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We investigate the log-concavity on the half-line of the Wright function $\phi(-\alpha,\beta,-x),$ in the probabilistic setting $\alpha\in (0,1)$ and $\beta \ge 0.$ Applications are given to the construction of generalized entropies associated to the corresponding Mittag-Leffler function. A natural conjecture for the equivalence between the log-concavity of the Wright function and the existence of such generalized entropies is formulated. The problem is solved for $\beta\geq\alpha$ and in the classical case $\beta = 1-\alpha$ of the Mittag-Leffler distribution, which exhibits a certain critical parameter $\alpha_*= 0.771667...$ defined implicitly on the Gamma function and characterizing the log-concavity. We also prove that the probabilistic Wright functions are always unimodal, and that they are multiplicatively strongly unimodal if and only if $\beta\geq\alpha$ or $\alpha\le 1/2$ and $\beta = 0.$, Comment: To appear in Constructive Approximation

We establish some identities in law for the convolution of a beta prime distribution with itself, involving the square root of beta distributions. The proof of these identities relies on transformations on generalized hypergeometric series obtained via Appell series of the first kind and Thomae's relationships for ${}_3F_2(1)$. Using a self-decomposability argument, the identities are applied to derive complete monotonicity properties for quotients of confluent hypergeometric functions having a doubling character. By means of probability, we also obtain a simple proof of Tur\'an's inequality for the parabolic cylinder function and the confluent hypergeometric function of the second kind. The case of Mill's ratio is discussed in detail., Comment: Minor corrections. To appear in Transactions of the American Mathematical Society

We define a class of discrete operators that, in particular, include the delta and nabla fractional operators., Comment: This is the version published in Journal of Fractional Calculus and Nonlinear Systems

In this work we wish to highlight some consequences of a recent result proved in [N. D. Cong and H. T. Tuan, Generation of nonlocal fractional dynamical systems by fractional differential equations, J. Integral Equations Appl. 29 (2017), no. 4, 585-608]. Particular emphasis will be given to its application on fractional variational problems of Herglotz type., Comment: To appear in Vietnam Journal of Mathematics

In this work we argue about the Lesche stability of some systems, that are motivated by the use of fractional derivatives., Comment: To appear in Journal of Applied Analysis (2022), Vol. 28

In this work we present a novel proof of the Saalschutz formula by using the theory of discrete fractional calculus. The proofs of some results within this theory, namely, the fractional power rule and the fractional Leibniz rule are revisited., Comment: Two typos detected: in Theorem 3.10, $\alpha\in\mathbb{R}\backslash\mathbb{N}^{0}$, and, in page 9, line 6, substitute $(\alpha)^{\underline{n}}$ by $(\alpha)_n$

The present work was primarily motivated by our findings in the literature of some flaws within the proof of the second-order Legendre necessary optimality condition for fractional calculus of variations problems. Therefore we were eager to elaborate a correct proof and it turns out that this goal is highly nontrivial, especially when considering final constraints. This paper is the result of our reflections on this subject. Precisely we consider here a constrained minimization problem of a general Bolza functional that depends on a Caputo fractional derivative of order 0 < $\alpha$ $\le$ 1 and on a Riemann-Liouville fractional integral of order $\beta$ > 0, the constraint set describing general mixed initial/final constraints. The main contribution of our work is to derive corresponding first-and second-order necessary optimality conditions, namely the Euler-Lagrange equation, the transversality conditions and, of course, the Legendre condition. A detailed discussion is provided on the obstructions encountered with the classical strategy, while the new proof that we propose here is based on the Ekeland variational principle. Furthermore we underline that some subsidiary contributions are provided all along the paper. In particular we prove an independent and intrinsic result of fractional calculus stating that it does not exist a nontrivial function which is, together with its Caputo fractional derivative of order 0 < $\alpha$ < 1, compactly supported. Moreover we also discuss some evidences claiming that Riemann-Liouville fractional integrals should be considered in the formulation of fractional calculus of variations problems in order to preserve the existence of solutions.

In this work we look at the original fractional calculus of variations problem in a somewhat different way. As a simple consequence, we show that a fractional generalization of a classical problem has a solution without any restrictions on the derivative-order $\alpha$., Comment: Minor changes of the first version. To be published in Fractional Calculus and Applied Analysis

In this work we derive some inequalities for fractional boundary value problems, that generalize the well-known de la Vall\'ee Poussin inequality. With our results we also were able to improve the intervals where some Mittag-Leffler functions don't possess real zeros., Comment: Some minor corrections to the previous version. To be published in Mathematical Inequalities & Applications

In this work we extend a recent result by Dyda et. al. [B. Dyda, A. Kuznetsov, M. Kwasnicki, Eigenvalues of the fractional Laplace equation in the unit ball, J. Lond. Math. Soc. (2) 95 (2017), 500-518.] to dimension 3., Comment: Title modification. To be published in Nonlinear Differential Equations and Applications

In this work, a generalization of the well known Bernoulli inequality is obtained by using the theory of discrete fractional calculus. As far as we know our approach is novel., Comment: To appear in Proceedings of the American Mathematical Society

In this paper we study isoperimetric problems of the calculus of variations with left and right Riemann-Liouville fractional derivatives. Both situations when the lower bound of the variational integrals coincide and do not coincide with the lower bound of the fractional derivatives are considered., Comment: Submitted 02-Oct-2009; revised 30-Jun-2010; accepted 10-May-2011; for publication in the journal Acta Mathematica Scientia

The recent theory of fractional $h$-difference equations introduced in [N. R. O. Bastos, R. A. C. Ferreira, D. F. M. Torres: Discrete-time fractional variational problems, Signal Process. 91 (2011), no. 3, 513--524], is enriched with useful tools for the explicit solution of discrete equations involving left and right fractional difference operators. New results for the right fractional $h$ sum are proved. Illustrative examples show the effectiveness of the obtained results in solving fractional discrete Euler-Lagrange equations., Comment: Submitted 15-Aug-2010; revised 16-Jan-2011 and 30-Jan-2011; accepted 31-Jan-2011; for publication in Applicable Analysis and Discrete Mathematics

We prove the Euler-Lagrange delta-differential equations for problems of the calculus of variations on arbitrary time scales with delta-integral functionals depending on higher-order delta derivatives., Comment: Submitted 26/Jul/2009; Revised 04/Aug/2010; Accepted 09/Aug/2010; for publication in "Applied Mathematics Letters"

We study problems of the calculus of variations and optimal control within the framework of time scales. Specifically, we obtain Euler-Lagrange type equations for both Lagrangians depending on higher order delta derivatives and isoperimetric problems. We also develop some direct methods to solve certain classes of variational problems via dynamic inequalities. In the last chapter we introduce fractional difference operators and propose a new discrete-time fractional calculus of variations. Corresponding Euler-Lagrange and Legendre necessary optimality conditions are derived and some illustrative examples provided., Comment: PhD thesis, University of Aveiro, 2010. Supervisor: Delfim F. M. Torres; co-supervisor: Martin Bohner. Defended 26/July/2010

We introduce a discrete-time fractional calculus of variations. First and second order necessary optimality conditions are established. Examples illustrating the use of the new Euler-Lagrange and Legendre type conditions are given. They show that the solutions of the fractional problems coincide with the solutions of the corresponding non-fractional variational problems when the order of the discrete derivatives is an integer value., Comment: Submitted 09-May-2009 to Discrete and Continuous Dynamical Systems (DCDS-B); revised 27-March-2010; accepted 04-July-2010

We introduce a discrete-time fractional calculus of variations on the time scale $h\mathbb{Z}$, $h > 0$. First and second order necessary optimality conditions are established. Examples illustrating the use of the new Euler-Lagrange and Legendre type conditions are given. They show that solutions to the considered fractional problems become the classical discrete-time solutions when the fractional order of the discrete-derivatives are integer values, and that they converge to the fractional continuous-time solutions when $h$ tends to zero. Our Legendre type condition is useful to eliminate false candidates identified via the Euler-Lagrange fractional equation., Comment: Submitted 24/Nov/2009; Revised 16/Mar/2010; Accepted 3/May/2010; for publication in Signal Processing.

We discuss the use of inequalities to obtain the solution of certain variational problems on time scales., Comment: To appear in Mathematical Inequalities & Applications (http://mia.ele-math.com). Accepted: 14.01.2010

We establish two nonlinear retarded integral inequalities. Bounds on the solution of some retarded equations are then obtained., Comment: 9 pages

We establish some linear and nonlinear integral inequalities of Gronwall-Bellman-Bihari type for functions with two independent variables on general time scales. The results are illustrated with examples, obtained by fixing the time scales to concrete ones. An estimation result for the solution of a partial delta dynamic equation is given as an application., Comment: Keywords: integral inequalities; Gronwall-Bellman-Bihari inequalities; time scales; two independent variables

We establish some nonlinear integral inequalities for functions defined on a time scale. The results extend some previous Gronwall and Bihari type inequalities on time scales. Some examples of time scales for which our results can be applied are provided. An application to the qualitative analysis of a nonlinear dynamic equation is discussed., Comment: This is a preprint of an article accepted (16/May/2008) for publication in the "Journal of Difference Equations and Applications"; J. Difference Equ. Appl. is available online at http://www.informaworld.com

We prove a necessary optimality condition for isoperimetric problems on time scales in the space of delta-differentiable functions with rd-continuous derivatives. The results are then applied to Sturm-Liouville eigenvalue problems on time scales., Comment: Changes suggested by the referee. This is the preprint version accepted (July 16, 2008) for publication in the Proceedings of the Conference on Nonlinear Analysis and Optimization, June 18-24, 2008, Technion, Haifa, Israel, and to appear in "Contemporary Mathematics"

The theory of the calculus of variations was recently extended to the more general time scales setting, both for delta and nabla integrals. The primary purpose of this paper is to further extend the theory on time scales, by establishing some basic diamond-alpha dynamic integral inequalities. We prove generalized versions of H\"{o}lder, Cauchy-Schwarz, Minkowski, and Jensen's inequalities. For the particular case when alpha is equal to one or alpha is equal to zero one gets, respectively, correspondent delta and nabla inequalities. If we further restrict ourselves by fixing the time scale to the real or integer numbers, then we obtain the classical inequalities, whose role in optimal control is well known. By analogy, we trust that the diamond-alpha integral inequalities we prove here will be important in the study of control systems on times scales., Comment: Accepted to the 8th Portuguese Conference on Automatic Control -- CONTROLO'2008, 21 to 23 July 2008, UTAD University, Vila Real, Portugal

We prove some new retarded integral inequalities. The results generalize those in [J. Math. Anal. Appl. 301 (2005), no. 2, 265--275]., Comment: Changes suggested by the referee done

The theory and applications of dynamic derivatives on time scales has recently received considerable attention. The primary purpose of this paper is to give basic properties of diamond-$\alpha$ derivatives which are a linear combination of delta and nabla dynamic derivatives on time scales. We prove a generalized version of Jensen's inequality on time scales via the diamond-$\alpha$ integral and present some corollaries, including H\"{o}lder's and Minkowski's diamond-$\alpha$ integral inequalities., Comment: This is a preprint of an article whose final and definitive form will appear in the \emph{Journal of Inequalities and Applications}, http://www.hindawi.com/journals/jia/. Accepted 07/April/2008

The calculus of variations is a classical subject which has gain throughout the last three hundred years a level of rigor and elegance that only time can give. In this note we show that, contrary to the classical field, available formulations and results on the recent calculus of variations on time scales are still at the heuristic level.

We prove a version of the Euler-Lagrange equations for certain problems of the calculus of variations on time scales with higher-order delta derivatives., Comment: Corrected minor typos

We study more general variational problems on time scales. Previous results are generalized by proving necessary optimality conditions for (i) variational problems involving delta derivatives of more than the first order, and (ii) problems of the calculus of variations with delta-differential side conditions (Lagrange problem of the calculus of variations on time scales)., Comment: 20 pages