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In the present study, an acid mediated steam explosion process was evaluated for pretreatment of elephant grass biomass in a bench scale reactor. Different combinations of H2SO4 concentration, reaction time and temperature (leading to different values of combined severity factor - CSF) were used for biomass pretreatment, and the impact of the resultant pretreatment conditions on biomass composition, structure and enzymatic hydrolysis was assessed. The optimal pretreatment conditions consisted in performing the steam explosion at 161°C during 11.5min, and using the biomass impregnated with 0.5% H2SO4 (CSF=1.42). Under these conditions, a pretreated solid containing 52.13% (w/w) cellulose and 31.00% (w/w) lignin was obtained. The modifications in the biomass structure resulting from the different pretreatment conditions were evaluated by scanning electron microscopy, thermogravimetric analysis and nuclear magnetic resonance spectroscopy analysis. Enzymatic hydrolysis of the pretreated material resulted in a cellulose saccharification yield of 55%. These results allow a better understanding about the pretreatment and enzymatic saccharification of elephant grass biomass and also reveal a great potential of this raw material for use in a biorefinery.

In the socio-technical transitions literature, local niche projects have been described as sources of knowledge, experience, actor networks, and (positive) expectations. Local niches and local designs can however also become stumbling blocks when local designs are non-compatible with an emerging global standard. In this paper we study the emergence of standards for electric vehicle recharging plugs to answer the question whether and how local niches and their outcomes may hamper the process of niche aggregation. Our analysis shows that distinct local recharging plug standards have emerged for both regular and fast charging. Especially the standards for regular charging are clearly designed to comply with local regime rules and that these rules have thus prevented the development of a global standard. With our analysis we show that the local context may indeed be so intrusive that it inscribes itself irreversibly in technical designs and standards and hence lead to local lock-ins that prevent further aggregation. Even more so, we recognize a tension between the need for local niche projects to comply with local rules and the need for the global niche to break free from such local rules in order to define universal designs instead.

The security of energy supply to the EU is examined in the context of two storylines. Markets and Institutions exemplifies an economically and politically integrated, multilateral world with effective institutions and markets, Regions and Empires involves a world broken up in rival political and economic blocks, competing for resources and markets via political, economic and military power. It is shown that these storylines have a significant impact on the development or the energy market, on the way in which energy Supply may be secured and on the effect and applicability of the several types of instruments available. The current EU is geared towards enlargement and a deepening of economic integration, based on the tenets of the post-1945 Multilateral world system. The present world tends towards Regions and Empires and Suggests that the EU may have to reorient its energy security policy. Energy Policy Must become an integral part of EU external trade and foreign relations and security policy. The EU should develop its own strategy, actively investing in dialogues with producer countries in the Persian Gulf and Africa and with Russia. Sustainable prosperity and governance in these regions will Support EU energy security. (c) 2005 Elsevier Ltd. All rights reserved.

The penetration level of plug-in electric vehicles (PEVs) has the potential to be notably increased in the near future, and as a consequence, power systems face new challenges and opportunities. In particular, PEVs are able to provide different types of power system ancillary services. The capability of storing energy and the instantaneous active power control of the fast-switching converters of PEVs are two attractive features that enable PEVs to provide various ancillary services, e.g., primary frequency control (PFC). However, concurrently, PEVs are obliged to be operated and controlled within limits, which curbs the grid support from PEVs. This paper proposes a new model for PEV using a participation factor, which facilitates the incorporation of several PEV fleets characteristics such as minimum desired state of charge (SOC) of the PEV owners, drive train power limitations, constant current and constant voltage charging modes of PEVs. In order to reduce computational complexity, an aggregate model of PEVs is provided using statistical data. In the end, the performance of PEVs for the provision of PFC is evaluated in a power system. Results show that PEV fleets can successfully improve frequency response, once all the operating constraints are respected. info:eu-repo/semantics/draft

In this contribution, we discuss the implementation of a novel microelectromechanical-systems (MEMS)-based energy harvester (EH) concept within the technology platform available at the ISAS Institute (TU Vienna, Austria). The device, already presented by the authors, exploits the piezoelectric effect to convert environmental vibrations energy into electricity, and presents multiple resonant modes in the frequency range of interest (i.e. below 10 kHz). The experimental characterisation of a sputter deposited aluminium nitride piezoelectric thin-film layer is reported, leading to the extraction of material properties parameters. Such values are then incorporated in the finite element method model of the EH, implemented in Ansys Workbench (TM), in order to get reasonable estimates of the converted power levels achievable by the proposed device solution. Multiphysics simulations indicate that extracted power values in the range of several mu W can be addressed by the EH-MEMS concept when subjected to mechanical vibrations up to 10 kHz, operating in closed-loop conditions (i.e. piezoelectric generator connected to a 100 k Omega resistive load). This represents an encouraging result, opening up the floor to exploitations of the proposed EH-MEMS device in the field of wireless sensor networks and zero-power sensing nodes.

Ligand exchange is a much-used method to increase the conductivity of colloidal quantum-dot films by replacing long insulating ligands on quantum-dot surfaces with shorter ones. Here we show that while some ligands indeed replace the original ones as expected, others may be used to controllably remove the native ligands and induce epitaxial necking of specific crystal facets. In particular, we demonstrate that amines strip lead oleate from the (100) surfaces of PbSe quantum dots. This leads to necking of QDs and results in cubic superlattices of epitaxially connected QDs. The number of amine head-groups as well as the carbon chain length of linear diamines is shown to control the extent of necking. DFT calculations show that removal of Pb(oleate)2 from (100) surfaces is exothermic for all amines, but the driving force increases as monoamines < long diamines < short diamines < tetramines. The neck formation and cubic ordering results in a higher optical absorption cross section and higher charge carrier mobilities, thereby showing that the use of the proper multidentate amine molecules is a powerful tool to create supercrystals of epitaxially connected PbSe QDs with controlled electronic coupling.

Swirling flow in combination with deformation still forms a major test case for many turbulence models. In order to better understand the relevant processes in such flows and to provide quantitative data for model validation, laboratory and numerical experiments are needed. Such data have been obtained on a simple flow: the passage of a swirling flow through a contraction. This flow can be considered as a prototype for flows that occur in cyclone separators and burners.

Artículos en revistas Wind power represents a significant percentage of the European generation mix and this will increase to fulfill the renewable energy targets. Different balancing rules are applied to wind power among the countries; for instance, to what extent wind power producers (WPPs) are responsible for the energy imbalances and how those imbalances are penalized. This paper discusses those different rules and evaluates their effects on WPP bidding strategies. To do so, a quantitative analysis is presented for an offshore wind farm, considering the differences in the balancing rules and prices of Belgium, Denmark, Germany and the Netherlands. The quantitative approach consists of a stochastic optimization model that maximizes the profits of a WPP by trading in different markets (day-ahead and intraday) and computes the final energy delivered. The model considers uncertainties of most important parameters such as wind energy forecasts and prices at different time frames. The results show that the imbalance pricing design and the allocation of balance responsibility significantly affect WPP revenues. Additionally, WPPs deviate differently from the expected energy depending on the balancing rules, which can impact the system. Furthermore, these balancing rules should be considered with other market regulations, such as the design of support schemes. info:eu-repo/semantics/publishedVersion