arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1306.3158cond-mat.stat-mechcond-mat.mes-hall
收藏

热涨落引起的可逆扩散

Reversible Diffusion by Thermal Fluctuations

A. Donev, T. G. Fai, and E. Vanden-Eijnden

摘要:

本文研究了在大施密特数的限制下,将示踪粒子的动力学耦合到流体的波动Stokes方程的液体扩散模型。在这个限制中,示踪剂的浓度被证明满足一个封闭形式的随机对流扩散方程,该方程用于调查流体动力学相关示踪剂的集体扩散通过欧拉和拉格朗日数值方法的组合。这一分析表明,在液体中的传输是完全不同于传统的菲克扩散图片。虽然整体平均浓度遵循菲克定律,扩散系数服从斯托克斯-爱因斯坦关系,但扩散混合过程的每个实例都表现出围绕其平均行为的长期巨大波动。我们构造了一类在不同观测尺度下的液体扩散介观模型,其中重正化扩散系数依赖于该尺度。这表明液体中的Fickian扩散系数不是材料常数,而是随着进行实验测量的尺度而变化。

英文摘要:

A model for diffusion in liquids that couples the dynamics of tracer particles to a fluctuating Stokes equation for the fluid is investigated in the limit of large Schmidt number. In this limit, the concentration of tracers is shown to satisfy a closed-form stochastic advection-diffusion equation that is used to investigate the collective diffusion of hydrodynamically-correlated tracers through a combination of Eulerian and Lagrangian numerical methods. This analysis indicates that transport in liquids is quite distinct from the traditional Fickian picture of diffusion. While the ensemble-averaged concentration follows Fick's law with a diffusion coefficient that obeys the Stokes-Einstein relation, each instance of the diffusive mixing process exhibits long-ranged giant fluctuations around its average behavior. We construct a class of mesoscopic models for diffusion in liquids at different observation scales in which the renormalized diffusion coefficient depends on this scale. This indicates that the Fickian diffusion coefficient in liquids is not a material constant, but rather, changes with the scale at which experimental measurements are performed.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

↑