@Misc{ 
  bucbuthen09,
  author = { Bucur, Dorin and Buttazzo, Giuseppe and Henrot, Antoine },
  title = { Minimization of $\lambda_2(\Omega)$ with a perimeter constraint },
  journal = {  },
  year = { 2009 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/1398/ },
  note = { cvgmt preprint}
}