Response kinetics in the complex chemotaxis signalling pathway of Rhodobacter sphaeroides

Chemotaxis is one of the best characterised signalling systems in biology. It is the mechanism by which bacteria move towards optimal environments and is implicated in biofilm formation, pathogenesis and symbiosis. The properties of the bacterial chemosensory response have been described in detail for the single chemosensory pathway of Escherichia coli. We have characterised the properties of the chemosensory response of Rhodobacter sphaeroides, an -proteobacterium with multiple chemotaxis pathways, under two growth conditions allowing the effects of protein expression levels and cell architecture to be investigated. Using tethered cell assays we measured the responses of the system to step changes in concentration of the attractant propionate and show that, independently of the growth conditions, R. sphaeroides is chemotactic over at least five orders of magnitude and has a sensing profile following Weber’s law. Mathematical modelling also shows that, like E. coli, R. sphaeroides is capable of showing Fold-Change Detection (FCD). Our results indicate that general features of bacterial chemotaxis such as the range and sensitivity of detection, adaptation times, adherence to Weber’s law and the presence of FCD may be integral features of chemotaxis systems in general, regardless of network complexity, protein expression levels and cellular architecture across different species

Package R copula : "Multivariate dependence with copulas", version 0.9-7

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Détermination expérimentale des atomes métastables d'argon et de néon à l'intérieur d'une cathode creuse fonctionnant en régime d'arc

The concentrations of metastable atoms of argon and neon in a low pressure arc discharge are measured. Under similar conditions of performance of gas discharge, the 3P2 metastable neon concentrations are about 30 times higher than the argon concentrations. The experimental results found in argon are in good agreement with previous theoretical predictions.Les concentrations d'atomes métastables d'argon et de néon sont mesurées à l'intérieur du canal cathodique d'une décharge d'arc à basse pression. Dans les conditions de fonctionnement de l'arc analogues, les niveaux métastables 3P2 du néon sont environ 30 fois plus peuplés que ceux de l'argon. Les résultats expérimentaux trouvés dans l'argon sont en bon accord avec des précédents résultats théoriques

Nonparametric rank-based tests of bivariate extreme-value dependence

cited By (since 1996)9International audienceA new class of tests of extreme-value dependence for bivariate copulas is proposed. It is based on the process comparing the empirical copula with a natural nonparametric rank-based estimator of the unknown copula under extreme-value dependence. A multiplier technique is used to compute approximate p-values for several candidate test statistics. Extensive Monte Carlo experiments were carried out to compare the resulting procedures with the tests of extreme-value dependence recently studied in Ben Ghorbal et al. (2009) [1] and Kojadinovic and Yan (2010) [19]. The finite-sample performance study of the tests is complemented by local power calculations. © 2010 Elsevier Inc