Technical Note: The air quality modeling system Polyphemus

International audiencePolyphemus is an air quality modeling platform which aims at covering the scope and the abilities of modern air quality systems. It deals with applications from local scale to continental scale, using two Gaussian models and two Eulerian models. It manages passive tracers, radioactive decay, photochemistry and aerosol dynamics. The structure of the system includes four independent levels with data management, physical parameterizations, numerical solvers and high-level methods such as data assimilation. This enables sensitivity and uncertainty analysis, primarily through multimodel approaches. On top of the models, drivers implement advanced methods such as model coupling or data assimilation

Use of Heating Configuration to Control Marangoni Circulation during Droplet Evaporation

The present work presents a numerical study of the evaporation of a sessile liquid droplet deposited on a substrate and subjected to different heating configurations. The physical formulation accounts for evaporation, the Marangoni effect, conductive transfer in the support, radiative heating, and diffusion-convection in the droplet itself. The moving interface is solved using the Arbitrary Lagrangian-Eulerian (ALE) method. Simulations were performed using COMSOL Multiphysics. Different configurations were performed to investigate the effect of the heating conditions on the shape and intensity of the Marangoni circulations. A droplet can be heated by the substrate (different natures and thicknesses were tested) and/or by a heat flux supplied at the top of the droplet. The results show that the Marangoni flow can be controlled by the heating configuration. An upward Marangoni flow was obtained for a heated substrate and a downward Marangoni flow for a flux imposed at the top of the droplet. Using both heat sources generated two vortices with an upward flow from the bottom and a downward flow from the top. The position of the stagnation zone depended on the respective intensities of the heating fluxes. Controlling the circulation in the droplet might have interesting applications, such as the control of the deposition of microparticles in suspension in the liquid, the deposition of the solved constituent, and the enhancement of the evaporation rate

Numerical and experimental study of convective heat transfer in a vertical porous channel using a non-equilibrium model

International audienceConvective heat transfer in a vertical porous channel heated by the wall and isolated on the other face was simulated numerically and experimentally. The porous medium is formed by a solid matrix of spherical beads. The considered fluid is air that saturates the solid matrix. The two-temperature model and the Darcy-Brinkman-Forchheimer equation are adopted to represent this system and the porosity is considered as variable in the domain. The numerical model was used to analyze the effect of several operating parameters on heat transfer enhancement. Heat transfer decreases with the increase of the form factor. When Biot number increases, heat transfer between the heated wall and the porous domain is increased. Heat transfer increases with Reynolds 1 number and with the thermal conductivity of the solid matrix. The influence of the thermal conductivity of the particles on heat transfer in the porous medium decreases with increase of the thermal conductivity of the metallic beads, principally when the diameter of the beads increases. An increase of the bead diameter induces a decrease of heat transfer. Nusselt numbers based on the particle diameter have been correlated with respect to Reynolds number and the particle diameter. Furthermore, simulation results have been validated by experiments

Sub-laser-cycle control of coupled electron–nuclear dynamics at a conical intersection

Nonadiabatic processes play a fundamental role in the understanding of photochemical processes in excited polyatomic molecules. A particularly important example is that of radiationless electronic relaxation at conical intersections (CIs). We discuss new opportunities for controlling coupled electron–nuclear dynamics at CIs, offered by the advent of nearly single-cycle, phase-stable, mid-infrared laser pulses. To illustrate the control mechanism, a two-dimensional model of the NO2 molecule is considered. The key idea of the control scheme is to match the time scale of the laser field oscillations to the characteristic time scale of the wave packet transit through the CI. The instantaneous laser field changes the shape and position of the CI as the wave packet passes through. As the CI moves in the laser field, it ‘slices’ through the wave packet, sculpting it in the coordinate and momentum space in a way that is sensitive to the carrier-envelope phase of the control pulse. We find that the electronic coherence imparted on the sub-laser-cycle time scale manifests during much longer nuclear dynamics that follow on the many tens of femtosecond time scale. Control efficiency as a function of molecular orientation is analyzed, showing that modest alignment is sufficient for showing the described effects.ERA-ChemistryDFG SMEU FP7 Marie Curie ITN CORINFMINECO:European Research Council: http://dx.doi.org/10.13039/501100000781Engineering and Physical Sciences Research Council: http://dx.doi.org/10.13039/501100000266CAM NANOFRONTMAGMINECO FPU (LMF)European Cooperation in Science and Technology: http://dx.doi.org/10.13039/501100000921Peer Reviewe

Use of Heating Configuration to Control Marangoni Circulation during Droplet Evaporation

The present work presents a numerical study of the evaporation of a sessile liquid droplet deposited on a substrate and subjected to different heating configurations. The physical formulation accounts for evaporation, the Marangoni effect, conductive transfer in the support, radiative heating, and diffusion–convection in the droplet itself. The moving interface is solved using the Arbitrary Lagrangian–Eulerian (ALE) method. Simulations were performed using COMSOL Multiphysics. Different configurations were performed to investigate the effect of the heating conditions on the shape and intensity of the Marangoni circulations. A droplet can be heated by the substrate (different natures and thicknesses were tested) and/or by a heat flux supplied at the top of the droplet. The results show that the Marangoni flow can be controlled by the heating configuration. An upward Marangoni flow was obtained for a heated substrate and a downward Marangoni flow for a flux imposed at the top of the droplet. Using both heat sources generated two vortices with an upward flow from the bottom and a downward flow from the top. The position of the stagnation zone depended on the respective intensities of the heating fluxes. Controlling the circulation in the droplet might have interesting applications, such as the control of the deposition of microparticles in suspension in the liquid, the deposition of the solved constituent, and the enhancement of the evaporation rate

Umbrella inversion of ammonia redux

Does Umbrella inversion motion of ammonia really correspond to a back-and-forth oscillation between its two equilibrium molecular structures, i.e., dynamical localization over the two potential wells, as described by the textbook picture?</jats:p

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En métrologie, une incertitude de mesure liée à un mesurage « caractérise la dispersion des valeurs attribuées à un mesurande, à parti des informations utilisées ». Une erreur de mesure, dans le langage courant, est « la différence entre la valeur donnée par la mesure et la valeur exacte d'une grandeur ». Sur une échelle nationale, le laboratoire national de métrologie et d'essais, est un organisme chargé de réaliser les mesures et essais de produits de toutes sortes en vue de leur certification pour leur mise sur le marché </p

Développement d'un modèle numérique de dispersion atmosphérique de particules à l'échelle d'un paysage hétérogène

*INRA CR Bordeaux, Unité de Bioclimatologie Diffusion du document : INRA CR Bordeaux, Unité de Bioclimatologie Diplôme : Dr. d'Universit