Surface wave scattering at nonuniform fluid interfaces

Effects of spatially varying interfacial parameters on the propagation of surface waves are studied. These variations can arise from inhomogeneities in coverage of surface active substances such as amphiphillic molecules at the fluid/gas interface. Such variations often occur in phase coexistence regions of Langmuir monolayers. Wave scattering from these surface inhomogeneities are calculated in the limit of small variations in the surface parameters by using the asymptotic form of surface Green's functions in the first order Born approximation. When viscosity and variations in surface elastic moduli become important, modes other than transverse capillary waves can change the characteristics of propagation. Scattering among these modes provides a mechanism for surface wave attenuation in addition to viscous damping on a homogeneous surfactant covered interface. Experimental detection of waves attenuation and scattering is also discussed.Comment: 11 pages; 8 figures on reques

Observations on the helminths of harbour porpoises ( Phocoena phocoena

peer reviewedBetween February 1990 and July 1991, 18 harbour porpoises (Phocoena phocoena) and 248 common guillemots (Uria aalge), found dead along the Belgian and German coasts, were examined for their burden of helminths. A total of three species were found in the guillemots (one cestode, one nematode and one pentastomid), and six species in the porpoises (one trematode, one cestode and four nematodes). Among the guillemots the burden of helminths was not statistically different between juvenile and adult birds. The deaths of the birds were apparently not related to the parasite infections. In contrast, the adult porpoises were more heavily parasitised than the juveniles, except for one young porpoise stranded on the Belgian coast. In the porpoises, four species of parasites had a pathological effect and Torynurus convolutus was responsible for the death of one animal from the Belgian coast and three from the German coast