Generation of umbilics by Poiseuille flows

  • P. PieranskiEmail author
Regular Article
Part of the following topical collections:
  1. Irreversible Dynamics: A topical issue dedicated to Paul Manneville


The Fredericks transition in homeotropic nematic layers submitted to an electric field can be described in terms of a 2D vectorial order parameter \(\vec c\). We have shown previously that umbilics which are point defects of the field \(\vec c\) can be generated in a controlled manner by magnetic fields. Here we report on a serendipitous discovery of generation of umbilics during cleaning of a sample and on a series of experiments which were performed with the aim to unveil conditions necessary for a controlled reproduction of this phenomenon. From the analysis of all circumstances in which umbilics were generated we conclude that umbilics are generated by Poiseuille flows and appear in π-walls in points where these walls are orthogonal to the flow direction. We discuss theoretical aspects of the action of Poiseuille flows on the field \(\vec c\) and unveil the relationship \(\vec c\)→ system π-walls. Finally we explain why and where umbilics are generated in π-walls.

Graphical abstract


Topical issue: Irreversible Dynamics: A topical issue dedicated to Paul Manneville 


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© EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  1. 1.Laboratoire de Physique des SolidesUniversité Paris-SudOrsay CedexFrance

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