COMMUNICATION | doi:10.20944/preprints202004.0130.v1
Subject: Medicine And Pharmacology, Pulmonary And Respiratory Medicine Keywords: COVID-19; LMIC; Quarantine Measures
Online: 8 April 2020 (12:03:43 CEST)
In response to the COVID-19 pandemic, the Philippines placed the majority of the country under enhanced community quarantine, restricting the movement of most of its 100 million plus population. These aggressive measures were initiated on March 15, 2020 and intensified on March 17. According to official data, the number of confirmed COVID-19 cases has exponentially increased during this period, but it is important to note that the number of patients tested also substantially increased during the same period. It is not conclusive that widespread transmission of COVID-19 only started in March and our analysis suggests that community transmission was happening earlier. In discussing extended quarantine measures, it is important to properly understand the trends and recognize the limitations of the data. The unintended consequences on the population, especially in lower-middle income countries with fragile health systems like the Philippines, must be carefully considered.
ARTICLE | doi:10.20944/preprints202311.0545.v1
Subject: Environmental And Earth Sciences, Other Keywords: sandstone; high-temperature; heating rate; physical and mechanical properties; acoustic emission; macroscopic de-structive characteristic; microscopic morphology
Online: 9 November 2023 (07:19:03 CET)
The physical and mechanical properties of rocks will change significantly after being subjected to high temperatures, which poses safety hazards to underground projects such as coal underground gasification. In order to investigate the effect of temperature on the macroscopic and microscopic properties of rocks, this paper has taken sandstone as the research object and conducted uniaxial compression tests on sandstone specimens at different temperatures (20-1000 ℃) and different heating rates (5-30 ℃/min) at 1200 ℃. At the same time, the acoustic emission (AE) test system was used to observe the acoustic emission characteristics of the rock damage process, and the microstructural changes after high temperature were analyzed with the help of a scanning electron microscope (SEM). The test results show that the effect of temperature on sandstone is mainly divided into three stages: Ⅰ (20-500 ℃) stage is the strengthening zone, the evaporation of water and the contraction of primary fissures, sandstone densification is enhanced. Specifically, the compressive strength and elastic modulus increase, the macroscopic damage mode is dominated by shear damage, and the fracture micro-morphology is mainly brittle fracture. Stage II (500-600°C) is the transition zone, 500°C is the threshold temperature for compressive strength and modulus of elasticity, and the damage mode changes from shear to cleavage damage, and the sandstone undergoes brittle-ductile transition in this temperature interval. Stage III is the physicochemical deterioration stage. The changes in physical and chemical properties make the sandstone compressive strength and modulus of elasticity continue to decline, the macroscopic damage mode is mainly dominated by cleavage damage, and the fracture microscopic morphology is more toughness fracture. The effect of different heating rates on the mechanical properties of sandstone was further studied, and it was found that the mechanical properties of the rock were more deteriorated under higher heating rates.
REVIEW | doi:10.20944/preprints202306.0522.v1
Subject: Chemistry And Materials Science, Physical Chemistry Keywords: Fischer-Tropsch synthesis; Fe-carbide; Mechanism; Synthesis gas; Fe carburization
Online: 7 June 2023 (08:58:31 CEST)
With an increase in energy consumption globally, Fischer-Tropsch (FT) synthesis is a good alternative for producing fuels and chemicals from coal, natural gas or biomass. Among them, coal to liquids has been put into production in countries that have large coal reserves. In this process, Fe-based catalysts are commonly used due to their earth abundance, comparatively wide operation range and ready availability to handle low H2/CO ratio from coal. Despite their extensive applications, the kinetic and mechanistic understandings of Fe carburization and FT reaction on Fe-carbides are relatively limited due to the complexity of phase composition of the applied catalysts. This review summarizes the current state of knowledge of FT synthesis on Fe-carbide with an emphasis on underlying mechanism. Specifically, the employment of model catalyst, such as Raney-Fe, could provide a convenient way to furnish kinetic information regarding Fe carburization and subsequent FT reaction. A major challenge for further understanding catalytic reactions occurring at the Fe-carbide surface is correlating FT activity and selectivity to specific active site. To address this issue, the advancements of both DFT calculations and surface science techniques are highly demanded.