基于动态核独立元统计量的石油管道泄漏检测

石油管道泄漏是受腐蚀、磨损、焊缝缺陷、振动、冲刷以及人为破坏等多种因素影响的连续动态过程,单纯基于压力信号的检测和基于高斯分布假设的信号分析方法不能适应其多变量、强耦合、动态特性。为此,综合考虑与管道泄漏有关的操作参数和环境参数,针对管道监测参数呈现时序自相关性、泄漏检测精度不高的问题,提出一种基于动态核独立分量分析(DKICA)的石油管道泄漏检测方法。首先引入动态特性确定算法(DOD)计算模型最佳参数阶次,解决动态过程导致的监测参数呈现时序自相关性问题;再采用核独立分量分析(KICA)在核主元空间提取独立元;最后通过考察独立元的T2、SPE联合指标判断泄漏发生。通过对某一输送场站采集的数据进行实验验证,结果表明采用联合指标D2的正常样本误检率和泄漏样本漏检率都远低于单独采用T2或SPE统计量;而引入动态特性的2阶DKICA对于正常样本的误检率和泄漏样本的漏检率都低于未引入动态特性的KICA方法。可见,所提出的基于动态核独立分量联合指标的石油管道泄漏检测方法是一种高效且可行的方法。     

分散电源并网对供电可靠性的影响分析

分析了分散电源并网对供电可靠性的影响.计算并对比了分散电源并网前后在重合闸、备自投、解列重合闸、孤岛等不同运行方式下的供电可靠性指标.推导出了分散电源并网可靠性预测评估的数学模型和SAIFI-Island曲线.分散电源并网后,不合理的运行方式将降低系统供电可靠性,与重合闸相结合的计划孤岛模式能较好地改善供电可靠性.     

沈阳市地下水库建设的技术可行性分析

地下水在我国尤其是北方地区城乡供水中占较大比例。地下水库因具有地表水与地下水资源联合调控、多年调蓄、水资源战略储备及应急供水等功能而受到越来越广泛的关注。在分析地下水库基本结构的基础上,提出了建设地下水库的基本条件,并以沈阳市为例进行分析,给出了论证地下水库补给水源、补给区、地下水库储水空间估算及开采条件的具体分析与计算方法。最后利用建立的地下水流数值模型,模拟预测了地下水库建成后分别按常规水源与应急水源两种方式所产生的供水规模。结果表明,在研究区建设地下水库具有较高可行性。     

Calculating first-order sensitivity measures: A benchmark of some recent methodologies

This work compares three different global sensitivity analysis techniques, namely the state-dependent parameter (SDP) modelling, the random balance designs, and the improved formulas of the Sobol’ sensitivity indices. These techniques are not yet commonly known in the literature. Strengths and weaknesses of each technique in terms of efficiency and computational cost are highlighted, thus enabling the user to choose the more suitable method depending on the computational model analysed. Two test functions proposed in the literature are considered. Computational costs and convergence rates for each function are compared and discussed.     

C语言实验教学考核评价指标及其观测内容分析

针对C程序设计语言实验教学考核的需要，阐述了制定实验考核评价指标的基本原则，确立了各项考核评价指标，比较详细地说明了各项指标的观测内容。该指标体系能够帮助教师对C语言的实验教学考核作出整体评价。     

Application of the Water Poverty Index at Different Scales: A Cautionary Tale

Abstract

The Water Poverty Index is an integrated tool developed on the basis of extensive consultation with a range of scientists, practitioners and policymakers. It is primarily designed for use at the community level to enable more holistic water-resource assessments on a site-specific basis. It can however be applied at different scales to suit different needs. One of the motivations to design such a tool was an attempt to move away from the conventional, purely deterministic, approaches to water assessment, relying primarily on models and large-scale data. In today's world such an approach is inappropriate, ill representing the complexities of modern water-allocation decisions where economic, political and social issues all have a powerful role to play. This paper highlights some applications of the Water Poverty Index at different spatial scales and discusses the implications of applying indicators at these different scales.     

Comparative study of indices used in toxicity evaluation of effluents

Several toxicological indices currently proposed (inter)nationally to aid decision-making tasks in effluent control were compared. To evaluate effluent ranking differences between the indices an inversion distance as a similarity measure was proposed. The major factor influencing effluent ranking were found to be a composition of test-battery. Differences in mathematical operator of the indices such as, e.g. arithmetic mean (used in averaging indices) or maximum one (used in an approach of the most sensitive test in a battery), affect the ranking similarity noticeably lesser than the modification of the percentage effect level of the measurement endpoints. Effluent and/or river flow parameters incorporated into the indices substantially modify ranking results of the effluent set. For the analysis, the toxicological information on 23 effluents from municipal wastewater treatment plants operating in cities and small towns of Lithuania as well as test-battery data on industrial effluents published elsewhere were used. It seems that the general statements achieved in the current study can be applied to any set of effluents.     

晶体光学中若干基本问题的讨论

本文论证了晶体光学中的若干基本问题,如各种类型光率体之间的关系、光性正负判别式、光轴角计算公式以及⊥B_(xa)和⊥B_x。切面的双折射率大小等,结合实例分析并修正了以往文献中关于这些问题不正确或不准确的结论。     

Statistical analysis of process capability indices with measurement errors

Process capability indices (PCIs) have been widely used in manufacturing industries to provide a quantitative measure of process potential and performance. While some efforts have been dedicated in the literature to the statistical properties of PCIs estimators, scarce attention has been given to the evaluation of these properties when sample data are affected by measurement errors. In this work we deal with the problem of measurement‐error effects on the performance of PCIs. The analysis is illustrated with reference to and , i.e. the two most common measures suggested to evaluate process capability. Copyright © 2002 John Wiley & Sons, Ltd.     

Impact of understory vegetation on forest canopy reflectance and remotely sensed LAI estimates

Forest leaf area index (LAI), is an important variable in carbon balance models. However, understory vegetation is a recognized problem that limits the accuracy of satellite-estimated forest LAI. A canopy reflectance model was used to investigate the impact of the understory vegetation on LAI estimated from reflectance values estimated from satellite sensor data. Reflectance spectra were produced by the model using detailed field data as input, i.e. forest LAI, tree structural parameters, and the composition, distribution and reflectance of the forest floor. Common deciduous and coniferous forest types in southern Sweden were investigated. A negative linear relationship (r² = 0.6) was observed between field estimated LAI and the degree of understory vegetation, and the results indicated better agreement when coniferous and deciduous stands were analysed separately. The simulated spectra verified that the impact of the understory on the reflected signal from the top of the canopy is important; the reflectance values varying by up to ± 18% in the red and up to ± 10% in the near infra-red region of the spectra due to the understory. In order to predict the variation in LAI due to the understory vegetation, model inversions were performed where the input spectra were changed between the minimum, average and maximum reflectance values obtained from the forward runs. The resulting variation in LAI was found to be 1.6 units on average. The LAI of the understory could be predicted indirectly from simple stand data on forest characteristics, i.e. from allometric estimates, as an initial step in the process of estimating LAI. It is suggested here that compensation for the effect of the understory would improve the accuracy in the estimates of canopy LAI considerably.