Hindawi Publishing Corporation Advances in Difference Equations Volume 2011, Article ID 237219, 14 pages doi:10.1155/2011/237219 Research Article Asymptotic Behavior of Solutions of Higher-Order Dynamic Equations on Time Scales Taixiang Sun,1 Hongjian Xi,2 and Xiaofeng Peng1 1 2 College of Mathematics and Information Science, Guangxi University, Nanning, Guangxi 530004, China Department of Mathematics, Guangxi College of Finance and Economics, Nanning, Guangxi 530003, China Correspondence should be addressed to Taixiang Sun, stx1963@163.com Received 18 November 2010; Accepted 23 February 2011 Academic Editor: Abdelkader Boucherif Copyright q 2011 Taixiang Sun et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. We investigate the asymptotic behavior of solutions of the following higher-order dynamic n n−1 equation xΔ t ft, xt, xΔ t, . . . , xΔ t 0, on an arbitrary time scale T, where the n function f is defined on T × R . We give sufficient conditions under which every solution x of n−1 this equation satisfies one of the following conditions: 1 limt → ∞ xΔ t 0; 2 there exist n−1 0, such that limt → ∞ xt/ i0 ai hn−i−1 t, t0 1, where constants ai 0 ≤ i ≤ n − 1 with a0 / hi t, t0 0 ≤ i ≤ n − 1 are as in Main Results. 1. Introduction In this paper, we investigate the asymptotic behavior of solutions of the following higherorder dynamic equation n n−1 xΔ t f t, xt, xΔ t, . . . , xΔ t 0, 1.1 on an arbitrary time scale T, where the function f is defined on T × Rn . Since we are interested in the asymptotic and oscillatory behavior of solutions near infinity, we assume that sup T ∞, and define the time scale interval t0 , ∞T {t ∈ T : t ≥ t0 }, where t0 ∈ T. By a solution of 1.1, we mean a nontrivial real-valued function n x ∈ Crd Tx , ∞T , R, Tx ≥ t0 , which has the property that xΔ t ∈ Crd Tx , ∞T , R and satisfies 1.1 on Tx , ∞T , where Crd is the space of rd-continuous functions. The solutions vanishing in some neighborhood of infinity will be excluded from our consideration. A solution x of 1.1 is said to be oscillatory if it is neither eventually positive nor eventually negative, otherwise it is called nonoscillatory. 2 Advances in Difference Equations The theory of time scales, which has recently received a lot of attention, was introduced by Hilger’s landmark paper 1 in order to create a theory that can unify continuous and discrete analysis. The cases when a time scale is equal to the real numbers or to the integers represent the classical theories of differential and of difference equations. Many other interesting time scales exist, and they give rise to many applications see 2 . Not only the new theory of the so-called “dynamic equations” unifies the theories of differential equations and difference equations but also extends these classical cases to cases “in between,” for example, to the so-called q-difference equations when T qN0 , which has important applications in quantum theory see 3 . On a time scale T, the forward jump operator, the backward jump operator, and the graininess function are defined as σt inf{s ∈ T : s > t}, ρt sup{s ∈ T : s < t}, μt σt − t, 1.2 respectively. We refer the reader to 2, 4 for further results on time scale calculus. Let p ∈ 0, for all t ∈ T, then the delta exponential function ep t, t0 is Crd T, R with 1 μtpt / defined as the unique solution of the initial value problem yΔ pty, yt0 1. 1.3 In recent years, there has been much research activity concerning the oscillation and nonoscillation of solutions of various equations on time scales, and we refer the reader to 5–18 . Recently, Erbe et al. 19–21 considered the asymptotic behavior of solutions of the third-order dynamic equations Δ Δ Δ ptfxt 0, at rtx t xΔΔΔ t ptxt 0, Δ γ Δ Δ ft, xt 0, at rtx t 1.4 respectively, and established some sufficient conditions for oscillation. Karpuz 22 studied the asymptotic nature of all bounded solutions of the following higher-order nonlinear forced neutral dynamic equation n xt Atxαt Δ f t, x βt , x γt ϕt. 1.5 Chen 23 derived some sufficient conditions for the oscillation and asymptotic behavior of the nth-order nonlinear neutral delay dynamic equations γ Δ Δn−1 α−1 n−1 λFt, xδt 0, atΨxt xt ptxτt xt ptxτtΔ 1.6 Advances in Difference Equations 3 on an arbitrary time scale T. Motivated by the above studies, in this paper, we study 1.1 and give sufficient conditions under which every solution x of 1.1 satisfies one of the following n−1 0, such conditions: 1 limt → ∞ xΔ t 0; 2 there exist constants ai 0 ≤ i ≤ n − 1 with a0 / n−1 that limt → ∞ xt/ i0 ai hn−i−1 t, t0 1, where hi t, t0 0 ≤ i ≤ n − 1 are as in Section 2. 2. Main Results Let k be a nonnegative integer and s, t ∈ T, then we define a sequence of functions hk t, s as follows: ⎧ ⎪ ⎪ ⎨1 hk t, s t ⎪ ⎪ ⎩ hk−1 τ, sΔτ if k 0, if k ≥ 1. 2.1 s To obtain our main results, we need the following lemmas. Lemma 2.1. Let n be a positive integer, then there exists Tn > t0 , such that hk1 t, t0 − hk t, t0 ≥ 1 for t ≥ Tn , 0 ≤ k ≤ n − 1. 2.2 Proof. We will prove the above by induction. First, if k 0, then we take T1 ≥ t0 2. Thus, h1 t, t0 − h0 t, t0 t − t0 − 1 ≥ 1 for t ≥ T1 . 2.3 Next, we assume that there exists Tm > t0 , such that hk1 t, t0 − hk t, t0 ≥ 1 for t ≥ Tm and 0 ≤ k ≤ m with 0 ≤ m < n − 1, then hm1 t, t0 − hm t, t0 t hm τ, t0 − hm−1 τ, t0 Δτ t0 Tm hm τ, t0 − hm−1 τ, t0 Δτ ≥ t0 Tm hm τ, t0 − hm−1 τ, t0 Δτ Tm t0 Tm t hm τ, t0 − hm−1 τ, t0 Δτ t 2.4 Δτ Tm hm τ, t0 − hm−1 τ, t0 Δτ t − Tm , t0 from which it follows that there exists Tm1 > Tm , such that hk1 t, t0 −hk t, t0 ≥ 1 for t ≥ Tm1 and 0 ≤ k ≤ m 1. The proof is completed. 4 Advances in Difference Equations Lemma 2.2 see 24 . Let p ∈ Crd T, 0, ∞, then 1 t t psΔs ≤ ep t, t0 ≤ e t0 psΔs 2.5 . t0 Lemma 2.3 see 2 . Let y, p ∈ Crd T, 0, ∞ and A ∈ 0, ∞, then yt ≤ A t yτpτΔτ, 2.6 ∀t ∈ T t0 implies yt ≤ Aep t, t0 , ∀t ∈ T. 2.7 Lemma 2.4 see 2 . Let n be a positive integer. Suppose that x is n times differentiable on T. Let n−1 α ∈ T κ and t ∈ T, then xt ρn−1 t n−1 k n hk t, αxΔ α hn−1 t, στxΔ τΔτ. 2.8 α k0 Lemma 2.5 see 2 . Assume that f and g are differentiable on T with limt → ∞ gt ∞. If there exists T > t0 , such that gt > 0, g Δ t > 0, 2.9 ∀t ≥ T, then f Δ t ft r or ∞. r or ∞ implies lim t → ∞ g Δ t t → ∞ gt lim 2.10 Lemma 2.6 see 23 . Let x be defined on t0 , ∞T , and xt > 0 with xΔ t ≤ 0 for t ≥ t0 and not eventually zero. If x is bounded, then n 1 limt → ∞ xΔ t 0 for 1 ≤ i ≤ n − 1, i 2 −1i1 xΔ t > 0 for all t ≥ t0 and 1 ≤ i ≤ n − 1. n−i Now, one states and proves the main results. Theorem 2.7. Assume that there exists t1 > t0 , such that the function ft, u0 , . . . , un−1 satisfies n−1 ft, u0 , . . . , un−1 ≤ pi t|ui |, i0 ∀t, u0 , . . . , un−1 ∈ t1 , ∞T × Rn , 2.11 Advances in Difference Equations 5 where pi t 0 ≤ i ≤ n − 1 are nonnegative functions on t1 , ∞T and lim eq t, t1 < ∞, 2.12 t→∞ with qt conditions: n−1 i0 pi thn−i−1 t, t0 t ≥ t1 , then every solution x of 1.1 satisfies one of the following 1 limt → ∞ xΔ t 0, n−1 0, such that 2 there exist constants ai 0 ≤ i ≤ n − 1 with a0 / lim n−1 t→∞ i0 xt ai hn−i−1 t, t0 1. 2.13 Proof. Let x be a solution of 1.1, then it follows from Lemma 2.4 that for 0 ≤ m ≤ n − 1, x Δm t n−m−1 hk t, t1 x Δkm ρn−m−1 t t1 hn−m−1 t, στxΔ τΔτ n for t ≥ t1 . 2.14 t1 k0 By 2.11 and Lemma 2.1, we see that there exists T > t1 , such that for t ≥ T and 0 ≤ m ≤ n − 1, m Δ x t ≤ hn−m−1 t, t0 n−1 t i Δ Δkm pi τx τΔτ . t1 x n−m−1 2.15 t1 i0 k0 Then we obtain m Δ x t ≤ hn−m−1 t, t0 Ft for t ≥ T, 0 ≤ m ≤ n − 1, 2.16 t n−1 i Ft A pi τxΔ τΔτ, 2.17 where T i0 with T n−1 i Δkm pi τxΔ τΔτ. t1 x A max 0≤m≤n−1 n−m−1 2.18 t1 i0 k0 Using 2.16 and 2.17, it follows that Ft ≤ A t n−1 T i0 pi τhn−i−1 τ, t0 FτΔτ for t ≥ T. 2.19 6 Advances in Difference Equations By Lemma 2.3, we have Ft ≤ Aeq t, T ∀t ≥ T, 2.20 with qt n−1 i0 pi thn−i−1 t, t0 . Hence from 2.12, there exists a finite constant c > 0, such that Ft ≤ c for t ≥ T . Thus, inequality 2.20 implies that m Δ x t ≤ hn−m−1 t, t0 c for t ≥ T, 0 ≤ m ≤ n − 1. 2.21 By 1.1, we see that if t ≥ T , then x Δn−1 t x Δn−1 t n−1 T − f τ, xτ, xΔ τ, . . . , xΔ τ Δτ. 2.22 T Since condition 2.12 and Lemma 2.2 implies that t n−1 lim t→∞ 2.23 pi τhn−i−1 τ, t0 Δτ < ∞, T i0 we find from 2.11 and 2.21 that the sum in 2.22 converges as t → ∞. Therefore, n−1 n−1 0, then it follows limt → ∞ xΔ t exists and is a finite number. Let limt → ∞ xΔ t a0 . If a0 / from Lemma 2.5 that xt n−1 lim xΔ t a0 , t → ∞ hn−1 t, t0 t→∞ 2.24 lim and x has the desired asymptotic property. The proof is completed. Theorem 2.8. Assume that there exist functions pi : t0 , ∞T → 0, ∞ 0 ≤ i ≤ n, and nondecreasing continuous functions gi : 0, ∞ → 0, ∞ 0 ≤ i ≤ n − 1, and t1 > t0 such that n−1 ft, u0 , . . . , un−1 ≤ pi tgi i0 |ui | hn−i−1 t, t0 pn t for t ≥ t1 , 2.25 with ∞ pi tΔt Pi < ∞ for 0 ≤ i ≤ n, t1 ∞ ε ds n−1 i0 gi s 2.26 ∞ for any ε > 0, Advances in Difference Equations 7 then every solution x of 1.1 satisfies one of the following conditions: 1 limt → ∞ xΔ t 0, n−1 2 there exist constants ai 0 ≤ i ≤ n − 1 with a0 / 0 such that lim n−1 t→∞ i0 xt ai hn−i−1 t, t0 1. 2.27 Proof. Let x be a solution of 1.1, then it follows from Lemma 2.4 that for 0 ≤ m ≤ n − 1, xΔ t m n−m−1 hk t, t1 xΔ km t1 ρn−m−1 t hn−m−1 t, στxΔ τΔτ n for t ≥ t1 . 2.28 t1 k0 By Lemma 2.1 and 2.25, we see that there exists T > t1 , such that for t ≥ T and 0 ≤ m ≤ n − 1, ⎛ i ⎞ ⎡ ⎤ ⎤ ⎡ Δ n−m−1 n−1 t km m τ x Δ Δ ⎠ pn τ⎦Δτ ⎦. t1 ⎣ pi τgi ⎝ x x t ≤ hn−m−1 t, t0 ⎣ hn−i−1 τ, t0 t1 i0 k0 2.29 Then, we obtain m Δ x t ≤ hn−m−1 t, t0 Ft, for t ≥ T, 0 ≤ m ≤ n − 1, 2.30 where ⎛ i ⎞ t n−1 xΔ τ ⎝ ⎠Δτ, Ft A pi τgi hn−i−1 τ, t0 T i0 2.31 with A max 0≤m≤n−1 ⎛ Δi ⎞ T n−1 x τ Δkm ⎠Δτ Pn . pi τgi ⎝ t1 x hn−i−1 τ, t0 t1 i0 n−m−1 k0 2.32 Using 2.30 and 2.31, it follows that Ft ≤ A t n−1 pi τgi FτΔτ T i0 for t ≥ T. 2.33 8 Advances in Difference Equations Write ut A t n−1 pi τgi FτΔτ T i0 G y y A 2.34 for t ≥ T, ds , n−1 i0 gi s 2.35 then Δ Δ Gut u t 1 G hut 1 − huσ tdh 0 $ 1 # n−1 pi tgi Ft n−1 0 i0 n−1 gi hut 1 − huσ t i0 pi tgi ut n−1 i0 gi ut ≤ ≤ i0 dh 2.36 n−1 pi t, i0 from which it follows that Gut ≤ GuT t n−1 T i0 pi τΔτ ≤ GuT n−1 Pi . 2.37 i0 Since limy → ∞ Gy ∞ and Gy is strictly increasing, there exists a constant c > 0, such that ut ≤ c for t ≥ T . By 2.30, 2.33, and 2.34, we have m Δ x t ≤ hn−m−1 t, t0 c for t ≥ T, 0 ≤ m ≤ n − 1. 2.38 It follows from 1.1 that if t ≥ T , then x Δn−1 t x Δn−1 t n−1 T − f τ, xτ, xΔ τ, . . . , xΔ τ Δτ. T 2.39 Advances in Difference Equations 9 Since 2.38 and condition 2.25 implies that t n−1 f τ, xτ, xΔ τ, . . . , xΔ τ Δτ T ⎛ i ⎞ ⎤ ⎡ t n−1 xΔ τ ⎠ pn τ⎦Δτ ≤ ⎣ pi τgi ⎝ hn−i−1 τ, t0 T i0 ≤ 2.40 n−1 Pi gi c Pn i0 M < ∞, we see that the sum in 2.39 converges as t → ∞. Therefore, limt → ∞ xΔ t exists and is a n−1 0, then it follows from Lemma 2.5 that finite number. Let limt → ∞ xΔ t a0 . If a0 / n−1 lim xt lim xΔ t a0 , n−1 t → ∞ hn−1 t, t0 2.41 t→∞ and x has the desired asymptotic property. The proof is completed. Theorem 2.9. Assume that there exist positive functions p : t0 , ∞T → 0, ∞, and nondecreasing continuous functions gi : 0, ∞ → 0, ∞ 0 ≤ i ≤ n − 1, and t1 > t0 , such that n−1 % ft, u0 , . . . , un−1 ≤ pt gi i0 |ui | hn−i−1 t, t0 for t ≥ t1 , 2.42 with ∞ ∞ ε ptΔt P < ∞, t1 2.43 ds &n−1 i0 gi s ∞, for any ε > 0, then every solution x of 1.1 satisfies one of the following conditions: 1 limt → ∞ xΔ t 0, n−1 2 there exist constants ai 0 ≤ i ≤ n − 1 with a0 / 0, such that lim n−1 t→∞ i0 xt ai hn−i−1 t, t0 1. 2.44 10 Advances in Difference Equations Proof. Arguing as in the proof of Theorem 2.8, we see that there exists T > t1 , such that for t ≥ T and 0 ≤ m ≤ n − 1, ⎛ Δi ⎞ ⎤ ⎡ n−1 n−m−1 t % km m x τ Δ Δ ⎠Δτ ⎦, pτgi ⎝ t1 x x t ≤ hn−m−1 t, t0 ⎣ hn−i−1 τ, t0 t1 i0 k0 2.45 from which we obtain m Δ x t ≤ hn−m−1 t, t0 Ft for t ≥ T, 0 ≤ m ≤ n − 1, 2.46 where Ft A T n−m−1 A max 0≤m≤n−1 Δ x ⎛ Δi ⎞ x τ ⎠, pτgi ⎝ hn−i−1 τ, t0 i0 t % n−1 km k0 ⎛ Δi ⎞ T n−1 x τ % ⎠. pτgi ⎝ t0 hn−i−1 τ, t0 t1 i0 2.47 2.48 Using 2.46 and 2.47, it follows that Ft ≤ A t % n−1 pτgi FτΔτ for t ≥ T. 2.49 for t ≥ T, 2.50 T i0 Write ut A t % n−1 pτgi FτΔτ T i0 G y y A ds , &n−1 i0 gi s 2.51 then Gut Δ uΔ t # n−1 % 1 G hut 1 − huσ tdh 0 ptgi Ft i0 &n−1 ≤ i0 ptgi ut &n−1 i0 gi ut pt, $ 1 0 &n−1 i0 dh gi hut 1 − huσ t 2.52 Advances in Difference Equations 11 from which it follows that Gut ≤ GuT t 2.53 pτΔτ ≤ GuT P. T The rest of the proof is similar to that of Theorem 2.8, and the details are omitted. The proof is completed. Theorem 2.10. Assume that the function ft, u0 , . . . , un−1 satisfies 1 ft, u0 , . . . , un−1 ptFu0 , . . . , un−1 for all t, u0 , . . . , un−1 ∈ t0 , ∞T × Rn , ∞ 2 pt ≥ 0 for t ≥ t0 and t0 hn−1 τ, t0 pτΔτ ∞, 3 u0 Fu0 , . . . , un−1 > 0 for u0 / 0 and Fu0 , . . . , un−1 is continuous at u0 , 0, . . . , 0 with u0 / 0, then (1) if n is even, then every bounded solution of 1.1 is oscillatory; (2) if n is odd, then every bounded solution xt of 1.1 is either oscillatory or tends monotonically to zero together with i xΔ t 1 ≤ i ≤ n − 1. Proof. Assume that 1.1 has a nonoscillatory solution x on t0 , ∞, then, without loss of generality, there is a t1 ≥ t0 , sufficiently large, such that xt > 0 for t ≥ t1 . It follows from n 1.1 that xΔ t ≤ 0 for t ≥ t1 and not eventually zero. By Lemma 2.6, we have lim xΔ t 0, i t→∞ −1 i1 Δn−i x for 1 ≤ i ≤ n − 1, 2.54 t > 0 ∀t ≥ t1 , 1 ≤ i ≤ n − 1, and xt is eventually monotone. Also xΔ t > 0 for t ≥ t1 if n is even and xΔ t < 0 for t ≥ t1 if n is odd. Since xt is bounded, we find limt → ∞ xt c ≥ 0. Furthermore, if n is even, then c > 0. We claim that c 0. If not, then there exists t2 > t1 , such that Fc, 0, . . . , 0 n−1 >0 F xt, xΔ t, . . . , xΔ t > 2 for t ≥ t2 , 2.55 since F is continuous at c, 0, . . . , 0 by the condition 3. From 1.1 and 2.55, we have xΔ t pt n Fc, 0, . . . , 0 ≤ 0, 2 2.56 for t ≥ t2 . Multiplying the above inequality by hn−1 t, t0 , and integrating from t2 to t, we obtain t t2 hn−1 τ, t0 xΔ τΔτ n t t2 hn−1 τ, t0 pτ Fc, 0, . . . , 0 Δτ ≤ 0, 2 for t ≥ t2 . 2.57 12 Advances in Difference Equations Since t n i1 Δn−i hn−1 τ, t0 x τΔτ ≥ −1 hn−i τ, t0 x τ t2 i1 t Δn t2 ≥ n 2.58 −1i hn−i t2 , t0 xΔ t2 −1n1 xt, n−i i1 we get n1 A −1 xt t hn−1 τ, t0 pτ t2 Fc, 0, . . . , 0 Δτ ≤ 0, 2 for t ≥ t2 , 2.59 ∞ n−i where A ni1 −1i hn−i t2 , t0 xΔ t2 . Thus, t2 hn−1 τ, t0 pτΔτ < ∞ since xt is bounded, which gives a contradiction to the condition 2. The proof is completed. 3. Examples Example 3.1. Consider the following higher-order dynamic equation: xΔ t n i n−1 1 xΔ t 0, βi h n−i−1 t, t0 i0 t 3.1 where t ≥ t1 > t0 > 0 and βi > 1 0 ≤ i ≤ n − 1. Let pi t 1/tβi hn−i−1 t, t0 0 ≤ i ≤ n − 1 and ft, u0 , . . . , un−1 n−1 1 ui , β i hn−i−1 t, t0 i0 t 3.2 then we have n−1 ft, u0 , . . . , un−1 ≤ pi t|ui |, ∀t, u0 , . . . , un−1 ∈ t1 , ∞T × Rn , i0 t n−1 t en−1 t, t1 en−1 βi t, t1 ≤ e 1 i0 pi thn−i−1 i0 1/t i0 1/τ βi Δτ 3.3 < ∞, by Example 5.60 in 4 . Thus, it follows from Theorem 2.7 that if x is a solution of 3.1 n−1 0, then there exist constants ai 0 ≤ i ≤ n − 1 with a0 with limt → ∞ xΔ t / 0, such that n−1 / limt → ∞ xt/ i0 ai hn−i−1 t, t0 1. Example 3.2. Consider the following higher-order dynamic equation: n−1 1 x t βi i0 t Δn # xΔ t hn−i−1 t, t0 i $αi 1 0, tβ n 3.4 Advances in Difference Equations 13 where t > t0 > 0, αi ∈ 0, 1 0 ≤ i ≤ n − 1, and βi > 1 0 ≤ i ≤ n. Let gi u uαi 0 ≤ i ≤ n − 1, pi t 1/tβi 0 ≤ i ≤ n, and ft, u0 , . . . , un−1 αi n−1 1 1 ui β . β i hn−i−1 t, t0 tn i0 t 3.5 It is easy to verify that ft, u0 , . . . , un−1 satisfies the conditions of Theorem 2.8. Thus, it follows n−1 0, then there exist constants ai 0 ≤ i ≤ that if x is a solution of 3.4 with limt → ∞ xΔ t / n−1 0, such that limt → ∞ xt/ i0 ai hn−i−1 t, t0 1. n − 1 with a0 / Example 3.3. Consider the following higher-order dynamic equation: # $αi i n−1 xΔ t 1% x t β 0, t i0 hn−i−1 t, t0 Δn where t > t0 > 0, αi ∈ 0, 1 0 ≤ i ≤ n − 1 with 0 < i ≤ n − 1, pt 1/tβ , and ft, u0 , . . . , un−1 n−1 n−1 % 1 i0 tβ i0 3.6 αi < 1 and β > 1. Let gi u uαi 0 ≤ ui hn−i−1 t, t0 αi . 3.7 It is easy to verify that ft, u0 , . . . , un−1 satisfies the conditions of Theorem 2.9. Thus, it follows n−1 0, then there exist constants ai 0 ≤ i ≤ that if x is a solution of 3.6 with limt → ∞ xΔ t / n−1 0, such that limt → ∞ xt/ i0 ai hn−i−1 t, t0 1. n − 1 with a0 / Acknowledgment This paper was supported by NSFC no. 10861002 and NSFG no. 2010GXNSFA013106, no. 2011GXNSFA018135 and IPGGE no. 105931003060. References 1 S. Hilger, “Analysis on measure chains—a unified approach to continuous and discrete calculus,” Results in Mathematics, vol. 18, no. 1-2, pp. 18–56, 1990. 2 M. Bohner and A. Peterson, Dynamic Equations on Time Scales: An Introduction with Applications, Birkhäuser, Boston, Mass, USA, 2001. 3 V. Kac and P. Cheung, Quantum Calculus, Universitext, Springer, New York, NY, USA, 2002. 4 M. Bohner and A. Peterson, Advances in Dynamic Equations on Time Scales, Birkhäuser, Boston, Mass, USA, 2003. 5 M. Bohner and S. H. 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