Stability of point defects of degree $\pm \frac 1 2$ in a   two-dimensional nematic liquid crystal model
  We study $k$-radially symmetric solutions corresponding to topological defects of charge $\frac{k}{2}$ for integer $k \neq 0$ in the Landau-de Gennes model describing liquid crystals in two-dimensional domains. We show that the solutions whose radial profiles satisfy a natural sign invariance are stable when $|k| = 1$ (unlike the case $|k|>1$ which we treated before). The proof crucially uses the monotonicity of the suitable components, obtained by making use of the cooperative character of the system. A uniqueness result for the radial profiles is also established. 
Radu Ignat, Luc Nguyen, Valeriy Slastikov and Arghir Zarnescu
math.AP