Department of Bioengineering and Robotics, Tohoku University, Sendai 980-8579, Japan.
Phys Rev Lett. 2011 Jul 8;107(2):028102. doi: 10.1103/PhysRevLett.107.028102. Epub 2011 Jul 7.
Coherent structures appear in a concentrated suspension of swimming bacteria. While transport phenomena in a suspension have been studied extensively, how energy is transported from the individual cell scale to the larger mesoscale remains unclear. In this study, we carry out the first successful measurement of the three-dimensional velocity field in a dense suspension of bacteria. The results show that most of the energy generated by individual bacteria dissipates on the cellular scale. Only a small amount of energy is transported to the mesoscale, but the gain in swimming velocity and mass transport due to mesoscale coherent structures is enormous. These results indicate that collective swimming of bacteria is efficient in terms of energy. This paper sheds light on how energy can be transported toward smaller wave numbers in the Stokes flow regime.
相干结构出现在密集的游动细菌悬浮液中。虽然悬浮液中的输运现象已经得到了广泛的研究，但能量如何从单个细胞尺度传递到更大的中间尺度仍然不清楚。在这项研究中，我们首次成功地测量了密集细菌悬浮液中的三维速度场。结果表明，大多数由单个细菌产生的能量都在细胞尺度上耗散掉了。只有少量的能量被传递到中间尺度，但由于中间尺度相干结构，游泳速度和质量传递的增益是巨大的。这些结果表明，细菌的集体游动在能量方面是高效的。本文揭示了在斯托克斯流场中，能量如何向较小的波数传递。
