Browsing by Issue Date, starting with "2011-10"
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- Educação e Diversidade Cultural: Notas de Antropologia da EducaçãoPublication . Vieira, Ricardo
- Problematiche di Modellazione nella Valutazione Sismica delle Strutture EsistentiPublication . Sousa, Romain; Bianchi, F.; Nascimbene, Roberto; Pinho, RuiProblemi di modellazione per l’analisi sismica delle strutture esistenti Molti edifici in c.a. del patrimonio edilizio esistente sono stati progettati per i soli carichi verticali, presentando un’inadeguata resistenza ai carichi laterali e scarsi dettagli costruttivi. Inoltre, il concetto di regolarità in pianta e in elevazione, tipico di una buona progettazione sismica, spesso è stato trascurato. Per valutare il comportamento sismico di tali edifici, alcune recenti normative in materia sismica - quali l’EC8 e le NTC08 - hanno introdotto diverse prescrizioni sulle tipologie di analisi, le distribuzioni di carico, l’eccentricità accidentale, ecc., lasciando, però, ai progettisti piena autonomia a proposito delle strategie di modellazione (es. impalcati, tamponamenti verticali, tipologia di elementi finiti, masse, ecc.). L’obiettivo del presente lavoro è quello di stimare, tramite l’esecuzione di analisi non-lineari (statiche e dinamiche) per un edificio reale, l’influenza di tali strategie nella valutazione sismica delle strutture, al fine di fornire indicazioni sull’importanza di ogni scelta progettuale.
- A divulgação da informação socialmente responsável nos estabelecimentos hoteleiros portuguesesPublication . Ferraz, Francisco António Vaz Guedes Delgado; Schön, Michael; Vázquez, Dolores GallardoAs organizações têm vindo a manifestar uma maior consciência a nível económico, social e ambiental, procurando minimizar problemas com que a sociedade se debate de uma forma sistemática, numa lógica de sustentabilidade e de longo prazo. Para esse efeito, procuram desenvolver um conjunto de iniciativas que implica a adopção de comportamentos coerentes e transparentes com objectivos de criação de valor, não apenas para a organização mas também para com todos aqueles com os quais a mesma se relaciona. Nesta óptica, a divulgação da sua actuação socialmente responsável, assume um papel importante como instrumento de Marketing Relacional com os seus Stakeholders, uma vez que numa perspectiva de longo prazo potenciará vantagens competitivas às organizações que as fomentem. Neste documento, pretende-se efectuar uma análise sobre a divulgação da diversa informação sobre Responsabilidade Social no sector Turístico Português baseando-se a mesma num estudo empírico realizado aos estabelecimentos hoteleiros classificados de três a cinco estrelas.
- A maximum independent set approach for collusion detection in voting poolsPublication . Araujo, Filipe; Farinha, Jorge; Domingues, Patrício; Silaghi, Gheorghe Cosmin; Kondo, DerrickFrom agreement problems to replicated software execution, we frequently find scenarios with voting pools. Unfortunately, Byzantine adversaries can join and collude to distort the results of an election. We address the problem of detecting these colluders, in scenarios where they repeatedly participate in voting decisions. We investigate different malicious strategies, such as naïve or colluding attacks, with fixed identifiers or in whitewashing attacks. Using a graph-theoretic approach, we frame collusion detection as a problem of identifying maximum independent sets. We then propose several new graph-based methods and show, via analysis and simulations, their effectiveness and practical applicability for collusion detection.
- A multi-objective simulated annealing approach to reactive power compensationPublication . Antunes, Carlos Henggeler; Lima, Paulo; Oliveira, Eunice; Pires, Dulce F.Reactive power compensation is an important problem in electrical distribution systems, involving the sizing and location of capacitors (sources of reactive power). The installation of capacitors also contributes to releasing system capacity and improving voltage level. A multi-objective simulated annealing approach to provide decision support in this problem is presented. This approach is able to compute a set of well-distributed and diversified solutions underlying distinct trade-offs, even for a challenging network. The characterization of the non-dominated front is relevant information for aiding planning engineers to select satisfactory compromise solutions (compensation schemes) to improve the network operation conditions.
- Preparation and Characterization of Films Based on Alginate and Aloe VeraPublication . Brás Pereira, Rúben Filipe; Tojeira, Ana; Barroso de Moura Cipreste Vaz, Daniela; Mendes, Ausenda; Bartolo, Paulo; Mendes, AusendaSodium alginate films with aloe vera extract were prepared by the casting/solvent evaporation technique. The resulting films were characterized by differential scanning calorimetry, Fourier transform-infrared spectroscopy, scanning electron microscopy, and mechanical and water absorption tests. The in vitro degradation of the films was also investigated over 14 days. Results show that aloe vera contributes to both enhancing the thermal and mechanical properties of the films and decreasing the weight loss during in vitro degradation.
- An instantaneous regulation for the wired and wireless super-resonant convertersPublication . Valtchev, Stanimir; Medeiros, Rui; Valtchev, Svilen S.; Klaassens, BenThe paper develops further the method presented in [12], [14], based on energy balance in the resonant tank. This method allows a stable operation of the switches and a higher efficiency of any Series Loaded Series Resonant (SLSR) power converter, especially when contactless energy transfer is concerned. The strategy is based on guaranteeing the correct portion of energy transported by the resonant tank to the load. The portion has to vary corresponding to the error signal taken from the output voltage and remains unchanged if the error signal from the output is at its minimum. In a certain way this method is similar to the Current Mode Control of the classical power converters.
- An iterative pilot-data aided estimator for OFDM-based relay-assisted systemsPublication . Neves, D.; Ribeiro, Carlos; Silva, A.; Gameiro, A.We propose and assess a pilot-data aided channel estimation scheme for realistic relay-assisted scenarios designed for the downlink SFBC OFDM-based systems. We consider that both the base station and the relay node are equipped with an antenna array whereas the user terminal is a single antenna device. The relay protocol considered is equalise-and-forward. The channel estimation method iteratively uses the information carried by the pilots and data to improve the estimate of the equivalent channels for the path Base Station - Relay Node - User Terminal. The MMSE criterion is used in the design of the estimator for both the pilot-based and data-aided iterations. The results show the benefits of cooperation in terms of MSE and also show that the proposed scheme allows, with a single data iteration, a reduction of the number of pilots when compared with non-data-aided schemes.
- Financial risk exposures and risk management: evidence from european nonfinancial firmsPublication . Jorge, Maria João Da Silva ; Augusto, Mário António GomesPrevious empirical studies concerning corporate risk management have attempted to show that the use of derivatives as a hedging mechanism can be value enhancing. Implicit to these tests has been the assumption that firms use derivatives solely for the purpose of hedging. There is substantial literature concerning nonfinancial firms that suggest that changes in financial prices affect firms' value. Furthermore, it is a common belief that financial price exposures are created via firms' real operations and are reduced through the implementation of financial hedging strategies. We use monthly returns of 304 European firms traded in Euronext over the period from 2006-2008 to analyse whether risk management practices are associated with lower levels of risk. We pursue Jorion (1990) and Allayannis and Ofek (2001) two stages framework to investigate, firstly, the relationship between firm value and financial risk exposures; subsequently, the risk behaviour inherent to firms' real operations and to the use of derivatives and other risk management instruments. So, we argue that hedging policies affect the firm's financial risk exposures; however, we do not discard the fact that the magnitude of a firm's exposure to risks affects hedging activities. The interaction between financial price exposures and hedging activities is tested by using the Seemingly Unrelated Regression (SUR) procedure. Our major findings are as follows: Firstly, we find evidence that the sample firms exhibit higher percentages of exposure to the three categories of risks analysed when compared to previous empirical studies. Secondly, we find that hedging is significantly associated with financial price exposure. Our results are also consistent with the idea that financial risk exposure and hedging activities are endogenously related, but only in what respects the exchange risk and commodity risk exposure.
- Genetic and local search algorithms applied to balanced communication networksPublication . Bernardino, Eugénia; Moreira Bernardino, Anabela; Sánchez-Pérez, Juan M.; Gómez-Pulido, Juan A.; Vega-Rodríguez, Miguel A.In this paper we describe the application of different heuristics to optimise large communication networks. We use Iterated Local Search (ILS), Tabu Search (TS), Simulated Annealing (SA) and Genetic Algorithm (GA) to minimise the link cost to form balanced communication networks. This paper makes a comparison among the effectiveness of ILS, TS, SA and GA on solving large communication networks. Simulation results verify the effectiveness of these algorithms.