Modelling of metal polluant leaching through a smectite.

International audienceLaboratory tests are performed to characterise the soaking and retention properties of a clay barrier (Fo-Ca) under controlled homogeneous conditions. A physical model that allows calculating the retention properties and kinetics observed during the test is then detailed, and lastly simulations are examined using various soaking conditions. The results show the model predictions of cumulative cation concentrations in leachates (i.e. copper retention by clay). These curves are accurately fit by the model with the experimental data for the leaching phenomena. Clay retention capacity until reaching a physical limit in the exchanges is evidenced as well, with this limit being input into the model as the clay CEC

Simulation of pollutant transport investigated through an expansive clay.

In the framework of domestic waste disposals, the in-situ compaction of soil is usually used to obtain engineered clay barriers with suitable confining properties. Permeability and pollutant retention are the major properties which should be investigated in this context for barrier evaluation. Considering clay barriers in contact with waste leachates, they may be saturated by solutes of various chemical compositions, including in particular toxic heavy metals. In this context, the expansive Fo-Ca clay, a natural Ca-smectite from the Paris basin of Ypersian (Sparnacian) age, was chosen because of its very low permeability and ability for pollutant retention through cationic exchanges. The smectic is associated with kaolinite (up to 20%), and minor quartz, calcite, goethite and gypsum

Improved VSF Algorithm for Smooth Surface Reconstruction from Sparse Medical Data

This paper presents a Modified Variational Splines Fitting (MVSF) algorithm for surface reconstruction using thin plate splines on scattered patches or points of originally smooth surfaces. In particular, a more accurate derivation of the discrete equations for the energy corresponding to the thin plate model is introduced. The results obtained on simulated data show that the proposed algorithm converges faster than the original VSF algorithm. Additionally, we discuss an approach for choosing the algorithm’s parameters using a cross validation technique. Results obtained with the modified algorithm are compared to those using a Frequency Fourier-based 3D Harmonic modelling (3DHM) algorithm and show that the proposed algorithm gives an improved performance under the small sample size condition. The developed model has been successfully applied for real biomedical data; in particular for the reconstruction of left ventricle of human heart

Chan-Vese based method to segment mouse brain MRI images: application to cerebral malformation analysis in trisomy 21

International audienceIn this paper, a semi automatic active contour method based on Chan-Vese model is proposed for the segmentation of mouse brain MR images. First, a 2 ½ D strategy is applied on the axial images to segment the 3D volume of interest. The method takes into account the special shape of the object to segment. Moreover, the user defines the limits where to search these contours and also provides an initial contour. This semi automatic method makes that human intervention is limited and the tedious manual handling is greatly reduced. Results have shown that the brain volumes estimated by the method are identical to expert manually estimated volumes. Last but not least, the new method was used in the analysis of the cerebral malformations linked to Trisomy 21: no significant difference of the brain volumes between Tri-somy 21 mice and the control ones were found

Transport de polluant à travers une argile gonflante : étude du cuivre infiltré sous pression dans un matériau argileux sous contrainte.

Actuellement, lors du stockage de déchets ménagers et industriels, une barrière argileuse est mise en place en fond et sur les flancs des alvéoles, pour respecter la réglementation en terme de perméabilité et permettre la rétention des polluants. Dans ce domaine, un des enjeux scientifiques est la prédiction du comportement à long terme des argiles gonflantes utilisées comme barrière de confinement. Dans cette optique, des essais de laboratoire reproduisant les conditions hydrauliques in situ d'un site de stockage ont été effectués à l'aide d'une cellule œdométrique munie d'un système d'injection approprié (Jullien et Lecomte, 2000). Les expériences ont été réalisées avec la Fo-Ca, matériau argileux naturel choisi pour ses propriétés de gonflement, sa faible perméabilité et sa capacité d'échanges cationiques. La Fo-Ca, d'âge Yprésien et issue du bassin de Paris, contient plus de 80% de minéraux argileux (dont 80% d'interstratifiés smectite-kaolinite et 20% de kaolinite) et comme phases mineures, du quartz, de la goethite, de la calcite et du gypse. Des travaux antérieurs (Jullien et al., 2002) ont permis de tester les performances de la Fo-Ca soumises à des sollicitations chimio-hydro-mécaniques lors de l'infiltration sous pression de solutions de nitrate de cuivre. Les lixiviats obtenus sont analysés par spectrométrie d'absorption atomique, caractérisant ainsi l'aptitude de rétention du matériau argileux en fonction du temps (figure 1). Ces échantillons d'argile compactés puis infiltrés peuvent ainsi être considérés comme un système soumis à un paramètre externe x(t) et délivrant une réponse y(t)

An Image Dependent Stopping Method for Iterative Denoising Procedures

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Atlas-assisted segmentation of cerebral structures of mice

International audienceThe segmentation of different cerebral structures of mice is becoming more and more important due to the growing interest in finding small animal models of human diseases. In this work, variational atlases are constructed by manual segmentation of various MRI brain images of reference and trisomy 21 mice. These atlases are then registered to assist the segmentation of fine cerebral structures such as the cerebellum and the hippocampus. A modified Chan-Vese segmentation method is used for the detection of these structures. Global as well as local comparison of the reconstructed surfaces and volumes are hence conducted to better understand the gene involved in the morphological malformations associated to trisomy

A new adaptive switching median filter

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A joint snake and atlas-based segmentation of plantar foot thermal images

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A joint snake and atlas-based segmentation of plantar foot thermal images

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