On the topic of noise, be aware that rotating machinery, no matter how well balanced, will still vibrate due to harmonic resonances if the numberofvanes is an even number.
对噪音问题，要知道旋转机械，无论怎样很好的平衡，仍然会由于谐波共振振动如果数字的叶片是一个偶数。
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Since then, however, scientists have found a numberof well-preserved theropod fossils with many more featherlike structures, corresponding to downy feathers and feathers with vanes.