Postprint version. Published in Journal of Sound and Vibration, Volume 227, Issue 2, October 21, 1999, pages 469-470.
At the time of publication, the author Mohammad N. Noori was affiliated with Worcester Polytechnic Institute. Currently, August 2008, he is the Dean of the College of Engineering at California Polytechnic State University - San Luis Obispo.
The definitive version is available at https://doi.org/10.1006/jsvi.1999.2334.