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Concentrations of Cr, Cu, Hg, Pb and Zn have been measured, by atomic absorption spectrophotometry, in the fine fraction (<63 μm) of surface sediments collected in 30 sites in the Palermo Gulf (Sicily, Italy) in order to assess the levels and the spatial distribution of these elements. Enrichment factors calculated with respect to clean areas have been considered to discriminate between levels due to background or to pollution contributions. The sampling stations, which form a grid inside these areas, are characterized by geographic proximity and by the presence of pollution sources. Ratio matching technique along with hierarchical clustering, minimum spanning tree and principal component analysis have been used for the statistical analysis of data, allowing to better describe the spatial distribution of metal levels. Our work allowed to assess the anthropogenic contribution to the pollution of the area under investigation through industrial and domestic wastes, presence of an harbour area and river inflow.

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Within a non-perturbative treatment of the multiphoton multichannel ionisation of helium we show for the first time that the angular distributions of the electrons ejected by elliptically polarised light exhibit the twofold symmetry recently observed experimentally on noble gases and already predicted by the authors for hydrogen. Several fine structures and details of the experimental angular distributions are successfully reproduced; a physical model for such asymmetries is provided, which is also able to explain why several approximations fail in reproducing them.