ESTG - Comunicações em conferências e congressos internacionais
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- Perfect DFT sequences transformed into orthogonal sequencesPublication . Pereira, J. S.; Silva, H. J. A. daIn this paper, we present a method and a code generator to transform perfect DFT (discrete Fourier transform) sequences into orthogonal sequences and into bipolar codes, with good correlation properties. These new sequences or codes produce a low peak-to-average power ratio (PAPR) and a low error probability in a code-division multiple access (CDMA) system. All these codes can also be useful in a pre-coded version of an orthogonal frequency-division multiplexing (OFDM) system.
- Subjective quality factors in packet 3D videoPublication . Pinto, L.; Carreira, J.; Faria, S.; Rodrigues, N.; Assunção, P.; Carreira, J.This paper presents an experimental study on subjective quality of 3D video under packet loss conditions. A priority network is assumed, such that the base view of a stereoscopic video stream is delivered through a guaranteed channel and the auxiliary view is subject to packet losses over a low priority channel. Due to the packetisation scheme, one frame is lost whenever a packet is lost. Three frame concealment methods are proposed to deal with frame losses and seven different 3DTV sequences are used. The subjective evaluation study was carried out for different packet loss ratios and concealment methods, using shutter glasses with synchronized display. The experimental results show that sequence disparity, type of loss concealment and packet loss pattern should be jointly considered as relevant quality factors in 3D video over packet networks.
- Experimental measurement of H3+/H5 + and D3+/D5+ mobilities in their parent gasesPublication . Neves, P.N.B.; Escada, J.; Borges, F.I.G.M.; Távora, L. M. N.; Conde, C.A.N.The experimental study of the reduced mobility K0 of the molecular ions H3+/H5+ in H 2 and D3+/D5+ in D 2 was carried out using a recently developed technique, that uses a Xe VUV flash lamp and a Gaseous Electron Multiplier (GEM) microstructure with a CsI deposit to produce the molecular ions by electron avalanche ionization. For both gases, the K0 values were obtained at room temperature (295 K) and at pressures from 5 to 50 Torr for uniform reduced electric fields E/N from 4 to 40 Td. The reduced mobility derived from the measurements is an average of the K0 value of the two molecular ions, and for the H 3+ and H5+ ions is 11.1 cm 2V-1s-1 while for D3+ and D5+ it ranges from 8.5 to 7.8 cm2V -1s-1, for pressure from 5 to 50 Torr. A discussion of the obtained results is presented.
- An Economical Model For Dumping by Dumping in a Cournot ModelPublication . Banik, Nilanjan; Ferreira, Fernanda A.; Martins, J.; Pinto, Alberto A.We consider an international trade economical model where two firms of different countries compete in quantities and can use three different strategies: (i) repeated collusion, (ii) deviation from the foreigner firm followed by punishment by the home country and then followed by repeated Cournot, or (iii) repeated deviation followed by punishment. In some cases (ii) and (iii) can be interpreted as dumping.We compute the profits of both firms for each strategy and we characterize the economical parameters where each strategy is adopted by the firms.
- State estimation model including synchronized phasor measurementsPublication . Vide, Paula S. Castro; Barbosa, Maciel; Ferreira, Isabel M.State estimation plays an important role in real time security monitoring and control of power systems. With increasing implementation of PMUs across the electric power grids and the ability of the Phasor Measurement Unit (PMU) to directly measure the system state, the use of these measurements to improve the precision of state estimator becomes imperative. In this paper, a new state estimator including voltage and current phasors and traditional measurements is proposed. The methodology is validated by simulation results on the 14 and 30 IEEE bus test systems. Several comparisons between the use of SCADA measurements and PMU measurements are exposed. Discussion concerning statistical robustness of the implemented state estimators is presented.
- Evolution of Artificial Terrains for Video Games Based on AccessibilityPublication . Frade, Miguel; Vega, Francisco Fernandez de; Cotta, CarlosDiverse methods have been developed to generate terrains under constraints to control terrain features, but most of them use strict restrictions. However, there are situations were more flexible restrictions are sufficient, such as ensuring that terrains have enough accessible area, which is an important trait for video games. The Genetic Terrain Program technique, based on genetic programming, was used to automatically evolve Terrain Programs (TPs - which are able to generate terrains procedurally) for the desired accessibility parameters. Results showed that the accessibility parameters have negligible influence on the evolutionary system and that the terminal set has a major role on the terrain look. TPs produced this way are already being used on Chapas video game.
- Power converter fault diagnosis in SRM drives based on the DC Bus current analysisPublication . Gameiro, Natália S.; Cardoso, A. J. MarquesThis paper presents a new fault diagnostic technique applied to switched reluctance motor (SRM) drives. A fault is detected when the measured amplitude of the DC bus current differs from its expected amplitude, assuming normal operating conditions. The information about phase currents amplitudes and the control states of all power switches permit to easily estimate the amplitude of the power converter supply current, since an asymmetric bridge converter is used. Open-and short-circuit fault occurrences in the converter power switches are presented. The proposed technique can early detect these fault occurrences and can also, in almost situations, identify not only the affected motor phase but also the faulty element. A short-circuit fault in a converter power switch of a SRM drive does not necessarily causes a short-circuit in the DC bus, unlike to what happens in many other converter-fed electrical machine drives. On the other hand, although a converter power switch open-circuit fault can be easily detected by the observation of the phase currents, the identification of the faulty element becomes impossible to achieve, if only phase currents are measured. This information is of paramount importance in the development of fault tolerant power converters.
- Islanding operation of active distribution grids using an agent-based architecturePublication . Issicaba, D.; Gil, N. J.; Lopes, J. A. PeçasThis paper presents a decentralized architecture for the islanding operation of distribution grids with large volume of distributed generation. This architecture involves the definition of network blocks which share the responsibility of frequency control. The control block abstraction was particularly designed to support the transition from regular grids to smart grids. In addition, the control schemes were developed using an agentbased paradigm. Hence, an agent-based simulation platform was implemented using libraries from the Java Agent Development Framework (JADE). The control schemes were evaluated using a test system with different sorts of distributed energy resources and modeled in the EUROSTAG environment. Simulation results show the effectiveness of the control architecture when different failure events are applied to the test system.
- Parallel AlineaGA: An island parallel evolutionary algorithm for multiple sequence alignmentPublication . Silva, Fernando José Mateus da; Pérez, Juan Manuel Sánchez; Pulido, Juan Antonio Gómez; Ródriguez, Miguel A. VegaMultiple sequence alignment is the base of a growing number of Bioinformatics applications. This does not mean that the accuracy of the existing methods corresponds to biologically faultless alignments. Searching for the optimal alignment for a set of sequences is often hindered by the size and complexity of the search space. Parallel Genetic Algorithms are a class of stochastic algorithms which can increase the speed up of the algorithms. They also enhance the efficiency of the search and the robustness of the solutions by delivering results that are better than those provided by the sum of several sequential Genetic Algorithms. AlineaGA is an evolutionary method for solving protein multiple sequence alignment. It uses a Genetic Algorithm on which some of its genetic operators embed a simple local search optimization. We have implemented its parallel version which we now present. Comparing with its sequential version we have observed an improvement in the search for the best solution. We have also compared its performance with ClustalW2 and T-Coffee, observing that Parallel AlineaGA can lead the search for better solutions for the majority of the datasets in study.
- Alternative Zigbee codes derived from orthogonal perfect DFT sequencesPublication . Pereira, João S.; Silva, Henrique J. A. daThe performance of a code-division multiple access (CDMA) system is directly related with the choice of adequate codes. The codes for use in CDMA communication systems should have a perfect aperiodic (or periodic) autocorrelation function and should be orthogonal to each other at all time shifts. A mathematical property that provides a way to find large sets of real perfect DFT (discrete Fourier transform) sequences is presented. These sequences can be transformed into real orthogonal perfect DFT sequences and also into bipolar codes that have better properties than the codes used in the Zigbee communication system. These new bipolar codes are approximately orthogonal and have nearly optimum periodic and aperiodic autocorrelation functions. We also evaluate our bipolar codes with an improved error probability model.