Machine learning techniques to select Be star candidates. An application in the OGLE-IV Gaia south ecliptic pole field

Statistical pattern recognition methods have provided competitive solutions for variable star classification at a relatively low computational cost. In order to perform supervised classification, a set of features is proposed and used to train an automatic classification system. Quantities related to the magnitude density of the light curves and their Fourier coefficients have been chosen as features in previous studies. However, some of these features are not robust to the presence of outliers and the calculation of Fourier coefficients is computationally expensive for large data sets. We propose and evaluate the performance of a new robust set of features using supervised classifiers in order to look for new Be star candidates in the OGLE-IV Gaia south ecliptic pole field. We calculated the proposed set of features on six types of variable stars and on a set of Be star candidates reported in the literature. We evaluated the performance of these features using classification trees and random forests along with K-nearest neighbours, support vector machines, and gradient boosted trees methods. We tuned the classifiers with a 10-fold cross-validation and grid search. We validated the performance of the best classifier on a set of OGLE-IV light curves and applied this to find new Be star candidates. The random forest classifier outperformed the others. By using the random forest classifier and colour criteria we found 50 Be star candidates in the direction of the Gaia south ecliptic pole field, four of which have infrared colours consistent with Herbig Ae/Be stars. Supervised methods are very useful in order to obtain preliminary samples of variable stars extracted from large databases. As usual, the stars classified as Be stars candidates must be checked for the colours and spectroscopic characteristics expected for them

Who uses Transport Network Companies?: Characterization of Demand and its Relationship with Public Transit in Medellín

Transport Network Companies (TNCs) have become a popular alternative for mobility due to their ability to provide on-demand flexible mobility services. By offering smartphone-based, ride-hailing services capable of satisfying specific travel needs, these modes have transformed urban mobility worldwide. However, to-date, few studies have examined the impacts in the Latin American context. This analysis is a critical first step in developing policies to promote efficient and sustainable transport systems in the Latin-American region. This research examines the factors affecting the adoption of on-demand ride services in Medellín, Colombia. It also explores whether these are substituting or competing with public transit. First, it provides a descriptive analysis in which we relate the usage of platform-based services with neighborhood characteristics, socioeconomic information of individuals and families, and trip-level details. Next, factors contributing to the election of platform-based services modeled using discrete choice models. The results show that wealthy and highly educated families with low vehicle availability are more likely to use TNCs compared to other groups in Medellín. Evidence also points at gender effects, with being female significantly increasing the probability of using a TNC service. Finally, we observe both transit complementary and substitution patterns of use, depending on the context and by whom the service is requested

Ensayos y pruebas de un calentador solar de agua operando por termosifón

En este artículo se presentan los diferentes ensayos y pruebas hechos a un colector solar para calentamiento de agua de consumo doméstico, operando por termosifón. Los ensayos se hacen con base en la norma técnica colombiana NTC 4368. Se presentan además los resultados de las pruebas y las conclusiones a las mismas

Ensayos y pruebas de un calentador solar de agua operando por termosifón

En este artículo se presentan los diferentes ensayos y pruebas hechos a un colector solar para calentamiento de agua de consumo doméstico, operando por termosifón. Los ensayos se hacen con base en la norma técnica colombiana NTC 4368. Se presentan además los resultados de las pruebas y las conclusiones a las mismas

Ensayos y pruebas de un calentador solar de agua operando por termosifón

En este artículo se presentan los diferentes ensayos y pruebas hechos a un colector solar para calentamiento de agua de consumo doméstico, operando por termosifón. Los ensayos se hacen con base en la norma técnica colombiana NTC 4368. Se presentan además los resultados de las pruebas y las conclusiones a las mismas

DISEÑO Y CONSTRUCCIÓN DE UN CALENTADOR SOLAR DE AGUA OPERANDO POR TERMOSIFÓN

En este artículo se presenta el proceso de diseño y construcción de un colector solar para calentamiento de agua de consumo doméstico, operando por termosifón. El diseño matemático, la selección de los materiales y el proceso de construcción, con base en las normas técnicas colombianas NTC 4368 y NTC 2461, se describen en este trabajo

DISEÑO Y CONSTRUCCIÓN DE UN CALENTADOR SOLAR DE AGUA OPERANDO POR TERMOSIFÓN

En este artículo se presenta el proceso de diseño y construcción de un colector solar para calentamiento de agua de consumo doméstico, operando por termosifón. El diseño matemático, la selección de los materiales y el proceso de construcción, con base en las normas técnicas colombianas NTC 4368 y NTC 2461, se describen en este trabajo

Deriving calibrations for Arawakan using archaeological evidence

NWOVl.Veni.191T.007Descriptive and Comparative Linguistic