Irene Brito

University of Minho · Departamento de Matemática e Aplicações (DMA)

In this paper, the performance of portfolios consisting of stocks selected with the recently proposed expected utility, entropy and variance (EU–EV) risk model is analysed. The portfolios were constructed using data of the PSI 20 index, from January 2019 to December 2020, by reducing the number of stock components to the half with the EU–EV risk mo...

Mathematics and Music are closely connected and their multifaceted relationship has been explored since ancient times. Pythagoras was one of the first who discovered and formalized one of those connections by studying the arithmetic of musical intervals, expressing them by numerical ratios and relating ratios to consonance/dissonance notions, being...

In the context of investment decision-making, the selection of stocks is important for a successful construction of portfolios. In this paper the expected utility, entropy and variance (EU-EV) model is applied for stock selection, which can be used as preselection model for mean–variance portfolio optimization problems. Based on the EU-EV risk, sto...

The normalized expected utility - entropy and variance (NEU-EV) decision model and associated risk measure are proposed for the analysis and modelling of decisions under risk. The model depends on normalized entropy and variance and expected utility, can be applied to decision problems depending on actions, where the states have different numbers o...

MVGEN is a multi-version question generation tool that allows creating multiple-choice questions with a large number of versions and multi-version tests using different randomisation techniques. These techniques include simple randomisation through shuffling of lists with keys and distractors or random selection of options from lists with several k...

Expected utility theory can be relevant for decision-making under risk, when different preferences should be taken into account. The goal of this paper is to present a quantitative risk analysis methodology, depending on expected utility, where the risk consequences are determined quantitatively, the risk is modelled using a loss random variable an...

In this work we show how concepts and methods from actuarial risk theory can be applied to risk analysis in industry. Risk analysis consists in identifying, quantifying and classifying or ordering risks. In the proposed methodology, the risks identified in industrial setting, are modeled by loss random variables. The loss random variables are used...

A decision model - the expected utility, entropy and variance (EU-EV) model – is proposed, where the decision criterion depends on the uncertainty risk factors entropy and variance and on the subjective expected utility. The EU-EV model is applied to decision problems existing in the literature, and it is shown that they can be well explained with...

It is shown that exact spherically symmetric solutions to Einstein’s field equations exist such that, over an open region of the spacetime, they are singularity free, satisfy the dominant energy condition, represent elastic matter with a well-defined constitutive function, and are such that elastic perturbations propagate causally. Two toy models a...

It is shown that exact spherically symmetric solutions to Einstein's Field Equations exist such that, over an open region of the spacetime, they are singularity free, satisfy the dominant energy condition, represent elastic matter with a well defined constitutive function, and are such that elastic perturbations propagate causally. Two toy-models a...

A question generating system developed in Perl that uses LaTeX as typographical language is presented, which, besides random generation of different question types, allows a random creation of a large number of different test versions. Examples of question types in mathematics (Linear Algebra and Discrete Mathematics) are provided and the associate...

The problem of generating solutions of the Einstein field equations with an elastic energy–momentum tensor from the Schwarzschild vacuum solution by means of conformal transformations is analyzed. Applying the formulation of relativistic elasticity, suitable conformal factors are obtained for static and non-static elastic spacetime configurations a...

A particular class of conformally flat spacetimes possessing isotropic and anisotropic pressure are investigated, using 1+3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document...

In this work we propose a methodology which permits the risk analysis and classification of occupational accidents in industrial settings. Data used in this study corresponds to accidents that occurred in the furniture industry in Portugal in 2010. A loss random variable is constructed in order to model the number of lost days implied by different...

This work is based on dry and lubricated friction properties of Polyoxymethylene (POM) plastics widely used in multimedia and electronic sector of automotive industries. The results show that lubrication does not seem to influence the static coefficient of friction; however, significantly influences the dynamic one and increases it by two-fold.

Paper aims This paper presents teachers and students perspectives of integration Science, Technology, Engineering and Mathematics (STEM) courses contents into the first year of Industrial Engineering and Management (IEM) program through Project-Based Learning (PBL). Originality These perspectives provide strategies that IEM teachers could use to ch...

The present study, conducted at the end of a PBL edition at the University of Minho, reports on the results of a questionnaire issued to the lecturers of the Project Supporting Courses of a semester-wide interdisciplinary PBL approach. The questionnaire was intended to gather the perceptions on a number of relevant aspects, such as on the validity...

We investigate a class of cylindrically symmetric inhomogeneous $\Lambda$-dust spacetimes which have a regular axis and some zero expansion component. For $\Lambda\ne 0$, we obtain new exact solutions to the Einstein equations and show that they are unique, within that class. For $\Lambda=0$, we recover the Senovilla-Vera metric and show that it ca...

Noise generation in modern vehicles cabin is mainly due to the contact among small mechanical parts integrated on systems such as steering angle sensors. Currently, to ensure that the noise produced by the steering angle sensors is below the limits, it is necessary to carry out tests in an anechoic environment. This work aims to compare the steerin...

We prove that, for a given spherically symmetric fluid distribution with tangential pressure on an initial spacelike hypersurface with a timelike boundary, there exists a unique, local in time solution to the Einstein equations in a neighbourhood of the boundary. As an application, we consider a particular elastic fluid interior matched to a vacuum...

This work is focused on the acoustic simulation of a steering wheel sensor for geometric design optimization. The sensor is located under the steering wheel inside the vehicle cabin, which may cause noise audible by the passengers and the driver. A common way of noise reduction from mechanical components is changing their structural rigidity. Simil...

Nowadays noise reduction constitutes a goal for every car manufacturer and a considerable effort is being made to produce components with low noise emission levels. Interactions between mechanisms undergoing friction are often associated with noise generation. This work is aimed to study the friction properties of two commercial plastics commonly u...

Purpose: Project-Based Learning (PBL) is considered to be an active learning methodology which can be used to develop both technical and transversal competences in engineering programs. This methodology demands a great deal of work effort from the students and also from the teachers and it requires a meticulous plan and a well-managed project as we...

Conformally flat spacetimes with an elastic stress energy tensor given by a diagonal trace-free anisotropic pressure tensor are investigated using 1+3 formalism. We show how the null tetrad Ricci components are related to the pressure components and energy density. The 1+3 Bianchi and Jacobi identities and Einstein field equations are written for t...

We analyse the geodesics' dynamics in cylindrically symmetric vacuum spacetimes with Λ > 0 and compare it to the Λ = 0 and Λ > 0 cases. When Λ > 0 there are two singularities in the metric which brings new qualitative features to the dynamics. We find that Λ = 0 planar timelike confined geodesics are unstable against the introduction of a sufficien...

Conformal transformations are applied in the context of general relativistic elasticity. Expressions relating relativistic elastic quantities and tensors are obtained for two conformal spacetimes, whose material metrics are also conformally related. Non-static shear-free spherically symmetric elastic solutions of the Einstein field equations are co...

We present a comparative study about the dynamics of geodesic orbits in static cylindrically symmetric vacuum spacetimes with and without a cosmological constant.. In particular, we analyze the orbital stability of the Lambda = 0 case with respect to the introduction of arbitrarily small values of vertical bar Lambda vertical bar and single out the...

This paper deals with the field of mathematics education where the aim is to generate exercises with randomized data. The process of exercise generation involves, first, identification of common errors that may be performed when solving the exercise, then, modeling of these errors by appropriate functions and recognition and distinction of errors t...

We consider static conformally flat cylindrically symmetric spacetimes with a cosmological constant and study the matching problem with the exterior Linet-Tian spacetime. We show that the matching is impossible if Λ < 0.

We investigate the geodesics’ kinematics and dynamics in the Linet–Tian metric with [TEX equation: \Lambda Keywords: Cylindrically symmetric spacetimes; Exact solutions; General relativity; Geodesics; Stability Document Type: Research Article DOI: http://dx.doi.org/10.1007/s10714-014-1681-7 Affiliations: 1: Centro de Matemática, Universidade do Min...

In this paper we concentrate on the field of mathematics education where the aim is to generate exercises going beyond those with answers of simple types (e.g. multiple-choice, Boolean, integer, or file comparison). We present three examples from introductory college mathematics and emphasize the key points that should be taken into account in orde...

In order to be robust and achieve multi-domain coverage, exercise generation systems usually work with answers of simple types (e.g. multiple-choice, Boolean, integer, or file comparison). In this paper we describe an exercise generation system Passarola, a simple, yet powerful, language that anyone with no computer science background, can use to d...

We investigate the matching, across cylindrical surfaces, of static cylindrically symmetric conformally flat spacetimes with a cosmological constant Λ, satisfying regularity conditions at the axis, to an exterior Linet-Tian spacetime [B. Linet, J. Math. Phys. 27, 1817–1818 (1986; Zbl 0593.53040)]. We prove that for Λ≤0 such matching is impossible....

The Einstein field equations are derived for a static cylindrically symmetric spacetime with elastic matter. The equations can be reduced to a system of two nonlinear ordinary differential equations and we present analytical and numerical solutions satisfying the dominant energy conditions. Furthermore, we show that the solutions can be matched at...

We consider a static cylindrically symmetric spacetime with elastic matter and study the matching problem of this spacetime with a suitable exterior. For the exterior, we take the Levi-Civita spacetime and its generalization including a cosmological constant, the Linet-Tian spacetime. We show that the matching is only possible with the Linet-Tian s...

In the context of relativistic elasticity it is interesting to study axially symmetric space-times due to their significance in modeling neutron stars and other astrophysical systems of interest. To approach this problem, here, a particular class of these space-times is considered. A cylindrically symmetric elastic space-time configuration is studi...

Given a space-time and a continuous medium with elastic properties described by a 3-dimensional material space, one can ask whether they are compatible in the context of relativistic elasticity. Here a non-static, spherically symmetric spacetime metric is considered and we investigate the conditions for that metric to correspond to different 3-dime...

The relativistic theory of elasticity is reviewed within the spherically symmetric context with a view towards the modelling of star interiors possessing elastic properties such as the ones expected in neutron stars. Emphasis is placed on generality in the main sections of the paper, and the results are then applied to specific examples. Along the...

Mathematics at an undergraduate level is frequently presented to the students in quite a traditional way. When implementing the Bologna education reform in Portuguese universities, the number of contact hours of the courses decreased (considerably in some cases), therefore increasing the need of a more self-responsible learning by the student. This...

Mathematics at an undergraduate level is frequently presented to the students in quite a traditional way. When implementing the Bologna education reform in Portuguese universities, the number of contact hours of the courses decreased, therefore increasing the need of a more self-responsible learning by the student. This means that the student has t...

The relativistic theory of elasticity is reviewed within the spherically symmetric context with a view towards the modeling of star interiors possessing elastic properties such as theones expected in neutron stars. Emphasis is placed on generality in the main sections of the paper, and the results are then applied to specific examples. Along the wa...

The elasticity difference tensor, used in [1] to describe elasticity properties of a continuous medium filling a space-time, is here analysed from the point of view of the space-time connection. Principal directions associated with this tensor are compared with eigendirections of the material metric. Examples concerning spherically symmetric and ax...

A tetrad, adapted to the principal directions of the unstrained reference tensor, is chosen and the elasticity difference tensor, as introduced in [1], is decomposed along those directions. The second order tensors obtained are studied and an example is presented.

An introduction is provided to the theory of elasticity in general relativity. Important tensors appearing in this context are presented. In particular, attention is focussed on the elasticity difference tensor, for which an algebraic analysis is performed. Applications are given to static and non-static spherically symmetric configurations. For th...

Dissertação de Mestrado em Estatística apresentada à Faculdade de Ciências da Universidade do Porto Neste trabalho consideram-se duas classes de processos que têm aplicações reais a séries de dados discretos: processos ramificados com imigração - BGWI, e processos aotorregressivos de valor inteiro - INAR.Os processos BGWI são processos estocásticos...