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A support tool for teaching grafcet : engineering students' perceptions
Leão, Celina Pinto; Oliveira, Filomena; Machado, José Mendes; Oliveira, P. B. de Moura; Cunha, J. BoaventuraModeling discrete event systems with sequential behavior can be a very hard and complex task. Some formalisms are used in this context, such as: Petri Nets, Statecharts, Finite automata, Grafcet and others. Among these, Grafcet seems to be a good choice because it is easy: to learn, to understand and to use. Teaching Grafcet is then relevant within engineering courses concerned with Industrial Automation. A vir...
Particle swarm optimization with fractional-order velocity
Pires, E. J. Solteiro; Machado, J. A. Tenreiro; Oliveira, P. B. Moura; Cunha, J. Boaventura; Mendes, LuísThis paper proposes a novel method for controlling the convergence rate of a particle swarm optimization algorithm using fractional calculus (FC) concepts. The optimization is tested for several well-known functions and the relationship between the fractional order velocity and the convergence of the algorithm is observed. The FC demonstrates a potential for interpreting evolution of the algorithm and to contro...
Adaptable control for electrical generation at irregural wind speeds
Puga, Ricardo; Ferreira, Judite; Cunha, J. Boaventura; Vale, ZitaThe main aims of this work are the development and the validation of one generic algorithm to provide the optimal control of small power wind generators. That means up to 40 kW and blades with fixed pitch angle. This algorithm allows the development of controllers to fetch the wind generators at the desired operational point in variable operating conditions. The problems posed by the variable wind intensity are...
Electrical skin phenomena: a fractional calculus analysis
Machado, J. A. Tenreiro; Jesus, Isabel S.; Galhano, Alexandra; Cunha, J. Boaventura; Tar, József K.The internal impedance of a wire is the function of the frequency. In a conductor, where the conductivity is sufficiently high, the displacement current density can be neglected. In this case, the conduction current density is given by the product of the electric field and the conductance. One of the aspects of the high-frequency effects is the skin effect (SE). The fundamental problem with SE is it attenuates ...
A fractional calculus perspective in the evolutionary design of combinational c...
Reis, Cecília; Machado, J. A. Tenreiro; Cunha, J. BoaventuraThis paper analyses the performance of a genetic algorithm (GA) in the synthesis of digital circuits using two novel approaches. The first concept consists in improving the static fitness function by including a discontinuity evaluation. The measure of variability in the error of the Boolean table has similarities with the function continuity issue in classical calculus. The second concept extends the static fi...
A silicon probe with integrated microelectronics for soil moisture measurements
Valente, A.; Cunha, J. Boaventura; Correia, J. H.; Couto, CarlosThis work presents an on-chip silicon bulk-micromachined Soil Moisture Sensor (SMS) suited for irrigation control and management applications. The same basic fabrication concepts and materials, which made microelectronics successful, are now being adapted to making low-cost, small, high-performance sensor systems with integrated electronics on the same chip. As a result, this system-on-a-chip includes the SMS, ...
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