As variáveis de processo determinam as propriedades dos produtos resultantes dos processos de fundição ou de soldagem, que são função da sua macro e microestrutura bruta de solidificação. Um dos parâmetros importantes para se determinar as propriedades de um produto é a posição da transição colunarequiaxial (CET) e, por este motivo, o entendimento dos fenômenos físicos que causam esta transição é essencial. Com o intuito de se prever a formação da CET, surgiram os métodos empíricos e os modelos matemáticos, que são divididos em dois grandes grupos: modelos determinísticos e modelos estocásticos. Estes dois grupos foram bem estudados, porém nunca foram comparados entre si, particularmente em relação à previsão da posição da CET. O presente trabalho tem como um primeiro objetivo preencher esta lacuna através da comparação entre estes modelos. No entanto, o objetivo principal é apresentar, implementar e validar um novo modelo matemático, denominado de híbrido estocástico-determinístico (CADE -\"Cellular Automaton Deterministic\"), que combine características importantes e vantajosas de cada um dos dois grupos de modelos. Inicialmente, um modelo representante do grupo dos modelos estocásticos foi implementado e validado frente a resultados disponíveis na literatura. Durante esta validação, foi necessária a elaboração de um critério baseado na razão de aspecto dos grãos para a identificação da CET nas macroestruturas calculadas pelo modelo. Estes resultados foram então comparados com os resultados de modelos determinísticos para, após cuidadosa discussão, possibilitar a proposta e implementação do modelo híbrido. Os modelos determinísticos que utilizam o critério mecânico para prever o bloqueio de grãos colunares e a ocorrência da CET mostram regiões colunares em geral maiores que as previstas pelo modelo estocástico. Por outro lado, os modelos determinísticos que utilizam um critério de bloqueio a partir da interação do campo de concentração de soluto ao redor dos grãos prevêem uma CET em posições semelhantes às calculadas pelos modelos estocásticos. O modelo implementado no presente trabalho é capaz de prever a macroestrutura bruta de solidificação e ainda utilizar as equações tradicionalmente empregadas nos modelos determinísticos, sem a necessidade de qualquer método extra para prever a posição da frente de crescimento colunar ou o seu bloqueio por grãos equiaxiais. / The processing variables determine many properties of the products obtained by casting and welding processes and these properties, on the other hand, are strongly affected by the as-cast micro and macrostructure. Particularly the position of the columnar-to-equiaxed transition (CET), which determines the amount of columnar and equiaxed grains in the macrostructure, has an important effect on the properties of as-cast parts. Therefore, understanding the important physical phenomena that cause and affect the formation of the CET plays a crucial role in predicting the ascast macrostructure. To predict the CET formation, empirical methods and mathematical models have been developed. These models are frequently divided into two main groups: deterministic and stochastic. Both groups have been thoroughly studied, but a comparison between them was never attempted, especially regarding the prediction of the CET position. One of the main objectives of the present work is to fulfill this gap by carefully comparing these models. Nevertheless, the most important objective is to propose, implement, and validate a hybrid stochastic-deterministic model, referred to as CADE (Cellular Automaton Deterministic), that combines some important and well-known features of each model. Initially, a model from the stochastic group was implemented and validated using results available in the literature and then used to analyze the effects of some processing variables on the CET prediction. To carry out this analyzes, a criteria based on the aspect ratio of the grains was proposed and developed to identify the CET region from macrostructure images calculated by the model. The results were compared with those obtained by deterministic models and finally led to the development of the new proposed model. This new model has some characteristics from each group of mathematical models and, for this reason, was denoted as hybrid. A deterministic model based on a mechanical blocking criterion to block columnar grains and define the CET position showed, for the most part, larger columnar regions than those predicted by the stochastic model. A deterministic model with a solutal blocking criterion to predict the CET showed results similar to those calculated with the stochastic model. The model proposed in the present work (CADE) was able to predict the as-cast macrostructure using the well-established deterministic equations, without the need for a new method to track columnar grains or predict their blocking by equiaxed grains.

Modelar a dinâmica de neurônios é relevante em estudos de neurociências. Neste trabalho, propõe-se um modelo computacional de neurônio baseado no comportamento dos canais iônicos presentes na sua membrana. O modelo combina elementos microscópicos, como o comportamento dos canais individuais, com elementos macroscópicos, como a tensão ao longo de um trecho de membrana. Simulações foram realizadas com o objetivo de reproduzir dados biológicos e resultados obtidos de modelos teóricos clássicos da área. Foi possível reproduzir com boa concordância o potencial de ação, o fenômeno da adaptação, a curva da corrente de entrada versus a frequência de disparos e o potencial excitatório pós-sináptico. / Modelling the dynamics of neurons is relevant in studies on neurosciences. In this work, a computational model of neuron based on the behavior of the ionic channels found in its membrane is proposed. The model comprises microscopic elements, as the behavior of the individual channels, and macroscopic elements, as the tension along a membrane patch. Simulations were performed with the aim of reproducing biological data and results derived from classical theoretical models of the field. It was possible to reproduce with good agreement the action potential, the phenomenon of adaptation, the curve of the input current versus the spike frequency, and the excitatory postsynaptic potential.

The objective of the research presented in this thesis has been to develop a physics-based dislocation density-based numerical framework to simulate microstructure evolution in severe plastic deformation (SPD) manufacturing processes for different materials. Different mechanisms of microstructure evolution in SPD manufacturing processes were investigated and summarized for different materials under dynamic or high strain rates over a wide temperature range. Thorough literature reviews were performed to clarify discrepancies of the mechanism responsible for the formation of nanocrystalline structure in the machined surface layer under both low-temperature and high-temperature conditions. Under this framework, metallo-thermo-mechanically (MTM) coupled finite element (FE) models were developed to predict the microstructure evolution during different SPD manufacturing processes. Different material flow stress responses were modeled subject to responsible plastic deformation mechanisms. These MTM coupled FE models successfully captured the microstructure evolution process for various materials subjected to multiple mechanisms. Cellular automaton models were developed for SPD manufacturing processes under intermediate to high strain rates for the first time to simulate the microstructure evolution subjected to discontinuous dynamic recrystallization and thermally driven grain growth. The cellular automaton simulations revealed that the recrystallization process usually cannot be completed by the end of the plastic deformation under intermediate to high strain rates. The completion of the recrystallization process during the cooling stage after the plastic deformation process was modeled for the first time for SPD manufacturing processes at elevated temperatures.

La formation de la structure de grains dans les métaux pendant la solidification est déterminante pour les propriétés mécaniques et électroniques des pièces coulées. En plus de la texture donnée au matériau, la germination et la croissance des grains sont liées en particulier avec la formation des phases thermodynamiques et les inhomogénéités en composition d'éléments d'alliage. La structure de grains est rarement modélisée à l'échelle macroscopique, d'autant plus que l'approximation 2D est très souvent injustifiée. Dans ces travaux, la germination et la croissance de chaque grain individuel sont suivies avec un modèle macroscopique 3D CAFE. La microstructure interne des grains n'est pas explicitement résolue. Pour valider les approximations faites sur cette microstructure, une comparaison directe avec un modèle microscopique "champ de phase" a été réalisée. Celle-ci a permis de valider les hypothèses de construction du modèle CAFE, de mettre en avant le lien entre données calculées par les modèles microscopiques et paramètres d'entrée des modèles à plus grande échelle, et les domaines de validité de chaque modèle. Dans un deuxième temps, un couplage avec la ségrégation chimique et les bases de données thermodynamiques a été mise en place et appliquée sur un alliage binaire étain-plomb. Une expérience de macroségrégation par convection naturelle a été simulée. L'accord entre les courbes de température expérimentales et simulées atteint une précision de l'ordre de 1K, et la recalescence est correctement prédite. Les cartes de compositions sont comparables qualitativement, ainsi que la structure de grains. Les avantages du suivi de la structure ont été mis en évidence par rapport à une simulation par éléments finis classique. De plus, il a été montré que le calcul 3D était ici indispensable. Enfin, une implémentation parallèle optimisée du code a permis d'appliquer le modèle CAFE à un lingot de silicium polycristallin industriel de dimensions 0,192 x 0,192 x 2,08m, avec une taille de cellules de 250µm. Au total, 4,9 milliards de cellules sont représentées sur le domaine, et la germination et la croissance de 1,6 million de grains sont suivies.

The heart is a muscular organ which acts as a biomechanical pump. Electrical impulses are generated in specialized cells and flow through the heart myocardium by the ion changes on the cell membrane which is the beginning of both the electrical and the mechanical activity. Both the electrical and the mechanical states of the organ will directly affect the pumping activity. The main motivation of this thesis is to better understand physiological and pathological properties of the heart muscle via studying the electro-mechanics of the heart. This model could be used to gain better solutions of the ill-posed inverse problem of ECG and Body Surface Potential Maps (BSPM) or to estimate the electrical propagation and mechanical response on patient specific heart geometry models which can be obtained by using MRI technique. Cellular automaton technique will be used to simulate the physiological function of the left ventricle to estimate the cardiac functions. To model the heart tissue firstly the anatomical knowledge of the heart will be used such as properties of the myocardium, fiber orientations, etc. to simulate the three dimensional electrical propagation. Then the mechanical activity consisting of contraction and relaxation will be simulated according to the material properties of the heart. Using this simulation, the effects of the cardiac arrhythmias such as reentry will be generated. In this study, electrical and mechanical properties of the heart tissue are modeled for normal heart beat and heart beat in case of ischemic heart tissue. Contraction of the tissue via electrical activation has also been considered in terms of time synchronization. &ldquo / Cellular automaton&rdquo / method is used for modeling the electromechanical interactions in the heart tissue. A simplified left ventricle model is used to observe the electrical and the mechanical behavior. Using this method, both the normal heart beat&rsquo / s electrical activation and the arrhythmia excitation could be taken on, without using complex differential equations. To consider the anisotropy of the heart tissue, fiber orientations have also been added to the model. In this thesis work, electro-mechanic models at cellular, macroscopic and heart left ventricle level are presented. The electro-mechanical adaptation is performed by cellular electrophysiology and cellular force development due to intercellular excitation propagation. Varying densities of transmembrane proteins, changes on concentration of calcium, metabolic and hormonal effects are neglected. Also in simplified ventricular model the fluid mechanics and mechanoelectrical feed-back is not taken into-account.

During braking, both the disc and pads in disc brakes are worn. Since disc brakes are not sealed,some of the wear particles generated can become airborne. Several studies have found anassociation between adverse health effects and the concentration of particles in the atmosphere,so it is of interest to improve our knowledge of the airborne wear particles generated by discbrakes. This thesis deals with experimental and computational methods focusing on airborne wearparticles from disc brakes. The eight appended papers discuss the possibility to both measure andnumerically determine the concentration and size distribution of airborne wear particles thatoriginate from the pad-to-disc contact. The objective is to increase the scientific knowledge ofairborne wear particles generated from disc brakes. Papers A, B and C describe tests of disc brake materials conducted in a modified pin-on-discmachine. The results show that the test set-up can be used to measure and rank disc brakematerials with respect to the concentration of airborne particles generated. Ultrafine (nanosized),fine and coarse airborne wear particles that contain metals such as iron, copper and tin werefound. Papers D and E describe a novel disc brake assembly test stand and tests of disc brake materialsconducted in it. The results show that the test set-up can be used to measure the concentrationand size distribution of airborne wear particles generated from disc brake materials. The resultsalso indicate an ability to rank different pad/disc combinations with respect to the concentrationof airborne wear particles. Furthermore, the results suggest that this test stand can be used tostudy rust layer removal from the disc and that airborne particles are generated even at low brakepressures, such as used to remove dirt from the disc. Paper F compares measurements made in passenger car field tests with measurements made in adisc brake assembly test stand and in a pin-on-disc machine. A promising correlation between thethree different test methods is found. Paper G presents and discusses a simulation methodology that numerically determines theconcentration and size distribution of airborne wear particles generated from the pad-to-disccontact in disc brakes by using general-purpose finite element software. Paper H discusses a cellular automaton model that describes the microscopic contact situationbetween the pad and disc in disc brakes. This model is used to numerically determine the amountof wear that leaves the contact. The results correlate qualitatively with experimental observationsfound in the literature. / QC 20110317

Caenorhabditis elegans is a natural predator of the mushroom pathogen Pseudomonas fluorescens NZI7. The bacterial mechanisms for reducing predation by the nematode through the secretion of secondary metabolites have been described, but not yet fully explored. The behaviour of nematodes is influenced by the different factors produced by the pseudomonads. In this thesis we develop a range of assays to link the behaviour of C. elegans to these factors to identify their role in bacteria-nematode interactions. We show that these factors play two distinct roles: they may either repel nematodes, or harm them. This permits the classification of mutants of P. fl. NZI7 lacking these factors as either attractive, edible or both. Many studies of C. elegans behaviour have demonstrated that the nematode can distinguish between different food sources. Our results show two distinct types of response: chemotaxis drives the response to attractive or repellent stimuli, and nematodes also show a choice behaviour that is independent of chemotaxis. This choice behaviour is determined by bacterial edibility and requires nematodes to come into contact with the bacteria. This contact is the foundation of the bacterial dispersal by nematodes. By making use of the luminescence property of the available bacterial mutants, we demonstrate an intimate link between the behaviour of C. elegans and the success with which bacteria are disseminated: if nematodes are induced to regularly leave a bacterial colony, whether through their genotype or the low edibility of the food, then they will spread bacteria effectively. Throughout this thesis, we use computational simulations based on a hybrid cellular automaton model to represent the nematode-bacteria interactions. These simulations recreate the observed behaviour of the system, thus they help to confirm our hypotheses and establish the fundamental aspects of the interactions between the two species.

As variáveis de processo determinam as propriedades dos produtos resultantes dos processos de fundição ou de soldagem, que são função da sua macro e microestrutura bruta de solidificação. Um dos parâmetros importantes para se determinar as propriedades de um produto é a posição da transição colunarequiaxial (CET) e, por este motivo, o entendimento dos fenômenos físicos que causam esta transição é essencial. Com o intuito de se prever a formação da CET, surgiram os métodos empíricos e os modelos matemáticos, que são divididos em dois grandes grupos: modelos determinísticos e modelos estocásticos. Estes dois grupos foram bem estudados, porém nunca foram comparados entre si, particularmente em relação à previsão da posição da CET. O presente trabalho tem como um primeiro objetivo preencher esta lacuna através da comparação entre estes modelos. No entanto, o objetivo principal é apresentar, implementar e validar um novo modelo matemático, denominado de híbrido estocástico-determinístico (CADE -\"Cellular Automaton Deterministic\"), que combine características importantes e vantajosas de cada um dos dois grupos de modelos. Inicialmente, um modelo representante do grupo dos modelos estocásticos foi implementado e validado frente a resultados disponíveis na literatura. Durante esta validação, foi necessária a elaboração de um critério baseado na razão de aspecto dos grãos para a identificação da CET nas macroestruturas calculadas pelo modelo. Estes resultados foram então comparados com os resultados de modelos determinísticos para, após cuidadosa discussão, possibilitar a proposta e implementação do modelo híbrido. Os modelos determinísticos que utilizam o critério mecânico para prever o bloqueio de grãos colunares e a ocorrência da CET mostram regiões colunares em geral maiores que as previstas pelo modelo estocástico. Por outro lado, os modelos determinísticos que utilizam um critério de bloqueio a partir da interação do campo de concentração de soluto ao redor dos grãos prevêem uma CET em posições semelhantes às calculadas pelos modelos estocásticos. O modelo implementado no presente trabalho é capaz de prever a macroestrutura bruta de solidificação e ainda utilizar as equações tradicionalmente empregadas nos modelos determinísticos, sem a necessidade de qualquer método extra para prever a posição da frente de crescimento colunar ou o seu bloqueio por grãos equiaxiais. / The processing variables determine many properties of the products obtained by casting and welding processes and these properties, on the other hand, are strongly affected by the as-cast micro and macrostructure. Particularly the position of the columnar-to-equiaxed transition (CET), which determines the amount of columnar and equiaxed grains in the macrostructure, has an important effect on the properties of as-cast parts. Therefore, understanding the important physical phenomena that cause and affect the formation of the CET plays a crucial role in predicting the ascast macrostructure. To predict the CET formation, empirical methods and mathematical models have been developed. These models are frequently divided into two main groups: deterministic and stochastic. Both groups have been thoroughly studied, but a comparison between them was never attempted, especially regarding the prediction of the CET position. One of the main objectives of the present work is to fulfill this gap by carefully comparing these models. Nevertheless, the most important objective is to propose, implement, and validate a hybrid stochastic-deterministic model, referred to as CADE (Cellular Automaton Deterministic), that combines some important and well-known features of each model. Initially, a model from the stochastic group was implemented and validated using results available in the literature and then used to analyze the effects of some processing variables on the CET prediction. To carry out this analyzes, a criteria based on the aspect ratio of the grains was proposed and developed to identify the CET region from macrostructure images calculated by the model. The results were compared with those obtained by deterministic models and finally led to the development of the new proposed model. This new model has some characteristics from each group of mathematical models and, for this reason, was denoted as hybrid. A deterministic model based on a mechanical blocking criterion to block columnar grains and define the CET position showed, for the most part, larger columnar regions than those predicted by the stochastic model. A deterministic model with a solutal blocking criterion to predict the CET showed results similar to those calculated with the stochastic model. The model proposed in the present work (CADE) was able to predict the as-cast macrostructure using the well-established deterministic equations, without the need for a new method to track columnar grains or predict their blocking by equiaxed grains.

Made available in DSpace on 2016-03-15T19:37:40Z (GMT). No. of bitstreams: 1 Alex Martins.pdf: 1863982 bytes, checksum: 63a3f4efd397697e6bc129fa070520d5 (MD5) Previous issue date: 2011-10-19 / Synchronization can be understood as a temporal organization of events, able of emerging in complex systems, as neural networks. Here, random graph and cellular automaton (CA) are used to represent neural networks, in order to investigate the occurrence of synchronism in such networks. The network coupling topology is of Newman-Watts type, formed by regular lattice with additional random connections. Two parts with this structure are connected by random links. Results obtained from numerical simulations with this model indicate variety of oscillatory behavior: there are cases in which both parts oscillate with equal, multiple and submultiple periods; and cases without oscillation. Investigations were performed concerning the relation among oscillatory behavior and maximum activity, the time to reach such an activity, the minimum average path length, size of the network, the percentage of random connections added and the rules of the CA state transition. Synchronous behavior was found in more than 75% of 28000 simulations accomplished. The system dynamics is influenced more by variations on the number of time steps in which a cell remains firing than by alterations on the lattice size or on the percentage of the randomly added links. / Pode-se entender sincronismo como uma organização temporal de eventos, possível de emergir em sistemas complexos, como redes neurais. Aqui, usam-se grafo aleatório e autômato celular (AC) para representar redes neurais, a fim de investigar a ocorrência de sincronismo em tais redes. A topologia de acoplamento da rede é do tipo Newman-Watts, formada por uma grade regular com ligações aleatórias acrescentadas. Duas partes com essa estrutura são conectadas por ligações aleatórias. Resultados obtidos por simulações numéricas com esse modelo indicam diversidade de comportamento oscilatório: há casos em que as duas partes oscilam em períodos iguais, múltiplos e submúltiplos; e casos sem oscilação. Investigaram-se as relações entre comportamento oscilatório e a atividade máxima, o tempo para se alcançar essa atividade, o comprimento do caminho mínimo médio, o tamanho da rede, a porcentagem de ligações aleatórias adicionadas, e as regras de transição de estado do AC. Comportamento síncrono foi encontrado em mais de 75% das 28.000 simulações realizadas. A dinâmica do sistema é mais influenciada por variações no número de passos de tempo em que a célula permanece disparando do que por alterações no tamanho do reticulado ou no percentual das ligações aleatórias adicionais.

Made available in DSpace on 2016-03-15T19:38:12Z (GMT). No. of bitstreams: 1 Douglas Nunes de Oliveira.pdf: 2639611 bytes, checksum: aa451c77b140c40c8a504474462ded1e (MD5) Previous issue date: 2008-09-17 / Probabilistic cellular automata can be used to model the spreading of contagious diseases in a population composed by susceptible, infected and recovered individuals. At each time step, a susceptible individual can either remain susceptible or contract the disease from infected individuals, where the probability related to the contagion depends on the number of infected individuals in contact with this susceptible individual. At each time step, an infected individual may (probabilistically) either remain infected or recuperate or die by the disease or die by other causes. A recovered individual, at each iteration, can either remain as he/she is or die. When an infected or recovered individual dies, a susceptible one appears in his/her place; thus, the population remains constant. Here, genetic algorithms are employed to identify the probability values concerning the processes of infection, cure and death, from epidemiological data from Arizona (USA) for measles. The goal is to obtain a model based on probabilistic rules of state transitions able of reproducing this time series and to verify the quality of the model prediction. This work reveals that the predictions are strongly influenced by the lattice dimension of the cellular automaton and by limitations imposed to the probability values. / Autômatos celulares probabilistas podem ser usados para modelar a propagação de doenças contagiosas numa população composta por indivíduos suscetíveis, infectados e recuperados da infecção. A cada passo de tempo, um indivíduo suscetível pode ou permanecer suscetível ou contrair a doença de infectados, sendo a probabilidade associada ao contágio dependente do número de infectados em contato com esse suscetível. A cada passo de tempo, um indivíduo infectado pode (probabilisticamente) permanecer infectado, ou se recuperar, ou morrer pela doença ou morrer de outras causas. Um indivíduo recuperado pode, a cada iteração, ou permanecer como está ou morrer. Quando um indivíduo infectado ou recuperado morre, nasce, em seu lugar, um suscetível, de modo que a população permanece constante. Aqui, algoritmos genéticos são empregados para identificar os valores das probabilidades associadas aos processos de infecção, recuperação e morte, a partir de dados epidemiológicos do Arizona (EUA) para catapora. O objetivo é obter um modelo baseado em regras probabilistas de transição de estados capaz de reproduzir essa série temporal e verificar a qualidade da previsão do modelo. Este trabalho revela que as previsões são fortemente influenciadas pelo tamanho do reticulado do autômato celular e por restrições impostas aos valores das probabilidades.