ABSTRACT
Predicting COVID-19 epidemic development in the upcoming warm season has attracted much attention in the hope of providing helps to fight the epidemic. It requires weather (environmental) factors to be included in prediction models, but there are few models to achieve it successfully. In this study, we proposed a new concept of environmental infection rate (RE), based on floating time of respiratory droplets in the air and inactivation rate of virus to solve the problem. More than half of the particles in the droplets can float in the atmosphere for 1-2 hours. The prediction results showed that high RE values (>3.5) are scattered around 30{degrees}N in winter (Dec.-Feb.). As the weather warms, its distribution area expands and extends to higher latitudes of northern hemisphere, reaching its maximum in April, and then shrinking northward. These indicated that the spread of COVID-19 in most parts of the northern hemisphere is expected to decline after Apr., but the risks in high latitudes will remain high in May. In the south of southern hemisphere, the RE values tend to subside from Apr. to July. The high modeled RE values up to July, however, suggested that warmer weather will not stop COVID-19 from spreading. Public health intervention is needed to overcome the outbreak.
ABSTRACT
The analysis of stable nitrogen isotopic composition (δ15 N) of individual amino acid was recognized as an effective method for estimating the trophic level of organisms and detecting the nitrogen flow in food webs. In this study, we evaluated a two-stage procedure of esterification followed by acylation, in which biological samples underwent hydrolysis in acid and the released individual amino acids were derivative into the corresponding N-pivaloyl-iso-propyl ( NPP ) esters for gas chromatography-combustion-isotope ratio mass spectrometric ( GC-C-IRMS) analysis. A total of 13 kinds of individual amino acid derivatives were baseline separated on a nonpolar gas chromatography column (DB-5ms). The amount of sample for each test was not less than 20 ng N on column. High correlations were observed between the δ15 N values respectively obtained by GC-C-IRMS and element analysis-isotope ration mass spectrometry (EA-IRMS). Furthermore, the mean precision of this method was better than 1‰. Cation-exchange chromatograph was used to purify the samples, and the difference of the detection δ15 N values before and after purification by the resin was within 1‰. This method was applied to estimate the trophic level of various natural freshwater organisms from Aha Lake. The present study provided a new idea for the application of stable nitrogen isotope (δ15 N ) in the trophic level estimation of organisms and metabolism analysis of amino acid.
