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Abstract
The onset of transient periodic dissipative structures (TPDS) is studied using the linear perturbation approximation when a sufficiently strong magnetic field (B) is impressed on the uniformly aligened director (n o) of a nematic confined to the annular space between two coaxial cylinders of radii R 2 and R 1 (R 2>R 1). Only TPDS with axial or azimuthal periodicity is considered. An approximate expression for the magnetic body force density is employed. The solutions mainly concern rigid anchoring. When n o is along the common axis, a radial field or an azimuthal field causes TPDS with periodicity along the axis when the calamitic nematic has positive diamagnetic anisotropy (χA>0); an axial field has a similar effect when χ A<0. The dependence of the rise time as well as the periodicity wavevector are studied as functions of the applied field strength and the ratio of the radii (R 21 = R 2/R 1). A weakening of director anchoring has a deletcrious effect on the formation of TPDS. When n o is azimuthal and χA0, a radial or an axial field may induce TPDS having an azimuthal periodicity wavevector which is an integer and related to the number of domains; continuous changes in control variables cause discontinuous changes in the wavevector. Using hypothetical material parameters, it is shown that an axial (or an azimuthal) field may induce TPDS with a continuously varying (or discontinuously varying) wavevector in a radially aligned discotic nematic having χA>0. If χA<0. a radial field may induce TPDS with modulation along both the axial and the azimuthal directions in a discotic nematic. When R 21 is close to unity, the results of this work go over to those obtained for a flat sample.