CMA - Centro de Matemática e Aplicações da UBI
Permanent URI for this community
CMA, Centre of Mathematics and Applications, is a research unit in Mathematics and Applications, hosted by University of Beira Interior (UBI). UBI provides the requested facilities, budget management, computing support and institutional framework to wards CMA’s activities.
Website CMABrowse
Browsing CMA - Centro de Matemática e Aplicações da UBI by Title
Now showing 1 - 10 of 145
Results Per Page
Sort Options
- 3-Form Cosmology: Phantom Behaviour, Singularities and InteractionsPublication . Morais, João; Bouhmadi Lopez, Mariam; Marto, JoãoThe latest cosmological observations by the Planck collaboration (and combined with others) are compatible with a phantom-like behaviour (w < − 1) for the dark energy equation of state that drives the current acceleration of the Universe. With this mindset, we look into models where dark energy is described by a 3-form field minimally coupled to gravity. When compared to a scalar field, these models have the advantage of more naturally accommodating a cosmological-constant and phantom-like behaviours. We show how the latter happens for a fairly general class of positive-valued potentials, and through a dynamical system approach, we find that in such cases the 3-form field leads the Universe into a Little Sibling of the Big Rip singular event into the future. In this work, we explore the possibility of avoiding such singularity via an interaction in the dark sector between cold dark matter and the 3-form field. For the kind of interactions considered, we deduce a condition for replacing the LSBR by a late time de Sitter phase. For specific examples of interactions that meet this condition, we look for distinctive imprints in the statefinder hierarchy { S 3 ( 1 ) ; S 4 ( 1 ) } , { S 3 ( 1 ) ; S 5 ( 1 ) } , and in the growth rate of matter, e ( z ) , through the composite null diagnostic (CND).
- Action of Curcumin on Glioblastoma Growth: A Systematic Review with Meta-Analysis of Animal Model StudiesPublication . Luís, Ângelo; Amaral, Leonor; Domingues, F.C.; Pereira, L.; Cascalheira, JoséGliomas are aggressive brain tumors with poor prognosis even after surgical removal and radio-chemotherapy, stressing the urgency to find alternative therapies. Several preclinical studies evaluating the anticancer effect of curcumin in animal models of glioma are reported, but a systematic review with meta-analysis of these studies, considering the different experimental conditions used, has not been made up to this date. A search in different databases (Pubmed, Web of Science, Scopus, and SciELO) following the PRISMA statement was conducted during November 2023 to systematically identify articles assessing the effect of curcumin in murine xenograft models of glioma and identified 15 articles, which were subdivided into 24 studies. Tumor volume before and after treatment with curcumin or vehicle was extracted and the efficacy of curcumin was evaluated by performing a random effects meta-analysis of the data. Publication bias and the impact of different experimental conditions on curcumin efficacy were assessed. Treatment with curcumin decreased tumor volume. Comparing curcumin with control groups, the overall weighted standardized difference in means was −2.079 (95% CI: −2.816 to −1.341; p-value < 0.001). The curcumin effect was observed for different animal models, types of glioma cells, administration routes, and curcumin formulations. Publication bias was identified but does not invalidate curcumin’s effectiveness. The findings suggest the potential therapeutic efficacy of curcumin against glioma.
- Analyzing the Gaver - Lewis Pareto Process under an Extremal PerspectivePublication . Ferreira, Marta; Ferreira, HelenaPareto processes are suitable to model stationary heavy-tailed data. Here, we consider the auto-regressive Gaver–Lewis Pareto Process and address a study of the tail behavior. We characterize its local and long-range dependence. We will see that consecutive observations are asymptotically tail independent, a feature that is often misevaluated by the most common extremal models and with strong relevance to the tail inference. This also reveals clustering at “penultimate” levels. Linear correlation may not exist in a heavy-tailed context and an alternative diagnostic tool will be presented. The derived properties relate to the auto-regressive parameter of the process and will provide estimators. A comparison of the proposals is conducted through simulation and an application to a real dataset illustrates the procedure.
- ANOVA with random sample sizes: An application to a Brazilian database on cancer registriesPublication . Nunes, Célia; Capistrano, Gilberto; Ferreira, Dário; Ferreira, Sandra S.ANOVA is routinely used in many situations, namely in medical research, where the sample sizes may not be previously known. This leads us to consider the samples sizes as realizations of random variables. The aim of this paper is to extend one-way random effects ANOVA to those situations and apply our results to a Brazilian database on cancer registries.
- Application domains for the Delta methodPublication . Nunes, Célia; Oliveira, Manuela M.; Mexia, João T.The Delta method uses truncated Lagrange expansions of statistics to obtain approximations to their distributions. In this paper, we consider statistics Y = g(μ + X), where X is any random vector.We obtain domains D such that, when μ ∈ D, we may apply the distribution derived from the Delta method. Namely, we will consider an application on the normal case to illustrate our approach.
- Approximate Normality of Low Degree Polynomials in Normal Independent VariablesPublication . Ferreira, Dário; Ferreira, Sandra S.; Nunes, Célia; Ramos, Luís; Mexia, João T.In this paper, we emphasize that polynomials are asymptotically linear functions and show, through Monte Carlo methods, that when the variation coefficients are small, low degree polynomials in normal independent variables are approximately normal. An application which illustrates the approach is presented.
- Arithmetic for closed ballsPublication . Beites, P. D.; Nicolás, A. P.; Vitoria, JoseInspired by circular complex interval arithmetic, an arithmetic for closed balls in Rn is pursued. In this sense, the properties of certain operations on closed balls in Rn, some of which related either to the Hadamard product of vectors or to the 2-fold vector cross product when n ∈ {3, 7}, are studied. In particular, known results for operations on closed balls in C, which can be identified with R2, are extended to closed balls in Rn.
- Asymptotic dependence of bivariate maximaPublication . Ferreira, Helena; Ferreira, MartaThe Ledford and Tawn model for the bivariate tail incorporates a coefficient, η, as a measure of pre-asymptotic dependence between the marginals. However, in the limiting bivariate extreme value model, G, of suitably normalized component-wise maxima, it is just a shape parameter without reflecting any description of the dependency in G. Under some local dependence conditions,we consider an index that describes the pre-asymptotic dependence in this context. We analyze some particular cases considered in the literature and illustrate with examples. A small discussion on inference is presented at the end.
- Autoimmune hepatitis in 828 Brazilian children and adolescents: clinical and laboratory findings, histological profile, treatments, and outcomesPublication . Porta, Gilda; Carvalho, Elisa; Santos, Jorge Luiz Dos; Gama, Jorge; Borges, Cristian V.; Seixas, Renata; Ferreira, Alexandre; Miura, Irene; Silveira, Themis Reverbel; Silva, Luciana; Fagundes, Eleonora; Brandao, MA Bellomo; Sawamura, Regina; Vieira, Sandra; Melere, Melina; Marques, Cibele D F; Pugliese, Renata P.; Danesi, Vera; Porta, Adriana; Marsillac, Marise; Valladares, Marcia Angélica; Menezes, Daniela G.; Kieling, Carlos; Paula, Mariana N. de; Vasconcelos, Juliana R.; Ferreira, Cristina T.; Perin, Nilza; Resende, Leonardo R.; Maia, Jussara; Tommaso, Adriana M.A. De; Hessel, Gabrielsentation, laboratory findings, histological profile, treatments, and outcomes of children andadolescents with autoimmune hepatitis.Methods: The medical records of 828 children and adolescents with autoimmune hepatitiswere reviewed. A questionnaire was used to collect anonymous data on clinical presentation,biochemical and histological findings, and treatments.Results: Of all patients, 89.6% had autoimmune hepatitis-1 and 10.4% had autoimmunehepatitis-2. The female sex was predominant in both groups. The median age at symptomonset was 111.5 (6; 210) and 53.5 (8; 165) months in the patients with autoimmune hepatitis1 and autoimmune hepatitis-2, respectively. Acute clinical onset was observed in 56.1% and58.8% and insidious symptoms in 43.9% and 41.2% of the patients with autoimmune hepatitis-1and autoimmune hepatitis-2, respectively. The risk of hepatic failure was 1.6-fold higher forautoimmune hepatitis-2. Fulminant hepatic failure occurred in 3.6% and 10.6% of the patientswith autoimmune hepatitis-1 and autoimmune hepatitis-2, respectively; the risk was 3.1-foldhigher for autoimmune hepatitis-2. The gamma globulin and immunoglobulin G levels were sig-nificantly higher in autoimmune hepatitis-1, while the immunoglobulin A and C3 levels werelower in autoimmune hepatitis-2. Cirrhosis was observed in 22.4% of the patients; biochem-ical remission was achieved in 76.2%. The actuarial survival rate was 93.0%. A total of 4.6%underwent liver transplantation, and 6.9% died (autoimmune hepatitis-1: 7.5%; autoimmunehepatitis-2: 2.4%).Conclusions: In this large clinical series of Brazilian children and adolescents, autoimmunehepatitis-1 was more frequent, and patients with autoimmune hepatitis-2 exhibited higherdisease remission rates with earlier response to treatment. Patients with autoimmune hepatitis-1 had a higher risk of death.
- Balanced prime basis factorial fixed effects model with random number of observationsPublication . 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.