A class of chemotaxis systems with growth source and nonlinear secretion

Abstract

In this paper, we are concerned with a class of parabolic-elliptic chemotaxis systems encompassing the prototype $$\left\{\begin{array}{lll} &u_t = \nabla\cdot(\nabla u-χu\nabla v)+f(u), & x\in Ω, t>0, \\[0.2cm] &0= Δv -v+u^κ, & x\in Ω, t>0 \end{array}\right. $$ with nonnegative initial condition for $u$ and homogeneous Neumann boundary conditions in a smooth bounded domain $Ω\subset \mathbb{R}^n(n\geq 2)$, where $χ>0$, $κ>0$ and $f$ is a smooth growth source satisfying $f(0)\geq 0$ and $$ f(s)\leq a-bs^θ, \quad s\geq 0, \text{with some} a\geq 0, b>0, θ>1. $$ Firstly, it is shown, either $$ κ<\frac{2}{n}\quad \& \quad f\equiv 0, $$ or $$θ>κ+1, $$ or $$ θ-κ=1, \ \ b\geq \frac{(κn-2)}{κn}χ, \eqno(*) $$ that the corresponding initial-value problem admits a unique classical solution that is uniformly bounded in space and time. Our proof is elementary and semigroup-free. Whilst, with the particular choices $θ=2$ and $κ=1$, Tello and Winkler \cite{TW07} use sophisticated estimates via the Neumann heat semigroup to obtain the global boundedness under the strict inequality in ($\ast$). Thereby, we improve their results to the "borderline" case $b=(κn-2)/(κn)χ$ in this regard. Next, for an unbounded range of $χ$, the system is shown to exhibit pattern formations, and, the emerging patterns are shown to converge weakly in $ L^θ(Ω)$ to some constants as $χ\rightarrow \infty$. While, for small $χ$ or large damping $b$, precisely $b>2χ$ if $f(u)=u(a-bu^κ)$ for some $a, b>0$, we show that the system does not admit pattern formation and the large time behavior of solutions is comparable to its associated ODE+algebraic system.