Asymmetric Partial Hydrosilylation of 2,2-Difluoro-1,3-diketones with Chiral Frustrated Lewis Pairs

Comprehensive Summary,The asymmetric partial reduction of 1,3-diketones stands as a straightforward pathway to access optically active β-hydroxyketones. In this paper, an asymmetric Piers-type hydrosilylation of 2,2-difluoro-1,3-diketones was successfully realized by using a frustrated Lewis pair of chiral borane and tricyclohexylphosphine as a catalyst, delivering a variety of α,α-difluoro-β-hydroxyketones in high yields with up to 99% ee. Significantly, no over-reduced diol products were observed even with an excess amount of silanes. The product can be conveniently converted to α,α-difluoro-β-hydroxyester or 1,3-anti-diol via an oxidation with m-CPBA or a reduction with DIBAL-H without obvious loss of ee.

滑动摩擦副表面非对称微织构空化效应数值分析

为探究滑动摩擦副表面非对称微织构空化效应及其影响因素,基于N-S方程建立了表面织构化滑动摩擦副数值计算模型并进行求解,讨论了凹槽型非对称微织构的结构参数、运动速度和润滑油黏度对凹槽内的气相分布、空化面积率、油膜承载力和摩擦系数等的影响.结果表明:凹槽型非对称微织构的承载力大于对称微织构,而其摩擦系数小于对称微织构;在考虑空化效应时,凹槽型非对称微织构比对称微织构能更显著地改善摩擦学性能,并且非对称微织构凹槽离入口距离越远,空化效应越显著;滑动摩擦副运动速度和润滑油黏度对空化效应有重要影响,运动速度越高、润滑油黏度越大,凹槽型非对称微织构的空化效应越明显,且提升承载力的能力明显优于对称微织构,该研究对滑动摩擦副表面微织构的设计和分析有一定的参考意义.

非对称轴向柱塞泵热力学建模与分析

为了精确分析非对称轴向柱塞泵各组件温度分布规律,考虑滑靴的自旋,建立非对称轴向柱塞泵摩擦副黏性摩擦功率损失和容积功率损失数学模型,利用Fluent软件对柱塞泵发热情况进行仿真计算,并讨论了柱塞泵转速、工作压力对柱塞泵组件发热情况的影响。结果表明:非对称柱塞泵最高温度出现在滑靴位置,转速和工作压力均会影响柱塞泵发热情况,其中转速的影响更为显著,当主轴转速由1000 r/min增大到2000 r/min时,最大功率损失增加幅值为269%,最高温升为12℃。

Electron-positron pair production in a strong asymmetric laser electric field

By solving the quantum Vlasov equation, electron positron pair production in a strong electric field with asymmetric laser pulses has been investigated. We consider three different situations of subcycle, cycle and supercycle laser pulses. It is found that in asymmetric laser pulse field, i.e.. when the pulse length of one rising or falling side is fixed while the pulse length of the other side is changed, the pair production rate and mnnber density can be significantly modified comparable to symmetric situation. For each ca,se of these three different cycle pulses, when one side pulse length is constant and the other side pulse length becomes shorter, i.e., the whole pulse is compressed, the more pairs can be produced than that in tile vice versa case, i.e., the whole pulse is elongated. In compressed pulse case there exists an optimum pulse length ratio of asylnmetric pulse lengths which makes the pair number density maximunn. Moreover, the created maximum pair number density by subcycle pulse is larger than that by cycle or/and supercycle pulse. In elongated pulse case, however, only for supercycle laser pulse the created pairs is enhanced and there exists also an optimum asymmetric pulse length ratio that maximizes the pair number density. On the other hand. surprisingly, in both cases of subcycle and cycle elongated laser pulses, the pair number density is monotonically decreasing as the asymmetry of pulse increases.

Asymmetric Hydrogenation of Phenanthridines with Chiral Boranes

The asymmetric hydrogenation of N-heteroarenes provides an efficient method for the synthesis of optically active cyclic secondary amines.In this paper,we described an asymmetric hydrogenation of phenanthridines using a chiral mono-alkene-derived borane.A variety of dihydrophenanthridines were furnished in high yields with up to 93%ee.The current catalytic system was very sensitive for the steric hindrance of phenanthridines.Bulky substituents at one phenyl group of phenanthridines were required to obtain the high enantioselectivity.But large substituents on the carbon of the C=N bonds would diminish the reactivity sharply.

Access to Enantioenriched Allylic Alcohols via Peptide-Mimic Phosphonium Salt-Catalyzed Asymmetric Aerobic Hydroxylation

The development of catalytic asymmetric methods that enable access to value-added functionalities or structures,exemplified by allylic alcohols,is a highly interesting yet challenging topic from both academic and industrial perspectives.However,before recent advances in chemical catalysis,there were scarce protocols toward constructing enantioenriched tertiary allylic alcohol scaffolds.In this context,peptide-mimic phosphonium salts were found to be highly efficient in catalytic asymmetricα-hydroxylation ofα,β-unsaturated and/orβ,Y-unsaturated compounds with satisfactory regio-and stereochemical outcomes(up to 97%yield and 95%ee).This methodology tolerates a broad array of substrates and thus provides an expeditious and unified platform for the assembly of enantioenriched tertiary allylic alcohols by avoiding the use of additional reductants and expensive metal catalysts.Furthermore,the power of this protocol is enlarged by simple conditions and the use of air as a source of hydroxyl functionality.

Asymmetricalπback-donation of hetero-dicationic Mo^(4+)-Mo^(6+)pairs for enhanced electrochemical nitrogen reduction

The breaking of nonpolar N≡N bond of dinitrogen is the biggest dilemma for electrocatalytic nitrogen reduction reaction(NRR)application,driving electron migration between catalysts and N≡N bond(termed“πback-donation”process)is crucial for attenuating interfacial energy barrier but still remains challenging.Herein,using density functional theory calculations,we revealed that constructing a unique hetero-dicationic Mo^(4+)-Mo^(6+)pair could effectively activate N≡N bond with a lying-down chemisorption configuration by an asymmetrical“πback-donation”process.As a proof-of-concept demonstration,we synthesized MoO_(2)@MoO_(3)heterostructure with double Mo sites(Mo^(4+)-Mo^(6+)),which are embedded in graphite,for electrochemical nitrogen reduction.Impressively,this hetero-dicationic Mo^(4+)-Mo^(6+)pair catalysts display more excellent catalytic performance with a high NH_(3)yield(60.9μg·h^(-1)·mg^(-1))and Faradic efficiency(23.8%)as NRR catalysts under ambient conditions than pristine MoO_(2)and MoO_(3).Operando characterizations using synchrotron-based spectroscopic techniques identified the emergence of a key^(*)N_(2)Hy intermediate on Mo sites during NRR,which indicates that the Mo sites are active sites and the NRR process tends to follow an associative mechanism.This novel type of hetero-dicationic catalyst has tremendous potential as a new class of transition metal-based catalysts with promising applications in electrocatalysis and catalysts for energy conversion and storage.

Coexistence of isospin I=0 and I=1 pairings in asymmetric nuclear matter

The coexistence of neutron-neutron(n-n),proton-proton(p-p),and neutron-proton(n-p)pairings is investigated by adopting an effective density-dependent contact pairing potential.These three types of pairings can coexist only if the n-p pairing is stronger than the n-n and p-p pairings for the isospin asymmetric nuclear matter.In addition,the existence of n-n and p-p pairs might enhance n-p pairings in asymmetric nuclear matter when the n-p pairing strength is significantly stronger than the n-n and p-p ones.Conversely,the n-p pairing is reduced by the n-n and p-p pairs when the n-p pairing interaction approaches n-n and p-p pairings.

Asymmetric pulse effects on pair production in polarized electric fields

Using the Dirac–Heisenberg–Wigner formalism,effects of the asymmetric pulse shape on the generation of electronpositron pairs in three typical polarized fields,i.e.,linear,middle elliptical and circular fields,are investigated.Two kinds of asymmetries for the falling pulse length,short and elongated,are studied.We find that the interference effect disappears with the shorter pulse length and that the peak value of the momentum spectrum is concentrated in the center of the momentum space.In the case of the extending falling pulse length,a multiring structure without interference appears in the momentum spectrum.Research results show that the momentum spectrum is very sensitive to the asymmetry of the pulse as well as to the polarization of the fields.We also find that the number density of electronpositron pairs under different polarizations is sensitive to the asymmetry of the electric field.For the short falling pulse,the number density can be significantly enhanced by over two orders of magnitude.These results could be useful in planning high-power and/or high-intensity laser experiments.

一种SM9数字签名及验证算法的快速实现方法

SM9算法在2016年被确定为国家密码行业标准(GM/T0044-2016)o该算法是一种标识密码算法,以用户的身份标识为基础产生公私钥,进行数据加解密、密钥交换以及数字签名等,具有广阔的应用场景。SM9算法的软硬件实现研究方面虽然取得了许多进步,但是该算法涉及的数学计算较为复杂,不断改进算法的计算性能仍是一个重要的研究课题。针对SM9算法的数字签名及验证过程进行研究,提出一些改进思路,有效降低了算法运算的复杂度。测试结果表明,该实现方法可有效提高SM9数字签名及验证算法的性能。

斜对称q^2-分圆陪集及其应用研究

引入斜对称q2-分圆陪集及斜非对称偶的概念,深入考察了n=q2m-1时斜对称分圆陪集及斜非对称偶的性质及确定方法。以此为基础研究了Hermite对偶包含BCH码的极大设计距离。解决了前人留下的一个疑难问题,并改进了前人的一个判别上界,所得到的界是紧的。再利用所得到的满足Hermite对偶包含条件的非狭义BCH码构造出一些具有很好参数的量子纠错码,这些量子码超过已有文献中由狭义BCH码构造的量子纠错码。

多种网络带宽测量算法及其比较

网络环境的复杂性造成测量网络带宽面临巨大困难。文章对现有的网络带宽测量算法进行了分类介绍,并对各种算法优缺点从滤波算法、时间分辨率、对网络交通影响、隐藏瓶颈、链接的多通道识别、可用带宽测量、带宽变化适用性的角度进行了比较。

并集对称合并和序偶非对称合并——句法演算的一个简约的新设想

本文提炼了Chomsky(2001)等文论中的句法推导原理,对“最简方案”中的并集对称合并和序偶非对称合并中的要害问题做了概括和批评,继而提出了包括重新定义成分统制者和被成分统制者等理论概念和句法操作原理在内的一些具有简约性的新建议。

素数阶群上基于非对称对的身份基环签名

针对已有身份基环签名的安全性证明难以在标准模型下实现的问题,提出标准模型下可证明安全的身份基环签名方案。首先,给出了身份基环签名安全模型和敌手模型的形式化定义。然后,基于素数阶群上的非对称对构造了一个具体的身份基环签名方案。最后,给出了该方案的安全性分析和性能分析。安全性分析结果表明,所提方案通过采用对偶系统加密技术实现了标准模型下的可证明安全性。性能分析结果表明,所提方案有效提升了方案中各算法的运行效率,与已有的基于对偶系统的身份基环签名方案相比,产生签名和验证签名的时间更短。

不对称数字用户线（ADSL）

本文对不对称数字用户线（ＡＤＳＬ）的基本概念，所能提供的宽带业务、技术性能、系统组成作了介绍和说明，并指出利用ＡＤＳＬ，把宽带信息沿普通电话线（铜线）送到千家万户，是数十年时间内过渡到光纤到家（ＦＴＴＨ）的有效传输手段。

叛逆者可追踪的非对称群组密钥协商协议

非对称群组密钥协商(Asymmetric Group Key Agreement,ASGKA)的概念在2009年欧密会上被首次提出,其协议结束时协商出来的只是一个共享的加密密钥。这个加密密钥可以被敌手访问,而且对应多个不同的解密密钥,每个群组用户都可以计算出一个对应该公钥的解密密钥。同时指出进一步研究的问题之一是如何实现叛逆者可追踪的ASGKA协议。设计了一个标准模型下可证安全的非对称密钥协商协议ASGKAwTT,该协议可以实现叛逆者追踪。

基于交织技术的非对称零相关区序列偶集构造

为了抑制或者消除准同步码分多址(QS-CDMA)通信系统的多址干扰(MAI)、多径干扰(MI)以及邻小区干扰,该文提出一类非对称零相关区(A-ZCZ)序列偶集的构造方法。基于给定的最佳自相关序列偶,运用交织操作,成功设计一类非对称零相关区序列偶集。新集合的每个子集均是零相关区序列偶集,且不同子集的序列偶间的互相关函数(CCF)具有更大的零互相关区(ZCCZ)。同时,该文提出的构造方法可以根据系统要求灵活地选择子集的零相关区宽度。

一种改进的非对称可搜索加密方案

云服务器端在缓解用户本地存储压力的同时,也存在对数据进行窃听的隐患,用户往往选择把数据的密文形式上传到云服务器端。然而,经典的数据加解密算法均未提供搜索功能,影响用户的使用效率。为此,提出一种非对称可搜索加密方案。该方案针对任何人均可生成陷门、密文可随意篡改、密钥对由用户各自生成、对身份进行加密、S形同虚设等5个漏洞作改进。分析结果表明,该方案在延用原方案类似框架的基础上,解决了原方案中的上述5个漏洞,使通信双方的信息语义得到保障。

汽车继电器触头系统研究新思路

论述了汽车继电器触头系统研究新思路。提出为提高汽车继电器通断能力和可靠性 ,需从触头本体对其结构进行改进 ,选择合适的触头材料 ,进行非对称配对 ;从外部利用电力电子器件对触头系统进行控制 ,实现无电弧通断。

一种改进的扩频非对称水印方案

在分析H artung提出的基于扩频的非对称水印方案的基础上,提出了一种新颖的公钥生成策略。此策略对嵌入水印时所需要的密钥进行随机双位循环变换生成水印检测时的公钥,生成的公钥和嵌入密钥有较好的相关性,并且攻击者利用生成的公钥无法估算出私钥,从而利用此策略改进的扩频非对称水印方案,提高了水印的检测效果,较好地保证了水印的安全性。