Intelectuales y sociedad civil en el periodo de la reforma

Just as the nature of the concept has changed in the last decades, the involvement of the intelligentsia has also gone through various phases. In this paper, we shall attempt to describe these successive attitudes and analyse the factors which underlie the changes that have taken place.Así como el concepto de sociedad civil ha sufrido cambios a lo largo de las últimas décadas, la implicación de los intelectuales chinos también ha pasado por diferentes fases. En este artículo trataremos de describir las sucesivas actitudes y analizaremos los factores subyacentes a los cambios que han tenido lugar

Input-output decoupling and linearization of nonlinear two-input two-output time-varying delay systems

International audienceIn this paper, we study the input-output decoupling and linearization of nonlinear two-input two-output time-varying delay systems. When working with delay systems, two problems may arise when constructing a feedback transformation for which the input-output map of the feedback modified systems is linear. The first issue is the boundedness of the control and the second one is its causality. We develop an algorithm allowing the construction of a causal and bounded feedback which permits to solve the input-output decoupling and linearization problem. The idea of our algorithm is to introduce, at each step, when the input-output decoupling is not possible, an artificial delay for the input that appears " too early " in the system. To that end, we propose, at each step, a precise procedure for defining a simple feedback transformation

Modified Cramér-Rao lower bound for TOA and symbol width estimation. An application to search and rescue signals

International audienceThis paper focuses on the performance of time of arrival estimators for distress beacon signals which are defined by pulses with smooth transitions. These signals are used in the satellite-based search and rescue Cospas-Sarsat system. We propose a signal model based on sigmoidal functions. Closed-form expressions for the modified Cramér-Rao bounds associated with the parameters of this model are derived. The obtained expressions are easy to interpret since they analytically depend on the system parameters. Simulations conducted on realistic search and rescue signals show good agreement with the theoretical results

Application of homogeneous observers with variable exponent to a mechatronic system

International audiencePreventive maintenance becomes nowadays more and more essential in many industrial applications. In fact, researchers are always looking for new techniques and analysis tools to monitor the dynamic behavior of their machines. In this context, firstly, we deal with the modeling of an electromechanical system which is accounted for by a hybrid model obtained by assembling the mechanical model of a gear element and the electrical model of an asynchronous motor. Secondly, we use Sliding Mode Observers to supervise the gear dynamic behavior. The observers parameters are suitably chosen to ensure rapid and accurate convergence between the real and the estimated system quantities. Finally, a comparative study between three simulations is presented in order to illustrate the observers performances and the influence of the mechanical dynamics on the electrical ones

Bornes de Cramér-Rao modifiées pour le temps d'arrivée et la période symbole. Application aux signaux de recherche et de sauvetage

National audienceCet article étudie la performance des estimateurs de temps d’arrivée de signaux de détresse qui sont définis par des formes d’onde ayant des transitions douces. Ces signaux sont utilisés dans le système de recherche et sauvetage par satellite Cospas-Sarsat. Nous proposons un modèle de signal basé sur des transitions sigmoïdales. Des expressions analytiques des bornes de Cramér-Rao modifiées associées aux paramètres de ce modèle sont déterminées. Les expressions obtenues sont faciles à interpréter, car elles dépendent analytiquement des paramètres du système. Des simulations effectuées avec des signaux réalistes concordent avec les résultats théoriques

Electro-mechanical system control based on observers

International audienceThe prediction of the gear behavior is becoming major concerns in many industries. For this reason, in this article, an electro-mechanical modeling is developed in order to simulate a gear element driven by an asynchronous motor. The electrical part, which is the induction motor, is simulated by using the Kron's model while the mechanical part, which is the single stage gear element, is accounted for by a torsional model. The mechanical model that simulates the pinion-gear pair is obtained by reducing the degree of freedom of the global spur or helical gear system. The electrical and mechanical state variables are combined in order to obtain a unique differential system that describes the dynamics of the elecro-mechanical system. The global coupled electro-mechanical model can be characterized by a unique set of non-linear state equations. The contribution of this work is to apply the control based on observers in order to supervise the electrical and mechanical behavior of the electro-mechanical system from only its inputs and its measurements outputs (sensors outputs). Some simulations on pinon/motor angular speed, electromagnetic torque, currents, are presented, which illustrate the system evolution (i.e., the electrical and mechanical quantities) and the good performances of the proposed observers

Periodic averaging with a second order integral error

International audienceIn this paper, we study a variation of second order periodic averaging that allows an asymptotic reconstruction of the " fast " variable. Our goal is to present a simpler method to obtain a second order estimate based on changing the initial condition of the averaged system and approaching a " moving " average of the solutions instead of the solutions themselves. This idea was already present in a publication by the first author, in the context of solving an optimal control problem with averaging techniques and application to low thrust orbit transfer. Namely, adding well suited second order terms to the average system, properly choosing the initial condition for the average system and measuring errors " in the mean " instead of point-wise yields an errors of order 2 with respect to ε on the slow variable and of order 1 for the fast variable

Further remarks on input-output linearization of SISO time-varying delay systems

International audienceIn this paper, the problem of input-output linearization of nonlinear single-input single-output time-varying delay systems (with delays in the input and the output) is discussed and illustrated via several examples. Sufficient conditions have been recently developed by the authors. Here, we propose to discuss these conditions and give some insight allowing to improve them