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Local controllability of 1D Schrödinger equations with bilinear control and minimal time
No full textInternational audienceWe consider a linear Schrödinger equation, on a bounded interval, with bilinear control. Beauchard and Laurent proved that, under an appropriate non degeneracy assumption, this system is controllable, locally around the ground state, in arbitrary time. Coron proved that a positive minimal time is required for this controllability, on a particular degenerate example. In this article, we propose a general context for the local controllability to hold in large time, but not in small time. The existence of a positive minimal time is closely related to the behaviour of the second order term, in the power series expansion of the solution
Shape optimization with a level set based mesh evolution method
No full textInternational audienceIn this article, we discuss an approach for geometry and topology optimization of structures which benefits from an accurate description of shapes at each stage of the iterative process - by means of a mesh amenable for mechanical analyses - while retaining the whole versatility of the level set method when it comes to accounting for their evolution. The key ingredients of this method are two operators for switching from a meshed representation of a domain to an implicit one, and conversely; this notably brings into play an algorithm for generating the signed distance function to an arbitrary discrete domain, and a mesh generation algorithm for implicitly-defined geometries
Quick reachability and proper extension for problems with unbounded controls
No full textParallel sessionInternational audienceFor a CONTROL SYSTEM of the form _ x = f (x; u; v) + Σm =1 g (x)u_ ; on [0;T]; (x; u)(0) = ( x; u); with x : [0;T] ! IRn; u : [0;T] ! U IRm; v : [0;T] ! V IRl ; we rely on the notion of LIMIT SOLUTION, and we investigate whether minimum problems with L1controls are PROPER EXTENSIONS of regular problems with more regular controls (AC or BV). Motivation: optimality conditions, numerical methods, etc
Global weak solutions to magnetic fluid flows with nonlinear Maxwell-Cattaneo heat transfer law
No full text28We discuss the equations describing the dynamic of the heat transfer in a magnetic fluid flow under the action of an applied magnetic field. Instead of the usual heat transfer equation we use a generalization given by the Maxwell-Cattaneo law which is a system satisfied by the temperature and the heat flux. We prove a global existence of weak solutions to the system having a finite energy
Wireless Flexible Strain Sensor Based on Carbon Nanotube Piezoresistive Networks for Embedded Measurement of Strain in Concrete
No full textInternational audienceThis work proposes a new type of low-cost strain sensor, based on piezoresistive carbon nanotube (CNT) network deposited on a flexible substrate. Experimental results show that the strain can be reliably measured thanks to the highly linear piezoresistive behaviour of the CNT network and thanks to temperature compensation capabilities. Moreover, the experimental results show the capability of measuring multiple loading cycles. The performance and the range of sensitivity of the device, suggest possible usage in the domain of embedded monitoring, in particular the detection of micro-strain and micro-cracking in concrete. In order to target this domain, a wireless RFID solution to embed the sensor into concrete is provided
Flexible Routes to Thiophenes
No full textThree convergent routes to thiophenes are described, hinging on the radical addition of α-xanthyl ketones to ethyl vinyl sulfide or to vinyl pivalate. The latter route ultimately proved to be the most versatile and efficient (61-94%)
Splitting trees with neutral mutations at birth
No full text26 pagesInternational audienceWe consider a population model where individuals behave independently from each other and whose genealogy is described by a chronological tree called splitting tree. The individuals have i.i.d. (non-exponential) lifetime durations and give birth at constant rate to clonal or mutant children in an infinitely many alleles model with neutral mutations. First, to study the allelic partition of the population, we are interested in its frequency spectrum, which, at a fixed time, describes the number of alleles carried by a given number of individuals and with a given age. We compute the expected value of this spectrum and obtain some almost sure convergence results thanks to classical properties of Crump-Mode-Jagers (CMJ) processes counted by random characteristics. Then, by using multitype CMJ-processes, we get asymptotic properties about the number of alleles that have undergone a fixed number of mutations with respect to the ancestral allele of the population
The quasi-electrostatic mode of chorus waves and electron nonlinear acceleration
No full textInternational audienceSelected Time History of Events and Macroscale Interactions During Substorms observationsat medium latitudes of highly oblique and high-amplitude chorus waves are presented and analyzed. Thepresence of such very intense waves is expected to have important consequences on electron energizationin the magnetosphere. An analytical model is therefore developed to evaluate the efficiency of the trappingand acceleration of energetic electrons via Landau resonance with such nearly electrostatic chorus waves.Test-particle simulations are then performed to illustrate the conclusions derived from the analytical model,using parameter values consistent with observations. It is shown that the energy gain can be much largerthan the initial particle energy for 10 keV electrons, and it is further demonstrated that this energy gain isweakly dependent on the density variation along field lines
D’Italie et d’ailleurs. Mélanges en l’honneur de Pierre Milza
No full textInternational audience[4e de couverture] Depuis le début de sa carrière, Pierre Milza est un passeur de frontières dans toutes les acceptions du mot, géographique et linguistique, académique et thématique. Il a ainsi construit une œuvre historique originale, féconde, en perpétuelle évolution, dans des domaines aussi divers que l’histoire de l’Italie, l’histoire de l’immigration et des relations internationales, l’histoire politique et culturelle, en particulier celle des fascismes et des extrêmes droites. En tant qu’enseignant et auteur de manuels du secondaire et du supérieur, il a aussi marqué des générations de lycéens et d’étudiants, particulièrement à Sciences Po.En rassemblant des textes inédits, dont les auteur(e)s ont pour la plupart mené leur doctorat sous sa direction, ce volume se propose de donner un aperçu du rayonnement de Pierre Milza sur l’historiographie contemporaine et de rendre hommage au caractère foisonnant, inventif et multiforme de ses travaux
The homogenized behavior of unidirectional fiber-reinforced composite materials in the case of debonded fibers
No full textInternational audienceThis paper is devoted to the analysis of the homogenized behavior of unidirectional composite materials once the fibers are debonded from (but still in contact with) the matrix. This homogenized behavior is built by an asymptotic method in the framework of the homogenization theory. The main result is that the homogenized behavior of the debonded composite is that of a generalized continuous medium with an enriched kinematics. Indeed, besides the usual macroscopic displacement field, the macroscopic kinematics contains two other scalar fields. The former one corresponds to the displacement of the matrix whereas the two latter ones correspond to the sliding and the rotation of the debonded fibers with respect to the matrix. Accordingly, new homogenized coefficients and new coupled equilibrium equations appear. This problem is addressed in a linear elastic three-dimensional setting