Precambrian-Cambrian boundary: recent state of knowledge

The principle of biostratigraphic delimitation of the type lower boundary of the Cambrian System has become generally accepted, despite a lack of recent results which further support this approach. The detection of the most ancient Vendian Ediacara softbodied forms and Cambrian skeletal fauna in a large number of localities worldwide has been the only obvious trend in recent investigations.The present agreement that the base of the Tommotion Stage is the most satisfactory position for the Precambrian—Cambrian boundary is based on the idea that the best type section of the boundary is to be found in the Siberian platform. Such a decision is based largely on the unsatisfactory nature of the arguments for alternative positions.     

A mapping finite element method for stress calculation in two-dimensions

A mapping finite element method is proposed for the solution of elastic problems in two-dimensions. This method, based on the logarithmic condensation of physical space, is found to give significantly greater accuracy than when the problem is solved in the physical plane using the standard FEM. Logarithmic condensation of space also permits the solution of large aspect-ratio problems of this type, accurately and economically.     

Distances from auroral zones to the magnetic and geographic equators

Distance from auroral zone is a fundamental parameter in studies of disturbances produced in the thermosphere and ionosphere through the action of the solar wind. Calculations showing the great variation of the distances of the auroral “zones” from the magnetic equator and geographic equator are presented in diagrams. An auroral zone proximity index is proposed for use in correlative studies of upper atmosphere and of ionospheric disturbances.     

The polarization of starlight in NGC 654 and IC 5146

Two very young star clusters, NGC 654 and IC 5146 are studied using photographic polarization measures with limiting magnitudeB=15m,with a view to determining the nature of magnetic fields in the vicinities of these clusters.Starlight from NGC 654 is found to be polarized in a direction parallel to the galactic plane, the fainter members being more strongly polarized than the brighter ones.Polarization of starlight in IC 5146 is found to be very variable in both magnitude and direction, indicating the presence of complex magnetic fields within the cluster.