A Study on the Development of Leisure Agriculture in Liaoning Province

Leisure agriculture in foreign countries has a long history of over 100 years,and China's leisure agriculture started in the 1980 s.With the earlier reform and opening up,Shenzhen first opened " Lychee Festival" in the macroscopic background,and leisure agriculture in Liaoning Province was also developed by leaps and bounds. This paper describes the basic situation of leisure agriculture in Liaoning Province,analyzes the three stages of leisure agriculture in Liaoning Province,and expounds the leisure agriculture in Liaoning's product development mode. Finally,it puts forward strategies for the development of leisure agriculture in Liaoning Province,in order to contribute to the development of leisure agriculture in Liaoning Province.

A 6n-Order Low-Frequency Mathematical Model of Multiple Inverters Based Microgrid

Microgrid stability analysis is a critical issue especially due to the inverters’low-inertia nature.The voltage and current control loops influences on stability are researched frequently most of which focus on medium and high-frequency characteristic.Although the complete state-space model aims at low-frequency characteristic,it is too complicated and the calculation amount is huge with the scale of the microgrid increasing.One available reduced-order model of an inverter is simple,but it is suitable for only single inverter without network dynamic in microgrid.To fill in these gaps,a novel modeling method is proposed in this paper to investigate the low-frequency instability phenomenon and describe the whole DG connected system including network.In consideration of the high penetration level of induction motor(IM)loads and constant power(CP)loads in practical applications,the low-frequency mathematical model of IM and CP loads on the basis of static load is also built in this paper.Simulation and experimental results verify the effectiveness of the proposed model.

A multi-provincial survey and analysis of radiation doses from pediatric CT in China

Objective:To survey and analyze the radiation doses of pediatric CT in some provinces(autonomous region)or municipalities in China,and compare them with the data released by the relevant domestic and international organizations,so as to identify the current status of Chinese pediatric CT radiation doses.Methods:Radiation doses of pediatric CT were collected during August and December 2016 from 40 hospitals(including 18 children’s hospitals)in 15 provinces,municipalities or autonomous regions across the China.The procedures of head CT,chest CT and abdomen CT were selected in these hospitals,and 10 patients in each group of 0-<1 y,1-<5 y,5-<10 y and 10-<15 y were collected at random for every procedure.Weighted CT dose index(CTDI_(w)),volumetric CT dose index(CTDI_(vol))and dose length product(DLP)were used as survey quantities.An independent sample Kruskal-Wallis rank sum test was performed for CTDI and DLP for each procedure for different age groups,and pairwise comparisons were performed for intra-group data.The same statistical method was also conducted for CTDI and DLP of the same procedure and age group in different provinces or municipalities.Results:The 75th percentiles of the distribution of CTDI and DLP in different age groups of 0-<1 y,1-<5 y,5-<10 y and 10-<15 y were as follows:36.5,43.4,49.1,51.1 mGy and 488,635,723,852 mGy.cm for head,6.1,6.4,6.8,9.6 mGy and 108,136,187,293 mGy.cm for chest,10.5,10.3,11.4,13.0 mGy and 251,284,353,523 mGy.cm for abdomen.The 50th percentiles of the distribution of the radiation doses for the same procedure varied with the ages(head,CTDI_(w):H=155.66,DLP:H=212.35,P<0.05;chest,CTDI_(vol):H=85.43,DLP:H=197.36,P<0.05;abdomen:H=62.29,DLP:H=173.22,P<0.05)and with lower dose at lower age.Radiation doses were close for head between 5-<10 y and 10-<15 y groups,for chest between 1-<5 y and 5-<10 y groups and between 5-<10 y and 10-<15 y groups,and for abdomen between 0-<1 y and 1-<5 y groups,with no statistically significant difference(the adjusted P>0.05).The dose levels of different provinces or municipalities in the same procedure and age group were not consistent,and the differences were statistically significant(P<0.05).The data were different from the domestic and international values of DRL.The 75th percentiles of CTDI_(w) and DLP values of head CT were close to the data from Japan and UK(United Kingdom),higher than the data from Korea and EC(European Commission).The 75th percentiles of CTDI values of all age groups were lower than the values of Japan and UK,and larger than that of Korea and EC in chest CT and abdomen CT.Conclusions:The 75th percentile values of the distribution of the pediatric CT doses obtained from the survey were inconsistent with those released by the relevant national and international organizations.It is necessary to update the national DRLs for pediatric CT on the basis of the actual survey data.