Étude comparée des communautés benthiques et ripicoles endogées d'un réseau méditerranéen perturbé : l'Arc (Bouches-du-Rhône, France)

L'utilisation des méthodes biologiques et plus particulièrement l'étude des communautés benthiques pour l'appréciation de la qualité des eaux est actuellement d'un usage général. L'impact des perturbations des milieux peut être déduit de la composition et de la structure des peuplements qu'ils hébergent. En est-il de même pour les peuplements d'invertébrés ripicoles endogés humides, soumis moins directement à t'influence du milieu aquatique? Pour répondre à cette question une étude comparée (par analyse factorielle des correspondances) a été entreprise sur le réseau hydrographique d'une rivière de la région méditerranéenne, l'Arc, présentant des situations hydrochimiques variées.L'A.F.C., à partir de l'axe I, sépare les prélèvements d'invertébrés benthiques des prélèvements d'invertébrés ripicoles. Sur l'axe II les couples, prélèvement benthique - prélèvement ripicole de chaque station, possèdent sensiblement la même valeur sur l'axe et s'ordonnent selon un gradient de trophie croissant de l'amont vers l'aval. Les communautés ripicoles endogées humides peuvent donc être considérées comme des bio-indicateurs de la chimie de l'eau de la même manière que les communautés benthiques. Par contre le facteur temporarité (axe III) a une influence plus importante sur les communautés benthiques que sur les communautés ripicoles.L'examen de la répartition des taxons sur les axes factoriels a permis de déterminer un certain nombre d'espèces qui, tout en étant représentées dans les 2 milieux, sont caractéristiques de l'habitat rivulaire endogé humide. La prise en compte des peuplements ripicoles, malgré des difficultés d'ordre taxonomique, pourrait être envisagée lors de la détermination de la qualité des eaux.Utilization of biological methods and particularly through the study of benthic communities in order to estimate the quality of the water is for the present time very common. The impact of the disturbances of the medium may be deducted from the composition and the structure of the populations living there. But is it altogether the same for endogenous riparian wet invertebrate populations less directly submitted to the influence of the aquatic medium?To answer to this question, a comparative study (Factorial Analysis of Correspondences) has been carried out on the hydrographic network of the Arc River (Mediterranean region) which exhibits diversified hydrochemical situations. From and after axis I, the F.A.C. separates the benthic invertebrate samples from the riparian invertebrate ones. On axis II, the couples "benthic samples-riparian samples" of each station appreciably posses the same value on the axis and are arranged according to a trophic gradient ascending from upstream to downstream. The wet endogenous riparian communities can therefore be considered as bioindicators of the chemistry of the water in the same way as benthic communities. In contrast, the temporality factor (axis III) has a more important influence on the benthic communities than on the riparian ones.Examination of the distribution of the taxons on the factorial axis leads to identify a certain number of species which, although present in both mediums are characteristic of the wet endogenous riverside habitat. Taking into account of the riparian populations, in spite of taxonomic difficulties, should be considered as a valuable method for the determination of the quality of the waters

Ruled Laguerre minimal surfaces

A Laguerre minimal surface is an immersed surface in the Euclidean space being an extremal of the functional \int (H^2/K - 1) dA. In the present paper, we prove that the only ruled Laguerre minimal surfaces are up to isometry the surfaces R(u,v) = (Au, Bu, Cu + D cos 2u) + v (sin u, cos u, 0), where A, B, C, D are fixed real numbers. To achieve invariance under Laguerre transformations, we also derive all Laguerre minimal surfaces that are enveloped by a family of cones. The methodology is based on the isotropic model of Laguerre geometry. In this model a Laguerre minimal surface enveloped by a family of cones corresponds to a graph of a biharmonic function carrying a family of isotropic circles. We classify such functions by showing that the top view of the family of circles is a pencil.Comment: 28 pages, 9 figures. Minor correction: missed assumption (*) added to Propositions 1-2 and Theorem 2, missed case (nested circles having nonempty envelope) added in the proof of Pencil Theorem 4, missed proof that the arcs cut off by the envelope are disjoint added in the proof of Lemma

Estimation of the hydraulic parameters of unsaturated samples by electrical resistivity tomography

In situ and laboratory experiments have shown that electrical resistivity tomography (ERT) is an effective tool to image transient phenomena in soils. However, its application in quantifying soil hydraulic parameters has been limited. In this study, experiments of water inflow in unsaturated soil samples were conducted in an oedometer equipped to perform three-dimensional electrical measurements. Reconstructions of the electrical conductivity at different times confirmed the usefulness of ERT for monitoring the evolution of water content. The tomographic reconstructions were subsequently used in conjunction with a finite-element simulation to infer the water retention curve and the unsaturated hydraulic conductivity. The parameters estimated with ERT agree satisfactorily with those determined using established techniques, hence the proposed approach shows good potential for relatively fast characterisations. Similar experiments could be carried out on site to study the hydraulic behaviour of the entire soil deposi

Gaudin Models and Bending Flows: a Geometrical Point of View

In this paper we discuss the bihamiltonian formulation of the (rational XXX) Gaudin models of spin-spin interaction, generalized to the case of sl(r)-valued spins. In particular, we focus on the homogeneous models. We find a pencil of Poisson brackets that recursively define a complete set of integrals of the motion, alternative to the set of integrals associated with the 'standard' Lax representation of the Gaudin model. These integrals, in the case of su(2), coincide wih the Hamiltonians of the 'bending flows' in the moduli space of polygons in Euclidean space introduced by Kapovich and Millson. We finally address the problem of separability of these flows and explicitly find separation coordinates and separation relations for the r=2 case.Comment: 27 pages, LaTeX with amsmath and amssym

Hypoxia up-regulates SERPINB3 through HIF-2\u3b1 in human liver cancer cells.

SERPINB3 is a cysteine-proteases inhibitor up-regulated in a significant number of cirrhotic patients carrying hepatocellular carcinoma (HCC) and recently proposed as a prognostic marker for HCC early recurrence. SERPINB3 has been reported to stimulate proliferation, inhibit apoptosis and, similar to what reported for hypoxia, to trigger epithelial-to-mesenchymal transition (EMT) and increased invasiveness in liver cancer cells. This study has investigated whether SERPINB3 expression is regulated by hypoxia-related mechanisms in liver cancer cells. Exposure of HepG2 and Huh7 cells to hypoxia up-regulated SERPINB3 transcription, protein synthesis and release in the extracellular medium. Hypoxia-dependent SERPINB3 up-regulation was selective (no change detected for SERPINB4) and operated through hypoxia inducible factor (HIF)-2\u3b1 (not HIF-1\u3b1) binding to SERPINB3 promoter, as confirmed by chromatin immuno-precipitation assay and silencing experiments employing specific siRNAs. HIF-2\u3b1-mediated SERPINB3 up-regulation under hypoxic conditions required intracellular generation of ROS. Immuno-histochemistry (IHC) and transcript analysis, performed in human HCC specimens, revealed co-localization of the two proteins in liver cancer cells and the existence of a positive correlation between HIF-2\u3b1 and SERPINB3 transcript levels, respectively. Hypoxia, through HIF-2\u3b1-dependent and redox-sensitive mechanisms, up-regulates the transcription, synthesis and release of SERPINB3, a molecule with a high oncogenic potential

A sampling method for quantifying the information content of IASI channels

There is a vast amount of information about the atmosphere available from instruments on board satellites. One example is the Infrared Atmospheric Sounding Interferometer (IASI) instrument, which measures radiances emitted from Earth’s atmosphere and surface in 8461 channels. It is difficult to transmit, store, and assimilate such a large amount of data. A practical solution to this has been to select a subset of a few hundred channels based on those that contain the most useful information. Different measures of information content for objective channel selection have been suggested for application to variational data assimilation. These include mutual information and the degrees of freedom for signal. To date, the calculation of these measures of information content has been based on the linear theory that is at the heart of operational variational data assimilation. However, the retrieval of information about the atmosphere from the satellite radiances can be highly nonlinear. Here, a sampling method for calculating the mutual information that is free from assumptions about the linearity of the relationship between the observed radiances and the state variables is examined. It is found that large linearization errors can indeed lead to large discrepancies in the value of mutual information. How this new estimate of information content can be used in channel selection is addressed, with particular attention given to the efficiency of the new method. It is anticipated that accounting for the nonlinearity in the channel selection will be beneficial when using nonlinear data assimilation methods currently in development

Ricerca del grano tenero in miscela con il duro negli sfarinati e nelle paste variamente essiccate

Il riconoscimento dell'uso del grano tenero nella produzione della pasta alimentare si basa sull'analisi gas cromatografica deli esteri degli steroli previo isolamento della frazione lipidica. Il metodo consente di calcolare la percentuale di grano tenero utilizzato sia negli sfarinati sia nelle paste