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881.
为应用d-电子合金设计理论(或新相分计算法(New PHACOMP))设计发展新型抗热腐蚀单晶高温合金,首先对高Cr抗热腐蚀IN738LC系列合金Ni—16Cr—9.5Al—4.0Ti-8.0Co—0.55Nb—0.06Zr—0.05B—0.47C-Ta—W—Mo(at-%)的相稳定性进行了综合评价得出抑制σ相析出的稳定性临界条件为Mdt<0.991或Mdγ<0.93同时证明这两个临界电子参数具有等价性,可以用Mdt代替Mdγ简化合金设计过程.这一结果可适用于其它高Cr系列抗热腐蚀镍基合金的d-电子合金设计 相似文献
882.
Creep lives of high Cr ferritic heat resisting steel weldments decrease due to Type Ⅳ fracture, which occurs as a result of formation and growth of creep voids and cracks on grain boundaries in fine-grained heat affected zone (HAZ). Because boron is considered to suppress the coarsening of grain boundary precipitates and growth of creep voids, we have investigated the effect of boron addition on the creep properties of 9Cr steel weldments. Four kinds of 9Cr3WSCoVNb steels with boron content varying from 4.7×10-5 to 1.8×10-4 and with nitrogen as low as 2.0×10-5 were prepared. The steel plates were welded by gas tungsten arc welding and crept at 923K. It was found that the microstructures of HAZ were quite different from those of conventional high Cr steels such as P91 and P92, namely the fine-grained HAZ did not exist in the present steel weldments. Boron addition also has the effect to suppress coarsening of grain boundary carbides in HAZ during creep. As a result of these phenomena, the welded join 相似文献
883.
HSn70-1B铜管在碱性NaCl溶液中的腐蚀行为 总被引:2,自引:0,他引:2
利用表面分析技术和电化学方法研究了HSn70- 1B 铜管在碱性NaCl溶液中的腐蚀行为.在自腐蚀状态下,HSn70-1B铜管表面生成以Cu2 O为主的表面膜;在阳极极化电位下表面CuCl的生成反应为一级反应,电极表面形成CuCl膜 后,存在极限电流密度;电化学阻抗频谱(EIS)有2个容抗弧,随Cl-含量的增加,容抗弧 逐渐收缩,弥散性增大. 相似文献
884.
885.
Downstream Ecological Impacts of Controlled Sediment Flushing in an Alpine Valley River: A Case Study 总被引:1,自引:0,他引:1
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Sediment flushing may be effective to tackle the loss of reservoir storage as a result of siltation. When operationally possible, the impact of this practice on the downstream aquatic environment can be mitigated by limiting the sediment concentration of the discharged waters (controlled sediment flushing). However, this topic is poorly documented, and concerns arise when limits are discussed. We present the results of a 3‐year field investigation concerning the controlled sediment flushing of a small reservoir on the Adda River, the main tributary of Lake Como—Italy. Two limits for suspended solid concentration (SSC) were adopted: 1.5 g L?1, as average value throughout the whole working day, and 3.0 g L?1, as alert threshold to adjust the ongoing activity. These constraints were essentially fulfilled in the course of the documented operations. The first year sediment flushing was more significant than the following year: 25 000 tons of fines below 2 mm in diameter were flushed in six non‐consecutive days in summer 2010, while, one year earlier, 75 000 tons were flushed in 16 non‐consecutive days. In the third year of investigation (2011), no sediment evacuation took place. The benthic macroinvertebrate and the fish communities were surveyed a short distance below the reservoir, that is, in the potentially more affected river reach. Clear pieces of evidence of environmental quality degradation were not detected; the adopted strategies can therefore be considered to be appropriate when planning sediment flushing management in comparable contexts. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
886.
城市化引起的诸多水生态、水环境及洪灾问题均与天然水文条件的破坏紧密相关;水文控制指标是海绵城市建设中的关键控制指标。在调研国际城市雨洪管理的演变及目前城市水文控制指标发展趋势的基础上,提出海绵城市建设所必需的水文控制指标体系概念。该体系包括维持河湖湿地基流与地下水补给的入渗控制指标,减少雨洪面源污染的水质控制指标,防止河道侵蚀的水土侵蚀控制指标,以及避免小量级洪涝和减轻极端洪涝灾害的洪水控制指标。在此基础上,分析了我国在海绵城市建设中缺乏完整水文控制指标体系的现状,并提出了我国目前在建立城市雨洪管理水文控制指标工作中亟待开展的工作,为海绵城市建设中合理确定适合各地具体条件的水文控制指标体系提供研究思路与参考。 相似文献
887.
Taneli Rantaharju Neil J. Mansfield Jussi M. Ala-Hiiro Thomas P. Gunston 《Ergonomics》2015,58(7):1071-1087
In this paper, alternative assessment methods for whole-body vibration and shocks are compared by means of 70 vibration samples measured from 13 work vehicles, deliberately selected to represent periods containing shocks. Five methodologies (ISO 2631-1:1997, BS 6841:1987, ISO 2631-5:2004, DIN SPEC 45697:2012 and one specified by Gunston [2011], ‘G-method’) were applied to the vibration samples. In order to compare different evaluation metrics, limiting exposures were determined by calculating times to reach the upper limit thresholds given in the methods. Over 10-fold shorter times to exposure thresholds were obtained for the tri-axial VDV (BS 6841) than for the dominant r.m.s. (ISO 2631-1) when exposures were of high magnitude or contained substantial shocks. Under these exposure conditions, the sixth power approaches (ISO 2631-5, DIN SPEC, G-method) are more stringent than a fourth power VDV method. The r.m.s. method may lead to misleading outcomes especially if a lengthy measurement includes a small number of severe impacts. In conclusion, methodologies produce different evaluations of the vibration severity depending on the exposure characteristics, and the correct method must be selected. 相似文献
888.
889.
为模拟植物在不同季节的颜色变化,提出一种在虚拟环境中实现对不同季节植物表观仿真的方法.采用基于二阶统计量的全局颜色传递算法,得到不同季节的纹理库;基于生成的纹理库实现对不同季节植物的表观仿真.为改善传递效果,引入高阶矩,调整目标图像的斜度和峰度分布,使之与样本图像一致.建立评估模型,从颜色和纹理两方面对传递效果进行评估,评估结果表明,该方法的仿真效果较好. 相似文献
890.