La réduction continuelle des dimensions dans les technologies CMOS a ouvert la porte à la conception de circuits complexes multi-cœurs (SoC). Malheureusement dans les technologies nanométriques, les performances des systèmes intégrés après fabrication ne sont pas complètement prédictibles. En effet, les variations des procédés de fabrication sont très importantes aux échelles des puces. Par conséquent, la conception de tels systèmes dans les technologies nanométriques est désormais contrainte par de nombreux paramètres tels que la robustesse aux variations des procédés de fabrication et la consommation d'énergie. Ceci implique de disposer d'algorithmes efficaces, intégrés dans la puce, susceptibles d'adapter le comportement du système aux variations des charges des processeurs tout en faisant face simultanément aux variations des paramètres qui ne peuvent pas être prédits ou modélisées avec précision au moment de la conception. Dans ce contexte, ce travail de thèse porte sur la conception de systèmes dit « GALS » (Globally Asynchronous Locally Synchronous) conçus autour d’un réseau de communication intégré à la puce (Network-on-Chip ou NoC) exploitant les nouvelles générations de technologie CMOS. Une nouvelle méthode permettant de contrôler dynamiquement la vitesse des différents îlots du NoC grâce à un contrôle de la tension et de la fréquence en fonction de la qualité locale des procédés de fabrication sur chaque îlot est proposée. Cette technique de contrôle permet d’améliorer les performances du système en consommation, et d’augmenter son rendement en fabrication grâce à l’utilisation des synergies au sein du système intégré. La méthode de contrôle est basée sur l’utilisation d'un anneau asynchrone programmable capable de prendre en compte la charge de travail dynamique et les effets de la variabilité des procédés de fabrication. Le contrôleur évalue en particulier la limite supérieure de fréquence de fonctionnement pour chaque domaine d'horloge. Ainsi, il n'est plus nécessaire de garantir les performances temporelles de chaque nœud au moment de la conception. Cela relâche considérablement les contraintes de fabrication et permet du même coup l'amélioration du rendement. / Continuous scaling of CMOS technology push circuit designs towards multi-core complex SoCs. Moreover, with the nanometric technologies, the integrated system performances after fabrication will not be fully predictable. Indeed, the process variations really become huge at the chip scale. Therefore the design of such complex SoCs in the nanoscale technologies is now constrained by many parameters such as the energy consumption and the robustness to process variability. This implies the need of efficient algorithms and built-in circuitry able to adapt the system behavior to the workload variations and, at the same time, to cope with the parameter variations which cannot be predicted or accurately modeled at design time. In this context, this thesis work addresses the design of GALS-based NoC architectures in the upcoming CMOS technologies. A novel methodology to dynamically control the speed of different voltage-frequency NoC islands according to the process variability impact on each domain is proposed. This control technique can improve the performances, the energy consumption, and the yield of future SoC architectures in a synergistic manner. The control methodology is based on the design of an asynchronous programmable self-timed ring where the controller takes into account the dynamic workload and the process variability effects. The controller especially considers the operating frequency limit which does not exceed the maximum locally allowed value for a given clock domain. With such an approach, it is no more required to separately guaranty the performance for each node. This drastically relaxes the fabrication constraints and helps the yield enhancement.

Submitted by Allan Victor Ribeiro null (allan_vr@fc.unesp.br) on 2017-07-12T19:01:29Z No. of bitstreams: 1 Tese - Allan Victor Ribeiro - Posmat.pdf: 17273743 bytes, checksum: 654df5020a2a453977468f1145d42794 (MD5) / Approved for entry into archive by Monique Sasaki (sayumi_sasaki@hotmail.com) on 2017-07-14T17:31:10Z (GMT) No. of bitstreams: 1 ribeiro_av_dr_bauru.pdf: 17273743 bytes, checksum: 654df5020a2a453977468f1145d42794 (MD5) / Made available in DSpace on 2017-07-14T17:31:10Z (GMT). No. of bitstreams: 1 ribeiro_av_dr_bauru.pdf: 17273743 bytes, checksum: 654df5020a2a453977468f1145d42794 (MD5) Previous issue date: 2017-04-28 / Gregory H. Wannier, em 1937, introduziu uma representação dos orbitais eletrônicos cristalinos em termos de funções ortogonais localizadas relacionadas com os orbitais atômicos. Posteriormente, tais funções foram denominadas de funções de Wannier. Nos últimos 30 anos, estudos têm apontado um crescente interesse da comunidade científica por estas funções, as quais se apresentam como uma poderosa ferramenta para a investigação de propriedades eletrônicas dos materiais. No presente trabalho, calculamos as funções de Wannier de sistemas nanométricos uni e bidimensionais. Inicialmente abordamos o cumuleno, que consiste em uma cadeia de átomos de carbono equidistantes. As funções de Bloch são obtidas por meio de uma aproximação tight binding e as funções de Wannier, usuais e generalizadas, são calculadas a partir delas. São discutidas as relações entre as funções de Wannier generalizadas obtidas por meio da aproximação tight binding e os orbitais híbridos sp. Isto é explicado mediante um cálculo alternativo das funções de Wannier, com a resolução de um problema de autovalores generalizado. As funções de Wannier das bandas pz do grafeno também são calculadas a partir das funções de Bloch obtidas por meio de uma aproximação tight binding. Elas assemelham-se a um par ligante-antiligante de orbitais moleculares, e suas propriedades de simetria e localização são discutidas. Finalmente, por meio de uma combinação dos pacotes PWscf (baseado em ondas planas e na teoria do funcional da densidade) e wannier90, são calculadas as funções de Bloch e as funções de Wannier de máxima localização para arranjos atômicos com periodicidade em uma (cumuleno) e duas (grafeno) dimensões. Há boa concordância qualitativa entre os resultados da aproximação tight binding e da teoria do funcional da densidade. Deve-se ressaltar que a primeira abordagem não usa réplicas dos sistemas nanométricos e permite aprofundar o entendimento das propriedades e do significado físico das funções de Wannier. / Gregory H. Wannier, in 1937, introduced a representation of crystalline electronic orbitals in terms of localized orthogonal functions related to the atomic orbitals. Subsequently, these functions were called as Wannier functions. Over the past 30 years, studies have shown a growing interest of the scientific community on these functions, which are presented as a powerful tool to investigate the electronic properties of materials. In this work, we calculate the Wannier functions of one and two-dimensional nanometric systems. Initially, we deal with cumulene, which consists of a chain of equidistant carbon atoms. The Bloch functions are obtained by means of a tight binding approximation, and the standard and the generalized Wannier functions are derived from them. The relations between the generalized Wannier functions and the sp hybrid orbitals is discussed. This is explained through an alternative calculation of the Wannier functions, solving a generalized eigenvalue problem. The pz Wannier functions of graphene are also calculated from the Bloch functions obtained by means of a tight binding approximation. They resemble a bonding-antibonding pair of molecular orbitals, and their symmetry and localization properties are discussed. Finally, by combining the computational codes PWscf (based on plane waves and the Density-functional Theory) and wannier90, the Bloch functions and the maximally localized Wannier functions are calculated for atomic arrangements which are periodic in one (cumulene) and two (graphene) dimensions. There is a good qualitative agreement between the results of the tight binding and density-functional approaches. It should be noted that the former does not involve replicas of the nanometric systems and allows a deeper understanding of the properties and the physical meaning of the Wannier functions.

Orientador: Peter Alexander Bleinroth Schulz / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-09T13:08:11Z (GMT). No. of bitstreams: 1 Caetano_RodrigoAndre_D.pdf: 1870062 bytes, checksum: 8848ab4c022cee347bb886bd1b5d15c5 (MD5) Previous issue date: 2007 / Resumo: Nesse trabalho estudamos as propriedades eletrônicas de alguns sistemas de dimensão nanométricas. Primeiramente, vemos os efeitos do emparelhamento de base em cadeias duplas desordenadas. Dois aspectos são considerados: Para um conjunto de parâmetros que simulam o DNA, o emparelhamento de base aumenta significativamente o comprimento de localização da função de onda. Para um outro determinado conjunto de parâmetros, há uma forte sugestão de uma transição de estados localizados-delocalizados. Investigamos tamb'em os efeitos da correlação no grau de localização em sistemas 2D. Propomos um modelo minimamente realista para descrever a correlação na formação de pontos quânticos auto formados. O modelo que propomos é a proibição de dois pontos quânticos serem primeiros vizinhos. Revelamos tanto os efeitos estruturais, como a formação de regiões de redes binárias ordenadas, quanto os efeitos na estrutura eletrônica. Verificamos que a Razão de Participação é cerca de três vezes maior quando a correlação é considerada. Finalmente, consideramos os efeitos do acoplamento spin-órbita em nanotubos de carbono. Levamos em conta dois tipos de acoplamento: O intrínseco, devido ao arranjo dos átomos de carbono no nanotubo e o acoplamento spin-órbita Rashba, devido a um campo elétrico externo. Mostramos que o acoplamento intrínseco abre um gap, se o nanotubo for metálico na ausência de spin-órbita, ou aumenta o gap se, na ausência de spin-órbita, o nanotubo não for metálico. Mostramos também que para nanotubos metálicos (na ausência do acoplamento spin-órbita) a dependência da amplitude do gap depende de forma universal com a amplitude do campo elétrico externo, no entando, para nanotubos que já apresentam gap mesmo sem levar o acoplamento spin-órbita em conta, a amplitude do gap depende fortemente da quiralidade do nanotubo. Por fim, mostramos que a degenerescência de spin é quebrada pelo acoplamento spin-órbita Rashba / Abstract: In this work, we study the electronic properties of some nanometric systems. Firstly, we look the effects of the base pairing em disordered double chain. Two aspects are considered: For a set of parameters which mimics the DNA, the base pairing enlarge significantly the spread of the wave function. For another determined set of parameters, there is a strong suggestion of a truly localization-delocalization transition. We also investigate the effects of correlation in the localization degree in 2D systems. We propose a minimally realist model in order to describe the correlation in the growth of self-assembled quantum dots. The model that we propose is: There are no quantum dots first neighbor. We reveal as the structural effects, like the formation of "quantum crystals", as the effects in the electronic structure. We report that the Participation Ratio is around three times bigger whenever the correlation is imposed. Finally, we consider the effects of the spin-orbit coupling in carbon nanotubes. We take into account two kinds of coupling: The intrinsic, due to the hexagonal arrangement of the carbon atoms in carbon nanotubes and the Rashba spin-orbit coupling, due to the external electric field. We show that the intrinsic opens a gap, if the nanotube is metallic in the absence of spin-orbit coupling, or increase the gap, if the nanotube is not metallic in the absence of spin-orbit coupling. We also show that for metallic nanotubes (in the absence of spin-orbit coupling) the gap amplitude depends in an universal way with the external electric field amplitude. However, for non metallic nanotubes (in the absence of spin-orbit coupling), the gap amplitude strongly depends on the carbon nanotube chirality. By the end, we show that the Rashba spin-orbit coupling lifts the spin degenerescency / Doutorado / Física da Matéria Condensada / Doutor em Ciências

Thesis (Ph. D. (Physics)) -- University of Limpopo, 2016. / Single and double doped nanometric powders of Single and double doped nanometric powders of titanium dioxide (TiO2) were synthesised by the sol-gel process using titanium isopropoxide (TTIP) as the precursor. For comparison, an undoped sample was also prepared. The metal dopants, Ag and Cu, were used at doping levels of 5% molar weight. The samples were dried at 100°C in air and post annealing was done at 300°C, 600°C, 900°C and 1100°C. Structural characterisation of the samples was carried out by X-ray Diffraction (XRD), Raman Spectroscopy, Scanning Electron Microscopy (SEM) and Energy dispersive X-ray Spectrometry (EDS) techniques. Most samples annealed at the 300°C temperature (and lower) revealed the predominantly-anatase phase, while those annealed at 900°C and above were rutile-only. The double-doped powder that was annealed at 300°C was found to be constituted by anatase and brookite phases (with the dopants incorporated into the TiO2 matrix), and the one annealed at 600°C was a mixture of brookite and rutile. The results suggest that multiple doping of titania may favour a two-phase structure at lower temperatures than singly-doped powders. The co-existence of brookite with anatase is believed to be responsible for the enhancement of anatase to rutile transformation in the double-doped sample. UV-visible (UV-vis) and Photoluminescence (PL) measurements were also carried out to study the optical properties of the TiO2 nanoparticles. This revealed the active PL band at around 440 nm. By narrowing the band gap, the double-doped powders that exhibited the brookite phase, again showed improved visible light photo absorption over the other samples, with a significant shift of the absorption edge to shorter wavelengths. Further, PL spectra revealed a change in PL intensity with phase change, as well as the presence of exciton energy levels at the base of the conduction band. The changes in the electrical conductivities of representative anatase and rutile TiO2 nanopowders upon exposure to water-vapour, ammonia (NH3) and hydrogen (H2) were also investigated. Sensing measurements for water-vapour was done at room temperature for various humidity levels ranging from 5.4% RH to 88.4% RH. The detection of NH3 and H2 gases were carried out at temperatures extending from room temperature to 350°C and over concentration ranges of 25 sccm to 500 sccm and 15 v sccm to 200 sccm respectively. The gas-sensing results show that the sol-gel fabricated TiO2 nanoparticles (particularly in anatase form), has excellent fast and stable dynamic responses to humidity, NH3 and H2. They feature good sensitivities, even at a low operating temperatures. However, acceptor behaviour, for which there was a conductivity switch from n-type to p-type, was recorded for the Ag-doped rutile powders at operating temperatures of 300ºC and 350ºC. Overall, the double-doped sample annealed at 300ºC was deemed the most promising candidate for gassensing. (TiO2) were synthesised by the sol-gel process using titanium isopropoxide (TTIP) as the precursor. For comparison, an undoped sample was also prepared. The metal dopants, Ag and Cu, were used at doping levels of 5% molar weight. The samples were dried at 100°C in air and post annealing was done at 300°C, 600°C, 900°C and 1100°C. Structural characterisation of the samples was carried out by X-ray Diffraction (XRD), Raman Spectroscopy, Scanning Electron Microscopy (SEM) and Energy dispersive X-ray Spectrometry (EDS) techniques. Most samples annealed at the 300°C temperature (and lower) revealed the predominantly-anatase phase, while those annealed at 900°C and above were rutile-only. The double-doped powder that was annealed at 300°C was found to be constituted by anatase and brookite phases (with the dopants incorporated into the TiO2 matrix), and the one annealed at 600°C was a mixture of brookite and rutile. The results suggest that multiple doping of titania may favour a two-phase structure at lower temperatures than singly-doped powders. The co-existence of brookite with anatase is believed to be responsible for the enhancement of anatase to rutile transformation in the double-doped sample. UV-visible (UV-vis) and Photoluminescence (PL) measurements were also carried out to study the optical properties of the TiO2 nanoparticles. This revealed the active PL band at around 440 nm. By narrowing the band gap, the double-doped powders that exhibited the brookite phase, again showed improved visible light photo absorption over the other samples, with a significant shift of the absorption edge to shorter wavelengths. Further, PL spectra revealed a change in PL intensity with phase change, as well as the presence of exciton energy levels at the base of the conduction band. The changes in the electrical conductivities of representative anatase and rutile TiO2 nanopowders upon exposure to water-vapour, ammonia (NH3) and hydrogen (H2) were also investigated. Sensing measurements for water-vapour was done at room temperature for various humidity levels ranging from 5.4% RH to 88.4% RH. The detection of NH3 and H2 gases were carried out at temperatures extending from room temperature to 350°C and over concentration ranges of 25 sccm to 500 sccm and 15 v sccm to 200 sccm respectively. The gas-sensing results show that the sol-gel fabricated TiO2 nanoparticles (particularly in anatase form), has excellent fast and stable dynamic responses to humidity, NH3 and H2. They feature good sensitivities, even at a low operating temperatures. However, acceptor behaviour, for which there was a conductivity switch from n-type to p-type, was recorded for the Ag-doped rutile powders at operating temperatures of 300ºC and 350ºC. Overall, the double-doped sample annealed at 300ºC was deemed the most promising candidate for gassensing.

Les enjeux médicaux et le contexte socio-économique des maladies respiratoires ont une importance majeure à l'échelle mondiale. Parmi les procédures mini-invasives classiques de traitement des maladies respiratoires, l’aérosolthérapie se distingue par sa capacité d’administrer des médicaments pour les pathologies locales, directement dans les voies respiratoires, comme les sinus ou l’arbre trachéaux-bronchique. Dans ce contexte, l’utilisation de nanoparticules à visée pulmonaire est objet de grandes avancées en aérosolthérapie car les aérosols nanométriques ont la capacité de contourner les obstacles dans les voies aériennes supérieures et se déposer dans le poumon profond, renforçant ainsi la performance thérapeutique et diagnostique de ces aérosols. Afin de contribuer à l’évolution des traitements par aérosolthérapie cette thèse s’est orientée vers le développement des nouvelles techniques de génération d’aérosols nanométriques et submicroniques, capables de cibler des régions spécifiques de l'appareil respiratoire d'un patient. La problématique majeure à être confrontée dans ce contexte est donc l’adaptation de la taille des particules de l’aérosol afin de promouvoir un dépôt ciblé chez le patient. Pour cela il est d’abord nécessaire d’avoir une large gamme de tailles d’aérosols, de micronique à nanométrique, puis déterminer la relation entre la taille des particules et leur site de dépôt dans les voies respiratoires. De ce fait, les objectifs principaux de cette thèse sont la caractérisation métrologique et l’évaluation des performances des aérosols nanométriques en termes de cartographie de dépôt. Les résultats obtenus ont démontré qu’il est possible de générer efficacement des aérosols submicroniques et nanométriques soit solides soit liquides. Les aérosols contenant une plus grande quantité de nanoparticules ont montré un dépôt plus important dans les poumons, ce qui contribue au développement des techniques d'administration de médicaments par aérosolthérapies ainsi que pour des études toxicologiques. / Medical and socio-economic issues of respiratory diseases have a major importance in world medicine. Among the conventional minimally invasive procedures in the treatment of respiratory diseases, the aerosoltherapy distinguishes itself by its ability to deliver medication directly into the respiratory tract, such as the sinuses or the tracheal-bronchial tree. In this context, the use of nanoparticles to target the lungs is object of great advances in aerosoltherapy as nanometric aerosols have the ability to overcome obstacles in the upper airways and deposit in the deep lung, increasing the therapeutic and diagnostic performance of these aerosols. In order to contribute with the advance of aerosoltherapy treatments this thesis is directed towards the development of new techniques of generation of nanometric and submicronic aerosols, able to target specific regions of the respiratory system of a patient. The major problem within this context is the adjustment of the aerosol’s particle size in order to promote a targeted deposition in a patient. Therefore, it is firstly necessary to have a wide range of aerosols sizes, from micronic to nanometric, and then it is needed to determine the relationship between particle size and deposition site in the respiratory tract. As a result, the main objectives of this thesis are the metrological characterization of nanometric aerosols and the evaluation of its performance in terms of its deposition in the respiratory tract. The achieved results have demonstrated that is possible to efficiently generate submicronic and nanometric aerosols, either with solid or liquid particles. Aerosols containing a higher amount of nanoparticles showed a larger deposit in the lungs that may contribute to the advancement of aerosoltherapy techniques as well as for toxicological studies.

Orientador: Cláudio Kitano / Resumo: A manufatura de micro e nano dispositivos vem se tornado um mercado de grande representação na indústria moderna, onde destacam-se a indústria médica, eletrônica e mecatrônica, que necessitam de dispositivos capazes de movimentar ou manipular elementos de dimensões microscópicas, tais como micro-pipetas em cirurgias, posicionamento de máscaras de chips, de amostras em microscópios de força atômica, entre outros. Neste contexto, os atuadores piezoelétricos flextensionais são dispositivos consagrados quanto ao uso na micro e nano manipulação. A solução analítica destes atuadores normalmente é muito complexa ou até mesmo impossível e, diante disso, há a necessidade de efetuar a caracterização experimental do atuador após sua confecção. A interferometria óptica é uma técnica muito precisa de medição de pequenos deslocamentos. O interferômetro volumétrico é normalmente montado sobre uma mesa óptica (breadboard) por meio de estruturas comerciais para montagem de experimentos ópticos. Diante disso, o atuador é fixado ao breadboard por estruturas como postes, deslocadores cinemáticos de translação, rotação e tilt, etc. Dessa forma, neste trabalho, levantou-se a resposta em frequência de um protótipo de atuador piezoelétrico flextensional multi atuado que foi projetado e confeccionado no Departamento de Engenharia Mecatrônica e de Sistemas Mecânicos da Escola Politécica da USP - EPUSP. Utilizou-se um interferômetro de Michelson em óptica volumétrica, e, posteriormente, um interferômet... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The manufacture of micro and nano devices has become a market of great prominence in the modern industry, where the medical, electronic and mechatronic industries stand out that need devices capable of repositioning or manipulating elements of microscopic dimensions, such as micro-pipettes in surgeries, positioning of chip masks, adjusting of samples in atomic force microscopes, among others. In this context, flextentional piezoelectric actuators are appropriated devices for use in micro and nano manipulation. The analytical solution of these actuators is usually very complex or even impossible, and there is a need to characterize the actuator after its manufacturing. Optical interferometry is a very precise technique for measuring small displacements and consequently, primissing for the caracterization of these piezoelectric atuators. The bulk interferometer is usually mounted on an optical table (breadboard) by means of commercial precision kinematic optical mounts, such as posts, tilt platformors, translations and rotation stages, and others. In this work, the frequency response of a multi-actuated flextensional piezoelectric actuator prototype, designed and manufactured at the Department of Mechatronics and Mechanical Systems of the Polytechnic School of USP - EPUSP, was investigated. Both, a Michelson interferometer and a double Michelson interferometer were applied for the simultaneousmeasurement of the displacement of the actuator in the X and Y directions. The frequen... (Complete abstract click electronic access below) / Mestre

Em trabalhos anteriores de nosso grupo de pesquisa foram desenvolvidos fios supercondutores nanoestruturados de Nb3Sn com introdução de centros de aprisionamento artificiais (CAAs) de Cu(Sn), numa tentativa de melhorar as propriedades supercondutoras. Porém, os perfis de tratamentos térmicos utilizados não foram otimizados. No presente trabalho as amostras desses fios compósitos foram utilizadas para otimização dos perfis de tratamentos térmicos visando determinar a influência destes perfis no processo de difusão atômica, reação e formação de fases nestes supercondutores nanoestruturados, e, com isso, otimizar a capacidade de transporte de corrente desses materiais. As micrografias e as análises composicionais obtidas produziram um conjunto de informações sobre os mecanismos de difusão e formação da fase supercondutora de Nb3Sn. As amostras foram analisadas quanto às suas propriedades e características supercondutoras. Com as medidas de transporte e magnetização pôde-se obter o comportamento global do supercondutor e o comportamento de cada filamento individual de Nb3Sn, respectivamente. Os compósitos otimizados apresentaram valores de temperatura crítica Tc próximos de 17 K, valores de Bc2 da ordem de 18 T, e densidades de corrente crítica tão altas quanto 1750 A/mm² a 4,2K e 12 T. Os máximos das curvas de força de aprisionamento aconteceram em campos magnéticos tão altos quanto 10 T, aproximadamente 0,5 Bc2, em distinção ao valor de 4,5 T (cerca de 0,2 Bc2) para Nb3Sn convencional, deslocamento que demonstra mudanças no comportamento de aprisionamento de fluxo nestes materiais. Um comportamento inédito e importante, que mistura os mecanismos de aprisionamento de fluxo devido aos contornos de grãos e as fases normais, está presente e pôde ser quantificado em detalhe. A análise dos comportamentos de todas as amostras possibilitou um entendimento satisfatório da influência dos CAAs na fase supercondutora e da influência do efeito de proximidade no aprisionamento de fluxo e nas propriedades de transporte destes materiais. / In previous works of our research group it was shown the development of Nb3Sn nanostructured superconducting wires with introduction of artificial pinning centers (APCs) of Cu(Sn), in an attempt to improve the superconducting properties. However, the used heat treatment profiles were not optimized. In the present work samples of these composite wires were used to optimize the heat treatment profile aiming to determine the influence of these profiles on the processes of atomic diffusion, reaction and formation of phases in these nanostructured superconductors and, consequently, optimize the transport properties of these materials. The obtained micrographs and compositional analysis gave a set of information about the diffusion mechanisms and formation of the Nb3Sn superconducting phase. The samples were analyzed in relation to their superconducting properties and characteristics. The transport and magnetization measurements showed the global behavior of the superconductor and the behavior of each individual Nb3Sn filament, respectively. The optimized composites presented values of critical temperature Tc around 17 K, values of Bc2 around 18 T, and critical current densities as large as 1750 A/mm2 at 4,2 K and 12 T. The peaks of the pinning force curves, occurred at magnetic fields as large as 10 T, approximately 0.5 Bc2, in distinction to the value of 4.5 T (about 0.2 Bc2) for conventional Nb3Sn, displacement that demonstrates changes on the flux pinning behavior in these materials. An inedit and important behavior, which mixes the flux pinning mechanisms due to the grain boundaries and to the normal phases, is present and could be quantified in detail. The behavior analysis of all samples enable a satisfactory understanding of the APCs influence on the superconducting phase and of the influence of the proximity effect on the flux pinning and on the transport properties of these materials.

Em trabalhos anteriores de nosso grupo de pesquisa foram desenvolvidos fios supercondutores nanoestruturados de Nb3Sn com introdução de centros de aprisionamento artificiais (CAAs) de Cu(Sn), numa tentativa de melhorar as propriedades supercondutoras. Porém, os perfis de tratamentos térmicos utilizados não foram otimizados. No presente trabalho as amostras desses fios compósitos foram utilizadas para otimização dos perfis de tratamentos térmicos visando determinar a influência destes perfis no processo de difusão atômica, reação e formação de fases nestes supercondutores nanoestruturados, e, com isso, otimizar a capacidade de transporte de corrente desses materiais. As micrografias e as análises composicionais obtidas produziram um conjunto de informações sobre os mecanismos de difusão e formação da fase supercondutora de Nb3Sn. As amostras foram analisadas quanto às suas propriedades e características supercondutoras. Com as medidas de transporte e magnetização pôde-se obter o comportamento global do supercondutor e o comportamento de cada filamento individual de Nb3Sn, respectivamente. Os compósitos otimizados apresentaram valores de temperatura crítica Tc próximos de 17 K, valores de Bc2 da ordem de 18 T, e densidades de corrente crítica tão altas quanto 1750 A/mm² a 4,2K e 12 T. Os máximos das curvas de força de aprisionamento aconteceram em campos magnéticos tão altos quanto 10 T, aproximadamente 0,5 Bc2, em distinção ao valor de 4,5 T (cerca de 0,2 Bc2) para Nb3Sn convencional, deslocamento que demonstra mudanças no comportamento de aprisionamento de fluxo nestes materiais. Um comportamento inédito e importante, que mistura os mecanismos de aprisionamento de fluxo devido aos contornos de grãos e as fases normais, está presente e pôde ser quantificado em detalhe. A análise dos comportamentos de todas as amostras possibilitou um entendimento satisfatório da influência dos CAAs na fase supercondutora e da influência do efeito de proximidade no aprisionamento de fluxo e nas propriedades de transporte destes materiais. / In previous works of our research group it was shown the development of Nb3Sn nanostructured superconducting wires with introduction of artificial pinning centers (APCs) of Cu(Sn), in an attempt to improve the superconducting properties. However, the used heat treatment profiles were not optimized. In the present work samples of these composite wires were used to optimize the heat treatment profile aiming to determine the influence of these profiles on the processes of atomic diffusion, reaction and formation of phases in these nanostructured superconductors and, consequently, optimize the transport properties of these materials. The obtained micrographs and compositional analysis gave a set of information about the diffusion mechanisms and formation of the Nb3Sn superconducting phase. The samples were analyzed in relation to their superconducting properties and characteristics. The transport and magnetization measurements showed the global behavior of the superconductor and the behavior of each individual Nb3Sn filament, respectively. The optimized composites presented values of critical temperature Tc around 17 K, values of Bc2 around 18 T, and critical current densities as large as 1750 A/mm2 at 4,2 K and 12 T. The peaks of the pinning force curves, occurred at magnetic fields as large as 10 T, approximately 0.5 Bc2, in distinction to the value of 4.5 T (about 0.2 Bc2) for conventional Nb3Sn, displacement that demonstrates changes on the flux pinning behavior in these materials. An inedit and important behavior, which mixes the flux pinning mechanisms due to the grain boundaries and to the normal phases, is present and could be quantified in detail. The behavior analysis of all samples enable a satisfactory understanding of the APCs influence on the superconducting phase and of the influence of the proximity effect on the flux pinning and on the transport properties of these materials.

Ce travail de thèse s’inscrit dans une approche fondamentale expérimentale de l’étude de suspensions céramiques, au travers de la mise en place d’un banc de mesure de diffusion dynamique de la lumière (DLS) sur une suspension en écoulement. L’étude a été effectuée sur des suspensions céramiques concentrées de silice nanométrique et de laponite dans une géométrie de Couette. La technique de mesure par DLS permet d’obtenir des informations locales telles que le taux de cisaillement et la vitesse locale des particules. À travers ces mesures et d’observation vidéo, les profils de vitesse ont permis de comprendre l’évolution du comportement rhéologique de ces suspensions concentrées. De plus, les suspensions concentrées en laponite forment un gel lorsque celles-ci sont au repos. Si ce gel subit un cisaillement, il se déstructure pour redevenir une suspension « liquide ». Cependant, du gel apparait sous cisaillement et sa formation a également été observée par DLS et par vidéo. / This thesis is part of a fundamental experimental approach to the study of ceramics suspensions, through the establishment of a panel of dynamic light scattering (DLS) measurement to a flowing suspension. The study was performed on ceramic concentrated suspensions of nanometric silica and laponite in Couette geometry. The measurement technique by DLS provides local information such as the shear rate and the local velocity of the particles. Through these measurements and video observation, velocity profiles have allowed to understand the evolution of the rheological behavior of concentrated suspensions. Moreover, concentrated suspensions of laponite form a gel when these are at rest. If this gel undergoes shear, this one deconstructs to become a « liquid » suspension. However, the gel appears under shear and its formation was also observed by DLS and camera.

Pjezoelektriniai keitikliai naudojami įvairiuose įrenginiuose, kur reikalingas itin didelis tikslumas, greitaveika ir nanometrų eilės matmenys. Šiame darbe pristatomas nanometrinės skyros cilindrinio pjezokeitiklio, naudojamo palydovo kameros pozicionavimui, tyrimas. Pirmame skyriuje aptartos fizikinės pjezokeraminių medžiagų savybės, pjezokeitiklių konstrukcijos, tvirtinimo sąlygos bei baigtinių elementų metodas. Antrame skyriuje pateikta išsami publikacijų, susijusių su cilindriniais pjezokeitikliais apžvalga. Trečiame skyriuje sprendžiamas cilindrinio pjezokeitiklio matmenų ir elektrodų schemos parinkimo uždavinys. Baigtinių elementų metodas naudojamas sprendžiant cilindrinio pjezokeitiklio savųjų reikšmių ir harmoninės analizės uždavinius. Cilindrinio pjezokeitiklio skaitinis modeliavimas atliktas naudojant ANSYS programinę įrangą. / Piezoelectric actuators are used in various devices where great precision, speed and nanometric scaling are needed. In this paper a nanometric scale piezoelectric actuator used for satellite camera's positioning is presented. In the first chapter physical properties of piezoeletric materials, piezoelectric constructions, support conditions and finite element method are presented. In the second chapter a wide review of literature related to cylindrical piezoelectric actuators is given. In the third chapter a problem of geometrical parameters and electrode schemes selection of cylindrical piezoelectric actuator is investigated. Finite element method is used for determining eigenfrequencies and performing harmonic analysis. Numerical modeling of piezoelectric actuator is carried out using ANSYS software.