No abstract

There is evidence that a uniquely Venusian type of channel may be at least partly erosional in origin. A number of published models discuss the erosion process on various planetary bodies. However, these relate to lavas of specifically different compositions. Here a numerical model is derived to investigate the sensitivity of the erosion process to various physical parameters of the lava and substrate, placing constraints on the physical characteristics required to obtain a suitably rapid erosion rate. The model allows for the effects of latent heat and also considers the presence of a liquid substrate boundary layer between the lava and solid substrate. The results indicate that the thermal erosion process is particularly sensitive to the melting temperature, when the melting temperature is doubled from 700 to 1400 K, the erosion rate decreases by approximately an order of magnitude. Also, the erosion rate associated with a venusian initial substrate temperature is approximately 1.5 times greater than the equivalent terrestrial one. Mechanical erosion is considered by altering the percentage of latent heat required to melt the substrate; as this percentage is varied from 0 to 100, the erosion rate decreases by about a factor of 2.

No abstract

Currently, the Genomic Threading Database (GTD) contains structural assignments for the proteins encoded within the genomes of nine eukaryotes and 101 prokaryotes. Structural annotations are carried out using a modified version of GenTHREADER, a reliable fold recognition method. The Gen THREADER annotation jobs are distributed across multiple clusters of processors using grid technology and the predictions are deposited in a relational database accessible via a web interface at http://bioinf.cs.ucl.ac.uk/GTD. Using this system, up to 84% of proteins encoded within a genome can be confidently assigned to known folds with 72% of the residues aligned. On average in the GTD, 64% of proteins encoded within a genome are confidently assigned to known folds and 58% of the residues are aligned to structures.

Abstract. Smrzstroms are giant landslides that travel kilometers within minutes. Data from terrestrial examples of 0.001-10 km 3 suggest that their runout lengths increase in proportion to the square root of their volume. This trend is investigated assming that runout is controlled by fragmental flow. The results indicate that runout lengths depend on the potential energy available for motion after initial collapse (itself a function of the dimensions of the collapse zone), on the degree of rock fragmentation, and on the rate of momentum loss by fragment collisions in a basal boundary layer, assumed to thicken with time by diffusion. A dependence on initial conditions during collapse would explain claims that a minimum volume is required for sturzstroms to form: Beneath a critical volume, insufficient energy is available to initiate fragmental flow, and so the unstable mass slumps downslope. The drop height (H) is often similar to the vertical extent of the collapse zone and so is linked by geometry to sturzstrom volume. The ratio of H to L (the horizontal distance of effective transport), normally interpreted as a measure of frictional resistance, is thus reinterpreted as an inverse measure of the energy available for runout after collapse. By providing a physical basis for observed trends, the analysis justifies use of empirical limits for forecasting the runout lengths of major landslides.