Results for "Sébastien Renaux-Petel"

total 974took 0.11s
Geometrical Destabilization of InflationOct 05 2015Sep 20 2016We show the existence of a general mechanism by which heavy scalar fields can be destabilized during inflation, relying on the fact that the curvature of the field space manifold can dominate the stabilizing force from the potential and destabilize inflationary ... More
On reaching the adiabatic limit in multi-field inflationMay 23 2014Dec 29 2014We calculate the scalar spectral index $n_s$ and the tensor-to-scalar ratio $r$ in a class of recently proposed two-field no-scale inflationary models in supergravity. We show that, in order to obtain correct predictions, it is crucial to take into account ... More
Perturbations in generalized multi-field inflationJan 07 2008May 31 2008We study the linear perturbations of multi-field inflationary models governed by a Lagrangian which is a general function of the scalar fields and of a global kinetic term combining their spacetime gradients with an arbitrary field space metric. Our analysis ... More
Flattened non-Gaussianities from the effective field theory of inflation with imaginary speed of soundMay 31 2018Nov 06 2018Inflationary perturbations in multi-field theories can exhibit a transient tachyonic instability as a consequence of their non-trivial motion in the internal field space. When an effective single-field description is applicable, the resulting theory is ... More
A Statistical Approach to Multifield Inflation: Many-field Perturbations Beyond Slow RollJul 02 2012Oct 02 2012We study multifield contributions to the scalar power spectrum in an ensemble of six-field inflationary models obtained in string theory. We identify examples in which inflation occurs by chance, near an approximate inflection point, and we compute the ... More
Multifield Cosmological Perturbations at Third Order and the Ekpyrotic TrispectrumJun 02 2009Sep 14 2009Using the covariant formalism, we derive the equations of motion for adiabatic and entropy perturbations at third order in perturbation theory for cosmological models involving two scalar fields. We use these equations to calculate the trispectrum of ... More
Primordial fluctuations and non-Gaussianities in sidetracked inflationApr 30 2018Jul 27 2018Heavy scalar fields can undergo an instability during inflation as a result of their kinetic couplings with the inflaton. This is known as the geometrical destabilization of inflation, as it relies on the effect of the negative curvature of the field-space ... More
Hyper non-Gaussianities in inflation with strongly non-geodesic motionFeb 08 2019Several recent proposals to embed inflation into high-energy physics rely on inflationary dynamics characterized by a strongly non-geodesic motion in negatively curved field space. This naturally leads to a transient instability of perturbations on sub-Hubble ... More
Nonlinear perturbations of cosmological scalar fields with non-standard kinetic termsOct 14 2008Dec 09 2008We adopt a covariant formalism to derive exact evolution equations for nonlinear perturbations, in a universe dominated by two scalar fields. These scalar fields are characterized by non-canonical kinetic terms and an arbitrary field space metric, a situation ... More
Primordial fluctuations and non-Gaussianities from multifield DBI Galileon inflationAug 01 2011Jan 03 2012We study a cosmological scenario in which the DBI action governing the motion of a D3-brane in a higher-dimensional spacetime is supplemented with an induced gravity term. The latter reduces to the quartic Galileon Lagrangian when the motion of the brane ... More
Massive Gravity on de Sitter and Unique Candidate for Partially Massless GravityJun 15 2012Jan 10 2013We derive the decoupling limit of Massive Gravity on de Sitter in an arbitrary number of space-time dimensions d. By embedding d-dimensional de Sitter into d+1-dimensional Minkowski, we extract the physical helicity-1 and helicity-0 polarizations of the ... More
Spectral distortions in the cosmic microwave background polarizationDec 16 2013Mar 21 2014We compute the spectral distortions of the Cosmic Microwave Background (CMB) polarization induced by non-linear effects in the Compton interactions between CMB photons and cold intergalactic electrons. This signal is of the $y$-type and is dominated by ... More
Primordial fluctuations and non-Gaussianities in multi-field DBI inflationApr 19 2008We study Dirac-Born-Infeld (DBI) inflation models with multiple scalar fields. We show that the adiabatic and entropy modes propagate with a common effective sound speed and are thus amplified at the sound horizon crossing. In the small sound speed limit, ... More
Multi-field DBI inflation: introducing bulk forms and revisiting the gravitational wave constraintsFeb 17 2009We study multi-field Dirac-Born-Infeld (DBI) inflation models, taking into account the NS-NS and R-R bulk fields present in generic flux compactifications. We compute the second-order action, which governs the behaviour of linear cosmological perturbations, ... More
Primordial perturbations and non-Gaussianities in DBI and general multi-field inflationJun 02 2008We study cosmological perturbations in general inflation models with multiple scalar fields and arbitrary kinetic terms, with special emphasis on the multi-field extension of Dirac-Born-Infeld (DBI) inflation. We compute the second-order action governing ... More
Neveu-Schwarz and operators algebras II: Unitary series and charactersOct 01 2010Oct 07 2010This paper is the second of a series giving a self-contained way from the Neveu-Schwarz algebra to a new series of irreducible subfactors. Here we give a unitary complete proof of the classification of the unitary series of the Neveu-Schwarz algebra, ... More
On rotarily transitive graphsMay 19 2016From the point of view of discrete geometry, the class of locally finite transitive graphs is a wide and important one. The subclass of Cayley graphs is of particular interest, as testifies the development of geometric group theory. Recall that Cayley ... More
Ergodicity and indistinguishability in percolation theoryOct 04 2012Nov 13 2014This paper explores the link between the ergodicity of the clus-ter equivalence relation restricted to its infinite locus and the indis-tinguishability of infinite clusters. It is an important element of the dictionary connecting orbit equivalence and ... More
Asymptotic Analysis of a Non-Linear Non-Local Integro-Differential Equation Arising from Bosonic Quantum Field DynamicsDec 19 2012We introduce a one parameter family of non-linear, non-local integro-differential equations and its limit equation. These equations originate from a derivation of the linear Boltzmann equation using the framework of bosonic quantum field theory. We show ... More
Precise measurement of the $K_{e2}/K_{μ2}$ branching ratio and search for new physics beyond the Standard ModelNov 08 2016The E36 experiment recently conducted at J-PARC by the TREK Collaboration will provide a precise mesurement of the decay ratio $ R_K = \Gamma(K^+ \rightarrow e^+\nu_e) / \Gamma(K^+ \rightarrow \mu^+\nu_{\mu}) $ with the aim of testing lepton universality, ... More
A fast Monte-Carlo method with a Reduced Basis of Control Variates applied to Uncertainty Propagation and Bayesian EstimationFeb 03 2012The Reduced-Basis Control-Variate Monte-Carlo method was introduced recently in [S. Boyaval and T. Leli\`evre, CMS, 8 2010] as an improved Monte-Carlo method, for the fast estimation of many parametrized expected values at many parameter values. We provide ... More
On geometric aspects of the SUSY Fokas-Gel'fand immersion formulaJun 20 2017Mar 09 2018In this paper, we develop a new geometric characterization for the supersymmetric versions of the Fokas--Gel'fand formula for the immersion of soliton supermanifolds with two bosonic and two fermionic independent variables into Lie superalgebras. In order ... More
Hybrid Inflation: Multi-field Dynamics and Cosmological ConstraintsSep 26 2011The dynamics of hybrid models is usually approximated by the evolution of a scalar field slowly rolling along a nearly flat valley. Inflation ends with a waterfall phase, due to a tachyonic instability. This final phase is usually assumed to be nearly ... More
Cellular automata on a $G$-setMay 26 2011We extend the usual definition of cellular automaton on a group in order to deal with a new kind of cellular automata, like cellular automata in the hyperbolic plane and we explore some properties of these cellular automata. This definition also allows ... More
Torus Knots in Lens Spaces & Topological StringsAug 26 2013Jun 22 2014We study the invariant of knots in lens spaces defined from quantum Chern-Simons theory. By means of the knot operator formalism, we derive a generalization of the Rosso-Jones formula for torus knots in L(p,1). In the second part of the paper, we propose ... More
Existence of 3D strong solutions for a system modeling a deformable solid inside a viscous incompressible fluidMar 01 2013Jul 07 2014In this paper we study a coupled system modeling the movement of a deformable solid immersed in a fluid. For the solid we consider a given deformation that has to obey several physical constraints. The motion of the fluid is modeled by the incompressible ... More
Stabilization of a fluid-solid system, by the deformation of the self-propelled solid. Part I: The linearized systemMar 27 2013Jan 02 2014This paper is the first part of a work which consists in proving the stabilization to zero of a fluid-solid system, in dimension 2 and 3. The considered system couples a deformable solid and a viscous incompressible fluid which satisfies the incompressible ... More
A fictitious domain approach for a mixed finite element method solving the two-phase Stokes problem with surface tension forcesJul 25 2018In this article we study a mixed finite element formulation for solving the Stokes problem with general boundary forces that induce a jump of the normal trace of the stress tensor, on an interface that splits the domain into two subdomains. Equality of ... More
Neveu-Schwarz and operators algebras I: Vertex operators superalgebrasOct 01 2010Oct 07 2010This paper is the first of a series giving a self-contained way from the Neveu-Schwarz algebra to a new series of irreducible subfactors. Here we present an elementary, progressive and self-contained approch to vertex operator superalgebra. We then build ... More
Directed Diffusion-Limited AggregationNov 13 2014Dec 22 2015In this paper, we define a directed version of the Diffusion-Limited-Aggregation model. We present several equivalent definitions in finite volume and a definition in infinite volume. We obtain bounds on the speed of propagation of information in infinite ... More
A counterexample to a question of Hof, Knill and SimonJul 05 2013In this article, we give a negative answer to a question of Hof, Knill and Simon (1995) concerning purely morphic sequences obtained from primitive morphism containing an infinite number of palindromes. Proven for the binary alphabet by B. Tan in 2007, ... More
Chern-Simons Invariants of Torus LinksMar 15 2010Jan 03 2011We compute the vacuum expectation values of torus knot operators in Chern-Simons theory, and we obtain explicit formulae for all classical gauge groups and for arbitrary representations. We reproduce a known formula for the HOMFLY invariants of torus ... More
On the coldness of the local Hubble flow: the role of baryonsFeb 24 2010Jun 14 2010(Abridged) Our aim is to investigate whether the presence of baryons can have any significant influence on the properties of the local Hubble flow which has proved to be "cold". We use two cosmological zoom simulations in the standard LCDM cosmology with ... More
A geometric derivation of the linear Boltzmann equation for a particle interacting with a Gaussian random fieldJul 05 2011Jun 25 2012In this article the linear Boltzmann equation is derived for a particle interacting with a Gaussian random field, in the weak coupling limit, with renewal in time of the random field. The initial data can be chosen arbitrarily. The proof is geometric ... More
A Greedy Algorithm to Cluster SpecialistsSep 13 2016Several recent deep neural networks experiments leverage the generalist-specialist paradigm for classification. However, no formal study compared the performance of different clustering algorithms for class assignment. In this paper we perform such a ... More
Low energy scales of Kondo lattices: mean-field perspectiveMar 11 2009A review of the low temperature properties of Kondo lattice systems is presented within the mean-field approximation, focusing on the different characteristic energy scales. The Kondo temperature, T_K, and the Fermi liquid coherence energy, T_0, are analyzed ... More
Some properties of meta-stable supersymmetry-breaking vacua in Wess-Zumino modelsJul 24 2006As a contribution to the current efforts to understand supersymmetry-breaking by meta-stable vacua, we study general properties of supersymmetry-breaking vacua in Wess-Zumino models: we show that tree-level degeneracy is generic, explore some constraints ... More
Johnson-Segalman -- Saint-Venant equations for viscoelastic shallow flows in the elastic limitNov 25 2016The shallow-water equations of Saint-Venant, often used to model the long-wave dynamics of free-surface flows driven by inertia and hydrostatic pressure, can be generalized to account for the elongational rheology of non-Newtonian fluids too. We consider ... More
Neveu-Schwarz and operators algebras III: Subfactors and Connes fusionOct 01 2010Oct 07 2010This paper is the third of a series giving a self-contained way from the Neveu-Schwarz algebra to a new series of irreducible subfactors. Here we introduce the local von Neumann algebra of the Neveu-Schwarz algebra, to obtain Jones-Wassermann subfactors ... More
Almost sure invariance principle for dynamical systems by spectral methodsJul 08 2009Feb 09 2011We prove the almost sure invariance principle for stationary R^d--valued processes (with dimension-independent very precise error terms), solely under a strong assumption on the characteristic functions of these processes. This assumption is easy to check ... More
Martin boundary of random walks with unbounded jumps in hyperbolic groupsFeb 21 2013Nov 03 2015Given a probability measure on a finitely generated group, its Martin boundary is a natural way to compactify the group using the Green function of the corresponding random walk. For finitely supported measures in hyperbolic groups, it is known since ... More
Higher order terms for the quantum evolution of a Wick observable within the Hepp methodFeb 19 2011The Hepp method is the coherent state approach to the mean field dynamics for bosons or to the semiclassical propagation. A key point is the asymptotic evolution of Wick observables under the evolution given by a time-dependent quadratic Hamiltonian. ... More
Bringing Information Credibility Back Into Transparency: The Case for a Global Monitoring System Of Green House Gas EmissionsJul 07 2016The goal of climate change governance is to stabilize greenhouse gas concentrations. This requires the reduction of anthropogenic global net emissions. In the pursuit of such a reduction, knowledge of greenhouse gas sources and sinks is critical to define ... More
Improved bounds for reduction to depth 4 and depth 3Apr 21 2013May 16 2014Koiran showed that if a $n$-variate polynomial of degree $d$ (with $d=n^{O(1)}$) is computed by a circuit of size $s$, then it is also computed by a homogeneous circuit of depth four and of size $2^{O(\sqrt{d}\log(d)\log(s))}$. Using this result, Gupta, ... More
Convex Optimization: Algorithms and ComplexityMay 20 2014Nov 16 2015This monograph presents the main complexity theorems in convex optimization and their corresponding algorithms. Starting from the fundamental theory of black-box optimization, the material progresses towards recent advances in structural optimization ... More
Analyticity of the entropy and the escape rate of random walks in hyperbolic groupsSep 23 2015We consider random walks on a non-elementary hyperbolic group endowed with a word distance. To a probability measure on the group are associated two numerical quantities, the rate of escape and the entropy. On the set of admissible probability measures ... More
The set of connective constants of Cayley graphs contains a Cantor spaceAug 11 2016Aug 14 2016The purpose of this note is to prove that the set of connective constants of Cayley graphs contains a Cantor space.
Supersymmetric and R symmetric vacua in Wess-Zumino modelsAug 16 2007In the context of supersymmetric Wess-Zumino models with an R symmetry, we find some simple conditions on the R-charge content of the theory that imply the presence or absence of supersymmetric and R-symmetric vacua. The main result of this work is that ... More
Persistent homoclinic tangencies and infinitely many sinks for residual sets of automorphisms of low degree in C^{3}Nov 07 2016We show that there exists a polynomial automorphism $f$ of $\mathbb{C}^{3}$ of degree 5 such that for every automorphism $g$ sufficiently close to $f$, $g$ admits a tangency between the stable and unstable laminations of some hyperbolic set. As a consequence, ... More
$3$-dimensional Continued Fraction Algorithms Cheat SheetsNov 26 2015Multidimensional Continued Fraction Algorithms are generalizations of the Euclid algorithm and find iteratively the gcd of two or more numbers. They are defined as linear applications on some subcone of $\mathbb{R}^d$. We consider multidimensional continued ... More
Stabilization of a fluid-solid system, by the deformation of the self-propelled solid. Part II: The nonlinear systemMar 27 2013Jan 02 2014In this second part we prove that the full nonlinear fluid-solid system introduced in Part I is stabilizable by deformations of the solid that have to satisfy nonlinear constraints. Some of these constraints are physical and guarantee the self-propelled ... More
Ballistic Impact of Dense Particle SuspensionsOct 14 2011The ballistic impact of various dense particle suspensions is of interest for the development of superior materials for personal protective equipment. The dynamic response of the fluids under impact of a fragment simulating projectile at various incident ... More
Inkjet-printed vertically emitting solid-state organic lasersMay 25 2016In this paper, we show that Inkjet Printing can be successfully applied to external-cavity vertically-emitting thin-film organic lasers, and can be used to generate a diffraction-limited output beam with an output energy as high as 33.6 uJ with a slope ... More
A Scalable Byzantine GridOct 17 2012Modern networks assemble an ever growing number of nodes. However, it remains difficult to increase the number of channels per node, thus the maximal degree of the network may be bounded. This is typically the case in grid topology networks, where each ... More
Electron-phonon scattering in topological insulatorsMar 01 2011We formulate and apply a theory of electron-phonon interactions for the surface state of a strong topological insulator. Phonons are modelled using an isotropic elastic continuum theory with stress-free boundary conditions and interact with the Dirac ... More
Deformations of constant mean curvature 1/2 surfaces in H2xR with vertical ends at infinityMar 04 2012Jul 19 2013We study constant mean curvature 1/2 surfaces in H2xR that admit a compactification of the mean curvature operator. We show that a particular family of complete entire graphs over H2 admits a structure of infinite dimensional manifold with local control ... More
Formulas for Continued Fractions. An Automated Guess and Prove ApproachJul 15 2015We describe a simple method that produces automatically closed forms for the coefficients of continued fractions expansions of a large number of special functions. The function is specified by a non-linear differential equation and initial conditions. ... More
The complexity of Shortest Common Supersequence for inputs with no identical consecutive lettersSep 02 2013Jan 08 2015The Shortest Common Supersequence problem (SCS for short) consists in finding a shortest common supersequence of a finite set of words on a fixed alphabet Sigma. It is well-known that its decision version denoted [SR8] in [Garey and Johnson] is NP-complete. ... More
Moving Toward High Precision Dynamical Modelling in Hidden Markov ModelsJul 01 2016Hidden Markov Model (HMM) is often regarded as the dynamical model of choice in many fields and applications. It is also at the heart of most state-of-the-art speech recognition systems since the 70's. However, from Gaussian mixture models HMMs (GMM-HMM) ... More
Factor Complexity of S-adic sequences generated by the Arnoux-Rauzy-Poincaré AlgorithmApr 16 2014The Arnoux-Rauzy-Poincar\'e multidimensional continued fraction algorithm is obtained by combining the Arnoux-Rauzy and Poincar\'e algorithms. It is a generalized Euclidean algorithm. Its three-dimensional linear version consists in subtracting the sum ... More
A systematic approach for doing an \textit{a priori} identifiability study of dynamical nonlinear modelsOct 23 2015Oct 10 2016This paper presents a method for investigating, through an automatic procedure, the (lack of) identifiability of parametrized dynamical models. This method takes into account constraints on parameters and returns parameters whose estimations make the ... More
Entropic CLT and phase transition in high-dimensional Wishart matricesSep 10 2015Sep 13 2015We consider high dimensional Wishart matrices $\mathbb{X} \mathbb{X}^{\top}$ where the entries of $\mathbb{X} \in {\mathbb{R}^{n \times d}}$ are i.i.d. from a log-concave distribution. We prove an information theoretic phase transition: such matrices ... More
The nature of the UV halo around the spiral galaxy NGC 3628Jan 22 2016Thanks to deep UV observations with GALEX and Swift, diffuse UV haloes have recently been discovered around galaxies. Based on UV-optical colours, it has been advocated that the UV haloes around spiral galaxies are due to UV radiation emitted from the ... More
A Chaining Algorithm for Online Nonparametric RegressionFeb 26 2015Jul 01 2015We consider the problem of online nonparametric regression with arbitrary deterministic sequences. Using ideas from the chaining technique, we design an algorithm that achieves a Dudley-type regret bound similar to the one obtained in a non-constructive ... More
Dynamical properties and characterization of gradient drift diffusionsDec 14 2006We study the dynamical properties of the Brownian diffusions having $\sigma {\rm Id}$ as diffusion coefficient matrix and $b=\nabla U$ as drift vector. We characterize this class through the equality $D^2_+=D^2_-$, where $D_{+}$ (resp. $D_-$) denotes ... More
Invertibility of random submatrices via tail decoupling and a Matrix Chernoff InequalityMar 15 2011Mar 19 2012Let $X$ be a $n\times p$ matrix with coherence $\mu(X)=\max_{j\neq j'} |X_j^tX_{j'}|$. We present a simplified and improved study of the quasi-isometry property for most submatrices of $X$ obtained by uniform column sampling. Our results depend on $\mu(X)$, ... More
Clustering of floaters on the free surface of a turbulent flow: an experimental studyOct 28 2014Jul 01 2016We present an experimental study of the statistical properties of millimeter-size spheres floating on the surface of a turbulent flow. The flow is generated in a layer of liquid metal by an electromagnetic forcing. By using two magnet arrays, we are able ... More
MCMC Louvain for Online Community DetectionDec 05 2016We introduce a novel algorithm of community detection that maintains dynamically a community structure of a large network that evolves with time. The algorithm maximizes the modularity index thanks to the construction of a randomized hierarchical clustering ... More
Large scale dynamics of the Persistent Turning Walker model of fish behaviorOct 26 2007This paper considers a new model of individual displacement, based on fish motion, the so-called Persistent Turning Walker (PTW) model, which involves an Ornstein-Uhlenbeck process on the curvature of the particle trajectory. The goal is to show that ... More
Learning nonsingular phylogenies and hidden Markov modelsFeb 18 2005Jul 05 2006In this paper we study the problem of learning phylogenies and hidden Markov models. We call a Markov model nonsingular if all transition matrices have determinants bounded away from 0 (and 1). We highlight the role of the nonsingularity condition for ... More
Refined Lower Bounds for Adversarial BanditsMay 24 2016We provide new lower bounds on the regret that must be suffered by adversarial bandit algorithms. The new results show that recent upper bounds that either (a) hold with high-probability or (b) depend on the total lossof the best arm or (c) depend on ... More
A macroscopic model for a system of swarming agents using curvature controlOct 26 2010In this paper, we study the macroscopic limit of a new model of collective displacement. The model, called PTWA, is a combination of the Vicsek alignment model and the Persistent Turning Walker (PTW) model of motion by curvature control. The PTW model ... More
Lifetime of dynamic heterogeneity in strong and fragile kinetically constrained spin modelsJun 24 2005Kinetically constrained spin models are schematic coarse-grained models for the glass transition which represent an efficient theoretical tool to study detailed spatio-temporal aspects of dynamic heterogeneity in supercooled liquids. Here, we study how ... More
Probabilistic Asynchronous Arbitrary Pattern FormationAug 15 2015Mar 14 2016We propose a new probabilistic pattern formation algorithm for oblivious mobile robots that operates inthe ASYNC model. Unlike previous work, our algorithm makes no assumptions about the local coordinatesystems of robots (the robots do not share a common ... More
The Random Bit Complexity of Mobile Robots ScatteringSep 25 2013Feb 24 2015We consider the problem of scattering $n$ robots in a two dimensional continuous space. As this problem is impossible to solve in a deterministic manner, all solutions must be probabilistic. We investigate the amount of randomness (that is, the number ... More
Minimax fast rates for discriminant analysis with errors in variablesJan 16 2012May 12 2015The effect of measurement errors in discriminant analysis is investigated. Given observations $Z=X+\epsilon$, where $\epsilon$ denotes a random noise, the goal is to predict the density of $X$ among two possible candidates $f$ and $g$. We suppose that ... More
The Quench ActionMar 15 2016Jul 15 2016We give a pedagogical introduction to the methodology of the Quench Action, which is an effective representation for the calculation of time-dependent expectation values of physical operators following a generic out-of-equilibrium state preparation protocol ... More
Comment on `Revisiting the Exact Dynamical Structure Factor of the Heisenberg Antiferromagnetic Model' by A. H. BougourziFeb 19 2014We point out the erroneous reasoning and disprove the conclusions contained in a recent preprint by A. H. Bougourzi (arxiv:1402.3855v1) concerning the spin structure factor of the Heisenberg model at zero field in the thermodynamic limit, as calculated ... More
Time evolution of a viscous protoplanetary disk with a free geometry: toward a more self-consistent pictureMar 25 2014Observations of protoplanetary disks show that some characteristics seem recurrent, even in star formation regions that are physically distant such as surface mass density profiles varying as $r^{-1}$, or aspect ratios about 0.03 to 0.23. Accretion rates ... More
Asymptotic behavior of the Eden model with positively homogeneous edge weightsAug 20 2015Aug 25 2015Let $d\in\mathbb N$, $\alpha\in\mathbb R$, and let $f :\mathbb R^d\setminus \{0\} \rightarrow (0,\infty)$ be locally Lipschitz and positively homogeneous of degree $\alpha$ (e.g. $f$ could be the $\alpha$th power of a norm on $\mathbb R^d$). We study ... More
Conception d'outils de communication spécifiques au contexte éducatifDec 11 2007In a distance learning context, providing usual communication tools (forum, chat, ...) is not always enough to create efficient interactions between learners and to favour collective knowledge building. A solution consists in setting-up collective activities ... More
Conceptions et usages des plates-formes de formation, Revue Sciences et Technologies de l'Information et de la Communication pour l'Éducation et la FormationDec 11 2007Educative platforms are at the heart of the development of online education. They can not only be reduced to technological aspects. Underlying models impact teaching and learning from the preparing of lessons to the learning sessions. Research related ... More
Stochastic embedding of dynamical systemsSep 30 2005Most physical systems are modelled by an ordinary or a partial differential equation, like the n-body problem in celestial mechanics. In some cases, for example when studying the long term behaviour of the solar system or for complex systems, there exist ... More
Discovering Network Topology in the Presence of Byzantine FaultsNov 22 2006We study the problem of Byzantine-robust topology discovery in an arbitrary asynchronous network. We formally state the weak and strong versions of the problem. The weak version requires that either each node discovers the topology of the network or at ... More
Physical measures for the geodesic flow tangent to a transversally conformal foliationDec 06 2015May 30 2016We consider a transversally conformal foliation $\mathcal{F}$ of a closed manifold $M$ endowed with a smooth Riemannian metric whose restriction to each leaf is negatively curved. We prove that it satisfies the following dichotomy. Either there is a transverse ... More
Exact Relation with Two-point Correlation Functions and Phenomenological Approach for Compressible Magnetohydrodynamic TurbulenceJan 11 2013Compressible isothermal magnetohydrodynamic turbulence is analyzed under the assumption of statistical homogeneity and in the asymptotic limit of large kinetic and magnetic Reynolds numbers. Following Kolmogorov we derive an exact relation for some two-point ... More
On two-dimensional supersymmetric quantum mechanics, pseudoanalytic functions and transmutation operatorsJul 01 2013Sep 09 2013Pseudoanalytic function theory is considered to study a two-dimensional supersymmetric quantum mechanics system. Hamiltonian components of the superhamiltonian are factorized in terms of one Vekua and one Bers derivative operators. We show that imaginary ... More
A d-dimensional extension of Christoffel wordsApr 15 2014In this article, we extend the definition of Christoffel words to directed subgraphs of the hypercubic lattice in arbitrary dimension that we call Christoffel graphs. Christoffel graphs when $d=2$ correspond to well-known Christoffel words. Due to periodicity, ... More
Continuum limit of self-driven particles with orientation interactionOct 01 2007We consider the discrete Couzin-Vicsek algorithm (CVA), which describes the interactions of individuals among animal societies such as fish schools. In this article, we propose a kinetic (mean-field) version of the CVA model and provide its formal macroscopic ... More
Arithmeticity of discrete subgroups containing horospherical latticesApr 30 2018Let $G$ be a semisimple real algebraic Lie group of real rank at least two and $U$ be the unipotent radical of a non-trivial parabolic subgroup. We prove that a discrete Zariski dense subgroup of $G$ that contains an irreducible lattice of $U$ is an arithmetic ... More
Tropical and non-Archimedean limits of degenerating families of volume formsMay 17 2016Dec 20 2016We study the asymptotic behavior of volume forms on a degenerating family of compact complex manifolds. Under rather general conditions, we prove that the volume forms converge in a natural sense to a Lebesgue-type measure on a certain simplicial complex. ... More
Phoretic self-propulsion at finite Péclet numbersMar 14 2014Phoretic self-propulsion is a unique example of force- and torque-free motion on small scales. The classical framework describing the flow field around a particle swimming by self-diffusiophoresis neglects the advection of the solute field by the flow ... More
On Byzantine Broadcast in Planar GraphsJan 14 2013Dec 07 2013We consider the problem of reliably broadcasting information in a multihop asynchronous network in the presence of Byzantine failures: some nodes may exhibit unpredictable malicious behavior. We focus on completely decentralized solutions. Few Byzantine-robust ... More
On Byzantine Broadcast in Loosely Connected NetworksSep 05 2012We consider the problem of reliably broadcasting information in a multihop asynchronous network that is subject to Byzantine failures. Most existing approaches give conditions for perfect reliable broadcast (all correct nodes deliver the authentic message ... More
An All-Sky Catalog of Bright M DwarfsAug 12 2011We present an all-sky catalog of M dwarf stars with apparent infrared magnitude J<10. The 8,889 stars are selected from the ongoing SUPERBLINK survey of stars with proper motion >40 mas/yr, supplemented on the bright end with the TYCHO-2 catalog. Completeness ... More
An original image slicer designed for Integral Field Spectroscopy with NIRSpec/JSWTDec 01 2005Integral Field Spectroscopy (IFS) provides a spectrum simultaneously for each spatial sample of an extended, two-dimensional field. It consists of an Integral Field Unit (IFU) which slices and re-arranges the initial field along the entrance slit of a ... More
Noisy classification with boundary assumptionsJul 12 2013We address the problem of classification when data are collected from two samples with measurement errors. This problem turns to be an inverse problem and requires a specific treatment. In this context, we investigate the minimax rates of convergence ... More
Friction of spheres on a rotating parabolic supportOct 27 2014This article illustrates the role of friction on the motion of a rolling sphere on pedagogical example. We use a parabolic support rotating around it axis to study the static equilibrium positions of a single sphere. Due to the particular choice of the ... More
Kondo screening by the surface modes of a strong topological insulatorApr 25 2013We consider a magnetic impurity deposited on the surface of a strong topological insulator and interacting with the surface modes by a Kondo exchange interaction. Taking into account the warping of the Fermi line of the surface modes, we derive a mapping ... More
Linear Sum Assignment with EditionMar 14 2016Mar 23 2016We consider the problem of transforming a set of elements into another by a sequence of elementary edit operations, namely substitutions, removals and insertions of elements. Each possible edit operation is penalized by a non-negative cost and the cost ... More