Why pebbles float to the surface

Article Abstract:

A computer simulation may account for why the larger particles rise to the top when a mixture of sand and pebbles is shaken in a pail. French researchers Remi Jullien, Paul Meakin and Andre Pavlovich used a computer model to determine that the smaller particles at the pail's bottom will remain there at each successive shaking, while the larger particles will always fall relatively later. The upshot of this process is that the larger particles can move upward only. However, the process apparently only works if the ratios of the large and small particles' diameters is larger than about 2.8.

Models, Usage, Particles, Particulate matter, Computer simulation, Sand, Sands, Sediments (Geology)

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Genetics helping molecular dynamics

Article Abstract:

The theory of natural evolution can be used to predict the structure of C60 where the standard molecular dynamics technique fails. The molecular dynamics technique selects the optimum equilibrium configuration on the basis of the least available free energy but this has not proved suitable for finding structures of molecules with a large number of atoms. However, the procedure adopted to find the C60 structure fails to find a reasonable structure for simpler molecules, such as C20.

Molecular structure, Chemical evolution, Molecular evolution, Buckminsterfullerene

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