Scanning and focusing mechanisms of METEOSAT radiometer

Two mechanisms, both of screw-jack type are described. The scanning mechanism, an oil lubricated and sealed unit drives and accurately positions the telescope of the METEOSAT radiometer. The dry lubricated focusing mechanism is used to adjust the focus of this telescope. The METEOSAT program is nearly completed, and the first flight model will be launched at the end of the year

Finite Time and Exact Time Controllability on Compact Manifolds

It is first shown that a smooth controllable system on a compact manifold is finite time controllable. The technique of proof is close to the one of Sussmann's orbit theorem, and no rank condition is required. This technique is also used to give a new and elementary proof of the equivalence between controllability for essentially bounded inputs and for piecewise constant ones. Two sufficient conditions for controllability at exact time on a compact manifold are then stated. Some applications, in particular to linear systems on Lie groups, are provided

Convergence Rate of Nonlinear Switched Systems

This paper is concerned with the convergence rate of the solutions of nonlinear switched systems. We first consider a switched system which is asymptotically stable for a class of inputs but not for all inputs. We show that solutions corresponding to that class of inputs converge arbitrarily slowly to the origin. Then we consider analytic switched systems for which a common weak quadratic Lyapunov function exists. Under two different sets of assumptions we provide explicit exponential convergence rates for inputs with a fixed dwell-time

Geometry of the Limit Sets of Linear Switched Systems

The paper is concerned with asymptotic stability properties of linear switched systems. Under the hypothesis that all the subsystems share a non strict quadratic Lyapunov function, we provide a large class of switching signals for which a large class of switched systems are asymptotically stable. For this purpose we define what we call non chaotic inputs, which generalize the different notions of inputs with dwell time. Next we turn our attention to the behaviour for possibly chaotic inputs. To finish we give a sufficient condition for a system composed of a pair of Hurwitz matrices to be asymptotically stable for all inputs

Isometries of almost-Riemannian structures on Lie groups

A simple Almost-Riemannian Structure on a Lie group G is defined by a linear vector field (that is an infinitesimal automorphism) and dim(G) -- 1 left-invariant ones. It is first proven that two different ARSs are isometric if and only if there exists an isometry between them that fixes the identity. Such an isometry preserves the left-invariant distribution and the linear field. If the Lie group is nilpotent it is an automorphism. These results are used to state a complete classification of the ARSs on the 2D affine and the Heisenberg groups

Stability of uniformly bounded switched systems and Observability

This paper mainly deals with switched linear systems defined by a pair of Hurwitz matrices that share a common but not strict quadratic Lyapunov function. Its aim is to give sufficient conditions for such a system to be GUAS.We show that this property of being GUAS is equivalent to the uniform observability on $[0,+\infty)$ of a bilinear system defined on a subspace whose dimension is in most cases much smaller than the dimension of the switched system.Some sufficient conditions of uniform asymptotic stability are then deduced from the equivalence theorem, and illustrated by examples.The results are partially extended to nonlinear analytic systems

Esprit critique et capacité à faire des choix: entre autorité et liberté - quels ingrédients et quelle mesure ?

Ce travail porte sur la manière de rendre les enfants autonomes psychiquement et en état de faire leur propres choix intérieurs. Afin d’être capable d’avoir une opinion personnelle sur soi et sur son environnement, l’enfant doit pouvoir créer sa propre identité, ainsi que savoir se conformer aux règles de vie en collectivité. Ces deux compétences, oscillants entre liberté d’être et autorité, peuvent être encouragées en structure d’accueil par le personnel éducatif. Ce mémoire tend à rechercher dans quelle mesure cette stimulation est apportée au quotidien, ceci en tenant compte des possibilités et des contraintes que peuvent rencontrer les professionnels(les). La transmission de ce savoir à la famille fait en outre l’objet d’une réflexion. Pour finir, une méditation sur notre capacité réelle à développer l’esprit critique des enfants conclura ce mémoire