Etude du comportement quasi-statique de la mousse polyuréthane : Comparaison entre les modèles de mémoire fractionnaire et entier

La mousse polyuréthane présente un comportement quasi-statique de type viscoélasticité linéaire. Les paramètres de deux modèles à mémoire, l'un fractionnaire, l'autre entier ont été déterminés grâce à des méthodes originales de minimisation et d'identification. Il a été vérifié que les paramètres trouvés respectent les conditions thermodynamiques. Enfin, Les résultats obtenus montrent une bonne concordance entre le comportement expérimental de la mousse polyuréthane et celui prédit par les deux modèles de mémoire

Analyse du comportement dynamique de mousses de polyuréthane par des tests vibratoires

L’objectif de cet article est de décrire les techniques expérimentales et l’identification des propriétés dynamiques de mousses de polyuréthane. En effet, le niveau de confort d’un siège automobile est établien considérant les propriétés quasi-statiques – densité, portance et résilience – et dynamiques – transmissibilité – de la mousse flexible de polyuréthane. Notre dispositif d’essai est un système à un degré de liberté, composé d’un dispositif expérimental reposant sur le vérin d’une machine d’essai dynamique. Ce dispositif expérimental est composé d’un plateau supérieur avec une masse libre et d’un plateau inférieur solidaire de la machine d’essai, entre lesquels est placé un échantillon de mousse de dimensions100x100x50 mm3. Les vibrations transmises à travers la mousse sont mesurées pour déterminerles caractéristiques dynamiques de l’échantillon et permettent de réaliser le diagramme de Bodede la transmissibilité de l’échantillon. Cinq types de mousses de polyuréthane utilisées dans l’automobile seront comparés dans cet article

Dynamics of nanodroplets on topographically structured substrates

Mesoscopic hydrodynamic equations are solved to investigate the dynamics of nanodroplets positioned near a topographic step of the supporting substrate. Our results show that the dynamics depends on the characteristic length scales of the system given by the height of the step and the size of the nanodroplets as well as on the constituting substances of both the nanodroplets and the substrate. The lateral motion of nanodroplets far from the step can be described well in terms of a power law of the distance from the step. In general the direction of the motion depends on the details of the effective laterally varying intermolecular forces. But for nanodroplets positioned far from the step it is solely given by the sign of the Hamaker constant of the system. Moreover, our study reveals that the steps always act as a barrier for transporting liquid droplets from one side of the step to the other.Comment: 44 pages, 25 figure

Genome-wide association analyses identify new Brugada syndrome risk loci and highlight a new mechanism of sodium channel regulation in disease susceptibility.

Brugada syndrome (BrS) is a cardiac arrhythmia disorder associated with sudden death in young adults. With the exception of SCN5A, encoding the cardiac sodium channel Na1.5, susceptibility genes remain largely unknown. Here we performed a genome-wide association meta-analysis comprising 2,820 unrelated cases with BrS and 10,001 controls, and identified 21 association signals at 12 loci (10 new). Single nucleotide polymorphism (SNP)-heritability estimates indicate a strong polygenic influence. Polygenic risk score analyses based on the 21 susceptibility variants demonstrate varying cumulative contribution of common risk alleles among different patient subgroups, as well as genetic associations with cardiac electrical traits and disorders in the general population. The predominance of cardiac transcription factor loci indicates that transcriptional regulation is a key feature of BrS pathogenesis. Furthermore, functional studies conducted on MAPRE2, encoding the microtubule plus-end binding protein EB2, point to microtubule-related trafficking effects on Na1.5 expression as a new underlying molecular mechanism. Taken together, these findings broaden our understanding of the genetic architecture of BrS and provide new insights into its molecular underpinnings

Extracorporeal Membrane Oxygenation for Severe Acute Respiratory Distress Syndrome associated with COVID-19: An Emulated Target Trial Analysis.

RATIONALE: Whether COVID patients may benefit from extracorporeal membrane oxygenation (ECMO) compared with conventional invasive mechanical ventilation (IMV) remains unknown. OBJECTIVES: To estimate the effect of ECMO on 90-Day mortality vs IMV only Methods: Among 4,244 critically ill adult patients with COVID-19 included in a multicenter cohort study, we emulated a target trial comparing the treatment strategies of initiating ECMO vs. no ECMO within 7 days of IMV in patients with severe acute respiratory distress syndrome (PaO2/FiO2 <80 or PaCO2 ≥60 mmHg). We controlled for confounding using a multivariable Cox model based on predefined variables. MAIN RESULTS: 1,235 patients met the full eligibility criteria for the emulated trial, among whom 164 patients initiated ECMO. The ECMO strategy had a higher survival probability at Day-7 from the onset of eligibility criteria (87% vs 83%, risk difference: 4%, 95% CI 0;9%) which decreased during follow-up (survival at Day-90: 63% vs 65%, risk difference: -2%, 95% CI -10;5%). However, ECMO was associated with higher survival when performed in high-volume ECMO centers or in regions where a specific ECMO network organization was set up to handle high demand, and when initiated within the first 4 days of MV and in profoundly hypoxemic patients. CONCLUSIONS: In an emulated trial based on a nationwide COVID-19 cohort, we found differential survival over time of an ECMO compared with a no-ECMO strategy. However, ECMO was consistently associated with better outcomes when performed in high-volume centers and in regions with ECMO capacities specifically organized to handle high demand. This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives License 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Memory integer model parameters based on polyurethane foam experimental compression tests

International audienceThe polyurethane foam (PU) undergoing large compressive deformation exhibits highly nonlinear elasticity and viscoelastic behaviour. The principal aim of this paper is to modeling this behaviour using a memory integer model which describes the nonlinearity by polynomial function and the viscoelasticity by convolution function. A unidirectional compression tests are considered to identify experimentally the mechanical parameters of model. The difference between force responses of foam in load and unload phases constitute the base element of the identification methodology. Many precautions are taken into account to find accurate results that verify thermodynamics conditions. Finally, the reliability and also the limits of the memory integer model are discussed

Technological knowledge and transfer of Roman pottery production in <i>Civitas Nerviorum</i> (northern France, central Belgium) during the 1st–3rd centuries CE

International audienceAspects of 1st to 3rd centuries CE Roman production technology and knowledge transfer in northern France and central Belgium (known as Civitas Nerviorum) were studied. To this aim, 43 pottery waste fragments from six workshops at Bavay, Pont-sur-Sambre, Blicquy, Cambrai, Les Rues-des-Vignes and Sains-du-Nord were studied macroscopically and analysed in thin section petrography and chemistry with X-ray fluorescence spectrometry. This permitted to reconstruct the production technologies employed at the six workshops, and to infer inter- and intra-site knowledge transfer. More specifically, potters at Bavay transferred their knowledge to craftsmen at Pont-sur-Sambre. The epigraphic evidence on the discarded pottery further suggests that they passed on their technological knowledge through kinship. Craftsmen at Cambrai and Les Rues-des-Vignes also appear to have shared aspects of their technological knowledge. The reconstructed technologies were then used to tentatively indicate the production location of three conspicuous types of pottery, which circulated widely within and beyond the study region but were hitherto not known from production waste contexts. To this aim, seven samples from settlement, burial and sanctuary sites at Famars, Blicquy and Sains-du-Nord were selected and analysed in thin section petrography and chemistry with X-ray fluorescence spectrometry

Harmonic Vibration Test for the Analysis of the Dynamic Behaviour of Polyurethane Foams

International audienceThe main goal of this paper is to describe experimental techniques and identification of dynamic properties offlexible polyurethane foam. Indeed, automotive seat comfort level is established with considering quasi-static -density core, hysteresis loss and compression set - and dynamic -transmissibility and damping - properties offlexible polyurethane foams. Our dynamic system, modeled as a single degree-of-freedom system, is composedof an experimental device with a free mass on the top and a shaker on the basement. The first one, a rigid block,is mounted on a 100x100x50 mm cube sample of foam material and the second one excites the device with harmonicvibration. The steady-state response of a polyurethane foam sample – after the same number of cycles –to harmonic vibration is analyzed for different excitation amplitude level and for different initial compression level,corresponding respectively to various road surface conditions and to various apparent-mass. The transmittedvibration between the shaker and the free mass is measured to determine the damping power and the filter bandof polyurethane foam, and enables to trace the Bode magnitude and phase plots of the dynamic stiffness functionof the system. The results presented here compare 3 types of OEM foams

Etude de l'efficacité mécanique d'une vis hydrodynamique

L'objectif de cet article est d'évaluer l'efficacité mécanique d'une vis hydrodynamique, dont le but est de convertir une puissance hydraulique en puissance électrique. Dans un premier temps, un modèle théorique issu de la littérature est présenté et implémenté afin d'étudier l'influence des différents paramètres d'un tel système sur son efficacité. Dans un second temps, une maquette à l'échelle 1/5 et son instrumentation sont présentées. Les résultats obtenus suite à une série d'essais permettent de recaler certains paramètres empiriques du modèle et d'effectuer une première comparaison entre efficacités réelles et théoriques.