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Projeto de investigação
Center for Mathematics and Applications
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Side-scan sonar imaging data of underwater vehicles for mine detection
Publication . Santos, Nuno Pessanha; Moura, Ricardo; Torgal, Gonçalo Sampaio; Lobo, Victor; Neto, Miguel de Castro; CMA - Centro de Matemática e Aplicações; Information Management Research Center (MagIC) - NOVA Information Management School; NOVA Information Management School (NOVA IMS); Elsevier BV
Unmanned vehicles have become increasingly popular in the underwater domain in the last decade, as they provide better operation reliability by minimizing human involvement in most tasks. Perception of the environment is crucial for safety and other tasks, such as guidance and trajectory control, mainly when operating underwater. Mine detection is one of the riskiest operations since it involves systems that can easily damage vehicles and endanger human lives if manned. Automating mine detection from side-scan sonar images enhances safety while reducing false negatives. The collected dataset contains 1170 real sonar images taken between 2010 and 2021 using a Teledyne Marine Gavia Autonomous Underwater Vehicle (AUV), which includes enough information to classify its content objects as NOn-Mine-like BOttom Objects (NOMBO) and MIne-Like COntacts (MILCO). The dataset is annotated and can be quickly deployed for object detection, classification, or image segmentation tasks. Collecting a dataset of this type requires a significant amount of time and cost, which increases its rarity and relevance to research and industrial development.
Assessing global satisfaction of Portuguese expatriate workers using PLSc-SEM
Publication . Grilo, Luís M.; Honrado, Graciete; Vitorino, Ricardo; CMA - Centro de Matemática e Aplicações
The impacts of globalization and changes in the paradigms of the international workforce have led to an increasing trend in the number of expatriates (either those who do so by decision of the company for which they work, or those who do so on their own initiative). This reality applies to Portuguese expatriate workers, with positive and negative points for the development of their career and personal life. For a better understanding of this phenomenon, a survey was carried out using a questionnaire (validated in previous studies) with manifest variables expressed in a Likert-type scale of seven categories, which resulted in a sample of 207 observations. We used the Structural Equation Modeling (SEM) to study the relationship between the available latent variables and we applied the consistent Partial Least Squares (PLSc) estimator, which provides a correction for estimates and retains some of the advantages of the traditional PLS, to estimate the proposed reflective model. The results obtained show that for Portuguese expatriate workers the Personal Satisfaction and Satisfaction with Destination Country have a statistically significant direct effect on their Global Satisfaction.
Regression-type analysis for multivariate extreme values
Publication . de Carvalho, Miguel; Kumukova, Alina; dos Reis, Gonçalo; CMA - Centro de Matemática e Aplicações; Springer
This paper devises a regression-type model for the situation where both the response and covariates are extreme. The proposed approach is designed for the setting where the response and covariates are modeled as multivariate extreme values, and thus contrarily to standard regression methods it takes into account the key fact that the limiting distribution of suitably standardized componentwise maxima is an extreme value copula. An important target in the proposed framework is the regression manifold, which consists of a family of regression lines obeying the latter asymptotic result. To learn about the proposed model from data, we employ a Bernstein polynomial prior on the space of angular densities which leads to an induced prior on the space of regression manifolds. Numerical studies suggest a good performance of the proposed methods, and a finance real-data illustration reveals interesting aspects on the conditional risk of extreme losses in two leading international stock markets.
A New Class of Generalized Probability-Weighted Moment Estimators for the Pareto Distribution
Publication . Caeiro, Frederico; Mateus, Ayana; CMA - Centro de Matemática e Aplicações; MDPI - Multidisciplinary Digital Publishing Institute
Estimation based on probability-weighted moments is a well-established method and an excellent alternative to the classic method of moments or the maximum likelihood method, especially for small sample sizes. In this research, we developed a new class of estimators for the parameters of the Pareto type I distribution. A generalization of the probability-weighted moments approach is the foundation for this new class of estimators. It has the advantage of being valid in the entire parameter space of the Pareto distribution. We established the asymptotic normality of the new estimators and applied them to simulated and real datasets in order to illustrate their finite sample behavior. The results of comparisons with the most used estimation methods were also analyzed.
From plactic monoids to hypoplactic monoids
Publication . Guilherme, Ricardo P.; CMA - Centro de Matemática e Aplicações; Springer
The plactic monoids can be obtained from the tensor product of crystals. Similarly, the hypoplactic monoids can be obtained from the quasi-tensor product of quasi-crystals. In this paper, we present a unified approach to these constructions by expressing them in the context of quasi-crystals. We provide a sufficient condition to obtain a quasi-crystal monoid for the quasi-tensor product from a quasi-crystal monoid for the tensor product. We also establish a sufficient condition for a hypoplactic monoid to be a quotient of the plactic monoid associated to the same seminormal quasi-crystal.
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Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
6817 - DCRRNI ID
Número da atribuição
UIDB/00297/2020