  We have discovered that the influence of the surrounding nanotubes in a
bundle is similar to that of a liquid having surface tension equal to the
surface energy of the nanotubes. This surprising behaviour is confirmed by the
calculation of the self-collapse diameters of nanotubes in a bundle. Other
systems, such as peapods, fullerites, are similarly treated, including the
effect of the presence of a solvent. Finally, we have evaluated the strength
and toughness of the nanotube bundle, with or without collapsed nanotubes,
assuming a sliding failure.
