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One fundamental physical process in mixing cohesionless particulate materials is interparticle percolation, the drainage of smaller particles in the mixture through the larger ones, normally under the influence of gravity and strain. A simple shear cell has been developed to study strain-induced interparticle percolation under closely controlled conditions. The uniform deformation in the cell allows percolation rates to be determined readily. The amount of percolation depends mainly on total strain, the relative sizes of large and small particles, and also on rate of strain, even at low strain rates. It is believed that this is the first extensive information on this mixing mechanism. The results indicate the potential significance of interparticle percolation in understanding solids mixing and in those chemical reaction systems in which the detailed distribution of particles is significant.

Measurements are reported on the open and closed-loop phase stability of a large-mode-area ytterbium-doped fiber amplifier. Phase fluctuations are characterized by a high-frequency low-amplitude jitter superimposed on a slow power-dependent drift. The amplifier may be phase locked to a precision of lambda/20 by using a low-bandwidth feedback loop.

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