Browsing by Author "Reis, Luís"
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- O Impacto da crise do petróleo na Força Aérea PortuguesaPublication . Reis, LuísA Força Aérea Portuguesa consome uma elevada quantidade de combustível no cumprimento da sua missão, o que a torna muito dependente do petróleo. A recente crise do petróleo veio levantar sérias preocupações em relação ao futuro do mercado de combustíveis. A incerteza quanto à sustentabilidade do mercado fez com que o valor do petróleo atingisse níveis históricos, e as economias sofreram um sério abalo devido à constante subida dos preços. Para que melhor se compreenda quais as variáveis envolvidas neste fenómeno, o estudo inicia-se com uma breve abordagem da crise do petróleo e das suas causas, seguindo-se uma análise da evolução do mercado do petróleo nas suas várias dimensões: as reservas de petróleo, a oferta, a procura e o preço. Ao abordar o impacto económico da crise do petróleo na Força Aérea, procurou-se não só medir a sua dimensão, mas também explicar a relação existente entre a subida do preço do petróleo e a variação da despesa com combustíveis. A projecção da despesa para o período entre 2009 e 2030, embora tratando-se de uma previsão, permitiu-nos antever as dificuldades que a Força Aérea Portuguesa poderá ter de enfrentar num futuro próximo, face à dependência que tem em relação aos combustíveis fósseis. No intuito de diminuir gradualmente essa dependência, elaborou-se um estudo das energias alternativas que melhor se adequam à realidade da Força Aérea e das possíveis medidas práticas que poderão ser adoptadas de forma a reduzir o consumo de combustível. A Força Aérea Portuguesa tem implementado algumas medidas no sentido de reduzir a despesa com combustíveis, o que revela uma crescente preocupação da Instituição face a esta problemática. Contudo, para que se consiga ir mais além, haverá ainda muito a fazer neste campo. Abstract: The Portuguese Air Force consumes a large amount of fuel to accomplish its mission thus becoming very dependant on oil. The recent oil crisis has brought serious concerns about the future of the fuel market. The uncertainty about the sustainability of the market has made the oil value reach historical levels and the economies have suffered a serious blow due to the constant rising prices. For a better understanding of the variables involved in this phenomenon, this study starts with a brief approach of the oil crisis and its causes, followed by an analysis of the market evolution on its various dimensions: oil reserves, supply, demand and price. By analysing the economic impact of the oil crisis on Air Force, we attempt not only to measure its dimension but also to explain the relation between the oil price rise and the variation of the expense with fuels. The projection of the expense for the period between 2009 and 2030, although its only a prevision, allowed us to foresee the difficulties that the Portuguese Air Force could have to deal with it in the near future due to its dependence on fossil fuels. Aiming to gradually diminish that dependence, we have studied the alternative energies that are best for the reality of the Air Force and the possible practical measures that could be adopted as a way to reduce the fuel consumption. The Portuguese Air Force has implemented some measures towards fuel expense reduction, which reveals a growing concern about this problem. However, there’s still a long way to go.
- Rotary fatigue testing machine to determine the fatigue life of NiTi alloy Wwres and endondontic filesPublication . Carvalho, André; Freitas, Manuel; Reis, Luís; Montalvão, Diogo; Fonte, M.Endodontic rotary file instruments used to treat root canals in dentistry suffered breakthrough transformations in recent years when stainless steel was replaced by Nickel-Titanium (NiTi). NiTi alloys used in Endodontics possess superelastic properties at body temperature (37C) that bring many advantages on the overall performance of the root-canal treatment. They can follow curved root canals more easily than stainless steel instruments and have been reported to be more effective in the removal of the inflamed pulp tissue and protection of the tooth structure. However, these instruments eventually fracture under cyclic bending loading due to fatigue, without any visible signals of degradation to the practitioner. This problem brought new challenges on how new instruments should be tested, as NiTi alloys are highly non-linear and present a large hysteresis cycle in the Elastic domain. Current existing standards are only available for Stainless Steel testing. Thus, many authors have attempted to design systems that can test NiTi endodontic files under fatigue loads. However, no approach has been universally adopted by the community yet, as in most cases they are based on empirical set ups. Following a more systematic approach, this work presents the results of rotary fatigue tests for several NiTi wires from different manufacturers (MemryTM and EuroflexTM). The tests were done on a versatile fully automatic rotary bending testing machine. The formulation is also presented, where the material strength reduction can be quantified from the determination of the strain and the number of cycles until failure.