An invariant set generated by the domain topology for parabolic semiflows with small diffusion
Nils Ackermann  Instituto de Matemáticas, Universidad Nacional Autónoma de México, México, D.F. C.P. 04510, Mexico (email) Abstract: We consider the singularly perturbed semilinear parabolic problem $u_td^2\Delta u+u=f(u)$ with homogeneous Neumann boundary conditions on a smoothly bounded domain $\Omega\subseteq \mathbb{R}^N$. Here $f$ is superlinear at $0$, and $\pm\infty$ and has subcritical growth. For small $d>0$ we construct a compact connected invariant set $X_d$ in the boundary of the domain of attraction of the asymptotically stable equilibrium $0$. The main features of $X_d$ are that it consists of positive functions that are pairwise noncomparable, and its topology is at least as rich as the topology of $\partial\Omega$ in a certain sense. If the number of equilibria in $X_d$ is finite, then this implies the existence of connecting orbits within $X_d$ that are not a consequence of a well known result by Matano.
Keywords: Semilinear Parabolic Equation, Singular Perturbation,
Neumann Boundary Condition, LusternikSchnirelmann Category,
Invariant Set, Connecting Orbit, Positive Equilibrium, Domain of
Attraction.
Received: November 2006; Revised: February 2007; Available Online: May 2007. 
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