Oscillation criteria for a class of nonlinear fourth order neutral differential equations

In this paper, sufficient conditions are obtained for oscillation of a class of nonlinear fourth order mixed neutral differential equations of the form (E) $$left( {frac{1} {{aleft( t right)}}left( {left( {yleft( t right) + pleft( t right)yleft( {t - tau } right)} right)^{prime prime } } right)^alpha } right)^{prime prime } = qleft( t right)fleft( {yleft( {t - sigma _1 } right)} right) + rleft( t right)gleft( {yleft( {t + sigma _2 } right)} right)$$ under the assumption $$intlimits_0^infty {left( {aleft( t right)} right)^{tfrac{1} {alpha }} dt} = infty .$$ where α is a ratio of odd positive integers. (E) is studied for various ranges of p(t).