Analyse par approche numérique mésoscopique des propriétés mécaniques résiduelles du béton après un chargement de type fluage

International audience Les modèles existants pour estimer le fluage du béton basés sur une modélisation rhéologique, supposent généralement que le béton est un matériau homogène. Par conséquent les incompatibilités de déformations entre la pâte de ciment et les granulats lorsque le béton est soumis à un chargement de type fluage ne peuvent pas être prise en compte alors qu'elles peuvent être à l'origine d'une microfissuration. Ces microfissures peuvent entrainer une diminution du module d'élasticité et de la résistance du béton, et une augmentation de la quantité de déformation par fluage sous le même niveau de chargement. Cette augmentation des déformations de fluage peut être considérée comme la source de non linéarités avec le niveau de contrainte. Pour étudier l'influence de ces microfissures, un modèle visco-élastique-endommageable a été adopté pour le calcul de fluage en utilisant une technique de maillage mésoscopique. Les résultats montrent qu'une part importante des non linéarités peut être expliquée par les microfissurations liées aux incompatibilités de déformations et que l'approche mésoscopique permet de reproduire fidèlement des essais de fluage jusqu'à la rupture. </div

Staufferia and Pilgerina: Two New Endemic Monotypic Arborescent Genera of Santalaceae from Madagascar

Two new arborescent species of Santalaceae, both endemic to Madagascar, are described in the new monotypic genera, Staufferia Z. S. Rogers, Nickrent & Malécot and Pilgerina Z. S. Rogers, Nickrent & Malécot. Based on available molecular and morphological data, the new species are part of a clade formed with Pyrularia Michx. of Asia and North America, the Indo-Malesian genus Scleropyrum Arn., and the central and western African Okoubaka Pellegr. & Normand. Staufferia is distinguished morphologically from Okoubaka by the smaller inflorescences (4 to 10 vs. 50 to 100 flowers); smaller (1.8–2 × 1.1–1.6 cm vs. ca. 9 × 5 cm), obovoidal (vs. ellipsoidal) fruits; smaller (ca. 1.5 mm vs. 7–8 mm diam.), persistent perianth; thinner (0.5–1 mm vs. 15–20 mm thick), 5-sulcate (vs. smooth) exocarp; and thinner (ca. 0.5 mm vs. 3–4 mm thick), smooth (vs. deeply striate or alveolate) mesocarp. Pilgerina differs from Scleropyrum by the smaller inflorescences (8 to 23 vs. 60 to 100 flowers); pedicellate (vs. sessile) flowers; smaller (1.2–1.9 × 1.7–2.7 cm vs. ca. 3 × 2 cm), broadly transversely ellipsoidal to subspheroidal (vs. obovoidal to pyriform) fruits; and thinner (ca. 0.5 mm vs. 1.5–3 mm thick), smooth or finely striate (vs. deeply striate or alveolate) mesocarp. Both species are illustrated and assigned an IUCN preliminary conservation status of Least Concern (LC)

Mesoscopic scale modeling of concrete under triaxial loading using X-ray tomographic images

This paper focuses on the discrete modeling of triaxial behaviour of concrete. The originality of this work comes from two points. The first one concerns the predictive feature of the model developed for simulating the response of concrete specimens; the behaviour of mortar, rock, and their interaction being identified a priori or by means of experimental tests on the mortar and the rock. The second originality relates to the construction method of the discrete element assembly based on the 3D segmentation of tomographic images. Such a method allows modeling of concrete at the mesoscopic scale with an internal structure similar to the one of the concrete tested experimentally. The comparisons between numerical and experimental results show the model is capable to reproduce the triaxial behavior of concrete for confining pressure varying from 0 to 650 MPa

Inhomogeneous turbulence in the vicinity of a large scale coherent vortex

We study the statistics of turbulent velocity fluctuations in the neighbourhood of a strong large scale vortex at very large Reynolds number. At each distance from the vortex core, we observe that the velocity spectrum has a power law ``inertial range'' of scales and that intermittency -- defined as the variation of the probability density function (PDF) of velocity increments as the length of the increment is varied -- is also present. We show that the spectrum scaling exponents and intermittency characteristics vary with the distance to the vortex. They are also influenced by the large scale dynamics of the vortex.Comment: submitted to europhys lett, 6 pages, 5 figure

Cross-linguistic study of vocal pathology: perceptual features of spasmodic dysphonia in French-speaking subjects

Clinical characterisation of Spasmodic Dysphonia of the adductor type (SD) in French speakers by Klap and colleagues (1993) appears to differ from that of SD in English. This perceptual analysis aims to describe the phonetic features of French SD. A video of 6 French speakers with SD supplied by Klap and colleagues was analysed for frequency of phonatory breaks, pitch breaks, harshness, creak, breathiness and falsetto voice, rate of production, and quantity of speech output. In contrast to English SD, the French speaking SD patients demonstrated no evidence pitch breaks, but phonatory breaks, harshness and breathiness were prominent features. This verifies the French authors’ (1993) clinical description. These findings suggest that phonetic properties of a specific language may affect the manifestation of pathology in neurogenic voice disorders

Characterizing Result Errors in Internet Desktop Grids

Desktop grids use the free resources in Intranet and Internet environments for large-scale computation and storage. While desktop grids offer a high return on investment, one critical issue is the validation of results returned by participating hosts. Several mechanisms for result validation have been previously proposed. However, the characterization of errors is poorly understood. To study error rates, we implemented and deployed a desktop grid application across several thousand hosts distributed over the Internet. We then analyzed the results to give quantitative, empirical characterization of errors rates. We find that in practice, error rates are widespread across hosts but occur relatively infrequently. Moreover, we find that error rates tend to not be stationary over time nor correlated between hosts. In light of these characterization results, we evaluated state-of-the-art error detection mechanisms and describe the trade-offs for using each mechanism. Finally, based on our empirical results, we conduct a benefit analysis of a recently proposed mechanism for error detection tailored for long-running applications. This mechanism is based on using the digest of intermediate checkpoints, and we show in theory and simulation that the relative benefit of this method compared to the state-of-the-art is as high as 45\%

Experimental characterization of interstitial pore pressure in concrete under high confinement

Le but de cette étude est de mesurer la pression interstitielle du béton sous haut niveau de confinement. Lorsque les structures de béton sont soumises à un chargement de type impact ou explosion, le matériau subit de très fortes contraintes triaxiales qui sont fortement influencées par le taux de saturation. Afin de mesurer la pression interstitielle d’eau à l’intérieur du béton sous fort chargement triaxial, un nouveau dispositif expérimental a été développé. Des éprouvettes de 14 cm de longueur et 7 cm de diamètre sont testées à l’aide de la presse GIGA. Dans le nouveau concept, la longueur de l’échantillon est réduite à 8 cm et une enclume de mesure de la pression interstitielle de longueur 6 cm a est incorporée. Des micro-trous sont percés sur sa face supérieure de sorte que la pression de l’eau libre dans l’échantillon puisse ainsi être transmise dans la cavité durant l’essai. Un capteur cylindrique équipé d’une jauge est placé dans la cavité permet de mesurer cette pression. Les résultats préliminaires d’un essai hydrostatique effectué sur un béton saturé indiquent que la pression interstitielle a augmenté jusqu’à 200 MPa pour 300 MPa de confinement.This study focuses on measuring the pore pressure of concrete under high confinement. When concrete structures are subjected to an impact loading, material exhibits high triaxial compressive stresses which are highly influenced by the saturation ratio. In order to measure the interstitial water pore pressure inside the concrete under mechanical loading, a new experimental device was developed. Usually, specimens of 14cm in length and 7cm in diameter are tested using the GIGA press. In the new concept, the specimen length is reduced to 8cm and a pore pressure measurement cell of 6 cm in length is incorporated. The cell has micro-holes on its upper face, so that, when the specimen is loaded water pressure is transmitted from concrete to the cell where a cylindrical sensor equipped with a gage is placed. Preliminary results indicate that concrete pore pressure increases up to 200 MPa during an hydrostatic test at 300 MPa of confinement

Accurate estimation of third-order moments from turbulence measurements

Politano and Pouquet's law, a generalization of Kolmogorov's four-fifths law to incompressible MHD, makes it possible to measure the energy cascade rate in incompressible MHD turbulence by means of third-order moments. In hydrodynamics, accurate measurement of third-order moments requires large amounts of data because the probability distributions of velocity-differences are nearly symmetric and the third-order moments are relatively small. Measurements of the energy cascade rate in solar wind turbulence have recently been performed for the first time, but without careful consideration of the accuracy or statistical uncertainty of the required third-order moments. This paper investigates the statistical convergence of third-order moments as a function of the sample size N. It is shown that the accuracy of the third-moment depends on the number of correlation lengths spanned by the data set and a method of estimating the statistical uncertainty of the third-moment is developed. The technique is illustrated using both wind tunnel data and solar wind data.Comment: Submitted to: Nonlinear Processes in Geophysic

Développement du procédé de micro-hydroformage de tubes

Le procéde d'hydroformage de tubes commence à être largement répandu dans l'industrie automobile pour la réalisation de pièces tubulaires complexes et mono-composant. Dans le cadre de cet article, on propose une miniaturisation de ce procédé à des structures de faibles dimensions (diamètres et épaisseurs respectivement inférieurs à 5mm et à 0,2mm). On présente iciun pilote expérimental instrumenté et les premiers tests effectués sur du gonflement libre en cavité ouverte sur des tubes de 4mm pour une épaisseur 0,1mm

DSL-Lab: a Platform to Experiment on Domestic Broadband Internet

This report presents the design and building of DSL-Lab, a platform for distributed computing and peer-to-peer experiments over the domestic broadband Internet. Experimental platforms such as PlanetLab and Grid'5000 are promising methodological approaches for studying distributed systems. However, both platforms focus on high-end services and network deployments on only a restricted part of the Internet, and as such, they do not provide experimental conditions of residential broadband networks. DSL-Lab is composed of 40 low-power and noiseless nodes, which are hosted by participants, using users' xDSL or cable access to the Internet. The objective is twofold: 1) to provide accurate and customized measures of availability, activity and performance in order to characterize and tune the models of such resources~; 2) to provide an experimental platform for new protocols, services and applications, as well as a validation tool for simulators and emulators targeting these systems. In this article, we report on the software infrastructure (security, resources allocation, power management) as well as on the first results and experiments achieved