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arXiv 2210.04414cond-mat.stat-mech
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球面上的分数布朗运动与标度布朗运动:长时间相关性对导航策略的影响

Fractional and scaled Brownian motion on the sphere: The effects of long-time correlations on navigation strategies

Adriano Valdés Gómez, Francisco J. Sevilla

AI总结:

本文分析了二维球面上的分数布朗运动与标度布朗运动,发现分数布朗运动的长时间相关性会与导航策略相互作用产生丰富传输特性,而标度布朗运动则与导航策略无关,且其解析与数值结果高度一致。

摘要:

我们分析了二维球面 $\mathbb{S}^{2}$ 上的分数布朗运动和标度布朗运动。我们发现,表征分数布朗运动的内禀长时间相关性与曲面上执行的具体动力学(导航策略)相互交织,产生了丰富的传输特性。我们重点研究两类导航策略:一类由为 $\mathbb{S}^2$ 选取的特定坐标系(本文选取球坐标系)诱导,我们发现与无此类长时间相关性时的情况相反,该策略会达到非平衡稳态分布。这些结果类似于受限一维和二维平直空间中报道的结果 [Guggenberger et al. New J. Phys. 21 022002 (2019), Vojta et al. Phys. Rev. E 102, 032108 (2020)],但在本文分析的球面情况中,并不存在影响运动的边界。相反,当所选导航策略对应于随粒子移动的参考系(Frenet-Serret 参考系)时,在长时间极限下会恢复球面上的平衡分布。对于这两种导航策略,向稳态分布的弛豫时间均取决于 Hurst 参数的具体数值。我们还证明,在 $\mathbb{S}^{2}$ 上,以具有幂律标度的时间依赖扩散系数为特征的标度布朗运动,与导航策略无关;通过求解 $\mathbb{S}^{2}$ 上的时间依赖扩散方程得到的解析计算结果,与通过我们的数值方法生成轨迹系综得到的数值结果取得了良好的一致性。

英文摘要:

We analyze \emph{fractional Brownian motion} and \emph{scaled Brownian motion} on the two-dimensional sphere $\mathbb{S}^{2}$. We find that the intrinsic long time correlations that characterize fractional Brownian motion collude with the specific dynamics (\emph{navigation strategies}) carried out on the surface giving rise to rich transport properties. We focus our study on two classes of navigation strategies: one induced by a specific set of coordinates chosen for $\mathbb{S}^2$ (we have chosen the spherical ones in the present analysis), for which we find that contrary to what occurs in the absence of such long-time correlations, \emph{non-equilibrium stationary distributions} are attained. These results resemble those reported in confined flat spaces in one and two dimensions [Guggenberger {\it et al.} New J. Phys. 21 022002 (2019), Vojta {\it et al.} Phys. Rev. E 102, 032108 (2020)], however in the case analyzed here, there are no boundaries that affects the motion on the sphere. In contrast, when the navigation strategy chosen corresponds to a frame of reference moving with the particle (a Frenet-Serret reference system), then the \emph{equilibrium} \emph{distribution} on the sphere is recovered in the long-time limit. For both navigation strategies, the relaxation times towards the stationary distribution depend on the particular value of the Hurst parameter. We also show that on $\mathbb{S}^{2}$, scaled Brownian motion, distinguished by a time-dependent diffusion coefficient with a power-scaling, is independent of the navigation strategy finding a good agreement between the analytical calculations obtained from the solution of a time-dependent diffusion equation on $\mathbb{S}^{2}$, and the numerical results obtained from our numerical method to generate ensemble of trajectories.

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