Mechanical damage, chemical damage and permeability in quasi-brittle cementitious materials

International audienceThe serviceability of concrete structures is a coupled problem in which fracture and damage are coupled with several environmental attacks. In this paper, we start with the description of chemo-mechanical damage and the case of calcium leaching which is relevant to waste containment vessels. The second example of implementation of continuum damage models discussed deals with coupled damage permeability effects. In the case of diffuse damage, the material permeability is controlled by the decrease of average stiffness due to micro-cracking. After a macro-crack has formed, permeability is controlled by a power function of the crack opening (Poiseuille flow). A relationship between permeability and damage, consistent with the two above asymptotic cases, is defined.La durabilité de structures en béton est un problème dans lequel la rupture et l'endommagement sont couplés aux différentes attaques de l'environnement. Nous commençons par illustrer un tel couplage avec la lixiviation et la modélisation chimiomécanique de l'endommagement dans les bétons. Les couplages entre l'endommagement et les propriétés de transport du béton sont le deuxième exemple traité. Dans le cas d'un endommagement diffus, la perméabilité du matériau est contrôlée par la diminution de raideur moyenne due à la microfissuration. Lorsqu'une macrofissure s'est formée, la perméabilité est contrôlée par une fonction puissance de l'ouverture de fissure (écoulement de Poiseuille). Une relation entre la perméabilité et l'endommagement est définie, en accord avec ces deux cas limites

Bootstrap methods applied to indirect measurement

A biased bootstrap technique is presented to obtain robust parameter and measurement estimates. Moreover, the estimation of a measurement probability density function (pdf) using classical bootstrap techniques is presented as our final goal. Most of the time, large scale repetition of an experiment is not economically feasible, the Monte Carlo method cannot be used for uncertainty characterization and bootstrap methods are proved to be a potentially useful alternative. The measurement characterization is driven by the pdf estimation in a non-linear non-Gaussian case and with limited observed data

Bootstrap methods applied to indirect measurement

A biased bootstrap technique is presented to obtain robust parameter and measurement estimates. Moreover, the estimation of a measurement probability density function (pdf) using classical bootstrap techniques is presented as our final goal. Most of the time, large scale repetition of an experiment is not economically feasible, the Monte Carlo method cannot be used for uncertainty characterization and bootstrap methods are proved to be a potentially useful alternative. The measurement characterization is driven by the pdf estimation in a non-linear non-Gaussian case and with limited observed data

An Interval Branch and Bound Algorithm for Parameter Estimation

International audienceThe parameter estimation problem is a widespread and challenging problem in engineering sciences consisting in computing the parameters of a parametric model that fit observed data. The computer vision community has proposed the RANSAC algorithm to deal with outliers in the observed data. This randomized algorithm is efficient but non-deterministic and therefore incomplete. Jaulin et al. propose a branch-and-contract algorithm that returns all the model instances fitting at least q observations. Assuming that at least q observed data are inliers, this algorithm achieves on the observations a relaxed intersection operator called q-intersection. First, this paper presents several improvements to Jaulin et al.'s algorithm. Second, an interval branch and bound algorithm is designed to produce a model that can explain the maximum number of observations within a given tolerance. Experiments are carried out on computer vision and image processing problems. They highlight a significant speedup w.r.t. Jaulin et al.'s interval method in 2D and 3D shape recognition problems. We have also investigated how the approach scales up in dimensions up to 7 for stereovision (estimation of essential and fundamental matrices)

Improving a Constraint Programming Approach for Parameter Estimation

International audienceThe parameter estimation problem is a widespread and challenging problem in engineering sciences consisting in computing the parameters of a parametric model that fit observed data. Calibration or geolocation can be viewed as specific parameter estimation problems. In this paper we address the problem of finding all the instances of a parametric model that can explain at least q observations within a given tolerance. The computer vision community has proposed the RANSAC algorithm to deal with outliers in the observed data. This randomized algorithm is efficient but non-deterministic and therefore incomplete. Jaulin et al. proposes a complete and combinatorial algorithm that exhaustively traverses the whole space of parameter vectors to extract the valid model instances. This algorithm is based on interval constraint programming methods and on a so called q-intersection operator, a relaxed intersection operator that assumes that at least q observed data are inliers. This paper proposes several improvements to Jaulin et al.'s algorithm. Most of them are generic and some others are dedicated to the shape detection problem used to validate our approach. Compared to Jaulin et al.'s algorithm, our algorithm can guarantee a number of fitted observations in the produced model instances. Also, first experiments in plane and circle recognition highlight speedups of two orders of magnitude

Drug Use on Mont Blanc: A Study Using Automated Urine Collection

Mont Blanc, the summit of Western Europe, is a popular but demanding high-altitude ascent. Drug use is thought to be widespread among climbers attempting this summit, not only to prevent altitude illnesses, but also to boost physical and/or psychological capacities. This practice may be unsafe in this remote alpine environment. However, robust data on medication during the ascent of Mont Blanc are lacking. Individual urine samples from male climbers using urinals in mountain refuges on access routes to Mont Blanc (Goûter and Cosmiques mountain huts) were blindly and anonymously collected using a hidden automatic sampler. Urine samples were screened for a wide range of drugs, including diuretics, glucocorticoids, stimulants, hypnotics and phosphodiesterase 5 (PDE-5) inhibitors. Out of 430 samples analyzed from both huts, 35.8% contained at least one drug. Diuretics (22.7%) and hypnotics (12.9%) were the most frequently detected drugs, while glucocorticoids (3.5%) and stimulants (3.1%) were less commonly detected. None of the samples contained PDE-5 inhibitors. Two substances were predominant: the diuretic acetazolamide (20.6%) and the hypnotic zolpidem (8.4%). Thirty three samples were found positive for at least two substances, the most frequent combination being acetazolamide and a hypnotic (2.1%). Based on a novel sampling technique, we demonstrate that about one third of the urine samples collected from a random sample of male climbers contained one or several drugs, suggesting frequent drug use amongst climbers ascending Mont Blanc. Our data suggest that medication primarily aims at mitigating the symptoms of altitude illnesses, rather than enhancing performance. In this hazardous environment, the relatively high prevalence of hypnotics must be highlighted, since these molecules may alter vigilance

Au large de Rogliano – Épave Tour d’Agnello 2

Un fragment de coque moderne a été déclaré en 1998 par Alain Dandé du club de plongée de Macinaggio au pied de la tour d’Agnello par 8 m de fond. L’expertise conduite par Hélène Bernard en 1999 a permis de constater que l’on avait affaire à un navire marchand de 40 à 60 m de long. Le sondage accordé en 2002 avait pour objectif de rechercher la limite occidentale du site, d’établir un relevé en coupe de la partie orientale et de prélever des éléments de cargaison et de mobilier de bord. Le vai..

Au large de Ersa – Ouest du Cap Corse

Située dans le chenal entre le cap Corse et l’île de la Giraglia existe une zone d’environ 1,5 ha dans laquelle ont été mis au jour des tessons d’amphores dispersés et deux lots d’ancres en fer antiques. La mission de 2009 avait pour but de trouver un éventuel amoncellement d’objets archéologiques qui permettrait une étude plus approfondie de ces sites. Les recherches effectuées par sondage et prospection visuelle à partir d’un lot d’ancres placées tête-bêche n’ont pas donné le résultat espér..