  We investigate similarities in the micro-structural dynamics between
externally driven and actively driven nematics. Walls, lines of strong
deformations in the director field, and topological defects are characteristic
features of an active nematic. Similar structures form in driven passive
nematics when there are inhomogeneities in imposed velocity gradients due to
non-linear flow fields or geometrical constraints. Specifically, pressure
driven flow of a tumbling passive nematic in an expanding-contracting channel
produces walls and defects similar to those seen in active nematics. We also
study the response of active nematics to external driving, confirming that
imposed shear suppresses the hydrodynamic instabilities. We show that shear
fields can lead to wall alignments and the localisation of active turbulence.
