@Misc{ belbucbut05, author = { Belhachmi, Zacharia and Bucur, Dorin and Buttazzo, Giuseppe and Sac-Epée, Jean-Marc }, title = { Shape optimization problems for eigenvalues of elliptic operators }, journal = { }, year = { 2005 }, pages = { }, URL = { http://cvgmt.sns.it/paper/756/ }, note = { cvgmt preprint} }