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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
281

Evolução morfológica e modularidade / Morphological evolution and modulatory

Melo, Diogo Amaral Rebouças 01 October 2012 (has links)
Sistemas morfológicos quantitativos são descritos por medidas contínuas. A relação genética entre essas características dos indivíduos é representada pela matriz de covariância genética aditiva, a matriz G. Entender a evolução da matriz G, portanto, é de suma importância para compreender os padrões de diversificação encontrados na natureza. Neste trabalho estudamos modelos computacionais para a evolução de traços contínuos em populações naturais, sujeitas a variados tipos de seleção e condições internas, focando no problema da evolução dos padrões de integração e modularidade nessas populações. Testamos dois modelos com diferentes combinações de parâmetros em sua capacidade de reproduzir e elucidar padrões naturais. Seleção direcional correlacionada se mostrou uma força importante na criação desses padrões de covariação e a seleção estabilizadora correlacionada se mostrou fundamental para a manutenção desses padrões / Quantitative morphological systems are described by continuous measurements. The genetic relation between these characteristics of the individuals is represented by the genetic additive co-variance matrix, the G matrix. Understanding the evolution of the G matrix is, therefore, of paramount importance for proper interpretation of the patterns of diversification we observe in nature. In this work we study computational models for the evolution of quantitative traits in natural populations, subject to different natural selection and internal conditions, focusing on the problem of the evolution of the pattern of morphological integration and modularity. We test two models with different sets of parameters in their ability to reproduce and elucidate natural patterns. Directional correlated selection was necessary for the shaping of the patterns of morphological integration, and correlated stabilizing selection was fundamental to the maintenance of these patterns
282

Avaliação da precisão da declividade da técnica de perfuração direcional horizontal para instalações de redes de esgoto / Evaluation of the gradient precision of the horizontal directional drilling technique for the installation of gravity sewers

Jamal, Fernando Galvanin 26 June 2008 (has links)
O presente trabalho está focado no método de perfuração direcional horizontal (HDD) para instalação de redes de esgoto gravitacional. Descrevem-se os resultados de diferentes técnicas com o objetivo de se atingir a exigência de declividade. Para tanto foram executados 4 furos experimentais simulando trechos daquelas redes, com extensão de 30 m e tubulação de PEAD com diâmetro externo de 125 mm. Estas instalações foram executadas na cidade de São Carlos, Brasil, em um solo classificado granulometricamente como uma areia argilosa. Para cada uma das 4 instalações, adotou-se um processo construtivo diferenciado. Esta diferenciação se deu a partir do diâmetro do alargador adotado, do número de passadas do mesmo e da execução de furos verticais para alívio de pressão no espaço anelar assim como medidas diretas de profundidade do furo piloto. Após a instalação dos dutos foram realizadas medidas altimétricas no interior dos mesmos possibilitando avaliar quantitativamente os resultados obtidos. Estes resultados indicam que ainda é necessário refinar a técnica de perfuração direcional para a execução das redes de esgoto. Entretanto é possível observar que as variações empregadas na execução de cada um dos furos conduzem a um caminho de melhoria nos resultados obtidos. Esta melhoria pode ser observada nos furos onde o alargador adotado apresentava menor diâmetro conduzindo a menores desvios na posição final do duto. Salientam-se também os benéficos resultados da execução dos furos verticais que conduziram a menores pressões no espaço anelar assim como possibilitaram medidas altimétricas diretas da posição do furo piloto. Desta forma, é provável que com um maior número de experimentos e incrementos tecnológicos se atinja o objetivo final, ou seja, executar redes de esgoto gravitacional com declividade constante e baixa. Em paralelo nas instalações executadas foram realizados testes para avaliação da precisão e acurácia do sistema de navegação responsável pelo fornecimento de informações de posição e temperatura da ferramenta de corte durante a execução do furo piloto. Este trabalho contempla ainda, a elaboração de uma nova solução para as instalações de esgoto executadas através do HDD. Esta solução propõe a aplicação de um esforço de tração a um elemento externo, uma geogrelha que envolve a tubulação, visando posicionar a mesma em declividade constante. Face a seu caráter inovador foram desenvolvidos equipamentos e procedimentos de ensaio de laboratório, para avaliar a aplicabilidade da solução na prática / The present work is focused on the horizontal directional drilling (HDD) method to install gravity sewers. The results of different techniques are described intending to meet the demands of gradient. Therefore, 4 experimental pilot bores were drilled simulating a section of those structures extending 30 m with HDPE pipelines of 125 mm external diameter. Those installations were engineered in the city of São Carlos, Brazil, in a clayey sand. For each of the 4 installations a distinct constructive process was adopted. Such characteristic was on account of the diameter of the selected reamer, the number of reamer steps and the vertical drills performed to relieve the pressure in the annular space, as well as the direct depth measurements of the pilot hole. After installing the pipes, altimetric measurements were performed inside them, hence enabling to quantitatively assess the obtained results. These results indicate the need to further refine the directional drilling technique for sanitary sewers. Yet it can be seen that the employed variations for each of the holes lead to an improved course of action with the observed results. Such improvement is perceived in the holes where the selected reamer had a smaller diameter, hence allowing for less displacement in the pipes final position. Also emphasized are the resulting benefits of the vertical drills that lead to less pressure in the annular space, as well as enabling altimetric measurements of the pilot hole position. Thus, it is presumed that with further experiments and technological developments the final objective is reached, meaning, putting into effect constant and low level gradient sewer networks. Tests for precision and accuracy assessment of the tracking system were also performed in each tube installed. The tracking system is responsible for providing information related to position and temperature of the drill head during the drilling operation. The steps for the development of a new HDD solution for sewer installation are presented. The idea is based on the application of a tensile force to an element external to the product, aiming at attaining a constant gradient. Equipments and procedures developed for this new technique are described.
283

Metodologia para a coordenação e seletividade da proteção direcional de sobrecorrente em sistemas de transmissão de energia elétrica / Methodology for the coordination and selectivity of directional overcurrent protection in electrical power transmission systems

Negrão, Danilo Luiz Alves 31 March 2015 (has links)
Este trabalho propõe uma nova metodologia para a solução do problema de coordenação de relés direcionais de sobrecorrente em sistemas de transmissão em malha. São utilizadas informações sobre a atuação do relé como dispositivo de proteção principal (ou retaguarda local no caso de se considerar o relé de distância) e também de sua atuação como proteção de retaguarda remota, fornecendo uma base mais sólida para definição dos ajustes. A partir de uma série de critérios determinados de acordo com a instalação, define-se uma área de ajuste do relé, diretamente sobre sua curva de atuação. Sobre esta área, aplica-se um método de otimização capaz de encontrar o melhor ajuste possível para o dispositivo em análise. A metodologia é aplicada sem a necessidade de uma análise topológica do sistema, sendo que as informações da localização do relé e sua integração com os outros dispositivos de proteção são resumidas durante o estudo de curto-circuito, que fornece os dados de entrada para a metodologia. O algoritmo resume os critérios de coordenação em pontos de referência, de modo que a análise é feita relé a relé, eliminando assim problemas comuns como o de tratamento de banco de dados e ganhando em agilidade e simplicidade no tratamento do problema. A resposta fornecida é bastante intuitiva, sendo fácil entender os resultados obtidos e quais seriam as implicações caso na prática sejam necessárias adequações à instalação. / This work proposes a new methodology to solve the problem of coordination of directional overcurrent relays in meshed transmission systems. Using information about the operation of the directional relay as primary protection (or local backup, in the case of considering the distance relay) and also its role as remote backup protection, the methodology provides a more solid basis for defining settings. Based on a series of criteria determined in accordance with the installation, an area of relay feasible settings is defined directly over their time-overcurrent curve. On this area, an optimization method is applied to find the best possible setting for the device under analysis. The method is applied without the need for topological analysis of the system, and the information of the relay location and its integration with other protective devices are summarized during the short circuit study, which provides the input data for the methodology. The algorithm summarizes the criteria of coordination in landmarks and the analysis is performed relay by relay, thus common problems are eliminated, such as database treatment, gaining agility and simplicity in treating the problem. The answer provided is extremely intuitive, making it easy to understand the results and what would be the implications in case of, in practice, be necessary to perform adjustments to fit with the installation.
284

Controlled drug release from oriented biodegradable polymers

Ambardekar, Rohan January 2015 (has links)
This research is the first systematic investigation of solid-state orientation as a novel method for controlling drug release from biodegradable polymers. The effect of various degrees of polymer orientation was studied in oriented Poly (L-lactic acid) (PLA) films containing curcumin and theophylline as model drugs. Additionally, direction specific drug release was studied from oriented PLA rods containing paracetamol. The films oriented to 2X uniaxial constant width (UCW) or 2X2Y biaxial draw ratio showed retardation of drug release, when their nematic structure was stabilised by the presence of crystalline theophylline. Contrarily, the same films when contained solid solution of curcumin, shrunk in the release medium and exhibited a release profile similar to the un-oriented films. All films oriented to the UCW draw ratio ≥ 3X contained α crystalline form of PLA and showed acceleration of drug release proportionate to the draw ratio. According to the proposed mechanism augmented formation of water filled channels in these films was responsible for faster drug release. Similarly, the paracetamol loaded PLA rods die-drawn to uniaxial draw ratios ≥ 3X exhibited enhancement of drug release. Importantly, the amount of drug released along the oriented chain axis was significantly larger than that in the perpendicular direction. Drug release from the die-drawn rods was accelerated by a greater degree than that observed from the oriented films. This can be correlated to the differences in their size, geometry and the crystalline form of PLA. In conclusion, the current study provided substantial evidence that solid-state orientation can offer a control over drug release from PLA.
285

Computational models for multilingual negation scope detection

Fancellu, Federico January 2018 (has links)
Negation is a common property of languages, in that there are few languages, if any, that lack means to revert the truth-value of a statement. A challenge to cross-lingual studies of negation lies in the fact that languages encode and use it in different ways. Although this variation has been extensively researched in linguistics, little has been done in automated language processing. In particular, we lack computational models of processing negation that can be generalized across language. We even lack knowledge of what the development of such models would require. These models however exist and can be built by means of existing cross-lingual resources, even when annotated data for a language other than English is not available. This thesis shows this in the context of detecting string-level negation scope, i.e. the set of tokens in a sentence whose meaning is affected by a negation marker (e.g. 'not'). Our contribution has two parts. First, we investigate the scenario where annotated training data is available. We show that Bi-directional Long Short Term Memory (BiLSTM) networks are state-of-the-art models whose features can be generalized across language. We also show that these models suffer from genre effects and that for most of the corpora we have experimented with, high performance is simply an artifact of the annotation styles, where negation scope is often a span of text delimited by punctuation. Second, we investigate the scenario where annotated data is available in only one language, experimenting with model transfer. To test our approach, we first build NEGPAR, a parallel corpus annotated for negation, where pre-existing annotations on English sentences have been edited and extended to Chinese translations. We then show that transferring a model for negation scope detection across languages is possible by means of structured neural models where negation scope is detected on top of a cross-linguistically consistent representation, Universal Dependencies. On the other hand, we found cross-lingual lexical information only to help very little with performance. Finally, error analysis shows that performance is better when a negation marker is in the same dependency substructure as its scope and that some of the phenomena related to negation scope requiring lexical knowledge are still not captured correctly. In the conclusions, we tie up the contributions of this thesis and we point future work towards representing negation scope across languages at the level of logical form as well.
286

Relação entre reflectâncias de imagens orbitais e transporte de sedimentos em suspensão no Rio Doce

Vilches, Thanira Thammy Bastos 11 March 2013 (has links)
Made available in DSpace on 2016-12-23T14:04:28Z (GMT). No. of bitstreams: 1 Thanira Thammy Bastos Vilches.pdf: 1736718 bytes, checksum: 0125ce265ba8a796bb53677bd39e82a4 (MD5) Previous issue date: 2013-03-11 / Suspended solids transport excess, caused by erosion, may limit water use and cause rivers siltation. Suspended solids concentration may be assessed by remote sensing because the reflectance of the scenes, in the visible and infrared ranges, is positively influenced. This work aims at the understanding of the variability of suspended sediments concentrations in a Doce river stretch located in Espírito Santo state, Brazil, through spectral analysis of satellite images data and analysis of field measurements results. There were analyzed suspended solids concentrations for samples collected in Regência and Colatina Doce river sections and images captured by LANDSAT 5 TM satellite. To obtain reflectance values, the following operations were performed: geometric correction, conversion of DN values to apparent FRB values, atmospheric correction, using the 6S model (FRB surface), and transformation of NCs values.The results showed that, for the images corrected from atmospheric effects, the values of the ND curve related to the apparent FRB are higher than the values of the surface s FRB curve in the visible region, due to the electromagnetic radiation scattering phenomenon. In the near-infrared regions, the reverse was observed, because of the absorption of electromagnetic radiation by the atmosphere. It was observed positive correlation between reflectance and suspended solids concentration, despite the difficulties in obtaining data from same satellite images and field sample collection dates. For Regência data, the best correlation was obtained for band 1, located in the visible range of the surface s FRB curve, suggesting less suspended sediment transport. For Colatina, the best correlation occurred for band 4, located in the near-infrared range of the same surface s FRB curve, indicating greater sediment transport in this part of the Doce river during the sampling dates. It was concluded that the surface reflectance best represents the water spectral curve and that the correlated data showed the following pattern: smaller reflectance corresponds to lower water suspended solids concentration / O transporte de sólidos em suspensão, causado por erosão, é um dos problemas que limitam o uso da água, podendo causar assoreamento nos rios. A concentração de sólidos suspensos pode ser avaliada através do sensoriamento remoto, pois a reflectância da cena, na faixa do visível e do infravermelho, é positivamente influenciada. Desta forma, este trabalho visa o conhecimento da variabilidade das concentrações de sedimentos em suspensão no trecho do rio Doce localizada no ES, através de análises de dados espectrais contidos nas imagens orbitais e de resultados de medições em campo. Para tanto, foram avaliados dados concentrações de sólidos suspensos em amostras coletadas em Regência e Colatina, e imagens TM do satélite LANDSAT 5. Para obtenção dos valores de reflectância, foram realizadas as seguintes operações: correção geométrica, conversão dos NDs para valores de FRB aparente, correção atmosférica com uso do modelo 6S (FRB superfície), e transformação de NCs em valores de reflectância. Os resultados mostraram que nas imagens corrigidas dos efeitos atmosféricos, os valores da curva de ND referentes aos FRBs aparentes são superiores aos valores da curva FRB de superfície na região do visível, devido ao fenômeno de espalhamento da radiação eletromagnética. Nas regiões do infravermelho próximo, ocorreu o inverso, uma vez que há absorção da radiação eletromagnética pela atmosfera. Quanto aos sólidos suspensos, foram encontradas correlações positivas entre a reflectância e a concentração dos sólidos suspensos, apesar das dificuldades de obtenção de dados concomitantes das datas de imagens orbitais com datas da coleta de campo. Para os dados de Regência, a melhor correlação ocorreu para banda 1, que se localiza na faixa do visível, da curva dos FRB de superfície, sugerindo menor transporte de sedimentos suspensos. Para Colatina, ocorreu para banda 4, que se encontra na faixa do infravermelho próximo, também para curva dos FRB de superfície, sugerindo maior transporte de sedimentos nesse trecho do rio Doce, para as datas de amostragem. Conclui-se que a reflectância que melhor representa a curva espectral da água é de superfície e os dados correlacionados seguiram o padrão de quanto menores as reflectâncias, menores as concentrações de sólidos suspensos na água
287

AnÃlise NumÃrica do Acoplador Duplo NÃo-Linear Baseado em Fibras de Cristais FotÃnicos (NLDC-PCF) Operando com PAM e PWM para ObtenÃÃo de Portas LÃgicas / Numerical Analysis of Nonlinear Dual Core Coupler Based on Photonic Crystal Fibers (PCF-NLDC) Operating with PAM and PWM for Obtaining Logic Gates

Marcos Benedito Caldas Costa 01 January 2013 (has links)
CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / Neste trabalho, apresentamos uma anÃlise numÃrica para a obtenÃÃo de portas lÃgicas totalmente Ãptica baseada em um acoplador direcional nÃo-linear simÃtrico (NLDC) em fibras de cristal fotÃnico (PCF). O projeto mais comumente usado para o NLDC-PCF à uma fibra holey, utilizada neste trabalho, em que a seÃÃo transversal à uma matriz periÃdica de buracos de ar que se prolonga por todo o comprimento da fibra, operando com dois pulsos de luz ultracurtos na forma de sÃlitons, de duraÃÃo mÃnima de 100fs (femtosegundos). Investigamos dois formatos de modulaÃÃo por pulsos, a modulaÃÃo por amplitude de pulso (PAM) na modalidade de chaveamento de mudanÃa de amplitude (ASK) e a modulaÃÃo por largura de pulso (PWM) para obter portas lÃgicas no NLDC-PCF duplo simÃtrico. Avaliamos o efeito resultante de um incremento no parÃmetro codificaÃÃo PAM (ε) e PWM (w), considerando a dispersÃo de segunda ordem (β2), a dispersÃo de terceira ordem (β3) e efeitos nÃo-lineares, tais como: SPM (Self Phase Modulation), SS (Self-Steepening) e IRS (lntrapulse Raman Scattering) em uma configuraÃÃo sem perdas. Os nossos resultados indicam que à possÃvel obter operaÃÃes lÃgicas utilizando um controle de fase entre os pulsos de entrada. / We present a numerical analysis for obtaining all-optical logic gates based on a nonlinear directional coupler symmetric (NLDC) based on photonic crystal fibers (PCF). The most commonly used to project the NLDC-PCF is a holey fiber, used here in cross section which is a periodic array of air holes extending through the length of the fiber, using two ultrashort light pulses in form of solitons, the minimum duration of 100fs (femtoseconds). We investigated two forms of modulation pulse, pulse amplitude modulation (PAM) in the form of amplitude shift keying (ASK) modulation and pulse width modulation (PWM) for logic gate NLDC-PCF symmetrical double. We evaluated the effect resulting from an increase in the offset parameter encoding PAM (ε) and PWM (w), considering the second order dispersion (β2), the third order dispersion (β3) and non-linear modulation effects SPM (Self Phase Modulation), SS (Self-Steepening) and IRS (lntrapulse Raman Scattering) in a configuration without loss. Our results indicate that logical operations can be obtained using a phase control between the input pulses.
288

Metodologia para a coordenação e seletividade da proteção direcional de sobrecorrente em sistemas de transmissão de energia elétrica / Methodology for the coordination and selectivity of directional overcurrent protection in electrical power transmission systems

Danilo Luiz Alves Negrão 31 March 2015 (has links)
Este trabalho propõe uma nova metodologia para a solução do problema de coordenação de relés direcionais de sobrecorrente em sistemas de transmissão em malha. São utilizadas informações sobre a atuação do relé como dispositivo de proteção principal (ou retaguarda local no caso de se considerar o relé de distância) e também de sua atuação como proteção de retaguarda remota, fornecendo uma base mais sólida para definição dos ajustes. A partir de uma série de critérios determinados de acordo com a instalação, define-se uma área de ajuste do relé, diretamente sobre sua curva de atuação. Sobre esta área, aplica-se um método de otimização capaz de encontrar o melhor ajuste possível para o dispositivo em análise. A metodologia é aplicada sem a necessidade de uma análise topológica do sistema, sendo que as informações da localização do relé e sua integração com os outros dispositivos de proteção são resumidas durante o estudo de curto-circuito, que fornece os dados de entrada para a metodologia. O algoritmo resume os critérios de coordenação em pontos de referência, de modo que a análise é feita relé a relé, eliminando assim problemas comuns como o de tratamento de banco de dados e ganhando em agilidade e simplicidade no tratamento do problema. A resposta fornecida é bastante intuitiva, sendo fácil entender os resultados obtidos e quais seriam as implicações caso na prática sejam necessárias adequações à instalação. / This work proposes a new methodology to solve the problem of coordination of directional overcurrent relays in meshed transmission systems. Using information about the operation of the directional relay as primary protection (or local backup, in the case of considering the distance relay) and also its role as remote backup protection, the methodology provides a more solid basis for defining settings. Based on a series of criteria determined in accordance with the installation, an area of relay feasible settings is defined directly over their time-overcurrent curve. On this area, an optimization method is applied to find the best possible setting for the device under analysis. The method is applied without the need for topological analysis of the system, and the information of the relay location and its integration with other protective devices are summarized during the short circuit study, which provides the input data for the methodology. The algorithm summarizes the criteria of coordination in landmarks and the analysis is performed relay by relay, thus common problems are eliminated, such as database treatment, gaining agility and simplicity in treating the problem. The answer provided is extremely intuitive, making it easy to understand the results and what would be the implications in case of, in practice, be necessary to perform adjustments to fit with the installation.
289

Integration of electric vehicles in a flexible electricity demand side management framework

Wu, Rentao January 2018 (has links)
Recent years have seen a growing tendency that a large number of generators are connected to the electricity distribution networks, including renewables such as solar photovoltaics, wind turbines and biomass-fired power plants. Meanwhile, on the demand side, there are also some new types of electric loads being connected at increasing rates, with the most important of them being the electric vehicles (EVs). Uncertainties both from generation and consumption of electricity mentioned above are thereby being introduced, making the management of the system more challenging. With the proportion of electric vehicle ownership rapidly increasing, uncontrolled charging of large populations may bring about power system issues such as increased peak demand and voltage variations, while at the same time the cost of electricity generation, as well as the resulting Greenhouse Gases (GHG) emissions, will also rise. The work reported in this PhD Thesis aims to provide solutions to the three significant challenges related to EV integration, namely voltage regulation, generation cost minimisation and GHG emissions reduction. A novel, high-resolution, bottom-up probabilistic EV charging demand model was developed, that uses data from the UK Time Use Survey and the National Travel Survey to synthesise realistic EV charging time series based on user activity patterns. Coupled with manufacturers' data for representative EV models, the developed probabilistic model converts single user activity profiles into electrical demand, which can then be aggregated to simulate larger numbers at a neighbourhood, city or regional level. The EV charging demand model has been integrated into a domestic electrical demand model previously developed by researchers in our group at the University of Edinburgh. The integrated model is used to show how demand management can be used to assist voltage regulation in the distribution system. The node voltage sensitivity method is used to optimise the planning of EV charging based on the influence that every EV charger has on the network depending on their point of connection. The model and the charging strategy were tested on a realistic "highly urban" low voltage network and the results obtained show that voltage fluctuation due to the high percentage of EV ownership (and charging) can be significantly and maintained within the statutory range during a full 24-hour cycle of operation. The developed model is also used to assess the generation cost as well as the environmental impact, in terms of GHG emissions, as a result of EV charging, and an optimisation algorithm has been developed that in combination with domestic demand management, minimises the incurred costs and GHG emissions. The obtained results indicate that although the increased population of EVs in distribution networks will stress the system and have adverse economic and environmental effects, these may be minimised with careful off-line planning.
290

Rétrodiffusion micro-onde par la surface océanique en incidence élevée : approche conjointe expérimentale et théorique / Microwave backscattering from the sea surface at large incidence angles : a joint theoretical and experimental approach

Guerraou, Zaynab 26 September 2017 (has links)
Un nombre croissant de données satellitaires et aéroportées acquises dans le domaine micro-ondes sur la surface demer est aujourd’hui disponible. L’interprétation correcte de ces observations dépend d’une part de la précision desmodèles de diffusion électromagnétiques, et d’une autre part de la maîtrise des propriétés hydrodynamiques etstatistiques de la surface. Ces dernières années ont connu une amélioration considérable des modèlesélectromagnétiques et spectraux. Cependant, certains phénomènes sont encore mal compris et non pris en comptepar ces modèles. En particulier, la variation angulaire de la surface de mer est à ce jour non totalement caractériséeet modélisée. Ce travail de thèse concerne l’étude de cette variation azimutale et des asymétries directionnelles de lasurface de mer. Une première étape consiste à effectuer une analyse expérimentale en se basant sur les données dela littérature mais également sur d’autres jeux de données acquises par l’ONERA et le DSTO. Cette analysepermettra de caractériser les asymétries directionnelles en fonction de la géométrie d’observation, l’état de mer et lafréquence électromagnétique. Une seconde étape consiste à proposer des mécanismes physiques pouvant être àl’origine des asymétries directionnelles. L’asymétrie upwind-crosswind étant essentiellement liée à la fonctiond’étalement du spectre directionnel, notre étude théorique a principalement porté sur la caractérisation del’asymétrie upwind-downwind. Nous étudions l’influence de la prise en compte des formes déferlantes, initialementà travers des formes simples de vagues fortement asymétriques, et ensuite à travers une distribution de pentesexpérimentale prenant en compte ces formes de vagues. Les asymétries obtenues par un modèle deux-échellesprenant en compte ces formes de vagues sont en accord qualitatif avec les asymétries observées pour les bandes defréquences X et L. Une étape supplémentaire consiste ensuite à calculer les asymétries obtenues par un code dediffusion rigoureux sur des profils numérisés d’une expérience en soufflerie et permet la validation des résultatsobtenus avec un modèle deux-échelles. / An increasing number of airborne and spaceborne data acquired in the microwave regime on the sea surface is nowavailable. The appropriate interpretation of these observations depends on the precision of the electromagneticscattering models as well as the knowledge of hydrodynamic and statistical properties of the sea surface. Aconsiderable improvement has been realized in electromagnetic and spectral models in the recent years. However,some phenomena are still poorly understood and not correctly taken into account in these models. In particular, theangular variation of the sea surface is still not totally characterized and modeled. This PhD work concerns the studyof this azimuthal variation and the related directional asymmetries. A first step consists in carrying out anexperimental analysis based on data of the literature and other datasets acquired by ONERA and DSTO. Thisanalysis enables the characterization of the directional asymmetries with respect to acquisition geometry, sea stateand electromagnetic frequency. A second step consists in suggesting and testing physical mechanisms that may beat the origin of these directional asymmetries. As the upwind-crosswind asymmetry is essentially related to thespreading function of the directional spectrum, our theoretical study focused on the study of the upwind-downwindasymmetry. We investigate the influence of the presence breaking waves, initially through simple forms of stronglyasymmetric waves, and then through an experimental slope distribution including these wave forms. Theasymmetries obtained by a two-scale model taking into account these wave forms are in qualitative agreement withthe asymmetries observed at X and L bands. A further step consists in calculating the asymmetries using a rigorousmodel on digitized wind tank experiment profiles and allows the validation of the results previously obtained usinga two-scale model.

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