Changyin Sun Xunming Li Chun-Bo Feng On Robust Periodicity of Delayed Dynamical Systems with Time-Varying Parameters. 32-37 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3173&spage=32 2004 conf/isnn/2004-1 ISNN (1) db/conf/isnn/isnn2004-1.html#SunLF04