Growth limiting conditions and denitrification govern extent and frequency of volume detachment of biofilms

This study aims at evaluating the mechanisms of biofilm detachment with regard of the physical properties of the biofilm. Biofilms were developed in Couette–Taylor reactor under controlled hydrodynamic conditions and under different environmental growth conditions. Five different conditions were tested and lead to the formation of two aerobic heterotrophic biofilms (aeHB1 and aeHB2), a mixed autotrophic and heterotrophic biofilm (MAHB) and two anoxic heterotrophic biofilms (anHB1 and anHB2). Biofilm detachment was evaluated by monitoring the size of the detached particles (using light-scattering) as well as the biofilm physical properties (using CCD camera and image analysis). Results indicate that volume erosion of large biofilm particles with size ranging from 50 to 500 lm dominated the biomass loss for all biofilms. Surface erosion of small particles with size lower than 20 lm dominates biofilm detachment in number. The extent of the volume detachment events was governed by the size of the biofilm surface heterogeneities (i.e., the absolute biofilm roughness) but never impacted more than 80% of the mean biofilm thickness due to the highly cohesive basal layer. Anoxic biofilms were smoother and thinner than aerobic biofilms and thus associated with the detachment of smaller particles. Our results contradict the simplifying assumption of surface detachment that is considered in many biofilm models and suggest that discrete volume events should be considered

Présentation d'un nouvel élément fini de contact

International audienceThis paper will present a new way to deal with contact within a finite element code. The detection of contact is realised with an analytical method using B-spline functions, and the analysis of the contact is done with a special finite element using a modified penalty method.Cet article présente une élément de contact spécifique, destiné à être implémenté dans un code de calcul par éléments finis implicite. La détection du contact est réalisée par mise en œuvre d'une méthode analytique basée sur l'utilisation des fonctions B-spline. Le traitement du contact est fait par la méthode des pénalités par élément de contact avec une raideur spéciale

Assimilation de données images dans un modèle de circulation océanographique

National audienceData assimilation allows to couple together a forecast model and observations. In this study we are interested in the association of a simulation model for oceanic circulation with data coming from image processing. We propose a processing chain to estimate circulation velocity from ocean temperature images, and the assimilation of this image observation in a forecast model.L'assimilation de données permet de coupler un modèle de prévision à des observations. Dans cette étude nous nous intéressons à l'intégration de caractéristiques images dans un modèle de simulation de la circulation océanique. Nous proposons une chaîne de traitement permettant d'estimer la vitesse de circulation sur une séquence d'images de température de l'océan et l'assimilation de cette observation image dans un modèle de prévision

Dimensionality reduction on ocean model's outputs: Application to motion estimation on satellite images

International audienceMotion fields describing the ocean surface dynamics live in vectorial spaces of high dimension. Consequently, their estimation from satellite images requires huge computational resources. The issue of dimensionality reduction, that is the determination of representative low dimensional structures in these high dimensional spaces, is of major importance for any application that demands real-time or short-term results. Proper Order Decomposition allows to determine such subspace of motion fields on which estimation may be assessed with reduced complexity. A reduced model is obtained by Galerkin projection of evolution equations on this subspace. Motion is estimated by assimilating the observed image sequence with the reduced model. The paper describes how to derive the reduced space from a database of ocean model’s outputs and explains how to estimate surface circulation from satellite sequences. Results are given on images acquired on the Black Sea basin by NOAA-AVHRR sensors

Validation of surface velocity estimated from satellite images

This report concerns the validation of surface velocity estimated from satellite images. The estimation is obtained with a dynamic model based on shallow-water equations. We first compare the stationary assumption to the shallow-water heuristics to justify our choice. Second, we quantify the quality of the estimation by measuring the misfit between the model output and the altimetry measures. Experiments are achieved on Sea Surface Temperature data acquired by the NOAA/AVHRR satellites over the Black Sea. The altimetry measures are obtained by two radar sensors: Envisat and GFO. The good adequacy between the shallow-water output and the altimetry data validates our motion estimation approach.Ce rapport de recherche concerne la validation de l'estimation de la vitesse de surface à partir d'images satellite. Cette estimation est effectuée avec un modèle de la dynamique, basé sur les équations shallow-water. Nous comparons d'abord l'hypothèse de stationnarité aux équations shallow-water afin de justifier notre choix. Puis, nous quantifions la qualité des estimations en mesurant l'écart entre la sortie du modèle et les mesures d'altimétrie. Les expérimentations sont effectuées en utilisant des données de température de surface, acquises au-dessus de la Mer Noire avec les satellites NOAA/AVHRR. Les mesures altimétriques proviennent de deux capteurs radar : Envisat et GFO. La bonne adéquation entre la sortie du modèle shallow-water et les données altimétriques valide notre approche d'estimation du mouvement