Finding apparent horizons and other two-surfaces of constant expansion

Apparent horizons are structures of spacelike hypersurfaces that can be determined locally in time. Closed surfaces of constant expansion (CE surfaces) are a generalisation of apparent horizons. I present an efficient method for locating CE surfaces. This method uses an explicit representation of the surface, allowing for arbitrary resolutions and, in principle, shapes. The CE surface equation is then solved as a nonlinear elliptic equation. It is reasonable to assume that CE surfaces foliate a spacelike hypersurface outside of some interior region, thus defining an invariant (but still slicing-dependent) radial coordinate. This can be used to determine gauge modes and to compare time evolutions with different gauge conditions. CE surfaces also provide an efficient way to find new apparent horizons as they appear e.g. in binary black hole simulations.Comment: 21 pages, 8 figures; two references adde

Carbonate platform facies reflected in carbonate basin facies (Triassic, northern Calcareous Alps, Austria)

A 95 m long section (Lacke section) located in the Norther Calcareous Alps of Austria was analyzed in detail. Detailed field measurements and point-counting of thin-sections revealed a distinct compositional variation of calciturbidites deposited in the Triassic Hallstatt Basin (Pedata-Pötschen Schichten). After a pilot study seven point-count groups were developed distinguishing input from different paleoenvironments. Statistical analysis of the point-count data using summary statistics, cluster-and correspondence analysis assisted in describing the compositional variation within the calcuturbidites. Alternated flooding and exposure of the platform as a result of sealevel fluctuations, creating and destroying shallow-water habitats on the flat platform top, produced the variations in turbidite composition