Propagation of microwaves in pulsar magnetospheres

We discuss the dispersion relation of linearly-polarized waves, propagating along a strong background magnetic field embedded in an electron-positron plasma. The results are then applied to the study of the propagation conditions of coherent curvature radio radiation inside neutron stars magnetospheres, as produced by electric discharges following current pulsar models.     

An Integrated Approach for Realtime Floodmap Forecasting on the Belgian Meuse River

The last important floods of the Meuse river have shown the need to design powerful and real-time forecasting tools. With the support of CESAME and the department of Civil and Environmental Engineering at UCL, the Service of Hydrologic Studies (SETHY) of the Walloon Ministry of Equipment and Transport developed two models. Hydromax and Hydroaxe. These two complementary and user-friendly applications work with the data provided by the measurement network of SETHY (raingauges, water levels, discharge measurements, weir-gate positions). Hydromax produces local river flow forecasting for the main natural tributaries of the Meuse. These predictions are used by Hydroaxe to compute discharge propagation and water levels all along the Meuse. In Hydromax, the predictions are produced by a grey box model which involves two main parts. A nonlinear production function computes the effective rainfall from the mean areal rainfall. This part is based on a conceptual approach, the river basin being modelled as a reservoir. In the second part, a linear ARX (AutoRegressive model with eXtra input) transfer function (black box), describes the superficial runoff of the effective rainfall towards the watershed outlet. This transfer function is used to compute short term river flow predictions. Hydroaxe uses a Preissmann finite difference scheme to solve the Saint-Venant equations of shallow-water, completed with the Exchange Discharge Model describing the momentum exchanges between the main channel and the floodplains. The optimisation of the computation time requires a one-dimensional approach, based on a dense (1 point/m2) and accurate (15 cm in x, y, z) topography provided by SETHY and carried out through an original combination of technologies: swath bathymetry and airborne laser (Lidar). With the help of a GIS (Geographic Information System) and the DTM (Digital Terrain Model), the water levels calculated by Hydroaxe are transformed in flooded areas, fitted for an easy and fast overview of the extent of the flood event.     

Crystal chemistry and evolution of the clinopyroxene in a suite of high pressure ultramafic nodules from the Newer Volcanics of Victoria,Australia

A clinopyroxene suite from lherzolite inclusions associated with the Victorian (Australia) “Newer Volcanics” has been investigated with the aim of understanding the clinopyroxene crystal-chemical response to increasing temperature (e.g. a melting model and/or crystallization processes prevailing at high pressure). The M1 clinopyroxene polyhedron dominates the intracrystalline physical-chemical variations, essentially given by the triple substitution Al^VIFe _M1 ² Ti⁴⁺⇌Cr³⁺ Fe³⁺Mg _M1 ²⁺ corresponding to an increase in the volume of M1 with increasing Mg/Mg+Fe²⁺ (mg) for the clinopyroxene. A relative Ca²⁺ increase in M2 ensures the necessary charge balance. However, Na⁺ occupancy of M2 persists to the highest mg values, i.e. maximum thermal stability, where the volume of M2 is the largest due to Fe _M2 ²⁺ depletion. The variations of M1 and M2 volumes are greater than, and opposite to, the variations in the volume of T (tetrahedron) by factors of ca. 3 and 1.5, respectively. Inclusions with relatively low clinopyroxene content (Mt. Porndon specimens) show distinct intracrystalline variations, essentially reflecting lower Al^VI, i.e. higher volume of M1, and implying a lower pressure regime compared to clinopyroxene-rich analogues (Mt. Leura specimens). The intracrystalline relationships of the Mt. Porndon clinopyroxene suggest that the host peridotite inclusions survived larger degree of mantle melting at shallower depths relative to the Leura analogues.     

Mixed function oxidase activity and cytochrome P-450 forms in black-headed gulls feeding in different areas

The aim of the present study was to evaluate the mixed function oxidase (MFO) system and the forms of supposed cytochrome P-450 in the liver of black-headed gulls (Larus ridibundus) feeding in a lagoon and on a garbage dump. Tissue levels of polychlorinated biphenyls (PCBs) were also determined. Ethoxyresorufin 10-deethylase (EROD) and aldrin epoxidase activities were higher in the dump gulls than in the lagoon gulls. A marked thickening of the proteins in the cytochrome P-450 area, particularly of P-450c and P-450d, was also found in the dump gulls. No relationship was found between MFO activity and tissue chlorinated hydrocarbon levels.     

Experimental study of the coastal thermocline height variations caused by an impulsively applied wind of limited along-shore extent

On the large rotating platform of Grenoble's University, a channel (8×2×0.6 m) has been built, equipped with a wind entrainment simulation effects mechanism. With a local wind, acting over a two-layered ocean, upwelling or downwelling patterns are induced, which are Kelvin-type height variations of the interface; propagating so that, in the northern hemisphere, they leave the coastline to the right of their direction of propagation, and having a profile exponentially decreasing from the coastline towards the open sea. The agreement between these observations and the recently proposed model of Crepon and Richez (1982) is very good at some distance from the excitation zone.However, this model, for its application, is limited to the situation in which the Ekman layer is of the same order of magnitude as the upper layer. Otherwise the oceanographic observations, as well as our observations, show a cross-shore current in the intermediate layer. Near the boundaries of the excitation zone (i.e., the wind zone), such a current is responsible for vortices which cause local upwelling. The model does not account for such local upwelling which is superimposed on the Kelvin-type height variation of the thermocline. These vortices may be explained by consideration of variations of relative vorticity. The experiments also show that a wind perpendicular to the coast may also induce upwelling or downwelling.     

Influence of magma composition and oxygen fugacity on the crystal structure of C2/c clinopyroxenes from a basalt-pantellerite suite

The crystallochemical variations of clinopyroxene in response to changes in f_{O 2} and melt composition have been determined for a basalt-pantellerite suite (Boseti Complex, Main Ethiopian Rift) by crystal structure refinement and microprobe analysis. The pyroxene evolutionary trend has both a “Ca-minimum” and late iron enrichment. During crystallization from basalts to trachytes, clinopyroxene geometry depends mainly on the relationships between T and M2 sites; for example, high SiO₂ activity in the magma causes high Si occupancy in T site, which in turn requires low Ca occupancy in M2 site in order to fulfill the local charge balance requirements. In contrast, clinopyroxene crystallized from acid melts is characterized by high Fe²⁺ (M1) content and therefore by a very large M1 site. Longer 〈M1-O1〉 and M1-O2 bond lengths require shorter T-O1 and T-O2 bond lengths and high Si occupancy in T site. It is concluded that the “Ca-minimum” in the clinopyroxene structure is regarded as the lowest value at which the charge balance requirements are satisfied in a C2/c clinopyroxene structure.