1. https://en.wikipedia.org/wiki/ List of countries by number of mobile phones in use.
2. Valentina, A., Andrea, G., and Luciano, P. 2009. How people react to a deadline: time distribution of conference registrations and fee payments. J. Cent. Eur. J. Phys., 2009 (3).
3. Ju. L. F., Ying F., Yang W. and Shou Y. W. 2014 Network analysis of terrorist activities. J. J. Syst. Sci. Complex, 2014 (6).
4. Liu Y., Xiao Y. and Gao S., et al. 2011. A Review of Human Mobility Research Based on Location Aware Devices. J. Geography and Lect. Notes. Comput. Sc., 2011, 27(4):8--7.
5. Chao G. K., Yi Z. and Xiu J. M., et al. 2013. Inferring properties and revealing geographical impacts of intercity mobile communication network of China using a subnet data set. J. Int. J. Geogr. Inf. Sci., 2013, 27(3):1--18.