Postprint version. Published in Journal of Sound and Vibration, Volume 227, Issue 2, October 21, 1999, pages 469-470. The definitive version can be found online at http://dx.doi.org/10.1006/jsvi.1999.2334
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.