P‐wave transmission across fractures with nonlinear deformational behaviour

Stress wave attenuation across fractured rock masses is a great concern of underground structure safety. When the wave amplitude is large, fractures experience nonlinear deformation during the wave propagation. This paper presents a study on normal transmission of P‐wave across parallel fractures with nonlinear deformational behaviour (static Barton–Bandis model). The results show that the magnitude of transmission coefficient is a function of incident wave amplitude, nondimensional fracture spacing and number of fractures. Two important indices of nondimensional fracture spacing are identified, and they divide the area of nondimensional fracture spacing into three parts (individual fracture area, transition area and small spacing area). In the different areas, the magnitude of transmission coefficient has different trends with nondimensional fracture spacing and number of fractures. In addition, the study reveals that under some circumstances, the magnitude of transmission coefficient increases with increasing number of fractures, and is larger than 1. Copyright © 2006 John Wiley & Sons, Ltd.     

交通流量分析与实时最优控制

通过将车流量的增大或减小转化为路长权重的变化。将交通流量的动态问题转化为静态问题，用解决最短路问题的Dijkstra方法，给出交通流量实时最优控制的可行性模型及其有效算法。     

BACKGROUND STUDY ON NON-RESIDUAL PHASE OF ELEMENTS IN CHANGJIANG AND HUANGHE ESTUARINE SEDIMENTS

Analysis of Zn, Cu, Pb, Co, Cr, Li, Ni, K, Al, Fe extracted by 1 mol/L HCl or 0.5 mol/LHCl/H_2O_2, showed concentrations of Zn, Cu, Pb, Co, Cr, Fe, Ni were significantly correlated with Li, Al,K, and clay. Two methods are used to indicate the background value of the non-residual phase of elementsin sediments, and are the same as the methods used to indicate the background value of totalconcentrations in sediments. The first method uses correlograms and regression equations,the second usesthe mean element concentrations normalized with grain size. Li, Al, K can be used as reference elements to determine the background value of Zn, Cu, Pb, Co,Cr, Ni, Fe, while the clay concentration's correlation with some extractable concentrations can be used tocalculate the background value of the non-residual phase of elements as a percentage of clay concentrationin the sediments. Based on this study, the concept of using the background value of the non-residualphase of elements to compare the pollution level in differ     

专项气象服务经济效益的评价理论与技术

当前，由于缺乏对气象服务投入量与产出量准确而完整的统计，要对气象服务的各种经济效益作出总体评价是困难的。然而，在专项气象服务中，却不乏原始、完整而准确的资料。作者从此出发，讨论了专项气象服务经济效益评价的理论。并通过实地调查，以彭州市气象局几项专项气象服务为例探讨了评价技术。     

△T球体异常的三元解释法

在△Ｔ异常解释课题中，一个新的角度参量─—视磁化特征角的拟定，最大限度地简化了球体磁场表达式。从而才有可能通过特殊解法，给出了球体磁场的极值与拐点公式。作者据此建立了四种不受正常场制约、仅需异常的局部持征曲线即可全面解释三度异常的解释方法。屏障分解、叠加判别、三元迭代的设计，为解释三度体叠加异常给出了简单而易行的途径。     

一类“强降水构造”的观测研究

木文根据1966～1986年20年的观测研究,提出大气中存在一类“强降水构造”,它直观地表现为云区的组合。这类“组合”具有互补性、多尺度性、准静止性和阶段性、利用这些属性,有可能从常规地面图上(站距100-300公里)分析和预报出尺度为10~2公里的大～暴雨区;在省的加密地面图上(站距40～70公里)有可能分析出尺度为10~1公里的局地强对流雨。     

试论国外河流地貌学的进展

本文分四个阶段论述国外河流地貌学研究的发展,阐述了现代河流地貌学在一些领域中取得的成就,以及研究方法和技术的进展。     

柴达木盆地北缘侏罗系不同沉积环境烃源岩生物标志物特征及其应用

柴达木盆地北缘地区侏罗系(中下侏罗统)的优质烃源岩主要发育于湖相与三角洲相环境。研究了不同时代、不同沉积环境中烃源岩的生物标志物组成特征,结果发现,有3类化合物的分布与组成差异显著,包括三环萜烷(C19、C20、C21)的分布型式、重排藿烷的丰度以及规则甾烷的相对组成。其中,不同时代的差异主要体现在规则甾烷组成上;而不同沉积环境的差异主要体现为三环萜烷(C19、C20、C21)的分布型式及重排藿烷的丰度。分析认为,这些差异与烃源岩的沉积环境及其生源组成有密切关系。据此,初步将这些参数应用于两方面研究,一是为划分地层沉积环境提供“生物标志物相标志”,二是研究油源对比,取得良好效果。因此,本文研究结果具有重要实用价值与参考意义。     

Soil n-alkane δD vs. altitude gradients along Mount Gongga, China

The altitude effect on the isotopic composition of precipitation and its application to paleoelevation reconstruction using authigenic or pedogenic minerals have been intensively studied. However, there are still no studies on variations in biomarker δD along altitude transects to investigate its potential as a paleoelevation indicator, although it has been observed that δD of higher plant lipid may record changes in precipitation δD (δD_p). Here, we present δD values of higher plant-derived C₂₇, C₂₉, and C₃₁n-alkanes from surface soil along the eastern slope of Mount Gongga, China with great changes in physical variables and vegetation over a range from 1000 to 4000 m above sea level. The weighted-mean δD values of these n-alkanes (δD_wax) show significant linear correlations with predicted δD_p values (R² = 0.76) with an apparent isotopic enrichment (ε_wax-p) of −137 ± 9‰, indicating that soil δD_wax values track overall δD_p variation along the entire altitudinal transect. Leaf δD_wax is also highly correlated with mountain altitude by a significant quadratic relationship (R² = 0.80). Evapotranspiration is found declining with altitude, potentially lowering δD_wax values at higher elevations. However, this evapotranspiration effect is believed to be largely compensated by the opposing effect of vegetation changes, resulting in less varied ε_wax-p values over the slope transect. This study therefore confirms the potential of using leaf δD_wax to infer paleoelevations, and more generally, to infer the δD of precipitation.     

The state of land subsidence and prediction approaches due to groundwater withdrawal in China

This article gives a general introduction to land subsidence with the prediction approaches due to withdrawal of groundwater in three subsided/subsiding regions in China: the deltaic plain of Yangtse River (YRDP), North China Plain (NCP), and Fenwei Plain (FP). On YRDP, Shanghai is the typical subsided/subsiding city; on NCP Tianjin is the typical subsided/subsiding city, and on FP Taiyuan is the typical subsided/subsiding city. The subsided area with subsidence over 200 mm on YRDP is about 10,000 km² and the maximum subsided value reached 2.9 m at Shanghai; on NCP the subsided area reached 60,000 km² with the maximum subsidence of 3.9 m at Tianjing; on FP the subsided area is relatively smaller than that on the other two plains and is about 1,135 km² with maximum subsidence of 3.7 m at Taiyuan city. In order to protect the civil and industrial facilities, it is necessary to predict the future development of land subsidence based on present state. Many researchers proposed several approaches to predict the land subsidence due to groundwater withdrawal according to different geological conditions and groundwater withdrawal practice. This article classifies these approaches into five categories: (i) statistical methods; (ii) 1D numerical method; (iii) quasi-3D seepage model; (iv) 3D seepage model; (v) fully coupled 3D model. In China, the former four categories are presently employed in the prediction practice and their merits and demerits are discussed. According to the prediction practice, 3D seepage model is the best method presently.