Peser la terre, peser les mondes de la «balance à peser les mondes» de Cavendish (1798) aux repetitions didactiques a l'université

An historical overview is given from the first XVIIIth century experiments «to determine the density of the Earth» to the recent determinations of the newtonian «big G» constant. The dominant role played in this story by the gravitational torsion balance —including recent measurements— is emphasized through a detailed study of Cavendish’s gravitational balance and its important technical, methodological and publishing innovations. In the framework of our «historical experiments » approach of Science and History of Science Teaching, the use of a modern pedagogical version of the Cavendish balance in a university classroom is described. The relationship of the «weighing the Earth» challenge with Astronomy is finally shortly evoked

Nucleation and growth of single wall carbon nanotubes

The nucleation and growth of single wall carbon nanotubes from a carbon-saturated catalytic particle surrounded by a single sheet of graphene is described qualitatively by using a very restricted number of elementary processes, namely Stone-Wales defects and carbon bi-interstitials. Energies of the different configurations are estimated by using a Tersoff energy minimization scheme. Such a description is compatible with a broad variety of size or helicity of the tubes. Several mechanisms of growth of the embryos are considered: one of them is made more favourable when the tubes embryos are arranged in an hexagonal network in the graphene plane. All the proposed mechanisms can be indefinitely repeated for the growth of the nanotubes.Comment: Solid state communications, in pres

Le Mot d’Or de la Traduction francophone

Une naissance tardive, mais sous d’heureux auspices ! Né en 2003, Le Mot d’Or de la Traduction francophone avait été précédé, dès 1989, par les Mots d’Or des apprenants et des professionnels décernés par notre association Actions pour promouvoir le français des affaires (APFA), placée sous le patronage de la Délégation générale à la langue française et aux langues de France (DGLFLF), de l’Organisation internationale de la Francophonie (OIF) et de l’Union internationale de la Presse francophon..

Electron Spin Dynamics of the Superconductor CaC6 probed by ESR

Conduction Electron Spin Resonance (CESR) was measured on a thick slab of CaC6 in the normal and superconducting state. A surprising increase of the CESR intensity below Tc can not be explained by the theoretically predicted change in spin susceptibility. It is interpreted as a vortex enhanced increase of the effective skin depth. Non-linear microwave absorption measurements in the superconducting state describe CaC6 as an anisotropic BCS superconductor. The study of the spin dynamics in the superconducting state and the discovery of the vortex enhanced increase of the skin depth poses a challenge to theory to provide a comprehensive description of the observed phenomena. CESR data in the normal state characterize CaC6 as a three-dimensional (3D) metal. The analysis suggests that the scattering of conduction electrons is dominated by impurities and supports the description of superconductivity in the dirty limit.Comment: 4 pages, 3 figure

Reconstitution de l’expérience des liqueurs de Blaise Pascal

Au tout début du XXe siècle, Félix Mathieu avait écorné l’image de Blaise Pascal en l’accusant d’avoir produit un faux pour s’attribuer les mérites de l’hypothèse des effets de la pression atmosphérique concernant l’expérience du Puy de Dôme. Félix Mathieu avait d’autre part remis en cause le témoignage de Roberval sur l’expérience des liqueurs faite par Pascal à Rouen, pour laquelle il aurait utilisé des tubes longs de 46 pieds (environ 15m) remplis d’eau et de vin. Selon lui, Pascal n’aurai..

Etude de la prévalence des infections à trypanosomes chez différentes espèces d'animaux sauvages du parc national de la Comoé en Côte d'Ivoire : résultats préliminaires sur la comparaison de trois méthodes de diagnostic

Si de nombreuses études portent sur la trypanosomoses chez les animaux domestiques, peu de rcherches ont été effectuées sur la faune sauvage d'Afrique occidentale. Les résultats préliminaires sur la comparaison de trois méthodes de dépistages des trypanosomes : le frottis de sang, la détection des antigènes circulants par le technique ELISA et l'isolement in vitro des trypanosomes par le "kit for in vitro isolation" (KIVI), chez les animaux sauvages du parc national de la Comoé en Côte d'ivoire, ont permis de confirmer l'existence de cette infection chez ces animaux sans toutefois identifier de façon précise les espèces de trypanosomes en cause. Des investigations ultérieures permettront d'affiner l'identification des souches de parasites isolées par KIVI. (Résumé d'auteur

Sustainable peeling of Kapok Tree (Ceiba pentandra) bark by the chimpanzees (Pan troglodytes verus) of Comoé National Park, Ivory Coast

Primates often consume either bark or cambium (inner bark) as a fallback food to complete their diet during periods of food scarcity. Wild chimpanzees exhibit great behavioral diversity across Africa, as studies of new populations frequently reveal. Since 2014, we have been using a combination of camera traps and indirect signs to study the ecology and behavior of wild chimpanzees (Pan troglodytes verus) in Comoé National Park, Ivory Coast, to document and understand the behavioral adaptations that help them to survive in a savanna–forest mosaic landscape. We found that Comoé chimpanzees peel the bark of the buttresses of kapok tree (Ceiba pentandra) trees to eat the cambium underneath. Individuals of all sex/age classes across at least six neighboring communities peeled the bark, but only during the late rainy season and beginning of the dry season, when cambium may represent an important fallback food. Baboons (Papio anubis) also target the same trees but mainly eat the bark itself. Most of the bark-peeling wounds on Ceiba trees healed completely within 2 years, seemingly without any permanent damage. We recorded chimpanzees visiting trees in early stages of wound recovery but leaving them unpeeled. Only 6% of peeled trees (N = 53) were reexploited after a year, suggesting that chimpanzees waited for the rest of the trees to regrow the bark fully before peeling them again, thus using them sustainably. Many human groups of hunter-gatherers and herders exploited cambium sustainably in the past. The observation that similar sustainable bark-peeling behavior evolved in both chimpanzees and humans suggests that it has an important adaptive value in harsh environments when other food sources become seasonally scarce, by avoiding the depletion of the resource and keeping it available for periods of scarcity

A new method to determine the diet of pygmy hippopotamus in Taï National Park, Côte d’Ivoire

This research was funded by “Fond des donations” of the University of Neuchâtel and the “Willy Müller Award” of the Centre Suisse de Recherches Scientifiques en Côte d’Ivoire.Diet determination of endangered species is an essential element in defining successful conservation strategies and optimising captive breeding programmes. In this study, we developed a new diet identification system, derived from standard faecal analysis, to determine the diet of an elusive and endangered herbivore, the pygmy hippopotamus (Choeropsis liberiensis). We collected faecal samples from 10 free-ranging individuals covering a combined home range area of about 50 km2 in Taï National Park, Côte d’Ivoire. In subsequent laboratory analyses, we extracted a large number of leaf epidermis fragments from spatially separated faecal samples and compared them with a reference plant database. Using Multiple Correspondence Analysis (MCA) of epidermis fragments combined with direct visual inspection, we identified the most frequently consumed plant species, which revealed that pygmy hippopotami qualified as intermediate feeders. Their diet was based on at least seven species of monocotyledonae, dicotyledonae and fern groups, with a preference for a small number of other plant species. We evaluate the merit of our method and discuss our findings for developing effective conservation and captive breeding strategies in an endangered species with a wild population of less than 2500 adult individuals.PostprintPeer reviewe