@unpublished{PikovskijFeudel2007,
  author  = {Arkadij Pikovskij and Ulrike Feudel},
  title   = {Characterizing strange nonchaotic attractors},
  institution = {Institut f{\"u}r Physik und Astronomie},
  series    = {NLD Preprints},
  number    = {2},
  year    = {2007},
}