DC Emergency Power Control Strategy for AC/DC Multi-Channel Interconnected System

Inter-regional transmission line fault often results in power flow transferring, tie-line overloading and system islanding. Traditional control methods such asgenerator tripping and load shedding are costly, and also have undesirable impacts on theloadside. In this paper, a new emergency power control strategy is proposed for multi-channel interconnected system by using the overload capacity of non-fault DC lines. First of all, the capacity of emergency power control can be acquired by critical transmission power of a certain tie-line for stability. Secondly, the shortest electric distance can be calculated by Dijkstra algorithm, and then the priority of emergency control of the DC lines can be obtained by the entropy weight method. When the inter-regional transmission power decreases and the effect of single DC line emergency control is poor, the multi-channel cooperative emergency control strategy is proposed to ensure the system stability. Simulation results verify the effectiveness of the method proposed.

Spatio-temporal Change Characteristics of Summer Mean Temperature in Northeast China during 1974-2004 Based on Geostatistics

[ Objective] The research aimed to study the spatio-temporal change characteristics of summer mean temperature in northeast China during 1974 -2004 based on geostatistics. [ Method ] By combining climate tendency rate with geostatistics, the spatio-temporal change characteris- tics of summer mean temperature in northeast China during 1974 -2004 were discussed. [ Result] Summer mean temperature distribution in north- east China for many years showed a trend of decreasing from south and west to north and east. Summer mean temperature in northeast China overall showed rise trend, and the biggest temperature rise magnitude was in Liaoning Province. Summer average temperature in 1994 was significantly higher than that in other years, and climate was abnormal. The rise speed of summer mean temperature in northeast China showed a trend of decreasing from southeast Jilin Province to other areas. [ Conclusion ] The research contributed to recognize spatio-temporal structure and change characteristics of the temperature in northeast China.

Tirofiban combined with Aspirin in the Treatment of Acute Penetrating Artery Territory Infarction (STRATEGY): protocol for a multicentre, randomised controlled trial

Background Perforating artery territorial infarction(PAI)caused by branch atheromatous disease(BAD)is prone to recurrence and early progression without an effective and well-documented antiplatelet treatment regimen.Tirofiban,an adjunctive antiplatelet agent,has shown great potential to treat acute ischaemic stroke.However,whether the combination of tirofiban and aspirin can improve the prognosis of PAI remains unclear.Aim To explore an effective and safe antiplatelet regimen for reducing the risk of recurrence and early neurological deterioration(END)in PAI caused by BAD by comparing the tirofiban and aspirin combination with placebo and aspirin combination.Methods Tirofiban combined with Aspirin in the Treatment of Acute Penetrating Artery Territory Infarction(STRATEGY)trial is an ongoing multicentre,randomised,placebo-controlled trial in China.Eligible patients shall be randomly assigned to receive standard aspirin with tirofiban or placebo on the first day and standard aspirin from days 2 to 90.The primary endpoint is a new stroke or END within 90 days.The primary safety endpoint is severe or moderate bleeding within 90 days.Discussion The STRATEGY trial will assess whether tirofiban combined with aspirin is effective and safe in preventing recurrence and END in patients with PAI.Trial registration number NCT05310968.

石家庄新型冠状病毒肺炎疫情新型冠状病毒分子流行病学特征

目的从分子层面分析石家庄新型冠状病毒的流行病学特征,揭示此次传播链的源头,为新型冠状病毒肺炎疫情防控提供科学依据。方法收集2021年1月2—8日来自石家庄市第五医院170例新型冠状病毒感染者共计404份新型冠状病毒核酸阳性样本,采用多重聚合酶链反应靶向测序技术对样本进行深度测序获得病毒一致性序列。采用PANGOLIN分类系统对170个毒株序列进行分析,采用T-test对数据进行统计学分析。结果在404份新型冠状病毒核酸阳性样本中,356份获得病毒的全长基因组序列(>95%,100×测序深度),剔除重复取样,得到170株全基因组序列,所有样本均属于B.1.1分支。病毒突变数18~22个,大部分突变不改变氨基酸信息。根据基因组突变个数和种类,所有毒株分为48个亚型,其中2个毒株占主导(分别为66株和31株)。结论本研究中所有新型冠状病毒肺炎患者来自单一源头的境外输入性病例,病毒在社区隐匿传播了一段时间,并且在传播的过程中发生了变异。

钒配合物及其催化乙烯与α-烯烃共聚的研究进展

乙烯与α-烯烃(如丙烯、1-丁烯、1-己烯和1-辛烯等)共聚可制备乙丙橡胶、线形低密度聚乙烯、聚烯烃热塑弹性体和烯烃多嵌段共聚物等聚烯烃材料.在乙烯与α-烯烃共聚过程中,催化剂起着至关重要的作用.本文总结了用于催化乙烯与α-烯烃共聚的钒配合物催化剂及其催化性能的研究进展,包括钒配合物中钒的价态及配体的结构对乙烯与α-烯烃共聚的催化活性、单体竞聚率、共聚组成、序列分布、分子量及分子量分布的影响.钒(Ⅲ)配合物主要包括含氮杂环卡宾单齿配体、N^N或N^O双齿配体以及三齿或四齿配体的钒(Ⅲ)配合物,其中含有双齿配体的钒(Ⅲ)配合物催化乙烯与1-己烯共聚活性可高达8820 kg mol^(-1)h^(-1),配体空间位阻的增大阻碍α-烯烃的插入,使乙烯的竞聚率提高,α-烯烃的竞聚率降低,从而使α-烯烃的插入率降低;增加配体齿数,催化活性和共聚单体插入率均降低.钒(Ⅳ)配合物主要包括含胺类单齿或双齿配体、含N^O双齿配体和含O^N^N^O四齿配体的钒(Ⅳ)配合物,含N^O双齿配体钒(Ⅳ)配合物的催化活性通常低于含有相同配体钒(Ⅲ)配合物的催化活性.钒(Ⅴ)配合物主要包括含氮杂环卡宾配体的钒(Ⅴ)配合物、亚胺钒(Ⅴ)配合物以及含螯合芳氧基配体的钒(Ⅴ)配合物,其中含螯合芳氧基配体的钒(Ⅴ)配合物催化乙烯与丙烯共聚的催化活性可高达144400 kg mol^(-1)h^(-1),但共聚产物中丙烯结构单元含量不高于15%(mol);含氮杂环卡宾(NHC)配体的钒(Ⅴ)配合物可用于乙烯与丙烯拟活性共聚,制备出丙烯结构单元含量高的超高分子量乙烯-丙烯无规共聚弹性体.

Recovery of natural active molecules using aqueous two-phase systems comprising of ionic liquids/deep eutectic solvents

Due to environmental protection requirements,extraction of bioactive compounds from plant materials using environment-friendly green solvents has always been a research hotspot.And great efforts of scholars have been made in this direction,as well as environment-friendly solvents have been used to develop many innovative extraction techniques.Ionic liquids(ILs)and deep eutectic solvents(DESs)are two kinds of typical designable green solvents,which are potential replacements for traditional volatile organic solvents used for extracting.Under the substances action of inorganic salts or polymers,ILs/DESs can form an aqueous two-phase system(ATPS),which has obvious advantages for separating natural products.This paper discussed the phase separation principle of ILs/DESs-based ATPSs and reviewed the applications in the extraction of natural active molecules in recent years,as well as to promote the development of separation of the active constituents in Chinese materia medica.

Health assessment of plantations based on LiDAR canopy spatial structure parameters

The Yellow River Delta(YRD)has China's largest artificial Robinia pseudoacacia forest,which was planted in the late 1970s and suffered extensive dieback in the 1990s.The health grade of the R.pseudoacacia forest(named canopy vigor grade,CVG)could be achieved by using high-resolution images and canopy vigor indicators(CVIs).However,a previous study showed that there was no significant correlation between CVG and the field-estimated aboveground biomass(AGB)of R.pseudoacacia forest.Therefore,this study aims to construct forest health indicators(FHIs)based on canopy spatial structure parameters extracted from LiDAR.The FHIs included Weibull_α(the scale parameter of the Weibull density function that reflects the shape of the tree canopy),VCI(vertical complexity index),sdCC(the standard deviation of canopy cover),H99(the 99th percentile height)and cvLAD(the coefficient of variation of leaf area density),and could significantly distinguish three forest health grades(FHG)(p<0.05).The FHG was positively correlated with forest AGB(rs=0.51,p=0.004),and the similarity value with CVG was 63.33%.The results of this study confirmed that the FHIs can reflect both canopy vigor and tree productivity,and distinguish forest health status without prior classification information.