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Discrete Dynamics in Nature and Society
Volume 2015, Article ID 816325, 7 pages
http://dx.doi.org/10.1155/2015/816325
Research Article

Periodic Solutions Generated by Impulses for State-Dependent Impulsive Differential Equation

School of Mathematics and Statistics, Central South University, Changsha, Hunan 410083, China

Received 6 August 2014; Accepted 26 September 2014

Academic Editor: Zhengrong Xiang

Copyright © 2015 Qizhen Xiao and Binxiang Dai. 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

We study the existence of periodic solutions for a class of state-dependent impulsive differential systems via geometrical analysis methods. Our results show that these periodic solutions are generated by impulses. Moreover, numerical simulations are used to examine the existence of the periodic solutions.

1. Introduction

It is known that many evolutionary processes are characterized by the fact that at certain moments of time the states change abruptly. Such processes often occur in biology, control theory, optimization theory, physics, and mechanics problems (e.g., [16]). It is natural to assume that these perturbations act instantaneously, that is, in the form of impulses.

The theory of impulsive differential equations (IDEs) is rather rich, especially for impulse at fixed time. There are many classical methods to study impulsive differential equations. For example, Chen et al. [7] obtained some new results concerning the existence of solutions to an impulsive first-order, nonlinear ordinary differential equation with periodic boundary conditions via differential inequalities and Schaefer’s fixed-point theorem. Wang et al. [8] got the existence of extreme solutions of a periodic boundary value problem for a second-order functional differential equation by using upper and lower solutions. Based on a nonlinear alternative principle of Leray-Schauder, together with a truncation technique, Chu and Nieto [9] studied the impulsive periodic solutions of first-order singular ordinary differential equations. By using a variational method and a variant fountain theorem, Dai and Zhang [10] considered the existence and multiplicity of solutions for a class of nonlinear impulsive problem on the half-line. For more related work, the reader is referred to [1113] and the references therein. As we know, state-dependent IDEs have become a hot topic in recent years due to their extensive application space, but it is also a difficult research field because of their essential properties: uncertainties for impulsive time and collision times. Very recently, many papers have been devoted to the analysis of IDEs with state-dependent impulsive effect. By using differential equation geometry theory and the method of successor functions, the existence and stability of periodic solution for pest management model with state feedback control strategy were discussed in [14, 15] and the homoclinic cycle and homoclinic bifurcation were analyzed for predator-prey model with state-dependent impulsive harvesting in [16, 17]. On the basis of rotated vector fields theory, Dai et al. [18] discussed the order-1 positive periodic solution and homoclinic cycles and homoclinic bifurcations for a general semicontinuous dynamic system. Considering the influence of Allee effect on prey species, the authors in [19, 20] investigated a prey-predator model with Allee effect and state-dependent impulsive harvesting and got the sufficient conditions for the existence of order-1 periodic solution and heteroclinic bifurcation via the geometry theory of semicontinuous dynamic systems. Some other related studies can be seen in [2123] and the references therein.

The aforementioned papers all assumed that the predator just lived on the prey. However, in practice, it is very likely that many enemies have some other food sources. Motivated by this, in this paper, we consider the following state-dependent predator-prey model in which the predator species display the logistic growth in the absence of prey species: where and denote population densities of prey and predator at time , respectively. All the parameters are positive constants, in addition, , , and is the point of intersection of and .

This paper is organized as follows. In Section 2, we present some preliminaries. Then in Section 3, we discuss the existence of positive periodic solution of system (1) for different cases. At last, in Section 4, some numerical simulations and conclusions are presented.

2. Preliminaries

Lemma 4 (see [27]). For Model (1), if there exist , satisfying successor function , then there must exist a positive periodic solution.

Lemma 3 (see [27]). Successor function is continuous.

Definition 2 (see [27]). Suppose that the impulse set and its phase set are both lines, as shown in Figure 1. Assume that the trajectory starting from in firstly intersects at point and then jumps to in due to the impulsive effect. Then, one defines as the successor point of , and the corresponding successor function of point is that ; here and are the ordinates of and .

Lemma 1. Consider Model (2), there are one trivial equilibrium and two boundary equilibria and . is always unstable; is a saddle. Moreover, if , then is a saddle and there exists a unique positive equilibrium which is globally asymptotically stable.

For Model (1), if there is no impulsive effect, we have the following subsystem: Followed by [24], the following results can be concluded.

Throughout this paper, we always assume that the condition holds true. Considering the biological background, we only discuss Model (1) in the region . Obviously, due to Lakshmikantham et al. [25] and Bainov and Simeonov [26], the global existence and uniqueness of solution for Model (1) are guaranteed by the smoothness properties of right-side functions.

To discuss the dynamics of Model (1), we define three cross sections and two regions:

Figure 1: Illustration of the successor function.

3. Existence of Positive Periodic Solution for System (1)

Considering the biological meaning, here we always assume that . Therefore, we have four cases to discuss: , , , and .

3.1. The Case of

About the existence of positive periodic solution, we have the following graph illustrations.

Take a point on , where is small sufficiently. Assuming that the trajectory of Model (1) starting from firstly intersects at point and then jumps to , obviously, is above ; that is to say,

On the other hand, assume that the trajectory starting from intersects at and then jumps to . For , if , then thus, Model (1) exists as a positive periodic solution whose initial point is between and ; see Figure 2(a). If , then Model (1) will keep on impulse until ; this returns to the situation of and the positive periodic solution can be seen in Figure 2(b).

Figure 2: The possible trajectories in the case of .

Theorem 5. Assume that . Then Model (1) exists as a positive periodic solution whose initial point is located between and .

3.2. The Case of

For this case, we have the following graph illustrations.

Assuming that the trajectory starting from firstly intersects at and then jumps to , here is the intersection point of and . For , we have the following two situations.(i)If , then On the other hand, choosing a point next to -axis on , the trajectory starting from firstly intersects at point and then jumps to on ; obviously, is above ; thus, Therefore, Model (1) exists as a positive periodic solution whose initial point is between and ; this is shown in Figure 3(a).(ii)If , then On the other hand, there must exist a trajectory starting from on that tangents at point and then intersects , at points , , respectively; due to impulsive effect, jumps to . For , if , then Therefore, Model (1) exists as a positive periodic solution whose initial point is between and ; this can be seen in Figure 3(b). If , then the trajectory starting from will ultimately stay in . (Here we always assume the impulsive phase set with initial point on will ultimately exceed point after one or finite times impulses. In fact, the assumption is reasonable as should be very small in practical problem.)

Figure 3: The possible trajectories in the case of .

Theorem 6. Assume that . If or , , then Model (1) exists as a positive periodic solution.

3.3. The Case of

For this case, there must exist a trajectory starting from at that firstly intersects , at , respectively, and then tangents at point . For , there are three possible situations.

3.3.1.

Obviously, there must exist a trajectory starting from at that tangents at point and then intersects , at , , respectively. Due to impulsive effect, jumps to . For , there are two cases.(i)If , obviously, this situation returns to (i) of case of Section 3.2; here we omit it.(ii)If , assume that the trajectory starting from intersects , , and at , , and , respectively. Obviously, for the orbit , is the smallest abscissa. For , there are two possible positives.(a)If , then Model (1) exists as a positive periodic solution whose initial point is between and ; this is shown in Figure 4(a).(b)If , then there must exist a trajectory starting from at that tangents at point and then intersects and at points and . For , it also has two possibilities:if , then Model (1) exists as a positive periodic solution whose initial point is between and ; this can be seen in Figure 4(b);if , then the trajectory starting from will tend to equilibrium and the trajectory starting from will ultimately stay in . (In this case, we still assume the impulsive phase set with initial point on will ultimately exceed point after one or finite impulses.)

Figure 4: The possible trajectories in the case of .

Theorem 7. Assume that . If or , or , , , then Model (1) exists as a positive periodic solution.

3.3.2.

Assuming that the trajectory intersects at points with , due to impulsive effect, jumps to . For , one has the following four situations to discuss.(i)If or , then or is an order- periodic solution.(ii)If , then it is easy to get that there exists an order- periodic solution; here we omit the details.(iii)If , assume that the trajectory starting from intersects at point . For , there exist two cases.(a)If , then Model (1) exists as a positive periodic solution whose initial point is between and (see Figure 5(a)).(b)If , then there must exist a trajectory starting from at that firstly intersects at point and then tangents to at point , and intersects , at points , , respectively. Due to impulsive effect, jumps to . For , we have the following two cases to discuss:if , then Model (1) exists as a positive periodic solution whose initial point is between and (see Figure 5(b));if , then the trajectory starting from will tend to equilibrium and the trajectory starting from will ultimately stay in .(iv)If , then the trajectory starting from       will tend to equilibrium and the trajectory starting from will ultimately stay in .

Figure 5: The possible trajectories in the case of .

Theorem 8. Assume that . If or , or , , , then Model (1) exists as a positive periodic solution.

Similarly, for the case with or , one can prove there is no positive periodic solution; here we omit it.

Remark 9. The positive periodic solutions for Model (1) obtained in Theorem 5Theorem 8 are generated by impulses. Here, we say that a solution is generated by impulses if this solution is nontrivial when impulsive effect exists, but it is trivial when there does not exist impulsive effect. For example, when , by Lemma 1 we know that Model (2) does not possess any positive periodic solution; then positive periodic solutions of Model (1) under state-dependent impulsive conditions are called positive periodic solution generated by impulses.

Remark 10. As we know, the previous papers concerning state-dependent impulsive effect all assumed that the predator just lived on the prey; here we point out that the predator has some other food resources; this is more practical. On the other hand, the existing state-dependent impulsive differential systems mainly discussed the properties of solutions, including existence, uniqueness, and orbitally asymptotical stability. Here, not aiming at the properties of solutions, we are focused on considering the influence of impulsive effect on the system itself. The theoretical results imply that if impulses do not exist, then the predator and prey species will tend to a point; if impulsive effect occurs, then the predator and prey species will be maintained at a periodic oscillation; that is, both the densities of these two species can change periodically. Therefore, our results demonstrate that impulsive effect takes an important role in ecological system.

4. Simulations and Conclusions

In this paper, we propose and analyse a state-dependent impulsive predator-prey model in which the predator species display a logistic growth. By using geometrical analysis methods, the existence of positive periodic solutions of Model (1) is given. Here we should point out that the positive periodic solutions are generated by impulses. For system (2), which does not exist as impulsive effect, the interior equilibrium is globally asymptotically stable, the phase trajectory and time series chart can be seen in Figures 6 and 7; therefore, system (2) does not exist as positive periodic solution and all the phase trajectories will tend to the interior equilibrium. When the impulsive effects are operated, system (1) can be gotten, the theoretical results demonstrate that system (1) exists as positive periodic solutions for some cases, and the numerical simulations also illustrate the existence of the periodic solutions; please see Figures 8, 9, and 10. Here , , , , , and . Therefore, the positive periodic solutions are generated by impulses.

Figure 6: The phase trajectory without impulse.
Figure 7: The time series chart for and without impulse.
Figure 8: Plots of the positive periodic solution when with , , , , and .
Figure 9: Plot of the positive periodic solution when with , , , , and .
Figure 10: Plot of the positive periodic solution when with , , , , and .

Conflict of Interests

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

Acknowledgments

Qizhen Xiao was partially supported by the Fundamental Research Funds for the Central Universities of Central South University (no. 2013zzts006). Binxiang Dai was partially supported by the National Natural Science Foundation of China (no. 11271371 and no. 51479215).

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