Publications

2013

• La conjecture de Syracuse -visualisation tridimensionnelle
  
  • Colonna Jean-François
  , 2013. The Syracuse conjecture -tridimensional display- (La conjecture de Syracuse -visualisation tridimensionnelle-)
• La conjecture de Syracuse -visualisation bidimensionnelle
  
  • Colonna Jean-François
  , 2013. The Syracuse conjecture -bidimensional display- (La conjecture de Syracuse -visualisation bidimensionnelle-)
• La conjecture de Syracuse -visualisation monodimensionnelle
  
  • Colonna Jean-François
  , 2013. The Syracuse conjecture -monodimensional display- (La conjecture de Syracuse -visualisation monodimensionnelle-)
• La conjecture de Syracuse -visualisation monodimensionnelle
  
  • Colonna Jean-François
  , 2013. The Syracuse conjecture -monodimensional display- (La conjecture de Syracuse -visualisation monodimensionnelle-)
• La conjecture de Syracuse -visualisation monodimensionnelle
  
  • Colonna Jean-François
  , 2013. The Syracuse conjecture -monodimensional display- (La conjecture de Syracuse -visualisation monodimensionnelle-)
• La conjecture de Syracuse -visualisation monodimensionnelle
  
  • Colonna Jean-François
  , 2013. The Syracuse conjecture -monodimensional display- (La conjecture de Syracuse -visualisation monodimensionnelle-)
• La conjecture de Syracuse -visualisation monodimensionnelle
  
  • Colonna Jean-Francois
  , 2013. The Syracuse conjecture -monodimensional display- (La conjecture de Syracuse -visualisation monodimensionnelle-)
• La conjecture de Syracuse -visualisation monodimensionnelle
  
  • Colonna Jean-Francois
  , 2013. The Syracuse conjecture -monodimensional display- (La conjecture de Syracuse -visualisation monodimensionnelle-)
• Les deux premières itérations de la construction de la courbe de von Koch
  
  • Colonna Jean-Francois
  , 2013. The first two iterations of the construction of the von Koch curve (Les deux premières itérations de la construction de la courbe de von Koch)
• Un 'double sphere' défini à l'aide de trois champs bidimensionnels
  
  • Colonna Jean-Francois
  , 2013. A 'double sphere' defined by means of three bidimensional fields (Un 'double sphere' défini à l'aide de trois champs bidimensionnels)
• L’opérateur de Laplace-Beltrami en Géométrie presque-Riemannienne
  
  • Boscain Ugo
  • Laurent Camille
  Annales de l'Institut Fourier, Association des Annales de l'Institut Fourier, 2013, 63 (5), pp.1739 - 1770. Two-dimensional almost-Riemannian structures are generalized Riemannian structures on surfaces for which a local orthonormal frame is given by a Lie bracket generating pair of vector fields that can become collinear. Generically, the singular set is an embedded one dimensional manifold and there are three type of points: Riemannian points where the two vector fields are linearly independent, Grushin points where the two vector fields are collinear but their Lie bracket is not and tangency points where the two vector fields and their Lie bracket are collinear and the missing direction is obtained with one more bracket. Generically tangency points are isolated. In this paper we study the Laplace-Beltrami operator on such a structure. In the case of a compact orientable surface without tangency points, we prove that the Laplace-Beltrami operator is essentially self-adjoint and has discrete spectrum. As a consequence a quantum particle in such a structure cannot cross the singular set and the heat cannot flow through the singularity. This is an interesting phenomenon since when approaching the singular set (i.e. where the vector fields become collinear), all Riemannian quantities explode, but geodesics are still well defined and can cross the singular set without singularities. This phenomenon appears also in sub-Riemannian structure which are not equiregular i.e. in which the grow vector depends on the point. We show this fact by analyzing the Martinet case. (10.5802/aif.2813)
  DOI : 10.5802/aif.2813
• Un cylindre défini à l'aide de trois champs bidimensionnels
  
  • Colonna Jean-Francois
  , 2013. A cylinder defined by means of three bidimensional fields (Un cylindre défini à l'aide de trois champs bidimensionnels)
• Une surface intermédiaire entre une 'double sphère' et un cylindre
  
  • Colonna Jean-Francois
  , 2013. A surface between a 'double sphere' and a cylinder (Une surface intermédiaire entre une 'double sphère' et un cylindre)
• Une surface intermédiaire entre une 'double sphère' et un cylindre
  
  • Colonna Jean-Francois
  , 2013. A surface between a 'double sphere' and a cylinder (Une surface intermédiaire entre une 'double sphère' et un cylindre)
• La conjecture de Goldbach
  
  • Colonna Jean-Francois
  , 2013. The Goldbach conjecture (La conjecture de Goldbach)
• La conjecture de Goldbach
  
  • Colonna Jean-Francois
  , 2013. The Goldbach conjecture (La conjecture de Goldbach)
• Une surface intermédiaire entre une 'double sphère' et un cylindre
  
  • Colonna Jean-Francois
  , 2013. A surface between a 'double sphere' and a cylinder (Une surface intermédiaire entre une 'double sphère' et un cylindre)
• An Optimal Affine Invariant Smooth Minimization Algorithm
  
  • d'Aspremont Alexandre
  • Guzmán Cristóbal
  • Jaggi Martin
  , 2013. We formulate an affine invariant implementation of the algorithm in Nesterov (1983). We show that the complexity bound is then proportional to an affine invariant regularity constant defined with respect to the Minkowski gauge of the feasible set. We also detail matching lower bounds when the feasible set is an ℓp ball. In this setting, our bounds on iteration complexity for the algorithm in Nesterov (1983) are thus optimal in terms of target precision, smoothness and problem dimension.
• Agrandissement d'un ensemble de Mandelbrot dans l'ensemble des pseudo-octonions (un 'Mandelbulb') pour seize éclairages différents -section tridimensionnelle
  
  • Colonna Jean-François
  , 2013. Close-up on a pseudo-octonionic Mandelbrot set (a 'Mandelbulb') for sixteen different lightings -tridimensional cross-section- (Agrandissement d'un ensemble de Mandelbrot dans l'ensemble des pseudo-octonions (un 'Mandelbulb') pour seize éclairages différents -section tridimensionnelle-)
• Energy and regularity dependent stability estimates for near-field inverse scattering in multidimensions
  
  • Isaev Mikhail
  Journal of Mathematics, Hindawi Publishing Corp., 2013, pp.DOI:10.1155/2013/318154. We prove new global Hölder-logarithmic stability estimates for the near-field inverse scattering problem in dimension $d\geq 3$. Our estimates are given in uniform norm for coefficient difference and related stability efficiently increases with increasing energy and/or coefficient regularity. In addition, a global logarithmic stability estimate for this inverse problem in dimension $d=2$ is also given. (10.1155/2013/318154)
  DOI : 10.1155/2013/318154
• On the asymptotics of a Robin eigenvalue problem
  
  • Cakoni Fioralba
  • Chaulet Nicolas
  • Haddar Houssem
  Comptes Rendus. Mathématique, Académie des sciences (Paris), 2013, 351, pp.517-521. The considered Robin problem can formally be seen as a small perturbation of a Dirichlet problem. However, due to the sign of the impedance value, its associated eigenvalues converge point-wise to −∞ as the perturbation goes to zero. We prove in this case that Dirichlet eigenpairs are the only accumulation points of the Robin eigenpairs with normalized eigenvectors. We then provide a criterion to select accumulating sequences of eigenvalues and eigenvectors and exhibit their full asymptotic with respect to the small parameter. (10.1016/j.crma.2013.07.022)
  DOI : 10.1016/j.crma.2013.07.022
• Asymptotic enumeration of Eulerian orientations for graphs with strong mixing properties
  
  • Isaev Mikhail
  • Kseniia Isaeva
  Journal of Applied and Industrial Mathematics / Sibirskii Zhurnal Industrial'noi Matematiki and Diskretnyi Analiz i Issledovanie Operatsii, MAIK Nauka/Interperiodica, 2013, 20 (6), pp.40-58. We prove an asymptotic formula for the number of Eulerian orientations for graphs with strong mixing properties and with vertices having even degrees. The exact value is determined up to the multiplicative error O(n^{-1+epsilon}), where n is the number of vertices.
• A homogenization approach for the motion of motor proteins
  
  • Mirrahimi Sepideh
  • Souganidis Panagiotis E.
  Nonlinear Differential Equations and Applications, Springer Verlag, 2013, 20, pp.129-147. We consider the asymptotic behavior of an evolving weakly coupled Fokker-Planck system of two equations set in a periodic environment. The magnitudes of the diffusion and the coupling are respectively proportional and inversely proportional to the size of the period. We prove that, as the period tends to zero, the solutions of the system either propagate (concentrate) with a fixed constant velocity (determined by the data) or do not move at all. The system arises in the modeling of motor proteins which can take two different states. Our result implies that, in the limit, the molecules either move along a filament with a fixed direction and constant speed or remain immobile. (10.1007/s00030-012-0156-3)
  DOI : 10.1007/s00030-012-0156-3
• Time-reversal in visco-elastic media.
  
  • Ammari Habib
  • Bretin Elie
  • Garnier Josselin
  • Wahab Abdul
  European Journal of Applied Mathematics, Cambridge University Press (CUP), 2013 (24), pp.565-600. In this paper, we consider the problem of reconstructing sources in a homogeneous viscoelastic medium from wavefield measurements. We first present a modified time-reversal imaging algorithm based on a weighted Helmholtz decomposition and justify mathematically that it provides a better approximation than by simply time reversing the displacement field, where artifacts due to the coupling betwe en the pressure and shear waves appear. Then, we investigate the source inverse problem in an elastic attenuating medium. We provide a regularized time-reversal imagin g which corrects the attenuation effect at the first order. The results of this paper yie ld the fundamental tools for solving imaging problems in elastic media using cross correl ation techniques
• Daphnias: from the individual based model to the large population equation
  
  • Metz J.A.J.
  • Tran Viet Chi
  Journal of Mathematical Biology, Springer, 2013, 66 (4-5), pp.915--933. The class of deterministic 'Daphnia' models treated by Diekmann et~al. (J Math Biol 61: 277--318, 2010) has a long history going back to Nisbet and Gurney (Theor Pop Biol 23: 114--135, 1983) and Diekmann et~al. (Nieuw Archief voor Wiskunde 4: 82--109, 1984). In this note, we formulate the individual based models (IBM) supposedly underlying those deterministic models. The models treat the interaction between a general size-structured consumer population ('Daphnia') and an unstructured resource ('algae'). The discrete, size and age-structured Daphnia population changes through births and deaths of its individuals and throught their aging and growth. The birth and death rates depend on the sizes of the individuals and on the concentration of the algae. The latter is supposed to be a continuous variable with a deterministic dynamics that depends on the Daphnia population. In this model setting we prove that when the Daphnia population is large, the stochastic differential equation describing the IBM can be approximated by the delay equation featured in (Diekmann et~al., l.c.). (10.1007/s00285-012-0619-5)
  DOI : 10.1007/s00285-012-0619-5