About theoretic calculation for lightning electromagnetic field, two analytical methods are raised, which are dipole method in time domain and time-varyingfield method in frequency domain.
在雷电电磁场的理论计算方面，提出了两种方法，即时域中的偶极子方法和频域中的时变场方法。
2
Magnetic particles also can have resonant response to a time-varying magnetic field with advantageous results related to the transfer of energy from the exciting field to the nanoparticles.
磁性颗粒能在时间变化磁场中产生共振响应，因而能很好地将能量从激发场转移到纳米颗粒中。
3
In the expanding process, the coal powder torch's expanding form is varying with the change of time, space, and air flow field.