271 resultados para Involution logistique


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Pós-graduação em Geografia - FCT

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La régression logistique est un modèle de régression linéaire généralisée (GLM) utilisé pour des variables à expliquer binaires. Le modèle cherche à estimer la probabilité de succès de cette variable par la linéarisation de variables explicatives. Lorsque l’objectif est d’estimer le plus précisément l’impact de différents incitatifs d’une campagne marketing (coefficients de la régression logistique), l’identification de la méthode d’estimation la plus précise est recherchée. Nous comparons, avec la méthode MCMC d’échantillonnage par tranche, différentes densités a priori spécifiées selon différents types de densités, paramètres de centralité et paramètres d’échelle. Ces comparaisons sont appliquées sur des échantillons de différentes tailles et générées par différentes probabilités de succès. L’estimateur du maximum de vraisemblance, la méthode de Gelman et celle de Genkin viennent compléter le comparatif. Nos résultats démontrent que trois méthodes d’estimations obtiennent des estimations qui sont globalement plus précises pour les coefficients de la régression logistique : la méthode MCMC d’échantillonnage par tranche avec une densité a priori normale centrée en 0 de variance 3,125, la méthode MCMC d’échantillonnage par tranche avec une densité Student à 3 degrés de liberté aussi centrée en 0 de variance 3,125 ainsi que la méthode de Gelman avec une densité Cauchy centrée en 0 de paramètre d’échelle 2,5.

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This study aimed to evaluate the effect of chloprostenol administration, at early or intermediary puerperium, under uterine involution, intrauterine fluid accumulation and ovarian activity return. 30 Murrah postpartum buffaloes were randomly divided into three groups: CONT (saline, n = 10); CLO2 (chloprostenol at days 2 and 5 postpartum, n = 10) and; CLO15 (chloprostenol at days 15 and 20 postpartum, n = 10). Gynecological exams were performed at days 2, 7, 14, 21 and 28 postpartum, when uterine involution degree (1 to 3 scale, by transrectal palpation), intrauterine fluid accumulation (0 to 3 scale, by ultrasound exam) and ovarian activity (B-mode ultrasound exam) were evaluated. CLO2 group presented higher uterine involution (2.00 +/- 0.23, 1.66 +/- 0.23, 1.58 +/- 0.23 for groups CLO2, CONT and CLO15, respectively) and faster ovarian activity return in relation to groups CONT and CLO15 (P < 0.05). Groups CLO2 and CLO15 showed lower intrauterine fluid accumulation compared to CONT group (2.04 +/- 0.20, 1.58 +/- 0.20, 1.92 +/- 0.20 for groups CONT, CLO2 and CLO15, respectively; P < 0.05). Prostaglandin analogue administration in postpartum buffalo benefited uterine involution, lochia expulsion and ovarian activity return, improving reproductive efficiency in this specie.

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Let D be a division ring with center k, and let D-dagger be its multiplicative group. We investigate the existence of free groups in D-dagger, and free algebras and free group algebras in D. We also go through the case when D has an involution * and consider the existence of free symmetric and unitary pairs in D-dagger.

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Background: The bovine yolk sac derives from visceral endoderm and its development occurs between days 18-23 of gestation. The study of this membrane is important for comparative data and has already been performed in rodents, sheep and in cattle, especially Bos taunts. In species Bos indicus the yolk sac has not quite been studied and is believed that there are morphological differences between these species. The yolk sac undergoes a process of involution and degeneration during embryonic development and none vestige of it is found in late gestation. The period in which occurs the involution of the yolk sac coincides with the period of increased pregnancy loss in cattle, and changes in the morphology of this membrane may indicate the reasons for such high loss rates. Thus, considering that the yolk sac is important for embryonic circulation and metabolic transmission, besides participating actively in the process of cattle placentation, this study aimed characterize morphologically the involution of the bovine yolk sac. Materials, Methods & Results: The early gestational period was determined between days 20 and 70 post-insemination (p.i), according to the exterior characteristics of embryo/fetus. For macroscopic analyzes the uterus was dissected to expose the fetal membranes and subsequently the embryo/fetus was photographed. The samples were fixed for light microscopy and transmission electron microscopy. The yolk sac that emerges from the ventral part of the embryo was prominent and composed by a central part with two thin peripheral projections of different lengths. The bovine yolk sac with about 9 cm on day 25 p. i. of pregnancy permanently decreased its total length during this study. Histologically, the yolk sac is composed of three cell layers: the mesothelium, the mesenchyme and the endoderm. In mesenchyme are found blood islets. In the endoderm are formed cells invaginations toward the mesenchyme originating small canaliculi. The ultrastructure of yolk cells presented many mitochondria, rough endoplasmic reticulum, vesicles, euchromatin and the presence of two nucleoli, Discussion: The real first blood circulation in the bovine is attached with the development of yolk sac, differently from other membranes, such as the corium, that does not present evidence of vascularization by the age of 20-30 days. The erythroblasts found in the yolk sac are related to vasculogenesis and the process of differentiation of blood cells during the erythropoiesis. It could be observed on the histology of the yolk sac, in embryos of 30-50 days old, the presence of canaliculi and small folds of the epithelium. The canaliculi collapse is associated with the degeneration of the endoderm wall of the yolk sac. The organelles present in the endoderm cells of the yolk sac are associated with the function of protein metabolism and in the exchange of substances between the mesenchyme and the mesothelium, For these findings, could be observed that the yolk sac epithelium is found active until the 50th day of gestation, and thereafter regresses. However, remnants of this membrane may be present until the 70th day, These features may represent a presence of an active chorionvitelline placenta in this period responsible for the maintenance of pregnancy whereas the chorioallantoic placenta is not definitively established.

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OBJECTIVE: The purpose of this study was to evaluate whether there is a relationship between the sonographic fetal thymus size and the presence of an intrauterine infection in patients with preterm labor. STUDY DESIGN: Thirty-one women who had been admitted with preterm labor and intact membranes between 24 and 32 weeks of gestation were included. Fetal thymus perimeter was measured sonographically, and amniocentesis for the microbiologic assessment of the amniotic cavity was performed. Placentas and umbilical cords were examined for the presence of chorioamnionitis/funisitis. RESULTS: The prevalence of preterm delivery and intra-amniotic infection was 51.6% (16/31 women) and 32.3% (10/31 women), respectively. In all cases with intrauterine infection and in 23.8% of cases without intrauterine infection, the fetal thymus perimeter was below the 5th percentile for gestational age (10/10 women vs 5/21 women; P < .01). Isolated histologic chorioamnionitis and funisitis were found in 22.6% and 25.8% of fetuses, respectively. The fetal thymus was below the 5th percentile for gestational age in 100%, 71.4%, and 12.5% of patients with histologic signs of funisitis and isolated chorioamnionitis and without histologic signs of infection, respectively. CONCLUSION: Fetal thymus involution in preterm labor patients is strongly associated with funisitis, which is the histologic manifestation of the fetal inflammatory response syndrome.

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Activated lymphocytes and lymphoid-tissue inducer cells express lymphotoxins (LTs), which are essential for the organogenesis and maintenance of lymphoreticular microenvironments. Here we describe that T-cell-restricted overexpression of LT induces fulminant thymic involution. This phenotype was prevented by ablation of the LT receptors tumor necrosis factor receptor (TNFR) 1 or LT beta receptor (LTbetaR), representing two non-redundant pathways. Multiple lines of transgenic Ltalphabeta and Ltalpha mice show such a phenotype, which was not observed on overexpression of LTbeta alone. Reciprocal bone marrow transfers between LT-overexpressing and receptor-ablated mice show that involution was not due to a T cell-autonomous defect but was triggered by TNFR1 and LTbetaR signaling to radioresistant stromal cells. Thymic involution was partially prevented by the removal of one allele of LTbetaR but not of TNFR1, establishing a hierarchy in these signaling events. Infection with the lymphocytic choriomeningitis virus triggered a similar thymic pathology in wt, but not in Tnfr1(-/-) mice. These mice displayed elevated TNFalpha in both thymus and plasma, as well as increased LTs on both CD8(+) and CD4(-)CD8(-) thymocytes. These findings suggest that enhanced T cell-derived LT expression helps to control the physiological size of the thymic stroma and accelerates its involution via TNFR1/LTbetaR signaling in pathological conditions and possibly also in normal aging.

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The contribution of recent thymic emigrants (RTEs) to the peripheral naïve T cell population is necessary to maintain diversity of the T cell receptor (TCR) repertoire and produce immune responses against newly encountered antigens. The thymus involutes with age, after irradiation or chemotherapy, and due to severe viral infections. Thymus involution results in decreased thymopoiesis and RTE output leading to a reduced diversity of peripheral T cells. This increases susceptibility to disease and impairs immune responsiveness to vaccines. Therefore, studies aimed at maintaining or regenerating thymic function are integral for maintaining and restoring peripheral TCR diversity. Mice that express a K5.CyclinD1 transgene expression have a severely hyperplastic thymus that fails to undergo involution. Both thymocyte and TEC development appear normal in these mice. We have used the K5.CyclinD1 transgenic model to test the hypothesis that preventing thymus involution will sustain RTE output and incorporation into the peripheral T cell pool to prevent naïve T cell depletion with age. The K5.CyclinD1 transgene was crossed to the RAG2p-GFP transgenic model so that RTEs could be tracked by the intensity of the GFP signal. The frequency and number of RTEs in naïve CD4 splenic T cells was analyzed at monthly intervals to 5 months of age. Using this double transgenic approach, we determined that preventing thymus involution does maintain or enhance the number of RTEs in the peripheral T cell pool before and after thymus involution.

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In Drosophila, the chromosomal region 75C1–2 contains at least three genes, reaper (rpr), head involution defective (hid), and grim, that have important functions in the activation of programmed cell death. To better understand how cells are killed by these genes, we have utilized a well defined set of embryonic central nervous system midline cells that normally exhibit a specific pattern of glial cell death. In this study we show that both rpr and hid are expressed in dying midline cells and that the normal pattern of midline cell death requires the function of multiple genes in the 75C1–2 interval. We also utilized the P[UAS]/P[Gal4] system to target expression of rpr and hid to midline cells. Targeted expression of rpr or hid alone was not sufficient to induce ectopic midline cell death. However, expression of both rpr and hid together rapidly induced ectopic midline cell death that resulted in axon scaffold defects characteristic of mutants with abnormal midline cell development. Midline-targeted expression of the baculovirus p35 protein, a caspase inhibitor, blocked both normal and ectopic rpr- and hid-induced cell death. Taken together, our results suggest that rpr and hid are expressed together and cooperate to induce programmed cell death during development of the central nervous system midline.

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Mode of access: Internet.

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Mode of access: Internet.

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Lebenslauf.