Influence de la mortalité des cacaoyers sur la stabilité de la production dans une plantation industrielle

Effect of Cocoa Tree Mortality on Production Stability in a Private Estate. Yields in a 1,674 ha cocoa estate were analysed in Indonesia. The plantation, which was set up between 1981 and 1990 at Ransiki (Papua province), benefited from suitable soil and climatic conditions: good rainfall distribution and rich soils. The planting material comprised hybrids of various origins, Amelonados and local selections. Density measurements inside the plantation revealed a gradual reduction in the number of cocoa trees, from 1,250 at the outset to 835 trees/ha after 21 years. At the same time, overall yields for the same period remained stable. Cocoa tree mortality, which was responsible for the gradual reduction in density, did not affect production; neither did it alter the uniformity of the plant cover in the plots. This situation reflected an increase in tree productivity. The conditions for stabilized cocoa yields appeared to be linked not only to suitable edapho-climatic conditions and limited parasite pressure, but also to the ability of cocoa trees to increase their yields in conditions of decreasing stand due to the natural thining of the original plant population

Fluctuations in Chemical Gelation

We study a chemical gelation model in two dimensions which includes both monomer aggregations and bond fluctuations. Our numerical simulation shows that a sol-gel transition occurs when an initial monomer concentration is above a critical concentration. Fractal aggregates grow until the sol-gel transition occurs. After the gelation, however, bond fluctuations break the fractal structure and a novel inhomogeneous gel fibre network appears instead. A pore size distribution of the inhomogeneous structure shows the existence of hierarchical structures in the gel phase. It is also found that slow dynamics appear near the critical concentration.Comment: 6 pages, 10figure

Pressure-induced structural transitions in MgH2{_2}

The stability of MgH$_2$ has been studied up to 20~GPa using density-functional total-energy calculations. At ambient pressure $\alpha$-MgH${_2}$ takes a TiO$_2$-rutile-type structure. $\alpha$-MgH$_2$ is predicted to transform into $\gamma$-MgH${_2}$ at 0.39~GPa. The calculated structural data for $\alpha$- and $\gamma$-MgH${_2}$ are in very good agreement with experimental values. At equilibrium the energy difference between these modifications is very small, and as a result both phases coexist in a certain volume and pressure field. Above 3.84~GPa $\gamma$-MgH${_2}$ transforms into $\beta$-MgH${_2}$; consistent with experimental findings. Two further transformations have been identified at still higher pressure: i) $\beta$- to $\delta$-MgH${_2}$ at 6.73 GPa and (ii) $\delta$- to $\epsilon$-MgH${_2}$ at 10.26~GPa.Comment: 4 pages, 4 figure

Structure and Thermodynamics of the Mixed Alkali Alanates

The thermodynamics and structural properties of the hexahydride alanates (M2M'AlH6) with the elpasolite structure have been investigated. A series of mixed alkali alanates (Na2LiAlH6, K2LiAlH6 and K2NaAlH6) were synthesized and found to reversibly absorb and desorb hydrogen without the need for a catalyst. Pressure-composition isotherms were measured to investigate the thermodynamics of the absorption and desorption reactions with hydrogen. Isotherms for catalyzed (4 mol% TiCl3) and uncatalyzed Na2LiAlH6 exhibited an increase in kinetics, but no change in the bulk thermodynamics with the addition of a dopant. A structural analysis using synchrotron x-ray diffraction showed that these compounds favor the Fm-3m space group with the smaller ion (M') occupying an octahedral site. These results demonstrate that appropriate cation substitutions can be used to stabilize or destabilize the material and may provide an avenue to improving the unfavorable thermodynamics of a number of materials with promising gravimetric hydrogen densities.Comment: 6 pages, 7 figures,3 tables, submitted to PR

Contrôle du Phomopsis, maladie émergente, en culture de carotte porte-graîne

The first triangular browning umbels caused by Diaporthe angelicae on carrot seed crops were observed in France in 2007. This fungal phytopathogen negatively impacted carrot seed production. Little is known about this fungus. In order to control it in carrot seed production, a better understanding of its life cycle and its epidemiology is required. So, this is the reason why a three-years research project named DIAPOCAR was initiated in 2012. It appears that flower is the main sensitive organ and flowering the most sensitive stage of the umbel. In the field, contaminations are particularly observed during flowering of the umbels of order I and II if the weather is favourable to disease. Field fungicide trials show significant efficacy differences between fungicides and only three of them are efficient against carrot phomopsis. Finally, model simulations with the sunflower phomopsis model are promising and this tool to aid decision-making can be used to apply fungicides only when the weather is favourable to the disease. It should help carrot seed growers to determine the best timing for fungicide applications. Thus, a greater understanding of the biology of this fungus has led to a better control of phomopsis on carrot seed crops

A new mechanism of SOX9 action to regulate PKC expression in the intestine epithelium

International audienceVariations of protein kinase C (PKC) expression greatly influence the proliferation-to-differentiation transition (PDT) of intestinal epithelial cells and might have an important impact on intestinal tumorigenesis. We demonstrate here that the expression of PKCalpha in proliferating intestinal epithelial cells is repressed both in vitro and in vivo by the SOX9 transcription factor. This repression does not require DNA binding of the SOX9 high-mobility group (HMG) domain but is mediated through a new mechanism of SOX9 action requiring the central and highly conserved region of SOXE members. Because SOX9 expression is itself upregulated by Wnt-APC signaling in intestinal epithelial cells, the present study points out this transcription factor as a molecular link between the Wnt-APC pathway and PKCalpha. These results provide a potential explanation for the decrease of PKCalpha expression in colorectal cancers with constitutive activation of the Wnt-APC pathway

Perception of Nuclear Energy and Coal in France and the Netherlands

This study focuses on the perception of large scale application of nuclear energy and coal in the Netherlands and France. The application of these energy-sources and the risks and benefits are judged differently by various group in society. In Europe, France has the highest density of nuclear power plants and the Netherlands has one of the lowest. In both countries scientists and social scientists completed a questionnaire assessing the perception of the large scale application of both energy sources. Furthermore, a number of variables relating to the socio cultural and political circumstances were measured. The results indicate that the French had a higher risk perception and a more negative attitude toward nuclear power than the Dutch. But they also assess the benefits of the use of nuclear power to be higher. Explanations for these differences are discussed