Rainwater harvesting case study: FCT/UNL campus

Dissertação apresentada para a obtenção do grau de Mestre em Engenharia do Ambiente, Perfil Engenharia SanitáriaWith increasing pressure on the environment, particularly on water resources, due to outside forces such as climate change and population growth, water is nowadays a scarce and a valuable resource. With the need to find new alternatives, rainwater harvesting should be seen as an important strategy for better management of water resources, once it constitutes a free source of potable water. Rainwater harvesting systems, which already have a global implementation, are a recognised way for urban buildings to reduce their reliance on the public mains supply. Its applications are predominantly non-potable, namely toilet flushing and gardening. The aim of this report is to produce a comprehensive assessment of rainwater harvesting and its potential use all over the world, as well as the potential economical and environmental benefits. It is provided a description of all the rainwater harvesting system components, as well as water quality requirements according to the water final purpose. A case study is presented, which main object is to evaluate the feasibility of rainwater harvesting for gardening, applied to the University Campus of the Faculty of Sciences and Technology of Universidade Nova, Lisbon (FCT/UNL). A detailed characterization of the existing irrigation system on campus is provided, as well as its potential ability to collect rainwater. According to the supply and demand balance, several scenarios are presented in order to provide the necessary information for the decision-makers to evaluate the best solution for the desired application. For such, all the available information was analyzed, in order to determine the environmental, technical and economical viability of the project

A DEMONOLOGIA DISJUNTIVA DE GARCÍA LORCA

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All-fibre wavelength versatile short pulsed laser sources

Pulsed lasers operating in the picosecond or femtosecond regimes find a wide range of applications in optical sciences, such as spectroscopy, laser surgery, material processing and optical communications. Among the existing sources of short-pulses, mode-locked fibre lasers play an important role mainly due to their robust and compact nature, and also due to their ability to generate outputs over a wide range of repetition-rates, pulse durations, pulse shapes, peak powers and optical wavelengths. Considering the case of wavelength versatility, Raman amplification can be used to fill the spectral gaps that are not covered by the emission band of traditional rare-earth doped elements such as ytterbium and erbium, allowing the generation of light at unconventional wavelengths. Additionally, another contribution has come from the recent development of new nanomaterials such as graphene and carbon nanotubes that can be used as saturable absorbers over a broadband wavelength range. The experimental work reported in this thesis is mainly focused in combining the wavelength versatility allowed by Raman gain and carbon nanotubes and graphene to generate short-pulsed fibre lasers at different wavelengths. High power ytterbium and erbium lasers and also a high power Raman laser operating at 1450 nm are used as pump sources to seed the Raman gain and carbon nanotubes and graphene are the saturable absorbers used as mode-lockers. All the fibres utilized in the oscillators are highly non-linear single mode silica fibres doped with GeO2. The lasers operate in the dissipative soliton regime, generating chirped pulses with durations on the order of hundred of picosecond that are suitable for external compression. We demonstrate for example an erbium-pumped Raman oscillator generating 500 ps pulses that are linearly compressed to 2 ps. The results presented in this document are a contribution towards making fibre based lasers more universal devices in terms of wavelength operation.Open Acces

On Sterile neutrino explanation of LSND and MiniBooNE anomalies

We examine the compatibility between existing experimental data and a recently proposed explanation of the LSND and MiniBooNE anomalies, given in terms of a sterile neutrino $N$ whose decay is dominated by a radiative mode. We find that current experimental data on $\tau\rightarrow \mu\nu\nu\gamma$ decays are compatible with the sterile neutrino parameters required for the explanation of the anomalies, but $K\rightarrow \mu\nu\gamma$ shows a marginal tension with those parameters. We also propose experimental cuts on radiative $K$ decays that could test the sterile neutrino hypothesis better. Finally, we study the contribution of this sterile neutrino to $K\to\mu\nu e e$, and find that measurements of this process would provide powerful tests for the sterile neutrino explanation of the LSND and MiniBooNE anomalies, if the experimental cut on the invariant mass of the $e^{+}e^{-}$ pair could be reduced from its current value of 145 MeV to a value below 40 MeV.Comment: 6 pages, 2 figures, experimental cut taken into account, some conclusions change

Spin injection across magnetic/non-magnetic interfaces with finite magnetic layers

We have reconsidered the problem of spin injection across ferromagnet/non-magnetic-semiconductor (FM/NMS) and dilute-magnetic-semiconductor/non-magnetic-semiconductor interfaces, for structures with \textit{finite} magnetic layers (FM or DMS). By using appropriate physical boundary conditions, we find expressions for the resistances of these structures which are in general different from previous results in the literature. When the magnetoresistance of the contacts is negligible, we find that the spin-accumulation effect alone cannot account for the $d$ dependence observed in recent magnetoresistance data. In a limited parameter range, our formulas predict a strong $d$ dependence arising from the magnetic contacts in systems where their magnetoresistances are sizable.Comment: 6 pages, 3 eps figs. (extended version- new title + two new figures added