半线性抛物型方程解在有限时刻猝灭与解整体存在的条件
2014-08-06孙仁斌
孙仁斌
(中南民族大学 数学与统计学学院,武汉 430074)
本文讨论如下具有奇性反应函数的半线性抛物型方程的初边值问题:
(1)
(2)
1 解在有限时刻猝灭
为了得到问题(1)的解在有限时刻猝灭的结果,需要函数f(w)、g(t)满足一些基本条件,设:
f′(w)>0,f″(w)>0,1 (3) 存在正常数c0,使g(t)≥c0,t>0. (4) 定理1 设f(s),g(t)满足(3),(4)式,m>0,则当区域Ω充分大,使得特征值问题(2)的第一特征值λ1 (5) 则问题(1)的解会在有限时刻发生猝灭,且猝灭时刻T满足: (6) (7) 由Green公式及边界条件,有: -λ1y(t),因此,由(4)、(7)式可得: 如果问题(1)的解是整体存在的,则t可以任意大,与条件(5)矛盾,因此一定存在有限时刻T,使问题(1)的解u(x,t)关于t只存在于[0,T]上,在时刻T,解发生猝灭,令t→T-,得到T满足(6)式,定理1证毕. 下面在定理1的条件满足的情况下,讨论在猝灭时刻ut的爆破性质. 引理1 设初值函数u0(x)与g(t)满足: (8) g′(t)>0,t>0. (9) 则ut(x,t)>0,(x,t)∈Ω×(0,T). 证明令v(x,t)=ut(x,t),在方程两边对t求导得: 利用(8),(9)式与极大值原理,得证. 引理2 在定理1的条件下,问题(1)的猝灭点集是Ω的一个紧子集. 证明我们可以假设初值函数u0(x)满足: (10) 否则,只要将初始时刻增加一些即可,其中n是∂Ω上的单位外法向量. 本段在球形区域内讨论解的整体存在性,设Ω={x∈RN,|x| (11) (12) (13) 则问题(1)的解是整体存在的. (14) 参 考 文 献 [1] Kawarada H.On solutions of initial-boundary value problem forut=uxx+1/(1-u)[J]. Publ Res Inst Math Sci, 1975,10:729-736. [2] Chang C Y, Chen C S. A numerical method for semilinear singular parabolic quenching problems[J]. Quart Appl Math, 1989,47:45-57. [3] Deng C K, Levine H A.On the blow-up ofutat quenching[J]. Proc Amer Math Soc, 1989,106: 1045-1056. [4] Guo J S.On the quenching behavior of the solution of a semilinear parabolic equation[J]. J Math Anal Appl, 1990,151:58-79. [5] Dai Q Y, Gu Y G.A short note on quenching phenomena for semilinear parabolic equations[J]. J Differential Equations, 1997,137:240-250. [6] Salin T.On quenching with logarithmic singularity[J].Nonlinear Analysis,2003,52:261-289. [7] Zhi Y H , Mu C L, Yuan D M.The quenching phenomenon of a nonlocal semilinear heat equation with a weak singularity [J].Appl Math Comput, 2008, 201:701-709. [8] Zhi Y H , Mu C L.The quenching behavior of a nonlocal parabolic equation with nonlinear boundary outflux [J].Appl Math Comput,2007,184:624-630. [9] Zhi Y H.The boundary quenching behavior of a semilinear parabolic equation[J].Appl Math Comput,2011,218:233-238. [10] Zhou S M, Mu C L, Du Q L, et al.Quenching for a reaction-diffusion equation with nonlinear memory[J].Communl Nonlinear Sci Numer Simulat,2012,17:754-763. [11] Chan W Y.Quenching for nonlinear degenerate parabolic problems[J].J Comp Appl Math,2011,235:3831-3840. [12] Yang Y , Yin J X, Jin C H.A quenching phenomenon for one-dimensionalp-Laplacian with singular boundary flux[J].Appl Math Lett,2010,23:955-959. [13] Marcelo M.Complete quenching for singular parabolic problems[J].J Math Anal Appl,2011, 384:591-596. [14] Chan C Y, Boonklurb R.Solution profikes beyond quenching for a radially symmetric multi-dimensional parabolic problem[J].Nonlinear Analysis, 2013, 76:68-79. [15] Jacques G, Paul S, Sergey S.Complete quenching for a quasilinear parabolic equation[J].J Math Anal Appl,2014, 410:607-624.2 解的整体存在性