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Ammar S.,Institute Superieur Dinformatique Et Du Multimedia Of Sfax | Hammami M.A.,University of Sfax | Jerbi H.,University of Sfax | Vivalda J.C.,French Institute for Research in Computer Science and Automation
Journal of Dynamical and Control Systems | Year: 2010

This work is a continuation of [2] and [1] in which the authors studied the preservation of the observability and observer under sampling. In this paper, by relaxing some hypotheses, we study the observability and stabilization problems for a sampled bilinear system. We give a characterization of the observability for such systems. Moreover, under some sufficient conditions, we show that the sampled of the bilinear system can be globally asymptotically stabilizable using a state observer. © 2010 Springer Science+Business Media, LLC. Source


Benabdallah A.,Institute Superieur Dinformatique Et Du Multimedia Of Sfax | Kallel J.,Institute Preparatoire Aux Etudes Dingenieurs Of Sfax
Nonlinear Dynamics | Year: 2011

In this paper we propose sufficient conditions for the robust stability of time-invariant uncertain piecewise-linear systems using homogeneous polynomial Lyapunov functions. The proposed conditions are expressed in terms of linear matrix inequalities, which can be numerically determined. We solve the stabilization of piecewise uncertain linear control systems by using state piecewise-linear feedback. We propose an illustrative example to show the efficiency of the proposed approach. © 2010 Springer Science+Business Media B.V. Source


Aouicha M.B.,CNRS Toulouse Institute in Information Technology | Tmar M.,Institute Superieur Dinformatique Et Du Multimedia Of Sfax | Boughanem M.,CNRS Toulouse Institute in Information Technology
Proceedings of the ACM Symposium on Applied Computing | Year: 2010

The goal of an XML retrieval system is to select from a set of XML documents all elements (nodes) that fit the user information need, usually expressed by a set of keywords with some structural conditions. Structural conditions are simply given by an ordered list of tag names that gives the target element where to search for relevant content. Consequently a potential relevant node should not only contain similar text to the query but also its localization path should fit the structural conditions. We describe in this paper a new approach for ranking XML content-and-structure queries based on a probabilistic combination of two independent scores assigned to each XML element: content score and structural score. Content score measures the content similarity between an element and a query, the structural score measures the path similarity between an element path and the structural conditions of a query. We showed experimentally that both scores follow well-known distributions. We then proposed a probabilistic combination of these distributions in order to assign a final score to each node. Some experiments have been undertaken on a dataset provided by INEX to show the effectiveness of our approach. We emphasize our experiments on the VVCAS task which is appropriate to our model. © 2010 ACM. Source


Ammar S.,Institute Superieur Dinformatique Et Du Multimedia Of Sfax | Feki H.,University of Sfax | Vivalda J.-C.,French Institute for Research in Computer Science and Automation | Vivalda J.-C.,University of Lorraine | Vivalda J.-C.,French National Center for Scientific Research
International Journal of Control | Year: 2014

This work is a continuation of the study of the problem of the preservation of the observability under sampling. In this paper, we establish that, for a bilinear system, the property of observability is preserved after sampling provided that the controls take their values in a compact space of Rm and do not vary too quickly. © 2013 © 2013 Taylor & Francis. Source


Ammar S.,Institute Superieur Dinformatique Et Du Multimedia Of Sfax | Mabrouk M.,Faculte des science de Gabes
International Journal of Control | Year: 2010

The objective of the work is twofold. First, we investigate the problem of observer design for a class of systems in cascade form. We suppose that an observer exists for each subsystem and then prove that this interconnection is an observer for the overall system. One of both nonlinear functions is assumed to be not Lipschitz (e.g. to satisfy a quadratic constraint on the unmeasured part of the state). This first main result may be viewed as an improvement of Besancon and Hammouri (Besancon, G., and Hammouri, H. (1998), 'On Observers Design for Interconnected Systems', Journal of Mathematical Systems, Estimation and Control, 8, 377-380) in which the authors discussed the problem of the synthesis of interconnected observers. The second part is a generalisation of Ammar, Mabrouk, and Vivalda (Ammar, S., Mabrouk, M., and Vivalda, J.-C. (2009), 'Observer and Global Output Feedback Stabilisation for Some mechanical Systems', International Journal of Control, 82, 1070-1081) in which the authors study the problem of output feedback stabilisation for a class of Euler-Lagrange systems. The problem of global output feedback stabilisation of the practical system called the two-link manipulator system is solved. The output feedback scheme presented has better performance than the one exhibited in Ammar et al. (2009). © 2010 Taylor & Francis. Source

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