EJUKWA, Justin Odadami; ESSI, Isaac Didi. Time-Varying Covariance in Major Energy Portfolios. Faculty of Natural and Applied Sciences Journal of Scientific Innovations , Port Harcourt, Nigeria, v. 6, n. 4, p. 31–44, 2025. DOI: 10.63561/fnas-jsi.v6i4.966. Disponível em: https://fnasjournals.com/index.php/FNAS-JSI/article/view/966. Acesso em: 6 oct. 2025.