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按照IEC 61000-4-4/GB 17626.4—1998的要求,首先应用PSPICE仿真确定电路中各元件的参数值,然后基于拉普拉斯变换用MATLAB求解二阶电路验证各元件参数。在此基础上研制了一台以开关电源作为高压直流电源、以氢闸流管作为主控开关的脉冲群电源。该电源体积小、重量轻、效率高、成本低廉。试验结果表明,其输出信号符合标准要求,可用于快速瞬变脉冲群抗扰度试验。 相似文献
115.
研究了Pt,Ru,Ni为活性金属的负载型催化剂上甲醇质量分数为5%的水溶液的液相重整反应。在合适的温度、体积空速下,Pt基催化剂表现出较好的反应性能,甲醇转化率可达99%,H2选择性达98%以上,产物中CO体积分数小于0.01%。Ni/Al2O3催化剂可使甲醇转化率最高达到98%以上,H2选择性随转化率升高而下降,但不低于80%。Ru/Al2O3催化剂上甲醇的转化率最高,可达到98%以上,但其H2选择性随着转化率的升高,从68%快速下降至20%,明显与Pt、Ni基催化剂上的反应机理不同。根据反应条件和产物组成变化,进一步探讨甲醇反应路径,当产物中H2与CH4选择性比值高于2/3时,反应路径以重整制氢为主;当比值低于2/3时,反应路径以甲烷化为主。 相似文献
116.
The electron spin resonance (ESR) spectra of end‐group spin labelled poly(ethylene oxide) (SLPEO) using 2,2,6,6‐tetramethyl‐piperdine‐1‐oxyl nitroxide and its blends with poly(styrene‐co‐4‐vinylphenol) (STVPhs) of different hydroxyl contents were recorded over a wide temperature range. For a blend of SLPEO and pure polystyrene (PS), the ESR spectrum was composed of a single motion component, indicating that PS was immiscible with PEO. For blends composed of SLPEO and different‐hydroxyl‐content STVPhs, two spectral components with different motion rates were observed over a certain temperature range. The difference between the motion rates should be attributed to micro‐heterogeneity in the blends, with the faster rate corresponding to a nitroxide radical motion trapped in the PEO‐rich domain and the slower rate corresponding to a nitroxide radical motion trapped in the STVPh‐rich domain. Variations in the values of a number of the ESR parameters (Ta, Td and T50G) and the apparent activation energy (Ea) with hydroxyl content in the blends indicated that the miscibility of the blends increased with increasing hydrogen‐bonding density due to specific interactions between the hydroxyl groups in STVPh and the ether oxygens in PEO. Copyright © 2004 Society of Chemical Industry 相似文献
117.
Yu. F. Smirnov 《Measurement Techniques》2007,50(3):293-297
Metrological characteristics of active hydrogen frequency standards are investigated on the basis of internal and external
comparisons. The stability of random changes and drift of hydrogen frequency standards and also the potential capabilities
of time scale preservation with effective consideration of systematic changes in their frequency are demonstrated.
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Translated from Izmeritel’naya Tekhnika, No. 3. pp. 42–45, March, 2007. 相似文献
118.
Organic‐acid‐catalyzed sol–gel route for preparing poly(methyl methacrylate)–silica hybrid materials
Jui‐Ming Yeh Kuan‐Yeh Huang Chung‐Feng Dai B. G. Chand Chang‐Jian Weng 《应用聚合物科学杂志》2008,110(4):2108-2114
In this study, a series of organic–inorganic hybrid sol–gel materials consisting of a poly(methyl methacrylate) (PMMA) matrix and dispersed silica (SiO2) particles were successfully prepared through an organic‐acid‐catalyzed sol–gel route with N‐methyl‐2‐pyrrolidone as the mixing solvent. The as‐synthesized PMMA–SiO2 nanocomposites were subsequently characterized with Fourier transform infrared spectroscopy and transmission electron microscopy. The solid phase of organic camphor sulfonic acid was employed to catalyze the hydrolysis and condensation (i.e., sol–gel reactions) of tetraethyl orthosilicate in the PMMA matrix. The formation of the hybrid membranes was beneficial for the physical properties at low SiO2 loadings, especially for enhanced mechanical strength and gas barrier properties, in comparison with the neat PMMA. The effects of material composition on the thermal stability, thermal conductivity, mechanical strength, molecular permeability, optical clarity, and surface morphology of the as‐prepared hybrid PMMA–SiO2 nanocomposites in the form of membranes were investigated with thermogravimetric analysis, differential scanning calorimetry, dynamic mechanical analysis, gas permeability analysis, ultraviolet–visible transmission spectroscopy, and atomic force microscopy, respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
119.
Despite the common use of tapping-mode atomic force microscopy to image composites or polymer blends, very few studies have focused on the measurement of the interdiffusion at an interface between two polymers in contact. In this study, we show how to assess the interphase between two polymers with two methods. First, stable and robust tapping conditions are established, and the problem of the phase contrast is discussed. Second, a contact-resonance method is presented: the tip in contact with the sample is electrostatically excited at its resonance frequency by a self-controlled oscillator. The gain and frequency images allow us to measure the interdiffusion width. Both methods (using high and weak mechanical solicitation) give the same assessment of the interdiffusion width. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
120.