Title: Defining and identifying communities in networks Authors: Filippo Radicchi, Claudio Castellano, Federico Cecconi, Vittorio Loreto, Domenico Parisi Comments: Revtex, final form, 14 pages, 6 figures Subj-class: Statistical Mechanics; Disordered Systems and Neural Networks; Quantitative Methods Journal-ref: Proc. Natl. Acad. Sci. USA 101, 2658-2663 (2004)