@article{WuZhouXiaoetal.2010,
  author    = {Ye Wu Wu and Changsong Zhou and Jinghua Xiao and J{\"u}rgen Kurths and Hans Joachim Schellnhuber},
  title     = {Evidence for a bimodal distribution in human communication},
  doi       = {10.1073/pnas.1013140107},
  url       = {http://www.sciencedirect.com/science/journal/03784371},
  year      = {2010},
}