By the critical point theory, infinitely many 4σ-periodic solutions are obtained for the system of delay differential equations , where and . It is shown that all the periodic solutions derived here are brought about by the time delay.
"Infinitely Many Periodic Solutions to Delay Differential Equations via Critical Point Theory." Abstr. Appl. Anal. 2013 (SI28) 1 - 7, 2013. https://doi.org/10.1155/2013/526350