Research Article | Open Access

Xin Wu, Taixiang Sun, Hongjian Xi, Changhong Chen, "Oscillation Criteria for Fourth-Order Nonlinear Dynamic Equations on Time Scales", *Abstract and Applied Analysis*, vol. 2013, Article ID 740568, 11 pages, 2013. https://doi.org/10.1155/2013/740568

# Oscillation Criteria for Fourth-Order Nonlinear Dynamic Equations on Time Scales

**Academic Editor:**Delfim F. M. Torres

#### Abstract

We establish some new oscillation criteria for nonlinear dynamic equation of the form on an arbitrary time scale with , where are positive rd-continuous functions. An example illustrating the importance of our result is included.

#### 1. Introduction

A time scaleis an arbitrary nonempty closed set of real numberswith the topology and ordering inherited from. The theory of time scales, which has recently received a lot of attention, was introduced by Hilger in his Ph.D thesis [1] in order to unify continuous and discrete analysis. The cases when a time scaleis equal toor the set of all integersrepresent the classical theories of differential and difference equations. Many results concerning differential equations carry over quite easily to corresponding results for difference equations, while other results seem to be completely different from their continuous counterparts. The study of dynamic equations on time scales reveals such discrepancies and helps avoid proving results twice once for differential equations and once again for difference equations. The general is to prove a result for a dynamic equation where the domain of the unknown function is a time scale. In this way results not only related to the set of real numbers or set of integers but those pertaining to more general time scales are obtained. Therefore, not only can the theory of dynamic equations unify the theories of differential equations and difference equations, but also extends these classical cases to cases “in between,” for example, to the so-called -difference equations when, which has important applications in quantum theory (see [2]). In the last years there has been much research activity concerning the oscillation and asymptotic behavior of solutions of some dynamic equations on time scales, and we refer the reader to the paper [3–8] and the references cited therein.

Recently, Hassan in [9] studied the third-order dynamic equation on a time scale, whereis the quotient of odd positive integers,andare positive rd-continuous functions on, and the so-called delay functionsatisfiesforandandand obtained some oscillation criteria, which improved and extended the results that have been established in [10–12].

Li et al. in [13] also discussed the oscillation of (1), whereis the quotient of odd positive integers,is assumed to satisfyfor, and there exists a positive rd-continuous functionon such thatfor. They established some new sufficient conditions for the oscillation of (1).

Wang and Xu in [14] extended the Hille and Nehari oscillation theorems to the third-order dynamic equation on a time scale, whereis a ratio of odd positive integers and the functionsare positive real-valued rd-continuous functions defined on.

Erbe et al. in [15] were concerned with the oscillation of the third-order nonlinear functional dynamic equation

on a time scale, whereis the quotient of odd positive integers,andare positive rd-continuous functions on, andsatisfiesand. The authors obtain some new oscillation criteria and extend many known results for oscillation of third-order dynamic equations.

Qi and Yu in [16] obtained some oscillation criteria for the fourth-order nonlinear delay dynamic equation

on a time scale, whereis the ratio of odd positive integers,is a positive real-valued rd-continuous function defined on,, and.

Grace et al. in [17] were concerned with the oscillation of the fourth-order nonlinear dynamic equation

on a time scale, whereis the ratio of odd positive integers,is a positive real-valued rd-continuous function defined on. They reduce the problem of the oscillation of all solutions of (5) to the problem of oscillation of two second-order dynamic equations and give some conditions ensuring that all bounded solutions of (5) are oscillatory.

Grace et al. in [18] establish some new criteria for the oscillation of fourth-order nonlinear dynamic equations

whereis a positive real-valued rd-continuous function satisfying that,is continuous satisfyingandforand. They also investigate the case of strongly superlinear and the case of strongly sublinear equations subject to various conditions.

Agarwal et al. in [19] were concerned with oscillatory behavior of a fourth-order half-linear delay dynamic equation with damping

on a time scalewith, whereis the ratio of odd positive integers,are positive real-valued rd-continuous functions defined on, andas. They establish some new oscillation criteria of (7).

Zhang et al. in [20] were concerned with the oscillation of a fourth-order nonlinear dynamic equation

on an arbitrary time scalewith , wherewithand there exists a positive constantsuch thatfor all; they give a new oscillation result of (8).

Motivated by the previous studies, in this paper, we will study the oscillation criteria of the following fourth-order nonlinear dynamic equation:
whereis a time scale with is a constant and. Throughout this paper, we assume that the following conditions are satisfied:(*H*_{1}) and .(*H*_{2})(*H*_{3})and there exists a positive constantsuch that for any,.

By a solution of (9), we mean a nontrivial real-valued functionwith, which has the property thatand satisfies (9) on, whereis the space of differentiable functions whose derivative is rd-continuous. The solutions vanishing in some neighborhood of infinity will be excluded from our consideration. A solutionof (9) is said to be oscillatory if it is neither eventually positive nor eventually negative; otherwise it is called nonoscillatory.

#### 2. Some Auxiliary Lemmas

We shall employ the following lemmas.

Lemma 1. *Assume thatis an eventually positive solution of (9). Then there existssufficiently large, such that, for, one of the following cases holds:*(1)*, , , ,*(2)*, , , ,*(3)*, , , ,*(4)*, , , .*

*Proof. *Letbe an eventually positive solution of (9). Then there is a, sufficiently large, such that,for. By (9) we have
which implies that is decreasing and one of the following two cases holds.(a)for.(b) There is asuch that.

If case (a) holds, thenis strictly increasing onand there exist the following two subcases.()for.() There exists asuch that.

If subcaseholds, then we claim. If not, there exists asuch thatfor. Thus, we get

which contradicts eventually. Therefore, we obtain case (4).

If subcaseholds, then let we get

Therefore, we obtain case (3).

If case (b) holds, then we claimfor. If not, there exists asuch thatfor. Integrating this inequality fromto, we get
Then, there exists a such thatfor. Integrating this inequality fromto, we get
which contradicts eventually. The proof is completed.

Lemma 2 (see [12]). *Assume that there existssuch thatsatisfies
**
Then
**
where.*

#### 3. The Main Result

Now we state and prove our main result.

Theorem 3. *Assume that one of the following conditions holds:
**
If there exist two positive functionssuch that for all sufficiently large, and, and some constant,
**
where
**
Then, every solutionof (9) is oscillatory.*

*Proof. *Assume that (9) has a nonoscillatory solutionon. Then, without loss of generality, there is a, sufficiently large, such thatfor. By Lemma 1, there exist the following four possible cases:(1), , ,(2), , ,(3), , ,(4), , .

If case (1) holds, then
which implies thatis decreasing on, and so
Dividing the previous inequality byand integrating the resulting inequality fromto, we get
Let, we obtain
Hence, there exists a constantsuch that
Integrating (28) fromto, we get
which implies that

which contradicts assumption (17).

Integrating (28) fromto, we get
Integrating the previous inequality fromtogives
which implies

which contradicts assumption (18).

Let. Integrating (27) fromtogives
Integrating (34) fromto, we get
Set
Then,forand
By (34), we get
Combining (36) with (38) gives
In view of (35), we get
From (39), we obtain
Integrating (41) fromtogives
which implies

Which contradicts assumption (19).

If case (2) holds, then set
andforand
On the other hand, letfor, where; it is easy to check thatIn view of
by, we get
Therefore, by Lemma 2, for any, there existssuch that
Then, we see that
Since
we get
In view of (49), we obtain that for all,
On the other hand, there existssuch that for any,
It follows from (52) and (53) that
Combining (45) with (54) gives
By (27) we get
Multiplying both sides of (55) withreplaced by, by, and integrating with respect tofromto, one gets
Thus,
which implies that

which contradicts assumption (20).

If case (3) holds, then since
we have
Hence, there existssuch that
which implies that
Hence, there existssuch that
Combining (62) with (64) gives
Write
Thus,and for any,
By (61) and (65), we get
Integrating the last inequality fromto, we get

which contradicts assumption (21).

If case (4) holds, then
Integrating the previous inequality fromto, we get
Lettingin this inequality, we obtain
Integrating the previous inequality fromto, we get
Lettingin this inequality, we obtain
Now we set
Thus,and for any ,
Since