@article{czirok1997spontaneously,
  title={Spontaneously ordered motion of self-propelled particles},
  author={Czir{\'o}k, Andr{\'a}s and Stanley, H Eugene and Vicsek, Tam{\'a}s},
  journal={Journal of Physics A: Mathematical and General},
  volume={30},
  number={5},
  pages={1375},
  year={1997},
  publisher={IOP Publishing}
}