Active nematic coherence probed under spatial patterns of distributed activity.

A photoresponsive variant of the paradigmatic active nematic fluid made of microtubules and powered by kinesin motors is studied in a conventional two-dimensional interface under blue-light illumination. This advantageously permits the system's performance to be assessed under conditions of spatially distributed activity. Both turbulent and flow aligning conditions are separately analyzed. Under uniform illuminating conditions, active flows get enhanced, in accordance with previous observations. In contrast, patterning the activity appears to disturb the effective activity measured in terms of the vorticity of the elicited flows. We interpret this result as alternative evidence of the important role played by the active length scale in setting not only the textural and flow characteristics of the active nematic but also, most importantly, the range of material integrity. Our research continues to explore perspectives that should pave the way for an effective control of such an admirable material.