Robust capacitated trees and networks with uniform demands

We are interested in the design of robust (or resilient) capacitated rooted Steiner networks in case of terminals with uniform demands. Formally, we are given a graph, capacity and cost functions on the edges, a root, a subset of nodes called terminals, and a bound k on the number of edge failures. We first study the problem where k = 1 and the network that we want to design must be a tree covering the root and the terminals: we give complexity results and propose models to optimize both the cost of the tree and the number of terminals disconnected from the root in the worst case of an edge failure, while respecting the capacity constraints on the edges. Second, we consider the problem of computing a minimum-cost survivable network, i.e., a network that covers the root and terminals even after the removal of any k edges, while still respecting the capacity constraints on the edges. We also consider the possibility of protecting a given number of edges. We propose three different formulations: a cut-set based formulation, a flow based one, and a bilevel one (with an attacker and a defender). We propose algorithms to solve each formulation and compare their efficiency

Elèves en rupture scolaire :: regards sur l’école, l’estime de soi et la réintégration

Le contenu de cette recherche vise à explorer ce que les élèves en rupture scolaire vivent dans leur quotidien. Afin que cette exploration soit réalisable, j’ai choisi de sélectionner trois axes. Le premier étant celui de la perception de l’école des élèves en rupture scolaire. Le second celui de l’estime de soi de ces derniers. Finalement, le dernier de ces axes vise à entendre ces élèves, sortis de leur classe ordinaire, au sujet de leur réinsertion dans leur classe. Pour ce faire, ce travail contient une problématique qui renseigne le lecteur sur mes intentions, puis, une partie théorique qui permet de se familiariser avec le sujet. Suite à cela, je propose une méthodologie qui présente très concrètement les structures d’accueil que j’ai eues la chance de visiter et le guide d’entretien que j’ai employé pour me rendre sur le terrain. Finalement, je termine mon mémoire par une analyse des données récoltées grâce au témoignage d’élèves en rupture scolaire et une conclusion qui me permettra de faire une synthèse de l’ensemble de mon mémoire

Confidence Bounds for the Estimation of the Volume Phase Fraction from a Single Image in a Nickel Base Superalloy

We propose an image-based framework to evaluate the uncertainty in the estimation of the volume fraction of specific microstructures based on the observation of a single section. These microstructures consist of cubes organized on a cubic mesh, such as monocrystalline nickel base superalloys. The framework is twofold: a model-based stereological analysis allows relating two-dimensional image observations to three-dimensional microstructure features, and a spatial statistical analysis allows computing approximate confidence bounds while assessing the representativeness of the image. The reliability of the method is assessed on synthetic models. Volume fraction estimation variances and approximate confidence intervals are computed on real superalloy images in the context of material characterizatio

Reformulation of a locally optimal heuristic for modularity maximization

National audienceA network, or graph, G = (V,E) consists of a set of vertices V = {1, . . . , n} and a set of edges E = {1, . . . ,m} connecting vertices. One of the most studied problems in the field of complex systems is to find communities, or clusters, in networks. A community consists of a subset S of the vertices of V where inner edges connecting pairs of vertices of S are more dense than cut edges connecting vertices of S to vertices of V \S. Many criteria have been proposed to evaluate partitions of V into communities

A batch scheduler with high level components

In this article we present the design choices and the evaluation of a batch scheduler for large clusters, named OAR. This batch scheduler is based upon an original design that emphasizes on low software complexity by using high level tools. The global architecture is built upon the scripting language Perl and the relational database engine Mysql. The goal of the project OAR is to prove that it is possible today to build a complex system for ressource management using such tools without sacrificing efficiency and scalability. Currently, our system offers most of the important features implemented by other batch schedulers such as priority scheduling (by queues), reservations, backfilling and some global computing support. Despite the use of high level tools, our experiments show that our system has performances close to other systems. Furthermore, OAR is currently exploited for the management of 700 nodes (a metropolitan GRID) and has shown good efficiency and robustness

La lagune de Saquarema (Brésil) : hydroclimat, seston et éléments biogéniques au cours d'un cycle annuel

La lagune de Saquarema (située entre 42° et 43° de longitude ouest et à environ 23° de latitude sud, de superficie et de profondeur respectivement égales à 23 km2 et 1,15 m) fait partie d'une série de lagunes cotières de l'Etat de Rio Janeiro soumises à des degrés divers à la pression anthropique. Une description de son environnement est présentée, portant sur l'évolution au cours de 1987, de l'hydroclimat, du seston et des éléments biogéniques dissous. Il est observé une grande variabilité temporelle contrôlée principalement par l'alternance brusque d'eaux d'origines continentale et marine et aussi un gradient spatial bien marqué provenant d'une subdivision de la lagune en un compartiment à plus forte influence marine atteint par la pollution domestique. Cette lagune passe d'un état modérément eutrophe en hiver (par exemple Chla = 28 à 40 microg/l) à un état hypereutrophe en été (par exemple Chla = 300 microg/l) qui peut conduire à une crise dystrophique suivie de mortalité de poissons (cas d'avril 1987). (Résumé d'auteur

Structure and equation of state of interaction site models for disc-shaped lamellar colloids

We apply RISM (Reference Interaction Site Model) and PRISM (polymer-RISM) theories to calculate the site-site pair structure and the osmotic equation of state of suspensions of circular or hexagonal platelets (lamellar colloids) over a range of ratios of the particle diameter over thickness. Despite the neglect of edge effects, the simpler PRISM theory yields results in good agreement with the more elaborate RISM calculations, provided the correct form factor, characterizing the intramolecular structure of the platelets, is used. The RISM equation of state is sensitive to the number of sites used to model the platelets, but saturates when the hard spheres, associated with the interaction sites, nearly touch; the limiting equation of state agrees reasonably well with available simulation data for all densities up to the isotropic-nematic transition. When properly scaled with the second virial coefficient, the equations of state of platelets with different aspect ratios nearly collapse on a single master curve.Comment: 10 Pages, 11 Figures, Typesetted using RevTeX