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61.
Atmospheric mixing ratios of carbonyl sulfide (COS) in Beijing were intensively measured from March 2011 to June 2013. COS mixing ratios exhibited distinct seasonal variation, with a maximum average value of 849 ± 477 pptv in winter and a minimal value of 372 ± 115 pptv in summer. The seasonal variation of COS was mainly ascribed to the combined effects of vegetation uptake and anthropogenic emissions. Two types of significant linear correlations (R2 > 0.66) were found between COS and CO during the periods from May to June and from October to March, with slopes (ΔCOS/ΔCO) of 0.72 and 0.14 pptv/ppbv, respectively. Based on the emission ratios of COS/CO from various sources, the dominant anthropogenic sources of COS in Beijing were found to be vehicle tire wear in summer and coal burning in winter. The total anthropogenic emission of COS in Beijing was roughly estimated as 0.53 ± 0.02 Gg/year based on the local CO emission inventory and the ΔCOS/ΔCO ratios. 相似文献
62.
Ye Cheng Chenglong Zhang Yuanyuan Zhang Hongxing Zhang Xu Sun Yujing Mu 《环境科学学报(英文版)》2015,28(2):163-170
Atmospheric mixing ratios of carbonyl sulfide(COS) in Beijing were intensively measured from March 2011 to June 2013. COS mixing ratios exhibited distinct seasonal variation, with a maximum average value of 849 ± 477 pptv in winter and a minimal value of 372 ± 115 pptv in summer. The seasonal variation of COS was mainly ascribed to the combined effects of vegetation uptake and anthropogenic emissions. Two types of significant linear correlations(R2 0.66) were found between COS and CO during the periods from May to June and from October to March, with slopes(ΔCOS/ΔCO) of 0.72 and 0.14 pptv/ppbv, respectively. Based on the emission ratios of COS/CO from various sources, the dominant anthropogenic sources of COS in Beijing were found to be vehicle tire wear in summer and coal burning in winter. The total anthropogenic emission of COS in Beijing was roughly estimated as 0.53 ± 0.02 Gg/year based on the local CO emission inventory and the ΔCOS/ΔCO ratios. 相似文献
63.
The microscopic characteristics of melting trace caused by copper wire fault are an important basis for the physical evidence identification of electrical fires. Metallography is an important method in electrical fire research, and computer-aided quantitative analysis on metallographic structure is common in materials aspect. In this study, the metallographic structure and phase composition characteristics of melting trace caused by overcurrent fault were explored with the aid of a metallographic microscope and an X-ray diffractometer (XRD). The results show that the grains are mainly slender dendritic and columnar crystals when the current is 128 A, while they are coarse dendritic and cellular crystals when the current is greater than 192 A; the average grain diameter of melting trace of copper wire grows with the increase in current. The main phases of melting trace caused by overcurrent fault of copper wire are α-Cu base and Cu2O, and the new phases Cu4Si and Cu2Mg are formed when the current is higher than 160 A. In addition, the solidification process of metallographic structure of copper wire under different currents was simulated by the Procast software. It is found that the simulation results are basically in agreement with the experimental data, which suggests that this model can effectively predict the microstructure characteristics of melting trace of copper wire under different currents. The research results can provide a sound basis for the physical evidence identification of electrical fire and improve the accuracy and scientificity of electrical fire investigation. 相似文献
64.
Ali Vazini Shayan Reza Azar Afza Reza Teimouri 《Journal of Manufacturing Processes》2013,15(4):644-658
This work deals with parametric study of dry wire EDM (WEDM) process of cemented tungsten carbide. Experiments have been conducted using air as dielectric medium to investigate effects of pulse on time, pulse off time, gap set voltage, discharge current and wire tension on cutting velocity (CV) surface roughness (SR) and oversize (OS). Firstly, a series of exploratory experiments were carried out to identify appropriate gas and its pressure. Afterward, preliminary experiments were conducted to investigate effects of process parameters on dry WEDM characteristics and find appropriate ranges for each factor. Then a central composite rotatable method was employed to design experiments based on response surface methodology (RSM). Empirical models were developed to create relationships between process factors and responses by considering to analysis of variances (ANOVA). To increase the predictability of the process, intelligent models have been developed based on back-propagation neural network (BPNN) and accuracy of these models was compared with mathematical models based on root mean square error (RMSE) and prediction error percent (PEP). In order to select optimal solutions in the cases of single-objective and multi-objectives optimization problems, optimization includes two main approaches. First approach was based on mathematical model and desirability function. Also second approach was designed based on neural network and particle swarm optimization. These approaches were applied in both cases of single-objective and multi-objectives optimization problems and their results were compared with together. Results indicated that selection of air at inlet pressure of 1.5 bar is really appropriate for conducting experiments of next stages. Also, the BPNN creates more accurate prediction rather than mathematical model. Moreover, the BPNN-PSO approach was more efficient in optimization of process rather than mathematical model-desirability function in respect with validation tests. 相似文献
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西南地区覆冰气象要素的变化特征及综合评估 总被引:5,自引:0,他引:5
论文采用西南地区(95°~110°E,25°~35°N)96个常规气象观测站1961年1月1日至2009年12月31日逐日气象要素资料,应用模糊信息分配方法对西南地区形成覆冰的主要气象要素配置进行研究。以连续覆冰日数为主,建立了该地区满足气象条件的覆冰综合评估指数。结果表明,当同时满足地面日最低气温在-10~1 ℃,相对湿度≥80%,日照时数≤2 h这3个条件时,最易发生电线覆冰现象。我国西南地区的云南、贵州、四川三省交界处以及云贵高原大部为电线覆冰最为严重的地方,且覆冰灾害有非常显著的年际及年代际变化规律。 相似文献
67.
为准确认定电气火灾事故中的过电流故障,模拟在不同电流条件下ZR-BV单芯铜线的过电流故障,通过逐帧分析高速影像研究导线发生过电流故障时的变化过程,使用金相分析技术分类研究过电流导线电弧熔化痕迹的组织特征。结果表明:当I≥4Ie时,导线发生熔断,断路电弧将引燃热分解后的绝缘热解气体,造成火灾的蔓延扩大;过电流导线电弧熔断痕与火烧熔痕的宏观特征较为相似,但喷溅熔痕和发散状熔痕是过电流导线所特有的;枝晶偏析组织是过电流电弧熔断痕的典型组织,且随着电流值的升高,枝晶偏析组织分布范围明显扩大,几乎不再出现等轴状组织。 相似文献
68.
本文基于煤矿安全规程要求,通过对煤矿提升钢丝绳的现状分析和钢丝绳电脑探伤仪的简要介绍及其在晋城矿区的应用实践,从技术研究的角度,提出保证钢丝绳运行安全的解决方案。 相似文献
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