Arrays of C60 molecules nested inside single-walled nanotubes represent a class of nanoscale materials having tunable properties. We report electronic measurements of this system made with a scanning tunneling microscope and demonstrate that the encapsulated C60 molecules modify the local electronic structure of the nanotube. Our measurements and calculations also show that a periodic array of C60 molecules gives rise to a hybrid electronic band, which derives its character from both the nanotube states and the C60 molecular orbitals.

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We demonstrate that stability criteria can be used to calculate the maximum angle of stability m of a granular medium composed of spherical particles in three dimensions and circular disks in two dimensions. The predicted angles are in good agreement with the experimental results. Furthermore, we determine the dependence of m on cohesive forces, applying the results to wet granular material by calculating the dependence of m on the liquid content of the material. We have also studied wet granular media experimentally and find good agreement between the theory and our experimental results. ͓S1063-651X͑97͒50512-5͔PACS number͑s͒: 83.70.Fn, 05.90.ϩm, 46.10.ϩz, 68.45.Ϫv