Browsing by Issue Date, starting with "2005-05"
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- Injecção de Falhas por Varrimento Periférico em ProcessadoresPublication . Fidalgo, André; Alves, Gustavo R.; Santos, Luis F.; Zenha-Rela, MárioAs técnicas de injecção de falhas mais utilizadas podem ser classificadas em técnicas de indução, técnicas de injecão por hardware e técnicas de injecção por software. Dentro das técnicas de injecção por hardware surgem as técnicas de injecção de falhas recorrendo à tecnologia de teste por varrimento periférico. Esta encontra-se fortemente implantada nos processadores mais recentes, fornecendo um método de acesso ao seu interior de forma a permitir operações de teste e depuração. A sua utilização para a injecção de falhas é um passo lógico e tem sido estudada desde os anos 90. Os trabalhos desenvolvidos nesta área são diversos e incluem soluções que não exigem qualquer alteração à infraestrutura normalizada e soluções que modificam as células e a infraestrutura de controlo de forma a suportarem esta funcionalidade. Estas alterações implicam atrasos temporais acrescidos e um aumento da área de silício destinada a funções de teste, tornando-se importante uma preocupação com a optimização para que a inclusão de capacidades de injecção de falhas não afecte significativamente o desempenho e o custo dos componentes onde são implementadas.
- Adaptive reduction of the order of derivation in the control of a hydraulic differential cylinderPublication . Tar, József K.; Bitó, János F.; Rudas, Imre J.; Tenreiro Machado, J. A.Servo valve controlled hydraulic differential cylinders are non-linear, strongly coupled multivariable electromechanical tools applicable for driving e.g. manipulators. When the piston has finite but considerable velocity with respect to the cylinder the system’s behavior can be “linearized” because the viscous friction i.e. the main source of disturbance is smooth function of this velocity and causes linear damping. When this velocity is in the vicinity of zero the effect of adhesion is the dominating disturbance force that abruptly changes direction depending on the sign of this velocity. Furthermore, at zero relative velocity adhesion can compensate arbitrary forces within certain limits keeping the piston fixed. In the paper a concise application of the Stribeck model of friction and adhesion is reported in an adaptive control in which varying fractional order derivatives are used to reduce the hectic behavior of friction in the case of “critical” trajectories that asymptotically converge to a fixed position and zero velocity. Simulation results made by INRIA’s Scilab are presented. It is concluded that the combined application of the two adaptive techniques reported accurate control can be achieved without knowing the accurate model of the piston-cylinder system.
- Logic circuits synthesis through genetic algorithmsPublication . Reis, Cecília; Tenreiro Machado, J. A.; Cunha, J. BoaventuraThis paper proposes a genetic algorithm for designing combinational logic circuits and studies four different case examples: the 2-to-1 multiplexer, the one-bit full adder, the four-bit parity checker and the two-bit multiplier. The objective of this work is to generate a functional circuit with the minimum number of logic gates. It is also studied the scalability problem that emerges from the exponential growth of the truth table when the circuits complexity increases. Furthermore, it is as well investigated the population size and the processing time for achieving a solution in order to establish a compromise between the two parameters.
- Experimental Set-up for vibration and impact analysis in roboticsPublication . Lima, Miguel F. M.; Tenreiro Machado, J. A.; Crisóstomo, ManuelIn this paper a laboratory apparatus is presented to study vibrations and phenomena. The experimental setup consists in real time acquisition and control system that acquires signals from internal and external robotic sensors. Several signals are acquired based on several experiments, both with vibrations and impacts caused by a flexible rod or a flexible beam, showing the capabilities of the system.
- Prenatal cocaine exposure: effects on locomotor activity in rat offspringPublication . Magalhães, Ana; Summavielle, Teresa; Melo, Pedro; Tavares, Maria Amélia; Sousa, Liliana de; Summavielle, TeresaThis study examines the developmental effects of prenatal exposure to cocaine in the rat, evaluated during the first month of life through open-field behavior. The offspring of Wistar dams that received 60 mg/kg of cocaine, from gestational day 8 to 22, were examined in the open-field during the second, third and fourth weeks of postnatal life in three consecutive 15-min daily sessions, starting on postnatal day (PND) 14, (PND 14–16), PND 21 (PND 21–23) and PND 28 (PND 28–30). Results show that prenatal exposure to cocaine increased total activity and rearing behavior on PND 22 and PND 29. Also, on PND 14, cocaine-exposed animals reared significantly more than control rats. There were no significant differences in the frequency of center and peripheral ambulation, nor in the defecation rate. The present results evidence alterations in the emotional behavior of rats prenatally exposed to cocaine. The delayed onset of exploration in the open-field observed in cocaine-exposed animals suggests that they take more time to become habituated to a novel and open environment.