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Steady state solutions of a reaction-diffusion system modeling chemotaxis. (English) Zbl 1002.35049
Summary: We study the following nonlinear elliptic equation $\begin{cases} \Delta u-\beta u+\lambda\left( {e^u\over\int_\Omega e^u}-{1\over |\Omega |}\right) =0\quad &\text{in }\Omega,\\ {\partial u\over\partial \nu}= 0\quad &\text{on }\partial \Omega\end{cases},$ where $$\Omega$$ is a smooth bounded domain in $$\mathbb{R}^2$$. This equation arises in the study of stationary solutions of a chemotaxis system proposed by Keller and Segel. Under the condition that $$\beta> {\lambda\over |\Omega |}-\lambda_1$$, $$\lambda\neq 4\pi m$$ for $$m=1,2,\dots,$$ where $$\lambda_1$$ is the first (nonzero) eigenvalue of $$-\Delta$$ under the Neumann boundary condition, we establish the existence of a solution to the above equation. Our idea is a combination of Struwe’s technique and blow up analysis for a problem with Neumann boundary condition.

##### MSC:
 35J65 Nonlinear boundary value problems for linear elliptic equations 35Q80 Applications of PDE in areas other than physics (MSC2000) 35B40 Asymptotic behavior of solutions to PDEs 35B45 A priori estimates in context of PDEs
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