中文摘要：

应用ART模型研究了Eb=520MeV／u的UU碰撞．探讨了在两种极端方位UU碰撞下，核子和π在反应平面内的横向流的时间演化以及对碰撞中心度的依赖关系．研究表明，流在高密区域发展并且在膨胀相稳定，因而它是高密区域反应动力学的一个敏感探针．对头头和体体UU碰撞，末态π相对于核子的横向流分别在大约b=9fm和b=2fm处存在明显的正向到负向的改变，π的这种行为是重子共振态和旁观者的遮蔽效应（再散射和再吸收）共同作用的结果．

英文摘要：

The ART（a Relativistic Transport） Model is applied for studying the UU collisions at a beam kinetic energy about 0.52GeV/nucleon. We discuss the time evolution and the centrality dependence for sideward flow of nucleons and pions at two extreme orientation UU collisions. It is found that the collective （side） flow is developed in the high density region and has a saturation in the expansion phase, so it is a sensitive probe for the reaction dynamics in the high density region. A distinct transition from pion flow to antiflow, which is relative to nucleons flow, occurs at the impact parameters of about 8fm and 2fm in tip-tip and body-body UU collisions, respectively. The pion flow is a result of the competition between the collective flow of baryon resonances and the shadowing of spectators through rescatterings and reabsorptions.