@unpublished{VossKurthsSchwarz2007,
  author  = {Henning Voss and J{\"u}rgen Kurths and Udo Schwarz},
  title   = {Reconstruction of grand minima of solar activity from Delta 14 C data : linear and nonlinear signal analysis},
  institution = {Institut f{\"u}r Physik und Astronomie},
  series    = {NLD Preprints},
  number    = {28},
  year    = {2007},
}