New strategic reactions for organic synthesis: catalytic asymmetric C-H activation alpha to oxygen as a surrogate to the aldol reaction

The C-H activation of silyl ethers by means of rhodium carbenoid-induced C-H insertion represents a very direct method for the stereoselective synthesis of silyl-protected beta-hydroxy esters. The reaction can proceed with very high regio-, diastereo-, and enantioselectivity and represents a surrogate to the aldol reaction. The reaction is catalyzed by the rhodium prolinate complex Rh(2)(S-DOSP)(4). A critical requirement for the high chemoselectivity is the use of donor/acceptor-substituted carbenoids such as those derived from methyl aryldiazoacetates. A range of silyl ethers may be used such as allyl silyl ethers, tetraalkoxysilanes, and even simple trimethylsilyl alkyl ethers. In general, C-H activation preferentially occurs at methylene sites, as the reactivity is controlled by a delicate balance between steric and electronic effects.     

我国农业非点源污染研究进展及其防治措施

随着点源污染的有效控制,非点源污染已经成为我国重要污染类型之一,其中由农业产生的非点源污染又是重中之重。本文介绍了农业非点源污染的特点、研究进展及其对环境的影响,并针对不同形式的污染源提出了相应的防治措施,以便实现对农业非点源污染从源到汇的全面治理,减少农业非点源污染对水体和对人类健康的危害。     

地铁车辆段咽喉区上盖建筑振动影响

城区地铁车辆段进行上盖物业开发可节约、集约利用地铁用地,缓解城市土地资源稀缺问题。地铁车辆段特别是其咽喉区振动是上盖物业开发的环境制约因素。为研究地铁车辆段咽喉区对上盖建筑的振动影响,建立轨道-地基土-上盖建筑三维有限元模型,采用等效荷载法,将实地采样的钢轨铅垂向振动加速度转化为列车钢轨铅垂向振动线荷载,作用于轨道上。在结合实测数据验证模型合理性的基础上,定量研究上盖平台厚度和离地高度、上盖建筑层数和结构等因素对室内环境振动(铅垂向Z振级VL_Zmax)的影响。结果表明,地铁车辆段咽喉区对高层建筑的振动影响整体大于多层建筑;由于振动波在屋顶自由端发生反射并与入射波叠加,导致不同楼层楼板中央VL_Zmax随楼层升高略有增加;框架结构建筑室内VL_Zmax大于剪力墙结构;增加上盖平台厚度可减小建筑室内VL_Zmax;上盖建筑室内VL_Zmax随上盖平台离地高度增加而增加(即随建筑楼层绝对离地高度增加而增大)。研究结果可为地铁车辆段上盖物业开发振动污染防治提供理论和工程技术依据。     

CsPbI3钙钛矿量子点的精细纯化及其高效发光二极管的研究

钙钛矿量子点发光二极管(QLEDs)因其色纯度高、颜色控制精准、色域广以及溶液可加工等特点,在显示和照明等领域有着极大的应用前景.针对红光钙钛矿CsPbI3量子点纯化过程中相变和表面配体损失造成的荧光退化问题,本工作发展了一种甲苯和乙酸乙酯协同的混合溶剂纯化策略,能够避免纯化过程中的相变问题,获得了纯立方相的CsPbI...     

72Ge40的低激发态能级研究

用低本底反康谱仪(HpGe–NaI)和HpGe–HpGe的三参数符合γ–γ–T系统,对72Ga的衰变γ单谱、符合谱进行了研究,实验共获得2.3×10⁷个符合事件.根据实验结果建立了含有26个能级、87条γ射线的72Ga的衰变能级纲图,其中包含首次测到7条γ射线225.92、826.97、1349.71、1475.32、1667.91、2105.28、2247.39keV和4个能级3248.01、3396.27、3806.10、3864.56keVS并为2939.83keV能级和112.59、937.97、2402.25、2939.95keV4条γ射线的存在提供了证据;实验没有发现113.5、1155.7、1192.4keVγ射线和能级3307.1keV存在的证据。并把317.72keVγ射线的跃迁,由原来的能级3757.26keV跃迁到3439.51keV能级,改为3565.85keV到3248.01keV能级跃迁.     

中国城市职业多样性：事实、演进与政策含义

从城市职业类型分布的角度测算中国城市的职业多样性和趋势,并探讨城市特征对于城市职业多样性的影响,可以为引导城市充分高质量就业提供参考。通过采用改进的赫芬达尔指数、面板数据固定效应模型和Oaxaca-Blinder分解等方法,研究发现,2002−2016年期间中国城市职业多样性呈现出先降后升的趋势,其原因在于城市产业结构的调整以及金融危机后新经济的出现;同时,城市规模越大、行政等级越高、经济越发达,对应的职业多样性程度越高。研究结论有助于直观了解不同城市的职业分布、产业结构和分工现状,评估城市的人力资源结构和经济发展潜能,进而为不同城市制定产业发展及人力资源规划提供政策建议。     

基于反射式布拉格光栅和Fabry-Perot标准具组合的Nd∶YVO4单频激光器

报道了一种激光二极管端面连续抽运的稳定单频主动调Q Nd∶YVO_4激光器。采用RBG与标准具组合的方式获得了稳定的高功率单频激光输出。RBG既作为输出耦合镜,又作为纵模选择元件,与标准具组合可进一步抑制多纵模,增长谐振腔的光学腔长,获得高功率输出。通过优化标准具的倾斜角度,可使标准具与RBG的中心波长匹配,并减小腔内插入损耗。最终在物理腔长为148.7mm的条件下,获得了功率为750mW,脉冲能量为75μJ@10kHz,脉宽为8.3ns的稳定的高功率单频激光输出。     

Intrinsic luminescence from metal nanostructures and its applications

Intrinsic luminescence from metal nanostructures complements conventional scattering and absorption behaviors and has many interesting and unique features. This phenomenon has attracted considerable research attention in recent years because of its various potential applications. In this review, we discuss recent advances in this field, summarize potential applications for this type of luminescence, and compare theoretical models to describe the phenomena. On the basis of the excitation process, the characteristic features and corresponding applications are summarized briefly in three parts, namely,continuous-wave light, pulsed laser, and electron excitation. A universal physical mechanism likely operates in all these emission processes regardless of differences in the excitation processes; however, there remains some debate surrounding the details of the theoretical model. Further insight into these luminescence phenomena will not only provide a deeper fundamental understanding of plasmonic nanostructures but will also advance and extend their applications.