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991.
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994.
Hua-You Chai Kok-Kwang Phoon Chang-Fu Wei Ying-Fa Lu 《Journal of Applied Geophysics》2011,73(1):49-58
In the wave field induced by active sources, the observed phase velocity of surface waves is influenced by both mode incompatibility (i.e. non-planar spread of surface waves is idealized as plane waves) and body waves. Effects of sources are usually investigated based on numerical simulations and physical models. Several methods have been proposed to mitigate the effects. In application, however, these methods may also have difficulties since the energy of the body waves depends on soil stratification and parameters. There are multiple modes of surface waves in layered media, among which the higher modes dominate the wave field for soils with the irregular shear velocity profiles. Considering the mode incompatibility and the higher modes, we derive analytical expressions for the effective phase velocity of the surface waves based on the thin layer stiffness method, and investigate the effects of the body waves on the observed phase velocity through the phase analysis of the vibrations of both the surface waves and the body waves. The results indicate that the effective phase velocity of the surface waves in layered media varies with the frequency and the spread distance, and is underestimated compared to that of the plane surface waves in the spread range less than about one wavelength. The oscillations that appeared in the observed phase velocity are due to the involvement of the body waves. The mode incompatibility can be ignored in the range beyond one wavelength, while the influence range of the body waves is far beyond one wavelength. The body waves have a significant influence on the observed phase velocity of the surface waves in soils with a soft layer trapped between the first and the second layers because of strong reflections. 相似文献
995.
José M. Marques Paula M. M. Carreira Luís Aires-Barros Rui C. Graça 《Environmental Geology》2000,40(1-2):53-63
At the northern part of the Portuguese mainland, the upflow zone of several hot and cold HCO3/Na/CO2-rich mineral waters is mainly associated with important NNE–SSW faults. Several geochemical studies have been carried out
on thermal and non-thermal hydromineral manifestations that occur along or near these long tectonic alignments. The slight
chemical differences that exist between these meteoric hot and cold HCO3/Na/CO2-rich mineral waters seem to be mainly caused by CO2. δ13C(TIDC) values observed in these groundwaters range between –6.00 and –1.00‰ versus V-PDB (V denotes Vienna, the site of the International
Atomic Energy Agency; PDB originates from the CaCO3 of the rostrum of a Cretaceous belemnite, Belemnitella americana, collected in the Peedee formation of South Carolina, USA) indicating a deep-seated (mantle) origin for most of the CO2. Nevertheless, in the case of the heavier δ13C(TIDC) values, the contribution of metamorphic CO2 or the dissolution of carbonate rock levels at depth cannot be excluded. Concerning the hot waters, the lack of a positive
18O-shift should be attributed to water-rock interaction in a low temperature environment, rather than to the isotopic influence
of CO2 on the δ18O-value of the waters.
Received: 9 August 1999 · Accepted: 8 March 2000 相似文献
996.
��˫��Դ������ǰ�۵�Ľ�һ��̽�� 总被引:1,自引:1,他引:0
陆明勇 《大地测量与地球动力学》2007,27(4):105-111
?????????????????????????????????ü?????????????????????????????????????????????????????,???????????????????????????????????:?????????????????????????????????????????????????????????????μ??????????????????????????????У??????????????????λ?????????????????????????Щ???????????????????????????????????????????????????????????????????????????? 相似文献
997.
Wen-yuan Huang Russ W. Keim Yao-chi Lu N. D. Uri Terry Kelley 《Environmental Geology》1998,34(2-3):116-127
The economic and environmental consequences of soil nitrogen tests can have significant impacts on agricultural production.
Some of these are explored here. The pre-side-dress soil N-test is evaluated for a hypothetical farmer growing corn at the
ARS Sustainable Agriculture Demonstration Farm site in southern Maryland. For a farmer not currently using a soil N-test,
adoption of this technology can lead to the enhancement of net farm income and the reduction in nitrogen loss to the environment.
This will transpire only if the farmer is currently underestimating nitrogen carryover by more than 25% or applying nitrogen
fertilizer based solely on an expected plateau-yield goal.
Received: 13 February 1997 · Accepted: 13 May 1997 相似文献
998.
��������ұ궨�Զ�����ϵͳ 总被引:1,自引:0,他引:1
?????Я???????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????? 相似文献
999.
LUHe-li LIUGui-fang QANLe-xiang 《中国地理科学(英文版)》2004,14(4):314-319
This paper attempts to summarize the disparities of lnternet development in China spatially-temporally. The major objective is to measure the differences between Eastern, Central and Western China. Methods of map presentation, correlation, Lorenz curve, Gini Coefficient and location quotient analysis are conductcd in this study.For convenience, the indicator of regional lnternet development is simplified as the number of domain names registered under .CN in each province. The data used are collected from the semi-annual surveys of the Statistical surrey Report on the Internet Development in China since 1999. There are several findings: 1)The number of domain names in each province (city) declines gradually from the east to the west. 2) The gap between the highest growth provinces (cities) and the lowest ones is rather large. 3) Although the absolute differences between the eastern, ccntral and western China have been enlarged, the relative diffcrences in each province (city) have remained constant.4) Provinces (cities) are classified into three types according to location quotient changes, namely, rising type,changeless type and declining type. Compared with industrial and economic growth, lnternet sector in the eastern and western China is relatively ascending, while that in the central China is descending. 5) The number of domain names at provincial level is not statistically consistent with GDP. 相似文献
1000.
Based on Hagget's theory of spatial structure,researches on the nodes and field of tourist origins to Huang-cheng Village in Shanxi Province of China have been explored.Nodal hierarchy structure of tourist origins is analyzed with cluster analysis and the gravity model.And field of tourist origins is analyzed with attraction radius index(R)and geography concentration index(G).In the field analysis,R and G of Huangcheng Village are compared with Xidi Village that is a world heritage located in Huangshan City of Anhui Province in China.According to comparison of loca-tions of two areas,influential factors for field area of Huangcheng Village are identified.It is concluded that:1)cluster analysis and gravity model can be complementary methods to each other for nodal hierarchy structure analysis of tour-ist origins;and 2)as far as location is concerned,the weak intensity effect of tourism resources in the tourist region is a major cause for explaining why tourist origins to Huangcheng Village are mainly its neighboring areas.Moreover,it is suggested that the regional effect of tourist resources should be regarded as a component of destination attractiveness when applying gravity model. 相似文献