Made available in DSpace on 2014-06-12T23:14:12Z (GMT). No. of bitstreams: 2 arquivo8465_1.pdf: 3125970 bytes, checksum: 11f3471380cf5a868017f997139c6ce2 (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2011 / Para o propósito de evitar os efeitos deletérios determinísticos e minimizar a ocorrência dos efeitos estocásticos, em pessoas expostas à radiação ionizante, se faz necessário conhecer as doses equivalentes ou absorvidas em órgãos e tecidos radiosensíveis do corpo humano. Entretanto, estes valores não podem ser medidos diretamente no indivíduo exposto e, por esta razão, são usados fantomas humanos, que são representações físicas ou computacionais, utilizados para determinar coeficientes de conversão entre a dose absorvida nos órgãos e tecidos e grandezas mensuráveis. O procedimento de uso dos fantomas físicos é sabido ser caro e demanda muito tempo, devido a um laborioso procedimento experimental e restrições de segurança. Com o advento dos métodos de simulação Monte Carlo e o surgimento dos computadores, tornou-se gradualmente possível estimar doses absorvidas em órgãos e tecidos em fantomas computacionais. Cada fantoma computacional define não somente as características exteriores do corpo humano, mas inclui detalhes sobre órgãos internos tais como seus volumes e formas. Quando são usadas informações sobre densidade e composição elementar dos tecidos, um fantoma computacional pode ser acoplado a um código de transporte de radiação Monte Carlo para simular interações teciduais e deposição de energia no corpo humano por diversos tipos de radiação. Embora a fonte da radiação tenha que ser matematicamente modelada, o procedimento computacional é, em geral, muito vantajoso em termos da sua versatilidade, eficiência, precisão e segurança. A mais recente geração de fantomas computacionais recebeu a denominação de fantomas mesh. Para sua construção não são essenciais imagens de tomografia computadorizada ou de ressonância magnética e sim a descrição anatômica detalhada das estruturas de interesse. Estes fantomas permitem representar o indivíduo em diferentes posturas e em diferentes estágios do desenvolvimento do corpo humano, e ainda evitam implicações éticas provocadas pelas técnicas de obtenção das imagens dos indivíduos. Neste trabalho são apresentados dois casais de fantomas mesh referenciais, para crianças com 5 anos e 10 anos de idade. Eles foram construídos utilizando-se ferramentas computacionais usadas pela comunidade de computação gráfica, para a criação de filmes de animação. Os parâmetros adotados para as massas dos diferentes órgãos e tecidos foram os recomendados pela publicação 89 da Comissão Internacional de Proteção Radiológica (ICRP), para estudos populacionais. Os volumes destes órgãos e tecidos foram calculados utilizando-se densidades fornecidas pela Comissão Internacional de Unidades e Medidas Radiológicas (ICRU). Quanto à disposição dos diferentes órgãos e tecidos, foram consultadas descrições da anatomia humana. As versões voxelizadas dos fantomas foram conectadas ao código Monte Carlo EGSnrc. As aplicações dosimétricas apresentadas mostram exemplos de que doses absorvidas para órgãos e tecidos, estimadas com estes fantomas infantis, são razoáveis e comparáveis com dados correspondentes obtidos em outros fantomas

[pt] Descreve-se o controle em malha fechada por malha pequena de um motor de passo de imã permanente (MIPIP), de forma a obter posicionamento preciso em tempo mínimo. A malha pequena é utilizada para, aplicar o modo de controle de alta velocidade (HISPEED); consegue-se dessa forma atingir velocidades muito superiores às obtidas em malha aberta. O principio de controle adotado pelo controlador de malha externa baseia-se na utilização de tabelas que possuam dados sobre as curvas de aceleração e desaceleração do MPIP. Dependendo do número de passos que faltam para atingir o alvo e da velocidade de rotação do eixo, as tabelas indicarão o modo de controle adequado de forma a não ultrapassar o alvo e atingi-lo em tempo mínimo. Um microcomputador implementa o controlador da malha externa e indica ao controle da malha interna o modo de operação adequado. / [en] This work describes the use of an inner loop for closed loop control of a permanent magnet step motor to achieve precise positioning in minimal time. The inner loop is used to apply a high speed control; this method gives speeds higher than those obtained with the open loop control. The outer loop controller is based on the use of acceleration and deceleration data of the motor. Depending on the number of steps needed to reach the desired position, and the actual speed, these tables indicate the best control mode to get to the target in minimal time and without overshooting it. This controller is implemented in a microcomputer.

This thesis work will investigate and implement a method for reconstructing an unstructured mesh sequence with evolving topology. The goal of the method is to increase frame-to-frame coherency of the triangulation. The motivation of the method is that many of current state-of-the-art mesh compression and decimation algorithms for mesh sequences are based on static connectivity.

The paper is concerned with algorithms for transforming hexahedral finite element meshes into tetrahedral meshes without introducing new nodes. Known algorithms use only the topological structure of the hexahedral mesh but no geometry information. The paper provides another algorithm which can be extented such that quality criteria for the splitting of faces are respected.

Wireless mesh networks has rapid development over the last few years. However, due to properties such as distributed infrastructure and interference, which strongly affect the performance of wireless mesh networks, developing technology has to face the challenge of architecture and protocol design issues. Traditional layered protocols do not function efficiently in multi-hop wireless environments. To get deeper understanding on interaction of the layered protocols and optimize the performance of wireless mesh network, more recent researches are focusing on cross-layer measurement schemes and cross-layer protocol design. The goal of this project is to implement a distributed monitoring mechanism for IEEE802.11 based wireless mesh networks. This module is event-based and has modular structure that makes it flexible to be extended. This project results a novel Cross-Layer Monitoring Module, CLMM, which is a prototype that monitors each layer of the nodes locally and dynamically, calculates the average values of the metrics, compares these values with thresholds and handles the cross-layer messages of each node. The CLMM also has a routing module structure that can be extended to distribute the metrics to its neighbors.

Voice over IP (VoIP) traffic in a multi-hop wireless mesh network (WMN) suffers from a large overhead due to mac/IP/UDP/RTP headers and time collisions. A consequence of the large overhead is that only a small number of concurrent VoIP calls can be supported in a WMN[17]. Hop-to-hop packet aggregation can reduce network overhead and increase the capacity. Packet aggregation is a concept which combines several small packets, destined to a common next-hop destination, to one large packet. The goal of this thesis was to implement packet aggregation on a Linux distribution and to increase the number of concurrent VoIP calls. We use as testbed a two-hop WMN with a fixed data rate of 2Mbit/s. Traffic was generated between nodes using MGEN[20] to simulate VoIP behavior. The results from the tests show that the number of supported concurrent flows in the testbed is increased by 135% compared to unaggregated traffic.

Reducing the number of vertices in a mesh is a problem that if solved correctly can save the user a lot of time in the entire process of handling the model. Most of the solutions today are focused on reducing the mesh in one big step by running a separate application. The goal of this implementation is to bring the reduction application into the users workspace as a plugin. Many of the modellers in the various computer graphics industries use Autodesk Maya the plugins intention is to create a efficient tool which also give the modellers as much freedom as possible without the need to ever leave Mayas workspace. During the process the possible issues and solutions of creating this tool in Maya will also examined to help introduce the process of creating a tool for Maya. This plugin has the potential to improve on the existing reduction tool in Maya by giving the user more options and a more exact solution.

The problem of selecting the connectivity of a triangulation in order to minimize a given cost function is studied. This problem is of great importance for applications, such as generating triangle mesh models of images and other bivariate functions. In early work, a well-known method named the local optimization procedure (LOP) was proposed by Lawson for solving the triangulation optimization problem. More recently, Yu et al. proposed a variant of the LOP called the LOP with lookahead (LLOP), which has proven to be more effective than the LOP. Unfortunately, each of the LOP and LLOP can only guarantee to yield triangulations that satisfy a weak optimality condition for most cost functions. That is, the triangulation optimized by the LOP or LLOP is only guaranteed to be such that no single edge flip can reduce the triangulation cost. In this thesis, a new optimality criterion named n-flip optimality is proposed, which has proven to be a useful tool for analyzing the optimality property. We propose a more general framework called the modified LOP (MLOP), with several free parameters, that can be used to solve the triangulation-cost optimization problem. By carefully selecting the free parameters, two MLOP-based methods called the MLOPB(L,M) and MLOPC(L) are derived from this framework. According to the optimality property introduced in the thesis, we have proven our proposed methods can satisfy a stronger optimality condition than the LOP and LLOP. That is, the triangulation produced by our MLOP-based methods cannot have their cost reduced by any single edge flip or any two edge flips. Due to satisfying this stronger optimality condition, our proposed methods tend to yield triangulations of significantly lower cost than the LOP and LLOP methods. In order to evaluate the performance of our MLOP-based methods, they are compared with two other competing approaches, namely the LOP and LLOP. Experimental results show that the MLOPB and MLOPC methods consistently yield triangulations of much lower cost than the LOP and LLOP. More specifically, our MLOPB and MLOPC methods yield triangulations with an overall median cost reduction of 16.36% and 16.62%, respectively, relative to the LOP, while the LLOP can only yield triangulations with an overall median cost reduction of 11.49% relative to the LOP. Moreover, our proposed methods MLOPB(2,i) and MLOPA(i) are shown to produce even better results if the parameter i is increased at the expense of increased computation time. / Graduate

The potential of Additive Manufacturing (AM) for microwave and mm-wave applications is increasingly being revealed thanks to recent advancements in research. AM empowers engineers with new capabilities to manufacture complex conformal geometries quicker and at lower costs. It allows, for instance, the embedding of RF front ends into functional structures. In this dissertation, two aspects of AM are explored: (a) The development and characterization of techniques that improve the performance of AM microwave circuits and antennas, and (b) study of complex geometries, such as meshed structures, as an alternative to reduce material usage, cost, and weight of the components. Micro-dispensing of silver paste (CB028) is extensively used in this work as a viable approach for manufacturing microwave planar transmission lines. However, the performance and upper-frequency range of these lines are limited by the cross-sectional shape and electrical conductivity of the printed paste, as well as the achievable minimum feature size which is typically around 100 μm. In this work a picosecond Nd:YAG laser is used to machine slots in a 20-25 μm-thick layer of silver paste (Dupont CB028) that is micro-dispensed on a Rogers RT5870 substrate, producing coplanar waveguide transmission lines with 16-20 μm-wide slots. It is shown that the laser solidifies 2 μm wide region along the edges of the slots, thus significantly increasing the effective conductivity of the film and improving the attenuation constant of the lines. The extracted attenuation constant at 20 GHz for laser machined CB028 is 0.74 dB/cm. CPW resonators and filters show that the effective conductivity is in the range from 10 MS/m to 30 MS/m, which represents a 100x improvement when compared to the values obtained with the exclusive use of micro-dispensing. Another main aspect of this dissertation is the study of meshed structures in coplanar waveguides. For most AM processes the materials utilized for the conductive layer are the most expensive ones; hence, there is value in minimizing the conductor surface area used in a circuit. In this work, the approach of meshed ground coplanar waveguide (MGCPW) is analyzed by simulating, fabricating and measuring a broad set of meshed ground geometry sizes. Furthermore, a physical-mathematical model is presented, which predicts the characteristic impedance and the capacitance per unit length of MGCPW with less than 5.4% error compared to simulated data. A set of filters is designed and fabricated in order to demonstrate the approach. The main parameter affected by meshing the ground plane is the attenuation constant of the waveguide. It is shown that 50% mesh density in the ground plane of a MGCPW line can be used with less than 25% increase in the loss. In contrast, the loss of finite ground coplanar waveguide (FGCPW) can increase by as much as 108% when the ground size is reduced by the same factor (50%). Both 3D printing (micro-dispensing) and traditional printed circuit board manufacturing are used in this work, and most of the propagation characterization is performed at 4 GHz. A meshing technique is also applied to rectangular waveguides, and its effects are studied. It is presented as an option for high power, low loss, but also reduced weight applications. A set of meshed Ku-band waveguides was fabricated using binder jetting 3D printing technology showing that the weight can be reduced by 22% with an increase in loss of only 5%, from 0.019 dB/cm for the solid part to 0.020 dB/cm average across the band with the meshed design. Further weight reduction is possible if higher loss is allowed. To demonstrate the concept, a comparison is made between non-meshed and meshed waveguide 4 pole Chebyshev filters. Finally, the BJ technology is characterized for Ku-Band rectangular waveguide and reflector antenna applications. This technology is characterized using electron beam microscopy (SEM) and energy dispersive spectroscopy (EDS). The RF performance of the 3D printed circuits is benchmarked with Ka-band cavity resonators, waveguide sections, and a filter. An unloaded resonator Q of 616 is achieved, and the average attenuation of the WR-28 waveguide section is 4.3 dB/m. The BJ technology is tested with a meshed parabolic reflector antenna, where the illuminating horn, waveguide feed, and a filter are printed in a single piece. The antenna shows a peak gain of 24.56 dBi at 35 GHz.

Philosophiae Doctor - PhD / Numerical simulations play a crucial role in testing current cosmological models of the formation and evolution of the cosmic structure observed in the modern Universe. Simulations of the collapse of both baryonic and non-baryonic matter under the influence of gravity have yielded important results in our understanding of the large scale structure of the Universe. In addition to the underlying large scale structure, simulations which include gas dynamics can give us valuable insight into, and allow us to make testable predictions on, the nature and distribution of baryonic matter on a wide range of scales. In this work we give an overview of cosmological simulations and the methods employed in the solution of many body problems. We then present three projects focusing on scales ranging from individual galaxies to the cosmic web connecting clusters of galaxies thereby demonstrating the potential and diversity of numerical simulations in the fields of cosmology and astrophysics. We firstly investigate the environmental dependance of neutral hydrogen in the intergalactic medium by utilising high resolution cosmological hydrodynamic simulations in Chapter 3. We find that the extent of the neutral hydrogen radial profile is dependant on both the environment of the galaxy and its classification within the group ie. whether it is a central or satellite galaxy. We investigate whether this effect could arise from ram pressure forces exerted on the galaxies and find good agreement between galaxies experiencing high ram pressure forces and those with a low neutral hydrogen content. In Chapter 4 we investigate the velocity–shape alignment of clusters in a dark matter only simulation and the effect of such an alignment on measurements of the kinetic Sunyaev–Zeldovich (kSZ) effect. We find an alignment not only exists but can lead to an enhancement in the kSZ signal of up to 60% when the cluster is orientated along the line-of-sight. Finally we attempt to identify shocked gas in clusters and filaments using intermediate resolution cosmological hydrodynamic simulations in Chapter 5 with a view to predicting the synchrotron emission from these areas, something that may be detectable with the Square Kilometer Array.