Fig. 2: Configurations of defects and viscometric surfaces.

a, Snapshot of the flow geometry around −1/2 and +1/2 nematic defects from the numerical simulations, illustrating three −1/2 defects in a strain-dominated region, in a vorticity-dominated region and on the \({{{\mathcal{Q}}}}=0\) border. Arrows show the instantaneous velocity field, dashed lines the director field and solid lines the \({{{\mathcal{Q}}}}=0\) contours, with the enclosed area coloured by circulation (red for clockwise and blue for anticlockwise). Blue trefoil symbols mark −1/2 defects and green comet-shaped symbols represent +1/2 defects. b, Prediction for ideal, solitary −1/2 defect (section ‘Stokesian solitary-defect model’). c–e, Snapshots of +1/2 defects for mirror symmetry (c) and broken mirror symmetry with an anticlockwise vortex (d) or clockwise vortex (e). f, Same as b for a solitary +1/2 defect. g, PDF of alignment angles between the defect orientation and the tangent of the associated viscometric (\({{{\mathcal{Q}}}}=0\)) line (section ‘Defects and viscometric surfaces’). The vertical blue dashed-dotted line indicates the ideally expected alignment from f (section ‘Stokesian solitary-defect model’). The grey dashed line indicates the alignment angle for a point active force (section ‘Stokesian line-force model of bend walls’).