos de Daphnia), considerando os seus efeitos interativos com o aumento de temperatura. Estes cenários permitiram-nos simular dois agentes importantes de mudanças ambientais. Apesar de ambos os fungicidas (cobre e tebuconazole) reduzirem a fecundidade e sobrevivência de Daphnia, a temperatura foi o factor mais preponderante no desempenho de Daphnia. Neste sentido, observou-se um padrão de toxicidade dependente da temperatura para ambos os fungicidas, apesar de altamente dependente do contexto. Em segundo lugar, os efeitos recíprocos destes poluentes e do parasitismo foram avaliados, usando o modelo experimental Daphnia- Metschnikowia. Enquanto os poluentes diminuiram o desempenho reprodutivo de Daphnia, o parasita afetou principalmente a sobrevivência do hospedeiro. Além disso, enquanto os efeitos do sulfato de cobre e do parasita foram maioritariamente independentes, o tebuconazole suprimiu a infeção de M. bicuspidata a concentrações ambientalmente relevantes (> 6,25 μg l-1). Em terceiro lugar, e tendo em conta o potencial da temperatura como moduladora de toxicidade dos contaminantes e das relações hospedeiro-parasita, avaliámos o desfecho da interação parasita × contaminante quando o modelo experimental foi exposto a duas temperaturas distintas. De facto, a temperatura revelou ser capaz de aumentar a virulência do parasita e de modular interações existentes entre a poluição e a doença (no caso do tebuconazole). Tendo em conta as evidências recolhidas até este ponto, o foco do nosso trabalho foi dirigido para o efeito anti-parasitário do tebuconazole, que hipotetizamos ser mais disseminado do que o reportado até agora. Assim, numa quarta etapa investigativa, a influência de diferentes cenários de exposição ao tebuconazole (tempo de exposição × concentração) foi determinada, usando o modelo experimental Daphnia-Metschnikowia. Os dados de infetividade revelaram um efeito “tudo-ou-nada” causado pelo tebuconazole, confirmado pela supressão da infeção dentro de uma gama estreita de concentrações (3,65–13,5 μg l-1). Com estes resultados, foi possível confirmar que o tebuconazole inibiu a esporulação de Metschnikowia, e possivelmente o crescimento vegetativo das células desta levedura. Finalmente, com o intuito de determinar se M. bicuspidata conseguiria adaptarse a esta pressão seletiva, promovemos experimentalmente a rápida evolução de linhagens de Metschnikowia ao tebuconazole. A infectividade, o número (carga) de esporos e o tempo de sobrevivência dos hospedeiros infetados revelaram que as linhagens expostas ao tebuconazole tiveram um pior desempenho quando comparados com as linhagens não expostas ao tebuconazole. Ainda assim, este efeito negativo foi facilmente revertido após a remoção desta pressão selectiva. Estas evidências demonstram custos transientes associados a uma exposição prolongada ao tebuconazole, sendo que o microparasita M. bicuspidata não revelou potencial para uma evolução rápida ao tebuconazole. Em conjunto, os nossos resultados confirmam que a exposição prolongada a concentrações ambientalmente relevantes de tebuconazole é nociva para comunidades de fungos não-alvo, podendo assim afetar numerosos microparasitas e decompositores, assim como os processos onde eles intervêm (doença e decomposição). O sulfato de cobre, por outro lado, revelou um padrão de toxicidade menos dependente do contexto, e sem qualquer interação com o parasitismo. As nossas descobertas demonstraram potenciais efeitos ecológicos negativos de agentes anti-fúngicos (que incluem agroquímicos e fármacos, muitos dos quais partilham o mesmo modo de ação), que poderão ter sido negligenciados até agora.
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Risemark, Eriksson Martin. "Environmental stress of electrical machine winding insulation." Thesis, Uppsala universitet, Elektricitetslära, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-326711.
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The conducting winding of an electrical machine is insulated in order to prevent any short circuits to occur within the machine. This insulation is during its lifetime exposed to several environmental stresses and therefore plays an important role in the life length of the machine. Accelerated stress tests are used to investigate what design and material is most suitable for a good endurance of a product. In this master thesis, new accelerated test methods for the insulation system in an electrical machine are developed and evaluated. The study resulted in four stress tests that simulate the thermal stress, the thermomechanical stress and the ambient stress from direct oil cooling. Three diagnosis tests and a material analysis were used in order to evaluate how these accelerated stress test methods affected the insulation. The diagnosis tests showed no clear sign of deterioration of the insulation in terms of change in electrical characteristics. However, the material analysis indicated deterioration of the insulation, such as cracks and oxidation of the material. These changes show that the test methods are capable to affect the insulation, but will need more time to cause a breakdown, since a stator of this kind is expected to have a very long life length. Therefore, in future work on this topic, these test methods should continue for a longer time and it would likely be interesting to look into other diagnosis tests.
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Jacobsson, Malin. "A Stress Free Workplace : Spatially planned office space to diminish environmental stress." Thesis, Mälardalens högskola, Akademin för innovation, design och teknik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:mdh:diva-20007.
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The main objective of this thesis was to understand the environmental variables that affect humans psychological states when it comes to stress. More specifically, the environmental variables at the company Maintpartner AB's new Swedish headquarters office in Årsta, Stockholm, a company concentrated on customized industrial maintenance and operation service. In my thesis I found evidence that open-plan solutions would be a stressor due to increase disturbance from coworkers. Open-plan offices could also be perceived as a stressor because of the limitation in personal control. Through implementing nature and/or integrating it via visual escape the space could be perceived as more attractive and less crowded. Maintpartner AB's administrative personnel has highly individual work tasks and therefore a need for customized workplaces. This resulted in a design concept with separated office rooms, individually designed to meet the staffs individual need. Some areas are designed to work as meeting areas for work or social related encounters
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Xavier, Ilungo Johnny. "Environmental stress response of the hyphomycetous entomopathogenic fungi." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ32803.pdf.
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Tarlykov, Pavel Victorovich. "Chemical approaches to probe environmental stress in Archaea." Thesis, Montana State University, 2009. http://etd.lib.montana.edu/etd/2009/tarlykov/TarlykovP0509.pdf.
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Little is known about strategies and mechanisms employed by thermophilic organisms to adapt to environmental stress. Sulfolobus solfataricus is a thermophile that belongs to Archaea, the third domain of life, and can be found in unusual habitats, such as the hot springs of Yellowstone National Park. This archaeon can tolerate high temperature, extreme acidity and high concentrations of heavy metals and other toxic substances. Thus, S. solfataricus has been chosen by many researchers as a model system for biochemical, structural, and genetic studies. In this work S. solfataricus has been exposed to hydrogen peroxide as a natural mild oxidant and arsenic as a common toxic metalloid. One of the aims was to quantitatively define the regulation of proteins upon treatment with hydrogen peroxide or arsenic species in different time periods and concentrations. In this sense, two-dimensional gel electrophoresis approach in conjunction with novel chemical tagging probes has been applied to detect changes on the level of regulation and chemical modification of individual proteins within the whole proteome in response to the stressors. Proteins expression levels have been monitored, redox-sensitive and phosphoproteomic profiles of the S. solfataricus proteome have been identified. Synthesis of the results has allowed a general scheme for how S. solfataricus fights H2O2- and As-induced stress. Lists of mapped proteins have been created and potential biomarkers for oxidative stress have been identified, which can guide further research to better understand mechanisms of proteomic response to the environmental stress in Archaea on the example of thermophilic archaeon S. solfataricus.
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Ryan, Annette Coralie. "Does isoprene protect plants against complex environmental stress?" Thesis, Lancaster University, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.539650.
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Komitopoulou, Evangelia. "Environmental sensing and stress resistance in Salmonella typhimurium." Thesis, University of Surrey, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.252342.
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Hall, Tavenner Marie. "Evaluating changes in strontium chemistry of stream water in response to environmental stress." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/54408.
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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1995.Includes bibliographical references (leaves 47-49).
by Tavenner Marie Hall.
M.S.
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Bishop, G. P., and Phillip R. Scheuerman. "Physiological Changes in Bacteria During Starvation Stress." Digital Commons @ East Tennessee State University, 1990. https://dc.etsu.edu/etsu-works/2889.
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MacCombe, Diane Martha Elizabeth. "The effect of mild acid stress on environmental microorganisms." Thesis, Queen's University Belfast, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.491881.
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The requirement to reduce biomass production & enhance polyphosphate production during the wastewater treatment process is necessary to ensure the process is environmentally sound & cost effective. The effect of mildly acidic pH (pH6.0) on . the biomass formation & polyphosphate production by a range ofenvironmental microorganisms was investigated, using activated sludge from a trial wastewater treatment plant & a range ofenvironmental isolates. Activated sludge obtained from a treatment plant operating at pH6.0, produced lower levels of biomass alongside a higher level ofphosphate removal & higher rates ofrespiration & substrate utilisation, compared to operation ofthe same plant at higher operational pH levels. Seven pure culture isolates were also characterised in terms of their phosphate removal & biomass yields over a range ofpH values (5-.5 to 7.5). Isolates could be identified as members ofone Qfthe following: (1) demonstrate reduced biomass yields & accumulate more polyphosphate at an acidic pH, e.g. Erwinia carotovora subsp. atroseptica, (2) exhibit reduced biomass yields & polyphosphate accumulation at acidic pH e.g. Pseudomonf:ls aeruginosa PAOl, and (3) display similar or higher biomass yields at acidic pH & accumulate higher levels ofpolyphosphate at these acidic pH levels, e.g. Burkholderia cepacia AM19. Three microorganisms were studied further in continuous culture at pH6.0. E. carotovora displayed lower levels of biomass yield coupled with higher substrate utilisation rates, ATP formation rates & total intracellular P levels. B. cepacia AM19 & P. aeruginosa PAOl, in contrast displayed similar levels ofbiomass production, P removal & substrate utilisation rates. The response by E. carotovorG&activated sludge to acidic pH would suggest an increase in maintenance energy at acidic pH, caused by an increased rate ofproton pumping in order to maintain a constant intracellular pH with polyphosphate playing a protective role at acidic pH.
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Smith, P. J. "Investigation into Environmental Stress Cracking in Processed Food Cans." Thesis, Imperial College London, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.520862.
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Callander, Davon Christina. "Effects of environmental stress on gene expression in mussels." Thesis, University of Canterbury. Biological Sciences, 2012. http://hdl.handle.net/10092/8088.
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The biogeographic distribution of organisms is determined by physiological characteristics that enable a population to persist in a specific location. Global climate change effects are anticipated to increase the physiological stress experienced by organisms. Consequently, it is important to understand physiological responses to environmental stress and the mechanisms used by animals to cope with variable conditions.
I investigated the physiological response to environmental stress in two species of mussel from New Zealand, Perna canaliculus and Mytilus galloprovincialis, using quantitative PCR and ecological field experiments. A series of laboratory and field experiments were done to manipulate stress levels and the expression levels of three heat shock protein genes (hsp24, hsp70, hsp90) were measured. A transcription regulatory gene (elf2) and a cell cycle regulatory gene (tis11d) were also measured. The dynamics of stress response gene expression in response to acute stress and gene expression changes in the natural population due to varying forms of environmental stress were tested.
Between-zone translocations of different sized M. galloprovincialis and P. canaliculus were done at two sites in both east and west regions of the South Island of New Zealand. Site was found to be the most important factor in stress response. Apparent low food and high exposure stress interacted to create the particularly elevated stress response at the Timaru site. The adaptive ability of mussels transplanted between sites with varying environmental conditions was also tested. Results suggest that acclimation may be limited under stressful conditions. Furthermore, I found that P. canaliculus, the predominantly low-zone species, had a lower stress response than M. galloprovincialis, which was contradictory to predictions.
The investigations described in this thesis suggest that interactive effects of abiotic stress and food limitations are particularly challenging for animals. With the severity of climate change scenarios predicted, changes in water quality and aerial and seawater temperature suggest mussel populations are likely to be negatively affected in the future. This work also illustrates the great potential to utilise molecular techniques for analysis of physiological processes of non-model organisms in a real-world setting.
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French, Mark Andrew. "Environmental degradation and stress corrosion of hybrid fibre composites." Thesis, Kingston University, 1990. http://eprints.kingston.ac.uk/20537/.
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Smith, Hannah. "Metabolic adaptations to micro-environmental stress in tumour spheroids." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:3651d265-ddc0-4258-b3f7-2a0242697d21.
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Alterations in energy metabolism due to factors including cellular stress from the hostile tumour micro-environment are a emerging cancer hallmark. Distinct hypoxic and quiescent cell populations develop, which are resistant to chemotherapy due to lack of proliferation, drug inactivity in the altered redox status of the cell and enhanced drug biotransformation. The present study characterises the metabolic strategies employed by these distinct populations of cancer cells. The in vitro 3-dimensional tumour spheroid model, which reflects tumour architecture and behaviour, cultured under different micro-environmental conditions was utilized in this study. Metabolic enzyme activity and expression, overall metabolic flux rates for nutrients, metabolomics profiles of specific pathways and tissue status were assessed. Metabolic adaptations consistent with the Warburg effect were observed in fully oxygenated, proliferative tumour spheroids, with glucose being metabolised to produce lactate. Additionally, metabolomics investigations determined glucose was metabolised by the pentose phosphate pathway, demonstrated by high enrichment of glucose-derived carbon in 6-phophogluconate. The extraction of 39.7 ± 7.6 μ moles (mg protein) -1 glutamine from the medium over 24 hours was observed in these spheroids, consistent with glutaminolysis pathway activity. A 2-fold higher rate of glycolytic flux (measured by production of 3h2O from 5-3H-glucose) was measured in hypoxic tumour spheroids, despite reduced levels of glycolytic enzymes being determined. Surprisingly, although lower rates of glycolysis (2.6-fold) were measured in quiescent spheroids, increased glycolytic enzyme activities (HK 1.9 fold, PK 2 fold and LDH 1.8 fold), glucose (1.9 fold over 24 hours) and glutamine uptake (5.5 fold over 12 hours) as well as lactate production (1.8 fold) were measured, relative to their proliferating counterparts. This study demonstrates that metabolic strategies employed by tumour spheroids differ upon exposure to distinct micro-environmental stresses, additionally identifying hexokinase as a potential therapeutic target for the inhibition of glycolysis under all micro-environmental stress conditions analysed.
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Gomes, Ana Cristina Esteves Oliveira. "The role of environmental stress on protein synthesis fidelity." Doctoral thesis, Universidade de Aveiro, 2012. http://hdl.handle.net/10773/9534.
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Doutoramento em BioquímicaEstudos recentes estabelecem uma ligação entre erros na tradução do mRNA e cancro, envelhecimento e neurodegeneração. RNAs de transferência mutantes que introduzem aminoácidos em locais errados nas proteínas aumentam a produção de espécies reactivas de oxigénio e a expressão de genes que regulam autofagia, ribofagia, degradação de proteínas não-funcionais e protecção contra o stress oxidativo. Erros na tradução do mRNA estão portanto relacionados com stress proteotóxico. Sabe-se agora que o mecanismo de toxicidade do crómio está associado à diminuição da fidelidade de tradução e à agregação de proteínas com malformações que destabilizam a sua estrutura terciária. Desta forma, é possível que os efeitos do stress ambiental ao nível da degeneração celular possam estar relacionados com a alteração da integridade da maquinaria da tradução. Neste estudo procedeu-se a uma avaliação alargada do impacto do stress ambiental na fidelidade da síntese de proteínas, utilizando S. cerevisiae como um sistema modelo. Para isso recorreu-se a repórteres policistrónicos de luciferase que permitiram quantificar especificamente a supressão de codões de terminação e o erro na leitura do codão AUG em células exposta a concentações não letais de metais pesados, etanol, cafeína e H2O2. Os resultados sugerem que a maquinaria de tradução é na generalidade muito resistente ao stress ambiental, devido a uma conjugação de mecanismos de homeostase que muito eficientemente antagonizam o impacto negativo dos erros de tradução. A nossa abordagem quantitativa permitiu-nos a identificar genes regulados por uma resposta programada ao stress ambiental que são também essenciais para mitigar a ocorrência de erros de tradução, nomeadamente, HSP12, HSP104 e RPN4. A exposição prolongada ao stress ambiental conduz à saturação dos mecanismos de homeostase, contribuindo para a acumulação de proteínas contendo erros de tradução e diminuindo a disponibilidade de proteínas funcionais directamente envolvidas na manutenção da fidelidade de tradução e integridade celular. Ao contrário de outras Hsps, a Hsp12p adopta normalmente uma localização membranar em condições de stress, que pode modular a fluidez e estabilidade membranar, sugerindo que a membrana plasmática é um alvo preferencial da perda de fidelidade da tradução. Para melhor compreender as respostas celulares aos erros de tradução, células contendo deleções em genes codificadores das Hsps foram transformadas com tRNAs mutantes que introduzem alterações no proteoma. Os nossos resultados demonstram que para além da resposta geral ao stress, estes tRNAs induzem alterações a nível do metabolismo celular e um aumento de aminoacilação com Metionina em vários tRNAs, sugerindo um mecanismo de protecção contra espécies reactivas de oxigénio. Em conclusão, este estudo sugere um papel para os erros de tradução na gestão de recursos energéticos e na adaptação das células a ambientes desfavoráveis.
Recent studies link mRNA mistranslation to cancer, neurodegeneration, aging and metabolic imbalances. It was shown previously that mutant tRNAs that mutagenise the proteome via mRNA misreading increase production of reactive oxygen species and up-regulate the expression of oxidative stress, autophagy and ribophagy genes, indicating that mistranslation is an important cause of proteotoxic stress. Interestingly, chromium toxicity is linked to increased mistranslation and protein aggregation suggesting that environmental stressors may cause cell degeneration and human disease through deregulation of protein synthesis fidelity. In this study, we investigate the impact of environmental on the fidelity of protein synthesis using S.cerevisiae as a model system. We used a dual luciferase reporter to quantify both AUG misreading and stop codon readthrough in cells exposed to sub-lethal concentrations of heavy metals, ethanol, caffeine and hydrogen peroxide. Our results suggest that the translational machinery is in general very resistant to environmental stress, due to a conjugation of homeostasis mechanisms that effectively antagonize the negative impact of protein synthesis errors to a level tolerated by cells. Additionally, our quantitative approach allowed us to identify genes under the control of the environmental stress response (ESR) that are essential to cope with induced amino acid misincorporation, namely HSP12, HSP104 and RPN4. Prolonged stress exposure drives saturation of protein homeostasis mechanisms, which contributes to accumulation of mistranslated protein into the cytoplasm and thereby decreases the availability of functional proteins directly involved in translational fidelity and cellular integrity. Unlike all other Hsps, Hsp12p associates with the plasma membrane under stress, which may help modulate membrane fluidity and stability, suggesting that protein synthesis errors target membrane components. To further understand the cellular responses to mistranslation and proteotoxic stress, cells harboring deletions in genes coding for small heat-shock proteins were transformed with a misreading tRNA. The data showed that besides a wide response to stress, constitutive mistranslation also promoted a shift in cellular metabolism. Finally, cells expressing misreading tRNAs show increased Met-misacylation, suggesting that methionine misincorporation into proteins protects against ROS. This study strongly supports a role for mistranslation in energy management and cell adaptation to suboptimal environmental conditions.
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Woods, Clare A. "Respiratory carbon loss in plant tissues under environmental stress." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:829338ba-7c5a-41b8-9cdd-ead4646e161e.
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Crop productivity is a balance between carbon gain by photosynthetic assimilation of CO2 and the release of fixed carbon as CO2 via respiration. Respiration is the process by which carbohydrates are oxidised to produce ATP to fuel biochemical reactions, whilst simultaneously releasing CO2 as a by-product; therefore, increased demand for ATP or decreased efficiency of ATP production by uncoupling of the mitochondrial electron transport chain results in greater CO2 production. ATP produced by respiration is either used to support processes involved in growth or to power cell maintenance processes, such as macromolecule turnover or maintenance of membrane ion gradients. Respiration increases when plants are exposed to high temperatures; a factor that will become increasingly important as we try to maximise food production as the global climate changes. However, it is unknown if increased respiration at high temperature is necessary to provide energy to support growth, is a consequence of increased ATP consumption for maintenance processes or is due to increased mitochondrial uncoupling at high temperature. Flux measurements showed that CO2 production by excised Arabidopsis thaliana roots increases with temperature up to 37°C. Although growth also increased up to 37°C resulting in increased respiration associated with growth processes, the majority of overall CO2 production at high temperatures could be accounted for by non-growth respiration. An analysis of ATP-consuming processes demonstrated that protein turnover and maintenance of ion gradients collectively account for the majority of maintenance respiration, but that ATP consumption for the maintenance of ion gradients is quantitatively more important than protein turnover at high temperature. Furthermore, a decrease in in vivo P/O ratio at high temperature was demonstrated; the results presented suggest that this is most likely due to increased basal proton leak across the inner mitochondrial membrane. It can be concluded that increased CO2 production at high temperature results from a combination of increased ATP consumption for the maintenance of ion gradients and a decrease in coupling of the mitochondrial electron transport chain through a common mechanism of increased membrane fluidity and ion leak.
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Shen, Bo. "The role of sugar polyols in environmental stress protection." Diss., The University of Arizona, 1997. http://hdl.handle.net/10150/289133.
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Although the protective effects of polyols against environmental stress have been demonstrated, mechanisms through which protection is accomplished are unknown. In this dissertation, the potential functions of sugar polyols in osmotic stress protection have been investigated. The function of mannitol as a hydroxyl radical scavenger in plant cells has been tested by using a transgenic plant approach. The presence of mannitol in transgenic plant cells enhanced the hydroxyl radical scavenging capacity and protected phosphoribulokinase from oxidative inactivation. Transgenic plants showed increased resistance to methylviologen (MV)-induced oxidative stress, as documented by increased retention of chlorophyll in transgenic leaf tissue following MV treatment. In addition, mesophyll cells from transgenic plants exhibited higher CO₂ fixation than wild type. It was concluded that mannitol localized in chloroplasts can supplement endogenous radical scavenging mechanisms and reduce oxidative damage of cells by hydroxyl radicals. The role of polyols in osmotic adjustment was evaluated in yeast. A bacterial mannitol-1-phosphate dehydrogenase gene and an apple sorbitol-6-phosphate dehydrogenase gene were introduced into a glycerol-deficient yeast mutant. The presence of sorbitol and mannitol in transformants provided remarkable protection against salt stress. However, this protection was much less than the protection provided by the same concentration of glycerol in the transformants of glycerol-3-P dehydrogenase gene (GPD1). The reduced protection by mannitol and sorbitol suggested that osmotic adjustment by glycerol was either not sufficient for acquisition of salt tolerance or that glycerol had specific functions for which mannitol and sorbitol could not substitute. To understand the role of glycerol in salt tolerance, salt-tolerant suppressor mutants were isolated from the glycerol-deficient mutants. One such suppressor mutant, sr13, partially suppressed the salt-sensitive phenotype of the glycerol-deficient mutant, most likely, due to the double amount of K⁺ accumulated under salt stress. The accumulation of K⁺ and extrusion of Na⁺ in sr13 were not inhibited by a calcineurin inhibitor (FK506), suggesting SR13 may function downstream of the calcineurin signaling pathway or in a separate pathway that regulated ion homeostasis under salt stress.
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Santarelli, Luca. "Organic semiconductor-based devices electrical reliability to environmental stress." Thesis, University College London (University of London), 2018. http://discovery.ucl.ac.uk/10043464/.
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In this thesis, I report on the characterisation of the response of organic semiconductor based devices, namely organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs) and organic photovoltaic diodes (OPVDs) to environmental stress factors such as electrostatic discharge (ESD) and neutrons irradiation. The ESD stress was obtained by means of a transmission line-pulsing (TLP), responsible to generate current pulses with an increasing amplitude and a duration of few tens of nanoseconds. The exposure to neutron irradiation was obtained in the pulsed neutron and muon source at ISIS part of the Rutherford Appleton Laboratories (RAL). The tested devices were: P3HT (poly(3-hexylthiophene)):PCBM ([6,6]- phenyl C61 butyric acid methyl ester) bulk heterojunction solar cells; PBTTT (poly(2,5-bis(3-hexadecylthiophen-2-yl)thieno[3,2- b]thiophene) and P3HT OFETs; F8BT (poly(9,9'-dioctylfluorene-alt-benzothiadiazole)) OLEDs. An analysis of both electrical (IV and JV curves, Electroluminescence (EL)) and optical (photoluminescence (PL), Raman Spectroscopy) characteristics of tested devices prior and following the exposure to various degrees of ESD, neutron irradiation or both is reported. For each tested device I obtained the respective TLP parameters (the leakage current (ILEAK), the TLP current (ITLP), the TLP voltage (VTLP), the TLP resistance (RTLP)) and the correlation of these with parameters extracted by means of their electrical/optical characterisation, namely: (i) the charge mobility, the threshold voltage (VTH) and the on/off ratio of OFETs; (ii) the current density (Jsc), the open-circuit voltage (Voc), the fill factor (FF) and the power conversion efficiency (η) of OPVs; (iii) the turn-on voltage (Von), the external quantum efficiency (EQE) and the EL maximum wavelength emission (λmax) of OLEDs. Importantly, the activity carried out in this thesis gives novel insights about the response of conjugated polymer-based devices with respect to the stressing stimuli (ESD events, cosmic rays) they are exposed to in their most suitable application fields (space, medicine, robotics), such as the energy necessary to cause a total or partial failure during ESD events, the requirements necessary to design electrical protections, the expected loss of device figures after a decade of exposure to cosmic rays. Interestingly, the results in this thesis reported point out, in most of the cases, an excellent robustness of these devices to both ESD and cosmic rays stress. In fact, whilst technology silicon-based is found to suffer a permanent failure in most of the cases for an applied TLP power lower than 400 W, polymer-based technology was found to withstand up to 800 W (OPVs and OLEDs) without suffering permanent damages. As regards the stress correlated to the same dose of neutrons irradiation, optoelectronic devices based on inorganic semiconductors suffer of a 90% reduction of their figures of merit (JSC, h), whilst the same figures are reduced of only 20% in polymer-based devices. Although previous works are reported in literature, the work reported in this thesis, at the best of my knowledge, is the first work reporting a systematic quantitative TLP characterisation of organic devices along with a qualitative description of the effects on the organic materials within these devices because of the conditions imposed by the TLP test (high-frequency, high-voltage). Therefore, this thesis opens a new scenario proposing an investigating tool aimed both at measuring parameters useful for the design of the devices and at highlighting organic materials properties that can lead organic electronics to gain its definitive momentum.
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Sequera, Mutiozabal Miren Iranzu. "Polyamine signaling pathway during environmental stress: Metabolomic approaches to elucidate spermine down-stream targets." Doctoral thesis, Universitat de Barcelona, 2015. http://hdl.handle.net/10803/315648.
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Environmental stress is increasingly wearing down crop productivity. Nowadays, one of the main aims of plant research is to elucidate tolerance mechanisms to diverse stresses, in order to provide solutions by generating stress-tolerant plants. In regard with this matter, polyamine signaling pathway is of crucial importance. The major polyamines in plants (putrescine, spermidine and spermine) tend to accumulate in response to stress and are associated with a protective role. The trend of their accumulation is related to the stress the plant is sensing; in fact, polyamine biosynthetic pathway is activated at different levels depending on the stimulus, which gives a selective role to these molecules. Spermine, one of the higher polyamines, is not essential for plant growth; however, it is presently known that this molecule plays diverse protective roles under several stress factors and triggers signaling cascades implicated in plant defense. Therefore, research on spermine down-stream targets has become necessary towards the elucidation of plant tolerance responses. By the use of model plant Arabidopsis thaliana this study demonstrated the implication of this polycation on enhancement of anti-oxidative capacity by signaling connections to central hub metabolites for sugar, lipid and amino acid metabolism such as pyruvate or myo-Inositol, as well as its involvement on root morphology.El estrés medioambiental está afectando de forma paulatina la productividad de los cultivos. En la búsqueda de soluciones, uno de los principales objetivos de la investigación en fisiología de plantas, es dilucidar los mecanismos de tolerancia que se presentan ante diversos estreses, con la finalidad de generar plantas con fenotipos resistentes. En referencia a este asunto, las poliaminas y sus rutas señalizadoras son de importancia crucial. Las más abundantes en plantas (putrescina, espermidina y espermina) tienden a acumularse en respuesta al estrés por lo cual se les asocia a un rol protector, sin embargo, las tendencias de acumulación dependen del tipo de estrés que la planta es capaz de percibir. De hecho, su ruta biosintética se activa a diferentes niveles dependiendo del estímulo, lo cual les confiere un carácter selectivo. La Espermina (una de las poliaminas superiores) no es esencial para el crecimiento de la planta, no obstante, actualmente se sabe que esta molécula ejerce diversos roles protectores en una gran variedad de condiciones y además activa cascadas señalizadoras implicadas en la respuesta defensiva de la planta. En consecuencia, para dilucidar los mecanismos de tolerancia, se ha hecho necesario profundizar en las dianas de señalización por parte de la espermina. Empleando como modelo experimental Arabidopsis thaliana, el presente estudio ha demostrado la implicación de este policatión en el aumento de la capacidad anti-oxidativa a través de conexiones con metabolitos centrales en el metabolismo de azucares, lípidos y aminoácidos como es el caso del piruvato y el mio-Inositol, así como también, la implicación de esta poliamina en la morfología y ramificación de las raíces, reforzando la noción de implicación esencial por parte de esta poliamina, en la fisiología del estrés en plantas.
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Palaniappan, Prema. "In-process stress analysis of flip chip assemblies during underfill cure and environmental stress testing." Thesis, Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/19138.
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Bishop, G. P., and Phillip R. Scheuerman. "Physiological Changes in Bacteria During Starvation Stress." Digital Commons @ East Tennessee State University, 1991. https://dc.etsu.edu/etsu-works/2890.
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Seward, Lori Welte. "A multiple stress, multiple component stress screening cost model." Thesis, Virginia Tech, 1985. http://hdl.handle.net/10919/41578.
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Environmental stress screening is used to enhance reliability by decreasing the number of failures experienced during customer use. It is suggested that added benefit can be gained by applying multiple stresses rather than a single stress, as is done presently. A further modification is to apply the stress at the assembly level, accelerating different types of components at the same time. Different component E A e acceleration effects must then be considered.
The problem these modifications present is how to choose the appropriate stress levels and the time duration of the stress screen. A cost model is developed that trades off the cost of a field failure with the cost of applying a multiple stress, multiple component stress screen. The objective is to minimize this cost function in order to find an economical stress regimen.
The problem is solved using the software package GINO. The interesting result is that if a stress is used at all during the stress screen, the maximum amount of stress is the economic choice. Either the cost of stressing is low enough to justify the use of a stress, in which case the maximum amount of stress is used, or the cost is too high and the stress is not used at all.
Master of Science
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Dahl, Joakim. "Detection of human-induced stress in streams : comparison of bioassessment approaches using macroinvertebrates /." Uppsala : Dept. of Environmental Assessment, Swedish Univ. of Agricultural Sciences, 2004. http://epsilon.slu.se/s332.pdf.
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Andersen, Bistra. "Investigations on environmental stress cracking resistance of LDPE/EVA blends." [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=972520481.
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Alvarsson, Jesper J. "Stress recovery during exposure to natural sounds and environmental noise." Thesis, Stockholm University, Department of Psychology, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-27894.
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Research suggests that physiological stress reactions may be reduced by visual impressions from natural environments as compared to urban or built-up environments. The present experiment tested whether similar effects might be found by auditory stimulation. Forty university students were tested in an experiment with four consecutive recovery sessions after stressful mental arithmetic tests. The independent variables were type of sound during recovery. The sound was either a natural sound environment (sounds from water and birdsong, at 50 dBA), or three types of noisy environments (traffic noises at 50 or 80 dBA or ambient background sound at 40 dBA). The main dependent variables were physiological recovery from stress, as measured by decrease in heart rate (HR) and skin conductance level (SCL) after the stressful arithmetic test. The main result was that SCL reduction was faster during nature sounds than during the various noises. For HR, no systematic effects of experimental sounds were found. The result for SCL lends some support the hypothesis that exposure to natural sounds facilitate physiological stress recovery.
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Gardeström, Johanna. "Coping with environmental stress : from the individual and population perspective." Doctoral thesis, Stockholm University, Department of Systems Ecology, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-7311.
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Natural stress and disturbances are important factors affecting the structure and function of ecosystems. However the magnitude of stress has escalated due to anthropogenic activities. Environmental monitoring and toxicity assessments try to protect ecosystems from unwanted human alterations. The aim of this Doctoral thesis was to increase the understanding of the complex effects that environmental stress has on individuals and invertebrate populations. The low saline environment in the Baltic Sea is perceived as stressful for most organisms living there. In Paper I, it was found that Baltic blue mussels living in the less saline northern Baltic Proper (~5 psu) had lower basal metabolism and were more susceptible to toxic exposure than the mussels in the south (~7 psu). There was no genetic differentiation between the mussels from the northern and southern areas while there were genetic differences between mussels from sites within the respective areas (Paper III), indicating that there is not a simple relationship between the health of the mussels and genetic diversity in the microsatellite loci studied. In Paper IV it was found that the heat tolerance of the intertidal dogwhelk Nucella lapillus is oxygen dependent. Increased oxygen levels resulted in higher survival rate. Protein expression profiles also became more similar to those of the controls, compared to the whelks exposed to high temperature and normal oxygen levels. In Paper V and VI it was found that exposure to a single toxicant for more than one generation decreased the genetic diversity in exposed copepod populations even though abundances remained unaltered. In Paper VI, exposure to naturally contaminated sediments, which contained of a mixture of toxicants, did not decrease genetic diversity. However the genetic divergence (FST) within the treatments was very high, probably due to small effective population sizes in the replicates. Likewise in Paper III, the very low blue mussel abundance in the north together with the stressful environment suggests a small effective population in the northern Baltic Proper. In conclusion, my studies show that, measuring effects on several levels, including both functional and structural endpoints will both increase the sensitivity of the tests and increase their ecological relevance.
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Morin, Felix. "Development and Environmental Application of Microbial Bioreporters of Oxidative Stress." Thesis, Université d'Ottawa / University of Ottawa, 2015. http://hdl.handle.net/10393/33027.
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There is a need for a sensitive, specific, rapid and cost-effective assay that can be used as an early warning signal of contamination of aquatic ecosystems. The purpose of this work was to develop a sensitive stress-specific microbial bioreporter responsive to pro-oxidants. Furthermore, the bioreporter was designed to be applicable in environments possibly affected by metal processing activities.
An E.coli bioreporter was developed containing a plasmid with the katG promoter sequence as the sensing sequence and with mCherry as the reporter protein. The bioreporter responded to metal pro-oxidants (Cd, As, Zn, Pb, Ag and Ag nanoparticles). A new assay growth-medium was developed and contributed to improve the sensitivity of our assay that has the best detection limit to inorganic pro-oxidants compared to other oxidative-stress sensitive bioreporters in the literature. The bioreporter detected pro-oxidants in environmental samples. The assay has a reasonable sensitivity, however, it still lacks sensitivity to detect pro-oxidants at concentrations lower than those shown to be toxic to many aquatic species. Within-lab reproducibility and robustness were determined to be acceptable.
For stress-specific bioreporters to be incorporated in regulative legislations and industrial monitoring programs there is a need to improve the sensitivity of these assays, they need to be calibrated with other relevant pro-oxidants, inter-lab reproducibility needs to be established and robustness to environmental samples needs to be further tested. To further validate the sensitivity and ecotoxicological relevance of the bioreporter as a relevant predictive tool, stress-specific bioreporter assays need to be performed in parallel with traditional ecotoxicological assays using contaminated environmental samples.
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Gardeström, Johanna. "Coping with environmental stress : from the individual and population perspective /." Stockholm : Department of Systems Ecology, Stockholm University, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-7311.
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Francis, Darlene Deborah. "Early environmental regulation of adult stress responses and maternal care." Thesis, McGill University, 2000. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=36805.
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Variations in maternal care permanently alter the expression of behavioral and endocrine responses to stress. Thus, in the rat, increased levels of maternal licking and grooming over the first week of life are associated with decreased hypothalamic-pituitary-adrenal and behavioural responses to stress in the offspring in adulthood. Interestingly, such variations in maternal care are associated with individual differences in the neurochemistry and fearfulness of the dams themselves. Adult female rats which are more fearful exhibit less licking and grooming of their pups than do less fearful mothers. These more fearful females also possess greater levels of corticotropin-releasing hormone (CRH) receptors in the amygdala and the locus coeruleus. Oxytocin receptor expression is also different in these animals. The females which exhibit greater levels of licking and grooming of their pups have more oxytocin receptors in the medial preoptic area (MPOA) as well as the bed nucleus of the stria terminalis (BNST). The differences in maternal behavior may constitute a mechanism for the non-genomic, transgenerational transmission of fearfulness from parent to the offspring. The results of these thesis studies support this idea and also demonstrate that environmental events during early development that decrease fearfulness can serve to break the cycle of transmission.
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Schuwerack, Petra-Manuela. "Environmental pollution and disease : multiple stress responses in freshwater hosts." Thesis, Royal Holloway, University of London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.272253.
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Chen, Chien-Cheng. "Regulation of sigma B of Bacillus subtilis by environmental stress." Thesis, University of Oxford, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.403707.
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Li, J. J. "Environmental stress cracking behaviour of cross-linked acrylic based resins." Thesis, Swansea University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637899.
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The environmental stress cracking behaviour of several cross-linked acrylic based resins has been investigated under various testing conditions (bending, creep and constant strain rate tension.). Urethane methacrylate resins were found to undergo crazing in organic liquids only, and the critical strains and critical stresses for craze initiation can be related to the solubility of the liquid environments. PMMA resins with different EGDMA contents (and thus different cross-link densities) underwent crazing in all the environments tested. Small amounts of EGDMA, up to 3% were found to have little effect on critical strains, although in general, materials with higher cross-link densities had higher resistance to crazing. This capability tended to be reduced in aggressive agents. Environmental diffusion was found to play a very important role in determining the ESC behaviour of these resins. There was always competition between diffusion enhanced crack initiation and growth, and diffusion promoted crack blunting. Under most testing conditions, conventional ESC was the main failure mechanism for these materials since such an attack could come into effect over a wide range of liquid uptakes. However, strong environmental diffusion was also found to lead to crack blunting by the mechanisms of surface softening and compression. This occurred when a plasticised layer developed either on the specimen surface before crack nucleation, or ahead of the crack tip. The effects of cross-linking the chains were to restrict environmental liquid diffusion, to suppress craze initiation and to increase crack growth rate, although these effects were only significant at high levels of cross-linking A combination of these effects determined the overall ESC behaviour of cross-linked polymers Amongst them, restriction to environmental diffusion by cross-linking, appeared to be the most important factors.
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Thomas, N. "Effects of environmental stress on some functions of marine molluscs." Thesis, Swansea University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.639186.
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The relationship between environmental factors and the general 'health' of several common marine molluscs was investigated at stations along the coast of south-west Wales and in the laboratory, utilising locally collected molluscs whose 'health' was rated by numerical scales covering condition factor, dry tissue weight, total lipid content etc. In addition, an attempt was made to relate degree of motility with environmental stress amongst motile gastropods. Lamellibranch molluscs were monitored in situ over an extended period, revealing variations in condition criteria in connection with location, vertical position, age, season and the presence or intensity of pollution. Alcohols of varying isomeric forms were presented as pollutants to specimens of the gastropod L. littorea; the toxic influences were, in some cases, found to be reversible and the toxicity order was found to be similar to that reported in higher mammals. A degree of tolerance was evident towards crude oil; the influence of the substratum was found to be relevant. Molluscs were monitored under laboratory conditions with varying feeding regimes, to investigate the influence on total lipid level etc. Some food-stuffs were found to be more acceptable than others, but little direct fatty-acid incorporation was evident. Elevated temperatures were found to have a profound influence on fatty acid metabolism. L. littorea specimens were observed under field and laboratory conditions, a natural tidal-related behaviour being evident. This rhythmic behaviour proved resilient to environmental pollutants but tended to fade after prolonged constant conditions. Spontaneous re-emergence of the rhythm was detected, but attempts by artificial means to produce the same result met with only partial success. Under field conditions behaviour was found to be influenced by season and vertical position. Various species of gastropod revealed differing behaviour patterns. One aspect of man's role in the degradation of the marine environment was thus determined.
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Mutwakil, Mohammed Zainy. "The nematode Caenorhabditis elegans as a bioindicator of environmental stress." Thesis, University of Nottingham, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285556.
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Za'aba, Nor. "Electrical, environmental and optical stress effects on PS-DNTT OTFTs." Thesis, Bangor University, 2018. https://research.bangor.ac.uk/portal/en/theses/electrical-environmental-and-optical-stress-effects-on-psdntt-otfts(d44daf1d-ab86-4c14-92ae-c0f21ba8f0de).html.
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Exposure to moisture and elevated temperatures in organic thin film transistor (OTFT) usually results in significant degradation in the electrical performance. In this thesis the effects of temperature, T, and relative humidity, RH, on PS-DNTT OTFTs are investigated. Device characteristics were measured after 30-min exposure to RH that was gradually increased from 20% to 80% with T fixed at 20 oC and also for T increasing from 20 oC to 90 oC with RH held at 10%. The turn-on and threshold voltages show a negative shift with minimal change in mobility upon exposure to higher RH and T. A very minimal change was observed in the deeper states in the density of states (DoS) that was extracted from transfer characteristics in the linear regime using the Grünewald approach. These results suggest that OTFT instability is due to the flatband voltage shift caused by hole trapping/detrapping in the polystyrene gate dielectric or at the polystyrene/DNTT interface. Understanding the origin of electrical instability in OTFTs over long periods of time is also essential to realize high performance circuits. In this thesis, the effects of bias stress on PS-DNTT OTFTs is investigated over a range of temperature and relative humidity. It was found that the threshold voltage, VT, always shifted in the direction of the applied gate voltage. It was also observed that the threshold voltage shift, ΔVT, reduced as the drain voltage increased. The time-dependences of ΔVT in both linear and saturation regimes are well described by the stretched exponential function. Contrary to most previous reports, the threshold voltage at long times, VT(∞), asymptotes to a value well below the applied gate voltage. The VT change is minimal with increasing humidity under saturation bias and temperature. In all cases, the DoS exhibits similar behavior with weak features appearing at the deeper states. This is unlikely to be related to DNTT as there is no change in the gate-voltage dependence of mobility, but rather due to a changing flat-band voltage when electron/hole occupancy of interface states changes as the device turns on. Effect of illumination on the electrical performance as well the underlying physics of these effects are important for the development of several applications such as the backplane for display technology and photosensors. In this thesis the effect of illumination on PS-DNTT OTFTs has been investigated with light of different wavelengths and intensities. The greatest effect was observed at 460 nm with significant changes occuring in the subthreshold slope. Interestingly the profile of the deeper states in the DoS spectrum did apparently change. It was also found that changes in threshold voltage, turn-on voltage, subthreshold slope and responsivity all appear to saturate at higher light intensity due to a trap limited effect. Since there is no significant change observed in mobility, the DoS changes can be explained by (i) trapping of photogenerated electrons, (ii) an unstable shift in the light-induced flat-band ΔVFB, caused by detrapping or neutralization of electrons as the transistor is turned on so that ΔVT(∞) < ΔVON(∞), (iii) accumulation of electrons in DNTT near to source contact or (iv) the effect of the electron quasi Fermi level, QFL. The effect of bias stress and illumination on PS-DNTT has also been investigated with different wavelengths, time and intensity. It was observed that the transfer characteristic shows a parallel shift toward more positive voltages under positive bias stress (PBS) regardless of the wavelength. However under negative bias stress (NBS) at λ ≥ 520 mm, the transfer characteristic shifts negatively due to the dominant effect of hole trapping at the PS-DNTT interface.
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Elnitsky, Michael A. "Tolerance and Physiological Response to Environmental Stress in Antarctic Arthropods." Miami University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=miami1216152581.
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Lopez-Martinez, Giancarlo. "Molecular Responses to Environmental Stress in Temperate and Polar Flies." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1211554713.
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Teets, Nicholas Mario. "Cellular and Molecular Mechanisms of Environmental Stress Tolerance in Insects." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1354542991.
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Mehrani, Hossein Carleton University Dissertation Chemistry. "Regulation of glycogen metabolism by protein phosphorylation during environmental stress." Ottawa, 1994.
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