Inertial dynamics of air bubbles crossing a horizontal fluid–fluid interface

The dynamics of isolated air bubbles crossing the horizontal interface separating two Newtonian immiscible liquids initially at rest are studied both experimentally and computationally. High-speed video imaging is used to obtain a detailed evolution of the various interfaces involved in the system. The size of the bubbles and the viscosity contrast between the two liquids are varied by more than one and four orders of magnitude,respectively, making it possible to obtain bubble shapes ranging from spherical to toroidal. A variety of flow regimes isobserved,including that of small bubbles remaining trapped at the fluid–fluid interface in a film-drainage configuration.In most cases, the bubble succeeds in crossing the interface without being stopped near its undisturbed position and, during a certain period of time, tows a significant column of lower fluid which sometimes exhibits a complex dynamics as it lengthens in the upper fluid. Direct numerical simulations of several selected experimental situations are performed with a code employing a volume of-fluid type formulation of the incompressible Navier–Stokes equations. Comparisons between experimental and numerical results confirm the reliability of the computational approach in most situations but also points out the need for improvements to capture some subtle but important physical processes, most notably those related to film drainage. Influence of the physical parameters highlighted by experiments and computations, especially that of the density and viscosity contrasts between the two fluids and of the various interfacial tensions, is discussed and analysed in the light of simple models and available theories

Dynamics of air bubbles crossing a horizontal interface

Air bubbles crossing a horizontal interface separating two fluids otherwise at rest are encountered in a wide variety of applications, from iron processing to liquid-liquid extraction and scenarios of nuclear accidents or ascent of plumes in the Earth's man-tle. In this talk we report on some findings obtained during an extensive investigation of that problem involving both experiments and direct numerical simulations. Experimentally, we let a single gas bubble rise by releasing it well below an interface between a lower phase made of water or water plus glycerin and an upper, slightly lighter, phase made of silicon oil. We vary the size of the bubble (typically for 1 mm to 20 mm), and the characteristics of the two fluids in order to explore a broad range of physical conditions. A detailed evolution of the various interfaces is obtained usingnhigh-speed video imaging and image processing techniques. Computations are carried out with two separate codes, both of which solve the full Navier-Stokes equa-tions with an Eulerian approach based on an interface-capturing technique. One of them handles the three-phase nature of the flow through a Volume of Fluid approach without interface reconstruction 3 while the other employs the phase-field formulation based on the Cahn-Hilliard equation. The problem depends on six dimensionless parameters, among which the bubble Archimedes (Ar) and Bond (Bo) numbers and the viscosity ratio [lambda] of the two liquids are those we may vary by several orders of magnitude. A variety of flow regimes and bubble shapes is observed, including that of small bubbles remaining trapped during a very long time below the fluid/fluid interface in a film-drainage configuration. In most cases, the bubble succeeds in crossing the interface without being stopped near its undisturbed position and, during a certain period of time, tows a column or tail of lower fluid which sometimes exhibits a complex dynamics as it lengthens in the upper fluid. Varying Bo, or rather the interfacial Bond number BoI , for fixed values of Ar and [lambda] makes it possible to shed light on the complex role of BoI in the system dy-namics. A simple model is set up to show how BoI in fluences the slowing down of the bubble at the fluid/fluid interface and why increasing it suficiently prevents the bub-ble from remaining trapped below it, leading to a tailing configuration. In contrast, tracking the computed evolution of the film thickness when the bubble stands just below the interface indicates that the larger BoI, the longer the time required to drain the film, in agreement with lubrication-type arguments and previous computational studies performed in the creeping flow limit using boundary integral techniques

Modeling heat transfer in gas-particle mixtures: Calculation of the macro-scale heat exchange in Eulerian–Lagrangian approaches using spatial averaging

Heat transfers in dilute gas-particle mixtures are often modeled using hybrid Euler–Lagrange descriptions, treating the carrier fluid via an Eulerian representation and following each particle in a Lagrangian framework. One of the focal issues in these models is the calculation of the macro-scale heat transfer between the continuous phase and particles. In the standard approach, the heat transfer for each particle is considered to vary linearly with the average temperature difference between the particle and the fluid. Here, we use the method of volume averaging with closure to filter the heat transfer equations at the micro-scale and derive a closed form of the heat transfer rate, which is significantly different from the standard case. The primary difference is that the heat transfer for a given particle does not only depend on the temperature of the particle but also depends on the temperatures of all other particles within the averaging volume. This yields a matrix of heat exchange coefficients that captures indirect particle–particle exchanges at macro-scale. Using simple model cases, we validate our approach, compare it to the standard heat transfer model and show that it degenerates toward the standard model only in specific cases

The Major Surface-Associated Saccharides of Klebsiella pneumoniae Contribute to Host Cell Association

Analysing the pathogenic mechanisms of a bacterium requires an understanding of the composition of the bacterial cell surface. The bacterial surface provides the first barrier against innate immune mechanisms as well as mediating attachment to cells/surfaces to resist clearance. We utilised a series of Klebsiella pneumoniae mutants in which the two major polysaccharide layers, capsule and lipopolysaccharide (LPS), were absent or truncated, to investigate the ability of these layers to protect against innate immune mechanisms and to associate with eukaryotic cells. The capsule alone was found to be essential for resistance to complement mediated killing while both capsule and LPS were involved in cell-association, albeit through different mechanisms. The capsule impeded cell-association while the LPS saccharides increased cell-association in a non-specific manner. The electrohydrodynamic characteristics of the strains suggested the differing interaction of each bacterial strain with eukaryotic cells could be partly explained by the charge density displayed by the outermost polysaccharide layer. This highlights the importance of considering not only specific adhesin:ligand interactions commonly studied in adherence assays but also the initial non-specific interactions governed largely by the electrostatic interaction forces

Les mutations contemporaines du droit de l’animal

Le droit de l’animal a connu des mutations d’ampleur au cours des vingt dernières années. Il s’est structuré en champ disciplinaire autonome, a pris une importance croissante dans le débat public et a fait l’objet de réformes remarquées. Le présent ouvrage rend compte de ces évolutions en publiant les actes d’une université d’automne qui s’est tenue à la faculté de droit d’Aix-en-Provence en octobre 2021. Il rassemble les contributions des auteurs – juristes, politistes et historiens – autour de sept thématiques : le droit de l’animal comme champ disciplinaire ; les mots du droit de l’animal ; la fabrique du droit de l’animal ; droit de l’animal et participation démocratique ; droit de l’animal, droits fondamentaux et droit constitutionnel ; la représentation des animaux devant les juridictions et l’action au nom et pour le compte d’un animal ; juridictions pénales et animaux. Le lecteur pourra apprécier, en les parcourant, l’intérêt et la richesse d’une matière en plein essor, particulièrement en phase avec les préoccupations de son temps

The great melting pot. Common sole population connectivity assessed by otolith and water fingerprints

Quantifying the scale and importance of individual dispersion between populations and life stages is a key challenge in marine ecology. The common sole (Solea solea), an important commercial flatfish in the North Sea, Atlantic Ocean and the Mediterranean Sea, has a marine pelagic larval stage, a benthic juvenile stage in coastal nurseries (lagoons, estuaries or shallow marine areas) and a benthic adult stage in deeper marine waters on the continental shelf. To date, the ecological connectivity among these life stages has been little assessed in the Mediterranean. Here, such an assessment is provided for the first time for the Gulf of Lions, NW Mediterranean, based on a dataset on otolith microchemistry and stable isotopic composition as indicators of the water masses inhabited by individual fish. Specifically, otolith Ba/Ca and Sr/Ca profiles, and delta C-13 and delta O-18 values of adults collected in four areas of the Gulf of Lions were compared with those of young-of-the-year collected in different coastal nurseries. Results showed that a high proportion of adults (>46%) were influenced by river inputs during their larval stage. Furthermore Sr/Ca ratios and the otolith length at one year of age revealed that most adults (similar to 70%) spent their juvenile stage in nurseries with high salinity, whereas the remainder used brackish environments. In total, data were consistent with the use of six nursery types, three with high salinity (marine areas and two types of highly saline lagoons) and three brackish (coastal areas near river mouths, and two types of brackish environments), all of which contributed to the replenishment of adult populations. These finding implicated panmixia in sole population in the Gulf of Lions and claimed for a habitat integrated management of fisherie

Adiponectin roles at the human fetal-maternal interface in first-trimester of pregnancy

L’implantation embryonnaire repose sur une synchronisation spatio-temporelle entre un placenta fonctionnel et un endomètre réceptif. La réceptivité endométriale requiert la différenciation des cellules stromales en cellules déciduales sous l’effet des hormones ovariennes (œstrogènes et progestérone). Le placenta est un organe transitoire constitué de deux types cellulaires. Le cytotrophoblaste villeux est responsable des échanges fœtaux maternels et de la fonction endocrine du placenta. Le cytotrophoblaste extravilleux présente des propriétés invasives et assure ainsi l’ancrage du placenta dans l’endomètre maternel. Un dialogue paracrine complexe entre les cellules placentaires et endométriales s’établit au cours des premières étapes de l’implantation.L’adiponectine est une adipokine produite majoritairement par le tissu adipeux. Elle contrôle le métabolisme glucido-lipidique et joue le rôle d’hormone insulino-sensibilisatrice. Dans de nombreux tissus, l’adiponectine exerce des effets anti-prolifératifs, pro-invasifs et pro-différenciants. L’adiponectine et ses récepteurs ADIPOR1 et ADIPOR2 sont présents à l’interface fœto-maternelle. Le placenta et l’endomètre sont donc des tissus cibles de l’adiponectine.Au cours de ce travail, nous nous sommes intéressés aux effets directs de l’adiponectine à l’interface foeto-maternelle au cours du premier trimestre de grossesse.Dans une première partie, nous avons observé que l’adiponectine exerce des effets anti-différenciants et anti-invasifs dans les cellules stromales endométriales.Dans un second temps, nous avons démontré que l’adiponectine favorise la production de glycogène dans les cellules déciduales. Inversement, l’adiponectine semble limiter l’entrée du glycogène dans les cellules placentaires. Ces résultats démontrent que l’adiponectine pourrait contrôler la nutrition histiotrophe du foetus.Dans une dernière partie, nous avons observé que l’adiponectine diminue l’expression des transporteurs de nutriments et exerce une action pro-apoptotique dans le trophoblaste villeux. Ces derniers résultats pourraient permettre de mieux comprendre le rôle de l’adiponectine dans les pathologies placentaires telles que le retard de croissance intra-utérin qui se caractérise par une diminution du poids foetal et une augmentation de l’apoptose des cellules trophoblastiques.L’ensemble de ces résultats montre que l’adiponectine est un acteur clé du dialogue foeto-maternel au cours de la grossesse précoce en contrôlant la maturation d’un endomètre fonctionnel et en régulant les échanges nutritifs transplacentaires.Embryo implantation requires a spatiotemporal synchronization between a functional placenta and a receptive endometrium. Endometrium receptivity based on the differentiation of stromal cells into decidual cells, under the influence of ovarian hormones (estrogens and progesterone). The placenta is a transient organ composed of two cell types. Villous trophoblast ensures fetal-maternal exchanges and the endocrine functions. Extravillous trophoblast acquire an invasive phenotype resulting in the placenta anchoring in the endometrium. Then, a complexe paracrine dialog between placental cells and endometrial cells is established during the first stages of the embryo implantation.Adiponectin is an adipokine predominantly produced by the adipose tissue. This cytokine has an important role in the control of energy metabolism and displays an insulin-sensitizing action. In some cell types, adiponectin limits proliferation, but promotes invasion and differentiation. Adiponectin and its receptors ADIPOR1 and ADIPOR2, are expressed at the fetal-maternal interface. Thus, endometrium and placenta are adiponectin targets.In this work, we aimed to determine adiponectin direct effects at the human fetal maternal interface during the first trimester of pregnancy.In a first part, we observed that adiponectin limits differentiation and invasion in endometrial stromal cells.In a second part, we showed that adiponectin promotes glycogen production by decidual cells. Conversely, adiponectin seems to limit glycogen uptake by placental cells. These results demonstrate that adiponectin could regulate histiotrophic nutrition to the fetus.In a last part, we demonstrated that adiponectin down-regulates the expression of nutrient transporters and promotes apoptosis in villous trophoblast. These last results could help to better understand the adiponectin roles in some placental pathologies, as intrauterine growth restriction, characterized by a decreased fetal weight and a enhanced trophoblastic apoptosis. Altogether, these results demonstrate that adiponectin is a key regulator of the fetal-maternal dialog by controlling the differentiation of a functional endometrium and by regulating transplacental nutrient exchanges

Rôles de l'adiponectine à l'interface foeto-maternelle humaine au cours du premier trimestre de grossesse

Embryo implantation requires a spatiotemporal synchronization between a functional placenta and a receptive endometrium. Endometrium receptivity based on the differentiation of stromal cells into decidual cells, under the influence of ovarian hormones (estrogens and progesterone). The placenta is a transient organ composed of two cell types. Villous trophoblast ensures fetal-maternal exchanges and the endocrine functions. Extravillous trophoblast acquire an invasive phenotype resulting in the placenta anchoring in the endometrium. Then, a complexe paracrine dialog between placental cells and endometrial cells is established during the first stages of the embryo implantation.Adiponectin is an adipokine predominantly produced by the adipose tissue. This cytokine has an important role in the control of energy metabolism and displays an insulin-sensitizing action. In some cell types, adiponectin limits proliferation, but promotes invasion and differentiation. Adiponectin and its receptors ADIPOR1 and ADIPOR2, are expressed at the fetal-maternal interface. Thus, endometrium and placenta are adiponectin targets.In this work, we aimed to determine adiponectin direct effects at the human fetal maternal interface during the first trimester of pregnancy.In a first part, we observed that adiponectin limits differentiation and invasion in endometrial stromal cells.In a second part, we showed that adiponectin promotes glycogen production by decidual cells. Conversely, adiponectin seems to limit glycogen uptake by placental cells. These results demonstrate that adiponectin could regulate histiotrophic nutrition to the fetus.In a last part, we demonstrated that adiponectin down-regulates the expression of nutrient transporters and promotes apoptosis in villous trophoblast. These last results could help to better understand the adiponectin roles in some placental pathologies, as intrauterine growth restriction, characterized by a decreased fetal weight and a enhanced trophoblastic apoptosis. Altogether, these results demonstrate that adiponectin is a key regulator of the fetal-maternal dialog by controlling the differentiation of a functional endometrium and by regulating transplacental nutrient exchanges.L’implantation embryonnaire repose sur une synchronisation spatio-temporelle entre un placenta fonctionnel et un endomètre réceptif. La réceptivité endométriale requiert la différenciation des cellules stromales en cellules déciduales sous l’effet des hormones ovariennes (œstrogènes et progestérone). Le placenta est un organe transitoire constitué de deux types cellulaires. Le cytotrophoblaste villeux est responsable des échanges fœtaux maternels et de la fonction endocrine du placenta. Le cytotrophoblaste extravilleux présente des propriétés invasives et assure ainsi l’ancrage du placenta dans l’endomètre maternel. Un dialogue paracrine complexe entre les cellules placentaires et endométriales s’établit au cours des premières étapes de l’implantation.L’adiponectine est une adipokine produite majoritairement par le tissu adipeux. Elle contrôle le métabolisme glucido-lipidique et joue le rôle d’hormone insulino-sensibilisatrice. Dans de nombreux tissus, l’adiponectine exerce des effets anti-prolifératifs, pro-invasifs et pro-différenciants. L’adiponectine et ses récepteurs ADIPOR1 et ADIPOR2 sont présents à l’interface fœto-maternelle. Le placenta et l’endomètre sont donc des tissus cibles de l’adiponectine.Au cours de ce travail, nous nous sommes intéressés aux effets directs de l’adiponectine à l’interface foeto-maternelle au cours du premier trimestre de grossesse.Dans une première partie, nous avons observé que l’adiponectine exerce des effets anti-différenciants et anti-invasifs dans les cellules stromales endométriales.Dans un second temps, nous avons démontré que l’adiponectine favorise la production de glycogène dans les cellules déciduales. Inversement, l’adiponectine semble limiter l’entrée du glycogène dans les cellules placentaires. Ces résultats démontrent que l’adiponectine pourrait contrôler la nutrition histiotrophe du foetus.Dans une dernière partie, nous avons observé que l’adiponectine diminue l’expression des transporteurs de nutriments et exerce une action pro-apoptotique dans le trophoblaste villeux. Ces derniers résultats pourraient permettre de mieux comprendre le rôle de l’adiponectine dans les pathologies placentaires telles que le retard de croissance intra-utérin qui se caractérise par une diminution du poids foetal et une augmentation de l’apoptose des cellules trophoblastiques.L’ensemble de ces résultats montre que l’adiponectine est un acteur clé du dialogue foeto-maternel au cours de la grossesse précoce en contrôlant la maturation d’un endomètre fonctionnel et en régulant les échanges nutritifs transplacentaires

An Elliptic Blending explicit algebraic Reynolds-stress model for wall-bounded flows

A new explicit algebraic Reynolds stress model is derived based on the elliptic blending strategy to account for near-wall blocking effects. The resulting model inherits some of the most important features of the underlying elliptic blending Reynolds stress model, especially the two-component limit of turbulence, but involves only one elliptic equation for the blending coefficient in addition to the standard two-equation k-ε model which serves here as a platform for the model. The algebraic relationship is developed following a direct solution method for two-and three-dimensional mean flows rather than using a projection over a truncated integrity basis. The resulting algebraic relation remains formally similar to standard expressions based on a linear pressure-strain model with the addition of a tensor related to wall orientation. An analytical solution of the nonlinear consistency equation for the production to dissipation ratio is provided for two-dimensional cases that serves as an initial guess to an iterative approach depending on the flow situation. The computations carried out on fully developed turbulent flows to validate the algebraic model demonstrate the good model performances and confirm the effectiveness of the iterative approach to reach self consistency

Modélisation du renoyage d'un lit de particules (contribution à l'estimation des propriétés de transport macroscopiques)

Ce travail porte sur la modélisation macroscopique des transferts de masse et de chaleur dans un milieu poreux surchauffé parcouru par un écoulement liquide-vapeur avec changement de phase. Dans le cadre du non équilibre thermique local entre les trois phases du système, un modèle macroscopique quasi-stationnaire à trois températures est établi par prise de moyenne volumique des équations de transport locales. Un des aspects attrayants de la technique de changement d'échelle réside ici dans le développement d'une forme fermée du taux d'évaporation à l'échelle macroscopique dépendant des températures moyennes et des propriétés effectives. Le modèle macroscopique résultant peut être vu comme une généralisation des modèles à trois températures existants obtenus dans le cadre d'une approche heuristique. Les principales différences sont la présence de termes de transport supplémentaires et un couplage entre les différents continuums (phase et interface) qui semble plus complexe. L'intérêt majeur de l'approche développée ici est de proposer des problèmes de fermeture permettant de déterminer les coefficients de transports effectifs, tels que les tenseurs de dispersion et les coefficients d'échange, à partir d'une description locale sur une cellule représentative du milieu considéré. Ces problèmes ont été résolus pour des cellules unitaires simples pour obtenir une première estimation des propriétés effectives. Pour ces cellules et pour des problèmes de diffusion-évaporation, des comparaisons avec des solutions numériques du problème local ont permis d'illustrer l'intérêt pratique et les potentialités du modèle macroscopique. Pour des cellules unitaires plus complexes, une simulation numérique directe de l'écoulement diphasique à l'échelle locale a été effectuée permettant d'avoir accès au champ de vitesse et à la topologie des interfaces. L'outil de simulation numérique directe développé est basé sur une méthode à interface diffuse. Ces méthodes sont bien adaptées aux longueurs caractéristiques à l'échelle locale du milieu poreux et les développements menés montrent que l'on peut envisager de prendre en compte le changement de phase dans le cadre des modèles de Cahn-Hilliard. Les résultats obtenus sur des cellules 2D soulignent le rôle important de la répartition des phases et indiquent que les corrélations pour les propriétés effectives, en fonction de la saturation et des nombres de Péclet, peuvent être relativement complexes.TOULOUSE-ENSEEIHT (315552331) / SudocSudocFranceF