Active sensing using impedance‐based ARX models and extreme value statistics for damage detection

In this paper, the applicability of an auto‐regressive model with exogenous inputs (ARX) in the frequency domain to structural health monitoring (SHM) is established. Damage sensitive features that explicitly consider non‐linear system input/output relationships are extracted from the ARX model. Furthermore, because of the non‐Gaussian nature of the extracted features, Extreme Value Statistics (EVS) is employed to develop a robust damage classifier. EVS provides superior performance to standard statistical methods because the data of interest are in the tails (extremes) of the damage sensitive feature distribution. The suitability of the ARX model, combined with EVS, to non‐linear damage detection is demonstrated using vibration data obtained from a laboratory experiment of a three‐story building model. It is found that the vibration‐based method, while able to discern when damage is present in the structure, is unable to localize the damage to a particular joint. An impedance‐based active sensing method using piezoelectric (PZT) material as both an actuator and a sensor is then investigated as an alternative solution to the problem of damage localization. Copyright © 2005 John Wiley & Sons, Ltd.     

崇明地震台FGE磁通门磁力仪D分量基线值的确定

基线值是考察记录仪运行是否稳定可靠的一个重要指标。本文以记录仪的D分量为例,通过认真仔细地分析与探索,使用数据处理的方法,解决了崇明台FGE磁通门磁力仪基线值不稳定的问题。这对基线值的确定和日常的数据处理都具有一定的指导意义。     

Adsorbable Organic Halogens (AOX) in Polish Rivers – Levels and Changes

This paper presents results of a study on the concentration of adsorbable organic halogens (AOX) in water samples of the Oder River and its tributaries collected from 1998 to 2002. The Vistula River water for AOX was analysed in the period 2001–2002. The investigated waters of the Vistula near the mouth (Kiezmark) were more contaminated with AOX than the Oder near the mouth (Widuchowa, Krajnik Dolny). In general, AOX levels in the Polish rivers are comparable to the values found in the European rivers, e.g. the Rhine and the Ton. The research has shown that AOX were correlated with pH, total suspended solids, and the riverine flow. No relation between dissolved oxygen and redox potential and AOX was found out. During the flood period AOX, inorganic halogens (TIX), and mineral substances (sulfates) were analysed.     

用实测沉降量反求土体压缩性指标

采用室内试验求取的压缩性指标,由于受样品扰动的影响,往往不能反映实际土体的变形特点.为了寻求一种合理确定压缩性指标的方法,根据目前实际中广泛采用的沉降量计算公式,以深港西部通道填海工程软土的实测沉降量为例,通过对沉降量计算公式中参数的合理选取,反算求得了压缩性指标,经验证,其结果符合实际情况.     

CM桩复合地基承载力试验结果分析

通过对“CM桩复合地基”(以下简称CM地基 )承载力试验结果的分析 ,获得了一些有益的结论 ,对其在徐州地区的推广和应用提供参考。     

北京城近郊区土壤中Cd的释放、形态转化与演变趋势

在对北京城近郊区主要类型土壤(潮土和褐土)中Cd形态分析的基础上,研究pH与土壤中Cd的释放量及其形态转化的关系。结果表明:潮土和褐土中Cd的释放量曲线都呈下凹的弧形,在pH=6～7之间释放量最低。pH对土壤中Cd释放的影响,其本质是土壤中Cd的化学形态发生了变化,各形态间的转化以水溶态为中介体。所有的形态转化中,pH对交换态和碳酸盐结合态影响最大,且这两者之间的转化对生物有效量起决定性作用。进而根据北京城近郊区土壤中生物有效Cd的分布状况,结合北京市近12年监测的大气pH值,对北京城近郊区土壤Cd污染进行预警。     

婺源县森林景观游憩价值的经济评价

文章在简要分析森林游憩价值经济评价方法的基础上，采用旅行费用法（TCM）对婺源县森林景观游憩价值进行了经济评价。采用整群随机抽样的方法对研究区的游客进行半访谈式问卷调查，根据调查资料，将婺源县游客来源划分为15个出发区，建立了游林率-旅行费用回归模型。结果表明，旅行费用与游林率呈极显著的负相关，文化程度与游林率呈显著的正相关；在此基础上制定了游憩需求曲线，计算得出研究区2002年森林景观游憩经济价值为1．02亿元。     

四川盆地秸秆还田与稻田新三熟制的农产品服务价值

四川省传统稻田种植模式为稻麦（油）轮作，中稻收后到小麦、油菜播栽前尚有2个月左右的休闲期，该时段的温光时资源占全年的20％左右，利用潜力大。经多年研究集成了以秸秆覆盖还田提升土壤有机质、提高稻田综合生产能力的“水稻-蔬菜-小麦”、“水稻-秋马铃薯-油菜”、“水稻-蔬菜-春马铃薯”稻田新三熟种植模式，对三种新模式的农产品服务价值研究结果表明：秸秆覆盖稻田新三熟显著提高了稻田的综合生产能力，“稻-芋／油”三熟新模式比传统“稻-油”两熟模式的生产力提高115．2％，产值达到42218．4元/a；“稻-菜-麦”和“稻-菜-芋”三熟新模式分别比传统“稻-麦”两熟模式生产力提高92．3％、168．3％，周年公顷产值达到35798．9元、49952．2元；“稻-油”保护性耕作两熟模式与传统“稻-油”农作模式相比，虽然生产力相当，但由于降低了生产成本，年农产品服务价值每公顷增加904．0元，增加8．7％，“稻-麦”保护性耕作两熟模式与传统“稻-麦”农作模式相比，年农产品服务价值每公顷增加5341．5元，增加57．5％；“稻-芋／油”三熟新模式比传统“稻-油”和保护性耕作两熟模式年农产品服务价值每公顷分别增加18006．2元、17102．2元；“稻-菜-麦”和“稻-菜-芋”三熟新模式分别比传统“稻-麦”两熟模式农产品服务价值增加16835．5元、25063．8元，比保护性耕作模式分别增加11494．0元、19722．3元。     

Climatically driven pH changes in two Norwegian alpine lakes

Two alpine lakes in the south-central part of Norway have been studied for recent changes in diatom assemblages preserved in their sediments. Both lakes experience a post 1980 AD increase in diatom valve accumulation rates possibly reflecting an increase in lake productivity. In addition there is an overall increase in diatom-inferred pH at both sites. Recovery from lake acidification can be disregarded as a possible cause of increased pH as the lakes are situated in catchments with high buffering capacities in areas that have received low amounts of acid deposition. We suggest that recent climate warming has influenced both sites with the important effect of increasing mineralization in the catchments, resulting in greater fluxes of nutrients and base cations to the lakes, leading to an increase in diatom-inferred pH. Taxa that have increased in abundance include Achnanthes minutissima, Achnanthes nodosa, Cyclotella spp., Navicula schmassmannii, Staurosirella lapponica, and S. pinnata. In one of the lakes, the maximum diatom-inferred pH values reached at the top of the core are as high as pH values reconstructed from the diatom assemblages deposited at the end of the Mid-Holocene thermal maximum c. 4000 cal. BP.     

用最小绝对偏差方法(LAD)估计极值分布参数的探讨

数理统计问题中的最小绝对偏差方法(Least Absolute Deviation)由于具有良好的稳健性,近年来备受重视。本文所研究的是如何将最小绝对偏差法及非线性回归模型相结合,应用于极值分布的参数估计,并与经典的参数估计法相比较。通过对徐州市降雨量数据的研究表明,改进后的参数估计法不仅提高了模型拟和的精确度,而且有良好的稳定性,可以推广到相关气象要素的预测、预报研究中。其中,将LAD法运用于极值分布模型是一个新的尝试。