Abstract and Applied Analysis

Volume 2015, Article ID 826020, 8 pages

http://dx.doi.org/10.1155/2015/826020

## Effect of Leakage Delay on Stability of Neutral-Type Genetic Regulatory Networks

^{1}School of Science, Jiangnan University, Wuxi 214122, China^{2}Key Laboratory of Advanced Process Control for Light Industry (Ministry of Education), Wuxi 214122, China^{3}Department of Mathematics, Huaiyin Normal University, Huaian 223300, China

Received 16 June 2014; Accepted 6 August 2014

Academic Editor: Yonghui Xia

Copyright © 2015 Li Li 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.

#### Abstract

The stability of neutral-type genetic regulatory networks with leakage delays is considered. Firstly, we describe the model of genetic regulatory network with neutral delays and leakage delays. Then some sufficient conditions are derived to ensure the asymptotic stability of the genetic regulatory network by the Lyapunov functional method. Further, the effect of leakage delay on stability is discussed. Finally, a numerical example is given to show the effectiveness of the results.

#### 1. Introduction

Biology networks are important research tools of complex biological phenomena, which have been attracting attention of scientists and engineers [1–4]. There are many kinds of biological networks, such as metabolic network, signal network, genetic regulatory network (GRN), and protein interaction network. GRN, which describes the complex interactions between genes (mRNA) and its products (proteins), is often modelled by a kind of dynamical system. The study of GRNs can help scientists understand many important and complex phenomena of living cells. Up to now, several models of GRNs have been established, for example, Boolean network models [5], Bayesian network models [6], Petri network models [7, 8], and the differential equation models. It is more convenient to analyze the dynamical behaviors by using differential equation models and have been widely studied by many experts [9–12].

As we all know, stability is one of the most important issues of longtime quality behavior of dynamical systems. Some important biological secrets have been revealed and many significant results have been reported [13–15]. On the other hand, time delay is a common phenomenon that describes the dynamical behaviors. The existence of time delay can make the dynamical behaviors more complicated and may cause destabilization, oscillation, bifurcation, and chaos. So time delay should be taken into consideration when modelling the genetic networks. There are many types of time delays such as discrete delays [16], continuous delays [17, 18], random delays [19], and mixed delays [20]. In recent years, the neutral delay has attracted attention because it can embody some important information about the derivation of the past state [21, 22]. In [23, 24], the authors considered asymptotic stability of BAM neural networks of neutral type. Lakshmanan and Balasubramaniam [25] obtained some new results of robust stability analysis for neutral-type neural networks with time-varying delays and Markovian jumping parameters. However, the stability analysis for genetic regulatory networks with neutral delay has been rarely investigated. In [26], Jung et al. discussed the stability for genetic regulatory network with neutral delay. Further, Jiao et al. [27] investigated the asymptotic stability of genetic regulatory network with neutral delay, which extended and improved the main results of Jung et al. [26]. On the other hand, leakage delay is another type of delay, which exists in the negative feedback term of system [28, 29]. So far, few studies have been paid to the stability analysis for GRNs with leakage delay. In [30], the authors discussed the global asymptotic stability for genetic regulatory networks with leakage delay. In [31], stability was investigated for a class of uncertain impulsive stochastic genetic regulatory networks with time-varying leakage delay. As far as we know, there is no result on the stability of genetic regulatory networks with neutral delays and leakage delays. Motivated by the discussion above, in this paper, we consider the stability of genetic regulatory networks of neutral type with leakage delay.

The paper is organized as follows. In Section 2, the problem is formulated and some preliminaries and assumption are given. In Section 3, the asymptotic stability of neutral-type genetic regulatory networks with leakage delay is investigated. In Section 4, an illustrative example is given to show the effectiveness of the theoretical results. Some conclusions are proposed in Section 5.

*Notations*. Throughout this paper, and denote the -dimensional Euclidean space and the set of all real matrices, respectively. denotes the transposition of matrix . Diag denotes the diagonal matrix. Asterisk represents the symmetric block of the symmetric matrix.

#### 2. Preliminaries

GRNs with mRNA and proteins can be modelled by the following differential equations:where and denote the concentrations of mRNA and protein of the th node at time , respectively. and are the degradation rates of the mRNA and protein, respectively. is the translation rate, is the feedback regulation delays, and is the translation delays satisfying , where and are constants. Consider , where is the Hill coefficient. is a positive constant which denotes the feedback regulation of the protein on the transcription. The coupling matrix of the GRNs is defined as follows:

Let be an equilibrium point of (1). The equilibrium point can be shifted to the origin by transformation: , . System (1) can be changed into the following compact matrix form:where , , , and with .

In this paper, we will consider the GRNs with neutral delays and leakage delays:where and denote the leakage delays. is the neutral delay and satisfies , .

The system (4) has the following equivalent form:

The initial conditions are given as follows: where and .

In this paper, we introduce the following assumption and lemmas.

*Assumption 1. *There exist constants such that the regulatory function satisfies for all , and .

*Remark 2. *In the above assumption, are some real constants, which may be positive, zero, or negative. Compared with the existing results in [32], this is less conservative and less restrictive.

The following lemmas will be used to derive our main results.

Lemma 3 (see [33]). *Given any real matrix of appropriate dimension and a vector function , such that the integrations concerned are well defined, then*

*Lemma 4 (see [34, 35]). For any diagonal matrices , if Assumption 1 holds, then where and .*

*3. Main Results*

*In this section, the asymptotic stability of system (5) is investigated. Some sufficient conditions are obtained to ensure the stability of system (5) based on the Lyapunov functional approach.*

*Theorem 5. Let Assumption 1 hold. Then the trivial solution of system (5) is asymptotically stable if there exist symmetric positive definite matrices , symmetric matrices , diagonal positive definite matrix , and positive definite matrices , , such that the following LMIs hold:where *

*Proof. *Consider the following Lyapunov-Krasovskii functional: where Calculating the derivative of along with the solution of the system (5), we haveIn addition, note thatFrom (9) to (21), we have where is defined in (11) and which implies . It is easy to prove , where . According to the Lyapunov stability theory, the GRNs (5) are asymptotically stable. The proof is complete.

*Remark 6. *If the leakage delay , the model is the same as that in [27]. We can also deduce the sufficient conditions for guaranteeing system stability. So the model in [27] is a special case of the model in this paper. In fact, the leakage delay has a large effect on the dynamic behaviors of the model. It often leads to the instability. This phenomenon can be observed in Figure 1. Considering the impact of leakage delay, we analyze GRNs with neutral delays and leakage delays simultaneously.