Hydrodynamics within the Electric Double Layer on slipping surfaces

We show, using extensive Molecular Dynamics simulations, that the dynamics of the electric double layer (EDL) is very much dependent on the wettability of the charged surface on which the EDL develops. For a wetting surface, the dynamics, characterized by the so-called Zeta potential, is mainly controlled by the electric properties of the surface, and our work provides a clear interpretation for the traditionally introduced immobile Stern layer. In contrast, the immobile layer disappears for non-wetting surfaces and the Zeta potential deduced from electrokinetic effects is considerably amplified by the existence of a slippage at the solid substrate.Comment: accepted for publication in Physical Review Letter

Large permeabilities of hourglass nanopores: From hydrodynamics to single file transport

In fluid transport across nanopores, there is a fundamental dissipation that arises from the connection between the pore and the macroscopic reservoirs. This entrance effect can hinder the whole transport in certain situations, for short pores and/or highly slipping channels. In this paper, we explore the hydrodynamic permeability of hourglass shape nanopores using molecular dynamics (MD) simulations, with the central pore size ranging from several nanometers down to a few Angstr{\"o}ms. Surprisingly, we find a very good agreement between MD results and continuum hydrodynamic predictions, even for the smallest systems undergoing single file transport of water. An optimum of permeability is found for an opening angle around 5 degree, in agreement with continuum predictions, yielding a permeability five times larger than for a straight nanotube. Moreover, we find that the permeability of hourglass shape nanopores is even larger than single nanopores pierced in a molecular thin graphene sheet. This suggests that designing the geometry of nanopores may help considerably increasing the macroscopic permeability of membranes

Tracking a genetic signal of extinction-recolonization events in a neotropical tree species: Voucapoua americana Aublet in French Guiana

Drier periods from the late Pleistocene and early Holocene have been hypothesized to have caused the disappearance of various rainforest species over large geographical areas in South America and restricted the extant populations to mesic sites. Subsequent improvement in climatic conditions has been associated with recolonization. Changes in population size associated with these extinction‐recolonization events should have affected genetic diversity within species. However, these historical hypotheses and their genetic consequences have rarely been tested in South America. Here, we examine the diversity of the chloroplast and nuclear genomes in a Neotropical rainforest tree species, Vouacapoua americana (Leguminosae, Caesalpinioideae) in French Guiana. The chloroplast diversity was analyzed using a polymerase chain reaction‐restriction fragment length polymorphism method (six pairs of primers) in 29 populations distributed over most of French Guiana, and a subset of 17 populations was also analyzed at nine polymorphic microsatellite loci. To determine whether this species has experienced extinction‐recolonization, we sampled populations in areas supposedly not or only slightly affected by climatic changes, where the populations would not have experienced frequent extinction, and in areas that appear to have been recently recolonized. In the putatively recolonized areas, we found patches of several thousands of hectares homogeneous for chloroplast variation that can be interpreted as the effect of recolonization processes from several geographical origins. In addition, we observed that, for both chloroplast and nuclear genomes, the populations in newly recolonized areas exhibited a significantly smaller allelic richness than others. Controlling for geographic distance, we also detected a significant correlation between chloroplast and nuclear population differentiation. This result indicates a cytonuclear disequilibrium that can be interpreted as a historical signal of a genetic divergence between fragmented populations. In conclusion, the spatial genetic structure of contemporary V. americana populations shows evidence that this species has experienced large extinction‐recolonization events, which were possibly caused by past climatic change

Numerical analysis of pulsed local plane-wave generation in a TREC

International audienceThe feasibility of generating arbitrary wavefronts within a time-reversal electromagnetic chamber (TREC) has been demonstrated both theoretically and experimentally. Though originally motivated for EMC tests, the generation of coherent wavefronts within a reverberating cavity has a potential interest in antenna testing, too. In this paper, the generation of locally planar wavefronts is addressed by means of numerical simulations involving a 2D cavity, for a scalar electric field. The relationship between the quality of the wavefronts and its defining parameters (bandwidth, curvature, phase center, etc.) is investigated

Liquid friction on charged surfaces: from hydrodynamic slippage to electrokinetics

Hydrodynamic behavior at the vicinity of a confining wall is closely related to the friction properties of the liquid/solid interface. Here we consider, using Molecular Dynamics simulations, the electric contribution to friction for charged surfaces, and the induced modification of the hydrodynamic boundary condition at the confining boundary. The consequences of liquid slippage for electrokinetic phenomena, through the coupling between hydrodynamics and electrostatics within the electric double layer, are explored. Strong amplification of electro-osmotic effects is revealed, and the non-trivial effect of surface charge is discussed. This work allows to reconsider existing experimental data, concerning Zeta potentials of hydrophobic surfaces and suggest the possibility to generate ``giant'' electro-osmotic and electrophoretic effects, with direct applications in microfluidics

L’innovation controversée : le débat sur les OGM comme expérimentation collective de nouveaux rapports entre science, marché et démocratie

Christophe Bonneuil, chargé de recherche au CNRS Pierre-Benoît Joly, directeur de recherche à l’INRAClaire Marris, chargée de recherche à l’INRA Compte rendu non communiqué

L’innovation controversée : le débat sur les OGM comme expérimentation collective de nouveaux rapports entre science, marché et démocratie

Christophe Bonneuil, chargé de recherche au CNRSPierre-Benoît Joly, directeur de recherche à l’INRAClaire Marris, chargée de recherche à l’INRA À partir du cas de la controverse publique sur les OGM qui s’est ouverte en France vers 1996, le séminaire a permis d’aborder trois évolutions majeures de ces dernières années : les transformations des modes de production et d’appropriation des connaissances scientifiques ; les mutations des rapports à la science, à l’innovation et au « progrès ». Rom..

In situ HT-XRD study of the UO2_2-PuO2_2-Pu2_2O3_3 sub-system

International audienc

The Landscape from Home : a GIS-based hedonic price valuation

International audienceWe estimate the hedonic price of landscape seen from houses in the urban fringe of Dijon (France). The viewshed and the land cover as seen from the ground are analyzed by geographic methods from satellite images and from a digital elevation model. The landscape attributes are then used in an econometric model based on the sales of 2667 houses, which deals with endogeneity, multicollinearity, and spatial correlations. The results show that woodland and farmland in the immediate vicinity of houses have positive prices and roads a negative price when these features can be seen by an observer located on the ground, while those prices are clearly lower (or insignificant) when such features cannot be seen: the view itself matters. The arrangement of features in fragmented landscapes commands positive hedonic prices. Landscapes and objects seen more than 100-300 m away all have insignificant hedonic prices

Unsupervised Individual Whales Identification: Spot the Difference in the Ocean

International audienceIdentifying organisms is a key step in accessing information related to the ecology of species. But unfortunately, this is difficult to achieve due to the level of expertise necessary to correctly identify and record living organisms. To try bridging this gap, enormous work has been done on the development of automated species identification tools such as image-based plant identification or audio recordings-based bird identification. Yet, for some groups, it is preferable to monitor the organisms at the individual level rather than at the species level. The automatizing of this problem has received much less attention than species identification. In this paper, we address the specific scenario of discovering humpack whales individuals in a large collections of pictures collected by nature observers. The process is initiated from scratch, without any knowledge on the number of individuals and without any training samples of these individuals. Thus, the problem is entirely unsupervised. To address it, we set up and experimented a scalable fine-grained matching system allowing to discover small rigid visual patterns in highly clutter background. The evaluation was conducted in blind in the context of the LifeCLEF evaluation campaign. Results show that the proposed system provides very promising results with regard to the difficulty of the task but that there is still room for improvements to reach higher recall and precision in the future