Dans ce travail, nous étudions les surfaces dont les composantes irréductibles sont des surfaces toriques. En particulier, nous donnons une formule pour calculer l'obstruction d'Euler locale de ces surfaces. Comme application de cette formule, nous calculons l'obstruction d'Euler locale pour certaines familles de surfaces déterminantales. De plus, nous définissons et donnons une formule pour calculer la caractéristique d'Euler évanescente d'une surface torique normale $X_{sigma}$. Nous montrons que ce nombre est relié à la seconde multiplicité polaire de $X_{sigma}$. Nous présentons aussi une formule pour l'obstruction d'Euler d'une fonction $f: X_{sigma} to mathbb{C}$ et pour le nombre de Brasselet d'une telle fonction. Comme application de ce résultat nous calculons l'obstruction d'Euler d'un type de polynôme sur une famille de surfaces déterminantales. / In this work we study surfaces with the property that their irreducible components are toric surfaces. In particular, we present a formula to compute the local Euler obstruction of such surfaces. As an application of this formula we compute the local Euler obstruction for some families of determinantal surfaces. Furthermore, we define the vanishing Euler characteristic of a normal toric surface $X_{sigma}$, we give a formula to compute it, and we relate this number with the second polar multiplicity of $X_{sigma}$. We also present a formula for the Euler obstruction of a function $f: X_{sigma} to mathbb{C}$ and for the Brasselet number of it. As an application of this result we compute the Euler obstruction of a type of polynomial on a family of determinantal surfaces.

Le transistor est la brique élémentaire des circuits intégrés présents dans tous les appareils électroniques. Années après années l’industrie de la microélectronique a amélioré les performances des circuits intégrés (rapidité, consommation énergétique) en réduisant les dimensions du transistor. De nos jours, en plus de la réduction de la taille du transistor d’autres techniques permettent de soutenir cette croissance: ce sont les « booster » technologiques. Les contraintes mécaniques ou encore le remplacement du Silicium par d’autres matériaux tels que germanium (Ge) et les matériaux semi-conducteurs de type III-V sont des exemples de booster technologiques. Grâce à la modélisation numérique, cette thèse propose d’étudier les effets de booster technologiques sur les performances électriques de la future génération de transistors. / The transistor is the elementary brick of Integrated circuits found in all electronic devices. Years after years the microelectronic industry has enhanced the performances of integrated circuits (speed and energy consumption) by downscaling the transistor. Nowadays besides the transistor’s downscaling, other techniques have been considered to maintain this growth: they are called technological boosters. Mechanical strain or new material, such as germanium (Ge) and III-V semiconductors, to replace Silicon are example of technological boosters. By the means of numerical quantum simulations and modeling, this these work propose a study of the effect of technological boosters on the electric performances of the next generation of transistors.

Submitted by JOSIANE SANTOS DE OLIVEIRA (josianeso) on 2018-09-24T12:37:05Z No. of bitstreams: 1 Tatiana Dilly Dexheimer_.pdf: 564022 bytes, checksum: dc30c0b4e680aa78777ee81a76700bb5 (MD5) / Made available in DSpace on 2018-09-24T12:37:05Z (GMT). No. of bitstreams: 1 Tatiana Dilly Dexheimer_.pdf: 564022 bytes, checksum: dc30c0b4e680aa78777ee81a76700bb5 (MD5) Previous issue date: 2018-06-19 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Esta dissertação de mestrado é um subprojeto de um projeto maior, intitulado “A mobilização do saber e do fazer: episteme e deonticidade na fala-em-interação institucional e na conversa cotidiana”. (OSTERMANN, 2016). Investigamos o tema de respostas não-conformativas no português brasileiro como resposta a perguntas polares e perguntas abertas do tipo específicas. O contexto de pesquisa é um hospital do SUS, localizado no sul do Brasil, e as interações gravadas consistem em aconselhamentos genéticos, ecografias obstétricas e morfológicas e ecocardiografias. A análise dos dados é realizada com base no aparato teórico-metodológico da Análise da Conversa. (SACKS; SCHEGLOFF; JEFFERSON, 1974). O objetivo desta dissertação é analisar e descrever as ações e implicações das respostas não-conformativas fornecidas por médicos/as a gestantes de médio e alto risco. Os resultados da investigação mostram que, no contexto investigado, as respostas não-conformativas apresentam características similares as respostas não-conformativas transformativas, indiretas e oracionais descritas em estudos anteriores em outras línguas. (STIVERS, HAYASHI, 2010; WALKER; DREW; LOCAL, 2011; FOX; THOMSPON, 2011). Evidenciamos, contudo, que as respostas transformativas de especificação e substituição geram trabalho interacional maior por parte do respondente, assim como as respostas transformativas de foco e pressuposição. Além disso, identificamos um tipo de resposta não-conformativa não descrita anteriormente na literatura: respostas transformativas que postergam o provimento da informação. Esse tipo de resposta foi identificado tanto como resposta para perguntas polares quanto para perguntas abertas do tipo específicas. Observamos que esse tipo de resposta ocorre em momentos que se revelam como interacionalmente ‘delicados’, tais como, comunicação de más notícias, de risco de morte fetal e de riscos decorrentes de procedimentos. Concluímos que as respostas transformativas que postergam o provimento da informação são uma forma de ajustar a fala levando em consideração o interlocutor e a potencial delicadeza das ações envolvidas naquela sequência interacional. Por fim, entendemos que as respostas transformativas permitem ao interagente resistir às imposições da pergunta e controlar, também, a pauta da interação. / This master’s dissertation consists of a subproject of a larger study, entitled “A mobilização do saber e do fazer: episteme e deonticidade na fala-em-interação institucional e na conversa cotidiana”. (OSTERMANN, 2016). It investigates non-conformative answers in Brazilian Portuguese to polar questions and wh-questions, more specifically, specifying questions. All the consultations audio recorded were held at a public health system hospital located in southern Brazil and the interactions consist of genetic counseling, morphological and fetal ultrasound and echocardiography. The data analysis is based on a conversational analytical perspective. (SACKS; SCHEGLOFF; JEFFERSON, 1974). The objective of this dissertation is to analyze and describe the actions and implications of non-conformative answers provided by doctors to moderate and high pregnancy women. The results indicate that non-conformative answers and transformative, indirect and clausal responses present similar characteristics. (STIVERS, HAYASHI, 2010; WALKER; DREW; LOCAL, 2011; FOX; THOMSPON, 2011). However, transformative answers of specification and replacement engender greater interactive work for the respondent, as well as transformative answers of focus and presupposition. Additionally, we have identified a kind of transformative answer that has not been described in the literature yet: transformative answers that postpone the provision of the information. These kind of answers have been identified as answers to polar questions as well as wh-questions on the kind of specifying questions. We have observed that these answers occur in moments that reveal to be interactionally delicate, for instance, delivery of bad news, fetal death risk, and risks arising from medical procedures. We have concluded that transformative answers that postpone the provision of the information are a way to adjust the talk taking into consideration the interlocutor and the potential delicacy of the actions involved in that interactional sequence. Finally, we understand that transformative answers allow the interlocutor to resist to the constraints of the questions and also control the agenda of the interaction.

How long has the extant flora been present in the Antarctic? Glaciological reconstructions propose that most areas in Antarctica were covered by thick ice sheets throughout the Last Glacial Maximum (LGM; ~22-18 kya) as well as previous glaciations, suggesting terrestrial life must have been extremely limited during these periods. In contrast, recent biogeographic and genetic studies support most extant groups of Antarctic terrestrial fauna having survived past glaciations in situ. However, studies on the origin and age of the Antarctic flora remain sparse. Applying population genetic, phylogeographic and divergence time analyses I assessed the global biogeography, origin and age of several abundant Antarctic moss species, including: four Polytrichaceae mosses, characterised by having bipolar distributions, the most common (~45% of species) distribution pattern amongst Antarctic mosses; the globally widespread moss Ceratodon purpureus; the bank-forming moss Chorisodontium aciphyllum, also known for its old sub-fossils in Antarctica and long-term viability from revival experiments; and, lastly, the genus Schistidium, the most species-rich moss genus in Antarctica, including many endemic species. Genetic analyses revealed evidence of long-term (multi-million year) survival of plants in Antarctica (several species of Schistidium, Ceratodon purpureus, and possibly Polytrichum juniperinum). However, evidence for a likely more recent (< 100 ky) arrival of Chorisodontium aciphyllum was also found. Some species revealed multiple separate dispersal events to the Antarctic, suggesting the region may be less isolated for spore-dispersed organisms than previously thought. Evidence for increased genetic diversity in the northern maritime Antarctic compared to other regions point at it including potential refugial areas. Furthermore, genetic patterns revealed geographic features that enable and limit the connectivity of bryophytes globally as well as in Antarctica. This study suggests that, despite the harsh polar climate during glaciation periods, many bryophytes have had a much longer presence in Antarctica than previously thought.

Submitted by Silvana Teresinha Dornelles Studzinski (sstudzinski) on 2016-04-26T12:07:26Z No. of bitstreams: 1 Paula Cortezi Schefer Cardoso_.pdf: 2371409 bytes, checksum: c7f5e8cb111a2ba9ca150a830fe8d1ac (MD5) / Made available in DSpace on 2016-04-26T12:07:26Z (GMT). No. of bitstreams: 1 Paula Cortezi Schefer Cardoso_.pdf: 2371409 bytes, checksum: c7f5e8cb111a2ba9ca150a830fe8d1ac (MD5) Previous issue date: 2016-01-13 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / FAPERGS - Fundação de Amparo à Pesquisa do Estado do Rio Grande do Sul / Esta dissertação de mestrado é um subprojeto de um estudo maior, intitulado “Uma mulher, um feto, e uma má notícia: a entrega de diagnósticos de síndromes e de malformações fetais – em busca de uma melhor compreensão do que está por vir e do que pode ser feito”. (OSTERMANN, 2013). Debruçamo-nos sobre o tema de perguntas no português brasileiro com base no aparato metodológico da Análise da Conversa (SACKS; SCHEGLOFF; JEFFERSON, 1974) e da Linguística Interacional. (OCHS; SCHEGLOFF; THOMPSON, 1996; SELTING; COUPER-KUHLEN, 2001). Tendo em vista que o objetivo desta dissertação é distinguir as ações de pedido de informação e pedido de confirmação nas perguntas polares no português brasileiro, analisamos 891 perguntas polares da fase da anamnese das dezessete primeiras consultas de aconselhamento genético reprodutivo. As consultas ocorreram em um setor que atende mulheres em gestação de médio ou alto risco de um hospital materno infantil do Sistema Único de Saúde (SUS) localizado no sul do Brasil. Os resultados da investigação apontam que, nesse contexto, as ações de pedido de informação e pedido de confirmação se distinguem pelo grau epistêmico do médico em relação à informação solicitada. Evidenciamos que os conhecimentos prévios podem ser provenientes de diferentes fontes, sendo elas: (a) a interação, (b) o conhecimento médico específico, (c) o grupo de medicina fetal do hospital analisado e/ou (d) o prontuário médico da gestante. No que concerne aos recursos interacionais que diferem essas duas ações, identificamos o uso de marcadores discursivos somente na ação de pedido de confirmação. No que tange à análise prosódica, com o intuito de descrever a curva de F0 dessas perguntas polares, a análise aconteceu em duas etapas. Inicialmente, realizamos a análise auditiva das 891 perguntas polares e, em seguida, realizados a análise acústica de 300 dessas perguntas por meio do software PRAAT. Corroborando a descrição da entoação das perguntas apresentada em gramáticas descritivas do português brasileiro (CASTILHO, 2014; PERINI, 2005), evidenciamos que algumas delas apresentam entoação final ascendente. No entanto, nossos dados também revelaram que essas perguntas polares podem apresentar entoação final descendente. Na coleção de perguntas polares analisadas, constatamos que algumas demonstravam uma orientação do médico em relação a tópicos delicados o que, por sua vez, consititui outra análise. Identificamos que, nos assuntos interacionalmente construídos como delicados pelo médico geneticista, o formato do turno com as expressões “chegaste a” e “chegou a”, nas solicitações de informação sobre o uso do ácido fólico e na realização do exame de translucência nucal, atribui menor responsabilização à gestante. Em contrapartida, nas sequências em que o médico solicita informação sobre os hábitos relacionados ao fumo, ao consumo de álcool e ao uso de drogas, há responsabilização das gestantes por meio de fechamentos com avaliação positiva. / This master’s dissertation consists of a subproject of a larger study, entitled “Uma mulher, um feto, e uma má notícia: a entrega de diagnósticos de síndromes e de malformações fetais – em busca de uma melhor compreensão do que está por vir e do que pode ser feito”. (OSTERMANN, 2013). It investigates questions in Brazilian Portuguese through a conversation analytical perspective (SACKS; SCHEGLOFF; JEFFERSON, 1974) and an interaction linguistics approach. (OCHS; SCHEGLOFF; THOMPSON, 1996; SELTING; COUPER-KUHLEN, 2001). Taking into consideration that the objective of this dissertation is to distinguish the actions of requesting for information and requesting for confirmation in polar questions in Brazilian Portuguese, 891 polar questions were analyzed during the anamnesis phase in 17 first-time genetic counseling consultations. All of these consultations audiorecorded were held at a public health system hospital specialized in moderate and high-risk pregnancy, located in southern Brazil. The results indicate that, in this context, the actions of asking for information and asking for confirmation differ by the doctor’s epistemic degree concerning the information being requested. It was noticed that such previous knowledge might be originated from different sources, which are: (a) the interaction itself, (b) medical knowledge, (c) information gained through the fetal medicine group and/or (d) information from medical records. Regarding the interactional resources that differentiate these two actions, we identified that discourse markers were only used in requests for confirmation. On what concerns their prosodic features, in order to describe the F0 curve of these polar questions, the analysis was done in two stages. Firstly, we conducted an auditory analysis of all the 891 polar questions and, then, by using the software PRAAT, we conducted the acoustic analysis in 300 of these polar questions. Confirming the intonation patterns of polar questions described in Brazilian Portuguese descriptive grammar (CASTILHO, 2014; PERINI, 2005), we also identified that polar questions may present rising intonation. However, our data also reveal that polar questions may present falling and flat intonation. In the set of analyzed polar questions, we observed that some demonstrated the doctor’s orientation to delicate topics and this subset was also submitted to analysis. We identified that only specific topics were interactionally constructed as delicate by the geneticist. We also observed that in the turns designed with the expression “did you happen to”, in requests of information about folic acid and nuchal translucency, the doctor removes the responsibility from the pregnant. On the other hand, in the sequences in which the doctor requests information about smoking, drinking and using drugs, by the offering closings with positive assessments and accounts, the doctor attributes the responsibility to the pregnant women.

Nous nous intéressons dans cette thèse à l’optimisation conjointe de forme et d’anisotropie pour les structures surfaciques. Nous nous focalisons dans un premier temps sur l’analyse de ces structures minces modélisées par des coques. Le modèle utilisé pour décrire le comportement mécanique est celui de Naghdi communément utilisé pour les coques modérément épaisses et qui permet de prendre en compte l’effet transverse de déformation. La discrétisation par méthode éléments finis est réalisée avec des éléments Lagrange standards de classe C0. Nous considerons la simulation d’assemblage de coques en utilisant la méthode des éléments finis avec joint (mortier). Cette méthode est flexible, elle est adaptée à l’utilisation de maillages localement raffinés et/ou non-conformes, c'est-à-dire non coïncidents. La deuxième partie se consacre à la définition d’un paramétrage pour la conception optimale de champ d’anisotropie. Notre approche se base sur l’utilisation conjointe du formalisme polaire pour représenter le tenseur d’élasticité et le principe isogéométrique permettant de paramétrer les champs d’anisotropie par des fonctions de type B-splines. La dernière partie est dédiée à l’optimisation conjointe de forme et de propriétés matériaux. Le nombre de paramètres d’optimisation dans l’approche proposée est maîtrisée puisque les paramètres d’optimisation sontles coordonnées des points de contrôle. Nous considérons principalement pour l’optimisation un critère detype compliance. / This thesis tackles the problem of the shape and anisotropy optimization of shell structures. The first part of this work focuses on the analysis of the shell model. The mechanical behavior of the structure is described using the Naghdi’s shell model which allows to take into account the transverse shear deformation. This model is typically used for shallow shells. We use a standard Lagrange C0 finite elements discretization and we numerically simulate the shell assemblings by means of the mortar technique. This approach enables the application of local refinements and the use of nonconforming mesh discretizations. The second part of this thesis aims at defining an effective parameterization for the optimal design of the shell’s distributed elastic properties. The method adopted is based on the joint use of a polar formalism to represent the elastic tensor and an isogeometric technique for the parameterization of the elastic tensor fields by CAD-based functions such as B-splines. The number of design variables thus only depends on the control points coordinates making the approach numerically manageable. The last part is devoted to the joint optimization of both the material properties and shape of the shell using the structure compliance as objective function.

Submitted by Cássia Santos (cassia.bcufg@gmail.com) on 2016-08-10T13:40:03Z No. of bitstreams: 2 Dissertação - Vanessa Ribeiro Soares - 2016.pdf: 11844437 bytes, checksum: 03d509603ea96f2647ea2764aea87d17 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2016-08-10T13:42:09Z (GMT) No. of bitstreams: 2 Dissertação - Vanessa Ribeiro Soares - 2016.pdf: 11844437 bytes, checksum: 03d509603ea96f2647ea2764aea87d17 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2016-08-10T13:42:09Z (GMT). No. of bitstreams: 2 Dissertação - Vanessa Ribeiro Soares - 2016.pdf: 11844437 bytes, checksum: 03d509603ea96f2647ea2764aea87d17 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2016-05-30 / This work has the purpose contribute to the improvement in some teaching contents of analytic geometry and trigonometry in high school . The content work was based on the National Curriculum Parameters, highlighting de nitions, theorems and properties necessary for the development of student learning. The theme was chosen after a practical experience involving the Naval Battle game in order to reduce the students' di culties. The playful work, as the game, has a practical application that does the student become familiar with the content. That's an interesting way to propose problems and solutions involving the content. Thus becomes something attractive to the student and encourages creativity in nding problems solutions. / O trabalho tem como objetivo contribuir para o aprimoramento no ensino de alguns conteúdos de Geometria Analítica e Trigonometria no Ensino Médio. Dentro dos Parâmetros Curriculares Nacionais, trabalhamos o conteúdo destacando de nições, teoremas e propriedades necessárias para o desenvolvimento de aprendizagem do aluno. O tema foi escolhido depois de uma experiência prática envolvendo o jogo Batalha Naval a m de diminuir as di culdades dos alunos. O trabalho lúdico, como o jogo, tem uma aplicação prática que faz o aluno se familiarizar com os conceitos. É uma forma interessante de propor problemas e soluções envolvendo o conceitos. Assim se torna algo atrativo para o aluno e favorece a criatividade na busca de soluções para os problemas.

Human-bear interactions are an important consideration of bear biology, as interactions can lead to destruction of property as well as injury or death for both human and bear. Successful analysis of why these interactions occur can lead to appropriate preventative measures and mitigation of further conflict. Bryce Canyon National Park (BRCA) is comprised of relatively poor bear habitat, but a black bear population exists on the Paunsaugunt Plateau, on which the park occupies the eastern edge. Park managers expressed interest in learning more about bear movements and, specifically, bear use of anthropogenic features following a number of human-bear incidents located at backcountry campsites within park boundaries. By analyzing data from GPS radio-collared bears, trail cameras, existing literature, park incident reports and in-depth campsite assessments, we were able to show how bears are using both natural and anthropogenic features on the Bryce landscape. Campsites were assessed for bear habitat, displacement and encounter potential in order to establish an overall human-bear conflict potential. AIC model selection and resource selection functions using GPS collar data showed that bears selected for some anthropogenic features (campsites, springs), while actively avoiding others (trails, roads). Trail camera data, existing literature and park incident reports all pointed toward use of trails. We then considered all data sources used in the analysis and compiled rankings of human-bear conflict potential for each of the backcountry campsites within BRCA, and submitted a detailed report of findings, conclusions and recommendations to NPS personnel. Second, we investigated human-bear interactions at polar bear dens sites on Alaska's North Slope. As parturient female polar bears in the Southern Beaufort Sea subpopulation increasingly construct maternal dens on coastal land features rather than sea ice, they become more likely to interact with industry and other human activity. We wanted to understand what levels of human interaction could lead to disturbance of denning polar bears, and what types of responses were being exhibited by bears following those interactions. We subdivided potential disturbance stimuli into groups based on their size, motion and sound and the used AIC model selection techniques and multinomial logistic regression to analyze records of human-bear interactions at den sites ranging from 1975 through the present day. We found significant probabilities of varying levels of bear disturbance response among a number of stimuli and intensities. However, denning bear families were overall more tolerant of human activity near den sites than expected. Den abandonments were rare, and we documented no cases of reproductive failure following a disturbance event. We hope that our results from the analysis can be used to further enhance management of industry when operating in polar bear denning habitat.

Dans le contexte actuel du réchauffement climatique, l'une des principales sources d'incertitude pour l'élévation du niveau de la mer est la contribution de la calotte Antarctique. L'étendue et les conditions météorologiques extrêmes de ce continent font de la télédétection spatiale un moyen utile pour son suivi sur le long terme. Les observations satellites altimétriques et radiométriques dans la gamme des micro-ondes rendent compte de l'évolution des propriétés du manteau neigeux de la calotte. L'altimétrie radar, par des mesures répétées de l'élévation de la topographie de surface, permet de quantifier les variations de volume sur l'ensemble du continent. Cependant, la pénétration de l'onde radar dans la neige affecte négativement cette quantification. Les méthodes proposées pour minimiser les erreurs de pénétration sont toutes basées sur des relations avec le coefficient de rétrodiffusion radar. La compréhension des variations annuelles et inter-annuelles du coefficient de rétrodiffusion est nécessaire pour améliorer la précision de l'estimation de l'élévation de la surface donc du bilan de volume de la calotte. Cette thèse a pour objectif d'étudier le coefficient de rétrodiffusion mesuré par les altimètres sur l'ensemble du continent, sujet qui jusqu'à aujourd'hui a reçu peu d'attention. Les altimètres radars embarqués à bord d'ENVISAT (bandes S et Ku) et de SARAL/AltiKa (bande Ka) ont des sensibilités différentes aux propriétés de la neige. Nous nous sommes intéressés aux caractéristiques annuelles et inter-annuelles des coefficients de rétrodiffusion dans ces trois bandes. Une étude de sensibilité a été réalisée avec un modèle électromagnétique afin de déterminer les propriétés du manteau neigeux qui dominent le signal saisonnier. On montre que le signal saisonnier est sensible à la densité et la rugosité de surface dans la bande S, à la température de la neige dans la bande Ka et à l'une ou à l'autre de ces variables selon la région dans la bande Ku. Les caractéristiques saisonnières du coefficient de rétrodiffusion sont ensuite comparées à celles des températures de brillance acquises par les radiomètres à bord de SARAL et de SSM/I. Les résultats indiquent une influence significative de la rugosité de surface sur les températures de brillance de la bande Ka, influence souvent considérée négligeable dans la modélisation de la température de brillance. Cette étude apporte une meilleure connaissance de la dynamique saisonnière des propriétés de proche surface de la calotte Antarctique. Elle fournit de nouveaux indices pour développer dans le futur des algorithmes robustes de correction de l'erreur de pénétration. Elle met également en lumière l'importance des missions altimétriques multi-fréquences et les possibilités qu'offrent le signal de la bande S pour l'étude des variabilités saisonnières de la rugosité de surface. En définitive, la rugosité de surface est un paramètre important à prendre en compte pour obtenir de meilleures estimations et modélisations des coefficients de rétrodiffusion et des températures de brillance. / In the context of global climate changes, the Antarctic ice sheet contribution to sea-level rise is one of the main uncertainty sources. The extent and extreme meteorological conditions of this continent render remote sensing a useful tool for long term monitoring. Altimetry and radiometry observations in the microwave range reveal variations of the volume of the ice sheet and surface properties of the snowpack. Radar altimeters, provide repeated observations of the surface topography elevation, which allow the quantification of volume variations of the ice sheet. However, the penetration of radar waves in dry and cold snowpack adversely affects the estimated surface elevation. Approaches to minimize the penetration error are all based on a relationship with the backscattering coefficient. Understanding the annual and interannual variations of the backscattering coefficient is thus a key issue in order to improve the estimation accuracy of the surface elevation and to refine the ice-sheet volume trend. This thesis aims at studying the backscattering coefficients acquired by radar altimeters, which until now have received little attention. Radar altimeters on board ENVISAT (S and Ku bands) and SARAL/AltiKa (Ka band) have different sensitivities to the snowpack properties. The annual and interannual variations of the backscattering coefficient at the three bands is investigated. Sensitivity tests are carried out with an electromagnetic model to determine the prevailing snowpack properties that drive the signal. The seasonal signal is sensitive to surface density and roughness at S band, to snow temperature at Ka band and to either snow surface density and roughness or temperature depending on the location on the continent at Ku band. The seasonal signal of the backscattering coefficient is then compared with that of the brightness temperature measured by radiometers on SARAL and SSM/I. The results show a significant influence of surface roughness on brightness temperatures at Ka band, which has often been neglected in brightness temperature modeling studies. This thesis provides a better understanding of the seasonal dynamics of the near surface properties of the Antarctic ice sheet. It also provides new clues to build a more robust corrections of the penetration errors in the future. It highlights the importance of multi-frequency altimetry missions and the potential of the S band to study the seasonal variability in surface roughness. In summary, surface roughness is an important property which should be taken into account for a better modeling of backscattering coefficient and brightness temperature.

Les bétaïne lipides (BL) sont des lipides polaires qui se distinguent des phospholipides (PL)par l’absence de phosphore (P). La réorientation métabolique induite par une limitation en P chez des microalgues produisant des BL (Tisochrysis lutea et Diacronema lutheri, Haptophytes) ou en produisant peu (Phaeodactylum tricornutum, Bacillariophyte) a été comparée à celle induite par une limitation en azote (N). Le devenir et le flux de carbone dans différentes voies de biosynthèse ont été étudiés par une approche pluridisciplinaire.La limitation nutritive en P ou en N affecte différemment le métabolisme du carbone selon les espèces microalgales. La limitation en P réduit fortement l’activité photosynthétique et la respiration chez P. tricornutum et T. lutea. Par conséquent, l’accumulation de carbone est plus élevée que sous limitation en N chez ces deux espèces. Les deux limitations stimulent en particulier la synthèse des lipides neutres et / ou des glucides. Le remplacement des PL par les BL a été observé chez P. tricornutum en condition de limitation en P. Ce résultat est en accord avec une augmentation de la transcription du gène codant la bétaïne lipide synthase. En revanche, cette limitation ne modifie pas les teneurs en BL rapportées au carbone chez T. lutea et D. lutheri. La composition en acides gras des différentes classes lipidiques est modifiée selon l’espèce microalgale et l’élément nutritif limitant. Une attention particulière a été portée aux acides gras de la série oméga-3, notamment l’acide eicosapentaénoïque (EPA, 20:5 ω3) et l’acide docosahexaénoïque (DHA, 22:6 ω3) dont les proportions varient en fonction de l’élément limitant,de l’espèce et de la classe lipidique. L’augmentation de la production des lipides neutres et / ou des lipides polaires, notamment des bétaïne lipides, riches en DHA et/ou EPA induite par un stress nutritif laisse envisager une valorisation de ces molécules d’intérêt dans différents domaines dont la nutrition et la santé. / Betaine lipids (BL) are P-free polar lipids, conversely to phospholipids (PL). The metabolic reorientation induced by phosphorus (P) limitation in microalgae producing BL (Tisochrysis lutea and Diacronema lutheri, Haptophyta) or producing low levels of BL (Phaeodactylum tricornutum, Bacillariophyta) was compared to that induced by nitrogen (N) limitation. The carbon destiny and flow in different biosynthetic pathways were studied with a multidisciplinary approach. P or N limitation differently affected carbon metabolism according to microalgal species. P limitation highly decreased photosynthetic activity and respiration of P. tricornutum and T. lutea. Consequently, carbon accumulation was higher than under N limitation in these two species. Both limitations stimulated the synthesis of neutral lipids and / or carbohydrates. Replacement of PL by BL was observed in P. tricornutum under P limitation. This result is in agreement with a transcription increase of the gene encoding BL synthase. On the other hand, this limitation did not modify BL contents in reference with carbon in T. lutea or D. lutheri. Fatty acid composition of the different lipid classes was modified according to the microalgal species and the limiting nutrient. Particular attention was paid to the fatty acids of the omega-3 series, notably eicosapentaenoic acid (EPA, 20:5 ω3) and docosahexaenoic acid (DHA, 22:6 ω3), the proportions of which vary according to the limiting element, species and lipid class. The increase in the production of neutral lipids and / or polar lipids, especially betaine lipids, rich in DHA and / or EPA induced by nutritive stress suggests a valorization of these molecules of interest in various areas including nutrition and health.