@article{palla2007quantifying,
  title={Quantifying social group evolution},
  author={Palla, Gergely and Barab{\'a}si, Albert-L{\'a}szl{\'o} and Vicsek, Tam{\'a}s},
  journal={Nature},
  volume={446},
  number={7136},
  pages={664--667},
  year={2007},
  publisher={Nature Publishing Group}
}