\documentclass[reqno]{amsart} \usepackage{hyperref} \AtBeginDocument{{\noindent\small \emph{Electronic Journal of Differential Equations}, Vol. 2015 (2015), No. 233, pp. 1--10.\newline ISSN: 1072-6691. URL: http://ejde.math.txstate.edu or http://ejde.math.unt.edu \newline ftp ejde.math.txstate.edu} \thanks{\copyright 2015 Texas State University - San Marcos.} \vspace{9mm}} \begin{document} \title[\hfilneg EJDE-2015/233 fractional differential inclusions\hfil ] {Boundary-value problems for Riemann-Liouville fractional differential inclusions in \\ Banach spaces} \author[S. Hamani, J. Henderson \hfil EJDE-2015/233\hfilneg] {Samira Hamani, Johnny Henderson} \address{Samira Hamani \newline D\'epartement de Math\'ematiques, Universit\'e de Mostaganem, B.P. 227, 27000, Mostaganem, Alg\'erie} \email{hamani\_samira@yahoo.fr} \address{Johnny Henderson \newline Department of Mathematics, Baylor University, Waco, TX 76798-7328, USA} \email{johnny\_henderson@baylor.edu} \thanks{Submitted July 10, 2014 Published September 11, 2015.} \subjclass[2010]{26A33, 34A60} \keywords{Differential inclusion; Riemann-Liouville fractional derivative; \hfill\break\indent fractional integral; Banach space; fixed point} \begin{abstract} In this article, we sudy the existence of solutions of boundary-value problems for Riemann-Liouville fractional differential inclusions of order $r\in (2,3]$ in a Banach space. \end{abstract} \maketitle \numberwithin{equation}{section} \newtheorem{theorem}{Theorem}[section] \newtheorem{lemma}[theorem]{Lemma} \newtheorem{definition}[theorem]{Definition} \allowdisplaybreaks \section{Introduction} This article concerns the existence of solutions for boundary-value problems (BVP for short), for fractional order differential inclusions. We consider the bound\-ary-value problem \begin{gather}\label{e1} D^ry(t)\in F(t,y), \quad\text{for a.e. } t\in J=[0,T],\\ \label{e2} y(0)=0, \quad y'(0)=0,\quad y''(T)=0, \end{gather} where $ 2 0$, and $$ B =\{ x\in E: |x| \leq R \},\quad U =\{ x\in C(J,E): \|x\| \leq R \}, $$ Clearly $U$ is a closed subset of $C(J,B)$. \begin{definition}[\cite{KiSrTr,Pod}] \label{def2.1} \rm The fractional (arbitrary) order integral of the function $h\in L^1([a,b],\mathbb{R}_+)$ of order $r\in\mathbb{R}_+$ is defined by $$ I^r_ah(t)=\int_a^t\frac{(t-s)^{r-1}}{\Gamma(r)}h(s)\,ds, $$ where $\Gamma$ is the gamma function. When $a=0$, we write $I^rh(t)=h(t)*\varphi_{r}(t)$, where $\varphi_{r}(t)=\frac{t^{r-1}}{\Gamma(r)}$ for $t>0$, and $\varphi_{r}(t)=0$ for $t\leq 0$, and $\varphi_{r}\to \delta(t)$\ as $r\to 0$, where $\delta$ is the delta function. \end{definition} \begin{definition}[\cite{KiSrTr,Pod}]\rm For a function $h$ given on the interval $[a,b]$, the $r $ Riemann-Liouville fractional-order derivative of $h$, is defined by \[ (D^r_{a+}h)(t)=\frac{1}{\Gamma(n-r)}\big(\frac{d}{dt}\big)^{n} \int_a^t(t-s)^{n-r-1}h(s)\,ds. \] Here $n=[r]+1$ and $[r]$ denotes the integer part of $r$. \end{definition} For convenience, we recall the definition of the Kuratowski measure of noncompactness. \begin{definition}[\cite{AkKaPaRoSa, BaGo}] \rm Let $E$ be a Banach space and let $\Omega_{E}$ be the family of bounded subsets of $E$. The Kuratowski measure of noncompactness is the map $ \alpha : \Omega_{E} \to [0,\infty ) $ defined by \[ \alpha (M)=\inf \{ \epsilon > 0 : M \subset \cup_{j=1}^{m}M_j, \operatorname{diam}(M_j)\leq \epsilon \}\,, \] where $ M \in \Omega_{E}$. \end{definition} \noindent\textbf{Properties:} \begin{itemize} \item[(1)] $ \alpha (M) = 0 \Leftrightarrow \overline{M}$ is compact ($M$ is relatively compact). \item[(2)] $ \alpha (M)=\alpha(\overline{M})$. \item[(3)] $ M_1\subset M_2 \Rightarrow \alpha (M_1)\leq \alpha (M_2)$. \item[(4)] $ \alpha (M_1+M_2)\leq \alpha (M_1)+\alpha (M_2)$. \item[(5)] $ \alpha ( cM)=c\alpha(M)$, $c\in \mathbb{R}$. \item[(6)] $ \alpha (\operatorname{conv} M)=\alpha(M)$. \end{itemize} More properties of $\alpha$ can be found in \cite{AkKaPaRoSa, BaGo}. \begin{definition} \rm A multivalued map $F: J \times E \to \mathcal{P}(E) $ is said to be Carath\'eodory if \begin{itemize} \item[(1)] $ t \to F(t,u) $ is measurable for each $u \in E$. \item[(2)] $ u \to F(t,u) $ is upper semicontinuous for almost all $t\in J$. \end{itemize} \end{definition} For each $ y \in C(J,E)$, define the set of selections of $F$ by $$ S_{F,y} =\{ v \in L^{1}(J,E) : v(t) \in F(t,y(t)) \text{ a.e. } t\in J \}. $$ \begin{theorem}[\cite{He}] \label{thm1} Let $E$ be a Banach space and $C\subset L^{1}(J,E) $ be countable with $|u(t)| \leq h(t) $ for a.e. $t\in J$, and every $u \in C$, where $h \in L^{1}(J,\mathbb{R}_{+})$. Then the function $\phi(t)= \alpha (C(t))$ belongs to $L^{1}(J,\mathbb{R}_{+})$ and satisfies $$ \alpha \Big( \Big\{ \int_{0}^{T}u(s) \,ds : u\in C \Big\}\Big) \leq 2 \int_{0}^{T} \alpha(C(s))\,ds. $$ \end{theorem} Let us now recall the set-valued analog of M\"{o}nch's fixed point theorem. \begin{theorem}[\cite{OrPr}] \label{thm2} Let $K$ be a closed, convex subset of a Banach space $E,U$ a relatively open subset of $K$, and $N:\overline{U} \to\mathcal{P}_c(K)$. Assume $\operatorname{graph}(N)$ is closed, $N$ maps compact sets into relatively compact sets, and that, for some $x_{0}\in U$, the following two conditions are satisfied: \begin{gather}\label{e3} \parbox{10cm}{ $M\subset \overline{U}$, $M \subset \operatorname{conv}(x_{0}\cup N(M))$ and $\overline{M}=\overline{U}$ with $C\subset M$ countable imply that $\overline{M}$ is compact}, \\ \label{e4} x \in (1-\lambda) x_{0}+\lambda N(x)\quad \text{for all } x \in \overline{U}\backslash U, \; \lambda \in (0,1). \end{gather} Then there exists $x \in \overline{U}$ with $x\in N(x)$. \end{theorem} \begin{lemma}[\cite{LaOp}] \label{lem0} Let $J$ be a compact real interval. Let $F$ be a Carath\'eodory multivalued map and let $\Theta$ be a linear continuous map from $L^{1}(J,E) \to C(J,E)$. Then the operator $$ \Theta \circ S_{F,y} :C(J,E) \to \mathcal{P}_{cp,c} (C(J,E)),\quad y \mapsto (\Theta \circ S_{F,y})(y)= \Theta(S_{F,y}) $$ is a closed graph operator in $C(J,E) \times C(J,E)$. \end{lemma} \section{Main results} Let us start by defining what we mean by a solution of the problem \eqref{e1}--\eqref{e2}. \begin{definition}\label{def1} \rm A function $y\in AC^{2}([0,T],E)$ is said to be a solution of \eqref{e1}--\eqref{e2} if there exist a function $v \in L^{1}(J,E)$ with $ v(t) \in F(t,y(t)) $, for a.e. $ t\in J$, such that $D^ry(t)=v(t)$ on $J$, and the condition $ y(0)=0$, $y'(0)=0$, $y''(T)=0$ are satisfied. \end{definition} For the existence of solutions for the problem \eqref{e1}--\eqref{e2}, we need the following auxiliary lemma. \begin{lemma}[\cite{BaLu}] \label{lem1} Let $r > 0 $, and $ h\in C(0,T)\cap L^1(0,T)$. Then $$ {I^r}D^rh(t)= h(t)+c_1t^{r-1}+c_2t^{r-2}+\ldots+c_{n}t^{r-n} $$ for some $c_{i}\in \mathbb{R}$, $i=1,\ldots,n$, where $n$ is the smallest integer greater than or equal to $r$. \end{lemma} \begin{lemma}\label{lem2} Let $2 < r \leq 3$ and let $ h:[0,T]\to E$ be continuous. A function $y$ is a solution of the fractional integral equation \begin{equation}\label{e5} \begin{aligned} y(t)&=\frac{1}{\Gamma(r)} \int_{0}^{t}(t-s)^{r-1}h(s)\,ds\\ &\quad - \frac{t^{r-1}}{(r-1)(r-2)\Gamma(r-2)} \int_{0}^{T}(T-s)^{r-3}h(s)\,ds. \end{aligned} \end{equation} if and only if $y$\ is a solution of the fractional BVP \begin{gather}\label{e6} D^ry(t)=h(t), \quad t\in[0,T], \\ \label{e7} y(0)=0,\quad y'(0)=0,\quad y''(T)=0. \end{gather} \end{lemma} \begin{proof} Assume $y$ satisfies \eqref{e5}. Then Lemma \ref{lem1} implies that $$ y(t)=c_1t^{r-1}+c_2t^{r-2}+c_{3}t^{r-3}+\frac{1}{\Gamma(\alpha)} \int_{0}^{t}(t-s)^{r-1}h(s)\,ds. $$ From \eqref{e7}, a simple calculation gives \begin{gather*} c_1=-\frac{1}{(r-1)(r-2)\Gamma (r-3)}\int_{0}^{T}(T-s)^{r-3}h(s)\,ds, \\ c_2=0,quad c_{3}=0\,. \end{gather*} Hence we get equation \eqref{e5}. Conversely, it is clear that if $y$ satisfies equation \eqref{e5}, then equations \eqref{e6}-\eqref{e7} hold. \end{proof} \begin{theorem} Assume the following hypotheses hold: \begin{itemize} \item[(H1)] $F: J\times \mathbb{R}\to \mathcal{P}_{cp,c}(\mathbb{R})$ is a Carath\'eodory multivalued map. \item[(H2)] For each $R> 0$, there exists a function $p\in L^{1}(J,E) $ and such that $$ \|F(t,u)\|_\mathcal{P} = \sup \{ |v| ,\: v(t) \in F(t,y) \}\leq p(t) $$ for each $(t,y) \in J \times E $ with $|y| \leq R $, and $$ \lim _{R \to +\infty} \inf \frac{\int_{0}^{T} p(t) dt }{R}=\delta <\infty . $$ \item[(H3)] There exists a Carath\'eodory function $\psi : J \times [0,2R] \to \mathbb{R}_{+} $ such that $$ \alpha (F(t,M))\leq \psi (t,\alpha(M)),\quad \text{a.e. $t \in J$ and each $ M\subset B$}, $$ and $\phi \equiv 0$ is the unique solution in $ C(J,[0,2R]) $ of the inequality \begin{equation}\label{e8} \begin{aligned} \phi(t) &\leq 2 [ \frac{1}{\Gamma(r)} \int_{0}^{t}(t-s)^{r-1}\varphi(s,\phi(s))\,ds \\ &\quad - \frac{t^{r-1}}{(r-1)(r-2)\Gamma(r-2)} \int_{0}^{T}(T-s)^{r-3}\varphi(s,\phi(s))\,ds], \end{aligned} \end{equation} for $t\in J$. \end{itemize} Then the BVP \eqref{e1}--\eqref{e2} has at least one solution on $C (J,B) $, provided that \begin{equation}\label{e11} \delta <\Big[\frac{T}{\Gamma(r+1)}+ \frac{T^{2}}{(r-1)(r-2)\Gamma(r-1)}\Big]. \end{equation} \end{theorem} \begin{proof} First we transform problem \eqref{e1}--\eqref{e2} into a fixed point problem. Consider the multivalued operator \begin{align*} N(y)=\Big\{&h\in C(J,E): (Ny)(t)=\frac{1}{\Gamma(r)} \int_{0}^{t}(t-s)^{r-1}v(s)\,ds\\ &-\frac{t^{r-1}}{(r-1)(r-2)\Gamma(r-2)} \int_{0}^{T}(T-s)^{r-3}v(s)\,ds,\; v \in S_{F,y}\Big\}. \end{align*} Clearly, from Lemma \ref{lem2}, the fixed points of $N$ are solutions to \eqref{e1}--\eqref{e2}. We shall show that $N$ satisfies the assumptions of the set-valued analog of M\"{o}nch's fixed point theorem. The proof will be given in several steps. \smallskip \noindent\textbf{Step 1:} $N(y)$ is convex for each $y\in C(J,E)$. Indeed, if $h_1,h_2$ belong to $N(y)$, then there exist $v_1, v_2\in S_{F,y}$ such that for each $t\in J$ we have \begin{align*} h_{i}(t)&=\frac{1}{\Gamma(r)} \int_{0}^{t}(t-s)^{r-1}v_{i}(s)\,ds\\ &\quad - \frac{t^{r-1}}{(r-1)(r-2)\Gamma(r-2)} \int_{0}^{T}(T-s)^{r-3}v_{i}(s)\,ds, \quad i=1,2. \end{align*} Let $0\leq d\leq 1$. Then, for each $t\in J$, we have \begin{align*} &(dh_1+(1-d)h_2)(t)\\ &=\frac{1}{\Gamma(r)} \int_{0}^{t}(t-s)^{r-1} [dv_1(s)+(1-d)v_2(s)]\,ds \\ &\quad+ \frac{t^{r-1}}{(r-1)(r-2)\Gamma(r-2)} \int_{0}^{T}(T-s)^{r-3}[dv_1(s)+(1-d)v_2(s)]\,ds. \end{align*} Since $S_{F,y}$ is convex (because $F$ has convex values), we have $dh_1+(1-d)h_2\in N(y)$. \smallskip \noindent\textbf{Step 2:} $N(M)$ is relatively compact for each compact $ M \subset \overline{U}$. Let $M \subset \overline{U}$ be a compact set and let $(h_{n})$ by any sequence of elements of $N(M)$. We show that $(h_{n})$ has a convergent subsequence by using the Arz\'ela-Ascoli criterion of compactness in $C(J,E)$. Since $h_{n} \in N(M)$ there exist $y_{n} \in M $ and $ v_{n} \in S_{F,y_{n}}$ such that \begin{align*} h_{n}(t) &=\frac{1}{\Gamma(r)} \int_{0}^{t}(t-s)^{r-1}v_{n}(s)\,ds\\ &\quad - \frac{t^{r-1}}{(r-1)(r-2)\Gamma(r-2)} \int_{0}^{T}(T-s)^{r-3}v_{n}(s)\,ds. \end{align*} Using Theorem \ref{thm1} and the properties of the measure of noncompactness of Kuratowski, we have \begin{equation} \label{e9} \begin{aligned} \alpha (\{h_{n}(t)\}) &\leq 2 [ \frac{1}{\Gamma(r)} \int_{0}^{t}\alpha (\{(t-s)^{r-1}v_{n}(s) \})\,ds \\ &\quad - \frac{t^{\alpha-1}}{(r-1)(r-2)\Gamma(r-2)} \int_{0}^{T}\alpha (\{(T-s)^{r-3} v_{n}(s)\})\,ds]. \end{aligned} \end{equation} On the other hand, since $M(s)$ is compact in $E$, the set $\{ v_{n}(s): n\geq 1\}$ is compact. Consequently, $\alpha (\{ v_{n}(s): n\geq 1\})=0 $ for a.e. $s\in J$. Furthermore \begin{gather*} \alpha (\{(t-s)^{r-1}v_{n}(s) \}) = (t-s)^{r-1}\alpha (\{ v_{n}(s): n\geq 1\})=0, \\ \alpha (\{(T-s)^{r-1}v_{n}(s) \}) = (T-s)^{r-1}\alpha (\{ v_{n}(s): n\geq 1\})=0, \end{gather*} for a.e. $t,s\in J$. Now \eqref{e9} implies that $\{ h_{n}(t): n\geq 1\}$ is relatively compact in $E$, for each $t\in J$. In addition, for each $t_1$ and $t_2$ from $J$, $t_1 R $ and \begin{align*} h(t)&= \frac{1}{\Gamma(r)} \int_{0}^{t}(t-s)^{r-1}v(s)\,ds\\ &\quad - \frac{t^{r-1}}{(r-1)(r-2)\Gamma(r-2)} \int_{0}^{T}(T-s)^{r-3}v(s)\,ds, \end{align*} for some $v \in S_{F,y}$. On the other hand, \begin{align*} R &\leq \|N(y)\|_\mathcal{P} \\ & \leq \frac{1}{\Gamma(r)} \int_{0}^{t}(t-s)^{r-1}|v(s)|\,ds\\ &\quad - \frac{t^{r-1}}{(r-1)(r-2)\Gamma(r-2)} \int_{0}^{T}(T-s)^{r-3}|v(s)|\,ds \\ & \leq \frac{T}{\Gamma(r+1)} \int_{0}^{t} p(s)\,ds\\ &\quad - \frac{T^{2}}{(r-1)(r-2)\Gamma(r-1)} \int_{0}^{T} p(s)\,ds \\ &\leq \big[\frac{T}{\Gamma(r+1)}+ \frac{T^{2}}{(r-1)(r-2)\Gamma(r-1)}\big] \int_{0}^{T} p(s)\,ds. \end{align*} Dividing both sides by $R$ and taking the lower limits as $R \to \infty$, we conclude that \[ \big[\frac{T}{\Gamma(r+1)}+\frac{T^{2}}{(r-1)(r-2)\Gamma(r-1)}\big] \delta \geq 1 \] which contradicts \eqref{e11}. Hence $N(\overline{U}) \subseteq \overline{U}$. As a consequence of Steps 1-5 and Theorem \ref{thm2}, we conclude that $N$ has a fixed point $y \in C(J,B)$ which is a solution of problem \eqref{e1}-\eqref{e2}. \end{proof} \begin{thebibliography}{00} \bibitem{AgBeHa} R. P. Agarwal, M. Benchohra, S. 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