共查询到20条相似文献,搜索用时 46 毫秒
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MS界面稳定性判据新探 总被引:3,自引:0,他引:3
给出了定向凝固平界面稳定性新的判据,(l+3k/y0)ξ +[1+(1+ k)y0/4k]≥1其中A为无量纲速度,ξ≡GLS/mGc,y0是有关A和ξ的一个二次方程的根.新判据的最大特点是可直接由凝固参数推断界面的稳定性,不用解高次方程.发现MS绝对稳定性速度Va仅在加权温度梯度GLS→0时才是界面稳定性的临界速度.当 GLS>0时,Va大于实际的临界速度.给出了一个新的绝对稳定性梯度条件,并求出了最小的绝对稳定性无量纲临界梯度. 相似文献
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本文用自变量取值范围为有限区间的频率特性曲线来代替原来的Popov频率特性曲线,从而改进和简化了PoPov频率判据。 相似文献
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在实际工程应用中,需要利用稳定性判据判断直流分布式电源系统(direct current distributed power system,DCDPS)的稳定性,以便采取合适的控制策略。因此,DCDPS稳定性判据成为国内外学者研究的热点。对基于等效源变换器(子系统)和负载变换器(子系统)的稳定性判据、基于母线电压控制变换器和母线电流控制变换器的稳定性判据、基于无源性的稳定性判据、大扰动信号情况下稳定性判据的基本思想、特点进行分析。指出这些稳定性判据的优点与不足,给出了DCDPS稳定性判据研究的趋势,提出了基于无源性的稳定性判据和其他判据相结合的稳定性判断新方法。 相似文献
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KF稳定性判据的进一步分析 总被引:2,自引:0,他引:2
对KF稳定性判据做了进一步分析,得到一个新的界面稳定性判据:G≥mGc-kΓV2/D2V/D,发现绝对稳定性不只出现在凝固速度极高的条件下,极高的温度梯度也会导致绝对稳定性.这个结果对快速凝固和激光表面处理技术具有指导意义. 相似文献
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本文主阐述了电厂锅炉热平衡试验的组织和准备工作、热平衡试验的求、热平衡试验测定内容、主参数的记录及数据的整理等问题。 相似文献
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Galina Zilberstein 《Materials Characterization》1997,39(2-5):687-695
A method of tungsten grain size analysis in coiled lamp filaments has been developed. It is shown to be a valuable tool in design and optimization of heat treatment schedules, predictions of sag rates, failure analyses as well as standardization and benchmarking of non-sag tungsten grain structure in coiled lamp filaments. The procedure consists of two measurements on a polished and etched cross-section of a lamp coil: a number of observed “grains” and a number of examined turns. The resulting figure of merit, a grain-per-turn ratio, provides a useful relative measure of grain size (grain aspect ratio) in recrystallized non-sag tungsten lamp coils. The method permits rapid measurement, does not require any special instrumentation, and is performed directly from a stage of a standard light microscope. 相似文献
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在温度量值复现与传递以及国际比对中经常需要对亮度温度进行波长修正.探讨了钨带灯结构与亮度温度模型的关系,计算了T型钨带灯在400~1100 nm亮度温度对波长的导数,并利用实验数据进行了大波长间隔的修正验证.定性分析了不同结构钨带灯与T型钨带灯亮度温度-波长特性的差异.利用钨带灯的亮度温度-波长特性进行波长修正可减小温度量值传递的不确定度,扩展钨带灯应用的光谱范围. 相似文献
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Zongkui Kou Tingting Wang Haijun Wu Lirong Zheng Shichun Mu Zhenghui Pan Zhiyang Lyu Wenjie Zang Stephen J. Pennycook John Wang 《Small (Weinheim an der Bergstrasse, Germany)》2019,15(19)
Synergistic integration of two active metal‐based compounds can lead to much higher electrocatalytic activity than either of the two individually, due to the interfacial effects. Herein, a proof‐of‐concept strategy is creatively developed for the successful fabrication of twinned tungsten carbonitride (WCN) nanocrystals, where W2C and WN are chemically bonded at the molecule level. High‐angle annular dark‐field scanning transmission electron microscopy (HAADF‐STEM) and X‐ray absorption fine structure (XAFS) spectroscopy analyses demonstrate that the intergrowth of W2C and WN in the WCN nanocrystals produces abundant N–W–C interfaces, leading to a significant enhancement in catalytic activity and stability for hydrogen evolution reaction (HER). Indeed, it shows 14.2 times higher and 140 mV lower in the respective turn‐over frequency (TOF) and overpotential at 10 mA cm?2 compared to W2C alone. To complement the experimental observation, the theoretical calculations demonstrate that the WCN endows more favorable hydrogen evolution reaction than the single W2C or WN crystals due to abundant interfaces, beneficial electronic states, lower work function, and more active W sites at the N–W–C interfaces. 相似文献
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N. I. Kuskova S. I. Tkachenko S. V. Koval 《International Journal of Thermophysics》1998,19(1):341-345
The dynamics of electrical explosion of tungsten wires under water in microsecond times was studied. A new optical method for temperature measurement has been developed. For tungsten, uniform heating took place at 1011<j(A·m–2)<1012, therefore one can use these regimes for the investigation of properties in the liquid phase. Temperature dependences of enthalpy, electrical resistivity, and specific heat for liquid tungsten are given and compared with literature values. 相似文献
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文章对药剂中粘合剂含量、延期体装药结构、装药压力等进行研究,从而提高产品质量.结果表明:采用秒量较高的过渡药、200MPa压药压力、药剂中造粒剂含量为1.5%时能明显提高延期药秒量精度和贮存稳定性. 相似文献
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The phase overvoltage in the course of nucleation of molybdenum- and tungsten-carbide crystals in oxide tungstate-molybdate-carbonate
melts is determined by the nature of the substrate material and the conditions of electrodeposition (melt temperature, current
density, and electrolysis duration). As the temperature grows, the processes of alloy formation can complicate crystallization.
The structural correspondence of deposits depends on the nature and structure of substrate crystals.
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Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 3, pp. 57 – 60, May – June, 2005. 相似文献