Browsing by Autor "L. Herrera"

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Conformally flat polytropes for anisotropic matter
(Springer Science+Business Media, 2014) L. Herrera; A. Di Prisco; W. Barreto; J. Ospino
Estudio de una intrusión de polvo sahariano en la atmósfera de Colombia
(University of Medellín, 2018) Juan Felipe Méndez-Espinosa; L. Herrera; Luis Carlos Belalcázar
El desierto del Sahara es una de las principales fuentes de material particulado (MP) en el mundo. Este MP tiene la capacidad de afectar la calidad del aire a miles de kilómetros de la fuente. Las intrusiones de este polvo en el Caribe están bien documentadas, sin embargo, no se han reportado intrusiones de este contaminante en grandes ciudades colombianas. En este artículo se analiza y determina la posible relación entre las emisiones de polvo del Sahara y un episodio de alta contaminación que se registró en Bogotá y Medellín a finales de junio de 2014. Se utilizaron los datos registrados por las redes de calidad del aire de Bogotá y Medellín, la densidad másica de columna de polvo del proyecto MERRA-2 y los resultados del modelo NMMB/BSC-Dust. Se rastrearon las trayectorias y origen de masas de aire implementando HYSPLIT y se obtuvo el tipo de aerosol mediante el sensor CALIOP-CALIPSO.
Public Health Impact Atribution due particulate matter from Biomass Burning Emissions
(2019) L. Herrera; Ricardo Morales Betancourt; Luis Jorge Hernández Flórez
Background: Biomass burning emissions have a substantial impact on regional air quality and climate, we evaluated the short-term effect of particulate matter on acute respiratory disease morbidity and mortality, determinated by the risk of childs under 5 years old and adults over 60 years old in Bogota 2016. Methods: Daily Emergency Department (ED) visit records for respiratory illnesses and selected diagnosis, besides daily concentrations of PM2.5 obtained in Bogota as a high altitude city, therefore we selected the back-trajectories of air masses reaching the receptor, that were linked with fire spots. Using conditional Poisson time series analysis we assessed the effect of air pollutants on health outcomes using single pollutant, controlling for meteorology and time trends. The percentages of change in the rate of ED visits and their 95% confidence interval were estimated for the joint effect of particulate matter. Results and Conclusions: On one hand in dry season, the amount of firespots increases as single-pollutant model increases particulate matter were associated with 5% increases in ED visits for respiratory diseases. On the other hand the during the wet season the incidence of ED visits decreases.
RadiatingC metric: An example of a proper Ricci collineation
(Springer Science+Business Media, 1984) L. Aulestia; Luis A. Núñez; Alberto Patiño-Vanegas; Héctor Rago; L. Herrera
STUDY OF A SAHARAN DUST INTRUSION INTO THE COLOMBIAN ATMOSPHERE : Impact on public health The case of Guajira
(2019) L. Herrera; Samuel David Osorio García; Juan Felipe Méndez-Espinosa
Sahara desert is one of the main sources of particulate matter (PM) in the world. This Particulate Matter has the potential to affect the air quality, thousands of kilometers away from the source. The dust intrusions in the Caribbean are well documented; however, there are no reports of this pollutant in Colombian large cities. In this article we analyze and establish the possible relation between the Sahara’s dust emissions and an episode of elevated PM levels registered at the end of June 2014 in the entire Country, these type of events are not atypical for coastal areas, that is why is pertinent to assess the impact on public health in this case for Guajira . For this purposes we used data collected by the automatic air quality monitoring stations installed in these cities, the column mass density of the MERRA-2 project, and results from the NMMB/BSC-Dust model. We also implemented the HYSPLIT model to determine the origins and trajectories of air masses during the episode. As results, the averages in the Medellin results were the highest values of 2014. According to the results obtained from MERRA-2, on June 27, 2014 an intrusion of Saharan dust occurred in approximately 95% of the national territory with a value greater than 90 Kg / Km2 of dust column density, and from the backward trayectories, the air masses were from saharan dust. The increase of reports of cardiovascular and respiratory illnesses for Maicao on Guajira Department are related to the increment of particulate matter due this transatlantic transport.
Supernovae: Where and why do they break off?
(Springer Science+Business Media, 1992) L. Herrera; L. A. N��ez
Supernovae: Where and Why Do They Break Off?
(1991) L. Herrera; Luis A. Núñez
Supernovae: Where and why do they break off?\n\n\n(Herrera, L.; Núñez, Luis)\n\n\nAbstract\n\n\nThe precise mechanism whereby gravitational collapse leads to a type II supernova event is one of the most controversial points in the understanding of the final stages of stellar evolution. The 'bounceshock' mechanism and the proposed `long-term neutrino mediated' processes compete to explain the ejection of the outer envelopes of the star. Despite their differences, both descriptions consider the shock as mainly responsible for the ejection of the outer mantle in a supernova burst. In this note we discuss results from collapse calculations in which the shock is considered as an interface separating the quasi-static stiff core from the outer mantle. In the models considered the shock fades out and becomes a new boundary surface delimiting the compact homogeneous remnant. The resulting pictures become intelligible in the light of a recently proposed generalization of the concept of adiabatic index for systems where radiation flux is present.\n\n\n\nArtículo publicado en: Astrophysical and Space Science. 188: 9-18 1992.