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arXiv 1910.03417cond-mat.soft
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布朗液体中的记忆诱导运动反转

Memory-induced motion reversal in Brownian liquids

Lucas L. Treffenstädt, Matthias Schmidt

摘要:

利用事件驱动的布朗动力学模拟和幂泛函理论研究了空间非均匀剪切下硬球的布朗动力学。我们研究密度和电流分布的稳态和瞬态动力学后,打开和关闭外部方波剪切力场。我们发现,一个致密的硬球流体(体积分数$\approx$ 0.35)进行全球运动反转后关闭剪切力场。我们使用幂泛函理论与空间非局部记忆内核来描述超绝热力的贡献,并获得良好的定量协议的理论结果与模拟数据。该理论为运动反转提供了一种解释:由于关闭后的记忆,内部超绝热非平衡力与外部驱动的电流相反。这种效应是真正的粘弹性:在稳定状态下,粘性力与电流相反,但在关闭后,它们弹性地产生相反的电流。

英文摘要:

We study the Brownian dynamics of hard spheres under spatially inhomogeneous shear, using event-driven Brownian dynamics simulations and power functional theory. We examine density and current profiles both for steady states and for the transient dynamics after switching on and switching off an external square wave shear force field. We find that a dense hard sphere fluid (volume fraction $\approx$0.35) undergoes global motion reversal after switching off the shear force field. We use power functional theory with a spatially nonlocal memory kernel to describe the superadiabatic force contributions and obtain good quantitative agreement of the theoretical results with simulation data. The theory provides an explanation for the motion reversal: Internal superadiabatic nonequilibrium forces that oppose the externally driven current arise due to memory after switching off. The effect is genuinely viscoelastic: in steady state, viscous forces oppose the current, but they elastically generate an opposing current after switch-off.

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