# New Existence Results for Higher-Order Nonlinear Fractional Differential Equation with Integral Boundary Conditions

- Meiqiang Feng
^{1}Email author, - Xuemei Zhang
^{2, 3}and - WeiGao Ge
^{3}

**2011**:720702

**DOI: **10.1155/2011/720702

© Meiqiang Feng et al. 2011

**Received: **16 March 2010

**Accepted: **5 July 2010

**Published: **20 July 2010

## Abstract

This paper investigates the existence and multiplicity of positive solutions for a class of higher-order nonlinear fractional differential equations with integral boundary conditions. The results are established by converting the problem into an equivalent integral equation and applying Krasnoselskii's fixed-point theorem in cones. The nonexistence of positive solutions is also studied.

## 1. Introduction

Fractional differential equations arise in many engineering and scientific disciplines as the mathematical modelling of systems and processes in the fields of physics, chemistry, aerodynamics, electrodynamics of complex medium, polymer rheology, Bode's analysis of feedback amplifiers, capacitor theory, electrical circuits, electron-analytical chemistry, biology, control theory, fitting of experimental data, and so forth, and involves derivatives of fractional order. Fractional derivatives provide an excellent tool for the description of memory and hereditary properties of various materials and processes. This is the main advantage of fractional differential equations in comparison with classical integer-order models. An excellent account in the study of fractional differential equations can be found in [1–5]. For the basic theory and recent development of the subject, we refer a text by Lakshmikantham [6]. For more details and examples, see [7–23] and the references therein. However, the theory of boundary value problems for nonlinear fractional differential equations is still in the initial stages and many aspects of this theory need to be explored.

where is the standard Rimann-Liouville fractional derivative of order , the nonlinearity may be singular at , and function may be singular at . The author derived the corresponding Green's function named by fractional Green's function and obtained some properties as follows.

Proposition 1.1.

Green's function satisfies the following conditions:

(i) for all ;

(ii)there exists a positive function such that

here .

for the fractional order cases. In Section 2, we will deduce some new properties of Green's function.

where is the standard Rimann-Liouville fractional derivative of order and may be singular at or/and at , is nonnegative, and .

For the case of , the boundary value problems () reduces to the problem studied by Eloe and Ahmad in [24]. In [24], the authors used the Krasnosel'skii and Guo [25] fixed-point theorem to show the existence of at least one positive solution if is either superlinear or sublinear to problem (). For the case of , the boundary value problems () is related to a m-point boundary value problems of integer-order differential equation. Under this case, a great deal of research has been devoted to the existence of solutions for problem (), for example, see Pang et al. [26], Yang and Wei [27], Feng and Ge [28], and references therein. All of these results are based upon the fixed-point index theory, the fixed-point theorems and the fixed-point theory in cone for strict set contraction operator.

The organization of this paper is as follows. We will introduce some lemmas and notations in the rest of this section. In Section 2, we present the expression and properties of Green's function associated with boundary value problem (). In Section 3, we discuss some characteristics of the integral operator associated with the problem () and state a fixed-point theorem in cones. In Section 4, we discuss the existence of at least one positive solution of boundary value problem (). In Section 5, we will prove the existence of two or positive solutions, where is an arbitrary natural number. In Section 6, we study the nonexistence of positive solution of boundary value problem (). In Section 7, one example is also included to illustrate the main results. Finally, conclusions in Section 8 close the paper.

The fractional differential equations related notations adopted in this paper can be found, if not explained specifically, in almost all literature related to fractional differential equations. The readers who are unfamiliar with this area can consult, for example, [1–6] for details.

Definition 1.2 (see [4]).

where , is called Riemann-Liouville fractional integral of order .

Definition 1.3 (see [4]).

where denotes the integer part of number , is called the Riemann-Liouville fractional derivative of order .

Lemma 1.4 (see [13]).

for some , where is the smallest integer greater than or equal to .

## 2. Expression and Properties of Green's Function

In this section, we present the expression and properties of Green's function associated with boundary value problem ().

Lemma 2.1.

Proof.

where is defined by (2.4).

where and are defined by (2.3), (2.4), and (2.5), respectively. The proof is complete.

From (2.3), (2.4), and (2.5), we can prove that and have the following properties.

Proposition 2.2.

The function defined by (2.4) satisfies

(i) is continuous for all ;

(ii)for all , one has

- (i)
It is obvious that is continuous on and when .

- (ii)
Since , it is clear that is increasing with respect to for .

Then, for given , we have arrives at maximum at when . This together with the fact that is increasing on , we obtain that (2.15) holds.

Remark 2.3.

Remark 2.4.

Remark 2.5.

Remark 2.6.

Remark 2.7.

Remark 2.8.

Proposition 2.9.

Proof.

For , we divide the proof into the following three cases for .

Case 1.

Case 2.

Case 3.

Letting and using (2.30), (2.33), and (2.36), it follows that (2.28) holds. This completes the proof.

Proposition 2.10.

If , then one has

(i) is continuous for all ;

(ii) .

Proof.

Using the properties of , definition of , it can easily be shown that (i) and (ii) hold.

Theorem 2.11.

If , the function defined by (2.3) satisfies

(i) is continuous for all ;

(ii) for each , and

is defined by (2.16), is defined in Proposition 2.9.

- (i)
From Propositions 2.2 and 2.10, we obtain that is continuous for all , and .

- (ii)
From (ii) of Proposition 2.2 and (ii) of Proposition 2.10, we have that for each .

Now, we show that (2.38) holds.

Then the proof of Theorem 2.11 is completed.

Remark 2.12.

From the definition of , it is clear that .

## 3. Preliminaries

To prove the existence of positive solutions for the boundary value problem (), we need the following assumptions:

() on any subinterval of (0,1) and , where is defined in Theorem 2.11;

() and uniformly with respect to on ;

() , where is defined by (2.37).

From condition , it is not difficult to see that may be singular at or/and at , that is, or/and .

where is defined by (2.3).

Lemma 3.1.

Let hold. Then boundary value problems () has a solution if and only if is a fixed point of .

Proof.

From Lemma 2.1, we can prove the result of this lemma.

Lemma 3.2.

Let hold. Then and is completely continuous.

Proof.

So, and hence . Next by similar proof of Lemma in [13] and Ascoli-Arzela theorem one can prove is completely continuous. So it is omitted.

To obtain positive solutions of boundary value problem (), the following fixed-point theorem in cones is fundamental which can be found in [25, page 94].

Lemma 3.3 (Fixed-point theorem of cone expansion and compression of norm type).

Let be a cone of real Banach space , and let and be two bounded open sets in such that and . Let operator be completely continuous. Suppose that one of the two conditions

(i) and

or

(ii) and

is satisfied. Then has at least one fixed point in .

## 4. Existence of Positive Solution

Theorem 4.1.

Assume that hold. In addition, one supposes that one of the following conditions is satisfied:

and (particularly, and ).

there exist two constants with such that is nondecreasing on

for all , and , and for all . Then boundary value problem () has at least one positive solution.

Proof.

Let be cone preserving completely continuous that is defined by (3.2).

Case 1.

where satisfies .

then .

Case 2.

Applying Lemma 3.3 to (4.4) and (4.8), or (4.10) and (4.12), yields that has a fixed point or with . Thus it follows that boundary value problems () has a positive solution , and the theorem is proved.

Theorem 4.2.

Assume that hold. In addition, one supposes that the following condition is satisfied:

and (particularly, and ).

Then boundary value problem () has at least one positive solution.

## 5. The Existence of Multiple Positive Solutions

Now we discuss the multiplicity of positive solutions for boundary value problem (). We obtain the following existence results.

Theorem 5.1.

Assume , and the following two conditions:

and (particularly, );

there exists such that

Proof.

We consider condition . Choose with .

Applying Lemma 3.3 to (5.2), (5.3), and (5.5) yields that has a fixed point , and a fixed point Thus it follows that boundary value problem () has at least two positive solutions and . Noticing (5.5), we have and . Therefore (5.1) holds, and the proof is complete.

Theorem 5.2.

Assume , and the following two conditions:

and ;

there exists such that

Theorem 5.3.

Assume that , and hold. If there exist positive numbers with such that

for and for

Then boundary value problem () has at least positive solutions satisfying

Theorem 5.4.

Assume that , and hold. If there exist positive numbers with such that

is nondecreasing on for all ;

, and

Then boundary value problem () has at least positive solutions satisfying

## 6. The Nonexistence of Positive Solution

Our last results corresponds to the case when boundary value problem () has no positive solution.

Theorem 6.1.

Assume and , then boundary value problem () has no positive solution.

Proof.

which is a contradiction, and complete the proof.

Similarly, we have the following results.

Theorem 6.2.

Assume and , then boundary value problem () has no positive solution.

## 7. Example

To illustrate how our main results can be used in practice we present an example.

Example 7.1.

thus it follows that problem (7.1) has a positive solution by .

## 8. Conclusions

In this paper, by using the famous Guo-Krasnoselskii fixed-point theorem, we have investigated the existence and multiplicity of positive solutions for a class of higher-order nonlinear fractional differential equations with integral boundary conditions and obtained some easily verifiable sufficient criteria. The interesting point is that we obtain some new positive properties of Green's function, which significantly extend and improve many known results for fractional order cases, for example, see [12–15, 19]. The methodology which we employed in studying the boundary value problems of integer-order differential equation in [28] can be modified to establish similar sufficient criteria for higher-order nonlinear fractional differential equations. It is worth mentioning that there are still many problems that remain open in this vital field except for the results obtained in this paper: for example, whether or not we can obtain the similar results of fractional differential equations with *p*-Laplace operator by employing the same technique of this paper, and whether or not our concise criteria can guarantee the existence of positive solutions for higher-order nonlinear fractional differential equations with impulses. More efforts are still needed in the future.

## Declarations

### Acknowledgments

The authors thank the referee for his/her careful reading of the manuscript and useful suggestions. These have greatly improved this paper. This work is sponsored by the Funding Project for Academic Human Resources Development in Institutions of Higher Learning Under the Jurisdiction of Beijing Municipality (PHR201008430), the Scientific Research Common Program of Beijing Municipal Commission of Education (KM201010772018), the 2010 level of scientific research of improving project (5028123900), the Graduate Technology Innovation Project (5028211000) and Beijing Municipal Education Commission (71D0911003).

## Authors’ Affiliations

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