We use continuum simulations to study the impact of friction on the ordering of defects in an active nematic. Even in a frictionless system, +1/2 defects tend to align side-by-side and orient antiparallel reflecting their propensity to form, and circulate with, flow vortices. Increasing friction enhances the effectiveness of the defect-defect interactions, and defects form dynamically evolving, large scale, positionally and orientationally-ordered structures which can be explained as a competition between hexagonal packing, preferred by the -1/2 defects, and rectangular packing preferred by the +1/2 defects.
@article{arxiv.2005.01164,
title = {Role of friction in multidefect ordering},
author = {Kristian Thijssen and Mehrana R. Nejad and Julia M. Yeomans},
journal= {arXiv preprint arXiv:2005.01164},
year = {2020}
}