Boundedness and asymptotics of a reaction-diffusion system with density-dependent motility (2005.11460v1)

Abstract: We consider the initial-boundary value problem of a system of reaction-diffusion equations with density-dependent motility \begin{equation*}\label{e1}\tag{$\ast$} \begin{cases} u_t=\Delta(\gamma(v)u)+\alpha u F(w) -\theta u, &x\in \Omega, ~~t>0,\ v_t=D\Delta v+u-v,& x\in \Omega, ~~t>0,\ w_t=\Delta w-uF(w),& x\in \Omega, ~~t>0, \frac{\partial u}{\partial \nu}=\frac{\partial v}{\partial \nu}= \frac{\partial w}{\partial \nu}=0,&x\in \partial\Omega, ~~t>0,\ (u,v,w)(x,0)=(u_0,v_0,w_0)(x), & x\in\Omega, \end{cases} \end{equation*} in a bounded domain $\Omega\subset\R^2$ with smooth boundary, $\alpha$ and $\theta$ are non-negative constants and $\nu$ denotes the outward normal vector of $\partial \Omega$. The random motility function $\gamma(v)$ and functional response function $F(w)$ satisfy the following assumptions: \begin{itemize} \item $\gamma(v)\in C^{3}([0,\infty)),~0<\gamma_{1}\leq\gamma(v)\leq \gamma_2, \ |\gamma'(v)|\leq \eta$ for all $v\geq0$; \item $F(w)\in C^1([0,\infty)), F(0)=0,F(w)>0 \ \mathrm{in}~(0,\infty)~\mathrm{and}~F'(w)>0 \ \mathrm{on}\ \ [0,\infty)$ \end{itemize} for some positive constants $\gamma_1, \gamma_2$ and $\eta$. Based on the method of weighted energy estimates and Moser iteration, we prove that the problem \eqref{e1} has a unique classical global solution uniformly bounded in time. Furthermore we show that if $\theta>0$, the solution $(u,v,w)$ will converge to $(0,0,w_)$ in $L^\infty$ with some $w_>0$ as time tends to infinity, while if $\theta=0$, the solution $(u,v,w)$ will asymptotically converge to $(u_,u_,0)$ in $L^\infty$ with $u_*=\frac{1}{|\Omega|}(|u_0|{L^1}+\alpha|w_0|{L^1})$ if $D>0$ is suitably large.