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arXiv 1108.3161math.AP
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heat equation的逐点估计。Dini系数障碍问题自由边界的应用

Pointwise estimates for the heat equation. Application to the free boundary of the obstacle problem with Dini coefficients

Erik Lindgren, Régis Monneau

摘要:

研究了抛物型方程解的点态正则性。作为第一个结果,我们证明了,如果平均振荡的模$Δu -u_t$在原点是Dini(在$L^p$平均),那么原点是一个勒贝格连续点(仍然在$L^p$平均)的$D^2 u$和$\dd_t u$。我们将这一点态正则性结果推广到Dini右手边的抛物障碍问题。特别是,我们证明了障碍物问题的解决方案,在正则点的自由边界,泰勒扩展到两个空间和一个时间(在$L^p$平均)。此外,我们还得到了泰勒展开式误差的定量估计。我们的方法是基于衰变估计矛盾,使用爆破参数和刘维尔型定理。作为我们的方法的一个副产品,我们推导出的规则点的自由边界局部包含在$C^1$超曲面的抛物线距离$\sqrt{x^2 +|t|}$。

英文摘要:

We study the pointwise regularity of solutions to parabolic equations. As a first result, we prove that if the modulus of mean oscillation of $Δu -u_t$ at the origin is Dini (in $L^p$ average), then the origin is a Lebesgue point of continuity (still in $L^p$ average) for $D^2 u$ and $\dd_t u$. We extend this pointwise regularity result to the parabolic obstacle problem with Dini right hand side. In particular, we prove that the solution to the obstacle problem has, at regular points of the free boundary, a Taylor expansion up to order two in space and one in time (in the $L^p$ average). Moreover, we get a quantitative estimate of the error in this Taylor expansion. Our method is based on decay estimates obtained by contradiction, using blow-up arguments and Liouville type theorems. As a by-product of our approach, we deduce that the regular points of the free boundary are locally contained in a $C^1$ hypersurface for the parabolic distance $\sqrt{x^2 +|t|}$.

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