Power-Law Distributions in Circulating Money: Effect of Preferential   Behavior
  We introduce preferential behavior into the study on statistical mechanics of money circulation. The computer simulation results show that the preferential behavior can lead to power laws on distributions over both holding time and amount of money held by agents. However, some constraints are needed in generation mechanism to ensure the robustness of power-law distributions. 
Ning Ding, Yougui Wang