1. Amster, P., Balderrama, R.: On the global dynamic behaviour for a generalized haematopoiesis model with almost periodic coefficients and oscillating circulation loss rate. Math. Methods Appl. Sci. 41, 3976–3997 (2018)
2. Berezansky, L., Braverman, E., Idels, L.: Mackey-Glass model of hematopoiesis with monotone feedback revisited. Appl. Math. Comput. 219, 4892–4907 (2013)
3. Jiang, W.H.: The existence of multiple positive periodic solutions for functional differential equations. Appl. Math. Comput. 208, 165–171 (2009)
4. Krasnosel’skii, M.A.: Positive Solutions of Operator Equations. Noordhoff, Groningen (1964)
5. Li, J.W., Du, C.X.: Existence of positive periodic solutions for a generalized Nicholson’s blowflies model. J. Comput. Appl. Math. 221, 226–233 (2008)