Oscillation theorems concerning non-linear differential equations of the second order

This paper concerns the oscillation of solutions of the differential eq. [r,(t) ψ(x(t)) ƒ (x(t))] + q(t) φ (g(x(t)), r(t)ψ(x(t))=0 where uφ(u,v) > 0 for all u ≠ 0, xg(x)>0, xf(x)>0 for all x ≠ 0, ψ(x)>0 for all x ∈ R, r(t)>0 for t≥t0>0 and q is of arbitrary sign. Our results complement the results in [A.G. Kartsatos, On oscillation of nonlinear quations of second order, J. Math. Anal. Appl. 24 (1968), 665-668], and improve a number of existing oscillation criteria. Our main results are illustrated with examples