Directed Asymmetric Nickel-Catalyzed Reductive 1,2-Diarylation of Electronically Unactivated Alkenes

Transition-metal catalyzed intermolecular 1,2-diarylation of electronically unactivated alkenes has emerged as an extensive research topic in organic synthesis. However, most examples are mainly limited to terminal alkenes. Furthermore, transition-metal catalyzed asymmetric 1,2-diarylation of unactivated alkenes still remains unsolved and is a formidable challenge. Herein, we describe a highly efficient directed nickel-catalyzed reductive 1,2-diarylation of unactivated internal alkenes with high diastereoselectivities. More importantly, our further effort towards enantioselective 1,2-diarylation of the unactivated terminal and challenging internal alkenes is achieved, furnishing various polyarylalkanes featuring benzylic stereocenters in high yields and with good to high enantioselectivities and high diastereoselectivities. Interestingly, the generation of cationic Ni-catalyst by adding alkali metal fluoride is the key to increased efficiency of this enantioselective reaction.     

衬底温度对HfO_2薄膜结构和光学性能的影响

采用直流磁控反应溅射法,分别在室温,200,300,400和500℃下制备了HfO2薄膜。利用X射线衍射(XRD)、椭圆偏振光谱(SE)和紫外可见光谱(UVvis)研究了衬底温度对HfO2薄膜的晶体结构和光学性能的影响。XRD研究结果显示:不同衬底温度下制备的HfO2薄膜均为单斜多晶结构;随衬底温度的升高,(-111)面择优生长更加明显,薄膜中晶粒尺寸增大。SE和UVvis研究结果表明:随衬底温度升高,薄膜折射率增加,光学带隙变小;制备的HfO2薄膜在250～850nm范围内有良好的透过性能,透过率在80%以上。     

Nonlinear empirical mode predictive drift extraction on fiber optical gyroscope

The integration drift of inertial unit is a fatal error on navigation and attitude determination system. Many approaches have been developed to extract and eliminate it. A novel fiber optical gyroscope drift extraction algorithm was proposed in this paper to ameliorate the performance of fiber optical gyroscope by extracting the trend component as the compensation. In this algorithm, the attitude quaternion of stellar sensor and the output of fiber optical gyroscope were imported into a nonlinear empirical mode predictive algorithm to extract the drift component of gyroscope. Combing the advantages of predictive filter and empirical mode decomposition in nonlinear signal processing, our proposal is more precise in drift extraction and data approximation. Software simulation and hardware verifications on gyroscope were launched, in which the results had proven the capability of the algorithm.     

High-resolution algorithms of sharp interface treatment for compressible two-phase flows

In this paper, a kind of arbitrary high order derivatives (ADER) scheme based on the generalised Riemann problem is proposed to simulate multi-material flows by a coupling ghost fluid method. The states at cell interfaces are reconstructed by interpolating polynomials which are piece-wise smooth functions. The states are treated as the equivalent of the left and right states of the Riemann problem. The contact solvers are extrapolated in the vicinity of contact points to facilitate ghost fluids. The numerical method is applied to compressible flows with sharp discontinuities, such as the collision of two fluids of different physical states and gas–liquid two-phase flows. The numerical results demonstrate that unexpected physical oscillations through the contact discontinuities can be prevented effectively and the sharp interface can be captured efficiently.     

覆黏弹层加肋双层板的声反射

为评估覆盖层的吸声性能,研究黏弹层在无限大周期加肋双层板背衬下的声反射。首先通过弯曲波与Lamb波的比较,揭示了板近似理论不适用于黏弹性板的原因。为此采用(黏)弹性理论处理(黏)弹性板,而肋板的处理则采用板近似理论,并用Hull提出的方法解决肋板和平板的耦合问题,得到反射声场的解。与板近似理论计算加肋双层板声反射的结果进行比较验证了本文方法的正确性,对反射系数进行计算分析了背衬对声反射的影响,定义平均反射系数比较了不同覆盖层的性能。结果表明,频率较低时覆盖层无法有效抑制背衬的影响,板间流体层与双层板的耦合作用引起共振散射,肋板与双层板的耦合作用降低声反射。      

A Facile Strategy for the Preparation of Azide Polymers via Room Temperature RAFT Polymerization by Redox Initiation

A new vinyl aryl azide monomer, 4‐azidophenyl methacrylate (APM), has been synthesized and characterized by ¹H NMR and FT‐IR spectroscopy. The thermal stability of APM has been investigated by temperature‐dependent FT‐IR spectroscopy and ¹H NMR, and the monomer has been demonstrated to be quite stable at ambient temperature. Reversible addition–fragmentation chain transfer (RAFT) homopolymerization and copolymerizations of APM with methyl acrylate, methyl methacrylate, and styrene have been carried out at room temperature using a redox initiator, benzoyl peroxide (BPO)/N,N‐dimethylaniline (DMA). The results show that the polymerizations bear all the characteristics of controlled/living free‐radical polymerizations. Moreover, the cycloaddition of azido group to carbon–carbon double bond can be avoided in the polymerization process at room temperature.

     

非线性系统参数辩识的一种频域模型

本文基于对非线性系统的可分离性假设，将非线性弹性力和阻尼力分别分解为物理坐标下各点间相对位移和相对速度的幂级数函数，导出了一般多自由度非线性系统在恒幅激励下的广义频率响应函数与输入输出之间的迭代关系式，提出了非线性系统中基本线性部分的概念，进而了一种在实验条件下的系统物理参数辩识方法。     

Monitor adsorption of acetone vapor to a room temperature ionic liquid 1-octyl-3-methylimidazolium bromide by a langasite crystal resonator

In this work, the responses of a Y-cut langasite crystal resonator (LCR) in liquid phases were investigated by an impedance analysis method. The resonant frequency (f_S) of the LCR decreases with increasing mass loading on the active surface of the resonator. The LCR can be operated at the resonant frequency that is down to about 60% of the fundamental frequency (f₀) under foreign mass loading. The frequency-mass coefficient of the Y-cut LCR is theoretically derived to be −1.282 × 10⁻⁶, which is supported by the experimental results. The resonant frequency of the LCR decreases linearly while its motional resistance (R_m) increases linearly with increasing (ρη)^1/2, where η and ρ are the viscosity and density of the liquid phase, respectively. The slopes of the plots of f_S versus (ρη)^1/2 and R_m versus (ρη)^1/2 are related to the region of (ρη)^1/2 because of the influence of surface roughness of the LCR. The changes in viscodensity of a room temperature ionic liquid (RTIL), 1-octyl-3-methylimidazolium bromide ([C₈MIM][Br]), were investigated in acetone vapor adsorption and ascending temperature processes by the LCR. The adsorption of acetone into [C₈MIM][Br] causes a significantly drop in viscosity of the [C₈MIM][Br] film, which induces an increase in f_S and a decrease in R_m for the RTIL modified LCR. When the thickness of [C₈MIM][Br] film is less than the decay distance of the thickness-shear wave, a mass effect model is observed in the early adsorption process. Based on the responses of the LCR, the viscodensity of the [C₈MIM][Br] film as well as the adsorbed amounts of acetone into film were monitored in real time during the adsorption or desorption processes.     

A Surface Enhanced Raman Scattering (SERS) microdroplet detector for trace levels of crystal violet

We report on a microfluidic platform that integrates a winding microdroplet chip and a surface-enhanced Raman scattering (SERS) detection system for trace determination of crystal violet (CV). Colloidal silver was applied to generate SERS. Compared to the continuous flow microfluidic system, the microdroplet based detection described here effectively eliminates any memory effects. Effects of flow pattern, droplet size, surfactant, and position of detection were optimized. Under optimal conditions, there is a linear correlation between signal and the concentration of CV in the 10 nM to 800 nM range, with a correlation coefficient (R²) of 0.9967. The limit of detection in water is 3.6 nM.

Palladium-catalyzed haloallylation of aromatic ynol ethers with allyl chlorides: a highly regio- and stereoselective approach to (1E)-α-chloroenol ethers

Described herein is a Pd-catalyzed haloallylation of aromatic ynol ethers and allyl chlorides, allowing facile access to (1E)-α-chloroenol ethers in a highly regio- and stereoselective manner. The synthetic utility of this method is demonstrated well by the synthesis of the stereodefined multisubstituted enol ethers and α-allylated carbonyl compounds.