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Coimbra, Portugal

The Polytechnical Institute of Coimbra is a public polytechnic institute of higher education in Coimbra, Portugal. It was created by decree of 1979, but its effective start up was only in 1988 through the creation and union of new and former schools. With an enrollment of 10,197 students, it is the third biggest polytechnic institute of Portugal. Wikipedia.

Malca J.,University of Coimbra | Malca J.,Polytechnic Institute of Coimbra | Freire F.,University of Coimbra
Renewable and Sustainable Energy Reviews | Year: 2011

Renewable energy sources, and particularly biofuels, are being promoted as possible solutions to address global warming and the depletion of petroleum resources. Nevertheless, significant disagreement and controversies exist regarding the actual benefits of biofuels displacing fossil fuels, as shown by a large number of life-cycle studies that have varying and sometimes contradictory conclusions. This article presents a comprehensive review of life-cycle studies of biodiesel in Europe. Studies have been compared in terms of nonrenewable primary energy requirement and GHG intensity of biodiesel. Recently published studies negate the definite and deterministic advantages for biodiesel presented in former studies. A high variability of results, particularly for biodiesel GHG intensity, with emissions ranging from 15 to 170 gCO2eq MJf -1 has been observed. A detailed assessment of relevant aspects, including major assumptions, modeling choices and results, has been performed. The main causes for this high variability have been investigated, with emphasis on modeling choices. Key issues found are treatment of co-product and land use modeling, including high uncertainty associated with N2O and carbon emissions from cultivated soil. Furthermore, a direct correlation between how soil emissions were modeled and increasing values for calculated GHG emission has been found. A robust biodiesel life-cycle modeling has been implemented and the main sources of uncertainty have been investigated to show how uncertainty can be addressed to improve the transparency and reliability of results. Recommendations for further research work concerning the improvement of biofuel life cycle modeling are also presented. © 2010 Elsevier Ltd. Source

Pereira A.J.C.,Polytechnic Institute of Coimbra | Saraiva J.T.,INESC Porto
Energy | Year: 2013

The Iberian power systems went through important changes at the legal, regulatory and organizational levels in the last 20 years. One of the most relevant ones was the increasing penetration of distributed generation, namely wind parks, together with the development of the common market involving Portugal and Spain. In Portugal, distributed generation is paid using feed in tariffs while in Spain it can choose between receiving a regulated feed in tariff or the market price plus a participation prize. The feed in scheme is now under discussion since it is argued that it represents an excessive cost that is internalized in the end user tariffs. However, this discussion is frequently conducted without complete knowledge of the real impact of wind power on the electricity market price, since it contributes to reduce the demand on the market thus inducing a price reduction. To clarify these issues we used a long term System Dynamics based model already reported in a previous publication to estimate the long term evolution of the market price. This model was applied to the Iberian generation system using different shares of wind power capacity to quantify the impact of wind power on the day-ahead electricity market price. © 2013 Elsevier Ltd. Source

Pereira A.J.C.,Polytechnic Institute of Coimbra | Saraiva J.T.,INESC Porto
Energy | Year: 2011

This paper presents a model to solve the Generation Expansion Planning (GEP), problem in competitive electricity markets. The developed approach recognizes the presence of several generation agents aiming at maximizing their profits and that the planning environment is influenced by uncertainties affecting the demand, fuel prices, investment and maintenance costs and the electricity price. Several of these variables have interrelations between them turning it important to develop an approach that adequately captures the long-run behavior of electricity markets. In the developed approach we used System Dynamics to capture this behavior and to characterize the evolution of electricity prices and of the demand. Using this information, generation agents can then prepare their individual expansion plans. The resulting individual optimization problems have a mixed integer nature, justifying the use of Genetic Algorithms (GAs). Once individual plans are obtained, they are input once again on the System Dynamics model to update the evolution of the price, of the demand and of the capacity factors. This defines a feedback mechanism between the individual expansion planning problems and the long-term System Dynamics model. This approach can be used by a generation agent to build a robust expansion plan in the sense it can simulate different reactions of the other competitors and also by regulatory or state agencies to investigate the impact of regulatory decisions on the evolution of the generation system. Finally, the paper includes a Case Study to illustrate the use and the results of this approach. © 2011 Elsevier Ltd. Source

Guine R.P.F.,Polytechnic Institute of Coimbra
International Journal of Food Properties | Year: 2013

In the present work, the pears were dried in two different systems, both having the sun as the energy source: a solar stove with ventilation (ESAV) and a solar drier with natural convection (ESTV). The objectives of this work were to evaluate how instrumental textural properties changed during maturation, storing, and drying, as well as to compare the two different drying methods. The results obtained allowed to see that drying affected the textural properties of pears in a way that hardness decreased very much during drying irrespective of the drying system used. © 2013 Copyright Taylor and Francis Group, LLC. Source

Martins P.,Polytechnic Institute of Coimbra
Computers and Operations Research | Year: 2012

Given a graph G=(V,E) and a clique C of G, the edge neighborhood of C can be defined as the total number of edges running between C and VC, being denoted by N(C). The density of the edge neighborhood N(C) can be set as the ratio (|N(C)|/(|C|·|V/C|)). This paper addresses maximum/minimum edge neighborhood and neighborhood density cliques in G. Two versions will be undertaken, by fixing, or not, the size of the cliques. From an optimization point of view these problems do not bring much novelty, as they can be seen as particular or special versions of weighted clique problems. However, from a practical point of view, they concentrate on certain kinds of properties of cliques, rather than their size, revealing clique's engagement in the graph. In fact, a maximum edge neighborhood clique should be strongly embraced in the graph, while a minimum edge neighborhood clique should reveal an almost isolated strong component. In particular, special versions of the new problems allow to distinguish among cliques of the same size, namely among possible tied maximum cliques in the graph. We propose node based formulations for these edge based clique related problems. Using these models, we present computational results and suggest applications where the new problems can bring additional insights. © 2011 Elsevier Ltd. All rights reserved. Source

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