Ⅱ型裂纹疲劳扩展中超载行为的研究

利用铝合金ＬＹ１２ＣＺ制十字型试样进行Ⅱ型裂纹的疲劳扩展试验，施加若干次短瞬的Ⅱ型超载。发现Ⅱ型裂纹的超载行为与Ⅰ型裂纹的不同，裂纹的扩展速率可几倍于未超载时相同应力强度因子幅度下的扩展速率；而且超载后的短瞬期间，裂纹在塑性区内仍保持较快的速率扩展。试验研究表明：Ⅱ型超载和Ⅰ型超载也许分别受不同的机制控制；它更类似于Ⅲ型超载。     

非交换Lipschitz-φ算子代数

本文引入由紧距离空间(K,d)到给定Banach代数A中的Lipschitz-φ算子构成的非交换Banach代数L~φ(K,A)与l~φ(K,A),证明了它们都是由K到A的全体连续算子构成的非交换Banach代数C(K,A)的子代数,并且关于范数||f||φ=L_φ(f)+||f||∞是Banach代数,研究了不同 Lipschitz尺度函数φ对应的大(小)Lipschitz代数之间的关系。特别当φ(t)=t~α时,引入了极限代数lim_(α→0+)l~α(K,A),lim_(α→+∞)l~α(K,A),lim_(α→0+)L~α(K,A)与lim_(α→+∞)L~α(K,A)以及距离空间的Lipschitz连通性,得到了lim_(α→+∞)l~α(K,A)=A的充要条件,也给出了lim_(α→0+)L~α(K,A)=C(K,A)的条件。     

The optical properties of MgxZnl-xO thin films

Mg_xZn_1-xO thin films have been prepared on silicon substrates by radio frequency magnetron sputtering at 60℃. The thin films have hexagonal wurtzite single-phase structure and a preferred orientation with the c-axis perpendicular to the substrates. The refractive indices of Mg_xZn_1-xO films are studied at room temperature by spectroscopic ellipsometry over the wavelength range of 400--760\,nm at the incident angle of 70℃. Both absorption coefficients and optical band gaps of Mg_xZn_1-xO films are determined by the transmittance spectra. While Mg content is increasing, the absorption edges of Mg_xZn_1-xO films shift to higher energies and band gaps linearly increase from 3.24.eV at x=0 to 3.90\,eV at x=0.30. These results provide important information for the design and modelling of ZnO/ Mg_xZn_1-xO heterostructure optoelectronic devices.     

Single-frequency terahertz source pumped by Q-switched fiber lasers based on difference-frequency generation in GaSe crystal

We demonstrate a unique terahertz (THz) source that is compact, utilizes recently developed all-fiber Q-switched lasers, and is based on difference-frequency generation in a GaSe crystal. A single piezo simultaneously Q switched the two fiber lasers by using stress-induced birefringence, to achieve the temporal overlap of pulses from the two fiber lasers. These correlated pulses then combine in the GaSe crystal to produce coherent and highly monochromatic THz pulses. The peak power for this THz source can reach 0.53 mW, corresponding to an average power of 0.43 microW and a conversion efficiency of 4.75 x 10(-7). The estimated linewidth of this THz source can be as narrow as approximately 35 MHz or 1.17 x 10(-3) cm(-1).     

Highly efficient high-power thulium-doped germanate glass fiber laser

A 64 W fiber laser at 1.9 microm with a slope efficiency of 68% with respect to the launching pump power at 800 nm was demonstrated in a one-end pump configuration using a piece of 20 cm long newly developed thulium-doped germanate glass double-cladding single-mode fiber. A quantum efficiency of 1.8 was achieved. An output laser power of 104 W at 1.9 microm was demonstrated from a piece of 40 cm long fiber with a dual-end pump configuration.     

Enantioselective Synthesis of Quaternary Carbon Stereocenters: Addition of 3‐Substituted Oxindoles to Vinyl Sulfone Catalyzed by Pentanidiums

A pentanidium‐catalyzed highly enantioselective conjugate addition of 3‐alkyloxindoles to phenyl vinyl sulfone has been demonstrated. This approach allows the construction of 3,3‐dialkyl‐substituted oxindole frameworks with high yield and excellent enantioselectivity (up to 99 %) under simple phase‐transfer conditions. A variety of oxindoles bearing all‐carbon quaternary stereogenic centers were obtained in the presence of 0.25 mol % pentanidium. Meanwhile, practicality was illustrated by a gram‐scale asymmetric synthesis of two 3,3‐dialkyl‐substituted oxindoles. The resulting adduct can be smoothly transformed to the natural product analogue in a short synthetic route.     

多金核二氧化铈空心球用于硝基苯酚催化加氢

催化剂的微观结构在催化还原反应、有机物氧化反应及有机物转化反应中起着关键作用。本文利用无模板方法合成了多金核中空二氧化铈微球催化剂。将制备好的二氧化铈中空微球浸渍到一定浓度的氯金酸溶液中,然后多次洗涤除去表面吸附的氯金酸离子,最后通过硼氢化钠还原制成中空氧化铈微球包覆的多金核的核壳结构催化剂。将该核壳结构材料用于硝基苯酚加氢反应与金纳米粒子及氧化铈微球相比,多金核中空二氧化铈核壳结构表现出优越的活性和稳定性。通过这种浸渍洗涤再还原的简单方法合成的多金核二氧化铈催化剂有望应用于生物医药和能源环境等领域。     

齐次分数次积分算子在变指标函数空间上的有界性

本文得到了齐次分数次积分算子在变指标Lebesgue空间、变指标Hardy空间和变指标Herz型Hardy空间上的一些有界性结果.