"Sigmelts": A web portal for electrical conductivity calculations in geosciences

International audienceElectrical conductivity measurements in the laboratory are critical for interpreting geoelectric and magnetotelluric profiles of the Earth's crust and mantle. In order to facilitate access to the current database on electrical conductivity of geomaterials, we have developed a freely available web application (SIGMELTS) dedicated to the calculation of electrical properties. Based on a compilation of previous studies, SIGMELTS computes the electrical conductivity of silicate melts, carbonatites, minerals, fluids, mantle materials as a function of different parameters, such as composition, temperature, pressure, water content, oxygen fugacity. Calculations on two-phase mixtures are also implemented using existing mixing models for different geometries. An illustration of the use of SIGMELTS is provided, in which calculations are applied to subduction zone related volcanic zone in the Central Andes. Along with petrological considerations, field and laboratory electrical data allow discrimination between the different hypotheses regarding the formation and rise from depth of melts and fluids and to quantify their storage conditions

Mise en oeuvre de modèles de réseaux 3-D pour l'étude du transport binaire en milieu poreux

Dans ce travail, nous nous concentrons sur l’étude de la relation entre d’une part la structure sous-jacente d’un milieu poreux à l’échelle du pore et d’autre part le tenseur de dispersion D* et le coefficient d’échange de masse a décrivant à l’échelle macroscopique (dans le cas binaire) le devenir d’un polluant peu miscible piégé dans un aquifère saturé. Le choix d’utiliser des modèles de réseaux "réalistes" (pour mettre pratiquement à l’échelle l’information microstructurale dans les équations macroscopiques de dispersion) nous conduit à proposer une stratégie globale, basée sur l’analyse d’images quantitative, dont nous développons plusieurs aspects (modèle stochastique, squelettisation, etc.) dans le but à terme de prendre en compte les effets sur D* et a des caractéristiques structurales de milieux poreux réels.In this work, we focus on the study of the relation between the structure of a porous medium at the pore scale, and the dispersion tensor D* and the mass exchange coefficient a describing at the macroscopic scale the fate of a pollutant of low miscibility (binary case) trapped in a saturated aquifer. The choice to use "realistic" pore network models (to practically upscale the microstructural information into the macroscopic dispersion equation) leads us to propose a global strategy based on quantitative image analysis. Several aspects of this global strategy are developed (random model, skeletonization, etc.) with the aim to take into account ultimately the effects of the structural characteristics of real porous media on D* and a

Segmentation of X-ray tomographic images : contribution to weathering analysis of building limestones originating from historical buildinds.

Historical monuments contributing to our cultural heritage undergo their environment that alters them and can results in their destruction. The observed macro-scale effects result from physico-chemical mechanisms (dissolution, transport, precipitation) occurring in the complex porous structure of the building stones at the pore scale. Understanding of weathering processes and more generally of water transfer properties of building stone requires a detailed knowledge of the pore and different solid phases distribution. Indeed, quantitative physical models (permeability, compressive strength...) rely on a precise and relevant description of the microstructure. The method presented here is a required step toward the understanding of the mechanisms of limestones weathering based on realistic geometrical information of the geomaterial, i.e. not based on a more or less complex mathematical model representing an ideal material

2D-Image analysis: A complementary tool for characterizing quarry and weathered building limestones.

International audienceUnderstanding of weathered processes and more generally of transfer properties of building stone requires a detailed knowledge of the porosity characteristics. This study aims at analyzing 2D-images of stones by using mathematical tools that enable the description of the pore and solid phase distribution. We selected two limestones that were widely used for different types of buildings: a quarried and weathered tuffeau, the latter being used in most Châteaux of the Loire and a quarried sebastopol stone used in numerous buildings in Paris. Backscattered electron scanning images obtained on thin section of the stones were studied by using autocorrelation function analysis and chord distributions. Our results showed that these mathematical tools are able to discuss quantitatively and statistically differences of pore and solid distribution between quarried limestones, and to discuss the weathering degree of stones collected on buildings. Thus, very small differences of pore and solid phase distribution between the samples studied were revealed by chord distribution analysis and autocorrelation function analysis. The resulting characteristics obtained with such an analysis are promising information for a better understanding of the weathering mechanisms

A simple methodology to segment X-ray tomographic images of a multiphasic building stone.

International audienceAssessment of the weathering of a particular limestone, the tuffeau, used in historical monuments requires an accurate description of its microstructure. An efficient tools to obtain such a description is X-ray microtomography. However the segmentation of the images of this multiphasic material is not trivial. As the identification of pertinent markers of the structural components to extract is difficult, a two steps filtering approach is chosen. Alternate sequential filters are shown to efficiently remove the noise but, as they destroy the structural components smaller than the structuring element used, they cannot be carried out far enough. Hence as a second step in the filtering process, a mosaic operator, relying on a pragmatic yet efficient marker determination, is implemented to simplify further the images

A METHODOLOGY TO SEGMENT X-RAY TOMOGRAPHIC IMAGES OF MULTIPHASE POROUS MEDIA: APPLICATION TO BUILDING STONES.

An image analysis technique based on mathematical morphology tools dedicated to the segmentation of X-ray tomographic images of porous media is presented in this article. It consists in an efficient denoising using alternate sequential filters and a watershed operation using an original starting marker. The image is transformed into a mosaic that is straightforward to segment. An application to building stones of heritage monuments illustrates the potentialities of this technique

A mixed model of active geodesic contours with gradient vector flows for X-ray microtomography segmentation

Actes de la conférence "Mathématiques pour l'image" - PUOInternational audienceThe structural characterization of weathered building stones of historical monuments can be achieved with a powerfull imagering technique, X-ray microtomography. It requires however a carefull extraction of each phase constituting the sample from the raw gray-level images obtained (the segmentation process). This contribution presents an original method of segmentation of such images that combines active contour models driven by gradient vector flows with a morphological preprocessing, alternate sequential filters. Preliminary results on high resolution, structuraly complex images are presented and compared to more classical approaches

A SIMPLE METHODOLOGY TO SEGMENT X-RAY TOMOGRAPHIC IMAGES OF A MULTIPHASIC BUILDING STONE

Assessment of the weathering of a particular limestone, the tuffeau, used in historical monuments requires an accurate description of its microstructure. An efficient tools to obtain such a description is X-ray microtomography. However the segmentation of the images of this multiphasic material is not trivial. As the identification of pertinent markers of the structural components to extract is difficult, a two steps filtering approach is chosen. Alternate sequential filters are shown to efficiently remove the noise but, as they destroy the structural components smaller than the structuring element used, they cannot be carried out far enough. Hence as a second step in the filtering process, a mosaic operator, relying on a pragmatic yet efficient marker determination, is implemented to simplify further the images

A new method of reconstructing the P-T conditions of fluid circulation in an accretionary prism (Shimanto, Japan) from microthermometry of methane-bearing aqueous inclusions

International audienceIn paleo-accretionary prisms and the shallow metamorphic domains of orogens, circulating fluids trapped in inclusions are commonly composed of a mixture of salt water and methane, producing two types of fluid inclusions: methane-bearing aqueous and methane-rich gaseous fluid inclusions. In such geological settings, where multiple stages of deformation, veining and fluid influx are prevalent, textural relationships between aqueous and gaseous inclusions are often ambiguous, preventing the microthermometric determination of fluid trapping pressure and temperature conditions. To assess the P-T conditions of deep circulating fluids from the Hyuga unit of the Shimanto paleo-accretionary prism on Kyushu, Japan, we have developed a new computational code, applicable to the H2O-CH4-NaCl system, which allows the characterization of CH4-bearing aqueous inclusions using only the temperatures of their phase transitions estimated by microthermometry: Tmi, the melting temperature of ice; Thyd, the melting temperature of gas hydrate and Th,aq, homogenization temperature. This thermodynamic modeling calculates the bulk density and composition of aqueous inclusions, as well as their P-T isochoric paths in a P-T diagram with an estimated precision of approximatively 10 %. We use this computational tool to reconstruct the entrapment P-T conditions of aqueous inclusions in the Hyuga unit, and we show that these aqueous inclusions cannot be cogenetic with methane gaseous inclusions present in the same rocks. As a result, we propose that pulses of a high-pressure, methane-rich fluid transiently percolated through a rock wetted by a lower-pressure aqueous fluid. By coupling microthermometric results with petrological data, we infer that the exhumation of the Hyuga unit from the peak metamorphic conditions was nearly isothermal and ended up under a very hot geothermal gradient. In subduction or collision zones, modeling aqueous fluid inclusions in the ternary H2O-CH4-NaCl system and not simply in the binary H2O-NaCl is necessary, as the addition of even a small amount of methane to the water raises significantly the isochores to higher pressures. Our new code provides therefore the possibility to estimate precisely the pressure conditions of fluids circulating at depth

Validation of Mesocyclops (Copepoda) and community participation as an effective combination for Dengue control in Northern Vietnam

The “Programme Meso-Vietnam” was implemented in Vietnam from October 2007 to December 2010 to reduce dengue and dengue hemorrhagic fever incidence and to improve the quality of life in the four project communes. This dengue control project was based on biological control using Mesocyclops, a larvivorous micro-crustacean, as well as on the establishment of a strong community involvement to educate the population on dengue transmission and to reduce Aedes breeding by removal of containers. During three years, a network of collaborators was responsible for introducing Mesocyclops in all the containers defined as key breeding-sites, and regular activities such as community training workshops, school programmes, clean-up campaigns and health promotion through IEC programmess were performed. To make this programme sustainable, local leadership has been strengthened as well. The use of these larvivorous micro-crustaceans as a biological control strategy against dengue over the medium and long term, when combined with community participation and effective health promotion, demonstrated a significant reduction in dengue vector populations and dengue cases.  In Vietnam, this study reconfirms that there is an ecological alternative to systematic use of insecticides to control dengue vector population. (Abstract word count: 186)Le " Programme Meso-Vietnam " a été mis en œuvre au Vietnam entre octobre 2007 et décembre 2010. Ce programme vise à réduire l'incidence de la dengue et de la fièvre hémorragique de la dengue et à améliorer la qualité de vie dans les quatre communes sélectionnées pour le projet. Ce projet de lutte contre la dengue était basé sur un contrôle biologique assuré par des Mésocyclopes, micro-crustacés larvivores, et sur l'établissement d'une forte implication de la communauté pour éduquer la population sur la transmission de la dengue et pour réduire la reproduction des moustiques Aedes par élimination des conteneurs leur servant de site de ponte. Pendant trois ans, un réseau de collaborateurs a été chargé d'introduire des Mésocyclopes dans tous les conteneurs définis comme des sites de reproduction clés, et des activités régulières telles que des ateliers de formation communautaires, des programmes scolaires, des campagnes de nettoyage et des activités de promotion de la santé via les programmes IEC ont été mises en place. En outre, pour assurer la pérennité de ce programme, le leadership local a été renforcé. L'utilisation de ces micro-crustacés larvivores comme stratégie de contrôle biologique de la dengue à moyen et long terme, associée à une participation communautaire et à une promotion efficace de la santé, a permis d'aboutir à une réduction significative des populations vecteurs de la dengue et des cas de dengue. Au Vietnam, cette étude confirme une fois de plus qu'il existe une alternative écologique à l'utilisation systématique d'insecticides pour lutter contre les vecteurs de la dengue.El “Programa Meso-Vietnam” se implementó en Vietnam desde octubre de 2007 hasta diciembre de 2010 para reducir la incidencia del dengue y la fiebre hemorrágica del dengue y para mejorar la calidad de vida en los cuatro municipios del proyecto. Este proyecto de control del dengue se basaba en el control biológico usando Mesocyclops, un microcrustáceo larvívoro, así como en el establecimiento de una fuerte implicación comunitaria para educar a la población sobre la transmisión del dengue y para reducir la cría de Aedes mediante la eliminación de recipientes. Durante tres años, una red de colaboradores fue responsable de la introducción de Mesocyclops en todos los recipientes definidos como sitios clave para la cría, y se realizaron actividades regulares tales como talleres de formación comunitaria, programas escolares, campañas de limpieza y promoción de la salud a través de programas de IEC. Para hacer sostenible este programa, también se reforzó el liderazgo local. El uso de estos microcrustáceos larvívoros como estrategia de control biológico contra el dengue a medio y largo plazo demostró una reducción significativa de las poblaciones de vectores del dengue y los casos de dengue cuando se combinaba con la participación comunitaria y la promoción eficaz de la salud. En Vietnam, este estudio vuelve a confirmar que existe una alternativa ecológica al uso sistemático de insecticidas para controlar la población de vectores del dengue