Geochronologic evidence for Early Cretaceous volcanic activity on Barton Peninsula, King George Island, Antarctica     

Hyeoncheol Kim  Jong IK Lee  Moon Young Chose  Moonsup Cho  Xiangshen Zheng  Haiquing Sang  Ji Qiu 《Polar research》2000,19(2):251-260

Ages of six volcanic and plutonic rocks on Barton Peninsula, King George Island, were determined using ⁴⁰Ar/³⁹Ar and K-Ar isotopic systems. The ⁴⁰Ar/³⁹Ar and K-Ar ages of basaltic andesite and diorite range from 48 My to 74 My and systematically decrease toward the upper stratigraphic section. Two specimens of basaltic andesite which occur in the lowermost sequence of the peninsula, however, apparently define two distinct plateau ages of 52-53 My and 119-120 My. The latter is interpreted to represent the primary cooling age of basaltic andesite, whereas the former is interpreted as the thermally-reset age caused by the intrusion of Tertiary granitic pluton. The isochron ages calculated from the isotope correlation diagram corroborate our interpretation based on the apparent plateau ages. It is therefore likely that volcanism was active during the Early Cretaceous on Barton Peninsula. When the K-Ar ages of previous studies are taken into account with our result, the ages of basaltic andesite in the northern part of the Barton Peninsula are significantly older than those in the southern part. Across the north-west-south-east trending Barton fault bounding the two parts, there are significant differences in geochronologic and geologic aspects.  相似文献   

Long-term variability of cold surges in Korea     

Kwang-Yul Kim  Seoyeon Lee  Maeng-Ki Kim  Chun-Ho Cho 《Asia-Pacific Journal of Atmospheric Sciences》2014,50(4):519-529

Cold surge statistics have been analyzed from the 52-year (1961–2012) winter temperature data archived at Korea Meteorological Administration. Despite a significant winter warming in South Korea, there is no statistically affirmable sign of the occurrence frequency, duration and total days of cold surges to have changed in the record; there is little abatement in the frequency, duration, and total days of cold surges. Thermal advection anomalies were also derived from the NCEP/NCAR and ERA interim reanalysis datasets. Cold surges defined in terms of thermal advection anomalies do not exhibit any statistically significant change either. The increased mean and the decreased variance of thermal advection both indicate that cold advection from north has, in fact, decreased gradually in South Korea. It appears that cold surges are statistically rare enough to be affected by increased mean and decreased variance of thermal advection. Polar warming is often interpreted as weakening of jet stream and increasing southward flux of cold air. Analysis of thermal advection, on the other hand, does not show increased advection of cold air from north in South Korea.  相似文献   

Geotechnical properties of deep oceanic sediments recovered from the hydrate occurrence regions in the Ulleung Basin, East Sea, offshore Korea   总被引：1，自引：0，他引：1  

Tae-Hyuk Kwon  Kang-Ryel Lee  Gye-Chun Cho  Joo Yong Lee 《Marine and Petroleum Geology》2011,28(10):1870-1883

This study presents comprehensive geotechnical data of the natural marine sediments cored from the hydrate occurrence regions during the Ulleung Basin Gas Hydrate Expedition 1 (UBGH1), East Sea, offshore Korea in 2007. Geotechnical soil index properties of the Ulleung Basin sediments, including grain size distribution, porosity, water content, Atterberg limits, specific gravity, and specific surface area, were experimentally determined. These soil index properties were correlated to geotechnical engineering parameters (e.g., shear strength and friction angle) by using well-known empirical relationships. By performing standard consolidation tests on both undisturbed specimens (as recovered from the original core liner after hydrate dissociation) and remolded specimens, stress-dependent mechanical and hydraulic properties (e.g., compressibility and hydraulic conductivity) were measured. The experimental results provide important engineering parameters, and demonstrate the effect of hydrate presence and consequential dissociation to index properties, engineering parameters, and innate sediment structures.  相似文献   

Vertical structure of the M<Subscript>2</Subscript> tidal current in the Yellow Sea   总被引：2，自引：0，他引：2  

Seok Lee  Heung-Jae Lie  Cheol-Ho Cho  Sok Kuh Kang  William J. Teague  Kyung-Il Chang  Kyu-Min Song  Kyung-Hee Oh 《Ocean Science Journal》2011,46(2):73-84

The vertical structure of the M₂ tidal current in the Yellow Sea is analyzed from data acquired using an acoustic Doppler current profiler. The observed vertical profiles of the M₂ tidal current are decomposed into two rotating components of counter-clockwise and clockwise, and restructured using a simple one-point model with a constant vertical eddy viscosity. The analyzed results show that the internal fictional effect dominates the vertical structure of the tidal current in the bottom boundary layer. In the Yellow Sea, the effect of the bottom friction reduces the current speed by about 20–40% and induces the bottom phase advance by about 15–50 minutes. In the shallower coastal regions, the effects of bottom topography are more prominent on the vertical structure of tidal currents. The vertical profile of the tidal current in summer, when the water column is strongly stratified, is disturbed near the pycnocline layer. The stratification significantly influences the vertical shear and distinct seasonal variation of the tidal current.  相似文献   

GATE A/B‐scale budget analysis     

Han‐Ru Cho  Robert M. Bloxam  Lawrence Cheng 《大气与海洋》2013,51(1):60-76

Abstract

Using GATE A/B‐scale U.S.S.R. ship data, heat and moisture budget analyses have been carried out for the three‐day period: 0000 GMT, 7 September to 2400 GMT, 9 September, 1974. The period has been subdivided into an undisturbed period (0000 GMT, 7 September ‐1800 GMT, 8 September) and a disturbed period (1800 GMT, 8 September ‐ 2400 GMT, 9 September) based on surface precipitation and satellite cloud observations. During the undisturbed period, precipitation was very light (1–3 mm day^‐1). On the other hand, the precipitation rate became well over 10 mm day^‐1 during the disturbed period. A/B‐scale heat and moisture budget results for both periods are presented.

It is found that during the undisturbed period, cumulus clouds have heating and moistening effects in the lower troposphere below 700 mb, and cooling and moistening effects in the upper troposphere above 600mb. In the disturbed period, clouds have strong heating and drying effects throughout the entire cloud layer.

Using the diagnostic scheme developed by Cho (1977), the collective properties of cumulus clouds for both the undisturbed and the disturbed periods are also determined. During the undisturbed period, some clouds reached as high as the 300‐mb level, however, little precipitation was produced. The total cloud mass flux is found to be negative in the upper troposphere and can be attributed to downdrafts induced by the evaporation of cloud liquid water. On the other hand, total cloud mass flux for the disturbed period is positive throughout the entire troposphere.  相似文献   

Origin of Coronal Shocks without Mass Ejections     

A. Shanmugaraju  Y.-J. Moon  K.-S. Cho  M. Dryer  S. Umapathy 《Solar physics》2006,233(1):117-127

We present an analysis of all the events (around 400) of coronal shocks for which the shock-associated metric type IIs were observed by many spectrographs during the period April 1997– December 2000. The main objective of this analysis is to give evidence for the type IIs related to only flare-blast waves, and thus to find out whether there are any type II-associated coronal shocks without mass ejections. By carefully analyzing the data from multi-wavelength observations (Radio, GOES X-ray, Hα, SOHO/LASCO and SOHO/EIT-EUV data), we have identified only 30 events for which there were actually no reports of CMEs. Then from the analysis of the LASCO and EIT running difference images, we found that there are some shocks (nearly 40%, 12/30) which might be associated with weak and narrow mass ejections. These weak and narrow ejections were not reported earlier. For the remaining 60% events (18/30), there are no mass ejections seen in SOHO/LASCO. But all of them are associated with flares and EIT brightenings. Pre-assuming that these type IIs are related to the flares, and from those flare locations of these 18 cases, 16 events are found to occur within the central region of the solar disk (longitude ≤45^∘). In this case, the weak CMEs originating from this region are unlikely to be detected by SOHO/LASCO due to low scattering. The remaining two events occurred beyond this longitudinal limit for which any mass ejections would have been detected if they were present. For both these events, though there are weak eruption features (EIT dimming and loop displacement) in the EIT images, no mass ejection was seen in LASCO for one event, and a CME appeared very late for the other event. While these two cases may imply that the coronal shocks can be produced without any mass ejections, we cannot deny the strong relationship between type IIs and CMEs.  相似文献   

Improved performance-based seismic coefficient for gravity-type quay walls based on centrifuge test results     

Lee  Moon-Gyo  Ha  Jeong-Gon  Cho  Hyung-Ik  Sun  Chang-Guk  Kim  Dong-Soo 《Acta Geotechnica》2021,16(4):1187-1204

Verifying the seismic performance of port structures when the force balance limit is exceeded is important for the performance-based seismic design of gravity-type quay walls. Over the last three decades, performance verification methods have been developed that consider the effects of the design earthquake motion, geotechnical conditions, and structural details on the deformation of a quay wall to accurately predict earthquake-induced damage. In this study, representative performance verification methods (i.e., simplified dynamic analysis methods extending from the Newmark sliding block method and performance-based seismic coefficients developed in Japan) were quantitatively assessed with actual cases of earthquake-damaged quay walls and the results of dynamic centrifuge tests previously conducted under various conditions (i.e., different wall heights, earthquake motions and the thickness of subsoil). The dynamic centrifuge test results suggested directions for improving the performance-based seismic coefficients of the representative methods, while their field applicability and reliability were confirmed according to the actual earthquake records.

  相似文献   

Development of a CO2 emission factor in Korea from sub-bituminous coal by the classification method     

Seungjin Kim  Jeongwoo Lee  Seehyung Lee  Chang-Sang Cho  Jae-Hwan Sa  Eui-Chan Jeon 《Environmental Earth Sciences》2014,72(7):2325-2332

While the Intergovernmental Panel on Climate Change classifies coal as anthracite, bituminous coal, and sub-bituminous coal, Korea only distinguishes coal as anthracite and bituminous coal while sub-bituminous coal is considered bituminous coal. As a result, Korea conducted research in the CO₂ emission factors of anthracite and bituminous coal, but largely ignored sub-bituminous coal. Therefore, the purpose of this research is to develop the CO₂ emission factor of sub-bituminous coal by classifying sub-bituminous coal from resources of bituminous coal activities collected in Korea between 2007 and 2011. The 2007–2011 average carbon content of sub-bituminous coal was analyzed to be 69.63 ± 3.11 %, the average hydrogen content 4.97 ± 0.37 %, the inherent moisture 12.60 ± 4.33 %, the total moisture 21.91 ± 5.45 %, and the dry-based gross calorific value was analyzed to be 5,914 ± 391 kcal/kg; using these analyzed values, the as-received net calorific value was found to be 20.75 ± 7.59 TJ/Gg and the CO₂ emission factor was found to be 96,241 ± 4,064 kg/TJ. In addition, the 62.7 million ton amount for the 2009 greenhouse gas emission from sub-bituminous coal as estimated with the analyzed value of this study is an amount that is equivalent to 11.1 % of the 2009 total greenhouse gas emission amount of 564.7 million tons, and this amount is larger than the 9.3 % for the industrial processes sector, 3.3 % for the agricultural sector and 2.5 % for the waste sector. Therefore, it is important to reflect the realities of Korea when estimating the greenhouse gas emission from such sub-bituminous coals.  相似文献   

Long-Wavelength Elastic Wave Propagation Across Naturally Fractured Rock Masses   总被引：1，自引：1，他引：0  

Mohd Mustaqim Mohd-Nordin  Ki-Il Song  Gye-Chun Cho  Zainab Mohamed 《Rock Mechanics and Rock Engineering》2014,47(2):561-573

Geophysical site investigation techniques based on elastic waves have been widely used to characterize rock masses. However, characterizing jointed rock masses by using such techniques remains challenging because of a lack of knowledge about elastic wave propagation in multi-jointed rock masses. In this paper, the roughness of naturally fractured rock joint surfaces is estimated by using a three-dimensional (3D) image-processing technique. The classification of the joint roughness coefficient (JRC) is enhanced by introducing the scan line technique. The peak-to-valley height is selected as a key indicator for JRC classification. Long-wavelength P-wave and torsional S-wave propagation across rock masses containing naturally fractured joints are simulated through the quasi-static resonant column (QSRC) test. In general, as the JRC increases, the S-wave velocity increases within the range of stress levels considered in this paper, whereas the P-wave velocity and the damping ratio of the shear wave decrease. In particular, the two-dimensional joint specimen underestimates the S-wave velocity while overestimating the P-wave velocity. This suggests that 3D joint surfaces should be implicated to obtain the reliable elastic wave velocity in jointed rock masses. The contact characteristic and degree of roughness and waviness of the joint surface are identified as a factor influencing P-wave and S-wave propagation in multi-jointed rock masses. The results indicate a need for a better understanding of the sensitivity of contact area alterations to the elastic wave velocity induced by changes in normal stress. This paper’s framework can be a reference for future research on elastic wave propagation in naturally multi-jointed rock masses.  相似文献   

Enhancing strategic defensive positioning and performance in the outfield     

Murray  Alan T.  Ortiz  Antonio  Cho  Seonga 《Journal of Geographical Systems》2022,24(2):223-240

Journal of Geographical Systems - Over the past 20&nbsp;years, professional and collegiate baseball has undergone a transformation, with statistics and analytics increasingly factoring into...  相似文献