The effect of multiple paternity on genetic diversity during and after colonisation

In metapopulations, genetic variation of local populations is influenced by the genetic content of the founders, and of migrants following establishment. We analyse the effect of multiple paternity on genetic diversity using a model in which the highly promiscuous marine snail Littorina saxatilis expands from a mainland to colonise initially empty islands of an archipelago. Migrant females carry a large number of eggs fertilised by 1 - 10 mates. We quantify the genetic diversity of the population in terms of its heterozygosity: initially during the transient colonisation process, and at long times when the population has reached an equilibrium state with migration. During colonisation, multiple paternity increases the heterozygosity by 10 - 300 % in comparison with the case of single paternity. The equilibrium state, by contrast, is less strongly affected: multiple paternity gives rise to 10 - 50 % higher heterozygosity compared with single paternity. Further we find that far from the mainland, new mutations spreading from the mainland cause bursts of high genetic diversity separated by long periods of low diversity. This effect is boosted by multiple paternity. We conclude that multiple paternity facilitates colonisation and maintenance of small populations, whether or not this is the main cause for the evolution of extreme promiscuity in Littorina saxatilis.Comment: 7 pages, 5 figures, electronic supplementary materia

Analytical and numerical stability analysis of Soret-driven convection in a horizontal porous layer

We present an analytical and numerical stability analysis of Soret-driven convection in a porous cavity saturated by a binary fluid. Both the mechanical equilibrium solution and the monocellular flow obtained for particular ranges of the physical parameters of the problem are considered. The porous cavity, bounded by horizontal infinite or finite boundaries, is heated from below or from above. The two horizontal plates are maintained at different constant temperatures while no mass flux is imposed. The influence of the governing parameters and more particularly the role of the separation ratio, characterizing the Soret effect and the normalized porosity, are investigated theoretically and numerically. From the linear stability analysis, we find that the equilibrium solution loses its stability via a stationary bifurcation or a Hopf bifurcation depending on the separation ratio and the normalized porosity of the medium. The role of the porosity is important, when it decreases, the stability of the equilibrium solution is reinforced. For a cell heated from below, the equilibrium solution loses its stability via a stationary bifurcation when the separation ratio >0(Le,), while for 0, while a stationary or an oscillatory bifurcation occurs if mono the monocellular flow loses stability via a Hopf bifurcation. As the Rayleigh number increases, the resulting oscillatory solution evolves to a stationary multicellular flow. For a cell heated from above and <0, the monocellular flow remains linearly stable. We verified numerically that this problem admits other stable multicellular stationary solutions for this range of parameters

La diversité génétique chez les plantes cultivées des régions tropicales = Genetic variability in tropical crops

Les activités de l'ORSTOM sur les ressources génétiques concernent une dizaine d'espèces tropicales d'intérêt agricole principalement en Afrique. Les chercheurs ont tout d'abord contribué à l'enrichissement des banques de gènes mondiales en matériel végétal original ; près de 20 000 échantillons sont conservés par le Centre ORSTOM de Montpellier. L'analyse de la diversité génétique des espèces a été privilégiée afin de connaître sa structuration et de comprendre son organisation dans son contexte évolutif (domestication, migration, sélection). Deux évolutions fondamentales ont guidé cette approche de la diversité génétique : 1) les concepts de "pools géniques" et de "complexe d'espèces" pour rendre compte des rapports entre les espèces cultivées et les formes apparentées sauvages ; 2) l'étude du polymorphisme moléculaire des protéines et de l'ADN, source quasi illimitée de marqueurs génétiques, dans leur majorité sélectivement neutres. Ainsi, la description de l'organisation génétique des espèces collectées a été réalisée et illustrée par l'exemple des riz. Afin de développer la conservation et la gestion des ressources génétiques, les chercheurs ORSTOM participent au développement de méthodologies adaptées : 1) la constitution de collections réduites (core collection) ; 2) la cryoconservation d'espèces à graines récalcitrantes et/ou à multiplication végétative ; 3) la conservation #in situ$ des formes spontanées dans leurs écosystèmes et des formes cultivées dans leurs agrosystèmes. Les ressources génétiques conservées prennent de la valeur ajoutée par leur évaluation, leur gestion et leur utilisation en sélection. Quelques-unes des perspectives de valorisation des recherches ORSTOM sont présentées, en particulier l'emploi de marqueurs moléculaires cartographiés dans le pilotage de l'introgression des caractères d'intérêt agronomique. (Résumé d'auteur

SECM study of a chromium-free anticorrosion adhesion primer for aluminum 2024

International audienceHexavalent chromium, largely used for anticorrosion surface treatments of aluminum in aeronautics, will soon be completely banned due to its high toxicity (REACH regulation). Looking for an innovative solution, regarding both anticorrosion and adhesion properties, a chromium free replacement treatment directly inspired by the diazonium chemistry has been developed by the CEA (LICSEN). The evolution of the surface electrochemical properties was followed before and after grafting by means of scanning electrochemical microscopy (SECM). These studies showed that the native aluminum oxide layer is etched during the organic grafting step, which is performed in sulfuric acid. SECM also evidenced that the polymeric grafted film is porous enough to allow the reconstruction of this native aluminum oxide layer after the treatment. On the strength of these results, we decided to extend the thickness of the aluminum oxide layer by an anodization treatment, in the idea that Al$_2$O$_3$ could be formed through the organic layer without altering it. In that purpose, SECM was used to characterize the films and allow the determination of the best parameters for the organic coating (concentration, immersion time, diazonium function, rinsing, cleaning, additives…) and for the anodization process (duration, applied tension…). Thus, bi-functional coatings were obtained, giving very satisfying results both in terms of corrosion protection and adhesion with painting. This simple and low cost process has been patented . It validates standardized tests and could be swiftly industrializable

Об'єктивність і правда в журналістиці

Головним принципом журналістики с не об’єктивність, а правда. Критерієм правди є справедливість, сприйнята як дотримання норм загальнолюдської моралі й орієнтація на ідеал повноцінного національного розвитку.Главным принципом журналистики является не объективность, а правда. Критерий правды - справедливость, воспринятая как соблюдение норм общечеловеческой морали и ориентация на идеал полноценного национального развития.The main principle of journalism is truth, not objectivity. Truth criterion is fairness perceived as observance of moral standard common to all mankind and orientation on an ideal of full national development

Radio Detection of Cosmic Ray Air Showers with Codalema

Studies of the radio detection of Extensive Air Showers is the goal of the demonstrative experiment CODALEMA. Previous analysis have demonstrated that detection around $5.10^{16}$ eV was achieved with this set-up. New results allow for the first time to study the topology of the electric field associated to EAS events on a event by event basis.Comment: 6 pages, 4 figures Proceedings of the Rencontres de Moriond, Very High Energy Phenomena in the Universe, La Thuile, Italy (March 12-19, 2005

Radio Detection of Extensive Air Showers with CODALEMA

The principle and performances of the CODALEMA experimental device, set up to study the possibility of high energy cosmic rays radio detection, are presented. Radio transient signals associated to cosmic rays have been identified, for which arrival directions and shower's electric field topologies have been extracted from the antenna signals. The measured rate, about 1 event per day, corresponds to an energy threshold around 5.10^16 eV. These results allow to determine the perspectives offered by the present experimental design for radiodetection of UHECR at a larger scale.Comment: 4 pages and 3 figures. To appear in the Proceedings of the 29th ICRC, Pune (2005