Mesures µPIV dans un modèle de milieu poreux

L'étude présentée porte sur la mesure des champs de vitesses dans un milieu poreux et en particulier dans les pores de tels milieux. Le milieu poreux utilisé possède des caractéristiques géométriques et dimensionnelles proches de celles observées dans le cas d'un sol. Les champs de vitesses sont déterminés à l'aide d'une méthode de micro vélocimétrie par image de particules (µPIV ) adaptée aux spécificités du modèle utilisé. Les résultats obtenus sont comparés à des observations réalisées sur un modèle similaire dans le cadre d'une étude portant sur la détermination des capacités de filtrage de ce type de milieu au regard de la taille des particules (phénomène de ségrégation). Les deux types de résultats sont en bon accord et les hypothèses formulées pour expliquer le filtrage partiel sont confirmées par la présente étude

Botanical Monography in the Anthropocene

Unprecedented changes in the Earth's biota are prompting urgent efforts to describe and conserve plant diversity. For centuries, botanical monographs — comprehensive systematic treatments of a family or genus — have been the gold standard for disseminating scientific information to accelerate research. The lack of a monograph compounds the risk that undiscovered species become extinct before they can be studied and conserved. Progress towards estimating the Tree of Life and digital information resources now bring even the most ambitious monographs within reach. Here, we recommend best practices to complete monographs urgently, especially for tropical plant groups under imminent threat or with expected socioeconomic benefits. We also highlight the renewed relevance and potential impact of monographies for the understanding, sustainable use, and conservation of biodiversity.Fil: Grace, Olwen M.. Royal Botanic Gardens, Kew; Reino UnidoFil: Pérez-Escobar, Oscar A.. Royal Botanic Gardens, Kew; Reino UnidoFil: Lucas, Eve J.. Royal Botanic Gardens, Kew; Reino UnidoFil: Vorontsova, Maria S.. Royal Botanic Gardens, Kew; Reino UnidoFil: Lewis, Gwilym P.. Royal Botanic Gardens, Kew; Reino UnidoFil: Walker, Barnaby E.. Royal Botanic Gardens, Kew; Reino UnidoFil: Lohmann, Lúcia G.. Universidade de Sao Paulo; BrasilFil: Knapp, Sandra. Natural History Museum; Reino UnidoFil: Wilkie, Peter. Royal Botanic Gardens; Reino UnidoFil: Sarkinen, Tiina. Royal Botanic Gardens; Reino UnidoFil: Darbyshire, Iain. Royal Botanic Gardens; Reino UnidoFil: Lughadha, Eimear Nic. Royal Botanic Gardens; Reino UnidoFil: Monro, Alexandre. Royal Botanic Gardens; Reino UnidoFil: Woudstra, Yannick. Universidad de Copenhagen; Dinamarca. Royal Botanic Gardens; Reino UnidoFil: Demissew, Sebsebe. Addis Ababa University; EtiopíaFil: Muasya, A. Muthama. University Of Cape Town; SudáfricaFil: Díaz, Sandra Myrna. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; ArgentinaFil: Baker, William J.. Royal Botanic Gardens, Kew; Reino UnidoFil: Antonelli, Alexandre. University of Oxford; Reino Unido. University Goteborg; Sueci

Global and Zonal-Mean Hydrological Response to Early Eocene Warmth

Earth's hydrological cycle is expected to intensify in response to global warming, with a “wet-gets-wetter, dry-gets-drier” response anticipated over the ocean. Subtropical regions (∼15°–30°N/S) are predicted to become drier, yet proxy evidence from past warm climates suggests these regions may be characterized by wetter conditions. Here we use an integrated data-modeling approach to reconstruct global and zonal-mean rainfall patterns during the early Eocene (∼56–48 million years ago). The Deep-Time Model Intercomparison Project (DeepMIP) model ensemble indicates that the mid- (30°–60°N/S) and high-latitudes (>60°N/S) are characterized by a thermodynamically dominated hydrological response to warming and overall wetter conditions. The tropical band (0°–15°N/S) is also characterized by wetter conditions, with several DeepMIP models simulating narrowing of the Inter-Tropical Convergence Zone. However, the latter is not evident from the proxy data. The subtropics are characterized by negative precipitation-evaporation anomalies (i.e., drier conditions) in the DeepMIP models, but there is surprisingly large inter-model variability in mean annual precipitation (MAP). Intriguingly, we find that models with weaker meridional temperature gradients (e.g., CESM, GFDL) are characterized by a reduction in subtropical moisture divergence, leading to an increase in MAP. These model simulations agree more closely with our new proxy-derived precipitation reconstructions and other key climate metrics and imply that the early Eocene was characterized by reduced subtropical moisture divergence. If the meridional temperature gradient was even weaker than suggested by those DeepMIP models, circulation-induced changes may have outcompeted thermodynamic changes, leading to wetter subtropics. This highlights the importance of accurately reconstructing zonal temperature gradients when reconstructing past rainfall patterns

RED BLOOD CELL GHOSTS FLOW IN MICRO CHANNEL

International audienceOptical characterization of high hematocrit whole blood flows in small to medium size vessels are of particular interest in many patho-physiological conditions. However, such characterizations remain challenging because of the optical properties of blood. Blood is a complex multiphasic fluid and its optical and rheological properties are governed by interactions between red blood cells (RBC) and plasma. In particular the transmission characteristics of such a suspension is ruled by the combined effect of absorption from some molecules and scattering from the cells. These combined effects make it globally difficult to image RBC at high hematocrit in depth larger than a few 10th of micrometers limiting therefore the studies to small size vessels or to wall regions . Major rheological and fluid mechanical behaviors are therefore not accessible with traditional laboratory instrumentation. As an example, the blunting of the velocity profile is a known effect in physiological high hematocrit flow conditions. Such a deviation from the traditionally accepted Poiseuille theory has a major consequence on the local flow conditions (shear rate/stress) and can hardly be observed because of the aforementioned limitations. To overcome such problems, transparent suspensions can be prepared by using RBC ghosts (i.e. hemoglobin free RBC) [1]. By such a technique one can obtain a transparent high hematocrit mixture that can be imaged over large depth of flow (Figure 1, right) in which high precision microscopic particle image velocimetry flow field measurements (microPIV) can be performed. To demonstrate this capacity and to have a close insight in the flow of a blood mimicking fluid in vessels larger than previously reported in the literature are the goals of this work

A simple model for the perfusion of porous hydrogel scaffolds under culture in a sustentation like bioreactor

International audienceOver the last decade hydrogels, and more recently porous hydrogels, have shown to be promising biocompatible, resorbable scaffolds for tissue engineering (Gloria et al, 2010). Such porous scaffolds generally show a poor mechanical behavior which makes them difficult to manipulate. Since one key issue of tissue engineering is to properly perfuse the scaffolds in order to promote cell seeding in 3D scaffold, increase mass transport and mechanically condition by shear and compressive forces the cells under culture, the perfusion strategy has to be adapted for such materials. As a matter of fact the use of such scaffolds in perfusion systems in which the scaffolds are clamped is prohibited and only bioreactors in which the scaffolds are freely suspended are possible. In order to quantify the perfusion performance of porous hydrogel scaffolds in such bioreactors we :1) characterized the free settling velocity, measured the permeability of the scaffolds,2) derived a simple model for the perfusion of the scaffolds under free falling suspension,3) compared the obtained perfusion characteristics with literature,4) designed and built a bioreactor system to host the scaffolds under proper flow conditions performed cell culture experiments. The present work relates to the 4 first steps, details of the 2 later ones can be found in Knapp et al (2012)

Characterization of dense particle suspensions under flow

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