6 research outputs found
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