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排序方式: 共有106条查询结果,搜索用时 156 毫秒
31.
Byoung‐Young Choi Seong‐Taek Yun Bernhard Mayer Gi‐Tak Chae Kyoung‐Ho Kim Kangjoo Kim Yong‐Kwon Koh 《水文研究》2010,24(3):317-330
We evaluated sources and pathways of groundwater recharge for a heterogeneous alluvial aquifer beneath an agricultural field, based on multi‐level monitoring of hydrochemistry and environmental isotopes of a riverside groundwater system at Buyeo, Korea. Two distinct groundwater zones were identified with depth: (1) a shallow oxic groundwater zone, characterized by elevated concentrations of NO3? and (2) a deeper (>10–14 m from the ground surface) sub‐oxic groundwater zone with high concentrations of dissolved Fe, silica, and HCO3?, but little nitrate. The change of redox zones occurred at a depth where the aquifer sediments change from an upper sandy stratum to a silty stratum with mud caps. The δ18O and δ2H values of groundwater were also different between the two zones. Hydrochemical and δ18O? δ2H data of oxic groundwater are similar to those of soil water. This illustrates that recharge of oxic groundwater mainly occurs through direct infiltration of rain and irrigation water in the sandy soil area where vegetable cropping with abundant fertilizer use is predominant. Oxic groundwater is therefore severely contaminated by agrochemical pollutants such as nitrate. In contrast, deeper sub‐oxic groundwater contains only small amounts of dissolved oxygen (DO) and NO3?. The 3H contents and elevated silica concentrations in sub‐oxic groundwater indicate a somewhat longer mean residence time of groundwater within this part of the aquifer. Sub‐oxic groundwater was also characterized by higher δ18O and δ2H values and lower d‐excess values, indicating significant evaporation during recharge. We suggest that recharge of sub‐oxic groundwater occurs in the areas of paddy rice fields where standing irrigation and rain water are affected by strong evaporation, and that reducing conditions develop during subsequent sub‐surface infiltration. This study illustrates the existence of two groundwater bodies with different recharge processes within an alluvial aquifer. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
32.
Rapid development of arctic cyclone in June 2008 simulated by the cloud resolving global model NICAM
In this study, we conducted a numerical simulation of a rapid development of an arctic cyclone (AC) that appeared in June 2008 using a cloud resolving global model, Nonhydrostatic ICosahedral Atmospheric Model (NICAM). We investigated the three dimensional structure and intensification mechanism of the simulated AC that developed to the minimum sea level pressure of 971 hPa in the model. According to the result, the AC indicates a barotropic structure with a warm core in the lower stratosphere and a cold core in the troposphere. The development of the AC is accompanied by an intense mesoscale cyclone (MC) showing baroclinic structure with a marked local arctic front. The upper level warm core of the AC is formed by an adiabatic heating associated with the downdraft in the lower stratosphere. The rapid development of the AC is caused by the combination of the intensification of the upper level warm core and the merging with the baroclinically growing MC in the lower level. The merging of the AC and MC and the vertical vortex coupling with the upper air polar vortex are the most important mechanisms for the rapid development of the arctic cyclone. 相似文献
33.
Martin Danišík Jaroslav Kadlec Christoph Glotzbach Anett Weisheit István Dunkl Milan Kohút Noreen J. Evans Monika Orvošová Brad J. McDonald 《Swiss Journal of Geoscience》2011,104(2):285-298
A combination of four thermochronometers [zircon fission track (ZFT), zircon (U–Th)/He (ZHe), apatite fission track (AFT)
and apatite (U–Th–[Sm])/He (AHe) dating methods] applied to a valley to ridge transect is used to resolve the issues of metamorphic,
exhumation and topographic evolution of the Nízke Tatry Mts. in the Western Carpathians. The ZFT ages of 132.1 ± 8.3, 155.1 ± 12.9,
146.8 ± 8.6 and 144.9 ± 11.0 Ma show that Variscan crystalline basement of the Nízke Tatry Mts. was heated to temperatures
>210°C during the Mesozoic and experienced a low-grade Alpine metamorphic overprint. ZHe and AFT ages, clustering at ~55–40
and ~45–40 Ma, respectively, revealed a rapid Eocene cooling event, documenting erosional and/or tectonic exhumation related
to the collapse of the Carpathian orogenic wedge. This is the first evidence that exhumation of crystalline cores in the Western
Carpathians took place in the Eocene and not in the Cretaceous as traditionally believed. Bimodal AFT length distributions,
Early Miocene AHe ages and thermal modelling results suggest that the samples were heated to temperatures of ~55–90°C during
Oligocene–Miocene times. This thermal event may be related either to the Oligocene/Miocene sedimentary burial, or Miocene
magmatic activity and increased heat flow. This finding supports the concept of thermal instability of the Carpathian crystalline
bodies during the post-Eocene period. 相似文献
34.
Sung Won Kim Sanghoon Kwon Hee Jae Koh Keewook Yi Youn-Joong Jeong M. Santosh 《Gondwana Research》2011,20(4):865-889
This study presents sensitive high-resolution ion microprobe (SHRIMP) U–Pb zircon ages, and whole-rock chemical and isotopic (Sr-Nd) compositions of representative Triassic plutons from South Korea. The plutons from the Gyeonggi massif (Hongseong, Namyang, Yangpyeong and Odesan), the central Okcheon belt (Baeknok and Yongsan), and the Yeongnam massif (Sangju, Gimcheon, Hamyang and Macheon) yield zircon U–Pb ages of ca. 232–226 Ma, 227–226 Ma, and 240–228 Ma, respectively. Among the Triassic plutonic suite in South Korea, those within the Gyeonggi massif are dominated by granite, syenite, monzonite, monzodiorite and gabbro. Plutons within the Okcheon belt are mainly by granite to quartz monzodiorite. The Yeongnam massif mainly incorporates granite to granodiorite and minor monzodiorite intrusions. The geochemical signatures of the Triassic plutons are characterized by Ta–Nb troughs, depletion of P and Ti, and enrichment of LILE. Most plutons except Macheon monzodioritic pluton show high initial 87Sr/86Sr ratios (0.708248–0.714678) and strongly negative εNd(T) (− 20.3 to − 7.7) values, suggesting contribution from middle to upper crust. In contrast, the Macheon monzodioritic pluton in the Yeongnam massif shows relatively low initial 87Sr/86Sr ratios (0.706547-0.706629) and negative εNd(T) (− 4.43 to − 3.62) values. The Middle Triassic syenite–monzonite–granite–gabbro series in and around the Gyeonggi massif possess high-K calc-alkaline and shoshonitic affinity suggesting a post-collisional magmatic event following the Permo–Triassic collision between the North and South China blocks. The Triassic plutons in the Yeongnam massif and the Okcheon belt, together with a Permian Yeongdeok pluton in the Gyeongsang basin, show features typical of high- to medium-K calc-alkaline magmatism with LREE and LILE enrichments. This together with a depletion of Y and HREE suggests their formation in a subduction setting. Our results provide robust evidence to consider the Gyeonggi massif as an extension of the Qinling–Dabie–Sulu belt between the North and South China blocks in central China. The Okcheon belt and Yeongnam massif in South Korea, together with the continental margin of South China, are marked by a common Permian to Triassic magmatic episode, probably related to the paleo-Pacific slab subduction. 相似文献
35.
Kohút Milan Hofmann Mandy Havrila Milan Linnemann Ulf Havrila Jakub 《International Journal of Earth Sciences》2018,107(1):321-335
International Journal of Earth Sciences - The Late Triassic timescale, especially the Carnian–Norian boundary, is poorly constrained mainly due to a paucity of high-precision radio-isotopic... 相似文献
36.
The present study examined actigraphically evaluated sleep on the days surrounding the greatest earthquake in Japanese history. The Great East Japan Earthquake occurred unexpectedly on the third day of a 1-week actigraphy measurement. The subjects were eight elderly (73.1 ± 4.3 years, mean ± SD) individuals living in Sendai city, one of the largest cities damaged by the earthquake. All of the subjects wore their actigraph devices until 2 days after the earthquake. The results showed that wake after sleep onset (WASO) was significantly increased (118 ± 29 min, mean ± SE) the first night after the earthquake compared with pre-earthquake values (35 ± 12 min). The subjects described being awoken by frequent aftershocks the first night. This sleep debt was recovered the next day through significant increases in daytime napping and the length of nocturnal sleep periods resulting from earlier bedtimes. An electrical blackout that lasted 2–3 days seemed to be associated with earlier bedtimes by inducing a dark and cold environment. One subject who evacuated to a school gymnasium after the earthquake suffered severely disturbed sleep due to cold temperatures (nocturnal WASO over 180 min). These findings suggest that the environmental factors related to disrupted infrastructure might have considerable impacts on sleep in the first several days after the catastrophic disaster. The findings should be considered for future disaster preparedness initiatives. 相似文献
37.
Koki Aizawa Yasuo Ogawa Masaaki Mishina Kosuke Takahashi Shintaro Nagaoka Nobumasa Takagi Shin'ya Sakanaka Takuya Miura 《Journal of Volcanology and Geothermal Research》2009,187(1-2):131-139
Magnetotelluric (MT) measurements were conducted at Iwate volcano, across the entirety of the mountain, in 1997, 1999, 2003, 2006, and 2007. The survey line was 18 km in length and oriented E–W, comprising 38 measurements sites. Following 2D inversion, we obtained the resistivity structure to a depth of 4 km. The surface resistive layer (~ several hundreds of meters thick) is underlain by extensive highly conductive zones. Based on drilling data, the bottom of the highly conductive zone is interpreted to represent the 200 °C isotherm, below which (i.e., at higher temperatures) conductive clay minerals (smectite) are rare. The high conductivity is therefore mainly attributed to the presence of hydrothermally altered clay. The focus of this study is a resistive body beneath the Onigajo (West-Iwate) caldera at depths of 0.5–3 km. This body appears to have impeded magmatic fluid ascent during the 1998 volcanic unrest, as inferred from geodetic data. Both tectonic and low-frequency earthquakes are sparsely distributed throughout this resistive body. We interpret this resistive body as a zone of old, solidified intrusive magma with temperatures in excess of 200 °C. Given that a similar relationship between a resistive body and subsurface volcanic activity has been suggested for Asama volcano, structural controls on subsurface magmatic fluid movement may be a common phenomenon at shallow levels beneath volcanoes. 相似文献
38.
Flow and Pollutant Transport in Urban Street Canyons of Different Aspect Ratios with Ground Heating: Large-Eddy Simulation 总被引:2,自引:2,他引:0
Xian-Xiang Li Rex E. Britter Leslie K. Norford Tieh-Yong Koh Dara Entekhabi 《Boundary-Layer Meteorology》2012,142(2):289-304
A validated large-eddy simulation model was employed to study the effect of the aspect ratio and ground heating on the flow
and pollutant dispersion in urban street canyons. Three ground-heating intensities (neutral, weak and strong) were imposed
in street canyons of aspect ratio 1, 2, and 0.5. The detailed patterns of flow, turbulence, temperature and pollutant transport
were analyzed and compared. Significant changes of flow and scalar patterns were caused by ground heating in the street canyon
of aspect ratio 2 and 0.5, while only the street canyon of aspect ratio 0.5 showed a change in flow regime (from wake interference
flow to skimming flow). The street canyon of aspect ratio 1 does not show any significant change in the flow field. Ground
heating generated strong mixing of heat and pollutant; the normalized temperature inside street canyons was approximately
spatially uniform and somewhat insensitive to the aspect ratio and heating intensity. This study helps elucidate the combined
effects of urban geometry and thermal stratification on the urban canyon flow and pollutant dispersion. 相似文献
39.
Hyerin Kim Sung-Hyun Cho Dongguen Lee Youn-Young Jung Young-Hee Kim Dong-Chan Koh Jeonghoon Lee 《Environmental Earth Sciences》2017,76(2):82
For water resources management, many studies for investigating flow paths from rainfall to subsurface have been conducted for last half century. A hydrograph separation based on end member mixing was carried out to evaluate the importance of the hydrological pathways providing the main sources of a small granitic watershed, Dorim-cheon, Seoul. An analysis of chloride, oxygen-18 and deuterium isotopes from precipitation and stream water during three storms was conducted with high-resolution data using 129 samples. Stream water, collected in advance of rain event, was assumed as a pre-event water (baseflow) component according to its dry condition and isotopic values compared with the values of different time periods. The contribution from vadose water was ignored due to the thin soil layer covering the study area. Using a two-component mixing model, hydrograph separation of the stream water in Dorim-cheon was conducted based on weighted mean values of rain water and pre-event water component with the high-resolution datasets. As a result of the analysis with water isotopes, contribution of groundwater was dominant during the entire study period (73–74%) except of instant dominance of rainfall at the earliest period. Using chloride as a tracer for hydrograph separation, a significant difference for the amount of pre-event water contribution was identified. This might be caused by the large variation of chloride concentration during the rain event and the end member determination. 相似文献
40.
By identifying changes in stiffness parameters, structural damage can be detected and monitored. Although considerable progress has been made in this research area, many challenges remain in achieving robust structural identification based on incomplete and noisy measurement signals. The identification task is made even more difficult if measurement of input force is to be eliminated. To this end, an output‐only structural identification strategy is proposed to identify unknown stiffness and damping parameters. A non‐classical approach based on genetic algorithms (GAs) is adopted. The proposed strategy makes use of the recently developed GA‐based method of search space reduction, which has shown to be able to accurately and reliably identify structural parameters from measured input and output signals. By modifying the numerical integration scheme, input can be computed as the parameter identification task is in progress, thereby eliminating the need to measure forces. Numerical and experimental results demonstrate the power of the strategy in accurate and efficient identification of structural parameters and damage using only incomplete acceleration measurements. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献