Spontaneous Patterning of Confined Granular Rods
  Vertically vibrated rod-shaped granular materials confined to quasi-2D containers self organize into distinct patterns. We find, consistent with theory and simulation, a density dependent isotropic-nematic transition. Along the walls, rods interact sterically to form a wetting layer. For high rod densities, complex patterns emerge as a result of competition between bulk and boundary alignment. A continuum elastic energy accounting for nematic distortion and local wall anchoring reproduces the structures seen experimentally. 
J. Galanis (1), D. Harries (1), D. L. Sackett (1), W. Losert (2) and   R. Nossal (1) ((1) National Institutes of Health, (2)...