Showing papers by "École normale supérieure de Cachan published in 2006"
TL;DR: It is shown how certain nonconvex optimization problems that arise in image processing and computer vision can be restated as convex minimization problems, which allows, in particular, the finding of global minimizers via standard conveX minimization schemes.
Abstract: We show how certain nonconvex optimization problems that arise in image processing and computer vision can be restated as convex minimization problems. This allows, in particular, the finding of global minimizers via standard convex minimization schemes.
1,142 citations
TL;DR: This note investigates process fault accommodation in a class of nonlinear continuous-time systems using a new fault estimation module, based on an adaptive estimator, to compensate for the effect of the faults by stabilizing the closed-loop system.
Abstract: This note investigates process fault accommodation in a class of nonlinear continuous-time systems. A new fault estimation module, based on an adaptive estimator, is first proposed. The fault tolerant controller is constructed to compensate for the effect of the faults by stabilizing the closed-loop system. A flexible joint robotic example is given to illustrate the efficiency of the proposed approach
712 citations
TL;DR: It is proved that the Gaussian unitary attack is optimal for all the considered bounds on the key rate when the first and second momenta of the canonical variables involved are known by the honest parties.
Abstract: We analyze the asymptotic security of the family of Gaussian modulated quantum key distribution protocols for continuous-variables systems. We prove that the Gaussian unitary attack is optimal for all the considered bounds on the key rate when the first and second momenta of the canonical variables involved are known by the honest parties.
387 citations
TL;DR: This paper first explains the staircase effect by finding the subjacent partial differential equation (PDE) of the neighborhood filter, and shows that this ill-posed PDE is a variant of another famous image processing model, the Perona-Malik equation, which suffers the same artifacts.
Abstract: Many classical image denoising methods are based on a local averaging of the color, which increases the signal/noise ratio. One of the most used algorithms is the neighborhood filter by Yaroslavsky or sigma filter by Lee, also called in a variant "SUSAN" by Smith and Brady or "Bilateral filter" by Tomasi and Manduchi. These filters replace the actual value of the color at a point by an average of all values of points which are simultaneously close in space and in color. Unfortunately, these filters show a "staircase effect," that is, the creation in the image of flat regions separated by artifact boundaries. In this paper, we first explain the staircase effect by finding the subjacent partial differential equation (PDE) of the filter. We show that this ill-posed PDE is a variant of another famous image processing model, the Perona-Malik equation, which suffers the same artifacts. As we prove, a simple variant of the neighborhood filter solves the problem. We find the subjacent stable PDE of this variant. Finally, we apply the same correction to the recently introduced NL-means algorithm which had the same staircase effect, for the same reason.
231 citations
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TL;DR: In this paper, a complete complexity table for logic fragments defined by varying the set of temporal operators and the number of registers is presented. But it is not decidable over finite data words, since adding past-time operators or 1 more register causes undecidability.
Abstract: A data word is a sequence of pairs of a letter from a finite alphabet and an element from an infinite set, where the latter can only be compared for equality. To reason about data words, linear temporal logic is extended by the freeze quantifier, which stores the element at the current word position into a register, for equality comparisons deeper in the formula. By translations from the logic to alternating automata with registers and then to faulty counter automata whose counters may erroneously increase at any time, and from faulty and error-free counter automata to the logic, we obtain a complete complexity table for logical fragments defined by varying the set of temporal operators and the number of registers. In particular, the logic with future-time operators and 1 register is decidable but not primitive recursive over finite data words. Adding past-time operators or 1 more register, or switching to infinite data words, cause undecidability.
196 citations
05 Jul 2006
TL;DR: It is shown in accordance with intuition that coercion-resistance implies receipt-freeness, which implies privacy, the basic anonymity property of voting protocols, as defined in previous work.
Abstract: In this paper we formally study important properties of electronic voting protocols. In particular we are interested in coercion-resistance and receipt-freeness. Intuitively, an election protocol is coercion-resistant if a voter A cannot prove to a potential coercer C that she voted in a particular way. We assume that A cooperates with C in an interactive fashion. Receipt-freeness is a weaker property, for which we assume that A and C cannot interact during the protocol: to break receipt-freeness, A later provides evidence (the receipt) of how she voted. While receipt-freeness can be expressed using observational equivalence from the applied pi calculus, we need to introduce a new relation to capture coercion-resistance. Our formalization of coercion-resistance and receipt-freeness are quite different. Nevertheless, we show in accordance with intuition that coercion-resistance implies receipt-freeness, which implies privacy, the basic anonymity property of voting protocols, as defined in previous work. Finally we illustrate the definitions on a simplified version of the Lee et al. voting protocol.
182 citations
TL;DR: It is proved that neighborhood filters are asymptotically equivalent to the Perona–Malik equation, one of the first nonlinear PDE’s proposed for image restoration, and an extremely simple variant of the neighborhood filter using a linear regression instead of an average is proposed.
Abstract: Denoising images can be achieved by a spatial averaging of nearby pixels. However, although this method removes noise it creates blur. Hence, neighborhood filters are usually preferred. These filters perform an average of neighboring pixels, but only under the condition that their grey level is close enough to the one of the pixel in restoration. This very popular method unfortunately creates shocks and staircasing effects. In this paper, we perform an asymptotic analysis of neighborhood filters as the size of the neighborhood shrinks to zero. We prove that these filters are asymptotically equivalent to the Perona–Malik equation, one of the first nonlinear PDE’s proposed for image restoration. As a solution, we propose an extremely simple variant of the neighborhood filter using a linear regression instead of an average. By analyzing its subjacent PDE, we prove that this variant does not create shocks: it is actually related to the mean curvature motion. We extend the study to more general local polynomial estimates of the image in a grey level neighborhood and introduce two new fourth order evolution equations.
176 citations
TL;DR: Osteoblastic cells could be successfully cultured inside the microdevices under dynamic conditions and their ALP activity was enhanced, promising for bone cell growth and differentiation as well as future tissue regeneration using larger 3D microfluidic microdevices.
171 citations
TL;DR: It is concluded that a single IN dimer at each extremity of viral DNA molecules is required for 3′-processing, with a dimer of dimers responsible for the subsequent full integration.
158 citations
TL;DR: Three-dimensional microfluidic systems in poly(dimethylsiloxane) (PDMS) were fabricated and used in conjunction with both custom-made and commercially available planar microelectrode arrays (pMEAs) to address the problem of in vitro culture of small neuronal networks with pre-defined topological features.
154 citations
TL;DR: A new electrofluorescent switch was prepared with an electroactive fluorescent tetrazine blend of polymer electrolyte using two indium-tin oxide plates as the two contact electrodes.
TL;DR: This correspondence aims to provide a sound proof of a result, i.e., asymptotic (in SNR) Gaussianity and efficiency of the CML estimator in the multiple parameters case, generally regarded as trivial but not so far demonstrated.
Abstract: In the field of asymptotic performance characterization of the conditional maximum-likelihood (CML) estimator, asymptotic generally refers to either the number of samples or the signal-to-noise ratio (SNR) value. The first case has been already fully characterized, although the second case has been only partially investigated. Therefore, this correspondence aims to provide a sound proof of a result, i.e., asymptotic (in SNR) Gaussianity and efficiency of the CML estimator in the multiple parameters case, generally regarded as trivial but not so far demonstrated
TL;DR: In this paper, a system coupling a kinetic equation for the droplets of Vlasov type and a (Euler-like) fluid equation for a gas is introduced, where the initial data are sufficiently smooth and their support has suitable properties.
Abstract: Sprays are complex flows made of liquid droplets surrounded by a gas. They can be modeled by introducing a system coupling a kinetic equation (for the droplets) of Vlasov type and a (Euler-like) fluid equation for the gas. In this paper, we prove that, for the so-called thin sprays, this coupled model is well-posed, in the sense that existence and uniqueness of classical solutions holds for small time, provided the initial data are sufficiently smooth and their support have suitable properties.
TL;DR: The main factors that could increase the lifetime expectancy of power modules in such harsh environments will be identified.
01 Jan 2006
TL;DR: In this article, the Navier-Stokes equations and wavelet revolution are discussed and a series of talks and preprints by Marie Farge and Paul Federbush are discussed.
Abstract: My interest in Navier-Stokes equations arose from the wavelet revolution. I was puzzled by (1) a series of talks and preprints by Marie Farge and (2) an intriguing paper by Paul Federbush entitled ‘Navier and Stokes meet the wavelets’. Both Marie Farge and Paul Federbush were convinced that wavelets could play an important role in fluid dynamics.
TL;DR: In this paper, the authors examine paths of commercial learning, where the environment is perceived as multi-referent and pluralistic The informationally rich category of scientist-entrepreneurs constitutes our research terrain This group represents the acme of strong science and enterprise interaction Data from a written questionnaire and extensive oral interviews of 41 people and information from four laboratory-enterprise micro-studies, form the basis of their description and conclusions.
TL;DR: In this paper, a new space and time finite elements discretization of the Landau-Lifshitz equations is proposed, which may be readily used for numerical computations.
Abstract: In this paper we propose a new space and time finite elements discretization of the Landau–Lifshitz equations which may be readily used for numerical computations. We then prove its convergence to a weak solution in the sense given by Alouges and Soyeur or Labbe in the literature.
TL;DR: The present paper will describe the complete process involved in functional tolerancing using the CLIC tolerancing method within an Excel software environment, and creates location and orientation specifications for influential parts using datum reference frames derived during the previous stage.
Abstract: The aim behind applying functional tolerancing to a mechanism is to widen the tolerances used in parts manufacturing according to the effective functional properties of the product. This step may be performed using CAD systems and geometrical specifications defined by ISO standards. The present paper will describe the complete process involved in functional tolerancing. The CLIC tolerancing method has been implemented within an Excel software environment. CAD models for parts have been imported via a STEP interface. According to this approach, the designer describes the assembly process; the CLIC system then determines the functional requirements corresponding to the joints between parts and generates all datum reference frames and tolerancing of set-up surfaces in compliance with ISO standards. CLIC also determines both the geometrical conditions of minimum distances in order to avoid interference between parts and the conditions for assembling small standard components. The designer next adds other functional requirements. For each such requirement, a tolerancing process creates location and orientation specifications for influential parts using datum reference frames derived during the previous stage. Excel formulae focusing on the sum of tolerances are generated using a three-dimensional statistical approach. Moreover, the tolerance database allows optimizing the tolerances and nominal dimensions of parts.
TL;DR: It is shown that vMIA decreases cell size, reduces actin polymerization, and induces cell rounding, which suggests that the cytopathic effect of CMV can be explained by vMia effects on mitochondrial bioenergetics.
Abstract: Replication of human cytomegalovirus (CMV) requires the expression of the viral mitochondria-localized inhibitor of apoptosis (vMIA). vMIA inhibits apoptosis by recruiting Bax to mitochondria, resulting in its neutralization. We show that vMIA decreases cell size, reduces actin polymerization, and induces cell rounding. As compared with vMIA-expressing CMV, vMIA-deficient CMV, which replicates in fibroblasts expressing the adenoviral apoptosis suppressor E1B19K, induces less cytopathic effects. These vMIA effects can be separated from its cell death-inhibitory function because vMIA modulates cellular morphology in Bax-deficient cells. Expression of vMIA coincided with a reduction in the cellular adenosine triphosphate (ATP) level. vMIA selectively inhibited one component of the ATP synthasome, namely, the mitochondrial phosphate carrier. Exposure of cells to inhibitors of oxidative phosphorylation produced similar effects, such as an ATP level reduced by 30%, smaller cell size, and deficient actin polymerization. Similarly, knockdown of the phosphate carrier reduced cell size. Our data suggest that the cytopathic effect of CMV can be explained by vMIA effects on mitochondrial bioenergetics.
TL;DR: In this paper, the question of existence and uniqueness for entropy solutions of scalar conservation laws with a flux function which is discontinuous with respect to the space variable is investigated, and it is shown that no extra assumption of convexity or genuine non-linearity is required for the problem to be wellposed and prove it.
Abstract: In this paper, the question of existence and uniqueness for entropy solutions of scalar conservation laws with a flux function which is discontinuous with respect to the space variable is investigated. We show that no extra assumption of convexity or genuine non-linearity with respect to the state variable of the flux function is required for the problem to be well-posed and prove it. The proof uses a kinetic formulation of the conservation law.
TL;DR: In this paper, the authors used optical confocal microscopy to study optical properties of diamond 50-nm nanocrystals first irradiated with an electron beam, then dispersed as a colloidal solution and finally deposited on a silica slide.
Abstract: We used optical confocal microscopy to study optical properties of diamond 50 nm nanocrystals first irradiated with an electron beam, then dispersed as a colloidal solution and finally deposited on a silica slide. At room temperature, under CW laser excitation at a wavelength of 514.5 nm we observed perfectly photostable single nitrogen-vacancy (NV) colour defects embedded in the nanocrystals. From the zero-phonon line around 575 nm in the spectrum of emitted light, we infer a neutral NV 0 type of defect. Such nanoparticle with intrinsic fluorescence are highly promising for applications in biology where long-term emitting fluorescent bio-compatible nanoprobes are still missing.
TL;DR: In this article, the authors tackle the issue of locating a public facility which provides a public good in a closed and populated territory, and introduce a common-agency lobbying game, where agents attempt to influence the location and provision decisions by the government.
Abstract: In this paper, we tackle the issue of locating a public facility which provides a public good in a closed and populated territory. This facility generates differentiated benefits to neighborhoods depending on their distance from it. In the case of a Nimby facility, the smaller is the distance, the lower is the individual benefit. The opposite is true in the case of an anti-Nimby facility. We first characterize the optimal location which would be chosen by a social planner. Then we introduce a common-agency lobbying game, where agents attempt to influence the location and provision decisions by the government. Some interesting results arise in the case where only a subset of neighborhoods lobby. First, the solution of the lobbying game can replicate the optimal solution. Second, under-provision and over-provision of the public good may be obtained both in the Nimby and the anti-Nimby cases. The provision outcome depends on the presence of either a congestion effect or an agglomeration effect. Third, some non-lobbying neighborhoods may be better off than in the case where all neighborhoods lobby, which raises the possibility of free-riding at the lobbying stage.
TL;DR: An efficient numerical model for solving fully nonlinear potential flow equations with a free surface using a high-order three-dimensional boundary-element method combined with mixed Eulerian–Lagrangian time updating, based on second-order explicit Taylor expansions with adaptive time-steps.
Abstract: An efficient numerical model for solving fully nonlinear potential flow equations with a free surface is presented. Like the code that was developed by Grilli et al. (Grilli et al. 2001 Int. J. Numer. Methods Fluids 35, 829–867), it uses a high-order three-dimensional boundaryelement method combined with mixed Eulerian–Lagrangian time updating, based on second-order explicit Taylor expansions with adaptive time-steps. Such methods are known to be accurate but expensive. The efficiency of the code has been greatly improved by introducing the fast multipole algorithm. By replacing every matrix–vector product of the iterative solver and avoiding the building of the influence matrix, this algorithm reduces the computing complexity from OðN 2 Þ to nearly OðN Þ, where N is the number of nodes on the boundary. The performance of the method is illustrated by the example of the overturning of a solitary wave over a three-dimensional sloping bottom. For this test case, the accelerated method is indeed much faster than the former one, even for quite coarse grids. For instance, a reduction of the complexity by a factor six is obtained for NZ6022, for the same global accuracy. The acceleration of the code allows the study of more complex physical problems and several examples are presented.
TL;DR: In this paper, a spherical actuator with two actuated degrees of freedom (DOFs) is described. But the authors focus on the performance of the actuator in terms of characteristic torque-speed and efficiency.
Abstract: This paper reports on the development of a spherical actuator with two actuated degrees of freedom (DOFs). The electromechanical conversion principle is that of an induction motor. The paper first discusses possibilities of adapting the actuator to a spherical rotor actuated with an unlimited angular range along two DOFs. These concepts are then characterized and compared by analytical and numerical modeling, and the final shape of the actuator, composed of a two-layer rotor with teeth surrounded by five inductors, is described. A prototype has been built, and its performance, in terms of characteristic torque-speed and efficiency, has been measured.
TL;DR: In this paper, a mechanically excited unimorph piezoelectric membrane transducer was used to generate a power of 0.65 mW at the resonance frequency (1.71 kHz) across a 5.6 kΩ optimal resistor and for a 80 n force.
TL;DR: The negative strain-rate dependence, which is attributed to dynamic strain aging, leads to serrated stress-strain curves, discontinuous plastic flow and propagating deformation bands during plastic straining (also denoted as the Portevin-Le Chatelier effect) as discussed by the authors.
Abstract: Experimental data from uniaxial tensile tests on smooth and notched specimens of aluminium alloy 5083-H116 show that the material exhibits negative strain-rate sensitivity for strain rates within a certain range. The negative strain-rate dependence, which is attributed to dynamic strain aging, leads to serrated stress–strain curves, discontinuous plastic flow and propagating deformation bands during plastic straining (also denoted as the Portevin–Le Chatelier effect). Band analysis and linear perturbation analysis are performed using simple elastic-viscoplastic constitutive equations that include negative strain-rate sensitivity in a simplified manner. The negative strain-rate sensitivity allows for jumps in the plastic strain rate, which in turn permits the existence of localisation bands for the elastic-viscoplastic model. The simple elastic-viscoplastic constitutive model has been implemented in LS-DYNA, and non-linear finite element simulations of smooth and notched tensile test specimens are performed, allowing more detailed investigations into the effects of the negative strain-rate sensitivity on the material's behaviour.
TL;DR: Photoluminescence of single emitters in natural diamond samples emitting in the near infrared under optical excitation has several striking features, including narrow-band (FWHM 2 nm) fully polarized emission around 780 nm, a short excited-state lifetime of about 2 ns, and perfect photostability at room temperature under excitation conditions.
Abstract: We present a detailed study of photophysical properties of single color centers in natural diamond samples emitting in the near infrared under optical excitation. Photoluminescence of these single emitters has several striking features, including narrow-band (FWHM 2 nm) fully polarized emission around 780 nm, a short excited-state lifetime of about 2 ns, and perfect photostability at room temperature under our excitation conditions. Development of a triggered single-photon source relying on this single color center is discussed for application to quantum key distribution.
TL;DR: In this paper, the main focus is on methods for time-dependent fully nonlinear water waves, but aspects of steady waves are also discussed, ranging from two-dimensional time-periodic waves over a flat bottom to unsteady three-dimensional waves over an arbitrary topography.
TL;DR: In this paper, the authors characterized strongly coupled microcavities in which optical hybridization occurs between the organic-dye zinc tetraphenyl-porphrin (ZnTPP) and a thin film of a self-assembled perovskite.
Abstract: We characterize strongly coupled microcavities in which optical hybridization occurs between the organic-dye zinc tetraphenyl-porphrin (ZnTPP) and a thin film of a self-assembled perovskite. Position-resolved reflectivity measurements demonstrate the formation of hybrid organic-inorganic exciton polaritons corresponding to a three-way admixture of the cavity photon with the electronic transitions of the ZnTPP and the perovskite. We find that such hybrid-polariton states can undergo radiative emission, despite the existence of a competing decay channel to lower-lying $Q$-band states. We argue that such hybrid polaritons can in principle act as an intermediate energy-transfer state between the organic and inorganic excitations.
TL;DR: In this article, an original form of the strain energy density function (W) was derived for isotropic and incompressible vulcanized natural rubbers (NR's) and that of quasi-incompressible carbon black filled vulcanised natural rubber (NR 70) by generalizing the neo-Hookean model.
Abstract: The mechanical behaviour of isotropic and incompressible vulcanized natural rubbers (NR's) and that of quasi-incompressible carbon black filled vulcanized natural rubbers (NR 70) are considered both theoretically and experimentally. We start by generalising the neo-Hookean model to derive an original form of the strain energy density function (W). W satisfies the hypothesis of the Valanis–Landel function, which allows reducing the number of needed experimental tests to identify the parameters of the model. In the present study, in the order to identity the analytical form of W, we undertake only simple tension tests. The two-dimensional field of in-plane homogeneous displacements is determined here using a home-developed image analysis cross-correlation technique. Our model is also identified using results taken from the literature in the case of (NR's) for different types of solicitations, including simple tension, equibiaxial tension and pure shear deformation. Comparison of numerical results with the experimental data indicates that the present model can characterise the hyperelastic behaviour of NR's and that of NR 70 for all the tested modes of deformation. Moreover, it seems to be valid over a wide range of deformation intervals.