Le nouveau régime de l’appel public à l’épargne.

Le nouveau régime de l’appel public à l’épargne français a un champ d’application plus restreint mais aussi des obligations légales renforcées. Cette réforme, qui entraîne des conséquences notables pour la Place de Paris, participe de la stabilité financière.Appel public à l’épargne, prospectus, investisseur qualifié, émetteur.

The Nuclear dsRNA Binding Protein HYL1 Is Required for MicroRNA Accumulation and Plant Development, but Not Posttranscriptional Transgene Silencing

AbstractMicroRNAs (miRNAs) are 21–24 nucleotides long molecules processed from imperfect double-stranded RNAs (dsRNAs). They regulate gene expression by targeting complementary mRNA for cleavage or interfering with their translation [1–6]. In Arabidopsis, point mutations in or short truncations of the nuclear DICER-LIKE1 (DCL1) or HEN1 protein reduce miRNA accumulation and increase uncleaved target mRNAs accumulation, resulting in developmental abnormalities [7–12]. Here, we show that miRNA accumulation also depends on the activity of HYL1, a nuclear dsRNA binding protein [13]. hyl1 mutants exhibit developmental defects overlapping with that of dcl1 and hen1 mutants, suggesting that DCL1, HEN1, and HYL1 act together in the nucleus. We validate additional target mRNAs and show that reduced miRNA accumulation in hyl1 correlates with an increased accumulation of uncleaved target mRNAs, including meristem- and auxin-related genes, providing clues for the developmental abnormalities of hyl1 and for the previous identification of hyl1 as a mutant with altered responses to phytohormones [13]. Lastly, we show that posttranscriptional transgene silencing occurs in hyl1, suggesting that HYL1 has specialized function in the plant miRNA pathway, whereas the HYL1-related RDE-4 and R2D2 proteins associate with DICER in the cytoplasm and act in the RNAi pathway in C. elegans and Drosophila, respectively [14–15]

Knapping tools in Magdalenian contexts: New evidence from Gough’s Cave (Somerset, UK)

Our knowledge of the recolonization of north-west Europe at the end of the Last Glacial Maximum depends to a large extent on finds from Gough's Cave (Somerset, UK). Ultra-high resolution radiocarbon determinations suggest that the cave was occupied seasonally by Magdalenian hunters for perhaps no more than two or three human generations, centred on 12,600 BP (~14,950-14,750 cal BP). They left behind a rich and diverse assemblage of Magdalenian lithic and osseous artefacts, butchered animal bones, and cannibalised human remains. The faunal assemblage from Gough's Cave is one of the most comprehensively studied from any Magdalenian site, yet new and unexpected discoveries continue to be made. Here, we record previously unrecognized flint-knapping tools that were identified during a survey of the Gough's Cave faunal collection at the Natural History Museum (London). We identified bones used as hammers and teeth manipulated as pressure-flakers to manufacture flint tools. Most of the pieces appear to be ad hoc (single-use?) tools, but a horse molar was almost certainly a curated object that was used over an extended period to work many stone tools. This paper explores how these knapping tools were used to support a more nuanced understanding of Magdalenian stone-tool manufacturing processes. Moreover, we provide a standard for identifying minimally-used knapping tools that will help to establish whether retouchers and other organic stone-working tools are as rare in the Magdalenian archaeological record as current studies suggest

Spatial distribution of emission in Unidentified Infrared Bands from Midcourse Space Experiment Survey

Recently the Midcourse Space Experiment (MSX) has surveyed the Galactic plane in mainly four infrared bands between 6 and 25 micron. Two of these bands cover several Unidentified Infrared emission Bands (UIBs). With the aim of extracting the spatial distribution of the UIB emission on a large scale, a scheme has been developed to model the MSX data with emission in the UIBs alongwith the underlying thermal continuum from the interstellar dust. In order to test this scheme, a sample of five Galactic compact H II regions (Sh-61, Sh-138, Sh-152, Sh-156, Sh-186; Zavagno & Ducci 2001) for which imaging study in some individual UIBs is available from ISOCAM measurements, has been studied. The results of this comparative study on small angular scale are as follows : (i) the morphological details extracted from our scheme agree very well with those from the superior ISOCAM measurements; (ii) the integrated strength of UIBs extracted from the MSX database correlates extremely well with the sum of the strengths of individual UIBs measured from ISOCAM. This tight correlation is very encouraging and promises the potential of MSX database for study of large scale spatial distribution of UIB emission (and the carriers of UIBs) in the entire Galactic plane.Comment: to be published in Astronomy & Astrophysics; (9 pages including 2 tables & 11 figures

Primer-dependent and primer-independent initiation of double stranded RNA synthesis by purified <i>arabidopsis</i> RNA-dependent RNA polymerases RDR2 and RDR6

Cellular RNA-dependent RNA polymerases (RDRs) are fundamental components of RNA silencing in plants and many other eukaryotes. In Arabidopsis thaliana genetic studies have demonstrated that RDR2 and RDR6 are involved in the synthesis of double stranded RNA (dsRNA) from single stranded RNA (ssRNA) targeted by RNA silencing. The dsRNA is subsequently cleaved by the ribonuclease DICER-like into secondary small interfering RNAs (siRNAs) that reinforce and/or maintain the silenced state of the target RNA. Models of RNA silencing propose that RDRs could use primer-independent and primer-dependent initiation to generate dsRNA from a transcript targeted by primary siRNA or microRNA (miRNA). However, the biochemical activities of RDR proteins are still partly understood. Here, we obtained active recombinant RDR2 and RDR6 in a purified form. We demonstrate that RDR2 and RDR6 have primer-independent and primer-dependent RNA polymerase activities with different efficiencies. We further show that RDR2 and RDR6 can initiate dsRNA synthesis either by elongation of 21- to 24- nucleotides RNAs hybridized to complementary RNA template or by elongation of self-primed RNA template. These findings provide new insights into our understanding of the molecular mechanisms of RNA silencing in plants

Possible contribution of olefins and heteroatoms to the Unidentified Infrared Bands

The current assignments of the 11.3 feature are shown to be incompatible with observations. An unbiased survey of correlation charts suggests that the olefinic group R2=CH2 is a good alternative candidate. For the 12.7 feature, the best fits are provided by nitrites, R-O-N=O, and amines, R-N=H2. Sulfones, SO2, exhibit strong features near 7.7 and 8.6 microns, which may contribute to the UIBs. These additional functional groups are likely to be attached to the main hydrocarbon dust skeleton previously hypothesized in the coal/kerogen model. They provide further leeway in modelling the large variety of relative band intensities observed in the sky.Comment: 5 pages, 1 figure, accepted by A and A Letter

Simulation 2D de la fissuration dans un matériau ductile endommageable avec X-FEM

Ce travail est consacré à la simulation numérique de la propagation d’une fissure dans un matériau dont la rupture résulte de la création, la croissance et la coalescence de vides. Nous avons ainsi considéré une plaque (cas des déformations planes) soumise à un chargement de type Mode I. Le comportement du matériau est décrit via un modèle de type Gurson [1] (en réalité GTN, voir Ref. [3]) prenant en compte les effets combinés de l’écrouissage, de l’adoucissement thermique, de la viscoplasticité et de l’endommagement par croissance de vides. Le matériau étudié est un acier. La méthode des éléments finis étendu (X-FEM) [2] a été retenue pour décrire les discontinuités fortes induites par la présence d’une fissure dans le maillage. Une méthode de propagation originale est proposée afin de coupler la X-FEM et le comportement fortement non linéaire du matériau. La simulation numérique de ce problème est réalisée à l’aide du code de calculs industriel par éléments finis, Abaqus. Cela à impliqué le développement i) d’un élément fini utilisateur (UEL dans Abaqus) afin de décrire les conséquences cinématiques de la présence d’une fissure et ii) d’un matériau utilisateur (UMAT dans Abaqus) pour décrire le comportement du matériau. Un schéma d’intégration implicite est utilisé dans le code de calculs. Considérant quelques simplifications, le travail présenté reproduit la propagation d’une fissure en 2D résultant de la croissance de vides induits par l’endommagement. [1] A.L. Gurson. Continuum theory of ductile rupture by void nucleation and growth : Part I - Yield criteria and flow rules for porous ductile media, J. Eng. Mat. Tech., 2-15, 1977. [2] N. Moës, J. Dolbow, T. Belytschko. A finite element method for crack growth without remeshing. Int. J. Num. Methods Eng., 131-150,1999. [3] V. Tvergaard, A. Needleman. Analysis of the cup-cone fracture in a round tensile bar, Acta Metall., page157- page169, 1984