This paper was retracted by the publisher as it was found that K. Ratchagit plagiarized a paper by Vu Ngoc Phat and Phan T. Nam published in the Electonic Journal of Differential Equations, vol. 2005 (2005), no. 58, pp. 1–8.
"[RETRACTION] Exponential Stability of Linear Nonautonomous Systems." Afr. Diaspora J. Math. (N.S.) 10 (1) 79 - 86, 2010.