A fast current-driven instability in relativistic collisionless shocks

We report here on a fast current-driven instability at relativistic collisionless shocks, triggered by the perpendicular current carried by the supra-thermal particles as they gyrate around the background magnetic field in the shock precursor. We show that this instability grows faster than any other instability studied so far in this context, and we argue that it is likely to shape the physics of the shock and of particle acceleration in a broad parameter range.Comment: 6 pages, 5 figures -- version to appear in EP

Multidimensional Poverty in Cameroon: Determinants and Spatial Distribution

The study examined the usefulness and relevance of the contingent valuation method (CVM) in community-based (CB) project planning and implementation. To elicit willingness to pay (WTP) values for the restocking of Lake Bamendjim with Tilapia nilotica and Heterotis niloticus fish species, the study used pre-tested questionnaires interviewer-administered to 1,000 randomly selected households in the Bambalang Region of Cameroon.The datawere elicitedwith the conventional referendumdesign and analysed using a referendum model. Empirical findings indicated that about 85% of the sampled households were willing to pay about CFAF1,054 (US$2.1) for the restocking project. This amount was found to be significantly related to the starting price used in the referendum design, household income, the gender of the respondent, the age of the respondent, household poverty status, and previous participation of a household in a community development project.The findings prompted the following recommendations. Firstly, in order to reduce community burden due to cash constraints, it is advisable for the mean estimate obtained for the scheme to be split into four instalments over a year. Secondly, since the success of the scheme largely depends on the governing roles of the scheme, it is further advisable for the community to allowthemanagement of the scheme to be handled by the elderly community members. Finally, it will be important during the financing of the scheme, to levy wealthier household heads an amount sufficient to subsidize poorer household heads who cannot afford to pay the threshold price.

Engagement associatif : ces retraités qui veulent être utiles aux autres...

National audienceCette communication présentée au deuxième congrès de l’Association Française de Sociologie (Bordeaux, 5-8 septembre 2006) fait un panorama de la participation associative des retraités aux débuts des années 2000 (en France), puis cherche à identifier ceux qui, par leur participation associative, ont la volonté d'agir sur leur environnement, proche ou lointain. Ne renonçant pas à certaines formes de militantisme, ils conçoivent leur action de façon altruiste au service de causes qui leur paraissent justes ; ils participent à des actions de solidarité qui dépassent la solidarité familiale intergénérationnelle. Dans cet article, nous qualifions ces retraités d' « engagés solidaires » et cherchons à les comptabiliser

LALNVIEW: a graphical viewer for pairwise sequence alignments

LALNVIEW is a graphical program for visualising local alignments between two sequences (protein or nucleic acids). Sequences are represented by coloured rectangles to give an overall picture of their similarities. LALNVIEW can display sequence features (exon, intron, active site, domain, propeptide, etc.) along with the alignment. When using LALNVIEW through our Web servers, sequence features are automatically extracted from database annotations (SWISS-PROT, GenBank, EMBL or HOVERGEN) and displayed with the alignment. LALNVIEW is a useful tool for analysing pairwise sequence alignments and for making the link between sequence homology and what is known about the structure or function of sequences. LALNVIEW executables for UNIX, Macintosh and PC computers are freely available from our server (http://expasy.hcuge.ch/sprot/lalnview.html

From the Phan-Thien Tanner / Oldroyd-B non-Newtonian model to the double shear thining Rabinowisch thin film model

International audienceIn this paper, an asymptotic expansion is used to derive a description of Phan-Tien Tanner~/ Oldroyd-B flows in the thin film situation without the classical "Upper Convective Maxwell'' assumption. We begin with a short presentation of the Phan-Thien Tanner~/ Oldroyd-B models which introduce viscoelastic effects in a solute-solvant mixture. The three dimensional flow is described using five parameters, namely the Deborah number (or the relaxation parameter), the viscosity ratio, the bulk fluid viscosity, the material slip parameter related to the "convected derivative'' and an elongation number. Then we focus on the thin film assumption and the related asymptotic analysis that allows us to derive a reduced model. A perturbation procedure for "not too small'' values of the elongation number allows us to obtain further results such as an asymptotic "effective viscosity / shear rate'' law which appears to be a perturbation of the double Rabinowisch model whose parameters are completely defined by those of the original three dimensional model. And last a numerical procedure is proposed based on a penalized Uzawa method, to compute the corresponding solution. This algorithm can also be used for any generalized double Newtonian shear thinning Carreau law

Viscoelastic fluids in a thin domain

The present paper deals with viscoelastic flows in a thin domain. In particular, we derive and analyse the asymptotic equations of the Stokes-Oldroyd system in thin films (including shear effects). We present a numerical method which solves the corresponding problem and present some related numerical tests which evidence the effects of the elastic contribution on the flow