Complex sentence: The second term is the frequency shift that results from the photoacoustic wave as it is observed by the ultrasonic transducer with the particle as a moving source H. Fang, K. Maslov, L.V. Wang.
Split into simpler sentences: The second term is the frequency shift that results from the photoacoustic wave as it is observed by the ultrasonic transducer. In this case, the particle is the moving source H. Fang, K. Maslov, L.V. Wang.