Convex circuit free coloration of an oriented graph

We introduce the \textit{convex circuit-free coloration} and \textit{convex circuit-free chromatic number} $\overrightarrow{\chi_a}(\overrightarrow{G})$ of an oriented graph $\overrightarrow{G}$ and establish various basic results. We show that the problem of deciding if an oriented graph verifies $\chi_a( \overrightarrow{G}) \leq k$ is NP-complete if $k \geq 3$ and polynomial if $k \leq 2$. We exhibit an algorithm which finds the optimal convex circuit-free coloration for tournaments, and characterize the tournaments that are \textit{vertex-critical} for the convex circuit-free coloration

Tournois sans intervalle acyclique.

Un intervalle X d'un tournoi T est un ensemble de sommets de T tel que tout sommet extérieur à X domine ou est dominé par tous les sommets de X. Nous caractérisons les tournois dont tous les intervalles acycliques non vides sont des singletons et qui sont critiques pour cette propriété, c'est-à-dire que la suppression d'un sommet quelconque du tournoi donne naissance à au moins un intervalle acyclique de plus de 2 sommets. Ces tournois sont exactement ceux construits comme la composition d'un tournoi quelconque avec des tournois circulants. Ce travail sur les intervalles acycliques a été motivé par la recherche de structures ordonnées dans des tournois pour lesquels aucun ordre médian ne s'impose naturellement

Molding direction constraints in structural optimization via a level-set method

International audienceIn the framework of structural optimization via a level-set method, we develop an approach to handle the directional molding constraint for cast parts. A novel molding condition is formulated and a penalization method is used to enforce the constraint. A first advantage of our new approach is that it does not require to start from a feasible initialization, but it guarantees the convergence to a castable shape. A second advantage is that our approach can incorporate thickness constraints too. We do not adress the optimization of the casting system, which is considered a priori defined. We show several 3d examples of compliance minimization in linearized elasticity under molding and minimal or maximal thickness constraints. We also compare our results with formulations already existing in the literature

Front-End Electronics of the ALICE dimuon trigger

This document presents the design and performance of the Front-End Electronics (FEE) developed for the ALICE dimuon trigger operating with Resistive Plate Chambers (RPCs) in streamer mode. This electronics, yet ready for production, is based on a dedicated ASIC designed at LPC Clermont-Fd

Thickness control in structural optimization via a level set method

International audienceIn the context of structural optimization via a level-set method we propose a framework to handle geometric constraints related to a notion of local thickness. The local thickness is calculated using the signed distance function to the shape. We formulate global constraints using integral functionals and compute their shape derivatives. We discuss diff erent strategies and possible approximations to handle the geometric constraints. We implement our approach in two and three space dimensions for a model of linearized elasticity. As can be expected, the resulting optimized shapes are strongly dependent on the initial guesses and on the speci fic treatment of the constraints since, in particular, some topological changes may be prevented by those constraints

Damage and fracture evolution in brittle materials by shape optimization methods

International audienceThis paper is devoted to a numerical implementation of the Francfort-Marigo model of damage evolution in brittle materials. This quasi-static model is based, at each time step, on the minimization of a total energy which is the sum of an elastic energy and a Griffith-type dissipated energy. Such a minimization is carried over all geometric mixtures of the two, healthy and damaged, elastic phases, respecting an irreversibility constraint. Numerically, we consider a situation where two well-separated phases coexist, and model their interface by a level set function that is transported according to the shape derivative of the minimized total energy. In the context of interface variations (Hadamard method) and using a steepest descent algorithm, we compute local minimizers of this quasi-static damage model. Initially, the damaged zone is nucleated by using the so-called topological derivative. We show that, when the damaged phase is very weak, our numerical method is able to predict crack propagation , including kinking and branching. Several numerical examples in 2d and 3d are discussed

Pediatric orthopedic surgery in humanitarian aid

Pediatric orthopedic surgery in humanitarian aid is conducted mainly in cooperation with emerging countries. Each mission is different, and depends on numerous parameters such as the country, the frequency of such missions, the pathologies encountered, the local structure and team, and the non-governmental organization (NGO) involved. Pathologies vary in etiology (tuberculosis, poliomyelitis) and severity. Each mission requires the presence of an experienced surgeon. Working conditions are often rudimentary. Surgical indications should be restricted to procedures that are going to be effective, with minimal postoperative complications, without any surgical "acrobatics". Teaching should be in association with the local university, and adapted to local needs. Mission objectives need to be realistic. Surgical indications should be adapted to local conditions, and the surgeon needs to be able to say "no" to procedures involving undue risk. The surgeon on mission should cooperate with local teams and be able to adapt to unusual situations. Assessment of results is essential to improving efficacy and evaluating the success of the mission