为了在单边核磁共振仪器外产生梯度恒定的磁场，提出利用基于拓扑优化和有限元法的优化设计方法。
To obtain a constant gradient magnetic field outside unilateral nuclear magnetic resonance (NMR), optimal design method based on finite element method (FEM) and topology optimization is proposed.
第二个比较幸运的地方是，遍布全世界的范围内都有一个恒定的垂直磁场。
The second piece of luck is that all over the Earth there is a constant vertical electrical field.
麦克斯韦方程中有某些特性是恒定不变的——磁场强度、电位移场以及描述电磁场电通量的坡印廷矢量。
Maxwell's equations conserve certain properties-the magnetic field intensity, the electric displacement field and the Poynting vector that describes the electric flux of an electromagnetic field.
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