Analytic shock-fronted solutions to a reaction–diffusion equation with negative diffusivity

IF 2.6 2区 数学 Q1 MATHEMATICS, APPLIED
Thomas Miller, Alexander K. Y. Tam, Robert Marangell, Martin Wechselberger, Bronwyn H. Bradshaw-Hajek
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引用次数: 0

Abstract

Reaction–diffusion equations (RDEs) model the spatiotemporal evolution of a density field u ( x , t ) $u({x},t)$ according to diffusion and net local changes. Usually, the diffusivity is positive for all values of u $u$ , which causes the density to disperse. However, RDEs with partially negative diffusivity can model aggregation, which is the preferred behavior in some circumstances. In this paper, we consider a nonlinear RDE with quadratic diffusivity D ( u ) = ( u a ) ( u b ) $D(u) = (u - a)(u - b)$ that is negative for u ( a , b ) $u\in (a,b)$ . We use a nonclassical symmetry to construct analytic receding time-dependent, colliding wave, and receding traveling wave solutions. These solutions are multivalued, and we convert them to single-valued solutions by inserting a shock. We examine properties of these analytic solutions including their Stefan-like boundary condition, and perform a phase plane analysis. We also investigate the spectral stability of the u = 0 $u = 0$ and u = 1 $u = 1$ constant solutions, and prove for certain a $a$ and b $b$ that receding traveling waves are spectrally stable. In addition, we introduce a new shock condition where the diffusivity and flux are continuous across the shock. For diffusivity symmetric about the midpoint of its zeros, this condition recovers the well-known equal-area rule, but for nonsymmetric diffusivity it results in a different shock position.

Abstract Image

具有负扩散性的反应-扩散方程的冲击前解析解
反应-扩散方程(RDE)根据扩散和局部净变化来模拟密度场的时空演变。通常情况下,扩散率在所有Ⅴ值下都为正值,这会导致密度分散。然而,部分扩散率为负的 RDE 可以模拟聚集,这在某些情况下是首选行为。在本文中,我们考虑了一种具有二次扩散性的非线性 RDE,该扩散性在......时为负。我们利用非经典对称性来构建解析的后退时变、碰撞波和后退行波解。这些解都是多值解,我们通过插入冲击波将它们转换为单值解。我们研究了这些解析解的特性,包括它们的类斯蒂芬边界条件,并进行了相平面分析。我们还研究了恒定解的频谱稳定性,并证明了后退行波具有一定的频谱稳定性。此外,我们还引入了一种新的冲击条件,即扩散率和通量在冲击两侧是连续的。对于围绕其零点中点对称的扩散性,该条件恢复了著名的等面积规则,但对于非对称扩散性,它导致了不同的冲击位置。
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来源期刊
Studies in Applied Mathematics
Studies in Applied Mathematics 数学-应用数学
CiteScore
4.30
自引率
3.70%
发文量
66
审稿时长
>12 weeks
期刊介绍: Studies in Applied Mathematics explores the interplay between mathematics and the applied disciplines. It publishes papers that advance the understanding of physical processes, or develop new mathematical techniques applicable to physical and real-world problems. Its main themes include (but are not limited to) nonlinear phenomena, mathematical modeling, integrable systems, asymptotic analysis, inverse problems, numerical analysis, dynamical systems, scientific computing and applications to areas such as fluid mechanics, mathematical biology, and optics.
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