@Article{ 
  DePVel13,
  author = { De Philippis, Guido and Velichkov, Bozhidar },
  title = { Existence and regularity of minimizers for some spectral functionals  with perimeter constraint },
  journal = { Appl. Math. Optim.  },
  year = { 2014 },
  volume = { 69 },
  number = { 2 },
  pages = { 199--231 },
  URL = { http://cvgmt.sns.it/paper/2110/ },
  note = { cvgmt preprint}
}