Rapidly spinning and loosely aggregated asteroids appear to take on diamond-shaped profiles, with elevated poles as well as equators. The evolutionary processes that form these characteristic shapes remain a matter of debate. In this paper, we propose a novel model, based on debris accretion, to explain these diamond-shaped profiles. We derive an analytic expression for the shapes of such rapidly spinning rubble piles based on the principle that as rubble is deposited it assumes a critical angle of repose. We show that this expression correctly reproduces diamond shaped profiles. We also conduct granular simulations of debris deposition and show that simulated shapes are in striking accord with both observations and analytical results. Our results suggest that non-uniform debris accumulation, which is overlooked in current models, may play a cardinal role in the formation of diamond-shaped asteroids.
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null (Ed.)Triboelectric charging has been linked to numerous industry hazards including dust explosions, damage to electrical devices and granular demixing, for example during pharmaceutical processing. In this work we demonstrate that triboelectric charging of peeling tape generates characteristic pat- terns that can be used to identify stick-slip events. We show that peeling tape from different materials (e.g. polymethylmeth- acrylate and polytetrafluoroethylene) generates distinct electrostatic as well as stick-slip patterns, which we identify us- ing electrically charged copier toners. This method is useful for laboratory character- ization of surface properties and may be translatable to industrial problems where control of stick-slip is desirable.more » « less
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