@Misc{ 
  madsol07,
  author = { Maddalena, Francesco and Solimini, Sergio },
  title = { Transport distances and irrigation models },
  journal = {  },
  year = { 2007 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/1448/ },
  note = { cvgmt preprint}
}