费马原理

The main contents include the ray phenomenon and its generation conditions; the deduction and physical illumination of wave action conservation equation and wave number conservation equation; ray theory for sinusoidal waves; Fermat's principle; the variation of amplitude in the case of straight and parallel depth contours and circular depth contours; the amplitude near the caustics; wave trapping; deduction of mild-slope equation and the relevant numerical solution methods.

讲授折射现象及其发生的条件；波作用守恒方程和波数守恒方程的推导及物理解释；稳恒正弦波的控制方程及射线方程；费马原理；利用射线方程研究等深线是平行直线和圆周线时波振幅的变化，特别是焦散线附近波高的变化以及由此而产生的波的俘获；缓坡方程的推导及有关的数值求解方法。

Fermat's principle ; ray tracing ; spline function ; gradient method ; target method

费马原理；射线追踪；样条函数；梯度法；打靶法

Fermat's principle: The raypath which seismic energy will follow between two points is that for which the first order variation with all neighboring paths is zero.

费马原理：两点之间地震波传播的射线路径，它与相邻路径的一阶差分为零。

In the days of sailing vessels the crew were afraid they would be becalmed on the ocean.

在使用帆船的时代，船员们担心他们会因为无风而无法在海洋上航行。

As long as foreign donors pay the PA's salary bill, few expect a new intifada.

只要外国继续为巴权力机构的薪水买单，希望发动新暴动的人便寥寥无几。