Spallation as an effect of laser-induced shock waves

Spallation resulting from laser-driven shock waves in metallic foils was investigated and the various stages of material failure were identified. The very high strain rate (10⁷sec^–1 ) characteristic of these experiments sets our results apart from those obtained by high explosives or hypervelocity impact. Numerical hydrodynamic simulations of the phenomenon were developed and are shown to be in qualitative agreement with the experimental results.     

Mobile users: To update or not to update?

Tracking strategies for mobile users in wireless networks are studied. In order to save the cost of using the wireless links mobile users should not update their location whenever they cross boundaries of adjacent cells. This paper focuses on three natural strategies in which the mobile users make the decisions when and where to update: the time-based strategy, the number of movements-based strategy, and the distance-based strategy. We consider both memoryless movement patterns and movements with Markovian memory along a topology of cells arranged as a ring. We analyze the performance of each one of the three strategies under such movements, and show the performance differences between the strategies.The work of this author was done when he was with IBM, T.J. Watson Research Center, Yorktown Heights, NY, USA.Part of the work of this author was done when he was visiting IBM, T.J. Watson Research Center, Yorktown Heights, NY, USA.