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Verma, Meera Mary. "On the effect of UV-irradiation on DNA replication in Escherichia coli." Title page, contents and summary only, 1985. http://web4.library.adelaide.edu.au/theses/09PH/09phv522.pdf.
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Manners, Vicki. "Molecular studies on the radiation-resistant bacteria Deinococcus radiodurans and Deinobacter grandis." Thesis, University of Edinburgh, 1989. http://hdl.handle.net/1842/12557.
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Li, Sha. "Potency of nanoparticles to amplify radiation effects revealed in radioresistant bacteria." Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112061/document.
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Les thérapies par irradiation sont utilisées pour traiter la plupart des cas de cancer. Une limitation majeure est l’induction de dommages dans les tissus sains. Par conséquent, l’amélioration du ciblage tumoral est un défi majeur. L'addition de nanoparticules (NPs) est proposée comme une nouvelle stratégie pour amplifier les effets des radiations dans les tumeurs (radiosensibilisation ). Les nanoparticules de Z élevé (platine, or, gadolinium) se révèlent être de bons candidats. Afin de développer de nouveaux nanoagents et d’améliorer les plans de traitement, il est nécessaire de mieux comprendre les mécanismes fondamentaux impliqués. Il a été observé que les radiosensibilisateurs augmentent l'effet létal des radiations (ions rapides ou rayons gamma). Ceci est attribué à une cascade d'événements multi-échelle qui comprend l'activation des NPs, leur relaxation, suivi de la production de radicaux responsables de la mort cellulaire (dans les eucaryotes). Il n'est pas encore clair laquelle des étapes, entre l’excitation/relaxation électronique des NPs ou la réponse biologique joue le rôle prédominant. Par conséquent, le défi de ma thèse était de tester les effets de radiosensibilisateurs (NPs d'or, de platine ou à base de gadolinium) sur des cellules autres que des cellules eucaryotes. Pour la première fois, l’effet des NPs a été testé sur la bactérie la plus radiorésistante jamais rapportée, D. radiodurans. Les NPs ont également été testées sur E. coli. Des études à l'échelle moléculaire ont été utilisées pour comprendre les mécanismes élémentaires. En résumé, ce travail montre que les NPs radiosensibilisantes amplifient les effets des rayons γ dans les bactéries radiosensibles et radiorésistantes. Ceci est attribué à la production de grappes de radicaux et à l’induction de dommages nanométriques dans l'ADN mais également dans les protéines de réparation. Finalement la radiosensibilisation est un phénomène «universel» qui peut être induite dans tout organisme vivant. En d'autres termes, les mécanismes élémentaires liés à l’excitation/relaxation de la NP jouent un rôle majeur par rapport à la réponse biologique de la cellule. Enfin, un ensemble de méthodes ont été optimisées pour évaluer la toxicité et observer l’internalisation des NPs dans les bactériesRadiation therapies are used to treat most of the cancer cases. One major limitation is the damage induced in the healthy tissues and tumor targeting is a major challenge. The addition of nanoparticles (NPs) is proposed as a novel strategy to amplify the radiations effects in the tumors (radiosensitization). The high-Z nanoparticles (platinum, gold, gadolinium) are found to be good candidates. To develop new nanoagents and improve treatment planning, a deeper knowledge of the fundamental mechanisms is required. It was found that radiosensitizers enhance the lethal effect of radiations (fast ions and gamma rays). This is attributed to a multiscale cascade of events, which includes the NPs activation and relaxation, the production of water radicals up to the biological impact in mammalian cells. It is not clear yet what from the early stage processes or from the (eukaryotic) cell response is the key stage of the radiosensitization. Hence, the challenge of my thesis was to probe the effects of radiosensitizers (gold, platinum and gadolinium based nanoparticles) on cells other than eukaryotic cells. For the first time, their effect was tested on the most radioresistant bacterium ever reported Deinoccocus radiodurans (D. radiodurans). For comparison, the nanoparticles were tested on the radiosensitive bacterium E.coli. Additional studies at molecular scale were used to understand the elementary mechanisms. In summary, this work demonstrates that the radiosensitizing nanoparticles amplify the effects of -rays in radiosensitive and also radioresistant bacteria. This is attributed to the production of radical clusters and to the inducetion of nano-size biodamages in DNA but also in repair proteins. Finally, this work proves that the radiosensitization is a “universal” phenomenon that can take place in all living organisms. In other words, it tells that elementary mechanisms play a major role compared to the biological response of the cell. A set of standardized methods for evaluating the cellular uptake and the toxicity of the potential nanodrug was established throughout this study
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Alkan, Ufuk. "The effects of solar radiation, adsorption and sedimentation of the population of enteric bacteria in marine waters." Thesis, University of Newcastle Upon Tyne, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359000.
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PEREIRA, MARCO A. dos S. "Estudo da acao da radiacao gama de sup(60)Co sobre Salmonella poona, Escherichia coli e Alicyclobacillus Acidoterrestris em polpa de manga congelada." reponame:Repositório Institucional do IPEN, 2009. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9425.
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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Kminek, Gerhard. "The effect of ionizing radiation on amino acids and bacterial spores in different geo- and cosmochemical environments /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2003. http://wwwlib.umi.com/cr/ucsd/fullcit?p3090438.
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BLAY, CLAUDIA C. "Analise comparativa da reducao bacteriana com irradiacao do laser Er:YAG ou ponta montada em alta rotacao apos remocao de tecido cariado em dentina: estudo in anima nobile." reponame:Repositório Institucional do IPEN, 2001. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10940.
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Dissertacao (Mestrado Profissionalizante em Lasers em Odontologia)
IPEN/D-MPLO
Intituto de Pesquisas Energeticas e Nucleares, IPEN/CNEN-SP; Faculdade de Odontologia, Universidade de Sao Paulo
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BORRELY, SUELI I. "Reducao da toxidade aguda de efluentes industriais e domesticos tratados por irradiacao com feixe de eletrons, avaliada com as especies Vibrio fischeri, Daphnia similis e Poecilia reticulata." reponame:Repositório Institucional do IPEN, 2001. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10943.
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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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BOIANI, NATHALIA F. "Remoção da toxicidade do fármaco propranolol e de sua mistura com cloridrato de fluoxetina em solução aquosa empregando irradiação com feixe de elétrons." reponame:Repositório Institucional do IPEN, 2016. http://repositorio.ipen.br:8080/xmlui/handle/123456789/27140.
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A saúde do meio ambiente vem sendo comprometida devido ao descarte incorreto de produtos e seus subprodutos. Dentre os contaminantes emergentes encontram-se os fármacos, causadores de problemas ambientais por serem descartados no meio ambiente através dos efluentes. As técnicas convencionais de tratamento são insuficientes na remoção de diversos fármacos, por apresentarem resíduos resistentes e baixa biodegradabilidade. Sendo assim os processos oxidativos avançados vêm sendo estudados como alternativa para o tratamento de diferentes tipos de efluentes. O objetivo desse trabalho foi aplicar o processo de irradiação com feixe de elétrons para reduzir os efeitos tóxicos do propranolol, e de sua mistura com cloridrato de fluoxetina, em solução aquosa. Foram realizados ensaios ecotoxicológicos com o fármaco propranolol, e de sua mistura com o cloridrato de fluoxetina, utilizando como organismos-teste o microcrustáceo Daphnia similis, e a bactéria Vibrio fischeri. Observamos que o organismo D. similis mostrou-se mais sensível as amostras de fármacos quando comparado à bactéria V.fischeri. Após serem submetidas ao tratamento com radiação ionizante, todas as doses aplicadas para o propranolol e a mistura, mostraram significativa redução de toxicidade, tendo como organismo-teste D. similis. Para a bactéria V. fischeri apenas na dose de 5,0 kGy foi verificada a redução da toxicidade para o fármaco propranolol. Quanto à mistura dos fármacos, apenas as doses de 2,5 e 5,0 kGy apresentaram eficiência de remoção da toxicidade. A dose 5,0 kGy mostrou-se a melhor, apresentando redução de 79,94% para D. similis, e 15,64% para V. fischeri, quando expostas ao fármaco propranolol. Quanto à mistura, apresentou 81,59% e 26,93%, para D.similis e V.fischeri, respectivamente.
Dissertação (Mestrado em Tecnologia Nuclear)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Almeida, Ana Rita Marques. "Combined effects of ultraviolet radiation and xenobiotics on zebrafish." Master's thesis, Universidade de Aveiro, 2013. http://hdl.handle.net/10773/12624.
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Mestrado em Biologia Aplicada - Microbiologia Clínica e AmbientalNowadays, climate changes are an imperative problem and multiple measurements made in the last years showed an increase of all wavelengths of solar radiance, specially the Ultraviolet radiation. In their natural environment organisms are not only affected by biotic and environmental factors, but also by abiotic factors such as xenobiotics. Besides, these both stressors can interact with each other being their combined effect unpredictable (producing additive, synergistic or antagonistic effect). This work aims to studying the combined effect of UV radiation and three xenobiotics: triclosan, potassium dichromate and prochloraz on zebrafish embryos (Danio rerio). Effects were assessed at two levels: i) effects on embryos mortality and ii) effects in the natural bacterial communities of zebrafish embryos. The organisms were exposed to concentrations of each chemical combined with several UV doses. Embryo’ mortality, were observed daily for 96 hours post fertilization (hpf) and natural bacterial communities’ evaluation was performed at 48 hpf. Results showed that different combined effect may occur compromising organism’s survival. Combined exposure of UV radiation with TCS revealed a synergism pattern when the UV radiation is the dominant stressor while PD and PCZ revealed antagonism at low dose levels or when the UV radiation is dominant in the mixture. Zebrafish natural bacterial communities were also affected by UV radiation and chemicals with the change of their structure; however, conclusions about interactive effects were difficult to be drawn because effects were not always translated into changes in the diversity indexes.
Hoje em dia, as alterações climáticas são um problema imperativo e múltiplas medições feitas nos últimos anos mostram um aumento de toda a radiação solar, especialmente a radiação Ultravioleta que chega á superfície da terra afetando todos os organismos expostos. No seu ambiente natural, os organismos não estão apenas sujeitos a fatores bióticos, mas também a fatores ambientais e abióticos como por exemplo os xenobióticos. Além disso, ambos os stressores podem interagir uns com os outros produzindo efeitos imprevisíveis nos organismos (efeitos sinergísticos ou antagonísticos). O presente trabalho tem como objetivo a avaliação dos efeitos combinados da radiação UV e três xenobioticos (triclosan, dicromato de potássio e procloraz) em embriões de peixe zebra (Danio rerio). A avaliação foi feita a dois níveis: i) efeitos na mortalidade de embriões e ii) efeitos a nível das comunidades bacterianas naturais dos embriões. Os organismos foram expostos a várias concentrações de cada químico, combinadas com várias doses de UV. A mortalidade foi registada diariamente durante 96 horas e as comunidades bacterianas naturais foram avaliadas às 48 horas pós fertilização (hpf). Os resultados mostram que diferentes efeitos combinados foram observados, alterando a ecotoxicidade esperada. A exposição combinada da radiação UV com o TCS revelou um patrão sinergístico quando a radiação UV é o stressor dominante, enquanto que, na combinação UV com PD e PCZ observou-se antagonismo a doses baixas ou quando a radiação UV era dominante na mistura. As comunidades bacterianas naturais do peixe zebra também foram afetadas pela radiação UV e químicos, com alterações na sua estrutura. No entanto, foi difícil tirar conclusões relativamente a possíveis interações entre stressors visto que os efeitos observados nem sempre se traduziam em variações no índice de diversidade.
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Jensen, Brandi Jean. "The role of infrared radiation in the evolution and ecology of anaerobic photosynthetic bacteria." Laramie, Wyo. : University of Wyoming, 2008. http://proquest.umi.com/pqdweb?did=1594477811&sid=1&Fmt=2&clientId=18949&RQT=309&VName=PQD.
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Meneghel, Julie. "Study of the cryopreservation-related stresses in the lactic acid bacterium Lactobacillus delbrueckii subsp. bulgaricus through a global and multi-scale approach." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLA030.
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La cryopréservation engendre des dégradations variables de l’activité biologique et des fonctionnalités des bactéries lactiques, notamment chez Lactobacillus delbrueckii subsp. bulgaricus, un starter de l’industrie laitière. Le but de ce travail a été d’identifier les marqueurs cellulaires de cryorésitance et de cryosensibilité afin de mieux comprendre les mécanismes de dégradation sous-jacents et d’améliorer les performances industrielles des bactéries lactiques. La cryopresérvation a ici été considérée comme une combination de deux stress majoritaires : froid et osmotique. Une attention particulière a été portée à l’analyse de la membrane cellulaire, un site majeur de dégradation lié à la congélation, mais également à la paroi cellulaire et aux protéines. De plus, les cellules ont été analysées à différentes échelles d’observation, de la population jusqu’à la cellule unique, afin de quantifier l’hétérogénéité des propriétés cellulaires existant au sein de populations. Dans une première partie de ce travail, des conditions de culture ont été comparées pour identifier deux souches de L. bulgaricus présentant des résistances contrastées vis-à-vis de la congélation. Une analyse génomique comparative des souches a également été menée dans le but de fournir des pistes de compréhension de ces comportements différents. Dans une seconde partie, des propriétés membranaires des cellules ont été évaluées en réponse aux stress froid et osmotique : composition en acides gras, organisation au niveau des chaînes d’acides gras et des têtes phospholipidiques, et fluidité.Leur fluidité membranaire a également été caractérisée à une échelle subcellulaire par microscopie de fluorescence au moyen du rayonnement synchrotron, permettant la quantification des hétérogénéités inter- et intra-cellulaires. Enfin, un développement technique et méthodologique a été entrepris afin de permettre l’analyse de bactéries individuelles en milieu aqueux par spectroscopie infrarouge à transformée de Fourier, et ainsi leur signature biochimique en conditions natives. Ces approches complémentaires et multidisciplinaires ont révélé l’existence de propriétés et d’organisation différentes de la membrane des deux souches de L. bulgaricus. Différents types d’interaction entre les molécules cryoprotectrices du milieu extracellulaire et la membrane des deux souches a été proposé, pouvant être à l’origine des dommages causés à la souche sensible. De plus, une hétérogénéité plus importante au sein de la population sensible a été identifiée, attribuée à des différences en termes de composition biochimique et d’organisation au niveau de la membrane et de la paroi. Finalement, ce travail suggère quelques marqueurs cellulaires d’évaluation de la cryorésistance des bactéries lactiques, et fournit des méthodes de caractérisation de l’hétérogénéité biochimique au sein des populations. Ceux-ci pourraient être appliqués à l’étude de toute autre étape critique du procédé de production des bactéries lactiques, et pourraient être utiles pour aller vers la production de ferments homogènes au niveau de leur résistanceCryopreservation leads to variable degradation of the biological activity and functionality among lactic acid bacteria (LAB), particularly Lactobacillus delbrueckii subsp. bulgaricus, a dairy starter of industrial relevance. The aim of this work was to identify cellular markers of cryoresistance or cryosensitivity for better understanding the mechanisms of cell cryoinjury and increasing LAB industrial performances. Cryopreservation was here considered as a combination of cold and osmotic stresses. A particular focus was given to the analysis of the cell membrane, recognised as a primary site of cryoinjury, but also of the cell wall and proteins. Moreover, cells were analysed from the population level down to the single-cell level to quantify the heterogeneity of cell properties within populations. In the first part of this work, bacterial cultivation conditions were compared to identify two L. bulgaricus strains with markedly different cell cryoresistance. Moreover, a comparative genomic analysis of the strains was performed to provide some clues for the explanation of their different behaviours. In the second part of this work, the membrane properties were evaluated in response to the cold and osmotic stresses: fatty acid composition, organisation of fatty acyl and phospholipid headgroups, and fluidity.Subcellular membrane fluidity was also characterised by fluorescence microscopy using synchrotron radiation, enabling the quantification of inter- and intra-cellular heterogeneities. Finally, original methodological and technical developments were undertaken to achieve the analysis of individual bacterial cells in an aqueous environment by Fourier transform infrared (FTIR) spectroscopy, for the analysis of the biochemical signature of cells under native conditions. These complementary multidisciplinary approaches revealed different properties and organisation of the membrane of both L. bulgaricus strains. It was proposed that different types of interaction between cryoprotectants of the extracellular matrix and the membrane of both strains could be at the origin of cryoinjury for the sensitive strain. Moreover, a high population heterogeneity characterised the cryosensitive strain, ascribed to differences in terms of biochemical composition and organisation of the membrane and cell wall. Altogether, this work suggests some cellular markers to evaluate LAB cryoresistance and provides methods to characterize population biochemical heterogeneity. These could be applied to any other stressful step of their production process, and should be useful for future production of homogeneous populations of resistant LAB
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Dijkstra, Camelia Elena. "Effect of diamagneic levitation on bacteria." Thesis, University of Nottingham, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.479268.
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Wahle, Peter Joseph 1961. "Radiation effects on power MOSFETs under simulated space radiation conditions." Thesis, The University of Arizona, 1989. http://hdl.handle.net/10150/277024.
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Application of power MOSFETs in spaceborne power converters was simulated by exposing devices to low-dose-rate ionizing radiation. Both radiation-hardened and nonhardened devices were tested with constant and switched gate biases during irradiation. In addition, some of the devices were under load. The threshold-voltage shifts were strongly bias dependent. The threshold-voltage shift of the nonhardened parts was approximately dose-rate independent, while the hardened parts exhibited significant dose-rate dependence. A pre-anneal dose-rate dependence was found for the interface-state buildup of the switched and positively biased devices, but the results for the switched devices were qualitatively different than those for the positively biased devices. The buildup of interface trapped charge was found to be the primary contributor to mobility degradation, which results in reduced drive capability and slower operation of the devices. These results indicate that new methods need to be utilized to accurately predict the performance of power MOSFETs in space environments.
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Martinez, Laura-Maria Madeleine. "Effect of solar radiation on cetaceans." Thesis, Queen Mary, University of London, 2011. http://qmro.qmul.ac.uk/xmlui/handle/123456789/2420.
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Despite the marked deceleration in the amount of ozone lost at the poles each year, high levels of solar ultraviolet radiation (UVR) continue to reach our biosphere, potentially threatening living organisms, which owing to their life-histories and physiological constraints, are unable to avoid exposure to UVR. I aimed to demonstrate that cetaceans are affected by UVR and that they have adaptive mechanisms against exposure. Using histological analyses of skin biopsies and high-quality photographs, I characterized and quantified UVR-induced lesions in 184 blue, fin and sperm whales sampled in the Gulf of California, Mexico, and estimated indices of skin pigmentation for each individual. To examine the molecular pathways by which whales counteract UVR-induced damage, levels of expression of genes involved in genotoxic stress pathways (heat shock protein 70: HSP70, tumour protein 53: P53, and KIN protein genes: KIN) and melanogenesis (tyrosinase gene: TYR) were quantified. I not only detected evidence of sun-induced cellular and molecular damage but also showed that lesions were more prevalent in blue whales, the study species with lightest pigmentation, and sperm whales, the species that spends longest periods at the surface. Furthermore, within species, darker whales exhibited fewer lesions and more apoptotic cells, suggesting that darker pigmentation is advantageous. When accounting for interspecific differences in melanocyte abundance, sperm and blue whales presented similar amounts of melanin, although sperm whales overexpressed HSP70 and KIN. This suggests that sperm whales may have limited melanin production capacity, but have molecular responses to counteract more sustained exposure to UVR. By contrast, increased UVR in the study area led to increases in melanin concentration and melanocyte abundance of blue whales, suggesting tanning capacity in this species. My study provides insights into the mechanisms with which cetaceans respond to UVR and reveals the central role played by pigmentation and DNA-repair mechanisms in cetaceans.
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Slaninová, Eva. "Metabolická a biofyzikální charakterizace bakteriálních buněk schopných akumulace PHA." Doctoral thesis, Vysoké učení technické v Brně. Fakulta chemická, 2021. http://www.nusl.cz/ntk/nusl-438297.
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This thesis deals with the characterization of bacterial cells capable of polyhydroxyalkanoates (PHA) accumulation. The dissertation thesis is written in the form of a discussed published publications which are attached to the thesis as appendixes. The work develops a study of the current topic of the protective functions of PHA and clarifies protective mechanisms against selected stressors. Firstly, we focused on the protective effects of PHA granules against UV radiation and osmotic stress, specifically hypotonic conditions. In the case of UV exposition, the cells protected themselves by scattering UV radiation on the intracellular granules protecting especially nucleoid. When exposed to osmotic stress, the amorphous state of PHA granules is very important since it is capable of stabilization of cell membranes under hypertonic stress, afterwards, bacterial cells can maintain their integrity during the subsequent hypotonic challenge. In general, the amorphous state of PHA granules is key to ensure the proper biological functions of PHA whether as storage or protective polymer. Therefore, in the next part of this work, we focused on the core of the stabilization mechanism that protects native PHA granules from crystallization and thus the intracellular polymer maintains in a thermodynamically unfavorable amorphous phase state. Based on experimental work, we applied selected stresses because we proposed a new model of stabilization of the amorphous state of PHA granules in vivo. It consists of two mechanisms, where small volumes of PHA granules reduce the rates of crystallization and at the same time the water present in the granules plays the role of a low molecular plasticizer. Due to the metabolic apparatus of bacterial cells, PHA are simultaneously synthesized and degraded which leads to an increment of intracellular concentration of monomers that also figure in the protective effect of PHA. In this context, we aimed at the description of the mechanism of cryoprotective effects of 3-hydroxybutyrate, the monomer of the most common of PHA, poly(3-hydroxybutyrate). Hence, we constructed an equilibrium and non-equilibrium phase diagram of the 3HB-water system to prove that 3HB is a very effective cryoprotectant. This fundamental understanding of the protective properties of PHA monomers could be also used in the food industry or cryopreservation of biological samples.
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Arrage, Andrew Anthony. "Characterization of DNA-repair potential in deep subsurface bacteria challenged by UV light, hydrogen peroxide, and gamma radiation." Thesis, This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-08182009-040256/.
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Caló, A. (Antonio). "Electron spectroscopy of atoms and molecules using synchrotron radiation, UV radiation and electron impact." Doctoral thesis, University of Oulu, 2007. http://urn.fi/urn:isbn:9789514286650.
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The present thesis investigates the electronic structure of selected atoms and molecules in vapor phase. Electron spectroscopy is applied for studying the electronic transitions following excitation and ionization with electron and photon bombardment. The work focuses on the photoionization and Auger decay of selected noble gasses, and on the photoionization and Auger decay of core ionized or resonant excited alkali halide molecules. The experimental results are compared with theoretical predictions.
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Johns, Desmond J. "Effect of pH on phytoplankton and bacteria production." College Park, Md.: University of Maryland, 2009. http://hdl.handle.net/1903/9487.
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Thesis (M.S.) -- University of Maryland, College Park, 2009.Thesis research directed by: Marine, Estuarine, Environmental Sciences Graduate Program. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Wadsworth, Jennifer Louise. "Microbial responses to extreme radiation environments." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/31217.
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Microorganisms are known to tolerate a variety of extreme environments, such as high and low pH, desiccation and a wide range of temperatures that would prove uninhabitable for most eukaryotic cells. However, extreme radiation exposure is a ubiquitous hazard to pro- and eukaryotic viability. Ionising and non-ionising radiation, and their associated high energies, cause damage to a cell in the form of DNA double-strand breaks, membrane deterioration, and lethal mutations. Radiation also induces secondary effects such as the production of reactive oxygen species, which attack and degrade organic compounds. It is therefore not surprising that radiation is considered by the scientific community to be one of the main influencing factors when regarding habitability on the early Earth, as well as other planets, such as present-day Mars. This thesis explores the response of select microbes that have been exposed to extreme radiation environments, i.e. both high and ultra-low radiation. Understanding how radiation affects the geochemical environment is key to the assessment of its potential to support life and to harbour molecules associated with life. The effect of radiation-induced photochemistry on the early terrestrial and present-day Martian surface is explored in conjunction with Fenton chemistry. Iron oxides are abundant on both Earth and Mars and act as catalysts in Photo-Fenton reactions, enabling the production of free radicals. The resulting consequences for habitability are shown to be antagonistic, with iron oxide enabling both the protection or destruction of cells, depending on the local geochemistry. In addition, the photo-reactivity of perchlorate is investigated. The UV-induced activation of the strong oxidant, and recently confirmed Martian surface constituent, is demonstrated, revealing its severe bacteriocidal effect on microbes. It is also shown to significantly reduce microbial viability when combined with further Martian soil constituents and components required for Photo-Fenton chemistry. In order to accurately analyse the effects of low earth orbit radiation on prokaryotic life, cyanobacterial samples were attached to the outside of the International Space Station as part of the EXPOSE-R2 mission for 1.5 years. The samples were subjected to various conditions, including exposure to a minimally filtered space radiation environment and simulated Mars conditions. The experiment is designed to test the protection that biogenic and non-biogenic substances may provide to cells. The results in this work present the post-flight analysis of the samples and demonstrate the ability of these substances to maintain cyanobacteria viability. They also show that the cyanobacterial cells themselves can effectively act as a shield for a secondary, co-cultured bacteria species. On the other end of the radiation dose scale, this work addresses the gaps in knowledge with regard to the little-understood effects of low, sub-background radiation on prokaryotes. Using the Boulby Underground Lab in the functioning Boulby Mine, Cleveland UK, microbes are cultivated under regulated, extremely low radiation environments to test multiple dose-response models. The results show no change in cell's growth rates or gradients in low radiation exposure when compared to surface-dose controls. They also fail to exhibit any enhanced susceptibility to stress factors, such as UV irradiation, as suggested by previous work in the field. These experiments mark the first extensive and tightly controlled research into microbial responses in the near-absence of radiation. This work illustrates the importance of understanding both primary and secondary effects of radiation on microbes and begins to bridge the knowledge gap from both ends of the dose axis. These approaches show the far-reaching influence radiation has on astrobiologically relevant topics, such as habitat geochemistry and life detection, and demonstrate the capacity of life to survive in extreme radiation environments.
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Vorster, Werner. "The effect of microwave radiation on mineral processing." Thesis, University of Birmingham, 2001. http://etheses.bham.ac.uk//id/eprint/309/.
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Between 50% and 70% of the total energy used in the extraction process may be attributed to comminution. Microwave pre-treatment has been suggested as a means to decrease the energy requirements. A variety of mineral ores have been investigated and the effects of microwave radiation quantified in terms of the mineralogy, changes in the Bond Work Index, flotability and magnetic separation. It has been shown that microwave pre-treatment is most effective for coarse grained ores with consistent mineralogy consisting of good microwave absorbers in a transparent gangue (up to a 90% decrease in Bond work index for Palabora copper ore) whereas fine grained ores consisting predominantly of good absorbers are not affected as well (a reduction of only 25% in work index for Mambula ore). Although the mineralogy of minerals are affected by exposure to microwave radiation, flotability and magnetic separation characteristics have been shown not to be adversely affected, unless the microstructure is completely destroyed after prolonged microwave exposure. Computer simulations have shown that significant changes to comminution circuits are possible as a result of microwave induced work index reductions (three mills reduced to one). Purpose-built microwave units may hold the solution for more efficient mineral extraction in the near future.
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Allred, Clark L. (Clark Lane) 1972. "Effect of radiation on silicon and borosilicate glass." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/29965.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2003.Includes bibliographical references (p. 245-255).
A study was made that is logically divided into two parts, both involving radiation damage effects. The first is a study of the effects of neutron and gamma radiation on the dimensions of two borosilicate glasses, Pyrex® and Hova SD-2®. These two glasses are commonly used as substrates for silicon microelectromechanical (MEMS) devices, and radiation-induced compaction in a substra.te can have deleterious effects on device performance. Results are presented for density changes induced in both glasses by neutron irradiation. Pyrex was shown to compact at a rate of (in [delta]p[rho]/p[rho] per n/cm2Ì) 8.14 x 10-Ì20 (thermal) and 1.79 x 10-Ì20 (fast). The corresponding results for Hoya SD-2 were 2.21 x 10-Ì21 and 1.71 x 10-Ì21, respectively. On a displacement per atom (dpa) basis, the compaction of the Pyrex was an order of magnitude greater than that of the Hoya SD-2. Our results are the first reported measurement of irridiation-induced densification in Hoya SD-2. The compaction of Pyrex agreed with a previous study. Our results for gamma irradiations were unexpected. Silicon MEMS strain gauges mounted on glass wafers were gamma-irradiated to hundreds of Mrad. Based on expectations from the literature, the Pyrex was supposed to compact to a level easily measurable by the MEMS strain gauges. Almost no substrate compaction registered in the strain gauges, however. It is hypothesized that the anodic bonding process (by which a silicon wafer was bonded to the glass before etching to create the MEMS strain gauges) was responsible for either 1) changing the bulk radiation response of the glass or 2) creating a layer near the bond interface which somehow prevented the MEMS strain gauges from registering the compaction that was occurring in the glass substrate. While not yet understood, this null result for apparent substrate compaction is of great importance to the problem of mechanically rad-hard MEMS, since it indicates that the response of an anodically bonded Si-glass system to radiation is not simply the sum of the effects on the unbonded materials. To investigate this further, glass samples were prepared in various stages of the anodic bonding process (which involves heating in the presence of an electric field), then irradiated with neutrons. No difference in bulk compaction was noted among the
(cont.) treated samples or the untreated glass, but this result may have been influenced by the high temperature at which the glass was irradiated; however, temperature alone could not have annealed away all the effects of treatment. We conclude that the unexpected results of the MEMS strain gauge experiment were caused by surface layer phenomena at the bonding interface, though we do not currently understand the exact mechanism for this. The second major topic of this study is the effect of neutron irradiation on the Young's modulus of silicon, the constancy of which is key to the operation of many MEMS devices. The elastic constants of defected and amorphous silicon simulation cells were calculated using EDIP. Simulation cells included some containing randomly generated defect distributions, as well as several that were completely amorphous and one containing a small amorphous region. An extensive and careful characterization of point defects was made ...
by Clark L. Allred.
Ph.D.
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Zemp, Franz Joseph, and University of Lethbridge Faculty of Arts and Science. "The bystander effect : animal and plant models." Thesis, Lethbridge, Alta. : University of Lethbridge, Faculty of Arts and Science, 2008, 2008. http://hdl.handle.net/10133/685.
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Bystander effects are traditionally known as a phenomenon whereby unexposed cells exhibit the molecular symptoms of stress exposure when adjacent or nearby cells are traversed by ionizing radiation. However, the realm of bystander effects can be expanded to include any systemic changes to cellular homeostasis in response to a number of biotic or abiotic stresses, in any molecular system. This thesis encompasses three independent experiments looking at bystander and bystander-like responses in both plant and animal models. In plants, an investigation into the regulation of small RNAs has given us some insights into the regulation of the plant hormone auxin in both stress-treated and systemic (bystander) leaves. Another plant model shows that a bystander-like plant-plant signal can be induced upon ionizing radiation to increase the genome instability of neighbouring unexposed (bystander) plants. In animals, it is shown that the microRNAome is largely affected in the bystander cells in a three-dimensional human tissue model. In silico and bioinfomatic analysis of this data provide us with clues as to the nature of bystander signalling in this human ‘in vivo’ model.xiv, 141 p. : ill. ; 29 cm.
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Hind, John. "The effect of antibiotics on bacteria under hyperbaric conditions." Thesis, Manchester Metropolitan University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.290430.
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Neto, Ricardo Francisco. "High pressure effect on malolactic bacteria growth and metabolism." Master's thesis, Universidade de Aveiro, 2013. http://hdl.handle.net/10773/11603.
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Mestrado em BiotecnologiaO Oenococcus oeni é uma espécie de bactéria de elevado interesse, nomeadamente enológico, porque é capaz de realizar a fermentação maloláctica (desacidificação do vinho) e reúne as condições essenciais para poder sobreviver às condições adversas do vinho. Por outro lado ao alta-pressão é uma tecnologia com grande potencial para explorar novas e promissoras aplicações na biotecnologia. Neste trabalho pretendeu-se avaliar o efeito de um tratamento de alta-pressão no metabolismo desta bactéria, nomeadamente na descarboxilação do ácido L-málico, no metabolismo de açúcares e no crescimento bacteriano. O tratamento de 50 MPa durante 8 h e 100 MPa durante 0.5 h não resultaram em alterações significativas no metabolismo das bactérias. O tratamento de 100 MPa, durante 8 e 60 h resultaram numa redução da quantidade de ácido L-láctico produzido, propondo-se que também foi produzido ácido D-láctico a partir do ácido L-málico. O tratamento de 300 MPa durante 0.5 h resultou na completa inactivação das bactérias. Assim conclui-se que alta-pressão é uma tecnologia que permite a alteração do metabolismo, nomeadamente a modificação da especificidade da enzima maloláctica, e a inactivação de Oenococcus oeni.
The Oenococcus oeni is a bacterial species with high interest, especially winemaking, because it is able to carry out malolactic fermentation (wine desacidification) and has the essentials conditions to be able to survive in the wine harsh conditions. On the other hand the high-pressure is a technology with great potential to explore new and promising applications in biotechnology. In this work the aim was to evaluate the effect of high pressure treatments in the metabolism of the bacteria, especially in the decarboxylation of L-malic acid, in the sugars metabolism and bacterial growth. The treatment of 50 MPa during 8 hours and 100 MPa during 0.5 h did not result in significant alterations in the bacteria metabolism. The treatment at 100 MPa during 8 and 60 h resulted in a reduction of the amount of L-lactic acid produced. It was proposed that was also produced D-lactic acid from L-malic acid. The treatment of 0.5 MPa during 300 h resulted in complete inactivation of bacteria. It is concluded that high pressure is a technology that allows the alteration of the metabolism, particularly change of malolactic enzyme specificity, and inactivation of Oenococcus oeni.
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MacPhail, Susan Helen. "Effect of intercellular contact on radiation-induced DNA damage." Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/27986.
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Chinese hamster V79-171B cells grown for about 24 hours in suspension culture display increased resistance to cell killing by ionizing radiation compared with cells grown as monolayers, an observation originally termed the "contact effect". More recently, development of that resistance was shown to be accompanied by changes in the conformation of the DNA which reduce its denaturation rate in high salt/weak alkali. These changes in DNA conformation, mediated by the cellular micro-environment, appear to be responsible for the contact effect.
The conditions necessary for the development of the effect are not, however, completely understood. In particular, when cells grown as monolayers on petri plates are suspended in spinner culture flasks, their growth characteristics change in three distinct ways. First, cells in suspension no longer have a solid substrate, so they remain round. Second, after several hours, they begin to aggregate to form "spheroids", so that three-dimensional intercellular cell contact develops. Third, cells in the stirred suspension cultures are not subjected to high local concentrations of metabolic by-products or surrounded by a zone depleted of nutrients, as are cells in monolayer culture. The studies described here were designed to determine how each of these factors influence changes in DNA conformation, as assayed using the alkali unwinding technique. Our results indicated that a round shape may not be an essential requirement, since cells spread out on the surface of cytodex beads in suspension culture, and sparsely-seeded cells in monolayer culture demonstrated at least a partial contact effect. Three-dimensional intercellular contact does not always seem necessary for the development of the contact effect. Cells grown in a methyl cellulose matrix developed radioresistance, even though the cells formed only small clusters of less than five cells. Similarly, suspension culture cells which were prevented from aggregating by frequent exposure to trypsin, also developed the contact effect. There was no evidence that nutrient depletion plays a role in the failure of cells grown as monolayers to develop a contact effect. However, cells grown as spheroids in the presence of monolayer cells, or in monolayer cell-conditioned medium, did not display a full contact effect. This indicates a role for monolayer cell-produced factors (possibly extracellular matrix proteins) in preventing the development of the contact effect.
We conclude that changes in DNA conformation and the increase in radiation resistance, seen in V79-171b cells grown as spheroids, are not the result of intercellular contact or round shape of the cells. This radioresistance appears to be the result of an absence of monolayer cell-produced factors which could control both cell shape and DNA conformation.Medicine, Faculty of
Pathology and Laboratory Medicine, Department of
Graduate
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Phillips, Stanley D. "Developing radiation hardening by design." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/29640.
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Thesis (M. S.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2010.Committee Chair: Cressler, John; Committee Member: Citrin, David; Committee Member: Shen, Shyh-Chiang. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Ho, Chiu Man. "Repression of photoreactivation and dark repair of coliform bacteria by TiO[subscript 2]-modified UV-C irradiation /." View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?CIVL%202009%20HO.
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Tangboonduangjit, Puangpen. "Intensity-modulated radiation therapy dose maps the matchline effect /." Access electronically, 2006. http://www.library.uow.edu.au/adt-NWU/public/adt-NWU20060724.095712/index.html.
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Young, Stephen Michael Radley. "The effect of intense laser radiation on atomic collisions." Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302895.
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Daar, Eman S. "Effect of ionizing radiation on hyaluronan and fibrous pericardium." Thesis, University of Surrey, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.540706.
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Chakravarthy, Usha. "The effect of gamma radiation on intraocular cellular proliferation." Thesis, Queen's University Belfast, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317046.
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Phorah, Motee William. "The effect of radiation and convection on stellar oscillations." Doctoral thesis, University of Cape Town, 2007. http://hdl.handle.net/11427/4426.
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Peters, Chris (Christopher Joseph) Carleton University Dissertation Engineering Electrical. "MOSFET based gamma radiation detector." Ottawa, 1992.
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Smith, Mark William 1961. "Effect of infrared reflectance on stem temperatures of saguaros." Thesis, The University of Arizona, 1989. http://hdl.handle.net/10150/277222.
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The role of high infrared (IR) reflectance in the temperature regulation of a single species of cactus, Cereus giganteus (saguaro cactus), was investigated. Two independent methods were used to determine the effect of high near-IR reflectance on C. giganteus stem temperatures. The first method was to measure the surface temperature of two individual plants of comparable size and health, one of which was partially shaded by a canopy of loose sun-screening material. The second method involved the numerical solution on a computer of the energy balance, or heat transfer, equation for C. giganteus. High reflectance at near-IR wavelengths was found to decrease the peak surface temperature reached by C. giganteus by 3.2 to 3.3°C. This figure is valid for the fairly mild environmental conditions encountered in the Sonoran Desert at an altitude of 940 m during late September and early October.
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Reinhard, Mark. "Radiation hardness study of high purity silicon and the development of a radiation damage monitoring system for silicon devices in mixed radiation fields /." Access electronically, 2003. http://www.library.uow.edu.au/adt-NWU/public/adt-NWU20040727.132611/index.html.
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Mo, Anthony John. "Effect of NaOH solutions on planktonic bacteria, biofilms, and lipopolysaccharide." Thesis, University of British Columbia, 2016. http://hdl.handle.net/2429/58354.
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Background: Eradicating bacteria, biofilms and harmful by-products such as LPS from the root canal system is important in providing successful endodontic treatment. To date no irrigant or medicament used in endodontics has been able to completely eradicate bacteria in the root canal system or detoxify all LPS. Aim: It is proposed that a novel solution containing NaOH (Sodium hydroxide), Sodium dodecyl sulfate (SDS) and an alcohol may have unique disinfective properties against bacterial factors highly relevant in endodontic treatment. Materials and Methods: Combinations of the proposed solution were tested and compared to NaOCl (sodium hypochlorite) against 1- Planktonic E. faecalis in direct contact and quantified by CFU counts 2 - Polymicrobial biofilms in an open model exposed to solutions and visualized with CLSM (Confocal Laser Scanning Microscopy) 3 – LPS using a biofunctional assay, stimulating IL-1ß production in RAW 264.7 macrophages with treated LPS aliquots and analyzed by ELISA. Results: Planktonic killing tests with E. faecalis showed that NaOCl was more effective than NaOH solutions. With potency from highest to lowest as follows: 6% NaOCl, 2% NaOCl, NaOH/SDS/Propanol, NaOH/Propanol. Biofilm tests showed that NaOCl killed more biofilm bacteria, however NaOH/SDS combinations removed more biofilm mass. Results showed that LPS samples treated with either 6% or 2% NaOCl produced no IL-1ß. Samples treated with NaOH/SDS combinations produced inconsistent results regarding IL-1ß release due to inefficient dialysis removal of toxic irrigants. Conclusions: Results suggest that NaOCl remains the irrigant of choice as it is most effective in killing bacteria either planktonically or within biofilm systems. The results of this study suggest that NaOCl is indeed effective in LPS detoxification which is contrary to suggestions by several previous studies. NaOH/SDS combinations while less effective in killing, appear to remove more biofilm mass when compared to NaOCl. This may be attributed to the surfactant properties of SDS.Dentistry, Faculty of
Graduate
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Kayagil, Fulya. "Effect Of Traditional Starter Cultures On Quality Of Cheese." Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/12607103/index.pdf.
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In this study, the physico-chemical chances occurring in white cheese and possible effects of starter culture combinations to the ripening period during 30 days storage examinated.
A total of thirty six lactic acid bacteria were isolated from a cheese made witohout using starter culture. For identification gram staining, catalase, gas production and coagulation tests were performed. For determination of species API50 CH (BioMérieux) and partial 16S rDNA gene sequence analysis were used. Four cheese were produced, one by using commercial starter culture [Lyofast CMS (Lactococcus lactic subs. lactis and Lactococcus lactis subs. cremoris)]as control the other three by using different combinations of isolates [Lactococcus lactic subs. lactis (13%) +Lactobacillus brevis (40%)+Lactobacillus paracasei (47%)
Lactococcus lactic subs. lactis (36%)+Lactobacillus paracasei (64%)
Lactococus lactis subs. lactis (24,5%)+ Lactobacillus paracasei (28,5%) + Lactobacillus brevis (47%)] Cheese were ripened in 15% saline solution 4 C for 30 days.Samples were taken from each treatment and analyzed on 2nd,15th and 30th days Sensory ,microbiological and chemical properties of the cheese preparations as pH, acidity ,salt,fat,moisture,protein contents during storage period were determined. In this respect effect of using different starter culture combinations on quality of Turkish white chee was determined and Lactococcus lactis subs. lactis(13%)+Lactobacillus brevis (40%)+Lactobacillus paracasei(47%) combination was found as the best and can be suggested as ideal combination for white cheese production.
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Johnson, William H. "Lost life expectancy rate survey meter." Thesis, Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/16408.
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Kabilan, Usha. "Studying the Effect of Low Doses of Ionization Radiation on Senescence in Human Lung Fibroblasts." Thesis, Université d'Ottawa / University of Ottawa, 2020. http://hdl.handle.net/10393/40982.
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The exposure to high doses of ionizing radiation (>5Gy) is unequivocally associated with increased cancer risk. However, there is substantial experimental evidence showing that in response to low doses of ionizing radiation (LDR: <100mGy), cells and organisms are benefitted with delayed ageing, improved immunity and reduced cancer growth. These intriguing findings have proposed the “Radiation Hormesis” hypothesis. Herein, I studied the senescence effects of LDR exposure to normal human HFL1 cells and examined transcriptional changes. I found that HFL1 cells exposed to 10 mGy of gamma radiation had delayed senescence measured at 12 weeks post-irradiation compared to unirradiated cells. Through qPCR array analysis, I found that genes involved in human cellular senescence functions are differentially regulated in 10 mGy exposed cells at 12 weeks compared to 1-week post-exposure. A nucleolar protein, SIRT7, that belongs to the family of proteins called Sirtuins with known roles in aging, was found to be upregulated transcriptionally in LDR-exposed HFL1 cells. Knocking out SIRT7 protein significantly accelerated senescence in HFL1 cells suggesting a direct role of SIRT7 in the deceleration of senescence and potentially in mediating radiation hormesis. Furthermore, overexpression of the HRAS oncogene strongly accelerated senescence in HFL1 cells through gene expression of cell cycle regulators and checkpoint proteins. Together, my studies revealed that LDR induces unique transcriptional changes resulting in a potentially radio adaptive protective cellular response. I also discuss the HRAS overexpression system as a time-efficient cellular model that could be used to more rapidly study the effect of LDR on senescence using primary cultures.
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Habeeb, Fatema. "Bacteria-cytokines interactions : effect of normal bacterial flora of pathogenic bacteria on pro-inflammatory cytokines production in human blood." Thesis, University of Strathclyde, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.501921.
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Itoh, Yoshito, Yasuo Kitane, and Paramashanti. "Long-term performance of rubber bearing considering solar radiation effect." 土木学会, 2010. http://hdl.handle.net/2237/18846.
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Marty, Christoph. "Surface radiation, cloud forcing and greenhouse effect in the Alps /." Zürich, 2000. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=13609.
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Xia, Zichao. "Effect of neutron radiation on the mechanical properties of B4C." Master's thesis, University of Central Florida, 2011. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5087.
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B4C is an important engineering ceramic used in a number of different applications. One of the promising applications of B4C is in the nuclear industry. B4C has a high neutron absorption cross-section (600 barns) and that is why it can absorb neutrons without forming long lived radio nuclides. As a result, B4C is extensively used as control rods, shielding material and as neutron detectors in nuclear reactors.
During the reactor’s operation, the B4C undergoes severe neutron radiation and defects, such as vacancies and helium bubbles, are generated in the structure. These defects are responsible for the degradation of mechanical performance of B4C and can make this material unsuitable for further exploitation. Therefore, both crystal structure and mechanical properties of B4C were studied before and after radiation, as well as for the case when irradiated by neutrons B4C samples has been annealed in order to heal the defects introduced by the radiation. Fully dense B4C ceramics were produced by hot pressing at 2100ºC, 30MPa, and 45 minutes dwell time. 120 small bars of 2×2.5×25mm were machined according to the MOR bar standard. 40 bars after machining were tested as they were, 80 bars were irradiated with neutrons in neutron source for 3.5 months. 40 out of the 80 irradiated bars were annealed at 400ºC for 1 hour with an attempt to heal the defects possibly introduced by the irradiation.
4-point bending strength, SEVNB fracture toughness, and Vickers hardness have been measured on as received B4C, B4C after radiation, and B4C after radiation and annealing. The Weibull parameters were determined for each set of the conditions. The fracture surfaces of the B4C samples before and after radiation as well as after radiation and annealing have also been analyzed using SEM. X-ray diffractometer was used to collect diffraction pattern of the B4C, and Raman spectrometer was used to evaluate the vibrational response of B4C. Thus the effect of neutron radiation and annealing on the mechanical performance and structure of B4C has been analyzed.ID: 029809317; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (M.S.)--University of Central Florida, 2011.; Includes bibliographical references (p. 94-107).
M.S.
Masters
Mechanical, Materials, and Aerospace Engineering
Engineering and Computer Science
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Millar, Samuel John. "The effect of ionising radiation on the appearance of meat." Thesis, Queen's University Belfast, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241420.
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Pattenden, Caroline Sarah. "The effect of radiation on the thermal stability of polyisobutylene." Thesis, University of Birmingham, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366649.
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Wyss, Rolf A. (Rolf Andreas). "Far-infrared radiation response of antenna-coupled quantum-effect devices." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/33537.
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Bolsa, Ferruz Marta. "Oxygen effect in medical ion beam radiation combined with nanoparticles." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS476/document.
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Environ 50% des patients recevant un traitement contre le cancer bénéficient de la radiothérapie. La radiothérapie conventionnelle consiste à utiliser des rayons X de haute énergie capables de traverser les tissus et de traiter des tumeurs situées en profondeur de façon non-invasive. Malheureusement, les rayons X ne font pas la distinction entre les tumeurs et les tissus sains, qui peuvent donc être endommagés. Cette non-sélectivité est à l’origine de graves effets secondaires, voire du développement de cancers secondaires. Par conséquent, l’amplification des effets radiatifs au sein de la tumeur par rapport aux tissus environnants représente un défi majeur.L’hadronthérapie (traitement par faisceaux de protons ou d’ions carbone) est considérée comme l’une des techniques les plus prometteuses car, contrairement aux rayons X, la quantité d’énergie déposée atteint son maximum en fin de trajectoire. Lorsque le faisceau est réglé de manière à ce que ce maximum atteigne la tumeur, aucun dommage n’est causé aux tissus situés au-delà. Un autre avantage majeur est que les ions lourds sont plus efficaces pour traiter les tumeurs radiorésistantes. L’utilisation de cette technique est cependant restreinte du fait des dommages – plus faibles mais néanmoins significatifs – causés aux tissus normaux situés sur la trajectoire du faisceau d’ions en amont de la tumeur. Afin d’améliorer les performances de l’hadronthérapie, l’équipe a développé à l’ISMO une nouvelle stratégie combinant l’utilisation de nanoparticules (NPs) métalliques avec l’irradiation par faisceaux d’ions. L’utilisation de NPs a pour but non seulement d’amplifier les effets des rayonnements dans la tumeur mais également d’améliorer l'imagerie médicale à l’aide des mêmes agents (théranostic). Les NPs possèdent une chimie de surface permettant leur fonctionnalisation avec des ligands capable d’améliorer la biocompatibilité, la stabilité ainsi que la circulation sanguine et l’accumulation dans la tumeur. L’équipe a déjà démontré que les petites NPs d’or et de platine (≈ 3 nm) avaient la capacité d’amplifier les effets causés par les faisceaux d’ions carbone médicaux en présence d’oxygène. Cependant, les tumeurs radiorésistantes sont susceptibles de contenir des régions hypoxiques. Il est donc urgent de quantifier et de caractériser l’influence de l’oxygène sur l’effet radio-amplificateur. Le but de ma thèse était d’étudier l’influence de l’oxygène lors d’irradiations par des faisceaux d’ions médicaux en présence de NPs d’or et de platine. Pour cela, deux lignes de cellules cancéreuses humaines radiorésistantes ont été testées: HeLa (col de l’utérus) et BxPC-3 (pancréas). Plusieurs techniques d’irradiation ont été utilisées : des faisceaux d’ions carbone et hélium générés par « passive scattering » et des faisceaux d’ions carbone générés par « pencil beam scanning ». Les principaux résultats de cette étude sont les suivants. En condition oxique (concentration d’O₂ = 20%), une amplification des effets radiatifs a été observée pour les deux types de NPs (à concentration de métal égale). Ce phénomène se réduit à mesure que la concentration d’oxygène diminue mais reste significatif jusqu’à 0.5%. Aucune différence significative n’a été observée entre les deux lignes cellulaires. Il est intéressant de noter que la dépendance à l’oxygène varie en fonction de la technique d’irradiation utilisée. Une tentative d’explication de l’influence de l’oxygène par des processus moléculaires est proposée. Des perspectives de développements ultérieurs sont suggéréesAbout 50% of the cancer patients who are treated benefit from radiation therapy. Conventional radiotherapy consists of high energy X-rays traveling through the tissues, so that deeply sited tumors are treated in a non-invasive way. Unfortunately, X-rays are not tumor selective and healthy tissues may be damaged. This lack of selectivity is responsible for severe side effects and/or secondary cancers. Hence, improving the differential of radiation effects between the tumor and surrounding tissues remains a major challenge. Particle therapy (treatment by protons or carbon ion beams) is considered as one of the most promising technique because, by opposition to X-rays, the energy deposition of ions is maximum at the end of their tracks. When the beam is tuned so that the maximum reaches the tumor, there is no damage induced in tissues siting after the tumor. Another important added value is that heavy ions are more efficient to treat radioresistant tumors. The use of this modality is however restricted by the low but significant damage that is induced to normal tissues located at the entrance of the track prior to reaching the tumor. To improve the performance of particle therapy, a new strategy based on the combination of high-Z nanoparticles with ion beam radiation has been developed by the group at ISMO. This approach aims at using nano-agents not only to increase radiation effects in the tumor but also to improve medical imaging with the same agent (theranostic). Nanoparticles present a remarkable surface chemistry, which allows functionalization with ligands able to improve biocompatibility, stability as well as blood circulation and accumulation in tumors. The group already demonstrated the efficiency of small (≈ 3 nm) gold and platinum nanoparticles to amplify the effects of medical carbon ions in normoxic conditions (in the presence of oxygen). However, radioresistant tumors may host hypoxic regions. It is thus urgent to quantify and characterize the influence of oxygen on the radio-enhancement effect. The goal of my thesis was to study the influence of oxygen on medical ion radiation effects in the presence of gold and platinum nanoparticles. This was performed using two radioresistant human cancer cell lines: HeLa (uterine cervix) and BxPC-3 (pancreas). Different radiation modalities were used: carbon and helium ion beams delivered by a passive scattering delivery system and carbon ion beams delivered by a pencil beam scanning system. The major results of this work are the following. In oxic conditions (O₂ concentration = 20%), an enhancement of ion radiation effects was observed for the two nanoparticles (at the same concentration in metal). This effect decreased with the oxygen concentration but remained significant for a concentration of 0.5%. No significant difference was found between the cell lines. Interestingly, the oxygen-dependence varied with the type of radiation. An attempt to explain the effect of oxygen by molecular processes is proposed. Perspectives of further developments are suggested
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Thurston, Gavin O. "Studies on the effect of radiation on 3T3 cell motility." Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/29441.
Full textAbstract:
The ability of mammalian cells to locomote is important in a variety of normal and pathological processes. Previous work has suggested that low doses of x-irradiation may perturb cell motility, a finding that may have important consequences in embryogenesis, cancer metastasis, and immune response. This thesis has sought to study in more detail the effect of radiation on mammalian cell motility.
Work performed in other laboratories used the colloidal gold assay and time lapse cinemicroscopy to study x-irradiation induced changes to 3T3 fibroblast motility in tissue culture. These studies were repeated here, with qualitative results similar to those reported earlier. However, these methods were not amenable to a detailed quantitative analysis. For this, spatial and temporal information on the motility and dynamic morphology of a large number of cells is required. Such a task would be impossible to perform manually, thus an automated microscope system was developed that used a computer-driven precision stage and a solid state optical sensor to track individual cells in tissue culture. Information on motility and morphology was concurrently extracted from many cells. As part of the thesis, several techniques were developed to analyze and display these data, and to correlate motility and morphology observations. These techniques were directed at preserving the actual process of 3T3 cell motility, and parameters were measured to quantify the short term persistence of cell movement (on a time scale of 0.5 to 2 hours), and the long term persistence of cells in maintaining certain characteristic behaviour (on a time scale of 3 to 12 hours). The response of 3T3 fibroblasts to x-irradiation was characterized by a number of parameters. The population average cell speed was measured following treatment, and a dose response and time response was determined in the range of 1.5 Gy. Other motility parameters indicate that the normal process of cell motility, evidenced by a series of motile segments, was disrupted by x-rays. This was thought to reflect perturbation to the control mechanisms of cell motility.
The morphology of 3T3 cells stained with Coomassie blue was examined in an effort to correlate the observed motility changes with changes in the fixed cell morphology. This stain is a general structural protein stain with higher affinity toward microfilaments. High doses of x-rays were required to produce significant perturbation to cell morphology, and in the dose regime of interest, the morphology of irradiated cells was not identifiably different from control. Of note is that it was the well spread, quiescent cells that seemed least perturbed by large doses of irradiation.
In summary, x-rays apparently disrupt the normal process of cell motility. Several lines of evidence suggest that actively migrating cells are the most perturbed by irradiation. This work has developed techniques to quantify cell motility in a meaningful way, and to characterize the x-ray induced perturbations.Science, Faculty of
Physics and Astronomy, Department of
Graduate
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Watson, Anna. "The effect of nutrient pulsing on competition between phytoplankton and bacteria." Thesis, Lancaster University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310355.
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