RT Journal T1 Stability of a Class of Nonlinear Hierarchical Age-Dependent Population Model A1 Zerong He,Zhiqiang Zhang,Yang Wang PB Acta mathematica scientia,Series A FD 2020-12-26 YR 2020 JF Acta mathematica scientia, Series A JO Acta mathematica scientia,Series A VO 40 IS 6 SP 1712 DO K1 ;Hierarchy of ages;Positive equilibria;Stability;Non-zero fixed points LK {http://121.43.60.238/sxwlxbA/EN/article/article_16276.shtml}