Application of Refined Land-Use Categories for High Resolution Mesoscale Atmospheric Modelling     

J. S. L. Lam  A. K. H. Lau  J. C. H. Fung 《Boundary-Layer Meteorology》2006,119(2):263-288

A comparison of two separate MM5 land-use datasets (i.e., ‘US Geological Survey (USGS)’ and ‘Pollutants in the Atmosphere and their Transport over Hong Kong (PATH)’, each with different parameter values and different spatial distributions) was performed to understand the importance of land-surface processes and land-atmosphere interactions in the evolution of mesoscale weather phenomena during a high pollution episode in Hong Kong from 28 December 1999 through 1 January 2000. Also, a series of high resolution mesoscale numerical experiments was performed to investigate the possible roles of various surface characteristics or land-use parameters in this high pollution episode. Specifically, the relative importance of six land-use parameters including the roughness length, thermal inertia, soil moisture availability, albedo, surface heat capacity and surface emissivity are studied. Results from this study suggest that the soil moisture availability is the most important controlling parameter on the flow pattern and on surface fluxes. Sensitivity tests also show that the general flow pattern is insensitive to the other five land-use parameters  相似文献   

Simple models for estimating period‐shift and damping in soil     

Hing‐Ho Tsang  Adrian M. Chandler  Nelson T. K. Lam 《地震工程与结构动力学》2006,35(15):1925-1947

This study describes the development of a simple, heuristic manual calculation procedure for estimating the site period‐shift factor and soil damping ratio, with appropriate considerations for the level of shaking, impedance contrast between soil and bedrock interface and the plasticity of the soil layers. Essentially, the analogy of a building shear‐frame has been used to represent the seismic response behaviour of a soil column. The proposed procedure has been verified by comparing the predictions with results obtained directly from non‐linear shear wave analyses of soil column models. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Field validation of antioxidant enzyme biomarkers in mussels (Perna viridis) and clams (Ruditapes philippinarum) transplanted in Hong Kong coastal waters   总被引：1，自引：1，他引：1  

Sharon B. De Luca-Abbott  Bruce J. Richardson  Katherine E. McClellan  Gene J. Zheng  Michael Martin  Paul K.S. Lam 《Marine pollution bulletin》2005,51(8-12):694

Green-lipped mussels, Perna viridis, and Manila clams, Ruditapes philippinarum were sourced from “clean” sites in the Hong Kong region, depurated in a laboratory using uncontaminated filtered seawater for 8 days, and transplanted to a suspected gradient of chemically polluted sites in Hong Kong. After 14- and 28-days of field exposure, several antioxidant parameters including glutathione S transferase (GST), catalase (CAT), glutathione peroxidase (GPx), and glutathione (GSH) were quantified in gill and hepatopancreas tissues. Whole body tissue concentrations of polycyclic aromatic hydrocarbons (PAHs), petroleum hydrocarbons (PHCs), polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCs) were determined in pooled site samples. Chemical analyses indicated that: (a) clams had higher levels of PAHs, PHCs, DDTs and PCBs, whereas mussels had higher hexachlorocyclohexane (HCHs) and there was no difference between species for dieldrin and remaining OCs; (b) Kat O should not be continued as a “clean” reference site for Hong Kong, because of the levels of contaminants measured and (c) PAH concentrations in the current survey were similar to those previously measured. Toxicological conclusions were: (a) antioxidant responses were different between species; (b) CAT and GST have highest utility in clams for field use in Hong Kong, whereas CAT in both gill and hepatopancreas tissue showed most potential in mussels; (c) significant induction of antioxidant responses over day 0 (excluding GPx in both tissues, and GST in mussel hepatic tissue); (d) groups of contaminants do not consistently induce antioxidant responses and (e) organochlorines and PCBs correlated significantly with CAT and GST in clam hepatopancreas and with CAT in mussel gill and hepatic tissue. Multivariate statistical techniques indicated little relationship between the site patterns for antioxidant responses and the contaminant gradients identified in body burden analysis.  相似文献   

Okadaic acid, a causative toxin of diarrhetic shellfish poisoning, in green-lipped mussels Perna viridis from Hong Kong fish culture zones: Method development and monitoring     

Kylie C.Y. Mak  H. Yu  M.C. Choi  Xiaoyun Shen  Michael H.W. Lam  M. Martin  Rudolf S.S. Wu  Patsy S. Wong  Bruce J. Richardson  Paul K.S. Lam   《Marine pollution bulletin》2005,51(8-12):1010

Green-lipped mussels (Perna viridis) were collected from seven fish culture zones (FCZs) in Hong Kong and analyzed for okadaic acid (OA). A conventional HPLC method was modified by incorporating a proteinase K digestion step. Results suggest that a higher recovery (2.5 times higher) of OA was obtained from spiked samples after the addition of 1.08 mg proteinase K in comparison with samples incubated without the proteolytic enzyme. For the hepatopancreas (HP) of individual field-collected mussels, the additional digestion step can enhance OA extraction by 3.1 times. Spatial and temporal variations in OA concentrations in the mussels from various FCZs were investigated. The highest concentration of OA in mussel HP samples was 1164.9 ng/g HP wet wt. With respect to OA concentrations in whole mussel tissues from seven sites and four seasonal samplings, the concentrations were between 70.0 and 131.0 ng/g wet wt., which did not exceed the generally recognized international regulatory criteria (>200 ng/g) for OA.  相似文献   

Longitudinal characteristics of Pc5 magnetic pulsations     

Lam Hing-Lan 《Planetary and Space Science》1980,28(11):1035-1050

Data from an East-West line of magnetometer stations stretching approximately along 67° geomagnetic latitude from western Alberta (290° geomagnetic longitude) to western Quebec (350° geomagnetic longitude) in Canada have been used to study the longitudinal characteristics of Pc5 geomagnetic pulsations. This paper concerns the analysis of 3 days' data of relatively intense pulsational activity which occurred around the middle of October in 1976. The intensity variations of Pc5 activity on longitude and time clearly show that the activity is localized in longitude in the morning sector and confused in the afternoon sector. Pulsational activity in the morning sector for two of the events studied appears to be markedly enhanced across the dawn terminator and midway through the pre-noon quadrant. A study of the longitudinal phase variation indicates that the eastern stations lead in phase before noon and lag in phase after noon. This implies that the signals propagate away from noon toward the dawn-dusk meridian. A systematic reversal in the sense of polarization in the horizontal plane was observed when the line of stations rotated across noon. The polarization characteristics in the vertical planes of the events recorded by stations in eastern Canada between 318° and 350° geomagnetic longitude appear to be stationary with respect to time suggesting that the polarization characteristics of pulsations are influenced by geoelectric structures. The implications of these morphological features will be discussed.  相似文献   

Mathematical modeling of PCB bioaccumulation in Perna viridis     

Yu KN  Lam PK  Cheung CC  Yip CW 《Marine pollution bulletin》2002,45(1-12):332-338

In the present work, we built a mathematical model of polychlorinated biphenyl (PCB) bioaccumulation in Perna viridis, namely, a one-compartment model with a time dependent incorporation rate R (μg g⁻¹ lipid per ppb water per day), with positive substrate cooperativity as the underlying physical mechanism. The temporal change of the PCB concentration Q (μg g⁻¹ lipid) in the soft tissues of the mussel depends on the competition of the input rate RW and the output rate kQ, where W is the concentration of PCB in water (ppb water) and k is the elimination rate (per day). From our experimental data, k=0.181±0.017 d⁻¹. The critical concentration in water W_c for positive substrate cooperativity was found to be 2.4 ppb. Below W_c, R is a constant. For a water concentration of 0.5 ppb Aroclor 1254, R=24.0±2.4 μg g⁻¹ lipid ppb⁻¹ d⁻¹. Above W_c, positive substrate cooperativity comes into effect and R becomes a function of time and dependent on the concentration Q in a form R=γQ/(Q+δ). This is the case for a water concentration of 5 ppb Aroclor 1254, where γ=15.1 μg g⁻¹ lipid ppb⁻¹ d¹ and δ≈200 μg g⁻¹ lipid. From this model, the uptake is exponentially increasing when the PCB concentration in the mussel is small compared to 200 μg g⁻¹ lipid, and hyperbolically increasing when the concentration is large compared to 200 μg g⁻¹ lipid, which are consistent with the experimental data. The model is useful for understanding the true processes taking place during the bioaccumulation and for risk assessment with higher confidence. Future experimental data which challenge the present model are anticipated and in fact desirable for improvement and perfection of the model.  相似文献   

Cyclic testing of unreinforced masonry walls in two‐way bending     

M. C. Griffith  J. Vaculik  N. T. K. Lam  J. Wilson  E. Lumantarna 《地震工程与结构动力学》2007,36(6):801-821

An experimental programme was conducted in which eight full‐scale unreinforced masonry walls were subjected to cyclic face loading using a system of airbags. Of the eight walls, six contained a window opening and four were subjected to vertical pre‐compression. Combined supports at the vertical and horizontal edges ensured that under face loading the walls underwent two‐way bending. The test walls were found to possess good post‐peak strength and displacement capacity as well as reasonable energy dissipation characteristics. Significant strength and stiffness degradation and non‐symmetry of strength in the positive and negative displacement directions were also evident. Discussion of the causes of the aforementioned trends and their implications towards the seismic response of masonry walls is provided. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Uptake and depuration of PAHs and chlorinated pesticides by semi-permeable membrane devices (SPMDs) and green-lipped mussels (Perna viridis)     

Richardson BJ  Tse ES  De Luca-Abbott SB  Martin M  Lam PK 《Marine pollution bulletin》2005,51(8-12):975-993

Semi-batch seawater experiments were conducted to follow the uptake and release of selected PAHs (anthracene, fluorathene, pyrene and B[a]P) and organochlorine pesticides (-HCH, aldrin, dieldrin, p,p′-DDT) in semi-permeable membrane devices (SPMDs) and green-lipped mussels (Perna viridis). Mathematical models were applied to describe the uptake and elimination curves of the contaminants for SPMDs, and kinetic parameters, such as uptake rate constants, and equilibrium triolein/water partitioning coefficients were calculated. SPMD data showed a good fit to estimate rate constant and partition coefficient equations, but only those contaminants which partitioned mainly in the dissolved phase (-HCH and dieldrin) were well explained for mussels. Poor conformity of the other contaminants indicated mussels uptake by routes other than diffusion, such as ingestion of algae. An apparent equilibrium state was only noted for -HCH in mussels. Aldrin was not detected in mussels in the first few days of exposure, indicating potential metabolism of this compound. B[a]P was not detected in the triolein of SPMDs, which suggests that the membrane may act as a reservoir. Loss of spiked B[a]P from the triolein was evident in a depuration experiment, which may indicate transfer to the membrane. Rate constants for mussels were higher than those for SPMDs, but the reverse was true for partition coefficients. Overall, mussels and SPMDs had similar uptake rates for all compounds in this study, excluding p,p′-DDT and dieldrin. Contaminant elimination took place more rapidly in mussels, implying that SPMDs are better candidates for detecting episodic discharge of organic contaminants.  相似文献   

Tangential‐projection algorithm for manifold representation in unidentifiable model updating problems     

Lambros S. Katafygiotis  Heung‐Fai Lam 《地震工程与结构动力学》2002,31(4):791-812

The problem of updating a structural model and its associated uncertainties by utilizing structural response data is addressed. In an identifiable case, the posterior probability density function (PDF) of the uncertain model parameters for given measured data can be approximated by a weighted sum of Gaussian distributions centered at a number of discrete optimal values of the parameters at which some positive measure‐of‐fit function is minimized. The present paper focuses on the problem of model updating in the general unidentifiable case for which certain simplifying assumptions available for identifiable cases are not valid. In this case, the PDF is distributed in the neighbourhood of an extended and usually highly complex manifold of the parameter space that cannot be calculated explicitly. The computational difficulties associated with calculating the highly complex posterior PDF are discussed and a new adaptive algorithm, referred to as the tangential‐projection (TP) algorithm, allowing for an efficient approximate representation of the above manifold and the posterior PDF is presented. Using this approximation, expressions for calculating the uncertain predictive response are established. A numerical example involving noisy data is presented to demonstrate the proposed method. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

An Evaluation of Four Different Wavelet Decomposition Procedures for Spatial Feature Discrimination in Urban Areas   总被引：2，自引：0，他引：2  

Soe Win Myint  Nina Lam  & John Tyler 《Transactions in GIS》2002,6(4):403-429

Texture or spatial arrangement of neighborhood objects and features plays an important role in the human visual system for pattern recognition and image classification. The traditional spectral–based image processing techniques have proven inadequate for urban land use and land cover mapping from images acquired by the current generation of fine–resolution satellites. This is because of the high frequency spatial arrangements or complex nature of urban features. There is a need for an effective algorithm to digitally classify urban land use and land cover categories using high–resolution image data. Recent studies using wavelet transforms for texture analysis have generally reported better accuracy. Based on a high–resolution ATLAS image, this study illustrates four different wavelet decomposition procedures – the standard, horizontal, vertical, and diagonal decompositions – for urban land use and land cover feature extraction with the use of 33×33 pixel samples. The standard decomposition approach was found to be the most efficient approach in urban texture analysis and classification. For comparison purposes and to better evaluate the accuracy of wavelet approaches in image classification, spatial autocorrelation techniques (Moran's I and Geary's C ) and the spatial co–occurrence matrix method were also examined. The results suggest that the wavelet transform approach is superior to all other approaches.  相似文献