Browsing by Issue Date, starting with "2006-09"
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- Interactive Exercises on Analysis Methods for DC Linear Electrical CircuitsPublication . Sousa, Pedro A.; Gericota, Manuel G.; Alves, Gustavo R.Electrical Engineering students must learn the fundamentals of electricity in a very short time, due to the increasing number and size of areas addressed on EE courses. While some students have been exposed to those fundamentals during secondary level education, others have not. These circumstances increase the complexity of devising a good approach to motivate all students for learning. One example occurs when teaching the analysis methods for DC Linear Electrical Circuits, where the number of all possible arbitrary choices grows exponentially with the number of circuit branches. While first-time-exposed students are required to learn first how to apply the different analysis methods, the remaining students are required to calculate the total number of possible set of equations that solve the circuit. To serve both student groups, we developed an application that helps understanding the way arbitrary choices affect the set of equations generated for solving a customizable circuit.
- Exploiting the IEEE 1149.1 Standard for Software Reliability Evaluation in Space ApplicationsPublication . Zenha-Rela, M.; Cunha, J.C.; Santos, L.E.; Gameiro, M.; Gonçalves, P.; Alves, Gustavo R.; Fidalgo, André Vaz; Fortuna, P.; Maia, R.; Henriques, L.; Costa, D.The IEEE 1149.1 standard (boundary-scan) was originally developed as a technology to provide in-circuit testing of digital devices. Its effectiveness lead to unanticipated successes such as its extension to support on-line monitoring and in-circuit emulation. Meanwhile, its applicability for fault-injection had already been demonstrated by academic prototypes. In this paper we describe the first commercial tool, the BSCAN4FI plug in for Xception®, that provides support for software reliability evaluation for aeronautics and space applications using the boundary-scan technology as a means for controlled fault-injection. This tool allows transparent integration testing without any modification to the original system to be deployed and was developed specifically for the SPARC V.7 TSC695f space processor. Besides extended fault models and test features only made possible through this technology, in-system non-intrusive monitoring capabilities are also made possible.
- Evolutionary Techniques in Circuit Design and OptimizationPublication . Reis, Cecília; Tenreiro Machado, J. A.; Cunha, J. BoaventuraSeveral Evolutionary Algorithms (EAs) are applied in the design and optimization of digital circuits, namely Genetic Algorithms (GAs), Memetic Algorithms (MAs) and swarm intelligence with Particle Swarm Optimization (PSO). GAs are optimization and search techniques based on the principles of genetics and natural selection. MAs are evolutionary algorithms that include a stage of individual optimization as part of its search strategy, being the individual optimization in the form of a local search. The combination of a global and a local search is a strategy used by many successful hybrid optimization approaches. PSO is a population-based search algorithm that starts with a population of random solutions called particles. In a PSO scheme each particle flies through the search space with a velocity that is adjusted dynamically according with its historical behavior. Therefore, the particles have a tendency to fly towards the best search area along the search process. In this line of thought, this paper presents the results for digital circuits design using the three above EAs.
- Particle swarm optimization versus genetic algorithm in manipulator trajectory planningPublication . Pires, E. J. Solteiro; Oliveira, P. B. Moura; Tenreiro Machado, J. A.; Cunha, J. BoaventuraThe aim of this study is the reduction of the computational burden associated with the evolutionary optimization of manipulator trajectory planning. This paper proposes the use of a particle swarm optimization algorithm to generate trajectories for robotic planar manipulators, based on direct kinematics. The design objective is to minimize the ripple in the trajectory time evolution. Several redundant and hyperredundant manipulators are considered. The particle swarm optimization algorithm is compared with genetic algorithm in solving the manipulator trajectory planning problem. Preliminary simulation results are presented.
- Optimum Gait Selection for Quadruped RobotsPublication . Silva, Manuel; Tenreiro Machado, J. A.This paper studies periodic gaits of quadruped animals and its application to multilegged artificial locomotion systems. The purpose is to determine the best set of gait and locomotion variables during walking, for different robot velocities and intrabody compliance characteristics, based on two formulated performance measures. A set of experiments reveals the influence of the gait and locomotion variables upon the proposed indices, namely that the gait and the locomotion parameters should be adapted to the robot forward velocity and to the robot intra-body compliance characteristics.
- Application of Genetic Algorithms to the Implementation of Fractional Electromagnetic PotentialsPublication . Jesus, Isabel S.; Tenreiro Machado, J. A.; Cunha, J. BoaventuraA genetic algorithm (GA) is a search technique based on the natural selection process. The GAs provide further flexibility and robustness that are unique for signal process. Recently, a closer look of some phenomena present in electrical systems, such as motors, transformers and lines, and the motivation towards the development of comprehensive models, seem to point out the requirement for a fractional calculus approach. Bearing these ideas in mind, we address the analysis and the synthesis of fractional-order multipoles, based in a GA optimization scheme.
- Comparison of Different Fractional Order PD0.5 Control Algorithm Implementations for Legged RobotsPublication . Silva, Manuel; Tenreiro Machado, J. A.; Barbosa, RamiroThis paper studies different Fractional Order (FO) PD0.5 algorithms applied to the leg joint control of a hexapod robot with two dof legs. For the implementation of the FO PD0.5 joint controllers both the Padé and the series approximations are considered, being compared their performance. For simulation purposes the robot prescribed motion is characterized through several locomotion variables and parameters and for the walking performance evaluation two indices are used, one of them based on the mean absolute density of energy per travelled distance and the other one on the hip trajectory errors. A set of simulation experiments reveals the influence of the different approximations and the order of the PD0.5 controllers tuning upon the proposed indices.
- Fractional PDª control of an hexapod robotPublication . Silva, Manuel; Tenreiro Machado, J. A.This paper studies the performance of a Fractional Order PDª controller in a hexapod robot with three dof legs and leg joint actuators having saturation. For that objective the robot prescribed motion is characterized in terms of several locomotion variables. Moreover, two indices measure the walking performance based on the mean absolute density of energy per travelled distance and on the hip trajectory errors. A set of simulation experiments reveals the influence of the different controller tuning upon the proposed indices.
- Prenatal exposure to cocaine and enriched environmentPublication . Magalhães, Ana; Summavielle, Teresa; Melo, Pedro; Rosa, Rui; Tavares, Maria Amélia; Sousa, Liliana deExposure to cocaine throughout gestation may produce several deleterious outcomes in the offspring that include effects on neurotransmitter systems and structure of the central nervous system. Such changes are most likely correlated with behavioral alterations. Environmental enrichment (EE) in early stages is a factor that affects structural and behavioral development. This article examines the effects, upon social interactions, of EE during the first month of life in rats prenatally exposed to cocaine. Wistar dams were subcutaneously exposed to 60 mg/kg of cocaine divided in two daily doses from gestational day (GD)8 to GD22. Pair-fed controls were given saline vehicle in the same protocol. Offspring were distributed to the different environments in four experimental groups. Group 1: offspring from dams prenatally exposed to cocaine as previously described and reared in EE from postnatal day (PND)1 to PND28; Group 2: pups from cocaine-exposed dams and reared in a standard environment (SE); Group 3: pups from pair-fed saline-exposed dams and reared in EE; Group 4: offspring from saline-exposed dams and reared in SE. On PND21, 24, and 28, rats were examined in several social behavioral categories (play fighting, social investigation, comfort behaviors, and solicitation to play) for 10 min. Animals reared in SE do not display any differences due to treatment in the behavioral categories analyzed. Control offspring reared in EE presented decreased play fighting, decreased solicitation to play, and decreased social investigation compared to the control SE group, while cocaine-exposed animals reared in EE did not present these variations. These results suggest that EE rearing may unmask hidden effects of prenatal cocaine exposure.
- MDA in adolescent male rats - decreased serotonin in the amygdala and behavioral effects in the elevated plus-maze testPublication . Faria, Raquel; Magalhães, Ana; Monteiro, Pedro; Silva, Joana Gomes da; Tavares, Maria Amélia; Summavielle, TeresaLong-term behavioral consequences of the neurotoxicity produced by 3,4-methylenedioxymethamphetamine (MDMA) in the adolescent rat are still mostly unknown. Here, adolescent male rats (postnatal day 45 PND [45]) were exposed to 10 mg/kg of MDMA, intraperitoneally, every 2 h for 6 h. Controls were given 0.9% saline in the same protocol. Ten days after exposure, the behavioral effects of MDMA were assessed in the elevated plus-maze (n = 6 per group). After behavioral testing, animals were sacrificed and the amygdalae were dissected and processed for HPLC determination of dopamine (DA), serotonin (5-HT), and metabolites. Results showed a significant decrease in the 5-HT content (P < 0.05), but no significant alterations in DA or its metabolites. Behavioral observation in the elevated plus-maze showed a decreased number of entries in the unprotected arms (P < 0.05), which were correlated to the number of entries and time spent in the central platform. Rearing was also decreased (P < 0.05). No differences were observed in head dips, grooming, or number of entries in the protected arms of the apparatus. Therefore, we conclude that, as in the adult rat, exposure to MDMA in the adolescent rat is associated to long-term depletion of the 5-HT content and increased anxiety-like behavior.