Injection moulding process optimization for microstructured parts production

Ao longo das ��ltimas d��cadas, a micromolda����o (u-molda����o) por inje����o de termopl��sticos ganhou um lugar de destaque no mercado de equipamentos eletr��nicos e de uma ampla gama de componentes mec��nicos. No entanto, quando o tamanho do componente diminui, os pressupostos geralmente aceites na molda����o por inje����o convencional deixam de ser v��lidos para descrever o comportamento reol��gico e termomec��nico do pol��mero na microimpress��o. Por isso, a compreens��o do comportamento din��mico do pol��mero �� escala micro bem como da sua carateriza����o, an��lise e previs��o das propriedades mec��nicas exige uma investiga����o mais alargada. O objetivo principal deste programa doutoral passa por uma melhor compreens��o do fen��meno f��sico intr��nseco ao processo da ��-molda����o por inje����o. Para cumprir com o objetivo estabelecido, foi efetuado um estudo param��trico do processo de ��-molda����o por inje����o, cujos resultados foram comparados com os resultados obtidos por simula����o num��rica. A caracteriza����o din��mica mec��nica das ��-pe��as foi efetuada com o objetivo de recolher os dados necess��rios para a previs��o do desempenho mec��nico das mesmas, a longo prazo. Finalmente, depois da calibra����o do modelo matem��tico do pol��mero, foram realizadas an��lises estruturais com o intuito de prever o desempenho mec��nico das ��-pe��as no longo prazo. Verificou-se que o desempenho mec��nico das ��-pe��as pode ser significativamente afetado pelas tens��es residuais de origem mec��nica e t��rmica. Estas ��ltimas, resultantes do processo de fabrico e das condi����es de processamento, por isso, devem ser consideradas na previs��o do desempenho mec��nico e do tempo de servi��o das u-molda����es.

Cooperative positioning for heterogeneous wireless systems

Future emerging market trends head towards positioning based services placing a new perspective on the way we obtain and exploit positioning information. On one hand, innovations in information technology and wireless communication systems enabled the development of numerous location based applications such as vehicle navigation and tracking, sensor networks applications, home automation, asset management, security and context aware location services. On the other hand, wireless networks themselves may bene t from localization information to improve the performances of di erent network layers. Location based routing, synchronization, interference cancellation are prime examples of applications where location information can be useful. Typical positioning solutions rely on measurements and exploitation of distance dependent signal metrics, such as the received signal strength, time of arrival or angle of arrival. They are cheaper and easier to implement than the dedicated positioning systems based on ngerprinting, but at the cost of accuracy. Therefore intelligent localization algorithms and signal processing techniques have to be applied to mitigate the lack of accuracy in distance estimates. Cooperation between nodes is used in cases where conventional positioning techniques do not perform well due to lack of existing infrastructure, or obstructed indoor environment. The objective is to concentrate on hybrid architecture where some nodes have points of attachment to an infrastructure, and simultaneously are interconnected via short-range ad hoc links. The availability of more capable handsets enables more innovative scenarios that take advantage of multiple radio access networks as well as peer-to-peer links for positioning. Link selection is used to optimize the tradeo between the power consumption of participating nodes and the quality of target localization. The Geometric Dilution of Precision and the Cramer-Rao Lower Bound can be used as criteria for choosing the appropriate set of anchor nodes and corresponding measurements before attempting location estimation itself. This work analyzes the existing solutions for node selection in order to improve localization performance, and proposes a novel method based on utility functions. The proposed method is then extended to mobile and heterogeneous environments. Simulations have been carried out, as well as evaluation with real measurement data. In addition, some speci c cases have been considered, such as localization in ill-conditioned scenarios and the use of negative information. The proposed approaches have shown to enhance estimation accuracy, whilst signi cantly reducing complexity, power consumption and signalling overhead.

An overview of chemosynthetic symbioses in bivalves from the North Atlantic and Mediterranean Sea

Deep-sea bivalves found at hydrothermal vents, cold seeps and organic falls are sustained by chemosynthetic bacteria that ensure part or all of their carbon nutrition. These symbioses are of prime importance for the functioning of the ecosystems. Similar symbioses occur in other bivalve species living in shallow and coastal reduced habitats worldwide. In recent years, several deep-sea species have been investigated from continental margins around Europe, West Africa, eastern Americas, the Gulf of Mexico, and from hydrothermal vents on the Mid-Atlantic Ridge. In parallel, numerous, more easily accessible shallow marine species have been studied. Herein we provide a summary of the current knowledge available on chemosymbiotic bivalves in the area ranging west-to-east from the Gulf of Mexico to the Sea of Marmara, and north-to-south from the Arctic to the Gulf of Guinea. Characteristics of symbioses in 53 species from the area are summarized for each of the five bivalve families documented to harbor chemosynthetic symbionts (Mytilidae, Vesicomyidae, Solemyidae, Thyasiridae and Lucinidae). Comparisons are made between the families, with special emphasis on ecology, life cycle, and connectivity. Chemosynthetic symbioses are a major adaptation to ecosystems and habitats exposed to reducing conditions. However, relatively little is known regarding their diversity and functioning, apart from a few ���model species��� on which effort has focused over the last 30 yr. In the context of increasing concern about biodiversity and ecosystems, and increasing anthropogenic pressure on oceans, we advocate a better assessment of the diversity of bivalve symbioses in order to evaluate the capacities of these remarkable ecological and evolutionary units to withstand environmental change.