首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 46 毫秒
1.
Several lines of evidence were presented in Gasperini et al. [Terra Nova (2007), vol. 19 , pp. 245–251] suggesting that Lake Cheko, a small lake close to the alleged epicentre of the 1908 Tunguska Event, might be a secondary impact crater. Collins et al. [Terra Nova (2008), this volume] argue against this hypothesis. We reply here arguing in favour of an impact origin for Lake Cheko.  相似文献   

2.
Tea bush is one of the plants cultivated in acidic soil, and is a typical hyper-accumulator of F and Al. Brick tea is a kind of brick-formed tea compressed using the older and coarse leaves and branches of tea trees. Brick tea mixed with milk is drunk as a daily indispensable beverage for Mongols, Ewenki, and other minority nationalities in the pastoral and semi-pastoral areas of Northwest China. It is reported that drinking brick tea can result in dental and skeletal fluorosis due to the high F content in it. Because Alzheimer＇s disease （AD） is related with Al in human brain, and Al has potential toxicities for skeletal and neural systems,  相似文献   

3.
Jiang  Yupeng  Zhao  Yidong  Choi  Clarence E.  Choo  Jinhyun 《Acta Geotechnica》2022,17(12):5597-5612
Acta Geotechnica - Granular impact—the dynamic intrusion of solid objects into granular media—is widespread across scientific and engineering applications including geotechnics....  相似文献   

4.
  相似文献   

5.
In total 27 short and one long sediment core, and 278 surface sediment samples from the Baltic Sea were analyzed for mercury (Hg), and organic carbon contents. Thirteen short cores and the long core were dated by radionuclide methods (210Pb, 137Cs, AMS14C). The dataset allows discriminating between natural and human induced changes on the Hg levels in Baltic Sea sediments. Preindustrial Holocene background concentrations vary between 20 and 50 μg Hg per kg dry sediment and are positively correlated with organic carbon changes. Strong human induced pollution is recorded for the second half of the past century and caused high Hg concentrations of up to several hundred μg Hg per kg dry sediment even in Baltic Sea basins. Maximum concentrations are found at industrial and war waste dumping sites (local hot spots). An Hg concentration decreasing trend toward the present day is observed at most coring sites, a result of environmental measures undertaken during the last two decades. At sites where it is possible to calculate Hg fluxes, the natural accumulation rates vary between 2.1 and 5.4 μg Hg per m2 per year. Anthropogenically sourced Hg accumulation rates vary in a wide range of 30 and 300 μg Hg per m2 per year for the time span of maximum pollution. In areas characterized by discontinuous sedimentation only “inventories” of human sourced Hg expressed as the total amount of deposited Hg (above the natural background) per m2 can be calculated. The inventories of the investigated cores vary in the range of 1 and 8 mg Hg per m2. Additionally, influences of sediment dynamics on spatial distribution pattern of Hg concentrations in surface and subsurface sediments are discussed.  相似文献   

6.
Acid rain has been a great threat to socioeconomic sustainable development of China; therefore, we develop an indicator system based on the sensitivity and adaptive capacity perspectives and employ the TOPSIS (Technique for Order Preference by Similarity to Ideal Solution) approach to investigate the impact of acid rain on socioeconomic vulnerability of China. Some empirical findings are obtained. First, there is significant provincial difference of socioeconomic vulnerability caused by acid rain in China. Specifically, Tibet, Qinghai, and Shanghai are the top three provinces with the largest vulnerability but Inner Mongolia, Xinjiang, and Jilin are bottom of the rankings. Second, adaptive capacity indicators overall appear more important than sensitivity indicators to measure the vulnerability of acid rain, and the most important indicators are population density and output value of agriculture, forestry, animal husbandry, and fishery while GDP per capita ranks the last. Third, upgrading energy structure and reducing outdated capacity in China prove to be effective means to mitigate vulnerability of acid rain, which has been validated in Guizhou and Hunan provinces. Finally, great attention should be attached to the population increase so as to curb the acid rain vulnerability, especially in Beijing and Tianjin. These results present a basis for future acid rain prevention planning and economic development in China.  相似文献   

7.
Ecotourism environmental impact assessment is a traveling activity relevant influence prediction and appraisal. And the setting-up of the index system is very important to implement the appraisal of environmental impact of ecological travel. According to …  相似文献   

8.
Fault damage zones in highly porous reservoirs are dominated by deformation bands that generally have permeability-reducing properties. Due to an absence of sufficiently detailed measurements and the irregular distribution of deformation bands, a statistical approach is applied to study their influence on flow. A stochastic model of their distribution is constructed, and band density, distribution, orientation, and flow properties are chosen based on available field observations. The sensitivity of these different parameters on the upscaled flow is analyzed. The influence of a heterogeneous permeability distribution was also studied by assuming the presence of high permeability holes within bands. The fragmentation and position of these holes affect significantly the block-effective permeability. Results of local upscaling with a diagonal and full upscaled permeability tensor are compared, and qualitatively similar results for the flow characteristics are obtained. Further, the procedure of iterative local–global upscaling is applied to the problem.  相似文献   

9.
As a comprehensive study on interaction between type form, spatial collocation of landscape unit and ecology process, landscape ecology emphasizes the interaction between spatial pattern, ecology process and scale. Thereby, landscape ecology is the same with whole assessment and function plan to ecology environment. Combining the eco-environment impact assessment of Wu-Kun highway, this essay discusses the application technique and method of landscape ecology in eco-environment impact assessment of highway project. This highway is not only a part of Lan-Mo （Lanzhou to Mohan） highway and Bei-Kun （Beijing to Kunming） highway, but also a section of ＂9210 framework highway net＂ Kun-De （Kunming to Deqin） highway. Numbers and areas of landscape patch in the assessment region after highway construction show that the land use pattern is changed after highway construction in the assessment region, but construction and operation of the highway project has little influence on landscape quality in the assessment region. The landscape diversity in the assessment region of Wu-Kun highway is 1.125 calculated by formula. The result showed landscape diversity in the assessment region of highway project descends despite its small scope of change. Therefore the influence of highway construction on landscape diversity is very small. Landscape patched index in the assessment region is 204.42 calculated by formula, which influences ecology environment and survival of rare and endangered wildlife to a certain extent. Wildlife mostly refer to birds whose living environment is not very strict, thus reinforcement of landscape patched degree will not bring important influence on wildlife in the assessment region of highway.  相似文献   

10.
This study draws attention to the fact that natural processes can mobilize thallium (Tl), a highly toxic metal, which may enter the food chain with severe health impacts on the local human population. A rural area having independent Tl mineralization in s…  相似文献   

11.
The region to the east of Palghat gap is of low elevation and nearly circular in shape. It forms a part of the Kaveri river basin. The predominantly gneissic terrain is surrounded by the charnockitic hill ranges, prominent among which are Nilgiris and Biligirirangan to the north; and Anaimalai and Kodaikanal to the south. The charnockite massifs have a steep slope facing the circular feature and a gentler slope in the opposite direction. Fractures/faults/shear zones are noticed in many parts. The Bouguer anomaly in the gneissic terrain is elliptical in shape and positive, relative to the surrounding elevated region. The magnetic contours are also elliptical and the magnetic basement is deeper by about one km compared to regions in the periphery. The shallow seismic velocity picture from Chennimalai to Palani indicates a graben structure. The velocity structure also depicts a 4–5 km Moho upwarp near Chennimalai. Junction between the gneissic and charnockitic terrain and even beyond, is marked by the presence of pseudotachylites and breccia. Field and petrographic studies indicate presence of suevite, Planar Deformation Features (PDF), Planar Fractures, diaplectic glass of quartz and plagioclase and spherical inclusion in suevite. These evidences taken together point to an extra-terrestrial impact which created a crater of approximately 120 km in diameter. Several lines of indirect evidences point to Neoproterozoic age for the impact. Kaveri Crater is the fourth largest crater on the surface of the Earth; other larger craters being Vredefort (160 km), Chicxulub (150 km) and Sudbury (130 km).  相似文献   

12.
《Comptes Rendus Geoscience》2018,350(7):347-353
After the well-reported record loss of Arctic stratospheric ozone of up to 38% in the winter 2010–2011, further large depletion of 27% occurred in the winter 2015–2016. Record low winter polar vortex temperatures, below the threshold for ice polar stratospheric cloud (PSC) formation, persisted for one month in January 2016. This is the first observation of such an event and resulted in unprecedented dehydration/denitrification of the polar vortex. Although chemistry–climate models (CCMs) generally predict further cooling of the lower stratosphere with the increasing atmospheric concentrations of greenhouse gases (GHGs), significant differences are found between model results indicating relatively large uncertainties in the predictions. The link between stratospheric temperature and ozone loss is well understood and the observed relationship is well captured by chemical transport models (CTMs). However, the strong dynamical variability in the Arctic means that large ozone depletion events like those of 2010–2011 and 2015–2016 may still occur until the concentrations of ozone-depleting substances return to their 1960 values. It is thus likely that the stratospheric ozone recovery, currently anticipated for the mid-2030s, might be significantly delayed. Most important in order to predict the future evolution of Arctic ozone and to reduce the uncertainty of the timing for its recovery is to ensure continuation of high-quality ground-based and satellite ozone observations with special focus on monitoring the annual ozone loss during the Arctic winter.  相似文献   

13.
Fine atmospheric dust includes mineral particles and aggregates, fibrous minerals and fibrous organic material. Generation, dislodgement and transport （deflation） of natural dust with the finer （〈4 microns） components suspended as silt-size aggregates, is widespread in and adjacent to the world＇s drylands, as well as deriving from volcanic vents. Silica is a highly fibrogenic agent in lung tissue. Long-term inhaling of siliceous dusts can lead to a number of fibrotic lung diseases, including natural （non-occupational） pneumoconioses （notably silicosis, but including asbestosis and others）. Different polymorphs of silica show different levels of toxicity in interaction with lung tissue. Particles with highly active surfaces may release radicals, causing cell damage. Some types of inhaled particulates are degraded by macrophages, but many are highly resistant and persist in the lungs, some stimulating fibroblastic cells to deposit collagen. Silicosis is an inflammation of the lung commonly caused by silicate mineral particles, leading to fibrosis. Three types are recognized： nodular pulmonary fibrosis （simple or chronic silicosis）, acute silicosis, and accelerated silicosis. Generally, finer particulates have greater oxidative capacity than the coarser fractions. They contain more reactive oxygen species, their greater bioreactivity making them more toxic to pulmonary tissue. Nevertheless, inhalation of large dust particles （〉 10μm） may constitute a health risk if the mineralogy is toxic, regardless of where the grains lodge in the respiratory system. Dust may absorb harmful gases, disease-generating bacteria and carcinogenic hydrocarbon compounds. Silica-related respiratory disease may also an exacerbate cardiac problem, and epidemiology suggests a link with tuberculosis. Quantification of dust loading and exposure requires study of spatial and temporal patterns, supported by meteorological analysis, airflow modeling and satellite-borne imagery. Some acute, short-term health impacts have been assessed using atmospheric and health records both before and after a dust storm or by comparison of populations within and outside such events. Analysis of the size, shape, mineralogy and geochemistry of ambient dust particulates provides information on natural dust sources, dust concentrations, and potential particulate toxicity, as well as providing a datum for assessment of human exposure levels.  相似文献   

14.
崔曼仪  周刚  张大弘  张世强 《冰川冻土》2022,44(6):1898-1911
Under the background of climate warming, the occurrence time, frequency, intensity, and impact of snowmelt flood disasters have changed significantly. Thus, establishing a global snowmelt flood disaster database is particularly important for disaster risk management. With the help of a web crawler, and based on multiple data sources such as natural disaster databases, documents, books, government agency websites, and news media, this study collected relevant information of snowmelt floods and mixed floods and established standards for identifying snowmelt flood events and their disaster impacts based on data from the different sources. Following the screening, sorting, fusion, and integration of snowmelt flood events, a global snowmelt flood disaster dataset containing 579 pieces of data with strong pertinence and reliability was constructed. The temporal and spatial distribution characteristics of global snowmelt flood disasters from 1900 to 2020 were preliminarily analyzed. The results showed that the snowmelt floods were mainly distributed between 30° N and 60° N, with more mixed floods south of 50° N and more snowmelt floods north of 50° N. Spring was the period of highest incidence of snowmelt flood disasters, followed by winter, summer, and autumn, respectively. The snowmelt floods that occurred in spring, autumn, and winter were mainly at 40°~50° N, and the snowmelt floods that occurred in summer were mainly at 30°~40° N. Compared with the snowmelt floods, the mixed floods were more frequent and more destructive, and their frequency increased with climate warming. The results provide a scientific basis for risk prevention and loss assessment of global snowmelt flood disasters. © 2022 Science Press (China).  相似文献   

15.
This paper focuses on the process of Jewish settlement in the West Bank and its economic consequences in the period from 1967 to the outbreak of the Intifada late in 1987. It attempts to show that this process is the practical application of Israeli objectives which are based on expansion and occupation of neighbouring Arab lands, facilitated by the fashioning of a dual or bifurcate economy there.After the war of June 1967, Israeli occupation authorities started to draw up plans with a view to settling Jews in the West Bank. There has been an increase in the numbers of settlements and settlers, estimated at 122 and 52,000 respectively in 1987. The pattern of settlement distribution is randomly dispersed, although it is concentrated in a region located to the NW of Jerusalem. The settlement began in the Jordan valley and extended gradually westward in the highlands.Jewish settlement has affected economic development of the West Bank, where there were many constraints on Arab agriculture and industry. Inequality is evident between settlers and Palestinians in an economy that has been structurally bifurcated: although settlers represent about 3% of total population of the West Bank, their economic activity constitutes at least 35% of the GDP of the West Bank.  相似文献   

16.
Adsorption and desorption are critical processes controlling the fate and transport of organic contaminants in natural environment. Numerous studies have shown that only a fraction of contaminants in soil or sediment can readily be desorbed to the aqueous phase, while desorption of the remaining fraction is very difficult and does not follow the conventional desorption models-a phenomenon typically referred to as ＂resistant desorption＂ or ＂sequestration＂ and is argued by many as the cause of reduced availability of contaminants in soil and sediment. While this reduced availability often reduces the effectiveness of soil and sediment remediation, the same effect can also greatly reduce risk of contaminated soil and sediment. The authors have conducted extensive lab and field studies to characterize the unique properties of sequestration of organic contaminants and to understand the mechanism（s） controlling sequestration. Thus far, over 50 different contaminant-soil/sediment combinations have been evaluated, using contaminants of varied physical-chemical properties （e.g., chlorinated benzenes, PAHs, PCBs, DDT, atrazine, hexachlorocyclohexane isomers, etc.）. Several unique characteristics of sequestration have been observed, and the most striking one is that despite the significant differences in chemical and soil properties, desorption of sequestered contaminants for all the contaminant-soil/sediment combinations exhibited very similar KOC （organic-carbon normalized partition coefficient） and very similar desorption kinetics.  相似文献   

17.
The Lockne impact structure in Jämtland (63°00'20"N, 14°49'30"E) formed in the Middle Ordovician at approximately 455 Ma. The structure is a concentric crater with a total diameter of 13.5 km. The impact took place in a marine environment. Seawater played an important role in the cratering process and in crater morphology and the amount of melt remaining in the structure. Seawater rushed back into the crater in a resurge, eroding and redepositing the ejecta among the resurge deposit. Seawater furthermore facilitated the hydrothermal system, which was driven by the residual heat in the structure. The Lockne structure hosts shocked quartz and an iridium anomaly. The rim wall round the crater collapsed in the modification stage of the crater and was annihilated by the resurge. The fractured basement and the impact breccia were initially rich in open cavities. These became partly filled with dominantly calcite. The filling contributed to a low-density contrast, generating a negative gravity anomaly of 22 gu. The gravity model indicates a central uplift and a NW-directed tilt of the structure. This tilt is also seen in the magnetic models. The apparent absence of any impact melt is probably real and related to the environment of impact.  相似文献   

18.
On 13 August 2010, significant debris flows were triggered by intense rainfall events in Wenchuan earthquake-affected areas, destroying numerous houses, bridges, and traffic facilities. To investigate the impact force of debris flows, a fluid–structure coupled numerical model based on smoothed particle hydrodynamics is established in this work. The debris flow material is modeled as a viscous fluid, and the check dams are simulated as elastic solid (note that only the maximum impact forces are evaluated in this work). The governing equations of both phases are solved respectively, and their interaction is calculated. We validate the model with the simulation of a sand flow model test and confirm its ability to calculate the impact force. The Wenjia gully and Hongchun gully debris flows are simulated as the application of the coupled smoothed particle hydrodynamic model. The propagation of the debris flows is then predicted, and we obtain the evolution of the impact forces on the check dams.  相似文献   

19.
Lead （Pb） is normally considered as a trace element in soils and sediments for geochemical study. However, the concentration of Pb in firing range soils is generally so high that it should be considered as a major element during the evaluation of the soil geochemical properties. Soil organic matter （SOM） has been reported as one of the major factors to expedite the corrosion of metallic lead （Pb） in acidic and organic-rich soils. The main impacts of SOM on the fate and transport of Pb in firing range soils lie in the following two aspects; （1） the complexation of organic matter with Pb, which has received lots of attention, and; （2） changes in soil redox potential due to the transformation of SOM and its subsequent impact on Pb speciation, which has rarely been investigated. Soils from 6 different firing ranges are selected for this study. These samples have been stored under a closed condition for more than 3 years. The soil moisture contents were well-retained, as all the samples were kept in closed plastic buckets. The analytical data showed that the summation of the soil total organic carbon content （TOC） and inorganic carbon contents （TIC） were consistent with soil total carbon contents （TC） measured in previous years, although the TOC and TIC contents have changed respectively after years of storage. In general, it is observed that the soil TOC decreased against an increase of TIC. The mass balance on such a transformation suggested a major conversion of organic carbon （Corg） to inorganic carbon （CO3^2-） in the stored soils.  相似文献   

20.
Goat Paddock in northern Western Australia is a ～5 km-diameter impact crater of Eocene age excavated in gently dipping Proterozoic sandstones. Roughly radial gorges formed by post-impact erosion provide cross-sectional views of the wall and rim zone. The predominant structural theme is one of synclinal rim folding with broad zones in which bedrock strata were deformed by impact to steep, vertical and overturned attitudes. Impact breccia is found craterward of deformed bedrock, on top of it, and downdropped into fault troughs roughly concentric to the crater. The bedrock?–?breccia contact is sharp in some places and gradational in others. In at least one section, the entire mass of upturned bedrock and breccia was displaced radially over essentially undisturbed bedrock, as indicated by slickensides on the horizontal contact. Talus deposits are similar to breccia, but show rough size sorting and clast orientation that dips steeply craterward, indicating that the talus formed as slides down the oversteepened crater wall immediately after crater formation. Shatter cones in some clasts indicate that allogenic material is incorporated in these deposits. Suevite, characterised by ropy flow textures, and by microclasts of quartz with planar deformation features, planar fractures, and of vesiculated silica glass, was found overlying deformed bedrock at a point where the surface of the bedrock forms a nearly horizontal bench midway up the crater wall. The crater was at least partially filled by later sediments, represented by bedded conglomerate close to the crater wall grading inward to sand, silt and mudstone recovered by drillholes on the crater floor. Some of the talus and conglomerate occupy re-entrants in the crater walls, suggesting an original scalloped outline to the crater. Two drillholes, one central and one halfway to the wall, both reached brecciated sandstone after penetrating 210 m of lake sediments. Goat Paddock has a flat floor with no indication of a central uplift and a depth/diameter ratio of ～0.073. This crater form, coupled with the modification of the crater walls by slumping and the scalloped outline of the crater rim suggests that Goat Paddock bridges the two traditional classes of impact crater: simple and complex.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号