Electronic Journal of Differential Equations,
Vol. 2004(2004), No. 30, pp. 1-18.

Title: Periodic Duffing equations with delay
       
Authors: Jean-Marc Belley (Univ. de Sherbrooke, Qc, Canada)
   Michel Virgilio (Univ. de Sherbrooke, Qc, Canada)
Abstract: 
 Assuming a priori bounds on the mean of
 a $T$-periodic function $p$, we show that the
 Duffing equation
 $$
 x''(t) +cx'(t) +g(t-\tau,x(t-\tau), x'(t-\tau)) =p(t),
 $$
 with delay $\tau$, admits a $T$-periodic solution.
  
Submitted January 22, 2004. Published March 3, 2004.
Math Subject Classifications: 34K13.
Key Words: Duffing equations; periodic solutions; delay equations;
           a priori bounds; contraction principle.