Showing papers by "École normale supérieure de Cachan published in 2005"

A non-local algorithm for image denoising

Abstract: We propose a new measure, the method noise, to evaluate and compare the performance of digital image denoising methods. We first compute and analyze this method noise for a wide class of denoising algorithms, namely the local smoothing filters. Second, we propose a new algorithm, the nonlocal means (NL-means), based on a nonlocal averaging of all pixels in the image. Finally, we present some experiments comparing the NL-means algorithm and the local smoothing filters.

Computing Large Deformation Metric Mappings via Geodesic Flows of Diffeomorphisms

Abstract: This paper examine the Euler-Lagrange equations for the solution of the large deformation diffeomorphic metric mapping problem studied in Dupuis et al. (1998) and Trouve (1995) in which two images I 0, I 1 are given and connected via the diffeomorphic change of coordinates I 0???1=I 1 where ?=?1 is the end point at t= 1 of curve ? t , t?[0, 1] satisfying .? t =v t (? t ), t? [0,1] with ?0=id. The variational problem takes the form $$\mathop {\arg {\text{m}}in}\limits_{\upsilon :\dot \phi _t = \upsilon _t \left( {\dot \phi } \right)} \left( {\int_0^1 {\left\| {\upsilon _t } \right\|} ^2 {\text{d}}t + \left\| {I_0 \circ \phi _1^{ - 1} - I_1 } \right\|_{L^2 }^2 } \right),$$ where ?v t? V is an appropriate Sobolev norm on the velocity field v t(·), and the second term enforces matching of the images with ?·?L 2 representing the squared-error norm. In this paper we derive the Euler-Lagrange equations characterizing the minimizing vector fields v t, t?[0, 1] assuming sufficient smoothness of the norm to guarantee existence of solutions in the space of diffeomorphisms. We describe the implementation of the Euler equations using semi-lagrangian method of computing particle flows and show the solutions for various examples. As well, we compute the metric distance on several anatomical configurations as measured by ?0 1?v t? V dt on the geodesic shortest paths.

Salt-and-pepper noise removal by median-type noise detectors and detail-preserving regularization

Abstract: This paper proposes a two-phase scheme for removing salt-and-pepper impulse noise. In the first phase, an adaptive median filter is used to identify pixels which are likely to be contaminated by noise (noise candidates). In the second phase, the image is restored using a specialized regularization method that applies only to those selected noise candidates. In terms of edge preservation and noise suppression, our restored images show a significant improvement compared to those restored by using just nonlinear filters or regularization methods only. Our scheme can remove salt-and-pepper-noise with a noise level as high as 90%.

On the trend to global equilibrium for spatially inhomogeneous kinetic systems: The Boltzmann equation

Abstract: As part of our study of convergence to equilibrium for spatially inhomogeneous kinetic equations, started in [21], we derive estimates on the rate of convergence to equilibrium for solutions of the Boltzmann equation, like O(t-∞). Our results hold conditionally to some strong but natural estimates of smoothness, decay at large velocities and strict positivity, which at the moment have only been established in certain particular cases. Among the most important steps in our proof are 1) quantitative variants of Boltzmann’s H-theorem, as proven in [52,60], based on symmetry features, hypercontractivity and information-theoretical tools; 2) a new, quantitative version of the instability of the hydrodynamic description for non-small Knudsen number; 3) some functional inequalities with geometrical content, in particular the Korn-type inequality which we established in [22]; and 4) the study of a system of coupled differential inequalities of second order, by a treatment inspired from [21]. We also briefly point out the particular role of conformal velocity fields, when they are allowed by the geometry of the problem.

TGV: theory, principles and algorithms: A tool for the automatic synthesis of conformance test cases for non-deterministic reactive systems

Abstract: This paper presents the TGV tool, which allows for the automatic synthesis of conformance test cases from a formal specification of a (non-deterministic) reactive system. TGV was developed by Irisa Rennes and Verimag Grenoble, with the support of the Vasy team of Inria Rhones-Alpes. The paper describes the main elements of the underlying testing theory, which is based on a model of transitions system which distinguishes inputs, outputs and internal actions, and is based on the concept of conformance relation. The principles of the test synthesis process, as well as the main algorithms, are explained. We then describe the main characteristics of the TGV tool and refer to some industrial experiments that have been conducted to validate the approach. As a conclusion, we describe some ongoing work on test synthesis.

Analysis of an electronic voting protocol in the applied pi calculus

Abstract: Electronic voting promises the possibility of a convenient, efficient and secure facility for recording and tallying votes in an election. Recently highlighted inadequacies of implemented systems have demonstrated the importance of formally verifying the underlying voting protocols. The applied pi calculus is a formalism for modelling such protocols, and allows us to verify properties by using automatic tools, and to rely on manual proof techniques for cases that automatic tools are unable to handle. We model a known protocol for elections known as FOO 92 in the applied pi calculus, and we formalise three of its expected properties, namely fairness, eligibility, and privacy. We use the ProVerif tool to prove that the first two properties are satisfied. In the case of the third property, ProVerif is unable to prove it directly, because its ability to prove observational equivalence between processes is not complete. We provide a manual proof of the required equivalence.

Design, Synthesis, Structural and Nonlinear Optical Properties of Photochromic Crystals: Toward Reversible Molecular Switches

Abstract: Two new anil molecules exhibiting photochromism in the crystalline state, N-(4-hydroxy)-salicylidene-amino-4-(methylbenzoate) (2) and N-(3,5-di-tert-butylsalicylidene)-4-aminopyridine (3), are obtained. Upon irradiation in the UV, the yellow crystals change color to red, owing to enol-keto intramolecular tautomerism. The red color disappears, when crystals are left in the dark or irradiated with visible light. 3 has the most stable keto form among all anil-type photochromic compounds (τ = 460 days at room temperature). Both exhibit nonlinear optical (NLO) properties and show powder second harmonic generation (SHG) of respectively 10 and 3 times vs urea. X-ray diffraction shows acentric structures where molecules line up “head-to-tail” through hydrogen bonds for 2 (space group Pc), or form a chiral helix 3 (space group P32). Evidence of reversible structural change is given for 3, and we demonstrate the functionality of this crystal as an NLO switching material, as SHG can be photomodulated by about 30%.

Nominal techniques in Isabelle/HOL

Abstract: In this paper we define an inductive set that is bijective with the α-equated lambda-terms. Unlike de-Bruijn indices, however, our inductive definition includes names and reasoning about this definition is very similar to informal reasoning on paper. For this we provide a structural induction principle that requires to prove the lambda-case for fresh binders only. The main technical novelty of this work is that it is compatible with the axiom-of-choice (unlike earlier nominal logic work by Pitts et al); thus we were able to implement all results in Isabelle/HOL and use them to formalise the standard proofs for Church-Rosser and strong-normalisation.

A mesoporous silica functionalized by a covalently bound calixarene-based fluoroionophore for selective optical sensing of mercury(II) in water

Abstract: With the aim of optical sensing of Hg2+ in water, a calixarene bearing two dansyl fluorophores was grafted on a large pore mesoporous silica material (SBA-15) via two long alkyl chains containing triethoxysilane groups. The characterization of the obtained material 2-SBA-15 shows that the organized structure is preserved after the post-grafting procedure. A detailed study of the complexing and fluorescence properties of 2-SBA-15 is reported. The functionalized material is able to reversibly detect Hg2+ with a response time of a few seconds and a detection limit of 3.3 × 10−7 mol L−1 in water. Furthermore, this system offers a high selectivity over several interfering cations (Na+, K+, Ca2+, Cu2+, Cd2+, Pb2+).

A characterization of convex calibrable sets in

Abstract: The main purpose of this paper is to characterize the calibrability of bounded convex sets in Open image in new window by the mean curvature of its boundary, extending the known analogous result in dimension 2. As a by-product of our analysis we prove that any bounded convex set C of class C1,1 has a convex calibrable set K in its interior, and and for any volume V ∈ [|K|,|C|] the solution of the perimeter minimizing problem with fixed volume V in the class of sets contained in C is a convex set. As a consequence we describe the evolution of convex sets in Open image in new window by the minimizing total variation flow.

Deciding security of protocols against off-line guessing attacks

Abstract: We provide an effective procedure for deciding the existence of off-line guessing attacks on security protocols, for a bounded number of sessions.The procedure consists of a constraint solving algorithm for determining satisfiability and equivalence of a class of second-order E-unification problems, where the equational theory E is presented by a convergent subterm rewriting system.To the best of our knowledge, this is the first decidability result to use the generic definition of off-line guessing attacks due to Corin et al. based on static equivalence in the applied pi calculus.

Smoothness of the Solution of the Spatially Homogeneous Boltzmann Equation without Cutoff

Abstract: For regularized hard potentials cross sections, the solution of the spatially homogeneous Boltzmann equation without angular cutoff lies in Schwartz's space 𝒮(ℝ N ) for all (strictly positive) time. The proof is presented in full detail for the two-dimensional case, and for a moderate singularity of the cross section. Then we present those parts of the proof for the general case, where the dimension, or the strength of the singularity play an essential role.

A kinetic model allowing to obtain the energy law of polytropic gases in the presence of chemical reactions

Abstract: We propose a kinetic model which describes a mixture of reactive gases, in which a unique continuous internal energy parameter is present. This model enables to recover at the level of its hydrodynamical limit the Euler equations of a mixture of reactive polytropic gases.

Distributed Monitoring of Concurrent and Asynchronous Systems

Abstract: In this paper we study the diagnosis of distributed asynchronous systems with concurrency. Diagnosis is performed by a peer-to-peer distributed architecture of supervisors. Our approach relies on Petri net unfoldings and event structures, as means to manipulate trajectories of systems with concurrency. This article is an extended version of the paper with same title, which appeared as a plenary address in the Proceedings of CONCUR?2003.

Synthesis and properties of new tetrazines substituted by heteroatoms: towards the world's smallest organic fluorophores.

Abstract: New tetrazines substituted by heteroatoms have been synthesized and their electrochemical and photochemical properties investigated. All compounds are reversibly electroactive with standard potentials shifting cathodically according to the donor character of the substituent. The tetrazine derivatives are also fluorescent with maximum emission wavelengths in the range 550-575 nm. Some of them show very long fluorescence lifetimes (several tens of ns) and remain fluorescent in the solid state without major changes in the spectral features. The fluorescence of one of the derivatives can be efficiently quenched by the presence of electron-rich compounds such as triphenylamines, phenol or anisole, which make them very promising compounds for sensor applications.

Synthesis, crystal structures, and nonlinear optical (NLO) properties of new Schiff-base nickel(II) complexes. Toward a new type of molecular switch?

Abstract: An H2L Schiff-base ligand that was obtained from the monocondensation of diaminomaleonitrile and 4-(diethylamino)salicylaldehyde is reported together with four related nickel(II) complexes formulated as [Ni(L)(L‘)] (L‘ = MePhCHNH2, iPrNH2, Py, and PPh3). Crystal structures have been solved for H2L, [Ni(L)(MePhCHNH2)], and [Ni(L)(iPrNH2)]. Surprisingly, the complexation process leads to the formation of a rather unusual nickel amido (−NH−NiII) bond by deprotonation of the primary amine of H2L. A reduction of the quadratic hyperpolarizability (β) from 38 × 10-30 to 17.5 × 10-30 cm5 esu-1 is evidenced on H2L upon metal complexation by the electric-field-induced second-harmonic (EFISH) technique. Qualitative ZINDO/SCI quantum chemical calculations indicate that, in [Ni(L)(MePhCHNH2)], the β orientation strongly depends on the laser wavelength. In particular, a β rotation strictly equal to 90° could be obtained with 1.022 μm incident light on passing from [Ni(L)(MePhCHNH2] to a hypothetical [Ni(HL)(MePhCHNH2]+...

On the Adequacy of Monetary Arrangements in Sub-Saharan Africa

Abstract: We examine the economic rationale for monetary union(s) in Sub-Saharan Africa through the use of cluster analysis on a sample of 17 countries. The variables used stem from the theory of optimum currency areas and from the fear-of-floating literature. It is found that the existing CFA franc zone cannot be viewed as an optimum currency area: CEMAC and UEMOA countries do not belong to the same clusters, and a 'core' of the UEMOA can be defined on economic grounds. The results support the inclusion of the Gambia, Ghana and Sierra Leone in an extended UEMOA arrangement, or the creation of a separate monetary union with the 'core' of the UEMOA and the Gambia, rather than the creation of a monetary union around Nigeria. Finally, the creation of the West African Monetary Zone (WAMZ) around Nigeria is not supported by the data.

Structural modulation of the dipolar-octupolar contributions to the NLO response in subphthalocyanines

Abstract: Second order nonlinear optical properties of a series of trinitrosubphthalocyanine (SubPc) isomers were studied experimentally by electric field induced second harmonic (EFISH) generation and hyper Rayleigh scattering (HRS). These experimental values were compared to the ones obtained theoretically employing both sum over states (SOS) and finite field (FF) methods. From these studies, it was shown that the dipolar contributions to the β tensor are very much dependent on the substitution pattern at the periphery of the subphthalocyanine macrocycle, whereas the octupolar contributions remain mostly unchanged. Consequently, it was deduced that SubPc is extremely well suited for the decoupling of octupolar and dipolar contribution to the NLO response.

The Viscous Watershed Transform

Abstract: The watershed transform is the basic morphological tool for image segmentation. Watershed lines, also called divide lines, are a topographical concept: a drop of water falling on a topographical surface follows a steepest descent line until it stops when reaching a regional minimum. Falling on a divide line, the same drop of water may glide towards one or the other of both adjacent catchment basins. For segmenting an image, one takes as topographic surface the modulus of its gradient: the associated watershed lines will follow the contour lines in the initial image. The trajectory of a drop of water is disturbed if the relief is not smooth: it is undefined for instance on plateaus. On the other hand, each regional minimum of the gradient image is the attraction point of a catchment basin. As gradient images generally present many minima, the result is a strong oversegmentation. For these reasons a more robust scheme is used for the construction of the watershed based on flooding: a set of sources are defined, pouring water in such a way that the altitude of the water increases with constant speed. As the flooding proceeds, the boundaries of the lakes propagate in the direction of the steepest descent line of the gradient. The set of points where lakes created by two distinct sources meet are the contours. As the sources are far less numerous than the minima, there is no more oversegmentation. And on the plateaus the flooding also is well defined and propagates from the boundary towards the inside of the plateau. Used in conjunction with markers, the watershed is a powerful, fast and robust segmentation method. Powerful: it has been used with success in a variety of applications. Robust: it is insensitive to the precise placement or shape of the markers. Fast: efficient algorithms are able to mimic the progression of the flood. In some cases however the resulting segmentation will be poor: the contours always belong to the watershed lines of the gradient and these lines are poorly defined when the initial image is blurred or extremely noisy. In such cases, an additional regularization has to take place. Denoising and filtering the image before constructing the gradient is a widely used method. It is however not always sufficient. In some cases, one desires smoothing the contour, despite the chaotic fluctuations of the watershed lines. For this two options are possible. The first consists in using a viscous fluid for the flooding: a viscous fluid will not be able to follow all irregularities of the relief and produce lakes with smooth boundaries. Simulating a viscous fluid is however computationally intensive. For this reason we propose an alternative solution, in which the topographic surface is modified in such a way that flooding it with a non viscous fluid will produce the same lakes as flooding the original relief with a viscous fluid. On this new relief, the standard watershed algorithm can be used, which has been optimized for various architectures. Two types of viscous fluids will be presented, yielding two distinct regularization methods. We will illustrate the method on various examples.

Cryptographic protocol analysis on real c code

Abstract: Implementations of cryptographic protocols, such as OpenSSL for example, contain bugs affecting security, which cannot be detected by just analyzing abstract protocols (e.g., SSL or TLS). We describe how cryptographic protocol verification techniques based on solving clause sets can be applied to detect vulnerabilities of C programs in the Dolev-Yao model, statically. This involves integrating fairly simple pointer analysis techniques with an analysis of which messages an external intruder may collect and forge. This also involves relating concrete run-time data with abstract, logical terms representing messages. To this end, we make use of so-called trust assertions. The output of the analysis is a set of clauses in the decidable class $\mathcal{H}_1$, which can then be solved independently. This can be used to establish secrecy properties, and to detect some other bugs.

Energy harvesting from vibration using a piezoelectric membrane

Abstract: In this paper we investigate the capability of harvesting the electric energy from mechanical vibrations in a dynamic environment through a unimorph piezoelectric membrane transducer. Due to the impedance matrices connecting the efforts and flows of the membrane, we have established the dynamic electric equivalent circuit of the transducer. In a first study and in order to validate theoretical results, we performed experiments with a vibrating machine moving a macroscopic 25 mm diameter piezoelectric membrane. A power of 1.8 mW was generated at the resonance frequency (2.58 kHz) across a 56 kQ optimal resistor and for a 2 g acceleration.

Computationally sound implementations of equational theories against passive adversaries

Abstract: In this paper we study the link between formal and cryptographic models for security protocols in the presence of a passive adversary. In contrast to other works, we do not consider a fixed set of primitives but aim at results for an arbitrary equational theory. We define a framework for comparing a cryptographic implementation and its idealization w.r.t. various security notions. In particular, we concentrate on the computational soundness of static equivalence, a standard tool in cryptographic pi calculi. We present a soundness criterion, which for many theories is not only sufficient but also necessary. Finally, we establish new soundness results for the exclusive OR and a theory of ciphers and lists.

Inhibition of human immunodeficiency virus type 1 reverse transcriptase, RNase H, and integrase activities by hydroxytropolones.

Abstract: Human immunodeficiency virus type I reverse transcriptase (RT) possesses distinct DNA polymerase and RNase H sites, whereas integrase (IN) uses the same active site to perform 3'-end processing and strand transfer of the proviral DNA. These four enzymatic activities are essential for viral replication and require metal ions. Two Mg2+ ions are present in the RT polymerase site, and one or two Mg2+ ions are required for the catalytic activities of RNase H and IN. We tested the possibility of inhibition of the RT polymerase and RNase H as well as the IN 3'-end processing and transfer activities of purified enzymes by a series of 3,7-dihydroxytropolones designed to target two Mg2+ ions separated by approximately 3.7 angstroms. The RT polymerase and IN 3' processing and strand transfer activities were inhibited at submicromolar concentrations, while the RNase H activity was inhibited in the low micromolar range. In all cases, the lack of inhibition by tropolones and O-methylated 3,7-dihydroxytropolones was consistent with the active molecules binding the metal ions in the active site. In addition, inhibition of the DNA polymerase activity was shown to depend on the Mg2+ concentration. Furthermore, selective inhibitors were identified for several of the activities tested, leaving some potential for design of improved inhibitors. However, all tested compounds exhibited cellular toxicity that presently limits their applications.

Image denoising by non-local averaging

Abstract: In this work, we present and analyze an image denoising method, the NL-means algorithm, based on a non local averaging of all pixels in the image. We also introduce the concept of method noise, that is, the difference between the original (always slightly noisy) digital image and its denoised version. Finally, we present some experiences comparing the NL-means results with some classical denoising methods.

A highly selective fluorescent molecular sensor for potassium based on a calix[4]bisazacrown bearing boron-dipyrromethene fluorophores

Abstract: The synthesis of a ditopic fluorescent sensor for cations associating a 1,3 alternate calix[4]bisazacrown-5 as an ionophore and substituted boron-dipyrromethene dyes as fluorophores is reported. Photophysical studies revealed that in medium and high polarity solvents an efficient charge transfer (CT) reaction occurs in the excited state leading to a dual emission and a strong quenching of fluorescence. This CT process is either totally suppressed by amino group protonation or hampered by cation complexation; in both cases, a strong fluorescence enhancement is observed. This “switching-on” of the emission is more pronounced when two cations are coordinated. The stability constants of complexes with sodium, potassium, caesium, calcium and barium cations were measured in acetonitrile and ethanol. The system shows a high sensitivity and selectivity for potassium over other metal ions. A test under physiological conditions was successfully achieved.

Combinatorial search on graphs motivated by bioinformatics applications: a brief survey

Abstract: The goal of this paper is to present a brief survey of a collection of methods and results from the area of combinatorial search [1,8] focusing on graph reconstruction using queries of different type. The study is motivated by applications to genome sequencing.