States of active nematics confined to annuli

Defects play an important role in active-matter systems. They are nucleated because of the bend instability and in steady-state are continuously created and annihilated. In this study, we investigate a 2D active nematic confined in an annulus in which the plus and minus half defects exhibit rich dynamical behavior. Confinement into an annulus effectively transforms the turbulent dynamics of the active nematic into a coherent flow. We measure the positional-orientational distribution of defects in different degrees of confinement, as well as the circulation order parameter, and finally, we classify the behavior into three distinct regimes.