Computational Particle Physics for Event Generators and Data Analysis

High-energy physics data analysis relies heavily on the comparison between experimental and simulated data as stressed lately by the Higgs search at LHC and the recent identification of a Higgs-like new boson. The first link in the full simulation chain is the event generation both for background and for expected signals. Nowadays event generators are based on the automatic computation of matrix element or amplitude for each process of interest. Moreover, recent analysis techniques based on the matrix element likelihood method assign probabilities for every event to belong to any of a given set of possible processes. This method originally used for the top mass measurement, although computing intensive, has shown its power at LHC to extract the new boson signal from the background. Serving both needs, the automatic calculation of matrix element is therefore more than ever of prime importance for particle physics. Initiated in the eighties, the techniques have matured for the lowest order calculations (tree-level), but become complex and CPU time consuming when higher order calculations involving loop diagrams are necessary like for QCD processes at LHC. New calculation techniques for next-to-leading order (NLO) have surfaced making possible the generation of processes with many final state particles (up to 6). If NLO calculations are in many cases under control, although not yet fully automatic, even higher precision calculations involving processes at 2-loops or more remain a big challenge. After a short introduction to particle physics and to the related theoretical framework, we will review some of the computing techniques that have been developed to make these calculations automatic. The main available packages and some of the most important applications for simulation and data analysis, in particular at LHC will also be summarized.Comment: 19 pages, 11 figures, Proceedings of CCP (Conference on Computational Physics) Oct. 2012, Osaka (Japan) in IOP Journal of Physics: Conference Serie

Pôles de compétitivité version 2.0 : les enjeux stratégiques et managériaux de la « clusterisation » des dynamiques compétitives

Expression la plus récente de la politique industrielle française, les pôles de compétitivité sont le fruit d'une démarche volontariste initiée en 2005 par le gouvernement français et récemment réaffirmée par l'annonce de la version 2.0. Le déploiement de cette politique peut être synthétisé en deux phases successives. La première période (2005-2008) correspond à une phase de formalisation et de structuration. La seconde phase (2009-2011), dite « version 2.0 » est marquée par l'évaluation des pôles de compétitivité. Les pôles de compétitivité sont le reflet d'une tendance internationale à la « clusterisation » de l'économie depuis le milieu des années quatre-vingt-dix. Cette clusterisation repose sur des idées parfois anciennes qui lient la performance économique à deux dimensions essentielles : le réseau et le territoire. La construction et le développement de véritables réseaux territoriaux d'organisations nécessitent cependant de réinterroger les conceptions stratégiques et managériales mobilisées dans d'autres cadres organisationnels. Ils se révèlent ainsi des terrains de recherche particulièrement riches pour les sciences de gestion.Pôle de compétitivité ; cluster ; territoire ; éco-système.

Enhanced visualization of polysaccharides from aqueous suspensions

Aqueous suspensions of polysaccharides such as those prepared for domestic and industrial applications or present in natural waters, although difficult to visualize by conventional transmission electron microscopy (TEM) because of their poor electron density, can be characterized at the ultrastructural level by using milden bloc staining and contrast enhancement by energy-filtered TEM (EF-TEM). The advantages and drawbacks of the proposed method are discussed in relation to the different parameters controlling the quality of final images. It is shown, with synthetic polysaccharides, purified algal fibrils and lacustrine exocellular polymers as key examples, that optimizing specimen preparation and visualization parameters allows unbiased identification of organic substructures never revealed or strongly degraded by classical microscopic procedure

Incertitude(s) et Stratégie(s)

Introduction au numéro spécial RFG-AIMS. Compilation de recherches francophones en management stratégique contribuant à la réflexion sur la manière dont cette discipline se saisit de l'incertitude contextuelle et générique.Stratégie - Incertitude -

In vitro and in vivo exploration of the cellobiose and cellodextrin phosphorylases panel in Ruminiclostridium cellulolyticum: implication for cellulose catabolism

International audienceBackground: In anaerobic cellulolytic microorganisms , cellulolysis results in the action of several cellulases gathered in extracellular multi-enzyme complexes called cellulosomes. Their action releases cellobiose and longer cellodex-trins which are imported and further degraded in the cytosol to fuel the cells. In Ruminiclostridium cellulolyticum, an anaerobic and cellulolytic mesophilic bacteria, three cellodextrin phosphorylases named CdpA, CdpB, and CdpC, were identified in addition to the cellobiose phosphorylase (CbpA) previously characterized. The present study aimed at characterizing them, exploring their implication during growth on cellulose to better understand the lifestyle of cellulolytic bacteria on such substrate. Results: The three cellodextrin phosphorylases from R. cellulolyticum displayed marked different enzymatic characteristics. They are specific for cellodextrins of different lengths and present different k cat values. CdpC is the most active enzyme before CdpA, and CdpB is weakly active. Modeling studies revealed that a mutation of a conserved histidine residue in the phosphate ion-binding pocket in CdpB and CdpC might explain their activity-level differences. The genes encoding these enzymes are scattered over the chromosome of R. cellulolyticum and only the expression of the gene encoding the cellobiose phosphorylase and the gene cdpA is induced during cellulose growth. Characterization of four independent mutants constructed in R. cellulolyticum for each of the cellobiose and cellodextrin phosphorylases encoding genes indicated that only the cellobiose phosphorylase is essential for growth on cellulose. Conclusions: Unexpectedly, the cellobiose phosphorylase but not the cellodextrin phosphorylases is essential for the growth of the model bacterium on cellulose. This suggests that the bacterium adopts a "short" dextrin strategy to grow on cellulose, even though the use of long cellodextrins might be more energy-saving. Our results suggest marked differences in the cellulose catabolism developed among cellulolytic bacteria, which is a result that might impact the design of future engineered strains for biomass-to-biofuel conversion

Étude expérimentale de l'éclatement tourbillonnaire en bordure d'une plaque immergée sous la houle

L'interaction de la houle avec une structure immergée génère des filaments tourbillonnaires très intenses qui ont un fort impact sur leur environnement proche. La dynamique de ces filaments présente des mécanismes de déstabilisation fortement tridimensionnels dont la caractérisation représente un défi expérimental. Pour identifier et comprendre ces mécanismes, nous avons utilisé l'holographie numérique dans l'axe, par afin d'accéder à la distribution tridimensionnelle des vitesses au sein du tourbillon et ainsi mieux comprendre la nature des processus intervenant dans sa déstabilisation. Ses mesures sont complétées par des mesures en stéréo-piv afin de valider les résultats obtenus par holographie