Quasi-one and two-dimensional transitions of gases adsorbed on nanotube   bundles
  Grand canonical Monte Carlo simulations have been performed to determine the adsorption behavior of Ar and Kr atoms on the exterior surface of a rope (bundle) consisting of many carbon nanotubes. The computed adsorption isotherms reveal phase transitions associated with the successive creation of quasi-one dimensional lines of atoms near and parallel to the intersection of two adjacent nanotubes. 
S. M. Gatica, M. J. Bojan, G. Stan, and M. W. Cole