They point to evidence of pole shifts in Earth's past and claim that these reversals can be calculated by studying sunspots or magnetic field theory.
他们指出，地球曾在过去发生磁极翻转，这是谁都无法否认的事实。通过研究太阳黑子或者磁场，我们可以对磁极翻转进行计算。
However the small size of the Moon's core and the required surface magnetic field strengths were problematic for this theory.
可是，月球磁芯有点小，并且用这个理论看，月球表面磁场力还存在一些疑问。
After that a monohedral magnet for MRI is presented according to the basic theory of magnetic field and the theory of a pair of magnetic dipoles.
然后根据磁场基础理论及磁偶极子对模型理论等基本电磁场原理，提出一种设计MRI单边主磁体初始结构的方法。
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