论文标题
理想气体中示踪剂的短时动力学
Short time dynamics of tracer in ideal gas
论文作者
论文摘要
沉浸在流体中的小标记粒子表现出布朗运动，并长期以来扩散。同时，在短时尺度上，标记粒子的动力学不能简单地用高斯噪声来描述，因为标记的粒子和流体粒子之间的碰撞数量很小。在这样的时间尺度上，我们应该明确考虑标记粒子和周围流体颗粒之间的单个碰撞事件。在这项研究中，我们分析了理想气体中标记粒子的短时动力学，在该动力中我们没有流体颗粒之间的静态或流体动力相关性。我们进行了事件驱动的硬球模拟，并表明即使在如此理想化的情况下，标记粒子的短时动力学也是相关的。也就是说，当标记的粒子相对较轻并且流体密度相对较高时，速度自相关函数将变为负。该结果可以归因于碰撞事件之间的动态相关性。为了研究导致动态相关性的物理机制，我们分析了连续碰撞事件之间的相关性。我们发现，标记的粒子可以与相同的理想气体粒子碰撞几次，并且这种碰撞导致速度的强大动力相关性。
A small tagged particle immersed in a fluid exhibits the Brownian motion and diffuses at the long-time scale. Meanwhile, at the short-time scale, the dynamics of the tagged particle cannot be simply described by the usual generalized Langevin equation with the Gaussian noise, since the number of collisions between the tagged particle and fluid particles is rather small. At such a time scale, we should explicitly consider individual collision events between the tagged particle and the surrounding fluid particles. In this study, we analyzed the short-time dynamics of the tagged particle in an ideal gas, where we do not have static nor hydrodynamic correlations between fluid particles. We performed event-driven hard sphere simulations and show that the short-time dynamics of the tagged particle is correlated even under such an idealized situation. Namely, the velocity autocorrelation function becomes negative when the tagged particle is relatively light and the fluid density is relatively high. This result can be attributed to the dynamical correlation between collision events. To investigate the physical mechanism, which causes the dynamical correlation, we analyzed the correlation between successive collision events. We found that the tagged particle can collide with the same ideal gas particle several times, and such collisions cause the strong dynamical correlation for the velocity.
