Improving resource utilization in hierarchy network by optimizing topological structure G.L. Liu, H.P. Peng, L.X. Li, F. Sun and Y.X. Yang Eur. Phys. J. B, 85 2 (2012) 63 Published online: 13 February 2012 DOI: 10.1140/epjb/e2012-20801-4