#### Abstract

Under some conditions concerning the first eigenvalues corresponding to the relevant linear operator, we obtain sharp optimal criteria for the existence of positive solutions for -Laplacian problems with integral boundary conditions. The main methods in the paper are constructing an available integral operator and combining fixed point index theory. The interesting point of the results is that the nonlinear term contains all lower-order derivatives explicitly. Finally, we give some examples to demonstrate the main results.

#### 1. Introduction

In this paper, we discuss the existence of positive solutions for the following -Laplacian integral boundary value problems:where , , , , is symmetric on the interval (i.e., and for ), is continuous, and are nonnegative symmetric on .

Boundary value problems of ordinary differential equations have become an important research field in recent years. Fourth-order -Laplacian boundary value problems arise in applied mathematics, physics, gas diffusion through porous media, engineering, elastic mechanics, electromagnetic waves of gravity driven flows, and the various areas of adiabatic tubular reactor processes, as well as biological problems; see [1–5] and the references therein.

In [6], by using the fixed point theorem for strict set contraction operator, Zhang et al. considered the existence of positive solutions for the following th-order impulsive boundary value problems with integral boundary conditions in Banach spaces:where , , , , , , and denotes the jump of at . They also gave the upper and lower bounds for these positive solutions.

In [7], by means of the fixed point index theory, Sun and Zhang studied the following singular nonlinear Sturm-Liouville problems:where and is allowed to be singular at and .

In [2], by making use of the theory of the spectrum, Sergejeva studied the regions of solvability for three-point boundary value problem:where , , and is a bounded function. The solvability results are established for the problem with .

Motivated and inspired greatly by the above mentioned works, the aim of the paper is to improve, generalize, and supplement the previous results. We obtain the existence results on nonlinear fourth-order integral boundary value problems with one-dimensional -Laplacian integral boundary value problem (1). The novelty of our results is in exploring some optimal criteria for the existence of positive solutions of problem (1). The methods used in our work will depend on an application of fixed point index theory together with the first eigenvalues corresponding to the relevant linear operator. It can also be seen that the nonlinear term involves all lower-order derivatives explicitly.

The paper is organized as follows. In Section 2, we state some lemmas and several preliminary results. The main results are formulated and proved in Section 3. Examples are given in Section 4.

#### 2. Preliminaries

Throughout the paper, we make the following assumptions:

(**H**_{1}) and , , are continuous and also and are symmetric on for all (i.e., , ).

(**H**_{2}) are all nonnegative and symmetric on , and is continuous on , and may be singular at and/or , and and , where

In what follows, we will consider the Banach space , , equipped with the maximum norm . Denote cone bythen, is a positive cone in .

Let for (), andHere , , and are Green’s functions of problem (1).

Lemma 1 (see [1]). *Suppose that ( H_{1}) and (H_{2}) hold; then, for , we have*(I)

*, , ;*(II)

*, where ;*(III)

*, , and ;*(IV)

*; , where , , , .*

Define an integral operator by

It is well known that is a solution of problem (1) if and only if is a fixed point of operator equation .

Lemma 2. *Suppose that ( H_{1}) and (H_{2}) hold, if is a solution of the following integral equation: *

*then, is a solution of problem (1).*

Lemma 3. *Suppose that ( H_{1}) and (H_{2}) hold; then, is a completely continuous operator.*

*Proof. *First, we prove that For every , we haveThus, , for all Hence, is nonnegative concave functional on .

By Lemma 1, for , we obtainHence, , and , which implies

Next, we show that is completely continuous.

For any natural number , setThen, is continuous, and , . LetObviously, is a completely continuous operator. From Lemma 1, we obtainwhere . Therefore, is a completely continuous operator. The proof is completed.

Now we define linear integral operator as follows:

It is easy to see that is a completely continuous linear operator, and

Lemma 4. *Assume that ( H_{1}) and (H_{2}) hold. Then, the operator defined by (15) is a completely continuous linear operator and , the spectral radius , and has a positive eigenfunction corresponding to its first eigenvalue .*

*Proof. *A simple modification of the argument in Lemma 3 yields that is a completely continuous linear operator and . By (**H**_{1}) and (**H**_{2}), there is such that . Choose constants and such that and , for all . Choose a nonnegative continuous functional such that , for all . Then, for any , we haveThus, there exists a constant such that , for all . By famous Krein-Rutman theorems, we know that the spectral radius and has a positive eigenfunction corresponding to its first eigenvalue ; that is, . This completes the proof.

Lemma 5 (see [8]). *Let be a cone in Banach space , and let be a bounded open set in . Suppose that is completely continuous. If there exists , such that , for all , Then, the fixed point index *

Lemma 6 (see [8]). *Let be a cone in Banach space , and let be a bounded open set in with . Suppose that is a completely continuous operator. If , for all , Then, the fixed point index *

Lemma 7 (see [9]). *Let and be cones in Banach space , and let be a bounded open set in . Suppose that is a completely continuous operator, and has no fixed point on . If there exist linear operators which satisfy , , , and , such that*(1)*, for certain natural number ,*(2)*, for all ,*(3)*, for all ,**then the fixed point index *

#### 3. Main Results

In this section, we establish sharp optimal criteria for the existence of positive solutions to problem (1) under superlinear cases and sublinear cases, respectively.

Theorem 8. *Suppose that ( H_{1}) and (H_{2}) hold. In addition, assume that*

*where is the first eigenvalue of defined by (15); then, problem (1) has at least one positive solution.*

To prove our main result, we need some preliminary results.

Lemma 9. *Suppose that ( H_{1}) and (H_{2}) hold. Define*

*where , , is the positive eigenfunction corresponding to its first eigenvalue ; that is, , and*

*then, is a cone in , and*

*Proof. *It is obvious that is a cone in . For any , we obtainThus, . The proof is completed.

*Proof of Theorem 8. *It follows from (17) that there exists , such that , for is sufficiently large. In view of (**H**_{1}), we see that there exists such thatLet , where and are defined by Lemma 9.

In the following, we prove thatwhere is a positive eigenfunction corresponding to its first eigenvalue .

Otherwise, there exist and , such thatSince and , we know from (24) that Therefore, it follows from (19) and (22) thatOn the other hand, it follows from (24) thatwhich is a contradiction; thus, by Lemma 5, we seeIt follows from (18) that there exists , such thatSuppose that there exist , , such that Without loss of generality, we may suppose that (otherwise, the proof is completed). Then,Multiplying and then integrating by (29), we haveBy maximum principle, and , ; then Hence, (30) implies which is a contradiction. So by Lemma 6, we haveIt follows from (27) and (31) thatThen, has at least one fixed point on . This means problem (1) has at least one positive solution. The proof is completed.

Corollary 10. *Suppose that ( H_{1}) and (H_{2}) hold. In addition, assume that*

*Then, for any*

*where is the first eigenvalue of defined by (15), the following -Laplacian integral boundary value problem*

*has at least one positive solution.*

*Proof. *By (34), we obtainTherefore, it follows from Theorem 8 that Corollary 10 holds.

Theorem 11. *Suppose that ( H_{1}) and (H_{2}) hold. In addition, assume that*

*where is the first eigenvalue of defined by (15); then, problem (1) has at least one positive solution.*

*Proof. *It follows from (37) that there exists such thatLet be the positive eigenfunction corresponding to its first eigenvalue . Then, ; that is,Hence, , for all Then, is nonnegative concave on . Thus,

Let , . Then, is a completely continuous linear operator, and ,

For any , it follows from (39) thatSetting , , denotes the identical operator, and , in Lemma 7. We haveIt follows from (38) that there exist and , such thatSet . Then, is a completely continuous linear operator, and Let

Now we prove that

Suppose that there exist , , such that Let ; then, from (43) we havewhere Thus, , Since , we have , , for It means that , LetFor any , denoteIt is easy to see thatSince , we have from (47) that , which contradicts (45). Thus, for any , , we have that Thus, from Lemma 6, we know thatFrom (42) and (48), we see thatThen, has at least one fixed point on . It means problem (1) has at least one positive solution. The proof is completed.

Corollary 12. *Suppose that ( H_{1}) and (H_{2}) hold. In addition, assume that*

*Then, for any*

*where is the first eigenvalue of defined by (15), problem (35) has at least one positive solution.*

*Proof. *By (51), we obtainIt follows from Theorem 11 that Corollary 12 holds. The proof is completed.

#### 4. Examples

*Example 1. *Consider the existence of positive solutions for the following -Laplacian integral boundary value problems:where . , , , , is symmetric on the interval , for is continuous, and are nonnegative symmetric on .

Let and let Obviously, , and

All conditions of Theorem 8 are satisfied. Consequently, following from Theorem 8, we know that the boundary value problem (53) has at least one positive solution.

*Example 2. *Consider the existence of positive solutions for the following -Laplacian integral boundary value problems:where , , , , is symmetric on the interval , for is continuous, and are nonnegative symmetric on . For ,Let

Obviously, , and

All conditions of Theorem 8 are satisfied. Consequently, following from Theorem 8, we know that the boundary value problem (55) has at least one positive solution.

#### Conflict of Interests

The author declares that she has no competing interests.

#### Acknowledgments

The author is very grateful to the editor and the anonymous referee for his/her careful reading of the first draft of the paper and making very valuable comments and helpful suggestions. She would like to express her gratitude to Professor Lishan Liu and Professor R. P. Agarwal for their many valuable comments. The author was supported financially by the Foundation of Shanghai Natural Science (13ZR1430100) and the Foundation of Shanghai Municipal Education Commission (DYL201105) and the NNSF of China (no. 11371095 and no. 2013M541455).