Shaping Segregation: Convexity vs. Concavity
  Controlling segregation is both a practical and a theoretical challenge. In this Letter we demonstrate a manner in which rotation-induced segregation may be controlled by altering the geometry of the rotating containers in which granular systems are housed. Using a novel drum design comprising concave and convex geometry, we explore a means by which radial size-segregation may be used to drive axial segregation, resulting in an order of magnitude increase in the axial segregation rate. This finding, and the explanations provided of its underlying mechanisms, could lead to radical new designs for a broad range of particle processing applications. 
S. Gonzalez and C. R. K. Windows-Yule and S. Luding and D. J. Parker   and A.R. Thornton
cond-mat.soft