Defects disclination pairs, 250-1 dislocations

Figure 4. Isolated topological defects in a triangular lattice, (a) Isolated -1 and +1 disclinations. A vector aligned along a local lattice direction is rotated by 60° upon parallel transport around a unit strength disclination. (6) An isolated dislocation. The heavy line represents a Burgers circuit around the dislocation, and the Burgers vector of the dislocation is the amount by which the circuit fails to close. The core of the dislocation is a tightly bound pair of +1 and -1 disclinations (Reproduced from [78] by permission of Oxford University Press.)...

A very plausible alignment mechanism involves movement of defects. Here, forces on defect structures in an electric field are described. The actual material contains a large number of defects in many configurations, so a full analysis would be prohibitively complex. However, it is instructive to consider instead some simple ca.ses a general wall defect, a +1/2, -1/2 pair of parallel disclination lines, and two compound edge dislocations with opposing Burgers vector. 

This texture distribution is common, but corresponds to a rather schematic model, indicating that high-energy defects, such as disclinations, are found mainly in the vicinity of the isotropic transition. Other situations are observed in thick preparations of cholesterics, for example, where planar domains can be interrupted by walls of vertical layers (Fig. 34 c and d), due to edge dislocations disjoining into disclina-tion pairs (see Fig. 5 d). Despite these par-... 

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