Ishikawa Takuji, Pedley T J
Department of Bioengineering and Robotics, Tohoku University, Sendai 980-8579, Japan.
Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge CB3 0WA, United Kingdom.
Phys Rev E Stat Nonlin Soft Matter Phys. 2014 Sep;90(3):033008. doi: 10.1103/PhysRevE.90.033008. Epub 2014 Sep 12.
Although diffusion properties of a suspension of swimming microorganisms in equilibrium have been studied intensively, those under nonequilibrium conditions remain unclear. In this study, we investigate the spreading of model microorganisms from high concentration to low by the Stokesian dynamics method. The results reveal that the spreading is neither purely diffusive nor ballistic. When the dipole component of the swimming velocity is small, the cells actively direct themselves towards lower concentrations. The concentration distribution shows stronger oscillations than would be expected for ballistic swimmers with constant orientations. The mechanism can be explained by the near-field hydrodynamic interactions between cells and the spatial gradient of the collision rate. Comparison of the numerical results with a simple continuum model and a Monte Carlo simulation shows that those conventional models can capture the basic features of the present results. These new findings pave the way towards a mathematical description of the dispersion of microorganisms in various environments.
尽管对处于平衡状态的游动微生物悬浮液的扩散特性已进行了深入研究，但非平衡条件下的扩散特性仍不清楚。在本研究中，我们通过斯托克斯动力学方法研究了模型微生物从高浓度向低浓度的扩散。结果表明，这种扩散既不是纯粹的扩散，也不是弹道式的。当游动速度的偶极分量较小时，细胞会主动向较低浓度方向移动。浓度分布显示出比具有恒定取向的弹道式游动者预期更强的振荡。该机制可以通过细胞间的近场流体动力学相互作用以及碰撞率的空间梯度来解释。将数值结果与一个简单的连续介质模型和蒙特卡罗模拟进行比较表明，那些传统模型能够捕捉到当前结果的基本特征。这些新发现为数学描述微生物在各种环境中的扩散铺平了道路。
