@Article{ bucbutste11, author = { Bucur, Dorin and Buttazzo, Giuseppe and Stefanelli, Ulisse }, title = { Shape flows for spectral optimization problems }, journal = { Interfaces Free Bound. }, year = { 2013 }, volume = { 14 }, pages = { 521--544 }, URL = { http://cvgmt.sns.it/paper/630/ }, note = { cvgmt preprint} }