http://repositorio.lneg.pt:80 The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material. 2012-02-05T11:55:45Z http://hdl.handle.net/10400.9/434 Title: Utilização de isótopos de azoto na avaliação e caracterização do impacte da agricultura na qualidade da água subterrânea : resultados preliminares do Sistema Aquífero dos Gabros de Beja Authors: Paralta, Eduardo; Fernandes, Rosa M.; Carreira, Paula M.; Ribeiro, Luís F. Abstract: Apresentam-se os resultados preliminares da utilização de isótopos de azoto na avaliação e caracterização do impacte da agricultura na qualidade da água subterrânea no âmbito das preocupações com a extensão da contaminação difusa no Sistema Aquífero dos Gabros de Beja e recente publicação da Zona Vulnerável de Beja (Portaria 1100/2004 de 3 Setembro). Os trabalhos de investigação são financiados pela Fundação para a Ciência e Tecnologia (POCTI/AGG/47223/2002) e decorrem na região de Beja (2004-2007). Os isótopos estáveis de azoto (ratio 15N/14N) podem ser usados na identificação das origens da contaminação difusa das águas subterrâneas, dado que nas áreas agrícolas as duas principais causas de nitrato na água subterrânea são a fertilização e a pecuária, que apresentam diferente assinatura isotópica de d15N. A contribuição relativa das duas principais origens de poluição das águas subterrâneas e superficiais podem ser medidas por balanço de massa. A análise conjunta dos isótopos d18O e d15N do ião nitrato constitui um processo válido na identificação das fontes da poluição. Os resultados preliminares obtidos não são conclusivos relativamente à origem agrícola do N-NO3 na água subterrânea. Será necessário realizar trabalhos adicionais em situação de ano hidrológico normal. Pretende-se com o projecto adquirir conhecimentos científicos inovadores no sentido de apoiar as decisões políticas relacionadas com o desenvolvimento sustentável e a preservação dos recursos hídricos em regiões afectadas por contaminação agrícola difusa e contribuir para a aplicação da legislação nacional e directivas comunitárias no domínio das Zonas Vulneráveis e da Directiva Quadro da Água. 2006-01-01T00:00:00Z http://hdl.handle.net/10400.9/1435 Title: Symbolic computation and the Rayleigh-Bénard stability problem Authors: Giestas, Margarida Canedo; Pina, H.L. Abstract: This paper analyzes the linear stability of an horizontal layer of fluid consisting of a mixture of water and salt. The layer is hotter at the bottom and cooler at the top thus having a tendency to destabilize. To counteract this a salt concentration gradient (denser at the bottom and lighter at the top) is sometimes present, either naturally as in the ocean or created artificially as in solar ponds. The relevant governing equations are the linearized continuum mechanics balance laws applied to an incompressible, heat-conducting and salt-diffusing fluid, leading to a system of partial differential equations, from which the stability of a given base state has to be assessed with respect to arbitrary initial perturbations. This problem involves intensive symbolic computations that can be much facilitated by the use of a Computer Algebra System (CAS). 2012-01-01T00:00:00Z http://hdl.handle.net/10400.9/1434 Title: Modelling of the IPS buoy wave energy converter including the effect of non-uniform tube cross-section Authors: Falcão, António F. de O.; Cândido, José J.; Justino, Paulo Alexandre; Henriques, João C. C. Abstract: An important class of floating wave energy converters (that includes the IPS buoy, the Wavebob and the PowerBuoy) comprehends devices in which the energy is converted from the relative (essentially heaving) motion between two bodies oscillating differently. The paper considers the case of the IPS buoy, consisting of a floater rigidly connected to a fully submerged vertical (acceleration) tube open at both ends. The tube contains a piston whose motion relative to the floater-tube system (motion originated by wave action on the floater and by the inertia of the water enclosed in the tube) drives a power take-off mechanism (PTO) (assumed to be a linear damper). To solve the problem of the end-stops, the central part of the tube, along which the piston slides, bells out at either end to limit the stroke of the piston. The use of a hydraulic turbine inside the tube is examined as an alternative to the piston. A frequency domain analysis of the device in regular waves is developed, combined with a one-dimensional unsteady flow model inside the tube (whose cross-section is in general nonuniform). Numerical results are presented for a cylindrical buoy in regular waves, including the optimization of the acceleration tube geometry and PTO damping coefficient for several wave periods. 2011-06-18T23:00:00Z http://hdl.handle.net/10400.9/1432 Title: Energetic and environmental evaluation of microalgae biomass fermentation for biohydrogen production Authors: Ferreira, A.; Ortigueira, J.; Alves, L.; Gouveia, L.; Moura, P.; Silva, C. Abstract: This paper presents an energetic and environmental evaluation of the fermentative hydrogen production from the sugars of Scenedesmus obliquus biomass hydrolysate by Clostridium butyricum. The main purpose of this work was to evaluate the potential of H2 production and respective energy consumptions and CO2 emissions in the global fermentation process: hydrolysis of S. obliquus biomass, preparation of the fermentation medium, degasification and incubation. The scale-up to industrial production was not envisaged. Energy consumption and CO2 emissions estimations were based on SimaPro 7.1 software for the preparation of the fermentation medium and the use of degasification gas, nitrogen. The functional unit of energy consumption and CO2 emissions was defined as MJ and grams per 1 MJ of H2 produced, respectively. The electricity consumed in all hydrogen processes was assumed to be generated from the Portuguese electricity production mix. The hydrogen yield obtained in this work was 2.9 ± 0.3 mol H2/mol sugars in S. obliquus hydrolysate. Results show that this process of biological production of hydrogen consumed 281-405 MJ/MJH2 of energy and emitted 24-29 kgCO2/ MJH2. The fermentation stages with the highest values of energy consumption and CO2 emissions were identified for future energetic and environmental process optimisation. 2011-11-10T00:00:00Z