The methods of statistical physics are increasingly being employed in a range of interdisciplinary areas. In particular, aspects of complex biological processes have been elucidated by bringing the problems down to the level of simple interactions studied in a statistical sense. In nonequilibrium statistical physics, a one dimensional lattice model known as the totally asymmetric simple exclusion processes (TASEP) has become prominent as a tool for modelling various cellular transport processes. Indeed the context in which the TASEP was first introduced (MacDonald et. al., 1968) was to model ribosome motion along mRNA during protein synthesis. In this work I study a variation of the TASEP in which particles hop along a one dimensional lattice which extends as they reach the end. We introduce this model to describe the unique growth dynamics of filamentous fungi, whereby a narrow fungal filament extends purely from its tip region while being supplied with growth materials from behind the tip. We find that the steady state behaviour of our model reflects that of the TASEP, however there is an additional phase where a dynamic shock is present in the system. I show through Monte Carlo simulation and theoretical analysis that the qualitative behaviour of this model can be predicted with a simple mean-field approximation, while the details of the phase behaviour are accurate only in a refined approximation which takes into account some correlations. I also discuss a further refined mean-field approximation and give a heuristic argument for our results. Next I present an extension of the model which allows the particles to interact with a second lattice, on which they diffuse in either direction. A first order meanfield continuum approximation suggests that the steady states of this system will exhibit some novel behaviour. Through Monte Carlo simulation I discuss the qualitative changes that arise due to the on-off dynamics. Finally I study a model for a second biological phenomenon: the length fluctuations of microtubules. The model describes stochastic polymerisation events at the tip of a microtubule. Using a mean-field theory, we find a transition between regimes where the microtubule grows on average, and where the length remains finite. For low rates of polymerisation and depolymerisation, the transition is in good agreement with Monte Carlo simulation.

<p>There are an increasing number of pupils leaving school with incomplete grades. Research indicates that the causes to this phenomenon may be individual- as well as school related and complicated to illuminate. The purpose of the study is to examine the processes of exclusion that have resulted in pupils´ incomplete degrees. Two research problems have been formulated. The first one is about the identification of exclusion and branding factors for pupils with incomplete degrees. The second one focuses on how the pupils processes of branding- and exclusion are shaped. Six in dept interviews with three pupils with incomplete degrees have been conducted from a life history perspective. Each pupil has been interviewed twice, at different occasions. Results show that the factors vary and are individual, and can be identified within the family as well as the school. In school, there may be a tendency to refer the problem to the pupil rather than to the entire context.</p><p>This brands pupils that already are in a difficult situation, but results also show that school can have including tendencies as well. The three pupils in the study have in common that they contribute to the branding- and exclusion process by excluding themselves. To conclude, there are several factors that are intertwined and that together contribute to the result of incomplete degrees. Two of the pupils´ stories were related to Goldman’s (1980) identified stages of branding, which resulted in an understanding of these pupils process of exclusion. The third pupils´ story however, differed from the other two, and as a consequence, differed from Goldman’s theory, which is discussed.</p> / <p>Allt fler svenska elever går ut grundskolan med ofullständiga betyg. Tidigare forskning indikerar att orsakerna till att så sker kan vara såväl individ- som skolrelaterade och komplicerade att utreda. Syftet med studien är att undersöka de exkluderingsprocesser som lett fram till att elever fått ofullständiga betyg i grundskolan. Två problem har formulerats. Det första problemet handlar om att identifiera exkluderings- och stämplingsfaktorerna i grundskolan för elever med ofullständiga grundskolebetyg. Det andra problemet fokuserar på hur elevernas stämplings- och exkluderingsprocesser ser ut. Sex djupintervjuer med tre elever med ofullständiga grundskolebetyg har genomförts utifrån ett livsberättelseperspektiv. Varje elev har intervjuats vid två olika tillfällen. Resultaten visar att stämplings- och exkluderingsfaktorerna varierar och är individuella, och kan återfinnas inom såväl den egna familjen som skolans värld.</p><p>En skolrelaterad faktor handlar om en tendens att problematisera eleverna snarare än kontexten, vilket ytterligare stämplar elever i en redan svår situation, men resultaten påvisar också exempel på hur skolan kan arbeta inkluderande. De tre eleverna har gemensamt att de alla bidrar till stämplings- och exkluderingsprocessen genom självexkludering. Resultaten visar att det är en rad faktorer som samverkar och flätas in i varandra under elevernas skolgång, och som tillsammans bidrar till elevernas ofullständiga grundskolebetyg. Två av eleverna följde Goldmans (1980) stämplingsstadier, vilket bidrog till förståelse av dessa elevers exkluderingsprocesser. Den tredje elevens stämplings- och exkluderingsprocess avvek från de övriga två, och därmed också från Goldmans teori, vilket utgjort underlag för diskussion.</p>

There are an increasing number of pupils leaving school with incomplete grades. Research indicates that the causes to this phenomenon may be individual- as well as school related and complicated to illuminate. The purpose of the study is to examine the processes of exclusion that have resulted in pupils´ incomplete degrees. Two research problems have been formulated. The first one is about the identification of exclusion and branding factors for pupils with incomplete degrees. The second one focuses on how the pupils processes of branding- and exclusion are shaped. Six in dept interviews with three pupils with incomplete degrees have been conducted from a life history perspective. Each pupil has been interviewed twice, at different occasions. Results show that the factors vary and are individual, and can be identified within the family as well as the school. In school, there may be a tendency to refer the problem to the pupil rather than to the entire context. This brands pupils that already are in a difficult situation, but results also show that school can have including tendencies as well. The three pupils in the study have in common that they contribute to the branding- and exclusion process by excluding themselves. To conclude, there are several factors that are intertwined and that together contribute to the result of incomplete degrees. Two of the pupils´ stories were related to Goldman’s (1980) identified stages of branding, which resulted in an understanding of these pupils process of exclusion. The third pupils´ story however, differed from the other two, and as a consequence, differed from Goldman’s theory, which is discussed. / Allt fler svenska elever går ut grundskolan med ofullständiga betyg. Tidigare forskning indikerar att orsakerna till att så sker kan vara såväl individ- som skolrelaterade och komplicerade att utreda. Syftet med studien är att undersöka de exkluderingsprocesser som lett fram till att elever fått ofullständiga betyg i grundskolan. Två problem har formulerats. Det första problemet handlar om att identifiera exkluderings- och stämplingsfaktorerna i grundskolan för elever med ofullständiga grundskolebetyg. Det andra problemet fokuserar på hur elevernas stämplings- och exkluderingsprocesser ser ut. Sex djupintervjuer med tre elever med ofullständiga grundskolebetyg har genomförts utifrån ett livsberättelseperspektiv. Varje elev har intervjuats vid två olika tillfällen. Resultaten visar att stämplings- och exkluderingsfaktorerna varierar och är individuella, och kan återfinnas inom såväl den egna familjen som skolans värld. En skolrelaterad faktor handlar om en tendens att problematisera eleverna snarare än kontexten, vilket ytterligare stämplar elever i en redan svår situation, men resultaten påvisar också exempel på hur skolan kan arbeta inkluderande. De tre eleverna har gemensamt att de alla bidrar till stämplings- och exkluderingsprocessen genom självexkludering. Resultaten visar att det är en rad faktorer som samverkar och flätas in i varandra under elevernas skolgång, och som tillsammans bidrar till elevernas ofullständiga grundskolebetyg. Två av eleverna följde Goldmans (1980) stämplingsstadier, vilket bidrog till förståelse av dessa elevers exkluderingsprocesser. Den tredje elevens stämplings- och exkluderingsprocess avvek från de övriga två, och därmed också från Goldmans teori, vilket utgjort underlag för diskussion.

La plupart des processus dans notre vie quotidienne sont des processus hors équilibre. Un exemple de système hors équilibre est la cellule biologique et le transport qui a lieu dedans. Dans cette thèse ce transport intracellulaire est modélisé par des processus stochastiques. Pour cela deux approches différentes ont été utilisées : d’une part une modélisation explicite de particules actives avec des degrés de liberté internes obtenus expérimentalement, d’autre part une description phénoménologique des effets collectifs, qui est réalisée au moyen de processus d’exclusion.Un des résultats principaux pour le modèle explicite est qu’il est crucial de prendre en compte les fluctuations des forces pour reproduire les caractéristiques principales du mou- vement. Un autre élément important est la prise en considération de l’environnement cellu- laire, qui peut produire des effets non-triviaux, comme par exemple une inversion du sens de déplacement moyen. Pour étudier les effets collectifs il est possible de représenter le mou- vement des particules d’une manière simplifiée, en utilisant un processus d’exclusion avec des particules ayant des états internes. Le désordre sur les taux de saut qui en résulte peut provoquer une condensation dépendant de la densité.Un autre modèle étudié est un processus d’exclusion sur un réseau à deux voies. On suppose que deux types de particules se déplacent dans une géométrie tubulaire, inspirée par les champignons filamenteux. Ces hypothèses définissent un modèle minimal qui présente une transition de phase d’une phase de basse densité vers une phase pulsante caractérisée par des oscillations de densité. / Most processes in our daily life are far from equilibrium. The prime example is a cell and the transport occurring within. In this thesis intracellular transport is modeled by means of stochastic processes. For this, two different approaches are applied: the explicit mod- eling of active particles with internal degrees of freedom with characteristics as they were determined experimentally. And secondly, the collective effects occurring in many particle systems are studied in a phenomenological way by means of exclusion processes.In the explicit model one important result is given by the fact that force fluctuations are essential to capture the relevant motion characteristics. Further, the influence of the cellular environment creates counter-intuitive effects, like a possible inversion of the bias. The motion characteristics can be represented in a coarse-grained manner as an exclusion process for particles with internal states. Due to the resulting disorder in the hopping rates a density-dependent condensation occurs.In a second part, a two-lane exclusion model is studied. Two species in a tubular geometry inspired by filamentous fungi are considered.This can be seen as a minimal model exhibiting a phase transition from a low density phase to an intriguing phase with periodically changing particle densities.

<p>This dissertation includes my research works during Ph.D. career about three different kinds of random walks in (dynamical) random environments. It includes my two published papers “Functional weak limit of random walks in cooling random environments” which has been published in electronic communications in probability in 2020, and “Variable speed symmetric random walk driven by the simple symmetric exclusion process” which is the joint work with Peterson and Menezes and has been published in electronic journals of probability in 2021. This dissertation also includes my two other projects, one is the joint work with Janjigian and Emrah about moderate deviation and exit time estimates in integrable directed polymer models. The other one is the joint work with Peterson and Conrado that extends the weak limit of random walks in cooling randon environments with underlying environment is in the transient case.</p>

Made available in DSpace on 2016-04-29T14:16:57Z (GMT). No. of bitstreams: 1 Thais C G Lima.pdf: 1944536 bytes, checksum: baad5428036fbb2c2e13726d6ca7a7e8 (MD5) Previous issue date: 2007-05-18 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / This study aims to analyze the social impact of the tourism, considering its influences on local development and social inclusion/exclusion. For its contributions to the local economy, with the employment and income generation to the resident population and the culture valorization of the localities, tourism has been presented by academic studies and official documents as an important development factor. The difficult situations in which live many resident populations on tourist destinations, however, instigate investigations related to the actual level that it occurs. It was analyzed the conceptions of these three keyelements: tourism, local development and social inclusion/exclusion. Understood as a social phenomenon, in contraposition to its merely economic character, tourism is taken as a practice and activity that involves cultural and symbolical exchanges, impacts on the nature and influences on social behaviors and relations. Regarding the local development, it s taken as a process that involves citizenship, obtained by negotiations of interests and priorities of the different social groups, and it centers on the human beings as citizens. The social inclusion is seen as a consequence of multiple factors that come from social processes, with no absolute character. To the data collection, it was used two questionnaires one to the residents of Paraty and another to the tourists and qualitative interviews. The study identifies differences and similarities among the perceptions of residents and tourists. To the residents, the importance of the tourism is strongly related to the valorization that it promotes of the city, of the local culture and of the social relations and cultural interactions that come from it, when it transforms a small historic city into a famous tourist destination, internationally known. The population also recognizes the contribution of the tourism to the employment and income generation on the city. Among the tourists, the more frequent vision refers to the local economy activation and the elevation of the local culture and artistic production visibility. The study reveals tourism as a fundamental factor to the progress, in terms of local development and social inclusion, in Paraty. It denotes the importance of the union between the tourist activity and public policies, conjugating tourism and actions towards the local development, with special attention to the education, health and infrastructure areas, which will benefit not only the resident population but also the tourists that visit the city / Resumo Este estudo visa a analisar o impacto social do turismo, considerando sua influência sobre o desenvolvimento local e a inclusão/exclusão social em Paraty. Por suas contribuições para a economia local, com a geração de empregos e renda para a população residente, juntamente com a valorização da cultura das localidades, o turismo tem sido apresentado na literatura e nos documentos oficiais como importante fator de desenvolvimento. As precárias situações em que vivem muitas populações residentes em destinações turísticas, entretanto, instigam investigações a respeito do efetivo grau em que isto se realiza. Foram analisadas as conceituações acerca destes três elementos-chave: turismo, desenvolvimento local e inclusão/exclusão social. Compreendido enquanto fenômeno social, em contraposição ao seu caráter meramente econômico, o turismo é tomado como prática e atividade que envolve trocas culturais e simbólicas, impactos ambientais e influências nos comportamentos e relações sociais. Quanto ao desenvolvimento local, este é entendido como um processo que envolve a cidadania, obtida por meio de negociações e embates de interesses e prioridades dos diversos grupos sociais, e centra-se nos seres humanos enquanto cidadãos. A inclusão social é vista como conseqüência de múltiplos fatores, decorrentes de processos sociais, sem caráter absoluto. Para a coleta de dados, foram utilizados dois questionários um destinado aos residentes de Paraty e outro, aos turistas e entrevistas qualitativas. O estudo identifica diferenças e semelhanças entre as percepções dos moradores e turistas. Para os residentes, a importância do turismo está fortemente ligada à valorização que ele promove da cidade, da cultura local e das relações sociais e interações culturais que dele decorrem, ao transformar uma pequena cidade histórica em um famoso destino turístico internacionalmente conhecido. A população reconhece, também, a contribuição do turismo para a geração de empregos e renda na cidade. Já para os turistas a visão mais recorrente refere-se à ativação da economia local, além do aumento da visibilidade da cultura e produção artística paratienses. O estudo revelou o turismo enquanto fator fundamental para avanços em termos de desenvolvimento local e inclusão social em Paraty. Apontou a importância da vinculação entre a atividade turística e políticas públicas, que aliem o turismo a ações voltadas ao desenvolvimento local, com especial atenção às áreas de educação, saúde e infra-estrutura que beneficiarão não apenas a população residente mas também os turistas que visitam a cidade