 Solution

A topological defect occurs where the local order cannot be continued smoothly while retaining its surrounding texture. At a nematic disclination core, the director model fails and the orientational order may decrease.

For a planar texture $\mathbf{n}=(\cos \varphi ,\sin \varphi )$,Because $\mathbf{n}\equiv -\mathbf{n}$, half-integer winding strengths are allowed. The original sketches use $\varphi =s\alpha +{\varphi }_0$ to show $s=+1/2,-1/2,+1$, corresponding to director turns $+\pi ,-\pi ,+2\pi$. A radial $+1$ pattern and an azimuthally rotated version have the same winding.

These are planar labels. In unrestricted three dimensions an integer line texture may escape by tilting out of the plane; half-integer lines have a different classification. A planar disclination strength must not be identified automatically with a three-dimensional hedgehog point charge.