Dynamics of s =1/2 disclinations in twisted nematics

Declination lines separating regions with opposite twist in a twisted structure of a nematic liquid crystal are studied theoretically and experimentally. A particular study is made of magnetic-field induced motions of the disclination lines. Comparison of theoretical and experimental results leads to an estimate of the size of the disclination core. The elastic energy of a disclination line is obtained as a side result. A simple physical picture is given for the combined effect of the magnetic, curvature induced and dissipative forces acting on a disclination line.