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871.
Qi-he Chen Ming-liang Fu Jin Liu Hai-feng Zhang Guo-qing He Hui Ruan 《Ultrasonics sonochemistry》2009,16(5):599-604
Betulin is an abundant naturally occurring triterpene, which makes it a potentially important raw material for a precursor of biologically active compounds. The objective of the current study was to determine the optimum UAE conditions for betulin from B. papyfera bark. The optimum conditions were evaluated with fractional factorial design and optimized using response surface methodology. High yields of betulin were observed from white birch bark by UAE technology. The solvent concentration and the ratio of material to solvent were the most significant parameters on betulin extraction as evaluated through FFD. The extraction conditions were further investigated with central composite design. The fitted second-order model revealed that the optimal conditions consisted of 98% ethonal concentration, 1:42 the ratio of white birch bark to solvent, extraction temperature 50 °C, ultrasonic frequency 5 kHz and extraction time 3 h. Under the optimized condition, the maximum productivity of betulin predicted is 23.17%. The extraction productivity and purity of betulin under the optimized extraction conditions were great higher than that of the non-optimized condition. The present study demonstrates that ultrasound is a great efficiency tool for the fast extraction of betulin from white birch bark. 相似文献
872.
This paper reports that the K x-ray spectra of the thin target 47Ag, 48Cd, 49In and 50Sn were measured by an HPGe semi-conductor detector in collisions with 84.5 MeV 6C4+ ions. Our experiment revealed the Kα x-ray energy shifts were not obvious and the Kβ1 x-ray energy shifts were about 90~110 eV. The simple model of Burch et al has been previously used to calculate the K x-ray energy shifts due to an additional vacancy in 2p orbit. The present work extends the model of Burch to calculate the x-ray energy shifts of multiple ionized atoms induced by heavy ions with kinetic energy of MeV/u. In addition to our experimental results, many other experimental results are compared with the calculated values by using the model. 相似文献
873.
Yanping Li Yixian Xiang Xiaowen Dong Jiaqiang Xu Fei Ruan Qingyi Pan 《Journal of solid state chemistry》2009,182(8):2041-2045
Molybdenum trioxide/polyaniline (MoO3/PANI) composite was prepared first by ion-exchange reaction between aniline (ANI) and dodecylamine (DDA) which was intercalated precursor, and then was formed under the polymerization of ANI within the interlayer space of MoO3 at 120 °C for 3 d in air. According to powder X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, infrared spectroscopy and electrochemical testing, MoO3/PANI composite has layered structure, and its interlayer spacing is 1.127 nm. Moreover, it has high thermal stability with the compound and completes its weight loss at 751.9 °C. Electrochemical investigation shows that MoO3 is the major active substance in the MoO3/PANI electrode, and MoO3/PANI electrode demonstrates better conductivity and electrochemical activity than pure MoO3 electrode, attributed to the promotion of Li+ and/or electron transport. In addition, the alternating current impedance proves that if the resistance of MoO3/PANI electrode reduces apparently, the electrochemical activity will increase correspondingly, the same as the relationship between the ohmic resistance and the electrical conductivity. 相似文献
874.
在NaHSO4作催化剂, 无溶剂下将水杨醛、活泼亚甲基化合物和尿素或硫脲进行Biginelli 反应, 高收率地合成了一系列monastrol类物质. 产物的结构通过IR, 1H NMR, 13C NMR光谱数据和单晶解析表征和确定. 对于不同活泼亚甲基化合物参与的反应, 形成了4-(2-羟基苯基)嘧啶衍生物2和氧桥嘧啶衍生物3两类物质, 活泼亚甲基化合物分子中醇酯基的结构是决定两种嘧啶衍生物结构的主要因素. 对于以前报道的Biginelli产物4-(2-羟基苯基)嘧啶衍生物2a和氧桥嘧啶衍生物3e的形成也进行了讨论. 相似文献
875.
在一些光学精密仪器的应用场合中,不仅需要脉冲电源在时间上能够提供精确的控制,而且需要具有高稳定度的输出,以提高光电系统的探测性能;运用基于高压开关的两级式方法,采用单级高功率MOSFET开关结合具有高稳定输出的直流电源的结构,设计了输出辐度可达2kV的高稳定负脉冲电源;测试结果表明,在输出脉冲宽度为8 μs时,脉冲前沿约为48 ns,系统延迟时间约为140 ns,负脉冲超调参数约为1%。该系统具有结构简单、可靠性高、高稳定性输出等优点,可以为特定的光电器件提供优质的控制方式。 相似文献
876.
Ruan Huojun Dai Meifeng Su Weiyi Dept. of Math. Zhejiang Univ. Hangzhou China. Dept. of Math. Jiangsu Univ. Zhenjiang China. Dept. of Math. Nanjing Univ. Nanjing China. 《高校应用数学学报(英文版)》2005,20(2):235-242
§ 1 IntroductionThe class of Cantor sets is a typical one of sets in fractal geometry.Mathematicianshave paid their attentions to such sets for a long time.Itis well known that the Hausdorffmeasure of the Cantor middle- third set is1(see[1]) .Recently,Feng[3] obtained the exactvalues of the packing measure for a class of linear Cantor sets.Using Feng s method,Zhuand Zhou[5] obtained the exactvalue of Hausdorff centred measure of the symmetry Cantorsets.In this papar,we consider the Ha… 相似文献
877.
The shape-from-moments problem is to reconstruct a planar polygon from a set of its complex moments. To reconstruct a polygon means to estimate the vertices and the ordering of the vertices. We notice that some coefficients are very important in finding out the ordering of the vertices. We introduce sensitive factors for the coefficients and use it to analyze sensitivity. These factors are also useful for the sensitivity of the vertices. 相似文献
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