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arXiv 1004.0573math.AP
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空间周期反应扩散方程的最小行波速度变分问题

A variational problem associated with the minimal speed of travelling waves for spatially periodic reaction-diffusion equations

Xing Liang, Xiaotao Lin, Hiroshi Matano

摘要:

我们考虑方程$u_t=u_{xx}+b(x)u(1-u),$ $x\in\mathbb R,$,其中$b(x)$是$\mathbb R$上的非负测度,其在$x.$中是周期性的。在$b(x)$是光滑周期函数的情况下,已知对于任何$c\geq c^*(b),$存在速度为$c$的行波,其中$c^*(b)$是取决于$b.$的某个正数。或\lq \lq周期性行波”,并且$c^*(b)$被称为\lq \lq最小速度”。在本文中,我们首先扩展了这个理论的存在性的最小速度$c^*(b)$的任何非负措施$b$与周期$L.$接下来,我们研究的问题,最大化$c^*(b)$下的约束$\int_{[0,L)}b(x)dx=αL,$其中$α$是一个任意给定的常数。这一问题与80年代后期数学生态学家研究的问题密切相关,但其答案一直没有得到解答。我们通过证明周期排列的狄拉克δ函数$αL\sum_{k\in\mathbb Z}δ(x+kL).$可以达到最大值来回答这个问题

英文摘要:

We consider the equation $u_t=u_{xx}+b(x)u(1-u),$ $x\in\mathbb R,$ where $b(x)$ is a nonnegative measure on $\mathbb R$ that is periodic in $x.$ In the case where $b(x)$ is a smooth periodic function, it is known that there exists a travelling wave with speed $c$ for any $c\geq c^*(b),$ where $c^*(b)$ is a certain positive number depending on $b.$ Such a travelling wave is often called a \lq\lq pulsating travelling wave" or a \lq\lq periodic travelling wave", and $c^*(b)$ is called the \lq\lq minimal speed". In this paper, we first extend this theory by showing the existence of the minimal speed $c^*(b)$ for any nonnegative measure $b$ with period $L.$ Next we study the question of maximizing $c^*(b)$ under the constraint $\int_{[0,L)}b(x)dx=αL,$ where $α$ is an arbitrarily given constant. This question is closely related to the problem studied by mathematical ecologists in late 1980's but its answer has not been known. We answer this question by proving that the maximum is attained by periodically arrayed Dirac's delta functions $αL\sum_{k\in\mathbb Z}δ(x+kL).$

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