@Article{ 
  MazPra11,
  author = { Mazzoleni, Dario and Pratelli, Aldo },
  title = { Existence of minimizers for spectral problems },
  journal = { J. Math. Pures Appl. },
  year = { 2013 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/1703/ },
  note = { cvgmt preprint}
}