@Misc{ 
  bucbut98,
  author = { Bucur, Dorin and Buttazzo, Giuseppe },
  title = { Results and Questions on Minimum Problems for Eigenvalues },
  journal = {  },
  year = { 1998 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/422/ },
  note = { cvgmt preprint}
}