随机因素对镍基合金应力腐蚀裂尖力学特性的影响

镍基合金的应力腐蚀开裂是核电站一回路中最重要的潜在安全隐患之一,考虑物理参数的随机性,基于氧化膜破裂理论,研究了镍基合金应力腐蚀裂尖力学特性的分散性规律。为了提高随机参数数值分析的效率,结合MATLAB和ABAQUS子模型技术的优点,完成了MATLAB对ABAQUS 的二次开发,将有限元数值模拟和拉丁超立方抽样方法相结合,获得了弹性模量、屈服强度等随机参数对应力腐蚀裂尖氧化膜和基体金属区域应力应变的影响规律,并验证了方法的可行性。结果表明,随机性的影响不容忽略,屈服应力的随机性对裂尖应力的分散性影响最大,而弹性模量的随机性对裂尖塑性应变分散性的影响最为显著。     

圆截面RC桥墩曲率极限状态和延性的概率分析

从变形能力的不确定方面研究了圆截面钢筋混凝土桥墩曲率极限状态和曲率延性系数。把截面的材料参数和几何尺寸看作随机变量,采用拉丁超立方体抽样模拟法分析了在不同的轴压比、纵筋配筋率和配箍率下桥墩截面无量纲屈服、服务和破坏控制曲率极限状态的概率特性。结果表明,截面的无量纲曲率极限状态近似服从正态分布,轴压比是影响无量纲屈服和服务水平曲率极限状态均值的主要因素;轴压比和配箍率是影响无量纲破坏控制水平曲率极限状态均值的主要因素;无量纲曲率极限状态的变异系数随着截面变形的增加而增加。另外,还分析了桥墩截面在服务和破坏控制极限状态下曲率延性系数的概率分布特征值,通过回归分析提出了用桥墩截面设计参数计算曲率延性系数特征值的近似计算公式。     

Evaluation on four sampling schemes for assessing indoor air quality

Continuous sampling is one of the common approaches for assessing indoor pollutant level. It is believed that the longer the measurement time, the higher the accuracy and confidence level of the measurement can be achieved. In 2003, the Hong Kong Environmental Protection Department (HKEPD) launched an Indoor Air Quality (IAQ) certification scheme to promote an acceptable IAQ in workplaces. However, measurement efforts and uncertainties associated with the sampling method have not been addressed. Alternative sampling schemes taking shorter measurements in the sampling period were proposed in some circumstances. In this study, the average carbon dioxide (CO₂) concentration of a workplace is selected as an indicator of the indoor air quality to investigate the probable errors and measurement efforts in four sampling schemes, regarding the sampling period: in Scheme A, it is from a continuous sampling throughout the measurement; in Scheme B, it is from two sampling periods of two equal sessions of the measurement; in Scheme C, it is from two structural sampling periods of the two sessions; and in Scheme D, the average concentration is from four sampling periods in four equal sessions of the measurement. In particular, a year-round indoor CO₂ concentration at 17 locations in a typical office in Hong Kong was used to evaluate the probable errors using these four sampling schemes. At certain confidence levels, the required measurement times of the alternative sampling schemes (Schemes B, C, D) were evaluated and compared with that of an 8-hour continuous one (Scheme A). It was found that Scheme C would offer a reduction of measurement effort up to 30%. It is recommended to specify the uncertainties and efforts of measurement in future codes, and to consider these sampling schemes in determining practical strategies for IAQ measurement.     

含大规模风电的互联系统联络线随机功率波动幅值估计

随着我国特高压电网的快速发展,大区电网实现互联是未来发展趋势。然而在特高压电网建设初期,互联系统的电气联系较弱,互联系统的联络线功率波动限制了其输送能力。文中提出了一种考虑负荷与风电随机波动特性的联络线波动幅值计算方法。首先深入研究了联络线输送功率的波动原理,给出了基于电力系统频率响应特性的联络线功率波动机制,并研究了风电与负荷波动的概率分布特性,在此基础上,提出了基于改进拉丁超立方抽样的联络线功率波动幅值估算方法。通过华北—华中互联系统算例分析验证了文中所提算法的准确性和有效性。     

产品抽样检验的风险与科学的抽样方法

抽样检验广泛用于产品生产、购销，贸易以及科研活动之中。如何抽样才科学合理，人们却普遍认识不足，对于抽样的风险概念更是缺乏了解。     

QK系列多功能取样钻机的研制

介绍了QK系列多功能取样钻机的类型、基本结构以及性能特点。该系列钻机在实际应用中,体现了结构设计合理先进,较好地突出了＂轻便、快捷、高效＂的特点与优势。     

汽车运输煤采样点选取方法浅析

针对《煤炭化验手册》等汽车运输煤车顶采样中易出现的问题,分析其原因,提出在卸车过程中采样,从而提高汽车运输煤采样的精确性.     

Revisiting private participation,governance and electricity sector performance in Latin America

This paper revisits the relationship between private participation, regulatory governance and the performance of the electricity sector in 18 Latin American countries over the last five decades. Private investment flows have been consistent overtime, providing around 55 % of total electricity investment in the region. We examine the nature, and resultant performance outcomes, of increased private sector involvement in electricity sub-sectors, including generation capacity, non-conventional renewable energy (NCRE), electricity access, electricity losses, and affordability. The results suggest that private investment and the quality of regulatory governance are positively associated with better performance of the electricity sector. Our long-term examination suggests that private investments strongly contribute to enhancing the quality and efficiency of the electricity sector's performance by increasing generation capacity, increasing the share of renewable energy, increasing access, and reducing electricity losses. Affordability of electricity services also improved in countries with high private participation, while subsidies to the electricity sector declined considerably. These outcomes seem to be enabled and reinforced by independent regulatory governance.     

烤烟留种田棉铃虫幼虫分布型与抽样技术研究

棉铃虫是陕西省烤烟留种田后期主要害虫之一。幼虫分布型调查表明,它主要为波松和负二项分布,且随密度而变化,但适合于Taylor幂法则:S2=1.07523m0.9931。经推导演算,得出理论抽样公式为:n=1.07523(t/D)2·m-1.0069适合烟田棉铃虫幼虫调查的序贯抽样模型为T'₀(n)=0.15n+1.96√0.1634nT₀n(n)=0.15n-1.96-1.96√0.1634n最多只需抽取16株。对各种机械抽样方法比较后,认为实践中用平行线10点100株取样比较合适。      

脉金矿取样与偏析问题的探讨

本文分析了脉金矿化验品位偏差较大的原因,提出取样代表性、制样方法同化验技术一样,对造成偏差具有同等重要的作用。提出了新的取样量计算式和避免偏析的制样方法。