Micro-arcsecond light bending by Jupiter

The detectors designed for Gaia, the next ESA space astrometry mission to be launched in 2011, will allow to observe repeatedly stars very close to Jupiter's limb. This will open a unique opportunity to test General Relativity by performing many Eddington-like experiments through the comparison between the pattern of a starfield observed with or without Jupiter. We have derived the main formulas relevant for the monopole and quadrupole light deflection by an oblate planet and developed a simulator to investigate the processing of the Gaia astrometric observation in the vicinity of the planet. The results show that such an experiment carried out with the Gaia data will provide a new fully independent determination of the PPN parameter gamma by means of differential astrometric measurements and, more importantly, for the first time will evidence the bending effect due to the quadrupole moment with a 3-sigma confidence level. Given the accuracy of the experiment for the monopole deflection, this will permit to test alternative modelling of the light bending by moving masses.Comment: 22 pages, 16 figures. submitted to Class. Quantum Gra

Recommendations for the quantitative analysis of landslide risk

This paper presents recommended methodologies for the quantitative analysis of landslide hazard, vulnerability and risk at different spatial scales (site-specific, local, regional and national), as well as for the verification and validation of the results. The methodologies described focus on the evaluation of the probabilities of occurrence of different landslide types with certain characteristics. Methods used to determine the spatial distribution of landslide intensity, the characterisation of the elements at risk, the assessment of the potential degree of damage and the quantification of the vulnerability of the elements at risk, and those used to perform the quantitative risk analysis are also described. The paper is intended for use by scientists and practising engineers, geologists and other landslide experts

Iron Limitation Modulates Ocean Acidification Effects on Southern Ocean Phytoplankton Communities

The potential interactive effects of iron (Fe) limitation and Ocean Acidification in the Southern Ocean (SO) are largely unknown. Here we present results of a long-term incubation experiment investigating the combined effects of CO2 and Fe availability on natural phytoplankton assemblages from the Weddell Sea, Antarctica. Active Chl a fluorescence measurements revealed that we successfully cultured phytoplankton under both Fe-depleted and Fe-enriched conditions. Fe treatments had significant effects on photosynthetic efficiency (Fv/Fm; 0.3 for Fe-depleted and 0.5 for Fe-enriched conditions), non-photochemical quenching (NPQ), and relative electron transport rates (rETR). pCO2 treatments significantly affected NPQ and rETR, but had no effect on Fv/Fm. Under Fe limitation, increased pCO2 had no influence on C fixation whereas under Fe enrichment, primary production increased with increasing pCO2 levels. These CO2-dependent changes in productivity under Fe-enriched conditions were accompanied by a pronounced taxonomic shift from weakly to heavily silicified diatoms (i.e. from Pseudo-nitzschia sp. to Fragilariopsis sp.). Under Fe-depleted conditions, this functional shift was absent and thinly silicified species dominated all pCO2 treatments (Pseudo-nitzschia sp. and Synedropsis sp. for low and high pCO2, respectively). Our results suggest that Ocean Acidification could increase primary productivity and the abundance of heavily silicified, fast sinking diatoms in Fe-enriched areas, both potentially leading to a stimulation of the biological pump. Over much of the SO, however, Fe limitation could restrict this possible CO2 fertilization effect