Diffraction of plane sh waves in a half-space

Scattering of antiplane shear waves (SH) in two dimensions by surface and near-surface defects in a homogeneous, isotropic elastic semi-infinite medium has been studied. Attention has been focused here in the range of medium to long wavelengths. A combined finite element and analytical technique has been used to study the problems of scattering by semi-circular and triangular canyons. The results for the former case are compared with the known exact solution and those for the latter case are compared with some available approximate solutions. Finally a problem of multiple scattering by a triangular canyon and a nearby circular tunnel is studied. Numerical results are presented showing the effects of multiple scattering and different angles of incidence. These results are of interest in earthquake engineering.     

Magma mixing in mafic alkaline volcanic rocks: the evidence from relict phenocryst phases and other inclusions

Green clinopyroxenes, commonly rounded and anhedral and richer in Fe, Na and Mn than the pyroxenes of the surrounding groundmass are a common feature of mafic alkaline volcanic rocks (e.g. basanites, monchiquites, leucitites). Some are accompanied by one or more of the following phases: Fe-rich kaersutite and biotite, anorthoclase, sodic plagioclase, apatite, magnetite, sphene, which are believed to be cognate with the green pyroxenes. We review evidence that these minerals have crystallized from mugearite, trachyte or phonolite magmas, and their presence in mafic alkaline rocks is due to magma mixing. The intermediate and salic magmas may sometimes be generated at mantle depths, possibly by melting of mantle material enriched in Fe, Na and volatiles.     

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Toxicity of No. 2 fuel oil to coon stripe shrimp

Bioassay of a No. 2 fuel oil dispersion with shrimp in a continuous flow system using measured waterborne oil as the indicator of oil concentrations reveals a treatment more definable than those previously described in terms of volume ratios and produces lower lethal concentrations. Shrimp 96-h LC₅₀ was 0.8 mg/l in this study as compared to values from 1.5 to 50 mg/l reported for other methods. Mean concentrations in tests do not give significant differences in concentration with respect to day of the test or spatial distribution in the exposure tanks.