A detecção de descargas parciais em transformadores consiste em importante metodologia de manutenção preventiva e preditiva. Neste contexto, a proposta desta pesquisa com o uso de sensores acústicos de piezoeletreto apresenta-se como um tema original e altamente relevante no desenvolvimento da tecnologia brasileira. A multidisciplinaridade do tema exigiu a realização de uma extensa pesquisa bibliográfica envolvendo os temas descargas parciais, métodos de detecção das descargas, piezeletricidade, eletretos, piezoeletretos, técnicas de manufatura do piezoeletreto proposto para a detecção de descargas e ferramentas de processamento de sinais, sendo a principal a deconvolução homomórfica. O Trabalho evoluiu para a elaboração de um primeiro protótipo laboratorial, constituído basicamente de um sensor piezoeletreto e um circuito amplificador, ambos abrigados em um invólucro metálico para assegurar uma blindagem eletromagnética. Os primeiros ensaios, em face da característica \"sui generis\" do protótipo, apontaram para a necessidade de novos circuitos e aprimoramento das metodologias desses ensaios laboratoriais, as quais também fazem parte do escopo deste trabalho. O desenvolvimento de um sistema de alta tensão autônomo, eletromagneticamente blindado e gerador de descargas elétricas impulsivas é um exemplo dos circuitos mencionados. A nova metodologia de testes buscou apresentar a evolução do comportamento acústico de uma descarga em diferentes ambientes, isto é, desde sinais sem ecos até sinais carregados com ecos e distorcidos pelo meio. Finalizando o trabalho, outra contribuição importante foi a decisão de analisar os sinais acústicos das descargas parciais pela deconvolução homomórfica, que mostrou ser essencial na remoção de ecos e na reconstrução do sinal acústico original. / Partial discharges acoustic detection is a very important preventive and predictive maintenance tool for transformers. In this research, a new acoustic piezoelectric sensor, based in Brazilian technology, was presented. However, before the construction of the prototype, an extensive literature was analyzed, including partial discharge, methods of discharges detection, piezoelectricity, electrets, piezoelectrets, manufacturing of the piezoelectret proposed to detection of discharges and signal processing tools, in special the homomorphic deconvolution. Basically, the prototype developed consists of a piezoelectret sensor and an amplifier circuit, assembled in a special metallic box, to shield any electromagnetic interference. During the tests, it was detected the need to create new circuits and to improve laboratory methodologies. A new impulse high-voltage generator electromagnetically shielded can be cited as an example of these circuits here developed. The new testing methodology aimed to present the evolution of the acoustic behavior of a discharge in different environments, in other words, from signals without echoes to signals containing echoes and distorted by the environment. In the processing signals context, another important contribution was the decision to analyze the acoustic signals of partial discharges by homomorphic deconvolution, which has allowed the reconstruction of the original acoustic signal without echo.

Os problemas de separação cega de fontes e desconvolução cega multiusuário vêm sendo intensamente estudados nas últimas décadas, principalmente devido às inúmeras possibilidades de aplicações práticas. A desconvolução multiusuário pode ser compreendida como um problema particular de separação de fontes em que o sistema misturador é convolutivo, e as estatísticas das fontes, que possuem alfabeto finito, são bem conhecidas. Dentre os desafios atuais nessa área, cabe destacar que a obtenção de soluções adaptativas para o problema de separação cega de fontes com misturas convolutivas não é trivial, pois envolve ferramentas matemáticas avançadas e uma compreensão aprofundada das técnicas estatísticas a serem utilizadas. No caso em que não se conhece o tipo de mistura ou as estatísticas das fontes, o problema é ainda mais desafiador. Na área de Processamento Estatístico de Sinais, soluções vêm sendo propostas para resolver casos específicos. A obtenção de algoritmos adaptativos eficientes e numericamente robustos para realizar separação cega de fontes, tanto envolvendo misturas instantâneas quanto convolutivas, ainda é um desafio. Por sua vez, a desconvolução cega de canais de comunicação vem sendo estudada desde os anos 1960 e 1970. A partir de então, várias soluções adaptativas eficientes foram propostas nessa área. O bom entendimento dessas soluções pode sugerir um caminho para a compreensão aprofundada das soluções existentes para o problema mais amplo de separação cega de fontes e para a obtenção de algoritmos eficientes nesse contexto. Sendo assim, neste trabalho (i) revisitam-se a formulação dos problemas de separação cega de fontes e desconvolução cega multiusuário, bem como as relações existentes entre esses problemas, (ii) abordam-se as soluções existentes para a desconvolução cega multiusuário, verificando-se suas limitações e propondo-se modificações, resultando na obtenção de algoritmos com boa capacidade de separação e robustez numérica, e (iii) relacionam-se os critérios de desconvolução cega multiusuário baseados em curtose com os critérios de separação cega de fontes. / Blind source separation and blind deconvolution of multiuser systems have been intensively studied over the last decades, mainly due to the countless possibilities of practical applications. Blind deconvolution in the multiuser case can be understood as a particular case of blind source separation in which the mixing system is convolutive, and the sources, which exhibit a finite alphabet, have well known statistics. Among the current challenges in this area, it is worth noting that obtaining adaptive solutions for the blind source separation problem with convolutive mixtures is not trivial, as it requires advanced mathematical tools and a thorough comprehension of the statistical techniques to be used. When the kind of mixture or source statistics are unknown, the problem is even more challenging. In the field of statistical signal processing, solutions aimed at specific cases have been proposed. The development of efficient and numerically robust adaptive algorithms in blind source separation, for either instantaneous or convolutive mixtures, remains an open challenge. On the other hand, blind deconvolution of communication channels has been studied since the 1960s and 1970s. Since then, various types of efficient adaptive solutions have been proposed in this field. The proper understanding of these solutions can suggest a path to further understand the existing solutions for the broader problem of blind source separation and to obtain efficient algorithms in this context. Consequently, in this work we (i) revisit the problem formulation of blind source separation and blind deconvolution of multiuser systems, and the existing relations between these problems, (ii) address the existing solutions for blind deconvolution in the multiuser case, verifying their limitations and proposing modifications, resulting in the development of algorithms with proper separation performance and numeric robustness, and (iii) relate the kurtosis based criteria of blind multiuser deconvolution and blind source separation.

Diffusion of water molecules in biological tissues depends on several microstructural properties. Therefore, diffusion Magnetic Resonance Imaging (dMRI) is a useful tool to infer and study microstructural brain changes in the context of human development, ageing and neuropathology. In this thesis, the state-of-the-art of advanced dMRI techniques is explored and strategies to overcome or reduce its pitfalls are developed and validated. Firstly, it is shown that PCA denoising and Gibbs artefact suppression algorithms provide an optimal compromise between increased precision of diffusion measures and the loss of tissue's diffusion non-Gaussian information. Secondly, the spatial information provided by the diffusion kurtosis imaging (DKI) technique is explored and used to resolve crossing fibres and generalize diffusion measures to cases not limited to well-aligned white matter fibres. Thirdly, as an alternative to diffusion microstructural modelling techniques such as the neurite orientation dispersion and density imaging (NODDI), it is shown that spherical deconvolution techniques can be used to characterize fibre crossing and dispersion simultaneously. Fourthly, free water volume fraction estimates provided by the free water diffusion tensor imaging (fwDTI) are shown to be useful to detect and remove voxels corrupted by cerebrospinal fluid (CSF) partial volume effects. Finally, dMRI techniques are applied to the diffusion data from the large collaborative Cambridge Centre for Ageing and Neuroscience (CamCAN) study. From these data, the inference provided by diffusion anisotropy measures on maturation and degeneration processes is shown to be biased by age-related changes of fibre organization. Inconsistencies of previous NODDI ageing studies are also revealed to be associated with the different age ranges covered. The CamCAN data is also processed using a novel non-Gaussian diffusion characterization technique which is invariant to different fibre configurations. Results show that this technique can provide indices specific to axonal water fraction which can be linked to age-related fibre density changes.

We have used a series of observations of HD119419, performed in 2012 and 2013at the European Southern Observatory 3.6-m telescope in La Silla, Chile. These are high resolutionspectropolarimetric observations with coverage in all four Stokes parameters. We performed a chemical abundance analysis of HD119419, in the absence of any being published previously for this star. We used a LLmodels stellar atmosphere code with effective temperature11500 K and surface gravity log g = 4.0, together with the spectrum synthesis code synmast. Abundances were adjusted until the synthetic spectra matched the mean observed spectra as well as possible, and these abundances were assumed to be representative of the photosphere of HD119419. We found good estimates for some Fe-peak elements and rare-earth elements. The abundance estimates were used to compute least-squares deconvolution Stokes spectra, from which we calculated how the longitudinal magnetic field and net linear polarization varies with rotational phase for HD119419. We calculated an improved rotational period for HD119419 using our longitudinal magnetic field measurements together with previous measurements from the literature, determining it to be 2.60059(1) days. We found that the Stokes QUV are unusually strong for the rare-earth elements in HD119419, considering their weaker Stokes I profiles compared to the Fe-peak elements in particular.

The continuous advancement in wireless communications technology demands new approaches to improving the capacity of existing radio links. The high data throughput required can be achieved by the complete utilization of space, time and polarization diversities inherent in any propagation environment. Among the different propagation scenarios, the indoor channels represent a particularly challenging problem given the number and complexity of interactions between the transmitted signal and the environment. This dissertation explores the interrelation between propagation physics and space-time-polarization diversity based on a novel high resolution channel sounding and reconstruction technique. First, a method to reconstruct the indoor complex channel response based on a limited set of samples and the elimination of the interference using deconvolution techniques is presented. Then, the results for the joint angle-of-arrival, delay characterization and depolarization of electromagnetic waves are presented. Finally, a novel approach to using depolarized multipath signals to boost the receiver signal-to-noise performance is presented. The current study shows that full utilization of the diversities of channel novel wireless systems can be proposed with significant improvement in capacity.

The continuous advancement in wireless communications technology demands new approaches to improving the capacity of existing radio links. The high data throughput required can be achieved by the complete utilization of space, time and polarization diversities inherent in any propagation environment. Among the different propagation scenarios, the indoor channels represent a particularly challenging problem given the number and complexity of interactions between the transmitted signal and the environment. This dissertation explores the interrelation between propagation physics and space-time-polarization diversity based on a novel high resolution channel sounding and reconstruction technique. First, a method to reconstruct the indoor complex channel response based on a limited set of samples and the elimination of the interference using deconvolution techniques is presented. Then, the results for the joint angle-of-arrival, delay characterization and depolarization of electromagnetic waves are presented. Finally, a novel approach to using depolarized multipath signals to boost the receiver signal-to-noise performance is presented. The current study shows that full utilization of the diversities of channel novel wireless systems can be proposed with significant improvement in capacity.

Ultra-wideband (UWB) technology is the next viable solution for applications in wireless personal area network (WPAN), body area network (BAN) and wireless sensor network (WSN). However, as application evolves toward a more realistic situation, wideband channel characteristics such as pulse distortion must be accounted for in channel modeling. Furthermore, application-oriented services such as ranging and localization demand fast prototyping, real-time processing of measured data, and good low signal-to-noise ratio (SNR) performance. Despite the tremendous effort being vested in devising new receivers by the global research community, channel-estimating Rake receiver is still one of the most promising receivers that can offer superior performance to the suboptimal counterparts. However, acquiring Nyquist-rate samples costs substantial power and resource consumption and is a major obstacle to the feasible implementation of the asymptotic maximum likelihood (ML) channel estimator. In this thesis, we address all three aspects of the UWB impulse radio (UWB-IR), in three separate contributions. First, we study the {\it a priori} dependency of the CLEAN deconvolution with real-world measurements, and propose a high-resolution, multi-template deconvolution algorithm to enhance the channel estimation accuracy. This algorithm is shown to supersede its predecessors in terms of accuracy, energy capture and computational speed. Secondly, we propose a {\it regularized} least squares time-of-arrival (ToA) estimator with wavelet denoising to the problem of ranging and localization with UWB-IR. We devise a threshold selection framework based on the Neyman-Pearson (NP) criterion, and show the robustness of our algorithm by comparing with other ToA algorithms in both computer simulation and ranging measurements when advanced digital signal processing (DSP) is available. Finally, we propose a low-complexity ML (LC-ML) channel estimator to fully exploit the multipath diversity with Rake receiver with sub-Nyquist rate sampling. We derive the Cram\'er-Rao Lower Bound (CRLB) for the LC-ML, and perform simulation to compare our estimator with both the $\ell_1$-norm minimization technique and the conventional ML estimator.

La polarisation du quark top produit par interaction électrofaible (single-top) en voie-t permet de tester la structure du vertex Wtb: le couplage vecteur gauche prévu dans le cadre du Modèle Standard (MS), ainsi que les couplages anormaux vecteur ou tenseur introduits par plusieurs théories au-delà du Modèle Standard. Le lot de données correspondant à une luminosité integrée de 4,7 fb-1 recolté dans les collisions proton-proton à une énergie de 7 TeV dans le centre de masse offre une chance de mesurer la polarisation du quark top. Cette thèse traite de la mesure de la polarisation du quark top grâce à l'étude des distributions angulaires polarisées dans des bases spécifiques avec les événements single-top produits en voie-t. Au début du document, le contexte théorique de production du quark top par interaction forte et électrofaible au LHC est introduit. Ensuite, le détecteur, les performances de reconstruction ainsi que la sélection d'événements avec une signature single-top en voie-t, sont décrits. Les méthodes d' "unfolding" et de "folding" sont présentées et testées avec différentes configurations afin de mesurer la polarisation du quark top. Les résultats obtenus, ainsi que les incertitudes théorique, expérimentales et statistiques, sont examinées. Il s'agit de la première mesure de polarisation du quark top avec le détecteur ATLAS. Les résultats sont compatibles avec les prédictions MS, et contribuent donc à contraindre de maniére significative les couplages anormaux sur le vertex Wtb. / The top quark polarization in electroweak production for single top t-channel allows to test the structure of the Wtb vertex: the left-handed vector coupling of the Standard Model (SM) as well as the anomalous couplings including the right-handed vector, the left-handed tensor and the right-handed tensor couplings. The 4.7 fb-1 data recorded by the ATLAS detector at the LHC with the center of mass energy at 7 TeV in 2011 provides a chance to measure the top polarization. This thesis discusses the measurement of the top polarization by studying the polarized angular distributions in specific bases with t-channel single top events. In the beginning of the thesis, a theoretical context of the top quark production via the strong interaction and the electroweak interaction at the LHC is introduced. Then the detector, the reconstruction performances as well as the event selections with a single top t-channel event signature are described. To measure the top polarization, the unfolding and folding methods are constructed and tested with different configurations. In the end, the measured results are examined with the estimated uncertainties from the theory, the detector response and modeling as well as the statistics. This is the first measurement of the top polarization with the ATLAS detector. The results are compatible with the SM predictions and contribute signicantly to constrain the anomalous couplings in the Wtb vertex

Ce travail de thèse porte sur l'imagerie multispectrale à haut contraste pour la détection et la caractérisation directe d'exoplanètes. Dans ce contexte, le développement de méthodes innovantes de traitement d'images est indispensable afin d'éliminer les tavelures quasi-statiques dans l'image finale qui restent à ce jour, la principale limitation pour le haut contraste. Bien que les aberrations résiduelles instrumentales soient à l'origine de ces tavelures, aucune méthode de réduction de données n'utilise de modèle de formation d'image coronographique qui prend ces aberrations comme paramètres. L'approche adoptée dans cette thèse comprend le développement, dans un cadre bayésien, d'une méthode d'inversion fondée sur un modèle analytique d'imagerie coronographique. Cette méthode estime conjointement les aberrations instrumentales et l'objet d'intérêt, à savoir les exoplanètes, afin de séparer correctement ces deux contributions. L'étape d'estimation des aberrations à partir des images plan focal (ou phase retrieval en anglais), est la plus difficile car le modèle de réponse instrumentale sur l'axe dont elle dépend est fortement non-linéaire. Le développement et l'étude d'un modèle approché d'imagerie coronographique plus simple se sont donc révélés très utiles pour la compréhension du problème et m'ont inspiré des stratégies de minimisation. J'ai finalement pu tester ma méthode et d'estimer ses performances en terme de robustesse et de détection d'exoplanètes. Pour cela, je l'ai appliquée sur des images simulées et j'ai notamment étudié l'effet des différents paramètres du modèle d'imagerie utilisé. J'ai ainsi démontré que cette nouvelle méthode, associée à un schéma d'optimisation fondé sur une bonne connaissance du problème, peut fonctionner de manière relativement robuste, en dépit des difficultés de l'étape de phase retrieval. En particulier, elle permet de détecter des exoplanètes dans le cas d'images simulées avec un niveau de détection conforme à l'objectif de l'instrument SPHERE. Ce travail débouche sur de nombreuses perspectives dont celle de démontrer l'utilité de cette méthode sur des images simulées avec des coronographes plus réalistes et sur des images réelles de l'instrument SPHERE. De plus, l'extension de la méthode pour la caractérisation des exoplanètes est relativement aisée, tout comme son extension à l'étude d'objets plus étendus tels que les disques circumstellaire. Enfin, les résultats de ces études apporteront des enseignements importants pour le développement des futurs instruments. En particulier, les Extremely Large Telescopes soulèvent d'ores et déjà des défis techniques pour la nouvelle génération d'imageurs de planètes. Ces challenges pourront très probablement être relevés en partie grâce à des méthodes de traitement d'image fondées sur un modèle direct d'imagerie. / This research focuses on high contrast multispectral imaging in the view of directly detecting and characterizing Exoplanets. In this framework, the development of innovative image post-processing methods is essential in order to eliminate the quasi-static speckles in the final image, which remain the main limitation for high contrast. Even though the residual instrumental aberrations are responsible for these speckles, no post-processing method currently uses a model of coronagraphic imaging, which takes these aberrations as parameters. The research approach adopted includes the development of a method, in a Bayesian Framework, based on an analytical coronagraphic imaging model and an inversion algorithm, to estimate jointly the instrumental aberrations and the object of interest, i.e. the exoplanets, in order to separate properly these two contributions. The instrumental aberration estimation directly from focal plane images, also named phase retrieval, is the most difficult step because the model of on-axis instrumental response, of which these aberrations depend on, is highly non-linear. The development and the study of an approximate model of coronagraphic imaging thus proved very useful to understand the problem at hand and inspired me some minimization strategies. I finally tested my method and estimated its performances in terms of robustness and exoplanets detection. For this, I applied it to simulated images and I studied the effect of the different parameters of the imaging model I used. The findings from this research provide evidence that this method, in association with an optimization scheme based on a good knowledge of the problem at hand, can operate in a relatively robust way, despite the difficulties of the phase retrieval step. In particular, it allows the detection of exoplanets in the case of simulated images with a detection level compliant with the goal of the SPHERE instrument. The next steps will be to verify the efficiency of this new method on simulated images using more realistic coronagraphs and on real images from the SPHERE instrument. In addition, the extension of the method for the characterization of exoplanets is relatively easy, as its extension to the study of larger objects such as circumstellar disks. Finally, the results of this work will also bring some crucial insights for the development of future instruments. In particular, the Extremely Large Telescopes have already risen some technical challenges for the next generation of planet finders, which may partly be addressed by an image processing method based on an imaging model.

Made available in DSpace on 2015-03-13T17:08:36Z (GMT). No. of bitstreams: 1 RafaelSR_DISSERT_.pdf: 4378179 bytes, checksum: dc5658a221c8891102c9990af4393c19 (MD5) Previous issue date: 2013-04-13 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The 3D gravity modeling of the Potiguar rift basin consisted of a digital processing of gravity and aeromagnetic data, subsidized by the results of Euler deconvolution of gravity and magnetic data and the interpretation of seismic lines and wells descriptions. The gravity database is a compilation of independent geophysical surveys conducted by several universities, research institutions and governmental agencies. The aeromagnetic data are from the Bacia Potiguar and Plataforma Continental do Nordeste projects, obtained from the Brazilian Petroleum Agency (ANP). The solutions of the Euler Deconvolution allowed the analysis of the behavior of the rift main limits. While the integrated interpretation of seismic lines provided the delimitating horizons of the sedimentary formations and the basement top. The integration of these data allowed a 3D gravity modeling of basement topography, allowing the identification of a series of internal structures of the Potiguar rift, as well intra-basement structures without the gravity effect of the rift. The proposed inversion procedure of the gravity data allowed to identify the main structural features of the Potiguar rift, elongated in the NE-SW direction, and its southern and eastern faulted edges, where the sedimentary infill reachs thicknesses up to 5500 m. The southern boundary is marked by the Apodi and Baixa Grande faults. These faults seem to be a single NW-SE oriented fault with a strong bend to NE-SW direction. In addition, the eastern boundary of the rift is conditioned by the NE-SW trending Carnaubais fault system. It was also observed NW-SE oriented faults, which acted as transfer faults to the extensional efforts during the basin formation. In the central part of the residual anomaly map without the gravity effect of the rift stands out a NW-SE trending gravity high, corresponding to the Or?s-Jaguaribe belt lithotypes. We also observe a gravity maximum parallel to the Carnaubais fault system. This anomaly is aligned to the eastern limit of the rift and reflects the contact of different crustal blocks, limited by the eastern ward counterpart of the Portalegre Shear Zone / A modelagem gravim?trica 3D do rifte da Bacia Potiguar, apresentada neste trabalho, constituiu de um processamento digital de dados gravim?tricos e aeromagn?ticos, subsidiados pelos resultados da Deconvolu??o de Euler de dados gravim?tricos e magn?ticos e pela interpreta??o de linhas s?smicas e descri??es de po?os. O banco de dados gravim?trico ? proveniente de um trabalho de compila??o de levantamentos geof?sicos independentes realizados por diversas universidades, institui??es de pesquisa e ?rg?os governamentais. Os dados aeromagn?ticos s?o proveniente dos projetos Bacia Potiguar e Plataforma Continental do Nordeste, obtidos junto ? Ag?ncia Nacional do Petr?leo, G?s Natural e Biocombust?veis (ANP). As solu??es da Deconvolu??o de Euler possibilitaram a an?lise do comportamento dos principais limites do rifte, enquanto que a interpreta??o integrada das linhas s?smicas propiciou a delimita??o dos relevos dos horizontes da base das forma??es sedimentares e do topo do embasamento do Rifte Potiguar. A integra??o desses dados permitiu uma modelagem gravim?trica 3D do relevo do embasamento da bacia, possibilitando a identifica??o de uma s?rie de estruturas do arcabou?o estrutural do Rifte Potiguar e do embasamento cristalino sem o efeito gravim?trico do rifte. Com o procedimento de invers?o dos dados gravim?tricos, foi poss?vel identificar as principais fei??es estruturais do rifte da Bacia Potiguar, alongadas na dire??o NE-SW, bem como suas bordas falhadas nos limites Sul e Leste do rifte, onde o pacote sedimentar atinge espessuras superiores a 5500 m. O limite Sul ? marcado pelas falhas de Apodi e Baixa Grande, aparentando tratar-se de uma ?nica falha de dire??o NW-SE, com forte inflex?o para NE-SW. Observa-se ainda o limite Leste do rifte condicionado pelo Sistema de Falha Carnaubais de dire??o preferencial NE-SW. Observa-se ainda falhas de dire??o NW-SE, que atuaram como falhas de transfer?ncia aos esfor?os distensionais de forma??o da bacia. No mapa de anomalias residuais do embasamento cristalino sem o efeito gravim?trico do rifte destaca-se, na sua parte central, um alto gravim?trico de dire??o NW-SE, correspondendo a litotipos da Faixa Or?s-Jaguaribe. Observa-se ainda um m?ximo gravim?trico paralelo ao Sistema de Falhas de Carnaubais. Tal anomalia encontra-se alinhada ao limite Leste do rifte e reflete o contato de blocos crustais distintos, limitados pela continua??o Nordeste da Zona de Cisalhamento Portalegre