@PHDTHESIS{Pe15,
  author = {Perl, Ricardo},
  title = {Isogeometric Approximation of Variational Problems for Shells},
  school = {University of Bonn},
  year = {2015},
  url = {http://hss.ulb.uni-bonn.de/2016/4359/4359.htm},
}