Asymptotic integration of second-order nonlinear differential equations via principal and nonprincipal solutions. - Türker Ertem; Agacik Zafer (Appl. Math. Comput., 2013)

Monotone positive solutions for a class of second-order nonlinear differential equations. - Türker Ertem; Agacik Zafer (J. Comput. Appl. Math., 2014)

Asymptotic integration of second-order nonlinear delay differential equations. - Ravi P. Agarwal; Türker Ertem; Agacik Zafer (Appl. Math. Lett., 2015)

Asymptotic integration of higher order nonlinear delay differential equations via principal solutions. - Ravi P. Agarwal; Türker Ertem; Agacik Zafer (Asymptot. Anal., 2017)