Self-organized angleworm-like and centipede-like patterns in ac-driven electroconvection of nematic liquid crystals

We report localized electroconvection (EC) discovered in nematic liquid crystals (NLC), which resembles life-like angleworms (AW) and centipedes (CP) in nature. In the presence or absence of superposed noise on an ac field, such localized EC patterns are self-organized. We investigated their spatial and dynamical features in terms of the spontaneous formation and evolution of patterns. In a planarly-aligned NLC cell, the AWs are discovered in the conduction (f < f_cd) and dielectric (f > f_cd) regimes which are divided by a characteristic frequency f_cd. Moreover, in a homeotropically-aligned NLC cell, two types of the CP (i.e., single CP and couple CP) are discovered slightly before f_cd. Considering the director field of NLC in the noise and/or ac fields, we explain the emergence of these noticeable dissipative structures that are not conventional wholly-occupying patterns in systems but localized ones, and that are not stationary but regularly dynamical. It is crucial to consider the redistribution of electric charges through additional noise effects or disclinations of NLC.