Correlation based networks of equity returns sampled at different time horizons M. Tumminello, T. Di Matteo, T. Aste and R. N. Mantegna Eur. Phys. J. B, 55 2 (2007) 209-217 Published online: 22 November 2006 DOI: 10.1140/epjb/e2006-00414-4