Endommagement, par érosion de sable, des structures en acier API 5L X52 destinées aux produits pétroliers

Nous traitons l’endommagement des structures métalliques destinées à transporter et stocker du gaz et du pétrole, sous impact de sable. Une étude expérimentale, sur éprouvettes entaillées, évalue la perte de masse et la ténacité en fonction du temps de sablage et du rayon d’entaille. Les résultats montrent que la perte de masse augmente avec le temps de sablage, mais la ténacité diminue. Des essais supplémentaires, en fatigue, ont montré l’effet bénéfique du sablage

Complex shape forming of a flax woven fabric; analysis of the tow buckling and misalignment defect

With the view to minimise the impact on the environment and to produce structural parts with a goodproduction-rate/cost-ratio, the sheet forming of woven flax based fabric was investigated in this study. Aflax fibre plain-weave fabric has been used to form a complex tetrahedron shape. This shape is of partic-ular interest as it contains several geometric singularities required by many automotive parts such asdouble or triple curvature and low-curvature edges. Globally, the complex tetrahedron shape wasobtained, but tow buckling (out of plane bending of tows) was observed in specific zones of the shape.The main mechanism at the origin of this defect has been defined. A reduction of the tow buckle sizewas obtained by increasing the membrane tension. The influence of fabric architecture at the mesoscopicand macroscopic scales on the appearance of the tow buckles was demonstrated and discussed. Solutionsto prevent the appearance of this defect based on the design of the fabric architecture at the tow or fabricscales were successfully proposed. As a consequence, when sheet forming of complex shapes is consid-ered, specific fabric architectures should be chosen to prevent the appearance of the buckling defec

Experimental characterisation and modelling of the thermo-viscoplastic behaviour of steel AISI 304 within wide ranges of strain rate at room temperature

In this investigation, thermo-viscoplastic behaviour of austenitic steel AISI 304 has been characterised in tension under wide ranges of strain rate at room temperature. This metal possesses an elevated strain hardening rate and ductility which enhance its capability for absorbing energy under mechanical loading. It has been observed that the rate sensitivity of the material is independent of plastic strain. Moreover, it has been noticed that beyond a certain level of loading rate the flow stress of the material sharply increases. In agreement with experimental evidences reported in the literature, this behaviour is assumed to be caused by the drag deformation mode taking place at high strain rates. Based on such considerations, the thermo-viscoplastic behaviour of the material has been macroscopically modelled by means of the extended Rusinek-Klepaczko model to viscous drag effects. Satisfactory matching has been found between the experiments and analytical predictions provided by the constitutive relation

Genetic information transfer promotes cooperation in bacteria

Many bacterial species are social, producing costly secreted “public good” molecules that enhance the growth of neighboring cells. The genes coding for these cooperative traits are often propagated via mobile genetic elements and can be virulence factors from a biomedical perspective. Here, we present an experimental framework that links genetic information exchange and the selection of cooperative traits. Using simulations and experiments based on a synthetic bacterial system to control public good secretion and plasmid conjugation, we demonstrate that horizontal gene transfer can favor cooperation. In a well-mixed environment, horizontal transfer brings a direct infectious advantage to any gene, regardless of its cooperation properties. However, in a structured population transfer selects specifically for cooperation by increasing the assortment among cooperative alleles. Conjugation allows cooperative alleles to overcome rarity thresholds and invade bacterial populations structured purely by stochastic dilution effects. Our results provide an explanation for the prevalence of cooperative genes on mobile elements, and suggest a previously unidentified benefit of horizontal gene transfer for bacteria

Population genetics of African Fruit Bats involved in ecology of Filoviridae (Ebola virus, Marburg virus) in West, Central and Southern Africa

peer reviewe

Nonstandard Errors

In statistics, samples are drawn from a population in a data-generating process (DGP). Standard errors measure the uncertainty in estimates of population parameters. In science, evidence is generated to test hypotheses in an evidence-generating process (EGP). We claim that EGP variation across researchers adds uncertainty-nonstandard errors (NSEs). We study NSEs by letting 164 teams test the same hypotheses on the same data. NSEs turn out to be sizable, but smaller for more reproducible or higher rated research. Adding peer-review stages reduces NSEs. We further find that this type of uncertainty is underestimated by participants

Non-Standard Errors

In statistics, samples are drawn from a population in a data-generating process (DGP). Standard errors measure the uncertainty in estimates of population parameters. In science, evidence is generated to test hypotheses in an evidence-generating process (EGP). We claim that EGP variation across researchers adds uncertainty: Non-standard errors (NSEs). We study NSEs by letting 164 teams test the same hypotheses on the same data. NSEs turn out to be sizable, but smaller for better reproducible or higher rated research. Adding peer-review stages reduces NSEs. We further find that this type of uncertainty is underestimated by participants

Etude de la nocivité d'un défaut de type éraflure sur une conduite destinée au transport de gaz naturel soumise à une pression d'hydrogène

Currently major research effort is focused on the use of hydrogen as a new energy vector both in Europe and the US. An obvious pragmatic solution for transporting hydrogen, which will be necessary to make the European hydrogen economy feasible, could be to transport a mixture of natural gas and hydrogen in the actual existing natural gas pipe network. Within the European project NATURALHY, 39 European partners have combined their efforts to assess the effects of the presence of hydrogen on the existing gas network. This study is in this context. It focuses on the mechanical properties decreasing of a steel API 5L X52 by hydrogen, obtained in a gas and an electrolytic solution. This effect is quantified by a high number of different tests (burst, fracture, crack propagation, fatigue lifetime). The hydrogen consequence on notch like defect, is analyzed by coupling a deterministic Modified Notch Failure Assessment Diagram (MNFAD) and SINTAP procedure.Study of the harmfulness of a defect like a scratch on a pipeline used to carry natural gas under a pressure of hydrogenActuellement, un effort de recherche important est orienté sur l'usage de l'hydrogène comme nouveau vecteur énergétique aussi bien en Europe qu'aux États-Unis. Une solution pragmatique pour que le transport de l'hydrogène soit économiquement viable, serait de le véhiculer mélangé avec le gaz naturel dans le réseau de gazoducs existant. Dans le cadre du projet européen NaturalHy, 39 partenaires européens ont conjugué leurs efforts pour évaluer les effets de la présence d'hydrogène sur le réseau de gaz existant. Cette étude s inscrit dans ce cadre. Elle s intéresse plus particulièrement à l impact sur les propriétés mécaniques d un acier API 5L X52 de l introduction d hydrogène sous une forme gazeuse ou électrolytique. Cet impact a été quantifiée par un nombre conséquent d essais de différentes natures (éclatement, rupture, propagation, endurance). La nocivité de l hydrogène en présence d un défaut représentatif de type éraflure simulé par une entaille, est analysée de manière déterministe en couplant le Diagramme Intégrité Rupture Modifié pour les entailles et la procédure SINTA

Nanomachines bactériennes impliquées dans le transfert horizontal de gènes : étude structurale des protéines de l'ICESt3, un élément intégratif et conjuguatif de Streptococcus thermophilus

Antibiotic resistance in bacteria has become part of our daily lives. These resistances are progressingfaster than new antibiotics can be found and/or synthesized : a growing problem that knows no boundaries.To acquire this resistance, bacteria exchange mobile genetic elements by horizontal transfer and by usingthe type IV secretion system (T4SS). These conjugative T4SSs are multiprotein membrane complexes, wellstudied in Gram-negative bacteria where several functional models exist. However, in Gram-positive bacteria,little information is available. The aim of this thesis was to initiate a structural work on the proteins of aT4SS ofStreptococcus thermophilus. More precisely, it is the T4SS of the integrative and conjugative elementICESt3 . On the one hand the crystallographic structure of the OrfG protein was determined and on theother hand the structure of OrfM was solved by nuclear magnetic resonance. A preliminary three-dimensionalmodel of OrfM is proposed, composed of a mixed 4-stranded sheet. The exploitation of this structure willallow the establishment of the structure-function relationships of OrfM which is supposed to act in pairwith OrfL as a helicase processivity factor for T4SS. OrfG is a protein homologous to the VirB8 proteinwhich is an assembly factor for Gram negative T4SSs. A script called MPSA_Viewer was developed in thePython language to compare OrfG to its structural homologues. This was necessary because the sequencesimilarities between these proteins were very low. All these proteins have a common fold called VirB8-likebut also disparities separating Gram-negative from Gram-positive models. These results could be correlatedto their quaternary structures. A functional dimeric assembly has been proposed in Gram-negative bacteria.The trimeric assembly of OrfG observed in the crystal and supported by the similar quaternary structuresof two other proteins of the same group suggests an original T4SS specific to Gram positive bacteriaLes résistances aux antibiotiques chez les bactéries font aujourd’hui partie de nos vies quotidiennes. Ces résistances progressent plus vite que l’on arrive à trouver et/ou synthétiser de nouveaux antibiotiques : un problème grandissant qui n’a aucune frontière. Pour acquérir cette résistance, les bactéries s’échangent des éléments génétiques mobiles par transfert horizontal et en utilisant le système de sécrétion de type IV (T4SS). Ces T4SS conjugatifs sont des complexes membranaires multiprotéiques, bien étudiés chez les bactéries à Gram négatif où plusieurs modèles fonctionnels existent. En revanche, chez les bactéries à Gram positif peu d’informations sont disponibles. Cette thèse avait pour but d’initier un travail structural sur les protéines d’un T4SS de Streptococcus thermophilus. Plus précisément, il s’agit du T4SS de l’élément intégratif et conjugatif ICESt3 . D’une part la structure cristallographique de la protéine OrfG a été déterminée et d’autre part lastructure d’OrfM a été résolue par résonance magnétique nucléaire. Un modèle tridimensionnel préliminaire d’OrfM est proposé, composé d’un feuillet mixte à 4 brins. L’exploitation de cette structure permettra l’établissement des relations structure-fonction d’OrfM qui est supposée agir de paire avec OrfL comme un facteur de processivité d’hélicase pour les T4SS. OrfG est une protéine homologue à la protéine VirB8 qui est un facteur d’assemblage des T4SS Gram négatif. Un script appelé MPSA_Viewer a été développé dans le langage Python pour comparer OrfG à ses homologues structuraux. Cela était nécessaire car les similarités de séquence entre ces protéines étaient très faibles. Toutes ces protéines possèdent un repliement commun appelé VirB8-like mais aussi des disparités séparant les modèles Gram négatif des modèles Gram positif. Ces résultats pourraient être corrélées à leurs structures quaternaires. Un assemblage dimérique fonctionnel a été proposé chez les bactéries à Gram négatif. L’assemblage trimérique d’OrfG observé dans le cristal et conforté par les structures quaternaires similaires de deux autres protéines du même groupe suggère un T4SS original et spécifique aux bactéries à Gram positif