<ref name="Hayashi_Shibayama_Ueda_Quasi-periodic_Oscillations_in_Self-oscillatory_Systems_with_External_Force"> {{cite journal | author=Hayashi C | author2=Shibayama H | author3=Ueda Y | title=Quasi-periodic Oscillations in Self-oscillatory Systems with External Force | journal=IECE Technical Report, Nonlinear Theory | year=1961 | date=16 December 1961 }} </ref> | <ref name="Hayashi_Shibayama_Ueda_Quasi-periodic_Oscillations_in_Self-oscillatory_Systems_with_External_Force"> {{cite journal | author=Hayashi C | author2=Shibayama H | author3=Ueda Y | title=Quasi-periodic Oscillations in Self-oscillatory Systems with External Force | journal=IECE Technical Report, Nonlinear Theory | year=1961 | date=16 December 1961 }} </ref> |