Chuangxia Huang Yigang He Lihong Huang Mingyong Lai Global exponential periodicity of three-unit neural networks in a ring with time-varying delays. 1595-1603 2008 71 Neurocomputing 7-9 http://dx.doi.org/10.1016/j.neucom.2007.04.009 db/journals/ijon/ijon71.html#HuangHHL08