Sufficient conditions are obtained so that every solution of $[y(t) - p(t)y(t-τ)]^{(n)} + Q(t)G(y(t-σ)) = f(t)$ where n ≥ 2, p,f ∈ C([0,∞),ℝ), Q ∈ C([0,∞),[0,∞)), G ∈ C(ℝ,ℝ), τ > 0 and σ ≥ 0, oscillates or tends to zero as $t→ ∞ $. Various ranges of p(t) are considered. In order to accommodate sublinear cases, it is assumed that $∫_0^{∞} Q(t)dt = ∞$. Through examples it is shown that if the condition on Q is weakened, then there are sublinear equations whose solutions tend to ±∞ as t → ∞.
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Some results concerning oscillation of second order self-adjoint matrix differential equations are obtained. These may be regarded as a generalization of results for the corresponding scalar equations.
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Oscillation criteria are obtained for nonlinear homogeneous third order differential equations of the form $y''' + q(t)y' + p(t)y^α = 0$ and y''' + q(t)y' + p(t)f(y) = 0, where p and q are real-valued continuous functions on [a,∞), f is a real-valued continuous function on (-∞, ∞) and α > 0 is a quotient of odd integers. Sign restrictions are imposed on p(t) and q(t). These results generalize some of the results obtained earlier in this direction.
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The lower bounds of the spacings b-a or a'-a of two consecutive zeros or three consecutive zeros of solutions of third order differential equations of the form y''' + q(t)y' + p(t)y = 0 (*) are derived under very general assumptions on p and q. These results are then used to show that $t_{n+1} - tₙ → ∞$ or $t_{n+2} - tₙ → ∞$ as n → ∞ under suitable assumptions on p and q, where ⟨tₙ⟩ is a sequence of zeros of an oscillatory solution of (*). The Opial-type inequalities are used to derive lower bounds of the spacings d-a or b-d for a solution y(t) of (*) with y(a) = 0 = y'(a), y'(c) = 0 and y''(d) = 0 where d ∈ (a,c) or y'(c) = 0, y(b) = 0 = y'(b) and y''(d) = 0 where d ∈ (c,b).
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Sufficient conditions are obtained for oscillation of all solutions of a class of forced nth order linear and nonlinear neutral delay differential equations. Also, asymptotic behaviour of nonoscillatory solutions of a class of forced first order neutral equations is studied.