论文标题
单粒子扩散的续订方程通过半透明界面
Renewal equations for single-particle diffusion through a semipermeable interface
论文作者
论文摘要
通过半透明界面的扩散具有广泛的应用,范围从分子传递通过生物膜到使用人工膜的逆渗透进行水纯化。在单粒子水平上,可以根据所谓的抢断布朗尼运动(BM)对具有恒定通透性$κ_0$的屏障的一维扩散进行建模。后者将连续反映的BMS连续缝合在一起,这些回合仅限于屏障的左侧或右侧。当屏障的布朗当地时间超过$κ_0$参数的指数随机变量时。然后,新的回合立即以同样的概率沿任一方向启动。最近已经显示,捕获BM的概率密度满足了将全密度与屏障两侧部分反映BM的概率密度联系起来的更新方程。此外,可以构建续签方程的广义版本,以结合非马克维亚,基于遭遇的吸收模型。在本文中,我们扩展了将BM捕集到有限域和较高空间维度的单粒子扩散的更新理论。我们还考虑了一个不对称界面的示例,在该界面中,每个吸收事件后的方向开关有偏见。最后,我们展示了如何通过球形对称界面合并基于接触的吸收模型,以进行单粒子扩散。我们发现,即使在界面的两侧使用相同的非马克维亚吸收模型,所产生的渗透性也是具有内存的不对称时间依赖性函数。此外,渗透函数往往是重尾的。
Diffusion through semipermeable interfaces has a wide range of applications, ranging from molecular transport through biological membranes to reverse osmosis for water purification using artificial membranes. At the single-particle level, one-dimensional diffusion through a barrier with constant permeability $κ_0$ can be modeled in terms of so-called snapping out Brownian motion (BM). The latter sews together successive rounds of partially reflecting BMs that are restricted to either the left or right of the barrier. Each round is killed (absorbed) at the barrier when its Brownian local time exceeds an exponential random variable parameterized by $κ_0$. A new round is then immediately started in either direction with equal probability. It has recently been shown that the probability density for snapping out BM satisfies a renewal equation that relates the full density to the probability densities of partially reflected BM on either side of the barrier. Moreover, generalized versions of the renewal equation can be constructed that incorporate non-Markovian, encounter-based models of absorption. In this paper we extend the renewal theory of snapping out BM to single-particle diffusion in bounded domains and higher spatial dimensions. We also consider an example of an asymmetric interface in which the directional switching after each absorption event is biased. Finally, we show how to incorporate an encounter-based model of absorption for single-particle diffusion through a spherically symmetric interface. We find that, even when the same non-Markovian model of absorption applies on either side of the interface, the resulting permeability is an asymmetric time-dependent function with memory. Moreover, the permeability functions tend to be heavy-tailed.