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# Eigenvalue criteria for existence of positive solutions of impulsive differential equations with non-separated boundary conditions

Ruixi Liang1* and Jianhua Shen2

### Author affiliations

1 Department of Mathematics and Statistics, Central South University, Changsha, Hunan, 410075, P.R. China

2 Department of Mathematics, Hangzhou Normal University, Hangzhou, Zhejiang, 310036, P.R. China

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Boundary Value Problems 2013, 2013:3  doi:10.1186/1687-2770-2013-3

 Received: 29 August 2012 Accepted: 28 December 2012 Published: 14 January 2013

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

### Abstract

In this paper, we discuss the existence of positive solutions for second-order differential equations subject to nonlinear impulsive conditions and non-separated periodic boundary value conditions. Our criteria for the existence of positive solutions will be expressed in terms of the first eigenvalue of the corresponding nonimpulsive problem. The main tool of study is a fixed point theorem in a cone.

MSC: 34B37, 34B18.

##### Keywords:
impulsive differential equation; positive solution; fixed point theorem; non-separated periodic boundary value condition

### 1 Introduction

Let ω be a fixed positive number. In this paper, we are concerned with the existence of positive solutions for the following boundary value problem (BVP) with impulses:

(1.1a)

(1.1b)

(1.1c)

Here, denotes the quasi-derivative of . The condition (1.1c) is called a non-separated periodic boundary value condition for (1.1a).

We assume throughout, and with further mention, that the following conditions hold.

(H1) Let , and , , , . , where (respectively ) denotes the right limit (respectively, the left limit) of at .

(H)

A function defined on is called a solution of BVP (1.1) ((1.1a)-(1.1c)) if its first derivative exists for each , is absolutely continuous on each close subinterval of , there exist finite values , the impulse conditions (1.1b) and the boundary conditions (1.1c) are satisfied, and the equation (1.1a) is satisfied almost everywhere on .

For the case of (), the problem (1.1) is related to a non-separated periodic boundary value problem of ODE. Atici and Guseinov [1] have proved the existence of a positive and twin positive solutions to BVP (1.1) by applying a fixed point theorem for the completely continuous operators in cones. In [2], Graef and Kong studied the following periodic boundary value problem:

(1.2)

where . Based upon the properties of Green’s function obtained in [1], the authors extended and improved the work of [1] by using topological degree theory. They derived new criteria for the existence of non-trivial solutions, positive solutions and negative solutions of the problem (1.2) when f is a sign-changing function and not necessarily bounded from below even over . Very recently, He et al.[3] studied BVP (1.1) without impulses and generalized the results of [1,4] via the fixed point index theory. The problem (1.2) in the case of , the usual periodic boundary value problem, has been extensively investigated; see [4-7] for some results.

On the other hand, impulsive differential equations are a basic tool to study processes that are subjected to abrupt changes in their state. There has been a significant development in the last two decades. Boundary problems of second-order differential equations with impulse have received considerable attention and much literature has been published; see, for instance, [8-17] and their references. However, there are fewer results about positive solutions for second-order impulsive differential equations. To our best knowledge, there is no result about nonlinear impulsive differential equations with non-separated periodic boundary conditions.

Motivated by the work above, in this paper we study the existence of positive solutions for the boundary value problem (1.1). By using fixed point theorems in a cone, criteria are established under some conditions on concerning the first eigenvalue corresponding to the relevant linear operator. More important, the impulsive terms are different from those of papers [8,9].

### 2 Preliminaries

In this section, we collect some preliminary results that will be used in the subsequent section. We denote by and the unique solutions of the corresponding homogeneous equation

(2.1)

under the initial boundary conditions

(2.2)

Put , then by [[1], Lemma 2.3], .

Definition 2.1 For two differential functions y and z, we define their Wronskian by

Theorem 2.1The Wronskian of any two solutions for equations (2.1) is constant. Especially, .

Proof Suppose that y and z are two solutions of (2.1), then

therefore, the Wronskian is constant. Further, from the initial conditions (2.2), we have . The proof is complete. □

Consider the following equation:

(2.3)

From Theorem 2.5 in [1], equation (2.3) has a Green function for all , which has the following properties:

() is continuous in t and s for all .

() If and , then .

()

Combining with Theorem 2.1, we can also prove that

()

Remark 1 From paper [1], we can get when () and ,

Especially, in the case of , (), Green’s function has the form

Define an operator

then it is easy to check that is a completely continuous operator. By virtue of the Krein-Rutman theorem, the authors in [3] got the following result.

Lemma 2.1The spectral radiusandThas a positive eigenfunction corresponding to its first eigenvalue.

In what follows, we denote the positive eigenfunction corresponding to by ϕ and . Define a mapping Φ and a cone K in a Banach space by

where , .

Lemma 2.2The fixed point of the mapping Φ is a solution of (1.1).

Proof Clearly, Φu is continuous in t. For ,

Using () and (), we have , and

which implies that the fixed point of Φ is the solution of (1.1). The proof is complete. □

The proofs of the main theorems of this paper are based on fixed point theory. The following two well-known lemmas in [18] are needed in our argument.

Lemma 2.3[18]

LetXbe a Banach space andKbe a cone inX. Supposeandare open subsets ofXsuch that, and suppose that

is a completely continuous operator such that

, forand, andforand, or

, forand, andforand.

Then Φ has a fixed point in.

Lemma 2.4[18]

LetXbe a Banach space andKbe a cone inX. Supposeandare open subsets ofXsuch that, and suppose that

is a completely continuous operator such that

There existssuch thatforand, for, or

There existssuch thatforand, for.

Then Φ has a fixed point in.

### 3 Main results

Recalling that δ was defined after Lemma 2.1, for convenience, we introduce the following notations. Assume that the constant and γ is some positive function on J,

Theorem 3.1Assume that there exist positive constantsα, βsuch that, , , and

(3.1)

Then (1.1) has at least one positive solutionusuch that.

Proof Clearly, , let , . Define the open sets

Then is completely continuous. By (3.1) and the definition of , , , , there exists such that

(3.2)

(3.3)

and

(3.4)

Let . We show that

(3.5)

If not, there exist and such that . Let . Noting that for any , we obtain that for ,

which implies that , a contradiction.

On the other hand, for , , we have

From Lemma 2.4 it follows that Φ has a fixed point . Furthermore, and , which means that is a positive solution of Eq. (1.1). The proof is complete. □

In the next theorem, we make use of the eigenvalue and the corresponding eigenfunction ϕ introduced in Lemma 2.1.

Theorem 3.2Assume that there exist positive constantsα, βsuch that, , , and

(3.6)

hereonJ. Then (1.1) has at least one positive solutionusuch that.

Proof Obviously, , put , . Define the open sets

At first, we show that . For any , from (), we have

On the other hand,

It is easy to check that is completely continuous.

Next, we show that

(3.7)

If not, there exist and such that . Hence,

(3.8)

Multiplying the first equation of (3.8) by ϕ and integrating from 0 to ω, we obtain that

(3.9)

One can find that

(3.10)

Substituting (3.10) into (3.9), we get

Noting that , therefore,

which implies that

Finally, we show that

Since and are negative for and , the condition (3.6) implies that . Hence, for and for any ,

Suppose that there exist and such that , that is,

(3.11)

Multiplying the first equation of (3.11) by ϕ and integrating from 0 to ω, we obtain that

(3.12)

One can get that

(3.13)

Substituting (3.13) into (3.12), we get

Noting that , therefore,

It is impossible for . When ,

From Lemma 2.3 it follows that Φ has a fixed point . Furthermore, and , which means that is a positive solution of Eq. (1.1). The proof is complete. □

Corollary 3.1Assume that, , , and

or

hereonJ. Then (1.1) has at least one positive solution.

Corollary 3.2Assume that there exists a constantαsuch that, (, αand ∞) and

hereonJ. Then there exists one open intervalsuch that (1.1) has at least two positive solutions for.

Example 1 Consider the equation

(3.14)

where , and

here and . Since , and , by Theorem 3.1, (3.14) has at least one positive solution for any .

Example 2 Consider the equation

(3.15)

where , .

It is well known that, for the problem consisting of the equation , , and the boundary condition

(3.16)

the first eigenvalue is 0 (see, for example, [[19], p.428]). It follows that the first eigenvalue is for the problem consisting of the equation

and the boundary condition (3.16). Meanwhile, we can obtain the positive eigenfunction corresponding to . It is also easy to check that , , and (here ). So, the right-hand side of the inequality in Corollary 3.2 is obviously satisfied. Considering the monotonicity of and , we can choose a sufficiently small positive constant α such that the left-hand side of the inequality is true. Therefore, by a direct application of Corollary 3.2, there exists one open interval such that (3.15) has at least two positive solutions for .

### Competing interests

The authors declare that they have no competing interests.

### Authors’ contributions

All authors contributed equally to the manuscript and read and approved the final manuscript.

### Acknowledgements

The authors would like to thank anonymous referees very much for helpful comments and suggestions which led to the improvement of presentation and quality of work. This research was partially supported by the NNSF of China (No. 11001274, 11171085) and the Postdoctoral Science Foundation of Central South University and China (No. 2011M501280).

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