Luo, Albert C.J., and Siyuan Xing. “Time-Delay Effects on Periodic Motions in a Periodically Forced, Time-Delayed, Hardening Duffing Oscillator”. Journal of Vibration Testing and System Dynamics, vol. 1, no. 1, Aug. 2026, pp. 73-91, https://doi.org/10.5890/JVTSD.2017.03.006.