The toxicity of marine sediments in Victoria Harbour, Hong Kong   总被引：4，自引：0，他引：4  

Y. S. Wong  N. F. Y. Tam  P. S. Lau  X. Z. Xue 《Marine pollution bulletin》1995,31(4-12):464-470

When the toxicity of marine sediment in Hong Kong was evaluated, it was found that the seven sediments collected within Victoria Harbour were severely contaminated with heavy metals, at concentrations many times higher than those in sediments collected from outside the harbour. The highest metal content was recorded in site VS14 (located near the airport runway and the industrialized area), with copper, zinc, lead and chromium values of 3789, 610, 138 and 601 mg kg⁻¹ dry wt, respectively. This site also had the greatest alkaline phosphatase activities (15 fluorescent intensity unit g⁻¹ wet wt), the largest number of total coliforms (910 CFU g⁻¹ wet wt) and sulphate-reducing bacteria (8.5 × 10⁴ cells g⁻¹ wet wt), implying that site VS14 was also contaminated with organic matter and nutrients. Sediment bioassays, Microtox and algal tests, demonstrated that sediment elutriates obtained from site VS14 were of greatest toxicity. The EC₁₀ value in Microtox tests was 17% elutriate, and the 96-h IC₅₀ values using Skeletonema costatum and Dunaliella tertiolecta were 40 and 79% elutriate, respectively. No toxic effects were found in sediment samples collected from the control site outside Victoria Harbour. Significant correlations were found between the results of the algal toxicity test (using S. costatum) and the coliform count and metal content of the sediments. The Microtox test was less sensitive than the algal bioassay, and no sediment elutriate, even from the site mostly contaminated by heavy metals, caused more than 50% inhibition of the light-emitting activity of the bacteria. In this study, S. costatum (the diatom) provided a more sensitive and reliable test species than D. tertiolecta (the flagellate) in differentiating the toxicity of marine sediments.  相似文献   

Diffraction of plane sh waves in a half-space     

A. H. Shah  K. C. Wong  S. K. Datta 《地震工程与结构动力学》1982,10(4):519-528

Scattering of antiplane shear waves (SH) in two dimensions by surface and near-surface defects in a homogeneous, isotropic elastic semi-infinite medium has been studied. Attention has been focused here in the range of medium to long wavelengths. A combined finite element and analytical technique has been used to study the problems of scattering by semi-circular and triangular canyons. The results for the former case are compared with the known exact solution and those for the latter case are compared with some available approximate solutions. Finally a problem of multiple scattering by a triangular canyon and a nearby circular tunnel is studied. Numerical results are presented showing the effects of multiple scattering and different angles of incidence. These results are of interest in earthquake engineering.  相似文献   

Effects of CO₂-H₂O and oblique collision on orogenesis—the european hercynides as an example     

How Kin Wong  Egon T. Degens 《Tectonophysics》1983,95(3-4)

The European Hercynides are considered the collisional result of Baltica and the microcontinents of Southern Europe, after subduction destroyed the intervening Rheic Ocean during the early Paleozoic. Their geotectonic development is assumed to consist of four overlapping stages:

1. (1) lithospheric thinning, upwelling of hot asthenospheric material, subsidence along listric faults, and basinal and geosynclinal development on the opposing shelves of the Rheic Ocean starting in pre-Devonian time;

2. (2) intermittent subduction of the Rheic Ocean interspersed with episodes of fracturing, volcanism, local uplift and subsidence, and basement reactivation as a result of compression with dextral megashear, particularly since the earliest Devonian;

3. (3) several phases of folding with a northward vergence, and thrusting and overthrusting along listric surfaces, the true orogenic stage;

4. (4) post-orogenic stage of massive granite intrusions and subsequent volcanism in the Permo-Triassic

.The high clastic content (as opposed to carbonates) of the sedimentary sequences involved in the subduction and folding processes and the consequent release of large amounts of meteoric water are held responsible for the synorogenic and post-orogenic magma rise, and for the wide zone of anatectic granites and migmatites. The dominant dextral megashear, the constant re-adjustment of the microcontinents of Southern Europe (oblique collision) and the scarcity of back-arc basins, oceanic plateaus and microcontinents led to the poor preservation of ophiolites and ultrabasic rocks, and to a wide (over 1500 km) Hercynian Foldbelt.During the Paleozoic, the depositional center of the Rhenish Massif shifted from south polar latitudes in the early Ordovician to tropical positions within a period of about 100 m.y. The sediment facies reflects this paleogeographic development.  相似文献   

Defining the geochemical baseline: a case of Hong Kong soils     

H. B. Zhang  Y. M. Luo  M. H. Wong  Q. G. Zhao  G. L. Zhang 《Environmental Geology》2007,52(5):843-851

A geochemical baseline provides the means to distinguish between the pedogenic origin and the anthropogenic origin of the trace element in the environmental compartments. We collected 271 soil samples representative of different parent rocks and soil types from the whole territory of Hong Kong and analyzed the composition of clay mineralogy and the contents of 15 chemical elements (Fe, Cd, As, etc.) for these samples. The baseline was predicted with the method of the normalization procedure combined with the relative cumulative frequency curve. The result indicated that Fe was the best reference element for the normalization procedure among the five potential reference elements (Fe, Al, Sc, Ti, and Mn), followed by Sc and Ti. A poor correlation was found between Sc, Ti, and Cu. The predicted baseline was much lower than the A-value of the Dutch List used usually in screening the polluted soil of Hong Kong, implying that the extent of heavy metal pollution might have been underestimated with respect to local lands. We also applied the cluster analysis to distinguish the geochemical associations of the trace elements due to its importance to the baseline. Approximately three major associations including the Fe–Mn-oxides related, Al oxides or Al-bearing-clay-mineralogy related and sulfide- related associations were observed from the dendrogram.  相似文献   

Living with floods: victims' perceptions in Beijiang, Guangdong, China   总被引：2，自引：0，他引：2  

Koon-Kwai Wong  & Xiaobin Zhao 《Area》2001,33(2):190-201

This study revealed the collective values of the flood victims in the Beijiang area, Guangdong, China, as a result of a hazardous flood in 1994. The victims were sceptical of large flood-prevention engineering structures. They believed that flooding was unavoidable, but by extending support networks, applying hazard-resistant designs, and developing loss-sharing adjustments the disastrous effects of a flood could be mitigated. Seemingly, victims were prepared to live with floods and adopted functional adjustments to lessen flood impact.  相似文献   

Long-term changes in water quality and phytoplankton characteristics in port shelter, Hong Kong, from 1988-1998.   总被引：6，自引：0，他引：6  

Y K Yung  C K Wong  K Yau  P Y Qian 《Marine pollution bulletin》2001,42(10):981-992

This study analysed monthly physico-chemical and phytoplankton data collected from 10 marine monitoring stations in Port Shelter Hong Kong, from 1988 to 1998. Cluster analysis based on all water quality parameters measured shows that the 10 monitoring stations can be grouped into three clusters: Cluster I consists of stations located in Outer Port Shelter; Cluster II consists of stations located in Inner Port Shelter and Cluster III consists of a single station in Hebe Heaven, a well-sheltered Bay in Inner Port Shelter. Factor analysis shows high positive loadings for nutrients and nutrient ratios in the first two factors of the three clusters, which indicates that the stations of the three clusters were primarily grouped according to their respective nutrient conditions. In Inner Port Shelter, and particularly Station PM5 in the sheltered Hebe Haven, the influence of surface runoff and pollution loading from the surrounding catchment area was apparent. Five stations located along a transect from Inner to Outer Port Shelter were selected for trend analysis. An increasing trend for temperature and a decreasing trend for pH are observed in all Stations except PM10 which is at the mouth of Port Shelter. The results of canonical analysis revealed that temperature and pH could also play an important role in determining the density and biovolume of the minor algal groups in Port Shelter.  相似文献   

Evaluation of response and energy in actively controlled structures     

Kevin K. F. Wong  Rong Yang 《地震工程与结构动力学》2001,30(10):1495-1510

A computational method of energy evaluation is derived to study the elastic responses and energy distribution of actively controlled single‐degree‐of‐freedom (SDOF) structures during earthquakes. Contrary to the common perception that applying active control force pumps energy into the structure, the applied control force can actually reduce the energy in the structure by reducing the input energy from earthquakes to the structure. In addition, applying control force can dissipate a large amount of energy in the structure when this control force is applied in the direction opposite to the displacement and velocity responses. To demonstrate this energy mechanism in active controlled structures, the two most popular control algorithms, optimal linear control (OLC) and instantaneous optimal control (IOC) algorithms, are used to calculate the control response and energy spectra. One‐step time delay is incorporated into the algorithms to take into consideration the practical aspect of active control. The effects of different earthquakes and damping ratios on control energy and response spectra are studied. These studies show that both OLC and IOC are very effective in reducing the structural displacement and velocity responses by reducing the input earthquake energy as well as dissipating a large amount of energy in the structure. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Effectiveness of structural control based on control energy perspectives     

Kevin K. F. Wong  Rong Yang 《地震工程与结构动力学》2001,30(12):1747-1768

A computational algorithm for maximizing the control efficiency in actively controlling the elastic structural responses during earthquake is proposed. Study of optimal linear control using a single degree of freedom shows that applying active control is very effective in reducing the structural displacement and velocity responses for long‐period structures, but at the same time it has an adverse effect in increasing the absolute acceleration response. The extent of this adverse effect reduces the effectiveness of the control system, and therefore it poses a limit on the maximum control force in order to provide maximum control efficiency. In view of this shortcoming, maximum control energy dissipation is used to define the most effective optimal linear control law. Less displacement and velocity response are expected as larger control force is applied, but there is always a limit that maximum control energy can be dissipated. This study shows that this limit depends on the structural characteristics as well as the input ground motion, and a general trend is that the maximum control energy decreases as damping increases. Finally, application of the proposed algorithm on a six‐storey hospital building is presented to show the effectiveness of using optimal linear control on a multi‐degree‐of‐freedom system from the control energy perspectives. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Active control of the seismic response of structures by combined use of base isolation and absorbing boundaries     

J. E. Luco  A. Mita  H. L. Wong 《地震工程与结构动力学》1992,21(6):525-541

The relative advantages of several control strategies to reduce the seismic response of multi-storey structures are studied. The strategies involve the separate or combined use of passive base isolation mechanisms and active control forces. The base isolation mechanism is modelled as an equivalent linear soft storey with high damping. The active control forces are selected so that an absorbing boundary is obtained at the top of the structure and non-reflecting or reflecting boundaries are obtained at the base of the building. It is found that the best results are obtained when a passive base isolation system is combined with an active absorbing boundary placed at the top of the building. However, the incremental gains resulting from adding a base isolation system to a structure already controlled by a roof-top active absorbing boundary are significant only for relatively soft base isolation systems. Also, the incremental gains appear to decrease as the number of storeys of the structure increases.  相似文献   

The Reliability of Using the Iterative Proportional Fitting Procedure*     

David W. S. Wong 《The Professional geographer》1992,44(3):340-348

This paper demonstrates the utility of the iterative proportional fitting procedure (IPF) in generating disaggregated spatial data from aggregated data and evaluates the performance of the procedure. Estimates of individual level data created by IPF using data of equal-interval categories are reliable, but the performance of the estimation can be improved by increasing sample size. The improvement usually is enough to offset the increase in error created by other factors. If the two variables defining the cross-classification have a significant interaction effect and the number of categories in each variable is larger than two, then IPF is preferred over an independent model.  相似文献