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张洁课题组在Physical Review Letters发表关于颗粒体系统计力学的最新研究成果Friction-controlled Entropy-stability Competition in Granular Systems

近日,上海交通大学自然科学研究院/物理与天文学院张洁课题组及其合作者在颗粒体系中发现了由摩擦所调控的,熵与稳定性竞争的关系,研究成果Friction-controlled Entropy-stability Competition in Granular Systems于2020年12月31日在线发表在Physical Review Letters杂志。

颗粒体系是由大量宏观粒子集合而成的体系。由于其中缺少热涨落的驱动,且存在各种耗散机制,颗粒体系通常被认为是典型的非平衡态体系。因此,如何结合传统的平衡态统计物理来研究颗粒体系,成为了相关领域中的一个长期难题。

不同摩擦系数的颗粒体系中,元胞序的概率分布

张洁课题组发现,在循环剪切驱动下的二维颗粒体系,其中的元胞序(cell order)遵循指数分布。这种指数分布在从弱摩擦到强摩擦系统中都可以观察到,并且可以用玻尔兹曼分布进行解释。这种玻尔兹曼分布可以理解为在颗粒体系中,元胞的位型熵与稳定性竞争,且熵占有主导地位的结果。他们通过对比发现,这种竞争关系由颗粒摩擦系数所调控。最后,该项研究发现了元胞快速演化的性质,揭示了颗粒体系类似于液体的性质。

元胞的快速演化

本项工作主要由博士生孙旭来完成,合作者有Walter Kob教授、Raphael Blumenfeld教授、童华副教授和王宇杰教授,通讯作者为张洁教授。该研究工作得到了国家自然科学基金的支持。

On 31st December 2020, Physical Review Letters published the research on granular statistical mechanics by Prof. Jie Zhang and his collaborator. The title of this paper is Friction-controlled Entropy-stability Competition in Granular Systems.

Granular system is defined as an assemble of macroscopic particles. Due to the lack of thermal fluctuations and existence of various dissipations, granular systems are recognized as typical non-equilibrium systems. Thus, how to apply traditional equilibrium statistical mechanics to granular systems has been a long-lasting puzzle in this field.

We find that, the cell order distribution in a cyclic-driven 2D granular system well obeys exponential law. This exponential law can be observed across a wide range of inter-particle friction, and can be explained by Boltzmann distribution. This Boltzmann distribution originates from an entropy-stability competition in granular systems, where entropy dominates. By comparison, we find that this competition relation is tuned by inter-particle friction. Finally, we show that cells are short-lived, implying that our systems are liquid-like, rather than glassy.

The first author is Ph.D. student Xulai Sun, the corresponding author is Prof. Jie Zhang, and Prof. Walter Kob, Prof. Raphael Blumenfeld, Assoc. Prof. Hua Tong and Prof. Yujie Wang are co-authors. This work is supported by NSFC