4 resultados para Growth from solutions
em Universidade do Minho
Resumo:
O sistema de colocação dos professores do ensino secundário em Portugal é um sistema centralizado, gerido pelo governo, mais precisamente pelo Ministério da Educação e Ciência. É um sistema que todos os anos apresenta problemas e, por esse motivo, é alvo de críticas por parte dos seus intervenientes, sobretudo pelos professores. Este artigo pretende identificar esses problemas, para isso efetuou-se uma revisão sistemática e uma meta análise de como é efetuada a colocação de professores em Portugal. Pretendeu-se ainda perceber e descrever como este sistema funciona na União Europeia. Para se encontrar soluções de melhoria para o sistema de colocação de professores efetuaram-se entrevistas a dirigentes escolares. Finalmente, a partir das soluções encontradas em países da União Europeia e das soluções oriundas das opiniões dos dirigentes escolares, são apresentados um conjunto de requisitos que o sistema de colocação de professores deve ter em atenção, de forma a evitar os problemas identificados.
Resumo:
Polymer blends based on poly(vinylidene fluoride), PVDF and poly(ethylene oxide), PEO, with varying compositions have been prepared by solvent casting, the polymer blend films being obtained from solutions in dimethyl formamide at 70ºC. Under these conditions PVDF crystallizes from solution while PEO remains in the molten state. Then, PEO crystallizes from the melt confined by PVDF crystalls during cooling to room temperature. PVDF crystallized from DMF solutions adopt predominantly the electroactive β-phase (85%). Nevertheless when PEO is introduced in the polymer blend the β-phase content decreases slightly to 70%. The piezoelectric coefficient (d33) in pristine PVDF is -5 pC/N and decreases with increasing PEO content in the PVDF/PEO blends. Blend morphology, observed by electron and atomic force microscopy, shows the confinement of PEO between the already formed PVDF crystals. On the other hand the sample contraction when PEO is extracted from the blend with water (which is not a solvent for PVDF) allows proving the co-continuity of both phases in the blend. PEO crystallization kinetics have been characterized by DSC both in isothermal and cooling scans experiments showing important differences in crystalline fraction and crystallization rate with sample composition.
Resumo:
Dissertação de mestrado em Comunicação, Arte e Cultura
Resumo:
The Portuguese housing sector experienced a significant growth throughout the 20th century, particularly in the last quarter, after the democratic revolution in 1974. In fact, the number of buildings built between 1970 and 1990 is more than one third of the buildings actually existing in Portugal. Therefore most of them were built before the publication of the first regulation concerning the energy efficiency in buildings. Regarding this scenario, it would be expected that rehabilitation activities would represent most of the current construction activities. However, given some remaining barriers from old social policies, this situation is not observed; actually building retrofitting is the least significant sector, accentuating the degradation level of major part of the Portuguese housing stock. Several studies show that the main problems are found in the buildings envelope elements, such as roofs and façades. Based on this context, the aim of this paper is to introduce some examples of building retrofitting systems that, adapted to the Portuguese main needs and requirements may represent sustainable solutions to overcome the identified needs of Portuguese buildings' envelope.