 the increasing sequence of stopping times $$\left\{\begin{array}{l} \eta_0 = 0\\ \\ \sigma_0 = \inf \{ t \geq 0 : U^{u,\varepsilon}(t,\cdot) \in {\partial}B_{r_0}\} \end{array}\right.$$ and for $n \in {{\mathbb N}}_0$ $$\left\{\begin{array}{l} \eta_{n+0} = \inf \{ t > \sigma_n : U^{u,\varepsilon}(t,\cdot) \in {\partial}B_{r_0}