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arXiv 1201.3196math.AP
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具有临界梯度吸收的奇异扩散方程的永恒解

Eternal solutions to a singular diffusion equation with critical gradient absorption

Razvan Gabriel Iagar, Philippe Laurencot

摘要:

研究了具有临界梯度吸收的奇异扩散方程的指数自相似型$u(t,x)=e^{-pβt/(2-p)} f_β(|x|e^{-βt};β)$方程\partial_{t} u-Δ p u+的非负径向对称永恒解的存在性|\nabla u| ^{p/2}=0 \quad \;\; \hbox{in} \;\;(0,\infty)\times \real^N其中$2N/(N+1) < p < 2$ .这样的解决方案被证明是存在的,只有当参数$β$的范围在一个有界的区间$(0,β_*]$,这是在鲜明的对比,与众所周知的奇异扩散方程,如$\partial_{t}ϕ-Δ_{p} ϕ=0$当$p=2N/(N+1)$或多孔介质方程$\partial_{t}ϕ-Δϕ^m=0$当$m=(N-2)/N$。此外,轮廓$f(r;β)$以$β=β_*$比$β\in (0,β_*)$更快的方式作为$r\to\infty$衰减到零,但是在两种情况下代数前导阶是相同的。事实上,对于大的$r$,$f(r;β_*)$衰减为$r^{-p/(2-p)}$,而$f(r;β)$在$β\in (0,β_*)$时表现为$(\log r)^{2/(2-p)} r^{-p/(2-p)}$。

英文摘要:

The existence of nonnegative radially symmetric eternal solutions of exponential self-similar type $u(t,x)=e^{-pβt/(2-p)} f_β(|x|e^{-βt};β)$ is investigated for the singular diffusion equation with critical gradient absorption \partial_{t} u-Δ_{p} u+|\nabla u|^{p/2}=0 \quad \;\;\hbox{in}\;\; (0,\infty)\times\real^N where $2N/(N+1) < p < 2$. Such solutions are shown to exist only if the parameter $β$ ranges in a bounded interval $(0,β_*]$ which is in sharp contrast with well-known singular diffusion equations such as $\partial_{t}ϕ-Δ_{p} ϕ=0$ when $p=2N/(N+1)$ or the porous medium equation $\partial_{t}ϕ-Δϕ^m=0$ when $m=(N-2)/N$. Moreover, the profile $f(r;β)$ decays to zero as $r\to\infty$ in a faster way for $β=β_*$ than for $β\in (0,β_*)$ but the algebraic leading order is the same in both cases. In fact, for large $r$, $f(r;β_*)$ decays as $r^{-p/(2-p)}$ while $f(r;β)$ behaves as $(\log r)^{2/(2-p)} r^{-p/(2-p)}$ when $β\in (0,β_*)$.

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