@Misc{ 
  butbuc09,
  author = { Bucur, Dorin and Buttazzo, Giuseppe },
  title = { On the characterization of the compact embedding of Sobolev spaces },
  journal = { Calc. Var. and PDEs },
  year = { 2012 },
  pages = { 19 },
  URL = { http://cvgmt.sns.it/paper/353/ },
  note = { cvgmt preprint}
}