In this work is presented stochastic model of binaural hearing in context of another alternative models. According to latest experimental data on mammals, inhibition plays a role in interaural time difference recognition, which is a key for low frequency sound source localization. The outputs of experiments may lead to the conclusion that the binaural hearing works differently in mammals compared to birds. Nowadays there are a few theoretical works addressing this new phenomena, but all of them are relaying on a very precise inhibition timing, which was never proved as physiologically valid. On the other hand, models described in this work are based on the fact, that every neuron has a random delay when reacting to an excitation. If this time jitter is taken into account and combined with inhibitory signal, delay in the neuronal circuit and coincidence detection, then the output firing rate corresponds to the azimuth of the sound source. In this work it is shown, that such a neuronal circuits are giving the same output results compared to experimental data. The models are supported by analytical computations and numerical simulations including simulation of cochlear implant.

Le poly(3-hexylthiophène) régiorégulier (rr-P3HT) est l’un des matériaux phare pour les applications en électronique plastique. Afin d’améliorer les performances des dispositifs, il est important de comprendre et de contrôler la structure et la morphologie de la couche active. Des films minces de rr-P3HT cristallins et orientés peuvent être obtenus par epitaxie directionnelle par cristallisation (DEC) de 1,3,5-trichlorobenzène (TCB). Dans ce travail de thèse, nous présentons les avantages de la méthode DEC pour (i) déterminer la structure cristalline du rr-P3HT et pour (ii) étudier les fibres « shish-kebab », une morphologie alternative du rr-P3HT. La première partie de ce manuscrit consiste en l’analyse structurale par diffraction électronique de la forme I du P3HT obtenue dans les films epitaxiés. Afin d’affiner le modèle structural, nous avons fait varier la conformation des chaînes latérales. Dans un deuxième temps, nous avons appliqué ce même protocole afin de résoudre la structure du second polymorphe du P3HT (forme II) grâce à l’obtention de monocristaux parself-seeding. La deuxième partie du manuscrit est consacrée à l’élaboration de fibres orientées dites en « shish-kebab » par épitaxie dans un mélange TCB/Pyridine. La cinétique de croissance ainsi que l’orientation des chaînes de P3HT sont étudiés afin d’optimiser la méthode de préparation des fibres. L’effet de la masse moléculaire sur leur formation a également été évalué. Finalement les propriétés de transport de charges au sein de ces fibres ont été étudiées grâce à l’élaboration de transistors à effet de champ. / Regioregular poly(3-hexylthiophene) (rr-P3HT) is one of the promising materials for plastic electronic applications. Understanding as well as controlling the structure and morphology of the active layer is essential to improve the device efficiency. Highly crystalline and highly oriented rr-P3HT thin films can be obtained via directional epitaxial crystallization (DEC) in 1,3,5-trichlorobenzene (TCB). In this dissertation, we present the benefits of DEC method to (i) determine the crystal structure of rr-P3HT and (ii) to study shish-kebab fibers, an alternative morphology of rr-P3HT. The first part of this dissertation is related to the structural analysis of rr-P3HT form-I by using electron diffraction analysis on the epitaxied film. Furthermore, the modification of side chain conformation is used to improve the structural model. Finally, the determination protocol is also applied to resolve the preliminary crystal structure of rr-P3HT form II prepared by self-seeding method. The second part of thisdissertation is related to highly oriented shish-kebab fibers of rr-P3HT prepared by epitaxial crystallization in a mixture of TCB and pyridine. The investigations of growth kinetics and orientation of P3HT chains in the fiber are performed in order to determine the optimization of preparation conditions and growth mechanism of the fibers. In addition, the effect of molecular weight on the formation of the fibers is investigated. Finally, the charge transport properties of the fibers are measured by using the field effect transistor configuration.

Este texto trata da estimação de espectro direcional de ondas a partir de movimentos de primeira ordem de sistemas oceânicos estacionários utilizando um método de inferência bayesiano. Após descrição do método e discutidas suas principais fontes de incertezas, este foi validado experimentalmente através de ensaios com dois tipos de embarcações para ondas irregulares e mares bimodais, e verificado com dados de monitoração em escala real. Uma comparação preliminar com dados provenientes de um radar próximo ao sistema monitorado também foi feita. Com base nestes resultados, discute-se a eficiência do método e suas limitações. / This text is about estimating directional wave spectra based on first order motions of stationary systems by means of a bayesian inference method. After being described the method and its main sources of uncertainties discussed, an experimental validation was carried out with two different types of hulls for irregular waves and bimodal seas, with a posterior verification using data from a real scale monitoring campaign. Also, a preliminary comparison with data from a radar in the vicinities of the monitored system was made. Based on those results, the methods efficiency is discussed, along with its limitations.

FundaÃÃo de Amparo à Pesquisa do Estado do Cearà / Apresentamos neste trabalho, uma analise numÃrica para obtenÃÃo de portas lÃgicas em acoplador nÃo-linear simÃtrico (NLDC) em fibras de cristal fotÃnico (PCF), que em sua secÃÃo transversal à formada com matriz periÃdica de buracos de ar, operando em pulso de luz ultracurtos na forma de sÃlitons, com duraÃÃo de 100fs (fentosegundos). Foram investigados formatos dos pulsos em modulaÃÃo por amplitude de pulso (PAM), com chaveamento de mudanÃa de amplitude (ASK), com objetivo de obter portas lÃgicas no NLDC-PCF triplo planar simÃtrico. Neste trabalho usamos acopladores duplos de fibra Ãptica na constituiÃÃo de um InterferÃmetro Mach-Zenhder para construir um sensor de corrente, sua funcionalidade à aplicada para investigar a qualidade da corrente alternada, quer seja na geraÃÃo, transmissÃo ou distribuiÃÃo de energia elÃtrica. Como o interferÃmetro de Mach-Zenhder usa um agente mecÃnico, usaremos o mesmo agente para construir o sensor de corrente constituÃdo de um PiezelÃtrico. Ao fazer o comparativo dos dois sensores, podemos destinar sua usabilidade em diferenciados consumidores / In this work, a numerical analysis to obtain gates in coupler symmetrical nonlinear (NLDC) in photonic crystal fibers (PCF), which in cross section is formed with periodic array of air holes, operating in light pulse ultrashort as solitons, lasting 100fs (fentosegundos). The pulses in pulse amplitude modulation formats were investigated (WFP), with amplitude shift keying (ASK), in order to obtain logic gates in the triple NLDC PCF-planar symmetrical. In this paper we use double couplers fiber optic in setting up a Mach-Zenhder Interferometer to build a current sensor, its functionality is applied to investigate the quality alternating current, whether in the generation, transmission or distribution of electricity. Since the interferometer of Mach-Zenhder uses a mechanical agent, agent will use the same for constructing the current sensor constituted of a piezoelectric. In making the comparison of the two sensors, we can allocate its usability in different consumers

Orientadores: Amauri Garcia, Jose Eduardo Spinelli / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-12T23:27:26Z (GMT). No. of bitstreams: 1 Silva_MariaAdrinaPaixaodeSouzada_M.pdf: 3527327 bytes, checksum: 88f3012a000dcdb2956852ed7fa40402 (MD5) Previous issue date: 2008 / Resumo: Ligas de alumínio dispersas com bismuto apresentam aplicações promissoras em componentes automotivos resistentes ao desgaste. Essas dispersões de elementos de baixa temperatura de fusão diminuem a dureza e escoam facilmente em condições de deslizamento, resultando em um comportamento tribológico favorável. Muitos estudos têm sido realizados a fim de melhor compreender as distintas morfologias obtidas pela reação monotética. Algumas pesquisas assumem que a evolução do espaçamento interfásico na liga monotética Al-Bi obedece à clássica relação utilizada para eutéticos: ?2v = C, onde v é a velocidade de solidificação e C é uma constante. Não há nenhum consenso a respeito dos valores de C encontrados. Além disso, tais estudos utilizaram fornos de aquecimento à resistência do tipo Bridgman para produzir a solidificação direcional de ligas monotéticas. Existe uma falta de estudos consistentes no desenvolvimento microestrutural de ligas monotéticas durante condições de fluxo de calor transitório, que são de importância primordial, uma vez que esse tipo de fluxo de calor engloba a maioria dos processos industriais de solidificação. No presente estudo, foram feitos experimentos de solidificação unidirecional em regime não-estacionário com as ligas hipomonotética Al-2,0%Bi e monotética Al-3,2%Bi. Os parâmetros térmicos como velocidades de crescimento, taxas de resfriamento e gradientes térmicos foram determinados experimentalmente por curvas de resfriamento adquiridas ao longo do comprimento do lingote. Os crescimentos celular e monotético foram caracterizados por técnicas metalográficas, e os espaçamentos celulares e interfásicos correlacionados com os parâmetros térmicos de solidificação. Verificou-se que a lei de crescimento ?2v = C pode ser expressa por um valor de C de 1,70 x10-12, que é em torno de duas ordens de magnitude maior do que aqueles reportados para o regime estacionário. Embora o fluxo convectivo induzido não tenha sido suficiente para mudanças consideráveis na magnitude dos espaçamentos interfásicos, as partículas ricas em bismuto foram afetadas pela direção do crescimento, diminuindo o diâmetro em condições de solidificação vertical descendente, quando comparadas com aquelas obtidas no modo vertical ascendente / Abstract: Aluminium alloys dispersed with bismuth show promising applications in wear-resistant automotive components. Such dispersions of low melting temperature elements decrease hardness and flow easily under sliding conditions, resulting in favorable tribological behavior. Much research has been devoted in order to better comprehend the distinct morphologies obtained by monotectic reaction. Some researches assume that the phase spacing evolution in the monotectic Al-Bi alloy follows the classical relationship used for eutectics: ?2v = C, where v is the solidification velocity and C a constant value. There is no consensus concerning the found C values. Other than, such studies have used Bridgman-type resistance heated furnaces to produce the directionally solidified monotectic samples. There is a lack of consistent studies on the microstructural development of monotectic Al-Bi alloy during transient heat flow conditions, which are of prime importance since this class of heat flow encompasses the majority of solidification industrial processes. In the present study, directional unsteady-state solidification experiments were carried out with hypomonotectic Al-2.0wt%Bi and monotectic Al-3.2wt%Bi alloys. The thermal parameters such as growth rates, cooling rates and thermal gradients were experimentally determined by cooling curves recorded along the casting length. The cellular and monotectic growths were characterized by metallography, being both the cell and the interphase spacing correlated with the thermal parameters. It is shown that the ?2v = C growth law can be expressed by a C value of 1,7x10-12, which is about two orders of magnitude higher than those reported for the steady-state regime. Although the induced convective flow was not enough to considerably change the interphase spacing's magnitude, the Bi-rich particle diameters have been affected by the direction of growth, decreasing in conditions of downward vertical solidification when compared with those grown vertically upwards / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica

Orientador: Amauri Garcia / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-09T07:59:55Z (GMT). No. of bitstreams: 1 Rosa_DanielMonteiro_D.pdf: 8184541 bytes, checksum: 0b8d932ad9a1091a507ea6b10e4185f8 (MD5) Previous issue date: 2007 / Resumo: As morfologias das estruturas de solidificação, caracterizadas principalmente por arranjos celulares e dendríticos, e suas grandezas representadas por espaçamentos celulares e dendríticos primários, secundários e terciários, controlam os perfis de segregação e a formação de segundas fases dentro das regiões intercelulares ou interdendríticas, que determinam as propriedades finais das estruturas fundidas. O presente trabalho pretende contribuir para o entendimento do desenvolvimento microestrutural de ligas binárias através da análise de dois sistemas binários que possuem elevada importância para a indústria na fabricação de peças fundidas automotivas e grades de baterias: Al-Si e Pb-Sb, respectivamente. Os experimentos realizados utilizaram dois diferentes dispositivos em que o calor é extraído somente pelo sistema de resfriamento a água, localizado no fundo (solidificação ascendente) e no topo (solidificação descendente) da lingoteira. As variáveis térmicas de solidificação foram determinadas pela leitura de temperaturas a partir de termopares posicionados dentro da lingoteira em diferentes posições em relação à superfície refrigerada. Estas variáveis térmicas foram confrontadas com as previsões teóricas de um modelo numérico de solidificação. Os aspectos macroestruturais e microestruturais foram caracterizados ao longo dos lingotes através de microscopia óptica. Para as ligas Al-Si foi realizada uma análise complementar do efeito da convecção térmica e constitucional nos espaçamentos dendríticos terciários na solidificação unidirecional transitória descendente. Ligas hipoeutéticas Pb-Sb foram utilizadas para analisar as influências das variáveis térmicas de solidificação e da concentração de soluto nas estruturas celulares, na transição celular/dendrítica e nas estruturas dendríticas. Os espaçamentos celulares e dendríticos foram comparados com as previsões teóricas fornecidas pelos principais modelos de crescimento estacionário e transitório da literatura. Foram também examinados os efeitos da taxa de resfriamento no crescimento celular da liga Pb 0,85%Sb e a influência do tamanho celular e do perfil de macrossegregação correspondente na resistência à corrosão / Abstract: The morphologies of as-cast microstructures, characterized mainly by cellular and dendritic patterns, and their scales represented by primary, secondary and tertiary arm spacings, control the segregation profiles and the formation of secondary phases within intercellular and interdendritic regions, which determine the final properties of castings. The present work aims to contribute to the understanding of microstructural development of binary alloys by analyzing two binary systems, which possess high industrial importance in the manufacture of as-cast automotive components and battery grids: Al-Si and Pb-Sb, respectively. Experiments have been carried out by using two castings assemblies, which were designed in such way that heat was extracted only through the water-cooled system, located at the bottom (upward solidification) and at the top (downward solidification) of the casting. The solidification thermal variables have been determined from thermal readings acquired by thermocouples located inside of the casting in different positions from the cooled surface. Such experimental thermal variables have been compared with theoretical predictions of a numerical model of solidification. Macrostructural and microstructural aspects along the casting were characterized by optical microscopy. For Al-Si alloys a complementary analysis of the influence of thermosolutal convection on the tertiary dendrite arm spacing during the downward unsteady-state directional solidification has been carried out. Hypoeutectic Pb-Sb alloys have been used to analyze the influences of solute concentrations and solidification thermal variables in the development of cellular structures, the cellular/dendritic transition and dendritic structures. Experimental cellular and dendritic spacings have been compared with the theoretical predictions furnished by the main steady-state and unsteady-state growth models from the literature. The effect of cooling rate on the cellular growth of a Pb 0.85wt%Sb alloy and the influences of cell size and of the corresponding macrosegregation profile on the resultant corrosion behavior have also been examined. / Doutorado / Materiais e Processos de Fabricação / Doutor em Engenharia Mecânica

Orientador: Amauri Garcia / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-11T19:19:04Z (GMT). No. of bitstreams: 1 Cruz_KleberAugustinSabatda_D.pdf: 13994845 bytes, checksum: c0766efdbf4acbaf7d07b0db50f1fe52 (MD5) Previous issue date: 2008 / Resumo: A procura por relações funcionais correlacionando parâmetros microestruturais e o comportamento mecânico de ligas metálicas é fundamental para a pré-programação do produto final. O presente estudo pretende contribuir para o entendimento sobre a influência dos parâmetros microestruturais na resistência ao desgaste e nas propriedades mecânicas de ligas de dois sistemas binários: AI-Sn e AI-Si. Tais ligas são bastante usadas em aplicações de engenharia, tais como mancais e camisas de cilindro de motores de combustão, respectivamente. Apesar do grande uso das ligas do sistema AI-Sn como material tribológico, são escassos os estudos sobre o desenvolvimento microestrutural destas ligas na literatura. Neste estudo, quatro ligas hipoeutéticas do sistema AI-Sn e três ligas hipoeutéticas do sistema AI-Si foram submetidas a solidificação unidirecional, na direção vertical e sentido ascendente, sob condições transitórias de fluxo de calor. Os espaçamentos dendríticos primários (À1) e secundários (À2) foram medidos nas direçõe.s transversal e longitudinal dos lingotes, respectivamente, e correlacionados com as variáveis térmicas que atuaram durante a solidificação. Uma abordagem teórico-experimental foi desenvolvida para determinar quantitativamente_as variáveis térmicas, tais como: coeficiente de transferência de calor na interface metal/molde, velocidade de deslocamento da isoterma liquidus, gradientes térmicos, taxa de resfriamento e tempo local de solidificação. Este estudo também aborda a influência do teor de soluto nos espaçamentos dendríticos das ligas estudadas. Os dados experimentais obtidos, concementes à solidificação das ligas AI-Sn, são comparados com modelos de crescimento dendrítico existentes na literatura. O comportamento mecânico das ligas AI-Sn e AI-Si foi analisado por meio de ensaios de tração e de desgaste. O ensaio de desgaste utilizado foi o ensaio de micro-abrasão por esfera rotativa fixa, sob condições a seco (sem óleo lubrificante ou solução abrasiva). As amostras submetidas aos ensaios de desgaste foram retiradas na direção transversal dos lingotes. A condição a seco foi adotada para impedir a interferência de elementos interfaciais na resposta da microestrutura com relação ao desgaste mecânico. O volume de desgaste é o parâmetro quantificador da resistência ao desgaste e, são obtidas equações que correlacionam o volume de desgaste com espaçamentos dendríticos, levando em consideração o tempo de ensaio, que está relacionado com a distância de deslizamento. / Abstract: The search for relationships between microstructural parameters and mechanical behavior of alloys is fundamental for the pre-programming of final properties of as-cast components. The present study aims to contribute to the understanding about the influence of microstructural parameters on the wear resistance and mechanical properties of alloys of two binary systems: Al-Sn and AI-Si. Such alloys are widely used in engineering applications, especially as bearing components such as journal bearings and cylinder liners, respectively. Despite the wide use of Al-Sn alloys as bearing materiaIs studies on the microstructural development of such alloys are rare.. In the present study, four Al-Sn and three AI-Si hypoeutectic alloys were directionally solidified under upward unsteady state heat flow conditions. The primary (1,,1) and secondary (Â.2) dendrite arm spacings were measured along the castings length and correlated with transient solidification thermal variables. A combined theoretical and experimental approach has been used to quantitatively determine such thermal variables, i.e., transient metaVmold heat transfer coefficients, tip growth rates, thermal gradients, tip cooling rates and local solidifÍcation time. This study also focuses on the dependence of dendrite arm spacings on the alloy solute content. Furthermore, the experimental data conceming the solidification of AI -Sn alloys are compared with the main predictive dendritic models from the literature. The mechanical behaviors ofthe AI-Sn and AlSi alloys were analyzed by wear and tensile tests. Micro-abrasive wear tests under dry sliding conditions and by using a fixed rotating sphere were applied to transversal samples collected along the casting. The dry condition is adopted to prevent effects of interfacial elements such as abrasive slurry or lubricant oil on the microstructural response during the tests. The wear volume was used to evaluate the wear resistance. Afterwards, equations correlating the wear volume and the dendritic arm spacing have been proposed taking into account the influence of time (sliding distance). / Doutorado / Materiais e Processos de Fabricação / Doutor em Engenharia Mecânica

O incessante aumento do volume de informações produzido por uma sociedade cada vez mais informatizada tem elevado drasticamente os requisitos quanto ao desenvolvimento de dispositivos capazes de suportar velocidades de operação cada vez mais elevadas em tamanhos cada vez mais reduzidos. No entanto, a contínua redução do tamanho desses dispositivos, celebrado através da lei de Moore, também produz um indesejável aumento na produção de calor durante a operação dos mesmos, comprometendo seu desempenho global. Uma alternativa promissora para aliviar, ou mesmo superar, estas limitações é oferecida pelos dispositivos ópticos integrados. No entanto, todo esse avanço esbarrava no fato de que as dimensões de tais dispositivos estavam restringidas fundamentalmente ao que é largamente conhecido como limite de difração (LD). Uma maneira de contornar essa limitação é obtida através da utilização de Plásmon Poláritons de Superfície, ou SPPs, que, de maneira simplificada, são ondas que se propagam ao longo da superfície de um condutor depositado sobre um dielétrico. Estas são essencialmente ondas de luz que são localizadas na superfície por causa de sua interação com os elétrons livres do condutor. Nesta interação, os elétrons livres respondem coletivamente oscilando em ressonância com a onda de luz. No presente trabalho, o fenômeno de geração de SPPs é estudado teoricamente e aplicado na modelagem de diversas estruturas de interesse científico e tecnológico, tais como acopladores direcionais e ressoadores. O objetivo principal é a obtenção de estruturas capazes de proporcionar propagação de SPPs por longas distâncias, permitindo, assim, estender ainda mais o leque de possíveis aplicações. As estruturas são investigadas prioritariamente no COMSOL Multiphysics, um aplicativo baseado em elementos finitos que permite solução vetorial de problemas eletromagnéticos. Os resultados obtidos até o momento permitem afirmar que o conceito de SPP de longa distância (long range SPP, LRSPP) podem ser aplicados com sucesso a estruturas geometricamente complexas como os ressoadores em anel e acopladores direcionais. / The continuous growth of knowledge produced by a society with increasing access to information technologies has demanded the development of communication devices capable of supporting high processing speeds at more and more reduced sizes. Nevertheless, the continuous reduction of the size of these devices, celebrated by the Moore\'s law, has also produced an undesirable increase of heat produced during the operation of the device itself, compromising its overall performance. A promising alternative to alleviate, or even overcome, these limitations has been offered by photonic integrated circuits. However, all the advance of photonic devices was restricted to what is known as diffraction limit. A fascinating way of circumventing this limit is now available to the scientific community, and consists in the generation of Surface Plasmon Polariton (SPP) waves. In a simplified manner, SPP waves are waves that propagate along a metal/dielectric interface. These waves are essentially localized at the metal/dielectric interface because of the interaction of light with free electrons of the metal. In this interaction, the free electrons respond collectively and oscillate resonantly with the incident light. In the present work, the phenomenon of SPP generation is theoretically investigated and applied to the modeling of several structures, such as directional couplers and resonators. The primary goal of this work is to design structures capable propagating SPP waves for long distances, known as long range SPP (LRSPP). The structures are investigated mostly with COMSOL Multiphysics, a finite elements based software that allows for the vectorial solution of electromagnetic problems. The results obtained so far are extremely encouraging, and prove that the LRSPP concept can be successfully applied to geometrically complex structures, such as couplers and ring resonators.

Made available in DSpace on 2016-08-18T18:19:25Z (GMT). No. of bitstreams: 1 Nivea Fernanda Correa.pdf: 9488427 bytes, checksum: d432cb6753ed95396a5af400756eea91 (MD5) Previous issue date: 2009-02-27 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / in chains of coupled guides. These chains can serve of model for the propagation of solitons optics in directional couplers or micro-structuralized optics fibers. Systems of linearly coupled non linear Schrödinger equations had been used as theoretical model for these chains. The used numerical methods had been the split- step Fourier method and the orthogonal collocation method. The process of transference of energy between guides was characterized by the transmittance in function of the coupling factor, length of the guide and the power of entrance. In the mapping of the transmittance the diverse regions of parameters with its different behaviors had been identified. The threshold of power and the length of coupling had been gotten. The conclusions on the chains had been made on the basis of the analysis of the results in function of the total number of guides, the number of intermediate and peripheral guides and of the arrangement of couplings. For coupling arrangement the changes in the transmittances had the same been significant when the total number of guides varies, therefore it diminished the coupling length and the power threshold increased with the number of guides. Chains with same total number of guides, but with arrangements of distinct couplings had presented transmittances with clear differences in the chains of the type opened in relation to too many. The increase of the number of couplings between the guides led to an increase of the value of the power threshold, while the values of coupling length had not presented significant variations. / ópticos em cadeias de guias acoplados. Essas cadeias podem servir de modelo para a propagação de solitons ópticos em acopladores direcionais ou fibras ópticas micro-estruturadas. Sistemas de equações não lineares de Schrödinger acopladas linearmente foram utilizados como modelo teórico para essas cadeias. Os métodos numéricos utilizados foram o método de Fourier com passo dividido e o método da colocação ortogonal. O processo de transferência de energia entre guias foi caracterizado pela transmitância em função do fator de acoplamento, comprimento do guia e da potência de entrada. No mapeamento da transmitância foram identificadas as diversas regiões de parâmetros com seus diferentes comportamentos. O limiar de potência e o comprimento de acoplamento foram obtidos. As conclusões sobre as cadeias foram feitas com base na análise dos resultados em função do número total de guias, do número de guias intermediários e periféricos e do arranjo de acoplamentos. Para o mesmo arranjo de acoplamento as mudanças nas transmitâncias foram significativas quando o número total de guias varia, pois diminuiu o comprimento de acoplamento e o limiar de potência aumentou com o número de guias. Cadeias com mesmo número total de guias, mas com arranjos de acoplamentos distintos apresentaram transmitâncias com nítidas diferenças nas cadeias do tipo aberta em relação às demais. O aumento do número de acoplamentos entre os guias levou a um aumento do valor do limiar de potência, enquanto os valores de comprimento de acoplamento não apresentaram variações significativas.

Solar cells convert sunlight into electrical energy using the photo effect. With a mar-ket share of 60%, multicrystalline silicon (mc-Si) is the most frequently used absorber material. Standard mc-Si ingots are directionally solidified in a fused silica (SiO2) crucible, which exhibits a silicon nitride (Si3N4) inner coating. After the entire raw material has been melted, the nucleation takes place on the Si3N4 inner coating at the bottom of the crucible. This results in an inhomogeneous initial grain structure and an increased fraction of dislocation clusters in the upper part of the ingot, which decrease the quality of standard mc-Si. Therefore, the global goal is the development of a cost-effective technology that reduces the formation of clusters and enhances the quality of mc-Si ingots. One way of achieving that goal is to produce the so-called \"high performance multi crystalline silicon\" (HPM-Si). During the directional solidification silicon raw material remains unmelted at the bottom of the SiO2 crucible, whereby crystallization does start on the silicon feedstock a few millimeters above the crucible bottom. Compared to standard mc-Si, a finer grained structure with many small grains is formed, which are separated by so-called random grain boundaries. Since the movement of dislocations across this grain boundary type has rarely been observed, the risk of formation of dislocation clusters, which have a negative impact on the efficiency of solar cells, is greatly reduced for HPM-Si. However, the disadvantage of the HPM-Si compared to the mc-Si is the yield loss resulting from the unmelted raw material at the crucible bottom. Hence, the aim of the present work is to produce mc-Si with a fine-grained structure in combination with a high fraction of random grain boundaries without the disad-vantage of yield loss. In order to investigate the grain structure in dependence of the nucleation conditions G1 ingots having a mass of 14.5 kg and dimensions of 220x220x130 mm³ were directional solidified in a furnace. The analysis of the grain structure with respect to the grain size, grain orientation and the random grain boundary length fraction and the comparison with the HPM-Si reference crystal took place on horizontal wafers with a thickness of 3mm. One possibility to influence the grain structure of mc-Si could be the variation of the cooling conditions before the start of crystallization at the crucible bottom. In a first series of experiments, a gas-flowed cooling plate, positioned below the crucible, was used. An increased gas flow increases the axial heat flow downwards and the cooling rate below the crucible bottom in the same direction. The detected cooling rate, measured by a thermocouple in the silicon melt 5 mm above the crucible bottom, varied in a range between 0.06-1.5 K/min. An increased cooling rate increases the supercooling, with a maximum of 2K. The analysis of the grain structure shows that a reduction in the cooling rate in combination with the lowest supercooling minimizes the average grain size and increases the fraction of random grain boundaries. However, an HPM-Si like grain structure (grain size and fraction of random grain boundaries comparable to HPM-Si) could not completely produced. Furthermore, due to the extended process time, the wafer yield is reduced, whereby the reduction of the cooling rate is not a preferable method for the industrial process. In a second experimental series, which took place under constant cooling rates, the influence of an additional nucleation layer on the initial grain structure was investigated. For this purpose, the additional nucleation layer was applied on the already existing Si3N4 inner coating on the crucible bottom. In order to adjust a HPM-Si like grain structure, the contact angle of the silicon melt on the additional nucleation layer should be lower than on the Si3N4 inner coating. The theoretical basis for this hypothesis is the relationship between the contact angle and the nucleation energy, which states that a reduced contact angle lowers the nucleation energy and can ultimately lead to more nuclei. Furthermore, in order to avoid melting, the additional nucleation layer must have a higher melting point than silicon. Suitable materials for the application as a foreign seed sample are SiC, SiO2 and Al2O3, which are used in the form of particles with different sizes. The production of the additional nucleation layer was carried out by a spraying as well as by an embedding procedure. These layers exhibit different thermal conductivity as well as surface roughness. Embedded nucleation layers generate higher roughness values than sprayed nucleation layers. The analysis of the grain structure identified the surface roughness as the main influencing factor on the initial grain size. While an increased surface roughness (Rq>100μm) results in a fine-grained structure (average grain size: <2mm²) comparable to HPM-Si, the average grain size increases (>2 mm²) with a reduced surface roughness (Rq<100μm). However, the analysis of the grain boundary relationship shows that the fraction of random grain boundaries does not correlate with the average grain size. Only a ma-terial dependency was detected. All SiO2 nucleation layers generate an increased fraction of random grain boundaries, comparable to the HPM-Si material. In contrast, the fraction of random grain boundaries was reduced for all SiC nucleation layers. This result is probably established with the different thermal conductivities of the used materials. The increased thermal conductivity of the sample with the SiC nucleation layers increases the cooling rate, promoting dendritic growth. In contrast the lower thermal conductivity of the SiO2 nucleation layers reduces the cooling rate and dendritic growth is suppressed. Since dendrites exhibit a Σ3 grain boundary relationship in the center, the fraction of this grain boundary type increases for SiC nucleation layers and the fraction of random grain boundaries decreases. In this thesis, various possibilities for influencing the grain structure have been pre-sented. A SiO2 nucleation layer with a roughness value Rq> 200μm represents an industrially relevant solution for the production of mc-Si with comparable properties to the HPM-Si without the disadvantages of yield loss. Hence, it was possible to in-crease the yield with comparable material quality, whereby the production costs could be reduced. Some first crucible manufacturers have already transferred the use of the SiO2 nucleation layers on top of the already existing Si3N4 inner coating at the crucible bottom to production.