Growth rates of the salp Thalia democratica in Tikehau atoll (Tuamotu is.)

Deux méthodes différentes et indépendantes l'une de l'autre, sont utilisées pour déterminer le taux de croissance de T. democratica : la méthode de Héron et Benham (1985), basée sur l'observation de paramètres décrivant la population et la méthode des rapports C : N : P, utilisant les mesures de physiologie et de composition élémentaire. Avec la première méthode, la longueur augmente de 25 à 28 % en une heure, ce qui équivaut à une augmentation horaire de poids de 53 à 60 %. La seconde méthode fournit des résultats voisins, quoiqu'un peu plus faibles, pour la croissance pondérale : 33 à 36 %. Ces valeurs sont les plus élevées pour cette espèce et même pour tout organisme zooplanctonique, à l'heure actuelle, et pourraient être dues à la richesse du lagon de l'atoll en particules organiques et à sa température, alors voisine de 30°C. (Résumé d'auteur

Non-Fickian dispersion in porous media : 2. Model validation from measurements at different scales

International audienceWe aim at testing and validating a mobile-immobile mass transfer model from a set of single-well injection withdrawal tracer tests in a heterogeneous porous aquifer. By varying the duration of the injection phase, different volumes of aquifer are investigated by the tracer. Hence, we focus the transport model validation not only on reproducing a single breakthrough curve (BTC) but also on the model's capacity to predict the amount of mixing as a function of the volume visited by the tracer. All the BTCs are strongly asymmetric, as expected when dispersion is controlled by diffusive mass transfers between the mobile water and the immobile water part of the porosity. However, the BTC cannot be modeled by a conventional mobile-immobile mass transfer model with a simple power law memory function. To account for that, we implement a continuous time random walk model in which the transition time distribution y (t), which is related to the excursion time probability of the tracer in the immobile domain, is a dual-slope power law distribution. The model best fits the BTC data set with a transitional regime controlled by y(t) t2 and an asymptotic regime characteristic of the conventional double-porosity model with y(t) t1.5 . This work emphasizes that high-resolution concentration measurement and multiple-scale tracer tests are required for assessing solute dispersion models in heterogeneous reservoirs and for subsequently obtaining reliable predictions

Decision Diagrams for Qualitative Biological Models

The modelisation of large biological systems such that metabolic networks or gene interaction networks, implies interpretations of heterogeneous biological knownledge. A common feature of observations accumulated by biologist on these systems is their qualitative nature. More over it often happens that the knownledge is based on comparisons between different experimental conditions. In previous papers variations in observed variables between two conditions was interpreted in terms of equilibria shift. This leads to use qualitative equations in a sign algebra. The present report gives details on the implementation and main algorithms involved

Mixing as a correlated aggregation process

Mixing describes the process by which scalars, such as solute concentration or fluid temperature, evolve from an initial heterogeneous state to uniformity under the stirring action of a fluid flow. Mixing occurs initially through the formation of scalar lamellae as a result of fluid stretching and later by their coalescence due to molecular diffusion. Owing to the linearity of the advection-diffusion equation, scalar coalescence can be envisioned as an aggregation process. While random aggregation models have been shown to capture scalar mixing across a range of turbulent flows, we demonstrate here that they are not accurate for most chaotic flows. In particular, we show that the spatial distribution of the number of lamellae in aggregates is highly correlated with their elongation and is also influenced by the fractal geometry that arises from the chaotic flow. The presence of correlations makes mixing less efficient than a completely random aggregation process because lamellae with similar elongations and scalar levels tend to remain isolated from each other. Based on these observations, we propose a correlated aggregation framework that captures the asymptotic mixing dynamics of chaotic flows and predicts the evolution of the scalar pdf based on the flow stretching statistics. We show that correlated aggregation is uniquely determined by a single exponent which quantifies the effective number of random aggregation events, and is dependent on the fractal dimension of the flow. These findings expand aggregation theories to a larger class of systems, which have relevance to various fundamental and applied mixing problems

Programme PROPPAC : hydrologie, nutrients, chlorophylle et zooplancton des campagnes SURTROPAC 07 à 13 (1987-1989)

Ce recueil présente les données de sels nutritifs, oxygène dissous, chlorophylle et zooplancton obtenues deux fois par an lors de la radiale SURTROPAC, de 20°S à 10°N le long 165°E. Les campagnes couvrent la période comprise entre janvier 1987 (SURTROPAC 07) et décembre 1989 (SURTROPAC 13). Les données sont présentées sous forme de coupes 20°S - 10°N et sous forme de tableaux. (Résumé d'auteur

Performance evaluation of equipment used for volumetric water content measurements

Various methods can be used to evaluate in situ volumetric water content; however, when continuous measurements are required, only dielectric methods can be used. For equipment based on these methods, in the mining environment and particularly in environments having high sulfide contents (or acid-generating minerals), the accuracy of measurements can be affected by the chemistry of the solid and liquid phases. To evaluate the real impact of water chemistry and mineralization on volumetric water content measurement, three instruments were tested on five materials with varying sulphur contents and two types of water mineralization. The results of these investigations show that: i) increasing sulfur content of mine tailings increases the response output of the tested probes; ii) the obtained volumetric water contents are systematically higher than the real volumetric water contents obtained gravimetrically; iii), time-domain reflectometry probes are able to provide measurements in materials with high sulphur contents; and iv) 5TM and GS3 probes are not suitable for use in reactive materials with higher sulphur contents

Characterization of the velocity field organization in heterogeneous media by conditional correlation

International audienceThe purpose of the present work is to quantify the correlation structure of simulated velocity fields in heterogeneous permeability fields and to discuss how to represent it in upscaled transport models. We investigate the velocity field correlation structure for multinormal log permeability fields. The simulated velocity distributions are analyzed in a Lagrangian framework, i.e., along the particles' paths.To quantify the different spatial organization of low- and high-velocity zones, we condition the estimated velocity correlation length and time on the initial particle velocity. The velocity correlation length is found to increase with the initial particle velocity, following a power law. Such an effect is likely due to the channeling of high-velocity zones, which implies that particles keep memory of their initial velocity over longer distances for high initial velocities than for low initial velocities. Two distinct regimes are identified for the velocity correlation time. For low initial particle velocity the correlation time is controlled by the large time needed to escape from the low- velocity zones. For high initial particle velocity it is controlled by the large time needed for particles to sample the whole velocity field, in particular low- velocity zones. One of the consequences of these results is that for such velocity fields the nonlinear dependence of both the correlation length and time on the particle initial velocity restricts the se of spatial or temporal Markovian assumptions for modeling velocity transitions in effective transport models