Semaine d'Etude Mathématiques et Entreprises 2 : Analyse de grands volumes de données en grande dimension

Le problème considéré ici provient de l'analyse de journaux d'événements informatiques. Ces journaux constituent des jeux de données en grande dimension, qui peuvent contenir de l'information sur d'éventuelles attaques contre un réseau. Comment rechercher des événements extraordinaires dans ces journaux et comment visualiser les données

In Vitro Reconstitution of SARS-Coronavirus mRNA Cap Methylation

SARS-coronavirus (SARS-CoV) genome expression depends on the synthesis of a set of mRNAs, which presumably are capped at their 5′ end and direct the synthesis of all viral proteins in the infected cell. Sixteen viral non-structural proteins (nsp1 to nsp16) constitute an unusually large replicase complex, which includes two methyltransferases putatively involved in viral mRNA cap formation. The S-adenosyl-L-methionine (AdoMet)-dependent (guanine-N7)-methyltransferase (N7-MTase) activity was recently attributed to nsp14, whereas nsp16 has been predicted to be the AdoMet-dependent (nucleoside-2′O)-methyltransferase. Here, we have reconstituted complete SARS-CoV mRNA cap methylation in vitro. We show that mRNA cap methylation requires a third viral protein, nsp10, which acts as an essential trigger to complete RNA cap-1 formation. The obligate sequence of methylation events is initiated by nsp14, which first methylates capped RNA transcripts to generate cap-0 7MeGpppA-RNAs. The latter are then selectively 2′O-methylated by the 2′O-MTase nsp16 in complex with its activator nsp10 to give rise to cap-1 7MeGpppA2′OMe-RNAs. Furthermore, sensitive in vitro inhibition assays of both activities show that aurintricarboxylic acid, active in SARS-CoV infected cells, targets both MTases with IC50 values in the micromolar range, providing a validated basis for anti-coronavirus drug design

Darwin’s wind hypothesis: does it work for plant dispersal in fragmented habitats?

Using the wind-dispersed plant Mycelis muralis, we examined how landscape fragmentation affects variation in seed traits contributing to dispersal. Inverse terminal velocity (Vt−1) of field-collected achenes was used as a proxy for individual seed dispersal ability. We related this measure to different metrics of landscape connectivity, at two spatial scales: in a detailed analysis of eight landscapes in Spain and along a latitudinal gradient using 29 landscapes across three European regions. In the highly patchy Spanish landscapes, seed Vt−1 increased significantly with increasing connectivity. A common garden experiment suggested that differences in Vt−1 may be in part genetically based. The Vt−1 was also found to increase with landscape occupancy, a coarser measure of connectivity, on a much broader (European) scale. Finally, Vt−1 was found to increase along a south–north latitudinal gradient. Our results for M. muralis are consistent with ‘Darwin’s wind dispersal hypothesis’ that high cost of dispersal may select for lower dispersal ability in fragmented landscapes, as well as with the ‘leading edge hypothesis’ that most recently colonized populations harbour more dispersive phenotypes.

SARGOS: Securing Offshore Infrastructures Through a Global Alert and Graded Response System

International audienceThe purpose of the project SARGOS is to develop a global alert and graded response system to answer the recent but strong need for securing critical civilian offshore infrastructures, vulnerable to piracy or terrorist actions from the sea. The challenge of protecting these infrastructures against malevolent intrusions requires to develop innovative strategies so as to ensure in a coordinate way the whole processing line: automatic surveillance, robust detection, continuous adjustment of the reaction plan and graded implementation of the relevant set of reactions. The system handles : Automatic and robust detection and classification of small size maritime targets in rough sea; Detection of suspicious behaviors in a security zone around the platform; Formalization and modeling of graded internal and external reactions, adapted to the dangerousness of the detected intrusion and taking into account security rules in force on the platform, geopolitical environment and legal aspects; Activation of progressive and reversible reactions, according to an intelligent situation analysis process. Reactions can go from a simple alert up to bringing non lethal reaction means into play. The project will materialize with the implementation of all the processing line in a single platform that will be used to carry out experimentations and to validate the overcoming of critical issues and the appropriateness of the proposed concept with regards to users' needs. SARGOS has been selected by the French Nationa

SARGOS : Système d'Alerte et Réponse Graduée Off Shore

National audienceLes champs de production d'hydrocarbures deviennent de plus en plus une cible de choix pour la piraterie maritime voire la menace terroriste. Or si les plates-formes et navires associés forment un réseau industriellement abouti en ce qui concerne l'exploitation, ils sont démunis face aux actes de malveillance intentionnels : de ce point de vue, ce sont des cibles isolées et exposées. Le projet SARGOS vise à répondre à l'émergence du besoin de sûreté des infrastructures offshore civiles vulnérables aux actions de malveillance, de piraterie ou de terrorisme menées à partir de la mer. Il propose le développement d'un système assurant de manière coordonnée la chaîne globale de protection : veille et surveillance automatisées ; détection d'intrusion ; évaluation de dangerosité ; plan de réaction gradué et piloté en temps réel pour rester constamment adapté au niveau de menace représenté par l'intrusion détectée. Une des capacités clefs est l'élaboration d'une stratégie complète et mutualisée de défense, incluant la mise en sûreté des personnes, la diffusion de l'alarme, la coordination des moyens d'assistance extérieure et la mise en oeuvre de moyens de dissuasion non létaux. Un enjeu fort est mis sur la prise en compte des modes de fonctionnement de l'infrastructure et des contraintes règlementaires et juridiques. SARGOS apporte une réponse nouvelle et innovante dans ce domaine de la sûreté maritime pour lequel il n'existe pas aujourd'hui de système opérationnel. Après un rappel de la problématique, cet article fait le point sur les différentes approches innovantes mises en oeuvre dans le développement du projet

Structure and Evolution of Nearby Stars with Planets. I. Short-Period Systems

Using the Yale stellar evolution code, we have calculated theoretical models for nearby stars with planetary-mass companions in short-period nearly circular orbits: 51 Pegasi, Tau Bootis, Upsilon Andromedae, Rho Cancri, and Rho Coronae Borealis. We present tables listing key stellar parameters such as mass, radius, age, and size of the convective envelope as a function of the observable parameters (luminosity, effective temperature, and metallicity), as well as the unknown helium fraction. For each star we construct best models based on recently published spectroscopic data and the present understanding of galactic chemical evolution. We discuss our results in the context of planet formation theory, and, in particular, tidal dissipation effects and stellar metallicity enhancements.Comment: 48 pages including 13 tables and 5 figures, to appear in Ap

SARS-Coronavirus Replication Is Supported by a Reticulovesicular Network of Modified Endoplasmic Reticulum

Positive-strand RNA viruses, a large group including human pathogens such as SARS-coronavirus (SARS-CoV), replicate in the cytoplasm of infected host cells. Their replication complexes are commonly associated with modified host cell membranes. Membrane structures supporting viral RNA synthesis range from distinct spherular membrane invaginations to more elaborate webs of packed membranes and vesicles. Generally, their ultrastructure, morphogenesis, and exact role in viral replication remain to be defined. Poorly characterized double-membrane vesicles (DMVs) were previously implicated in SARS-CoV RNA synthesis. We have now applied electron tomography of cryofixed infected cells for the three-dimensional imaging of coronavirus-induced membrane alterations at high resolution. Our analysis defines a unique reticulovesicular network of modified endoplasmic reticulum that integrates convoluted membranes, numerous interconnected DMVs (diameter 200–300 nm), and “vesicle packets” apparently arising from DMV merger. The convoluted membranes were most abundantly immunolabeled for viral replicase subunits. However, double-stranded RNA, presumably revealing the site of viral RNA synthesis, mainly localized to the DMV interior. Since we could not discern a connection between DMV interior and cytosol, our analysis raises several questions about the mechanism of DMV formation and the actual site of SARS-CoV RNA synthesis. Our data document the extensive virus-induced reorganization of host cell membranes into a network that is used to organize viral replication and possibly hide replicating RNA from antiviral defense mechanisms. Together with biochemical studies of the viral enzyme complex, our ultrastructural description of this “replication network” will aid to further dissect the early stages of the coronavirus life cycle and its virus-host interactions