覆盖和耕作对黄土高原冬小麦土壤入渗特性的影响   总被引：3，自引：0，他引：3  

牛伊宁  沈禹颖  高崇岳  K.Y.Chan  南志标 《山地学报》2006,24(1):13-18

用人工模拟降雨器对黄土高原冬小麦收获后6个耕作措施:不翻耕(NT),不翻耕 覆盖(NTC),浅翻耕(LT),浅翻耕 覆盖(LTC),深翻耕(DT),深翻耕 覆盖(DTC)处理下土壤的入渗进行了研究,测定了土壤表面结皮、粗糙度等指标因子。结果表明,在模拟降雨强度为66 mm/h的条件下,覆盖处理的稳定入渗率>60 mm/h,降雨开始的40 m in内,平均入渗量>93%;深翻耕(DT)的稳定入渗率(26.4 mm/h)是浅翻耕(LT)(13.0 mm/h)的2倍,是不翻耕(NT)(6.4 mm/h)的4.1倍,降雨历时20m in时,深翻耕(DT)和浅翻耕(LT)分别比不翻耕处理(NT)减少径流28%和7%,40 m in时,浅翻耕(LT)和不翻耕(NT)处理径流量相当,深翻耕(DT)比这两个处理减少径流30%左右,土壤翻耕后在前期能提高土壤的入渗率,表现出经长年耕作后土壤退化的强烈特征,是“耕地越深,入渗越快”观念的根源;地表结皮是影响降雨入渗的主要因素,覆盖等保护性耕作更有利于土壤入渗。  相似文献   

Environmental impact and geochemistry of old tailing pile from the Sanggok mine creek, Republic of Korea     

Chan Hee Lee  Hyun Koo Lee 《Environmental Geology》2004,46(6-7):727-740

This study evaluates the pollution load on a creek based on the physicochemical and mineralogical properties of old tailings. The Sanggok mine is one of the largest lead–zinc producers in the Hwanggangri mining district, Republic of Korea. The vertical profile of the old tailings in the mine area can be divided into three units based on color change, and mineralogical and textural variations, as well as physical and chemical properties. Unit I (surface accumulation and oxidized heterogeneous tailing soil) has lower pH and higher Eh than unit II (originally unoxidized dumped tailing soil) and unit III (pebble-bearing bottom soil). The conductivity data indicates that unit I and II have very high values compared to unit III and basement. The mine area consists mainly of carbonate rocks; however, mineral constituents of tailing soil and sediments near the mine were mainly composed of quartz, mica, feldspar, amphibole, calcite, dolomite, magnesite, and clay minerals. Units I and II are characterized by high abundances of siderite, locally pyrite, and dolomite. Precipitates in the mining drainage mainly included: smectite, illite, berthierine, quartz, siderite, hexahydrite, and Ca-ferrate. Among the separated metallic minerals, tailing soils and sediments of highly concentrated toxic metals are found: some pyrite, arsenopyrite, chalcopyrite, sphalerite, galena, malachite, goethite, various hydroxide, and uncertain secondary minerals. Units I and II are characterized by relatively high concentrations of Ca, Fe, Mn and low contents of Al, Mg, K, Na, Ti, rare earth elements (REEs) that correlated with the proportion of secondary minerals. Potentially toxic elements such as Ag, As, Cd, Cu, Pb, Sb, and Zn are highly enriched in the upper two units. This metal concentration can be influenced by changes in the depth because of oxic and suboxic zonal distribution. The removal zone (unit I) has probably migrated below the elevation of the maximum enrichment layer due to deepening of the oxic/suboxic boundary. In most of the materials, the enrichment index is higher than 3.62. The highest value of 42.55 is found in the oxidation surface soils of the tailing pile. An average enrichment index of the profiles and precipitates are 27.62 and 22.62, respectively. Rocky basement soils have an average enrichment index of 6.63, which is influenced by overlying the tailing pile. The water quality and habitat of the Sanggok creek are severely polluted. Polluted surface water may also negatively impact the agricultural soil and groundwater.  相似文献   

Characteristics of the asymmetric circulation associated with tropical cyclone motion     

J. C. L. Chan  K. K. W. Cheung 《Meteorology and Atmospheric Physics》1998,65(3-4):183-196

Summary This paper examines the characteristics of the asymmetric flow associated with tropical cyclone (TC) motion using the Final Analysis dataset produced after the Tropical Cyclone Motion Experiment (TCM-90). The wind data vertically-integrated between 850 and 300 hPa around a TC are first separated into an environment flow and a vortex circulation using the filtering algorithm of Kurihara et al. (1995). The latter is then Fourier-decomposed azimuthally to obtain the symmetric and asymmetric components. Nine TCs that occurred during the TCM-90 Experiment are examined.For generally westward-moving TCs, the wavenumber-1 (WN-1) component is found to dominate the asymmetric flow. However, its pattern does not always exhibit a pair of counterrotating gyres as would be expected from previous modelling results (Fiorino and Elsberry, 1989). Further, the ventilation flow associated with WN-1 does not necessarily point towards the northwest. For a TC undergoing recurvature, the WN-2 flow becomes significant, and even has a larger magnitude than the WN-1 component, starting from about one day before recurvature. Consistent with the modelling results of Williams and Chan (1994), the WN-2 component also rotates counter-clockwise with time.The growth and decay of the asymmetric components result from the interaction between the environmental flow and the symmetric flow of the TC through an energy exchange, in addition to such exchanges between the asymmetric components. Energy generally flows from the environment and the symmetric circulation of the TC to the WN-1 component during intensification but vice versa when the TC is weakening. The growth of the WN-2 component in recurving TCs is due to a transfer of energy from the environment, the symmetric circulation and the WN-1 flow. It is for this reason that the WN-1 flow becomes weaker than the WN-2 flow in such cases. The WN-1 component of fast-moving TCs is found to extract energy from the WN-2 component, in addition to those from the environment and the symmetric flow.With 15 Figures  相似文献   

Elastic and inelastic drift performance optimization for reinforced concrete buildings under earthquake loads     

Chun‐Man Chan  Xiao‐Kang Zou 《地震工程与结构动力学》2004,33(8):929-950

This paper presents an effective optimization technique for the elastic and inelastic drift performance design of reinforced concrete buildings under response spectrum loading and pushover loading. Attempts have been made to develop an automatic optimal elastic and inelastic drift design of concrete framework structures. The entire optimization procedure can be divided into elastic design optimization and inelastic design optimization. Using the principle of virtual work, the elastic drift response generated by the response spectrum loading and the inelastic drift response produced by the non‐linear pushover loading can be explicitly expressed in terms of element sizing design variables. The optimization methodology for the solution of the explicit design problem of buildings is fundamentally based on the Optimality Criteria approach. One ten‐story, two‐bay building frame example is presented to illustrate the effectiveness and practicality of the proposed optimal design method. While rapid convergence in a few design cycles is found in the elastic optimization process, relatively slow but steady and smooth convergence of the optimal performance‐based design is found in the inelastic optimization process. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

一例由蓄水诱发的库岸边坡变形   总被引：7，自引：0，他引：7  

邓建辉  D.H.Chan  C.D.Martin  N.R.Morgenstern 《中国地质灾害与防治学报》2002,13(1):21-24

加拿大Oldman坝的库岸边坡主要由近水平、互层的砂岩及泥岩构造，自1993年开始蓄水以来库岸边坡一直处于变形之中。文章在简介区域地质条件、工程地质条件和水库蓄水诱发变形的基础上，对变形诱发机制进行了讨论。基于监测资料分析：（1）由于水库库边坡的卸荷裂隙十分发育， 提供了快速的水力通道， 蓄水期水对库岸边坡稳定存在不利影响；（2）该例的泥岩不存在膨胀性；（3）库岸边坡变形是由于水的快速渗透导致有效应力降低和泥岩软化，库岸边坡应力重新调整引起的；（4）对于软岩边坡，特别是库岸软岩边坡变形稳定分析比强度稳定分析更重要。  相似文献   

The relationship between administrative hierarchy position and city size development in China   总被引：1，自引：0，他引：1  

Roger C.K. Chan  X.B. Zhao 《GeoJournal》2002,56(2):97-112

China's urbanization process in the past 20 years has drawn much academic attention, and as a result, many attempts to explain the uniqueness of China's urbanization have emerged. Some argued that Tolley's model (1987), the well known theory explaining global urbanization, or the `Murray-Szelenyi' thesis (1984), which focus on the investigation of urbanization in socialist countries, can be applied in China. Most western literature, however, claimed either a `rural-bias' or an `urban-bias' from the state took place in China's urbanization process. This paper suggests another perspective in the analysis of this process, as it argues that it was the state bias for the allocation of production and human resources in the cities of higher hierarchical ranking that is behind China's urbanization. The objective of the paper is to test it through two hypotheses. The first hypothesis suggests that the higher the city is in the urban hierarchy, the more population it has; and the second argues the higher administrative position a city has, the better social and economic performance it will show. Using statistical data to validate these two hypotheses, this paper attempts to justify the role of `state-bias' of resources allocation and the dominance of the administrative hierarchy in China's urbanization process. Lastly, the paper argues, the state itself is a major factor or source for China's urbanization development.  相似文献   

Similarity functions D for water vapor in the unstable atmospheric boundary layer     

Wilfried Brutsaert  Frederick K. -F. Chan 《Boundary-Layer Meteorology》1978,14(4):441-456

An analysis was performed of experimental data obtained at fixed ship stations during AMTEX 1974 and 1975. This allowed the calculation of the bulk transfer relationships for water vapor and sensible heat in the atmospheric boundary layer for different interpretations of the thickness scale of the boundary layer. It was found that scaling based on the observed thickness, which herein was taken as the height of the lowest value in the potential temperature profile under unstable conditions, produces least scatter in the calculations. The results obtained for the similarity function c( _i ) of the bulk heat transfer coefficient are in good agreement with the results of previous studies. As observed earlier (Brutsaert and Mawdsley, 1976; Mawdsley and Brutsaert, 1977), under unstable conditions the similarity functions D() of the bulk water vapor transfer coefficient are smaller than the corresponding C() functions for sensible heat. In the case of inversion height scaling, the results can be represented by d( _i ) = 0.65 c( _i ).  相似文献   

Tutorial on the numerical modeling of edge diffracted waves by the ray method     

F. Hron  G. H. Chan 《Studia Geophysica et Geodaetica》1995,39(2):103-137

Summary The concept of diffracted rays introduced by Keller (1962) opened the way for a ray approach in the numerical modeling of the diffraction phenomena frequently seen in the seismic field records. Unlike the computation of travel times, which has never caused any difficulties being governed by the same eikonal equation as are the rays of ordinary seismic body waves, the evaluation of the diffracted ray amplitude has been another story. In this paper we give a tutorial account of a highly promising technique for the computation of the ray amplitude of seismic waves diffracted by linear edges on seismic interfaces originally presented by Klem-Musatov (1980, 1995). We demonstrate the adequacy of this technique on a series of SH synthetic traces containing diffracted arrivals, some of them diffracted more than once. Our computer program is based on a successful combination of Klem-Musatov's approach with the zero order approximation of the Asymptotic Ray Theory (Červeny and Hron, 1980). We showed in the paper that both techniqúes are ideally suited for such a combination, since the ray amplitude evaluation in each of them is based on the same transport equation. In our tutorial review we present all formulae which are needed for a practical implementation of the method and provide their physical interpretation, wherver possible, by using the numerical examples presented in the paper.  相似文献   

Multidisciplinary assessment of pollution at three sites in Long Island Sound     

William D. Gronlund  Sin-Lam Chan  Bruce B. McCain  Robert C. Clark  Mark S. Myers  John E. Stein  Donald W. Brown  John T. Landahl  Margaret M. Krahn  Usha Varanasi 《Estuaries and Coasts》1991,14(3):299-305

Winter flounder (Pseudopleuronectes americanus) were sampled from three sites located near Norwalk, New Haven, and Niantic, Connecticut, in Long Island Sound during February 1987, to evaluate the degree of chemical contamination and to determine possible effects of contaminant exposure. At each site, sediment and infaunal invertebrates were also collected and analyzed for trace metals and organic chemicals. Specimens of liver and kidney from winter flounder were examined for histopathological conditions, including the presence of macrophage aggregates in liver tissue. Liver samples were also analyzed for DNA damage (i.e., the formation of adducts between DNA and chemical contaminants). Blood samples were collected and analyzed for erythrocyte micronuclei. The sampling site near New Haven was determined to be the most affected site, from the standpoints of greater chemical contamination and possible effects on winter flounder. Concentrations of aromatic hydrocarbons (AHs) and polychlorinated biphenyls (PCBs) were highest in sediment from this site, and the highest prevalences of the histopathological changes and DNA alterations were also found in the livers of winter flounder from this site. No differences in the concentrations of contaminants in fish or in frequencies of erythrocyte micronuclei in fish blood were found between sites. None of the sites sampled had contaminant levels or prevalences of lesions as high as previously found at other East Coast locations (e.g., Boston Harbor, Massachusetts, Raritan Bay, New York). Overall, our results indicate moderate levels of pollution at two of the urban sites in Long Island Sound and provide a framework for expanded studies to better define the extent and impact of chemical pollution in Long Island Sound.  相似文献   

青藏高原地表热状况对夏季东亚大气环流影响的数值模拟   总被引：9，自引：1，他引：9  

刘晓东  罗四维  钱永甫 《高原气象》1989,(3)

本文利用有限区域有地形的5层原始方程模式,对青藏高原地区地表热状况在夏季东亚大气环流中的作用进行了一些数值试验和分析。结果表明:高原地面反照率、拖曳系数、蒸发系数以及土壤温度等的变化对大气加热增强时可造成高原上空及孟加拉湾一带的大气热源显著增强;对流层上层的青藏高压增强范围变大,并向西北方向偏移;热带东风急流加强北移;对流层低层西南季风加大;索马里、印度南侧和澳大利亚北侧的越赤道气流也增强;海平面上的大陆低压加深。同时,中南半岛地区及江淮流域的上升运动增强,降水增大,而我国东南沿海一带上升运动减弱,降水减少。  相似文献