大气湍流对斜程传输准单色高斯-谢尔光束时间相干性的影响

由第一类零阶贝塞尔函数的级数展开推导出波结构函数在任意湍流条件下的近似表达式。由广义惠更斯-菲涅耳原理、随高度变化的Hufnagel-Valley湍流廓线模型以及波结构函数在任意湍流条件下的近似表达式,导出了斜程传输时准单色高斯-谢尔光束互相干函数的解析式。然后,利用表征光束时间相干性的纵向相干长度(可由互相干函数导出),研究了斜程传输时大气湍流对准单色高斯-谢尔光束时间相干性的影响。研究结果表明,准单色高斯-谢尔光束的时间相干性在整个斜程传输过程中保持不变。最后,对该结果在物理上给予了定性解释。     

超临界CO2技术制备超细SiO2的研究

本文以水玻璃为硅源,利用超临界CO2(sc CO2)技术制备出超细SiO2粉体,研究了压力、温度对超细SiO2粒子粒径和Zeta电位的影响,采用Zeta电位及激光粒度分析仪、X射线衍射(XRD)、自动吸附仪等测试方法对粉体的结构和性能进行了分析表征.结果表明:当压力为8 MPa,温度为50℃时,所得超细SiO2粒子粒径分布较窄且平均粒径最小,为472.9 nm,且Zeta电位取得较小值,为-55.68 mV;所得超细SiO2粒子属于非晶态,且与市售的T36-5 SiO2粒子相比,其孔结构更加致密.     

Retrotransposon‐microsatellite amplified polymorphism,an electrophoretic approach for studying genetic variability among Schistosoma japonicum geographical isolates

In the present study, retrotransposon‐microsatellite amplified polymorphism (REMAP) was used to examine genetic variability among Schistosoma japonicum isolates from different endemic provinces in mainland China, using S. japonicum from Japan and the Philippines for comparison. Of the 50 primer combinations screened, eight produced highly reproducible REMAP fragments. Using these primers, 190 distinct DNA fragments were generated in total, of which 147 (77.37%) were polymorphic, indicating considerable genetic variation among the 43 S. japonicum isolates examined. The percentage of polymorphic bands (PPB) among S. japonicum isolates from mainland China, Japan, and the Philippines was 77.37%; PPB values of 18.42% and 53.68% were found among isolates from southwestern (SW) China and the lower Yangtze/Zhejiang province in eastern (E) China, respectively. Based on REMAP profiles, unweighted pair‐group method with arithmetic averages (UPGMA) dendrogram analysis revealed that all of the S. japonicum samples grouped into three distinct clusters: parasites from mainland China, Japan, and the Philippines were clustered in each individual clade. Within the mainland China cluster, SW China isolates (from Sichuan and Yunnan provinces) grouped together, whereas worms from E China (Zhejiang, Anhui, Jiangxi, Jiangsu, Hunan, and Hubei provinces) grouped together. These results demonstrated that the REMAP marker system provides a reliable electrophoretic technique for studying genetic diversity and population structures of S. japonicum isolates from mainland China, and could be applied to other pathogens of human and animal health significance.     

Retraction: Divergent synthesis of 5-substituted pyrimidine 2′-deoxynucleosides and their incorporation into oligodeoxynucleotides for the survey of uracil DNA glycosylases

Retraction of ‘Divergent synthesis of 5-substituted pyrimidine 2′-deoxynucleosides and their incorporation into oligodeoxynucleotides for the survey of uracil DNA glycosylases’ by Ai Tran et al., Chem. Sci., 2020, 11, 11818–11826, DOI: 10.1039/D0SC04161K.

The Royal Society of Chemistry hereby wholly retracts this Chemical Science article due to concerns about the reproducibility of the data.The Royal Society of Chemistry has been contacted by the authors of this article to alert us that recent experiments by their group have shown that some results are not reproducible, especially the yields of several key intermediates. Given the focus on the easy access to epigenetically important nucleosides and related ODNs, unreliable yields significantly impact the confidence in the results. In addition, it was discovered that one of the biological samples provided to the authors was mislabelled. The human stem cells were actually mouse stem cells, hence some discussion and conclusions in the article may no longer apply. Ahead of a thorough re-examination of the entire study, in order to preserve the rigor of the scientific record, the signing authors have chosen to retract the article and they would like to apologise for any inconvenience this may have caused for readers.Signed: Ai Tran, Song Zheng, Dawanna S. White, Alyson M. Curry and Yana CenRetraction endorsed by May Copsey, Executive Editor, Chemical Science     

一种新的长周期光纤光栅制作方法

提出了长周期光纤光栅的一种新的制作方法,通过对光纤周期性刻槽并加热拉伸引入纤芯形变,而使得纤芯折射率产生周期性变化。文中给出实验结果,并对其基本原理进行了理论分析。这种长周期光经行光栅可应用于需要宽阻滞滤波器的波分复用系统。     

Plant Natural Products: Promising Resources for Cancer Chemoprevention

Cancer is a major factor threatening human health and life safety, and there is a lack of safe and effective therapeutic drugs. Intervention and prevention in premalignant process are effective ways to reverse carcinogenesis and prevent cancer from occurring. Plant natural products are rich in sources and are a promising source for cancer chemoprevention. This article reviews the chemopreventive effects of natural products, especially focused on polyphenols, flavonoids, monoterpene and triterpenoids, sulfur compounds, and cellulose. Meanwhile, the main mechanisms include induction of apoptosis, antiproliferation and inhibition of metastasis are briefly summarized. In conclusion, this article provides evidence for natural products remaining a prominent source of cancer chemoprevention.     

基于企业网络舆情的客户满意度分析及管理方法

社交网络平台的迅速发展,促使网络舆情成为企业获取商业情报、扩大竞争优势的重要信息来源。本文针对网络舆情环境下的企业客户关系管理问题展开研究。通过构建企业客户推动式信息反馈模型,描述了企业客户、网络用户与企业网络舆情间的联系,并依据信息反馈模型,提出变尺度聚类算法。该算法将传统聚类方法的求解过程由单一尺度分析扩展到多尺度分析,克服了实际数据聚类应用过程中的聚类结果特征不显著问题。本文选取新浪微博作为数据源,利用企业网络舆情数据集和企业客户数据集进行数据分析实验。实验结果表明,企业可以通过获取与其主营业务相关的网络舆情信息,实现客户满意度预测;同时,变尺度聚类算法结果能够为企业进一步制定销售战略和销售战术提供决策支持。     

铕对Pt—Sn／γ—A12O3重整催化剂性能的影响

研究了添加RE2O3(RE＝Eu)的Pt—Sn／γ—A12O3重整催化剂的反应性能．研究结果表明添加稀土后，催化剂的液收增加，芳产增加，积炭降低．采用氢氧滴定(TPT)、程序升温还原(TPR)、吡啶红外光谱(IRS)、程序升温氧化(TPO)等对催化剂进行了物化表征．结果表明，催化剂中添加RE2O3之后，催化剂中Pt的两种活性中心不变，但改变了两种活性中心的相对比率，低温活性中心降低，高温活性中心增加；稀土与Pt和Sn之间发生相互作用，产生了电子效应，使得它们的还原峰温向低温移动；载体的酸量减少，酸性减弱．     

基于Agent的分布计算环境模型研究

针对未来的计算环境的分布、开放、不断进化的演变和发展,本文首先对Ａｇｅｎｔ的基本特性、体系结构及行为模式进行了介绍．在此基础上提出了一个基于Ａｇｅｎｔ的分布计算环境模型．     

不同模式耦合下偏振模色散几率分布的研究

研究了偏振模色散的统计特性,在不同模式耦合条件下,应用蒙特-卡罗方法模拟偏振模色散矢量的几率分布,并对模拟结果进行了函数拟合。发现随着耦合次数增加差分群时延的几率分布从一个类似δ函数分布逐渐过渡到麦克斯韦分布;在一定的耦合下,几率分布可以呈现高斯分布。对偏振模矢量的两个方向余弦进行统计分析,发现随着耦合次数的增加,偏振模矢量两个方向余弦函数的分布从高斯分布和δ函数分布都变为均匀分布。