# Homogeneous and heterogeneous populations of active rods in two-dimensional channels

## TL;DR

This study models and simulates the collective behavior of homogeneous and heterogeneous active rod-like bacteria in two-dimensional channels, revealing how boundary effects influence swarm segregation based on motility differences.

## Contribution

It introduces a simple molecular dynamics model for heterogeneous active rods and investigates the impact of heterogeneity and confinement on swarm dynamics and segregation.

## Key findings

- Boundary confinement drives segregation in mixed populations.
- Motility-to-steric force ratio governs swarm dynamics.
- Heterogeneity influences collective behavior and spatial organization.

## Abstract

Active swarms, consisting of individual agents which consume energy to move or produce work, are known to generate a diverse range of collective behaviors. Many examples of active swarms are biological in nature (e.g., fish shoals and bird flocks) and have been modeled extensively by numerical simulations. Such simulations of swarms usually assume that the swarm is homogeneous; that is, every agent has exactly the same dynamical properties. However, many biological swarms are highly heterogeneous, such as multispecies communities of micro-organisms in soil, and individual species may have a wide range of different physical properties. Here we explore heterogeneity by developing a simple model for the dynamics of a swarm of motile heterogeneous rodlike bacteria in the absence of hydrodynamic effects. Using molecular dynamics simulations of active rods confined within a two-dimensional rectangular channel, we first explore the case of homogeneous swarms and show that the key parameter governing both dynamics is ratio of the motility force to the steric force. Next we explore heterogeneous or mixed swarms in which the constituent self-propelled rods have a range of motilities and steric interactions. Our results show that the confining boundaries play a strong role in driving the segregation of mixed populations.