@article{SpahnKatzorkePetzschmannetal.1997,
  author    = {Spahn, Frank and Katzorke, Ines and Petzschmann, Olaf and Schwarz, Udo and Kurths, J{\"u}rgen},
  title     = {Cluster instabiliy of granular assemblies},
  year      = {1997},
  language  = {en}
}
@article{SpahnSchwarzKurths1997,
  author    = {Spahn, Frank and Schwarz, Udo and Kurths, J{\"u}rgen},
  title     = {Clustering of granular assemblies with temperature dependent restitution under Keplerian differential rotation},
  year      = {1997},
  language  = {en}
}
@article{FeudelJansenKurthsetal.1997,
  author    = {Feudel, Ulrike and Jansen, Wolfgang and Kurths, J{\"u}rgen and Schwarz, Udo and Voss, Henning U.},
  title     = {Solar variability : simple models and proxy data},
  isbn      = {4-274-90187-4},
  year      = {1997},
  language  = {en}
}