@unpublished{WittKurthsKrauseetal.2007,
  author  = {Annette Witt and J{\"u}rgen Kurths and F. Krause and K. Fischer},
  title   = {On the validity of a model for the reversals of the Earth's magnetic field},
  institution = {Institut f{\"u}r Physik und Astronomie},
  series    = {NLD Preprints},
  number    = {4},
  year    = {2007},
}