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Vandœuvre-lès-Nancy, France

Wood B.D.,Oregon State University | Golfier F.,Laboratoire Environnement | Quintard M.,CNRS Fluid Dynamics Institute of Toulouse
International Journal of Environment and Waste Management

In this work, we continue our study of upscaling biofilm processes in porous media from the pore scale to the Darcy scale. We adopt a continuum-level description of biofilms at the pore scale on the basis of work reported in Wood et al. (2002b). We upscale from the pore scale to the Darcy scale using the method of volume averaging and we predict the effective dispersion tensor with two- and three-dimensional closure problems. Our results indicate that, for a one-equation local mass equilibrium theory, the primary influence of the biofilm is that the effective diffusion coefficient is smaller than it would be without the presence of biofilm. This effect is important primarily at low Péclet numbers. Copyright © 2011 Inderscience Enterprises Ltd. Source

Philippe A.M.,CNRS Mechanical Energy, Theories, and Applications Laboratory | Baravian C.,CNRS Mechanical Energy, Theories, and Applications Laboratory | Baravian C.,University of Caen Lower Normandy | Bezuglyy V.,CNRS Mechanical Energy, Theories, and Applications Laboratory | And 4 more authors.

In the present study, we investigate the evolution with shear of the viscosity of aqueous suspensions of size-selected natural swelling clay minerals for volume fractions extending from isotropic liquids to weak nematic gels. Such suspensions are strongly shear-thinning, a feature that is systematically observed for suspensions of nonspherical particles and that is linked to their orientational properties. We then combined our rheological measurements with small-angle X-ray scattering experiments that, after appropriate treatment, provide the orientational field of the particles. Whatever the clay nature, particle size, and volume fraction, this orientational field was shown to depend only on a nondimensional Péclet number (Pe) defined for one isolated particle as the ratio between hydrodynamic energy and Brownian thermal energy. The measured orientational fields were then directly compared to those obtained for infinitely thin disks through a numerical computation of the Fokker-Plank equation. Even in cases where multiple hydrodynamic interactions dominate, qualitative agreement between both orientational fields is observed, especially at high Péclet number. We have then used an effective approach to assess the viscosity of these suspensions through the definition of an effective volume fraction. Using such an approach, we have been able to transform the relationship between viscosity and volume fraction (ηr = f into a relationship that links viscosity with both flow and volume fraction (ηr = f(Pe)). © 2013 American Chemical Society. Source

Guillon T.,French National Agency for Nuclear Waste Management ANDRA | Guillon T.,Laboratoire Environnement | Giot R.,Laboratoire Environnement | Giraud A.,Laboratoire Environnement | Armand G.,French National Agency for Nuclear Waste Management ANDRA
Acta Geotechnica

The French National Agency for Nuclear Waste Management is currently studying the Callovo-Oxfordian claystone as a potential repository for nuclear waste. This study focuses on the hydromechanical (HM) unsaturated response of the rock subjected to hydraulic loading. Static atmosphere drying tests highlighted the HM coupling and mechanical anisotropy of the samples. A coupled poroelastic model was proposed, involving highly nonlinear equations. Numerical simulations were performed using the finite element code Code_Aster. Through a sensitivity analysis, the most suitable parameters for estimation were found to be the Biot coefficient and 3 of the 4 independent parameters of the Van Genuchten-Mualem relations. The parameters were estimated according to an inverse procedure that minimizes a cost functional. The estimates could not outline any hysteretic behavior, but they appeared to be divided into two groups (depending on their fitted values). The convergence and stability of the inverse algorithm were studied, and the results showed that direct computations must be run prior to the inversion to ensure its convergence. No plasticity occurred in the samples (according to the model), whereas irreversible phenomena do take place in situ. © 2012 Springer-Verlag. Source

Guillon T.,French National Agency for the Nuclear Waste Management | Giot R.,Laboratoire Environnement | Giraud A.,Laboratoire Environnement | Armand G.,French National Agency for the Nuclear Waste Management
Computational Geomechanics, COMGEO II - Proceedings of the 2nd International Symposium on Computational Geomechanics

The French Agency for Nuclear Waste Management (ANDRA) is currently studying the Callovo-Oxfordian argillites (COxA) as a possible repository for nuclear wastes. The aim of this work is to focus on the hydromechanical unsaturated response of the COxA subjected to hydraulic loading. A coupled model is proposed, and is enhanced with a plastic part. First, the mechanical behaviour of the rock is obtained from triaxial tests. The observed inelastic strains are attributed to plasticity (Chiarelli et al., 2003) and a non-associated plastic law is proposed. Later, drying tests are performed to estimate poroelastic parameters. These tests are interpreted using EDF's Code-Aster finite element software as the model involves highly non-linear equations. Source

Erice G.,French National Institute for Agricultural Research | Louahlia S.,Laboratoire Environnement | Irigoyen J.J.,University of Zaragoza | Sanchez-Diaz M.,University of Zaragoza | Avice J.-C.,French National Institute for Agricultural Research
Journal of Plant Physiology

The predicted worldwide increase of arid areas and water stress episodes will strongly affect crop production. Numerous plants have developed specific morphological and physiological mechanisms as a means to increase their tolerance to drought. Water stress modifies dry matter partitioning and morphological components such as leaf area ratio (LAR), specific leaf area (SLA) and leaf weight ratio (LWR). Alfalfa has a wide-ranging distribution and is thus expected to show differing levels of drought tolerance. The aim of our study was to determine the effect of progressive drought and subsequent recovery in four alfalfa genotypes differing in drought sensitivity: three cultivars adapted to a Mediterranean climate, Tafilalet (TA), Tierra de Campos (TC) and Moapa (MO), and another representative of an oceanic climate, Europe (EU). Mild drought did not affect biomass production or water status in the studied varieties. Under moderate drought conditions, TA and MO showed decreased leaf production, which may help them to maintain relative water content (RWC). Despite observations that water stress did not affect root growth, after the recovery period, TA increased its root biomass, making higher water soil prospecting possible. Mediterranean cultivars modified LAR and SLA depending on water availability, whereas EU alters LWR. At the end of the experiment, TC was the most productive cultivar, but severe drought did not predict differences among cultivars. Severe water stress increased the root/shoot ratio in order to diminish water consumption and increase absorption of water. In spite of all cultivars showing a decreased LWR, TA also decreased SLA, which may suggest higher drought resistance. Morphological traits from Mediterranean cultivars, including the ability to alter SLA or LAR may be used for drought-tolerant cultivar improvement. © 2009 Elsevier GmbH. All rights reserved. Source

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