@Article{ 
  XiaXu11,
  author = { Xia, Qinglan and Xu, Shaofeng },
  title = { On the Ramified Optimal Allocation Problem },
  journal = { Networks and Heterogeneous Media },
  year = { 2013 },
  volume = { 8 },
  number = { 2 },
  pages = { 591-624 },
  URL = { http://cvgmt.sns.it/paper/5245/ },
  note = { cvgmt preprint}
}