@Misc{ 
  morsan07,
  author = { Morel, Jean-Michel and Santambrogio, Filippo },
  title = { The regularity of optimal irrigation patterns },
  journal = { Arch. Ration. Mech. Anal. },
  year = { 2008 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/1293/ },
  note = { cvgmt preprint}
}