The Montado agroforestry system microclimatic specificity in the context of global change

The effects of oak trees on microclimatic parameters in Quercus rotundifolia Lam. woodland in the Alentejo, Southern Portugal, are reported. Results show that oak tree create a marked differentiation in the grass matrix, between open and undercanopy areas. Compared to open areas, it presents lower soil moisture beneath the oak canopy, lower soil temperatures and lower photosynthetically active radiation (PAR). Soil temperatures outside trees canopy were generally higher than undercanopy areas, reaching twice its values during the winter. The decrease of soil water content is more rapid in areas outside the trees canopy action, but the replenishment starts early and is faster in those areas. PAR intercepted by tree canopy is greater than 60%, and affects dramatically herbaceous production. Different climatic conditions due to the presence of the tree, associated with greater variability in chemistry environment undercanopy, if combined with the IPCC forecasts for Mediterranean region, pose new challenges in the management of the montado areas

Caracterização energética e segurança na utilização de recuperadores de calor para lareiras

Os recuperadores de calor para lareiras são dispositivos de aquecimento doméstico cuja utilização está em expansão. A sua correcta utilização, quer no que respeita à segurança quer ao desempenho energético requer a caracterização destes equipamentos. Desta necessidade nasceu o projecto RECUPERA realizado em parceria entre a EST–ADEM da Universidade do Algarve e a empresa Vale–Montanha L.da., fabricante destes equipamentos. Foram realizados ensaios segundo a norma europeia em vigor EN 13299:2001 dos quais se obteve a distribuição de temperaturas nos recuperadores e envolvente, potência média, carga de lenha recomendada, emissões de CO e rendimento térmico. O presente artigo tem por objectivo apresentar os resultados obtidos nos ensaios, descrevendo a metodologia seguida e comparando os custos de operação entre vários equipamentos de aquecimento doméstico alternativos

Insights into tunnel FET-based charge pumps and rectifiers for energy harvesting applications

In this paper, the electrical characteristics of tunnel field-effect transistor (TFET) devices are explored for energy harvesting front-end circuits with ultralow power consumption. Compared with conventional thermionic technologies, the improved electrical characteristics of TFET devices are expected to increase the power conversion efficiency of front-end charge pumps and rectifiers powered at sub-µW power levels. However, under reverse bias conditions the TFET device presents particular electrical characteristics due to its different carrier injection mechanism. In this paper, it is shown that reverse losses in TFET-based circuits can be attenuated by changing the gate-to-source voltage of reverse-biased TFETs. Therefore, in order to take full advantage of the TFETs in front-end energy harvesting circuits, different circuit approaches are required. In this paper, we propose and discuss different topologies for TFET-based charge pumps and rectifiers for energy harvesting applications.Peer ReviewedPostprint (author's final draft

A battery-less, self-sustaining RF energy harvesting circuit with TFETs for µW power applications

This paper proposes a Tunnel FET (TFET) power management circuit for RF energy harvesting applications. In contrast with conventional MOSFET technologies, the improved electrical characteristics of TFETs promise a better behavior in the process of rectification and conversion at ultra-low power (µW) and voltage (sub-0.25 V) levels. RF powered systems can not only benefit from TFETs in front-end rectifiers by harvesting the surrounding energy at levels where conventional technologies cannot operate but also in the minimization of energy required by the power management circuit. In this work we present an energy harvesting circuit for RF sources designed with TFETs. The TFET controller emulates an adequate impedance at the output of the rectifier in order to allow maximum transfer of power from the RF source to the input of the boost converter. The output load is activated once the output capacitor reaches a voltage value of 0.5 V. The results show an efficiency boost of 89 % for an output load consuming 1 µW with an available RF power of -25 dBm.Postprint (published version

Nine years of project‐based learning in engineering

Este foi um número monográfico dedicado à Aprendizagem Baseada em ProjetosThe engineering programmes offered at the Higher Education Polytechnic School of Águeda, University of Aveiro, have been organised, since 2001, around the Project Based Learning paradigm. This paper will briefly set the scene for the educational development and will then proceed to describe the curricula implementation that is nowadays on the field, reflecting the accumulated nine-years’ experience of running the programmes. Finally, the author will offer his personal perspective on the difficulties of the development and its implementation, as an actor engaged in the process.Los programas de ingeniería impartidos en la Escuela Politécnica Superior de Educación de Águeda, Universidad de Aveiro, se han venido organizando desde 2001 bajo el paradigma de Aprendizaje Basado en Proyectos. Este breve artículo se propone mostrar el marco del desarrollo educativo y proceder a continuación a describir la implementación actual de los planes de estudio en este campo, de acuerdo con la experiencia acumulada durante nueve años de funcionamiento. Por último, el autor ofrece su personal visión sobre las dificultades del proceso de desarrollo e implementación, en su calidad de actor comprometido con el proceso

Temas clássicos na Internet: voo de Dédalo ou queda de Ícaro?

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Projecto de execução de uma passagem inferior de três vãos em betão armado e pré-esforçado

O presente trabalho foi realizado no âmbito do Trabalho Final de Mestrado em Engenharia Civil do Instituto Superior de Engenharia de Lisboa. O trabalho consistiu em realizar um Projecto de Execução de uma Passagem Inferior de três Vãos em Betão Armado e Pré- Esforçado. O trabalho divide-se em: PEÇAS ESCRITAS - Memória Descritiva e Justificativa, Cálculos Justificativos, Anexos de Cálculo e PEÇAS DESENHADAS. Os regulamentos utilizados foram o Regulamento de Segurança e Acções para Edifícios e Pontes (RSA) e o Regulamento de Betão Armado e Pré-Esforçado (REBAP). Para a análise estrutural foi utilizado o programa SAP2000

A China na obra de D. Jerónimo Osório

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