École normale supérieure de Cachan

About: École normale supérieure de Cachan is a education organization based out in Cachan, Île-de-France, France. It is known for research contribution in the topics: Decidability & Nonlinear system. The organization has 2717 authors who have published 5585 publications receiving 175925 citations.

Redox-controlled fluorescence modulation (electrofluorochromism) in triphenylamine derivatives

Abstract: The study of the chemical and electrochemical fluorescence switching properties of a family of substituted triphenylamine derivatives is reported. First of all, the synthesis of a family of six compounds is described. They are characterized by electrochemistry, UV-vis and fluorescence spectroscopy and spectroelectrochemistry. Theoretical calculations were performed in order to corroborate the experimental results. While these compounds emit blue to green light under UV irradiation with a large quantum yield (37%) in the case of one molecule, the fluorescence intensity is quenched upon oxidation. The fluorescence behavior can be switched between the strong fluorescent (neutral) state and the non-fluorescent (oxidized) state with a high contrast (around 1500 for the fluorescence intensity for one of these molecules). Furthermore, the chromatic contrast of three of these molecules reaches 70% that can be important for further applications.

A variational model for the restoration of MR images corrupted by blur and Rician noise

Abstract: In this paper, we propose a variational model to restore images degraded by blur and Rician noise. This model uses total variation regularization with a fidelity term involving the Rician probability distribution. For its numerical solution, we apply and compare the L2 and Sobolev (H1) gradient descents, and the iterative method called split Bregman (with a convexified fidelity term). Numerical results are shown on synthetic magnetic resonance imaging (MRI) data corrupted with Rician noise and Gaussian blur, both with known standard deviations. Theoretical analysis of the proposed model is briefly discussed.

Light-Driven Directed Motion of Azobenzene-Coated Polymer Nanoparticles in an Aqueous Medium

Abstract: Azobenzene-coated polymer nanoparticles in the 16-nm-diameter range act as phototriggered nanomotors combining photo to kinetic energy conversion with optical control through light intensity gradients. The grafted dyes act as molecular propellers: their photoisomerization supplies sufficient mechanical work to propel the particles in an aqueous medium toward the intensity minima with velocities of up to 15 μm/s. It is shown that nanoparticles can be driven over tens of micrometers by translating the intensity gradients in the plane. The analysis of the particles motion demonstrates the decisive role of photoisomerization in the transport with a measured driving force that is 3 to 4 orders of magnitude higher than optical forces.

Thermal tempering simulation of glass plates: inner and edge residual stresses

Abstract: Narayanaswamy's model is used to describe the thermomechanical behavior of glass. It includes both stress relaxation (to take into account the viscous aspect of glass) and structural relaxation (to take into account the structure state of glass). The necessary thermal and mechanical characteristics are given for the float soda-lime silicate glass. The thermal tempering of thin glass plates is simulated. Transient and residual stresses are given for the inner part of the plate. Computational results are compared with experimental results of previous works. This comparison validates Naranaswamy's model associated with material characteristics given previously. The edge effect (variation of stresses close to the edges) is described for thin plates. The thermal tempering of thick plates is simulated, and computational results are validated with optical measurements and a fractographic analysis.

Guarded Negation

Abstract: We consider restrictions of first-order logic and of fixpoint logic in which all occurrences of negation are required to be guarded by an atomic predicate. In terms of expressive power, the logics in question, called GNFO and GNFP, extend the guarded fragment of first-order logic and the guarded least fixpoint logic, respectively. They also extend the recently introduced unary negation fragments of first-order logic and of least fixpoint logic.We show that the satisfiability problem for GNFO and for GNFP is 2ExpTime-complete, both on arbitrary structures and on finite structures. We also study the complexity of the associated model checking problems. Finally, we show that GNFO and GNFP are not only computationally well behaved, but also model theoretically: we show that GNFO and GNFP have the tree-like model property and that GNFO has the finite model property, and we characterize the expressive power of GNFO in terms of invariance for an appropriate notion of bisimulation.Our complexity upper bounds for GNFO and GNFP hold true even for their “clique-guarded” extensions CGNFO and CGNFP, in which clique guards are allowed in the place of guards.