1. O. Arino, E. Sanchez, R. Bravo de la Parra, and P. Auger, A singular perturbation in an age-structured population, SIAM J. Appl. Math. 60 (1999–2000), no. 2, 408–436.
2. J. Banasiak and L. Arlotti, Perturbations of positive semigroups with applications, Springer, 2006.
3. J. Banasiak and A. Goswami, Singularly perturbed population models with reducible migration matrix. 1. Sova-Kurtz theorem and the convergence to the aggregated model, Discr. Cont. Dyn. Syst. A 35 (2015), no. 2, 617–635.
4. Banasiak J., Goswami A., Shindin S.: Aggregation in age and space structured population models: an asymptotic analysis approach. J. Evol. Equ. 11, 121–154 (2011)
5. J. Banasiak, A. Goswami, and S. Shindin, Singularly perturbed population models with reducible migration matrix: 2. Asymptotic analysis and numerical simulations, Mediterr. J. Math. 11 (2014), no. 2, 533–559.