Inertial manifolds on squeezed domains

Abstract

Let $\Omega$ be an arbitrary smooth bounded domain in $\R^2$ and $\epsilon>0$ be arbitrary. Squeeze $\Omega$ by the factor $\epsilon$ in the $y$-direction to obtain the squeezed domain $\Omega_\epsilon=\{(x,\epsilon y)\mid (x,y)\in\Omega \}$. In this paper we study the family of reaction-diffusion equations $$ \alignedat 2 u_t&=\Delta u+f(u),&\quad &t>0, (x,y)\in\Omega_\epsilon \partial_{\nu_\epsilon} u&=0,& & t>0, (x,y)\in\partial\Omega_\epsilon,\endalignedat\tag $E_\epsilon$ $$ where $f$ is a dissipative nonlinearity of polynomial growth. In a previous paper we showed that, as $\epsilon\to 0$, the equations $(E_\epsilon)$ have a limiting equation which is an abstract semilinear parabolic equation defined on a closed linear subspace of $H^1(\Omega)$. We also proved that the family ${\Cal A}_\epsilon$ of the corresponding attractors is upper semicontinuous at $\epsilon=0$. In this paper we prove that, if $\Omega$ satisfies some natural assumptions, then the limiting equation can be characterized as a reaction-diffusion equation on a finite topological graph. Moreover, there is a family $\Cal M_\epsilon$ of inertial $C^1$-manifolds for $(E_\epsilon)$, of some fixed finite dimension $\nu$, and, as $\epsilon\to 0$, the flow on $\Cal M_\epsilon$ converges in the $C^1$-sense to the limit flow on $\Cal M_0$.