@Article{ gramad06, author = { Granieri, Luca and Maddalena, Francesco }, title = { Optimal shapes in force fields }, journal = { J. Convex Analysis }, year = { 2008 }, volume = { 15 }, number = { 17-37 }, pages = { }, URL = { http://cvgmt.sns.it/paper/476/ }, note = { cvgmt preprint} }