The Scaling of Human Contacts in Reaction-Diffusion Processes on   Heterogeneous Metapopulation Networks
  We present new empirical evidence, based on millions of interactions on Twitter, confirming that human contacts scale with population sizes. We integrate such observations into a reaction-diffusion metapopulation framework providing an analytical expression for the global invasion threshold of a contagion process. Remarkably, the scaling of human contacts is found to facilitate the spreading dynamics. Our results show that the scaling properties of human interactions can significantly affect dynamical processes mediated by human contacts such as the spread of diseases, and ideas. 
Michele Tizzoni, Kaiyuan Sun, Diego Benusiglio, M\'arton Karsai,   Nicola Perra
physics.soc-ph q-bio.PE