As ligas de alumínio vêm sendo amplamente usadas nas indústrias aeronáuticas e automobilísticas por suas propriedades mecânicas superiores às do metal puro. Entretanto, como as propriedades de corrosão dessas ligas variam, sendo piores do que as do alumínio puro, surge a necessidade de estudos de diferentes métodos de proteção contra a corrosão. O uso de coberturas protetoras é uma alternativa para diminuir os processos corrosivos e, desta maneira, aumentar a vida útil desses materiais. Das coberturas de conversão existentes, as mais usadas ainda são à base de cromo, porém o cromo tem se mostrado danoso ao meio ambiente e à saúde humana. Por outro lado, as coberturas de conversão à base de óxidos de cério, ambientalmente mais corretas e menos nocivas, já têm sido usadas com sucesso para este propósito. Ademais, partindo do consenso sobre o bom desempenho da polianilina (PAni) em proteger metais oxidáveis contra a corrosão, inclusive o alumínio e suas ligas, o presente estudo propõe o desenvolvimento de proteção anticorrosiva de ligas de alumínio pela combinação de camadas de conversão à base de óxidos de cério associada com camadas de PAni nas ligas de alumínio das séries AA1xxx e AA6xxx. A combinação de camadas duplex surge como uma alternativa promissora por: (i) possibilitar a formação de pontos de ancoragem sobre a superfície, promovidos pelas camadas de conversão à base de óxidos de cério, para a posterior deposição de PAni; (ii) ampliar o uso das camadas de conversão à base de óxidos de cério isoladamente ou combinadas com PAni e (iii) promover o melhor sinergismo na proteção contra a corrosão das ligas de alumínio e de outros materiais pela associação e maior interação desses sistemas. / Aluminium alloys have been widely used in automobile and aircraft industries for their superior mechanical properties to the pure metal. However, as the corrosion properties of these alloys vary, being worse than those of pure aluminium, there is a need for studies of different methods of corrosion protection. The use of protective coverings appears as an alternative to reduce the corrosion process and thereby increase the useful life of these materials. Conversion of existing coverage, the most used are still based on chrome, but chrome has proven harmful to the environment and human health. Furthermore, coverage of cerium-based conversion, more environmentally friendly and healthy, have already been successfully used for this purpose. Furthermore, based on the consensus on the proper performance of polyaniline (PAni) to protect oxidizable metals against corrosion, including aluminium and its alloys, this study proposes the development of corrosion protection of aluminium alloys by combining layers of cerium conversion associated with layers of polyaniline on aluminium alloys AA1xxx and AA6xxx series. The combination of double layers arises as a promising alternative, which may: (i) facilitating formation of anchor points on the surface, driven by layers of cerium conversion, for the subsequent deposition of PAni (ii) expand the use of cerium conversion coatings alone or combined with PAni and (iii) promote synergy in protection against corrosion of aluminium alloys and other materials by the association and greater interaction of these systems.

Made available in DSpace on 2016-04-26T20:25:32Z (GMT). No. of bitstreams: 1 Tese Olavo Pezzotti.pdf: 1221100 bytes, checksum: 9b893bec55a7f37d6dbd1b7a7ca769cf (MD5) Previous issue date: 2007-06-05 / The theme related with the attitudes or positionings that the defendant can adopt in the civil process, especially in the ordinary procedure, is quite vast and complex. Multiples are the possibilities introduced to the defendant, both to attack the procedural relationship or to refute the merit, direct or indirectly. The hypotheses that allow to the defendant exceptionally to present counterattack to the author s pretension, or to obtain for himself court protection of merit, demand requirements and present convergent characteristics and others that differentiate them. Among the cases before referred, this work approaches the denominated action duplex and counterclaim. In an perfunctory exam of these afirmations, it could be considered redundant to treat the action duplex and the counterclaim, since they would be synonymous or related institutes. In order to reach the desideratum of distinguishing the several species of defendant s counterattack and their implications related to the litigious object of the process, the dissertation was divided in four chapters. In the first chapter, it approaches the contradictory and the wide defense, the defendant s legitimacy and the eventual interference of the positionings by him adopted on the litigious object. In the second, it discourses on the several attitudes that the defendant can adopt in the civil process. In the third chapter, it examines the action duplex, both in the Civil Process Code and in the extravagant procedural legislation. In the fourth chapter, it approaches the counterclaim, comparing the convergence points and divergencies among the counterclaim species foreseen for using by the defendant. In the conclusions, it detaches the common points and divergencies between the action duplex and the other hypotheses that permit the defendant to formulate a request to obtain for him a life good, confronting them with the counterclaim, as well as the implication, application and its relationship with institutes like provisional remedy, default, reconvention and others / O tema relacionado com as atitudes ou posicionamentos que o réu pode adotar no processo civil, especialmente no que tange ao procedimento ordinário, se mostra bastante vasto e complexo. Múltiplas são as possibilidades que se apresentam ao réu, quer para atacar a relação processual, quer para impugnar o mérito, direta ou indiretamente. As hipóteses que permitem ao réu excepcionalmente apresentar contra-ataque à pretensão do autor, ou obter para si uma tutela jurisdicional de mérito, exigem requisitos e apresentam características convergentes e outras que as diferenciam. Entre os casos antes referidos, este trabalho aborda as denominadas ações dúplices e o pedido contraposto. Em um exame perfunctório da assertiva supra, poder-se-ia considerar redundante tratar de ações dúplices e do pedido contraposto, já que seriam institutos sinônimos ou correlatos. A fim de permitir alcançar o desiderato de distinguir as várias espécies de contraataque do réu e suas implicações quanto ao objeto litigioso do processo, a dissertação foi dividida em quatro capítulos. No primeiro capítulo, aborda o contraditório e a ampla defesa, a legitimidade do réu e a eventual interferência dos posicionamentos por ele adotados sobre o objeto litigioso. No segundo capítulo, discorre sobre as várias atitudes que o réu pode vir a adotar no processo civil. No terceiro capítulo, examina as ações dúplices, seja no Código de Processo Civil, seja na legislação processual extravagante. No quarto capítulo, aborda o pedido contraposto, cotejando os pontos de convergência e divergência entre as espécies de contra-ataque previstas para utilização pelo réu. Nas conclusões, destaca os pontos comuns e divergentes entre as ações dúplices e as demais hipóteses nas quais se permite ao réu formular pedido para obtenção de um bem da vida para si, confrontando-as com o pedido contraposto, bem como a implicação, aplicação e sua relação com institutos como da tutela antecipada, revelia, reconvenção e outros

A cirurgia de restauração circulatória arterial no paciente portador de isquemia crítica de membros inferiores apresenta indicações clínicas e técnica operatória já bastante estudadas e definidas. Ainda hoje, no entanto, um considerável número de enxertos evolui para oclusão. Entre as causas relacionadas à falência precoce, podemos destacar a resistência do leito distal receptor do enxerto. Interessou-nos estudar a existência de correlação hemodinâmica entre a Ecografia-Doppler, a Arteriografia pré-operatória, e medidas diretas intra-operatórias de resistência do leito arterial receptor do enxerto. Foram estudadas 68 operações de revascularização de membros inferiores portadores de isquemia crítica. A Ecografia-Doppler foi considerada tecnicamente satisfatória em 93,2%. Foi verificada a presença de correlação hemodinâmica positiva entre os métodos descritos acima (Teste de Pearson), particularmente para as artérias distais. Concluímos que a Ecografia-Doppler, além de definir as características anatômicas da artéria a ser revascularizada, pode auxiliar no estudo hemodinâmico do leito arterial receptor do enxerto e dessa forma auxiliar na definição do prognóstico do enxerto e no estabelecimento da melhor estratégia terapêutica a ser tomada ainda no período pré-operatório / The clinical indications and the surgical technique regarding arterial revascularization in patients with critical lower limb ischemia have been thoroughly studied and well determined in the literature. However, a considerable number of grafts evolutes to occlusion even nowadays. Among the factors known to contribute to early graft failure the resistance of the outflow arterial bed stands out. The purpose of this study is to verify Duplex Scanning hemodynamic correlation power with preoperative arteriography and direct intraoperative resistance measurements. Sixty-eight (68) lower limb revascularizations were studied. Preoperative Duplex Scanning was considered satisfactory in 93,2% of the cases. A positive hemodynamic correlation among the methods described above (Pearson\'s correlation test), particularly for distal arteries, has been verified. We conclude that preoperative Duplex Scanning, apart from defining the anatomic characteristics of the artery to be revascularized, can be helpful in the hemodynamic study of the arterial bed receiving the graft, making it easier to establish the graft prognosis and define the best therapeutic strategy to be adopted in the preoperative period.

Os aços inoxidáveis dúplex possuem uma estrutura bifásica (ferrita e austenita) geralmente em frações aproximadamente iguais. Devido aos altos teores de Cr e Ni, esses aços apresentam alta resistência à corrosão e, por isso, são usados principalmente nas indústrias química, petroquímica e nuclear. Dependendo da sua composição química, os aços dúplex podem sofrer transformação martensítica induzida por deformação, com a transformação de austenita (γ) em martensita (α\'). Essa transformação pode ser revertida mediante tratamento térmico. A austenita é paramagnética, enquanto que a ferrita e a martensita são ambas ferromagnéticas. O objetivo desse trabalho foi estudar a relação entre a estabilidade microestrutural e as propriedades magnéticas de um aço dúplex UNS S32304, o qual apresenta transformação martensítica induzida por deformação. Amostras desse aço com redução em espessura de 80% foram recozidas isotermicamente em várias temperaturas até 800ºC por 1 h e resfriadas em água. A partir de laços de histerese obtidos em temperatura ambiente foram obtidos os valores de magnetização de saturação (Ms) e campo coercivo (Hc) para essas amostras. Além das medidas magnéticas essas amostras foram caracterizadas via difração de raios X, testes de dureza, microscopias óptica (MO) e eletrônica de varredura (εEV). Em relação ao εEV foram utilizadas as técnicas de EBSD (do inglês \"eléctron backscatter diffraction\") e ECCI (do inglês \"electron channeling contrast imaging\"). Medidas de magnetização (in situ) em função da temperatura (até 1000ºC) também foram obtidas para o material deformado, a partir das quais foi determinada a temperatura de Curie (Tc) do mesmo. Uma simulação das fases presentes no material em função da temperatura foi obtida utilizando-se o software Thermo-Calc©. Para as amostras recozidas isotermicamente, a inspeção metalográfica mostrou que para 600-700ºC o material apresenta um aspecto fragmentado na microestrutura. Esse aspecto fragmentado é uma evidência da reversão da martensita em austenita. Para a amostra recozida em 700ºC precipitados foram encontrados principalmente na austenita, a qual parece estar recristalizada. Indícios de recristalização da ferrita também foram observados para essa amostra. De acordo com o Thermo-Calc© os precipitados observados são provavelmente do tipo M23C6 (M = Fe, Cr) e Cr2N. A dureza do material apresenta uma queda evidente a partir de 500ºC, relacionada aos fenômenos de recristalização do material e reversão da martensita. Tal como a dureza, Ms e Hc também decaem a partir de ~ 500ºC. A reversão da martensita em austenita e a decomposição da ferrita (α) contribuem para a diminuição de Ms. As medidas magnéticas in situ também forneceram evidências da transformação α → γ + precipitados a partir do comportamento de Tc. Apesar do aspecto fragmentado da microestrutura e da precipitação, não foi observado um comportamento de \"pico\" em Hc em consequência da reversão da martensita em austenita. Isso indica que, no presente estudo, o fator que mais influenciou Hc foi a maior mobilidade das paredes de domínios magnéticos na fase ferrítica, em consequência dos efeitos de recuperação e recristalização. / Duplex stainless steels have a two-phase structure (ferrite and austenite) in approximately equal fractions. Due to their high Cr and Ni contents, these steels present a high corrosion resistance and, in consequence, they are mainly used in chemical, petrochemical and nuclear industries. Depending on their chemical composition, duplex steels may undergo strain induced martensite, with the austenite (γ) transformation in martensite (α\'). This transformation can be reversed by annealing. The austenite is paramagnetic, whereas ferrite and martensite are both ferromagnetic. The goal of this work was to study the relationship between microstructural stability and magnetic properties of a UNS S32304 duplex steel, which presents strain induced martensite. Samples of this steel with 80% thickness reduction were isotermally annealed at several temperatures up to 800ºC for 1 h and water-cooled. From hysteresis loops taken at room temperature, both saturation magnetization (Ms) and coercive field (Hc) were obtained for these samples. In addition to magnetic measurements these samples were characterized using X-ray diffraction, hardness testing, optical (OM) and scanning electron (SEM) microscopies. Regarding SEM were used both EBSD (eléctron backscatter diffraction) and ECCI (electron channeling contrast imaging) techniques. In situ magnetization measurements in function of temperature (up to 1000ºC) were also performed for the deformed material, from which was determined its Curie temperature (Tc). A simulation of the phases present in the material as a function of temperature was performed using the Thermo-Calc© software. For the isothermally annealed samples, metallographic analysis showed that for 600-700ºC the material presents a fragmented microstructure. Such fragmentation is an evidence of the martensite-to-austenite reversion. For the sample annealed at 700ºC precipitates were found mainly in the austenitic phase, which appears to be recrystallized. Evidences of recrystallization were also found for the ferritic phase in the same sample. According to Thermo-Calc© the observed precipitates are probably M23C6 (M = Fe,Cr) and Cr2N. Material\'s hardness present an evident drop for temperatures higher than 500ºC, due to both recrystallization and martensite-to-austenite reversion phenomena. Like hardness, both Ms and Hc also drop in temperatures higher than 500ºC. The martensite-toaustenite reversion and the ferrite decomposition contribute to Ms decreasing. From the Tc behavior, the in situ magnetic measurements also provided evidences of the transformation α → γ + precipitates. In spite of microstructure fragmentation and precipitation, it was not observed a \"pick\" effect in Hc behavior as a consequence of the martensite-to-austenite reversion. This indicates that, in the present study, the factor that most influenced Hc was the higher mobility of magnetic domain walls in the ferritic phase, due to both recovery and recrystallization effects.

Etude des micro-contraintes dans les matériaux texturés hétérogènes par diffraction et modèles de comportement L'objectif de ce travail est le développement d'une méthodologie d'analyse des contraintes utilisant des modèles théoriques pour décrire le comportement élasto-plastique des matériaux polycristallins. L'étude vise d'abord l'interprétation de résultats expérimentaux par des modèles de déformation qui décrivent la création des champs de contrainte dans les matériaux polycristallins déformés. Une attention particulière est portée à l'explication des phénomènes physiques à l'origine des contraintes résiduelles et à la prédiction de leur évolution et de leur influence sur les propriétés du matériau. Dans le premier chapitre, la méthode classique, dite des sin2y, d'analyse des contraintes est présentée. Ensuite, la nouvelle méthode d'analyse, méthode de multiréflexions, basée sur les mesures de déformation en utilisant plusieurs réflexions hkl est introduite. Dans cette méthode, tous les pics de diffraction sont analysés simultanément et la distance interréticulaire dhkl est remplacée par une distance équivalente a. Aussi, sont présentées les méthodes de calcul des constantes élastiques radiocristallographiques qui jouent un rôle crucial dans la détermination des contraintes. La détermination de ces constantes est indispensable pour l'interprétation des différents résultats expérimentaux. De nouvelles méthodes de calculs des constantes élastiques radiocristallographiques utilisant le modèle autocohérent ont été développées et testées. Une attention particulière a été portée au calcul par ce nouveau modèle autocohérent dans le cas des couches superficielles (surface libre). Dans ce modèle, le calcul des forces et contraintes normales à la surface est effectué selon le modèle de Reuss et pour les deux autres directions, c'est le modèle auto-cohérent qui est utilisé. Cette méthode de calcul est particulièrement adaptée au cas de la diffraction des rayons X où seulement une couche superficielle du matériau est examinée (généralement de quelques mm d'épaisseur). Dans le chapitre suivant, deux modèles de déformation ont été développés et utilisés pour déterminer l'évolution des contraintes et analyser les propriétés du matériau. Le premier modèle (LF) est basé sur les formulations de Leffers (Lefers 1968) qui ont été reprises et développées par Wierzbanowski (Wierzbanowski 1978, 1982). Le second est le modèle autocohérent (SC) (Hutchinson 1964, Berveiller et Zaoui 1979). Dans ce travail, le calcul est réalisé à partir de l'algotithme développé par Lipinski et Berveiller (Lipinski et Berveiller 1989). Dans cette approche, le tenseur de Green est utilisé pour décrire les interactions entre les grains. Les grains du polycristal sont considérés comme des inclusions ellipsoïdales (en 3D) dans une matrice homogène. Ces deux modèles de déformation elasto-plastique (LW et SC) sont des outils très utiles pour l'étude des propriétés mécaniques des matériaux polycristallins. Ils permettent la prédiction des propriétés macroscopiques du matériau (texture, courbes contrainte-déformation, surfaces d'écoulement plastique, densité des dislocations, état final des contraintes résiduelles, etc.) à partir de ses caractéristiques microsructurales (systèmes de glissement, loi d'écrouissage, texture initiale, état initial des contraintes résiduelles, etc.) (Wierzbanowski 1978). Des résultats typiques: de texture, écrouissage et énergie stockée, obtenus par ces modèles, ont été comparés aux résultats expérimentaux. Le chapitre 3 est consacré principalement à l'explication des origines physiques des contraintes et de la prédiction de leur évolution, ainsi qu'à leur influence sur les propriétés du matériau. Les contraintes internes sont classées en trois types selon l'échelle : contraintes d'ordre I, II ou III. Une attention particulière est portée aux contraintes d'ordre I et II car ce sont les seules qui sont déterminées à partir de la position des pics de diffraction. Les modèles de déformation ont été utilisés pour l'analyse des contraintes à l'échelle des grains (contraintes du second ordre). L'évaluation quantitative de ce type de contraintes ne peut pas être effectuée directement par des mesures mais elle est possible grâce aux modèles. Les matériaux multi-phasés ont été également étudiés. Pour ces matériaux, l'interprétation des données expérimentales est plus complexe que celle du cas des matériaux monophasés en raison de la nécessité de prendre en compte l'interaction entre les phases. C'est pourquoi, une nouvelle méthode adaptée aux matériaux multi-phasés a été développée et appliquée au cas des aciers inoxydables austéno-ferritiques (aciers Duplex). Les paramètres de déformation plastique ( ph c t - scission critique résolu et Η ph - paramètre d'écrouissage) de chacune des phases ont pu être déterminés. Lors de la déformation plastique, l'évolution des contraintes dans les phases et la création de contraintes d'incompatibilité de second ordre, sont observées et l'influence de la texture cristallographique et de l'anisotropie élastique est étudiée. La méthodologie développée et utilisée dans ce travail a, donc, permis de déterminer quantitativement les contraintes du premier et du second ordre, pour chaque phase. Il a été montré qu'une bonne corrélation entre les déformations déterminées expérimentalement et les résultats théoriques, n'est obtenue que si l'influence des contraintes du second ordre est prise en compte. Aussi, le meilleur lissage des courbes expérimentales est obtenu quand les calculs intègrent les constantes d'élasticité anisotropiques et la texture réelle initiale de l'échantillon. Les méthodes de détermination des contraintes du premier et du second ordre, présentées au troisième chapitre, sont employées pour l'étude des contraintes résiduelles dans des alliages écrouis par laminage croisé (Chapitre 4). Le laminage croisé a été retenu pour ajouter une symétrie de la texture cristallographique et, donc, de réduire l'anisotropie de la pièce (comparé au laminage uniaxial). Les résultats sont présentés pour des séries d'éprouvettes en acier et en alliage de cuivre. Dans le cas de l'alliage de cuivre, les résultats montrent de très faibles niveaux de contraintes d'incompatibilité de second ordre qui peuvent être négligées. Par contre, dans le cas de la ferrite, il faut en tenir compte car leur niveau s'avère important. Les oscillations observées sur les courbes des sin2y peuvent être expliquées, dans ce cas, principalement par la présence de contraintes du second ordre. Enfin, au chapitre 5, une nouvelle méthode d'analyse des contraintes utilisant un faisceau de rayons X avec un angle d'incidence faible et constant (méthode de diffraction en incidence rasante GID-sin2y). Cette méthode présente l'avantage d'une profondeur de pénétration des rayons X constante, contrairement à la méthode des sin2y classique qui présente l'inconvénient d'une forte variation de la pénétration avec l'angle y. C'est pour cette raison que la méthode classique des sin2y est mal adaptée pour l'étude des matériaux à forts gradients de contraintes. Moyennant un choix optimisé des angles d'incidence et du type de rayonnement, la nouvelle méthode s'avère efficace pour l'étude des matériaux à forts gradients de contraintes, en permettant des mesures dans différentes couches proches de la surface. L'incertitude des mesures a été évaluée et le rôle de l'absorption, de l'indice de réfraction et des facteurs de Lorentz-polarisation et de diffusion atomique ont été étudiés. A partir de mesures sur des poudres de référence, l'influence de chacun de ces paramètres a été évaluée et prise en compte dans la détermination de la position des pics de diffraction. Les analyses effectuées ont confirmé la faible influence de l'absorption et des facteurs de Lorentz-polarisation et de diffusion atomique sur la contrainte déterminée. Par contre, ils ont révélé un effet important de l'indice de réfraction, en particulier aux petits angles d'incidence. Pour des angles d'incidence a£100, les corrections sont importantes et modifient les résultats des contraintes d'une manière significative (la correction peut atteindre 70 MPa dans le cas de la poudre). Cet effet et, donc, la correction nécessaire décroît quand l'angle d'incidence augmente.

Ce travail traite de l'évolution de la texture et de la microstructure dans les soudures d'acier inoxydable duplex 2205 traitées thermiquement. L'analyse microstructurale a montré que la ZAT est caractérisée par une forte teneur en ferrite alors que le centre du métal fondu contient plus d'austénite. Les traitements thermiques effectués dans le domaine 800-1000°C ont causé la précipitation de la phase σ et des carbures de chrome M23C6 aux interfaces γ / δ qui sont les sites privilégiés de germination. Au-delà de 1050°C la fraction volumique de la ferrite augmente avec la température. Les propriétés mécaniques optimales du joint soudé sont obtenues suite à un traitement d'hypertrempe à 1050 °C pendant 1h. Le passage de la température d'hypertrempe de 1050 à 1250 °C retarde la précipitation de la phase σ et favorise celle de l'austénite secondaire γ2. L'étude de la cinétique de précipitation de la phase σ dans les différentes zones de la soudure montre que celle-ci suit le modèle modifié de JMA. Les résultats obtenus montrent une dépendance significative de la précipitation de la phase σ par rapport à la température d'hypertrempe. L'analyse par EBSD de la texture cristallographique du métal fondu a permis de déterminer la relation d'orientation exacte entre l'austénite et la ferrite comme étant une rotation de 44.2° autour d'un axe <0.16, 0.16, 0.97>. La texture du métal de base reste quasiment stable suite à l'opération de soudage et aux traitements thermiques effectués au moment où une petite dispersion vient perturber légèrement la relation d'orientation dans le métal fondu.

Nucleoside 5-triphosphates are the building blocks to synthesis of nucleic acids. Nucleic acids (RNA and DNA) participate in many important biological functions in living systems, including genetic information storage, gene expression, and catalysis. Nucleoside 5- triphosphates have many important therapeutic and diagnostic applications. To understand how these triphosphates are utilized in living systems, numerous synthetic mimics have been prepared and used as active metabolites of certain drugs and molecular probes. Over the years, nucleic acids have been modified at the nucleobase, sugar moiety and phosphate backbone with the aim of understanding their structures and functions. We have site-specifically replaced selected oxygen atoms of nucleosides and nucleotides with selenium atom in order to enzymatically synthesize selenium-derivatized DNAs for obtaining insights into the DNA flexibility, duplex recognition and stability. Although triphosphates have important biological and medicinal significance, they are however, very difficult to synthesize and isolate in high purity and yield. There are many approaches to the synthesis of nucleoside 5-triphosphates, but there is no general strategy that allows simple and direct synthesis of nucleoside triphosphates. To face the challenges, we have developed a new approach in the absence of protecting groups to quickly and efficiently synthesized native deoxynucleoside 5-triphosphates and deoxynucleoside 5-(α- P-seleno)- P-seleno)triphosphates. Syntheses of the triphosphates containing selenium-derivatized nucleobases were also successfully accomplished. After replacing the oxygen atoms at the 4-position of thymidine and uridine, and the 6-position of guanosine, we observed most strikingly, a large bathrochromic shift of over 100 nm, relative to their native counterparts of UV absorbance of 260 nm. Consequently, the synthesized selenium base modified triphosphates are yellow. We also synthesized 2-selenothymidine and 5-methylseleno thymidine 5-triphosphates. We conducted stability study on the colored 4-selenothymidine and used the 5- triphosphate analog (4-SeTTP) as substrate for polymerase recognition. The Klenow polymerase incorporated the 4-SeTTP with efficiency equal to that of the native counterpart. Finally, 4-SeTTP was used to demonstrate UVdamage resistance of selenium-derivatized DNAs and plasmid.

Cooperative wireless communication has received significant attention during recent years due to several reasons. First, since the received power decreases rapidly with distance, the idea of multi-hopping is becoming of particular importance. In multi-hopped communication, the source exploits some intermediate nodes as relays. Then the source sends its message via those relays to the destination. Second, relays can emulate some kind of distributed transmit antennas to form spatial diversity and combat multi-path fading effect of the wireless channel. Parallel Relay Channel is an information theoretical model for a communication system whereby a sender aims to communicate to a receiver with the help of relay nodes. It represents the simplest model for a multi–hop wireless network and a full understanding of the limits of communication over such a channel can potentially shed light on the design of more efficient wireless networks. However, the capacity of the relay channel has been established only for few special cases and little progress has been made toward solving the general case since the early 1980s. In this dissertation, motivated by practical constraints, we study the information theoretical limits of the half-duplex Gaussian Parallel Relay channel , as well as, the transmission strategies for the parallel relay channel with bandwidth mismatch between the first and the second hops. Chapter 2 investigates the problem of communication for a network composed of two half-duplex parallel relays with additive white Gaussian noise (AWGN). There is no direct link between the source and the destination. However, the relays can communicate with each other through the channel between them. Two protocols, i.e., \emph{Simultaneous} and \emph{Successive} relaying, associated with two possible relay scheduling are proposed. The simultaneous relaying protocol is based on \emph{Broadcast-multiaccess with Common Message (BCM)} scheme. For the successive relaying protocol: (i) a \emph{Non-Cooperative} scheme based on the \emph{Dirty Paper Coding (DPC)}, and (ii) a \emph{Cooperative} scheme based on the \emph{Block Markov Encoding (BME)} are considered. The composite scheme of employing BME in \emph{at most} one relay and DPC in \emph{at least} another one is shown to achieve at least the same rate when compared to the \emph{Cooperative} and \emph{Non-Cooperative} schemes. A \emph{``Simultaneous-Successive Relaying based on Dirty paper coding scheme" (SSRD)} is also proposed. The optimum scheduling of the relays and hence the capacity of the half-duplex Gaussian parallel relay channel in the low and high signal-to-noise ratio (SNR) scenarios is derived. In the low SNR scenario, it is revealed that under certain conditions for the channel coefficients, the ratio of the achievable rate of the simultaneous relaying based on BCM to the cut-set bound tends to be 1. On the other hand, as SNR goes to infinity, it is proved that successive relaying, based on the DPC, asymptotically achieves the capacity of the network. Schein and Gallager introduced the Gaussian parallel relay channel in 2000. They proposed the Amplify-and-Forward (AF) and the Decode-and-Forward (DF) strategies for this channel. For a long time, the best known achievable rate for this channel was based on the AF and DF with time sharing (AF-DF). Recently, a Rematch-and-Forward (RF) scheme for the scenario in which different amounts of bandwidth can be assigned to the first and second hops were proposed. In chapter 3, we propose a \emph{Combined Amplify-and-Decode Forward (CADF)} scheme for the Gaussian parallel relay channel. We prove that the CADF scheme always gives a better achievable rate compared to the RF scheme, when there is a bandwidth mismatch between the first hop and the second hop. Furthermore, for the equal bandwidth case (Schein's setup), we show that the time sharing between the CADF and the DF schemes (CADF-DF) leads to a better achievable rate compared to the time sharing between the RF and the DF schemes (RF-DF) as well as the AF-DF.

In the present work the effect of isothermal ageing treatment on the microstructure and on the localized corrosion resistance of a duplex stainless steel (DSS) was investigated. Specimens taken from a hot rolled cylindrical duplex stainless bar with 22% Cr grade were solution annealed at 1050&deg / C and then sensitization heat treatments were conducted at 650, 725 and 800&deg / C with duration ranging from 100 to 31622 min. The microstructural changes were examined by the light optical microscopy (LOM) and scanning electron microscopy (SEM). XRD technique and EDS analysis were used for microstructural evolution. Double Loop Electrochemical Potentiodynamic Reactivation (DLEPR) and standard weight loss immersion acid tests were performed in order to determine the degree of sensitization (DOS) to intergranular corrosion. The surfaces remained after the DLEPR test and the weight loss immersion test were also examined to observe the attack locations and their relationship with the chromium depleted zones. The degree of sensitization is measured by determining the ratio of the maximum current generated by the reactivation (reverse) scan to that of the anodic (forward) scan, (Ir/Ia) x 100. Ir is very small (less than 10-5 A/cm2) for solution annealed samples at 1050&deg / C for 1 hr and those aged at 650&deg / C for 100 and 316 min after the solution heat treatment, with the Ir/Ia ratios of 0.027634%, 0.033428% and 0.058928% respectively. Hence these samples were considered as unsensitized and their microstructure was composed of primary ferrite and austenite. However, Ir increased to values as high as 10-2 A/cm2 and even approached Ia for all samples aged for other temperatures and times, associated with high Ir/Ia ratios. The increased degree of sensitization can be attributed to stronger effect of chromium and molybdenum depleted areas. The microstructure was composed of primary ferrite and austenite including also sigma phase and the secondary austenite that would be responsible for the localized chromium impoverishment. The time required for sensitization was shorter in samples aged at higher temperatures. Accordingly ageing times of 1000 min at 725&deg / C and of 316 min at 800&deg / C were sufficient, whereas times longer than 10000 min was needed to achieve a sensitized structure at 650&deg / C.

This dissertation is aimed at examining signal integrity degradation factors and realizing signal integrity enhancement circuits for both wired and wireless communication systems. For wired communication systems, an optical coherent system employing an electrical equalization circuit is studied as a way of extending the transmission distance limited by optical fiber dispersion mechanisms. System simulation of the optical coherent receiver combined with the feed-forward equalizers is performed to determine the design specification of the equalizer circuit. The equalization circuit is designed and implemented in a 0.18 µm complementary metal-oxide semiconductor (CMOS) process and demonstrates the capability to extend the transmission reach of long-haul optical systems over single-mode fiber to 600 km. Additionally, for wireless applications, signal integrity issues found in a full-duplex wireless communication network are examined. Full-duplex wireless systems are subject to interference from their own transmitter leakage signals; thus, a transmitter leakage cancellation circuit is designed and implemented in a 0.18 µm CMOS technology. The proposed cancellation circuit is integrated with a low-noise amplifier and demonstrates over 20 dB of transmitter leakage signal suppression.