Dr Vittoria Colizza, Complex Systems Lagrange Lab, ISI Foundation, Turin Italy

Abstract: "The rich are different from you and me," said F. Scott Fitzgerald. But do the rich — the well connected and highly influential — really form an exclusive club? Do they attract and exchange among themselves the vast majority of resources available in the system, or do they tend to avoid one another? In network theory, 'rich' nodes are generally defined as the highly connected nodes, and the 'rich-club' phenomenon refers to their tendency to form tighter interconnected groups than randomly expected, pointing to the presence of dominant subgroups in the system. By shifting the attention from the bare topology of a network to its weighted nature, it is possible to explore the associations between prominence and control of resources in a networked system. The weighted rich-club phenomenon provides a new general framework that enables to investigate the tendency of prominent elements to form clubs with exclusive control over the majority of resources circulating in a system. The results shed a new light on the distribution of traffic in transportation networks, the allocation of resources among scientists in collaborative endeavors, and the deepening of social relationships among users in online communication.