A new hederagenin glycoside from <Emphasis Type="Italic">Nephelium lappaceum</Emphasis>

A new oleane-type triterpene oligoglycoside, hederagenin 3-O-(3-O-acetyl-β-D-xylopyranosyl)-(1→3)-α-L-arabinopyranoside (2), together with four known compounds, hederagenin (1), hederagenin 3-O-(4-O-acetyl-α-L-arabinopyranosyl)-(1→3)-α-L-rhamnopyranosyl-(1→2)-α-L-arabinopyranoside (3), hederagenin 3-O-α-L-arabinopyranosyl-(1→3)-α-L-rhamnopyranosyl-(1→2)-α-L-arabinopyranoside (4), hederagenin 3-O-β-D-glucopyranosyl-(1→3)-α-L-rhamnopyranosyl-(1→4)-β-D-xylopyranoside (5), was isolated from the hull of Nephelium lappaceum. All the isolates were obtained from the hull of rambutan for the first time.     

逐步增加Ⅱ型截尾下指数分布恒加试验的统计分析

本文对逐步增加Ⅱ型截尾下指数分布场合恒定应力加速寿命试验进行了统计分析,得到参数的最大似然估计存在唯一的充要条件。最后通过模拟例子表明最大似然估计是有效的。     

Influence of polymer dielectric surface energy on thin‐film transistor performance of solution‐processed triethylsilylethynyl anthradithiophene (TES‐ADT)

This study investigates the correlation between surface energy of polymer dielectrics and the film morphology, microstructure, and thin‐film transistor performance of solution‐processed 5,11‐bis(triethylsilylethynyl) anthradithiophene (TES‐ADT) films. The low surface energy polyimide (PI) dielectric induced large grains with strong X‐ray reflections for spin‐cast TES‐ADT films in comparison to high surface en‐ ergy poly(4‐vinyl phenol) (PVP) dielectric. Furthermore, thin‐film transistors based on spin‐cast TES‐ADT films on PI dielectric exhibited enhanced electrical performance, small hysteresis, and high stability under bias stress with carrier mobility as high as 0.43 cm²/Vs and a current on/off ratio of 10⁷. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

氢化物生成原子荧光法快速测定锑精矿中的砷、汞、硒、铋和锡

锑精矿;砷;汞;硒;铋;锡;氢化物发生 原子荧光     

传动装置密封环摩擦磨损性能研究

为分析车辆传动装置密封环在高速高压工作环境下的磨损失效,利用自主研制的试验台研究了速度、接触压力和介质油温对密封摩擦副摩擦磨损特性的影响;利用扫描电子显微镜观察了磨损程度不同的密封环端面的表面形貌,并探讨了其磨损机理.结果表明,在设定的试验条件下,密封摩擦副的摩擦系数随着压力的增大和转速的升高先急剧减小再降幅减缓后趋于稳定,而压力对摩擦状态的影响要比转速显著.密封环端面温度与摩擦状态之间存在相互影响的特征.密封介质性质同样影响着密封环的摩擦状态.在稳定磨损阶段,密封环的磨损机理以磨粒和黏着磨损为主导,当进入到剧烈磨损期后,磨粒磨损和疲劳磨损的影响更为突出.     

Effects of adhesive thickness on global and local Mode-I interfacial fracture of bonded joints

The interfacial fracture of adhesively bonded structures is a critical issue for the extensive applications to a variety of modern industries. In the recent two decades, cohesive zone models (CZMs) have been receiving intensive attentions for fracture problems of adhesively bonded joints. Numerous global tests have been conducted to measure the interfacial toughness of adhesive joints. Limited local tests have also been conducted to determine the interface traction-separation laws in adhesive joints. However, very few studies focused on the local test of effects of adhesive thickness on the interfacial traction-separation laws. Interfacial toughness and interfacial strength, as two critical parameters in an interfacial traction-separation law, have important effect on the fracture behaviors of bonded joints. In this work, the global and local tests are employed to investigate the effect of adhesive thickness on interfacial energy release rate, interfacial strength, and shapes of the interfacial traction-separation laws. Basically, the measured laws in this work reflect the equivalent and lumped interfacial fracture behaviors which include the cohesive fracture, damage and plasticity. The experimentally determined interfacial traction-separation laws may provide valuable baseline data for the parameter calibrations in numerical models. The current experimental results may also facilitate the understanding of adhesive thickness-dependent interface fracture of bonded joints.     

The Blocking Ability and Flowing Characteristics of Steady Foams in Porous Media

Foam flow experiments were carried out to study the influence factors such as surfactant concentration, foam quality, injection rate of liquid and gas, permeability of porous media, temperature, and oil saturation on blocking ability and flowing characteristics of steady foams in porous media. Foam blocking mechanisms and flowing characteristics were summarized according to the experimental results and foam migration behavior. The results showed that the pressure distribution of flowing foams was linearly descending in porous media at steady state. The results further showed that the foam size and quality in pores along the sand pack were almost uniform, that is, foam generation and destruction gradually reached dynamic equilibrium at steady state. In porous media, the blocking ability of steady foams increased with the concentration of the foaming agent and the increase in the permeability of porous media, but the blocking ability decreased with the increase in the temperature, the shearing rate, and the oil saturation of the porous media. Foam resistance factor reached maximal value at the foam quality of 85% in porous media.     

A <Emphasis Type="Italic">VU</Emphasis>-decomposition method for a second-order cone programming problem

A vu-decomposition method for solving a second-order cone problem is presented in this paper. It is first transformed into a nonlinear programming problem. Then, the structure of the Clarke subdifferential corresponding to the penalty function and some results of itsvu-decomposition are given. Under a certain condition, a twice continuously differentiable trajectory is computed to produce a second-order expansion of the objective function. A conceptual algorithm for solving this problem with a superlinear convergence rate is given.     

Collinear Velocity-map Photoelectron Imaging Spectrometer for Cluster Anions

We describe a collinear velocity-map photoelectron imaging spectrometer, which combines a Wiley-McLaren time-of-flight mass analyzer with a dual-valve laser vaporization source for investigating size-selected cluster and reaction intermediate anions. To generate the reaction anions conveniently, two pulsed valves and a reaction channel are employed instead of premixing carrier gas. The collinear photoelectron imaging spectrometer adopts modified velocity-map electrostatic lens, and provides kinetic energy resolution better than 3%. The performance of the instrument is demonstrated on the photodetachment of Si₄^- at 532 and 355 nm, and Si₃C^- at 532 nm, respectively. In both cases, photoelectron spectra and anisotropy parameters are obtained from the images. For Si₄^-, the spectra show two well-resolved vibrational progressions which correspond to the ground state and the first excited state of the neutral Si₄ with peak spacing of 330 and 312 cm^-1, respectively. Preliminary results suggest that the apparatus is a powerful tool for characterizing the electronic structure and photodetachment dynamics of cluster anions.     

金属钾和碳酸钠高压合成金刚石

以金属钾和碳酸钠为反应原料, 在压力为2 GPa, 温度为500 ℃的密封白金坩埚中反应18 h, 所得产物通过粉末X射线衍射和显微拉曼分析进行了表征, 证实合成出了微米级的金刚石. 对金刚石的合成机理进行了研究, 推测其反应过程为碳酸钠在铂和钾的作用下分解出CO2, CO2与钾反应得到金刚石. 研究结果表明金刚石可以在温和的条件下合成.