Caractérisation du mouvement déformable dans une séquence d'images par la localisation de points singuliers

L'analyse d'image numérique est une voie d'investigation de plus en plus pertinente pour l'étude de phénomènes physiques et de leurs évolutions au cours du temps. Dans ce cadre, l'analyse du mouvement déformable 2D est l'un des problèmes importants à étudier. L'interprétation d'un tel champ de vecteurs 2D peut généralement se formuler par la caractérisation d'un modèle linéaire sur un voisinage approprié de points dits singuliers. Cet article décrit une méthode performante, basée sur une approche statistique, qui répertorie explicitement ces problèmes, et nous permet de localiser, caractériser et suivre ces points singuliers dans une séquence d'images. Cette méthode ne nécessite pas le calcul préalable du champ des vitesses. Elle a été validée par des expériences réalisées à l'aide d'exemples synthétiques et réels correspondant à des séquences d'images météorologiques

Archaebacterial histone-like protein MC1 can exhibit a sequence-specific binding to DNA.

The binding of MC1 protein, the major chromosomal protein of the archaebacterium Methanosarcina sp. CHTI 55, to the region preceding the strongly expressed genes encoding methyl coenzyme reductase in a closely related micro-organism has been investigated. By gel retardation and DNAase I footprinting assays, we identified a preferential binding sequence in an open reading frame of unknown function. The large area of DNA protected against DNAase I is interrupted by a strong cleavage enhancement site on each strand. By circular permutation assays, we showed that the DNA bends upon MC1 binding. Furthermore we observed that the presence of a sequence outside the binding site can induce an unusual electrophoretic behaviour in some complexes

Geochemistry and age of the Nouméa Basin lavas, New Caledonia: Evidence for Cretaceous subduction beneath the eastern Gondwana margin

International audienceThe Nouméa Basin in New Caledonia is perhaps the best preserved sequence of in-situ Late Cretaceous marine sediments and volcanic rocks in the western Pacific region. Previous tectonic interpretations suggest that the basin formed during a period of large-scale extension between New Caledonia and Antarctica during the break-up of the eastern Gondwana margin. However, new geochemical analyses have identified continental arc signatures in the lavas, suggesting a well-developed Late Cretaceous volcanic arc system active in the New Caledonia sector of the eastern Gondwana margin, possibly extending as far south as New Zealand. There are two distinct suites of lavas in the Nouméa Basin. The older lavas are predominately mafic, low to high-K, and have a calc-alkaline fractionation trend. Chondrite normalised trace element plots show patterns that are light rare earth element (LREE) enriched, and mid-ocean ridge basalt (MORB) normalised trace element plots show enrichment of most incompatible trace elements with discernable negative Nb, Ta and Ti anomalies. Trace element ratios identify a continental arc signature in these lavas which were generated from an N-MORB-like source. Overlying the mafic lavas is a sequence of younger voluminous siliceous, generally subalkaline lavas (+/−88 Ma). These lavas are LREE enriched with slight positive Nb-Ta anomalies and negative Eu and Ti anomalies. The geochemical data indicates these lavas have within plate characteristics with minor continental affinities and an enriched source. We propose that the older mafic lavas were generated during large scale subduction under the eastern Gondwana margin during the Late Cretaceous. Whereas the younger lavas may have been generated during extension; caused by slab roll-back of the subduction system along the Southwest Pacific plate boundary. The presence of fragments of a detached slab in this process would result in lavas chemically similar to those found in the Nouméa Basin, with minor continental characteristics, and generated from an enriched mantle source. What is of fundamental importance is the evidence that the arc system extended from New Caledonia southwards to New Zealand and was likely contemporaneou

MRS and electrical prospection in the context of weathered peridotite rocks in the South of New Caledonia.

International audienceIn November 2011 and July 2012 were conducted geophysical prospections in the southern part of New Caledonia. Both electrical tomography (ERT) and Magnetic Resonance Sounding (MRS) were performed to obtain a better understanding of the water storage and circulation. The geological context is the weathering profile of peridotite rock (Maurizot and Vendé-Leclerc, 2009). We present a review of the various ERT and MRS responses observed in this context

Radiolytic signature of Z-DNA.

Ionizing radiations induce various damages in DNA via the hydroxyl radical OH. generated by the radiolysis of water. We compare here the radiosensitivity of B- and Z-DNA, by using a Z-prone stretch included in a plasmid. In the supercoiled plasmid, the stretch is in the Z-form, whereas it is in the B-form when the plasmid is relaxed. Frank strand breaks (FSB) and alkali-revealed breaks (ARB) were located and quantified using sequencing gel electrophoresis. We show that B- and Z-DNA have the same mean sensitivity towards radiolytic attack, for both FSB and ARB. Nevertheless, the guanine sites are more sensitive, and the cytosine sites less sensitive in Z- than in B-DNA, leading to a characteristic signature of the Z-form. The comparison of experiments with the outcome of a Monte Carlo simulation of OH. radical attack suggests that transfer of initial damage from a guanine base to its attached sugar or the adjacent 3' cytosine is more important in Z-DNA than in B-DNA