As famílias rurais do semiárido vivem sob constante vulnerabilidade climática, cujas atividades agropecuárias são comprometidas pela instabilidade hídrica, pela produção em solos empobrecidos e também pela demanda de altos investimentos na modernização dos seus sistemas produtivos. A consequência é um povo marginalizado, pobre, sem acesso a alimentação em quantidade e qualidade suficientes, desencadeando na migração para grandes centros ou ainda, a exploração e degradação dos recursos da Caatinga na tentativa de desenvolver suas atividades e assim permanecer no campo. Diante a problemática da seca, muitas estratégias de convivência com o semiárido são promovidas, as quais favorecem o acesso à água e a inclusão social. No entanto, o cenário atual enfatiza a necessidade de medidas mais eficientes para o fortalecimento da agricultura familiar, que devem ser condizentes à realidade do agricultor e harmoniosas com o meio ambiente. Portanto, para elucidar questões sobre a realidade de agricultores familiares do semiárido e gerar informações como subsídio a atuação de agentes externos, o presente trabalho compreendeu as vulnerabilidades dos meios de vida de agricultores familiares. Bem como, a importância e o impacto dos recursos (água, produção e área consolidada) dos meios de vida de agricultores familiares. Foram realizadas entrevistas com 23 famílias distribuídas em municípios da Bacia do Jacuípe e aplicados quatros métodos multivariados, por meio da (i) análise de agrupamentos, (ii) análise de componentes principais, (iii) análise de fatores e (iv) análise de seleção das variáveis. Os resultados apontaram para a produção que aqueles com maior número de matrizes (vacas em lactação ou caprinos para carne) diversificam suas rendas com a venda de galinhas e ovos e possuem RL com entrada de animais. Enquanto aquelas com propriedades entre 0-20 ha trabalham, somente, com a produção de hortaliças, cuja fonte de renda é o próprio negócio. Famílias com propriedades entre 20-66 ha criam caprinos, não possuem APP e não utilizam equipamentos via associações ou empréstimos. Quanto as famílias com propriedades entre 66-80 ha, embora criem caprinos, sua comercialização não é a principal fonte de renda. Assim, concluiu-se que os meios de vida das famílias rurais do semiárido apresentam maior vulnerabilidade nos seguintes recursos: financeiro (devido ao baixo retorno econômico de suas atividades e à comercialização de seus produtos, bem como às dificuldades de acesso ao crédito) e social (falta de conhecimentos técnicos resultando em práticas agropecuárias defasadas e insustentáveis, desencadeando uma má utilização dos recursos locais). O acesso aos programas sociais disponíveis e a participação em associações ou cooperativas são fundamentais para viabilizar as estratégias de convivência com o semiárido. A gestão da água (acesso e bom uso do recurso) e a aplicação dos conhecimentos tradicionais favorecem a segurança alimentar das famílias rurais. As principais estratégias de convivência com o semiárido focam no acesso a água e em alternativas para suprir a falta de alimento para o animal. O tamanho da propriedade e de produção impactam a conservação da caatinga, assim como, o tamanho da propriedade influencia no foco de produção agropecuário. Por fim, o uso eficiente da água depende de tecnologias e boas práticas que permitam o seu melhor aproveitamento. / Countryside families who lives in the semi-arid region are under constant climate vulnerability, whose agricultural activities are compromised by water instability, production in impoverished soils and by the demand for high investments in the modernization of their productive systems. The consequence is a marginalized, poor people, without access to food in sufficient quantity and quality, triggering the migration to big centers or the exploitation and degradation of Caatinga resources in attempt to develop their activities and thus remain in rural areas. Faced with drought problem, many strategies for living with the semi-arid are promoted, which favor access to water and social inclusion. However, the current scenario emphasizes the need for more efficient alternatives to strengthen family farming, which must be applicable to reality of farmers and harmonious with environment. Based on the assumption that more financial resources favor the development of family agriculture, but also the awareness of use and better exploitation of local resources available in their lives, the present work understood importance and use of resources of the livelihoods (human, Social, physical, financial and natural) through the methodology Sustainable Livelihoods. interviews were conducted with 23 families included on a program called Adapta Sertão, selected with a focus on production and size of the property, distributed in municipalities of the Jacuípe Basin. To verify the impact of family farmer livelihoods, 20 factors were generated based on 99 observed variables and four multivariate methods were applied, through (i) cluster analysis, (ii) principal component analysis, (iii) analysis of factors and (iv) analysis of selection of variables. The results showed that, based on the production focus, most of the families work with milk production, and there is a direct relationship between a higher production of animals and, consequently, a lower presence of APP. Families with higher numbers of animals (lactating cows or goats for meat) are those that diversify their family income through the sale of chickens and eggs, but who have RL with animals. Families with properties between 0-20 ha are those that produce only vegetables and have their own business as main source of income (they do not work with raising goats and selling milk). Families with properties between 20-66 ha, have no APP and do not use equipment via associations or loans. However, they are those that work with the creation of goats. Regarding families with properties between 66-80 ha, although they raise goats, their commercialization is not the main source of income. Thus, it was concluded that the guarantee of food security of countryside families who lives in the semi-arid region are vulnerable in the following resources: financial (due to the low economic return of their activities and the commercialization of their products, as well as the difficulties of access to credit) and (Lack of technical knowledge resulting in lagging and unsustainable agricultural practices, triggering misuse of local resources). Access to available social programs and participation in associations or cooperatives are fundamental to enable the strategies to coexist with the semi-arid region.

One of the most promising routes to create advanced materials is self-assembly. Self-assembly refers to the self-organisation of building blocks to form ordered structures. As the properties of the self-assembled materials will inherit the properties of the basic building blocks, it is then possible to engineer the properties of the materials by tailoring the properties of the building blocks. In order to create mesoscale materials, the self-assembly of molecular building blocks of different sizes and interactions is important. Mesoscopic materials can be obtained by using larger building blocks such as nano and colloidal particles. Colloidal particles are particularly attractive as building blocks because it is possible to design interparticle interactions by controlling both the chemistry of the particles' surface and the properties of the solvent in which the particles are immersed. The self-assembly of spherical colloidal particles has been widely reported in the literature. However, advances in experimental techniques to produce particles with different shapes and sizes have opened new opportunities to create more complex structures that cannot be formed using spherical particles. Indeed, the particles' shape and effective interactions between them dictate the spatial arrangement and micro-structure of the system, which can be engineered to produce functional materials for a wide range of applications. The driving forces determining the self-assembly of colloidal particles can be modified by the use of external influences such as geometrical confinement and electromagnetic forces. Geometrical confinement, for example, has been used to design quasi two-dimensional materials such as multi-layered structures of spheres, dimers, rods, spherical caps, and monolayers of platelets with various geometries and symmetries. In this dissertation, we present three computer simulations studies using Monte Carlo and Molecular Dynamics simulations determining the self-assembly of monolayer colloidal platelets with different shapes confined in two dimensions. These particles have been selected due to recent experiments in colloidal particles with similar shapes. All the particles' models are represented by planar polygons, and three different effects affecting their self-assembly have been analysed: (a) the curvature of the particles' vertices; (b) the curvature of the particles' edges; and finally (c) the addition of functional groups on the particles' surface. These studies aim to demonstrate that the subtle changes on the particle's shape can be used to engineer complex patterns for the fabrication of advanced materials. Monte Carlo simulations are performed to study the self-assembly of colloidal platelets with rounded corners with 4, 5, and 6-fold symmetries. Square platelets provide a rich phase behaviour that ranges between disorder-order and order-order phase transitions. Suprisingly, the disk-like shape of pentagons and hexagons prevents the total crystallisation of these systems, even at a high pressure state. A hysteresis gap is observed by the analysis of compression and expansion runs for the case of square platelets and the thermodynamic method known as direct coexistence method is used to be accurately determined the point of the order-order transition. Further, unexpected results are obtained by performing Molecular Dynamics simulations in systems with platelets with 3, 4, 5, and 6-fold symmetries when all the sides of each polygon are curved. Macroscopic chiral symmetry breaking is observed for platelets with 4 and 6-fold symmetries, and for the first time a rule is promoted to explain when these chiral structures can be formed driven only by packing effects. This unique rule is verified also for platelets with the same curved sides as previously when functional chains tethered to either vertices or sides. Indeed, square platelets with curved sides confined in two dimensions can form chiral structures at medium densities when flexible chains tethered to either vertices or sides. Triangular platelets with curved sides can form chiral structures only when the chains are tethered to the corners, since the chains experience an one-hand rotation to sterically protect one side. When the chains are symmetrically tethered to the sides, local chiral symmetry breaking is observed as both left-hand and right-hand sides on each vertex are sterically protected allowing the same probability for rotation either in clockwise or anticlockwise direction.

Orientador: Guillermo Gerardo Cabrera Oyarzun / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-09-24T18:55:27Z (GMT). No. of bitstreams: 1 Garcia_FernandoAssis_M.pdf: 623202 bytes, checksum: ec47f534b74f1dafc10e8a0d7c031968 (MD5) Previous issue date: 2007 / Resumo: Esta dissertação tem como objetivo apresentar um estudo da simetria do parâmetro de ordem em supercondutores ferromagnéticos. Nossa abordagem é inspirada na teoria de Landau para Transições de Fase de Segunda Ordem ou, de maneira mais precisa, na idéia que uma transição de fase de segunda ordem está acompanhada por uma redução na simetria do sistema. A nova fase passa a ser descrita por um subgrupo da fase de alta simetria, implicando consequências para o parâmetro de ordem, que em nosso caso determina a estrutura do gap supercondutor. A recente descoberta da coexistência de supercondutividade e ferromagnetismo revelou o problema da classificação das possíveis simetrias do parâmetro de ordem supercondutor quando o estado normal não possui simetria de reversão temporal. Veremos que o problema é resolvido quando a simetria do estado normal é descrita por grupos magnéticos ( ou co-grupos) e que a classificação dos estados supercondutores deve agora ser feita em termos das co-representações destes grupos / Abstract: In this dissertation, we present a study of the order-parameter symmetry in ferromagnetic superconductors. Our approach is inspired on the Landau Theory of Phase Trasition or, more precisely, on the idea that a second order phase transition is a symmetry breaking process where the ordered phase of the system is described by a subgroup of the highly symmetric one, leading to important consequences for the order parameter. In our case, it imposes constraints to the superconducting gap structure. The recent discovery of the coexistence of superconductivity and ferromagnetism brought the problem of the classification of such structures in the situation where time reversal symmetry is broken on the normal state. We argue that this problem is solved when one consider the description of such normal state by magnetic groups (or cogroups) and that the classification of the superconducting states must be done in terms of the corepresentations of such cogroups / Mestrado / Física da Matéria Condensada / Mestre em Física

O estudo tenta investigar quais são as fontes de privações que impedem a expansão das liberdades dos agricultores familiares no semiárido norte-mineiro e se a presença do Microcrédito Produtivo Rural (o Agroamigo) e dos Programas de Formação e Mobilização para a Convivência com o Semiárido: Um Milhão de Cisternas Rurais (P1MC/P1 +2) apresenta alguma eficácia com vistas à redução dos níveis de privações destes agricultores. A hipótese central que guia o itinerário deste trabalho tenta confirmar que as políticas e programas voltados para a região do semiárido norte-mineiro, mesmo que articulados, ainda são insuficientes para causar grandes efeitos na agricultura familiar. O que se observa também é a falta, por parte dos agricultores, de uma formação contextualizada para conviver com o semiárido por meio da adoção de tecnologias apropriadas e de estratégias para o enfrentamento à seca. O estudo demandou como aportes teóricos o pensamento crítico do semiárido e a abordagem das capacitações com a finalidade de explicar a realidade da base empírica. Para tanto, foram coletadas 92 amostras em seis comunidades rurais no município de Januária/MG, cujos dados foram operacionalizados e, posteriormente, analisados com base na abordagem das capacitações. A construção do Índice de Liberdade do Agricultor Familiar no Semiárido Norte-Mineiro (ILAF-SAM) deu suporte para mensurar os níveis de privações identificadas nos grupos de funcionamentos de cada liberdade instrumental. Os resultados revelaram ILAF-SAM muito baixo (0,387) na liberdade “A formação contextualizada e a convivência com o semiárido norte-mineiro”, enquadrando-se no nível extremamente alto de privação de liberdade para os agricultores conviverem com o fenômeno da seca. As oportunidades sociais (ILAF-SAM = 0,599), as facilidades econômicas (ILAF-SAM = 0,598), a segurança protetora (ILAF = 0,502) e as garantias de transparência (ILAF-SAM = 0,640), compuseram as principais fontes de privações que cerceiam os agricultores de ampliarem as suas liberdades. Observou-se também fraca articulação entre os programas de convivência e o Microcrédito Produtivo Rural a fim de reduzir as fontes de privações dos agricultores familiares. Mesmo assim, os resultados encontrados em algumas variáveis, isoladamente, foram relevantes no sentido de complementar este estudo e abrir novas perspectivas de pesquisas no semiárido norte-mineiro. / The study attempts to investigate what are the sources of deprivations that prevent the expansion of the freedoms of family farmers in the semiarid of northern Minas Gerais and whether the presence of the Rural Productive Microcredit (Agroamigo) and of the Training and Mobilization Programs for Coexistence with Semiarid Conditions: One Million Rural Cisterns (P1MC/P1 +2) has some efficacy in reducing the levels of deprivation of these farmers. The central hypothesis guiding the itinerary of this paper tries to confirm that policies and programs for the semiarid region of the northern Minas Gerais, even when conjoined, are insufficient to cause major positive effects on family farming. What is also observed is the lack, on the part of the farmers, of a contextualized training for living in the semiarid through the adoption of appropriate technologies and strategies for coping with drought. The study demanded as theoretical supports the critical thinking of the semiarid and the capabilities approach in order to explain the reality of the empirical basis. Therefore, 92 samples were collected in six rural communities in the municipality of Januária / MG, whose data were operationalized and subsequently analyzed using the capabilities approach. The construction of the Index of Freedom of the Family Farmer in the semiarid northern Minas Gerais (ILAFSAM) supported measuring the levels of deprivation identified in the groups of each instrumental freedom. The results revealed a very low (0.387) ILAF-SAM for the freedom "Contextualized training and coexistence with the semiarid northern Minas Gerais", characterizing an extremely high level of deprivation of freedom for farmers to live with the phenomenon of drought. Social opportunities (ILAF-SAM = 0.599), the economic possibilities (ILAF-SAM = 0.598), protective security (ILAF = 0.502) and guarantees of transparency (ILAF-SAM = 0.640), along with the previous one, composed the main sources of deprivation that curtail farmers from extending their freedoms.We also observed weak connections between these programs for living with the semiarid and the Rural Productive Microcredit with the aim of reducing the sources of deprivations for family farmers.Even so, the results in some isolated variables were relevant in order to complement this study and open new perspectives for research in the semiarid northern Minas Gerais.

We used demographic methods to address one of the main challenges facing ecological science: forecasting the effect of climate change on plant communities. Ecological forecasts will be crucial to inform long-term planning in wildland management and demographic methods are ideal to quantify changes in plant abundance. We carried out our research in the sagebrush steppe, one of the most extensive plant ecosystems of Western North America. Our research intended to inform ecological forecasts on an exotic invader, cheatgrass (Bromus tectorum). Moreover, we investigated the general question asking: to what degree competition among plants influences the outcome of ecological forecasts on the effect of climate change? We carried out two field experiments to test the hypothesis that warming will increase cheatgrass abundance in the sagebrush steppe. This hypothesis was strongly supported by both experiments. Warming increased cheatgrass abundance regardless of elevation, neighboring vegetation or cheatgrass genotype. Moreover, we found cheatgrass was hindered by snow cover. Therefore, warming increases cheatgrass growth directly by increasing temperature, and indirectly by decreasing or removing snow cover. In our last experiment, we tested whether forecasts of climate change effects on rare species can ignore competition from neighbors. This should occur because rare species should have little niche overlap with other species. The lower the niche overlap, the less competition with other species. To test this hypothesis, we used a long-term data set from an Idaho sagebrush steppe. We built population models that reproduced the dynamics of the system by simulating climate and competition. Model simulations supported our hypothesis: rare species have little niche overlap and little competitive interactions with neighbor species.

Les gestionnaires forestiers sont demandeurs d'une aide à la décision pour la conservation du mélange Sapin et Epicéa en forêt de montagne. Pour répondre à leur attente, nous avons modélisé, pour les deux espèces, les fonctions démographiques (croissance, mortalité et recrutement) et les fonctions d'allométries à partir de données de terrain. Ces fonctions ont été implémentées dans un modèle de dynamique forestière afin d'améliorer les connaissances sur la dynamique naturelle des deux espèces et d'envisager des tests de scénarios sylvicoles. L'estimation statistique des paramètres des modèles a été effectuée dans un cadre bayésien hiérarchique. Elle a permis de mettre en évidence et de quantifier les différences entre espèces : le Sapin, espèce tolérante à l'ombre comparativement à l'Epicéa, est moins sensible à l'autoéclaircie, a une croissance plus forte et un taux de recrutement plus important à faibles niveaux de lumière que l'Epicéa. Les modèles développés ont pris en compte l'incertitude sur les observations et la variabilité spatio-temporelle des processus. La variabilité individuelle (ou intraspécifique) et temporelle (interannuelle et intra-individuelle) est forte et tend à égaliser la fitness des deux espèces en inversant la hiérarchie des espèces localement dans l'espace ou sporadiquement dans le temps. Les premières simulations à l'aide du simulateur Samsara2 indiquent un meilleur comportement du modèle lorsque la variabilité spatio-temporelle est inclue dans les processus. La variabilité assure une structuration en hauteur et en diamètre ainsi qu'une évolution de la surface terrière qui correspondent à des patterns plus réalistes que lorsque la variabilité n'est pas prise en compte. A l'issue des premières simulations sur un peuplement test en mélange, on observe une exclusion compétititve systématique de l'Epicéa par le Sapin. Les mécanismes égaliseurs associés à la variabilité ne parviennent pas à contrebalancer l'avantage compétitif du Sapin sur l'Epicéa. Toutefois, la dynamique transitoire du système est lente et la coexistence apparente des deux espèces peut s'étaler sur plusieurs centaines d'années.

Cette thèse présente une approche phénoménologique des membranes <>, ces bicouches de lipides sur lesquelles sont greffées des macromolécules. Les membranes poilues sont des systèmes biomimétiques qui permettent d'appréhender le couplage entre la courbure de la membrane et l'organisation bidimensionnelle des macromolécules. Dans une première partie, nous mettons en évidence les forces exercées par des chaines polymères greffées sur la membrane, qui tendent à courber cette dernière. Un paramètre important que prend en compte ce travail est la fluidité de la bicouche lipidique. Cette propriété permet au manteau de polymère de s'adapter aux contraintes exercées sur la membrane. Ainsi, une courbure locale engendre la réorganisation à grande échelle des polymères. Par ailleurs, une étude préparatoire montre que la coexistence de la membrane poilue avec des polymères en solution ne modifie pas qualitativement ces résultats. La seconde partie est consacrée à l'étude de macromolécules greffées dans la membrane par plusieures ancres. Ces dernières sont modélisées par des chaînes polymères en bon solvant. Nous établissons le catalogue des différentes conformations qu'une chaîne peut adopter, ainsi que la déformation qui en découle. Nous montrons ainsi que l'effet du polymère sur la membrane domine la courbure spontanée. Le polymère devient alors un paramètre de contrôle maniable de l'état de surface de la membrane.

Cette thèse présente une approche phénoménologique des membranes <>, ces bicouches de lipides sur lesquelles sont greffées des macromolécules. Les membranes poilues sont des systèmes biomimétiques qui permettent d'appréhender le couplage entre la courbure de la membrane et l'organisation bidimensionnelle des macromolécules. Dans une première partie, nous mettons en évidence les forces exercées par des chaines polymères greffées sur la membrane, qui tendent à courber cette dernière. Un paramètre important que prend en compte ce travail est la fluidité de la bicouche lipidique. Cette propriété permet au manteau de polymère de s'adapter aux contraintes exercées sur la membrane. Ainsi, une courbure locale engendre la réorganisation à grande échelle des polymères. Par ailleurs, une étude préparatoire montre que la coexistence de la membrane poilue avec des polymères en solution ne modifie pas qualitativement ces résultats. La seconde partie est consacrée à l'étude de macromolécules greffées dans la membrane par plusieures ancres. Ces dernières sont modélisées par des chaînes polymères en bon solvant. Nous établissons le catalogue des différentes conformations qu'une chaîne peut adopter, ainsi que la déformation qui en découle. Nous montrons ainsi que l'effet du polymère sur la membrane domine la courbure spontanée. Le polymère devient alors un paramètre de contrôle maniable de l'état de surface de la membrane.

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Les membranes modèles représentent un outil indispensable pour l'étude des membranes biologiques, elles ont en effet grandement contribué à leur description. Dans ce travail, nous nous sommes intéressés à l'étude de la coexistence de phases liquide-ordonnée (lo) et liquide-désordonnée (ld) au sein de membranes modèles de type LUV (« Large Unilamellar Vesicle »). Nous avons cherché en premier lieu à mettre au point une méthodologie permettant de détecter la formation de la phase lo et d'estimer quantitativement la fraction membranaire Φo en phase lo dans des LUVs de composition ternaire PC/SM/Chol (phosphatidylcholine / sphingomyéline / cholestérol), capable d'induire une coexistence de phase. Pour cela, les propriétés d'auto-extinction de fluorescence et de distribution sélective en fonction de la phase lipidique d'une sonde fluorescente unique (C12NBD-PC) ont été mises à profit. La deuxième partie de notre travail a été consacrée à l'étude de la solubilisation par le détergent Triton X-100 des membranes de LUVs présentant une coexistence de phase lo/ld. Nous avons cherché à démontrer qu'il était possible d'extraire la fraction membranaire se trouvant strictement en phase lo. Pour cela, les transitions de structure induites par l'interaction du Triton X-100 avec des LUVs à 4°C ont été étudiées par une procédure de séparation par gradient de densité. Nous avons tenté d'évaluer le rapport effectif approprié détergent/lipides nous permettant d'isoler les fractions résistantes correspondant aux domaines en phase lo existant au niveau de la membrane des LUVs avant l'addition de détergent.