## Nonlinear Dynamics in Financial Systems: Advances and Perspectives

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Hua Wang, Li Liu, Yanxiang Tan, "Dynamics of Third-Order Nonlinear Neutral Equations", *Discrete Dynamics in Nature and Society*, vol. 2014, Article ID 917913, 4 pages, 2014. https://doi.org/10.1155/2014/917913

# Dynamics of Third-Order Nonlinear Neutral Equations

**Academic Editor:**Taishan Yi

#### Abstract

The aim of this paper is to study oscillatory and asymptotic properties of the third-order nonlinear neutral equation with continuously distributed delays of the form . Applying suitable generalized Riccati transformation and integral averaging technique, we present new criteria for oscillation or certain asymptotic behavior of nonoscillatory solutions of this equation. Obtained results essentially improve and complement earlier ones.

#### 1. Introduction

In recent years, the dynamics theory such as oscillation theory and asymptotic behavior of differential equations and their applications have been and still are receiving intensive attention [1–4]. In fact, in the last few years several monographs and hundreds of research papers have been written; see, for example, the monograph [5]. Determining oscillation criteria for particular second-order differential equations has received a great deal of attention in the last few years [6–8]. For example, [9] considered and obtained oscillatory criteria of Philos type. In [10], by means of Riccati transformation technique, Han et al. established some new oscillation criteria for the second-order Emden Fowler delay dynamic equations on a time scale : However, compared to second-order differential equations, the study of oscillation and asymptotic behavior of third-order differential equations has received considerably less attention in the literature [11–15]. In [16], Qiu investigated the oscillation criteria for the third-order neutral differential equations taking the following form: By using a generalized Riccati transformation and integral averaging technique, Zhang et al. [17] established some new sufficient conditions which ensure that every solution of the following equation oscillates or converges to zero: As we know, the dynamics theory such as oscillation theory and asymptotic behavior of the following equation have not been investigated up to now: With the help of a generalized Riccati transformation and integral averaging technique, this paper aims to establish some new sufficient conditions of Philos type which ensure that every solution of (5) oscillates or converges to zero. Our results improve and complement the corresponding results in [6, 11–17]. We should point out that, in this paper, is any quotient of odd positive integers and ; it is more general than that reported in [17] where .

We are interested in (5) in the case of . Throughout this paper, we assume that the following hypotheses hold:; ; is not a decreasing function for , and ;; is not a decreasing function for , such that ;.

We also define the following function: As far as a solution of (5) is concerned, we mean a nontrivial function , , which has the property and satisfies (5) on .

We restrict our attention to those solutions of (5) which satisfy for all . A solution of (5) is said to be oscillatory on if it is neither eventually positive nor eventually negative. Otherwise it is called nonoscillatory.

The rest of this paper is organized as follows. In Section 2, we will present some lemmas which are useful for the proof of our main results. In Section 3, we present new criteria of Philos type for oscillation or certain asymptotic behavior of nonoscillatory solutions of (5).

#### 2. Several Lemmas

Lemma 1. *Let be a positive solution of (5), and . Then which is defined as in (6) has only one of the following two properties:*(*I*)*;
*(*II*)*. *

*Proof. *Letting be a positive solution of (5) on , from (6), we have and . Then is a decreasing function and of one sign, and following and where and are odd positive integers, we have that and have the same sign, so is either eventually positive or eventually negative on ; that is, or . If , then there exists a constant , such that . By integrating from to , we get
Letting and using , we have . Thus eventually; since and , we have , which contradicts assumption , so . Therefore, has only one of the two properties (I) and (II).

Lemma 2. *Let be a positive solution of (5), and correspondingly has property . Assume that
**
Then
*

*Proof. *Let be a positive solution of (5). Since has property (II), then there exists finite limit . We assert that . Assuming that , then we have , for all . Choosing , we obtain
where . Using and , from (5), we find that
Note that has property and ; we have
where . Integrating inequality (13) from to , we get
Using , then we have
Integrating inequality (15) from to , we have
Integrating the last inequality from to , we obtain
we have a contradiction with (8) and so it follows that .

Lemma 3 (see [18]). *Let . Then, for each , there exists such that
*

Lemma 4 (see [19]). *Letting , then there exist and such that
*

Lemma 5. *For all , then for all , one has
*

*Proof. *Let . We investigate the maximal value and minimal value of the function .

At first, for all , the derivative of function is . It is clear that when , we have , and when , we have . Hence the function attains its maximum value at . This completes the proof.

#### 3. Main Result

Theorem 6. *Assume that the condition of Lemma 2 holds, and there exists , such that and
**
where
**
Then every solution of (5) either is oscillatory or converges to zero.*

*Proof. *Assume that (5) has a nonoscillatory solution . Without loss of generality we may assume that , and is defined as in (6). By Lemma 1, we have that has property (I) or property (II). At first, when has property (I), we obtain
Using and , we get
where
Let
Then
so
Letting , from Lemma 3, we obtain
Using Lemma 4, we get
Hence
where is defined as (21). Letting , we have that
and, from Lemma 5, we obtain
Integrating inequality (33) from to ,
we obtain
which contradicts (21). If has property (II), since (8) holds, then the conditions in Lemma 2 are satisfied. Hence .

This completes the proof.

#### Conflict of Interests

The authors declare that there is no conflict of interests regarding the publication of this paper.

#### Acknowledgments

This work is supported by the Scientific Research Funds of Hunan Provincial Science and Technology Department of China (no. 12FJ4252 and no. 2013SK3143), National Natural Science Foundation of China (nos. 11101053, 11326116).

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Copyright © 2014 Hua Wang 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.