Evolution of the Dok Do seamounts,Ulleung Basin,East Sea: constraints based on the reconstruction of virtual geomagnetic poles using paleomagnetic data     

Chang Hwan Kim  Chan Hong Park  Eui Young Jeong  Jong Sun Hwang  Young Tak Ko 《Geo-Marine Letters》2009,29(3):161-169

In the Ulleung Basin, East Sea, the Dok Do seamount group comprises Dok Do (Dok Island), consisting of very small islets/rocks and a large submerged volcanic edifice, and two voluminous tablemounts, Simheungtaek and Isabu. We attempted to reconstruct the evolution of these seamounts, using virtual geomagnetic poles (VGPs) determined by the least-squares and the seminorm magnetization methods, with 1,500 m upward continued magnetic anomalies. The VGPs of Dok Do with normal dipole anomaly, and of Simheungtaek with normal dipole anomaly are located near the present magnetic pole. The VGP of Isabu with normal dipole anomaly is located at low latitude, presumably due to overprints of reversals in the Tertiary, and the distortion of magnetization and structures associated with volcanism after its formation. In contrast to the tablemounts, magnetic anomalies over Dok Do are a combination of both normal polarity and reversed polarity dipoles in the northern hemisphere, indicating that Dok Do has had at least two major eruptions, one during normal and another during reversed polarity intervals. From these results, and information on the ages of the seamounts (either published radiometric ages of subaerial volcanic rocks, or ages reconstructed in terms of reported elastic thickness incorporated into an existing cooling plate model), we tentatively propose that (1) Isabu formed first, during a normal polarity interval after the opening of the East Sea had ceased; (2) this was followed by an initial and subsequent large eruption of Dok Do during a normal polarity and a reversed polarity interval after about 5 Ma; and (3) the formation of Simheungtaek occurred in between that of Isabu and Dok Do in a normal polarity interval. The pattern of normal/reversed magnetization is not inconsistent with the geomagnetic polarity timescale for at least the last 5 Ma. Nevertheless, precise ages of formation would need verification by additional geophysical/geochemical constraints. Evaluating various possible models explaining the successive formation of the Dok Do seamounts, we currently favor fracturing and volcanism related to compression-induced weakening of the extensional field from the late Miocene to Pliocene after the opening of the East Sea.  相似文献   

Antioxidant efficacy of extracts from a variety of seaweeds in a cellular system     

You Ah Kim  Chang Suk Kong  Young Ran Um  Jung Im Lee  Taek Jeong Nam  Youngwan Seo 《Ocean Science Journal》2008,43(1):31-37

As a part of an ongoing search for antioxidants frodm marine sources, antioxidant activities of 24 kinds of seaweeds (4 green algae, 8 brown algae, and 12 red algae) were investigated. The seaweeds were extracted by acetone/ dichloromethane and methanol, respectively. The antioxidant properties of both extracts were evaluated using four different activity tests, including degree of occurrence of intracellular reactive oxygen species (ROS), NO, lipid peroxidation, and GSH (glutathione) in mouse macrophage Raw 264.7 cells. The levels of intracellular reactive oxygen species (ROS) and GSH were measured using 2’,7’-dichlorofluorescin diacetate (DCF-DA) and monobromobimane as fluorescence probe, respectively. Moreover, the generation of NO and lipid peroxidation products were determined by each method based on the Griess reaction and TBARS assay. Solvent extracts from seaweeds such asScytosiphon lomentaria, Prionitis cornea, Laruencia okamurae,Callophyllis japonica, Sargassum horneri, Dictyopteris divaricat a,Lomentaria catenata, Corallina confuse, Ishige okamurae, andAhnfeltiopsis flabelliformi exhibited high antioxidant activities in cellular oxidizing systems.  相似文献   

Spatial pore characteristics of unsaturated soils caused by dielectric geometric factors under permittivity method with 1 GHz frequency range     

Man-Il Kim  Nam-Won Kim  Il-Moon Chung  Gyo-Cheol Jeong 《Environmental Earth Sciences》2010,60(6):1153-1164

A dielectric measurement device called a frequency domain reflectometry (FDR) has been designed and constructed for the dielectric measurement of unsaturated soil consisting of a volumetric soil water content of about 0.1, 0.2, and 0.3 m³/m³ with different soil porosity around 0.40–0.45, respectively. The dielectric constant is measured in the frequency range 1 GHz. Soil calibration tests and tracer injection tests on standard sand and river sand are carried out in the laboratory. FDR measurement probes at different soil depths allow volumetric soil water content and dielectric constant measurements. The tracer concentration in the pore water is monitored by determining the dielectric constant, from the soil impedance. From the relationship between volumetric soil water content and dielectric constant, the specific calibration equations for the unsaturated soils were derived, and one can easily estimate the volumetric soil water content from the response of the measured dielectric constant for the soils. In the study of dielectric mixture models using α-value of 0.5 which is dielectric geometric factor, the effective porosity for the soils was computed to a range of 87–92% compared with the soil porosity.  相似文献   

Potential impact of vegetation feedback on European heat waves in a 2 x CO 2 climate     

Su-Jong Jeong  Chang-Hoi Ho  Kwang-Yul Kim  Jinwon Kim  Jee-Hoon Jeong  Tae-Won Park 《Climatic change》2010,99(3-4):625-635

Inclusion of the effects of vegetation feedback in a global climate change simulation suggests that the vegetation–climate feedback works to alleviate partially the summer surface warming and the associated heat waves over Europe induced by the increase in atmospheric CO₂ concentrations. The projected warming of 4°C over most of Europe with static vegetation has been reduced by 1°C as the dynamic vegetation feedback effects are included.. Examination of the simulated surface energy fluxes suggests that additional greening in the presence of vegetation feedback effects enhances evapotranspiration and precipitation, thereby limiting the warming, particularly in the daily maximum temperature. The greening also tends to reduce the frequency and duration of heat waves. Results in this study strongly suggest that the inclusion of vegetation feedback within climate models is a crucial factor for improving the projection of warm season temperatures and heat waves over Europe.  相似文献   

The SAURON project – XIII. SAURON–GALEX study of early-type galaxies: the ultraviolet colour–magnitude relations and Fundamental Planes     

Hyunjin Jeong  Sukyoung K. Yi  Martin Bureau  Roger L. Davies  Jesús Falcón-Barroso  Glenn van de Ven †  Reynier F. Peletier  Roland Bacon  Michele Cappellari  Tim de Zeeuw  Eric Emsellem  Davor Krajnovi&#;  Harald Kuntschner  Richard M. McDermid  Marc Sarzi  Remco C. E. van den Bosch 《Monthly notices of the Royal Astronomical Society》2009,398(4):2028-2048

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CGCM3 predictors used for daily temperature and precipitation downscaling in Southern Québec, Canada     

Dae Il Jeong  André St-Hilaire  Taha B. M. J. Ouarda  Philippe Gachon 《Theoretical and Applied Climatology》2012,107(3-4):389-406

This study provides some guidance on the choice of predictor variables from both reanalysis products and the third version of the Canadian Coupled Global Climate Model (CGCM3) outputs for regression-based statistical downscaling models (SDMs) for climate change application in southern Québec (Canada). Twenty CGCM3 grid points and four surface observation sites in the study area were employed. Twenty-five deseasonalized predictors and four deseasonalized predictands (daily maximum and minimum temperatures, precipitation occurrence and wet day precipitation amount) were used to investigate correlation coefficients among predictors and to evaluate their predictive ability when used in a multiple linear regression (MLR) downscaling model. The basic statistical characteristics of vorticity at 1,000-, 850- and 500-hPa levels, U-component of velocity at 1,000-hPa level, temperature at 2?m (T ₂) and wind direction at 1,000- and 500-hPa level of CGCM3 showed a larger difference with those of the NCEP reanalysis data. Therefore, those seven variables require high caution to be included as predictors in statistical downscaling models. Specific humidity at 1,000-, 850- and 500-hPa levels, geopotential height at 850- and 500-hPa levels and T ₂ were the most sensitive predictors for future climate conditions (i.e. A1B and A2 emission scenarios). Specific humidity and geopotential height at different levels and T ₂ were important explainable predictors for the daily temperatures. Mean sea level pressure, specific humidity, U and V components and divergence showed potential as predictors for daily precipitation. Spatial explained variance of MLRs between predictors of every different CGCM3 grid points and the four predictands showed large values at the CGCM3 grid points located near the observation sites, whereas relatively small values were shown at the CGCM3 grid points located more than 400?km from the sites. The explained variance of the downscaled predictands by predictors of three or four CGCM3 grid points located near the observation site produced 2–5% larger R-squares than those by predictors of the nearest grid point. The results illustrated that the use of predictors from more than one AOGCM grid points located near the observation site can increase the skill of the MLR downscaling models.  相似文献   

Greening in the circumpolar high-latitude may amplify warming in the growing season   总被引：1，自引：0，他引：1  

Jee-Hoon Jeong  Jong-Seong Kug  Baek-Min Kim  Seung-Ki Min  Hans W. Linderholm  Chang-Hoi Ho  David Rayner  Deliang Chen  Sang-Yoon Jun 《Climate Dynamics》2012,38(7-8):1421-1431

We present a study that suggests greening in the circumpolar high-latitude regions amplifies surface warming in the growing season (May–September) under enhanced greenhouse conditions. The investigation used a series of climate simulations with the Community Atmospheric Model version 3—which incorporates a coupled, dynamic global vegetation model—with and without vegetation feedback, under both present and doubled CO₂ concentrations. Results indicate that climate warming and associated changes promote circumpolar greening with northward expansion and enhanced greenness of both the Arctic tundra and boreal forest regions. This leads to additional surface warming in the high-latitudes in the growing season, primarily through more absorption of incoming solar radiation. The resulting surface and tropospheric warming in the high-latitude and Arctic regions weakens prevailing tropospheric westerlies over 45–70N, leading to the formation of anticyclonic pressure anomalies in the Arctic regions. These pressure anomalies resemble the anomalous circulation pattern during the negative phase of winter Arctic Oscillation. It is suggested that these circulation anomalies reinforce the high-latitude and Arctic warming in the growing season.  相似文献   

Evaluating observed and projected future climate changes for the Arctic using the K?ppen-Trewartha climate classification     

Song Feng  Chang-Hoi Ho  Qi Hu  Robert J. Oglesby  Su-Jong Jeong  Baek-Min Kim 《Climate Dynamics》2012,38(7-8):1359-1373

The ecosystems in the Arctic region are known to be very sensitive to climate changes. The accelerated warming for the past several decades has profoundly influenced the lives of the native populations and ecosystems in the Arctic. Given that the K?ppen-Trewartha (K-T) climate classification is based on reliable variations of land-surface types (especially vegetation), this study used the K-T scheme to evaluate climate changes and their impact on vegetation for the Arctic (north of 50°N) by analyzing observations as well as model simulations for the period 1900–2099. The models include 16 fully coupled global climate models from the Intergovernmental Panel on Climate Change Fourth Assessment. By the end of this century, the annual-mean surface temperature averaged over Arctic land regions is projected to increase by 3.1, 4.6 and 5.3°C under the Special Report on Emissions Scenario (SRES) B1, A1b, and A2 emission scenarios, respectively. Increasing temperature favors a northward expansion of temperate climate (i.e., Dc and Do in the K-T classification) and boreal oceanic climate (i.e., Eo) types into areas previously covered by boreal continental climate (i.e., Ec) and tundra; and tundra into areas occupied by permanent ice. The tundra region is projected to shrink by ?1.86?×?10⁶?km² (?33.0%) in B1, ?2.4?×?10⁶?km² (?42.6%) in A1b, and ?2.5?×?10⁶?km² (?44.2%) in A2 scenarios by the end of this century. The Ec climate type retreats at least 5° poleward of its present location, resulting in ?18.9, ?30.2, and ?37.1% declines in areal coverage under the B1, A1b and A2 scenarios, respectively. The temperate climate types (Dc and Do) advance and take over the area previously covered by Ec. The area covered by Dc climate expands by 4.61?×?10⁶?km² (84.6%) in B1, 6.88?×?10⁶?km² (126.4%) in A1b, and 8.16?×?10⁶?km² (149.6%) in A2 scenarios. The projected redistributions of K-T climate types also differ regionally. In northern Europe and Alaska, the warming may cause more rapid expansion of temperate climate types. Overall, the climate types in 25, 39.1, and 45% of the entire Arctic region are projected to change by the end of this century under the B1, A1b, and A2 scenarios, respectively. Because the K-T climate classification was constructed on the basis of vegetation types, and each K-T climate type is closely associated with certain prevalent vegetation species, the projected large shift in climate types suggests extensive broad-scale redistribution of prevalent ecoregions in the Arctic.  相似文献   

Load transfer analysis of rock-socketed drilled shafts by coupled soil resistance     

Hoonil Seol  Sangseom Jeong  Yongmin Kim 《Computers and Geotechnics》2009

The load distribution and deformation of rock-socketed drilled shafts subjected to axial loads are evaluated by a load transfer method. The emphasis is on quantifying the effect of coupled soil resistance in rock-socketed drilled shafts using 2D elasto-plastic finite element analysis. Slippage and shear-load transfer behavior at the pile–soil interface are investigated by using a user-subroutine interface model (FRIC). It is shown that the coupled soil resistance acts as pile-toe settlement as the shaft resistance is increased to its ultimate limit state. Based on the results obtained, the coupling effect is closely related to the ratio of the pile diameter to soil modulus (D/E_s) and the ratio of total shaft resistance against total applied load (R_s/Q). Through comparison with field case studies, the 2D numerical analysis reasonably estimated load transfer of pile and coupling effect, and thus represents a significant improvement in the prediction of load deflections of drilled shafts.  相似文献   

Numerical analysis of passive pile groups in offshore soft deposits   总被引：1，自引：0，他引：1  

Sangseom Jeong  Donghee Seo  Youngho Kim   《Computers and Geotechnics》2009,36(7):1164-1175

The performance of pile foundations in offshore soft deposits is frequently dominated by passive loading from approach embankments for reclaimed land in Korea. This is mainly because of a Korean offshore soil profile, involving an over 30 m normally consolidated soil, with a strength that varies linearly with depth. This paper presents the results of an investigation on short- and long-term passive loading on the piles using two dimensional elastoplastic-consolidation coupled FEM analyses with large strain mode. This numerical scheme is essentially based on an updated Lagrangian formulation, which is favorably validated in cases of both centrifuge tests and field measurements. Although a parametric study is limited by some of the application, it is shown that passive pile loading is primarily affected by soil profile, pile head boundary condition, magnitude of embankment load, and average degree of consolidation. Simultaneously, time-dependent effect of shear transfer at the pile head is explicitly identified and a useful starting point in design is recommended for passive pile loading in construction (short-term) and consolidation (long-term) phases.  相似文献