Browsing by Issue Date, starting with "2012"
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- Energy storage for wind integration: hydropower and other contributionsPublication . Estanqueiro, Ana; Ardal, Atle Rygg; O'Dwyer, Ciara; Flynn, Damian; Huertas-Hernando, Daniel; Lew, Debra; Gomez-Lázaro, E.; Ela, Erik; Revuelta, Javier; Kiviluoma, Juha; Rodrigues, L.; Amelin, Mikael; Holttinen, HanneleThe amount of wind power and other timevariable non-dispatchable renewable energy sources (RES) is rapidly increasing in the world. A few power systems are already facing very high penetrations from variable renewables which can surpass the systems’ consumption during no-load periods, requiring the energy excess to be curtailed, exported or stored. The limitations of electric energy storage naturally lead to the selection of the well-known form of storing potential energy in reservoirs of reversible hydropower stations, although other technologies such as heat storage are also being used successfully. This paper reviews the storage technologies that are available and may be used on a power system scale and compares their advantages and disadvantages for the integration of fast-growing renewables, such as wind power, with a special focus on the role of pumped hydro storage.
- Contribuição para a reconstrução da produtividade primária no Pacífico Sul durante o último ciclo climático : registo das diatomáceasPublication . Mateus, Sandra Isabel Alves
- Constraints on the structure of Maio Island (Cape Verde) by a three-dimensional gravity model : imaging partially exhumed magma chambersPublication . Represas, Patricia; Catalão, João; Montesinos, Fuensanta G.; Madeira, José; Mata, João; Antunes, Carlos; Moreira, Mário
- Synchrotron radiation (SR) in materials science : a brief retrospective on first approaches towards the use of SR at European research facilitiesPublication . Figueiredo, M. OndinaA brief quasi-historical survey is presented on the primary joint efforts developed by Portuguese researchers towards the use of synchrotron radiation at European Instrumental Facilities, emphasizing some original contributions and mentioning a few decisive steps towards the adhesion of Portugal to the European Synchrotron Research Facility (ESRF, Grenoble/France).
- Nanodiamond dispersions in nanostructured metalsPublication . Nunes, D.; Correia, J.B.; Carvalho, Patricia Almeida
- Heuristic algorithm for the piecewise linear segmentation of multiple time-series for solar thermal systems inverse modellingPublication . Lopes, Vitor V.; Ferro, Filipa; Carvalho, Maria João; Novais, Augusto Q.This paper presents a novel algorithm for the piecewise linear segmentation of multivariate time-series and proposes its application to the analysis of hot water thermal solar systems (TSS). The ISO 9459-5:2007 norm describes a non-intrusive dynamic test for the performance assessment of TSS. This allows to characterize the system heat losses and the thermal stratification properties, as well as to predict its long-term performance. The application of this norm requires an inverse modeling approach where the parameters of a simplified plug flow storage model, based on simulation runs, are determined through an optimization procedure aiming at the adjustment of the predicted results to those obtained by a predefined experimental test sequence (3-5 days). This paper proposes a new method to decrease the computation time required for the model simulation, which is based on the segmentation of the multivariate time-series into a piecewise linear approximation, where the number of segments is critically selected. An illustrative example is presented consisting in the simulation of a real 3-day experimental dataset with 26873 points and a 15 s sampling rate.
- Deconstruction of the hemicellulose fraction from lignocellulosic materials into simple sugarsPublication . Gírio, Francisco; Carvalheiro, Florbela; Duarte, Luís C.; Lukasik, Rafal M.Hemicelluloses hold a great promise for the production of added-value compounds in the biorefinery framework. Specifically, the xylan-rich hemicelluloses from hardwoods and agro-industrial residues present themselves as effective feedstock choices for the biotechnological production of xylitol. This paper reviews the various hemicellulose structures present in such materials and critically evaluates the available processing options to produce xylose-rich fermentable hydrolysates. Currently, acid-based processes still present the best trade-off between operation easiness and xylose yield and recovery. Nevertheless, concerns regarding the impact of the fractionation processes on the overall upgradability of all biomass fractions (namely, cellulose and specially lignin) may turn the route to other strategies. Specifically, the combined/sequential use of processes targeting hemicellulose dissolution and hydrolysis might hold great promise for the economical production of pentoses.
- Indium-carrier minerals in polymetallic sulphide ore deposits : a crystal chemical insight into an indium binding state supported by X-ray absorption spectroscopy dataPublication . Figueiredo, M. Ondina; Silva, Teresa; de Oliveira, Daniel Pipa Soares; Rosa, Diogo
- Carta geológica da Guiné-Bissau: de 1982 a 2011Publication . Alves, Paulo; Figueiredo, Vera
- Assessment of PV and wind microgeneration's impact in the power quality of low and medium voltage distribution networksPublication . Bonifácio, Paulo; Viana, Susana; Rodrigues, L.; Estanqueiro, AnaElectric power systems face an ever-growing penetration (PV) and other microgeneration as well as non-linear loads such as electric vehicles. This is a common link between these : the extensive use of power electronics converters. These devices are a source of medium-to-high frequency harmonic distortion and their impact on the local distribution grid must be carefully assessed in order to evaluation possible network unbalances, demaging power line resonance conditions, transformer core saturation and overhearing.