Space-time correlations in urban population flows
  Evidences are presented concerning tantalizing regularities in cities' population-flows in what regards to space and time correlations. The former exhibit a distance-behavior (for large distances) compatible with the inverse square law, following an overall Lorentzian dependence with an scale-parameter of $74\pm6$ km. The later decay exponentially with a characteristic time of $17.2\pm1.3$ years. These features can be explained by a dynamical model for cities' population-growth of a Lagevinian nature. Numerical simulations based on the model confirm its applicability. The model also allows for the identification of collective normal modes of city-growth dynamics that can be empirically identified. 
A. Hernando, A. Plastino
stat.AP physics.soc-ph