Introduction of a pentagon-heptagon pair defect into the perfect hexagonal network of two carbon nanotubes could change the helicity of the tube and alter its electronic structure. Using a tight binding method to calculate the electronic structure of such a system, it was shown that this pentagon-heptagon pair defect in the nanotube structure was responsible not only for the change in nanotube diameter, but also governed the electronic behavior around the Fermi level. This configuration was explored in order to understand the influence of the defect upon the electronic properties of the system. Topological aspects associated with the presence of the defect were also considered. Electronic Properties of Carbon Nanotubes with Pentagon-Heptagon Pair Defects. H.F.Hu, Y.B.Li, H.B.He: Diamond and Related Materials, 2001, 10[9-10], 1818-23