Editorial

¹ ETH Zürich, Kreuzplatz 5, Zürich, 8032, Switzerland
² Northeastern University, 360 Huntington Ave., Boston, Massachusetts, 02115, USA
³ Institute for Scientific Interchange Foundation, Via Alassio 11/c, Turin, 10126, Italy

^* e-mail: fschweitzer@ethz.ch
^** e-mail: a.vespignani@neu.edu

Received: 25 November 2011
Accepted: 18 May 2012
Published online: 18 May 2012

This article has no abstract.