The Marangoni flow of soluble amphiphiles

Surfactant distribution heterogeneities at a fluid/fluid interface trigger the Marangoni effect, i.e. a bulk flow due to a surface tension gradient. The influence of surfactant solubility in the bulk on these flows remains incompletely characterized. Here we study Marangoni flows sustained by injection of hydrosoluble surfactants at the air/water interface. We show that the flow extent increases with a decrease of the critical micelle concentration, i.e. the concentration at which these surfactants self-assemble in water. We document the universality of the surface velocity field and predict scaling laws based on hydrodynamics and surfactant physicochemistry that capture the flow features.Comment: 5 pages, 4 figures, submitte

Traffic signal detection from in-vehicle GPS speed profiles using functional data analysis and machine learning

International audienceThe increasing availability of large-scale Global Positioning System (GPS) data stemming from in-vehicle embedded terminal devices enables the design of methods deriving road network cartographic information from drivers' recorded traces. Some machine learning approaches have been proposed in the past to train automatic road network map inference, and recently this approach has been successfully extended to infer road attributes as well, such as speed limitation or number of lanes. In this paper, we address the problem of detecting traffic signals from a set of vehicle speed profiles, under a classification perspective. Each data instance is a speed versus distance plot depicting over a hundred profiles on a 100-meter-long road span. We proposed three different ways of deriving features: the first one relies on the raw speed measurements; the second one uses image recognition techniques; and the third one is based on functional data analysis. We input them into most commonly used classification algorithms and a comparative analysis demonstrated that a functional description of speed profiles with wavelet transforms seems to outperform the other approaches with most of the tested classifiers. It also highlighted that Random Forests yield an accurate detection of traffic signals, regardless of the chosen feature extraction method, while keeping a remarkably low confusion rate with stop signs

a planned ancillary analysis of the coVAPid cohort

Funding: This study was supported in part by a grant from the French government through the «Programme Investissement d’Avenir» (I-SITE ULNE) managed by the Agence Nationale de la Recherche (coVAPid project). The funders of the study had no role in the study design, data collection, analysis, or interpreta tion, writing of the report, or decision to submit for publication.BACKGROUND: Patients with SARS-CoV-2 infection are at higher risk for ventilator-associated pneumonia (VAP). No study has evaluated the relationship between VAP and mortality in this population, or compared this relationship between SARS-CoV-2 patients and other populations. The main objective of our study was to determine the relationship between VAP and mortality in SARS-CoV-2 patients. METHODS: Planned ancillary analysis of a multicenter retrospective European cohort. VAP was diagnosed using clinical, radiological and quantitative microbiological criteria. Univariable and multivariable marginal Cox's regression models, with cause-specific hazard for duration of mechanical ventilation and ICU stay, were used to compare outcomes between study groups. Extubation, and ICU discharge alive were considered as events of interest, and mortality as competing event. FINDINGS: Of 1576 included patients, 568 were SARS-CoV-2 pneumonia, 482 influenza pneumonia, and 526 no evidence of viral infection at ICU admission. VAP was associated with significantly higher risk for 28-day mortality in SARS-CoV-2 (adjusted HR 1.70 (95% CI 1.16-2.47), p = 0.006), and influenza groups (1.75 (1.03-3.02), p = 0.045), but not in the no viral infection group (1.07 (0.64-1.78), p = 0.79). VAP was associated with significantly longer duration of mechanical ventilation in the SARS-CoV-2 group, but not in the influenza or no viral infection groups. VAP was associated with significantly longer duration of ICU stay in the 3 study groups. No significant difference was found in heterogeneity of outcomes related to VAP between the 3 groups, suggesting that the impact of VAP on mortality was not different between study groups. INTERPRETATION: VAP was associated with significantly increased 28-day mortality rate in SARS-CoV-2 patients. However, SARS-CoV-2 pneumonia, as compared to influenza pneumonia or no viral infection, did not significantly modify the relationship between VAP and 28-day mortality. CLINICAL TRIAL REGISTRATION: The study was registered at ClinicalTrials.gov, number NCT04359693.publishersversionpublishe

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/)

Convergence ou résilience ? Une analyse de classification hiérarchique des régimes providentiels des pays avancés

Dans la foulée des travaux de Gøsta Esping-Andersen, plusieurs études ont défini divers régimes providentiels en Europe occidentale et en Amérique du Nord. L’examen d’un ensemble d’indicateurs sociaux au moyen d’analyses de classification hiérarchique permet de confirmer l’existence de tels modèles, qui correspondent à des articulations spécifiques entre la famille, l’État et le marché pour produire les ressources nécessaires au bien-être des individus. En fait, notre analyse permet de distinguer quatre ensembles de pays, correspondant aux trois régimes identifiés à l’origine par Esping-Andersen — social-démocrate, libéral, conservateur — auxquels s’ajoute, comme l’avaient anticipé plusieurs auteurs, un régime distinct de ce dernier, le régime latin. Ces résultats, qui persistent quand on passe des années 1980 aux années 1990, relèvent aussi l’existence de liens étroits et durables de causalité réciproque entre l’organisation des programmes sociaux dans les sociétés analysées, les situations sociales qui sont en partie le résultat des politiques élaborées, et, enfin, le niveau de participation civique, qui conduit les gens à se mobiliser (ou non) collectivement pour donner forme aux programmes sociaux. Cette analyse comparative permet de situer le Canada parmi les mondes du « capitalisme providentiel ».Following the seminal work of Esping-Andersen, many studies have identified a variety of welfare regimes in Western Europe and North America. This study examines a set of quantitative social indicators, using hierarchical cluster analysis, in order to identify such regimes, which display specific arrangements between markets, the State and families in the production and distribution of the resources required for the well-being of people. Indeed, our empirical analyses reveal the existence of the three regimes originally identified by Esping-Andersen — social-democratic, liberal, and conservative — to which one must add, as many authors had pointed out, a fourth regime, distinct from the latter, called Latin. These results pertain whether one turns to data from the 80s or the 90s. The data also reveal strong and durable relations of mutual causality between the configuration of social programs in the various societies under analysis, the social situations which largely result from these social programs, and, lastly, the level of civic participation, which leads (or not) people to collective mobilization which in turn shapes social programs. Our comparative analysis allows us to identify Canada’s place in the worlds of welfare capitalism.En la continuidad de los trabajos de Gosta Esping-Andersen, varios estudios identificaron diversos regímenes providenciales en Europa occidental y en América del norte. El examen de un conjunto de indicadores sociales a través de análisis de clasificación jerárquica permite confirmar la existencia de tales modelos, que corresponden a articulaciones específicos entre la familia, el Estado y el mercado para producir los recursos necesarios al bienestar de los individuos. De hecho, nuestro análisis permite identificar 4 conjunto de países, correspondiendo a los tres regímenes identificados al comienzo por Esping-Andersen— social-demócrata, liberal, conservador — a los cuales se añade, como lo habían anticipado varios autores, un régimen distinto de éstos últimos, el regimen latín. Estos resultados, que persisten cuando se pasa de los años 1980 a los años 90, señalan también la existencia de lazos estrechos y durables de causalidad recÌproca entre la organización de los programas sociales en las sociedades analizadas, las situaciones sociales que son en parte el resultado de las polÌticas elaboradas y al fin el nivel de participación civica, que conduce a la gente a movilizarse (o nó) colectivamente para dar forma a los programas sociales. Este an·lisis comparativo permite situar al Canad· entre los mundos del « capitalismo providencial »

Aqueous foam slip and shear regimes determined by rheometry and multiple light scattering

International audienceBy using simultaneously rheometry and a multiple light scattering technique, diffusing wave spectroscopy (DWS), we have studied the steady flows of three-dimensional aqueous foams. A number of parameters--the surfactants, the liquid volume fraction, and the roughness of the rheometer surfaces--are widely varied in order to determine which quantities have an impact on the macroscopic flow behaviors. By comparing to previous theoretical and experimental results, we show that flow regimes can either be slip or shear dominated. Two opposite slip regimes are identified; the transition from one to the other is obtained either by changing the surfactant or the liquid fraction, and we quantitately discuss which regime is selected for any given foam properties. Similarly, different shear regimes are also found, and we discuss the link between the macroscopic rheometry measurements, the nature of the flow, and the interfacial microscopic properties. Despite the occurrence of slip, we show how we can recover the actual shear rate by DWS, and how we can quantitatively explain the measured slip velocities

Oscillatory rheometry of aqueous foams : surfactant, liquid fraction, aging and protocol effects

International audienceWe report a new set of rheological data on well controlled aqueous foams. We investigate and analyze how the linear viscoelastic regime, the foam yielding and the non-linear regimes above yielding actually depends on the interfacial properties, bubble size, liquid fraction and foam age. Results are compared to previous works on foams and emulsions, and to models. The viscoelastic linear properties and yield stress are strongly dependent on the liquid fraction, and for a low molecular weight surfactant, providing "fluid-like" interfaces, a universal behavior is recovered. However, discrepancies are observed for protein foams, and are discussed in relation to the interface and thin film properties. We also discuss the features of the non linear regimes above the yield stress, which cannot be fully explained by recent models. As the foam ages, the evolution of the viscoelastic properties can be interpreted in terms of foam drainage and coarsening; nevertheless, some of the aging effects remain unexplained. We also present the results of a new mode of oscillatory experiments, at constant shear rate the macroscopic results obtained with this new protocol turn out to be strikingly well correlated to microscopic measurements at the bubble scale. We then show that a same solid-liquid transition is obtained either by applying a deformation, or by the foam coarsening; we propose that the transition is controlled by a Deborah number De, which can be seen either as a frequency ratio or a deformation ratio. For De 1)

Surfactant spreading at an oil-water interface: From surfactant amphiphilicity to macroscopic flows

International audienc

Enhanced interfacial deformation in a Marangoni flow: A measure of the dynamical surface tension

International audienceWe investigate the flows and deformations resulting from the deposition of awater solublesurfactant at a bare oil-water interface. Once the surfactant is deposited, we show thatthe oil-water interface is deformed with a water bump rising upward into the oil. For agiven oil, the maximal deformation—located at the surfactant deposition point—decreaseswith the oil-layer thickness. We also observe a critical oil-layer thickness below whichthe deformation becomes as large as the oil layer, leading to the rupture of this layer andan oil-water dewetting. Experimentally, it is found that this critical thickness depends onthe oil density and viscosity. We then provide an analytical modelization that explainsquantitatively all these experimental features. In particular, our analysis allows us to derivean analytical relationship between the vertical profile of the oil-water interface and thein-plane surface tension profile. Therefore, we propose that the monitoring of the interfacevertical shape can be used as a new spatially resolved tensiometry technique

Patrimoine scientifique : le temps des doutes ?

Le patrimoine scientifique fait l’objet, en France, depuis le début des années 1990, d’une veille patiente ainsi que d’une recension la plus exhaustive possible. Les risques de destruction de certains lieux ou de disparition de certains instruments ne sont certes pas totalement écartés ; les conditions de protection et de valorisation du patrimoine scientifique ne sont pas optimales. Toutefois, un réseau hétérogène de conservateurs, d’historiens et de scientifiques poursuit un travail de conservation qui permet une stabilisation du corpus patrimonial. Ce nouvel équilibre fournit l’occasion d’une double réflexion sur la portée des actions menées et le cadre épistémologique dans lequel elles s’effectuent. Ce numéro spécial des Cahiers François Viète se propose de redéployer les problématiques patrimoniales en s’appuyant sur les travaux les plus récents en histoire, en sociologie et en muséographie. Les différents textes réunis saisissent les différentes dimensions des pratiques mémorielles et patrimoniales sans se départir des questionnements inquiets qui les accompagnent. Ce numéro a donc pour ambition d’étudier, dans leur grande diversité, les pratiques sociales et les politiques qui organisent les rapports à la mémoire scientifique. Since the beginning of the 1990s, scientific heritage in France has been the subject of patient monitoring and the most exhaustive survey possible. The risks of destruction of certain places or the disappearance of certain instruments have certainly not been completely eliminated; the conditions for protecting and promoting scientific heritage are not optimal. However, a heterogeneous network of curators, historians and scientists is carrying out conservation work that is stabilising the heritage corpus. This new balance provides the opportunity for a double reflection on the scope of the actions carried out and the epistemological framework in which they are carried out. This special issue of the Cahiers François Viète proposes to redefine heritage issues by drawing on the most recent work in history, sociology and museography. The various texts gathered together grasp the different dimensions of memory and heritage practices without abandoning the anxious questions that accompany them. The aim of this issue is therefore to study, in their great diversity, the social practices and policies that organise the relationship with scientific memory