Nonadditivity of Polymeric and Charged Surface Interactions: Consequences for Doped Lamellar Phases

We explore theoretically the modifications to the interactions between charged surfaces across an ionic solution caused by the presence of dielectric polymers. Although the chains are neutral, the polymer physics and the electrostatics are coupled; the intra-surface electric fields polarise any low permittivity species (e.g., polymer) dissolved in a high permittivity solvent (e.g., water). This coupling enhances the polymer depletion from the surfaces and increases the screening of electrostatic interactions with respect to a model which treats polymeric and electrostatic effects as independent. As a result, the range of the ionic contribution to the osmotic interaction between surfaces is decreased, while that of the polymeric contribution is increased. These changes modify the total interaction in a nonadditive manner. Building on the results for parallel surfaces, we investigate the effect of this coupling on the phase behaviour of polymer-doped smectics.Comment: 29 pages, 11 figures, v2: minor corrections added, published version available at http://dx.doi.org/10.1021/la050173

Water temperature modeling in the Garonne River (France)

Stream water temperature is one of the most important parameters for water quality and ecosystem studies. Temperature can influence many chemical and biological processes and therefore impacts on the living conditions and distribution of aquatic ecosystems. Simplified models such as statistical models can be very useful for practitioners and water resource management. The present study assessed two statistical models – an equilibrium-based model and stochastic autoregressive model with exogenous inputs – in modeling daily mean water temperatures in the Garonne River from 1988 to 2005. The equilibrium temperature-based model is an approach where net heat flux at the water surface is expressed as a simpler form than in traditional deterministic models. The stochastic autoregressive model with exogenous inputs consists of decomposing the water temperature time series into a seasonal component and a short-term component (residual component). The seasonal component was modeled by Fourier series and residuals by a second-order autoregressive process (Markov chain) with use of short-term air temperatures as exogenous input. The models were calibrated using data of the first half of the period 1988–2005 and validated on the second half. Calibration of the models was done using temperatures above 20 ◦C only to ensure better prediction of high temperatures that are currently at stake for the aquatic conditions of the Garonne River, and particularly for freshwater migrating fishes such as Atlantic Salmon (Salmo salar L.). The results obtained for both approaches indicated that both models performed well with an average root mean square error for observed temperatures above 20 ◦C that varied on an annual basis from 0.55 ◦C to 1.72 ◦C on validation, and good predictions of temporal occurrences and durations of three temperature threshold crossings linked to the conditions of migration and survival of Atlantic Salmon

Le progrès technique de la procédure civile

9 pagesNational audienceWhat are the conditions under which civil action may be technically perfect?Dans quelles conditions peut-on parler d'un progrès technique de la procédure civile

A genome-wide scan for genes under balancing selection in Drosophila melanogaster

In the history of population genetics balancing selection has been considered as an important evolutionary force, yet until today little is known about its abundance and its effect on patterns of genetic diversity. Several well-known examples of balancing selection have been reported from humans, mice, plants, and parasites. However, only very few systematic studies have been carried out to detect genes under balancing selection. We performed a genome scan in Drosophila melanogaster to find signatures of balancing selection in a derived (European) and an ancestral (African) population. We screened a total of 34 genomes searching for regions of high genetic diversity and an excess of SNPs with intermediate frequency. In total, we found 186 candidate genes: 141 in the European population and 45 in the African one, with only three genes shared between both populations. The difference between both populations is mainly due to a striking excess of candidate genes on the European X chromosome. For the European population, many GO terms are enriched including a main group of which many genes are related to cell morphogenesis involved in differentiation. Furthermore, some of the top genes we identified are involved in innate immunity. However, only two GO terms are found in the African population. Our results revealed evidence of genes under balancing selection in European and African populations. More candidate genes, in particular on the X chromosome, have been found in the European population. They are involved in many different functions

Gyrotactic swimmer dispersion in pipe flow: testing the theory

Suspensions of microswimmers are a rich source of fascinating new fluid mechanics. Recently we predicted the active pipe flow dispersion of gyrotactic microalgae, whose orientation is biased by gravity and flow shear. Analytical theory predicts that these active swimmers disperse in a markedly distinct manner from passive tracers (Taylor dispersion). Dispersing swimmers display non-zero drift and effective diffusivity that is non-monotonic with Péclet number. Such predictions agree with numerical simulations, but hitherto have not been tested experimentally. Here, to facilitate comparison, we obtain new solutions of the axial dispersion theory accounting both for swimmer negative buoyancy and a local nonlinear response of swimmers to shear, provided by two alternative microscopic stochastic descriptions. We obtain new predictions for suspensions of the model swimming alga Dunaliella salina, whose motility and buoyant mass we parametrise using tracking video microscopy. We then present a new experimental method to measure gyrotactic dispersion using fluorescently stained D. salina and provide a preliminary comparison with predictions of a non-zero drift above the mean flow for each microscopic stochastic description. Finally, we propose further experiments for a full experimental characterisation of gyrotactic dispersion measures and discuss the implications of our results for algal dispersion in industrial photobioreactors