3 research outputs found
Ablation des matériaux carbonés (lien entre la nanotexturation et la réactivité)
La problématique énoncée par l utilisation de matériaux composites C/C denses implique la connaissance et la maîtrise des processus de dégradation auxquels ils sont soumis. L utilisation de moyens de caractérisation in-situ de ces voies de dégradation constitue alors un atout considérable pour leur anticipation. Ainsi, l utilisation de la MEBE en Température associée à une caractérisation cristallographique par MET et une confrontation ex-situ par Analyse thermogravimétrique a abouti à l obtention de lois cinétiques caractérisant la propagation de l oxydation dans toutes les directions de l espace. A la suite de cette étape expérimentale, une approche numérique basée sur l utilisation d algorithmes de Monte-Carlo Cinétique, a alors été mise en place pour modéliser ces observations tant sur le plan atomique avec la modélisation de la loi cinétique d oxydation linéique, que meso et macroscopique par la simulation de la loi cinétique de perte de masse dans le cas particulier du HOPG.The problem stated by the use of composites C / C dense implies knowledge and control of degradation processes to which they are subjected. The use of in-situ characterization of these means of degradation pathways then is a considerable asset for their advance. Thus, the use of ESEM in temperature associated with a crystallographic characterization by TEM and ex situ confrontation by thermogravimetric analysis resulted in obtaining kinetic laws characterizing the propagation of oxidation in all directions. Following this experimental stage, a numerical approach based on the use of algorithms Kinetic Monte-Carlo, was then introduced to model these observations both at the atomic level with the modeling of the oxidation kinetics law linear, as meso-and macro-simulation by the kinetic law of mass loss in the case of HOPG.BORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF
STS-40 descent BET products: Development and results
Descent Best Estimate Trajectory (BET) Data were generated for the final Orbiter Experiments Flight, STS-40. This report discusses the actual development of these post-flight products: the inertial BET, the Extended BET, and the Aerodynamic BET. Summary results are also included. The inertial BET was determined based on processing Tracking and Data Relay Satellite (TDRSS) coherent Doppler data in conjunction with observations from eleven C-band stations, to include data from the Kwajalein Atoll and the usual California coastal radars, as well as data from five cinetheodolite cameras in the vicinity of the runways at EAFB. The anchor epoch utilized for the trajectory reconstruction was 53,904 Greenwich Mean Time (GMT) seconds which corresponds to an altitude at epoch of approximately 708 kft. Atmospheric data to enable development of an Extended BET for this mission were upsurped from the JSC operational post-flight BET. These data were evaluated based on Space Shuttle-derived considerations as well as model comparisons. The Aerodynamic BET includes configuration information, final mass properties, and both flight-determined and predicted aerodynamic performance estimates. The predicted data were based on the final pre-operational databook, updated to include flight determined incrementals based on an earlier ensemble of flights. Aerodynamic performance comparisons are presented and correlated versus statistical results based on twenty-two previous missions
Statistical methods for the selection of differentially expressed genes from DNA array data : application to the analysis of the gene expression induced in sugarcane by phosphate deficiency
Orientador: Marcelo Menossi Teixeira, Aluisio de Souza PinheiroTese (doutorado) - Universidade Estadual de Campinas, Instituto de BiologiaResumo: Arranjos de DNA são uma poderosa técnica de monitoramento da expressão gênica em larga escala. No entanto, a grande quantidade de dados gerados com esse tipo de experimento requer um tratamento estatÃstico adequado à s suas caracterÃsticas. Uma aplicação importante dos arranjos de DNA é a identificação de genes diferencialmente expressos em diferentes amostras de RNA. Essa seleção demanda testes estatÃsticos apurados, capazes de distinguir, entre o grande número de genes usualmente presentes nos arranjos, aqueles cuja
expressão é significativamente diferenciada. Neste trabalho nós desenvolvemos algoritmos para a análise estatÃstica dos dados provenientes de arranjos de DNA, eficientes em lidar com os problemas usuais nesse tipo de dados, como o número limitado de réplicas. Aplicados a dados simulados, os algoritmos desenvolvidos mostraram-se competitivos com outros métodos de análises descritos na literatura, superando-os em algumas situações. A aplicação desses algoritmos foi também demonstrada em um experimento voltado à identificação de genes de cana-deaçúcar diferencialmente expressos em resposta a deficiência de fosfato. O fósforo é um macronutriente essencial, captado pelas plantas principalmente na forma de fosfato inorgânico (Pi). A deficiência de fosfato é freqüente na natureza, especialmente nos solos ácidos das regiões tropicais e subtropicais. Devido a grande importância econômica da cana-de-açúcar, a identificação de genes diferencialmente expressos em resposta à deficiência de fosfato nesta espécie é de grande interesse cientÃfico e agronômico. Algoritmos de agrupamento foram também aplicados aos dados de expressão obtidos no experimento, identificando padrões de expressão gênica nos diferentes estágios da resposta da cana a esse estresse e proporcionando assim uma caracterização adicional da mesma. Futuramente, os resultados desse trabalho podem conduzir ao desenvolvimento de linhagens de cana-de-açúcar com melhor desempenho em solos pobres de fosfato, o que seria de extremo interesse agronômicoAbstract: DNA arrays are a powerful technique for monitoring gene expression in large scale. However, the great amount of data generated by this kind of experiment requires a statistical treatment adequate to its characteristics. An important application of DNA arrays is the identification of differentially expressed genes in different RNA samples. This selection demands refined statistical tests, able of distinguish among the great number of genes usually present in the arrays those which expression is significantly different. In this work, we have developed algorithms for the analysis of DNA array data, efficient in handling the usual problems in this kind of data, as the limited number of replicates. When applied to data simulations the developed algorithms showed to be competitive with other methods of analysis described in the literature and widely used, overperforming them in some situations. The application of these algorithms was also demonstrated in an experiment devoted to the identification of sugarcane genes differentially expressed in response to phosphate deficiency. Phosphorous is an
essential macronutrient, absorbed by plants mostly in the form of inorganic phosphate (Pi). The phosphate deficiency is frequent in the nature, especially in the acid soils of tropical and subtropical areas. Because of the great economical importance of sugarcane, the identification of genes that are differentially expressed in response to phosphate deficiency in this species is of great scientific and agronomic interest. Clustering algorithms were also applied to the expression data obtained in the experiment, identifying patterns of gene expression in the different stages of the sugarcane response to the stress, thus providing an additional characterization of it. In the future, the results of this work can lead to the development of sugarcane cultivars that have better performance in phosphate deficient soils, what would be of great agronomic interestDoutoradoBioinformáticaDoutor em Genetica e Biologia Molecula