A nonlinear random walk approach to concentration-dependent contaminant transport in porous media

We propose a nonlinear random walk model to describe the dynamics of dense contaminant plumes in porous media. A coupling between concentration and velocity fields is found, so that transport displays non-Fickian features. The qualitative behavior of the pollutant spatial profiles and moments is explored with the help of Monte Carlo simulation, within a Continuous Time Random Walk approach. Model outcomes are then compared with experimental measurements of variable-density contaminant transport in homogeneous and saturated vertical columns.Comment: 8 pages, 9 figure

FVCA8 benchmark for the Stokes and Navier-Stokes equations with the TrioCFD code

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FVCA8 benchmark for the Stokes and Navier-Stokes equations with the TrioCFD code – benchmark session

International audienceThis paper is devoted to the study of convergence orders of several numericalmethods that are implemented in the TrioCFD code dedicatedto the simulation of turbulent flows and heat transfer in nuclear engineering applications. The spatialdiscretization is based on Finite Difference-Volume or Finite Element-Volumemethods. A projection method is applied to update the velocity andthe pressure. The time scheme can be either explicit or implicit, and hexahedral or tetrahedral meshes can be used for simulations. In this paper,the test cases are relative to steady Stokes problems, steady and unsteady Navier-Stokes problems, and finally the well-known lid-driven cavity flow case.The latter proposes several comparisons between our simulations and numerical data already published inthe literature, while the other cases yield the values of convergence orders by using the analytical solutions.The accuracy of the results obtained with TrioCFDdiffers according to the types of mesh used for simulations, theviscosity values or the source terms in the equations

Flavan-3-ol aggregation in model ethanolic solutions: incidence of polyphenol structure, concentration, ethanol content, and ionic strength

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Poly(l-proline) interactions with flavan-3-ols units: Influence of the molecular structure and the polyphenol/protein ratio

International audienceThe interaction of proline-rich proteins with flavan-3-ol monomers was studied using poly(L-proline) as a model. Several parameters were varied: (i) the galloylation and trihydroxylation of the flavan-3-ols and (ii) the polyphenol/protein ratio. The systems were characterized by means of UV-Vis spectroscopy, dynamic light scattering and cryo-electron microscopy. Strong differences were observed between epicatechin and epigallocatechin, that did not form aggregates with poly(L-proline), and epicatechin gallate, epigallocatechin gallate, and catechin, which did. This highlighted the strong influence of structural details on the interactions. When complexes were formed, their stability depended on the monomer/protein ratio and on the initial protein concentration. For low galloylated flavan-3-ol/protein ratios (up to 17) and low poly(L-proline) concentration (0.03 mM), interactions led to the formation of relatively stable particles (average hydrodynamic diameter between 30 and 120 nm). When the ratio was further increased to 27, the particles formed were less stable and equilibrium was reached after a longer time. For the highest ratios (27 and 33), aggregation finally led to precipitation. Increasing the protein concentration (1.06 mM) strongly enhanced polyphenol-protein complexation, resulting in much larger particles and more extensive precipitatio

In situ diffusion experiments in Callovo-Oxfordian mudstone

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