arXiv subjects

Haruki Hayano

Publications and source records attributed to Haruki Hayano.

4 recordsLinked to original sources

arXiv2026

Near-field Hydrodynamics Disentangles Angular Correlations in Confined Active Suspensions

Spatial confinement profoundly impacts the transport and self-organization of active matter across diverse biological systems. While the collective orders in confined active matter have been extensively characterized, how geometric constraints reshape near-field flows and the resulting inter-particle correlations remains largely unexplored. In this study, we combine experiments and hydrodynamic simulations to investigate inter-particle correlations within quasi-two-dimensional Chlamydomonas reinhardtii suspensions. We reveal two disentangled modes characterizing cell pairs: a dipolar mode and an entrainment mode, which exhibit a density- and distance-dependent competition. Combining single-cell flow field analysis, hydrodynamic simulations, and active-passive mixtures, we link these two modes to singular hydrodynamics and lubrication-induced entrainment. Our results demonstrate that spatiotemporal correlations in confined active matter are fundamentally rooted in the interplay of these two hydrodynamic mechanisms.

cond-mat.soft↗

arXiv2025

Neural-Network-Assisted Boltzmann Approach for Dilute Microswimmer Suspensions

We introduce a neural-network-assisted Boltzmann framework that learns the binary-collision map of microswimmers directly from data and uses it to evaluate collision integrals efficiently. Using a representative model swimmer, the learned map quantitatively predicts translational and rotational diffusivities and enables a linear-stability analysis of isotropy against polar ordering in dilute suspensions. The resulting predictions closely match direct simulations. The present framework is agnostic to active matter models and broadly applicable: once two-body collision data are obtained -- either from simulations or experiments -- the same surrogate can be used to evaluate kinetic transport across dilute conditions where binary collisions dominate. Because the workflow relies only on pre- and post-collision statistics, the present approach provides a general data-driven route linking particle-scale interactions to macroscopic transport and collective behavior in active suspensions.

cond-mat.soft↗

arXiv2024

Anomalous rheology of puller-type microswimmer suspensions

We explore the mechanism underlying the anomalous rheology of puller-type microswimmer suspensions through direct hydrodynamic simulations. Puller-type swimmers generate contractile flow fields along their swimming direction, leading to hydrodynamic interactions that cause the swimmers to align vertically. Our simulations reveal that this alignment effect, along with the resultant orientational order of swimming motion, becomes particularly pronounced near boundary walls, where local swimmer density is amplified, predominantly controlling the overall swimming dynamics and rheological properties of the suspension. These findings contrast with our previous simulations of pusher-type swimmers, which hydrodynamically interact through extensile flow fields, whereby they exhibit weak orientational order in the bulk region, which primarily determines their steady-state properties. Furthermore, we demonstrate that the steady-state behavior near the walls is strongly influenced by the aspect ratio of the microswimmers and the degree of confinement between the walls. Our results highlight the crucial role of microswimmer characteristics, such as shape and swimming mechanisms, in determining the rheological properties of active suspensions.

cond-mat.soft↗

arXiv2023

Hydrodynamic interactions in anomalous rheology of active suspensions

We explore a mechanism of the anomalous rheology of active suspensions by hydrodynamic simulations using model pusher swimmers. Our simulations demonstrate that hydrodynamic interactions under shear flow systematically orient swimmers along the extension direction, which is responsible for determining the global swimming states and the resulting significant viscosity reduction. The present results indicate the essential role of hydrodynamic interactions in the elementary processes controlling the rheological properties in active suspensions. Furthermore, such processes may be the substance of the previously proposed scenario for anomalous rheology based on the interplay between the rotational diffusivities and the external shear flow.

cond-mat.soft↗