Suchergebnisse

AbstractOne of the significant features of Chinese economic development in the 1980s was that grain imports increased sharply, while the whole economy experienced rapid growth and reform. This paper attempts to measure the domestic resources costs (DRC) of rice and wheat production in China (two of the most important grains in the Chinese grain sector) during the period 1981–87 and to examine the questions of whether, or to what extent, the level of comparative advantage in grain production can explain the performance of China's grain trade. Substantial comparative advantage in China's rice production and considerable comparative disadvantage in wheat production have been found by the measurement. These preliminary results suggest that the relative costs incurred by China's domestic grain sector were likely to have played some role in determining both the structure of its grain trade and its large scale of net wheat importation in the 1980s.

Abstract
During the coronavirus disease 2019 (COVID-19) pandemic, many countries recommended social distances to prevent aerosol transmission. But in some cases, if there is insufficient ventilation condition especially in a stagnant air space, or other ventilation conditions, droplets from coughs or sneezes may have different potential infection impacts.
In this study, a TSI Aerodynamic Particle Sizer® (APS™) 3321 spectrometer was used to measure the aerosol size distributions of coughs and sneezes from volunteer subjects. The APS detects particles in the 0.37 to 20 μm range, with high-resolution sizing from 0.5 to 20 μm aerodynamic diameter. And it was placed in the sitting breathing area (80 cm height) in front of the volunteers in a testing chamber (2.0*2.0*2.1 m³). The social distance was 6 feet. The APS was used to sample for 1 minute after each action and was continued to sample the self-preserving distribution for aerosol coagulation for 30 minutes. The results showed after continuous monitoring for 30 minutes, the sneezing droplet range of male and female was between 0.523 ~ 5.425 μm, and the coughing droplet was in 0.523 ~ 4.371 μm; the mode droplet size of sneezing was 17.154 μm (0.08 mg/m³) for male and was about 14.855 μm (0.11 mg/m³) for female. Moreover, the mode droplet size of coughing for male was 10.366 μm (0.06 mg/m³), and 11.14 μm (0.02 mg/m³) for female, the droplet of a sneeze was larger and heavier than that of a cough while maintaining social distance after 30 minutes' suspension and coagulation.