Highly stereoselective construction of tetrahydroquinolines via cascade aza-Michael-Michael reaction: Formal [4+2] cycloaddition of β,γ-unsaturated α-ketoesters with 2-aminochalcones

An efficient cascade aza-Michael-Michael sequence for the preparation of tetrahydroquinolines has been established. Three contiguous stereogenic centers are created with high levels of enantioselectivities (79–99% ee) and exclusive diastereoselectivities in the presence of a bifunctional squaramide. This approach is compatible with a broad range of β,γ-unsaturated α-ketoesters and 2-aminochalcones. Our protocol indicated that β-site of β,γ-unsaturated α-ketoester is an available pro-nucleophilic site.     

Double Michael addition of nitromethane to divinyl ketones: A remarkably positive effect of additive

An efficient double Michael addition of nitromethane to divinyl ketones was established in good to high yields (75–99%). A wide range of cyclohexanones were obtained with excellent diastereocontrol (up to >20:1 dr) and enantioinduction (91–99% ee) in a one-pot fashion. The involvement of basic additive significantly enhanced the reactivity of this cascade sequence.     

离子束作用下KDP晶体表面粗糙度研究

为了避免传统加工过程对KDP( Potassium dihydrogen phosphate)晶体表面产生损伤、嵌入杂质等降低晶体抗激光损伤阈值的不利因素,文章探索采用离子束抛光技术实现KDP晶体的加工.本文主要分析了离子束抛光作用下KDP晶体表面粗糙度的演变过程,采用垂直入射和倾斜45°入射两种方式研究KDP晶体表面粗糙度,利用倾斜45°入射的加工方式提高了KDP晶体的表面质量,其表面均方根粗糙度值由初始的3.07 nm减小到了1.95 nm,实验结果验证了离子束抛光加工KDP晶体的可行性.     

Polymerizable Molecular Silsesquioxane Cage Armored Hybrid Microcapsules with In Situ Shell Functionalization

We prepared core–shell polymer–silsesquioxane hybrid microcapsules from cage‐like methacryloxypropyl silsesquioxanes (CMSQs) and styrene (St). The presence of CMSQ can moderately reduce the interfacial tension between St and water and help to emulsify the monomer prior to polymerization. Dynamic light scattering (DLS) and TEM analysis demonstrated that uniform core–shell latex particles were achieved. The polymer latex particles were subsequently transformed into well‐defined hollow nanospheres by removing the polystyrene (PS) core with 1:1 ethanol/cyclohexane. High‐resolution TEM and nitrogen adsorption–desorption analysis showed that the final nanospheres possessed hollow cavities and had porous shells; the pore size was approximately 2–3 nm. The nanospheres exhibited large surface areas (up to 486 m² g^?1) and preferential adsorption, and they demonstrated the highest reported methylene blue adsorption capacity (95.1 mg g^?1). Moreover, the uniform distribution of the methacryloyl moiety on the hollow nanospheres endowed them with more potential properties. These results could provide a new benchmark for preparing hollow microspheres by a facile one‐step template‐free method for various applications.     

High-birefringence nematic liquid crystal for broadband THz applications

Liquid crystals (LCs) have been studied extensively in the visible range for their dielectric tunability, and the characterisation in the terahertz (THz) range has gained increasing interest due to the need for active THz modulation and switching devices. In this paper, we use THz time-domain spectroscopy to measure the frequency-dependent birefringence and the absorption coefficient of a number of commercial and non-commercial nematic LCs, including E7, BL037, MDA-98-1602, LCMS-107, GT3-23001 and 1825, over a range of bias voltages at room temperature. Furthermore, several basic components of LC mixture are analysed to establish their contributions to birefringence and theoretical model is used to fit the absorption spectra. The large tunability and low loss measured for a range of samples show that the LCs are useful tunable dielectrics for compact, efficient and broadband THz devices.     

de Sitter空间中法联络平坦的完备类空子流形

该文证明了de Sitter空间中具有平行平均曲率向量的常数量曲率完备类空子流形,如果其法联络是平坦的,且M的截面曲率小于0,或M的第二基本形式模长平方‖σ‖相似文献   

基于低功耗双边沿D触发器的任意进制异步计数器设计

从D触发器激励表入手，分别给出了采用单边沿D触发器和双边沿D触发器的2^n进制异步加法计数器、减法计数器的设计方法．在此基础上，采用逻辑函数修改技术，通过实例讨论了基于单边沿D触发器和双边沿D触发器的异步任意进制计数器的设计．该设计方法方便，快速，具有一定的实用意义．     

X波段长脉冲高功率微波产生的实验研究

 获得长脉冲高功率微波（HPM）输出是HPM源技术追求的重要目标之一。从物理机理上分析了影响慢波结构HPM器件实现长脉冲HPM输出的因素,并利用长脉冲脉冲功率源和过模慢波结构HPM器件,开展了X波段长脉冲HPM产生实验。实验中,采用介质-铜阴极,并在慢波结构表面镀Cr,在导引磁场约0.7 T、二极管电压约400 kV、电流约10 kA、束流脉宽200 ns的条件下,获得了功率500 MW、脉宽约100 ns、主模为TM₀₁的X波段长脉冲HPM输出。对实验结果的分析表明,脉冲功率源与HPM器件的阻抗不匹配,是导致HPM器件输出微波脉宽比电子束脉宽短、以及HPM器件输出微波功率效率较低的主要原因。     

Yb3Cu9(OH)19Cl8 单晶的生长和低温磁性研究

本文介绍了新型kagomé 晶格化合物 Yb3Cu9 (OH)19Cl8 单晶的生长及磁性质研究. 利用水热法制备了高品质的 Yb3Cu9 (OH)19Cl8 单晶,X 射线衍射的精修结果表明,Cu2+ 离子在ab 面内形成kagomé 结构,Yb3+ 离子处在kagomé 六角晶格的中心. 磁化率结果表明 Yb3Cu9 (OH)19Cl8 在温度低至2 K 仍没有磁有序转变, 表现出明显的顺磁行为. 居里-外斯拟合结果显示, 磁性离子间具有强的反铁磁耦合相互作用. 温度低至2 K 的比热曲线上没有明显的磁相变行为的出现, 而是表现出典型的肖特基特征     

“神光-Ⅱ”装置倍频激光直接驱动冲击波平面性的实验研究

 设计了3套针对“神光-Ⅱ”倍频激光直接驱动的透镜阵列均匀辐照系统，并对冲击波的平面性进行了实验研究。结果表明，冲击波的平面性与透镜阵列参数、平面靶厚度、靶面位置等有关，采用列阵元数为121的透镜阵列进行激光束匀滑驱动的冲击波平面性最好，间接说明它在靶面的激光辐照是最均匀的；另外，随着靶厚的增加，冲击波平面性变差，平面区变小；而且冲击波平面性随靶面离焦位置的变化成一定的周期性变化，第2套透镜阵列焦点处的冲击波平面性最好。