Recent experiments [1] have shown unexpected patterns when a suspension of non-neutrally buoyant particles is rotated about a horizontal axis. Numerical simulations within the Stokes-flow approximation show that observed the formation of axial bands is correlated with an inhomogeneous particle distribution in the radial plane [2]. An order parameter, based on the average angular velocity of the particles, characterizes two distinct phases: a low frequency segregated phase and a high frequency dispersed phase. The axial band structure develops during the transition between these two phases. In Fig. 1 we show numerical results for a small number of particles in a short tube.
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