[S0739-3717(00)00704-2]

Dr. Shahruz claims that Theorem 2 in 1 is stronger than Theorem 1 in 2. Since Dr. Shahruz proves his claim by showing an example, not a mathematical derivation, I feel his argument is not convincing. Also it indicates clearly in 2, that the main purpose of the Theorem in 2 is to use damping to eliminate the parametric resonance. So there is no need for considering a time-varying damping.

1.
Gil, M. L., Stability of Finite and Infinite Systems, Kluwer Academic, Dordrecht, 1998.
2.
Wu
,
J. W.
, and
Fung
,
R. F.
,
1999
,
ASME J. Vibr. Acoust.
,
121
, pp.
509
511
.