In PNAS this week: *PHYSICAL SCIENCES / APPLIED PHYSICAL SCIENCES* * Extracting the hierarchical organization of complex systems* * Marta Sales-Pardo, Roger Guimerà, André A. Moreira, and Luís A. Nunes Amaral^* * Department of Chemical and Biological Engineering and Northwestern Institute on Complex Systems, Northwestern University, Evanston, IL 60208 Edited by H. Eugene Stanley, Boston University, Boston, MA, and approved July 22, 2007 (received for review April 23, 2007) Extracting understanding from the growing "sea" of biological^ and socioeconomic data is one of the most pressing scientific^ challenges facing us. Here, we introduce and validate an unsupervised^ method for extracting the hierarchical organization of complex^ biological, social, and technological networks. We define an^ ensemble of hierarchically nested random graphs, which we use^ to validate the method. We then apply our method to real-world^ networks, including the air-transportation network, an electronic^ circuit, an e-mail exchange network, and metabolic networks.^ Our analysis of model and real networks demonstrates that our^ method extracts an accurate multiscale representation of a complex^ system.^ cellular metabolism | complex networks | multiscale representatiom http://www.pnas.org/cgi/content/abstract/104/39/15224?etoc I haven't seen the paper itself yet. Cheers, Roeland