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arXiv 1012.0700math.AP
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有界区域上快速扩散方程的近灭绝性态

Behaviour near extinction for the Fast Diffusion Equation on bounded domains

Matteo Bonforte, Gabriele Grillo, Juan Luis Vazquez

摘要:

研究了在有界光滑区域$Ω\subset \RR^d$上的快速扩散方程$u_t=Δu^m$,其指数范围为$m_s=(d-2)_+/(d+2)<m<1$ .已知这类问题的有界正解$u(t,x)$在有限时间$T$内熄灭,并且这类解逼近一个分离变量解$u(t,x)\sim (T-t)^{1/(1-m)}S(x)$,称为$t\to T^-$ .在这里,我们感兴趣的是描述灭绝时间附近的解决方案的行为。我们首先表明,收敛$u(t,x)\,(T-t)^{-1/(1-m)}$ $S(x)$发生一致的相对误差范数。然后,我们研究了重标流的收敛速度问题。对于$m$接近于1的情形,我们通过熵方法和加权Poincaré不等式得到了这样的速率。后一点的分析,使一个必要的使用相关的固定椭圆问题$-ΔS^m= {\bf c} S$在极限$m\to 1$的优良性能,这样的研究有一个独立的利益。

英文摘要:

We consider the Fast Diffusion Equation $u_t=Δu^m$ posed in a bounded smooth domain $Ω\subset \RR^d$ with homogeneous Dirichlet conditions; the exponent range is $m_s=(d-2)_+/(d+2)<m<1$. It is known that bounded positive solutions $u(t,x)$ of such problem extinguish in a finite time $T$, and also that such solutions approach a separate variable solution $u(t,x)\sim (T-t)^{1/(1-m)}S(x)$, as $t\to T^-$. Here we are interested in describing the behaviour of the solutions near the extinction time. We first show that the convergence $u(t,x)\,(T-t)^{-1/(1-m)}$ to $S(x)$ takes place uniformly in the relative error norm. Then, we study the question of rates of convergence of the rescaled flow. For $m$ close to 1 we get such rates by means of entropy methods and weighted Poincaré inequalities. The analysis of the latter point makes an essential use of fine properties of the associated stationary elliptic problem $-ΔS^m= {\bf c} S$ in the limit $m\to 1$, and such a study has an independent interest.

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