## Compactness Conditions in the Theory of Nonlinear Differential and Integral Equations

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Hilmi Ergören, Adem Kiliçman, "Some Existence Results for Impulsive Nonlinear Fractional Differential Equations with Closed Boundary Conditions", *Abstract and Applied Analysis*, vol. 2012, Article ID 387629, 15 pages, 2012. https://doi.org/10.1155/2012/387629

# Some Existence Results for Impulsive Nonlinear Fractional Differential Equations with Closed Boundary Conditions

**Academic Editor:**Beata Rzepka

#### Abstract

We investigate some existence results for the solutions to impulsive fractional differential equations having closed boundary conditions. Our results are based on contracting mapping principle and Burton-Kirk fixed point theorem.

#### 1. Introduction

This paper considers the existence and uniqueness of the solutions to the closed boundary value problem (BVP), for the following impulsive fractional differential equation: where is Caputo fractional derivative, , , with and has a similar meaning for , where , , , and are real constants with .

The boundary value problems for nonlinear fractional differential equations have been addressed by several researchers during last decades. That is why, the fractional derivatives serve an excellent tool for the description of hereditary properties of various materials and processes. Actually, fractional differential equations arise in many engineering and scientific disciplines such as, physics, chemistry, biology, electrochemistry, electromagnetic, control theory, economics, signal and image processing, aerodynamics, and porous media (see [1–7]). For some recent development, see, for example, [8–14].

On the other hand, theory of impulsive differential equations for integer order has become important and found its extensive applications in mathematical modeling of phenomena and practical situations in both physical and social sciences in recent years. One can see a noticeable development in impulsive theory. For instance, for the general theory and applications of impulsive differential equations we refer the readers to [15–17].

Moreover, boundary value problems for impulsive fractional differential equations have been studied by some authors (see [18–20] and references therein). However, to the best of our knowledge, there is no study considering closed boundary value problems for impulsive fractional differential equations.

Here, we notice that the closed boundary conditions in (1.1) include quasi-periodic boundary conditions and interpolate between periodic and antiperiodic boundary conditions.

Motivated by the mentioned recent work above, in this study, we investigate the existence and uniqueness of solutions to the closed boundary value problem for impulsive fractional differential equation (1.1). Throughout this paper, in Section 2, we present some notations and preliminary results about fractional calculus and differential equations to be used in the following sections. In Section 3, we discuss some existence and uniqueness results for solutions of BVP (1.1), that is, the first one is based on Banach’s fixed point theorem, the second one is based on the Burton-Kirk fixed point theorem. At the end, we give an illustrative example for our results.

#### 2. Preliminaries

Let us set , , , and introduce the set of functions:

, and there exist and , with and

, , and there exist and , with which is a Banach space with the norm where .

The following definitions and lemmas were given in [4].

*Definition 2.1. *The fractional (arbitrary) order integral of the function of order is defined by
where is the Euler gamma function.

*Definition 2.2. *For a function given on the interval , Caputo fractional derivative of order is defined by
where the function has absolutely continuous derivatives up to order .

Lemma 2.3. *Let , then the differential equation
**
has solutions
*

The following lemma was given in [4, 10].

Lemma 2.4. *Let , then
**
for some , , .*

The following theorem is known as Burton-Kirk fixed point theorem and proved in [21].

Theorem 2.5. *Let be a Banach space and , two operators satisfying: *(a)* is a contraction, and *(b)* is completely continuous.* *Then either (i) the operator equation has a solution, or(ii) the set is unbounded for .*

Theorem 2.6 (see [22], Banach’s fixed point theorem). *Let be a nonempty closed subset of a Banach space , then any contraction mapping of into itself has a unique fixed point. *

Next we prove the following lemma.

Lemma 2.7. *Let and let be continuous. A function is a solution of the fractional integral equation:
**
if and only if is a solution of the fractional BVP
**
where*

*Proof. *Let be the solution of (2.7). If , then Lemma 2.4 implies that
for some .

If , then Lemma 2.4 implies that
for some . Thus we have
Observing that
then we have
hence, for ,
If , then Lemma 2.4 implies that
for some . Thus we have
Similarly we observe that
thus we have
Hence, for ,
By a similar process, if , then again from Lemma 2.4 we get
Now if we apply the conditions:
we have
In view of the relations (2.8), when the values of and are replaced in (2.9) and (2.20), the integral equation (2.7) is obtained.

Conversely, assume that satisfies the impulsive fractional integral equation (2.6), then by direct computation, it can be seen that the solution given by (2.6) satisfies (2.7). The proof is complete.

#### 3. Main Results

*Definition 3.1. *A function with its -derivative existing on is said to be a solution of (1.1), if satisfies the equation on and satisfies the conditions:

For the sake of convenience, we define The followings are main results of this paper.

Theorem 3.2. *Assume that *(A1)* the function is continuous and there exists a constant such that , for all , and ,*(A2)*, are continuous, and there exist constants and such that , for each and .**Moreover, consider the following:
**
Then, BVP (1.1) has a unique solution on .*

*Proof. *Define an operator by
Now, for and for each , we obtain
Therefore, by (3.3), the operator is a contraction mapping. In a consequence of Banach’s fixed theorem, the BVP (1.1) has a unique solution. Now, our second result relies on the Burton-Kirk fixed point theorem.

Theorem 3.3. *Assume that (A1)-(A2) hold, and*(A3)* there exist constants , , such that , , for each and .**Then the BVP (1.1) has at least one solution on . *

*Proof. *We define the operators by
It is obvious that is contraction mapping for
Now, in order to check that is completely continuous, let us follow the sequence of the following steps.*Step *1 ( is continuous). Let be a sequence such that in . Then for , we have
Since is continuous function, we get
*Step *2 ( maps bounded sets into bounded sets in ). Indeed, it is enough to show that for any , there exists a positive constant such that for each , we have . By (A3), we have for each ,
*Step *3 ( maps bounded sets into equicontinuous sets in ). Let with and let be a bounded set of as in Step 2, and let . Then
where
This implies that is equicontinuous on all the subintervals , . Therefore, by the Arzela-Ascoli Theorem, the operator is completely continuous.

To conclude the existence of a fixed point of the operator , it remains to show that the set is bounded.

Let , for each , Hence, from (A3), we have Consequently, we conclude the result of our theorem based on the Burton-Kirk fixed point theorem.

#### 4. An Example

Consider the following impulsive fractional boundary value problem: Here, , , , , , , . Obviously, , , , , . Further, Since the assumptions of Theorem 3.2 are satisfied, the closed boundary value problem (4.1) has a unique solution on . Moreover, it is easy to check the conclusion of Theorem 3.3.

#### Acknowledgments

The authors would like to express their sincere thanks and gratitude to the reviewer(s) for their valuable comments and suggestions for the improvement of this paper. The second author also gratefully acknowledges that this research was partially supported by the University Putra Malaysia under the Research University Grant Scheme 05-01-09-0720RU.

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#### Copyright

Copyright © 2012 Hilmi Ergören and Adem Kiliçman. 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.