The distribution of zeros of oscillatory solutions for second order nonlinear neutral delay differential equations

In this paper, the distance between adjacent zeros of oscillatory solutions for second order nonlinear neutral delay differential equations (a(t)z′(t))′+q(t)f(x(t−σ))=0,t≥t0, where z(t)=x(t)+p(t)x(t−τ) is investigated. By means of inequality techniques, specific function sequences and nonincreasing solutions for corresponding first order differential inequality, some new estimates for the distribution of zeros of oscillatory solutions have been presented, which have extended and improved some known results.