Browsing by Issue Date, starting with "1998"
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- Curva de Laffer - enquadramento, estudos e consideraçõesPublication . Castro, ConceiçãoCurva de Laffer - Enquadramento, Estudos e Considerações
- Fractional-order derivative approximations in discrete-time control systemsPublication . Machado, J. A. TenreiroThe theory of fractional calculus goes back to he beginning of the theory of differential calculus but its inherent complexity postponed the application of the associated concepts. in the last decade the progress in the areas of chaos and fractals revealed subtle relationships with the fractional calculus leading to an increasing interest in the development of the new paradigm. in the area of automatic control preliminay work has already been carried out but the proposed algorithms are restricted to the frequency domain. The paper discusses the design of fractional-order discrete-time controllers. the algorithms and discrete-time implementation.
- Multi-μ: an Ada 95 based architecture for fault tolerance support of real-time systemsPublication . Pinho, Luís Miguel; Vasques, FranciscoThis paper presents an architecture (Multi-μ) being implemented to study and develop software based fault tolerant mechanisms for Real-Time Systems, using the Ada language (Ada 95) and Commercial Off-The-Shelf (COTS) components. Several issues regarding fault tolerance are presented and mechanisms to achieve fault tolerance by software active replication in Ada 95 are discussed. The Multi-μ architecture, based on a specifically proposed Fault Tolerance Manager (FTManager), is then described. Finally, some considerations are made about the work being done and essential future developments.
- Analisis del impacto de latecnologia en los sistemas de información de la banca portuguesaPublication . Silva, Eduardo Sá eAnalisis del impacto de latecnologia en los sistemas de información de la banca portuguesa
- Clube de História 7Publication . Maia, Cristina; Neves, Pedro Almiro; Baptista, Dalila
- Real-time fieldbus communications using Profibus networksPublication . Tovar, Eduardo; Vasques, FranciscoThis paper provides a comprehensive study on how to use Profibus fieldbus networks to support real-time industrial communications, that is, on how to ensure the transmission of real-time messages within a maximum bound time. Profibus is base on a simplified timed token (TT) protocol, which is a well-proved solution for real-time communication systems. However, Profibus differs with respect to the TT protocol, thus preventing the application of the usual TT protocol real-time analysis. In fact, real-time solutions for networks based on the TT protocol rely on the possibility of allocating specific bandwidth for the real-time traffic. This means that a minimum amount of time is always available, at each token visit, to transmit real-time messages, transversely, with the Profibus protocol, in the worst case, only one real-time message is processed per token visit. The authors propose two approaches to guarantee the real-time behavior of the Profibus protocol: (1) an unconstrained low-priority traffic profile; and (2) a constrained low-priority traffic profile. The proposed analysis shows that the first profile is a suitable approach for more responsive systems (tighter deadlines), while the second allows for increased nonreal-time traffic throughput
- Soluções globais de suporte aos sistemas de informação do século XXIPublication . Babo, Rosalina; Machado, Altamiro
- On the describing function method and the prediction of limit cycles in nonlinear dynamical systemsPublication . Azenha, Abílio; Machado, J. A. TenreiroThis paper analyses the limit cycle characteristics of systms with nonlinear friction or dynamics backlash. The study is based on the describing function (DF) of nonlinear systems being the nonlinear blocks composed on a mass subected to nonlinear friction or two masses subjected to backlash. the rehability of the method is analysed through the extended harmonic content of the systems DFs and using the Nyquist plot of the dynamic response used in the DFs calculations. The overall systems performance is tested using classical PID controllers.
- On the Statistical/Harmonic modelling of mechanical manipulatorsPublication . Machado, J. A. Tenreiro; Galhano, Alexandra M. S. F.A new approach to the analysis and design of robot manipulators is presented. The novel feature resides on a non-standard formulation to the modelling problem. Usually, system descriptions are based on a set of differential equations which in general, require laborious computations and may be difficult to analyze. These facts motivate the need of alternative models based on different mathematical concepts. The proposed statistical approach to the Fourier modelling gives clear guidelines towards the optimization of the robot kinematics and point out structural characteristics of the trajectory planning algorithms.