Boundary-layer profile of a singularly perturbed non-local semi-linear problem arising in chemotaxis

TL;DR

This paper analyzes the boundary-layer behavior of solutions to a singularly perturbed non-local semi-linear PDE modeling chemotaxis, revealing unique solutions with boundary layers of order epsilon and curvature-dependent asymptotic profiles.

Contribution

It establishes the existence and uniqueness of boundary-layer solutions for the problem and derives refined asymptotic profiles considering boundary curvature effects.

Findings

Solutions exhibit boundary layers of thickness proportional to epsilon.

The boundary-layer slope decreases with boundary curvature.

Boundary-layer thickness increases with boundary curvature.

Abstract

This paper is concerned with the following singularly perturbed non-local semi-linear problem \begin{equation} \label{h} \tag{$\ast$} \begin{cases} \varepsilon^2 \Delta u=\frac{m}{\int_{\Omega}e^{u}{\mathrm{d}x}}u e^u\quad &\mathrm{in}~\Omega,\\ u= u_0~&\mathrm{on}~\partial\Omega, \end{cases} \end{equation} which corresponds to the stationary problem of a chemotaxis system describing the aerobic bacterial movement, where $\Omega$ is a smooth bounded domain in $\mathbb{R}^N (N\geq 1)$, $\varepsilon, m$ and $u_0$ are positive constants. We show that the problem \eqref{h} admits a unique classical solution which is of boundary-layer profile as $\varepsilon \to 0$, where the boundary-layer thickness is of order $\varepsilon$. When $\Omega=B_R(0)$ is a ball with radius $R>0$, we find a refined asymptotic boundary layer profile up to the first-order expansion of $\varepsilon$ by which we find that the slope of the layer profile in the immediate vicinity of the boundary decreases with respect to (w.r.t.) the curvature while the boundary-layer thickness increases {w.r.t.} the curvature.