A phenomenological model of cell-cell adhesion mediated by cadherins

International audienceWe present a phenomenological model intended to describe at the protein population level the formation of cell-cell junctions by the local recruitment of homophilic cadherin adhesion receptors. This modeling may have a much wider implication in biological processes since many adhesion receptors, channel proteins and other membrane-born proteins associate in clusters or oligomers at the cell surface. Mathematically, it consists in a degenerate reaction-diffusion system of two partial differential equations modeling the time-space evolution of two cadherin populations over a surface: the first one represents the diffusing cadherins and the second one concerns the fixed ones. After discussing the stability of the solutions of the model, we perform numerical simulations and show relevant analogies with experimental results. In particular, we show patterns or aggregates formation for a certain set of parameters. Moreover, perturbing the stationary solution, both density populations converge in large times to some saturation level. Finally, an exponential rate of convergence is numerically obtained and is shown to be in agreement, for a suitable set of parameters, with the one obtained in some in vitro experiments

LʼOccident grec de Marseille à Mégara Hyblaea

La recherche sur l’expansion grecque en Méditerranée occidentale à l’époque archaïque a largement progressé en France pendant les quarante dernières années grâce aux travaux d’Henri Tréziny et aux pistes qu’il a lancées dans l’interprétation des découvertes archéologiques de Sicile et du Sud de la Gaule. En présentant ces études sur l’urbanisme, l’architecture et divers artefacts de la vie matérielle dans ces régions occupées par les Grecs à partir du VIIIe siècle av. J.-C., ses amis, collègues et élèves ont voulu lui rendre hommage en centrant en particulier leurs réflexions sur les deux sites qui ont constitué les piliers de sa carrière, Marseille et Mégara Hyblaea. Vingt-trois contributions dues à quelques-uns des meilleurs spécialistes de ces questions, français, italiens et espagnols, mettent ici en évidence le dynamisme de la recherche dans ces régions périphériques du monde grec où populations locales et Grecs ont constitué une culture spécifique, faite de brassages et d’emprunts respectifs dans les domaines de la ville, de la religion ou des pratiques culturelles. Le volume s’ouvre sur la publication de découvertes récentes des chercheurs turcs à Phocée, la métropole de Marseille et une des cités grecques les plus actives dans cette expansion vers l’Ouest

Interférométrie avec des guides d'ondes optiques. Théorie et applications

Jury: Pierre Benech (président), Stuart Shaklan (rapporteur), Michel Tallon (rapporteur), Romain Petrov (examinateur), Alain Chelli (directeur de thèse), Fabien Malbet (codirecteur de thèse)Interferometry is the technique that produces interferences from an astrophysical target between the output of several independent apertures. Interferometry with optical waveguides is one important subclass of interferometry for which the beams propagate in optical waveguides, the most popular ones being optical fibers. Optical waveguides are special optical components which are often not well understood by the astronomical community. They are often presented as a funnel for photons, where the number of injected photons are computed from the injection coupling factor. Neither the propagation inside the waveguide, nor the effect on the spatial spectrum of the input source are considered. The goal of the work presented in this document is to get deeper understanding of how single-mode filtering works. After an introductory chapter recalling why optical waveguides have been introduced into astronomical interferometry, I will present the physics of modal filtering from a theoretical point of view. A special emphasis has been be put on the normalization problem of Radiation Modes inside a guiding structure. A new mathematical approach for solving this problem has been derived which can be applied for any number multi-layered strong or weakling guiding dielectric structure. Application of the method to the round optical fiber has led to the computation of the spectral density of power and rejection of radiated modes launched be a perfect or perturbated Airy pattern. It is shown that rejection dynamics is fast at the beginning but slows with the optical path. Furthermore interference phenomena between radiation modes and the fundamental one can locally give rise to an optimum for the rejection in terms of the size to be used for flux integration in the tranversal plane of the waveguide. The second part of this work is dedicated to the study of the object image relationship of a fibered interferometer. On a rigorous mathematical basis we study how partial coherence propagates through interferometric combination of single-mode beams in ground-based multi-aperture long-baseline optical interferometers. We show actually that the measured visibility is biased due to field of view limitations.L'interférométrie astronomique est une technique observationnelle qui forme des interférences avec le rayonnement d'une source à la sortie de différentes ouvertures indépendantes. L'interférométrie monomode (optique fibrée ou optique intégrée) est une catégorie importante de l'interférométrie pour laquelle les faisceaux se propagent à l'intérieur des guides d'onde, les plus populaires étant les fibres optiques. Les guides d'ondes ne sont pas très bien connus de la communauté astronomique. Ils sont souvent présentés comme des entonnoirs à photons, où le nombre de photons injectés est simplement calculé à partir d'un taux de couplage. Ni la propagation dans la fibre, ni l'effet du guide sur le spectre spatial de la source ne sont considérés. Le but de ce travail est de mieux comprendre comment marche le filtrage optique monomode. Après avoir rappelé pourquoi et dans quel contexte les guides d'ondes ont été introduits interférométrie, je vais présenter la physique du filtrage modal sous un angle théorique. Une attention particulière sera portée au problème de la normalisation des modes rayonnés dans une structure guidante. Une approche mathématique originale a été développée et permet de calculer les modes rayonnés de n'importe qu'elle structure multicouche fortement ou faiblement guidante. L'application de la méthode à la fibre optique circulaire bi-couche a permis de calculer la densité spectrale et dévaluer la réjection des modes rayonnés excités par une tâche d'Airy. Nous montrons que la dynamique de la réjection est rapide mais ralentit dans la longueur du guide. De plus des phénomènes interférentiels entre le mode guidé et le paquet d'ondes rayonnés conduisent à la notion d'optimum local pour la réjection en terme de taille de région d'intégration du flux dans le plan transverse du guide. La seconde partie de ce travail est dédiée à l'étude formelle de la relation objet-image dans un interféromètre fibré. Sur une base mathématique rigoureuse nous étudions comment se propage la cohérence partielle à travers le système optique. Nous montrons que les mesures de visibilité sont biaisées à cause de la réduction du champ de vue induite par la présence des guides

Morphological and mineralogical analysis of East Candor Chasma in Valles Marineris on Mars

+ PosterInternational audienc

Bipolar H ii regions produced by cloud–cloud collisions

17 pages, 6 figuresInternational audienceWe suggest that Bipolar H{\sc ii} Regions may be the aftermath of collisions between clouds. Such a collision will produce a shock-compressed layer, and a star cluster can then condense out of the dense gas near the centre of the layer. If the clouds are sufficiently massive, the star cluster is likely to contain at least one massive star, which emits ionising radiation, and excites an H{\sc ii} region, which then expands, sweeping up the surrounding neutral gas. Once most of the matter in the clouds has accreted onto the layer, expansion of the H{\sc ii} Region meets little resistance in directions perpendicular to the mid-plane of the layer, and so it expands rapidly to produce two lobes of ionised gas, one on each side of the layer. Conversely, in directions parallel to the mid-plane of the layer, expansion of the H{\sc ii} Region stalls due to the ram-pressure of the gas that continues to fall towards the star cluster from the outer parts of the layer; a ring of dense neutral gas builds up around the waist of the Bipolar H{\sc ii} Region, and may spawn a second generation of star formation. In this paper we present a dimensionless model for the flow of ionised gas in a Bipolar H{\sc ii} Region created according to the above scenario, and predict the characteristics of the resulting freefree continuum and recombination-line emission. This dimensionless model can be scaled to the physical parameters of any particular system. Our intention is that these predictions will be useful in testing the scenario outlined above, and thereby providing indirect support for the role of cloud/cloud collisions in triggering star formation

Could β-Lactam Antibiotics Block Humoral Immunity?

International audienceIt has been reported that treatment with b-lactam antibiotics induces leukopenia and candidemia, worsens the clinical response to anticancer immunotherapy and decreases immune response to vaccination. b-lactamases can cleave b-lactam antibiotics by blocking their activity. Two distincts superfamilies of b-lactamases are described, the serine b-lactamases and the zinc ion dependent metallo-b-lactamases. In human, 18 metallo-b-lactamases encoding genes (hMBLs) have been identified. While the physiological role of most of them remains unknown, it is well established that the SNM1A, B and C proteins are involved in DNA repair. The SNM1C/Artemis protein is precisely associated in the V(D)J segments rearrangement, that leads to immunoglobulin (Ig) and T-cell receptor variable regions, which have a crucial role in the immune response. Thus in humans, SNM1C/Artemis mutation is associated with severe combined immunodeficiency characterized by hypogammaglobulinemia deficient cellular immunity and opportunistic infections. While catalytic site of hMBLs and especially that of the SNM1 family is highly conserved, in vitro studies showed that some b-lactam antibiotics, and precisely third generation of cephalosporin and ampicillin, inhibit the metallo-b-lactamase proteins SNM1A & B and the SNM1C/Artemis protein complex. By analogy, the question arises as to whether b-lactam antibiotics can block the SNM1C/Artemis protein in humans inducing transient immunodeficiency. We reviewed here the literature data supporting this hypothesis based on in silico, in vitro and in vivo evidences. Understanding the impact of b-lactam antibiotics on the immune cell will offer new therapeutic clues and new clinical approaches in oncology, immunology, and infectious diseases

Full-scale fire test on a high-rise RC wall

International audienceThis paper describes a full-scale test carried out on a high-rise reinforced concrete wall subjected to fire loading conditions in the special Vulcain furnace (very large and modular gas furnace) at CSTB, France. The test sample was designed to represent a slender wall with a very large height/thickness ratio. The experimental results showed a large deflection of the high wall in fire conditions (almost equal to the wall height/24) even for a fire exposure time of 90 min. Such a deflection was significantly higher than the maximum value recommended by design codes (about the wall height/30 for 120 min of fire exposure). Furthermore, other test results (full-field displacements in the 3 directions, residual deformed shape after the heating and cooling phases) may also provide additional useful experimental data for validating available or future models (which are usually based on some specific assumptions). In addition, the measurements of thermal-induced deformed shape of the wall are compared to those predicted by an analytical solution derived from a simplified one-dimensional (1D) beam model, as well as to those obtained from non-linear finite-element simulations (with 2D plate elements), in order to assess the practical applicability of these simulations. These comparisons show a reasonably good agreement between the experimental results and the predictions of these models, thereby providing a first validation of the latter