Community analysis in social networks A. Arenas, L. Danon, A. Díaz-Guilera, P. M. Gleiser and R. Guimerà Eur. Phys. J. B, 38 2 (2004) 373-380 Published online: 14 May 2004 DOI: 10.1140/epjb/e2004-00130-1