Here, we present an assessment of long-term trends in the O₃ weekend effect (WE) occurrences and spread within the Mexico City (MCMA), Guadalajara (GMA), and Monterrey (MMA) metropolitan areas, which are the three largest metropolitan areas (MAs) of Mexico and concentrate around 33% of the total population in the country. Daytime averages and peak differences in O₃ concentrations from weekdays to weekends were used as a proxy of WE occurrence. All MAs exhibited the occurrence of WE in all years at least in one monitoring site. Substantial differences in O₃ daytime averages and peaks from weekdays to weekends have decreased over time in all MAs, and since 1998 and 2013 for the MCMA and GMA, respectively, higher O₃ levels during weekends are typical during most of the year. The largest variations in the O₃ WE were observed at downwind and urban core sites of the MCMA and GMA. Significant increasing trends (p < 0.05) in the O₃ WE magnitude were observed for Sundays at all sites within the MCMA, with trends in annual averages ranging between 0.33 and 1.29 ppb O₃ yr⁻¹. Within the GMA, for Sundays, fewer sites exhibited increasing trends in the WE occurrence and at lower growth rates (0.32 and 0.48 ppb yr⁻¹, p < 0.1) than within the MCMA, while within the MMA no apparent trends were observed in marked contrast with the MCMA and GMA. Our findings suggest that policies implemented have been successful in controlling weekday ground-level O₃ within the MCMA and GMA, but further actions must be introduced to control the increases in the O₃ WE magnitude and spread.

Communicability functions quantify the flow of information between two nodes of a network. In this work, we use them to explore the concept of the influence of a paper in a citation network. These functions depend on a parameter. By varying the parameter in a continuous way we explore different definitions of influence. We study six citation networks, three from physics and three from computer science. As a benchmark, we compare our results against two frequently used measures: the number of citations of a paper and the PageRank algorithm. We show that the ranking of the articles in a network can be varied from being equivalent to the ranking obtained from the number of citations to a behaviour tending to the eigenvector centrality, these limits correspond to small and large values of the communicability-function parameter, respectively. At an intermediate value of the parameter a PageRank-like behaviour is recovered. As a test case, we apply communicability functions to two sets of articles, where at least one author of each paper was awarded a Nobel Prize for the research presented in the corresponding article.

Los errores son parte del proceso en la investigación científica. Las correcciones a estos errores se hacen normalmente en artículos llamados, entre otros nombres, errata o erratum. La investigación sobre estas erratas ha sido, en áreas de investigación y revistas, muy específica. Así, en este artículo estudiamos la tasa de erratas en las veintisiete áreas de investigación definidas en la base de datos Scopus. Nos enfocamos en el periodo 2003-2017 para analizar la distribución de las veintisiete áreas en cuartiles, de acuerdo con el porcentaje de erratas. En paralelo, analizamos la tendencia de esos porcentajes por cada área durante el periodo señalado. Encontramos que esas equivocaciones son útiles como un indicador de diferencias notables entre áreas del conocimiento. Con información de la Web of Science, nos enfocamos en cuatro áreas del conocimiento, particularmente en la proporción de erratas por revista. Encontramos que la mayoría de éstas no tienen erratas publicadas, que en general la correlación entre el factor de impacto y el porcentajede aquéllas no es significativa y que la distribución de esos por revista se ajusta bien a una distribución log-normal.

The centrality measures of the nodes and edges of the street networks are related to various urban phenomena. In particular, betweenness centrality correlates with the spatial distribution of economic activities, the levels of congestion, and the structural changes in cities. In this work, we study how betweenness tends to concentrate in a small set of edges and develop a model to analyse this concentration throughout the growth of graphs. We show that random planar graphs tend to betweenness concentration as the number of nodes increases. The evolution of Paris and Tijuana street networks shows the same behaviour but at a higher rate. A set of 300 street networks worldwide follows a similar relationship between the number of nodes and the betweenness concentration. We find a significant correlation between congestion ranks and betweenness concentration.

Este artículo presenta un análisis de la concentración de la intermediación en las redes de vialidades de las zonas metropolitanas de México y su impacto en la congestión vehicular. Se muestra que el tamaño de la red y su casi planaridad determinan la proporción de aristas (calles) que concentran la mayor parte de la intermediación de la red. Esta proporción explica entre el 50 y el 70% de la varianza en la cantidad de horas perdidas debido a la congestión. Los resultados indican que es casi imposible disminuir significativamente los niveles de congestión modificando la conectividad localmente, como la creación de puentes o pasos a desnivel. Esto fortalece las propuestas de invertir en transporte público masivo y en infraestructura para la movilidad activa, así como en el desarrollo de ciudades con mezclas de usos de suelo que eviten los desplazamientos largos.

The occurrence of higher ground-level O₃ concentrations on weekends rather than on weekdays, despite reduced anthropogenic activity in urban areas, is known as the O₃ weekend effect (OWE). Here, we present an approach to analyse OWE spatio-temporal variations in urban areas, integrated by the trend, prediction and network representation. We used data from ten monitoring sites geographically distributed within the Mexico City Metropolitan Area (MCMA) recorded during 1994-2018. The OWE occurrence within the MCMA ranged typically between 40 and 60 % of the total weeks per year. The annual differences between weekday and weekend O₃ peaks (magnitudes) showed were most significant on Sundays. Naive, Linear and Auto-regressive Integrated Moving Average models were tested for predicting the OWE annual occurrences and magnitudes. There was no single model that outperformed significantly for predicting OWE at all sites. The proposed concept of generalised OWE (GOWE) implies that at least half of the sites under study exhibited simultaneous OWE occurrence. GOWE is represented as a network and its integration with prediction models is useful to determinate the OWE spread over the MCMA in the following years. The GOWE occurrence showed an increasing trend interpreted as the spread of VOC-limited conditions over most of the MCMA. Predicted data suggest that, with the current emission control policies, the GOWE will continue occurring. The integrated methodology presented permits the acquisition of valuable insights into the design of potential air quality control strategies.