An exact solution for the nonlinear birefringent medium model is obtained by using SO(3) rotation group property.

本文利用SO（3）旋转群性质得到了非线性双折射介质模型的一个严格解。

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It is very difficult to get analytic solution except some very specific cases for the model owing to nonlinear partial differential equation.

由于非饱和流动的数学模型归结为非线性的偏微分方程，除了一些很特殊的情况外，很难得到解析解。

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This paper also gives the differential equation of the nonlinear vibration model, and obtains its asymptotic solution by means of singular perturbation methods.

文中给出了这一非线性振动模型的微分方程，并用奇异摄动法求得了渐近解。

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