茂名油页岩沉积有机质特征及古气候意义

基于海洋沉积确定的始新世晚期至渐新世早期(约33.5 Ma)的气候过渡期是新生代全球性气候事件,但长期以来相关的陆相沉积记录研究则比较缺乏。本文对形成于始新世晚期至渐新世早期的茂名油柑窝组油页岩样品进行了有机质丰度、烃类组成、单体烃碳同位素组成等分析,以期研究低纬度陆相沉积有机质对古近纪始新世-渐新世气候过渡期(EOT)的响应。研究结果显示,埋藏较浅的上部层位样品正构烷烃碳同位素组成显著正偏,为-19.1‰~-25.9‰,平均值为-22.2‰;而下部层位样品正构烷烃碳同位素组成在-23.7‰~-30.2‰,平均值为-26.3‰。两个样品正构烷烃碳同位素组成之差在1.5‰~8.1‰,平均值之差为4.6‰。正构烷烃碳同位素组成的显著差异指示了EOT低纬度陆相古气候变化引起的陆相有机质响应,而这种响应与当时大气CO2浓度和海洋温度降低导致的气候和植物群落变化密切相关,即可能存在着C3植物向C4植物的转化、C4植物的迅速增加并最终导致沉积有机质碳同位素组成的变化;也可能是由于大气CO2浓度降低导致的大气CO2碳同位素组成整体正偏的结果。很显然,进一步详细的连续剖面分析将对研究古近纪EOT低纬度陆相古气候变化提供重要科学依据。     

一种顾及GNSS系统间偏差的伪距单点定位方法

对系统间偏差的成分和影响因素进行分析,发现各项改正后残余误差对系统间偏差估值的影响可归结为与卫星编号和广播星历更新相关。提出一种新的顾及参与解算卫星构成的系统间偏差估计方案,新方案能够在仅有4颗多模GNSS卫星可见时提供可靠的位置服务。     

Residual drift demands in moment‐resisting steel frames subjected to narrow‐band earthquake ground motions

This paper presents the main results of the evaluation of residual inter‐story drift demands in typical moment‐resisting steel buildings designed accordingly to the Mexican design practice when subjected to narrow‐band earthquake ground motions. Analytical 2D‐framed models representative of the study‐case buildings were subjected to a set of 30 narrow‐band earthquake ground motions recorded on stations placed in soft‐soil sites of Mexico City, where most significant structural damage was found in buildings as a consequence of the 1985 Michoacan earthquake, and scaled to reach several levels of intensity to perform incremental dynamic analyses. Thus, results were statistically processed to obtain hazard curves of peak (maximum) and residual drift demands for each frame model. It is shown that the study‐case frames might exhibit maximum residual inter‐story drift demands in excess of 0.5%, which is perceptible for building's occupants and could cause human discomfort, for a mean annual rate of exceedance associated to peak inter‐story drift demands of about 3%, which is the limiting drift to avoid collapse prescribed in the 2004 Mexico City Seismic Design Provisions. The influence of a member's post‐yield stiffness ratio and material overstrength in the evaluation of maximum residual inter‐story drift demands is also discussed. Finally, this study introduces response transformation factors, T_p, that allow establishing residual drift limits compatible with the same mean annual rate of exceedance of peak inter‐story drift limits for future seismic design/evaluation criteria that take into account both drift demands for assessing a building's seismic performance. Copyright © 2013 John Wiley & Sons, Ltd.     

Coping with water scarcity in Kashafroud G-WADI Basin,Iran: climate change or growing demands?

This paper assesses the various factors contributing to climate change in the region of the Kashafroud G-WADI Basin in Iran; quantifies the local impacts of climate change, especially local water scarcity; and simulates and discusses several proposed methods to combat these impacts. Hydrologic and climatic data are statistically analyzed and VENSIM modeling is used for various simulations of water resources in the basin. Results show that the natural climate changes affecting Kashafroud Basin include increased temperature, less rainfall, more frequent droughts, and changes in rainfall patterns, all of which are local symptoms of climate change in recent years. However, the most important challenge in the basin is the overexploitation of surface and groundwater resources to meet the growing water demands, especially domestic needs. Changes in land use, reallocation of water uses, groundwater depletion, and degradation of the quality of surface waters have all contributed to significant changes in the environmental features of this basin, and are the main reason why water demands now exceed the renewal capacity of the basin. Proposed response measures include reallocation of resources among different uses, inter-basin water transfers, drawing water from six small dams on the Kashafroud River, reducing groundwater extraction, and replacing groundwater extraction for agriculture by reuse of urban wastewater. This study concludes that although changes in global climatic parameters have altered environmental features in the basin, local factors, such as water utilization beyond the renewable capacity of the basin, are more significant in worsening the impacts of climate change.