Application d'une modélisation de la relation pluie brute - pluie efficace à la prévision des crues sur le Haut-Aveyron

Après une brève synthèse bibliographique, une modélisation de la relation pluie brute - pluie efficace est présentée, dans le cadre général des relations pluie-débit. Ce modèle fait appel à une expression de forme quadratique, et l'estimation de la pluie efficace est bien sûr fonction de l'état de saturation des sols, par l'intermédiaire d'un indice d'humidité. On associe cette fonction de production, pour laquelle une méthode simple de calage est exposée, à une fonction de transfert pluie efficace-débit déterminée par la méthode DPFT bien connue. Le calage est réalisé sur le haut-bassin de l'Aveyron, puis l'on procède à la validation sur des crues-tests. Les résultats semblent satisfaisants, au vu des critères d'adéquation préalablement définis. (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

Discrimination of Semi-Quantitative Models by Experiment Selection: Method and Application in Population Biology

Modeling an experimental system often results in a number of alternative models that are justified equally well by the experimental data. In order to discriminate between these models, additional experiments are needed. We present a method for the discrimination of models in the form of semiquantitative differential equations. The method is a generalization of previous work in model discrimination. It is based on an entropy criterion for the selection of the most informative experiment which can handle cases where the models predict multiple qualitative behaviors. The applicability of the method is demonstrated on a real-life example, the discrimination of a set of competing models of the growth of phytoplankton in a bioreactor

Time-resolved 3D characterisation of flow and dissolution patterns in a single rough-walled fracture

Chapter 43International audienceAn application of X-ray computed microtomography (XCMT) for 3D measurement of fracture geometry is presented. The study demonstrates the ability of XCMT to non-invasively measure the fracture walls and aperture during the course of a reactive flow experiment. The method allows estimation of both the local and global scale dissolution kinetics of a fractured limestone sample percolated by acidic water. The measured fracture geometry was then used as an input for flow modelling, in order to compare the hydraulic aperture calculated by numerical simulation with different evaluations of the aperture: hydraulic aperture measured from pressure drop during the flow experiment, mechanical aperture measured with XCMT, and chemical aperture deduced from calcium removal in the sample. The effects of reactive transport on geometry and fluid flow are discussed. Dissolution appears heterogeneous at both the small scale due to the presence of insoluble clays in the rock, and at larger scales with the formation of preferential flow pathways. These heterogeneous dissolution patterns are not predictable simply by the identification of the areas of higher fluid velocity, where transport of the chemical reaction products (i.e. rate of aperture increase) is presumed to be higher

Current Care and Investigational Therapies in Achondroplasia.

The goal of this review is to evaluate the management options for achondroplasia, the most common non-lethal skeletal dysplasia. This disease is characterized by short stature and a variety of complications, some of which can be quite severe. Despite several attempts to standardize care, there is still no widely accepted consensus. This is in part due to absence of concrete data on the incidence of sudden unexplained death in infants with achondroplasia and the best investigation for ascertaining which individuals could benefit from foramen magnum decompression surgery. In this review, we identify the different options of care and management for the various orthopedic, neurologic, and respiratory complications. In parallel, several innovative or drug repositioning therapies are being investigated that would restore bone growth but may also prevent complications. Achondroplasia is the most common non-lethal skeletal dysplasia. It is characterized by short stature and a variety of complications, some of which can be quite severe. Despite several attempts to standardize care, there is still no widely accepted consensus. This is in part due to absence of concrete data on the incidence of sudden unexplained death in infants with achondroplasia and the best investigation for ascertaining which individuals could benefit from foramen magnum decompression surgery. In this review, we identify the different options of care and management for the various orthopedic, neurologic, and respiratory complications. In parallel, several innovative or drug repositioning therapies are being investigated that would restore bone growth but may also prevent complications

Numerical computations of rock dissolution and geomechanical effects for CO 2 geological storage

International audienceThe paper is motivated by the long term safety analysis of the CO 2 geological storage. We present a methodology for the assessment of the ge-omechanical impact of progressive rock dissolution. The method is based on the use of X-ray tomography and the numerical dissolution technique. The influence of evolution of the microstructure on the macroscopic properties of the rock is analysed by using periodic homogenization method. The numerical computations show progressive degradation of all components of the stiffness (orthotropic) tensor. Moreover, the evolution of associated mass transfer properties (as tortuosity and conductivity tensors), by using the periodic homogenization method, is also calculated. The correlation between the mechanical parameters and the transfer properties during the dissolution pro-cess is presented. The results show that the highest increase of the hydraulic conductivity (in direction Y) is not associated with the highest decrease of Young modulus in this direction. Moreover, the highest decrease of Young modulus (in the direction X) is not associated with percolation in this direction. Finally, an incremental law to calculate settlement, in case of a rock with evolving microstructure, is proposed. The solution of the macroscopic settlement problem under constant stress and drained conditions showed that the geomechanical effects of the rock dissolution are rather limited

L'articulation entre efficacité et justice dans la conception du marché chez Amartya K. Sen

Dans Un nouveau modèle économique (1999a), Sen déclare : "Si les mérites du marché sont aujourd'hui largement reconnus, les raisons pour lesquelles nous souhaitons son existence ne sont pas assez expliquées" (Sen, 1999a, p. 154). Cette phrase contient deux aspects. D'une part, la première partie, qui donne un jugement plutôt favorable au marché, peut paraître étonnante au regard de la volonté de Sen de proposer une voie alternative à l'économie traditionnelle en prônant la "nécessité d'un examen critique du rôle des marchés" (op.cit., p. 168). D'autre part, la deuxième partie de la phrase identifie un manque : celui de la justification des raisons pour lesquelles nous recourrons au marché. C'est pour cela que Sen établit un argumentaire pour justifier le recours au mécanisme de marché concurrentiel dans l'analyse économique. En fait, les deux aspects de cette phrase peuvent être traités et analysés de manière complémentaire. L'argumentation de Sen pour justifier l'existence et le recours au marché se scinde en deux : d'une part, le marché est justifié par Sen au sein d'une argumentation de philosophie politique directement inspirée de Smith (1776) pour le penchant à l'échange, de Marx (1867) pour qui l'apparition du contrat de travail est constitutif de la liberté des individus d'entrer sur le marché du travail et de Hayek (1944) condamnant le planisme et l'absence de marchés ; d'autre part, Sen se fonde sur une justification purement économique autour des deux "théorèmes de l'économie du bien-être". Ce deuxième volet de l'argumentation contraste avec le premier dans la mesure où le marché n'est plus vu comme la possibilité de satisfaire le simple désir de participer à un échange mais comme la possibilité d'aboutir à une situation optimale au sens de Pareto. Ces deux volets participent d'une démarche sénienne consistant à "faire discuter l'économie et la philosophie ou l'éthique" (Bonvin et Farvaque, 2008, p. 17). En effet, cette séparation entre deux volets d'argumentation n'est que formelle car Sen va les allier au sein d'un raisonnement consistant à démontrer qu'il est possible d'aboutir à une situation qui soit optimale au sens de Pareto, non pas en termes d'utilités mais de libertés. Sen intègre de cette manière la liberté, correspondant à ce qu'il appelle le versant éthique de l'économie, à un raisonnement économique, correspondant au versant mécaniste de l'économie. Sen propose donc une manière originale d'articuler sa conception de la justice et l'efficacité marchande. La question qui se pose est donc celle de savoir de quelle manière Sen opère cette articulation et comment il se place vis-à-vis de traditions antérieures de conciliation entre justice et marché. Notre démarche consiste donc à suivre la manière dont Sen entend concilier la justice et l'efficacité et à la comparer à d'autres conceptions telles que celles de Walras, de Arrow et Debreu (auteurs auxquels Sen se réfère explicitement) et de Varian (avec la justice comme non-envie)

Non-Fickian dispersion in porous media explained by heterogeneous microscale matrix diffusion

International audienceMobile-immobile mass transfer is widely used to model non-Fickian dispersion in porous media. Nevertheless, the memory function, implemented in the sink/source term of the transport equation to characterize diffusion in the matrix (i.e., the immobile domain), is rarely measured directly. Therefore, the question can be posed as to whether the memory function is just a practical way of increasing the degrees of freedom for fitting tracer test breakthrough curves or whether it actually models the physics of tracer transport. In this paper we first present a technique to measure the memory function of aquifer samples and then compare the results with the memory function fitted from a set of field-scale tracer tests performed in the same aquifer. The memory function is computed by solving the matrix diffusion equation using a random walk approach. The properties that control diffusion (i.e., mobile-immobile interface and immobile domain cluster shapes, porosity, and tortuosity) are investigated by X-ray microtomography. Once the geometry of the matrix clusters is measured, the shape of the memory function is controlled by the value of the porosity at the percolation threshold and of the tortuosity of the diffusion path. These parameters can be evaluated from microtomographic images. The computed memory function compares well with the memory function deduced from the field-scale tracer tests. We conclude that for the reservoir rock studied here, the atypical non-Fickian dispersion measured from the tracer test is well explained by microscale diffusion processes in the immobile domain. A diffusion-controlled mobileimmobile mass transfer model therefore appears to be valid for this specific case