Geometrical optics approach can only calculate the high frequency approach solution of drilling bit vibration source wave equation in non caustic area but it become invalid in caustic area.

由于几何光学法求解钻头震源波动方程的高频近似解有局限性，即在焦散区失效，故只能计算非焦散区的高频近似解。

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This approach can work because in some systems "0" is invalid ports, When you attempt to use a normally closed the port connecting to it will produce different results.

这一方法能够工作是因为在一些系统中“0”是无效端口，当你试图使用一种通常的闭合端口连接它时将产生不同的结果。

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They argue that the referendum was invalid and have decried the United Kingdom for pushing a colonialist approach onto the territory.

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