K. Nagai

Experimental investigations of collective motion of self-propelled particles

Using minimal models described by simple rules like the Vicsek model, collective motion of self-propelled particles is well studied. Recently, we found that the predicted long-range orderd phase with the giant number flucuations exists in the real world using E. coli (D. Nishiguchi, KHN, et al. 2017), which indicates that unified descriptions of collective motion in the real world actually exists.

The particles in the Vicsek model change their direction randomly. However, there are various kinds of self-propelled particle that keeps its rotation rate for a long time such as an E. coli close to wall and a mycoplasma on a glass plate. Using an agent-based model like the Vicsek model, we elucidated the role of memory of rotation rate in collective motion of self-propelled particles. We found that the collective motions observed using our model were formed microtubules running on a glass grafted by dyneins (Y. Sumino, KHN, et al. 2012, KHN, et al. 2015). The recent results of experiments using C. elegans on a substrate, which keeps its rotation rate for a while, were also well-reproduced by our model. These results indicate that there exist unified descriptions of rotating self-propelled particles.