论文标题
各向异性Ornstein-Uhlenbeck过程的精确解决方案
Exact solution for the Anisotropic Ornstein-Uhlenbeck Process
论文作者
论文摘要
活动物质模型通常考虑具有恒定模量和随机方向的力(速度)的颗粒。一些模型还包括粒子位移(Wiener过程)中的随机噪声,导致短时间尺度的扩散运动。另一方面,Ornstein-Uhlenbeck过程考虑了粒子速度的Langevin动力学,并预测在短时间尺度上没有扩散的运动。但是,实验表明,迁移细胞可能会出现不同的速度以及短期扩散行为。尽管Ornstein-Uhlenbeck过程可以描述不同的速度,但主动的Mater模型可以解释短期扩散行为。各向同性模型无法同时解释:短期扩散使瞬时速度不确定,因此阻碍了考虑速度时间衍生物的动力学方程。另一方面,这两个模型都申请迁移的生物细胞,并且必须在一定程度上产生相同的可观察到的预测。在这里,我们提出并分析解决了一个各向异性的Ornstein-uhlenbeck过程,该过程考虑了极化颗粒,具有langevin动力学,用于粒子在极化方向上的粒子运动,同时遵循正交方向的维也纳过程。我们的表征提供了一种理论上可靠的方法,可以将无量纲模拟中的运动与尺寸实验中的运动进行比较,此外还提出了一种在实验或模拟中处理必然有限精度效应的程序。
Active Matter models commonly consider particles with overdamped dynamics subject to a force (speed) with constant modulus and random direction. Some models include also random noise in particle displacement (Wiener process) resulting in a diffusive motion at short time scales. On the other hand, Ornstein-Uhlenbeck processes consider Langevin dynamics for the particle velocity and predict a motion that is not diffusive at short time scales. However, experiments show that migrating cells may present a varying speed as well as a short-time diffusive behavior. While Ornstein-Uhlenbeck processes can describe the varying speed, Active Mater models can explain the short-time diffusive behavior. Isotropic models cannot explain both: short-time diffusion renders instantaneous velocity ill-defined, hence impeding dynamical equations that consider velocity time-derivatives. On the other hand, both models apply for migrating biological cells and must, in some limit, yield the same observable predictions. Here we propose and analytically solve an Anisotropic Ornstein-Uhlenbeck process that considers polarized particles, with a Langevin dynamics for the particle movement in the polarization direction while following a Wiener process for displacement in the orthogonal direction. Our characterization provides a theoretically robust way to compare movement in dimensionless simulations to movement in dimensionful experiments, besides proposing a procedure to deal with inevitable finite precision effects in experiments or simulations.