Tests on low‐ductility RC frames under high‐ and low‐frequency excitations

The response of low‐ductility reinforced concrete (RC) frames, designed typically for a non‐seismic region, subjected to two frequencies of base excitations is studied. Five half‐scaled, two‐bay, two‐storey, RC frames, each approximately 5 m wide by 3.3 m high, were subjected to both horizontal and/or vertical base excitations with a frequency of 40 Hz as well as a lower frequency of about 4 Hz (close to the fundamental frequency) using a shake table. The imposed acceleration amplitude ranged from 0.2 to 1.2g. The test results showed that the response characteristics of the structures differed under high‐ and low‐frequency excitations. The frames were able to sustain high‐frequency excitations without damage but were inadequate for low‐frequency excitations, even though the frames exhibited some ductility. Linear‐elastic time‐history analysis can predict reasonably well the structural response under high‐frequency excitations. As the frames were not designed for seismic loads, the reinforcement detailing may not have been adequate, based on the crack pattern observed. The effect of vertical excitation can cause significant additional forces in the columns and moment reversals in the beams. The ‘strong‐column, weak‐beam’ approach for lateral load RC frame design is supported by experimental observations. Copyright © 2001 John Wiley & Sons, Ltd.     

野外型断层活动连续监测系统

介绍野外型断层活动连续监测系统的组成、布设及主要技术指标。     

Variability of East Asian Winter Monsoon in Quaternary Climatic Extremes in North China

In order to examine high-frequency variations of East Asian winter monsoon in Quaternary climatic extremes, two typical loess–paleosol sequences in the Chinese Loess Plateau were investigated. Sandy layers in the loess deposits, the “Upper sand” and “Lower sand” (layers L9 and L15, respectively), which represent a high-resolution record of paleomonsoon changes, have been sampled at intervals of 5–6 cm from sections at Luochuan and Xifeng. The grain size and magnetic susceptibility was measured for all samples. The grain-size results (a proxy of winter monsoon strength) indicate that the winter monsoon strength fluctuated on a millennial timescale during cold climatic extremes, with climatic events of a few hundred to a few thousand years. However, the winter monsoon was relatively stable during warm periods. The magnetic susceptibility signal (a proxy of summer monsoon intensity) is practically constant over the same period. This is tentatively explained by the assumption that the summer monsoon intensity was too low to be recorded in the magnetic susceptibility signal. The intensified winter monsoon events show periodicities in a range of 1000 to 2770 yr, with a dominant cycle of approximately 1450 yr. The detection of this oscillation in older glacial stages strongly suggests that it may be a pervasive cycle of the cold climatic phases of the Quaternary. Millennial-scale variations of the winter monsoon may be caused by instability of the westerly jet, which is determined by temperature differences between the polar and the equatorial regions.     

DNQ3型能见度仪故障分析及校准方法研究

为有效提高国家地面气象观测站能见度仪观测数据准确性和设备运行稳定性,对能见度仪开展日常维护、核查校准、数据质控和故障修复等工作显得尤为重要。该文通过对DNQ3型前向散射能见度仪硬件结构和基本工作原理的介绍,以及对一些典型故障进行分析,总结出能见度仪的检测维修流程,归纳了对应的故障解决措施,凝练出该型能见度仪的核查校准和疑误数据质控方法,为一线业务人员开展能见度仪常规维护、故障排查、运行监控等提供借鉴。     

Luminescence dating of sand–loess sequences and response of Mu Us and Otindag sand fields (north China) to climatic changes

The sand–loess transition zone in north China is sensitive to climate change, and is an ideal place to investigate past environmental changes. However, past climate change at millennial–centennial timescales in this region has not been well reconstructed because of limited numerical dating. Alternations of sandy loam soils with aeolian sand layers in the Mu Us and Otindag sand fields, which lie along the sand–loess transition zone, indicate multiple intervals of dune activity and stability. This change is probably a response to variations of the East Asian monsoon climate during the late Quaternary. The single aliquot regeneration (SAR) optically stimulated luminescence (OSL) dating protocol, which has been successfully applied to aeolian deposits worldwide, is applied to these two sand fields in this study. The OSL ages provide reliable constraints for reconstruction of past climate changes at suborbital timescale. Sections in both sand fields contain aeolian sand beds recording millennial‐scale episodes of dry climate and widespread dune activation, including episodes at about the same time as Heinrich Event 5 and the Younger Dryas in the North Atlantic region. These results demonstrate the potential of aeolian sediments in semi‐arid north China to record millennial‐scale climatic events, and also suggest that dry–wet climate variation at the desert margin in China may be linked to climatic change elsewhere in the Northern Hemisphere, through atmospheric circulation. This article was published online on 27 November 2008. An error was subsequently identified. This notice is included in the online and print versions to indicate that both have been corrected (16 December 2008). Copyright © 2008 John Wiley & Sons, Ltd.     

气候异常对我国北方地区沙尘暴的影响及其对策

利用(1951～2000年)气温、降水资料分析我国北方地区沙尘暴的演变趋势,探讨沙尘暴的机理和形成机制,重点研究了气候异常事件对今春我国北方沙尘天气频发的可能影响.指出,为加深对沙尘暴的认识并减轻其对社会经济可持续发展的影响,应加强对沙尘暴形成机理的科学研究建立沙尘暴监测、预警系统,同时对荒漠化土地进行科学的治理.     

火电厂粉煤灰的矿物磁性及其环境意义

火电厂排放的粉煤灰是重要的大气颗粒污染物之一,利用粉煤灰的磁性监测环境污染是新近发展的新手段。应用矿物磁测技术和X射线衍射对浙江省主要电厂排放的粉煤灰的矿物磁性特征和磁性矿物学,以及与重金属元素的关系进行了研究,结果表明粉煤灰具有较高的磁化率（X）、软剩磁（IRM20mT）和饱和等温剩磁（SIRM）值,粉煤灰频率磁化率（Xfd）的平均值为2．5％,磁性矿物以多畴（MD）颗粒存在,粉煤灰的剩磁矫顽力（BCR）在42～53mT之间。矿物测试结合X射线衍射分析表明粉煤灰中的氧化铁矿物以FeO4和Fe2O3-α为主,粉煤灰的磁化率与Fe、Mn、Pb、Zn、Cu、CA含量呈显著线性正相关,相关系数（r）分别是0．924,0．866,0．725,0．756,0．945和0．867,磁化率可作为粉煤灰中重金属元素含量的代用指标。     

论卡以头组的时代

中国科学院南京地质古生物研究所的有关人员 (1980 )曾做过大量地层古生物工作 ,证实卡以头砂页岩层或卡以头组的时代为三叠纪最早期 ,是飞仙关组底部地层的相变。“论卡以头组”一文认为该组下部的时代为二叠纪 ,上部则属三叠纪。对该文提供的地层古生物资料进行分析后 ,本文作者认为该论点缺乏证据 ,不能成立 ;将陆相的威宁哲觉剖面代替标准地点宣威羊场的过渡相剖面作为卡以头组的标准剖面 ,也是不合适的     

澳大利亚西北陆架中生界生储盖组合特征

澳大利亚西北陆架是一个贫油富气的地区,在近年的勘探开发中显示出广阔的前景。区域上包含4个盆地和1个造山带:北卡那封盆地、柔布克盆地、布劳斯盆地、波拿巴盆地和帝汶—班达褶皱带。西北陆架油气绝大多数集中在中生界。中生界发育4套主要烃源岩:三叠系湖相泥页岩、下—中侏罗统海相和海陆交互相碳质泥岩和煤系、上侏罗统海相页岩及下白垩统海相泥页岩;主要储集岩为中—上三叠统三角洲—边缘海相砂岩、下—中侏罗统砂岩、上侏罗统砂岩和白垩系砂岩;主要区域性盖层是下白垩统海相泥页岩。根据生储盖组合的沉积环境,主要发育海生海储海盖型和陆生陆储陆盖型两大生储盖组合类型。海生海储海盖型生储盖组合广泛分布于西北大陆架,是区域最重要的成藏组合。     

一次西南低涡过程的地面场中尺度分析

本文运用带通滤波分析方法,对四川省1981年7月由西南低涡等天气系统引起的大暴雨过程作了地面气象要素场的中尺度诊断分析。结果表明,带通滤波后的场具有明显的中尺度特征,其中一些物理量场的适当配置与6小时后的暴雨中心有较好的对应关系。说明了此带通滤波方法在实际业务预报中具有一定的使用价值。