Population growth in Bejing: trends and countermeasures     

Zhaoliang Hu  Francis Yee  George Chusheng Lin 《中国地理科学(英文版)》1991,1(3):212-220

Beijing’ population has experienced a dramatic increase eversince the founding of the People’s Republic of China. Population growthin Beijing can be broadly broken down into three major components:natural increase, immigration, and the growth of floating population. Thecontinuous growth of Beijing’s population is closely linked with its centralized multi-function. The comprehensive countermeasures to control Beijing’s population growth are proposed, for example, decentralizing economicfunctions, including developing the suburbs, developing the metropolitan areaand creating counter-magnetic centers, reforming the administrative and economic systems.  相似文献   

High-order Taylor series expansion methods for error propagation in geographic information systems   总被引：2，自引：1，他引：1  

Jie Xue  Yee Leung  Jiang-Hong Ma 《Journal of Geographical Systems》2015,17(2):187-206

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The Completion of the C-Response Function For Utilization In Exact Inversion Procedures     

E. Yee  K. V. Paulson 《Geophysical Journal International》1989,97(1):41-50

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First-Order Inconsistencies Caused by Rogue Trajectories     

John V. Postma  Eugene Yee  John D. Wilson 《Boundary-Layer Meteorology》2012,144(3):431-439

A theoretical requirement of the Interaction by Exchange with the Conditional Mean (IECM) micromixing model is that the mean concentration field produced by it must be consistent with the mean concentration field produced by a traditional Lagrangian stochastic (LS) marked particle model. We examine the violation of this requirement that occurs in a coupled LS–IECM model when unrealistically high particle velocities occur. No successful strategy was found to mitigate the effects of these rogue trajectories. It is our hope that this work will provide renewed impetus for investigation into rogue trajectories and methods to eliminate them from LS models.  相似文献   

An integrated web-based air pollution decision support system – a prototype     

Yee Leung  Kwong-Sak Leung  Man-Hong Wong  Terrence Mak  Kwan-Yau Cheung  Leung-Yau Lo 《International journal of geographical information science》2018,32(9):1787-1814

To efficiently and effectively monitor and mitigate air pollution in the urban environment, it is of paramount importance to integrate into a unified whole air pollutant concentration databases coming from different sources including the ground-based stations, mobile sensors, remote sensing, atmospheric-chemical-transport models and social media for the analysis and unraveling of the complex air pollution processes in space and time. This study constructs and implements for the first time a prototype of the fully integrated air pollution decision support system (APDSS) that put together in an integrated manner all relevant multi-scale, multi-type and multi-source data for decision-making on urban air pollution. The prototype contains the main system that handles the multi-source, multi-type and multi-scale databases, queries, visualization and data mining algorithms and the integrated modules that individually and holistically capitalize on the power of the ground-based stations, ground and aerial mobile sensors, satellite-borne remote-sensing technologies, atmospheric-chemical-transport models and social media. It renders a solid scientific foundation and system development methodology for the study of the spatiotemporal air pollution profiles crucial to the mitigation of urban air pollution. Real-life applications of the prototype are employed to illustrate the functionality of the APDSS.  相似文献   

Numerical Study of Dual-Plume Interference in a Turbulent Boundary Layer     

Shahin N. Oskouie  Bing-Chen Wang  Eugene Yee 《Boundary-Layer Meteorology》2017,164(3):419-447

Direct numerical simulation is used to investigate the interference arising from the dispersion of passive scalar plumes released from a pair of point sources in a fully-developed wall-bounded shear flow. Four different lateral separations of the two sources for both near ground-level and elevated releases are considered. The downwind evolution of the correlation between the plume concentrations along the centreline between the two sources and the behaviour of the lateral profiles of the correlation at various locations downwind of the two sources are examined in detail. Differences in the exceedance probability over a high concentration level for a single plume and the total plume are highlighted and studied, and the effects of destructive and constructive interferences on the exceedance probabilities for the total plume are used to explain these differences. One significant result is that all higher-order (third-order and above) moments of the total concentration can be inferred from the application of a clipped-gamma distribution using the information embodied in only the first- and second-order concentration moments of each single plume, and in the cross-correlation coefficient of the instantaneous concentration of the two plumes.  相似文献   

Effect of rising atmospheric CO2 on sediment and water 15N interactions in experimental riparian wetland     

Swe Hlaing Htar  Wei Zhu  Jingyu Huang  Philip Nti Nkrumah 《Environmental Earth Sciences》2013,70(7):3185-3195

The experiment was conducted to ascertain net production and consumption rates of ¹⁵NH₄ ⁺ and ¹⁵NO₃ ^? for water and sediment in a wetland. This was done using ¹⁵N isotope pool dilution methodology under ambient and elevated atmospheric CO₂ concentrations in experimental riparian wetlands to obtain the gross N transformation rates. The ¹⁵N budget for sediment was also estimated. The results suggested that the differences in high proportion of ¹⁵N concentration in the overlying water body under elevated CO₂ could be attributed to the low production and high consumption rates of ¹⁵NH₄ ⁺ in sediment. The elevated CO₂ effect on production and consumption of NH₄ ⁺ decreased by 144 % (P = 0.014) and increased by 153 % (P = 0.009), respectively. Thereby, ¹⁵NH₄ ⁺ production rates are negatively related with ¹⁵NO₃ ^? consumption rates and this accounted for the decreases in net ¹⁵NO₃ ^? consumption under CO₂ enrichment in the wetland sediment by 11 % (P = 0.528). Therefore, ¹⁵NO₃ ^? production and consumption rates may strongly depend on NH₄ ⁺ production. Inorganic ¹⁵N and total ¹⁵N exported from sediment to overlying water body by the effect of CO₂ were 41 % (P = 0.071) and 18 % (P = 0.000), respectively. Therefore, low net ¹⁵NH₄ ⁺ production and high ¹⁵NH₄ ⁺ consumption rates under elevated CO₂ may partly explain the significant reduction of N from the sediment.  相似文献   

Seasonal changes in imposex and tissue burden of butyltin compounds in Thais clavigera populations along the coastal area of Mirs Bay, China     

Ka Ming Chan  Kenneth Mei Yee Leung  Kwai Chung Cheung  Ming Hung Wong  Jian-Wen Qiu   《Marine pollution bulletin》2008,57(6-12):645

We assessed the current status of tributyltin (TBT) contamination of Thais clavigera (Gastropoda) along the coastal area of Mirs Bay, China for the first time. The snail samples were collected from 10 different sites in the summer (June) and winter (December) of 2006, respectively. They were analyzed for imposex status, i.e. relative penis size index (RPSI) and vas deferens sequence index (VDSI), followed by quantification of butyltins in their tissues. Most of the collected females suffered from imposex, but the level of butyltin contamination varied with the distance from Yantian Port, which is currently the fourth busiest container port in the world. The tissue concentration of TBT varied with season. For a particular site, the winter samples in general contained much higher concentration of TBT than the summer samples. RPSI, VDSI and organotin concentrations were higher in T. clavigera collected from sites closer to the Port, such as the Seafood Street and Kat O. Both RPSI and VDSI were positively correlated with the tissue burden of tributyltin. VDSI exhibited little seasonal variability, whereas RPSI showed marked seasonal variability, with lower values in the summer samples. The current results will serve as an important reference for long-term monitoring of butyltin contamination in this area.  相似文献   

The effects of intermediate principle stress on the mechanical behavior of transversely isotropic rocks: Insights from DEM simulations     

Saad Ali Faizi  Chung Yee Kwok  Kang Duan 《国际地质力学数值与分析法杂志》2020,44(9):1262-1280

The discrete element method (DEM) is used to study the response of anisotropic rocks under true triaxial testing. Numerical samples of seven different bedding orientations (β = 0^o, 15^o, 30^o, 45^o, 60^o, 75^o, and 90^o) are created. Six series of test simulations (σ₃ = 0, 10, 30, 50, 70, and 100 MPa) are conducted on each sample, with five different σ₂ values, varied from σ₃ to σ₁. The effects of anisotropy and intermediate stress on the peak strength, brittle-ductile transition, and degree of anisotropy are subsequently explained through underlying micromechanics. Results show a “fan-shaped” variation of the peak strength with σ₂, displaying an ascending-then-descending trend. An increasing brittleness with σ₂ is observed at lower confining pressures for all, but medium anisotropy angles. For higher confining pressures, increasing ductility with σ₂ is seen for every anisotropy angle. A U-shaped variation of peak strength with anisotropy angles is noted that flattens under high intermediate stress. Hence, for numerical models of Posidonia shale under normalized σ₂ higher than 0.76, the anisotropy effect is found to be negligible. Micromechanical analyses reveal that the stress asymmetry, suppression of weak plane action as well as the localization and coalescence of microcracks in the intact rock matrix, due to σ₂, are the contributors towards the obtained trends. Since existing failure criteria do not weigh in these features in geotechnical assessments, this paper helps future studies by providing a deeper understanding of these effects and a comprehensive data set for the analyses of anisotropic rocks under polyaxial stress conditions.  相似文献   

EFFECT OF DUNE MIGRATION ON SCOUR AT BRIDGE PIERS     

Yee Meng CHIEW 《国际泥沙研究》1992,(1)

This paper examines the effect of dune migration on local scour around bridge piers. Experiments show that local scour depths fluctuate in response to the translation of dunes past the scour hole. The scour depths measured in a model study conducted in live-bed conditions contain both scour due to the pier and that due to dunes. The con' tribution from scour due to the dunes may form a significant fraction of the total scour depth measured in model investigations. Therefore, it is imperative to separate these two components of scour for analysis and comparison. The study proposes that an equilibrium or time-average scour depth normalized using pier diameter be used for analysis, and the contribution from dunes to the total scour depth be added independently. Dune size, in the absence of field or measured data, may be estimated using published predictive curves. Comparisons between computed and measured scour depths show a good correlation, and 90% of all the data tested fall within a scatter of 15%.  相似文献