Browsing by Issue Date, starting with "2009-04"
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- The QCD critical end point in the PNJL modelPublication . Costa, P.; Sousa, C. A. de; Ruivo, M. C.; Hansen, H.; Costa, PedroWe investigate the role played by the Polyakov loop in the dynamics of the chiral phase transition in the framework of the so-called PNJL model in the SU(2) sector. We present the phase diagram where the inclusion of the Polyakov loop moves the critical points to higher temperatures, compared with the NJL model results. The critical properties of physical observables, such as the baryon number susceptibility and the specific heat, are analyzed in the vicinity of the critical end point, with special focus on their critical exponents. The results with the PNJL model are closer to lattice results and we also recover the universal behavior of the critical exponents of both the baryon susceptibility and the specific heat.
- Marketing database knowledge extraction - towards a domain ontologyPublication . Pinto, Filipe Mota; Gago, Pedro; Santos, Manuel Filipe; Mota Pinto, Filipe; Gago, PedroOntologies are currently the most prominent computer science research area under development. With this paper we use ontologies at an almost unexplored research area within the marketing discipline, throughout ontological approach to the database marketing. We propose a generic framework supported by ontologies for the knowledge extraction from marketing databases. Therefore this work has two purposes: to integrate ontological approach in Database Marketing and to create domain ontology with a knowledge base that will enhance the entire process at both levels: marketing and knowledge extraction techniques. This research was developed according to two methodological principles, ontology domain double articulation and ontology modularization. At the end of our work we use ontologies to pre-generalize the Database Marketing knowledge through a knowledge base.
- Analysis of finite oscillating GIX/M(m)//N queueing systemsPublication . Ferreira, Fátima; Pacheco, António; Ribeiro, Helena; Ribeiro, Helena;In this work we investigate oscillating GIX/M(m)//N systems, which are queueing systems whose service mechanism reacts to the congestion of the system; namely, the service rates oscillate between two forms according to the evolution of the number of customers in the system. Resorting to Markov chain embedding, we address the time-dependent and limit analysis of the number of customers in the system at batch prearrivals and seen by customers at their arrival to the system. These results are then used to derive the continuous-time limit distribution of the number of customers in the system. In addition, we provide some numerical examples that illustrate our approach.
- On ECG Signal Compression With 1-D Multiscale Recurrent Patterns Allied to Preprocessing TechniquesPublication . Filho, E.B.L.; Rodrigues, N.M.M.; Silva, E.A.B. da; Carvalho, M.B. de; Faria, S.M.M. de; Silva, V.M.M. da; M. M. Rodrigues, Nuno; Faria, SergioThis paper presents the results of a multiscale pattern-matching-based ECG encoder, which employs simple preprocessing techniques for adapting the input signal. Experiments carried out with records from the Massachusetts Institute of Technology-Beth Israel Hospital database show that the proposed scheme is effective, outperforming some state-of-the-art schemes described in the literature.
- Predictable impact of lighting control on the energy consumption of a building through computational simulationPublication . Bernardo, H.; Leitão, S.; Neves, L.; Amaral, P.; Bernardo, Hermano; Pires Neves, LuísBuilding energy simulation tools provide accurate predictions of the energetic performance of buildings and thermal comfort of its occupants, allowing an evaluation of the impact of proposed improvement measures, in order to support choice for the more economically viable. This paper aims at determining the energy saving potential that can be obtained by adequate measures and investments. It presents the simulated values of the impact on the energy consumptions of a building, caused by artificial lighting control systems set to maximize use of natural lighting. Results show that optimization measures have a significant impact on energy consumptions reduction, and lead to important economical savings.
- INTCare: On-line knowledge discovery in the intensive care unitPublication . Gago, Pedro; Fernandes, C.; Pinto, Filipe; Santos, M.F.In our work aim to automate the knowledge discovery process. In this paper we present the INTCare system, an intelligent decision support system for intensive care medicine. INTCare is an agent based system that has (autonomous) agents responsible both for data acquisition and model updating thus reducing the need for human intervention. In the present, INTCare is predicting organ failure and probability of in-hospital death. Reliable prediction results facilitate a change from the current reactive behavior to a pro-active one thus enhancing the quality of service. The functional and structural aspects are presented as are some results obtained using data collected from the bedside monitors.
- Improving Visualization, Scalability and Performance of Multiclass Problems with SVM Manifold LearningPublication . Silva, Catarina; Bernardete RibeiroWe propose a learning framework to address multiclass challenges, namely visualization, scalability and performance. We focus on supervised problems by presenting an approach that uses prior information about training labels, manifold learning and support vector machines (SVMs). We employ manifold learning as a feature reduction step, nonlinearly embedding data in a low dimensional space using Isomap (Isometric Mapping), enhancing geometric characteristics and preserving the geodesic distance within the manifold. Structured SVMs are used in a multiclass setting with benefits for final multiclass classification in this reduced space. Results on a text classification toy example and on ISOLET, an isolated letter speech recognition problem, demonstrate the remarkable visualization capabilities of the method for multiclass problems in the severely reduced space, whilst improving SVMs baseline performance.
- Channel Estimation Schemes for OFDM Relay-Assisted SystemsPublication . Neves, Darlene; Ribeiro, Carlos; Silva, Adao; Gameiro, AtilioThe aim of this paper is to adapt and evaluate the performance of two classical pilot-aided channel estimation schemes designed for OFDM systems: least square and minimum mean square error, in a relay-assisted scenario. We consider the Amplify-and-Forward, which is the simplest relay protocol for cooperative systems. Also, we consider the use of a single antenna at all the terminals: base station, user terminal and relay node. In our scenario, it is assumed that some of the user terminals deployed in a certain area could act as relaying-able terminals for the communications of other users. In this communication we show that the classical channel estimation techniques designed for conventional wireless communications can be extended for relay-assisted based systems under some modifications.
- Design Optimization of Radio Frequency Discrete Tuning VaractorsPublication . Moreira Mendes, Luís Miguel; Pires, Eduardo J. Solteiro; Oliveira, Paulo B. de Moura; Machado, José A. Tenreiro; Ferreira, Nuno M. Fonseca; Vaz, João Caldinhas; Rosário, Maria J.This work presents a procedure to automate the design of Si-integrated radio frequency (RF) discrete tuning varactors (RFDTVs). The synthesis method, which is based on evolutionary algorithms, searches for optimum performance RF switched capacitor array circuits that fulfill the design restrictions. The design algorithm uses the ε-dominance concept and the maximin sorting scheme to provide a set of different solutions (circuits) well distributed along an optimal front in the parameter space (circuit size and component values). Since all the solutions present the same performance, the designer can select the circuit that is best suited to be implemented in a particular integration technology. To assess the performance of the synthesis procedure, several RFDTV circuits, provided by the algorithm, were designed and simulated using a 0.18μm CMOS technology and the Cadence Virtuoso Design Platform. The comparisons between the algorithm and circuit simulation results show that they are very close,poi ting out that the proposed design procedure is a powerful design tool.
- Simulation of the effect of voltage transients on an induction motor with ATP/EMTPPublication . Gonçalves, José; Baptista, José; Pires Neves, Luís; Oliveira, Filipe TadeuThe present study aims at understanding the behaviour of the induction motor when subject to different kinds of disturbances. The intention was to broaden the study of some disturbances by using a transient simulation software, ATP/EMTP, and comparing results with laboratory measurements. Obtained simulation results approached very closely the laboratory measurements, with small differences probably due to the model simplifying assumptions and uncertainties associated to the model parameter estimation process. However, although this theoretical model presents a response very similar to the actual model, improvements could be made by better modelling of the mechanical load, and by using different kinds of dynamic loads. Also, the use of more accurate laboratory equipment, and namely, programmable power supplies could lead to more accurate comparisons and better learning.