1. School of Arts and Humanities, The University of Texas at Dallas, Richardson, TX 75080, USA.
2. Chair of Sociology, in particular of Modeling and Simulation (SOMS), Eidgenössische Technische Hochschule (ETH) Zurich, CH-8092 Zurich, Switzerland.
3. Center for Complex Network Research, Department of Physics, Biology and Computer Science, Northeastern University, Boston, MA 02115, USA.
4. Department of Physics, University of Miami Coral Gables, Coral Gables, FL 33146, USA.
5. School for Informatics and Computing, Indiana University Bloomington, Bloomington, IN 47405, USA.
6. Department of Medicine, Harvard Medical School, and Center for Cancer Systems Biology, Dana-Farber Cancer Institute, Boston, MA 02115, USA.
7. Center for Network Science, Central European University, Budapest 1052, Hungary.