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Spreading speeds of nonlocal KPP equations in almost periodic media
Journal of Functional Analysis ( IF 1.7 ) Pub Date : 2020-08-06 , DOI: 10.1016/j.jfa.2020.108723
Xing Liang , Tao Zhou

In this paper, we investigate the spreading phenomena of the general nonlocal KPP equation in almost periodic media()ut=Ru(t,xy)dμ(y)u+a(x)u(1u)t>0,xR, where μ is a probability measure on R and a is a positive almost periodic function with infxRa(x)>0.

Two constants ω+ and ω are called the spreading speeds of () in the positive and negative directions respectively provided the following two statements hold:

(i) For any nonnegative initial function u0L(R)C(R) with a compact support, limt+supx(ω++ϵ)t|u(t,x)|=limt+supx(ωϵ)t|u(t,x)|=0,ϵ>0;

(ii) There is some L>0 such that for any nonnegative initial function u0L(R)C(R), if u0(x)>0 on an interval longer than L, thenlimt+sup(ω+ϵ)tx(ω+ϵ)t|u(t,x)1|=0,ϵ>0.

In this paper, we show that if the heterogeneity of the media can be averaged by the diffusion, then () has spreading speeds. Precisely, let E1 be the support of μ, E be the closed additive subgroup generated by E1{0} and H(a,S):={a(+s)|sS}, we have the following theorem:

Theorem 0.1

Let a be an almost periodic function with infxRa(x)>0. Then () has spreading speeds ω+ and ω provided H(a,E)=H(a,R).

We also give another description of this result by analyzing the basis of frequencies of a.

Let {βk}k=1N,NZ+{} be an at most countable set of real numbers. Suppose that for any q=(q1,,qn)Qn{0}, k=1nqkβk0 for any nZ+ and nN. SetA={r|nZ+,q=(q1,,qn)Qnwith qn0 s.t.rk=1nqkβk2πQ}.

Theorem 0.2

If the support of μ sptμrZ for any rA, then for any almost periodic function a with infxRa(x)>0 and {βk}k=1N being a basis of frequencies of a, () has spreading speeds.

If sptμrZ for some rA, then there is some almost periodic function a with infxRa(x)>0 and {βk}k=1N being a basis of frequencies of a such that () has no spreading speeds.

As the main tools in this paper, we also develop the theory of generalized principal eigenvalues and the homogenization method for nonlocal diffusion problems.



中文翻译:

非局部KPP方程在几乎周期介质中的传播速度

在本文中,我们研究了一般非局部KPP方程在几乎周期介质中的扩散现象üŤ=[RüŤX-ÿdμÿ-ü+一种Xü1个-üŤ>0X[R其中μ是对[R并且a是一个正的几乎周期函数,具有信息X[R一种X>0

两个常数 ω+ω- 被称为传播速度 分别在以下两个方面保持正向和负向:

(i)对于任何非负初始函数 ü0大号[RC[R 在紧凑的支撑下, Ť+SUPXω++ϵŤ|üŤX|=Ť+SUPX-ω--ϵŤ|üŤX|=0ϵ>0;

(ii)有一些 大号>0 这样对于任何非负初始函数 ü0大号[RC[R如果 ü0X>0间隔大于L,则Ť+SUP-ω-+ϵŤXω+-ϵŤ|üŤX-1个|=0ϵ>0

在本文中,我们表明,如果可以通过扩散将介质的异质性平均化,则 传播速度快。准确地,让Ë1个μ的支持,Ë 是由生成的封闭加法子组 Ë1个{0}H一种小号={一种+s|s小号},我们有以下定理:

定理0.1

设a是一个几乎周期性的函数 信息X[R一种X>0。然后 传播速度快 ω+ ω- 提供 H一种Ë=H一种[R

我们还通过分析a频率的基础来对此结果进行另一个描述。

{βķ}ķ=1个ññž+{}是最多可数的实数集。假设对于任何q=q1个qññ{0}ķ=1个ñqķβķ0 对于任何 ñž+ññ。组一种={[R|ñž+q=q1个qññ与 qñ0 ST[Rķ=1个ñqķβķ2π}

定理0.2

如果支持μ sptμ[Rž 对于任何 [R一种,则对于任何几乎周期函数a 信息X[R一种X>0 {βķ}ķ=1个ñ 作为a频率的基础, 传播速度快。

如果 sptμ[Rž 对于一些 [R一种,然后有一些几乎周期性的函数 信息X[R一种X>0 {βķ}ķ=1个ñ 作为频率的基础 没有传播速度。

作为本文的主要工具,我们还开发了广义本征值理论和非局部扩散问题的均化方法。

更新日期:2020-08-06
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