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arXiv 2002.07937math.APcond-mat.soft
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非退化非线性扩散方程的长时间渐近性

Long-time asymptotics of non-degenerate non-linear diffusion equations

Ivan C. Christov, Akif Ibraguimov, Rahnuma Islam

摘要:

研究了典型非线性扩散方程的长时间渐近性。具体来说,我们考虑的情况下,一个非退化的扩散函数,这是一个(非负)多项式的因变量的问题。我们激励这些类型的方程使用爱因斯坦的随机游动范式,导致非散度型的偏微分方程。另一方面,利用守恒原理导出了一个散度型的偏微分方程。将派生一个转换来处理这两种情况。然后,证明了一个最大值原理(在无界和有界区域上),以获得非线性扩散问题解的时间演化的上下界。具体来说,这些界限是基于线性问题的基本解(所谓的阿伦森格林函数)。因此,夹在线性问题的两个基本解之间的非线性问题的解的长时间渐近性,我们证明了,不同于退化扩散的情况下,非退化扩散方程的解决方案收敛到线性扩散解决方案在很长的时间。选择数值例子支持数学定理,并说明收敛过程。我们的研究结果的影响,如何解释潜在的异常扩散过程(如在流动的颗粒物质),已在应用物理文献中讨论的渐近标度。

英文摘要:

We study the long-time asymptotics of prototypical non-linear diffusion equations. Specifically, we consider the case of a non-degenerate diffusivity function that is a (non-negative) polynomial of the dependent variable of the problem. We motivate these types of equations using Einstein's random walk paradigm, leading to a partial differential equation in non-divergence form. On the other hand, using conservation principles leads to a partial differential equation in divergence form. A transformation is derived to handle both cases. Then, a maximum principle (on both an unbounded and a bounded domain) is proved, in order to obtain bounds above and below for the time-evolution of the solutions to the non-linear diffusion problem. Specifically, these bounds are based on the fundamental solution of the linear problem (the so-called Aronson's Green function). Having thus sandwiched the long-time asymptotics of solutions to the non-linear problems between two fundamental solutions of the linear problem, we prove that, unlike the case of degenerate diffusion, a non-degenerate diffusion equation's solution converges onto the linear diffusion solution at long times. Select numerical examples support the mathematical theorems and illustrate the convergence process. Our results have implications on how to interpret asymptotic scalings of potentially anomalous diffusion processes (such as in the flow of particulate materials) that have been discussed in the applied physics literature.

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