@Article{ 
  BucButVel13,
  author = { Bucur, Dorin and Buttazzo, Giuseppe and Velichkov, Bozhidar },
  title = { Spectral optimization problems for potentials and measures },
  journal = { SIAM J. Math. Anal. },
  year = { 2014 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/2245/ },
  note = { cvgmt preprint}
}