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排序方式: 共有137条查询结果,搜索用时 15 毫秒
41.
研究非线性电容RLC串联电路,应用多尺度法,得到非线性振动系统主共振的一次近似解并进行数值计算,分析电阻、电感、电容和电动势对主共振幅频响应的影响.结果表明:RLC串联电路的主共振响应有跳跃和滞后现象;随着电动势的增加,主共振的振幅和共振区增大;随着电阻的增大,主共振的振幅和共振区减小. 相似文献
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用化学镀法制备 Pd/Ag 膜时膜厚和组成的控制 总被引:1,自引:0,他引:1
研究了不同 Pd2+含量的镀液在多孔陶瓷载体上的化学沉积规律, 发现当 Pd 沉积层厚度达到约 5 μm 后, 即使镀液中反应物的消耗比例很小, 膜厚增长也明显变缓, 沉积反应主要受膜层表面的催化活性位控制; 当镀液中 Pd2+含量只能沉积形成小于 4 μm 的 Pd 膜时, 在 323 K 化学镀 180 min 后, 镀液中 Pd2+的转化率高于 90%. 与之相似, 当 Ag 镀液中的 Ag+含量等于 0.5~2 μm 的 Ag 膜层所需量时, 在 333 K 化学镀 120 min 后, Ag+的转化率可达 95%. Ag+的高转化率与 Ag 颗粒的择向生长特性有关. 根据 Pd 和 Ag 的化学镀沉积规律, 通过调节镀液中金属离子的含量能够预先设计和精确控制超薄 Pd/Ag 膜的膜厚和组成. 相似文献
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Weiwei Zhang Xin Zhang Gaofeng Zeng Kang Wang Wenchao Zhang Rongjie Yang 《先进技术聚合物》2019,30(12):3061-3072
Flamability is one of the major issues for utilization of bisphenol A–type vinyl ester resin (VER) polymeric composites in practical applications. The thermal stability and mechanical property of VER composites containing octaphenyl polyhedral oligomeric silsesquioxane (OPS) were investigated and discussed in detail. With increasing the mass ratio of OPS, the residues yield at 800°C and bending strength at break of the VER/OPS composites were enhanced, accompanied with the gradually decreased values of the peak heat release rate, total heat release, and total smoke release due to the formation of dense carbon/silica protective layers that acted as a barrier to heat and mass transfer. In addition, the flame‐retardant mechanisms of condensed phase and gas phase were analyzed by XPS, TGA‐FTIR, and GC‐MS. The results showed that when OPS was incorporated to the resin matrix, the characteristic peaks intensity of the gaseous products was reduced obviously due to some of the characteristic groups still retained in condensed phase. Therefore, the significance of this work is providing an optional method to fabricate flame‐retarding VER composites with excellent mechanical properties. 相似文献
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Almost automorphic is a particular case of the recurrent motion, which has been studied in differential equations for a long time. We introduce square-mean pseudo almost automorphic and some of its properties, and then study the pseudo almost automorphic solution in the distribution sense to stochastic differential equation driven by Lévy process. 相似文献
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Hongda?Zhang Taohong?YeEmail author Gaofeng?Wang Peng?Tang Minghou?Liu 《Flow, Turbulence and Combustion》2017,98(3):841-885
A sub-grid scale (SGS) combustion model by combining dynamic thickened flame (DTF) with flamelet generated manifolds (FGM) tabulation approach (i.e. DTF-FGM) is developed for investigating turbulent premixed combustion. In contrast to the thickened flame model, the dynamic thickening factor of the DTF model is determined from the flame sensor, which is obtained from the normalized gradient of the reaction progress variable from the one-dimensional freely propagating premixed flame simulations. Therewith the DTF model can ensure that the thickening of the flame is limited to the regions where it is numerically necessary. To describe the thermo-chemistry states, large eddy simulation (LES) transport equations for two characteristic scalars (the mixture fraction and the reaction progress variable) and relevant sub-grid variances in the DTF-FGM model are presented. As to the evaluation of different SGS combustion models, another model by utilizing the combination of presumed probability density function (PPDF) and FGM (i.e. PPDF-FGM) is also described. LES of two cases with or without swirl in premixed regime of the Cambridge swirl burner flames are performed to evaluate the developed SGS combustion model. The predicted results are compared with the experimental data in terms of the influence of different LES grids, model sensitivities to the thickening factor, the wrinkling factor, and the PPDF of characteristic scalars, the evaluation of different modelling approaches for the sub-grid variances of characteristic scalars, and the predictive capability of different SGS combustion models. It is shown that the LES results with the DTF-FGM model are in reasonable agreement with the experimental data, and better than the results with the PPDF-FGM approach due to its ability to predict better in regions where flame is not resolved. 相似文献
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甘肃省舟曲8.7特大泥石流调查研究 总被引:7,自引:0,他引:7
本文通过对甘肃省舟曲县城后山三眼峪沟和罗家峪沟特大泥石流灾害的现场调查,从泥石流形成的地形、地质和降雨条件入手,分析了特大泥石流灾害的特征与成因:三眼峪沟和罗家峪沟泥石流形成区在2010年8月7日23~24时的1h降雨量达77.3mm,暴雨形成强大洪水依次冲毁两条沟内的天然堆石坝和人工拦挡坝,形成规模巨大的高容重黏性泥石流,泥石流冲出总量和泥沙总量分别为 144.2×104m3和97.7×104m3; 泥石流携带具有强大冲击力的巨石冲毁房屋5500余间; 在白龙江内形成长约550m,宽约70m,高约10m的堰塞坝并形成堰塞湖,堰塞湖回水长3km,使县城一半被淹; 泥石流造成1744人死亡和失踪。分析研究表明,三眼峪沟和罗家峪沟泥石流如果在近期遭遇强降雨还会暴发泥石流,但规模比87特大泥石流小;如果强降雨发生在数年后,暴发的泥石流规模比87特大泥石流略小;在20a或更长的时期内,没有发生新的地震影响下,在三眼峪沟和罗家峪沟经历一次大规模泥石流暴发后,泥石流的规模将回到汶川地震前的水平。 相似文献
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各级化学竞赛中有不少以结构高度对称的化合物为素材的试题,该类题目不仅可以考查学生空间想象能力,还可以考查如何将化学问题抽象为数学问题,利用数学方法解决化学问题的能力。本文讨论几种结构高度对称化合物的试题的解题思路。1由正八面体引出的对称问题【例1】已知[Co(NH3) 相似文献