  A wide range of living and artificial active matter exists in close contact
with substrates and under strong confinement, where in addition to dipolar
active stresses, quadrupolar active stresses can become important. Here, we
numerically investigate the impact of quadrupolar non-equilibrium stresses on
the emergent patterns of self-organisation in non-momentum conserving active
nematics. Our results reveal that beyond having stabilising effects, the
quadrupolar active forces can induce various modes of topological defect motion
in active nematics. In particular, we find the emergence of both polar and
nematic ordering of the defects, as well as new phases of self-organisation
that comprise topological defect chains and topological defect asters. The
results contribute to further understanding of emergent patterns of collective
motion and non-equilibrium self-organisation in active matter.
