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41.
UPb geochronology provides an absolute time framework for the evolution of the Sigma gold deposit and surrounding rocks at Val d'Or, southern Abitibi subprovince. The Bourlamaque batholith, the largest pluton in the area, gives a 2699.8 ± 1.0 Ma UPb zircon age. This pluton cuts the Val d'Or Formation which hosts the mineralization. A UPb zircon age of 2704.9 ± 1.1 Ma on a felsic volcanic rock, the Colombière “rhyolite”, 13 km east of the mine dates that formation. The gold-bearing quartz vein system at Sigma is hosted by andesites and two generations of porphyry intrusions, all metamorphosed to the greenschist facies. The oldest porphyry (“porphyritic diorite”) shows the same deformation as the volcanic rocks, and has a 2703.7 ± 2.5 Ma UPb zircon age. The porphyritic diorite and volcanic rocks are cut by feldspar-porphyry dykes which post-date regional folding and have a 2694.0 ± 2.2 Ma UPb zircon age.Regional greenschist metamorphism has been dated directly, with a UPb date of 2684 ± 7 Ma on rutile in the Colombière “rhyolite”. The mineralization and hydrothermal alteration in the mine are superimposed on the metamorphic minerals. Hydrothermal rutile, from an alteration halo around the veins in andesite, has a 2599 ± 9 Ma UPb age. Textural evidence clearly indicates that the wall-rock alteration and vein filling are contemporaneous, and hence the vein system and gold mineralization appear to have developed at least 80 m.y. after the formation and metamorphism of host greenstones. 相似文献
42.
回顾分析Matilda医院超速CT室筛选首批病人中99例中国人资料,很明显从通常采用130-100Hounsfield单位作为检出冠状血管钙化的基数应用至中国人身上其阈值数目需要降低,同时,我们也发现如果病人年龄按每10年范围分组(21-30,30-40,41-50,51-60)而计算其超速CT的钙化指数会较随机男女一起按平均计算更易区分其差异.进一步分析显示,男性中年时候超速CT指数已达最高值,而女性则晚10年方达最高值,因此,为了更易探测冠脉循环内钙化倾向应作出超速CT检出钙化的指数数目.这些实践经验对动脉粥样硬化过程的预测或预防有实际意义. 相似文献
43.
The toxicity of marine sediments in Victoria Harbour, Hong Kong 总被引:4,自引:0,他引:4
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
44.
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
45.
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
46.
T. Wang H. Guo D. R. Blake Y. H. Kwok I. J. Simpson Y. S. Li 《Journal of Atmospheric Chemistry》2005,52(3):295-317
We present a 16-month record of ozone (O3), carbon monoxide (CO), total reactive nitrogen (NOy), sulphur dioxide (SO2), methane (CH4), C2 – C8 non-methane hydrocarbons (NMHCs), C1 – C2 halocarbons, and dimethyl sulfide (DMS) measured at a southern China coastal site. The study aimed to establish/update seasonal
profiles of chemically active trace gases and pollution tracers in subtropical Asia and to characterize the composition of
the `background' atmosphere over the South China Sea (SCS) and of pollution outflow from the industrialized Pearl River Delta
(PRD) region and southern China. Most of the measured trace gases of anthropogenic origin exhibited a winter maximum and a
summer minimum, while O3 showed a maximum in autumn which is in contrast to the seasonal behavior of O3 in rural eastern China and in many mid-latitude remote locations in the western Pacific. The data were segregated into two
groups representing the SCS background air and the outflow of regional continental pollution (PRD plus southern China), based
on CO mixing ratios and meteorological conditions. NMHCs and halocarbon data were further analyzed to examine the relationships
between their variability and atmospheric lifetime and to elucidate the extent of atmospheric processing in the sampled air
parcels. The trace gas variability (S) versus lifetime (τ) relationship, defined by the power law, Slnx = Aτ− b, (where X is the trace gas mixing ratio) gives a fit parameter A of 1.39 and exponent b of 0.42 for SCS air, and A of 2.86 and b of 0.31 for the regional continental air masses. An examination of ln[n-butane]/ln[ethane] versus ln[propane]/ln[ethane] indicates that their relative abundance was dominated by mixing as opposed
to photochemistry in both SCS and regional outflow air masses. The very low ratios of ethyne/CO, propane/ethane and toluene/benzene
suggest that the SCS air mass has undergone intense atmospheric processing since these gases were released into the atmosphere.
Compared to the results from other polluted rural sites and from urban areas, the large values of these species in the outflow
of PRD/southern China suggest source(s) emitting higher levels of ethyne, benzene, and toluene, relative to light alkanes.
These chemical characteristics could be unique indicators of anthropogenic emissions from southern China. 相似文献
47.
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
48.
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
49.
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
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
50.
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