PIEKARSKI, Sławomir. The method of the deformation operator in quantum acoustics – a formulation of perturbation calculus. Archives of Acoustics, [S. l.], v. 8, n. 2, p. 155–168, 2016. Disponível em: https://acoustics3.ippt.pan.pl/index.php/aa/article/view/3252. Acesso em: 25 apr. 2025.