O oceano desempenha papel fundamental na configuração e manutenção do clima da Terra, sendo considerado um dos componentes principais do sistema climático.Diversos estudo foram conduzidos para avaliar as mudanças nos processos climáticos e como o clima, em contrapartida, é afetado por tais mudanças. O presente trabalho visa investigar o impacto das mudanças climáticas na formação de massas de água do oceano austral. Foram analisados resultados de simulação numérica para os séculos XX e XXI pelo modelo CCSM3 para os cenários 20c3m e SRESA1B do IPCC. Através da técnica de separação de mássas de água Análise Otimizada de Parâmetros Múltiplos (OMP) foram identificadas 3 massas de água no Mar de Ross: Água Profunda Circumpolar (CDW); Água da Plataforma de Gelo (ISW); Água de Plataforma de Baixa Salinidade (LSSW). A ISW, precursora da Água de Fundo Antártica (AABW), apresenta maior variação espacial tornando-se mais rasa no século XX e assumindo camadas mais profundas no século XXI. A variação da ISW está relacionada à variação do Modo Anular Sul (SAM) e à variação do gelo marinho. / It has been known for a long time that the ocean plays the most important role on Earth\'s heat budget, what turns it into a major component of the global climate system. Therefore, many studies have been made to assess whether features of climate processes are changing and how may climate itself be affected by these changes. This work aims to look at the impact of climate changes on water masses formation in the Southern Ocean. Results from the 20th century and SRESA1b CCSM3/NCAR simulation (1870 to 2100) were analyzed using the Optimum Multiparameter Analysis (OMP) to separate water masses. Three water masses were identified in the Ross Sea: Circumpolar Deep Water (CDW); Ice Shelf Water (ISW); Low Salinity Shelf Water (LSSW). Simulation results have shown that the ISW gets shallower during the 20th century and then, during the 21stcentury, it gets deeper and occupies the deepest layer by 2100 while it flows towards higher latitudes as AABW. Much closely to what has been shown by observational studies, water masses formation in the Southern Ocean is intrinsically linked to atmospheric vaiability modes, such as the southern annular mode--SAM, and to sea ice variation.

O oceano desempenha papel fundamental na configuração e manutenção do clima da Terra, sendo considerado um dos componentes principais do sistema climático.Diversos estudo foram conduzidos para avaliar as mudanças nos processos climáticos e como o clima, em contrapartida, é afetado por tais mudanças. O presente trabalho visa investigar o impacto das mudanças climáticas na formação de massas de água do oceano austral. Foram analisados resultados de simulação numérica para os séculos XX e XXI pelo modelo CCSM3 para os cenários 20c3m e SRESA1B do IPCC. Através da técnica de separação de mássas de água Análise Otimizada de Parâmetros Múltiplos (OMP) foram identificadas 3 massas de água no Mar de Ross: Água Profunda Circumpolar (CDW); Água da Plataforma de Gelo (ISW); Água de Plataforma de Baixa Salinidade (LSSW). A ISW, precursora da Água de Fundo Antártica (AABW), apresenta maior variação espacial tornando-se mais rasa no século XX e assumindo camadas mais profundas no século XXI. A variação da ISW está relacionada à variação do Modo Anular Sul (SAM) e à variação do gelo marinho. / It has been known for a long time that the ocean plays the most important role on Earth\'s heat budget, what turns it into a major component of the global climate system. Therefore, many studies have been made to assess whether features of climate processes are changing and how may climate itself be affected by these changes. This work aims to look at the impact of climate changes on water masses formation in the Southern Ocean. Results from the 20th century and SRESA1b CCSM3/NCAR simulation (1870 to 2100) were analyzed using the Optimum Multiparameter Analysis (OMP) to separate water masses. Three water masses were identified in the Ross Sea: Circumpolar Deep Water (CDW); Ice Shelf Water (ISW); Low Salinity Shelf Water (LSSW). Simulation results have shown that the ISW gets shallower during the 20th century and then, during the 21stcentury, it gets deeper and occupies the deepest layer by 2100 while it flows towards higher latitudes as AABW. Much closely to what has been shown by observational studies, water masses formation in the Southern Ocean is intrinsically linked to atmospheric vaiability modes, such as the southern annular mode--SAM, and to sea ice variation.

The cosmic expansion history tests the dynamics of the global evolution of the universeand its energy density contents, while the cosmic growth history tests the evolution of theinhomogeneous part of the energy density. By comparing both histories, we can distinguishthe nature of the physics responsible of the acceleration of the universe: dark energy or modified gravity. Most of the observational evidence for the accelerating universe comes fromgeometrical tests that measure directly H(z) = ˙ a/a, the expansion rate of the universe, suchas measurements of the luminosity distance using standard candles (Sn Ia) or measurementsof the angular distance using standard rulers as baryonic acoustic oscillations. Observationsof the cosmic expansion history alone can not distinguish dark energy from modified gravity,since the expansion history H(z) can be reproduced by any modified gravity model, by changing the energy equation of state "w". The additional observational input that is required is the growth function delta(z) = (delta-ro / ro)(z) of the linear matter density contrast as a function of redshift (usually used as the normalized growth function D(z) = delta(z)/delta(0)).In the first part of the thesis, we study the Integrated Sachs-Wolfe effect (ISW), through thecross-correlation between large scale clustering, traced by galaxies (in our case from the catalog SDSS) and primordial temperature fluctuations from CMB (using the catalog WMAP).Photons that come from the last scattering surface can be red or blue shifted by the time evolution of fluctuations in the gravitational potentials created by large scale structures, which are traced by the large scale galaxy distribution. The ISW effect gives us information about dark energy (DE), because DE modifies the evolution of dark matter gravitational potential.In principle, the ISW effect can probe dark energy independently from other observations,such as Supernovae Ia.The correlation between galaxies in redshift space can also be used to study the evolution ofthe dark matter gravitational potential in a way that is complementary to the cross-correlationof galaxies with CMB photons. In the second part of the thesis, we will study this effect in theluminous red galaxies of the SDSS. These galaxies trace very large volumes which is important to have more signal, and they have a known evolution which make easy to work with them.KEY WORDS: cosmology, large scale structure, growth of perturbations, ISW effect, redshiftdistortions, LRG. / CATALÀ:En la primera part de la tesi, estudiem l'efecte Integrat Sachs-Wolfe (ISW), a través de lacorrelació creuada entre estructura a gran escala, traçada per les galàxies (en el nostre cas usem el catàleg SDSS) i fluctuacions primordials de temperatura del fons c-osmic de microones (amb el catàleg WMAP). Els fotons que provenen de la superfície d'última interacció poden ser moguts cap al blau o vermell a causa de l'evolució en el temps de les fluctuacions dels potencials gravitacionals, creats per l'estructura a gran escala. L'efecte ISW ens d´ona informació de l'energia fosca, perquè aquesta modifica l'evolució dels potencials gravitacionals de matèria fosca. En principi, l'efecte ISW pot provar l'energia fosca independentment d'altres observacions, com Supernoves Ia.La correlació entre galàxies en l'espai de velocitats també es pot utilitzar en l'estudi del'evolució dels potencials gravitacionals de manera complementària a l'obtinguda amb l'efecteISW. En la segona part de la tesi, estudiem les distorsions en l'espai de velocitats en lesgalàxies lluminoses vermelles del catàleg SDSS. Aquestes galàxies tracen volums molt grans, essencial per a obtenir un bon senyal, i tenen una evolució coneguda, facilitant el seu estudi. / RESUMEN CASTELLANO:En la primera parte de la tesis, estudiamos el efecto Integrado Sachs-Wolfe (ISW), a travésde la correlaci´on cruzada entre la estructura a gran escala trazada por galaxias (aquí usamosel catálogo SDSS) y las fluctuaciones primordiales de temperatura del fondo cósmico de microondas (catálogo WMAP). Los fotones que provienen de la superficie de última interacciónpueden ser movidos hacia el azul o rojo por la evolución en el tiempo de las fluctuacionesen los potenciales gravitacionales, creados por la estructura a gran escala. El efecto ISW dainformación de la energía oscura, porque esta modifica la evolución de los potenciales gravitacionales de materia oscura. En principio, el efecto ISW puede probar la energía oscura independientemente de otras observaciones, como Supernovas Ia.La correlación entre galaxias en el espacio de velocidades también se puede utilizar enel estudio de la evolución de los potenciales gravitacionales de forma complementaria a laobtenida mediante el efecto ISW. En la segunda parte de la tesis, estudiamos las distorsionesen el espacio de velocidades para las galaxias luminosas rojas del catálogo SDSS. Estas galaxias trazan volúmenes grandes, esencial para obtener una buena señal, y además tienen una evolución conocida, facilitando su estudio.

Dans le cadre scolaire, la recherche d'information sur le web (RIW) assistée par les moteurs de recherche joue un rôle croissant dans l'enseignement et l'apprentissage. Mais si les lycéens effectuent beaucoup de RIW, peu d'études leur sont consacrées : on ne sait pas comment ils conduisent les RIW et quelles démarches ils suivent. La RIW est variée en fonction du contexte de recherche ainsi que de la situation rencontrée dans le processus même de recherche. Deux épreuves avec plusieurs tâches de recherche définies par le chercheur ont été passées avec 79 lycéens vietnamiens. Si elles ne rendent compte que partiellement des RIW des lycéens, elles permettent d'enregistrer les démarches utilisées, faisant l'hypothèse que les démarches mises en œuvre ont une certaine stabilité.En essayant de simplifier la RIW des participants, un schéma général de RIW est conçu avec cinq actions élémentaires de recherche identifiées : lecture de tâche, formulation de requêtes, consultation de page de résultats, lecture de page web et notation de réponses. Ce schéma permet de visualiser des caractéristiques de RIW des participants : les moteurs sont l'outil principal ; la recherche utilise davantage la formulation de requêtes que la navigation web ; les pages de résultats sont le centre de la recherche ; la navigation web s'effectue à partir des pages de résultats et est plutôt en largeur d'abord, selon le modèle « Hub and spoke ».En nous centrant sur les requêtes, quatre démarches élémentaires de RIW sont reconnues : top-down, bottom-up, spécifique et générale. Les participants ont tendance à utiliser une démarche élémentaire spécifique pour une tâche fermée ; une démarche élémentaire générale pour une tâche ouverte. Quand la tâche est difficile, les participants ont tendance à changer plus souvent leurs démarches élémentaires au cours de recherche et utiliser plus de processus, d'outils et plus de techniques de recherche.Pendant une période de deux ans entre deux épreuves, nous constatons des changements de comportements des lycéens vietnamiens : augmentation de la croyance dans la fiabilité de Wikipédia, de l'utilisation de Wikipédia comme un outil de recherche, de l'utilisation des options de traduction de Google et de requêtes en anglais ; la diminution de l'utilisation des guillemets, des opérateurs booléens dans l'écriture de requêtes. / In school, the information search on the web (ISW) assisted by the search engines play a growing role in teaching and learning. But if the students do a lot of ISW, there are few studies on the high school students; we do not know how they do the ISW and what approaches they follow. The ISW is varied according to the search context and the situation met in the search process itself. Two tests with several search tasks defined by the researcher were passed with 79 vietnamese high school students. If they report only partially ISW of the participants, they allow to register the approaches used, making the hypothesis that the approaches implemented have some stability.In trying to simplify the ISW of the participants, a general schema of ISW is designed with five elementary search actions identified: reading of task, formulation of queries, consultation of page of results, reading of web page and notation of answers. This schema allows to visualize characteristics of ISW of the participants: search engines are the main tool; the search uses more the formulation of queries than the web navigation; the pages of results are the center of the search; the web navigation is made from the pages of results is rather in breadth-first and according to the model "Hub and spoke".By focusing on the queries, four elementary approaches of ISW are recognized: top-down, bottom-up, specific and general. The participants tend to use a specific elementary approach for a closed task; a general elementary approach for an opened task. When the task is difficult, the participants tend to change more often their elementary approaches during the search and to use more processes, tools and more search techniques.During a period of two years between two tests, we notice changes of behavior of the vietnamese high school students: the increase of the belief in the reliability of Wikipédia, the use of Wikipédia as a search tool, the use of the options of translation of Google and the increase of queries in English; the decrease of the use of quotation marks, Boolean operators in the writing of queries.

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