Crystal structure, electronic, and magnetic properties of the bilayered rhodium oxide Sr3Rh2O7

The bilayered rhodium oxide Sr3Rh2O7 was synthesized by high-pressure and high-temperature heating techniques. The single-phase polycrystalline sample of Sr3Rh2O7 was characterized by measurements of magnetic susceptibility, electrical resistivity, specific heat, and thermopower. The structural characteristics were investigated by powder neutron diffraction study. The rhodium oxide Sr3Rh2O7 [Bbcb, a = 5.4744(8) A, b = 5.4716(9) A, c = 20.875(2) A] is isostructural to the metamagnetic metal Sr3Ru2O7, with five 4d electrons per Rh, which is electronically equivalent to the hypothetic bilayered ruthenium oxide, where one electron per Ru is doped into the Ru-327 unit. The present data show the rhodium oxide Sr3Rh2O7 to be metallic with enhanced paramagnetism, similar to Sr3Ru2O7. However, neither manifest contributions from spin fluctuations nor any traces of a metamagnetic transition were found within the studied range from 2 K to 390 K below 70 kOe.Comment: To be published in PR

Towards a better characterisation of deep-diving whales’ distributions by using prey distribution model outputs?

In habitat modelling, environmental variables are assumed to be proxies of lower trophic levels distribution and by extension, of marine top predator distributions. More proximal variables, such as potential prey fields, could refine relationships between top predator distributions and their environment. In situ data on prey distributions are not available over large spatial scales but, a numerical model, the Spatial Ecosystem And POpulation DYnamics Model (SEAPODYM), provides simulations of the biomass and production of zooplankton and six functional groups of micronekton at the global scale. Here, we explored whether generalised additive models fitted to simulated prey distribution data better predicted deepdiver densities (here beaked whales Ziphiidae and sperm whales Physeter macrocephalus) than models fitted to environmental variables. We assessed whether the combination of environmental and prey distribution data would further improve model fit by comparing their explanatory power. For both taxa, results were suggestive of a preference for habitats associated with topographic features and thermal fronts but also for habitats with an extended euphotic zone and with large prey of the lower mesopelagic layer. For beaked whales, no SEAPODYM variable was selected in the best model that combined the two types of variables, possibly because SEAPODYM does not accurately simulate the organisms on which beaked whales feed on. For sperm whales, the increase model performance was only marginal. SEAPODYM outputs were at best weakly correlated with sightings of deep-diving cetaceans, suggesting SEAPODYM may not accurately predict the prey fields of these taxa. This study was a first investigation and mostly highlighted the importance of the physiographic variables to understand mechanisms that influence the distribution of deep-diving cetaceans. A more systematic use of SEAPODYM could allow to better define the limits of its use and a development of the model that would simulate larger prey beyond 1,000 m would probably better characterise the prey of deep-diving cetaceans.En prens

Morphological discrimination of Aphis gossypii (Hemiptera : Aphididae) populations feeding on Compositae

Aphis gossypii Glover is a polyphagous aphid pest with a worldwide distribution. However, there is evidence that on a global scale the name A. gossypii is being applied to a number of forms with different life cycles and/or host-plant associations. Morphometric variation of A. gossypii samples from crops and non-cultivated plants in many parts of the world was examined, to determine whether this variation is correlated with the hosts from which the aphids originated. Samples of A. gossypii were collected from Cucurbitaceae and Malvaceae in Europe, and from Compositae in various parts of the world. Morphometric data for 13 parameters measured from 97 clonal lineages (728 specimens) and 27 field-collected samples (313 specimens) were analysed by a series of canonical variates analyses, using the field sample/clonal lineage as grouping factor. Clonal lineages were reared on a common host in controlled conditions to standardize the effect of host and environment on morphology. The analyses provided a clear morphometric separation of the aphids originating from Compositae and those collected on Cucurbitaceae and Malvaceae, regardless of the geographical origin of the aphids and the host plant on which they were reared. This indicates that within A. gossypii there are two widely distributed host races or subspecies with different plant family associations. The taxonomic implications are discussed