The authors study the existence of positive periodic solutions for the nonautonomous functional differential equation
where , , , , , , are -periodic functions, and is a constant. Here, , denote, respectively, the right and the left-hand side limits of at , and the following hypotheses are assumed , , , for a certain positive integer in such a way that .
The results included in this paper are connected with those given in the papers of A. Wan, D. Jiang and X. Xu [Comput. Math. Appl. 47, 1257–1262 (2004; Zbl 1073.34082)], and A. Wan and D. Jiang [Kyushu J. Math. 56, 193–202 (2002; Zbl 1012.34068)] for the nonimpulsive case.
The new results extend those in [Comput. Math. Appl. 47, 1257–1262 (2004; Zbl 1073.34082)], and their proof is based on the application of fixed-point theorems in cones [see K. Deimling, Nonlinear Functional Analysis. Springer-Verlag, New York (1985; Zbl 0559.47040), and K. Lan and J. R. L. Webb, J. Differ. Equations 148, 407–421 (1998; Zbl 0909.34013)]. The calculus of the Green’s function associated with problem (1) is also essential in their procedure.
To this purpose, the authors consider an impulsive ‘linear’ problem related to (1) which is written on its equivalent integral form. This expression is useful to write problem (1) as an integral equation. As a particular case of the main result, it is analyzed the case of sublinear and superlinear behavior. Finally, the authors include some examples which illustrate the applicability of the new results to some problems with biological meaning.