Showing papers by "École normale supérieure de Cachan published in 1997"
TL;DR: An experimental analysis using Gabor filters, and in particular a comparison to quadratic distances, shows the efficiency and robustness of the method.
Abstract: We define a distance between textures for texture classification from texture features based on windowed Fourier filters. The definition of the distance relies on an interpretation of our texture attributes in terms of spectral density when the texture can be considered as a Gaussian random field. The distance between textures is then defined as a symmetrized Kullback distance which is a simple function of the attributes and does not require any normalization. An experimental analysis using Gabor filters, and in particular a comparison to quadratic distances, shows the efficiency and robustness of the method.
194 citations
TL;DR: In this article, photochromic N-salicylidene-4-bromoaniline was obtained and studied for their second-order nonlinear optical properties.
Abstract: Noncentrosymmetric crystals of photochromic N-salicylidene-4-bromoaniline are obtained and studied for their second-order nonlinear optical properties. Second harmonic light is generated and can be seen by the naked eye. Moreover, photochromism in the bulk state yields totally reversible photoswitching of the second harmonic intensity.
155 citations
TL;DR: In this paper, the authors considered the Euler equations for the propagation of gravity waves on the surface of an ideal, incompressible, inviscid fluid, and the asymptotic decay of solitary waves to a quiescent state away from their principal elevation.
120 citations
TL;DR: In this article, the basic aspects of a damage meso-model with delay effects for laminated composites are presented for fracture prediction under severe and multiaxial dynamic loading.
Abstract: The basic aspects of a damage meso-model with delay effects for laminated composites are presented. The applications concern fracture prediction under severe and multiaxial dynamic loading. In order to illustrate the possibilities and the mechanical significance of the proposed model for the prediction of rupture, especially the role of the delay effect, various simulations of one-dimensional wave propagation are performed. Then, a more complex finite element calculation is presented in order to show the ability of the model to predict the response of a composite structure until complete fracture.
104 citations
TL;DR: A new nonlinear control strategy is proposed for a permanent-magnet salient-pole synchronous motor which achieves accurate torque control and copper losses minimization without recurring to an internal current loop nor to any feedforward compensation.
Abstract: In this paper, a new nonlinear control strategy is proposed for a permanent-magnet salient-pole synchronous motor. This control strategy simultaneously achieves accurate torque control and copper losses minimization without recurring to an internal current loop nor to any feedforward compensation. It takes advantage of the rotor saliency by allowing the current (i/sub d/) to have nonzero values. This, in turn, allows us to increase the power factor of the machine and to raise the maximum admissible torque. We apply input-output linearization techniques where the inputs are the stator voltages and the outputs are the torque and a judiciously chosen new output. This new output insures a well-defined relative degree and is linked to the copper losses in such a way that, when forced to zero, it leads to maximum machine efficiency. The performance of our nonlinear controller is demonstrated by a real-time implementation using a digital signal processor (DSP) chip on a permanent-magnet salient-pole synchronous motor with sinusoidal flux distribution. The results are compared to the ones obtained with a scheme which forces the i/sub d/ current to zero.
94 citations
TL;DR: In economics, the use of sympathy and empathy has been used in two different senses: the first sense refers to cases where the concern for others directly affects an individual's own welfare; the second sense is associated with interpersonal comparisons of the extended sympathy type.
Abstract: In modern economics, the use of sympathy and empathy shows significant ambiguity. Sympathy has been used in two different senses. First, it refers to cases where the concern for others directly affects an individual's own welfare (Sen, 1977). Second, the term has served the purposes of welfare economics, where it is associated with interpersonal comparisons of the extended sympathy type, that is, comparisons between one's own situation in a social state and someone else's in a different social state (Arrow, 1963 [1951]). On the other hand, empathy has been used interchangeably with sympathy either to render the idea of interdependent utility functions (Leibenstein, 1976), or to convey the imaginative process of imagining oneself in someone else's place (Harsanyi, 1977).
88 citations
TL;DR: In this article, the authors deal with error estimators based on residuals on the constitutive relation which have been developed for the past 20 years at Cachan and deal with the construction of equilibrated stress fields from the computed finite element solution.
85 citations
TL;DR: In this article, the authors studied some explicit functions introduced by Riemann, Jordan, Levy, and Kahane, and proved that they are examples of multifractal functions.
Abstract: We study some explicit functions introduced by Riemann, Jordan, Levy, Kahane… These functions share the property of having a dense set of discontinuities. We prove that they are examples of multifractal functions.
68 citations
TL;DR: In this paper, a mechanical law with a simple elementary model of membrane deflection is used to demonstrate the static instability of such a system under electrostatic actuation and provide an analytical solution for the membrane position.
Abstract: Having developed a mechanical law with a simple elementary model of membrane deflection, we demonstrate the static instability of such a system under electrostatic actuation and provide an analytical solution for the membrane position. This allows us to highlight the sticking effect and the hysteresis phenomenon of the pump strike volume due to the nonlinearity of such excitation. We determine a parameter optimization procedure for the dimensions of the electrostatic actuated membrane in order to achieve maximum volume displacement.
61 citations
58 citations
TL;DR: It is shown that the use of new magnetic materials, such as the amorphous or the nanocrystalline, can improve large-current low-frequency operations, while preserving the smallest possible probe size.
Abstract: Current measurements in power electronics or in EMI domains require high-performance probes. These probes must have a very wide bandwidth, be insensitive to electromagnetic interferences, and be able to measure large direct and alternating currents (AC-DC) without distortion. This paper is limited to AC current probes. Various principles are reviewed, in particular those based on the current transformer (CT); their limitations are analyzed, and a solution based on a two-stage transformer are proposed to extend low- and high-frequency performance. It is shown that the use of new magnetic materials, such as the amorphous or the nanocrystalline, can improve large-current low-frequency operations, while preserving the smallest possible probe size. Various solutions are provided to improve high-frequency operations. Different developments are depleted; frequency and time-domain results are presented.
TL;DR: The definition of the Voronoi surfaces is extended to this new distance, and it is shown that it is possible to localize a small binary pattern in an image.
TL;DR: In this article, the role of residual hydroxyl groups is investigated and the linear electron-phonon coupling can be controlled with the choice of the organic group in organic/inorganic matrices.
TL;DR: In this paper, the gap condition between frequencies does not hold any more and a trigonometric inequality of Ingham's type for nonharmonic Fourier series is proved.
Abstract: We prove a trigonometric inequality of Ingham’s type for nonharmonic Fourier series when the gap condition between frequencies does not hold any more.
TL;DR: In this article, a remark on the asymptotic behavior of solutions of -Δu=λ ǫ(u) quand λ tend to be zero is made.
Abstract: Resume Soit Ω un domaine borne regulier de C, on s'interesse au comportement asymptotique des solutions de l'equation -Δu=λƒ(u) quand λ tend vers zero, ou ƒ est une fonction reguliere, positive, non lineaire, de comportement exponentiel a l'infini. En particulier, on generalise le resultat de Nagasaki-Suzuki (voir [7]) sur ce probleme. A remark on the asymptotic behavior of solutions of -Δu=λƒ(u)
TL;DR: In this paper, the authors studied the regularity of critical points of an energy which stems from micromagnetism theory and showed that in dimension two critical points are smooth in B 2, and in three dimensions the stationary critical points were smooth except in a subset of one dimensional Hausdorff measure zero.
Abstract: We study the regularity of critical points of an energy which stems from micromagnetism theory. First we show that in dimension two critical points are smooth in B
2
. In the three dimensional case we prove that the stationary critical points of the energy are smooth except in a subset of one dimensional Hausdorff measure zero. The particularity of this work is the non local character of one term of the energy.
29 Jun 1997
TL;DR: It is proved that ground reducibility is EXPTIME-complete in the general case and emptiness of such an automaton can be decided in time polynomial in the number of its states and exponential in the size of its constraints.
Abstract: We prove that ground reducibility is EXPTIME-complete in the general case. EXPTIME-hardness is proved by encoding the computations of an alternating Turing machine whose space is polynomially bounded. It is more difficult to show that ground reducibility belongs to DEXPTIME. We associate first an automaton with disequality constraints A/sub R,t/ to a rewrite system R and a term t. This automaton is deterministic and accepts a term u if and only if t is not ground reducible by R. The number of states of A/sub R,t/ is O(2/sup /spl par/R/spl par//spl times//spl par/t/spl par//) and the size of the constraints are polynomial in the size of R,t. Then we prove some new pumping lemmas, using a total ordering on the computations of the automaton. Thanks to these lemmas, we can give an upper bound to the number of distinct subtrees of a minimal successful computation of an automaton with disequality constraints. It follows that emptiness of such an automaton can be decided in time polynomial in the number of its states and exponential in the size of its constraints. Altogether, we get a simply exponential deterministic algorithm for ground reducibility.
TL;DR: It is proved that boundedness and reachability tree finiteness are undecidable for systems of two identical automata communicating via two perfect unbounded one-way FIFO channels and constructed solely from cycles about their initial states.
TL;DR: In this paper, a measurement of the time-resolved and steady-state fluorescence anisotropies of C60 and C70 in low-temperature organic glasses was performed.
TL;DR: In this paper, a confocal microscope setup is developed for time-resolved fluorescence measurements, which allows both decay lifetime and anisotropy relaxation time determination, and it is added to a traditional cuvette timeresolved setup, with a pumped Ti-Sa light source.
Abstract: A confocal microscope setup is developed for time-resolved fluorescence measurements. It is added to a traditional cuvette time-resolved setup, with a pumped Ti-Sa light source. The temporal resolution of 37 ps (FWHM) is not degraded, in comparison with the cuvette setup also described. These setups allow both decay lifetime and anisotropy relaxation time determination. Fluorescence correlation spectroscopy (FCS) is used to determine the observation point size. When associated with the calcium probe calcium green, calcium concentration in single cells can be determined in 10 ms by simultaneous acquisition of early and late fluorescence photons.
15 Sep 1997
TL;DR: A real-time camera-based system designed for gaze tracking focused on human-computer communication using a CCD camera placed between the keyboard and the screen that detects the user presence, locates his position and then tracks his face, nose and both eyes.
Abstract: We present a real-time camera-based system designed for gaze tracking focused on human-computer communication. We aim to equip computer systems with a tool which can provide visual information about the user. This tool must satisfy interaction constraints and not intrusive. Therefore, we use a CCD camera placed between the keyboard and the screen. The system detects the user presence, locates his position and then tracks his face, nose and both eyes. The detection is performed by combining image processing techniques and pattern recognition methods.
TL;DR: In this article, the fine structure fluorescence spectra of tetra(pentafluorophenyl)chlorin present as a contaminant in the samples have been fully analyzed.
TL;DR: In this article, during the leaching of simulated highly sulphated OPC/BFS cements, cured at room temperature and containing U-phase, sodium sulphate, and ettringite, physico-chemical transformations have been pointed out (transformation of U -phase into ettricite).
TL;DR: In this article, a time-resolved red shift in the transient fluorescence spectra has been interpreted as a diffusion process of the excited probe from the apolar core to the water interface of the micelle where an energy barrier prevents the diffusion of BOA toward the interface.
Abstract: The spectroscopic properties of the recently synthesized molecule 10,10‘-bis(2-ethylhexyl)-9,9‘-bianthryl (BOA) and of its parent molecule 9,9‘-bianthryl (BA) have been studied in micelles. A time-resolved red shift in the transient fluorescence spectra has been interpreted as a diffusion process of the excited probe from the apolar core to the water interface of the micelle where the excited probe is trapped. The dynamics of the diffusion process are governed by the chemical potential profile of the excited probe through the Smoluschowski equation. The diffusion of excited molecules of BA occurs on a potential surface presenting an attractive well about the water interface, whereas an energy barrier prevents the diffusion of BOA toward the interface. The height of this barrier has been estimated at 7kT in CTACl micelles. The diffusive nature of the red shift is shown by its dependence on viscosity. In CTACl micelles the viscosities measured from the rotational and the translational movement of the probe ...
TL;DR: In this paper, the 2D motion of independent point particles colliding with a periodic array of circular obstacles is described by a total accommodation reflection law, and the density of particles is approximated by the solution of a diffusion equation in the long time and large scale regime.
Abstract: We study the 2D motion of independent point particles colliding with a periodic array of circular obstacles. The interaction between the particles and the obstacles is described by a total accommodation reflection law. Assuming that the array of scatterers has finite horizon, the density of particles is approximated by the solution of a diffusion equation in the long-time and large-scale regime. The proof relies on a multiscale asymptotics and gives the order of approximation.
TL;DR: In this paper, a new orthonormal bases of improved time frequency atoms are constructed, similar to R. Baraniuk's chirplets, which are used to unfold frequency modulated signals in the time frequency plane.
TL;DR: In this article, the authors present a numerical implementation of such a model, written in the framework of viscoplasticity with a threshold, in a parallel version of the F.E. code ZeBuLoN, used to simulate the mechanical response of a biaxial specimen developed at Laboratoire de Mecanique et Technologie de Cachan.
TL;DR: In this article, a film of polyvinylpyrrolidone containing zinc tetraphenylporphyrin was formed and studied by spectrophotometric methods.