Asymptotic behavior of solutions of a semilinear heat equation with localized reaction

Abstract

We consider non-negative solutions to the Dirichlet problem of a semilinear heat equation with localized reaction in $\Omega$: $u_t = \Delta u +f(u(x_0(t),t))$, where $\Omega$ is a smooth bounded domain, $x_0(t)$ is a locally Hölder continuous function from $[0,\infty)$ into $\Omega$ and $f$ satisfies $f(0)=f'(0)=0$ and some blow-up condition. We show that, if $x_0(t)$ remains in some compact subset of $\Omega$ as $t\to\infty$, then all global solutions are bounded in $\Omega\times(0,\infty)$ and, if $x_0(t)$ approaches the boundary of $\Omega$ as $t\to \infty$, then some unbounded global solution (infinite time blow-up solution) exists. These results are parts of our main results on the classification of all solutions.