Showing papers by "École normale supérieure de Cachan published in 2000"
TL;DR: The main classes of fluorescent molecular sensors for cation recognition are presented: they differ by the nature of the cation-controlled photoinduced processes: photoinduced electron transfer, photoinduced charge transfer, excimer formation or disappearance as discussed by the authors.
2,128 citations
1,084 citations
TL;DR: A new representation of an image which is contrast independent is set out, which is decomposed into a tree of "shapes" based on connected components of level sets, which provides a full and nonredundant representation of the image.
Abstract: This paper sets out a new representation of an image which is contrast independent. The image is decomposed into a tree of "shapes" based on connected components of level sets, which provides a full and nonredundant representation of the image. A fast algorithm to compute the tree, the fast level lines transform (FLLT), is explained in detail. Some simple and direct applications of this representation are shown.
372 citations
01 Oct 2000
TL;DR: It is said that an observed geometric event is “meaningful” if the expectation of its occurences would be very small in a random image, and this methodology is applied to the detection of alignments in images.
Abstract: We propose a method for detecting geometric structures in an image, without any a priori information. Roughly speaking, we say that an observed geometric event is “meaningful” if the expectation of its occurences would be very small in a random image. We discuss the apories of this definition, solve several of them by introducing “maximal meaningful events” and analyzing their structure. This methodology is applied to the detection of alignments in images.
362 citations
TL;DR: In this paper, a formulation for anisotropic damage is established in the framework of the principle of strain equivalence, where the damage variable is still related to the surface density of microcracks and microvoids and, as its evolution is governed by the plastic strain, it is represented by a second order tensor and is orthotropic.
Abstract: A formulation for anisotropic damage is established in the framework of the principle of strain equivalence The damage variable is still related to the surface density of microcracks and microvoids and, as its evolution is governed by the plastic strain, it is represented by a second order tensor and is orthotropic The coupling of damage with elasticity is written through a tensor on the deviatoric part of the energy and through a scalar taken as its trace on the hydrostatic part The kinetic law of damage evolution is an extension of the isotropic case Here, the principal components of the damage rate tensor are proportional to the absolute value of principal components of the plastic strain rate tensor and are a nonlinear function of the effective elastic strain energy The proposed damage evolution law does not introduce any other material parameter Several series of experiments on metals give a good validation of this theory The coupling of damage with plasticity and the quasi-unilateral conditions of partial closure of microcracks naturally derive from the concept of effective stress Finally, a study of strain localization makes it possible to determine the critical value of the damage at mesocrack initiation
326 citations
TL;DR: In this article, Boltzmann's collision operator for long-range interactions is studied without Grad's angular cut-off assumption and a functional inequality showing that the entropy dissipation controls smoothness of the distribution function is established.
Abstract: We study Boltzmann's collision operator for long-range interactions, i.e., without Grad's angular cut-off assumption. We establish a functional inequality showing that the entropy dissipation controls smoothness of the distribution function, in a precise sense. Our estimate is optimal, and gives a unified treatment of both the linear and the nonlinear cases. We also give simple and self-contained proofs of several useful results that were scattered in previous works. As an application, we obtain several helpful estimates for the Cauchy problem, and for the Landau approximation in plasma physics.
311 citations
TL;DR: In this paper, the authors studied the Cauchy problem for the homogeneous Landau equation of kinetic theory in the case of hard potentials and proved that for a large class of initial data, there exists a unique weak soluti...
Abstract: We study the Cauchy problem for the homogeneous Landau equation of kinetic theory, in the case of hard potentials. We prove that for a large class of initial data, there exists a unique weak soluti...
236 citations
TL;DR: In this article, the first-order hyperpolarizabilities of a series of mono-, bi-, and trinuclear organometallic compounds were determined using Hyper-Rayleigh Scattering at 1.06 μm.
132 citations
TL;DR: In this article, the photophysics of a fluorescent drug Piroxicam was used to probe the intramicellar region of nonionic microemulsions of Triton X-100/cyclohexane/water, using both steady-state and transient (picosecond resolution) techniques.
124 citations
TL;DR: In this article, the authors developed a damage model for concrete materials exhibiting a residual hysteretic behavior at a fixed level of damage, which is obtained by coupling damage mechanics and friction phenomena.
Abstract: This paper is concerned with the development of a damage model for concrete materials exhibiting a residual hysteretic behaviour at a fixed level of damage. This feature is obtained by coupling damage mechanics and friction phenomena. In its complete form, the damage variable by means of which the stiffness decrease is obtained in an orthotropic second-order tensor. Its evolution is governed by the tensile part of the strain tensor. The sliding between the crack lips is assumed to have a plasticity-like behaviour with non-linear kinematic hardening. The sliding stress depends on the level of damage. Such a model assumes the evolution of two yield surfaces: a fracture one and a sliding one. If unilateral effects need to be taken into account for cyclic loading analysis (crack closure modelling), the damage evolution remains isotropic. The effectiveness of this model in reproducing a part of damping when subjected to dynamic loading is exemplified through two structural case studies. Copyright © 2000 John Wiley & Sons, Ltd.
102 citations
TL;DR: In this article, it was shown that the global minimizer of the Ginzburg-Landau functional of superconductors in an external magnetic field is, below the first critical field, the vortex-less solution found in (S. Serfaty, to appear).
Abstract: We prove that the global minimizer of the Ginzburg–Landau functional of superconductors in an external magnetic field is, below the first critical field, the vortex-less solution found in (S. Serfaty, to appear).
TL;DR: In this article, the Ginzburg-Landau energy of superconductors submitted to a possibly non-uniform magnetic field was studied in the limit of a large GLE parameter κ and it was shown that the induced magnetic fields associated to minimizers of the energy-functional converge as κ →+∞ to the solution of a free-boundary problem.
Abstract: We study the Ginzburg–Landau energy of superconductors submitted to a possibly non-uniform magnetic field, in the limit of a large Ginzburg–Landau parameter κ . We prove that the induced magnetic fields associated to minimizers of the energy-functional converge as κ →+∞ to the solution of a free-boundary problem. This free-boundary problem has a nontrivial solution only when the applied magnetic field is of the order of the “first critical field”, i.e. of the order of log κ . In other cases, our results are contained in those we had previously obtained [15, 16, 14]. We also derive a convergence result for the density of vortices.
TL;DR: In this paper, a model for concrete with an emphasis on tension and compaction is developed, based on mechanics of porous materials, damage and plasticity, and simulations of a split Hopkinson test performed on confined concrete and on a concrete rod submitted to an impact have been carried out.
TL;DR: In this article, the Ginzburg-Landau energy of superconductors with high κ, put in a prescribed external field hex, for hex varying between the two critical fields Hc1 and Hc3.
Abstract: We study the Ginzburg–Landau energy of superconductors with high κ, put in a prescribed external field hex, for hex varying between the two critical fields Hc1 and Hc3. As κ → +∞, we give the leading term in the asymptotic expansion of the minimal energy and show that energy minimizers have vortices whose density tends to be uniform and equal to hex.
TL;DR: The origin of the optical nonlinearity in azo-azulene is discussed in relation with crystal structures and semiempirical calculations within the INDO/SOS formalism, and compared with that of the well known disperse red one (DR1) organic dye.
Abstract: The molecular and solid state nonlinear optical (NLO) properties of several (phenylazo)-azulenes are investigated. In particular, (4-nitrophenylazo)-azulene (2 b) exhibits a quadratic hyperpolarizability (βvec) of 80×10−30 cm5 esu recorded at 1.907 μm by the electric field-induced second-harmonic (EFISH) technique. This molecular material, which crystallizes in the monoclinic noncentrosymmetric space group Pc, exhibits an efficiency 420 times that of urea in second-harmonic generation. The origin of the optical nonlinearity in azo-azulene is discussed in relation with crystal structures and semiempirical calculations within the INDO/SOS formalism, and compared with that of the well known disperse red one (DR1) organic dye.
TL;DR: This work decomposes images into shapes, based on connected components of level sets, which can be put in a tree structure, which yields a peculiar kind of scale-space, where the information present at each scale is already present in the original image.
TL;DR: In this paper, the main features of a numerical model predicting the behavior of hydrated cement systems subjected to freezing temperatures are presented, where all equations are written at the microscopic scale and then averaged over an elementary volume of the material (mesoscopic scale).
21 Aug 2000
TL;DR: It is proved, in the spirit of the correspondence between automata and temporal logics, that the models of a Lp+ formula are recognized by a piecewise flat counter machine; this shows that validity and model-checking positive formulas are undecidable for Lp+.
Abstract: We propose an extension, called Lp+, of the temporal logic LTL, which enables talking about finitely many register values: the models are infinite words over tuples of integers (resp. real numbers). The formulas of Lp+ are flat: on the left of an until, only atomic formulas or LTL formulas are allowed. We prove, in the spirit of the correspondence between automata and temporal logics, that the models of a Lp+ formula are recognized by a piecewise flat counter machine; for each state q, at most one loop of the machine on q may modify the register values.
Emptiness of (piecewise) flat counter machines is decidable (this follows from a result in [9]). It follows that satisfiability and model-checking the negation of a formula are decidable for Lp+. On the other hand, we show that inclusion is undecidable for such languages. This shows that validity and model-checking positive formulas are undecidable.
TL;DR: The Rayleigh-Taylor instability in linear density profiles is considered and the exact analytic expressions of the growth rates and associated eigenfunctions are derived.
Abstract: We consider the Rayleigh-Taylor instability in linear density profiles and we derive the exact analytic expressions of the growth rates and associated eigenfunctions. We study the behavior of the multiple eigenvalues in both the short- and the long-wavelength limit. As the largest eigenvalue ${\ensuremath{\gamma}}_{\mathrm{max}}$ reduces to the classical Rayleigh growth rate; the other eigenvalues vanish as the front thickness tends to zero. Furthermore, the simple expression of ${\ensuremath{\gamma}}_{\mathrm{max}}$ exact to first order in the long-wavelength limit differs from the widely used estimate $\sqrt{{Akg/(1+AkL}_{0})},$ where g is the acceleration, A the Atwood number, k the wave number of the perturbation, and ${L}_{0}$ the minimum density gradient scale length.
TL;DR: In this article, a thorough study of the reactivity of the X transient towards different organic and inorganic substrates in acetonitrile and in water was performed, and the bimolecular reaction between X and the substrates was shown to occur on the nanosecond time-scale, either by H atom or electron transfer, and leads to the formation of the reduced form Y of decatungstate.
Abstract: Previous studies have put into evidence the key role of a charge transfer excited state, noted X, in the primary steps of laser photolysis of sodium decatungstate solutions. In this work, we report a thorough study of the reactivity
of the X transient towards different organic and inorganic substrates in acetonitrile and in water.
The bimolecular reaction between X and the substrates is shown to occur on the nanosecond time-scale, either
by H atom or electron transfer, and leads to the formation of the reduced form Y of decatungstate.We find
that H atom transfer reactions are ruled by Z–H (Z=C, N, O) binding energies and lead to Y formation quantum yields that may reach the X formation quantum yield, whereas electron transfer reactions are ruled by the substrates' oxidation potential (Marcus reorganisation energy λ=1.0–1.3 eV for
aromatics
in acetonitrile)
and lead to Y formation
quantum yields similar to that obtained in the pure solvent.
TL;DR: In this paper, the authors discuss the finite element implementation of the internal constraints in a 3D geometrically exact beam model which can be formulated as holonomic constraint relationships.
Posted Content•
TL;DR: In this article, the Ginzburg-Landau energy of superconductors with a term $a_\ep$ modelling the pinning of vortices by impurities was studied.
Abstract: We study the Ginzburg-Landau energy of superconductors with a term $a_\ep$ modelling the pinning of vortices by impurities in the limit of a large Ginzburg-Landau parameter $\kappa=1/\ep$. The function $a_\ep$ is oscillating between 1/2 and 1 with a scale which may tend to 0 as $\kappa$ tends to infinity.
Our aim is to understand that in the large $\kappa$ limit, stable configurations should correspond to vortices pinned at the minimum of $a_\ep$ and to derive the limiting homogenized free-boundary problem which arises for the magnetic field in replacement of the London equation.
The method and techniques that we use are inspired from those of Sandier-Serfaty (in which the case $a_\ep \equiv 1$ was treated) and based on energy estimates, convergence of measures and construction of approximate solutions. Because of the term $a_\ep(x)$ in the equations, we also need homogenization theory to describe the fact that the impurities, hence the vortices, form a homogenized medium in the material.
TL;DR: Amphiphilic cationic polyenic push-pull chromophores have been synthesized and their optical nonlinearities studied for the first time by electric field induced second harmonic (EFISH) generation in solution.
08 Oct 2000
TL;DR: In this paper, the authors presented a synchronous machine with stator ferrite permanent magnets and a salient passive rotor, which, when supplied with current by a three-phase bridge converter, produces continuous torque.
Abstract: The aim of this paper is to present the structure of a new synchronous machine with stator ferrite permanent magnets and a salient passive rotor (a robust and low-cost technology) which, when supplied with current by a three-phase bridge converter, produces continuous torque. This feature serves to place our machine on a par with the best synchronous machines available (e.g. high-energy rotor magnets with flux concentration). Furthermore, the electrical characteristics of this machine make it possible to apply the well-known flux weakening technique, which enhances the performance of the entire energy-conversion system. In theory, an operating area at constant power with unlimited speed can be obtained merely by taking into account the ohmic tension drops in the coils. Experimental results demonstrate that taking both magnetic losses and windage losses into account is necessary in order to identify the maximum mechanical output power characteristics.
TL;DR: In this article, the authors studied the squeeze flow behavior of highly concentrated suspensions of spheres in a Newtonian fluid and found that the transition between the two regimes is a result of a competition between the viscous shear forces due the flow of the suspension and the damping force caused by the filtration of the fluid through the porous media made up by the particles.
Abstract: The squeeze flow behaviour of highly concentrated suspensions of spheres in a Newtonian fluid is studied experimentally. Analysing the evolution of the squeeze force as a function of time for different controlled velocities, the suspension is found to present two main flow regimes. The first regime is characterised by the situation in which the force decreases when the velocity decreases, which corresponds to a viscous flow of the suspension. In the second regime, the force increases when the velocity decreases, which is shown to correspond to a filtration of the solvent through the particle skeleton that behaves then as a deformable porous media. By varying the concentration, the sphere diameter and the solvent viscosity, it is found that the transition between the two regimes is a result of a competition between the viscous shear forces due the flow of the suspension and the damping force caused by the filtration of the fluid through the porous media made up by the particles.
TL;DR: The designed method is a leading way for identification of potent integrase inhibitors using in silico experiments and there is no direct correlation between the binding energy of the drugs with the Mg(2+) dication and their in vitro inhibitory effect.
Abstract: Styrylquinoline derivatives, known to be potent inhibitors of HIV-1 integrase, have been experimentally tested for their inhibitory effect on the disintegration reaction catalyzed by catalytic cores of HIV-1 and Rous sarcoma virus (RSV) integrases. A modified docking protocol, consisting of coupling a grid search method with full energy minimization, has been specially designed to study the interaction between the inhibitors and the integrases. The inhibitors consist of two moieties that have hydroxyl and/or carboxyl substituents: the first moiety is either benzene, phenol, catechol, resorcinol, or salicycilic acid; the hydroxyl substituents on the second (quinoline) moiety may be in the keto or in the enol forms. Several tautomeric forms of the drugs have been docked to the crystallographic structure of the RSV catalytic core. The computed binding energy of the keto forms correlates best with the measured inhibitory effect. The docking procedure shows that the inhibitors bind closely to the crystallogra...
TL;DR: In this paper, the authors consider the stability of shape-dependent energy functional shapes and prove weak-coercivity of the second derivative uniformly in a "strong" neighborhood of the equilibrium shape.
Abstract: We discuss the stability of "critical" or "equilibrium" shapes of a shape-dependent energy functional. We analyze a problem arising when looking at the positivity of the second derivative in order to prove that a critical shape is an optimal shape. Indeed, often when positivity -or coercivity- holds, it does for a weaker norm than the norm for which the functional is twice differentiable and local optimality cannot be a priori deduced. We solve this problem for a particular but significant example. We prove "weak-coercivity" of the second derivative uniformly in a "strong" neighborhood of the equilibrium shape.
TL;DR: A hierarchy of models for gas-liquid two-phase flows in the limit of infinite density ratio, when the liquid is assumed to be incompressible is derived, and the system of pressureless gases with constraint and undetermined pressure is obtained.
Abstract: We derive a hierarchy of models for gas-liquid two-phase flows in the limit of infinite density ratio, when the liquid is assumed to be incompressible. The starting model is a system of nonconservative conservation laws with relaxation. At first order in the density ratio, we get a simplified system with viscosity, while at the limit we obtain a system of two conservation laws, the system of pressureless gases with constraint and undetermined pressure. Formal properties of this constraint model are provided, and sticky blocks solutions are introduced. We propose numerical methods for this last model, and the results are compared with the two previous models.
TL;DR: In this paper, an application of the finite element method to modeling of flexible multibody systems employing geometrically exact structural elements is discussed, and two different approaches to handle constraints, one based on the Lagrange multiplier procedure and another based on release degrees of freedom, are examined in detail.
Abstract: In this work we discuss an application of the finite elementmethod to modeling of flexible multibody systems employing geometricallyexact structural elements. Two different approaches to handleconstraints, one based on the Lagrange multiplier procedure and anotherbased on the use of release degrees of freedom, are examined in detail.The energy conserving time stepping scheme, which is proved to be wellsuited for integrating stiff differential equations, gouverning themotion of a single flexible link is appropriately modified and extendedto nonlinear dynamics of multibody systems.
TL;DR: In this article, the Ladeveze mesoscale damage model was used to study the large strain response of [±45]s laminates of graphite-fiber/polyimide-matrix composite.