Fuentes informativas en tiempos de Covid-19: Cómo los medios en Chile narraron la pandemia a través de sus redes sociales

This study analyzes the use of social media sources by nine news outlets in Chile in regard to Covid-19. We identified the most frequently used types of sources, their evolution over time, and the differences between the various social media platforms used by the Chilean media during the pandemic. Specifically, we extracted 838,618 messages published by Chilean media on Facebook, Instagram, and Twitter between January and December 2020. An initial machine learning (MA) process was applied to automatically identify 168,250 messages that included keywords that link their content to Covid-19. Based on a list of 2,130 entities, another MA process was used to apply a set of rules based on the appearance of declarative verbs or common expressions used by the media when citing a source, and the use of colons or quotation marks to detect the presence of different types of sources in the news content. The results reveal that Chilean media outlets’ use of different voices on social media broadly favored political sources followed by health, citizen, academic-scientific, and economic ones. Although the hierarchy of the most important sources used to narrate the public health crisis tended to remain stable, there were nuances over time, and its variation depended on key historic milestones. An analysis of the use of sources by each platform revealed that Twitter was the least pluralist, giving space to a more restricted group of voices and intensifying the presence of political sources over the others, particularly citizen sources. Finally, our study revealed significant differences across media types in the use of political, health, and citizen sources, with television showing a greater presence than in other types of media. Resumen Se analiza el uso de fuentes en redes sociales de nueve medios de información de referencia en Chile frente al Covid-19. Se identificaron los tipos de fuentes más utilizados, su evolución en el tiempo, así como las diferencias encontradas entre distintas plataformas de redes sociales de los medios chilenos. Específicamente, se extrajeron 838.618 publicaciones de medios nacionales desde Facebook, Instagram y Twitter entre enero y diciembre de 2020. A ese corpus se aplicó un primer proceso de machine learning (MA) para filtrar automáticamente 168.250 publicaciones que incluían palabras claves que identifican su contenido con el Covid-19. A partir de una lista de 2.130 entidades, se utilizó otro proceso de MA para aplicar un conjunto de reglas basadas en la presencia de verbos declarativos o de expresiones comunes usadas por los medios cuando se cita a una entidad, así como el uso de dos puntos o de comillas, con el objeto de detectar distintos tipos de fuentes en el contenido informativo. Los resultados muestran que el uso que los medios chilenos dieron a distintas voces en sus redes sociales favoreció ampliamente a las fuentes políticas, seguidas por las fuentes de salud, y más desde lejos por las ciudadanas, académico-científicas y económicas. Aunque la jerarquía de las fuentes que se usó para narrar la crisis sanitaria tendió a mantenerse estable, tuvo matices a lo largo del tiempo y su variación dependió de los hitos que marcaron la historia del país. Al analizar el uso de fuentes según plataforma, se observa a Twitter como menos pluralista, dando espacio a un grupo más restringido de voces e intensificando la presencia de las fuentes políticas por sobre las demás; en especial, por sobre las ciudadanas. Finalmente, nuestro estudio reveló diferencias significativas en las fuentes utilizadas por publicaciones de origen televisivo, particularmente en el uso de fuentes políticas, de salud y ciudadanas, las cuales tuvieron una presencia mayor que en los demás tipos de medios

Best Lag Window for Spectrum Estimation of Law Order MA Process

In this article, we investigate spectrum estimation of law order moving average (MA) process. The main tool is the lag window which is one of the important components of the consistent form to estimate spectral density function (SDF). We show, based on a computer simulation, that the Blackman window is the best lag window to estimate the SDF of MA1 and MA2 at the most values of parameters βi and series sizes n, except for a special case when β=−1 and n≥40 in MA1. In addition, the Hanning–Poisson window appears as the best to estimate the SDF of MA2 when β1=β2=−0.5 and n≥40.

Mechanically alloyed NiTiO3/transition metal heterostructures: introducing oxygen vacancies for exceptionally enhanced hydrogen evolution reaction activity

This work reports that a convenient and straightforward MA process can produce top-performing heterostructured catalysts for the HER in alkaline media.

A comprehensive study on synthesis behavior of nanostructured Al-Zn-Mg-Cu alloy powder with and without 3 wt.% Al2O3 particles during mechanical alloying

The mechanical alloying (MA) process was applied to synthesize nanostructured Al-Zn-Mg-Cu alloy powder and its composite with 3 wt.% Al2O3 particles. Both the alloy and the composite powders were produced by simultaneous milling of the constituents for different milling times (0–50 hours), with fixed milling technical parameters. The produced powders were characterized by the X-ray diffraction (XRD) analysis to detect the generated phases. Also, a scanning electron microscope (SEM) and a transmission electron microscope (TEM) were used to observe the morphologies and measure the crystallite size of the powders, respectively. It was found that during the production of the composite powder, the size of Al2O3 particle changed which led to unexpected outcomes. In the alloy state, the average particle size and the crystallite size were lower and the microhardness values were higher than those in the composite powder. Also, the steady state was achieved after a shorter MA time in the alloy state compared to the composite state. The major reason for these results was the changes of alumina particle size in the composite powders at the first stages of the MA process due to consuming a noticeable amount of energy, which made them ineffective. In addition, the compressibility in the composite powders was lower than that of the alloy powders due to the presence of alumina particles. Moreover, in both powders, the compressibility decreased with increasing the MA time because of the increased work hardening and the reduced flow properties.

Influence of the mechanical alloying process on the sintering behaviour of astaloy CrM powder mixture with silicon carbide addition

Due to an excellent combination of toughness and strength, bainitic-austenitic dual phase steels with silicon addition have many applications in the industry. However, silicon has a high affinity to oxygen and, therefore, its introduction to the alloy is problematic during the classical sintering processes of mixing powders. Mechanical alloying (MA) offers one of the most attractive alternatives to the introduction of silicon to Astaloy CrM powders. The aim of the present study was to determine the influence of the MA process on changes in particle size distribution, work hardening and sintering behaviour of the investigated powder mixture - Astaloy CrM powder with the addition of 2 wt.% stearic acid and 2 wt.% silicon carbide alloyed under different conditions. The practical aspect of this study was to develop and apply a common and inexpensive method of die-pressing to compact a powder mixture prepared by the MA process.

Researches Regarding the Properties of Sintered Electrical Contacts Obtained From Mechanically Alloyed W-Cu Powders

In this paper are presented the experimental results regarding the elaboration of electrical contacts using W-Cu composite powders obtained by mechanical alloying (MA) process. For the research commercial powders with a particle size between [10-80] µm were used. Three types of mixtures with different concentrations as follow: 90W-10Cu; 80W-20Cu; 70W-30Cu were mechanically alloyed for 2 up to 6 hours using a planetary ball mill. The mixtures obtained after MA process were pressed in a cylindrical die at 400 respective 600 MPa. The evolution of green densities function the compaction pressure and Cu content was studied. The green billets were sintered in an electrical furnace at 1180 oC and maintained 60 minutes at the sintering temperature in argon atmosphere. The evolution of densities, microstructures and electrical properties of the sintered samples function the Cu content and compaction pressure were studied.

Preparation of Nanostructured Al-4.5wt%Mg Powder via Mechanical Alloying Process

In this work, the preparation of nanostructured Al-4.5wt%Mg powder through the mechanical alloying (MA) process was evaluated. The X-ray diffraction (XRD) technique was used to calculate the crystallite size and microstrain. Scanning electron microscopy (SEM) was used not only to study the morphology of the powders but also to show the fact that the Mg powders were distributed during the MA process. Transmission electron microscopy (TEM) was also used to demonstrate whether the produced powders are nanostructured or not. XRD results showed that microstrain and crystallite size of milled powder (after 10 h milling at the ball-to-powder weight ratio (BPR) of 20:1) were ≈-0.34% and ≈20nm respectively. XRD and TEM results showed that Al12Mg17has been formed during MA process. This means that during this process, mutual diffusion of Al and Mg has occurred.