[Epidemiological characteristics of novel coronavirus pneumonia in Shijiazhuang, China].

Objective: To analyze the epidemiological characteristics of an outbreak of novel coronavirus pneumonia (COVID-19) in Shijiazhuang, Hebei Province in 2021 and to provide scientific basis for developing improved strategies to prevent and control the outbreak of COVID-19. Methods: Descriptive analysis of the outbreak of COVID-19 in Shijiazhuang, Hebei Province was performed with SPSS 21.0 and Excel software. The statistical analysis of the incubation period was performed using the rstan package in R4.0.4. Results: As of February 14th 2021, a total of 942 local confirmed cases were reported in Hebei Province, 869 cases in Shijiazhuang, of which 847 cases were available for case information. This outbreak was mainly in rural areas, with the largest number of confirmed cases in Xiaoguozhuang village, 249 (29.4%); followed by Nanqiaozhai village, 128 (15.1%); and Liujiazuo village, 85 (10.0%). The outbreak lasted from January 2nd, 2021 to February 14th, 2021, and was mainly transmitted among the farmers as well as the students through dining parties, public gatherings and family contacts, showing an obvious time and occupation concentration trend. An analysis of 116 local confirmed cases in this outbreak with specific exposure time and onset time indicated that the median incubation period was 6 [interquartile range(IQR): 3.3, 10.0] days; whereas another report including 264 local confirmed cases with specific exposure time window showed that a median incubation period was 8.5 [95% confidence interval (CI): 1.8-18.8] days. Conclusions: This outbreak was mainly related to rural areas, and was associated with parties, public gatherings and family gatherings. Self-protection and isolation of key areas and populations at risk should be effectively implemented to avoid close contact and other measures to reduce the occurrence of COVID-19 aggregation. Based on the results of the incubation period of this outbreak, the isolation period could be recommended to be extended to three weeks.

[Simulation of gas chromatographic peak motion process].

Solute motion process under different temperature, pressure and/or flow program conditions is simulated with the aid of numerical calculation of the differential equation. It is demonstrated that there exist some differences between the normalized average linear velocity and the normalized local linear velocity. As time develops, they intercept, and may not reach the column end at the same time, thus may result in errors in retention time simulation. In constant pressure process, where the compressibility factor (j) does not change, simulation results in a model index of 1, and no model difference can be found when the integrate equation is used. In pressure varying process, where j changes by time, simulation results in an model index which deviates to 1, and positive (for a j decrease process) or negative (for a j increase process) error can be found when the integrate equation is used. The numerical solution of the differential equation is singular under given programs, which corresponds to a specific space line in z, t, u coordinates.