People often focus on the existence of light and often neglect the shadow function, in fact, the light and shadow is not two hostile concepts, but interdependent and complementary dual phenomenon.

Its natural frequency falls into two parts when the loads exerted on generator rotor are asymmetrical. Dual resonance phenomenon appears based on the former single frequency vibration.

As a special social psychological phenomenon, the Dual Image occupies a very important position in the psychobiography.