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arXiv math/0509359math.AP
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非线性波动力学中的线性叠加

Linear superposition in nonlinear wave dynamics

A. Babin, A. Figotin

摘要:

本文研究了R^{d}中由双曲型偏微分方程描述的非线性色散波系统和格点Z^{d}上的差分方程。系统包含两个小参数:一个是慢、快时间尺度之比,另一个是小、大空间尺度之比。我们证明了包括非线性Schrodinger方程、Maxwell方程、Fermi-Pasta-Ulam模型和许多其它不完全可积系统在内的广泛的一类系统满足叠加原理。该原理本质上指出,如果波的非线性演化最初作为一般波包(定义为几乎单色波)的总和开始,则具有高精度的该波仍然是经历独立非线性演化的单独波包波的总和。演化被认为是足够长的时间间隔来观察充分发展的非线性现象所涉及的波包。特别是,我们的方法提供了一个简单的理由,数值观察到的效果几乎没有相互作用的孤子通过彼此没有任何求助于完全可积性。我们的分析并不依赖于任何的anonymous或常见的渐近展开的两个小参数,但它使用相当明确的和建设性的代表性的解决方案作为功能的解析系列的形式的初始数据的功能。

英文摘要:

We study nonlinear dispersive wave systems described by hyperbolic PDE's in R^{d} and difference equations on the lattice Z^{d}. The systems involve two small parameters: one is the ratio of the slow and the fast time scales, and another one is the ratio of the small and the large space scales. We show that a wide class of such systems, including nonlinear Schrodinger and Maxwell equations, Fermi-Pasta-Ulam model and many other not completely integrable systems, satisfy a superposition principle. The principle essentially states that if a nonlinear evolution of a wave starts initially as a sum of generic wavepackets (defined as almost monochromatic waves), then this wave with a high accuracy remains a sum of separate wavepacket waves undergoing independent nonlinear evolution. The time intervals for which the evolution is considered are long enough to observe fully developed nonlinear phenomena for involved wavepackets. In particular, our approach provides a simple justification for numerically observed effect of almost non-interaction of solitons passing through each other without any recourse to the complete integrability. Our analysis does not rely on any ansatz or common asymptotic expansions with respect to the two small parameters but it uses rather explicit and constructive representation for solutions as functions of the initial data in the form of functional analytic series.

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