Academic literature on the topic 'Rats – Effets du stress sur'
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Journal articles on the topic "Rats – Effets du stress sur"
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Mellouk, Z., M. Agustina, M. Ramirez, K. Pena, and J. Arivalo. "Effets thérapeutiques de la supplémentation en huile de krill (Euphausia superba) sur les marqueurs du stress oxydant et des dommages de l’ADN chez des rats soumis au régime cafétéria." Annales de Cardiologie et d'Angéiologie 65, no. 3 (June 2016): 223–28. http://dx.doi.org/10.1016/j.ancard.2016.04.008.
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Scaps, Patrick, Christian Retière, Gaston Desrosiers, and Gilles Miron. "Effets de la ration alimentaire, de la densité intraspécifique et des relations entre individus sur la croissance des juvéniles de l'espèce Nereis diversicolor (Annelida: Polychaeta)." Canadian Journal of Zoology 71, no. 2 (February 1, 1993): 424–30. http://dx.doi.org/10.1139/z93-059.
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We studied the effects of food intake, intraspecific density, and interactions between individuals on the growth of laboratory-raised juveniles of Nereis diversicolor fed different quantities of Tetramin. A daily intake of 3.33 mg of Tetramin per individual resulted in an optimal mean mass gain. At densities above 3000 individuals/m2, not only was the growth rate reduced, but biomass and survival rates were also diminished. Frequent handling and the thermodifferential shock that ensured created a stress that had the same negative effects. Variations in responses to aggregation or isolation were high, as revealed by groups of juveniles captured in winter or in spring reacting differently: growth was not affected by the breeding conditions in the winter-caught worms but was faster in spring-caught individuals kept in isolation.
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Kuligowski, Janine, Michèle Ferrand, and Éliane Chenou. "Effets d'un choc thermique sur le métabolisme des ARN et des protéines au cours de l'embryogenèse d'une fougère aquatique, le Marsilea vestita." Canadian Journal of Botany 67, no. 9 (September 1, 1989): 2655–62. http://dx.doi.org/10.1139/b89-342.
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A mild, 2-h cold shock treatment, from 24 to 16 °C, was applied during the different stages of Marsilea vestita embryogenesis. For each main stage (proembryo, globular embryo, and completed embryo with a bilateral symmetry), cold-induced modifications in RNA and protein synthesis were studied by autoradiography of the cells after incorporation of [5-3H]uridine and [3H]leucine. In both controls and treated specimens, proembryogenesis was characterized by a lack of transcriptional activity and no labelling was detected in the cytoplasm until the 16-cell stage. Even in the absence of de novo RNA synthesis in cooled samples, proteins necessary for the first cleavages of the embryo were being synthesized, but always at a rate lower than in the reference material. These results lead us to postulate that long-lived mRNA is stored in the cytoplasm of young embryos. Transcription, slowed down by the cold treatment, starts at the 8- to 16-cell stage and increases during the globular embryo stage. In lowered temperature conditions, transport of new RNA transcripts to the cytoplasm, which was strongly inhibited during the transition from the 16- to the 64-cell stage, appears to be less sensitive to cold shock as the embryo gets older. Our results show a difference in the response to temperature between RNA and protein synthesis. However, in both cases, sensitivity to cold temperature stress decreases with age. It is the physiological status reached by the embryo when the cold temperature stress is applied that determines the intensity of the response. [Journal translation]
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Esquivel-Gutiérrez, Edgar Romualdo, Lilia Alcaraz-Meléndez, Roberto Hernández-Herrera, Amada Torres, and Carmen Rodríguez-Jaramillo. "Effects of damiana (Turnera diffusa; var. diffusa and var. aphrodisiaca) on diabetic rats." Acta Universitaria 28, no. 6 (February 7, 2019): 84–92. http://dx.doi.org/10.15174/au.2018.1761.
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Turnera diffusa (damiana) grows wild in Baja California Sur (BCS), Mexico. It is traditionally used for its aphrodisiac effects and for diabetes treatment. Two varieties (var.) have been identified: diffusa and aphrodisiaca. To evaluate the effects of water-ethanol extracts from both varieties, measurements on blood glucose, body weight, biochemical parameters, and cell blood counts were performed in a diabetic rat model. Oxidative stress was also evaluated when var. diffusa was administered. No significant reductions in blood glucose levels, in biochemical parameters, or in cell blood counts with any variety of damiana were observed; however, it helped diabetic animals to keep their body weight. Damiana var. diffusa did not modify the mitochondrial nitric oxide levels and superoxide dismutase activity; however, thiobarbituric acid reactive species diminished. In conclusion, damiana can be utilized reliably in the management of diabetes because of its antioxidant potential; it promoted body weight loss in healthy animals and helped to preserve it in diabetes.
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Oyeniyi, F. G., and E. O. Ewuola. "A review of strategies aimed at adapting livestock to volatile climatic conditions in Nigeria." Nigerian Journal of Animal Production 48, no. 4 (March 8, 2021): 79–93. http://dx.doi.org/10.51791/njap.v48i4.3018.
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Despite their crucial importance, limited information exists about how livestock are affected by climate change in Nigeria. Changing climatic patterns are manifested through occurrences like abrupt temperature increase, dwindling rainfall pattern, rise in spells of drought and flood. These conditions exert different effects across the geographical landscape of the country, which can broadly be classed as Semiarid, Sahel and Derived Savannah, respectively as well as Forest and Montane. Livestock provide humans with the full complement of amino acids, which are the only known natural suppliers of Vitamin B12 and equally supply iron, calcium, iodine and zinc. In addition, livestock accounts for 40% of Agricultural Gross Domestic Product and significantly contributes to enhancing rural livelihood. Stress conditions are induced in livestock by harsh weather conditions that reduce the feed available to them as well as impede growth rate and reproduction efficiency and disease incidence which may eventually result in death. In the light of the livestock benefits to humanity, it is necessary to devise means of making their climate resilient. Some of the proven strategies include animal genetic improvement for stress tolerance, growing disease resistant, early maturing and drought tolerant crops, selecting for and rearing climate tolerant animal species and breeds.
Malgré leur importance cruciale, il existe peu d'informations sur la manière dont le bétail est affecté par le changement climatique au Nigéria. Le changement des modèles climatiques se manifeste par des événements tels que l'augmentation brutale de la température, la diminution des précipitations, l'augmentation des périodes de sécheresse et d'inondation. Ces conditions exercent des effets différents sur le paysage géographique du pays, qui peuvent être globalement classés comme semi-aride, sahélien et savane dérivée, respectivement, ainsi que forêt et montagne. Le bétail fournit aux humains le complément complet d'acides aminés, qui sont les seuls fournisseurs naturels connus de vitamine B12 et fournissent également du fer, du calcium, de l'iode et du zinc. En outre, l'élevage représente 40% du produit intérieur brut agricole et contribue de manière significative à l'amélioration des moyens d'existence ruraux. Les conditions de stress sont induites chez le bétail par des conditions météorologiques difficiles qui réduisent les aliments disponibles pour eux et entravent le taux de croissance, l'efficacité de la reproduction et l'incidence des maladies qui peuvent éventuellement entraîner la mort. À la lumière des avantages de l'élevage pour l'humanité, il est nécessaire de concevoir des moyens de rendre leur résilient climatique. Certaines des stratégies éprouvées comprennent l'amélioration génétique animale pour la tolérance au stress, la culture de cultures résistantes aux maladies, à maturation précoce et à la sécheresse, la sélection et l'élevage d'espèces et de races animales tolérantes au climat.
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CAPEL, F., L. DEMAISON, B. MORIO, V. RIMBERT, P. PATUREAU-MIRAND, and L. MOSONI. "Rôle des mitochondries dans le développement d’un stress oxydant dans le muscle squelettique au cours du vieillissement." INRAE Productions Animales 19, no. 4 (September 14, 2006): 305–18. http://dx.doi.org/10.20870/productions-animales.2006.19.4.3498.
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Le vieillissement s’accompagne d’une perte de masse musculaire qui contribue à l’affaiblissement des capacités de défenses de l’organisme, et à la réduction de la mobilité et de l’autonomie des personnes âgées. Ce travail a été entrepris pour déterminer si le stress oxydant pouvait être impliqué dans ce phénomène, et en particulier la mitochondrie, forte productrice d’espèces actives de l’oxygène.
Nous avons montré dans les muscles glycolytiques que la production mitochondriale d’H2O2 (PMH) induite par le flux inverse d’électrons entre les complexes II et I augmentait avec l’âge. Dans les muscles oxydatifs, la PMH induite par un flux d’électrons à partir du complexe I augmentait également. La PMH semble donc augmenter avec l’âge dans tous les types musculaires et la réduction de l’activité de la GPX dans les muscles glycolytiques pourrait accroître les conséquences de ce phénomène. Cependant, d’autres paramètres mitochondriaux (respiration, activités des complexes II à IV) n’étaient pas modifiés. De plus, un stress calcique provoqué par l’injection d’un ionophore (A23187) n’a pas eu d’effet chez des rats jeunes, alors qu’il a induit une atrophie du muscle soleus et un accroissement de la PMH dans le muscle gastrocnemius chez les rats âgés.
L’ensemble de nos résultats suggère donc que l’augmentation de la PMH au cours du vieillissement n’a pas d’effet majeur à court terme sur le vieillissement musculaire. Elle pourrait avoir un effet à long terme, notamment dans le grand âge et/ou contribuer à accentuer la fragilisation du tissu âgé, en particulier en réponse à un stress.
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Kirstetter, P., F. Lagneau, O. Lucas, J. Krupa, and J. Marty. "Effets de l'isoflurane sur des anneaux aortiques de rats cirrhotiques." Annales Françaises d'Anesthésie et de Réanimation 15, no. 6 (January 1996): 826. http://dx.doi.org/10.1016/0750-7658(96)84433-9.
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Lourel, Marcel, and Nicolas Guéguen. "L'interface "vie privée ? vie au travail?. Effets sur l'implication organisationnelle et sur le stress perçu." Les cahiers internationaux de psychologie sociale Numéro 74, no. 2 (2007): 49. http://dx.doi.org/10.3917/cips.074.0049.
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Dolcos, Florin, and Ekaterina Denkova. "Dissocier les effets facilitants et les effets délétères de l’émotion sur la cognition." Santé mentale au Québec 41, no. 1 (July 5, 2016): 15–34. http://dx.doi.org/10.7202/1036964ar.
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L’émotion est une « arme à double tranchant » qui peut soit améliorer, soit détériorer des aspects divers de notre cognition et de notre comportement. Par exemple, la charge émotionnelle d’un événement peut attirer l’attention et renforcer la mémoire de cet événement, par contre une information émotionnelle, sans pertinence pour la tâche cognitive en cours, peut être considérée comme une distraction et ainsi entraîner la détérioration de la performance à cette tâche. Ces effets opposés de l’émotion peuvent être identifiés à différents niveaux, à la fois au sein du même processus cognitif et à travers des processus cognitifs différents, ou à un niveau plus général, comme dans le cas de la réponse au stress. Cette revue présente des données nouvelles qui permettent de mieux comprendre les facteurs qui influencent les effets opposés de l’émotion sur la cognition chez le sujet sain ainsi que dans le cas de dysfonctionnements liés à des désordres affectifs. Les questions discutées dans cette revue sont d’une grande importance pour arriver à mieux comprendre les mécanismes impliqués dans les relations entre émotion et cognition dans le fonctionnement sain ainsi que dans les troubles émotionnels où les effets de l’émotion sur la cognition sont intensifiés. Globalement, la présente revue souligne la nécessité de considérer et identifier les facteurs qui peuvent avoir une influence sur les effets de facilitation et les effets de dégradation des émotions sur la cognition.
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Mami-Soualem, Z., N. Brixi, C. Beghdad, and M. Belarbi. "Effet antioxydant et antihyperglycémiant du seigle (Secale cereale L.) et du sorgho (Sorghum bicolor L.) chez le rat Wistar rendu diabétique." Phytothérapie 16, S1 (September 5, 2018): S273—S283. http://dx.doi.org/10.3166/phyto-2018-0013.
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Le changement des habitudes alimentaires au cours de ces dernières années a abouti à l’apparition des maladies dites de civilisation, parmi elles le diabète sucré. Des approches diétothérapeutiques privilégient la consommation des produits céréaliers sous la forme la plus complète possible. Ce travail a pour but de tester l’efficacité des régimes expérimentaux préparés à base des grains complets des deux céréales, le sorgho (Sorghum bicolor L.) et le seigle (Secale cereale L.), sur la correction de l’hyperglycémie et des marqueurs du stress oxydant associés au diabète chez le rat mâle Wistar. Les résultats montrent que les rats diabétiques, soumis au régime seigle pendant quatre semaines, présentent une diminution significative de la glycémie qui atteint les 53,95 % à la fin de l’expérimentation, ce qui fait que leur taux en glycémie se rapproche de celui des normoglycémiques. Le sorgho blanc présente, d’une part, une diminution significative de la peroxydation lipidique intracellulaire et, d’autre part, une augmentation de l’activité de la glutathion peroxydase, la glutathion réductase ainsi que la vitamine C. Ces approches méthodologiques peuvent, en améliorant la connaissance de l’importance des céréales (fibres alimentaires solubles et des polyphénols) dans l’évolution du diabète, aboutir à des recommandations et à une éducation nutritionnelle du diabétique.
Dissertations / Theses on the topic "Rats – Effets du stress sur"
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Dumont, Frédéric. "Étude de l'altération de la réponse ventilatoire à l'hypercapnie, chez le rat adulte, induite par un stress néonatal." Thesis, Université Laval, 2011. http://www.theses.ulaval.ca/2011/28354/28354.pdf.
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Ammari, Mohamed. "Effets des champs électromagnétiques sur le comportement : le stress oxydant et le métabolisme oxydatif cérébral chez le rat." Paris 7, 2008. http://www.theses.fr/2008PA077118.
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L'exposition aux champs électromagnétiques a pris dans les dernières décennies une ampleur importante. En parallèle, de nombreux troubles de santé dans la population ont été attribués à ce facteur non perceptible et mal connu. Le système nerveux central est l'organe coordinateur des informations périphériques, et si une sensibilité aux champs électromagnétiques existe, elle a de fortes chances de se manifester sur ce système. Le but de ce travail a été d'étudier dans un premier temps l'influence de deux types de champs électromagnétiques, un champ magnétique statique et un champ radiofréquence de type GSM 900 MHz, sur le comportement chez le rat (anxiété, mémoire, processus de rappel et l'attention). Ensuite, des effets biologiques d'une exposition à un signal GSM 900 MHz à des débits d'absorption spécifique de 1,5 et 6W/Kg ont été recherchés au niveau du système nerveux central : stress oxydant, métabolisme oxydatif et évolution des cellules gliales. Nos résultats montrent qu'une exposition sub-aiguë à un champ magnétique statique de 128 mT n'induit pas de perturbation du comportement émotionnel et du processus de rappel chez le rat, malgré une tendance à une diminution des performances. De même, une exposition sub-chronique (2 mois) et chronique (6 mois) "tête seule" à un signal GSM n'induit pas de perturbation de l'apprentissage et de la mémorisation des rats à long terme. Par contre l'exposition à un signal GSM 900 MHz (DAS de 6 W/Kg) induit : i) une perturbation de l'activité des enzymes antioxydantes ii) une modification de l'activité cérébrale et une modification de l'activité de la cytochrome C oxydase iii) l'apparition d'une astrogliose réactionnelle au niveau cérébral chez les rats exposés. Cette astrogliose peut être associée à des dommages neuronaux sous-jacents. Compte tenu des différences morphologiques entre les rats et les humains, le DAS calculé chez un individu tel que défini dans les recommandations et les normes, serait égal à quatre fois le DAS moyenne sur le cerveau du rat, ce qui rend l'extrapolation de ces résultats à l'homme rassuranteExposure to electromagnetic fields has arisen in recent decades a large concern. In parallel, many symptoms experienced by some people have been attributed to this factor. The central nervous System is the most integrative tissue for information, and if a sensitivity to electromagnetic fields exists, it is likely to manifest itself on this System. The aim of this work was to study as a first step the effect of two types of electromagnetic fields, a static magnetic field and a radio frequency GSM 900 MHz, on the behavior in rats (anxiety, memory and attention). Then, biological effects of exposure to GSM 900 MHz signal to specific absorption rates of 1. 5 or 6 W/Kg were sought in the central nervous System: on oxidative stress, on oxidative metabolism and on glial cells. Our results show that sub-acute exposure to a static magnetic field of 128 mT did not disturb emotional behavior and recall process in rats, despite a trend towards a decrease in performance. Similarly, a sub-chronic (2 months) and chronic (6 months) "head only" exposure to GSM signal did not disturb learning and memory in rats. However, exposure to GSM 900 MHz signal (DAS 6 W/kg) induced: i) a disturbance of the antioxidant enzymes activity ii) a change in neuronal activity by a change in the activity of the cytochrome c oxidase iii) a reactive astrogliosis (increased GFAP expression) in the brain of exposed rats. Astrogliosis may be associated with underlying neuronal damage. Given the morphological differences between rats and humans, the SAR calculated from an individual as defined in the recommendations and standards, would be equal to four times the average SAR in the rat brain, making the extrapolation of these results to humans reassuring
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Vincent, Annabelle Carole. "Effets de la suppression du stress de la naissance et de l'adoption sur le développement et le comportement de jeunes rats." Rouen, 2003. http://www.theses.fr/2003ROUEL458.
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Chez les Mammifères au moins, la naissance représente un stress physique important pour le nouveau né. Notre étude a pour objet de déterminer les effets de la suppression de ce "stress de la naissance" chez des rats nés à terme, suivis jusqu'à l'âge adulte. Notre recherche s'intéresse également aux conséquences à court et long terme de l'adoption à la naissance. Nous avons conduit plusieurs expériences dans lesquelles nous avons fait varier, d'une part, le mode de naissance (par césarienne ou par voie vaginale) la césarienne permettant aux fœtus d'éviter de subir le stress dû à leur compression dans les voies génitales lors des contractions utérines et la situation d'hypoxie, d'autre part, l'environnement de développement post-natal (adoption ou élévage par la mère biologique). Les mères adoptives mettent bas naturellement soit deux jours avant, soit à la même période que les autres mères et leur comportement est aussi étudié. Les résultats et les comparaisons statistiques ont montré que : -la corticostéronémie, à la naissance, est plus faible chez les ratons nés par césarienne que chez ceux nés par voie vaginale, suggérant que la naissance naturelle est bien un évenement stressant. -l'adoption intra-lignée modifie seulement certaines composantes, orientées directement vers les jeunes, du comportement des mères, mais le mode de naissance des ratons n'engendre pas d'effets majeurs sur leurs conduites. -l'adoption provoque une mortalitée immédiatement suivant la procédure, qui se poursuit au moins jusqu'à l'âge d'un mois chez les rats adoptés par des mères ayant mis bas deux jours avant associée à une lente évolution pondérale néonatale, un accroissement de l'anxiété de trait, des modifications du comportement social, ainsi qu'une atteinte des fonctions mnésiques seulement à court terme. - la naissance par césarienne a des effets dramatiques sur la survie ainsi que sur la croissance pondérale au moins pendant toute la période néonatale, entraîne une hyper-activité durable uniquement chez les rats adoptés par des mères ayant mis bas deux jours avant l'adoption, des perturbations du comportement émotionnel, des changements comportementaux au cours d'interactions sociales, ainsi qu'une modification des capacités menésiques à court ou long terme. Ansi une légère modification des conditions de naissance ou un changement précoce de l'environnement maternel suffit à influencer le développement des jeunes et le comportement émotionnel et cognitif des animaux adultesAt least in mammals, birth represents an important physical stress for the newborn. The present study was aimed to dtermine the effects of elimination of this "birth stress" on development and behavior of young term rats, observed until the adult stage. The second aim of this study was to determine the short-and-long-term consequences of fostering at birth. Several experiments were organized to test the influence of the mode of delivery (cesarean section or spontaneous vaginal delivery), the cesarean delivery allowing the avoidance by fetuses of suffering stress due to their compression of the genital tract during strong uterine contractions and acute birth hypoxia, and the postnatal development environment (fostering or rearing by the natural mother). The foster dams were spontaneously dillivered two days peviously or at the same time than other biological dams, and their behavior was also studied. The results show that : - corticoid secretion, at birth, was lower in rat pups delivered by cesarean section than in those naturally born, indicating that natural birth is indeed a stressful event. - in-fostering modified dam's activities directly towards the pups, but the mode of pups'birth seemed to have no major effect on maternal behavior - in-fostering per se resulted in mortality of neonates soon following adoption but; which continued at least throughout the first month of life, with a neonatal growth retardation of surviving pups fostered by dams which were delivered two days previously, an enhanced trait anxiety, modifications of social behavior, and impairments of working memory. - cesarean section birth had catastrophic effects on death and weight gain of survivors at least throughout the neonatalperiod, and elicited a long-lasting hyperactivity only in rats fostered by dams which delivered two days previously, disturbances of emotional behavior, behavioral modifications during social interactions and dysfunction in short-or long-term memory. Thus, mild modification of birth conditions or early change of maternal environment is sufficient to influence the development of young and the emotional and cognitive functions of adult
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Foligné, Benoît. "Vieillissement de l'appareil digestif et nutrition : impact d'un régime supplémenté en yaourt sur la trophicité intestinale du rat âgé sur un modèle in vivo de détresse digestive." Paris 7, 2002. http://www.theses.fr/2002PA077082.
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Marinesco, Stéphane. "Étude des effets du stress d'immobilisation sur le sommeil du rat et des régulations exercées par la corticostérone et la sérotonine." Lyon 1, 1998. http://www.theses.fr/1998LYO1T172.
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Martin, Jessica. "Les effets interactifs du stress et de la diète sur la prise alimentaire et l'activité neuronale." Thesis, Université Laval, 2011. http://www.theses.ulaval.ca/2011/28025/28025.pdf.
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Patin, Valentine. "Effets d'un stress prénatal appliqué à des rates gestantes sur leur comportement maternel et sur le développement, l'anxiété et l'apprentissage de leur progéniture." Rouen, 2001. http://www.theses.fr/2001ROUES036.
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Chez l'homme, certaines modifications telles que l'hyperémotivité, les troubles du sommeil, le retard de développement neurologique chez l'enfant peuvent être engendrés suite à une période de stress maternel pendant la grossesse. Les recherches que nous avons entreprises ont permis de préciser les conséquences engendrées par un stress émotionnel de type écologique, la mise en présence d'un chat de façon ponctuelle, au cours de la gestation, sur la descendance mais également sur le comportement maternel. Les effets du stress prénatal ont été mesurés dans plusieurs expériences dans lesquelles nous avons fait varier le jour du stress (10ème jour : moment de la formation du tube neural ou 14ème jour : moment de la différentiation nerveuse) et l'intensité du stress (aigue͏̈ ou répétée). Les résultats et les comparaisons statistiques ont montré que : la mise en présence d'un chat à proximité de la rate gestante produit une réponse physiologique (taux de corticostérone) qui présente les caractéristiques du stress. Le stress prénatal, quel qu'il soit, a des effets délétères sur le comportement maternel. Les petits prénatalement stressés ont un fort taux de mortalité et une lente évolution pondérale. Ils montrent également un développement plus lent et cela de façon plus flagrante pour les petits nés de mères stressées de façon aigue͏̈ au 10ème jour de gestation. Le stress prénatal à un moment ponctuel de la gestation (10ème ou 14ème jour), qu'il soit aigu ou répété n'engendre pas d'effet sur l'anxiété de trait. Par contre, il engendre des effets sur l'anxiété d'état pour les animaux stressés au 10ème jour de façon aigue͏̈ et pour les animaux stressés au 14ème jour de façon répétée. Le stress prénatal entraîne des modifications dans le comportement social des animaux qui semblent moins agressifs ou plus soumis et ceci de façon plus flagrante pour les animaux nés de mères stressées de façon répétée. Toutes ces études montrent bien qu'un stress prénatal appliqué à un jour donné de la gestation influence le développement des fonctions cognitives des jeunes.
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Isner-Horobeti, Marie-Eve. "Comparaison des effets de deux modalités d'entraînement (excentrique vs. Concentrique) sur le muscle squelettique chez le rat jeune et agé : Etude de la fonction mitochondriale." Strasbourg, 2011. http://www.theses.fr/2011STRA6126.
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L’activité physique permet le développement de la performance aérobie en modifiant à la fois la morphologie et le métabolisme musculaires. Parmi les modalités d’entraînement, l’exercice peut se faire en mode concentrique ou excentrique, et ce à différentes intensités. Comparé à l’exercice concentrique classique, l’exercice excentrique permet de développer une puissance musculaire supérieure à moindre coût. Il est clairement établi que la mitochondrie joue un rôle dans les réponses à l’exercice et est une des sources principales de production des radicaux libres, dont les ROS (espèces réactives oxygénées) font partie. A ce jour, peu d’études ont été consacrées aux effets de l’exercice excentrique sur la respiration mitochondriale et la production de ROS. La première partie de ce travail a montré que, in vitro, l’exercice excentrique, n’augmente pas la respiration mitochondriale musculaire, quel que soit le phénotype musculaire, mais augmente la production de ROS. Le dommage musculaire induit par l’exercice excentrique joue un rôle dans l’augmentation des ROS, car un taux trop élevé constitue un facteur délétère pour la biogénèse mitochondriale. La seconde partie de ce travail a montré qu’il n’y a pas de différence pour les capacités oxydatives en réponse à l’entraînement excentrique chez les sujets âgés comparés aux sujets jeunes, suggérant que les phénomènes d’adaptations incluant la fonction mitochondriale n’étaient pas altérés. Dans la dernière partie de ce travail, nous avons montré l’intérêt et la pertinence de l’utilisation de microbiopsies musculaires, moins invasives pour l’Homme, et qui permettent d’obtenir des valeurs de respiration mitochondriale musculaire superposables à celles obtenues avec la technique de Bergström, classiquement utilisée. Ces travaux ont permis de préciser les adaptations mitochondriales après exercice excentrique ainsi que le rôle du dommage musculaire et du stress oxydant dans ce mode de contraction aussi bien chez le sujet jeune que chez le sujet âgéPhysical activity allows the development of aerobic performance by modifying both muscular morphology and metabolism. Among the training modalities, the exercise can be performed in either concentric or eccentric mode, and at various intensities. Compared to concentric training, eccentric training allows reaching at equal intensity a superior muscular strength at a lesser metabolic cost. It has been clearly established that mitochondria plays a role in the responses to exercise and is one of the main sources of production of free radicals, to which the ROS (reactive oxygen species) belong. However, only few studies have been devoted to the effects of eccentric training on mitochondrial respiration and ROS production. The first part of this work has shown that, in vitro, eccentric training, performed at the same mechanical power as concentric exercise, does not increase the muscular mitochondrial respiration, whatever the muscular phenotype, but increases ROS production. The muscular damage induced by eccentric training contributes to ROS enhancement, and yet a too high rate has deleterious effects on mitochondrial biogenesis. The second part of this work has shown that there is no difference for oxidative capacities in response to eccentric training in older subjects compared to younger subjects, suggesting that the adaptation mechanisms including the mitochondrial function were not altered. In the last part of this work, we have shown the interest and the relevance of the use of muscular microbiopsies, less invasive in Humans, and which allow obtaining muscular mitochondrial respiration values superimposable on those obtained with the usually used Bergström technique. These works have allowed clarifying the mitochondrial adaptations following eccentric training, as well as the role of muscular damage and oxidative stress in this contraction modality, in either younger or older subjects
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Ebabe, Elle Etienne Raymond. "Le double aspect des nanoparticules manufacturées sur les métabolismes oxydatifs et inflammatoires : effets délétères et effets protecteurs." Thesis, Montpellier, 2016. http://www.theses.fr/2016MONTT008/document.
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On étudie les effets des nanoparticules (d'argent et de silice) manufacturées sur les métabolismes oxydatifs et inflammatoire. La première partie étudie la toxicité in vivo de l'ingestion de nanoparticules d'argent, pendant 11 semaines, sur un modèle animal - rat Sprague Dawley. Nous y avons mis en évidence l'action toxique des nanoparticules d'argent notamment une hausse de la production d'anion superoxyde par les NADPH oxydases hépatiques et cardiaques, des dyslipidémies, une cytolyse hépatique, une augmentation de cytokines pro-inflammatoires et une tendance à la baisse de l'activité d'enzymes antioxydantes. Ceci nous a conduit à aborder l'étude in vitro, sur des modèles cellulaires intestinaux (Caco-2) et cutanés (HaCaT). Au cours de cette étude, des nanoparticules de silice, fonctionnalisées ou non avec des antioxydants, ont été incubées pendant 24 H en présence des cellules. Nous montrons que la modification de la surface des nanoparticules réduit considérablement leur toxicité en limitant la production d'espèces radicalaires et la mortalité cellulaire. D’autre part, le couplage avec un antioxydant permet d’augmenter la stimulation de voie de signalisation du facteur Nrf2. Cette voie est impliquée dans la protection de l’organisme contre les troubles liés aux espèces radicalaires. En somme, ce travail met en avant les potentialités de la vectorisation d’antioxydants avec des nanoparticules à des fins thérapeutiquesThe purpose of this study is to explore the effects of nanoparticles (silver and silica) manufactured on oxidative and inflammatory metabolism. In the first part of this work, we explored the in vivo toxicity from ingestion of silver nanoparticles, for 11 weeks, in an animal model - Sprague Dawley rat. This enabled us to demonstrate the toxic properties of silver nanoparticles including superoxide anion production by hepatic and cardiac NADPH oxidases, dyslipidemia, hepatic cytolysis, an increase in proinflammatory cytokines and a downward trend the activity of antioxidant enzymes. This led us to address the in vitro study on intestinal cell models (Caco-2) and cutaneous (HaCaT). During this study, silica nanoparticles, functionalized or not with anti-oxidants, were incubated for 24 hours in the presence of the cells. We show that the modification of the surface of the nanoparticles significantly reduces their toxicity limiting the production of free radical species and cell death. Furthermore, the coupling with an anti-oxidant increases the stimulation of Nrf2 factor that involves the protection of the body against disorders associated with radical species. In summary, this work highlights the potential of vectorization of antioxidants with nanoparticles for therapeutic purposes
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Hassan, Sahar. "Etude des effets protecteurs du trans-resvératrol sur les lésions induites par une ischémie-reperfusion hépatique chez le rat." Paris 5, 2008. http://www.theses.fr/2008PA05P617.
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Liver ischemia-reperfusion (IR) occurs in many clinical conditions; including liver surgery and transplantation. Early phase of reprfusion is associated with excessive production of reactive oxygen species and proinflammatory cytokines. We investigated the effects of trans-resveratrol (T-res) (molecule reported to have multiple effects, of wich antioxidant and antiinflammatory properties) on liver injury induced by IR. After 1 hour of ischemia, administered 5 minutes prior to 3 hours of reperfusion, T-res was hepatoprotective at low doses (0. 2 and 0. 02 mg/Kg) by decreasing plasmatic aminotransferase levels and improving sinusoidal dilatation. T-res preserved antioxidant defense by preventing total and reduced glutathion depletion caused by IR. At 0. 2 mg/kg, T-res significantly increased glutathione reductase, Cu/Zn–superoxide dismutase, and catalase activities. We also found that T-res, at low doses (0. 02 and 0. 2 mg/Kg) was able to decrease IL-1β and TNF-α hepatic mRNA expression induced by IR, with a reduction in plasma concentrations of IL-6 and IL-1β. T-res did not modify mRNA and protein expression of NOS III, DDAH activity or plasma concentrations of nitrites. NOSII protein or mRNA were undetected after IR or after T-res treatment. T-res decreased HO1 transcription without altering HSP-70 transcription induced by hepatic IR. In conclusion, a prereperfusion treatment by T-res only at low doses decreases liver injury induced by IR by protecting against antioxidant defense failure and by inhibiting proinflammatory cytokines induction. Our data present T-res as a molecule with potential therapeutic use against lesions secondary to liver surgery or hepatic allograftLiver ischemia-reperfusion (IR) occurs in many clinical conditions; including liver surgery and transplantation. Early phase of reprfusion is associated with excessive production of reactive oxygen species and proinflammatory cytokines. We investigated the effects of trans-resveratrol (T-res) (molecule reported to have multiple effects, of wich antioxidant and antiinflammatory properties) on liver injury induced by IR. After 1 hour of ischemia, administered 5 minutes prior to 3 hours of reperfusion, T-res was hepatoprotective at low doses (0. 2 and 0. 02 mg/Kg) by decreasing plasmatic aminotransferase levels and improving sinusoidal dilatation. T-res preserved antioxidant defense by preventing total and reduced glutathion depletion caused by IR. At 0. 2 mg/kg, T-res significantly increased glutathione reductase, Cu/Zn–superoxide dismutase, and catalase activities. We also found that T-res, at low doses (0. 02 and 0. 2 mg/Kg) was able to decrease IL-1β and TNF-α hepatic mRNA expression induced by IR, with a reduction in plasma concentrations of IL-6 and IL-1β. T-res did not modify mRNA and protein expression of NOS III, DDAH activity or plasma concentrations of nitrites. NOSII protein or mRNA were undetected after IR or after T-res treatment. T-res decreased HO1 transcription without altering HSP-70 transcription induced by hepatic IR. In conclusion, a prereperfusion treatment by T-res only at low doses decreases liver injury induced by IR by protecting against antioxidant defense failure and by inhibiting proinflammatory cytokines induction. Our data present T-res as a molecule with potential therapeutic use against lesions secondary to liver surgery or hepatic allograft
Books on the topic "Rats – Effets du stress sur"
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Treshow, Michael. Plant stress from air pollution. Chichester [England]: Wiley, 1989.
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M, Orcutt David, and Thompson Laura K, eds. The physiology of plants under stress. New York: Wiley, 1987.
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Perrin, Louis F. Le psychisme, le stress et l'immunité: La santé est en nous. Paris: Jacob, 2003.
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Hawkins, Christopher David Borden. SIVE, a new stock quality test: The first approximation. Victoria, B.C: Forestry Canada, 1992.
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Lin, Zhengxi. Les effets des ordinateurs sur le stress au travail, la sécurité d'emploi et l'intérêt que présente le travail au Canada: Rapport final. Hull, Qué: Direction générale de la recherche appliquée, Développement des ressources humaines Canada, 2002.
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Lin, Zhengxi. The effects of computers on workplace stress, job security and work interest in Canada: Final report. [Hull, Quebec]: Applied Research Branch, Human Resources Development Canada, 2002.
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L, Key Joe, Kosuge Tsune, ARCO Plant Cell Research Institute., and University of California, Los Angeles., eds. Cellular and molecular biology of plant stress: Proceedings of an ARCO Plant Cell Research Institute--UCLA symposium held at Keystone, Colorado, April 15-21, 1984. New York: Alan R. Liss, 1985.
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Frank, Pendl, Canada Forestry Canada, British Columbia. Ministry of Forests., Forest Resource Development Agreement (Canada), and Canada/BC Economic & Regional Development Agreement., eds. Plantation performance related to Canadian Fire Weather Index System: 10-year consequence of a time-of-planting study in the coast-interior transition zone. Victoria, B.C: Forestry Canada, 1990.
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Peter, Hall J., North American Forestry Commission. Atmospheric Changes and Forests Study Group., and Canada. Forestry Canada. Science and Sustainable Development Directorate, eds. Health of North American forests. Ottawa: Canadian Forest Service, Science and Sustainable Development Directorate, 1995.
Find full textBook chapters on the topic "Rats – Effets du stress sur"
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Oxenkrug, G. F., and P. J. Requintina. "The effect of MAO-A inhibition and cold-immobilization stress on N-acetylserotonin and melatonin in SHR and WKY rats." In MAO — The Mother of all Amine Oxidases, 333–36. Vienna: Springer Vienna, 1998. http://dx.doi.org/10.1007/978-3-7091-6499-0_35.
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McKechnie, Andrew E. "Physiological and morphological effects of climate change." In Effects of Climate Change on Birds, 120–33. Oxford University Press, 2019. http://dx.doi.org/10.1093/oso/9780198824268.003.0010.
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The direct impacts of higher temperatures on birds are manifested over timescales ranging from minutes and hours to years and decades. Over short timescales, acute exposure to high temperatures can lead to hyperthermia or dehydration, which among arid-zone species occasionally causes catastrophic mortality events. Over intermediate timescales of days to weeks, high temperatures can have chronic sub-lethal effects via body mass loss or reduced nestling growth rates, negatively affecting sev eral fitness components. Long-term effects of warming manifested over years to decades involve declining body mass or changes in appendage size. Key directions for future research include elucidating the role of phenotypic plasticity and epigenetic processes in avian adaptation to climate change, examining the role of stress pathways in mediating responses to heat events, and understanding the consequences of higher temperatures for species that traverse hot regions while migrating.
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"Nutrients in Salmonid Ecosystems: Sustaining Production and Biodiversity." In Nutrients in Salmonid Ecosystems: Sustaining Production and Biodiversity, edited by Megan S. Sterling and Kenneth I. Ashley. American Fisheries Society, 2003. http://dx.doi.org/10.47886/9781888569445.ch17.
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<em>Abstract.</em>—A solid briquette fertilizer for use in the Pacific Northwest streams and elsewhere was identified from a variety of slow-release formulations (26 were tested with varying N:P<sub>2</sub>O<sub>5</sub>:K<sub>2</sub>O ratios and binders) using indoor trough and controlled field experiments. The use of a slow-release fertilizer is an innovative method for adding inorganic nutrients to nutrientpoor (oligotrophic) streams to increase autotrophic production and aid in the restoration of salmonid populations. A series of indoor trough experiments demonstrated that the majority of samples containing binders of molasses, hydrated lime, vegetable oil, bentonite, starch, acrawax, candle wax, and Daratak® XB-3631 (unpolymerized Saran™) dissolved too slowly. The fastest dissolution rates occurred with fertilizer briquettes having no binder or vegetable oil. Further trough and field studies using fertilizer with no binder and vegetable oil as binder examined the effects of varying N:P<sub>2</sub>O<sub>5</sub>:K<sub>2</sub>O ratios. Dissolution rates were varied by using different percentages of magnesium ammonium phosphate (MagAmP; its formula 7:40:0 N:P<sub>2</sub>O<sub>5</sub>:K<sub>2</sub>O) and urea (46:0:0). Optimal continual nutrient release for a period of four months was achieved with a fertilizer formulation of 17:30:0 (percent by weight N:P<sub>2</sub>O<sub>5</sub>:K<sub>2</sub>O), with a ratio of 75% MagAmP to 25% urea, and containing no binder. The dissolution rate for this product ranged from 4.6% to 6.6% per week (for field and trough experiments, respectively) in water of 0.15 m/s average velocity. These studies indicate that a slow-release fertilizer product can be manufactured to last approximately four months when applied in the spring to stimulate autotrophic production in nutrient deficient streams, thereby increasing forage and salmonid production.
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Smith, Robert B., and Lee J. Siegel. "The Broken Earth: Why the Tetons Are Grand." In Windows into the Earth. Oxford University Press, 2000. http://dx.doi.org/10.1093/oso/9780195105964.003.0009.
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On a summer morning when the breeze blows cool, it is easy to re the lakes and sagebrush-covered glacial plains of Wyoming’s Jackson Hole sit at nearly 7,000 feet elevation. Yet the altitude of this gorgeous valley is diminished by the view to the west: The precipitous east front of the Teton Range towers above the valley floor, with 13,770-foot Grand Teton and other rugged, snowclad peaks catching the first golden rays of daybreak. This is one of the most spectacular mountain vistas in America. Whether at chill dawn, in glistening light after a torrential afternoon thunderstorm, or during summer evenings when the sun descends behind the lagged Tetons, it is a view that brings solace and peace. Yet the serene splendor of Grand Teton National Park belies a hidden fury. It is not volcanism, which is concealed beneath the gentle pine-covered Yellowstone Plateau to the north. Instead, this defiant topography was born of seismic disaster as the Teton fault repeatedly and violently broke the earth, producing a few thousand magnitude-7 to -7.5 earthquakes during the past 13 million years. During each major jolt, Jackson Hole dropped downward and the Teton Range rose upward, increasing the vertical distance between the valley and the mountains by 3 to 6 feet and sometimes more. Now, after 13 million years of earthquakes, the tallest peaks tower almost 7,000 feet above the valley floor. Actual movement on the fault has been even greater. Jackson Hole dropped downward perhaps 16,000 feet during all those earthquakes. Rock eroded from the Teton Range and other mountains by streams and glaciers filled Jackson Hole with thousands of feet of sediment, disguising how much the valley sank. Combine the uplift of the mountains and the sinking of Jackson Hole, and the best estimate—although still plagued by uncertainty—is that movement on the Teton fault has totaled 23,000 feet during the past 13 million years. That is a tiny fraction of Earth’s 4.6-billion-year history. Consider the effects of repeated episodes of mountain-building during eons before the Teton fault was born: The oldest rocks high in the Teton Range are 2.8-billion-year-old gneisses and schists and 2.4-billion-year-old granites.
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Agrawal, Ravi. "Big Brothers: Internet Shutdowns and Internet.org." In India Connected. Oxford University Press, 2019. http://dx.doi.org/10.1093/oso/9780190858650.003.0013.
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The rat-a-tat of automatic gunfire burst through the morning air in Anantnag. For the locals of this troubled district in the south of Kashmir, it came as a shock but no longer a surprise. Separatist militants had once again clashed with army forces. Several civilians were caught in the crossfire. One died; three others were wounded. It was Saturday, July 1, 2017. Hours earlier, at midnight, India had adopted a new national sales tax, designed to stitch the country’s twentynine states together into one economic union. The new system—known as the Goods and Services Tax, or GST—was heralded as an economic reform that would spur growth, enlarge the tax base, and make it easier to do business. Kashmir was the only state still debating whether to join. It was a symbolic outlier. Some distance from the gunfire, sixteen-year-old Zeyan Shafiq was just waking up. He hadn’t heard the shooting; his home was well insulated. When he opened his eyes, he told me, the first thing he did was to reach for his iPhone. He looked at the screen and sighed. The wireless internet at home was down. So was mobile data. Shafiq got out of bed, put on his slippers, and shuffled toward the front door, where he knew he would have a stronger mobile signal. No luck. He couldn’t catch the internet. Shafiq looked up at the skies, opened his lungs, and let out a bellow of frustration. For Shafiq, it was easy to guess what had happened. There must have been what locals called an encounter—a skirmish between Kashmiri separatists and the state. These days, encounters were inevitably followed by the government shutting down the internet. The digital blackouts weren’t aimed at stopping separatists or terrorists from communicating. They were usually already dead. The shutdowns were to prevent people from sharing videos and photos of the violence on social media. In effect, 13 million Kashmiris were collateral damage, unable to do something as simple as check email. There was a time when curfews were merely physical, imposed with barbed wire, barriers, and troops on the streets.
Conference papers on the topic "Rats – Effets du stress sur"
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Rombado, Gabriel, David A. Baker, Lars M. Haldorsen, Pedro Craidy, Jim H. Feiger, and Stephen J. Hudak. "Corrosion-Fatigue Crack Growth Performance of Titanium Grade 29 Welds in Tapered Stress Joints." In ASME 2019 38th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/omae2019-95175.
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Abstract Design of steel catenary risers (SCRs) requires the use of connection hardware to decouple the large bending moments induced by the host floater at the hang-off location. Reliability of this connection hardware is imperative, especially in those applications involving high pressure and temperature fluids. One option for connection hardware is the metallic tapered stress joint. Because of its inherent density, strength and stiffness, steel is not well suited for these applications as it would result it excessive length and weight for deepwater applications. Titanium grade 29 (Ti 29) has been identified as an attractive material candidate for demanding stress joint applications due to its unique mechanical properties including greater flexibility, excellent fatigue performance, and high resistance to sour fluids. Industry has successfully used this technology in over 60 SCR applications. Titanium stress joints (TSJs) for deep-water applications are typically not fabricated as a single piece due to titanium ingot/billet volume limitations, thus making an intermediate girth weld necessary to satisfy length requirements. Fracture and fatigue performance of these welds in the presence of cathodic potential in seawater and galvanic potentials in sour production fluids that may produce hydrogen embrittlement effects must be assessed to ensure long term weld integrity. This paper describes a joint industry project (JIP) performed to qualify titanium stress joints welds for ultra-deep water applications under harsh service and environmental conditions. Fatigue crack growth rate (FCGR) results for Ti 29 1G/PA gas tungsten arc welding (GTAW) specimens in air, seawater under cathodic potential and sour brine environments under galvanic potentials are presented and compared to vendor recommended design curves.
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Bahrami, Amir, Yanhui Zhang, and Peter Tubby. "Effects of Microstructure and Hydrogen Charging on Fatigue Performance of Duplex and Superduplex Stainless Steels." In ASME 2011 30th International Conference on Ocean, Offshore and Arctic Engineering. ASMEDC, 2011. http://dx.doi.org/10.1115/omae2011-49130.
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Steel Catenary Risers (SCRs) are a viable solution for production and export of offshore hydrocarbons in many deepwater developments. In addition to exposure to seawater from the outside, the pipes and their girth welds in an SCR are often exposed to aggressive environments on the inside surfaces due to the produced fluids. The fatigue life of pipe girth welds in aggressive environments is dependent on the material-environment interactions. Duplex and superduplex stainless steels are particularly good candidate materials for construction of corrosion resistant steel centenary risers. However, these steels have shown susceptibility to hydrogen induced stress cracking (HISC) when in seawater and under cathodic protection (CP). In addition there is very little published knowledge related to their sour service performance under fatigue loading. This paper provides new fatigue endurance data for superduplex riser girth welds tested in air, seawater with CP and sour environment. It further compares the fatigue crack growth rate (FCGR) in the same welded material in air and sour environment. Finally preliminary results of investigations made on the effect of frequency, microstructure and grain coarseness on FCGR in parent superduplex and duplex materials in seawater and under cathodic protection are presented.
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Miyachika, Kouitsu, Satoshi Oda, and Hiroshige Fujio. "Effect of Gear-Side Case-Hardening on Residual Stresses of Case-Hardened Gears." In ASME 2000 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2000. http://dx.doi.org/10.1115/detc2000/ptg-14385.
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Abstract This paper presents a study on effects of the case depth, the case-hardened part, the face width, the rim thickness and the standard pressure angle on residual stresses of case-hardened gears. A heat conduction analysis and an elastic-plastic stress analysis for the case-hardening process of spur gears were carried out by the three-dimensional finite-element method (3D-FEM), and then residual stresses were obtained. It was found that the compressive residual stress σ*θ = 30° at Hofer’s critical section of the end of the face width is smaller in magnitude than that of the middle of the face width, and that the absolute value of σ*θ = 30° of the middle of the face width decreases owing to case-hardening the gear-side and the decreasing rate increases with an increasing case depth and a decreasing face width.
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Safari, Javad, Ramgopal Thodla, Ian Merchant, and John Hamilton. "Fatigue Crack Growth Rate of Reeled Pipe in Sour Environments." In ASME 2015 34th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/omae2015-41028.
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Fatigue Crack Growth Rate (FCGR) of reeled pipe (strained & aged) in sour environments was investigated. FCGR frequency scans on different microstructures, i.e. heat affected zone (HAZ), and weld center line (WCL), revealed that, FCGR in corrosive environments increased with decreasing frequency and reached a plateau value at low frequencies of 10mHz to 3mHz. At these ‘plateau frequencies’, FCGR in the moderately sour environment that was investigated were found to be about 10–18× or 30× higher than the in-air values for the WCL and HAZ, respectively. There was no effect of the reeling cycles on the FCGR of the WCL or HAZ specimens. The FCGRs of the WCL were consistently lower than that of the HAZ by about a factor of 2–3× under various conditions. The reason for the lower FCGR of the WCL is not well understood. It is possible that it may be due to the higher yield strength (YS) of the overmatched welds, differing hydrogen concentration and/or diffusion coefficient or possibly due to the differences in the microstructure between the HAZ and WCL. Paris law curves, FCGRs as a function of ΔK (stress intensity factor range), were measured on the HAZ, and WCL (both intrados) at the plateau frequency (10mHz), representative of flowline cyclic loading. They were also measured at a higher frequency of 0.33Hz, representative of Steel Catenary Risers (SCR) cyclic loading associated with wave motion. Comparisons of measured Paris law curves in corrosive environments to those in air were consistent with the results of the frequency scans. There was no effect of number of cycles of reeling on the Paris law curves in the sour environment tested for WCL and HAZ specimens at both the plateau frequency and 0.33Hz. The results of the test program suggest FCGR of WCL and HAZ in the sour environment tested are not affected by number of cycles (up to 5) of straining on the intrados side for the strain level (1.93% per cycle) used in this study.
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Rawlings, A. L. K., A. J. Birnbaum, J. G. Michopoulos, J. C. Steuben, A. P. Iliopoulos, and H. Ryou. "Simulation Informed Effects of Solidification Rate on 316L Single Tracks Produced by Selective Laser Melting." In ASME 2020 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/detc2020-22451.
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Abstract The formation of sub-grain cellular structures generated during the rapid solidification associated with selective laser melting (SLM) typically yields enhanced mechanical properties in terms of yield stress without considerable loss in ductility when compared with those of wrought material. The extent to which the sub-grain structure appears under standard metallographic preparation shows dependence on multiple systematic conditions. This study identifies the effects of solidification and cooling rate on the grain and sub-grain structure in stainless steel through varying the processing parameters (laser power, scan velocity and spot size) of single tracks on both as-received, small grain and annealed, giant grain substrates. The process parameters, in conjunction with the initial substrate microstructure, are key components in understanding the resulting microstructure. Process parameters, particularly scan velocity, dictate the solidification rate and primary regrowth directions while the initial microstructure and its thermomechanical history dictate the propensity for stored strain energy density. Modeling the thermal process allows for experimental analysis within the context of predicted location within processing space as it pertains to local interface velocity and temperature gradient. Furthermore, it highlights the fact that this specific material system behaves in a manner that is inconsistent with classical solidification theory.
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Jeong, Jae-Ho, Jin Yoo, Kwi-Lim Lee, and Kwi-Seok Ha. "Investigation of Wire Effect in a Wire-Wrapped 37-Pin Fuel Assembly." In ASME/JSME/KSME 2015 Joint Fluids Engineering Conference. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/ajkfluids2015-09805.
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The wire effect in a wire-wrapped 37-pin fuel assembly mock-up of a Japanese loop-type sodium-cooled fast reactor (SFR), Monju, has been investigated through a numerical analysis using a general-purpose commercial computational fluid dynamics (CFD) code, CFX. Complicated and vortical flow phenomena in the wire-wrapped 37-pin fuel assembly were captured by a Reynolds-Averaged Navier-Stokes (RANS) flow simulation with a shear stress transport (SST) turbulence model. The CFD results show good agreement with Rehme’s friction factor correlation model, which can consider the number of wire-wrapped pins in the fuel assembly. Three-dimensional multi-scale vortex structures start to be formed by an interaction between secondary flows around each wire-wrapped pin. Large-scale and small-scale vortex structures are generated in the corner and edge, and interior sub-channel, respectively. The behavior of the large-scale vortex structures in the corner and edge sub-channel are closely related to the relative position between the hexagonal duct wall and the wire spacer. Regardless of the relative position between the adjacent rod and wire spacer, a small-scale vortex is axially developed in the interior sub-channels. Furthermore, a driving force on each wire spacer surface is closely related to the relative position between the hexagonal duct wall and wire spacer. It is expected that the multi-scale vortex structures in the fuel assembly play a significant role in the convective heat transfer characteristics.
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Hammond, R. I., and D. P. Baxter. "Corrosion Fatigue of Simulated C-Mn Steel HAZs in Sour Produced Fluids." In ASME 2008 27th International Conference on Offshore Mechanics and Arctic Engineering. ASMEDC, 2008. http://dx.doi.org/10.1115/omae2008-57149.
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Steel Catenary Risers are subjected to both fatigue loading (from waves and tides) and corrosive environments (internal and external). The financial benefit of using C-Mn steels for SCRs is significant, therefore there is a need to establish the limitations of the material. These limitations are likely to be controlled by the HAZ, as HAZ microstructures are typically more susceptible than parent steel to cracking during exposure to a sour environment, especially if they have high hardness. Samples of API 5L X65 line pipe steel were heat treated to provide materials exhibiting two microstructures comparable to those seen in girth weld HAZs with two levels of hardness. Fatigue tests were then performed in a sour environment to determine the influence of microstructure, frequency and crack depth on the observed crack growth rate. Tests were performed using a ‘frequency scanning’ technique which involved maintaining a constant ΔK by continually monitoring and shedding the applied load range as crack length increased during the test. Frequency was varied in the range 10–0.01Hz. As there was a concern that the effect of frequency might be masked by an effect of crack depth, a second series of tests was also carried out on each microstructure to explicitly investigate the effect of this latter variable. A stress ratio of 0.5 was used to ensure a relatively high mean stress, to simulate the presence of a tensile residual stress. Test data suggested that harder material exhibited a higher fatigue crack growth rate in the sour environment, and that frequency had only a small effect over the range examined. A second series of tests suggested that crack growth rate was independent of crack depth for crack depths greater than 6mm, although there was some evidence that for shallower flaws the crack growth rate may be higher. It is suggested that when performing fracture mechanics calculations using fatigue crack growth rate data, it is important to ensure that the latter are associated with tests performed on material exhibiting a comparable microstructure to the component being modelled. For relatively shallow flaws it may be the case that crack growth rates in a sour environment are higher (for a given ΔK) than for longer flaws. It should therefore be recognised that in certain applications, defect assessments which use crack growth rate data derived from tests using deeply-cracked specimens may result in non-conservative life predictions.
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Lu, Baotong, Stephen J. Hudak, and Carl F. Popelar. "Role of Crack Closure in Crack-Size-Dependent Corrosion-Fatigue Crack Growth of X65 Steel Exposed to Sour Brine Environment." In ASME 2018 37th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/omae2018-77002.
Full textAbstract:
Corrosion-fatigue in sour brine (SB) environments is a significant design consideration in deepwater floating production systems. Extensive testing over the past 20 years has shown that sour brine environments can reduce the fatigue life of line pipe steels by factors of 10× to 50× compared to fatigue lives measured in laboratory air; moreover, the extent of material degradation depends on a multitude of loading, environmental, and materials variables. Thus, in 2010 Southwest Research Institute (SwRI) embarked on an industry-supported Joint Industry Project (JIP) to develop a quantitative model to predict the effects of these variables on corrosion-fatigue crack growth rate (CFCGR) in offshore structure steels exposed to sour brine environments. Phase 1 of this JIP had successfully developed and validated such a model in the intermediate fatigue crack growth rate regime — i.e., with CFCGRs between 10−4 ∼ 10−2 mm/cycle. However, the Phase 1 model gave overly conservative CFCGRs at rates in the low growth rate regime below 1 × 10−4 mm/cycle, corresponding to S-N corrosion-fatigue lives in the high-cycle fatigue regime. It was hypothesized that these conservative predictions might result from the fact that the model did not consider effects of crack closure that could significantly reduce the effective crack-driving force in this low growth rate regime, a process that might also give rise to crack-size effects. Thus, the primary objective of the current study was to assess whether or not crack closure is responsible for the conservativism in the Phase 1 CFCGR model, as well as to explore related crack-size effects that in theory would not be predictable with conventional linear elastic fracture mechanics. Both of these possible effects are explored here using critical CFCGR experiments on X65 steel in sour brine under loading conditions for which the nominally applied mechanical driving force (ΔK), as well as the stress ratio (Rσ) and loading frequency were held constant, while crack closure measurements were made as the crack grew from 2 mm to about 10 mm. The crack closure measurements were made using elastic compliance measurements made with a specially designed, high-sensitivity clip gage. Results indicate that a crack-size dependence of CFCGR did occur and could be correlated using a crack-closure-corrected effective stress intensity factor (ΔKeff). These results have provided a foundation for extending the JIP’s Phase 1 CFCGR model into the low growth rate regime in the ongoing Phase 2 of the JIP.
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Prabhakaran, Ramprashad, and Ajit K. Roy. "The Effect of Environmental and Mechanical Variables on Stress Corrosion Cracking of a Martensitic Stainless Steel for Transmutation Applications." In 12th International Conference on Nuclear Engineering. ASMEDC, 2004. http://dx.doi.org/10.1115/icone12-49399.
Full textAbstract:
Extensive work has been performed on Type 422 stainless steel (SS), to characterize environment-induced degradations in aqueous environments of different pH values at ambient and elevated temperatures. The test material was thermally treated prior to the evaluation of stress-corrosion-cracking (SCC) behavior by slow-strain-rate (SSR) and constant-load (CL) testing techniques, using smooth and notched tensile specimens. Cyclic potentiodynamic polarization (CPP) testing was performed to evaluate localized corrosion behavior using a three-electrode polarization technique in similar environments. Fractographic and metallographic evaluations of broken specimens were also performed by scanning electron microscope (SEM) and optical microscope, respectively.
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Sura, Venkata S., and Sankaran Mahadevan. "Vertical Split Rim Failure Analysis in Railroad Wheels." In 2010 Joint Rail Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/jrc2010-36024.
Full textAbstract:
Vertical split rim cracking, rapid unstable propagation of a sub-surface crack parallel to the front rim face, is one of the dominant railroad wheel failure types observed in North America. Wheel impact load is believed to be a trigger for this unstable crack growth. This rapid crack growth rate depends on several factors, such as wheel geometry (wheel diameter and rim thickness), load magnitude, load location, residual stresses in the rim, worn tread profile, and material defects in the rim (size, shape, location, and orientation). This paper investigates the effect of these parameters on vertical split rim cracking, using finite element analysis and fracture mechanics. Vertical split rim cracking is modeled using a three-dimensional, multiresolution, elastic-plastic finite element analysis. Material defects are modeled as mathematically sharp cracks. Wheel impacts are simulated by applying a high axle load on the tread surface. The residual stress and wheel wear effects are also included in modeling vertical split rim cracking.