Change of groundwater chemistry from 1896 to present in the Mid-Levels area, Hong Kong   总被引：1，自引：0，他引：1  

Chi-man Leung  Jiu Jimmy Jiao 《Environmental Geology》2006,49(7):946-959

In this study, groundwater quality information collected in 1896 (well waters), 1980/1981 (piezometric and seepage samples) and 2002/2003 (seepage samples) in the regions centered by the Mid-Levels area, Hong Kong Island, was compared to illustrate how groundwater quality has changed over a century and the processes controlling it. As shown by saline ammonia and nitrate levels in the late nineteenth century, groundwater was severely polluted by widespread and obvious leakage from poorly designed wastewater collection systems, although groundwater was still a drinking water source for local residents. The extremely high residual chlorines in groundwater demonstrated that large doses of disinfection agents were added to wells at that time. In view of the decline in saline ammonia and nitrate levels, groundwater became less organically polluted in the 1980s probably due to significant improvement of the design of underground sewers. However, more leakage from sources such as salty flushing water and fresh water pipes emerged in the past few decades which added complexity to groundwater chemical systems. Some chemicals were used to identify possible locations of leakages. The temporal variations of the distribution of these chemicals over the area may shed light on the rate of leakage. Leakage from service pipes seems to have improved from the early 1980s to 2002/2003. However, the area is still suffering from widespread and small-scale leakage from service pipes. More efforts should be paid to control small leakages in the future. The findings will be instructive to various government organizations such as the Water Supplies Department and Drainage Services Department to identify possible locations of unobvious leakages in the area.  相似文献   

遥感影像配准误差传递模型及模拟分析   总被引：3，自引：0，他引：3  

葛咏  梁怡  马江洪  王劲峰 《遥感学报》2006,10(3):299-305

在遥感影像配准过程中,通常假设控制点是“完美的”。然而,在实际情况中,由于控制点本身不可避免的带有一定的误差导致这种假设在一定情况下并不成立,并且将会影响遥感影像几何校正的精度。普通最小二乘方法OLS(O rd inary Least Square)是遥感影像配准常用的校正估计模型,令人遗憾的是,在控制点存在误差的情况下,它的估计是有偏的,并且不能够正确传递和估计校正影像的误差大小。引入一致校正最小二乘方法CALS(ConsistentAd justed Least Squares),在此基础上提出的一个改进的方法,称之为松弛一致校正最小二乘方法RCALS(Relaxed ConsistentAd justed Least Squares)。这类回归模型具有改正控制点(解释变量)中的误差和跟踪回归模型中的误差传递的能力。为了验证CALS和RCALS模型的有效性,本文利用模拟影像进行分析。这里着重分析OLS,CALS和RCALS模型在几何校正过程中的比较。结果表明,RCALS和CALS的结果优于OLS估计结果。  相似文献   

Weather and traffic accidents in Hong Kong     

Yuk Yee Yan Department of Geography Hong Kong Baptist University Kowloon Tong  Hong Kong 《地理学报(英文版)》1998,(3)

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Simple model for transient soil loading in earthquake analysis. II. Non-associative models for sands     

M. Pastor  O. C. Zienkiewicz  K. H. Leung 《国际地质力学数值与分析法杂志》1985,9(5):477-498

This paper extends the bounding surface, generalized plasticity, model of Part I to reproduce the behaviour of sands under both static and transient loading. The essential features of the first model are preserved but the following changes are introduced:

• (i) The shape of the yield surface is modified.
• (ii) A non-associative flow rule is introduced.
• (iii) The hardening parameter of the bounding surface includes not only volumetric but also deviatoric plastic strain.
• (iv) Plastic volumetric and deviatoric strains are introduced during unloading.

Each of these modifications can be introduced separately in a hierarchical manner to model in an improved way the behaviour of sands. Good comparison with experimental observations is recorded. The simplicity of the original model is preserved with modifications being introduced progressively to model rising complexity of the phenomena.  相似文献   

Spreadsheets for the Analysis of Aquifer-Test and Slug-Test Data     

Jiu Jimmy Jiao  Chi-man Leung 《Ground water》2003,41(1):9-10

  相似文献   

Structural vibration control by shape memory alloy damper     

Yu‐Lin Han  Q. S. Li  Ai‐Qun Li  A. Y. T. Leung  Ping‐Hua Lin 《地震工程与结构动力学》2003,32(3):483-494

A damper device based on shape memory alloy (SMA) wires is developed for structural control implementation. The design procedures of the SMA damper are presented. As a case study, eight such SMA dampers are installed in a frame structure to verify the effectiveness of the damper devices. Experimental results show that vibration decay of the SMA damper controlled frame is much faster than that of the uncontrolled frame. The finite‐element method is adopted to conduct the free and forced vibration analysis of the controlled and uncontrolled frame. The experimental and numerical results illustrate that the developed SMA dampers are very effective in reducing structural response and have great potential for use as efficient energy dissipation devices with the advantages of good control of force and no lifetime limits, etc. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

X-ray absorption fine structure determination of pH-dependent U-bacterial cell wall interactions     

S.D KellyK.M Kemner  J.B FeinD.A Fowle  M.I Boyanov  B.A BunkerN Yee 《Geochimica et cosmochimica acta》2002,66(22):3855-3871

X-ray absorption fine structure (XAFS) measurements was used at the U L3-edge to directly determine the pH dependence of the cell wall functional groups responsible for the absorption of aqueous UO₂²⁺ to Bacillus subtilis from pH 1.67 to 4.80. Surface complexation modeling can be used to predict metal distributions in water-rock systems, and it has been used to quantify bacterial adsorption of metal cations. However, successful application of these models requires a detailed knowledge not only of the type of bacterial surface site involved in metal adsorption/desorption, but also of the binding geometry. Previous acid-base titrations of B. subtilis cells suggested that three surface functional group types are important on the cell wall; these groups have been postulated to correspond to carboxyl, phosphoryl, and hydroxyl sites. When the U(VI) adsorption to B. subtilis is measured, observed is a significant pH-independent absorption at low pH values (<3.0), ascribed to an interaction between the uranyl cation and a neutrally charged phosphoryl group on the cell wall. The present study provides independent quantitative constraints on the types of sites involved in uranyl binding to B. subtilis from pH 1.67 to 4.80. The XAFS results indicate that at extremely low pH (pH 1.67) UO₂²⁺ binds exclusively to phosphoryl functional groups on the cell wall, with an average distance between the U atom and the P atom of 3.64 ± 0.01 Å. This U-P distance indicates an inner-sphere complex with an oxygen atom shared between the UO₂²⁺ and the phosphoryl ligand. The P signal at extremely low pH value is consistent with the UO₂²⁺ binding to a protonated phosphoryl group, as previously ascribed. With increasing pH (3.22 and 4.80), UO₂²⁺ binds increasingly to bacterial surface carboxyl functional groups, with an average distance between the U atom and the C atom of 2.89 ± 0.02 Å. This U-C distance indicates an inner-sphere complex with two oxygen atoms shared between the UO₂²⁺ and the carboxyl ligand. The results of this XAFS study confirm the uranyl-bacterial surface speciation model.  相似文献   

Effects of heavy metals on the survival and feeding behaviour of the sandy shore scavenging gastropod Nassarius festivus (Powys)     

S. G. Cheung  K. K. Tai  C. K. Leung  Y. M. Siu 《Marine pollution bulletin》2002,45(1-12)

The effects of Cu, Cd, Zn and Cr on the survival and feeding behaviour of the sandy shore scavenging gastropod Nassarius festivus were compared. The 96-h LC₅₀ for Cu, Cd, Zn and Cr were 0.36, 1.52, 1.76 and 36.9 mg l⁻¹, respectively. Four sublethal concentrations of each metal plus a control were prepared and the snails were exposed to experimental solutions for 96 h. Feeding behaviour was studied after the snails were starved for five days. As compared with the control, the number of individuals feeding was significantly reduced by exposure to 0.05 mg l⁻¹ Cu, 0.2 mg l⁻¹ Zn, 0.5 mg l⁻¹ Cd and 5 mg l⁻¹ Cr. The time spent feeding was greater for individuals exposed to greater concentrations of Zn and Cd but no effect was found for Cu and Cr. Chemoreception of food was studied by placing the snails at a fixed distance of 15 cm from the bait. The success rate of reaching the bait was less for individuals exposed to Cr but no effect was found for Zn, Cu or Cd. The time required for an individual to reach the bait decreased as the concentration of Zn increased. In contrast, a longer time was required for individuals exposed to Cr whereas the effect of Cd and Cu was insignificant. The potential of using feeding behaviour and chemoreception in contaminant evaluations is discussed.  相似文献   

Elevation Dependence of Winter Wheat Production in Eastern Washington State with Climate Change: A Methodological Study     

Allison M. Thomson  Robert A. Brown  Steven J. Ghan  R. Cesar Izaurralde  Norman J. Rosenberg  L. Ruby Leung 《Climatic change》2002,54(1-2):141-164

Crop growth models, used in climate change impact assessments to project production on a local scale, can obtain the daily weather information to drive them from models of the Earth's climate. General Circulation Models (GCMs), often used for this purpose, provide weather information for the entire globe but often cannot depict details of regional climates especially where complex topography plays an important role in weather patterns. The U.S. Pacific Northwest is an important wheat growing region where climate patterns are difficult to resolve with a coarse scale GCM. Here, we use the PNNL Regional Climate Model (RCM) which uses a sub-grid parameterization to resolve the complex topography and simulate meteorology to drive the Erosion Productivity Impact Calculator (EPIC) crop model. The climate scenarios were extracted from the PNNL-RCM baseline and 2 × CO₂ simulationsfor each of sixteen 90 km² grid cells of the RCM, with differentiation byelevation and without correction for climate biases. The dominant agricultural soil type and farm management practices were established for each grid cell. Using these climate and management data in EPIC, we simulated winter wheat production in eastern Washington for current climate conditions (baseline) and a 2 × CO₂ `greenhouse' scenario of climate change.Dryland wheat yields for the baseline climate averaged 4.52 Mg ha^–1 across the study region. Yields were zero at high elevations where temperatures were too low to allow the crops to mature. The highest yields (7.32 Mgha^–1) occurred at intermediate elevations with sufficientprecipitation and mild temperatures. Mean yield of dryland winter wheat increased to 5.45 Mg ha^–1 for the 2 × CO₂ climate, which wasmarkedly warmer and wetter. Simulated yields of irrigated wheat were generally higher than dryland yields and followed the same pattern but were, of course, less sensitive to increases in precipitation. Increases in dryland and irrigated wheat yields were due, principally, to decreases in the frequency of temperature and water stress. This study shows that the elevation of a farm is a more important determinant of yield than farm location in eastern Washington and that climate changes would affect wheat yields at all farms in the study.  相似文献   

An Improved Workflow for Permeability Estimation from Image Logs with Uncertainty Quantification     

Rezvandehy  Mehdi  Leung  Juliana Y.  Ren  Weishan  Hollands  Ben  Pan  Guoai 《Natural Resources Research》2019,28(3):777-811

Natural Resources Research - Production forecasts are extremely sensitive to the spatial distribution of certain reservoir parameters, especially permeability, which controls fluid flow and...  相似文献