South Atlantic paleobathymetry since early Cretaceous

We present early Cretaceous to present paleobathymetric reconstructions and quantitative uncertainty estimates for the South Atlantic, offering a strong basis for studies of paleocirculation, paleoclimate and paleobiogeography. Circulation in an initially salty and anoxic ocean, restricted by the topography of the Falkland Plateau, Rio Grande Ridge and Walvis Rise, favoured deposition of thick evaporites in shallow water of the Brazilian-Angolan margins. This ceased as sea oor spreading propagated northwards, opening an equatorial gateway to shallow and intermediate circulation. This gateway, together with subsiding volcano-tectonic barriers would have played a key role in Late Cretaceous climate changes. Later deepening and widening of the South Atlantic, together with gateway opening at Drake Passage would lead, by mid-Miocene (∼15 Ma) to the establishment of modern-style thermohaline circulation

New approach for the determination of aerosol refractive indices - Part II: Experimental set-up and application to amorphous silica particles

International audienceThis article is the Part II of a work aimed at proposing a new method for determining the optical constants of aerosols. The Part I detailed the theoretical and numerical basis of an algorithm devoted to retrieve the imaginary and the real part of complex refractive indices from extinction spectra of aerosols. This algorithm associates the Mie theory, the single subtractive Kramers-Kronig relation, and an optimal estimation method in an iterative process. This Part II presents the experimental set-up developed to record simultaneously high spectral resolution extinction spectra and size distributions of airborne silica particles. Extinction spectra are measured with a high spectral resolution on a broad spectral range, including both infrared (650 - 2 , 500cm-1) and UV-visible (9 , 000 - 32 , 500cm-1) spectral regions. Experimental data were used to retrieve the complex refractive indices of aerosol particles. By associating the numerical procedure presented in the first paper and this experimental set-up, complex refractive indices of silica spherical aerosol particles have been determined under controlled experimental conditions. Additional comparison between experimental and simulated extinction spectra from retrieved complex refractive indices shows that this new methodology provides optical properties representative of the material

Atmospheric plasma: a simple way of improving the interface between natural polysaccharides and polyesters

International audienceIn this study, a novel simple and fast method was developed of immobilizing a natural polysaccharide (chitosan) on a polylactide (PLA) surface. In order to overcome the lack of surface adhesion between the chitosan and the PLA due to incompatibility issues, atmospheric pressure plasma was used. The plasma activation was able to modify the PLA surface by generating surface chemistry proper for stabilizing the chitosan layer. The activation of the surface was monitored through water contact angle (WCA) measurements and X-ray photoelectron spectroscopy (XPS). Indeed, the introduction of new functionalities lowers the hydrophobicity of the PLA surface allowing an effective spreading and immobilization of the chitosan layer. The presence of chitosan on the polyester’s surface was proven by Fourier transform infrared spectroscopy (FTIR)

Lattice Boltzmann scheme for diffusion on triangular grids

In this paper we present a Lattice Boltzmann scheme for diffusion on it unstructured triangular grids. In this formulation of a LB for irregular grids there is no need for interpolation, which is required in other LB schemes on irregular grids. At the end of the propagation step the lattice gas particles arrive exactly at neighbouring lattice sites, as is the case in LB schemes on Bravais lattices. The scheme is constructed using the constraints that the moments of the equilibrium distribution equals that of the Maxwell-Boltzmann distribution. For a special choice of the relaxation parameter ($\omega =1$) we show that our LB scheme is identical to a cell centered Finite Volume scheme on an unstructured triangular grid

Boiling in porous media: Model and simulations

International audienceWe present a modelization of the heat and mass transfers within a porous medium, which takes into account phase transitions. Classical equations are derived for the mass conservation equation, whereas the equation of energy relies on an entropy balance adapted to the case of a rigid porous medium. The approximation of the solution is obtained using a finite volume scheme coupled with the management of phase transitions. This model is shown to apply in the case of an experiment of heat generation in a porous medium. The vapor phase appearance is well reproduced by the simulations, and the size of the two-phase region is correctly predicted. A result of this study is the evidence of the discrepancy between the air - water capillary and relative permeability curves and water - water vapor ones