Helium and neon isotopes in São Miguel island basalts, Azores Archipelago: New constraints on the “low 3He” hotspot origin

Lavas from the São Miguel Island, Azores Archipelago, have peculiar isotopic compositions, including radiogenic lead and strontium and un-radiogenic neodymium. The peculiar isotopic trend of São Miguel is evident in the lead-lead diagram where both 207Pb/204Pb and 208Pb/204Pb ratios are high for a given 206Pb/204Pb ratio compared to other oceanic island basalts. This signature is unique among OIBs and is particularly evident in the Nordeste area, the oldest part of São Miguel island (≥1 Ma). Only a few olivine samples from the Nordeste volcanic complex have been analyzed for helium. They show radiogenic helium signatures with 4He/3He up to 174,000 (R/Ra ~4) [Moreira et al., Helium and lead isotope geochemistry in the Azores archipelago, Earth Planet. Sci. Lett. 169: 189–205, 1999]. However, because the Nordeste volcano has an age between 1 and 4 Ma and because these samples have low helium concentrations, these radiogenic helium isotopic ratios must be considered with caution as they can also reflect post eruptive radiogenic production. In this paper we present a detailed study of the helium and neon isotopic ratios obtained from 17 Nordeste samples in order to better constrain the helium isotopic signature of the São Miguel mantle source. By coupling helium and the other isotopic systems, we propose that the São Miguel source contains non-degassed material, enriched in U and Th, that was stored in the mantle for the last ~3 Ga. As suggested by Elliot et al. [Elliott et al., The origin of enriched mantle beneath São Miguel, Azores, Geochim. Cosmochim. Acta 71: 219–240, 2007], underplated magma intruded into oceanic lithosphere and subducted ~3 Ga ago is a possible explanation for the peculiar São Miguel source isotopic signatures

Civic Education in Basic School: Problems and Challenges in the Digital Age

This paper focus on the analysis of preliminary data of an ongoing study involving Portuguese teachers and students, in the non-disciplinary curricular area of Civic Education. The project aims at encouraging collaborative behaviour in educational communities, involving teachers and students in the development of digital contents, and at exploring different issues on citizenship education, under a case-based methodology. We believe this action research study is of relevance because it can unveil examples of good practices and innovative teaching strategies that need to be disseminated in this compulsory subject taking into account the results of recent studies, which exposed some of the inefficiency of the strategies adopted so far

Local minimizers in spaces of symmetric functions and applications

We study $H^1$ versus $C^1$ local minimizers for functionals defined on spaces of symmetric functions, namely functions that are invariant by the action of some subgroups of $\mathcal{O}(N)$. These functionals, in many cases, are associated with some elliptic partial differential equations that may have supercritical growth. So we also prove some results on classical regularity for symmetric weak solutions for a general class of semilinear elliptic equations with possibly supercritical growth. We then apply these results to prove the existence of a large number of classical positive symmetric solutions to some concave-convex elliptic equations of H\'enon type

Sapo Campus: what users really think about an institutionally supported PLE

Resumo não disponível..

Contribuição dos revestimentos poliméricos para a durabilidade de betões em ambientes agressivos

Dissertação de Mestrado em Engenharia Civil - Área de Materiais e Reabilitação da ConstruçãoActualmente é consensual que a principal degradação do betão deve-se a acções que ocorrem do exterior para o interior, devido à penetração de humidade, gases activos e iões agressivos, por métodos mecânicos, físicos e químicos, que frequentemente ocorrem juntos. Uma baixa porosidade, permeabilidade e penetração no betão de humidade e gases, são a primeira linha de defesa contra vários mecanismos de deterioração. A durabilidade do betão depende em grande medida da facilidade com que os fluidos (água, dióxido de carbono, oxigénio) na forma líquida ou gasosa, conseguem migrar através do betão. Um dos possíveis métodos de proteger o betão consiste na utilização de revestimentos por pintura, que funcionam como uma barreira entre o ambiente e o betão. Na selecção dos revestimentos por pintura deve ser dada a máxima importância às propriedades de difusão, permeabilidade, durabilidade e resistência química. Os revestimentos por pintura devem ser capazes de impedir a penetração da água e atrasar a influência de agentes agressivos (CO 2 , SO 2 , Cl − ), permitindo que a estrutura “respire” através de um mecanismo de difusão de vapor de água. Uma avaliação das propriedades de transporte da camada superficial deverá fornecer informação quanto à durabilidade de determinado betão. Virtualmente, todos os revestimentos são suficientemente permeáveis à água para serem pouco eficazes no controlo da corrosão mas não da permeabilidade iónica que é mais baixa. O presente trabalho de investigação pretende contribuir para uma melhor compreensão do desempenho do betão revestido em ambientes agressivos, apresentando resultados de capilaridade, permeabilidade, porosidade, difusão iónica, resistividade eléctrica e resistência a soluções agressivas de vários revestimentos por pintura utilizados para proteger o betão. Assim, foi feita a avaliação de nove ensaios diferentes, utilizados para medir parâmetros de durabilidade do betão revestido. Foram utilizados provetes pintados e não pintados, três tipos de resinas poliméricas (silicone, acrílica e epoxídica) e três tipos de composições de betões. Os resultados obtidos mostraram que os revestimentos contribuem para o aumento da durabilidade do betão, em particular os revestimentos epoxídicos que mostraram o melhor desempenho. Os vernizes de silicone tiveram alguns resultados surpreendentes mostrando ser um produto com uma excelente relação qualidade/preço.It is common knowledge that the highest concrete degradation occurs due to external influences, with effects in the bulk material. Mechanical, physical and chemical component mechanisms that frequently act together origins the penetration of moisture, active gases and aggressive ions inside the concrete. A low porosity, permeability and concrete penetration to moisture and gases are the first protective measures to be taken against several deterioration mechanisms. The concrete durability depends largely on how easy fluids in liquid or gas form, particularly water, carbon dioxide, and oxygen, migrate through the material. One of the possible methods to protect the concrete is by using paint coatings that act as a barrier between the environment and the bulk material. When selecting the paint coating for concrete protection, importance should be given to the critical properties of diffusion, permeability, durability and chemical resistance. The paint coatings should be able to stop the penetration of water and delay the influence of aggressive agents (CO 2 , SO 2 , Cl − ions), allowing the structure to “breathe” trough a water vapour diffusion mechanism. An evaluation of the surface layer transport properties should give some information on the durability of a particular concrete. Virtually all coatings are permeable to water, enough to be little effective controlling the corrosion but not the ionic permeability, which is much lower. The present work intends to contribute to a better understanding of the performance of coated concrete in aggressive environments. For this, results are presented for the capillarity, permeability, porosity, ion diffusion, electrical resistivity and resistance to aggressive solutions of several coatings used to protect concrete. The evaluation of nine different trials used to determine coated concrete durability parameters, was performed. Painted and unpainted specimens, three different types of resins (silicone, acrylic and epoxy) and three different concrete compositions were used. The results obtained showed that, in general, all coatings used contribute to the increasing of the concrete durability, in particular the epoxy resins which had the best performance. The silicone varnishes showed surprising results by presenting high quality/price rates