Center of Mathematics and Applications of University of Beira Interior

Funder

Organizational Unit

Publications

Random sample sizes in orthogonal mixed models with stability

Publication . Nunes, Célia; Mário, Anacleto César Xavier; Ferreira, Dário; Ferreira, Sandra S.; Mexia, João T.

In this work, we presente a new approach that considers orthogonal mixed models, under situations of stability, when the sample dimensions are not known in advande. In this case, samples are considered realizations of independente rendom variables. We apply this methodology to the case where there is na upper bound for the sample dimensions, which may not be attained since failures may occur. Based on this, we assume that sample sizes are binomially distributed. We consider na application on the incidence of unemployed persons in the European Union to illustrate the proposed methodology. A simulation study is also conduced. The obtained results show the relevance of the proposed approach in avoiding false rejections.

2019Journal article

Restricted access

Balanced prime basis factorial fixed effects model with random number of observations

Publication . Oliveira, Sandra; Nunes, Célia; Moreira, Elsa; Fonseca, Miguel; Mexia, João T.

Factorial designs are in general more efficient for experiments that involve the study of the effects of two or more factors. In this paper we consider a p^U factorial model with U factors, each one having a p prime number of levels. We consider a balanced (r replicates per treatment) prime factorial with fixed effects. Our goal is to extend these models to the case where it is not possible to known in advance the number of treatments replicates, r. In these situations is more appropriate to consider r as a realization of a random variable R, which will be assumed to be geometrically distributed. The proposed approach is illustrated through an application considering simulated data.

2019Journal article

Restricted access

On polynomial equation rings and radicals

Publication . Mendes, D. I. C.; Ochirbat, B.; Tumurbat, S.

The notion of n-polynomial equation ring, for an arbitrary but fixed positive integer n, is introduced. A ring A is called an n- polynomial equation ring if γ(A[Xn]) = γ(A)[ Xn], for all radicals γ. If this equation holds for all hereditary radicals γ, then A is said to be a hereditary n-polynomial equation ring. Various characterizations of these rings are provided. It is shown that, for any ring A, the zero-ring on the additive group of A is an n- polynomial equation ring and that any Baer radical ring is a hereditary n- polynomial equation ring. New radicals based on these notions are introduced, one of which is a special radical with a polynomially extensible semisimple class.

2019-09-27Journal article

Restricted access

Aproximação numérica de equações diferenciais parciais com p-Laplaciano e memória

Publication . Mário, Belchior César Xavier; Duque, José Carlos Matos; Almeida, Rui Manuel Pires

Neste trabalho, faz-se um estudo sobre a aplicação do método dos elementos finitos na resolução de uma equação diferencial parcial não linear do tipo parabólico com memória da forma [...]

2023-06-19Doctoral thesis

Open access

Straighten out coordinates for volume-preserving actions

Publication . Bessa, Mario; Morais, Pedro

In this short note we obtain a canonical form for commuting divergence-free vector fields.

2019Journal article

Restricted access