完全发展的主动湍流：通过非平衡相变定义
Fully developed active turbulence defined through a non-equilibrium phase transition
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中文总结 AI 辅助
本研究通过实验与模拟揭示主动湍流的起始对应活性驱动的非平衡相变，以涡度节点线渗流和涡旋中心刚性团簇为标志，为定义完全发展的主动湍流提供了实验可及标准。
中文摘要 AI 辅助
非平衡系统对平衡统计物理学中相和相变的标准定义提出了挑战。例如，在主动流体中，微观尺度的连续能量注入使系统本质上处于非平衡状态。这一过程产生了集体湍流状流动，其起始点至今定义不清。在此，我们表明该起始点对应一个由活性驱动的相变，其特征是涡度节点线的系统尺度贯穿临界骨架的出现。结合两个独立实验——微管驱动蛋白主动向列相和密集悬浮的游动细菌——以及主动向列相和涨落向列流体动力学的大规模模拟，我们证明该相变发生在临界活性阈值处。低于此阈值，涡度结构是碎片化的，涡旋中心仅形成有限的、机械上柔性的网络。高于此阈值，涡度场的节点线发生渗流，涡旋中心形成刚性的、系统尺度的团簇。几何相变以涡度节点线出现临界渗流统计为特征，而机械相变则反映涡旋构型的出现，该构型对涡旋中心表现出刚性渗流统计。我们证明，在满足细致平衡的平衡系统中，这两种相变均不存在，从而表明该相变本质上是非平衡的。这些结果确立了完全发展的主动湍流的实验可及定义，将微观活性与宏观几何及生命系统的力学联系起来。
英文摘要
Non-equilibrium systems challenge the standard definitions of phases and phase transitions from equilibrium statistical physics. For example, in active fluids continuous energy injection at the microscale drives the system intrinsically out of equilibrium. This process gives rise to collective turbulent-like flows whose onset remains poorly defined. Here we show that the onset corresponds to an activity-driven phase transition, marked by the emergence of a system-spanning critical backbone of vorticity nodal lines. Combining two independent experiments, microtubule kinesin active nematics and dense suspensions of swimming bacteria, with large-scale simulations of active nematics and fluctuating nematohydrodynamics, we show that this transition occurs at a critical activity threshold. Below this threshold, vorticity structures are fragmented and vortex centres form only finite, mechanically floppy networks. Above this threshold, the nodal lines of the vorticity field percolate and the vortex centres form a rigid, system-spanning cluster. The geometric transition is characterised by the emergence of critical percolation statistics for the vorticity nodal lines, while the mechanical transition reflects the emergence of a vortex configuration that shows rigidity percolation statistics for vortex centres. We show that both transitions are absent in equilibrium systems that obey detailed balance, demonstrating that the transition is intrinsically non-equilibrium. These results establish an experimentally accessible definition of fully developed active turbulence, linking microscopic activity to macroscopic geometry, and mechanics of living systems.
发表机构
- Niels Bohr Institute, University of Copenhagen（哥本哈根大学尼尔斯·玻尔研究所）
- Universitat de Barcelona（巴塞罗那大学）
- Institute of Nanoscience and Nanotechnology, IN2UB, Universitat de Barcelona（巴塞罗那大学纳米科学与技术研究所）
- Northwest University（西北大学）
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