@Article{ 
  BraNitPra11,
  author = { Brasco, Lorenzo and Nitsch, Carlo and Pratelli, Aldo },
  title = { On the boundary of the attainable set of the Dirichlet spectrum },
  journal = { Z. Angew. Math. Phys. },
  year = { 2012 },
  number = { 64 },
  pages = { 591-597 },
  URL = { http://cvgmt.sns.it/paper/1721/ },
  note = { cvgmt preprint}
}