Novel phase transition in collective motion with appearance of abnormal   agents
  We introduce a novel type of abnormal agents that proceed in the opposite direction of that defined for the normal agents. A new order parameter, $y$, is introduced to describe the characteristic of the system. Many interesting phenomenons emerge as the number of abnormal agents number shifts, e.g., the system may transform into a new phase (from $y\sim 1$ to $y\sim -1$) suddenly with abnormal agents getting denser, or stay disordered forever. A variety of other properties like size effect, agent speed and sight radii that have impacts on the new collective dynamics are also studied in detail. We suggest that our model or its modified versions can be applied to explain a variety of phenomenons with multiple kinds of particles interacting with each other and shape the system dynamics. 
Han Yan, Yu-Jian Li, Zhen-Dong Xi and Bing-Hong Wang
cond-mat.dis-nn