arXiv subjects

Hiroki Matsukiyo

Publications and source records attributed to Hiroki Matsukiyo.

2 recordsLinked to original sources

arXiv2026

Oscillating edge current in polar active fluid

Dense bacterial suspensions exhibit turbulent behaviour called ``bacterial turbulence''. The behavior of the bulk unconstrained bacterial turbulence is described well by the Toner-Tu-Swift-Hohenberg (TTSH) equation for the velocity field. However, it remains unclear how we should treat boundary conditions on bacterial turbulence in contact with some boundaries (e.g. solid walls). To be more specific, although the importance of the ``edge current'', the flow along the boundary, has been demonstrated in several experimental studies on confined bacterial suspensions, previous numerical studies based on the TTSH equation employ non-slip boundary conditions and do not seem to describe properly the behavior of bacteria near the boundaries. In this study, we impose a slip boundary condition on the TTSH equation to describe the bacterial motion at boundaries. We develop a method to implement the slip boundary condition. Using this method, we have successfully produced edge current and discovered that the direction of the edge current temporally oscillates. The oscillation can be attributable to the advection term in the TTSH equation. Our work demonstrates that boundary conditions could play an important role in the collective dynamics of active systems.

cond-mat.soft↗

arXiv2026

Defect configuration of an active nematic around a circular obstacle

To enhance the understanding of the behavior of active nematic, it is important to understand the behavior of topological defects. In this paper, we study the configuration of topological defects of a two-dimensional active nematic around a circular obstacle. In the case of a passive nematic liquid crystal, the equilibrium configuration of defects can be easily identified by the method of image charges. In the case of an active nematic, however, one must take account of the flow field generated by active constituents, and the problem of identifying the defect configuration becomes complicated. We first perform numerical simulations and investigate how the stationary defect configuration deviates from the passive case. Furthermore, we carry out a theoretical calculation based on an analytical expression relating the defect velocity with the force exerted on the defect. Our theoretical calculation qualitatively reproduces the simulation results. Our study may be applied to describing the behaviour of e.g. cell populations in the presence of obstacles, and has the potential to benefit related fields, e.g., developmental biology.

cond-mat.soft↗