Abstract It is no longer contested that migrant transnational linkages are becoming a replacement social organization where nation-states’ institutions and regulatory capacities are increasingly failing to guarantee decent livelihoods or, at least peace, to their citizens, and where potential destination countries’ policies are restrictive of immigrants. This essay explores the patterns and correlates of the contemporary migration decision-making and its timing, focusing on the role of transnational networks in that process. It is a quantitative study that uses a comprehensive dataset that Forced Migration Studies Programme collected in 2006 on the South African, Mozambican, Congolese and Somali immigrants residing in the Inner-city of Johannesburg. Based on personal experience of 594 international immigrants among those, the study challenges the well established argument in international migration theories that position economic opportunities as the primary explanatory factor underlying the contemporary migration decisions. While the study recognize the importance of economic factors, the study reveals that the entrenched history of migration between countries of origin and destinations and the resultant web of transnational ties explain better than economic factors the contemporary African migration decisions and their timing. With its relatively new approach to analysis of the patterns and correlates of migration decision timing, the study manages to position the importance of transnational ties in migration decisions and to show how they command the swiftness of migration decision-making processes.

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Este estudo doutoral enseja a contribuição com o avanço das reflexões acerca da migração e escravidão por dívida na Amazônia Paraense, no amplo espectro conceitual da geografia humana, perscrutando as narrativas de trabalhadores rurais do Maranhão submetidos à condição análoga a de escravo no Estado do Pará, através da metodologia da história oral entrecruzada com a geografia humana e geografia social, no que chamamos de geografia oral, amealhada a outras fontes documentais como hemerográficas, judiciárias e relatórios técnico-institucionais, com o intento de geografar as memórias e identidades forjadas por estes trabalhadores e suas intrínsecas relações com o território e a migração temporária, enquanto categorias geográficas para compreender o processo de escravidão por dívida, escopo de nosso trabalho. Defendemos, pois, a noção de trabalho escravo, enquanto escolha político-militante, por entender que nossos narradores assim são tratados na Amazônia. O universo pesquisado foi composto por uma cuidada análise entrevistas realizadas com trabalhadores de 19 a 84 anos de idade, no município de Açailândia/MA, localizado na Amazônia Maranhense, fronteira entre os Estados do Tocantins, Maranhão e Pará, palco de pujantes conflitos e impactos que tem sua origem na implantação do Programa Grande Carajás em meados dos anos 80, favorecendo a formação de um cenário de contradições sociais, econômicas e ambientais. Neste contexto, consubstanciamos uma discussão histórico-geográfica da noção de territorialidade migratória, acessada através das narrativas construídas pelos protagonistas deste estudo e as dimensões identitárias que emergem da análise de seu processo de [des/re]territorialização. Outrossim, discutimos filigranadamente os conceitos de território e migração à luz da ciência geográfica, cotejando-os. Nestes termos, pretende-se lançar novas perspectivas de análise e reflexão a este candente objeto de estudo. / This doctoral study expects to contribute with the advance of the reflections about immigration and slavery by debt in the Paraense Amazon, in the broad conceptual spectrum of human geography, peering the narratives of Maranhão rural workers submitted to the analogous condition of slave in the state of Pará, through the methodology of oral history, intertwined with human geography and social geography, in what we call oral geography, gathered to other documentary sources, such as hemerographic, judiciary and technical-institutional reports, itains to map the memories and identities forged by those workers and their intrinsic relations with the territory and the temporary migration, as geographical categories, to understand the process of slavery by debt, the scope of our research work. We defend, therefore, the notion of slave labor as a political militant choice, by understanding that our narrators are treated like that in the Amazon. The universe researched was composed by a prudent analysis of interviews, conducted with workers between 19 and 84 years old, in the county of Açailândia/Maranhão, localized in the Pre-Maranhense Amazon, border among the states of Tocantins, Maranhão and Pará, stage of thriving conflicts and impacts whose origins the implantation of Grande Carajás Program, mid 80s, favoring the formation of this scenery with social, economic and environmental contradictions. In this context, we consubstantiate a historical-geographic discussion about the notion of migratory territoriality, accessed through narratives built by the protagonists of this study and the identity dimensions that emerge from the analyses of deterritorialization, reterritorialization and territorialization processes. Furthermore, we filigreed discuss the concepts of territory and migration under the light of geographic science, collating them. In these terms, we intend to approach new perspectives of analyses and discussion to this ardent object of study.

Esta pesquisa tem como tema central analisar o processo emigratório/imigratório chileno ocorrido nas três últimas décadas do século XX e evidenciar os dilemas da construção de identidade imigrante neste processo por meio da história oral de vida. Para tanto, foram utilizados os procedimentos metodológicos do Núcleo de Estudos em História Oral da Universidade de São Paulo (NEHO/USP), trabalhando com sete histórias de vida de chilenos da cidade de Campinas/SP. Contextualização histórica e cultural do Chile, contextualização dos chilenos no exterior e conceituação dos termos migratórios foram alguns dos assuntos abordados utilizando a bibliografia selecionada. Razões da emigração, o porquê da escolha do Brasil, quais as formas de adaptação no novo país e a questão do retorno foram alguns dos temas analisados a partir das histórias de vida feitas para a pesquisa. Inserida na problemática principal os dilemas da construção de identidade imigrante a constituição de uma comunidade chilena foi assunto abordado. A descrição de todo o processo investigador também é parte fundamental da dissertação. / The aim of this research is to analize the migratory/immigrate process of Chileans which was occurred on the last three decades of the last century (twentieth ones) and also highlighting the structure of immigrant identity process and their dilemmas throughout some oral history life. For this, we were based on the Oral History Research Office at University of São Paulo (NEHO/USP - Núcleo de Estudos em História Oral da Universidade de São Paulo), a methodological procedures which works with life stories and, in this case, we have worked with seven Chilean persons who live in Campinas city (a small city close to São Paulo). By using a selected bibliography, we tried to contextualize Chile in a cultural and historical way and Chilean people overseas, in terms of migrate concepts. The reasons for migrating, the answer(s) for the choice of Brazil, in which forms they were adapting themselves in the new country, and, the problem of returning to Chile, were the topics analyzed from their oral history life in this reseach. We have also added into the topic of the dilemmas of immigrant identity process, the creation of a \"Chilean community\". The whole investigative method description was also the fundamental part of this research.

Esta pesquisa tem como tema central analisar o processo emigratório/imigratório chileno ocorrido nas três últimas décadas do século XX e evidenciar os dilemas da construção de identidade imigrante neste processo por meio da história oral de vida. Para tanto, foram utilizados os procedimentos metodológicos do Núcleo de Estudos em História Oral da Universidade de São Paulo (NEHO/USP), trabalhando com sete histórias de vida de chilenos da cidade de Campinas/SP. Contextualização histórica e cultural do Chile, contextualização dos chilenos no exterior e conceituação dos termos migratórios foram alguns dos assuntos abordados utilizando a bibliografia selecionada. Razões da emigração, o porquê da escolha do Brasil, quais as formas de adaptação no novo país e a questão do retorno foram alguns dos temas analisados a partir das histórias de vida feitas para a pesquisa. Inserida na problemática principal os dilemas da construção de identidade imigrante a constituição de uma comunidade chilena foi assunto abordado. A descrição de todo o processo investigador também é parte fundamental da dissertação. / The aim of this research is to analize the migratory/immigrate process of Chileans which was occurred on the last three decades of the last century (twentieth ones) and also highlighting the structure of immigrant identity process and their dilemmas throughout some oral history life. For this, we were based on the Oral History Research Office at University of São Paulo (NEHO/USP - Núcleo de Estudos em História Oral da Universidade de São Paulo), a methodological procedures which works with life stories and, in this case, we have worked with seven Chilean persons who live in Campinas city (a small city close to São Paulo). By using a selected bibliography, we tried to contextualize Chile in a cultural and historical way and Chilean people overseas, in terms of migrate concepts. The reasons for migrating, the answer(s) for the choice of Brazil, in which forms they were adapting themselves in the new country, and, the problem of returning to Chile, were the topics analyzed from their oral history life in this reseach. We have also added into the topic of the dilemmas of immigrant identity process, the creation of a \"Chilean community\". The whole investigative method description was also the fundamental part of this research.

The VAD Wind Profile (VWP), a time-height display of winds computed by the National Weather Service's WSR-88D radar, is known on occasion to have errors at night during the fall and spring seasons. Several studies, such Haro and Gauthreaux (1998), confirm that migrating birds often contaminate the VWP output. By means of telescopic observations of a full moon, birds were observed flying on two nights when VWP contamination was suspected. The nature of the VWP errors is consistent with migrating birds due to the seasonality, nocturnal nature, and the magnitude of the errors found (greater than 10 knots). With careful selection of data, two clusters of points on the Velocity-Azimuth Display (VAD) are found to exist at certain altitudes when birds begin migrating. One cluster of points is due to radar sample volumes containing birds, and the other cluster is from radar sample volumes without birds. Being able to determine which cluster represents the wind could allow the wind to be calculated by the VWP. Present limitations with the Radar Product Generator's processor and memory prohibit a very advanced detection algorithm. Two simple objective techniques to determine the existence of the two clusters, and determine the wind, were tested. While they show some promise, these methods require further operational testing to determine their usefulness for real-time warning of bird contamination and the reporting of the true wind.

Este estudo doutoral enseja a contribuição com o avanço das reflexões acerca da migração e escravidão por dívida na Amazônia Paraense, no amplo espectro conceitual da geografia humana, perscrutando as narrativas de trabalhadores rurais do Maranhão submetidos à condição análoga a de escravo no Estado do Pará, através da metodologia da história oral entrecruzada com a geografia humana e geografia social, no que chamamos de geografia oral, amealhada a outras fontes documentais como hemerográficas, judiciárias e relatórios técnico-institucionais, com o intento de geografar as memórias e identidades forjadas por estes trabalhadores e suas intrínsecas relações com o território e a migração temporária, enquanto categorias geográficas para compreender o processo de escravidão por dívida, escopo de nosso trabalho. Defendemos, pois, a noção de trabalho escravo, enquanto escolha político-militante, por entender que nossos narradores assim são tratados na Amazônia. O universo pesquisado foi composto por uma cuidada análise entrevistas realizadas com trabalhadores de 19 a 84 anos de idade, no município de Açailândia/MA, localizado na Amazônia Maranhense, fronteira entre os Estados do Tocantins, Maranhão e Pará, palco de pujantes conflitos e impactos que tem sua origem na implantação do Programa Grande Carajás em meados dos anos 80, favorecendo a formação de um cenário de contradições sociais, econômicas e ambientais. Neste contexto, consubstanciamos uma discussão histórico-geográfica da noção de territorialidade migratória, acessada através das narrativas construídas pelos protagonistas deste estudo e as dimensões identitárias que emergem da análise de seu processo de [des/re]territorialização. Outrossim, discutimos filigranadamente os conceitos de território e migração à luz da ciência geográfica, cotejando-os. Nestes termos, pretende-se lançar novas perspectivas de análise e reflexão a este candente objeto de estudo. / This doctoral study expects to contribute with the advance of the reflections about immigration and slavery by debt in the Paraense Amazon, in the broad conceptual spectrum of human geography, peering the narratives of Maranhão rural workers submitted to the analogous condition of slave in the state of Pará, through the methodology of oral history, intertwined with human geography and social geography, in what we call oral geography, gathered to other documentary sources, such as hemerographic, judiciary and technical-institutional reports, itains to map the memories and identities forged by those workers and their intrinsic relations with the territory and the temporary migration, as geographical categories, to understand the process of slavery by debt, the scope of our research work. We defend, therefore, the notion of slave labor as a political militant choice, by understanding that our narrators are treated like that in the Amazon. The universe researched was composed by a prudent analysis of interviews, conducted with workers between 19 and 84 years old, in the county of Açailândia/Maranhão, localized in the Pre-Maranhense Amazon, border among the states of Tocantins, Maranhão and Pará, stage of thriving conflicts and impacts whose origins the implantation of Grande Carajás Program, mid 80s, favoring the formation of this scenery with social, economic and environmental contradictions. In this context, we consubstantiate a historical-geographic discussion about the notion of migratory territoriality, accessed through narratives built by the protagonists of this study and the identity dimensions that emerge from the analyses of deterritorialization, reterritorialization and territorialization processes. Furthermore, we filigreed discuss the concepts of territory and migration under the light of geographic science, collating them. In these terms, we intend to approach new perspectives of analyses and discussion to this ardent object of study.

La thèse vise principalement à étudier la décision de migration aussi bien interne qu’internationale des femmes et des hommes individuels ou en couple. Nous essayerons d'étudier les facteurs déterminants de la migration interne et internationale masculine et féminine en Tunisie, et de voir particulièrement comment les relations de genre influencent la décision de migrer, les raisons de la migration et la destination des femmes et des hommes individuels et en couple. Nous stipulons que le phénomène migratoire est en grande partie lié aux exigences économiques. Les inégalités régionales de développement sont la cause principale des flux migratoires internes et internationaux. Mais, nous considérons que les hommes et les femmes n’ont pas les mêmes contraintes, les mêmes conditions de vie, et ne sont pas autant susceptibles de migrer |'un que l’autre. Bien que les relations de genre aient évolué en Tunisie, la décision de migrer est encore influencée par le modèle social et culturel traditionnel. Nos analyses se situent à la croisée de plusieurs disciplines et de plusieurs approches: démographiques, économiques, sociologiques, etc. Nous utilisons plusieurs méthodes d'analyse, notamment l’analyse descriptive, l'analyse multivariée et l'analyse multiniveaux. Notre principale source des données est l'Enquête nationale «Population et emploi » (2005-2006). Mais nous avons également eu recours à d’autres sources de données telles que : les données individuelles de l’enquête Papfam (2001), les données individuelles du recensement général de la population réalisé en 2004, et des séries des indicateurs statistiques officiels publiés par l’institut national de la statistique. / The thesis aims mainly to study the decision to migrate, both intemally and intemationally, for women and men, individual or in couple. We will try to study the determinant factors of internal and intemational migration of men and women in Tunisia, and especially to see how gender relations influence the decision to migrate, the reasons for migration and the destinations for women and men, individual or in couple. We stipulate that migration is largely due to the economic requirements. Regional inequalilies in development are the main cause of intemal and international migration. But we believe that women and men do not have the same constraints, the same living conditions, and have not the same chance to migrate. Although gender relations have changed in Tunisia, the decision to migrate is still influenced by the social and cultural traditional model. Our analyses are at the crossroads of several disciplines and several approaches: demographic, economic, sociological, etc. We use several methods of analysis, including descriptive analysis, multivariate analysis and multilevel analysis. Our main data source is the National Survey "Population and Employment" (2005-2006). But we also used other sources of data such as individual data from the survey PAPFAM (2001), the individual data of the population census conducted in 2004, and series of ofücial statistical indicators published by the National institute of Statistics.

Scientific computing is used frequently in an increasing number of disciplines to accelerate scientific discovery. Many such computing problems involve the numerical solution of partial differential equations (PDE). In this thesis we explore and develop methodology for high-performance implementations of PDE solvers for shared-memory multiprocessor architectures. We consider three realistic PDE settings: solution of the Maxwell equations in 3D using an unstructured grid and the method of conjugate gradients, solution of the Poisson equation in 3D using a geometric multigrid method, and solution of an advection equation in 2D using structured adaptive mesh refinement. We apply software optimization techniques to increase both parallel efficiency and the degree of data locality. In our evaluation we use several different shared-memory architectures ranging from symmetric multiprocessors and distributed shared-memory architectures to chip-multiprocessors. For distributed shared-memory systems we explore methods of data distribution to increase the amount of geographical locality. We evaluate automatic and transparent page migration based on runtime sampling, user-initiated page migration using a directive with an affinity-on-next-touch semantic, and algorithmic optimizations for page-placement policies. Our results show that page migration increases the amount of geographical locality and that the parallel overhead related to page migration can be amortized over the iterations needed to reach convergence. This is especially true for the affinity-on-next-touch methodology whereby page migration can be initiated at an early stage in the algorithms. We also develop and explore methodology for other forms of data locality and conclude that the effect on performance is significant and that this effect will increase for future shared-memory architectures. Our overall conclusion is that, if the involved locality issues are addressed, the shared-memory programming model provides an efficient and productive environment for solving many important PDE problems.

Cette thèse vise à contribuer à une meilleure compréhension des facteurs qui agissent sur la décision de migrer des individus. Dans le chapitre 1, nous montrons qu’au Portugal, les immigrés occupent souvent des postes pour lesquels ils sont surqualifiés, et que cette non-adéquation entre profils et emplois occupés influence la sélection dans la migration. Les phénomènes de surqualification, plus marqués chez les individus les plus qualifiés, entrainent une sélection négative des migrants, tandis qu’une bonne adéquation entre profils et emplois conduit à une sélection positive.Dans le chapitre 2, nous tirons profit d’une expérimentation sur le terrain pour comprendre comment les décisions de migrer illégalement vers l’Europe des jeunes gambiens sont influencées par l’information qu’ils ont sur les risques associés à cette mobilité. Nous montrons d’abord que les participants au jeu surestiment à la fois le risque de périr en route et la probabilité d’obtenir un statut légal en Europe. Nos résultats suggèrent par ailleurs que la décision de migrer illégalement est influencée par l’une et l’autre probabilité. Informer les candidats au départ sur les risques réels encourus pourrait ainsi les aider à prendre des décisions en connaissance de cause et contribuerait peut-être à sauver des vies. Dans le chapitre 3, nous examinons les liens entre structure familiale et migration, en étudiant l’influence du type d’union des mères sur le comportement migratoire de leurs enfants. Nous trouvons que les enfants nés de mères en union polygame sont plus enclins à migrer vers l’étranger. Nous expliquons ce résultat par la rivalité fraternelle qui en découle. / The purpose of this thesis is to contribute to a better understanding of the drivers of international migration. In Chapter 1, we document that immigrants in Portugal face a high incidence of occupational-skill mismatch, and show how it affects the selection into migration. We find that the incidence of over-education leads to negative selection while correct occupational-skill matches lead to positive selection. In Chapter 2, we rely on a lab-in-the-field experiment to understand the willingness to migrate illegally of young males aged 15 to 25 in The Gambia. We first show that potential migrants overestimate both the risk of dying en route to Europe, and the probability of obtaining legal residency status. The experimental results suggestthat the willingness to migrate illegally is affected by information on the chances of dying en route and of obtaining a legal residence permit. Providing providing potential migrants with official numbers on both probabilities thus affect their likelihood of migrating. This has the potential to help migrants make informed decisions and perhaps save lives. In Chapter 3, we investigate the impact of family structure on international migration decisions. We find that children of mothers in polygynous unions are more likely to migrate internationally. We provide further evidence suggesting that this result is due to sibling rivalry: having full- or half-siblings in migration increases the likelihood of migrating. Our evidence suggests that co-wives’ rivalry as documented elsewhere trickles down to children’s rivalry in migration, suggesting that while neglected in the literature, family structure is crucial to understanding migration.