Sistemas estruturais constituídos por perfis de aço são, em geral, dimensionados de uma forma \"indireta\", isto é, cada componente é analisado e verificado segundo suas capacidades teóricas individualmente, normalmente associando-se condições de extremidade e comprimentos teóricos para cada barra de modo a aproximar a sua capacidade portante sob a condição real. Contudo, importantes efeitos como a transmissão do empenamento entre as barras devido à torção e/ou distorção, as restrições localizadas impostas por sistemas de contraventamento ou componentes diversos, e também a compatibilidade de deslocamentos locais/globais entre barras conectadas não alinhadas entre si, são desconsiderados, uma vez que o estudo de tais efeitos envolve, normalmente, custosos trabalhos de modelagem através de elementos finitos de casca (e/ou sólidos), soluções numéricas complexas e demoradas, e/ou estudos experimentais caros e trabalhosos. Neste contexto, alguns recentes trabalhos apontam para um vasto campo de aplicações das inovadoras potencialidades da Teoria Generalizada de Vigas (GBT), permitindo, em particular, a análise de sistemas estruturais que consideram os diversos efeitos provocados por condições de apoio arbitrárias, diferentes posições do carregamento e efeitos decorrentes das ligações entre as barras. Contudo, apesar de tais recursos ampliarem as aplicações da GBT na análise de estabilidade de sistemas estruturais, apenas um conjunto limitado de problemas pode ser atendido, especialmente quanto às ligações entre as barras. Os recentes trabalhos envolvendo a aplicação da GBT para a análise de estabilidade de pórticos metálicos dedicaram-se ao estudo de alguns casos específicos de ligações rígidas, isto é, assumem a hipótese de transferência completa dos deslocamentos generalizados entre as barras. Assim, uma vez que a rigidez de tais ligações pode ser responsável por mudanças significativas no comportamento do sistema estrutural em questão, este trabalho procura fornecer uma solução capaz de considerar a semirrigidez das ligações metálicas associada aos parâmetros modais típicos da GBT. Além disso, dada a possibilidade de ampliar os tipos de ligações analisadas por meio da GBT, incluindo as configurações mais comumente utilizadas na prática, apresentam-se novos conjuntos de relações cinemáticas desenvolvidas para tal, assim como as referidas validações, que são realizadas por meio de análises utilizando o programa computacional ANSYS®. / Steel structural systems are usually associated with an \"indirect approach\", i.e., each component of the respective structure is analysed and verified according to its theoretical individual capacity. Normally, in order to approximate the real behaviour of the structural system, specific support conditions and effective length concepts are used to analyse each structural member separately. However, some important effects are disregarded in this procedure, like the warping transmission at frame joints (due to torsion and/or distortion), or those stemming from localized supports associated with bracing systems, as well as the local/global displacements compatibility of the cross-section walls at the joint region. Additionally, studies considering the above mentioned effects involves rather complicated and time-consuming numerical analyses using shell and/or solid finite elements, and/or expensive experimental investigation. On the other hand, some recent studies revealed a large field for application of the Generalized Beam Theory (GBT) in the context of the stability, first and second order analyses of structural systems, considering, particularly, the effects caused by arbitrary support conditions, different load positions, and the effects caused by connections between members. Nonetheless, all the recent works applying GBT for stability analysis of steel frames are focused on some specific cases of rigid connections, i.e., they assume the full transfer of the generalized displacements between the non-aligned members. Thus, given the well-known fact that the rigidity of connections may lead to considerable changes of the structural behaviour of steel structural systems, this work deals with the development of a solution to incorporate the semi-rigidity of the steel frame connections to the modal parameters of the GBT. Furthermore, given the possibility to expand the connection types analysed by means of GBT, including the most commonly used configurations adopted in practice, it is presented the related new kinematic relations developed, as well as the validation studies carried out in the software ANSYS®.

Sistemas estruturais constituídos por perfis de aço são, em geral, dimensionados de uma forma \"indireta\", isto é, cada componente é analisado e verificado segundo suas capacidades teóricas individualmente, normalmente associando-se condições de extremidade e comprimentos teóricos para cada barra de modo a aproximar a sua capacidade portante sob a condição real. Contudo, importantes efeitos como a transmissão do empenamento entre as barras devido à torção e/ou distorção, as restrições localizadas impostas por sistemas de contraventamento ou componentes diversos, e também a compatibilidade de deslocamentos locais/globais entre barras conectadas não alinhadas entre si, são desconsiderados, uma vez que o estudo de tais efeitos envolve, normalmente, custosos trabalhos de modelagem através de elementos finitos de casca (e/ou sólidos), soluções numéricas complexas e demoradas, e/ou estudos experimentais caros e trabalhosos. Neste contexto, alguns recentes trabalhos apontam para um vasto campo de aplicações das inovadoras potencialidades da Teoria Generalizada de Vigas (GBT), permitindo, em particular, a análise de sistemas estruturais que consideram os diversos efeitos provocados por condições de apoio arbitrárias, diferentes posições do carregamento e efeitos decorrentes das ligações entre as barras. Contudo, apesar de tais recursos ampliarem as aplicações da GBT na análise de estabilidade de sistemas estruturais, apenas um conjunto limitado de problemas pode ser atendido, especialmente quanto às ligações entre as barras. Os recentes trabalhos envolvendo a aplicação da GBT para a análise de estabilidade de pórticos metálicos dedicaram-se ao estudo de alguns casos específicos de ligações rígidas, isto é, assumem a hipótese de transferência completa dos deslocamentos generalizados entre as barras. Assim, uma vez que a rigidez de tais ligações pode ser responsável por mudanças significativas no comportamento do sistema estrutural em questão, este trabalho procura fornecer uma solução capaz de considerar a semirrigidez das ligações metálicas associada aos parâmetros modais típicos da GBT. Além disso, dada a possibilidade de ampliar os tipos de ligações analisadas por meio da GBT, incluindo as configurações mais comumente utilizadas na prática, apresentam-se novos conjuntos de relações cinemáticas desenvolvidas para tal, assim como as referidas validações, que são realizadas por meio de análises utilizando o programa computacional ANSYS®. / Steel structural systems are usually associated with an \"indirect approach\", i.e., each component of the respective structure is analysed and verified according to its theoretical individual capacity. Normally, in order to approximate the real behaviour of the structural system, specific support conditions and effective length concepts are used to analyse each structural member separately. However, some important effects are disregarded in this procedure, like the warping transmission at frame joints (due to torsion and/or distortion), or those stemming from localized supports associated with bracing systems, as well as the local/global displacements compatibility of the cross-section walls at the joint region. Additionally, studies considering the above mentioned effects involves rather complicated and time-consuming numerical analyses using shell and/or solid finite elements, and/or expensive experimental investigation. On the other hand, some recent studies revealed a large field for application of the Generalized Beam Theory (GBT) in the context of the stability, first and second order analyses of structural systems, considering, particularly, the effects caused by arbitrary support conditions, different load positions, and the effects caused by connections between members. Nonetheless, all the recent works applying GBT for stability analysis of steel frames are focused on some specific cases of rigid connections, i.e., they assume the full transfer of the generalized displacements between the non-aligned members. Thus, given the well-known fact that the rigidity of connections may lead to considerable changes of the structural behaviour of steel structural systems, this work deals with the development of a solution to incorporate the semi-rigidity of the steel frame connections to the modal parameters of the GBT. Furthermore, given the possibility to expand the connection types analysed by means of GBT, including the most commonly used configurations adopted in practice, it is presented the related new kinematic relations developed, as well as the validation studies carried out in the software ANSYS®.

Graphene base transistors (GBTs) have been, recently, proposed to overcome the intrinsic limitations of the graphene field effect transistors (GFETs) and exploit the graphene unique properties in high frequency (HF) applications. These devices utilize single layer graphene as the base material in the vertical hot-electron transistors. In an optimized GBT, the ultimate thinness of the graphene-base and its high conductivity, potentially, enable HF performance up to the THz region.  This thesis presents an experimental investigation on the GBTs as well as integration process developments for the fabrication of graphene-based devices. In this work, a full device fabrication and graphene integration process were designed with high CMOS compatibility considerations. To this aim, basic process modules, such as graphene transfer, deposition of materials on graphene, and formation of tunnel barriers, were developed and optimized. A PDMS-supporting graphene transfer process were introduced to facilitate the wet/dry wafer-scale transfer from metal substrate onto an arbitrarily substrate. In addition, dielectric deposition on graphene using atomic layer deposition (ALD) was investigated. These dielectric layers, mainly, served as the base-collector insulators in the fabricated GBTs. Moreover, the integration of silicon (Si) on the graphene surface was studied. Using the developed fabrication process, the first proof of concept devices were demonstrated. These devices utilized 5 nm-thick silicon oxide (SiO2) and about 20 nm-thick aluminum oxide (Al2O3) as the emitter-base insulator (EBI) and base-collector insulator (BCI). The direct current (DC) functionality of these devices exhibited &gt;104 on/off current ratios and a current transfer ratio of about 6%. The performance of these devices was limited by the non-optimized barrier parameters and device manufacturing technology. The possibility to improve and optimize the GBT performance was demonstrated by applying different barrier optimization approaches. Comparing to the proof of concept devices, several orders of magnitude higher injection current density was achieved using a bilayer dielectric tunnel barrier. Utilizing the novel TmSiO/TiO2 (1 nm/6 nm) dielectric stack, this tunnel barrier prevents defect mediated tunneling and, simultaneously, promotes the Fowler-Nordheim tunneling (FNT) and step tunneling (ST). Furthermore, it was shown that Si/graphene Schottky junction can significantly improve the current gain by reducing the electron backscattering at the base-collector barrier. In this thesis, a maximum current transfer ratio of about 35% has been achieved. / <p>QC 20160503</p>

Radio astronomy is the science of observing the heavens at radio frequencies, from a few kHz to approximately 300 GHz. In recent years, radio astronomy has faced a growing interference problem as radio frequency (RF) bandwidth has become an increasingly scarce commodity. A programmable real-time DSP least-mean-square interference canceller was developed and demonstrated as a successful method of excising satellite down-link signals from both an experimental platform at BYU, and the Green Bank Telescope at the National Radio Astronomy Observatory in West Virginia. A performance analysis of this cancellation system in the radio astronomy radio frequency interference (RFI) mitigation regime constitutes the main contribution of this thesis. The real-time BYU test platform consists of small radio telescopes, low noise RF receivers, and a state-of-the-art DSP platform. This programmable real-time radio astronomy RFI mitigation tool is the first of its kind. Basic tools needed for radio astronomy observations and the analysis and implementation of interference mitigation algorithms were also implemented in the DSP platform, including a power spectral density estimator, a beamformer, and an array signal correlator.