We have studied the early time evolution of granular segregation patterns ina horizontal rotating cylinder partially filled with a sand/salt mixture. Thegrowth of concentration fluctuations starting from premixed initial conditionswas analyzed using Fourier techniques. In one mixture, we observed generallymerging dynamics in the segregated bands up to the onset of saturation. At thethreshold of saturation, we found a spectrum of wavelengths with a broad peak.The peak position was nearly independent of the tube rotation rate. The overallgrowth rate of Fourier modes had a maximum at a particular value of the angularrotation frequency. In a slightly different mixture, we observed transienttraveling waves when the larger grains were in the majority. We measured thewave speed as a function of several parameters using presegregated initialconditions to launch waves of various wavelengths.
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