ANH, N. D.; KHIEM, N. T. Sub harmonic oscillations in first order systems with delay. Vietnam Journal of Mechanics, Hanoi, Vietnam, v. 12, n. 1, p. 1–6, 1990. DOI: 10.15625/0866-7136/10272. Disponível em: https://vjs.ac.vn/index.php/vjmech/article/view/10272. Acesso em: 29 mar. 2024.