Browsing by Issue Date, starting with "2006-02"
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- Fractional order electrical impedance of fruits and vegetablesPublication . Jesus, Isabel S.; Tenreiro Machado, J. A.; Cunha, J. Boaventura; Silva, ManuelThe idea of fractional calculus is not new. Fractional derivatives are almost as old as integer-order definition. In 1695 Leibniz discussed this problem with L’Hospital, but many other contributions are due to investigators such as Liouville, Abel, Heaviside and Riemann, that formalized the theory of the non-integer order systems. The area of fractional calculus has primarily been the domain of mathematicians, and only had the theoretical foundation. Nowadays, this concept is employed in physics, engineering, biology, economy and other scientific fields. In our work, we apply the concepts of fractional calculus and the theory of electrical impedance to botanical elements. The fractional order behaviour of these type of systems are studied and the relation with the electrical impedance is formulated.
- Modeling and simulation of walking robots with 3 dof legsPublication . Silva, Manuel; Tenreiro Machado, J. A.; Jesus, Isabel S.This paper describes a simulation model for a multilegged locomotion system with 3 dof legs and leg joint actuators having saturation. For that objective the robot prescribed motion is characterized in terms of several locomotion variables. Moreover, the robot body is divided into several segments in order to emulate the behavior of an animal spine. A non-linear spring-dashpot system models the foot-ground interaction, being its parameters computed from studies on soil mechanics. To conclude, the performance of the developed model is evaluated through a set of experiments while the robot leg joints are controlled using a proportional and derivative algorithm.
- OCD-FI, On-Chip Debugging and Fault Injection for validating microprocessor based dependable systemsPublication . Fidalgo, André Vaz; Alves, Gustavo R.; Ferreira, José M.This paper proposes a set of modifications to the on-chip debugging infrastructures present in many actual microprocessor cores, with the objective of supporting the validation and verification steps of fault-tolerant mechanisms through fault injection campaigns. A synthesisable microprocessor core for programmable components was used as a target system an. a debugging infrastructure compliant with the NEXUS 5001 proposed standard for on- chip debugging was implemented on this target. To improve the process of real-time memory fault injection, an upgraded infrastructure designated as On-Chip Debugging and Fault Injection (OCD-FI) was developed. The complete system was analysed in terms of area overhead and fault injection capabilities and performance. All elements were designed as synthesizable VHDL modules and evaluated in simulation.
- Assessing Defragmentation Strategies for FPGAsPublication . Gericota, Manuel G.; Alves, Gustavo R.; Lemos, Luís; Ferreira, José M.Fragmentation on dynamically reconfigurable FPGAs is currently a major obstacle to the efficient management of its logic space. When resource allocation decisions have to be made at run-time a relocation of currently running functions may be necessary to release enough contiguous resources to implement incoming functions. Relocation should have into account any specifics of function’s functionality and also those of the FPGA’s architecture as to not affect system’s performance. A simple and fast method to assess performance degradation of a function during relocation is proposed in this paper. This method is based on previous function labelling and on the new concept of proximity vectors.