Abstract
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.

Abstract
Actually, the electric energy has a high importance in all activities, namely, the economic activity and on its development. Sectors of activity like, communications, transports, illumination and many others industrial processes are sustained. With the increase of the global energy needs, and considering the Kyoto's protocol, the importance of green power as been increased. Based in that scenario, it's easy to understand the appearance of new low capacity producers, which should satisfy certain operation parameters to be connected to the network. Connections of small electric energy producers lead to some problems related with the voltage stability on transport and distribution systems, being crucial the satisfaction of several parameters with the objective to guarantee the electric system stability. In this article, the state of the art for the stability problems in power systems is made, being specially analyzed the Portuguese case. It's also analyzed lower producers response on voltage collapse and the parameters that they should satisfy in those situations.

Abstract
Voltage stability has been of the major concern in power system operation. To prevent these problems, technical staff evaluates frequently the distance of the operation state to the voltage collapse point. This distance normally is calculated with power flow equations. This classic technique is very slow for electric power systems with large dimension. In abnormal exploration situations it may introduce serious limitation in the voltage stability analysis process. So, the application of a fast and reliable evaluation technique is very important to diminish the evaluation time. This paper presents a study of the application of artificial neural network (ANN) to the evaluation of this distance to the voltage collapse point. To detection the point of collapse the new method FSQV was used.

Abstract
The paper proposes a simulation model which enables the evaluation of IEEE 802.11e EDCA networks, focusing in the behavior of the Enhanced Distributed Channel Access (EDCA) function associated to Quality of Service (QoS) stations. When compared with currently used simulation models, the proposed model provides a more accurate implementation of some aspects (timeouts, EIFS), a flexible implementation, and an easiness of use. Besides, a large number of different types of performance measures can be obtained. The model is based on a high level Stochastic Petri Net formalism referred as Stochastic Activity Networks (SAN), able to produce very compact and efficient models, and which is supported by the Mobius tool.

Abstract

Abstract
A partial component is a process which fails or dies at some stage, thus exhibiting a finite, more ephemeral behaviour than expected. Partiality-which is the rule rather than exception in formal modelling-can be treated mathematically via totalization techniques. In the case of partial functions, totalization involves error values and exceptions. In the context of a coalgebraic approach to component semantics, this paper argues that the behavioural counterpart to such functional techniques should extend behaviour with try-again cycles preventing from component collapse, thus extending totalization or transposition from the algebraic to the coalgebraic context. We show that a refinement relationship holds between original and totalized components which is reasoned about in a coalgebraic approach to component refinement expressed in the pointfree binary relation calculus. As part of the pragmatic aims of this research, we also address the factorization of every such totalized coalgebra into two coalgebraic components-the original one and an added front-end-which cooperate in a client-server style.