1. Amsterdam School of Communication Research (ASCoR), University of Amsterdam, PO Box 15793, 1001 NG Amsterdam, The Netherlands
2. Centre for Science and Technology Studies (CWTS), Leiden University, Leiden, The Netherlands & SPRU (Science Policy Research Unit), University of Sussex, UK
3. Center for Complex Networks and Systems Research, The Luddy School of Informatics, Computing, and Engineering, Indiana University, Bloomington, USA