L'hévéa en association avec les cultures pérennes, fruitières ou forestières dans les agroforêts de type simple ou complexe. Synthèse bibliographique

Alors que la monoculture est le fait des grandes exploitations industrielles, les petits paysans accordent souvent l'hévéa aux systèmes de cultures déjà existants et pratiquent généralement des associations culturales. Ils utilisent des systèmes de cultures que l'on peut qualifier de systèmes agroforestiers simples (hévéa associé à un nombre limité de cultures pérennes ou annuelles) ou complexes (hévéa associé à plusieurs espèces dont l'ensemble forme plusieurs strates de végétation). Le système agroforestier complexe le plus connu est le "jungle rubber ". Il s'agit, en Indonésie, d'un système de culture extensif où la forêt secondaire est associée à l'hévéa. Nous définirons plus précisément ces termes dans la première partie de ce document consacrée à une typologie des systèmes de cultures hévéicoles existants. Si l'association culturale utilisant des cultures vivrières en intercalaire durant la phase immature de l'hévéa est un type de valorisation de l'espace et du travail bien développé, favorisé dans les projets hévéicoles récents et faisant l'objet de nombreuses études il n'en va pas de même pour les associations incluant des cultures pérennes ou forestières. Pourtant un certain nombre de petits planteurs traditionnels pratiquent depuis longtemps ce système de culture en particulier en Indonésie. C'est ce constat qui a motivé la présente recherche. L'objectif est de faire le point sur les associations culturales pratiquées ou recommandées entre l'hévéa et les cultures pérennes ou forestières, de réaliser une typologie de ces systèmes et de dégager l'intérêt de telles pratiques ainsi que les perspectives de recherche. (Résumé d'auteur

Antiferro-quadrupolar correlations in the quantum spin ice candidate Pr2Zr2O7

We present an experimental study of the quantum spin ice candidate pyrochlore coumpound \przr\ by means of magnetization measurements, specific heat and neutron scattering up to 12 T and down to 60 mK. When the field is applied along the $[111]$ and $[1\bar{1}0]$ directions, ${\bf k}=0$ field induced structures settle in. We find that the ordered moment rises slowly, even at very low temperature, in agreement with macroscopic magnetization. Interestingly, for $H \parallel [1\bar{1}0]$, the ordered moment appears on the so called $\alpha$ chains only. The spin excitation spectrum is essentially {\it inelastic} and consists in a broad flat mode centered at about 0.4 meV with a magnetic structure factor which resembles the spin ice pattern. For $H \parallel [1\bar{1}0]$ (at least up to 2.5 T), we find that a well defined mode forms from this broad response, whose energy increases with $H$, in the same way as the temperature of the specific heat anomaly. We finally discuss these results in the light of mean field calculations and propose a new interpretation where quadrupolar interactions play a major role, overcoming the magnetic exchange. In this picture, the spin ice pattern appears shifted up to finite energy because of those new interactions. We then propose a range of acceptable parameters for \przr\, that allow to reproduce several experimental features observed under field. With these parameters, the actual ground state of this material would be an antiferroquadrupolar liquid with spin-ice like excitations

Etude en sciences sociales de grandes expéditions naturalistes contemporaines françaises,

social studies of sciences; Biodiversity inventories; systematicsInternational audienceCet article présente le projet de recherche interdisciplinaire, Expebiodiv visant à réaliser une étude interdisciplinaire des expeditions naturalistes contemporaines. Le cas étudié est celui du projet "La planète revisitée" qui est lancé pour 10 ans par le Museum d'Histoires Naturelle de Paris et l'ONG Pronatura International

Long term highly saturated fat diet does not induce NASH in Wistar rats

BACKGROUND: Understanding of nonalcoholic steatohepatitis (NASH) is hampered by the lack of a suitable model. Our aim was to investigate whether long term high saturated-fat feeding would induce NASH in rats. METHODS: 21 day-old rats fed high fat diets for 14 weeks, with either coconut oil or butter, and were compared with rats feeding a standard diet or a methionine choline-deficient (MCD) diet, a non physiological model of NASH. RESULTS: MCDD fed rats rapidly lost weight and showed NASH features. Rats fed coconut (86% of saturated fatty acid) or butter (51% of saturated fatty acid) had an increased caloric intake (+143% and +30%). At the end of the study period, total lipid ingestion in term of percentage of energy intake was higher in both coconut (45%) and butter (42%) groups than in the standard (7%) diet group. No change in body mass was observed as compared with standard rats at the end of the experiment. However, high fat fed rats were fattier with enlarged white and brown adipose tissue (BAT) depots, but they showed no liver steatosis and no difference in triglyceride content in hepatocytes, as compared with standard rats. Absence of hepatic lipid accumulation with high fat diets was not related to a higher lipid oxidation by isolated hepatocytes (unchanged ketogenesis and oxygen consumption) or hepatic mitochondrial respiration but was rather associated with a rise in BAT uncoupling protein UCP1 (+25–28% vs standard). CONCLUSION: Long term high saturated fat feeding led to increased "peripheral" fat storage and BAT thermogenesis but did not induce hepatic steatosis and NASH

Experimental infection with Mycoplama galliseptioum in chikens, turkeys, laying hens and chick embryos

Le pouvoir pathogène de la souche Mycoplasma gallisepticum R est exacerbé par 10 passages successifs sur poulets exempts d’organismes patho gènes spécifiés (EOPS). La souche réisolée MGR P10 est inoculée à des pou lets et des dindonneaux EOPS, des poules pondeuses conventionnelles et des embryons de poule de 19 jours d’incubation. Les symptômes et lésions observés chez ces hôtes révèlent le tropisme respiratoire et le fort pouvoir pathogène de la souche MGR P10. Un léger décrochement de la courbe de ponte est enregistré chez les poules pondeuses et une mortalité impor tante et rapide est observée après inoculation à l’embryon de 19 jours. Le pouvoir de diffusion de la souche est également mis en évidence.The Mycoplasma gallisepticum R strain is serially passaged ten times through specific pathogen free (SPF) chickens in order to exacerbate its potential pathogenicity. The recovered MGR P10 strain is inoculated in SPF chickens and turkeys, commercial laying fowl and nineteen-day-old chick embryos. The inoculation induces general and respiratory symptoms in the different hosts. Mortality occurs in the chicks hatched from inoculated embryos. A drop in egg production is observed in the laying hens. The strain is also shown to be able to spread from bird to bird

Solvent contribution to the stability of a physical gel characterized by quasi-elastic neutron scattering

The dynamics of a physical gel, namely the Low Molecular Mass Organic Gelator {\textit Methyl-4,6-O-benzylidene-$\alpha$ -D-mannopyranoside ($\alpha$-manno)} in water and toluene are probed by neutron scattering. Using high gelator concentrations, we were able to determine, on a timescale from a few ps to 1 ns, the number of solvent molecules that are immobilised by the rigid network formed by the gelators. We found that only few toluene molecules per gelator participate to the network which is formed by hydrogen bonding between the gelators' sugar moieties. In water, however, the interactions leading to the gel formations are weaker, involving dipolar, hydrophobic or $\pi-\pi$ interactions and hydrogen bonds are formed between the gelators and the surrounding water. Therefore, around 10 to 14 water molecules per gelator are immobilised by the presence of the network. This study shows that neutron scattering can give valuable information about the behaviour of solvent confined in a molecular gel.Comment: Langmuir (2015