有机催化不对称Diels-Alder反应的研究进展

综述了国内外不对称Diels-Alder反应的最新研究成果,就Lewis碱、Bronsted碱、有机双功能催化剂以及Br(o|¨)nsted酸作为催化剂来催化该反应分别进行了较全面的阐述。     

左旋多巴醇在不对称还原中的应用研究

在NaBH4/Cd2+、NaBH4/Co2+、NaB4/Ce3+、NaBH4/Ni3+还原体系中,采用加入手性源左旋多巴醇和不加入左旋多巴醇两种方法,分别对苯乙酮进行不对称还原,结果表明,加入手性源左旋多巴醇后,反应速度快,产率高.同时在这4种还原体系中NaBH4/Ce3+的催化效果最好.     

手性相转移催化剂在Michael加成反应中的应用研究进展

一些手性Michael加成产物是医药、农药、香料的重要产品或其中间体.因此,Michael加成产物的不对称催化合成一直是有机化学领域的热点课题.综述了手性相转移催化剂在不对称Michael加成反应中的应用研究进展.     

具有领航者的时延多智能体系统的一致性

本文研究了具有不同通信时延和不同输入时延的移动多智能体算法的一致性.假设多智能体系统有n个智能体和一个Leader组成,网络连接拓扑是非对称有向加权图,智能体Leader为拓扑图的全局可达节点.应用频域控制理论和广义Nyquist判据研究了时延多智能体算法的一致性,得到保证系统一致性的收敛条件.该一致性条件是一个应用节...     

一种基于微带开口环的双通带滤波器设计

文中提出了一种基于微带开口环的双通带滤波器设计,对比了非对称开口环结构与传统对称结构的传输特性,讨论了非对称结构中两端馈线位置,双环耦合间距以及环线宽度对于滤波器性能的影响,然后在此基础上,利用两级级联耦合开口环设计了一个用于接收机中抑制镜像的双通带滤波器,带外抑制度较高。     

自旋对非对称量子点中弱耦合束缚磁极化子基态能量的影响

采用Tokuda修正的线性组合算符和幺正变换方法,研究了非对称量子点中弱耦合束缚磁极化子的性质。推导出了磁极化子基态能量随量子点横向、纵向受限长度和磁场的变化关系。进行了数值计算,计算结果表明：考虑自旋影响时,束缚磁极化子基态能量分裂成自旋向上（向下）两个分支。并且磁极化子基态能量、自旋向上（向下）分裂能随量子点横向、纵向受限长度的增加而减少,随磁场强度的增加而增大。     

Control Strategies of Asymmetric Strip Shape in Six-High Cold Rolling Mill

 It is a complicated problem for cold-rolled strip to improve asymmetric strip shape in strip production. A roll system and strip coupled model of six-high cold rolling mill was established with finite element method to estimate the effect of intermediate roll shifting, tilting, symmetric and asymmetric bending technologies on strip profile. To reduce asymmetric defects of strip shape as much as possible, some control strategies were proposed, including tilting and asymmetric bending of intermediate roll and work roll. The combinations of these three control strategies can effectively eliminate asymmetric strip shape defects. Finally, the closed-loop control model of asymmetric flatness at the last stand was given, and the flatness control system with the function of asymmetric strip shape control was also designed for cold tandem mill.     

旋转非对称项面形误差绝对检测的仿真分析

为满足光学元件的高精度检测要求,绝对检测技术取代传统相对检测技术被越来越多的用于光学检测过程中.然而传统绝对检测法检测都有各自适用的范围且检测过程复杂对实验仪器的精度要求较高.在某些只需要获得旋转非对称面型误差的检测领域旋转平均法成为一种简单易行的绝对检测手段.旋转平均法适用于平面、球面与非球面旋转非对称面型检测.本文...     

Asymmetric Supercapacitors Based on Graphene/MnO2 and Activated Carbon Nanofiber Electrodes with High Power and Energy Density

Asymmetric supercapacitor with high energy density has been developed successfully using graphene/MnO₂ composite as positive electrode and activated carbon nanofibers (ACN) as negative electrode in a neutral aqueous Na₂SO₄ electrolyte. Due to the high capacitances and excellent rate performances of graphene/MnO₂ and ACN, as well as the synergistic effects of the two electrodes, such asymmetric cell exhibits superior electrochemical performances. An optimized asymmetric supercapacitor can be cycled reversibly in the voltage range of 0–1.8 V, and exhibits maximum energy density of 51.1 Wh kg^?1, which is much higher than that of MnO₂//DWNT cell (29.1 Wh kg^?1). Additionally, graphene/MnO₂//ACN asymmetric supercapacitor exhibits excellent cycling durability, with 97% specific capacitance retained even after 1000 cycles. These encouraging results show great potential in developing energy storage devices with high energy and power densities for practical applications.     

非对称非线性定向耦合器开关特性研究

利用拉格朗日变分法原理,分析了非对称非线性定向耦合器的开关特性.研究表明:增大第一纤芯的相速度能够降 低开关的阈值功率,但开关的陡峭性变差,且当相位失配量增大到一定程度,输入低功率脉冲时,光脉冲的部分能量将一直保 持在直通纤芯臂内不能耦合到第二纤芯.增大第一纤芯的有效模场面积将导致开关的阈值增大.同时,当两纤芯都为反常...