@Article{ 
  fer05,
  author = { Ferriero, Alessandro },
  title = { The approximation of higher-order integrals of the calculus of variations and the Lavrentiev phenomenon },
  journal = { SIAM J. Control Optim. },
  year = { 2005 },
  volume = { 44 },
  number = { 1 },
  pages = { 99-110 },
  URL = { http://cvgmt.sns.it/paper/303/ },
  note = { cvgmt preprint}
}