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Measurements of axial segregation of binary mixtures of glass beads having different diameters in a rotating horizontal cylinder are reported. For rotation speeds of ~ 15 rpm a mixed state quickly (within a few minutes) segregates into sharp bands of alternating large and small glass beads along the axis of rotation. Decreasing the rotation speed to ~ 5 rpm causes the bands to disappear, restoring the mixed state. This process is reversible upon increasing the rotation rate, though the exact location and width of the bands vary from run to run. The axial segregation phenomena are analyzed in terms of a diffusion equation where the effective diffusion coefficient is the difference between segregating drift and normal Fickian diffusion.

Transient coherent neural oscillations, as indicated by local field potentials, are thought to underlie key perceptual and cognitive events. We report a transient, state-dependent 50 Hz oscillation recorded from electrodes placed in the striatum of awake, behaving rats. These coherent oscillations, which we term gamma(50), occurred in brief (150 ms) events co-incident with the initiation of movement. On navigation tasks, the animal's speed increased dramatically at the precise moment of the gamma(50) event. This synchronous oscillation may provide a key to understanding striatal function, as well as basal ganglia pathology, which often impairs the control of voluntary movements.

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