Facultad de Ciencias Básicas

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A bimodal discrete shifted poisson distribution. A case study of tourists' length of stay
(2020) Gómez-Déniz, E.; Pérez-Rodríguez, J.V.; Reyes, J.; Gómez, H.W.
A Bivariate Power Lindley Survival Distribution
(2024) Guillermo Martínez Flórez; Barry C. Arnold; Héctor W. Gómez
We introduce and investigate the properties of new families of univariate and bivariate distributions based on the survival function of the Lindley distribution. The univariate distribution,to reflect the nature of its construction, is called a power Lindley survival distribution. The basic distributional properties of this model are described. Maximum likelihood estimates of the parameters of the distribution are studied and the corresponding information matrix is identified. A bivariate power Lindley survival distribution is introduced using the technique of conditional specification.The corresponding joint density and marginal and conditional densities are derived. The product moments of the distribution are obtained, together with bounds on the range of correlations that can be exhibited by the model. Estimation of the parameters of the model is implemented by maximizing the corresponding pseudo-likelihood function. The asymptotic variance–covariance matrix of these estimates is investigated. A simulation study is performed to illustrate the performance of these parameter estimates. Finally some examples of model fitting using real-world data sets are described
A Gamma-type distribution with applications
(2020) Iriarte, Y.A.; Varela, H.; Gómez, H.J.; Gómez, H.W.
A Modified Cure Rate Model Based on a Piecewise Distribution with Application to Lobular Carcinoma Data
(2024) Yolanda M. Gómez; John L. Santibañez; Vinicius F. Calsavara; Héctor W. Gómez; Diego I. Gallardo
A novel cure rate model is introduced by considering, for the number of concurrent causes, the modified power series distribution and, for the time to event, the recently proposed power piecewise exponential distribution. This model includes a wide variety of cure rate models, such as binomial, Poisson, negative binomial, Haight, Borel, logarithmic, and restricted generalized Poisson. Some characteristics of the model are examined, and the estimation of parameters is performed using the Expectation–Maximization algorithm. A simulation study is presented to evaluate the performance of the estimators in finite samples. Finally, an application in a real medical dataset from a population-based study of incident cases of lobular carcinoma diagnosed in the state of São Paulo, Brazil, illustrates the advantages of the proposed model compared to other common cure rate models in the literature, particularly regarding the underestimation of the cure rate in other proposals and the improved precision in estimating the cure rate of our proposal.
A New Generalization of the Truncated Gumbel Distributionwith Quantile Regression and Applications
(2024) Héctor J. Gómez; Karol I. Santoro; Diego Ayma; Isaac E. Cortés; Isaac E. Cortés; Tiago M. Magalhães
In this article, we introduce a new model with positive support. This model is an extension of the truncated Gumbel distribution, where a shape parameter is incorporated that provides greater flexibility to the new model. The model is parameterized in terms of the p-thquantile of the distribution to perform quantile regression in this model. An extensive simulation study demonstrates the good performance of the maximum likelihood estimators in finite samples. Finally, two applications to real datasets related to the level of beta-carotene and body mass index are presented.
A parametric quantile regression model for asymmetric response variables on the real line
(2020) Gallardo, D.I.; Bourguignon, M.; Galarza, C.E.; Gómez, H.W.
A power maxwell distribution with heavy tails and applications
(2020) Segovia, F.A.; Gómez, Y.M.; Venegas, O.; Gómez, H.W.
A reliability model based on the incomplete generalized integro-exponential function
(2020) Astorga, J.M.; Reyes, J.; Santoro, K.I.; Venegas, O.; Gómez, H.W.
A transmuted version of the generalized half-normal distribution
(2019) Salinas, H.S.; Iriarte, Y.A.; Astorga, J.M.
A Weighted Skew-Logistic Distribution with Applicationsto Environmental Data
(2024) Isaac Cortés; Jimmy Reyes; Yuri A. Iriarte
Skewness and bimodality properties are frequently observed when analyzing environmental data such as wind speeds, precipitation levels, and ambient temperatures. As an alternative to modeling data exhibiting these properties, we propose a flexible extension of the skew-logistic distribution. The proposal corresponds to a weighted version of the skewed logistic distribution, defined by a parametric weight function that allows shapes with up to three modes for the resulting density.Parameter estimation via the maximum likelihood approach is discussed. Simulation experiments are carried out to evaluate the performance of the estimators. Applications to environmental data illustrating the utility of the proposal are presented.
Accurate Analytical Approximation for the Bessel Function J2(x)
(2024) Pablo Martin; Juan Pablo Ramos Andrade; Fabián Caro Pérez; Freddy Lastra
We obtain an accurate analytic approximation for the Bessel function 𝐽2(𝑥) using an improved multipoint quasirational approximation technique (MPQA). This new approximation is valid for all real values of the variable x, with a maximum absolute error of approximately 0.009. These errors have been analyzed in the interval from 𝑥=0 to 𝑥=1000, and we have found that the absolute errors for large x decrease logarithmically. The values of x at which the zeros of the exact function 𝐽2(𝑥) and the approximated function 𝐽˜2(𝑥) occur are also provided, exhibiting very small relative errors. The largest relative error is for the second zero, with 𝜀rel=0.0004 , and the relative errors continuously decrease, reaching 0.0001 for the eleventh zero. The procedure to obtain this analytic approximation involves constructing a bridge function that connects the power series with the asymptotic approximation. This is achieved by using rational functions combined with other elementary functions, such as trigonometric and fractional power functions.
An asymmetric bimodal distribution with application to quantile regression
(2019) Gómez, Y.M.; Gómez-Déniz, E.; Venegas, O.; Gallardo, D.I.; Gómez, H.W.
An asymmetric distribution with heavy tails and its expectation-maximization (EM) algorithm implementation
(2019) Olmos, N.M.; Venegas, O.; Gómez, Y.M.; Iriarte, Y.A.
An Extension of the Akash Distribution: Properties, Inference and Application
(2024) Yolanda M. Gómez; Luis Firinguetti Limone; Diego I. Gallardo; Héctor W. Gómez
In this article we introduce an extension of the Akash distribution. We use the slash methodology to make the kurtosis of the Akash distribution more flexible. We study the general probability density function of this new model, some properties, moments, skewness and kurtosis coefficients. Statistical inference is performed using the methods of moments and maximum likelihood via the EM algorithm. A simulation study is carried out to observe the behavior of the maximum likelihood estimator. An application to a real data set with high kurtosis is considered, where it is shown that the new distribution fits better than other extensions of the Akash distribution.
An Extension of the Fréchet Distribution and Applications
(2024) Yolanda M. Gómez; Inmaculada Barranco Chamorro; Jaime S. Castillo; Héctor W. Gómez
This paper presents the Slash-Exponential-Fréchet distribution, which is an expanded version of the Fréchet distribution. Through its stochastic representation, probability distribution function, moments and other relevant features are obtained. Evidence supports that the updated model displays a lighter right tail than the Fréchet model and is more flexible as for skewness and kurtosis. Results on maximum likelihood estimators are given. Our proposition’s applicability is demonstrated through a simulation study and the evaluation of two real-world datasets.
Aqueous Dried Extract of Skytanthus acutus Meyen as Corrosion Inhibitor of Carbon Steel in Neutral Chloride Solutions
(2021) Luis Cáceres; Yohana Frez; Felipe Galleguillos; Alvaro Soliz; Benito Gómez-Silva; Jorge Borquez
The implementation of corrosion engineering control methods and techniques is crucial to extend the life of urban and industrial infrastructure assets and industrial equipment affected by natural corrosion. Then, the search of stable and environmentally friendly corrosion inhibitors is an important pending task. Here, we provide experimental evidence on the corrosion inhibitory activity of aqueous extracts of Skytanthus acutus Meyen leaf, a native plant from the Atacama Desert in northern Chile. Skytanthus extracts as a powder should be prepared at 55 °C to avoid thermal decomposition and loss of corrosion inhibitory activity. Corrosion of carbon steel AISI1020 immersed in 0.5 M NaCl was evaluated in the presence of different doses of Skytanthus extract by complementary and simultaneous linear polarization, electrochemical impedance spectroscopy, and weight-loss technique under high hydrodynamic conditions. Mixed Potential Theory was applied to confirm the electrochemical activity of the extract inhibitory capabilities. The Skytanthus extracts reached a 90% corrosion inhibitory efficiency when tested at 100 to 1200 ppm in a time span of 48 h, through an electrochemical interaction between the extract inhibitor component and the carbon steel surface. The corrosion inhibition activity observed in Skytanthus dry extracts involves a protective film formation by a mechanism that includes an iron dissolution at the expense of either oxygen reduction and/or hydrogen evolution, followed by a ferrous-ferric iron cycling, the formation of an iron complex and adsorption to the metal surface, and, finally, desorption or degradation of the protecting film. The water-soluble plant extract was subjected to HPLC-MS analyses that rendered 14 major signals, with quinic acid, protocatechuic acid, chlorogenic acid isomers, vanillic acid hexoside, and patuletin 3-methoxy-7-glucoside as the most abundant components. Then, we propose that a phenolic derivative is responsible for the corrosion inhibitory activity found in Skytanthus extracts.
Betel and tobacco chewing habit and its relation to risk factors for periodontal disease
(2018) Giovannoni, M.L.; Valdivia-Gandur, I.; Lozano de Luaces, V.; Varela Véliz, H.; Balasubbaiah, Y.; Chimenos-Küstner, E.
Bimodal extension based on the skew-t-normal distribution
(2019) Amiri, M.; Gómez, H.W.; Jamalizadeh, A.; Towhidi, M.
Bivariate power-skew-elliptical distribution
(2020) Martínez-Flórez, G.; Tovar-Falón, R.; Gómez, H.W.
Censored bimodal symmetric-asymmetric families
(2018) Martínez-Flórez, G.; Bolfarine, H.; Gómez, H.W.

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