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.
- 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.
- Market orientation and performance: modelling a neural networkPublication . Silva, Manuela; Moutinho, Luiz; Coelho, Arnaldo; Marques, AlziraPurpose: This paper aims to investigate the impact of market orientation (MO) on performance using a neural network model in order to find new linkages and new explanations for this relationship. Design/methodology/approach: This investigation is based on a survey data collection from a sample of 192 Portuguese companies. A neural network model has been developed to identify the effects of each dimension of MO on each dimension of performance. Findings: Relationship among MO and performance was corroborated but MO's impact is poor and based on its first dimension, market intelligence generation. Research limitations/implications: Further research in this field should be conducted using other tools offered by neural network modelling. Practical implications: Managers should give more attention to cross-functional co-ordination in order to improve market intelligence dissemination and responsiveness and, thus, global performance. Originality/value: The paper presents the development of a neural network model to analyse this relationship.
- Sensing methodologies to determine automotive damper condition under vehicle normal operationPublication . Ferreira, Carlos Daniel Henriques; Ventura, Paulo; Morais, Raul; Valente, António L.G.; Neves, Carlos; Reis, Manuel C.Vehicles rely on the efficiency of dampers to dissipate energy from the motion of vehicle body and wheels, maintaining the vehicle more stable, and improving the contact between tires and the road surface. To achieve an effective monitoring of dampers (or shock absorbers), two different methodologies, capable of assessing, under vehicle normal operation, the condition of the automotive dampers are presented. The proposed methodologies are based in acceleration, temperature and pressure sensing to determine the shock absorber condition, and are therefore suitable for future implementation in low cost fabrication technologies. The results shown that it is possible to have an effective monitoring device, installed in the damper body, capable of continuously determining shock absorber status, and therefore enabling real time diagnosis. Such a diagnosis system can reduce the number of vehicles riding with defective suspension systems and increase the overall vehicle safety.
- Regional input-output tables and modelsPublication . Sargento, Ana; Ramos, Pedro; Hewings, GeoffreyThe present research concerns the study of input-output modelling and input-output table construction, when applied at the regional level. Input-output models, at the national or regional level, are known as a fundamental tool for economic analysis. Yet, in order to apply such models, the researcher must have access to the correspondent input-output tables. National-level tables are currently published by the national statistical offices according to well-defined conventions. The same, however, cannot be said about regional tables which are not provided as a rule by official statistics organisms. Being so, a great part of input-output research is still dedicated to the study of techniques for input-output table gathering. This dissertation is, in such context, divided into three chapters. The first one is mainly theoretical, aiming to review the basic principles underlying input-output analysis at the regional level. The second and third chapters constitute the research’s practical contribution, focused on two major issues, respectively: 1) interregional trade estimation and 2) input-output modelling on the basis of total-use rectangular table at purchasers’ prices. In most countries, survey-based interregional trade data does not exist. However, even when some simplifying assumptions are used in the model, a minimum amount of data on interregional trade is always necessary, in order for the model to succeed in capturing spillover and feedback effects caused by the interregional linkages. In order to evaluate the reasonability of using indirect interregional trade flows estimates, a comparison was made between alternative methodologies (with special focus on gravitational models), assessing the sensitivity of the model results. Such comparison allowed to conclude that the results of the input-output model are not greatly affected by the insertion of different trade flow values. Thus, the results obtained do not reject the reasonability of using indirect estimates for interregional trade, whenever survey-based data is unavailable. The official input-output tables are published on a total-use rectangular format, which is different from the lay-out upon which traditional input-output models were developed (domestic use symmetric tables). The objective here was to demonstrate the equivalence in the results of the input-output model between two alternative procedures: 1) to convert the available input-output table into a domestic-flow symmetric table at basic prices and then implement the input-output model; 2) to perform the direct modelling of the original table (the total-flow rectangular table at purchasers’ prices). It has been concluded that, when the same set of hypotheses is used, there is no advantage in making a previous transformation of the original tables into the symmetric format and a previous calculation of domestic flows, since the results of the model are exactly the same.