RESUMO
Experimental observations and theoretical studies show that nonlinear internal waves occur widely in shallow water and cause acoustic propagation effects including ducting and mode coupling. Horizontal ducting results when acoustic modes travel between internal wave fronts that form waveguide boundaries. For small grazing angles between a mode trajectory and a front, an interference pattern may arise that is a horizontal Lloyd mirror pattern. An analytic description for this feature is provided along with comparisons between results from the formulated model predicting a horizontal Lloyd mirror pattern and an adiabatic mode parabolic equation. Different waveguide models are considered, including boxcar and jump sound speed profiles where change in sound speed is assumed 12 m/s. Modifications to the model are made to include multiple and moving fronts. The focus of this analysis is on different front locations relative to the source as well as on the number of fronts and their curvatures and speeds. Curvature influences mode incidence angles and thereby changes the interference patterns. For sources oriented so that the front appears concave, the areas with interference patterns shrink as curvature increases, while convexly oriented fronts cause patterns to expand.
RESUMO
The study was designed to assess the effect of heavy metal fallouts in industrial areas on the development of primary palatal cleft in Northern Moravia and Silesia over a period of five years (1985-1990). The study involved a total of 110 children; fallout levels in their places of residence were determined. Heavy metal fallout levels were measured in the ashes of needles and forest soil in the nearest possible locality to the place of birth of the child. The data obtained show a striking correlation between increases in cadmium and cobalt levels and the development of primary palatal cleft.