Cristalização de Biomateriais Vitrocerâmicos e Mineralização em Meio Fisiológico Simulado

We propose new theoretical models, which generalize the classical Avrami-Nakamura models. These models are suitable to describe the kinetics of nucleation and growth in transient regime, and/or with overlapping of nucleation and growth. Simulations and predictions were performed for lithium disilicate based on data reported in the literature. One re-examined the limitations of the models currently used to interpret DTA or DSC results, and to extract the relevant kinetic parameters. Glasses and glass-ceramics with molar formulation 0.45SiO2? (0.45-x)MgO?xK2O?0.1(3CaO.P2O5) (0?x?0.090) were prepared, crystallized and studied as potential materials for biomedical applications. Substitution of K+ for Mg2+ were used to prevent devritification on cooling, to adjust the kinetics of crystallization and to modify the in vitro behaviour of resulting biomaterials. The crystallization of the glass frits was studied by DTA, XRD and SEM. Exothermic peaks were detected corresponding to bulk crystallization of whitlockite-type phosphate, Ca9MgK(PO4)7, at approximately 900ºC, and surface crystallization of a predominant forsterite phase (Mg2SiO4) at higher temperatures. XRD also revealed the presence of diopside (CaMgSi2O6 in some samples. The predominant microstructure of the phosphate phase is of the plate-type, seemingly crystallizing by a 2-dimensional growth mechanism. Impedance spectroscopy revealed significant changes in electrical behaviour, associated to crystallization of the phosphate phase. This showed that electrical measurements can be used to study the kinetics of crystallization for cases when DTA or DSC experiments reveal limitations, and to extract estimates of relevant parameters from the dependence of crystallization peak temperature, and its width at half height. In vitro studies of glasses and glass-ceramics in acelular SBF media showed bioactivity and the development of apatite layers The morphology, composition and adhesion of the apatite layer could be changed by substitution of Mg2+ by K+. Apatite layers were deposited on the surface of glass-ceramics of the nominal compositions with x=0 and 0.09, in contact with SBF at 37ºC. The adhesion of the apatite layer was quantified by the scratch test technique, having been related with SBF?s immersion time, with composition and structure of the glass phase, and with the morphology of the crystalline phase of the glass-ceramics. The structure of three glasses (x=0, 0.045 and 0.090) were investigated by MAS-NMR ( 29Si and 31P), showing that the fraction of Q3 structural units increases with the contents of Mg, and that the structure of these glasses includes orthophosphate groups (PO43-) preferentially connected to Ca2+ ions. Mg2+ ions show preference towards the silicate network. Substitution of Mg2+ by K+ allowed one to change the bioactivity. FTIR data revealed octacalcium phosphate precipitation (Ca8H2(PO4)6.5H2O) in the glass without K, while the morphology of the layer acquires the shape of partially superimposed hemispheres, spread over the surface. The glasses with K present a layer of acicular hidroxyapatite, whose crystallinity and needles thickness tend to increase along with K content.

Incentivos governamentais em PPP: uma análise por opções reais

Em novembro de 2005, o Governo do Estado lançou edital de licitação para serviços de transporte de passageiros da Linha 4 do Metrô de São Paulo. Neste trabalho, utilizamos a metodologia de opções reais para modelar o impacto dos incentivos governamentais existentes no contrato de concessão sobre o valor do projeto, determinar o grau de redução de risco obtido e o seu custo para o Estado. Os resultados indicam que estes incentivos são eficazes em reduzir o risco do projeto e aumentam o seu resultado em 36%, a um custo para o Estado de 5% do valor total do projeto. Adicionalmente, analisamos também a relação custo/benefício para o Estado de modelos alternativos de mitigação de risco e mostramos que, sem aumentar o custo para o Governo, a eficácia desse mecanismo pode ser incrementada aumentando-se o peso da parcela de garantia de demanda em relação à parcela de contraprestação.

As formas de participação na construção do projecto político pedagógico : diferentes realidades escolares

RESUMO: Na sociedade da comunicação e da informação, as escolas ainda não conseguiram compreender o seu papel de facilitadoras do conhecimento que o mundo está promovendo entre a realidade da escola e o interesse do educando. Um dos fatores para isso é o crescimento das escolas ao longo dos séculos e a necessidade de superação decorrente do alargamento da educação, que têm gerado um conhecimento complexo que descreve as reflexões e conscientizações sobre o nosso próprio desenvolvimento humano e sobre a nossa participação no mundo em que estamos vivendo. Essas complexidades possibilitam mudanças, principalmente nas questões epistemológicas e paradigmáticas, que proporcionaram outra forma de conceber o conhecimento e os saberes, chamado de “ecologia dos saberes”. Nesse contexto, existe a necessidade de se fazer uma leitura crítica na e da escola e de sua participação junto à comunidade escolar, objetivando minimizar as relações de dominação, de normatizações, de disciplinamento, de concentração de poder, para direcionar a educação num processo emancipatório, democrático, consciente das mudanças, de forma a incluir todos os saberes possíveis para acompanhar e valorizar a realidade escolar, através da participação de alta intensidade na construção e reconstrução do seu projeto político pedagógico. Para tanto, iremos discorrer sobre três escolas, a partir da análise de cada uma dentro da realidade construída por elas, buscando demonstrar que as escolas, dentro dos seus contextos educacionais, possuem diferentes realidades que não podem ser generalizadas, mas que devem ser compreendidas no sentido de que sejam promovidas a autonomia escolar e o fortalecimento da democracia educacional, objetivando a superação das condições atuais da educação para se adequar à sociedade e ao mundo atual. ABSTRACT: In the present society of communication and information, schools have not yet been able to understand their roles as facilitators of the knowledge that the world is promoting between the reality of school and the interest of the learner. One of the reasons for that is the growth of schools along the centuries as well as their constant need for getting over old problems, due to the expansion of education. These questions lead to a complex knowledge which describes reflections on our own human development and on our participation in the world we live in. These complexities lead to changes, especially in epistemological and paradigmatic questions, making it possible for new ways of conceiving knowledge, known as “ecology of knowledge”. In this context, there is a need for making a critical reading about school and its participation in the school community, with the objective to minimize the relations of domination, power concentration and discipline and to direct education towards a process of emancipation and democracy, in which there is conscience of the necessary changes to include all possible knowledge as a way to value the reality of school through a high intensity participation in the construction and reconstruction of its political and pedagogical project. Thus, this study will discuss three schools, basing this discussion on the analysis of each school within the reality built by them, trying to demonstrate that, within their educational contexts, each one possesses different realities that cannot be generalized. These differences must, however, be understood, in order to allow the promotion of school autonomy and the strengthening of educational democracy with the objective to get over education`s present conditions and adjust them to society and to the present world.