Une galaxie est un système complexe au sens où, autant des phénomènes se produisant à l'échelle du milieu interstellaire, comme des explosions de supernovæ ou l'activité d'un trou noir supermassif, que des interactions entre galaxies au sein de groupes ou d'amas, comme l'effeuillage par effet de marée ou par effet de bélier, influencent et conditionnent l'évolution de la galaxie dans son ensemble. Comme les processus œuvrant dans de tels systèmes font intervenir une gamme d'échelle de temps et de distance considérable, allant de l'étoile individuelle aux amas de galaxies tout entier, leur modélisation constitue un immense défi qui ne peut être relevé ni par une approche purement analytique ni par l'entremise de techniques exclusivement numériques.Cette thèse, à l'interface entre modèles semi-analytique et analyse de simulations numériques, se concentre sur l'étude de l'effeuillage des étoiles des galaxies satellites par effet de marée et sur les rétro-actions induites par les supernovæ.Ce manuscrit présente, d'une part, un modèle d'occupation des halos permettant de contraindre la masse d'étoiles perdue par les galaxies satellites depuis leur entrée dans leur groupe ou leur amas ainsi qu'un modèle d'effeuillage impulsif prédisant la masse stellaire arrachée aux satellites. Ce dernier est confronté, par le truchement du modèle d'occupation des halos, aux observations des fonctions de masses des groupes et des amas.Il expose, d'autre part, l'étude des rétro-actions des supernovæ implémenté dans les simulations numériques du projet NIHAO, conduite en séparant en différentes composantes le gaz des simulations et en comptabilisant les échanges entre ces dernières, laquelle a permis de mettre en évidence trois processus distincts par le biais desquels les supernovæ réduisent ou suppriment la formation stellaire.Enfin, il détaille les améliorations techniques et scientifiques apportées au modèle semi-analytique GalICS. / A galaxy is a complex system since as many phenomena take place at the scale of the interstellar medium, such as supernovae explosions or the activity of supermassive black holes, as interactions between galaxies within groups or clusters, such as tidal or ram pressure stripping, affect and condition the evolution of the galaxy itself as a whole. Because the processes acting in such systems involve a considerable range of times and distances, going from individual stars to entire clusters of galaxies, they modelling constitutes an immense challenge that cannot be met neither by a purely analytical approach nor by solely numerical technics.This thesis, being at the interface between semi-analytical models and the analysis of numerical simulations, focuses on the study of star stripping in satellite galaxies by tidal effects and on the supernovae induced feedback.This manuscript presents, on one hand, an halo occupation model that allows to constrain the stellar mass lost by satellite galaxies since they entered their group or their cluster, and a model of impulsive stripping that predicts the stellar mass ripped out of satellites. The latter is compared, through the halo occupation model, to the observed mass functions of groups and clusters.It exposes, on the other hand, the study of the supernovae feedback implemented in the numerical simulations of the NIHAO project, performed separating the simulated gas into different components and counting the exchanges that take place between them. This allowed for the highlighting of three distinct processes through which supernovae reduce or suppress their star formation.

<p>Inter-Vehicle Communication (IVC) is a vital part of Intelligent Transportation System (ITS), which has been extensively researched in recent years. Dedicated Short Range Communication (DSRC) is being seriously considered by automotive industry and government agencies as a promising wireless technology for enhancing transportation safety and efficiency of road utilization. In the DSRC based vehicular ad hoc networks (VANETs), the transportation safety is one of the most crucial features that needs to be addressed. Safety applications usually demand direct vehicle-to-vehicle ad hoc communication due to a highly dynamic network topology and strict delay requirements. Such direct safety communication will involve a broadcast service because safety information can be beneficial to all vehicles around a sender. Broadcasting safety messages is one of the fundamental services in DSRC. In order to provide satisfactory quality of services (QoS) for various safety applications, safety messages need to be delivered both timely and reliably. To support the stringent delay and reliability requirements of broadcasting safety messages, researchers have been seeking to test proposed DSRC protocols and suggesting improvements. A major hurdle in the development of VANET for safety-critical services is the lack of methods that enable one to determine the effectiveness of VANET design mechanism for predictable QoS and allow one to evaluate the tradeoff between network parameters. Computer simulations are extensively used for this purpose. A few analytic models and experiments have been developed to study the performance and reliability of IEEE 802.11p for safety-related applications. In this thesis, we propose to develop detailed analytic models to capture various safety message dissemination features such as channel contention, backoff behavior, concurrent transmissions, hidden terminal problems, channel fading with path loss, multi-channel operations, multi-hop dissemination in 1-Dimentional or 2-Dimentional traffic scenarios. MAC-level and application-level performance metrics are derived to evaluate the performance and reliability of message broadcasting, which provide insights on network parameter settings. Extensive simulations in either Matlab or NS2 are conducted to validate the accuracy of our proposed models.</p> / Dissertation

Made available in DSpace on 2014-12-17T14:09:18Z (GMT). No. of bitstreams: 1 JulianaAA_TESE.pdf: 2312979 bytes, checksum: 31c1a19cbf37d537febd576ec54e5eb2 (MD5) Previous issue date: 2013-09-13 / Discrepancies between classical model predictions and experimental data for deep bed filtration have been reported by various authors. In order to understand these discrepancies, an analytic continuum model for deep bed filtration is proposed. In this model, a filter coefficient is attributed to each distinct retention mechanism (straining, diffusion, gravity interception, etc.). It was shown that these coefficients generally cannot be merged into an effective filter coefficient, as considered in the classical model. Furthermore, the derived analytic solutions for the proposed model were applied for fitting experimental data, and a very good agreement between experimental data and proposed model predictions were obtained. Comparison of the obtained results with empirical correlations allowed identifying the dominant retention mechanisms. In addition, it was shown that the larger the ratio of particle to pore sizes, the more intensive the straining mechanism and the larger the discrepancies between experimental data and classical model predictions. The classical model and proposed model were compared via statistical analysis. The obtained p values allow concluding that the proposed model should be preferred especially when straining plays an important role. In addition, deep bed filtration with finite retention capacity was studied. This work also involves the study of filtration of particles through porous media with a finite capacity of filtration. It was observed, in this case, that is necessary to consider changes in the boundary conditions through time evolution. It was obtained a solution for such a model using different functions of filtration coefficients. Besides that, it was shown how to build a solution for any filtration coefficient. It was seen that, even considering the same filtration coefficient, the classic model and the one here propposed, show different predictions for the concentration of particles retained in the porous media and for the suspended particles at the exit of the media / Discrep?ncias encontradas entre dados experimentais e previs?es feitas a partir do modelo cl?ssico foram relatadas por v?rios autores. Para entender essas discrep?ncias, um modelo anal?tico cont?nuo para a filtra??o profunda ? proposto. Neste modelo, cada mecanismo de reten??o est? associado a um coeficiente de filtra??o diferente. Foi mostrado que os coeficientes de filtra??o n?o podem ser somados e considerados em um ?nico coeficiente de filtra??o global como se apenas um mecanismo de reten??o atuasse no sistema, o que ? feito no modelo cl?ssico. Al?m disso, foram obtidas solu??es expl?citas para o sistema de equa??es que representam o modelo proposto. Tais solu??es foram usadas para ajustar os dados experimentais, e um bom ajuste foi obtido. Comparando os resultados obtidos com rela??es emp?ricas dispon?veis na literatura foi poss?vel identificar o mecanismo de reten??o mais atuante na filtra??o. Foi mostrado ainda, que quanto maior o tamanho das part?culas injetadas, mais atuante ? o mecanismo de exclus?o pelo tamanho e maiores as discrep?ncias entre o modelo proposto e o modelo cl?ssico. Os modelos cl?ssico e proposto foram comparados atrav?s de uma an?lise estat?stica. Tal an?lise mostrou que os ajustes feitos com o modelo proposto s?o significativamente melhores que os ajustes feitos com o modelo cl?ssico, principalmente quando o mecanismo de exclus?o pelo tamanho ? o mais atuante na filtra??o. Neste trabalho foi, tamb?m, estudado a filtra??o de part?culas em meio poroso com capacidade finita de filtra??o. Observou-se, neste caso, que ? necess?rio considerar mudan?as nas condi??es de fronteira com a evolu??o do tempo. Foi obtida a solu??o para tal modelo para diferentes fun??es de coeficiente de filtra??o. Al?m disso, foi mostrado como construir a solu??o para um coeficiente de filtra??o qualquer. Observou-se que, ainda que se considere o mesmo coeficiente de filtra??o, o modelo cl?ssico e o modelo proposto apresentam previs?es distintas para as concentra??es de part?culas retidas no meio e de part?culas em suspens?o na sa?da do meio