Inviscid instability of a stably stratified boundary layer

International audienceThe three-dimensional stability of an inflection-free boundary layer flow of length scale L and maximum velocity U0 in a stably stratified fluid of constant Brunt-Väisälä frequency N is examined in an inviscid Boussinesq framework. The plane of the boundary layer is assumed to be inclined with an angle θ with respect to the vertical direction of stratification. The stability analysis is performed using both numerical and theoretical methods for all the values of θ and Froude number F = U0 /(LN ). The boundary layer flow is found to be unstable whatever F as soon as θ ̸= 0. The growth rate of the most unstable mode is shown to increase with the inclination angle to reach its maximum for a vertical boundary layer θ = π/2. The unstable modes are 3D in nature. The mechanism of instability is shown to be associated with internal gravity wave emission. In the weakly stratified limit, both the oscillation frequency and the growth rate are found to scale with the Brunt-Väisälä frequency N. In the strongly stratified limit, frequency and growth rate become independent of the Froude number and proportional to the sine of the inclination angle (as long as F / sin θ ≪ 1)

Haptic feedback in teleoperation in Micro-and Nano-Worlds.

International audienceRobotic systems have been developed to handle very small objects, but their use remains complex and necessitates long-duration training. Simulators, such as molecular simulators, can provide access to large amounts of raw data, but only highly trained users can interpret the results of such systems. Haptic feedback in teleoperation, which provides force-feedback to an operator, appears to be a promising solution for interaction with such systems, as it allows intuitiveness and flexibility. However several issues arise while implementing teleoperation schemes at the micro-nanoscale, owing to complex force-fields that must be transmitted to users, and scaling differences between the haptic device and the manipulated objects. Major advances in such technology have been made in recent years. This chapter reviews the main systems in this area and highlights how some fundamental issues in teleoperation for micro- and nano-scale applications have been addressed. The chapter considers three types of teleoperation, including: (1) direct (manipulation of real objects); (2) virtual (use of simulators); and (3) augmented (combining real robotic systems and simulators). Remaining issues that must be addressed for further advances in teleoperation for micro-nanoworlds are also discussed, including: (1) comprehension of phenomena that dictate very small object (< 500 micrometers) behavior; and (2) design of intuitive 3-D manipulation systems. Design guidelines to realize an intuitive haptic feedback teleoperation system at the micro-nanoscale level are proposed

Instabilités rayonnantes tri-dimensionnelles d'un jet plan stratifié

La stabilité tri-dimensionnelle d'un jet plan de Bickley est étudiée sous l'hypothèse de Boussinesq en faisant varier l'angle formé par le plan de cisaillement et la stratification. Nous analysons dans quelle mesure le mode de Kelvin-Helmholtz peut avoir une structure rayonnante et plus généralement comment des ondes internes (ou ondes de gravité) associées à des modes rayonnants instables, peuvent être générées spontanément

Cerebral perturbations during exercise in hypoxia.: The brain during hypoxic exercise

International audienceReduction of aerobic exercise performance observed under hypoxic conditions is mainly attributed to altered muscle metabolism due to impaired O(2) delivery. It has been recently proposed that hypoxia-induced cerebral perturbations may also contribute to exercise performance limitation. A significant reduction in cerebral oxygenation during whole body exercise has been reported in hypoxia compared with normoxia, while changes in cerebral perfusion may depend on the brain region, the level of arterial oxygenation and hyperventilation induced alterations in arterial CO(2). With the use of transcranial magnetic stimulation, inconsistent changes in cortical excitability have been reported in hypoxia, whereas a greater impairment in maximal voluntary activation following a fatiguing exercise has been suggested when arterial O(2) content is reduced. Electromyographic recordings during exercise showed an accelerated rise in central motor drive in hypoxia, probably to compensate for greater muscle contractile fatigue. This accelerated development of muscle fatigue in moderate hypoxia may be responsible for increased inhibitory afferent signals to the central nervous system leading to impaired central drive. In severe hypoxia (arterial O(2) saturation <70-75%), cerebral hypoxia per se may become an important contributor to impaired performance and reduced motor drive during prolonged exercise. This review examines the effects of acute and chronic reduction in arterial O(2) (and CO(2)) on cerebral blood flow and cerebral oxygenation, neuronal function, and central drive to the muscles. Direct and indirect influences of arterial deoxygenation on central command are separated. Methodological concerns as well as future research avenues are also considered

Bayesian inverse problems with non-commuting operators

The Bayesian approach to ill-posed operator equations in Hilbert space recently gained attraction. In this context, and when the prior distribution is Gaussian, then two operators play a significant role, the one which governs the operator equation, and the one which describes the prior covariance. Typically it is assumed that these operators commute. Here we extend this analysis to non-commuting operators, replacing the commutativity assumption by a link condition. We discuss its relation to the commuting case, and we indicate that this allows to use interpolation type results to obtain tight bounds for the contraction of the posterior Gaussian distribution towards the data generating element.Comment: This is an update of the previously uploaded version, improving the readabilit

Vanin-1 licenses inflammatory mediator production by gut epithelial cells and controls colitis by antagonizing peroxisome proliferator-activated receptor γ activity

Colitis involves immune cell–mediated tissue injuries, but the contribution of epithelial cells remains largely unclear. Vanin-1 is an epithelial ectoenzyme with a pantetheinase activity that provides cysteamine/cystamine to tissue. Using the 2,4,6-trinitrobenzene sulfonic acid (TNBS)-colitis model we show here that Vanin-1 deficiency protects from colitis. This protection is reversible by administration of cystamine or bisphenol A diglycidyl ether, a peroxisome proliferator-activated receptor (PPAR)γ antagonist. We further demonstrate that Vanin-1, by antagonizing PPARγ, licenses the production of inflammatory mediators by intestinal epithelial cells. We propose that Vanin-1 is an epithelial sensor of stress that exerts a dominant control over innate immune responses in tissue. Thus, the Vanin-1/pantetheinase activity might be a new target for therapeutic intervention in inflammatory bowel disease

Muscle strength is associated with COVID-19 hospitalization in adults 50 years of age or older.

Funder: Natural Sciences and Engineering Research Council of Canada (NSERC) : RGPIN‐2021‐03153; Id: http://dx.doi.org/10.13039/100000049Funder: Max Planck Society for the Advancement of Science; Id: http://dx.doi.org/10.13039/501100004189Funder: German Ministry of Education and ResearchFunder: European Commission; Id: http://dx.doi.org/10.13039/501100000780BACKGROUND: Weak muscle strength has been associated with a wide range of adverse health outcomes. Yet, whether individuals with weaker muscle strength are more at risk for hospitalization due to severe COVID-19 is still unclear. The objective of this study was to investigate the independent association between muscle strength and COVID-19 hospitalization. METHODS: Data from adults 50 years of age or older were analysed using logistic models adjusted for several chronic conditions, body-mass index, age, and sex. Hand-grip strength was repeatedly measured between 2004 and 2017 using a handheld dynamometer. COVID-19 hospitalization during the lockdown was self-reported in summer 2020 and was used as an indicator of COVID-19 severity. RESULTS: The study was based on the Survey of Health, Ageing and Retirement in Europe (SHARE) and included 3600 older adults (68.8 ± 8.8 years, 2044 female), among whom 316 were tested positive for the severe acute respiratory syndrome coronavirus 2 (8.8%), and 83 (2.3%) were hospitalized due to COVID-19. Results showed that higher grip strength was associated with a lower risk of COVID-19 hospitalization [adjusted odds ratio (OR) per increase of 1 standard deviation in grip strength = 0.64, 95% confidence interval (95% CI) = 0.45-0.87, P = 0.015]. Results also showed that age (OR for a 10 -year period = 1.70, 95% CI = 1.32-2.20, P < 0.001) and obesity (OR = 2.01, 95% CI = 1.00-3.69, P = 0.025) were associated with higher risk of COVID-19 hospitalization. Sensitivity analyses using different measurements of grip strength as well as robustness analyses based on rare-events logistic regression and a different sample of participants (i.e. COVID-19 patients) were consistent with the main results. CONCLUSIONS: Muscle strength is an independent risk factor for COVID-19 severity in adults 50 years of age or older

Control Architecture Concepts and Properties of an Ontology Devoted to Exchanges in Mobile Robotics

National audienceA specific ontology is proposed in the scope of the development of a platform devoted to exchanges between academics and industrials of the robotic domain. This paper presents the tools used for knowledge elicitation, the concepts and properties linked with control architecture, the use of the resulting ontology for description of some scenarios and the tracks for the development of a domain specific language grounded on the ontology. Knowledge elicitation is performed in web ontology language thanks to Protégé ontology editor. The ontology is structured as a set of modules organized around a kernel. Modules addressing systems, information, robot and mission include concepts and properties for control architecture description. The expressivity of the ontology is demonstrated describing architectures for a set of scenarios; urban robotic scenario, air-ground scenario, landmark search scenario and military unmanned aerial vehicles scenario. Finally some tracks for the use of the ontology for developing a domain specific language are given

Des exemples de briques technologiques dans le cadre d'une application pour l'industrie du futur

International audienceLa quatrième révolution industrielle est à l'évidence bien en marche. Tous les jours nous en avons la démonstration au travers de nouveaux modes d'organisation autant marchands qu'industriels de la société. Nous sommes confrontés à des ruptures majeures aussi bien liées à l'évolution des technologies qu'à la mondialisation de l'économie avec l'émergence et la maturité de nouveaux acteurs : le défi de la transition énergétique, la révolution du numérique, la protection de notre planète, les convergences entre les sciences du vivant et des sciences dures… Cet article présente des applications implémentées dans le cadre de la mise en place de technologie " Internet of Things " par l'utilisation d'un réseau Profinet. Ces applications peuvent être utilisées sur l'ensemble des processus de l'entreprise dans le cadre de l'Industrie du Futur. Le standard OPC est apparu au milieu des années 90 pour faciliter les échanges entre le monde des automatismes et celui de la supervision basée sur PC. Les dernières spécifications d'OPC UA (Unified Architecture) sont aujourd'hui validées. Avec cette nouvelle version, la fondation OPC révolutionne son standard de communication entre équipements industriels. OPC UA rompt les liens qui le rendaient indissociable de Windows, pour se déployer sur tous types de plateformes

A map and a database for flint-bearing formations in Southern France: A tool for Petroarchaeology

Une carte des principales formations à silex du sud de la France est en cours de réalisation. Elle propose, à tous les préhistoriens, une base nécessaire au développement d’études interrégionales sur la circulation des silex. Elle est le fruit d’une collaboration entre des acteurs impliqués dans la problématique de caractérisation de la provenance des silex. Elle regroupe les résultats de leurs prospections systématiques ou ciblées dans six régions (Aquitaine, Auvergne, Languedoc-Roussillon, Midi-Pyrénées, Provence-Alpes-Côte-d’Azur, Rhône-Alpes). Elle intègre, en plus, le dépouillement d’un grand nombre de documents : i) les principaux articles et thèses traitant des formations à silex du sud de la France ; ii) plus de 200 fiches issues de la base de données du sous-sol BSS du BRGM, qui permettent de visualiser des logs ou des documents scannés ; iii) 529 cartes géologiques à 1/50 000 et leurs notices. La carte est organisée en trois couches de données superposables : une carte des affleurements ou gîtes primaires, une carte des altérites et des formations superficielles remaniées et une carte des formations alluviales. La carte existera dans deux versions numériques aisément actualisables : une version dans un format PDF et une version sous la forme d’un SIG. C’est l’ensemble de la formation contenant le ou les même(s) type(s) de silex qui est prise en compte, le terme de formation désignant un terrain possédant des caractères communs et qui constitue un ensemble cartographiable. Chacune des formations recensées fait l’objet d’une notice simplifiée qui décrit l’encaissant et - le ou les - type(s) de silex présent(s). Ces notices descriptives et explicatives contiennent des photos à toutes les échelles (de la formation à l’échelle microscopique). Des références bibliographiques géologiques et archéologiques complèteront chaque notice. La version définitive de ces notices constituera un atlas. Les archéologues et géologues disposeront ainsi de fiches descriptives pour chaque type de silex et son encaissant. Elles serviront aux diagnoses analytiques (structures, textures et compositions minéralogiques).A map of the main flint bearing formations in the South of France is under construction. It will provide an essential basis to develop interregional studies about flint procurements and travels. It results from collaboration between actors involved in topic flint sourcing. It includes results of their systematic surveys and studies in six regions (Aquitaine, Auvergne, Languedoc-Roussillon, Midi-Pyrenees, Provence-Alpes - Côte d’Azur, Rhône-Alpes). Moreover, it includes a large number of associated data : i) The main papers and those dealing with flint bearing formations of southern France, ii) more than 200 records from the under-soil database BSS BRGM, which give access to logs or scanned documents iii) 529 geological maps at 1/50 000 and their leaflets. The map is organized in three superimposed layers : a map of outcrops or primary deposits, a map of surficial weathered formation and a revised map of alluvial formations. The map is available in two versions which are easily updatable : a PDF version and an interactive GIS version. In this document, every formation containing the same type (s) (s) of flint is taken into account and forms a mappable entity. Every listed formation is linked to a text which describes the parent rock and/or the type(s) of flint(s). These records contain descriptive and explanatory pictures at different scale (naked eye to microscopic scale). Geological and archaeological references complement every record. The final version will constitute an atlas. Archaeologists and geologists will find description sheets of every type of flint and bearing rock. They will help for analytical diagnoses (structure, texture and mineralogical composition)