Effect of fingerprints orientation on skin vibrations during tactile exploration of textured surfaces

In humans, the tactile perception of fine textures is mediated by skin vibrations when scanning the surface with the fingertip. These vibrations are encoded by specific mechanoreceptors, Pacinian corpuscules (PCs), located about 2 mm below the skin surface. In a recent article, we performed experiments using a biomimetic sensor which suggest that fingerprints (epidermal ridges) may play an important role in shaping the subcutaneous stress vibrations in a way which facilitates their processing by the PC channel. Here we further test this hypothesis by directly recording the modulations of the fingerpad/substrate friction force induced by scanning an actual fingertip across a textured surface. When the fingerprints are oriented perpendicular to the scanning direction, the spectrum of these modulations shows a pronounced maximum around the frequency v/lambda, where v is the scanning velocity and lambda the fingerprints period. This simple biomechanical result confirms the relevance of our previous finding for human touch.Comment: Addendum to: Scheibert J, Leurent S, Prevost A, Debr\'egeas G. The role of fingerprints in the coding of tactile information probed with a biomimetic sensor. Science 2009; 323:1503?6 3 pages, 1 figur

Hydrodynamic and mass transfer efficiency of ceramic foam packing applied to distillation.

In addition to a high void volume and specific area, solid foams possess other properties (low density, good thermal, mechanical, electrical, and acoustical behaviour) that make them attractive for applications such as heat exchangers and reformers. Applications using foams as catalysts or structured catalyst supports have demonstrated higher performance than classical catalysts. Several studies have explored the hydrodynamic behaviour of foams in monophasic and counter current systems and have reported very low pressure drops. This paper describes the application of ceramic foam to distillation. The β-SiC foam contains 5 pores per inch (PPI) with a 91% void volume and a surface area of 640 m2/m3. Performance parameters including pressure drop for the dry and wet packing, flooding behaviour, and dynamic liquid hold-up were measured in a column of 150 mm internal diameter. The mass transfer efficiency in terms of the height equivalent to theoretical plate (HETP) was determined by total reflux experiments using a mixture of n-heptane and cyclohexane at atmospheric pressure. The experimental results were used to develop a set of correlations describing pressure drop and liquid hold-up in terms of a dimensionless number. The hydrodynamic performance and mass transfer efficiency were compared with classical packing materials used in distillation

Mécanique du contact rugueux et perception tactile

5 pages, 2 figuresNational audienceDans un contact entre solides rugueux, l'interface constitue la partie la plus déformable. Son comportement mécanique détermine les contraintes s'établissant dans les deux solides, ainsi que la dynamique de frottement. Deux nouvelles méthodes expérimentales, fondées respectivement sur une observation optique directe et sur l'utilisation d'un microcapteur de force MEMS, permettent de sonder la mécanique locale de ces interfaces. Le dispositif MEMS, qui est un analogue très rudimentaire de l'extrémité du doigt humain, nous a permis de proposer un rôle possible des empreintes digitales dans la transduction de l'information tactile

Probing the micromechanics of a multi-contact interface at the onset of frictional sliding

Digital Image Correlation is used to study the micromechanics of a multi-contact interface formed between a rough elastomer and a smooth glass surface. The in-plane elastomer deformation is monitored during the incipient sliding regime, i.e. the transition between static and sliding contact. As the shear load is increased, an annular slip region, in coexistence with a central stick region, is found to progressively invade the contact. From the interfacial displacement field, the tangential stress field can be further computed using a numerical inversion procedure. These local mechanical measurements are found to be correctly captured by Cattaneo and Mindlin (CM)'s model. However, close comparison reveals significant discrepancies in both the displacements and stress fields that reflect the oversimplifying hypothesis underlying CM's scenario. In particular, our optical measurements allow us to exhibit an elasto-plastic like friction constitutive equation that differs from the rigid-plastic behavior assumed in CM's model. This local constitutive law, which involves a roughness-related length scale, is consistent with the model of Bureau \textit{et al.} [Proc. R. Soc. London A \textbf{459}, 2787 (2003)] derived for homogeneously loaded macroscopic multi-contact interfaces, thus extending its validity to mesoscopic scales.measurements allow for the first quantitative test of Cattaneo and Mindlin (CM) classical model of the incipient sliding of a smooth interface. Small deviations are observed and interpreted as a result of the finite compliance of the rough interface, a behavior which contrasts with Amontons' law of friction assumed to be valid locally in CM's model. We illustrate how these measurements actually provide a method for probing the rheology of the rough interface, which we find to be of the elasto-plastic type.Comment: 11 page

1D model of precursors to frictional stick-slip motion allowing for robust comparison with experiments

We study the dynamic behaviour of 1D spring-block models of friction when the external loading is applied from a side, and not on all blocks like in the classical Burridge-Knopoff-like models. Such a change in the loading yields specific difficulties, both from numerical and physical viewpoints. To address some of these difficulties and clarify the precise role of a series of model parameters, we start with the minimalistic model by Maegawa et al. (Tribol. Lett. 38, 313, 2010) which was proposed to reproduce their experiments about precursors to frictional sliding in the stick-slip regime. By successively adding (i) an internal viscosity, (ii) an interfacial stiffness and (iii) an initial tangential force distribution at the interface, we manage to (i) avoid the model's unphysical stress fluctuations, (ii) avoid its unphysical dependence on the spatial resolution and (iii) improve its agreement with the experimental results, respectively. Based on the behaviour of this improved 1D model, we develop an analytical prediction for the length of precursors as a function of the applied tangential load. We also discuss the relationship between the microscopic and macroscopic friction coefficients in the model.Comment: 13 pages, 14 figures, accepted in Tribology Letter

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/)

Place de la maison médicale de garde de Limoges dans la permanence des soins

Les maisons médicales de garde (MMG) sont un nouveau mode d organisation des gardes en médecine générale. Elles répondent aux besoins actuels de notre société en termes de qualité des soins, de confort de travail et de sécurité. Ces structures expérimentales permettent la prise en charge des patients en ambulatoire lors de la permanence des soins (PDS). Elles sont financées essentiellement par le Fonds d Aide à la Qualité des Soins de Ville (FAQSV). La MMG de Limoges a été récemment évaluée selon trois approches : une autoévaluation annuelle interne, une évaluation externe par l Observatoire Régional de la Santé (ORS) du Limousin, et une évaluation à partir de sa base de données de dossiers médicaux HelloDoc®. Elles sont toutes les trois développées dans cette thèse. Ouverte depuis plus de 4 ans, la MMG de Limoges apparaît bien implantée parmi les acteurs de la PDS. Elle représente un quart de l activité de garde de la ville, et permet d éviter certaines visites au profit de consultations dans ses locaux. Les patients la fréquentant sont jeunes, et la pédiatrie représente un tiers des consultations. Les pathologies traitées sont principalement infectieuses, viennent ensuite la prise en charge de la douleur et la traumatologie. Les patients et les médecins sont globalement satisfaits de ce mode d organisation. Le statut des MMG est en voie de légitimation, et leur place sera sûrement centrale dans la future organisation de la permanence des soins.LIMOGES-BU Médecine pharmacie (870852108) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

Toucher digital humain et mécano-transduction

National audienc

Auto-inflammation de mélanges pauvres assistée par plasma

Le durcissement des normes d émission, tout autant que l impératif d économie,poussent à étudier de nouveaux modes de combustion pour les moteurs. L autoallumage decharges homogènes à basse température offre de bonnes perspectives quant au rejet de NOx,suies, et CO2. Cependant son control reste délicat, car il est extrêmement sensible à latempérature et la cinétique de l hydrocarbure. L assistance par plasma hors-équilibre pourraitfournir une solution. Les expériences sont menées dans une MCR avec des mélanges pauvresd isooctane/air et un prototype d allumeur Renault. La combustion obtenue identifiée commeSICI se déroule en deux phases: la propagation d une flamme comprime les gaz restantjusqu à leur autoallumage. Le réchauffement du système expérimental est intégré dans leprotocole d exploitation, afin de quantifier l effet SICI relativement à l autoallumage pur.L effet du plasma semble avant tout dépendre de l énergie déposée, bien qu il convergerapidement, quel que soit l avance du déclenchement. Le comportement asymptotique à hauteénergie s explique par la thermalisation des filaments, soulignée par comparaison avec l effetSICI d un arc classique. A l inverse, le seuil minimal d énergie nécessaire semble lié à lacapacité à générer un noyau de flamme viable, rapprochant le phénomène d un problèmeclassique d allumage en conditions difficiles. La propagation de la flamme détermine ledéclenchement de l autoallumage selon une caractéristique linéaire particulièrementremarquable, car indépendante des conditions thermodynamiques du mélange. L existenced une flamme froide est mise en avant par des acquisitions de PLIF formaldéhyde. Lapréréaction semble accélérer la propagation du front de flamme.Emission standards tightening as well as economical needs urge to study newcombustion modes for engines. Low-temperature homogeneous charge auto-ignition offersgood prospects for NOx, soot, and CO2 emissions. However, its control remains sharp for it isextremely influenced by temperature and fuel chemistry. Assisting non-equilibrium plasmascould provide a solution. Experiments are RCM managed with lean isooctane/air mixtures andprototype Renault ignition devise. Combustion occurs in a two steps mode known as SICI:flame propagation compresses the remaining gas to auto-ignition. The experimental settemperature rise is computed in order to measure the SICI effect compared to pure autoignition.The plasma seems to act mainly through the energy dropped, albeit its effect quicklyreaches a maximum, no matter how early it starts. This asymptomatic high energy behaviorrelies on the streamers overheating, as underlined by the look-like SICI effect from a regulararc discharge. On the contrary, minimal required energy appears to be linked to the capabilityof generating a sustainable flame kernel, making it closer to a standard ignition issue in roughconditions. Flame propagation sets auto-ignition start, according to an astonishingly linearcharacteristic not even influenced by charge s thermodynamic conditions. Cool flame is putforward through formaldehyde PLIF imaging. Prereaction seems to enhance front propagationspeed.POITIERS-ENS Mécanique Aérot (860622301) / SudocSudocFranceF