Publications 2020


165.  Bioestatística: síntese teórica e exercícios

Freitas, Adelaide and Cruz, João Pedro

Edições Sílabo

Sem resumo disponível.

164.  Atletas das Contas: 50 desafios matemáticos desportivos

Pinto, Hélder and Silva, Cristina

Cultura Editora

Sem resumo disponível.

163.  Dynamic logic: new trends and applications

Martins, Manuel A. and Sedlár, Igor


This book constitutes the proceedings of the Third International Workshop on Dynamic Logic, DaLí 2019, held in Prague, Czech Republic in October 2020. Due to COVID-19 the workshop has been held online. The 17 full papers presented together with 6 short papers were carefully reviewed and selected from 31 submissions. The theoretical relevance and practical potential of dynamic logic is a topic of interest in a number of scientific venues, from wide-scope software engineering conferences to modal logic specific events. The DaLí 2020 workshop is exclusively dedicated to Dynamic logic and aims at filling this gap and creating a heterogeneous community of colleagues, from Academia to Industry, from Mathematics to Computer Science. | doi

Book Chapters

162.  A note on robust estimation of the extremal index

Miranda, M. Cristina Souto and Gomes, M. Ivette and Miranda, M. Manuela Souto

Nonparametric Statistics


Many examples in the most diverse fields of application show the need for statistical methods of analysis of extremes of dependent data. A crucial issue that appears when there is dependency is the reliable estimation of the extremal index (EI), a parameter related to the clustering of large events. The most popular EI-estimators, like the blocks’ EI-estimators, are very sensitive to anomalous cluster sizes and exhibit a high bias. The need for robust versions of such EI-estimators is the main topic under discussion in this paper. | doi | Peer Reviewed

161.  A new mathematical model for the efficiency calculation

Galindro, Aníbal and Santos, Micael and Torres, Delfim F. M. and Marta-Costa, Ana

Recent Advances in Modeling, Analysis and Systems Control: Theoretical Aspects and Applications. Studies in Systems, Decision and Control

Springer Nature

During the past sixty years, a lot of effort has been made regarding the productive efficiency. Such endeavours provided an extensive bibliography on this subject, culminating in two main methods, named the Stochastic Frontier Analysis (parametric) and Data Envelopment Analysis (non-parametric). The literature states this methodology also as the benchmark approach, since the techniques compare the sample upon a chosen “more-efficient” reference. This article intends to disrupt such premise, suggesting a mathematical model that relies on the optimal input combination, provided by a differential equation system instead of an observable sample. A numerical example is given, illustrating the application of our model’s features. | doi | Peer Reviewed

160.  Parametric identification of the dynamics of inter-sectoral balance: modelling and forecasting

Kostylenko, Olena and Rodrigues, Helena Sofia and Torres, Delfim F. M.

Recent Advances in Modeling, Analysis and Systems Control: Theoretical Aspects and Applications. Studies in Systems, Decision and Control


This work is devoted to modelling and identification of the dynamics of the inter-sectoral balance of a macroeconomic system. An approach to the problem of specification and identification of a weakly formalized dynamical system is developed. A matching procedure for parameters of a linear stationary Cauchy problem with a decomposition of its upshot trend and a periodic component, is proposed. Moreover, an approach for detection of significant harmonic waves, which are inherent to real macroeconomic dynamical systems, is developed. | doi | Peer Reviewed

159.  Mathematics Exercise Generator: the language of parameterized exercises

Oliveira, Paula and Carvalho, Paula

Developing Technology Mediation in Learning Environments

IGI Global

Nowadays, the process of teaching and learning is changing from a traditional model in which teachers were the source of information for a model in which teachers appear as advisors who carefully observe students, assist in the selection of information by identifying their learning needs and support students in their autonomous study. In this chapter, the authors describe an approach used in curricular units of first year in Science and Engineer degrees, which results from a connection of three projects born in University of Aveiro: MEGUA, SIACUA and PmatE, and the interconnections of their informatics platforms. Although any scientific area besides mathematics can use this tool, the authors focus in a case study using an example on a specific topic of Calculus courses for first year students on Engineering: Sequences and Series of Functions. The methodology described allows teachers to achieve further goals on learning strategies and students to have enough material to practice. | Peer Reviewed

158.  A four-valued hybrid logic with non-dual modal operators

Costa, Diana and Martins, Manuel A.

Dynamic logic: new trends and applications

Springer International Publishing

Hybrid logics are an extension of modal logics where it is possible to refer to a specific state, thus allowing the description of what happens at specific states, equalities and transitions between them. This makes hybrid logics very desirable to work with relational structures. However, as the amount of information grows, it becomes increasingly more common to find inconsistencies. Information collected about a particular hybrid structure is not an exception. Rather than discarding all the data congregated, working with a paraconsistent type of logic allows us to keep it and still make sensible inferences. In this paper we introduce a four-valued semantics for hybrid logic, where contradictions are allowed both at the level of propositional variables and accessibility relations. A distinguishing feature of this new logic is the fact that the classical equivalence between modal operators will be broken. A sound and complete tableau system is also presented. | doi | Peer Reviewed

157.  An extension of the fractional Gronwall inequality

Almeida, Ricardo and Malinowska, Agnieszka B. and Odzijewicz, Tatiana

Advances in Non-Integer Order Calculus and Its Applications


In this work, we prove a generalization of the Gronwall type inequality. This relation can be used in the qualitative analysis of the solutions to fractional differential equations with the ψ-fractional derivatives. | doi | Peer Reviewed

156.  A note on controlled invariance for behavioral nD systems

Pereira, Ricardo and Rocha, Paula

Algebraic and Symbolic Computation Methods in Dynamical Systems


In this chapter we extend the notion of invariance of nD behaviors introduced in Pereira and Rocha (European Control Conference 2013, ECC’13. ETH Zurich, Switzerland, pp. 301–305, 2013) [4], Rocha and Wood (Int. J. Appl. Math. Comput. Sci. 7(4):869–879, 1997) [7] to the controlsetting. More concretely, we introduce a notion which is the behavioral counterpart of classical controlled invariance, using the framework of partial interconnections. In such interconnections, the variables are divided into two sets: the variables to-be-controlled and the variables on which it is allowed to enforce restrictions (called control variables). In particular we focus on regular partial interconnection, i.e., interconnections in which the restrictions of the controller do not overlap with the ones already implied by the laws of the original behavior. For some particular cases, complete characterizations of controlled invariance and controller construction procedures are derived for both 1D and nD behaviors. | doi | Peer Reviewed

155.  Extremal index estimation: application to financial data

Miranda, Maria Cristina Souto

Handbook of Research on Accounting and Financial Studies

IGI Global

In finance it is crucial to understand the risk of occurrence of extreme events such as currency crises or stock market crashes. It is important to model the distribution of extreme events. Extreme value theory is known to accurately estimate quantiles and tail probabilities of financial asset returns. These kinds of data are usual related to heavy tailed distributions, where a relevant parameter is the tail index. Fitting data to heavy tail distributions usually assumes independent observations. However, the most usual real market scenario describes clusters of extreme events rather than isolated records over some period of time. In that case, estimating tail probabilities includes estimating the extremal index. This chapter describes the usual extremal index estimators based in different approaches and illustrates their values for a real financial data set. Computations are provided by the use of suitable R packages. | doi | Peer Reviewed

154.  Comparing learning objects for effective learning in Mathematics

Descalço, L. and Carvalho, P.

EDULEARN20 Proceedings


The too high number of students per class, situation typically found in higher education in Portugal, makes it difficult to adopt an approach were the student work is taken as the center of the learning process. The use of digital contents in this context is helpful for the students to build their own appropriate environment outside the classroom, using all support and learning material built up for that purpose. A fundamental problem we have in Mathematics is that many students are not well prepared in previous concepts. We have been developing and using several kinds of learning objects (LO) for calculus in the recent years, some of them dedicated to recall previous concepts. Among all kinds of contents, students valorize more learning objects that simultaneously challenge them and give them useful feedback. In this paper, we compare the usefulness of different kinds of LO, using computers, in a calculus course for students from several sciences and engineering, with a population of 290 students, based on a survey answered by 40% of them. The learning objects include multiple-choice questions with detailed solutions, quizzes, formative tests, short videos, and others. We present a quantitative analysis comparing different kinds of LO, considering students of several study areas. Together with the quantitative analysis, we add some qualitative considerations based on student’s answers to open questions concerning the learning methodology adopted. | Peer Reviewed

153.  On SICA models for HIV transmission

Silva, Cristiana J. and Torres, Delfim F. M.

Mathematical Modelling and Analysis of Infectious Diseases. Studies in Systems, Decision and Control


We revisit the SICA (Susceptible-Infectious-Chronic-AIDS) mathematical model for transmission dynamics of the human immunodeficiency virus (HIV) with varying population size in a homogeneously mixing population. We consider SICA models given by systems of ordinary differential equations and some generalizations given by systems with fractional and stochastic differential operators. Local and global stability results are proved for deterministic, fractional, and stochastic-type SICA models. Two case studies, in Cape Verde and Morocco, are investigated. | doi | Peer Reviewed

152.  A survey on sufficient optimality conditions for delayed optimal control problems

Lemos-Paião, Ana P. and Silva, Cristiana J. and Torres, Delfim F. M.

Mathematical Modelling and Analysis of Infectious Diseases. Studies in Systems, Decision and Control


The aim of this work is to make a survey on recent sufficient optimality conditions for optimal control problems with time delays in both state and control variables. The results are obtained by transforming delayed optimal control problems into equivalent non-delayed problems. Such approach allows to use standard theorems that ensure sufficient optimality conditions for non-delayed optimal control problems. Examples are given with the purpose to illustrate the results. | doi | Peer Reviewed

151.  PLS visualization using biplots: an application to team effectivenes

Silva, Alberto and Dimas, Isabel Dórdio and Lourenço, Paulo Renato and Rebelo, Teresa and Freitas, Adelaide

Computational Science and Its Applications: ICCSA 2020

Springer Nature

Based on a factorization provided by the Partial Least Square (PLS) methodology, the construction of a biplot for both exploratory and predictive purposes was shown to visually identify patterns among response and explanatory variables in the same graph. An application on a team effectiveness research, collected from 82 teams from 57 Portuguese companies and their respective leaders, containing two effectiveness criteria (team performance and the quality of the group experience as response variables), was considered and interpretation of the biplot was analyzed in detail. Team effectiveness was considered as the result of the role played by thirteen variables: team trust (two dimensions), team psychological capital (four dimensions), collective behavior, transformational leadership, intragroup conflict (two dimensions), team psychological safety, and team cohesion (two dimensions). Results revealed that the biplot approach proposed was able to capture the most critical variables for the model and correctly assigned the signals and the strength of the regression coefficients. Regarding the response variable team performance, the most significant variables to the model were team efficacy, team optimism, and team psychological safety. Concerning the response variable quality of the group experience, intragroup conflict, team-trust, and team cohesion emerged as the most relevant predictors. Overall, the results found are convergent with the literature on team effectiveness. | doi | Peer Reviewed

150.  Freedman’s paradox: a solution based on normalized entropy

Macedo, Pedro

Theory and applications of time series analysis


In linear regression models where there are no relationships between the dependent variable and each of the potential explanatory variables – a usual scenario in real-world problems – some of them can be identified as relevant by standard statistical procedures. This incorrect identification is usually known as Freedman's paradox. To avoid this disturbing effect in regression analysis, an info-metrics approach based on normalized entropy is discussed and illustrated in this work. As an alternative to traditional statistical methodologies currently used by practitioners, the simulation results suggest that normalized entropy is a powerful procedure to identify pure noise models. | doi | Peer Reviewed

149.  Teaching-learning process under a Multidirectional Efficiency and Canonical Correlation Analysis

Murillo, K. and Rocha, E.

EDULEARN20 Proceedings


The detailed study of the agents and factors involved in the teaching-learning process is vital to advance in the proposal of strategies that contribute to their improvement in all aspects (methodology, evaluation, resource management, between others). Today, many theoretical studies on the quality of education are known, which makes this a broad topic of discussion. However, education is a universe in constant motion which imposes the necessity of new systematic studies from different and relevant perspectives. This work aims to contribute to the study of the quality of higher education, evaluating the teachinglearning process, under two approaches. First, examining the technical efficiency of the institutions of higher education (approach 1), and also evaluating the performance of the students of these institutions, in accordance with the influence of the training of the teachers assigned to them (approach 2). Specifically, the use case study relates to 335 data units representing Colombian higher education institutions, corresponding to 165 institutions in the year 2016 (47 publics and 118 privates), and 170 institutions in the year 2017 (48 publics and 122 privates). The analysis considers variables of training/research for teacher and variables of graduation/performance for students. For the estimation of the efficiency (approach 1) has used a non-parametric, method based on the Multidirectional Efficiency Analysis (MEA). The study is focused on efficiency score, efficiency ratios and analysis of the output inefficiency index. For the exploration of the relationship, academic qualification/performance (approach 2), is executed a Canonical Correlation Analysis (CCA). Box-Cox transformations and filtering analysis to deal with outliers are applied. The statistical significance of the canonical correlations found, are shown with different statistical tests. The greatest contribution of this work is the appropriate combination of the MEA and CCA methodologies, which allows a broader vision of what happens in the scheme: institution efficiency/student performance/teacher training. Our results allow us to characterize the institutions in terms of efficiency, discriminating them into seven groups according to the training offer (doctoral programs, masters, specialization, etc.) and comparatively establish the most relevant relationships between teacher training / research and performance of the student. | doi | Peer Reviewed

148.  Reversal Fuzzy Switch Graphs

Campos, Suene and Santiago, Regivan and Martins, Manuel A. and Figueiredo, Daniel

Formal Methods: Foundations and Applications. SBMF 2020.


Fuzzy Switch Graphs (FSG) generalize the notion of Fuzzy Graphs by adding high-order arrows and aggregation functions which update the fuzzy values of arrows whenever a zero-order arrow is crossed. In this paper, we propose a more general structure called Reversal Fuzzy Switch Graph (RFSG), which promotes other actions in addition to updating the fuzzy values of the arrows, namely: activation and deactivation of the arrows. RFSGs are able to model dynamical aspects of some systems which generally appear in engineering, computer science and some other fields. The paper also provides a logic to verify properties of the modelled system and closes with an application. | doi | Peer Reviewed


147.  Inventory models with reverse logistics for assets acquisition in a liquefied petroleum gas company

Lopes, Cristina and Correia, Aldina and Silva, Eliana Costa e and Monteiro, Magda and Lopes, Rui Borges

Journal of Mathematics in Industry


This paper addresses a case study regarding inventory models for acquiring liquefied petroleum gas (LPG) cylinders. This is an industrial challenge that was proposed at an European Study Group with Industry, by a Portuguese energy company, for which the LPG cylinder is the main asset of its LPG business. Due to the importance of this asset, an acquisition plan must be defined in order to determine the amount of LPG cylinders to acquire, and when to acquire them, in order to optimize the investment. As cylinders are returned and refilled, the reverse logistic flows of these assets must be considered. As the classical inventory models are not suitable for this case study, three new inventory models, which account for the return of LPG cylinders, are proposed in this work. The first proposed model considers deterministic constant demand and continuous returns of LPG cylinders, with discrete replenishment from the supplier. The second model is similar, but for the case when the returned cylinders cover for the demand. A third model is also proposed considering that both the demand and the returns are stochastic in nature and the replenishment from the supplier is discrete. The three models address different scenarios that the company is either currently facing or is expecting to occur in the near future. | doi | Peer Reviewed

146.  Algorithmic determination of immobile indices in convex SIP problems with polyhedral index sets

Kostyukova, O. I. and Tchemisova, T. V.

INFOR: Information Systems and Operational Research

Taylor & Francis

The concepts of immobile indices and their immobility orders are objective and important characteristics of feasible sets of semi-infinite programming (SIP) problems. They can be used for the formulation of new efficient optimality conditions without constraint qualifications. Given a class of convex SIP problems with polyhedral index sets, we describe and justify a finite constructive algorithm (algorithm DIIPS) that allows to find in a finite number of steps all immobile indices and the corresponding immobility orders along the feasible directions. This algorithm is based on a representation of the cones of feasible directions in the polyhedral index sets in the form of linear combinations of extremal rays and on the approach proposed in our previous papers for the cases of immobile indices’ sets of simpler structures. A constructive procedure of determination of the extremal rays is described, and an example illustrating the application of the DIIPS algorithm is provided. | doi | Peer Reviewed

145.  Maximum principles for some quasilinear elliptic systems

Leonardi, Salvatore and Leonetti, Francesco and Pignotti, Cristina and Rocha, Eugénio and Staicu, Vasile

Nonlinear Analysis: Theory, Methods and Applications


We give maximum principles for solutions u:Ω→ℝ N to a class of quasilinear elliptic systems whose prototype is [Formula presented]where α∈{1,…,N} is the equation index and Ω is an open, bounded subset of ℝ n . We assume that coefficients [Formula presented] are measurable with respect to x, continuous with respect to y∈ℝ N , bounded and elliptic. In vectorial problems, when trying to bound the solution by means of the boundary data, we need to bypass De Giorgi's counterexample by means of some additional structure assumptions on the coefficients [Formula presented]. In this paper, we assume that off-diagonal coefficients [Formula presented], α≠β, have support in some staircase set along the diagonal in the y α ,y β plane | doi | Peer Reviewed

144.  Product preservation and stable units for reflections into idempotent subvarieties

Xarez, João J. and Xarez, Isabel A.

Categories and General Algebraic Structures with Applications

Shahid Beheshti University

We give a necessary and sufficient condition for the preservation of finite products by a reflection of a variety of universal algebras into an idempotent subvariety. It is also shown that simple and semi-left-exact reflections into subvarieties of universal algebras are the same. It then follows that a reflection of a variety of universal algebras into an idempotent subvariety has stable units if and only if it is simple and the above-mentioned condition holds. | Peer Reviewed

143.  Variable exponent Besov-Morrey spaces

Almeida, Alexandre and Caetano, António

Journal of Fourier Analysis and Applications

Springer Verlag

In this paper we introduce Besov-Morrey spaces with all indices variable and study some fundamental properties. This includes a description in terms of Peetre maximal functions and atomic and molecular decompositions. This new scale of non-standard function spaces requires the introduction of variable exponent mixed Morrey-sequence spaces, which in turn are defined within the framework of semimodular spaces. In particular, we obtain a convolution inequality involving special radial kernels, which proves to be a key tool in this work. | doi | Peer Reviewed

142.  Extremal graphs for Estrada indices

Andrade, Enide and Lenes, Eber and Mallea-Zepeda, Exequiel and Robbiano, María and Rodríguez Z., Jonnathan

Linear Algebra and its Applications


Let $mathcal{G}$ be a simple undirected connected graph. The signless Laplacian Estrada, Laplacian Estrada and Estrada indices of a graph $mathcal{G}$ is the sum of the exponentials of the signless Laplacian eigenvalues, Laplacian eigenvalues and eigenvalues of $mathcal{G}$, respectively. The present work derives an upper bound for the Estrada index of a graph as a function of its chromatic number, in the family of graphs whose color classes have order not less than a fixed positive integer. The graphs for which the upper bound is tight is obtained. Additionally, an upper bound for the Estrada Index of the complement of a graph in the previous family of graphs with two color classes is given. A Nordhaus-Gaddum type inequality for the Laplacian Estrada index when {$mathcal{G}$ is a bipartite} graph with color classes of order not less than $2$, is presented. Moreover, a sharp upper bound for the Estrada index of the line graph and for the signless Laplacian index of a graph in terms of connectivity is obtained. | doi | Peer Reviewed

141.  Matrix Toda and Volterra lattices

Moreno, Ana Foulquié and Branquinho, Amílcar and García-Ardila, Juan C.

Applied Mathematics and Computation


We consider matrix Toda and Volterra lattice equations and their relation with matrix biorthogonal polynomials. From that relation, we give a method for constructing a new solution of these systems from another given one. An illustrative example is presented. | doi | Peer Reviewed

140.  Maximal commutators and commutators of potential operators in new vanishing Morrey spaces

Almeida, Alexandre

Nonlinear Analysis


We study mapping properties of commutators in certain vanishing subspaces of Morrey spaces, which were recently used to solve the delicate problem of describing the closure of nice functions in Morrey norm. We show that the vanishing properties defining those subspaces are preserved under the action of maximal commutators and commutators of fractional integral operators. | doi | Peer Reviewed

139.  On the invariance of certain vanishing subspaces of Morrey spaces with respect to some classical operators

Alabalik, Aysegul Ç. and Almeida, Alexandre and Samko, Stefan

Banach Journal of Mathematical Analysis


We consider subspaces of Morrey spaces defined in terms of various vanishing properties of functions. Such subspaces were recently used to describe the closure of C∞0(Rn) in Morrey norm. We show that these subspaces are invariant with respect to some classical operators of harmonic analysis, such as the Hardy–Littlewood maximal operator, singular type operators and Hardy operators. We also show that the vanishing properties defining those subspaces are preserved under the action of Riesz potential operators and fractional maximal operators. | doi | Peer Reviewed

138.  Fundamental solution for natural powers of the fractional Laplace and Dirac operators in the Riemann-Liouville sense

Teodoro, A. Di and Ferreira, M. and Vieira, N.

Advances in Applied Clifford Algebras


In this paper, we study the fundamental solution for natural powers of the $n$-parameter fractional Laplace and Dirac operators defined via Riemann-Liouville fractional derivatives. To do this we use iteration through the fractional Poisson equation starting from the fundamental solutions of the fractional Laplace $Delta_{a^+}^alpha$ and Dirac $D_{a^+}^alpha$ operators, admitting a summable fractional derivative. The family of fundamental solutions of the corresponding natural powers of fractional Laplace and Dirac operators are expressed in operator form using the Mittag-Leffler function. | doi | Peer Reviewed

137.  Variable exponent Triebel-Lizorkin-Morrey spaces

Caetano, António and Kempka, Henning

Journal of Mathematical Analysis and Applications


We introduce variable exponent versions of Morreyfied Triebel-Lizorkin spaces. To that end, we prove an important convolution inequality which is a replacement for the Hardy-Littlewood maximal inequality in the fully variable setting. Using it we obtain characterizations by means of Peetre maximal functions and use them to show the independence of the introduced spaces from the admissible system used. | doi | Peer Reviewed

136.  On the energy of singular and non singular graphs

Andrade, Enide and Carmona, Juan R. and Poveda, Alex and Robbiano, María

MATCH Communications in Mathematical and in Computer Chemistry

University of Kragujevac

Let $G$ be a simple undirected graph with $n$ vertices, $m$ edges, adjacency matrix $A$, largest eigenvalue $rho$ and nullity $kappa$. The energy of $G,$ $mathcal{E}(G)$ is the sum of its singular values. In this work lower bounds for $mathcal{E}(G)$ in terms of the coefficient of $mu^{kappa}$ in the expansion of characteristic polynomial, $p(mu)=det{(mu I-A)}$ are obtained. In particular one of the bounds generalizes a lower bound obtained by K. Das, S. A. Mojallal and I. Gutman in $2013$ to the case of graphs with given nullity. The bipartite case is also studied obtaining in this case, a sufficient condition to improve the spectral lower bound $2rho.$ Considering an increasing sequence convergent to $rho$ a convergent increasing sequence of lower bounds for the energy of $G$ is constructed. | doi | Peer Reviewed

135.  A lower bound for the energy of hypoenergetic and non hypoenergetic graphs

Andrade, Enide and R. Carmona, Juan and Infante, Geraldine and Robbiano, María

MATCH Communications in Mathematical and in Computer Chemistry

University of Kragujevac, Faculty of Science

Let $G$ be a simple undirected graph with $n$ vertices and $m$ edges. The energy of $G,$ $mathcal{E}(G)$ corresponds to the sum of its singular values. This work obtains lower bounds for $mathcal{E}(G)$ where one of them generalizes a lower bound obtained by Mc Clelland in $1971$ to the case of graphs with given nullity. An extension to the bipartite case is given and, in this case, it is shown that the lower bound $2sqrt{m}$ is improved. The equality cases are characterized. Moreover, a simple lower bound that considers the number of edges and the diameter of $G$ is derived. A simple lower bound, which improves the lower bound $2sqrt{n-1}$, for the energy of trees with $n$ vertices and diameter $d$ is also obtained. | Peer Reviewed

134.  Numerical optimal control of HIV transmission in Octave/MATLAB

Campos, Carlos and Silva, Cristiana J. and Torres, Delfim F. M.

Mathematical and Computational Applications


We provide easy and readable GNU Octave/MATLAB code for the simulation of mathematical models described by ordinary differential equations and for the solution of optimal control problems through Pontryagin’s maximum principle. For that, we consider a normalized HIV/AIDS transmission dynamics model based on the one proposed in our recent contribution (Silva, C.J.; Torres, D.F.M. A SICA compartmental model in epidemiology with application to HIV/AIDS in Cape Verde. Ecol. Complex. 2017, 30, 70–75), given by a system of four ordinary differential equations. An HIV initial value problem is solved numerically using the ode45 GNU Octave function and three standard methods implemented by us in Octave/MATLAB: Euler method and second-order and fourth-order Runge–Kutta methods. Afterwards, a control function is introduced into the normalized HIV model and an optimal control problem is formulated, where the goal is to find the optimal HIV prevention strategy that maximizes the fraction of uninfected HIV individuals with the least HIV new infections and cost associated with the control measures. The optimal control problem is characterized analytically using the Pontryagin Maximum Principle, and the extremals are computed numerically by implementing a forward-backward fourth-order Runge–Kutta method. Complete algorithms, for both uncontrolled initial value and optimal control problems, developed under the free GNU Octave software and compatible with MATLAB are provided along the article. | doi | Peer Reviewed

133.  Regional enlarged observability of Caputo fractional differential equations

Zouiten, Hayat and Boutoulout, Ali and Torres, Delfim F. M.

Discrete and Continuous Dynamical Systems - Series S

American Institute of Mathematical Sciences (AIMS)

We consider the regional enlarged observability problem for fractional evolution differential equations involving Caputo derivatives. Using the Hilbert Uniqueness Method, we show that it is possible to rebuild the initial state between two prescribed functions only in an internal subregion of the whole domain. Finally, an example is provided to illustrate the theory. | doi | Peer Reviewed

132.  Some new aspects of main eigenvalues of graphs

Abreu, Nair and Cardoso, Domingos M. and França, Francisca A. M. and Vinagre, Cybele T. M.

Computational and Applied Mathematics


An eigenvalue of the adjacency matrix of a graph is said to be main if the all-1 vector is non-orthogonal to the associated eigenspace. This paper explores some new aspects of the study of main eigenvalues of graphs, investigating specifically cones over strongly regular graphs and graphs for which the least eigenvalue is non-main. In this case, we characterize paths and trees with diameter-3 satisfying the property. We may note that the importance of least eigenvalues of graphs for the equilibria of social and economic networks was recently uncovered in literature. | doi | Peer Reviewed

131.  Graphs with clusters perturbed by regular graphs: Aα-spectrum and applications

Cardoso, Domingos M. and Pastén, Germain and Rojo, Oscar

Discussiones Mathematicae Graph Theory

De Gruyter

Given a graph $G$, its adjacency matrix $A(G)$ and its diagonal matrix of vertex degrees $D(G)$, consider the matrix $A_{alpha}left( Gright) = alpha Dleft( Gright) +(1-alpha)Aleft(Gright)$, where $alpha inleft[ 0,1right)$. The $A_{alpha}-$ spectrum of $G$ is the multiset of eigenvalues of $A_{alpha}(G)$ and these eigenvalues are the $alpha-$ eigenvalues of $G$. A cluster in $G$ is a pair of vertex subsets $(C,S)$, where $C$ is a set of cardinality $|C| ge 2$ of pairwise co-neighbor vertices sharing the same set $S$ of $|S|$ neighbors. Assuming that $G$ is connected and it has a cluster $(C,S)$, $G(H)$ is obtained from $G$ and an $r-$ regular graph $H$ of order $|C|$ by identifying its vertices with the vertices in $C$, eigenvalues of $A_{alpha}(G)$ and $A_{alpha}(G(H))$ are deduced and if $A_{alpha}(H)$ is positive semidefinite then the $i$-th eigenvalue of $A_{alpha}(G(H))$ is greater than or equal to $i$-th eigenvalue of $A_{alpha}(G)$. These results are extended to graphs with several pairwise disjoint clusters $(C_1,S_1), ldots, (C_k,S_k)$. As an application, the effect on the energy, $alpha$-Estrada index and $alpha$-index of a graph $G$ with clusters when the edges of regular graphs are added to $G$ are analyzed. Finally, the $A_{alpha}-$ spectrum of the corona product $G circ H$ of a connected graph $G$ and a regular graph $H$ is determined. | doi | Peer Reviewed

130.  CGO-Faddeev approach for complex conductivities with regular jumps in two dimensions

Pombo, Ivan

Inverse Problems

IOP Publishing

Researchers familiar with the state of the art are aware that the development of close-formed solutions for the EIT problem was not able to overpass the case of once-time differentiable conductivities beside the well known particular Astala–Päivärinta result for zero frequency. In this paper, we introduce some new techniques for the inverse conductivity problem combined with a transmission problem and achieve a reconstruction result based on an adaptation of the scattering data. The idea for these techniques, in particular the concept of admissible points is coming from Lakshtanov and Vainberg. Moreover, we are going to establish the necessary groundwork for working with admissible points which will be required in any further research in this direction. | doi | Peer Reviewed

129.  A survey on graphs with convex quadratic stability number

Cardoso, Domingos M.


Taylors & Fancis

A graph with convex quadratic stability number is a graph for which the stability number is determined by solving a convex quadratic program. Since the very beginning, where a convex quadratic programming upper bound on the stability number was introduced, a necessary and sufficient condition for this upper bound be attained was deduced. The recognition of graphs with convex quadratic stability number has been deeply studied with several consequences from continuous and combinatorial point of view. This survey starts with an exposition of some extensions of the classical Motzkin-Straus approach to the determination of the stability number of a graph and its relations with the convex quadratic programming upper bound. The main advances, including several properties and alternative characterizations of graphs with convex quadratic stability number are described as well as the algorithmic strategies developed for their recognition. Open problems and a conjecture for a particular class of graphs, herein called adverse graphs, are presented, pointing out a research line which is a challenge between continuous and discrete problems. | doi | Peer Reviewed

128.  On Hermite-Hadamard type inequalities for harmonical h-convex interval-valued functions

Dafang Zhao and Tianqing An and Guoju Ye and Torres, Delfim F. M.

Mathematical Inequalities and Applications


We introduce and investigate the concept of harmonical h-convexity for interval-valued functions. Under this new concept, we prove some new Hermite-Hadamard type inequalities for the interval Riemann integral. | doi | Peer Reviewed

127.  On the spectra of some g-circulant matrices and applications to nonnegative inverse eigenvalue problem

Andrade, Enide and Arrieta, Luis and Manzaneda, Cristina and Robbiano, María

Linear Algebra and its Applications


A $g$-circulant matrix $A$, is defined as a matrix of order $n$ where the elements of each row of $A$ are identical to those of the previous row, but are moved $g$ positions to the right and wrapped around. Using number theory, certain spectra of $g$-circulant real matrices are given explicitly. The obtained results are applied to Nonnegative Inverse Eigenvalue Problem to construct nonnegative, $g$-circulant matrices with given appropriated spectrum. Additionally, some $g$-circulant marices are reconstructed from its main diagonal entries. | doi | Peer Reviewed

126.  Traveling wave solutions of some important Wick-type fractional stochastic nonlinear partial differential equations

Hyunsoo Kim and Sakthivel, Rathinasamy and Debbouche, Amar and Torres, Delfim F. M.

Chaos, Solitons and Fractals


In this article, exact traveling wave solutions of a Wick-type stochastic nonlinear Schrödinger equation and of a Wick-type stochastic fractional Regularized Long Wave-Burgers (RLW-Burgers) equation have been obtained by using an improved computational method. Specifically, the Hermite transform is employed for transforming Wick-type stochastic nonlinear partial differential equations into deterministic nonlinear partial differential equations with integral and fraction order. Furthermore, the required set of stochastic solutions in the white noise space is obtained by using the inverse Hermite transform. Based on the derived solutions, the dynamics of the considered equations are performed with some particular values of the physical parameters. The results reveal that the proposed improved computational technique can be applied to solve various kinds of Wick-type stochastic fractional partial differential equations. | doi | Peer Reviewed

125.  Boolean dynamics revisited through feedback interconnections

Chaves, Madalena and Figueiredo, Daniel and Martins, Manuel A.

Natural Computing


Boolean models of physical or biological systems describe the global dynamics of the system and their attractors typically represent asymptotic behaviors. In the case of large networks composed of several modules, it may be difficult to identify all the attractors. To explore Boolean dynamics from a novel viewpoint, we will analyse the dynamics emerging from the composition of two known Boolean modules. The state transition graphs and attractors for each of the modules can be combined to construct a new asymptotic graph which will (1) provide a reliable method for attractor computation with partial information; (2) illustrate the differences in dynamical behavior induced by the updating strategy (asynchronous, synchronous, or mixed); and (3) show the inherited organization/structure of the original network’s state transition graph. | doi | Peer Reviewed

124.  The stability and stabilization of infinite dimensional Caputo-time fractional differential linear systems

Zitane, Hanaa and Boutoulout, Ali and Torres, Delfim F. M.



We investigate the stability and stabilization concepts for infinite dimensional time fractional differential linear systems in Hilbert spaces with Caputo derivatives. Firstly, based on a family of operators generated by strongly continuous semigroups and on a probability density function, we provide sufficient and necessary conditions for the exponential stability of the considered class of systems. Then, by assuming that the system dynamics is symmetric and uniformly elliptic and by using the properties of the Mittag-Leffler function, we provide sufficient conditions that ensure strong stability. Finally, we characterize an explicit feedback control that guarantees the strong stabilization of a controlled Caputo time fractional linear system through a decomposition approach. Some examples are presented that illustrate the effectiveness of our results. | doi | Peer Reviewed

123.  A mathematical model for vineyard replacement with nonlinear binary control optimization

Galindro, Aníbal and Cerveira, Adelaide and Torres, Delfim F. M. and Matias, João and Marta-Costa, Ana

Discontinuity, Nonlinearity, and Complexity

L&H Scientific Publishing

Vineyard replacement is a common practice in every wine-growing farm since the grapevine production decays over time and requires a new vine to ensure the business sustainability. In this paper, we formulate a simple discrete model that captures the vineyard’s main dynamics such as production values and grape quality. Then, by applying binary nonlinear programming methods to find the vineyard replacement trigger, we seek the optimal solution concerning different governmental subsidies to the target producer. | doi | Peer Reviewed

122.  A fuzzy modal logic for fuzzy transition systems

Jain, Manisha and Madeira, Alexandre and Martins, Manuel A.

Electronic Notes in Theoretical Computer Science


This paper intends to contribute with a new fuzzy modal logic to model and reason about transition systems involving uncertainty in behaviours. Our formalism supports fuzziness at transitions and on the proposition symbols assignment levels. Against of other approaches in the literature, our bisimulation and bisimilarity notions generalise the analogous standard notions of classic modal logic and of process algebras. Moreover, the outcome of our logic is also fuzzy, with the semantic interpretation of connectives supported by the Gödel algebra. | doi | Peer Reviewed

121.  Introducing synchrony in fuzzy automata

Gomes, Leandro and Madeira, Alexandre and Barbosa, Luis Soares

Electronic Notes in Theoretical Computer Science


This paper introduces a sort of automata and associated languages, often arising in modelling natural phenomena, in which both vagueness and simultaneity are taken as first class citizens. This requires a fuzzy semantics assigned to transitions and a precise notion of a synchronous product to enforce the simultaneous occurrence of actions. The expected relationships between automata and languages are revisited in this setting; in particular it is shown that any subset of a fuzzy synchronous language with the suitable signature forms a synchronous Kleene algebra. | doi | Peer Reviewed

120.  Errata to "Modeling and optimal control of HIV/AIDS prevention through PrEP", Discrete Contin. Dyn. Syst. Ser. S 11 (2018), no. 1, 119–141

Silva, Cristiana J. and Torres, Delfim F. M.

Discrete and Continuous Dynamical Systems - Series S

American Institute of Mathematical Sciences (AIMS)

No abstract available. | doi | Peer Reviewed

119.  Enlarged controllability and optimal control of sub-diffusion processes with Caputo fractional derivatives

Karite, Touria and Boutoulout, Ali and Torres, Delfim F. M.

Progress in Fractional Differentiation and Applications

Natural Sciences Publishing (NSP)

We investigate the exact enlarged controllability and optimal control of a fractional diffusion equation in Caputo sense. This is done through a new definition of enlarged controllability that allows us to extend available contributions. Moreover, the problem is studied using two approaches: a reverse Hilbert uniqueness method, generalizing the approach introduced by Lions in 1988, and a penalization method, which allow us to characterize the minimum energy control. | doi | Peer Reviewed

118.  New convolutions and their applicability to integral equations of Wiener-Hopf plus Hankel type

Castro, Luis P. and Guerra, Rita C. and Tuan, Nguyen Minh

Mathematical Methods in the Applied Sciences


We propose four new convolutions exhibiting convenient factorization properties associated with two finite interval integral transformations of Fourier-type together with their norm inequalities. Moreover, we study the solvability of a class of integral equations of Wiener-Hopf plus Hankel type (on finite intervals) with the help of the factorization identities of such convolutions. Fourier-type series are used to produce the solution formula of such equations and a Shannon-type sampling formula is also obtained. | doi | Peer Reviewed

117.  Probing multi-step electroweak phase transition with multi-peaked primordial gravitational waves spectra

Morais, António P. and Pasechnik, Roman

Journal of Cosmology and Astroparticle Physics

IOP Publishing

Multi-peaked spectra of the primordial gravitational waves are considered as a phenomenologically relevant source of information about the dynamics of sequential phase transitions in the early Universe. In particular, such signatures trace back to specific patterns of the first-order electroweak phase transition in the early Universe occurring in multiple steps. Such phenomena appear to be rather generic in multi-scalar extensions of the Standard Model. In a particularly simple extension of the Higgs sector, we have identified and studied the emergence of sequential long- and short-lasting transitions as well as their fundamental role in generation of multi-peaked structures in the primordial gravitational-wave spectrum. We discuss the potential detectability of these signatures by the proposed gravitational-wave interferometers. | doi | Peer Reviewed

116.  Mathematical modeling of COVID-19 transmission dynamics with a case study of Wuhan

Ndaïrou, Faïçal and Area, Iván and Nieto, Juan J. and Torres, Delfim F. M.

Chaos, Solitons and Fractals


We propose a compartmental mathematical model for the spread of the COVID-19 disease with special focus on the transmissibility of super-spreaders individuals. We compute the basic reproduction number threshold, we study the local stability of the disease free equilibrium in terms of the basic reproduction number, and we investigate the sensitivity of the model with respect to the variation of each one of its parameters. Numerical simulations show the suitability of the proposed COVID-19 model for the outbreak that occurred in Wuhan, China. | doi | Peer Reviewed

115.  Synchronization and self-organization in complex networks for a tuberculosis model

Silva, Cristiana J. and Cantin, Guillaume

Mathematics in Computer Science


In this work, we propose and analyze the dynamics of a complex network built with non identical instances of a tuberculosis (TB) epidemiological model, for which we prove the existence of non-negative and bounded global solutions. A two nodes network is analyzed where the nodes represent the TB epidemiological situation of the countries Angola and Portugal. We analyze the effect of different coupling and intensity of migratory movements between the two countries and explore the effect of seasonal migrations. For a random complex network setting, we show that it is possible to reach a synchronization state by increasing the coupling strength and test the influence of the topology in the dynamics of the complex network. All the results are analyzed through numerical simulations where the given algorithms are implemented with the python 3.5 language, in a Debian/GNU-Linux environment. | doi | Peer Reviewed

114.  Systematic maximum sum rank codes

Almeida, Paulo and Martínez-Peñas, Umberto and Napp, Diego

Finite Fields and Their Applications


In the last decade there has been a great interest in extending results for codes equipped with the Hamming metric to analogous results for codes endowed with the rank metric. This work follows this thread of research and studies the characterization of systematic generator matrices (encoders) of codes with maximum rank distance. In the context of Hamming distance these codes are the so-called Maximum Distance Separable (MDS) codes and systematic encoders have been fully investigated. In this paper we investigate the algebraic properties and representation of encoders in systematic form of Maximum Rank Distance (MRD) codes and Maximum Sum Rank Distance (MSRD) codes. We address both block codes and convolutional codes separately and present necessary and sufficient conditions for an encoder in systematic form to generate a code with maximum (sum) rank distance. These characterizations are given in terms of certain matrices that must be superregular in a extension field and that preserve superregularity after some transformations performed over the base field. We conclude the work presenting some examples of Maximum Sum Rank convolutional codes over small fields. For the given parameters the examples obtained are over smaller fields than the examples obtained by other authors. | doi | Peer Reviewed

113.  Qualitatively-improved identified parameters of prestressed concrete catenary poles using sensitivity-based Bayesian approach

Alkam, F. and Pereira, I. and Lahmer, T.

Results in Engineering


Prestressed, spun-cast ultrahigh-strength concrete catenary poles have been used widely for electric train systems; for example, thousands of these poles have been installed along high-speed train tracks in Germany. Given the importance of the functionality of train systems, adequate attention has not been paid to catenary poles in research and the literature. Questions regarding the integrity of catenary poles still exist. This study contributes to identify the actual material properties of the poles of interest because the parameter identification is an essential process for any subsequent evaluation of the integrity of catenary poles. Accordingly, a sensitivity-based Bayesian parameter identification approach is developed to estimate the real material properties of the poles using measurements from multiple experiments and numerical models. This approach integrates the sensitivity of time-dependent measurements into the Bayesian inference, which improves the quality of inferred parameters considerably in comparison with classic Bayesian approaches applied in similar case of studies. Furthermore, the proposed approach combines observations of multiple experiments conducted on full-scale poles using a probabilistic uncertainty framework, which provides informative data used in the parameter identification process. Besides, Bayesian inference quantifies the uncertainty of inferred parameters and estimates the hyperparameters, such as the total errors of the observations. The proposed approach utilizes the efficiency of the transitional Markov Chain Monte Carlo algorithm for sampling from the posterior in both levels of Bayesian inference, namely, the unknown parameters and the hyperparameters. The results show the significant influence of the sensitivity concept in improving the quality of the posterior and highlight the importance of identifying the real material properties during the evaluation of the behavior of existing structures, rather than using the characteristic properties from the datasheet. Applying the proposed approach looks very promising when applied to similar applied case studies. | doi | Peer Reviewed

112.  An exploration of locally spherical regular hypertope

Fernandes, Maria Elisa and Leemans, Dimitri and Weiss, Asia Ivić

Discrete & Computational Geometry

Springer Nature

Hypertope is a generalization of the concept of polytope, which in turn generalizes the concept of a map and hypermap, to higher rank objects. Regular hypertopes with spherical residues, which we call regular locally spherical hypertopes, must be either of spherical, euclidean, or hyperbolic type. That is, the type-preserving automorphism group of a locally spherical regular hypertope is a quotient of a finite irreducible, infinite irreducible, or compact hyperbolic Coxeter group. We classify the locally spherical regular hypertopes of spherical and euclidean type and investigate finite hypertopes of hyperbolic type, giving new examples and summarizing some known results. | doi | Peer Reviewed

111.  A multi-model methodology for forecasting sales and returns of liquefied petroleum gas cylinders

Correia, Aldina and Lopes, Cristina and Silva, Eliana Costa e and Monteiro, Magda and Lopes, Rui Borges

Neural Computing and Applications


In the liquefied petroleum gas (LPG) cylinder business, one of the most important assets is the LPG cylinder. This work addresses the asset acquisition planning for the LPG cylinder business of a company from the energy sector which has recently started this activity. In order to make the acquisition plan, it was necessary to forecast the sales and the LPG cylinder return rate. For that purpose, an ensemble method using time series techniques, multiple linear regression models and artificial neural networks was employed. Sales forecast was obtained using time series techniques, in particular, moving averages and exponential smoothing. Then, forecast of bottled propane gas sales and return rate was also addressed through multiple linear regression and artificial neural networks. A probability density function was defined for each of the different approaches. Afterward, using Monte Carlo simulation, the forecast values are obtained by a linear combination of the probability density functions, thus producing the final forecast. Results show that the company’s expectation of growth is larger than that predicted by the proposed methodology, which means the company should reflect on its current asset acquisition strategy. By combining different approaches, the proposed multi-model methodology allowed to obtain an accurate forecasting, without requiring a lot of historical data. | doi | Peer Reviewed

110.  On leader-following consensus in multi-agent systems with discrete updates at random times

Almeida, Ricardo and Girejko, Ewa and Hristova, Snezhana and Malinowska, Agnieszka



This paper studies the leader-following consensus problem in continuous-time multi-agent networks with communications/updates occurring only at random times. The time between two consecutive controller updates is exponentially distributed. Some sufficient conditions are derived to design the control law that ensures the leader-following consensus is asymptotically reached (in the sense of the expected value of a stochastic process). The numerical examples are worked out to demonstrate the effectiveness of our theoretical results. | doi | Peer Reviewed

109.  Optimal control of aquatic diseases: a case study of Yemen’s cholera outbreak

Lemos-Paião, Ana P. and Silva, Cristiana J. and Torres, Delfim F. M. and Venturino, Ezio

Journal of Optimization Theory and Applications


We propose a mathematical model for the transmission dynamics of some strains of the bacterium Vibrio cholerae, responsible for the cholera disease in humans. We prove that, when the basic reproduction number is equal to one, a transcritical bifurcation occurs for which the endemic equilibrium emanates from the disease-free point. A control function is introduced into the model, representing the distribution of chlorine water tablets for water purification. An optimal control problem is then proposed and analyzed, where the goal is to determine the fraction of susceptible individuals who should have access to chlorine water tablets in order to minimize the total number of new infections plus the total cost associated with the distribution of chlorine water tablets, over the considered period of time. Finally, we consider real data of the cholera outbreak in Yemen, from April 27, 2017 to April 15, 2018, choosing the values of the parameters of the uncontrolled model that fit the real data. Using our optimal control results, we show, numerically, that the distribution of chlorine water tablets could have stopped, in a fast way, the worst cholera outbreak that ever occurred in human history. Due to the critical situation of Yemen, we also simulate the case where only a small percentage of susceptible individuals has access to chlorine water tablets and obtain an optimal control solution that decreases, substantially, the maximum number of infective individuals affected by the outbreak. | doi | Peer Reviewed

108.  Time Series components separation based on Singular Spectral Analysis visualization: an HJ-biplot method application

Silva, Alberto Oliveira da and Freitas, Adelaide

Statistics, Optimization and Information Computing

International Academic Press

The extraction of essential features of any real-valued time series is crucial for exploring, modeling and producing, for example, forecasts. Taking advantage of the representation of a time series data by its trajectory matrix of Hankel constructed using Singular Spectrum Analysis, as well as of its decomposition through Principal Component Analysis via Partial Least Squares, we implement a graphical display employing the biplot methodology. A diversity of types of biplots can be constructed depending on the two matrices considered in the factorization of the trajectory matrix. In this work, we discuss the called HJ-biplot which yields a simultaneous representation of both rows and columns of the matrix with maximum quality. Interpretation of this type of biplot on Hankel related trajectory matrices is discussed from a real-world data set. | doi | Peer Reviewed

107.  Constructions of MDS convolutional codes using superregular matrices

Lieb, Julia and Pinto, Raquel

Journal of Algebra Combinatorics Discrete Structures and Applications

Jacodesmath Institute

Maximum distance separable convolutional codes are the codes that present best performance in error correction among all convolutional codes with certain rate and degree. In this paper, we show that taking the constant matrix coefficients of a polynomial matrix as submatrices of a superregular matrix, we obtain a column reduced generator matrix of an MDS convolutional code with a certain rate and a certain degree. We then present two novel constructions that fulfill these conditions by considering two types of superregular matrices. | Peer Reviewed

106.  Functional differential equations involving the ψ-Caputo fractional derivative

Almeida, Ricardo

Fractal and Fractional


This paper is devoted to the study of existence and uniqueness of solutions for fractional functional differential equations, whose derivative operator depends on an arbitrary function. The introduction of such function allows generalization of some known results, and others can be also obtained. | doi | Peer Reviewed

105.  Older people’s preferences for self-involvement in decision-making if faced with serious illness

Jorge, Rafaela and Calanzani, Natália and Freitas, Adelaide and Nunes, Rui and Sousa, Liliana

Geriatrics, Gerontology and Aging

Brazilian Society of Geriatrics and Gerontology (SBGG)

OBJECTIVES: To examine older people’s preferences for self-involvement in end-of-life care decision-making in scenarios of mental capacity (competency) and incapacity, and to identify associated factors. METHODS: A cross-sectional survey was conducted including 400 individuals aged 60+ years living in the city of Belo Horizonte, Brazil. RESULTS: Among 400 respondents, 95.3% preferred self-involvement when capable (due to the high percentage, associated factors were not calculated) and 64.5% preferred self-involvement when incapable through, for example, a living will. Considering that participants could choose multiple answers, the most frequent combinations in the capacity scenario were “yourself” and “other relatives” (76.8%) and “yourself” and “the doctor” (67.8%). In the incapacity scenario, the most frequent combinations were “yourself” and “other relatives” (usually their “ children and, less often, their grandchildren) (59.3%) and “yourself” and “the doctor” (48.5%). Three factors were associated with a preference for self-involvement in an incapacity scenario. Those who were married or had a partner (widowed; adjusted odds ratio [AOR] = 0.37; 95% confidence interval [CI] 0.19-0.68) and those who were male (female; AOR = 0.62; 95%CI 0.38-1.00) were less likely to prefer self-involvement. Those who were younger, as in age bands 60-69 years (80+; AOR = 2.35; 95%CI 1.20-4.58) and 70-79 years (80+; AOR = 2.45; 95%CI 1.21-4.94), were more likely to prefer self-involvement. CONCLUSIONS: Most participants preferred self-involvement in both scenarios of capacity and incapacity. Preference for self-involvement was higher in the scenario of capacity, while preference for the involvement of other relatives (usually their children) was greater in the scenario of incapacity. | doi | Peer Reviewed

104.  Orthogonal gyrodecompositions of real inner product gyrogroups

Ferreira, Milton and Suksumran, Teerapong



In this article, we prove an orthogonal decomposition theorem for real inner product gyrogroups, which unify some well-known gyrogroups in the literature: Einstein, Möbius, Proper Velocity, and Chen’s gyrogroups. This leads to the study of left (right) coset partition of a real inner product gyrogroup induced from a subgyrogroup that is a finite dimensional subspace. As a result, we obtain gyroprojectors onto the subgyrogroup and its orthogonal complement. We construct also quotient spaces and prove an associated isomorphism theorem. The left (right) cosets are characterized using gyrolines (cogyrolines) together with automorphisms of the subgyrogroup. With the algebraic structure of the decompositions, we study fiber bundles and sections inherited by the gyroprojectors. Finally, the general theory is exemplified for the aforementioned gyrogroups. | doi | Peer Reviewed

103.  Dynamical analysis of a fractional SIR model with treatment and quarantine

Almeida, Ricardo

Chaotic Modeling and Simulation

We propose a fractional SIR model with treatment and quarantine policies, whose dynamics is described by the Caputo fractional derivative. Local stability of the equilibrium points is studied, and the threshold value R0 is found. Finally, some numerical simulations are presented for different values of the parameters. | Peer Reviewed

102.  Cartesian closed exact completions in topology

Clementino, Maria Manuel and Hofmann, Dirk and Ribeiro, Willian

Journal of Pure and Applied Algebra


Using generalized enriched categories, in this paper we show that Rosický’s proof of cartesian closedness of the exact completion of the category of topological spaces can be extended to a wide range of topological categories over Set, like metric spaces, approach spaces, ultrametric spaces, probabilistic metric spaces, and bitopological spaces. In order to do so we prove a sufficient criterion for exponentiability of (T, V)-categories and show that, under suitable conditions, every injective (T, V)-category is exponentiable in (T, V)-Cat. | doi | Peer Reviewed

101.  A stochastic fractional calculus with applications to variational principles

Zine, Houssine and Torres, Delfim F. M.

Fractal and Fractional


We introduce a stochastic fractional calculus. As an application, we present a stochastic fractional calculus of variations, which generalizes the fractional calculus of variations to stochastic processes. A stochastic fractional Euler-Lagrange equation is obtained, extending those available in the literature for the classical, fractional, and stochastic calculus of variations. To illustrate our main theoretical result, we discuss two examples: one derived from quantum mechanics, the second validated by an adequate numerical simulation. | doi | Peer Reviewed

100.  Automatic adjoint differentiation for gradient descent and model calibration

Goloubentsev, Dmitri and Lakshtanov, Evgeny

International Journal of Wavelets, Multiresolution and Information Processing

World Scientific Publishing

In this work, we discuss the Automatic Adjoint Differentiation (AAD) for functions of the form G=12∑m1(Eyi−Ci)2, which often appear in the calibration of stochastic models. We demonstrate that it allows a perfect SIMDa parallelization and provides its relative computational cost. In addition, we demonstrate that this theoretical result is in concordance with numerical experiments. a Single Input Multiple Data. | doi | Peer Reviewed

99.  Lyapunov functions for fractional-order systems in biology: methods and applications

Boukhouima, Adnane and Hattaf, Khalid and Lotfi, El Mehdi and Mahrouf, Marouane and Torres, Delfim F. M. and Yousfi, Noura

Chaos, Solitons & Fractals


We prove new estimates of the Caputo derivative of order α ∈ (0, 1] for some specific functions. The estimations are shown useful to construct Lyapunov functions for systems of fractional differential equations in biology, based on those known for ordinary differential equations, and therefore useful to determine the global stability of the equilibrium points for fractional systems. To illustrate the usefulness of our theoretical results, a fractional HIV population model and a fractional cellular model are studied. More precisely, we construct suitable Lyapunov functionals to demonstrate the global stability of the free and endemic equilibriums, for both fractional models, and we also perform some numerical simulations that confirm our choices. | doi | Peer Reviewed

98.  Hausdorff coalgebras

Hofmann, Dirk and Nora, Pedro

Applied Categorical Structures


As composites of constant, (co)product, identity, and powerset functors, Kripke polynomial functors form a relevant class of $mathsf{Set}$-functors in the theory of coalgebras. The main goal of this paper is to expand the theory of limits in categories of coalgebras of Kripke polynomial functors to the context of quantale-enriched categories. To assume the role of the powerset functor we consider "powerset-like" functors based on the Hausdorff $mathsf{V}$-category structure. As a starting point, we show that for a lifting of a $mathsf{SET}$-functor to a topological category $mathsf{X}$ over $mathsf{Set}$ that commutes with the forgetful functor, the corresponding category of coalgebras over $mathsf{X}$ is topological over the category of coalgebras over $mathsf{Set}$ and, therefore, it is "as complete" but cannot be "more complete". Secondly, based on a Cantor-like argument, we observe that Hausdorff functors on categories of quantale-enriched categories do not admit a terminal coalgebra. Finally, in order to overcome these "negative" results, we combine quantale-enriched categories and topology emph{`a la} Nachbin. Besides studying some basic properties of these categories, we investigate "powerset-like" functors which simultaneously encode the classical Hausdorff metric and Vietoris topology and show that the corresponding categories of coalgebras of "Kripke polynomial" functors are (co)complete. | doi | Peer Reviewed

97.  Inference for bivariate integer-valued moving average models based on binomial thinning operation

Silva, Isabel and Silva, Maria Eduarda and Torres, Cristina

Journal of Applied Statistics

Taylor & Francis

Time series of (small) counts are common in practice and appear in a wide variety of fields. In the last three decades, several models that explicitly account for the discreteness of the data have been proposed in the literature. However, for multivariate time series of counts several difficulties arise and the literature is not so detailed. This work considers Bivariate INteger-valued Moving Average, BINMA, models based on the binomial thinning operation. The main probabilistic and statistical properties of BINMA models are studied. Two parametric cases are analysed, one with the cross-correlation generated through a Bivariate Poisson innovation process and another with a Bivariate Negative Binomial innovation process. Moreover, parameter estimation is carried out by the Generalized Method of Moments. The performance of the model is illustrated with synthetic data as well as with real datasets. | doi | Peer Reviewed

96.  New developments in the forecasting of monthly overnight stays in the North Region of Portugal

Silva, Isabel and Alonso, Hugo

Journal of Applied Statistics

Taylor & Francis

The Tourism sector is of strategic importance to the North Region of Portugal and is growing. Forecasting monthly overnight stays in this region is, therefore, a relevant problem. In this paper, we analyze data more recent than those considered in previous studies and use them to develop and compare several forecasting models and methods. We conclude that the best results are achieved by models based on a non-parametric approach not considered so far for these data, the singular spectrum analysis. | doi | Peer Reviewed

95.  Mixed impedance boundary value problems for the Laplace–Beltrami equation

Castro, Luis and Duduchava, Roland and Speck, Frank-Olme

Journal of Integral Equations and Applications

Rocky Mountain Mathematics Consortium

This work is devoted to the analysis of the mixed impedance-Neumann-Dirichlet boundary value problem (MIND~BVP) for the Laplace-Beltrami equation on a compact smooth surface $mathcal{C}$ with smooth boundary. We prove, using the Lax-Milgram Lemma, that this MIND BVP has a unique solution in the classical weak setting $mathbb{H}^1(mathcal{C})$ when considering positive constants in the impedance condition. The main purpose is to consider the MIND~BVP in a nonclassical setting of the Bessel potential space $mathbb{H}^s_p(mathcal{C})$, for $s> 1/p$, $11/p$ and $1 | doi | Peer Reviewed

94.  A História da Matemática nos cursos de Educação Básica em Portugal: uma reflexão para a formação de professores

Pinto, Hélder and Costa, Cecília

Revista Paradigma

Centro de Investigaciones Educacionales Paradigma (CIEP)

A História da Matemática (HM) é uma ferramenta que poderá ser muito útil em contexto educativo. Contudo, a HM é um corpo de saber muito extenso e é necessário refletir qual a HM que deverá ser ensinada na formação inicial de professores dos primeiros anos de escolaridade. Neste artigo fazemos essa reflexão tentando justificar quais os conteúdos de HM verdadeiramente essenciais para os professores e para as suas práticas profissionais futuras. Na nossa opinião, os conteúdos de HM deverão centrar-se nos temas: sistemas de numeração de diversos povos, diferentes algoritmos para realizar operações aritméticas e resolver equações, tópicos de geometria, bem como o conhecimento de vários pontos de HM local/nacional. Fazemos ainda uma breve descrição do que são os cursos de Educação Básica em Portugal, dando especial enfoque nas matemáticas lecionadas nesses cursos. Por outro lado, apresentamos também várias referências a estudos internacionais onde se atesta a importância da utilização da HM em contexto de sala de aula. | doi | Peer Reviewed

93.  Corrigendum to "Mathematical Modeling of COVID-19 Transmission Dynamics with a Case Study of Wuhan" [Chaos Solitons Fractals 135 (2020), 109846]

Ndaïrou, Faïçal and Area, Iván and Bader, Georg and Nieto, Juan J. and Torres, Delfim F. M.

Chaos, Solitons and Fractals


We correct some numerical results of [Chaos Solitons Fractals 135 (2020), 109846], by providing the correct numbers and plots. The conclusions of the paper remain, however, the same. In particular, the numerical simulations show the suitability of the proposed COVID-19 model for the outbreak that occurred in Wuhan, China. This time all our computer codes are provided, in order to make all computations reproducible. The authors would like to apologize for any inconvenience caused. | doi | Peer Reviewed

92.  Fractional variational principle of Herglotz for a new class of problems with dependence on the boundaries and a real parameter

Almeida, Ricardo and Martins, Natália

Journal of Mathematical Physics

American Institute of Physics

The fractional variational problem of Herglotz type for the case where the Lagrangian depends on generalized fractional derivatives, the free endpoints conditions, and a real parameter is studied. This type of problem generalizes several problems recently studied in the literature. Moreover, it allows us to unify conservative and non-conservative dynamical processes in the same model. The dependence of the Lagrangian with respect to the boundaries and a free parameter is effective and transforms the standard Herglotz’s variational problem into a problem of a different nature. | doi | Peer Reviewed

91.  Spectral inequalities for Kubo-Ando operator means

Lemos, Rute and Soares, Graça

Linear Algebra and its Applications


Eigenvalue and singular value inequalities, involving Kubo-Ando operator connections or means, are established. Previous results from Lemos and Soares in 2018 are generalized or complemented, some log-majorizations are included. As a consequence, a refinement of an independent result by Ando and by Visick in 1995 on the eigenvalues of the Hadamard product is derived. Some singular value inequalities by Zou in 2017 are further extended. | doi | Peer Reviewed

90.  Application of Bernoulli polynomials for solving variable-order fractional optimal control-affine problems

Nemati, Somayeh and Torres, Delfim F. M.



We propose two efficient numerical approaches for solving variable-order fractional optimal control-affine problems. The variable-order fractional derivative is considered in the Caputo sense, which together with the Riemann--Liouville integral operator is used in our new techniques. An accurate operational matrix of variable-order fractional integration for Bernoulli polynomials is introduced. Our methods proceed as follows. First, a specific approximation of the differentiation order of the state function is considered, in terms of Bernoulli polynomials. Such approximation, together with the initial conditions, help us to obtain some approximations for the other existing functions in the dynamical control-affine system. Using these approximations, and the Gauss--Legendre integration formula, the problem is reduced to a system of nonlinear algebraic equations. Some error bounds are then given for the approximate optimal state and control functions, which allow us to obtain an error bound for the approximate value of the performance index. We end by solving some test problems, which demonstrate the high accuracy of our results. | doi | Peer Reviewed

89.  Promover o raciocínio geométrico em alunos com Perturbação do Espectro do Autismo através de um ambiente digital

Santos, Maria Isabel Gomes dos and Breda, Ana Maria Reis d’Azevedo and Almeida, Ana Margarida Pisco

Bolema: Boletim de Educação Matemática

UNESP - Universidade Estadual Paulista

O raciocínio e a construção do sentido espacial são capacidades essenciais em todos os processos de aprendizagem e compreensão matemática de crianças com desenvolvimento típico. Em crianças com Perturbação do Espectro do Autismo (PEA), estas capacidades se tornam ainda muito mais significativas, considerando o papel relevante que desempenham para uma vida independente bem-sucedida. O uso da tecnologia é referido como uma forma eficaz de trabalhar o conteúdo acadêmico com crianças com PEA, possibilitando a criação de ambientes criativos e construtivos onde se podem desenvolver atividades diferenciadas, significativas e de qualidade. No entanto, o desenvolvimento de aplicações tecnológicas para crianças e jovens com PEA continua a merecer pouca atenção, nomeadamente as que dizem respeito ao desenvolvimento do pensamento geométrico. O objetivo deste artigo é relatar os principais resultados obtidos com crianças com PEA utilizando o ambiente digital Learning Environment on Mathematics for Autistic Children desenvolvido, particularmente, no que se refere à promoção das suas capacidades matemáticas fundamentais em geometria. O “PISA 2015 Mathematics Framework” foi a base teórica utilizada para a recolha dos dados, cuja análise, para além de situar o pensamento geométrico dos alunos participantes entre parcialmente estruturado e estruturado, apontou, também, para o redesenho de algumas das atividades implementadas no ambiente digital, tendo em vista a promoção do pensamento geométrico. | doi | Peer Reviewed

88.  Global solution of the initial value problem for the focusing Davey-Stewartson II system

Lakshtanov, Evgeny and Vainberg, Boris

Pure and Applied Functional Analysis

Yokohama Publishers

We consider the two dimensional focusing Davey-Stewartson II system and construct the global solution of the Cauchy problem for a dense in L 2 (C) set of initial data. We do not assume that the initial data is small. So, the solutions may have singularities. We show that the blow-up may occur only on a real analytic variety and the variety is bounded in each strip t ≤ T. | Peer Reviewed

87.  Small-scale distribution of microbes and biogeochemistry in the Great Barrier Reef

Carreira, Cátia and Carvalho, Júlia Porto Silva and Talbot, Samantha and Pereira, Isabel and Lønborg, Christian



Microbial communities distribute heterogeneously at small-scales (mm-cm) due to physical, chemical and biological processes. To understand microbial processes and functions it is necessary to appreciate microbes and matter at small scales, however, few studies have determined microbial, viral, and biogeochemical distribution over space and time at these scales. In this study, the small-scale spatial and temporal distribution of microbes (bacteria and chlorophyll a), viruses, dissolved inorganic nutrients and dissolved organic carbon were determined at five locations (spatial) along the Great Barrier Reef (Australia), and over 4 consecutive days (temporal) at a coastal location. Our results show that: (1) the parameters show high small-scale heterogeneity; (2) none of the parameters measured explained the bacterial abundance distributions at these scales spatially or temporally; (3) chemical (ammonium, nitrate/nitrite, phosphate, dissolved organic carbon, and total dissolved nitrogen) and biological (chl a, and bacterial and viral abundances) measurements did not reveal significant relationships at the small scale; and (4) statistically significant differences were found between sites/days for all parameter measured but without a clear pattern. | doi | Peer Reviewed

86.  Distributed-order non-local optimal control

Ndaïrou, Faïçal and Torres, Delfim F. M.



Distributed-order fractional non-local operators were introduced and studied by Caputo at the end of the 20th century. They generalize fractional order derivatives/integrals in the sense that such operators are defined by a weighted integral of different orders of differentiation over a certain range. The subject of distributed-order non-local derivatives is currently under strong development due to its applications in modeling some complex real world phenomena. Fractional optimal control theory deals with the optimization of a performance index functional, subject to a fractional control system. One of the most important results in classical and fractional optimal control is the Pontryagin Maximum Principle, which gives a necessary optimality condition that every solution to the optimization problem must verify. In our work, we extend the fractional optimal control theory by considering dynamical system constraints depending on distributed-order fractional derivatives. Precisely, we prove a weak version of Pontryagin’s maximum principle and a sufficient optimality condition under appropriate convexity assumptions. | doi | Peer Reviewed

85.  Mathematical modeling of Japanese encephalitis under aquatic environmental effects

Ndaïrou, Faïçal and Area, Iván and Torres, Delfim F. M.



We propose a mathematical model for the spread of Japanese encephalitis with emphasis on the environmental effects on the aquatic phase of mosquitoes. The model is shown to be biologically well-posed and to have a biologically and ecologically meaningful disease-free equilibrium point. Local stability is analyzed in terms of the basic reproduction number and numerical simulations presented and discussed. | doi | Peer Reviewed

84.  A stochastic time-delayed model for the effectiveness of Moroccan COVID-19 deconfinement strategy

Zine, Houssine and Boukhouima, Adnane and Lotfi, El Mehdi and Mahrouf, Marouane and Torres, Delfim F. M. and Yousfi, Noura

Mathematical Modelling of Natural Phenomena

EDP Sciences

Coronavirus disease 2019 (COVID-19) poses a great threat to public health and the economy worldwide. Currently, COVID-19 evolves in many countries to a second stage, characterized by the need for the liberation of the economy and relaxation of the human psychological effects. To this end, numerous countries decided to implement adequate deconfinement strategies. After the first prolongation of the established confinement, Morocco moves to the deconfinement stage on May 20, 2020. The relevant question concerns the impact on the COVID-19 propagation by considering an additional degree of realism related to stochastic noises due to the effectiveness level of the adapted measures. In this paper, we propose a delayed stochastic mathematical model to predict the epidemiological trend of COVID-19 in Morocco after the deconfinement. To ensure the well-posedness of the model, we prove the existence and uniqueness of a positive solution. Based on the large number theorem for martingales, we discuss the extinction of the disease under an appropriate threshold parameter. Moreover, numerical simulations are performed in order to test the efficiency of the deconfinement strategies chosen by the Moroccan authorities to help the policy makers and public health administration to make suitable decisions in the near future. | doi | Peer Reviewed

83.  Spherical electro-vacuum black holes with resonant, scalar Q-hair

Herdeiro, C. A. R. and Radu, E.

European Physical Journal C

The asymptotically flat, spherical, electro-vacuum black holes (BHs) are shown to support static, spherical configurations of a gauged, self-interacting, scalar field, minimally coupled to the geometry. Considering a Q-ball type potential for the scalar field, we dub these configurations Q-clouds, in the test field approximation. The clouds exist under a resonance condition, at the threshold of (charged) superradiance. This is similar to the stationary clouds supported by Kerr BHs, which exist for a synchronisation condition, at the threshold of (rotational) superradiance. In contrast with the rotating case, however, Q-clouds require the scalar field to be massive and self-interacting; no similar clouds exist for massive but free scalar fields. First, considering a decoupling limit, we construct Q-clouds around Schwarzschild and Reissner-Nordstrom BHs, showing there is always a mass gap. Then, we make the Q-clouds backreact, and construct fully non-linear solutions of the Einstein-Maxwell-gauged scalar system describing spherical, charged BHs with resonant, scalar Q-hair. Amongst other properties, we observe there is non-uniqueness of charged BHs in this model and the Q-hairy BHs can be entropically preferred over Reissner-Nordstrom, for the same charge to mass ratio; some Q-hairy BH solutions can be overcharged. We also discuss how some well known no-hair theorems in the literature, applying to electro-vacuum plus minimally coupled scalar fields, are circumvented by this new type of BHs. | doi | Peer Reviewed

82.  Stationary Black Holes and Light Rings

Cunha, P. V. P. and Herdeiro, C. A. R.

Physical Review Letters

American Physical Society

The ringdown and shadow of the astrophysically significant Kerr black hole (BH) are both intimately connected to a special set of bound null orbits known as light rings (LRs). Does it hold that a generic equilibrium BH must possess such orbits? In this Letter we prove the following theorem. A stationary, axisymmetric, asymptotically flat black hole spacetime in 1 + 3 dimensions, with a nonextremal, topologically spherical, Killing horizon admits, at least, one standard LR outside the horizon for each rotation sense. The proof relies on a topological argument and assumes C-2 smoothness and circularity, but makes no use of the field equations. The argument is also adapted to recover a previous theorem establishing that a horizonless ultracompact object must admit an even number of nondegenerate LRs, one of which is stable. | doi | Peer Reviewed

81.  Rotating axion boson stars

Delgado, J. F. M. and Herdeiro, C. A. R. and Radu, E.

Journal of Cosmology and Astroparticle Physics

IOP Publishing

We construct and study rotating axion boson stars (RABSs). These are the spinning generalisations of the spherical gravitating solitons recently introduced in [1]. RABSs are asymptotically flat, stationary, axially symmetric, everywhere regular solutions of the Einstein-Klein-Gordon theory, in the presence of a periodic scalar potential arising in models of axion-like particles. The potential is characterised by two parameters: the mass of the scalar field m(a), and the decay constant f(a). We present an overview of the solution space, for different values of f(a), and analyse some of their phenomenological properties. For large decay constants the solutions become identical to the standard spinning mini boson stars. For small decay constants, on the other hand, the solutions develop distinctive features. In particular, we analyse their compactness, the emergence of ergoregions, light rings and the distribution of stable and unstable equatorial timelike circular orbits, including the inner-most stable circular orbit. We also establish the occurrence of violations of the strong energy condition for physical observers, for some RABSs. We observe some analogy between RABSs and spinning gravitating Q-balls. | doi | Peer Reviewed

80.  Higher dimensional black hole scalarization

Astefanesei, D. and Herdeiro, C. A. R. and Oliveira, J. and Radu, E.

Journal of High Energy Physics


In the simplest scalar-tensor theories, wherein the scalar field is non-minimally coupled to the Ricci scalar, spontaneous scalarization of electrovacuum black holes (BHs) does not occur. This ceases to be true in higher dimensional spacetimes, d > 4. We consider the scalarization of the higher dimensional Reissner-Nordstrom BHs in scalar-tensor models and provide results on the zero modes for different d, together with an explicit construction of the scalarized BHs in d = 5, discussing some of their properties. We also observe that a conformal transformation into the Einstein frame maps this model into an Einstein-Maxwel- scalar model, wherein the non-minimal coupling occurs between the scalar field and the Maxwell invariant (rather than the Ricci scalar), thus relating the occurence of scalarization in the two models. Next, we consider the spontaneous scalarization of the Schwarzschild- Tangherlini BH in extended-scalar-tensor-Lovelock gravity in even dimensions. In these models, the scalar field is non-minimally coupled to the (d/2)(th) Euler density, in d spacetime dimensions. We construct explicitly examples in d = 6, 8, showing the properties of the four dimensional case are qualitatively generic, but with quantitative differences. We compare these higher d scalarized BHs with the hairy BHs in shift-symmetric Horndeski theory, for the same d, which we also construct. | doi | Peer Reviewed

79.  A class of solitons in Maxwell-scalar and Einstein-Maxwell-scalar models

Herdeiro, C. A. R. and Oliveira, J. M S. and Radu, E.

European Physical Journal C


Recently, no-go theorems for the existence of solitonic solutions in Einstein-Maxwell-scalar (EMS) models have been established (Herdeiro and Oliveira in Class Quantum Gravity 36(10):105015, 2019). Here we discuss how these theorems can be circumvented by a specific class of non-minimal coupling functions between a real, canonical scalar field and the electromagnetic field. When the non-minimal coupling function diverges in a specific way near the location of a point charge, it regularises all physical quantities yielding an everywhere regular, localised lump of energy. Such solutions are possible even in flat spacetime Maxwell-scalar models, wherein the model is fully integrable in the spherical sector, and exact solutions can be obtained, yielding an explicit mechanism to de-singularise the Coulomb field. Considering their gravitational backreaction, the corresponding (numerical) EMS solitons provide a simple example of self-gravitating, localised energy lumps. | doi | Peer Reviewed

78.  On the inexistence of self-gravitating solitons in generalised axion electrodynamics

Herdeiro, C. A. R. and Oliveira, J. M. S.

Physics Letters B


Building upon the methods used recently in [1], we establish the inexistence of self-gravitating solitonic solutions for both static and strictly stationary asymptotically flat spacetimes in generalised axion electrodynamics. This is an Einstein-Maxwell-axion model, where the axion field theta is non-minimally coupled to the electromagnetic field. Considering the standard QCD axion coupling, we first present an argument for the absence of static axionic solitons, i.e. localised energy axionic-electromagnetic configurations, yielding an everywhere regular, horizonless, asymptotically flat, static spacetime. Then, for generic couplings f(theta) and g(theta) (subject to mild assumptions) between the axion field and the electromagnetic field invariants, we show there are still no solitonic solutions, even when dropping the staticity assumption and merely requiring a strictly stationary spacetime, regardless of the spatial isometries. (C) 2019 The Author(s). Published by Elsevier B.V. | doi | Peer Reviewed

77.  Static black holes without spatial isometrics: From AdS multipoles to electrovacuum scalarization

Herdeiro, C. A. R. and Radu, E.

International Journal of Modern Physics D

World Scientific Publishing

We review recent results on the existence of static black holes (BHs) without spatial isometrics in four spacetime dimensions and propose a general framework for their study. These configurations are regular on and outside a horizon of spherical topology. Two different mechanisms allowing for their existence are identified. The first one relies on the presence of a solitonic limit of the BHs; when the solitons have no spatial isometrics, the BHs, being a nonlinear bound state between the solitons and a horizon, inherit this property. The second one is related to BH scalarization, and the existence of zero modes of the scalar field without isometrics around a spherical horizon. When the zero modes have no spatial isometrics, the back-reaction of their nonlinear continuation makes the scalarized BHs inherit the absence of spatial continuous symmetries. A number of general features of the solutions are discussed together with possible generalizations. | doi | Peer Reviewed

76.  Lensing and shadow of a black hole surrounded by a heavy accretion disk

Cunha, P. V. P. and Eiro, N. A. and Herdeiro, C. A. R. and Lemos, J. P. S.

Journal of Cosmology and Astroparticle Physics

IOP Publishing

We consider a static, axially symmetric spacetime describing the superposition of a Schwarzschild black hole (BH) with a thin and heavy accretion disk. The BH-disk configuration is a solution of the Einstein field equations within the Weyl class. The disk is sourced by a distributional energy-momentum tensor and it is located at the set of fixed points of the geometry's Z(2) symmetry, i.e., at the equatorial plane. It can be interpreted as two streams of counter-rotating particles, yielding a total vanishing angular momentum. The phenomenology of the composed system depends on two parameters: the fraction of the total mass in the disk, m, and the location of the inner edge of the disk, a. We start by determining the sub-region of the space of parameters wherein the solution is physical, by requiring the velocity of the disk particles to be sub-luminal and real. Then, we study the null geodesic flow by performing backwards ray-tracing under two scenarios. In the first scenario the composed system is illuminated by the disk and in the second scenario the composed system is illuminated by a far-away celestial sphere. Both cases show that, as m grows, the shadow becomes more prolate. Additionally, the first scenario makes clear that as m grows, for fixed a, the geometrically thin disk appears optically enlarged, i.e., thicker, when observed from the equatorial plane. This is to due to light rays that are bent towards the disk, when backwards ray traced. In the second scenario, these light rays can cross the disk (which is assumed to be transparent) and may oscillate up to a few times before reaching the far away celestial sphere. Consequently, an almost equatorial observer sees different patches of the sky near the equatorial plane, as a chaotic "mirage". Indeed, for neighbouring observation angles, different sets of oscillating light rays can end up on distinct regions of the far away sky. As m -> 0 one recovers the standard test, i.e., negligible mass, disk appearance. | doi | Peer Reviewed

75.  Stationary scalar and vector clouds around Kerr-Newman black holes

Santos, N. M. and Herdeiro, C. A. R.

International Journal of Modern Physics D

World Scientific Publishing

Massive bosons in the vicinity of Kerr-Newman black holes can form pure bound states when their phase angular velocity fulfills the synchronization condition, i.e. at the threshold of superradiance. The presence of these stationary clouds at the linear level is intimately linked to the existence of Kerr black holes with synchronized hair at the nonlinear level. These configurations are very similar to the atomic orbitals of the electron in a hydrogen atom. They can be labeled by four quantum numbers: n, the number of nodes in the radial direction; l, the orbital angular momentum; j, the total angular momentum; and m(j), the azimuthal total angular momentum. These synchronized configurations are solely allowed for particular values of the black holes mass, angular momentum and electric charge. Such quantization results in an existence surface in the three-dimensional parameter space of Kerr-Newman black holes. The phenomenology of stationary scalar clouds has been widely addressed over the last years. However, there is a gap in the literature concerning their vector cousins. Following the separability of the Proca equation in Kerr(-Newman) spacetime, this paper explores and compares scalar and vector stationary clouds around Kerr and Kerr-Newman black holes, extending previous research. | doi | Peer Reviewed

74.  Shadows of charged rotating black holes: Kerr-Newman versus Kerr-Sen

Xavier, S. V. M. C. B. and Cunha, P. V. P. and Crispino, L. C. B. and Herdeiro, C. A. R.

International Journal of Modern Physics D

World Scientific Publishing

Celebrating the centennial of its first experimental test, the theory of General Relativity (GR) has successfully and consistently passed all subsequent tests with flying colors. It is expected, however, that at certain scales new physics, in particular, in the form of quantum corrections, will emerge, changing some of the predictions of GR, which is a classical theory. In this respect, black holes (BHs) are natural configurations to explore the quantum effects on strong gravitational fields. BH solutions in the low-energy effective field theory description of the heterotic string theory, which is one of the leading candidates to describe quantum gravity, have been the focus of many studies in the last three decades. The recent interest in strong gravitational lensing by BHs, in the wake of the Event Horizon Telescope (EHT) observations, suggests comparing the BH lensing in both GR and heterotic string theory, in order to assess the phenomenological differences between these models. In this work, we investigate the differences in the shadows of two charged BH solutions with rotation: one arising in the context of GR, namely the Kerr-Newman (KN) solution, and the other within the context of low-energy heterotic string theory, the Kerr-Sen (KS) solution. We show and interpret, in particular, that the stringy BH always has a larger shadow, for the same physical parameters and observation conditions. | doi | Peer Reviewed

73.  Spinning black holes in shift-symmetric Horndeski theory

Delgado, J. F. M. and Herdeiro, C. A. R. and Radu, E.

Journal of High Energy Physics


We construct spinning black holes (BHs) in shift-symmetric Horndeski theory. This is an Einstein-scalar-Gauss-Bonnet model wherein the (real) scalar field couples linearly to the Gauss-Bonnet curvature squared combination. The BH solutions constructed are stationary, axially symmetric and asymptotically flat. They possess a non-trivial scalar field outside their regular event horizon; thus they have scalar hair. The scalar "charge" is not, however, an independent macroscopic degree of freedom. It is proportional to the Hawking temperature, as in the static limit, wherein the BHs reduce to the spherical solutions found by Sotirou and Zhou. The spinning BHs herein are found by solving non-perturbatively the field equations, numerically. We present an overview of the parameter space of the solutions together with a study of their basic geometric and phenomenological properties. These solutions are compared with the spinning BHs in the Einstein-dilaton-Gauss-Bonnet model and the Kerr BH of vacuum General Relativity. As for the former, and in contrast with the latter, there is a minimal BH size and small violations of the Kerr bound. Phenomenological differences with respect to either the former or the latter, however, are small for illustrative observables, being of the order of a few percent, at most. | Peer Reviewed

72.  Electromagnetic dual Einstein-Maxwell-scalar models

Herdeiro, C. A. R. and Oliveira, J. M. S.

Journal of High Energy Physics


Electromagnetic duality is discussed in the context of Einstein-Maxwell-scalar (EMS) models including axionic-type couplings. This family of models introduces two non-minimal coupling functionsf(phi) andg(phi), depending on a real scalar field phi. Interpreting the scalar field as a medium, one naturally defines constitutive relations as in relativistic non-linear electrodynamics. Requiring these constitutive relations to be invariant under the SO(2) electromagnetic duality rotations of Maxwell's theory, defines 1-parameter, closedduality orbitsin the space of EMS models, connecting different electromagnetic fields in "dual" models with different coupling functions, but leaving both the scalar field and the spacetime geometry invariant. This mapping works as a solution generating technique, extending any given solution of a specific model to a (different) solution for any of the dual models along the whole duality orbit. We illustrate this technique by considering the duality orbits seeded by specific EMS models wherein solitonic and black hole solutions are known. For dilatonic models, specific rotations are equivalent toS-duality. | doi | Peer Reviewed

71.  Black hole spontaneous scalarisation with a positive cosmological constant

Brihaye, Y. and Herdeiro, C. A. R. and Radu, E.

Physics Letters B


A scalar field non-minimally coupled to certain geometric [or matter] invariants which are sourced by [electro]vacuum black holes (BHs) may spontaneously grow around the latter, due to a tachyonic instability. This process is expected to lead to a new, dynamically preferred, equilibrium state: a scalarised BH. The most studied geometric [matter] source term for such spontaneous BH scalarisation is the Gauss-Bonnet quadratic curvature [Maxwell invariant]. This phenomenon has been mostly analysed for asymptotically flat spacetimes. Here we consider the impact of a positive cosmological constant, which introduces a cosmological horizon. The cosmological constant does not change the local conditions on the scalar coupling for a tachyonic instability of the scalar-free BHs to emerge. But it leaves a significant imprint on the possible new scalarised BHs. It is shown that no scalarised BH solutions exist, under a smoothness assumption, if the scalar field is confined between the BH and cosmological horizons. Admitting the scalar field can extend beyond the cosmological horizon, we construct new scalarised BHs. These are asymptotically de Sitter in the (matter) Einstein-Maxwell-scalar model, with only mild difference with respect to their asymptotically flat counterparts. But in the (geometric) extended-scalartensor-Gauss-Bonnet-scalar model, they have necessarily non-standard asymptotics, as the tachyonic instability dominates in the far field. This interpretation is supported by the analysis of a test tachyon on a de Sitter background. (C) 2020 The Authors. Published by Elsevier B.V. | doi | Peer Reviewed

70.  Einstein-Maxwell-scalar black holes: The hot, the cold and the bald

Blazquez-Salcedo, J. L. and Herdeiro, C. A. R. and Kunz, J. and Pombo, A. M. and Radu, E.

Physics Letters B


The phenomenon of spontaneous scalarisation of charged black holes (BHs) has recently motivated studies of various Einstein-Maxwell-scalar models. Within these models, different classes of BH solutions are possible, depending on the non-minimal coupling function f (phi), between the scalar field and the Maxwell invariant. Here we consider the class wherein both the (bald) electrovacuum Reissner-Nordstrom (RN) BH and new scalarised BHs co-exist, and the former are never unstable against scalar perturbations. In particular we examine the model, within this subclass, with a quartic coupling function: f (Phi)) = 1+ alpha Phi(4). The domain of existence of the scalarised BHs, for fixed alpha, is composed of two branches. The first branch (cold scalarised BHs) is continuously connected to the extremal RN BH. The second branch (hot scalarised BHs) connects to the first one at the minimum value of the charge to mass ratio and it includes overcharged BHs. We then assess the perturbative stability of the scalarised solutions, focusing on spherical perturbations. On the one hand, cold scalarised BHs are shown to be unstable by explicitly computing growing modes. The instability is quenched at both endpoints of the first branch. On the other hand, hot scalarised BHs are shown to be stable by using the S-deformation method. Thus, in the spherical sector this model possesses two stable BH local ground states (RN and hot scalarised). We point out that the branch structure of BHs in this model parallels the one of BHs in five dimensional vacuum gravity, with [Myers-Perry BHs, fat rings, thin rings] playing the role of [RN, cold scalarised, hot scalarised] BHs. (C) 2020 The Author(s). Published by Elsevier B.V. | doi | Peer Reviewed

69.  Dynamically and thermodynamically stable black holes in Einstein-Maxwell-dilaton gravity

Astefanesei, D and Blazquez-Salcedo, J. L. and Herdeiro, C. A. R. and Radu, E. and Sanchis-Gual, N.

Journal of High Energy Physics


We consider Einstein-Maxwell-dilaton gravity with the non-minimal exponential coupling between the dilaton and the Maxwell field emerging from low energy heterotic string theory. The dilaton is endowed with a potential that originates from an electromagnetic Fayet-Iliopoulos (FI) term in N = 2 extended supergravity in four spacetime dimensions. For the case we are interested in, this potential introduces a single parameter alpha. When alpha -> 0, the static black holes (BHs) of the model are the Gibbons-Maeda-Garfinkle- Horowitz-Strominger (GMGHS) solutions. When alpha -> infinity, the BHs become the standard Reissner-Nordstrom (RN) solutions of electrovacuum General Relativity. The BH solutions for finite non-zero a interpolate between these two families. In this case, the dilaton potential regularizes the extremal limit of the GMGHS solution yielding a set of zero temperature BHs with a near horizon AdS(2) x S-2 geometry. We show that, in the neighborhood of these extremal solutions, there is a subset of BHs that are dynamically and thermodynamically stable, all of which have charge to mass ratio larger than unity. By dynamical stability we mean that no growing quasi-normal modes are found; thus they are stable against linear perturbations (spherical and non-spherical). Moreover, non-linear numerical evolutions lend support to their non-linear stability. By thermodynamical stability we mean the BHs are stable both in the canonical and grand-canonical ensemble. In particular, both the specific heat at constant charge and the isothermal permittivity are positive. This is not possible for RN and GMGHS BHs. We discuss the different thermodynamical phases for the BHs in this model and comment on what may allow the existence of both dynamically and thermodynamically stable BHs. | doi | Peer Reviewed

68.  Black holes with synchronised Proca hair: linear clouds and fundamental non-linear solutions

Santos, N. M. and Benone, C. L. and Crispino, L. C. B. and Herdeiro, C. A. R. and Radu, E.

Journal of High Energy Physics


Recent studies have made key progress on the black hole/solitonic solutions of the Einstein-Proca system. Firstly, fully non-linear dynamical evolutions of the Kerr black hole superradiant instability, triggered by a Proca field, have shown the formation of a new equilibrium state, a spinning black hole with synchronised Proca hair. Secondly, non-linear evolutions of spinning Proca stars have established that they are dynamically stable, unlike their scalar cousins. Thirdly, separability of the Proca equation on the Kerr background has been achieved. Motivated by these results, in this paper we reconsider Kerr black holes with synchronised Proca hair. The separability of the Proca equation on the Kerr background allows us to examine the stationary Proca clouds in greater detail, in particular their dependence on the different quantum numbers. These stationary clouds occur at a set of existence lines in the Kerr parameter space, from which the black holes with synchronised Proca hair bifurcate. We construct the domain of existence of these black holes, comparing the fundamental states missed in the original study with the first excited states and with the cousin scalar model, giving illustrative examples of Kerr-like and non- Kerr-like BHs. In the vanishing event horizon limit, these hairy black holes connect to the fundamental states of spinning Proca stars, which include the dynamically stable solutions. | doi | Peer Reviewed

67.  Dynamical l-boson stars: Generic stability and evidence for nonspherical solutions

Jaramillo, V. and Sanchis-Gual, N. and Barranco, J. and Bernal, A. and Degollado, J. C. and Herdeiro, C. A. R. and Nunez, D.

Physical Review D

American Physical Society

l-boson stars are static, spherical, multifield self-gravitating solitons. They are asymptotically flat, finite energy solutions of Einstein's gravity minimally coupled to an odd number of massive, complex scalar fields. A previous study assessed the stability of l-boson stars under spherical perturbations, finding that there are both stable and unstable branches of solutions, as for single-field boson stars (l = 0). In this work we probe the stability of l-boson stars against nonspherical perturbations by performing numerical evolutions of the Einstein-Klein-Gordon system, with a 3D code. For the timescales explored, the l-boson stars belonging to the spherical stable branch do not exhibit measurable growing modes. We find, however, evidence of zero modes; that is, nonspherical perturbations that neither grow nor decay. This suggests the branching off toward a larger family of equilibrium solutions: we conjecture that l-boson stars are the enhanced isometry point of a larger family of static (and possibly stationary), nonspherical multifield self-gravitating solitons. | doi | Peer Reviewed

66.  Temporal constraints and device management for the Skill VRP: mathematical model and lower bounding techniques

Cappanera, Paola and Requejo, Cristina and Scutellà, Maria Grazia

Computers & Operations Research


We study a generalization of the Skill VRP that incorporates time windows aspects, precedence and synchronization constraints. Specifically, we are given a logistic network where nodes correspond to customers, and where each customer requires a set of (partially ordered) operations. A set of technicians is available to perform such operations, and each technician is qualified to execute only a subset of them, depending on his skill. By referring to a specific context such as Health Care, customers are patients while technicians are caregivers. In a Field Service context, instead, customers are usually referred to as clients while technicians as field technicians. The innovative aspect is that some operations may require a special device, which must be transported at the customer site and must be present at the customer location together with a technician qualified to use it. Given technician dependent traveling costs, we address the problem of defining the tours for the technicians and for the special device, while respecting the skill compatibility between customers and technicians, and the time windows, precedence and synchronization constraints. We propose a Mixed Integer Linear Programming (MILP) model for the generalized Skill VRP, and present some lower bounding techniques based on the proposed formulation. Preliminary computational experiments show that some lower bounding techniques may rapidly produce good lower bounds, thanks to quite effective valid inequalities. The returned percentage optimality gaps, estimated also thanks to a simple matheuristic, are in fact quite small for several scenarios of medium to large size, by encouraging the use of the proposed lower bounding techniques both as building blocks for designing exact approaches, and also as valuable tools to evaluate the efficacy of more sophisticated heuristic approaches to the problem. | doi | Peer Reviewed

65.  Efficient lower and upper bounds for the weight-constrained minimum spanning tree problem using simple Lagrangian based algorithms

Requejo, Cristina and Santos, Eulália

Operational Research


The weight-constrained minimum spanning tree problem (WMST) is a combinatorial optimization problem for which simple but effective Lagrangian based algorithms have been used to compute lower and upper bounds. In this work we present several Lagrangian based algorithms for the WMST and propose two new algorithms, one incorporates cover inequalities. A uniform framework for deriving approximate solutions to the WMST is presented. We undertake an extensive computational experience comparing these Lagrangian based algorithms and show that these algorithms are fast and present small integrality gap values. The two proposed algorithms obtain good upper bounds and one of the proposed algorithms obtains the best lower bounds to the WMST. | doi | Peer Reviewed

64.  Robust inventory theory with perishable products

Santos, Marcio Costa and Agra, Agostinho and Poss, Michael

Annals of Operations Research


We consider a robust inventory problem where products are perishable with a given shelf life and demands are assumed uncertain and can take any value in a given polytope. Interestingly, considering uncertain demands leads to part of the production being spoiled, a phenomenon that does not appear in the deterministic context. Based on a deterministic model we propose a robust model where the production decisions are first-stage variables and the inventory levels and the spoiled production are recourse variables that can be adjusted to the demand scenario following a FIFO policy. To handle the non-anticipativity constraints related to the FIFO policy, we propose a non-linear reformulation for the robust problem, which is then linearized using classical techniques. We propose a row-and-column generation algorithm to solve the reformulated model to optimality using a decomposition algorithm. Computational tests show that the decomposition approach can solve a set of instances representing different practical situations within reasonable amount of time. Moreover, the robust solutions obtained ensure low losses of production when the worst-case scenarios are materialized. | doi | Peer Reviewed

63.  Heuristics for a vehicle routing problem with information collection in wireless networks

Flores-Luyo, Luis and Agra, Agostinho and Figueiredo, Rosa and Ocaña, Eladio

Journal of Heuristics


We consider a wireless network where a given set of stations is continuously generating information. A single vehicle, located at a base station, is available to collect the information via wireless transfer. The wireless transfer vehicle routing problem (WTVRP) is to decide which stations should be visited in the vehicle route, how long shall the vehicle stay in each station, and how much information shall be transferred from the nearby stations to the vehicle during each stay. The goal is to collect the maximum amount of information during a time period after which the vehicle returns to the base station. The WTVRP is NP-hard. Although it can be solved to optimality for small size instances, one needs to rely on good heuristic schemes to obtain good solutions for large size instances. In this work, we consider a mathematical formulation based on the vehicle visits. Several heuristics strategies are proposed, most of them based on the mathematical model. These strategies include constructive and improvement heuristics. Computational experiments show that a strategy that combines a combinatorial greedy heuristic to design a initial vehicle route, improved by a fix-and-optimize heuristic to provide a local optimum, followed by an exchange heuristic, affords good solutions within reasonable amount of running time. | doi | Peer Reviewed

62.  Bending of light in axion backgrounds

McDonald, Jamie I. and Ventura, Luís B.

Physical Review D

American Physical Society

In this work we examine refraction of light by computing full solutions to axion electrodynamics. We also allow for the possibility of an additional plasma component. We then specialise to wavelengths which are small compared to background scales to determine if refraction can be described by geometric optics. In the absence of plasma, for small incidence angles relative to the optical axis, axion electrodynamics and geometric optics are in good agreement, with refraction occurring at O(g 2 aγγ). However, for rays which lie far from the optical axis, the agreement with geometric optics breaks down and the dominant refraction requires a full wave-optical treatment, occurring at O(gaγγ). In the presence of sufficiently large plasma masses, the wave-like nature of light becomes suppressed and geometric optics is in good agreement with the full theory for all rays. Our results therefore suggest the necessity of a more comprehensive study of lensing and ray-tracing in axion backgrounds, including a full account of the novel O(gaγγ) wave-optical contribution to refraction.

61.  Optical properties of dynamical axion backgrounds

McDonald, Jamie I. and Ventura, Luís B.

Physical Review D

American Physical Society

We discuss spectral distortions, time delays and refraction of light in an axion or axion-plasma background. This involves solving the full set of geodesic equations associated to the system of Hamiltonian optics, allowing us to self-consistently take into account the evolution of the momentum, frequency and position of photons. We support our arguments with analytic approximations and full numerical solutions. Remarkably, the introduction of a plasma enhances the sensitivity to axion-induced birefringence, allowing these effects to occur at linear order in the axion-photon coupling even when the axion background is not present at either the emission or detection points. This suggests a general enhancement of axion-induced birefringence when the background refractive index is different from one. | doi | Peer Reviewed

60.  Towards recognizing the light facet of the Higgs boson

Alves, Alexandre and Freitas, Felipe F.

Machine Learning: Science and Technology

IOP Publishing

The Higgs boson couplings to bottom and top quarks have been measured and agree well with the Standard Model predictions. Decays to lighter quarks and gluons, however, remain elusive. Observing these decays is essential to complete the picture of the Higgs boson interactions. In this work, we present the perspectives for the 14 TeV LHC to observe the Higgs boson decay to gluon jets assembling convolutional neural networks, trained to recognize abstract jet images constructed embodying particle flow information, and boosted decision trees with kinetic information from Higgs-strahlung ZH → ℓ +ℓ− + gg events. We show that this approach might be able to observe Higgs to gluon decays with a significance of around 2.4σ improving significantly previous prospects based on cut-and-count analysis. An upper bound of BR(H → gg)≤1.74 × BRSM (H → gg) at 95% confidence level after 3000 fb−1 of data is obtained using these machine learning techniques. | doi | Peer Reviewed

59.  Deep learnig analysis of the inverse seesaw in a 3-3-1 model at the LHC

Cogollo, D. and Freitas, F. F. and Pires, C. A. de S. and Oviedo-Torres, Yohan M. and Vasconcelos, P.

Physics Letters B


Inverse seesaw is a genuine TeV scale seesaw mechanism. In it active neutrinos with masses at eV scale requires lepton number be explicitly violated at keV scale and the existence of new physics, in the form of heavy neutrinos, at TeV scale. Therefore it is a phenomenologically viable seesaw mechanism since its signature may be probed at the LHC. Moreover it is successfully embedded into gauge extensions of the standard model as the 3-3-1 model with the right-handed neutrinos. In this work we revisit the implementation of this mechanism into the 3-3-1 model and employ deep learning analysis to probe such setting at the LHC and, as main result, we have that if its signature is not detected in the next LHC running with energy of 14 TeVs, then, the vector boson $Z^{prime}$ of the 3-3-1 model must be heavier than 4 TeVs. | doi | Peer Reviewed

58.  Developing an app to interpret chest X-rays to support the diagnosis of respiratory pathology with artificial intelligence

Elkins, Andrew and Freitas, Felipe F. and Sanz, Verónica

Journal of Medical Artificial Intelligence

AME Publishing Company

Background: Medical images, including results from X-rays, are an integral part of medical diagnosis. Their interpretation requires an experienced radiologist. One of the main problems in developing countries is access to timely medical diagnosis. Lack of investment in health care infrastructure, geographical isolation and shortage of trained specialists are common obstacles to providing adequate health care in many areas of the world. In this work we show how to build and deploy a Deep Learning computer vision application for the classification of 14 common thorax disease using X-rays images. Methods: We make use of the FAST.AI and pytorch framework to create and train the DenseNet-121 model to classify the X-ray images from the ChestX-ray14 data set which contains 112,120 frontal-view X-ray images of 30,805 unique patients. After training and validate our model we create a web-app using Heroku, this web-app can be accessed by any mobile device with internet connection. Results: We obtained 70% for detecting pneumothorax for the one-vs-all task. Meanwhile, for the multilabel-multiclass task we are able to achieve state-of-the-art accuracy with fewer epochs, reducing drastically the training time of the model. We also demonstrate the feature localization of our model by using the Grad-CAM methodologies, feature which can be useful for early diagnostic of dangerous illnesses. Conclusions: In this work we present our study of the use of machine learning techniques to identify diseases using X-ray information. We have used the new framework of Fast.AI, and imported the resulting model to an app which can be tested by any user. The app has an intuitive interface where the user can upload an image and obtain a likelihood for the given image be classified as one of the 14 labeled diseases. This classification could assist diagnosis by medical providers and broaden access to medical services to remote areas. | doi | Peer Reviewed

57.  SO(2) gauged Skyrmions in 4 + 1 dimensions

Navarro-Lérida, Francisco and Radu, Eugen and Tchrakian, D. H.

Physical Review D

American Physical Society

We study the simplest SO(2) gauged O(5) Skyrme models in 4 + 1 (flat) dimensions. In the gauge decoupled limit, the model supports topologically stable solitons (Skyrmions) and after gauging, the static energy of the solutions is bounded from below by a “baryon number”. The studied model features both Maxwell and Maxwell–Chern-Simons dynamics. The considered configurations are subject to biazimuthal symmetry in the R 4 subspace resulting in a two dimensional subsystem, as well as subject to an enhanced symmetry relating the two planes in the R 4 subspace, which results in a one dimensional subsystem. Numerical solutions are constructed in both cases. In the purely magnetic case, fully biazimuthal solutions were given, while electrically charged and spinning solutions were constructed only in the radial (enhanced symmetric) case, both in the presence of a Chern-Simons term, and in its absence. We find that, in contrast with the analogous models in 2+1 dimensions, the presence of the Chern-Simons term in the model under study here results only in quantitative effects. | doi | Peer Reviewed

56.  Gravitational Chern–Simons, and Chern–Simons gravity in all dimensions

Radu, Eugen and Tchrakian, D. H.

Physics of Particles and Nuclei Letters

Springer Verlag; MAIK Nauka/Interperiodica

The construction of Chern–Simons gravities (CSG) and gravitational Chern–Simons densities (GCS) are considered. Since both these are definied the non-Abelian (nA) Chern–Simons densities (CS) in the appropriate representations, and the latter are defined only in odd dimensions, so are the CSG and the GCS. To overcome this restriction, it is proposed that instead of employing nA CS densities, the Higgs–CS (HCS) densities are employed, the latter being defined in all dimensions and hence leading to their gravitational counterparts, HCS-Gravity (HCSG) Lagrangians and gravitational-HCS (GHCS) densities, not all of them restricted to odd dimensions. A detailed definition for a GHCS density in 3 + 1 dimensions is presented, and, a new result in black hole solutions in CSG gravity models in all odd dimensions is presented. | doi | Peer Reviewed

55.  Gravitational footprints of massive neutrinos and lepton number breaking

Addazi, Andrea and Marcianò, Antonino and Morais, António P. and Pasechnik, Roman and Srivastava, Rahul and Valle, José W. F.

Physics Letters B


We investigate the production of primordial Gravitational Waves (GWs) arising from First Order Phase Transitions (FOPTs) associated to neutrino mass generation in the context of type-I and inverse seesaw schemes. We examine both “high-scale” as well as “low-scale” variants, with either explicit or spontaneously broken lepton number symmetry U(1)L in the neutrino sector. In the latter case, a pseudo-Goldstone majoron-like boson may provide a candidate for cosmological dark matter. We find that schemes with softly-broken U(1)L and with single Higgs-doublet scalar sector lead to either no FOPTs or too weak FOPTs, precluding the detectability of GWs in present or near future measurements. Nevertheless, we found that, in the majoron-like seesaw scheme with spontaneously broken U(1)L at finite temperatures, one can have strong FOPTs and non-trivial primordial GW spectra which can fall well within the frequency and amplitude sensitivity of upcoming experiments, including LISA, BBO and u-DECIGO. However, GWs observability clashes with invisible Higgs decay constraints from the LHC. A simple and consistent fix is to assume the majoron-like mass to lie above the Higgs-decay kinematical threshold. We also found that the majoron-like variant of the low-scale seesaw mechanism implies a different GW spectrum than the one expected in the high-scale seesaw. This feature will be testable in future experiments. Our analysis shows that GWs can provide a new and complementary portal to test the neutrino mass generation mechanism. | doi | Peer Reviewed

54.  What can a heavy U(1)B−L Z 0 boson do to the muon (g − 2)µ anomaly and to a new Higgs boson mass?

Pasechnik, Roman and Morais, António P. and Rodrigues, João Pedro

Chinese Physics C

IOP Publishing

The minimal $U(1)_{B-L}$ extension of the Standard Model (B-L-SM) offers an explanation for neutrino mass generation via a seesaw mechanism as well as contains two new physics states such as an extra Higgs boson and a new $Z'$ gauge boson. The emergence of a second Higgs particle as well as a new $Z^prime$ gauge boson, both linked to the breaking of a local $U(1)_{B-L}$ symmetry, makes the B-L-SM rather constrained by direct searches at the Large Hadron Collider (LHC) experiments. We investigate the phenomenological status of the B-L-SM by confronting the new physics predictions with the LHC and electroweak precision data. Taking into account the current bounds from direct LHC searches, we demonstrate that the prediction for the muon $(g-2)_mu$ anomaly in the B-L-SM yields at most a contribution of approximately $8.9 times 10^{-12}$ which represents a tension of $3.28$ standard deviations, with the current $1sigma$ uncertainty, by means of a $Z^prime$ boson if its mass lies in a range of $6.3$ to $6.5$ TeV, within the reach of future LHC runs. This means that the B-L-SM, with heavy yet allowed $Z^prime$ boson mass range, in practice does not resolve the tension between the observed anomaly in the muon $(g-2)_mu$ and the theoretical prediction in the Standard Model. Such a heavy $Z^prime$ boson also implies that the minimal value for a new Higgs mass is of the order of 400 GeV. | doi | Peer Reviewed

53.  How low-scale trinification sheds light in the flavor hierarchies, neutrino puzzle, dark matter, and leptogenesis

Cárcamo Hernández, A. E. and Huong, D. T. and Kovalenko, Sergey and Morais, António and Pasechnik, Roman and Schmidt, Ivan

Physical Review D

American Physical Society

We propose a low-scale renormalizable trinification theory that successfully explains the flavor hierarchies and neutrino puzzle in the Standard Model (SM), as well as provides a dark matter candidate and also contains the necessary means for efficient leptogenesis. The proposed theory is based on the trinification SUð3ÞC × SUð3ÞL × SUð3ÞR gauge symmetry, which is supplemented with an additional flavor symmetry Uð1ÞX × Zð1Þ 2 × Zð2Þ2 . In the proposed model the top quark and the exotic fermions acquire tree-level masses, whereas the lighter SM charged fermions gain masses radiatively at one-loop level. In addition, the light active neutrino masses arise from a combination of radiative and type-I seesaw mechanisms, with the Dirac neutrino mass matrix generated at one-loop level | doi | Peer Reviewed

52.  Anomalies in B-meson decays and the muon g-2 from dark loops

Huang, Da and Morais, António P. and Santos, Rui

Physical Review D

American Physical Society

We explore a class of models which can provide a common origin for the recently observed evidence for lepton flavor universality violation in b→sl+l- decays, the dark matter (DM) problem, and the long-standing muon (g-2) anomaly. In particular, both anomalies in the B meson decays and the muon (g-2) can be explained by the additional one-loop diagrams with DM candidates. We first classify several simple models according to the new fields' quantum numbers. We then focus on a specific promising model and perform a detailed study of both DM and flavor physics. A random scan over the relevant parameter space reveals that there is indeed a large parameter space which can explain the three new physics phenomena simultaneously, while satisfying all other flavor and DM constraints. Finally, we discuss some of the possible new physics signatures at the Large Hadron Collider | doi | Peer Reviewed

51.  A note on Newton's problem of minimal resistance for convex bodies

Plakhov, Alexander

Calculus of Variations and Partial Differential Equations


We consider the following problem: minimize the functional f (∇u(x)) dx in the class of concave functions u : D → [0, M], where D ⊂ R2 is a convex body and M > 0. If f (x) = 1/(1 + |x|^2) and D is a circle, the problem is called Newton’s problem of least resistance. It is known that the problem admits at least one solution. We prove that if all points of ∂D are regular and (1 + |x|) f (x)/(|y| f (y)) → +∞ as (1 + |x|)/|y| → 0 then a solution u to the problem satisfies u|_∂D = 0. This result proves the conjecture stated in 1993 in the paper by Buttazzo and Kawohl (Math Intell 15:7–12, 1993) for Newton’s problem. | doi | Peer Reviewed

50.  Optimal impulse control of a SIR epidemic

Piunovskiy, Alexey and Plakhov, Alexander and Tumanov, Mikhail

Optimal Control Applications and Methods

John Wiley and Sons; Wiley

Based on our recent results on the optimal impulse control, we solve explicitly an optimal isolation problem for a specific SIR (susceptible-infective-removed) epidemic model describing, eg, the spread of AIDS. | doi | Peer Reviewed

49.  Tidal Love numbers of Proca stars

Herdeiro, Carlos A. R. and Panotopoulos, Grigoris and Radu, Eugen

Journal of Cosmology and Astroparticle Physics

IOP Publishing; International School for Advanced Studies (SISSA)

Proca stars [1] are everywhere regular, asymptotically flat self-gravitating solitons composed of complex, massive vector bosons, forming a macroscopic, star-sized, Bose-Einstein condensate. They have been suggested as a classical, dynamical model of exotic compact objects, black hole mimickers and dark matter candidates. In spherical symmetry, they are qualitatively similar to their scalar cousins, the standard (scalar) boson stars in all respects studied so far. Here we study the tidal deformability and the quadrupolar tidal Love numbers, both electric-type and magnetic-type, of spherically symmetric Proca stars. The equations for the perturbations are derived and the numerical values of the Love numbers for some concrete background solutions are computed. We observe that both Love numbers are qualitatively similar to the ones of the scalar boson stars; in particular, the electric-type (magnetic-type) quadrupolar Love numbers are positive (negative) for Proca stars. Quantitatively, for the same compactness, the electric and magnetic Love numbers in the Proca case are closer (in magnitude) than in the scalar case, with the electric Love numbers having a slightly larger magnitude than the magnetic ones. | doi | Peer Reviewed

48.  Spinning black holes with a separable Hamilton–Jacobi equation from a modified Newman–Janis algorithm

Junior, Haroldo C. D. Lima and Crispino, Luís C. B. and Cunha, Pedro V. P. and Herdeiro, Carlos A. R.

The European Physical Journal C

EDP Sciences; Società Italiana di Fisica; Springer Verlag

Obtaining solutions of the Einstein field equations describing spinning compact bodies is typically challenging. The Newman–Janis algorithm provides a procedure to obtain rotating spacetimes from a static, spherically symmetric, seed metric. It is not guaranteed, however, that the resulting rotating spacetime solves the same field equations as the seed. Moreover, the former may not be circular, and thus expressible in Boyer–Lindquist-like coordinates. Amongst the variations of the original procedure, a modified Newman–Janis algorithm (MNJA) has been proposed that, by construction, originates a circular, spinning spacetime, expressible in Boyer–Lindquist-like coordinates. As a down side, the procedure introduces an ambiguity, that requires extra assumptions on the matter content of the model. In this paper we observe that the rotating spacetimes obtained through the MNJA always admit separability of the Hamilton–Jacobi equation for the case of null geodesics, in which case, moreover, the aforementioned ambiguity has no impact, since it amounts to an overall metric conformal factor. We also show that the Hamilton–Jacobi equation for light rays propagating in a plasma admits separability if the plasma frequency obeys a certain constraint. As an illustration, we compute the shadow and lensing of some spinning black holes obtained by the MNJA. | doi | Peer Reviewed

47.  Synchronized gravitational atoms from mergers of bosonic stars

Sanchis-Gual, Nicolas and Zilhão, Miguel and Herdeiro, Carlos and Di Giovanni, Fabrizio and Font, José A. and Radu, Eugen

Physical Review D

American Physical Society

If ultralight bosonic fields exist in nature as dark matter, superradiance spins down rotating black holes (BHs), dynamically endowing them with equilibrium bosonic clouds, here dubbed synchronized gravitational atoms (SGAs). The self-gravity of these same fields, on the other hand, can lump them into (scalar or vector) horizonless solitons known as bosonic stars (BSs). We show that the dynamics of BSs yield a new channel forming SGAs. We study BS binaries that merge to form spinning BHs. After horizon formation, the BH spins up by accreting the bosonic field, but a remnant lingers around the horizon. If just enough angular momentum is present, the BH spin up stalls precisely as the remnant becomes a SGA. Different initial data lead to SGAs with different quantum numbers. Thus, SGAs may form both from superradiance-driven BH spin down and accretion-driven BH spin up. The latter process, moreover, can result in heavier SGAs than those obtained from the former: in one example herein, ∼ 18 % of the final system’s energy and ∼ 50 % of its angular momentum remain in the SGA. We suggest that even higher values may occur in systems wherein both accretion and superradiance contribute to the SGA formation. | doi | Peer Reviewed

46.  Circular economy in plastic waste: efficiency analysis of European countries

Robaina, Margarita and Murillo, Kelly and Rocha, Eugénio and Villar, José

Science of the Total Environment


The way plastics are currently produced, used and disposed does not capture the economic benefits of a more 'circular' approach and is dramatically harming the environment. It is relevant to determine which European countries can be considered more or less efficient in the end-of-life of plastic products processes, what the sources of the inefficiencies are, and how those less efficient countries could improve their performance towards a more circular economy. Although some countries have developed a variety of quantitative indicators, there is scarcity of adequate metrics for performance measurements. This paper estimates the efficiency of 26 European countries in the context of Circular Economy, for the period 2006-2016, considering the generation of waste, recovery and recycling of plastic, with a methodology based on the Multidirectional Efficiency Analysis. Apart from identifying the most efficient countries in the studied period, results show that efficiency increases for most countries with time, and that many countries reach the full efficiency by the end of the study period, and especially by 2016. Input analysis shows that increasing capital seems to be a main driver towards efficiency, since the other inputs are used with a similar efficiency by most countries. Output analysis suggest that the difference among countries efficiency is not in their reduction of total waste or emissions, but rather in the improvement of their economic growth in a circular way, that is, improving GDP but also the recovering and recycling activities. These results could be useful to design policies towards a more efficient and circular use of plastics. | doi | Peer Reviewed

45.  Factors influencing the economic behavior of the food, beverages and tobacco industry: a case study for Portuguese enterprises

Murillo, Kelly P. and Rocha, Eugénio M.

World Journal of Applied Economics

World Economic Research Institute (WERI)

In today's world, it is increasingly important to conduct economic and financial analyzes of enterprises in all sectors to determine strengths, identify weaknesses and adopt strategies that allow them to be at the highest competitive level. In particular, the food sector plays an essential role in the economy of any country, representing a significant contribution to gross domestic product, total employment, and disposable income of households. In this work, we adopt a methodology for measuring efficiency based on the multidirectional efficiency analysis and other mathematical techniques (the calculation of the normal distribution intersection coefficient (NC value), analysis of clusters and principal components, and model fitting) in order to examine the factors that influence the performance of Portuguese enterprises in the food, beverages and tobacco industry for the period of 2006-2013. The results show a characterization of the financial structure of the sector and diagnosis through indexes that identify the strategic positioning of the enterprises in terms of efficiency scores. In addition, we also show that an analysis of the variables that must be approached differently to obtain better results regarding economic performance. Although there is an increase in credit with the acquisition of long-term debts, there is no evidence that this implies the ability of enterprises to grow faster, which affects profitability. | doi | Peer Reviewed

44.  Complete j-MDP convolutional codes

Almeida, Paulo J. and Lieb, Julia

IEEE Transactions on Information Theory


Maximum distance profile (MDP) convolutional codes have been proven to be very suitable for transmission over an erasure channel. In addition, the subclass of complete MDP convolutional codes has the ability to restart decoding after a burst of erasures. However, there is a lack of constructions of these codes over fields of small size. In this paper, we introduce the notion of complete j-MDP convolutional codes, which are a generalization of complete MDP convolutional codes, and describe their decoding properties. In particular, we present a decoding algorithm for decoding erasures within a given time delay T and show that complete T-MDP convolutional codes are optimal for this algorithm. Moreover, using a computer search with the MAPLE software, we determine the minimal binary and non-binary field size for the existence of (2, 1, 2) complete j-MDP convolutional codes and provide corresponding constructions. We give a description of all (2, 1, 2) complete MDP convolutional codes over the smallest possible fields, namely F13 and F16 and we also give constructions for (2, 1, 3) complete 4-MDP convolutional codes over F128 obtained by a randomized computer search. | doi | Peer Reviewed

43.  A new compartmental epidemiological model for COVID-19 with a case study of Portugal

Lemos-Paião, Ana P. and Silva, Cristiana J. and Torres, Delfim F. M.

Ecological Complexity


We propose a compartmental mathematical model for the spread of the COVID-19 disease, showing its usefulness with respect to the pandemic in Portugal, from the first recorded case in the country till the end of the three states of emergency. New results include the compartmental model, described by a system of seven ordinary differential equations; proof of positivity and boundedness of solutions; investigation of equilibrium points and their stability analysis; computation of the basic reproduction number; and numerical simulations with official real data from the Portuguese health authorities. Besides completely new, the proposed model allows to describe quite well the spread of COVID-19 in Portugal, fitting simultaneously not only the number of active infected individuals but also the number of hospitalized individuals, respectively with a $L^2$ error of $9.2152e-04$ and $1.6136e-04$ with respect to the initial population. Such results are very important, from a practical point of view, and far from trivial from a mathematical perspective. Moreover, the obtained value for the basic reproduction number is in agreement with the one given by the Portuguese authorities at the end of the emergency states. | doi | Peer Reviewed

42.  An adaptive bolus calculator to minimize the impact of inaccurate insulin to carbohydrate ratio

Miranda, Francisco and Abreu, Carlos and Felgueiras, Paula

AIP Conference Proceedings

AIP Publishing

Patients with type 1 diabetes mellitus use intensive insulin therapy to suppress their insulin needs and avoid the adverse consequences of chronic hyperglycemia. Intensive insulin therapy consists of a combination of basal insulin and bolus insulin. While the basal insulin dose is periodically adjusted in collaboration with the healthcare team, patients have to estimate the bolus insulin dose by themselves, before each meal. To accurately estimate the bolus insulin dose, patients must know the carbohydrates content of each meal and their insulin to carbohydrate ratio. The insulin to carbohydrate ratio is initially calculated by experienced diabetologists using high-quality data. However, regarding the glucose complex metabolism, it varies over the day due to several factors. Consequently, daily, patients use approximate values to estimate their bolus insulin. Thus, depending on the error of the insulin to carbohydrate ratio estimates, the patient could experience hypo or hyperglycemic events. Therefore, to avoid the consequences of inaccurate bolus insulin and to improve the patient's glycemic control, this work presents an adaptive insulin bolus calculator that uses the patient's glycemic data to dynamically adjust the mealtime bolus and compensate for the adverse effects of inaccurate insulin to carbohydrate ratio estimates. | doi | Peer Reviewed

41.  Assessing the impact of inaccurate insulin-to-carbohydrate ratio on the patient's glycemic targets and lifestyle management

Miranda, Francisco and Abreu, Carlos and Felgueiras, Paula

AIP Conference Proceedings

AIP Publishing

To mitigate the adverse consequences of chronic hyperglycemia, patients with type 1 diabetes mellitus must provide their bodies with insulin to control their blood glucose. In most cases, insulin therapy consists of a combination of basal insulin and bolus insulin, the so-called basal-bolus insulin therapy. To determine the bolus insulin, patients must know not only the carbohydrate content of each meal but also the values of the insulin-to-carbohydrate ratio and the insulin sensitivity factor. Although important, the blood glucose complex dynamics make determining these parameters a difficult and error-prone task, usually performed by experienced diabetologists using high-quality data. Moreover, the insulin-to-carbohydrate ratio and the insulin sensitivity factor vary over the day due to several factors. Thus, daily, patients use approximate values to determine their prandial bolus. In this paper, we propose an analytic method to find the safe maximum interval for the error in the estimates of the insulin-to-carbohydrate ratio and, therefore, avoid dysglycemia. Our study suggests that slimmer patients with smaller insulin-to-carbohydrate ratios need to be more careful when estimating it. Another significant finding of our work is that in such cases, having small meals reduces the adverse effect of inaccurate insulin-to-carbohydrate ratio estimates in the postprandial blood glucose. | doi | Peer Reviewed

40.  Theoretical simulation of different 3D separator geometries for lithium-ion batteries

Miranda, D. and Gonçalves, R. and Miranda, F. and Almeida, A. M. and Costa, C. M. and Lanceros-Méndez, S.

AIP Conference Proceedings

AIP Publishing

The battery separator is an essential component of batteries and affects their cycling performance. In this work, the effect of different 3D geometries of the battery separator on battery performance was studied keeping the same volume. It was observed that the different geometries affect the cycling performance, the best geometry being the perforated one that cycled up to 90 C. The cycling performance is affected by parameters such as the separator thickness and the electrolyte volume. Through the control of the battery separator geometry it is possible to obtain high performance lithium-ion batteries. | doi | Peer Reviewed

39.  Preface of the “5th Symposium on Modelling and Simulation in Computer Sciences and Engineering”

Miranda, Francisco and Abreu, Carlos and Miranda, Daniel

AIP Conference Proceedings

AIP Publishing

The 5th Symposium on Modelling and Simulation in Computer Sciences and Engineering was held in the 17th International Conference of Numerical Analysis and Applied Mathematics (ICNAAM 2019), Rhodes, Greece, 23-28 September 2019. | doi | Peer Reviewed

38.  Cone geometry optimization and thermal behavior for lithium-ion battery separators

Miranda, D. and Gonçalves, R. and Miranda, F. and Vilhena, E. and Lanceros-Méndez, S. and Costa, C. M.

AIP Conference Proceedings

AIP Publishing

A 3D cone separator geometry for lithium-ion batteries has been optimized taking into account the increase of radius size of one side. Theoretical simulations have been carried out for evaluating the influence of radius size in the cone structure at different discharge rates (1 C and 60 C) in which it was also determined the produced ohmic heat. The value of the discharge capacity in the cone structure depends on the increases of the radius, which is correlated with the electrolyte volume and interface between free electrolyte/cathode. The optimum balance of these parameters is essential for obtaining higher battery performance through this geometry that can be used in the next generation of lithium-ion batteries. | doi | Peer Reviewed

37.  Dynamical bar-mode instability in spinning bosonic stars

Di Giovanni, Fabrizio and Sanchis-Gual, Nicolas and Cerdá-Durán, Pablo and Zilhão, Miguel and Herdeiro, Carlos and Font, José A. and Radu, Eugen

Physical Review D

American Physical Society

Spinning bosonic stars (SBSs) can form from the gravitational collapse of a dilute cloud of scalar/Proca particles with nonzero angular momentum, via gravitational cooling. The scalar stars are, however, transient due to a nonaxisymmetric instability which triggers the loss of angular momentum. By contrast, no such instability was observed for the fundamental ( m = 1 ) Proca stars. In [N. Sanchis-Gual et al., Phys. Rev. Lett. 123, 221101 (2019)] we tentatively related the different stability properties to the different toroidal/spheroidal morphology of the scalar/Proca models. Here, we continue this investigation, using three-dimensional numerical-relativity simulations of the Einstein-(massive, complex)Klein-Gordon system and of the Einstein-(complex)Proca system. First, we incorporate a quartic self-interaction potential in the scalar case to gauge its effect on the instability. Second, we investigate toroidal ( m = 2 ) Proca stars to assess their stability. Third, we attempt to relate the instability of SBSs to the growth rate of azimuthal density modes and the existence of a corotation point in the unstable models. Our results indicate that: (a) the self-interaction potential can only delay the instability in scalar SBSs but cannot quench it completely; (b) m = 2 Proca stars always migrate to the stable m = 1 spheroidal family; (c) unstable m = 2 Proca stars and m = 1 scalar boson stars exhibit a pattern of frequencies for the azimuthal density modes which crosses the angular velocity profile of the stars in the corotation point. This establishes a parallelism with rotating neutron stars affected by dynamical bar-mode instabilities. Finally, we compute the gravitational waves emitted by SBSs due to the nonaxisymmetric instability. We investigate the detectability of the waveforms comparing the characteristic strain of the signal with the sensitivity curves of a variety of detectors, computing the signal-to-noise ratio for different ranges of masses and for different source distances. Moreover, by assuming that the characteristic damping timescale of the bar-like deformation in SBSs is only set by gravitational-wave emission and not by viscosity (unlike in neutron stars), we find that the postcollapse emission could be orders of magnitude more energetic than that of the bar-mode instability itself. Our results indicate that gravitational-wave observations of SBSs might be within the reach of future experiments, offering a potential means to establish the existence of such stars and to place tight constraints on the mass of the bosonic particle. | doi | Peer Reviewed

36.  Spectral properties of the n-Queens' graphs

Cardoso, Domingos M. and Costa, Inês Serôdio and Duarte, Rui


The n-Queens’ graph, Q(n), is the graph associated to the n×n chessboard (a generalization of the classical 8×8 chessboard), with n 2 vertices, each one corresponding to a square of the chessboard. Two vertices of Q(n) are adjacent if and only if they are in the same row, in the same column or in the same diagonal of the chessboard. After a short overview on the main combinatorial properties of Q(n), its spectral properties are investigated. First, a lower bound on the least eigenvalue of an arbitrary graph is obtained using clique edge partitions and a sufficient condition for this lower bound be attained is deduced. For the particular case of Q(n), we prove that for every n, its least eigenvalue is not less than −4 and it is equal to −4 with multiplicity (n − 3)2 , for every n ≥ 4. Furthermore, n − 4 is also an eigenvalue of Q(n), with multiplicity at least n−2 2 when n is even and at least n+1 2 when n is odd. A conjecture about the integer eigenvalues of Q(n) is presented. We finish this article with an algorithm to determine an equitable partition of the n-Queens’ graph, Q(n), for n ≥ 3, concluding that such equitable partition has (⌈n/2⌉+1)⌈n/2⌉ 2 cells.

35.  Asymptotically flat, spherical, self-interacting scalar, Dirac and Proca stars

Herdeiro, Carlos A. R. and Radu, Eugen



We present a comparative analysis of the self-gravitating solitons that arise in the Einstein–Klein–Gordon, Einstein–Dirac, and Einstein–Proca models, for the particular case of static, spherically symmetric spacetimes. Differently from the previous study by Herdeiro, Pombo and Radu in 2017, the matter fields possess suitable self-interacting terms in the Lagrangians, which allow for the existence of Q-ball-type solutions for these models in the flat spacetime limit. In spite of this important difference, our analysis shows that the high degree of universality that was observed by Herdeiro, Pombo and Radu remains, and various spin-independent common patterns are observed. | doi | Peer Reviewed

34.  Higgs–Chern–Simons Gravity Models in d = 2n + 1 Dimensions

Radu, Eugen and Tchrakian, D. H.



We consider a family of new Higgs–Chern–Simons (HCS) gravity models in 2n+1 dimensions (n=1,2,3). This provides a generalization of the (usual) gravitational Chern–Simons (CS) gravities resulting from non-Abelian CS densities in all odd dimensions, which feature vector and scalar fields, in addition to the metric. The derivation of the new HCS gravitational (HCSG) actions follows the same method as in the usual-CSG case resulting from the usual CS densities. The HCSG result from the HCS densities, which result through a one-step descent of the Higgs–Chern–Pontryagin (HCP), with the latter being descended from Chern-Pontryagin (CP) densities in some even dimension. A preliminary study of the solutions of these models is considered, with exact solutions being reported for spacetime dimensions d=3,5. | doi | Peer Reviewed

33.  Preservation of certain vanishing properties of generalized Morrey spaces by some classical operators

Alabalik, Aysegul Ç. and Almeida, Alexandre and Samko, Stefan

Mathematical Methods in the Applied Sciences


We show that certain vanishing properties defining closed subspaces of generalized Morrey spaces are preserved under the action of various classical operators of harmonic analysis, such as maximal operators, singular-type operators, Hardy operators, and fractional integral operators. Those vanishing subspaces were recently used to deal with the delicate problem on the description of the closure of nice functions in Morrey norm. | doi | Peer Reviewed

32.  A comprehensive analysis of age and gender effects in European Portuguese oral vowels

Albuquerque, Luciana and Oliveira, Catarina and Teixeira, António and Sá-Couto, Pedro and Figueiredo, Daniela

Journal of Voice


The knowledge about the age effects in speech acoustics is still disperse and incomplete. This study extends the analyses of the effects of age and gender on acoustics of European Portuguese (EP) oral vowels, in order to complement initial studies with limited sets of acoustic parameters, and to further investigate unclear or inconsistent results. A database of EP vowels produced by a group of 113 adults, aged between 35 and 97, was used. Duration, fundamental frequency (f0), formant frequencies (F1 to F3), and a selection of vowel space metrics (F1 and F2 range ratios, vowel articulation index [VAI] and formant centralization ratio [FCR]) were analyzed. To avoid the arguable division into age groups, the analyses considered age as a continuous variable. The most relevant age-related results included: vowel duration increase in both genders; a general tendency to formant frequencies decrease for females; changes that were consistent with vowel centralization for males, confirmed by the vowel space acoustic indexes; and no evidence of F3 decrease with age, in both genders. This study has contributed to knowledge on aging speech, providing new information for an additional language. The results corroborated that acoustic characteristics of speech change with age and present different patterns between genders. | doi | Peer Reviewed

31.  The effect of an exercise intervention program on bone health after bariatric surgery: a randomized controlled trial

Diniz-Sousa, Florêncio and Veras, Lucas and Boppre, Giorjines and Sá-Couto, Pedro and Devezas, Vítor and Santos-Sousa, Hugo and Preto, John and Vilas-Boas, João Paulo and Machado, Leandro and Oliveira, José and Fonseca, Hélder

Journal of Bone and Mineral Research

Wiley; American Society for Bone and Mineral Research

Exercise has been suggested as a therapeutic approach to attenuate bone loss induced by bariatric surgery (BS), but its effectiveness remains unclear. Our aim was to determine if an exercise-training program could induce benefits on bone mass after BS. Eighty-four patients, submitted to gastric bypass or sleeve gastrectomy, were randomized to either exercise (EG) or control group (CG). One month post-BS, EG underwent a 11-month supervised multicomponent exercise program, while CG received only standard medical care. Patients were assessed before BS and at 1, 6, and 12 months post-BS for body composition, areal bone mineral density (BMD), bone turnover markers, calciotropic hormones, sclerostin, bone material strength index, muscle strength, and daily physical activity. A primary analysis was conducted according to intention-to-treat principles and the primary outcome was the between-group difference on lumbar spine BMD at 12 months post-BS. A secondary analysis was also performed to analyze if the exercise effect depended on training attendance. Twelve months post-BS, primary analysis results revealed that EG had a higher BMD at lumbar spine (+0.024 g∙cm-2 [95% confidence interval (CI) 0.004, 0.044]; p = .015) compared with CG. Among total hip, femoral neck, and 1/3 radius secondary outcomes, only 1/3 radius BMD improved in EG compared with CG (+0.013 g∙cm-2 [95% CI 0.003, 0.023]; p = .020). No significant exercise effects were observed on bone biochemical markers or bone material strength index. EG also had a higher lean mass (+1.5 kg [95% CI 0.1, 2.9]; p = .037) and higher number of high impacts (+51.4 [95% CI 6.6, 96.1]; p = .026) compared with CG. In addition, secondary analysis results suggest that exercise-induced benefits may be obtained on femoral neck BMD but only on those participants with ≥50% exercise attendance compared with CG (+5.3% [95% CI 2.0, 8.6]; p = .006). Our findings suggest that an exercise program is an effective strategy to ameliorate bone health in post-BS patients. © 2020 American Society for Bone and Mineral Research (ASBMR). | doi | Peer Reviewed

30.  Nursing workload assessment in an intensive care unit: a 5-year retrospective analysis

Simões, João Lindo and SáCouto, Pedro and Simões, Carlos Jorge and Oliveira, Cátia and Santos, Neuza Maia dos and Mateus, José and Magalhães, Carlos and Martins, Matilde

Journal of Clinical Nursing


Aims: To study the correlation between the workload of intensive care nursing teams and the sociodemographic, anthropometric and clinical characteristics of patients in critical condition in a Portuguese Intensive Care Unit (ICU) during a 5‐year period. Background: Currently, indices of nursing workload quantification are one of the resources used for planning and evaluating ICUs. Evidence shows that there are several factors related to critical patients and their hospitalisation which potentially influence the nursing workload. Design: Retrospective cohort analysis of a health record database from adult patients admitted to a Portuguese ICU between January 1, 2015, and December 31, 2019. Methods: Simplified Therapeutic Intervention Scoring System (TISS‐28) scores of 730 adult patients. Three TISS‐28 assessments were considered: first assessment, last assessment and average. The STROBE guidelines were used in reporting this study. Results: The TISS‐28 has an average of 34.2 ± 6.9 points at admission, which is considered a high nursing workload. A somewhat lower result was found for the discharge and average assessments. It shows that basic activities accounted for the highest percentage of time spent (38.0%), followed by the cardiovascular support category (26.5%). The TISS‐28 shows consistent results throughout the study period, despite a small trend reduction in the last 2 years. Conclusions: Lower workloads were found for age ≤ 44 years and with a shorter length of stay. Higher workload was more probable in patients classified in Cullen Class IV (OR = 2.5) and with a normal to higher weight percentile (OR = 1.9 and 1.5, respectively). Relevance to clinical practice: Knowledge of the factors influencing the nursing workload facilitates the implementation of rules to improve performance in nursing interventions, based on the redefinition of care priorities, increased productivity, human resources management and reduction of additional costs to the organisation, related to possible adverse events, among others. | doi | Peer Reviewed

29.  Effects of a short health education intervention on physical activity, arterial stiffness and cardiac autonomic function in individuals with moderate-to-high cardiovascular risk

Bohn, Lucimére and Sá-Couto, Pedro and Castro, Ana Ramoa and Ribeiro, Fernando and Oliveira, José

Patient Education and Counseling


Objective: This study evaluated the effects of a short health education and counseling intervention program, in a primary healthcare setting, on daily physical activity (PA), arterial stiffness, and cardiac autonomic function in individuals with moderate-to-high risk of cardiovascular disease. Methods: This was a parallel-group study with a 4-month-long intervention, plus 8 months of follow-up. 164 individuals with moderate-to-high cardiovascular risk were allocated to either an intervention (n = 87) or a control group (n = 77). The intervention consisted of 3 walking and face-to-face group sessions plus text messages. Primary outcome was daily PA (sedentary time, light and moderate-to-vigorous PA, all in min/day); secondary outcomes were arterial stiffness i.e., carotid-femoral pulse wave velocity (cfPWV, m/s)] and cardiac autonomic function [(i.e., standard deviation of all N-N intervals (SDNN, ms) and absolute high frequency (HF, ms2)]. Results: There were not significant group*time interactions for sedentary time [−7.4 (7.6); p = 0.331)], light PA [4.4 (6.4); p = 0.491] or moderate-to-vigorous PA [0.1 (2.6); p = 0.938]. Considering secondary outcomes, there were not significant group*time interactions for cfPWV [0.09 (0.18); p = 0.592], Ln_SDNN [0.09 (0.06); p = 0.148], or Ln_HF [0.16 (0.14); p = 0.263]. Conclusion: The program did not improve daily PA, arterial stiffness, or the autonomic cardiac function. Practice Implications: Primary care staff should consider longer or other types of intervention to improve daily PA. | doi | Peer Reviewed

28.  Simulation of image-guided intervention in medical imaging education

Carramate, Lara F. N. D. and Rodrigues, Alexandre and Simões, João Lindo and Sá-Couto, Pedro and Pereira, Rui M. and Pinto, Serafim and Francesco, Silvia de

Journal of Medical Imaging and Radiation Sciences


Introduction/Background: Medical imaging education programs across Europe, despite their variability, include clinical practice as a guarantee of quality because learning in a clinical context is more effective and allows for constructive qualification of students. Learning in a clinical simulation context is a strategy to promote simulated clinical experience and assure patient safety. In this work, a learning experience, consisting of simulating a pacemaker implantation, implemented over 3 years with students pursuing the Medical Imaging and Radiotherapy degree at the University of Aveiro was evaluated. Methods: A pacemaker implantation simulation with fluoroscopic support was performed with students (third year) pursuing the Medical Imaging and Radiotherapy degree at the Simulation Centre of our institution over 3 years (2016, 2017–2018), addressing all the simulation phases. An operating theater, video recording system, high-fidelity full-body manikin with remote control and monitoring, anesthesia, and fluoroscopic C-arm imaging equipment were used for the simulation. After the simulation activity, students completed a questionnaire evaluated the importance of this learning experience for their educational process. Results: Overall, the mean score results were consistent, even considering the three independent groups (one for each academic year). Students considered this experience valuable for their education, strongly agreeing that the simulation environment helped their learning process and allowed them to acquire, consolidate, and deepen knowledge. Furthermore, they considered that it impressed on them the necessity to continue to improve their learning, and that they would like to participate in other simulation scenarios. Discussion/Conclusion: This simulation activity was a valuable experience for the learning process of the students because it facilitated the acquisition and consolidation of knowledge. It also allowed the students to be aware of the importance of being engaged in their own education. The results were highly consistent over the 3 years, reinforcing the positive feedback from this experience. | doi | Peer Reviewed

27.  Perceção de estudantes de Matemática sobre a aprendizagem a distância: um caso de estudo no contexto da pandemia COVID-19

Freitas, Adelaide and Neves, António Jorge and Carvalho, Paula

Indagatio Didactica

Centro de Investigação Didática e Tecnologia na Formação de Formadores (CIDTFF/UA)

Como consequência da pandemia COVID-19, foram suspensas, em 16 de março de 2020, todas as atividades presenciais nas instituições de ensino em Portugal, obrigando a alterações abruptas nas metodologias de ensino e de aprendizagem. Emergente desta realidade, importa conhecer experiências de ensino e de aprendizagem vivenciadas por professores e estudantes. O presente trabalho foca-se num caso de estudo: um grupo de estudantes universitários inscritos no ano letivo de 2019/2020 na Licenciatura em Matemática de uma Instituição de Ensino Superior (IES) pública. Tem como objetivo analisar a perceção de estudantes de Matemática sobre a sua aprendizagem a distância (online) que lhes foi exigida, com adaptação a novos métodos de ensino a distância, aquisição de novos processos de aprendizagem e hábitos de trabalho, entre outras mudanças, no contexto da primeira vaga da pandemia COVID-19. Para o efeito, foi elaborado um questionário para recolha de informação e, com ele, aplicado um inquérito a todos os estudantes de Matemática inscritos naquela IES. Neste artigo, descrevem-se e analisam-se as respostas dos estudantes que, de forma anónima, participaram no inquérito. Uma análise quantitativa descritiva dessas respostas mostra que, apesar de, na sua maioria, estes estudantes manifestarem preferência por um ensino maioritariamente presencial, também reportam aspetos positivos do ensino a distância, tais como, a interação entre estudantes promovida por atividades em grupo. Não obstante, são refletidos aspetos menos positivos, nomeadamente, ser menos eficaz na esperada interação aluno-professor, assim como na criação de um ambiente favorável à sua participação no processo de aprendizagem. | doi | Peer Reviewed

26.  Immobile indices and CQ-free optimality criteria for linear copositive programming problems

Kostyukova, O. I. and Tchemisova, T. V. and Dudina, O. S.

Set-Valued and Variational Analysis


We consider problems of linear copositive programming where feasible sets consist of vectors for which the quadratic forms induced by the corresponding linear matrix combinations are nonnegative over the nonnegative orthant. Given a linear copositive problem, we define immobile indices of its constraints and a normalized immobile index set. We prove that the normalized immobile index set is either empty or can be represented as a union of a finite number of convex closed bounded polyhedra. We show that the study of the structure of this set and the connected properties of the feasible set permits to obtain new optimality criteria for copositive problems. These criteria do not require the fulfillment of any additional conditions (constraint qualifications or other). An illustrative example shows that the optimality conditions formulated in the paper permit to detect the optimality of feasible solutions for which the known sufficient optimality conditions are not able to do this. We apply the approach based on the notion of immobile indices to obtain new formulations of regularized primal and dual problems which are explicit and guarantee strong duality. | doi | Peer Reviewed

25.  CQ-free optimality conditions and strong dual formulations for a special conic optimization problem

Kostyukova, Olga and Tchemisova, Tatiana

Statistics, Optimization & Information Computing

International Academic Press

In this paper, we consider a special class of conic optimization problems, consisting of set-semidefinite (orK-semidefinite) programming problems, where the setKis a polyhedral convex cone. For these problems, we introduce theconcept of immobile indices and study the properties of the set of normalized immobile indices and the feasible set. Thisstudy provides the main result of the paper, which is to formulate and prove the new first-order optimality conditions inthe form of a criterion. The optimality conditions are explicit and do not use any constraint qualifications. For the case of alinear cost function, we reformulate theK-semidefinite problem in a regularized form and construct its dual. We show thatthe pair of the primal and dual regularized problems satisfies the strong duality relation which means that the duality gap is vanishing. | doi | Peer Reviewed

24.  Linear semidefinite programming problems: regularisation and strong dual formulations

Kostyukova, O. I. and Tchemisova, T. V.

Journal of the Belarusian State University: Mathematics and Informatics

Belarusian State University

Regularisation consists in reducing a given optimisation problem to an equivalent form where certain regularity conditions, which guarantee the strong duality, are fulfilled. In this paper, for linear problems of semidefinite programming (SDP), we propose a regularisation procedure which is based on the concept of an immobile index set and its properties. This procedure is described in the form of a finite algorithm which converts any linear semidefinite problem to a form that satisfies the Slater condition. Using the properties of the immobile indices and the described regularisation procedure, we obtained new dual SDP problems in implicit and explicit forms. It is proven that for the constructed dual problems and the original problem the strong duality property holds true. | doi | Peer Reviewed

23.  On strong duality in linear copositive programming

Kostyukova, O. I. and Tchemisova, T. V.


The paper is dedicated to the study of strong duality for a problem of linear copositive programming. Based on the recently introduced concept of the set of normalized immobile indices, an extended dual problem is deduced. The dual problem satisfies the strong duality relations and does not require any additional regularity assumptions such as constraint qualifications. The main difference with the previously obtained results consists in the fact that now the extended dual problem uses neither the immobile indices themselves nor the explicit information about the convex hull of these indices. The strong duality formulations presented in the paper have similar structure and properties as that proposed in the works of M. Ramana, L. Tuncel, and H. Wolkovicz, for semidefinite programming, but are obtained using different techniques.

22.  On equivalent representations and properties of faces of the cone of copositive matrices

Kostyukova, O. I. and Tchemisova, T. V.


The paper is devoted to a study of the cone COPp of copositive matrices. Based on the known from semi-infinite optimization concept of immobile indices, we define zero and minimal zero vectors of a subset of the cone COPp and use them to obtain different representations of faces of COPp and the corresponding dual cones. We describe the minimal face of COPp containing a given convex subset of this cone and prove some propositions that allow to obtain equivalent descriptions of the feasible sets of a copositive problems and may be useful for creating new numerical methods based on their regularization.

21.  Clustering genomic words in human DNA using peaks and trends of distributions

Tavares, Ana Helena and Raymaekers, Jakob and Rousseeuw, Peter J. and Brito, Paula and Afreixo, Vera

Advances in Data Analysis and Classification


In this work we seek clusters of genomic words in human DNA by studying their inter-word lag distributions. Due to the particularly spiked nature of these histograms, a clustering procedure is proposed that first decomposes each distribution into a baseline and a peak distribution. An outlier-robust fitting method is used to estimate the baseline distribution (the ‘trend’), and a sparse vector of detrended data captures the peak structure. A simulation study demonstrates the effectiveness of the clustering procedure in grouping distributions with similar peak behavior and/or baseline features. The procedure is applied to investigate similarities between the distribution patterns of genomic words of lengths 3 and 5 in the human genome. These experiments demonstrate the potential of the new method for identifying words with similar distance patterns. | doi | Peer Reviewed

20.  Does induction of labor at term increase the risk of cesarean section in advanced maternal age? A systematic review and meta-analysis

Fonseca, Maria João and Santos, Fernanda and Afreixo, Vera and Silva, Isabel Santos and Almeida, Maria do Céu

European Journal of Obstetrics & Gynecology and Reproductive Biology


Background: Women of advanced maternal age, defined as >= 35 years at delivery, are at increased risk of multiple complications during pregnancy, with perinatal death being one of the most feared. For instance, the risk of stillbirth at term in this subgroup of women is higher than in younger women, and particularly high beyond 39 weeks of gestation. Induction of labor at 39–40 weeks might help prevent some cases of perinatal death, however, the fact that induction of labor has been historically associated with an increased risk of cesarean delivery and the knowledge that advanced maternal age is an independent risk factor for cesarean delivery are some of the major reasons why clinicians are reluctant to offer elective induction of labor in this particular group. Objective: The aim of the study was to assess if induction of labor in advanced maternal age was associated with increased rates of cesarean delivery when compared to expectant management. Material and methods: We performed an electronic search limited to published articles available between January 2000 and March 2020. Randomized clinical trials and retrospective studies with large cohorts comparing induction of labor with expectant management in singleton pregnancies at term, of women aged >= 35 years were included. The primary outcome was the rate of cesarean delivery in induction of labor versus expectant management, and secondary outcomes were the occurrence of assisted vaginal delivery and postpartum hemorrhage. Results: Eight studies, including 81151 pregnancies (26,631 in the induction group and 54,520 expectantly managed), were included in the analysis. Six of the included studies were randomized clinical trials with the remaining two being observational and retrospective cohort studies. Induction of labor was not associated with a significant increased risk of cesarean delivery (OR 0.97, 95 % CI 0.86–1.1), assisted vaginal delivery (OR 1.12, 95 % CI 0.96–1.32) or postpartum hemorrhage (OR 1.11, 95 % CI 0.88–1.41). Discussion: The belief that induction of labor is associated with an increased risk of cesarean delivery is based on the results of retrospective studies comparing induction with spontaneous labor at the same gestational age. However, at any point in a pregnancy, the comparison should be between induction of labor and expectant management, with the latter contributing to a pregnancy of greater gestation age and not always leading to spontaneous labor. When comparing induction to expectant management, our study shows no significant increase of cesarean section, assisted vaginal delivery or postpartum hemorrhage. Our study was not powered to assess neonatal outcomes, and additional research is needed to confirm whether induction of labor might have a positive effect in preventing stillbirth. Conclusion: Induction of labor at term in advanced maternal age has no significant impact on cesarean delivery rates, assisted vaginal delivery or postpartum hemorrhage, giving additional reassurance to obstetricians who would consider this intervention in this particular subgroup. | doi | Peer Reviewed

19.  Estrogen receptors in urogenital schistosomiasis and bladder cancer: estrogen receptor alpha-mediated cell proliferation

Bernardo, Carina and Santos, Júlio and Costa, Céu and Tavares, Ana and Amaro, Teresina and Marques, Igor and Gouveia, Maria João and Félix, Vítor and Afreixo, Vera and Brindley, Paul J. and Costa, José Manuel and Amado, Francisco and Helguero, Luisa and Santos, Lúcio L.

Urologic Oncology: Seminars and Original Investigations


Estrogen-like metabolites have been identified in S. haematobium, the helminth parasite that causes urogenital schistosomiasis (UGS) and in patients´ blood and urine during UGS. Estrogen receptor (ER) activation is enriched in the luminal molecular subtype bladder cancer (BlaCa). To date, the significance of ER to these diseases remains elusive. We evaluated ERα and ERβ expression in UGS-related BlaCa (n = 27), UGS-related non-malignant lesions (n = 35), and noninfected BlaCa (n = 80). We investigated the potential of ERα to recognize S. haematobium-derived metabolites by docking and molecular dynamics simulations and studied ERα modulation in vitro using 3 BlaCa cell lines, T24, 5637 and HT1376. ERα was expressed in tumor and stromal cells in approximately 20% noninfected cases and in 30% of UGS-related BlaCa, predominantly in the epithelial cells. Overall, ERα expression was associated with features of tumor aggressiveness such as high proliferation and p53 positive expression. ERα expression correlated with presence of schistosome eggs. ERβ was widely expressed in both cohorts but weaker in UGS-related cases. molecular dynamics simulations of the 4 most abundant S. haematobium-derived metabolites revealed that smaller metabolites have comparable affinity for the ERα active state than 17β-estradiol, while the larger metabolites present higher affinity. Our in vitro findings suggested that ERα activation promotes proliferation in ERα expressing BlaCa cells and that this can be reverted with anti-estrogenic therapy. In summary, we report differential ER expression between UGS-related BlaCa and noninfected BlaCa and provide evidence supporting a role of active ERα during UGS and UGS-induced carcinogenesis. | doi | Peer Reviewed

18.  On the existence of optimal consensus control for the fractional Cucker–Smale model

Almeida, R. and Kamocki, R. and Malinowska, A. B. and Odzijewicz, T.

Archives of Control Sciences


This paper addresses the nonlinear Cucker–Smale optimal control problem under the interplay of memory effect. The aforementioned effect is included by employing the Caputo fractional derivative in the equation representing the velocity of agents. Sufficient conditions for the existence of solutions to the considered problem are proved and the analysis of some particular problems is illustrated by two numerical examples. | doi | Peer Reviewed

17.  Multivariate and multiscale complexity of long-range correlated cardiovascular and respiratory variability series

Martins, Aurora and Pernice, Riccardo and Amado, Celestino and Rocha, Ana Paula and Silva, Maria Eduarda and Javorka, Michal and Faes, Luca



Assessing the dynamical complexity of biological time series represents an important topic with potential applications ranging from the characterization of physiological states and pathological conditions to the calculation of diagnostic parameters. In particular, cardiovascular time series exhibit a variability produced by different physiological control mechanisms coupled with each other, which take into account several variables and operate across multiple time scales that result in the coexistence of short term dynamics and long-range correlations. The most widely employed technique to evaluate the dynamical complexity of a time series at different time scales, the so-called multiscale entropy (MSE), has been proven to be unsuitable in the presence of short multivariate time series to be analyzed at long time scales. This work aims at overcoming these issues via the introduction of a new method for the assessment of the multiscale complexity of multivariate time series. The method first exploits vector autoregressive fractionally integrated (VARFI) models to yield a linear parametric representation of vector stochastic processes characterized by short- and long-range correlations. Then, it provides an analytical formulation, within the theory of state-space models, of how the VARFI parameters change when the processes are observed across multiple time scales, which is finally exploited to derive MSE measures relevant to the overall multivariate process or to one constituent scalar process. The proposed approach is applied on cardiovascular and respiratory time series to assess the complexity of the heart period, systolic arterial pressure and respiration variability measured in a group of healthy subjects during conditions of postural and mental stress. Our results document that the proposed methodology can detect physiologically meaningful multiscale patterns of complexity documented previously, but can also capture significant variations in complexity which cannot be observed using standard methods that do not take into account long-range correlations. | doi | Peer Reviewed

16.  Modelling irregularly spaced time series under preferential sampling

Monteiro, Andreia and Menezes, Raquel and Silva, Maria Eduarda


Instituto Nacional de Estatística

Irregularly spaced time series are commonly encountered in the analysis of time series. A particular case is that in which the collection procedure over time depends also on the observed values. In such situations, there is stochastic dependence between the process being modeled and the times at which the observations are made. Ignoring this dependence can lead to biased estimates and misleading inferences. In this paper, we introduce the concept of preferential sampling in the temporal dimension and we propose a model to make inference and prediction. The methodology is illustrated using artificial data as well a real data set. | Peer Reviewed

15.  Treatment priorities among older people if faced with serious illness: improving the quality of life or extending life?

Jorge, Rafaela and Freitas, Adelaide and Sousa, Liliana

Journal of Statistics on Health Decision

Universidade de Aveiro; Centro Hospitalar do Baixo Vouga

Objective: This study aimed to analyse older people`s end-of-life care priorities and to identify factors associated with these priorities. Methods: A cross-sectional face-to-face survey with 400 individuals aged ≥60 living in the city of Belo Horizonte, Brazil was conducted. Participants were asked their treatment priorities if faced with a serious illness with limited time to live. Multinomial logistic regressions were used to identify the associated factors. The possible instability of the factors in the final multivariable model were assessed by bootstrap resampling. Results: Most participants (65.3%) chose the option ‘improve quality of life for the time they had left’. Only 4% said extending life was the most important priority while the option ‘both equally important’ (quality and extension) was chosen by 30.8 of respondents. Participants in the age group 60-69 years were more likely to choose both quality and life extension than choose to extend life alone (AOR=0.18, 95% CI:0.05-0.72; ref: 80+ years). The group comprised of single + widowers is more likely to prioritize both quality and extension than to prioritize just extending life (AOR=0.28, 95% CI:0.09- 0.89; ref: the others marital status) and or just improving the quality of life (AOR=0.62, 95% CI:0.40-0.95; ref: the others marital status). Conclusion: The findings indicated that treatment for improving the quality of life was the most important priority. Two factors influenced the priorities (age group and marital status). To meet people's treatment priorities at end of life, policies need to be formulated to develop palliative care services, train health-care professionals, and educate patients | doi | Peer Reviewed

14.  Design of pulmonary rehabilitation programmes during acute exacerbations of COPD: a systematic review and network meta-analysis

Machado, Ana and Matos Silva, Pedro and Afreixo, Vera and Caneiras, Cátia and Burtin, Chris and Marques, Alda

European Respiratory Review

European Respiratory Society

This systematic review aimed to systematise the different designs used to deliver pulmonary rehabilitation during acute exacerbations of COPD (AECOPD) and explore which ones are the most effective. PubMed, Scopus, Web of Science, EBSCO and Cochrane were searched. Randomised controlled trials comparing pulmonary rehabilitation or at least one of its components with usual care or comparing different components of pulmonary rehabilitation were included. Network meta-analysis was conducted in MetaXL 5.3 using a generalised pairwise modelling framework. Pooled effects compared each treatment to usual care. 42 studies were included. Most studies were conducted in an inpatient setting (57%) and started the intervention 24-48 h after hospital admission (24%). Exercise training (71%), education and psychosocial support (57%) and breathing techniques (55%) were the most used components. Studies combining exercise with breathing techniques presented the larger effects on exercise capacity (weighted mean difference (WMD) -41.06, 95% CI -131.70-49.58) and health-related quality of life (WMD 16.07, 95% CI 10.29-21.84), and breathing techniques presented the larger effects on dyspnoea (WMD 1.90, 95% CI 0.53-3.27) and length of hospitalisation (effect size =0.15, 95% CI -0.28-0.57). A few minor adverse events were found.Pulmonary rehabilitation is a safe intervention during AECOPD. Exercise, breathing techniques, and education and psychosocial support seem to be the core components for implementing pulmonary rehabilitation during AECOPD. Studies may now focus on comparisons of optimal timings to start the intervention, total duration of the intervention, duration and frequency of sessions, and intensity for exercise prescription. | doi | Peer Reviewed

13.  Prospects for new physics from gauge left-right-colour-family grand unification hypothesis

Morais, António P. and Pasechnik, Roman and Porod, Werner

The European Physical Journal C


Given the tremendous phenomenological success of the Standard Model (SM) framework, it becomes increasingly important to understand to what extent its specific structure dynamically emerges from unification principles. In this study, we present a novel anomaly-free supersymmetric (SUSY) Grand Unification model based upon gauge trinification [SU(3)]3 symmetry and a local SU(2)F×U(1)F family symmetry, with particle spectra and gauge symmetries inspired by a possible reduction pattern E8→E6×SU(2)F×U(1)F, with subsequent E6→[SU(3)]3 symmetry breaking step. In this framework, higher-dimensional operators of E6 induce the threshold corrections in the gauge and Yukawa interactions leading, in particular, to only two distinct Yukawa couplings in the fundamental sector of the resulting [SU(3)]3×SU(2)F×U(1)F Lagrangian. Among the appealing features emergent in this framework are the Higgs-matter unification and a unique minimal three Higgs doublet scalar sector at the electroweak scale as well as tree-level hierarchies in the light fermion spectra consistent with those observed in nature. In addition, our framework reveals a variety of prospects for New Physics searches at the LHC and future colliders such as vector-like fermions, as well as rich scalar, gauge and neutrino sectors. | doi | Peer Reviewed

12.  The main vertices of a star set and related graph parameters

Anđelić, Milica and Cardoso, Domingos M. and Simić, Slobodan K. and Stanić, Zoran


A vertex v ∈ V (G) is called λ-main if it belongs to a star set X ⊂ V (G) of the eigenvalue λ of a graph G and this eigenvalue is main for the graph obtained from G by deleting all the vertices in X {v}; otherwise, v is λ-non-main. Some results concerning main and non-main vertices of an eigenvalue are deduced. For a main eigenvalue λ of a graph G, we introduce the minimum and maximum number of λ-main vertices in some λ-star set of G as new graph invariant parameters. The determination of these parameters is formulated as a combinatorial optimization problem based on a simplex-like approach. Using these and some related parameters we develop new spectral tools that can be used in the research of the isomorphism problem. Examples of graphs for which the maximum number of λ-main vertices coincides with the cardinality of a λ-star set are provided.

11.  Représentation de la courbe intersection d’une quadrique et d’une quartique

Breda, Ana and Trocado, Alexandre and Neves, António and Santos, José dos


Cet article présente l’implémentation dans le langage Geogebra de deux algorithmes pour calculer la courbe intersection d’une quadrique et d’une quartique. Nous présentons deux méthodes de calcul et de visualisation de cette courbe avec GeoGebra. La première utilise un logiciel de Calcul formel pour obtenir une paramétrisation de la courbe et sa représentation. La seconde est basée sur le calcul d’une projection plane de la courbe intersection, sur la détermination de son allure et de ses singularités, et sur son relèvement dans l’espace à trois dimensions. Ce problème met en évidence les difficultés innérentes à l’implémentaion dans Geogebra d’un algorithme géométrique basé sur les équations algébriques définissant les surfaces. Nous nous intéressons également à l’utilisation de ces techniques de calcul comme outil pédagogique dans l’enseignement supérieur.

10.  Mapification of n-dimensional abstract polytopes and hypertopes

Breda d'Azevedo, António

Ars Mathematica Contemporanea

The n-dimensional abstract polytopes and hypertopes, particularly the regular ones, have gained great popularity over recent years. The main focus of research has been their symmetries and regularity. The planification of a polyhedron helps its spatial construction, yet it destroys symmetries. No “planification” of n-dimensional polytopes do exist, however it is possible to make a “mapification” of an n-dimensional polytope; in other words it is possible to construct a restrictedly-marked map representation of an abstract polytope on some surface that describes its combinatorial structures as well as all of its symmetries. There are infinitely many ways to do this, yet there is one that is more natural that describes reflections on the sides of (n-1)-simplices (flags or n-flags) with reflections on the sides of n-gons. The restrictedly-marked map representation of an abstract polytope is a cellular embedding of the flag graph of a polytope. We illustrate this construction with the 4-cube, a regular 4-polytope with automorphism group of size 384. This paper pays a tribute to Lynne James’ last work on map representations. | doi | Peer Reviewed

9.  Strong map-symmetry of SL(3, K) and PSL(3, K) for every finite field K

Breda d'Azevedo, António and Catalano, Domenico A.

Journal of Algebra and Its Applications

World Scientific Publishing

In this paper, we show that for any finite field K, any pair of map-generators (that is when one of the generators is an involution) of SL(3,K) and PSL(3,K) has a group automorphism that inverts both generators. In the theory of maps, this corresponds to say that any regular oriented map with automorphism group SL(3,K) or PSL(3,K) is reflexible, or equivalently, there are no chiral regular maps with automorphism group SL(3,K) or PSL(3,K). As remarked by Leemans and Liebeck, also SU(3,K) and PSU(3,K) are not automorphism groups of chiral regular maps. These two results complete the work of the above authors on simples groups supporting chiral regular maps. | doi | Peer Reviewed

8.  New convolutions associated with the Mellin transform and their applications in integral equations

Castro, L. P. and Silva, A. S. and Tuan, N. M.

Journal of Classical Analysis


In this paper, we introduce two new convolutions associated with the Mellin transform which exhibit factorization properties upon the use of certain weight functions. This is applied to the solvability analysis of classes of integral equations. In particular, we present sufficient conditions for the solvability of an integral equation and a system of integral equations of convolution type. | doi | Peer Reviewed

7.  On the equivalence of the integral and differential Bellman equations in impulse control problems

Dufour, Francois and Piunovskiy, Alexey and Plakhov, Alexander

International Journal of Control

Taylor & Francis

When solving optimal impulse control problems, one can use the dynamic programming approach in two different ways: at each time moment, one can make the decision whether to apply a particular type of impulse, leading to the instantaneous change of the state, or apply no impulses at all; or, otherwise, one can plan an impulse after a certain interval, so that the length of that interval is to be optimized along with the type of that impulse. The first method leads to the differential Bellman equation, while the second method leads to the integral Bellman equation. The target of the current article is to prove the equivalence of those Bellman equations. Firstly, we prove that, for the simple deterministic optimal stopping problem, the equations in the integral and differential form are equivalent under very mild conditions. Here, the impulse means that the uncontrolled process is stopped, i.e., sent to the so called cemetery. After that, the obtained result immediately implies the similar equivalence of the Bellman equations for other models of optimal impulse control. Those include abstract dynamical systems, controlled ordinary differential equations, piece-wise deterministic Markov processes and continuous-time Markov decision processes. | doi | Peer Reviewed

6.  A behavioral approach to estimation in nD systems

Pereira, Ricardo and Rocha, Paula


Elsevier; International Federation of Automatic Control (IFAC)

In this paper we study the problem of estimation for multidimensional systems within the context of the behavioral approach. We consider the case where there are no disturbances as well as the case where the system dynamics is perturbed, and provide necessary conditions for the solvability of the corresponding estimation problems together with the construction of a solution, if it exists. Such solution is an estimator that is asymptotic, in the sense that the error trajectories are stable with respect to a pre-specified nD stability cone. | doi | Peer Reviewed


5.  World Health Organization Quality of Life-BREF: versão Aphasia-Friendly

Araújo, Ana and Sá-Couto, Pedro and Valente, Paula and Matos, Maria

14.º Congresso Português do AVC

Sociedade Portuguesa do AVC

Sem resumo disponível. | Peer Reviewed

4.  Classification of HRV using Long Short-Term Memory networks

Leite, Argentina and Silva, Maria Eduarda and Rocha, Ana Paula

2020 11th Conference of the European Study Group on Cardiovascular Oscillations (ESGCO)


This work focus on detection of diseases from Heart Rate Variability (HRV) series using Long Short-Term Memory (LSTM) networks. First, non-linear models are used to extract sequences of features that characterize the HRV series. These time sequences are then used as input for the LSTM. HRV recordings from the Noltisalis database are used for training and testing this approach. The results indicate that the procedure provides accuracy scores in the range of 86.7% to 90.0% on the test set. | doi | Peer Reviewed

3.  Vector Autoregressive Fractionally Integrated models to assess multiscale complexity in cardiovascular and respiratory time series

Martins, Aurora and Amado, Celestino and Rocha, Ana Paula and Silva, Maria Eduarda and Pernice, Riccardo and Javorka, Michal and Faes, Luca

2020 11th Conference of the European Study Group on Cardiovascular Oscillations (ESGCO)


Cardiovascular variability is the result of the activity of several physiological control mechanisms, which involve different variables and operate across multiple time scales encompassing short term dynamics and long range correlations. This study presents a new approach to assess the multiscale complexity of multivariate time series, based on linear parametric models incorporating autoregressive coefficients and fractional integration. The approach extends to the multivariate case recent works introducing a linear parametric representation of multiscale entropy, and is exploited to assess the complexity of cardiovascular and respiratory time series in healthy subjects studied during postural and mental stress. | doi | Peer Reviewed

2.  On the use of neural networks for stock price forecasting

Sousa, Virgínia and Alonso, Hugo

Economic and Social Development: 62nd International Scientific Conference on Economic and Social Development: book of proceedings

Varazdin Development and Entrepreneurship Agency; University North

Having the ability to predict the price of a particular stock share is undoubtedly a major challenge, because of the complexity and implied volatility of the financial markets. This is a topic of great interest to researchers and market players, as the effectiveness of the forecast might translate into huge monetary gains. This work aims to demonstrate the use of neural networks for stock price forecasting. Two financial titles are considered: Microsoft and Apple. The initial choice of the predictor variables comprises the most used and referenced in the scientific papers published on this subject. This work demonstrates the importance of a careful selection of some of those variables for a good neural network performance. | Peer Reviewed

1.  Situational pricing: the role of wine consumption occasion on price decision

Candeias, Teresa and Alonso, Hugo

Economic and Social Development: 62nd International Scientific Conference on Economic and Social Development: book of proceedings

Varazdin Development and Entrepreneurship Agency; University North

Wine companies are usually operating in larger and diverse markets and consumers show different needs. Given resource constraints, companies must segment the market, because they cannot cover the entire market or, if they do, they need to adopt and implement an appropriate marketing strategy. Market segmentation enables to treat consumers differently through a marketing strategy geared to this purpose. There are several segmentation criteria and one of them is the wine consumption occasion. Here, like other authors do, we consider the following five situations where the consumer pays for a bottle of wine: to drink at home, to drink at home with friends, to drink at a restaurant, to give as a gift and in businesses. We asked to 133 consumers, randomly selected, how much they were willing to pay in each situation: < 1 Euro; 1 – 2 Euros; 2 – 5 Euros; 5 – 10 Euros; 10 – 20 Euros; > 20 Euros. We concluded that the price decision depends on the wine consumption occasion (Friedman test, p-value=0,000). This is in accordance with the literature. Furthermore, we found something that, to our knowledge, is new: at a 5% level of significance, there is no difference between the situations “to drink at home” and “to drink at home with friends” and also between “to drink at a restaurant”, “to give as a gift” and “in businesses”; the difference lies between the former two situations and the latter three. This means that, for market segmentation, we can consider two instead of five wine consumption occasions. We further investigate how this conclusion depends on consumer gender. | Peer Reviewed
(latest changes on 2021-09-13 18:39)

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