Dinh, Nguyen Van. “A Modified Asymptotic Method for a Van-Der-Pol Oscillator With Large Cubic Restoring Nonlinearity”. Vietnam Journal of Mechanics 26, no. 2 (June 1, 2004): 122–128. Accessed May 25, 2022. https://vjs.ac.vn/index.php/vjmech/article/view/5696.