The recent extension of muskwari sorghums in northern Cameroon

The extension of transplanted sorghum in northern Cameroon began in the 1950s and is now attaining remarkable proportions. It concerns from 150,000 to 200 000 ha throughout the plains in the extreme north according to the climatic conditions of the year. This spread has been caused mainly by the increase in food crop requirements resulting from population increase and also the development of cotton growing on land previously used for rainfed food crops. Studies have been performed at the local area ('terroir') level to gain a better understanding of the reasons for the phenomenon and its effects on farming systems. The spread can be as much as 200% in 20 years and is on vertisols and also seemingly less propitious vertic soils. It has been made possible by the perfecting of cultivation techniques and the endogenous dissemination of farming know-how, with an astonishing diversity of environments and varieties cultivated. Growers using the cropping system are encountering new constraints-especially weed growth- and are calling for external aid. An R&D programme initiated by the DPGT project (Développement Paysannal et Gestion des Terroirs) is leading to support services managed collectively by farmers' organisations. (Résumé d'auteur

Reliable ABC model choice via random forests

Approximate Bayesian computation (ABC) methods provide an elaborate approach to Bayesian inference on complex models, including model choice. Both theoretical arguments and simulation experiments indicate, however, that model posterior probabilities may be poorly evaluated by standard ABC techniques. We propose a novel approach based on a machine learning tool named random forests to conduct selection among the highly complex models covered by ABC algorithms. We thus modify the way Bayesian model selection is both understood and operated, in that we rephrase the inferential goal as a classification problem, first predicting the model that best fits the data with random forests and postponing the approximation of the posterior probability of the predicted MAP for a second stage also relying on random forests. Compared with earlier implementations of ABC model choice, the ABC random forest approach offers several potential improvements: (i) it often has a larger discriminative power among the competing models, (ii) it is more robust against the number and choice of statistics summarizing the data, (iii) the computing effort is drastically reduced (with a gain in computation efficiency of at least fifty), and (iv) it includes an approximation of the posterior probability of the selected model. The call to random forests will undoubtedly extend the range of size of datasets and complexity of models that ABC can handle. We illustrate the power of this novel methodology by analyzing controlled experiments as well as genuine population genetics datasets. The proposed methodologies are implemented in the R package abcrf available on the CRAN.Comment: 39 pages, 15 figures, 6 table

A subspace fitting method based on finite elements for fast identification of damages in vibrating mechanical systems

International audienceIn this paper, a method based on subspace fitting is proposed for identification of faults in mechanical systems. The method uses the modal information from an observability matrix, provided by a stochastic subspace identification. It is used for updating a Finite Element Model through the Variable Projection algorithm. Experimental example aims to demonstrate the ability and the efficiency of the method for diagnosis of structural faults in a mechanical system

A Subspace Fitting Method based on Finite Elements for Identification and Localization of Damage in Mechanical Systems

International audienceIn this work, a subspace fitting method based on finite elements for identification of modal parameters of a mechanical system is proposed. The technique uses prior knowledge resulting from a coarse finite element model (FEM) of the structure. The proposed technique is applied to identify the parameters of several mechanical systems under deterministic and stochastic excitations. Numerical experiments highlight the relevance of the technique compared to the conventional identification techniques. Identification, localization and estimation of severity of damages are carried out

Parameter uncertainties quantification for finite element based subspace fitting approaches

International audienceThis paper addresses the issue of quantifying uncertainty bounds when updating the finite element model of a mechanical structure from measurement data. The problem arises as to assess the validity of the parameters identification and the accuracy of the results obtained. In this paper, a covariance estimation procedure is proposed about the updated parameters of a finite element model, which propagates the data-related covariance to the parameters by considering a first-order sensitivity analysis. In particular, this propagation is performed through each iteration step of the updating minimization problem, by taking into account the covariance between the updated parameters and the data-related quantities. Numerical simulations on a beam show the feasibility and the effectiveness of the method

State Space Estimation Method for Robot Identification

In this paper, we study the identification of robot dynamic models. The usual technique, based on the Least-Squares method, is carefully detailed. A new procedure based on Kalman filtering and fixed interval smoothing is developed. This new technique is compared to usual one with simulated and experimental data. The obtained results show that the proposed technique is a credible alternative, especially if the system bandwidth is unknown

WIDDE: a Web-Interfaced next generation database for genetic diversity exploration, with a first application in cattle

Background The advent and democratization of next generation sequencing and genotyping technologies lead to a huge amount of data for the characterization of population genetic diversity in model and non model-species. However, efficient storage, management, cross-analyzing and exploration of such dense genotyping datasets remain challenging. This is particularly true for the bovine species where many SNP datasets have been generated in various cattle populations with different genotyping tools. Description We developed WIDDE, a Web-Interfaced Next Generation Database that stands as a generic tool applicable to a wide range of species and marker types (http://widde.toulouse.inra.fr). As a first illustration, we hereby describe its first version dedicated to cattle biodiversity, which includes a large and evolving cattle genotyping dataset for over 750,000 SNPs available on 129 (89 public) different cattle populations representative of the world-wide bovine genetic diversity and on 7 outgroup bovid species. This version proposes an optional marker and individual filtering step, an export of genotyping data in different popular formats, and an exploration of genetic diversity through a principal component analysis. Users can also explore their own genotyping data together with data from WIDDE, assign their samples to WIDDE populations based on distance assignment method and supervised clustering, and estimate their ancestry composition relative to the populations represented in the database. Conclusion The cattle version of WIDDE represents to our knowledge the first database dedicated to cattle biodiversity and SNP genotyping data that will be very useful for researchers interested in this field. As a generic tool applicable to a wide range of marker types, WIDDE is overall intended to the genetic diversity exploration of any species and will be extended to other species shortly. The structure makes it easy to include additional output formats and new tools dedicated to genetic diversity exploration. (Résumé d'auteur

Interactions of ammonium smectite with low molecular weight carboxylic acids.

International audienceThis study aims at better understanding the interaction between an ammonium smectite and carboxylic acids. The SWy-2 (Wyoming smectites) has been exchanged with NH4 + and then batched with carboxylic acids (acetic, formic, chloroacetic and oxalic) in concentrations between 0,01M and 1M. The obtained solid phases have been chemically analyzed and characterized by infrared absorption spectroscopy and X-ray powder diffraction. The ionic chromatography has been used for the quantitative measurement of ammonium in the solution after interaction. For the four acids, the interaction is characterized by a cationic exchange of NH4+ to H3O+. A partial exchange to Al3+ due to a partial dissolution of the sample in strong acidic medium is observed with chloroacetic and oxalic acids. For these two last acids, the adsorption of molecules on the clay sample occurs, mainly through H-bonding with the cation. Moreover, the intercalation of oxalic acid in the interlayer space has been highlighted

Caractérisation physico-chimique et comportement hydromécanique d'une argile échangée avec l'ammonium dans le contexte des sites de stockage

International audienceEn 2007, près de 38 millions de tonnes de déchets d'origine ménagère ont été collectés par les collectivités en France (ADEME, 2009). Malgré l'essor constant du recyclage et du compostage, 31% de ces déchets municipaux traités ont été envoyé dans des installations de stockage des déchets non dangereux (ISDND) cette même année. A l'échelle européenne, ce pourcentage augmente considérablement. Dans ces sites de stockage, la percolation de l'eau à travers les déchets produit une grande quantité de lixiviats chargés en polluants de diverses natures. L'étanchéité en fond de site est notamment assurée par une couche argileuse (barrière passive). Son rôle est notamment de limiter la pollution des sols et des nappes phréatiques. Les argiles utilisées en fond de site de stockage sont principalement des smectites qui possèdent une forte capacité de rétention. Dans les analyses de lixiviats, de nombreux auteurs ont mis en évidence une très grande quantité d'ammonium susceptible de s'échanger avec le sodium ou le calcium initialement présent la barrière argileuse. Si ces dernières ont largement été décrites dans la littérature, les argiles ammoniées sont beaucoup moins connues. Le travail présenté ici s'est donc intéressé à la caractérisation complète d'une argile totalement échangée avec des cations ammonium. L'objectif de ce travail est de mieux comprendre et appréhender le comportement d'une argile ammoniée dans le contexte de la mise en décharge des déchets. En raison du poids des déchets, la barrière d'argile en fond de site subit des pressions élevées. Le deuxième objectif est de comprendre les phénomènes microscopiques et macroscopiques liées au comportement hydromécanique des matériaux argileux. Des cellules oedométriques équipées d'un système d'injection sous pression contrôlée ont été utilisés. Des différences significatives sur les capacités d'hydratation de l'argile ammoniée et sur la perméabilité de cette dernière ont été mises en évidence au cours de ce travail. L'ensemble des résultats présentés souligne l'importance du suivi des sites de stockage sur le long terme, notamment pour prévenir des pollutions des nappes phréatiques

NH4-smectite: Characterization, hydration properties and hydro mechanical behaviour

International audienceLeachates in waste landfills are characterized by the presence of ammonium ions in large excess. These ammonium ions can be exchanged with the interlayer cations in clay and modify the physical and chemical properties of clay geochemical barriers in waste landfills and drive to environmental problems. The purpose of this study was to understand the hydro-physical changes of a smectite in the presence of ammonium ions. An ammonium smectite was prepared by cation exchange from a natural montmorillonite (Wyoming). The samples were characterized and their properties were compared by the use of a set of complementary techniques (X-ray diffraction, infrared spectroscopy, N2 adsorption-desorption BET technique, thermal analysis, and percolation experiments). The main effect was a modification of the porosity and its network, and reduced crystalline swelling. These effects changed the hydraulic conductivity and macroscopic swelling of the clay. The oedometer experiments, which allow simulating the pressure on small amounts of samples, proved the strong increase of the permeability of NH4-smectite. This last point is of great importance in an environment point of view and raises questions on the impermeability behaviour on the long term of the clay geochemical barriers with the presence of ammonium ions in waste landfills