Title: Asymptotic behavior of semilinear parabolic equations on the circle with time almost-periodic/recurrent dependence,
Abstract: We study topological structure of the $\omega$-limit sets of the skew-product
semiflow generated by the following scalar reaction-diffusion equation
\begin{equation*} u_{t}=u_{xx}+f(t,u,u_{x}),\,\,t>0,\,x\in
S^{1}=\mathbb{R}/2\pi \mathbb{Z}, \end{equation*} where $f(t,u,u_x)$ is
$C^2$-admissible with time-recurrent structure including almost-periodicity and
almost-automorphy. Contrary to the time-periodic cases (for which any
$\omega$-limit set can be imbedded into a periodically forced circle flow), it
is shown that one cannot expect that any $\omega$-limit set can be imbedded
into an almost-periodically forced circle flow even if $f$ is uniformly
almost-periodic in $t$.
More precisely, we prove that, for a given $\omega$-limit set $\Omega$, if
${\rm dim}V^c(\Omega)\leq 1$ ($V^c(\Omega)$ is the center space associated with
$\Omega$), then $\Omega$ is either spatially-homogeneous or
spatially-inhomogeneous; and moreover, any spatially-inhomogeneous $\Omega$ can
be imbedded into a time-recurrently forced circle flow (resp. imbedded into an
almost periodically-forced circle flow if $f$ is uniformly almost-periodic in
$t$). On the other hand, when ${\rm dim}V^c(\Omega>1$, it is pointed out that
the above embedding property cannot hold anymore. Furthermore, we also show the
new phenomena of the residual imbedding into a time-recurrently forced circle
flow (resp. into an almost automorphically-forced circle flow if $f$ is
uniformly almost-periodic in $t$) provided that $\dim V^c(\Omega)=2$ and $\dim
V^u(\Omega)$ is odd. All these results reveal that for such system there are
essential differences between time-periodic cases and non-periodic cases.