A power management strategy for a stand-alone photovoltaic/fuel cell energy system for a 1kW application

In this paper a power management strategy is presented for a stand-alone photovoltaic (PV)/fuel cell (FC) energy system. PV is the primary power source of the system and an FC-electrolyzer combination is used as a backup and a long-term storage system. The energy in the hybrid system is balanced by the common dc bus voltage regulation. A simple hysteresis voltage control is used for dc bus voltage regulation. In this way, the fuel cell and the electrolyzer can be protected from unnecessary utilization or irregular operation (reduction of frequent start-ups and shutdowns). Simulation results obtained using Matlab and Simulink are presented to verify the effectiveness of the proposed control algorithm

Performance of a solar-hydrogen stand-alone system for residential applications

Hydrogen, as an energy storage medium, is considered a promising solution to overcome the limitation of intermittent renewable energy sources. In this paper, a residential scale solar-hydrogen based stand-alone energy system is designed, modelled and the simulated system performance under real end-use load, representative of standard European domestic electrical energy consumption, and meteorological conditions is analyzed. The sun is the primary energy source of the system and a fuel cell-electrolyzer combination is used as a backup and a long-term storage system. A battery bank is also used as energy buffer and for short time storage. Matlab/Simulink® is used for the overall system modelling and simulation. The results show that the designed solar-hydrogen system is in principle capable of operating autonomously and in a sustainable manner. The designed system is able to convert 7.6% of the total energy irradiated in one year

Experimental investigation of quantum key distribution with position and momentum of photon pairs

We investigate the utility of Einstein-Podolsky-Rosen correlations of the position and momentum of photon pairs from parametric down-conversion in the implementation of a secure quantum key distribution protocol. We show that security is guaranteed by the entanglement between downconverted pairs, and can be checked by either direct comparison of Alice and Bob's measurement results or evaluation of an inequality of the sort proposed by Mancini et al. (Phys. Rev. Lett. 88, 120401 (2002)).Comment: 6 pages, 6 figures, subimitted for publicatio

Pulsed DC reactive magnetron sputtering of vanadium dioxide thermochromic thin films

Vanadium oxides are an important class of materials with a large diversity of physical and chemical properties which derive from a range of single or mixed valences and a large variety of structures. They are already being used in many technological applications such as electrical and optical switching devices, light detectors, temperature sensors, etc. There has been a great interest in a particular phase, VO2(M), due to its thermochromic behaviour near room temperature which allows the development of smart windows with active control of the solar spectrum, for energy efficiency purposes. However, stoichiometric VO2 is difficult to deposit because of a narrow stability range due to the complex vanadium–oxygen reactive system. In this work, vanadium oxide thin films were synthesised on glass substrates by reactive pulsed direct current magnetron sputtering from a vanadium metal target in an O2/Ar atmosphere. Different processing conditions have been chosen in order to evaluate their influence on the crystal phases formed, surface morphologies and thicknesses and optical performance. The films were characterised by X-ray diffractometry in order to examine the crystal structure and identify the phases present in different films. The obtained VO2(M) films were thereafter analysed in terms of surface morphology by scanning electron microscopy and the characteristic reversible semiconductor-metal transition of the VO2 films was evaluate by optical spectrophotometry in the ultraviolet-visible-near infrared.Fundação para a Ciência e a Tecnologia (FCT) SFRH/BD/40512/2007

Avaliação de um plano de formação : o trabalho de campo no ensino da Geologia

Apresentam-se os resultados de uma avaliação de um plano de formação relativo ao trabalho de campo no ensino da geologia aplicado a seis professores de duas escolas secundárias de Vila do Conde, distrito do Porto, no Noroeste de Portugal. O estudo apresentado permite verificar o impacto positivo do plano de formação através da análise de snapshots (pequenos questionários) preenchidos pelos formandos e pelo formador no final de cada uma das cinco sessões que integraram a formação

Irrigação do cajueiro-anão-precoce na região de Teresina.

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On the dynamics of bubbles in boiling water

We investigate the dynamics of many interacting bubbles in boiling water by using a laser scattering experiment. Specifically, we analyze the temporal variations of a laser intensity signal which passed through a sample of boiling water. Our empirical results indicate that the return interval distribution of the laser signal does not follow an exponential distribution; contrariwise, a heavy-tailed distribution has been found. Additionally, we compare the experimental results with those obtained from a minimalist phenomenological model, finding a good agreement.Comment: Accepted for publication in Chaos, Solitons & Fractal