An Oracle Approach for Interaction Neighborhood Estimation in Random Fields

We consider the problem of interaction neighborhood estimation from the partial observation of a finite number of realizations of a random field. We introduce a model selection rule to choose estimators of conditional probabilities among natural candidates. Our main result is an oracle inequality satisfied by the resulting estimator. We use then this selection rule in a two-step procedure to evaluate the interacting neighborhoods. The selection rule selects a small prior set of possible interacting points and a cutting step remove from this prior set the irrelevant points. We also prove that the Ising models satisfy the assumptions of the main theorems, without restrictions on the temperature, on the structure of the interacting graph or on the range of the interactions. It provides therefore a large class of applications for our results. We give a computationally efficient procedure in these models. We finally show the practical efficiency of our approach in a simulation study.Comment: 36 pages, 10 figure

Exhaustive Search for Small Dimension Recursive MDS Diffusion Layers for Block Ciphers and Hash Functions

This article presents a new algorithm to find MDS matrices that are well suited for use as a diffusion layer in lightweight block ciphers. Using an recursive construction, it is possible to obtain matrices with a very compact description. Classical field multiplications can also be replaced by simple F2-linear transformations (combinations of XORs and shifts) which are much lighter. Using this algorithm, it was possible to design a 16x16 matrix on a 5-bit alphabet, yielding an efficient 80-bit diffusion layer with maximal branch number.Comment: Published at ISIT 201

Geometric analysis of the linear Boltzmann equation I. Trend to equilibrium

This work is devoted to the analysis of the linear Boltzmann equation in a bounded domain, in the presence of a force deriving from a potential. The collision operator is allowed to be degenerate in the following two senses: (1) the associated collision kernel may vanish in a large subset of the phase space; (2) we do not assume that it is bounded below by a Maxwellian at infinity in velocity. We study how the association of transport and collision phenomena can lead to convergence to equilibrium, using concepts and ideas from control theory. We prove two main classes of results. On the one hand, we show that convergence towards an equilibrium is equivalent to an almost everywhere geometric control condition. The equilibria (which are not necessarily Maxwellians with our general assumptions on the collision kernel) are described in terms of the equivalence classes of an appropriate equivalence relation. On the other hand, we characterize the exponential convergence to equilibrium in terms of the Lebeau constant, which involves some averages of the collision frequency along the flow of the transport. We handle several cases of phase spaces, including those associated to specular reflection in a bounded domain, or to a compact Riemannian manifold

Electric-field induced dipole blockade with Rydberg atoms

High resolution laser Stark excitation of np (60 < n < 85) Rydberg states of ultra-cold cesium atoms shows an efficient blockade of the excitation attributed to long-range dipole-dipole interaction. The dipole blockade effect is observed as a quenching of the Rydberg excitation depending on the value of the dipole moment induced by the external electric field. Effects of eventual ions which could match the dipole blockade effect are discussed in detail but are ruled out for our experimental conditions. Analytic and Monte-Carlo simulations of the excitation of an ensemble of interacting Rydberg atoms agree with the experiments indicates a major role of the nearest neighboring Rydberg atom.Comment: 4 page

Dipole blockade through Rydberg Forster resonance energy transfer

High resolution laser excitation of np Rydberg states of cesium atoms shows a dipole blockade at F\"{o}rster resonances corresponding to the resonant dipole-dipole energy transfer of the np + np &#8594; ns + (n + 1)s reaction. The dipole-dipole interaction can be tuned on and off by the Stark effect, and such a process observed for relatively low n (25 &#8722; 41) is promising for quantum gate devices. Both Penning ionization and saturation in the laser excitation can limit the range of observation of the dipole blockadeComment: number of pages:

Segmentation Propagation in ImageNet

Abstract. ImageNet is a large-scale hierarchical database of object classes. We propose to automatically populate it with pixelwise segmentations, by leveraging existing manual annotations in the form of class labels and bounding-boxes. The key idea is to recursively exploit images segmented so far to guide the segmentation of new images. At each stage this propagation process expands into the images which are easiest to segment at that point in time, e.g. by moving to the semantically most related classes to those segmented so far. The propagation of segmentation occurs both (a) at the image level, by transferring existing segmentations to estimate the probability of a pixel to be foreground, and (b) at the class level, by jointly segmenting images of the same class and by importing the appearance models of classes that are already segmented. Through an experiment on 577 classes and 500k images we show that our technique (i) annotates a wide range of classes with accurate segmentations; (ii) effectively exploits the hierarchical structure of ImageNet; (iii) scales efficiently; (iv) outperforms a baseline GrabCut [1] initialized on the image center, as well as our recent segmentation transfer technique [2] on which this paper is based. Moreover, our method also delivers state-of-the-art results on the recent iCoseg dataset for co-segmentation.

The Discriminatory Effect of Domestic Regulations on International Trade in Services: Evidence from Firm-Level Data

URL des Documents de travail : http://centredeconomiesorbonne.univ-paris1.fr/bandeau-haut/documents-de-travail/Documents de travail du Centre d'Economie de la Sorbonne 2013.19 - ISSN : 1955-611XIn order to promote international trade in services, the WTO-GATS aims at progressively eliminating discriminatory regulations, which apply to foreign suppliers, byguaranteeing equal national treatment. This paper looks instead at the trade effect of domestic regulations, which apply to all firms indifferently and do not intend to exclude foreign suppliers. We propose a theory-based empirical test to determine whether or not these domestic regulations affect foreign suppliers more than local ones. We take this test to the data by using French firm-level exports of professional services to OECD countries. Our econometric results show that domestic regulations in the importing markets matter significantly for trade in services. They reduce both the decision to export and the individual exports. These results tend to prove that domestic regulations are de facto discriminatory even if they are not de jure.Afin de promouvoir le commerce international de services, l'AGCS (OMC) a pour but l'élimination des régulations discriminantes qui s'appliquent aux entreprises étrangères, en garantissant un accès au marché identique à toutes les entreprises. Dans cet article, nous nous intéressons aux régulations qui sont non discriminantes par nature, et s'appliquent de manière identique aux entreprises domestiques et étrangères. Nous proposons un test empirique basé sur un modèle simple de commerce international avec firmes hétérogènes, afin de déterminer si ces régulations affectent plus les entreprises étrangères que les entreprises domestiques. Nous utilisons des données individuelles sur les exportations de services professionnels par les entreprises françaises vers les pays de l'OCDE. Nos résultats montrent que les régulations dans les secteurs des services des pays importateurs constituent une barrière importante au commerce international de services. Ces régulations réduisent à la fois la probabilité d'exporter, et les exportations individuelles. Ces résultats montrent que les régulations domestiques sont discriminantes de facto, même si elles ne le sont pas de jure

A semi-adaptive frequency control law for flexible structures

Piloting flexible structures has become a major concern for control law designers. robustness to parameters variation of the flexible modes is necessary to guarentee stability. The method introduced in this paper makes use of a semi-adaptive frequency control law. Performance for the rigid dynamics of the structure is obtained through a classical linear controller. The adaptive part of the control deals only with updating a controller in charge of following the flexible modes fluctuation. Doing so our global strategy satisfies both the robustness and the performance requirements