Browsing by Issue Date, starting with "2009-11"
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- A contratação a termo na Administração PúblicaPublication . Machado, Maria JoãoSumário: Introdução. Natureza imperativa do regime. Fundamentos. Forma e formalidades. Duração. Renovação. Caducidade. Proibição de conversão do contrato de trabalho a termo em funções públicas. Regime de protecção dos trabalhadores contratados a termo (Contratos sucessivos. Obrigação de prestar informações. Obrigações sociais. Preferência na admissão. Igualdade de tratamento. Formação profissional. Taxa social única.). Conformidade com a Directiva 1999/70/CE, do Conselho, de 28 de Junho de 1999.
- Simple Adaptive Dynamical Control of Vehicles Driven by Omnidirectional WheelsPublication . Tar, J. K.; Rudas, I. J.; Nagy, I.; Kozłowski, K. R.; Tenreiro Machado, J. A.Precise control of Automatic Guided Vehicles (AGVs) navigating between the aisles of manufacturing systems by the use of local markers is an important task. On the basis of the geometric model of the workspace and the vehicles and that of the sensor uncertainties precise trajectories were recently generated along which the vehicle safely can move. In order to achieve precise trajectory tracking the effects of the system’s dynamical uncertainties (modeling errors and possible external perturbations) have to be compensated. In the present paper a simple, fixed point transformations based adaptive control is proposed for this purpose. The proposed method is tested via simulation for a vehicle of triangular shape, driven by three omnidirectional wheels. The method is also able to monitor and evade the conditions that may lead to turning over the vehicle.
- Performance of fractional-order control of cooperative robotsPublication . Ferreira, N. M Fonseca; Tenreiro Machado, J. A.In this paper it is studied the implementation of fractional-order algorithms in the position/force control of two cooperating robotic manipulators. The system performance is analyzed in the time and frequency domains. The effect of backlash and flexibility at the robot joints is also investigated.
- Particle swarm optimization with fractional EvolutionPublication . Pires, E. J. Solteiro; Tenreiro Machado, J. A.; Oliveira, P. B. de MouraThis work presents a new perspective of the particle swarm optimization algorithm where the integer velocity is replaced by one of fractional order. The algorithm is tested for several well known functions and the relationship between the fractional order velocity and the convergence of the algorithm is observed. The fractional order velocity is analyzed showing that influences directly the algorithm convergence rate. The fractional calculus demonstrates a potencial for interpreting evolution of the algorithm and to control its convergence.
- Implementation of fractional electric potential using genetic algorithmsPublication . Jesus, Isabel S.; Tenreiro Machado, J. A.A fresh look of several phenomena present in electrical systems induced an approach based in the fractional calculus (FC) viewpoint. The problem of point multipoles with electrical charges is an important subject in the field of electromagnetism. In this work, it is applied the concept of FC to implement the electrical potential of fractional order through a genetic algorithm (GA) optimization scheme. The work is complemented by analyzing the locus of charge versus position distribution of the required electrical charges.