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21.
Laboratory testing of rectangular beams using a synthetic rock was used to investigate the onset of dilation and spalling.
The beams are axially compressed and subjected to 4-point bending to provide non-uniform compressive stresses. The maximum
tangential stress occurs at the top of the beam and rapidly decreases with distance from the top of the beam. This stress
distribution was used to simulate the maximum tangential stress distribution found around circular excavations. The results
showed using this beam test configuration that the onset of dilation based on beam displacement and visually observed spalling
began at approximately the same stress level. Discrete element numerical analyses (particle flow code) were used to evaluate
the stress path at various locations in the beams. The analyses revealed that spalling and dilation in the beams occurred
well below the peak strength failure envelope determined from conventional laboratory tests. The findings suggest that the
onset of dilation in laboratory tests appears to be a good indicator for assessing the stress magnitudes required to initiate
spalling. 相似文献
22.
John M. Zachara Steve M. Heald Byong-Hun Jeon Chongxuan Liu Alice C. Dohnalkova 《Geochimica et cosmochimica acta》2007,71(9):2137-2157
The subsurface behaviour of 99Tc, a contaminant resulting from nuclear fuels reprocessing, is dependent on its valence (e.g., IV or VII). Abiotic reduction of soluble Tc(VII) by Fe(II)(aq) in pH 6-8 solutions was investigated under strictly anoxic conditions using an oxygen trap (<7.5 × 10−9 atm O2). The reduction kinetics were strongly pH dependent. Complete and rapid reduction of Tc(VII) to a precipitated Fe/Tc(IV) form was observed when 11 μmol/L of Tc(VII) was reacted with 0.4 mmol/L Fe(II) at pH 7.0 and 8.0, while no significant reduction was observed over 1 month at pH 6.0. Experiments conducted at pH 7.0 with Fe(II)(aq) = 0.05-0.8 mmol/L further revealed that Tc(VII) reduction was a combination of homogeneous and heterogeneous reaction. Heterogeneous reduction predominated after approximately 0.01 mmol/L of Fe(II) was oxidized. The heterogeneous reaction was more rapid, and was catalyzed by Fe(II) that adsorbed to the Fe/Tc(IV) redox product. Wet chemical and Fe-X-ray absorption near edge spectroscopy measurements (XANES) showed that Fe(II) and Fe(III) were present in the Fe/Tc(IV) redox products after reaction termination. 57Fe-Mössbauer, extended X-ray adsorption fine structure (EXAFS), and transmission electron microscopy (TEM) measurements revealed that the Fe/Tc(IV) solid phase was poorly ordered and dominated by Fe(II)-containing ferrihydrite with minor magnetite. Tc(IV) exhibited homogeneous spatial distribution within the precipitates. According to Tc-EXAFS measurements and structural modeling, its molecular environment was consistent with an octahedral Tc(IV) dimer bound in bidentate edge-sharing mode to octahedral Fe(III) associated with surface or vacancy sites in ferrihydrite. The precipitate maintained Tc(IV)aq concentrations that were slightly below those in equilibrium with amorphous Tc(IV)O2·nH2O(s). The oxidation rate of sorbed Tc(IV) in the Fe/Tc precipitate was considerably slower than Tc(IV)O2·nH2O(s) as a result of its intraparticle/intragrain residence. Precipitates of this nature may form in anoxic sediments or groundwaters, and the intraparticle residence of sorbed/precipitated Tc(IV) may limit 99Tc remobilization upon the return of oxidizing conditions. 相似文献
23.
Elevated levels of nitrate in groundwater are an important concern for health and the environment. The overapplication of nitrogen fertilizer to croplands is one of the major sources of high nitrate content in groundwater. In this study, we analyse the nitrate concentrations in Korean groundwater based on data from groundwater quality monitoring wells (n = 1,022–2,072), which were sampled twice annually over a recent 13‐year analysis period (2001–2013). We report that groundwater nitrate levels are decreasing, despite steadily increasing groundwater use. The maximum nitrate concentration decreased from 168.91 to 48.11 mg/L, whereas the mean values also show a gradual decreasing trend. Non‐parametric Mann–Kendall tests on nitrate concentrations also confirm the decreasing trend. The nitrate decrease is more clearly evident in agricultural groundwater as compared to domestic and drinking groundwaters. This decrease of nitrate in groundwater coincides with a large decline in nitrogen fertilizer application due to reduced cropland areas, more sustainable agricultural practices, and progressive improvement of sewage disposal services. This study proposes that the long‐term adoption of best practices in agriculture has had a positive impact on groundwater nitrate control. 相似文献
24.
To enhance the understanding of solute dynamics within the stream‐to‐riparian continuum during flood event‐driven water fluctuation (i.e., flood wave), a variable saturated groundwater flow and solute transport model were developed and calibrated against in situ measurements of the Inbuk stream, Korea, where seasonal flooding prevails. The solute dynamics were further investigated for flood waves (varying by amplitude [A], duration [T], roundness [r], and skewness [tp]) that were parameterised by real‐time stream stage fluctuations. We found that the solute transferred faster and farther in the riparian zone, especially within the phreatic zone, above which in the variable saturated zone the concentration required a significantly longer time, particularly at higher altitudes, to return to the initial state. By comparison, solute transferred shallowly in the streambed where the solute plume exhibited an exponential growth trend from the centre to the bank. The dynamic changes of solute flux and mass along the stream–aquifer interface and stream concentration were linked to the shape of flood wave. As the flood wave became higher (A↗), wider (T↗), rounder (r↘), and less skewed (tp↗), the maximum solute storage in aquifer increased. Maximum stream concentration (Cstr?max) not only presented a positive linear relationship with A or tp but also showed a negative logarithmic trend with increasing T or r. The sensitivity of Cstr_max to A was approximately two times that of tp, and between these values, the r was slightly more sensitive than T. Cstr?max linearly increased as hydraulic conductivity increased and logarithmically increased as longitudinal dispersivity increased. The former relationship was more sensitive than the latter. 相似文献
25.
26.
We have studied the relatively recently discovered object 2-7-0122, with a V magnitude of 17 m , and have confirmed that it is an SX Phe variable star. Our photometry at the 1.8 m telescope of the Boyhunsan Observatory and the 1.0 m telescope of the Mount Lemon Observatory has enabled us to refine the photometric elements and to perform a frequency analysis of the light curve. We demonstrate the presence of two close frequencies, f 1 = 24.6539 cycles/day and f 2 = 24.8173 cycles/day, one of them possibly non-radial, and of several combinational frequencies. The star’s metallicity is at least two orders of magnitude lower than that of the Sun, making the star the most metal-poor SX Phe object in the Galactic field. We confirm variability of another star in the field of view, and have determined its light elements and its possible variability type (RRc). 相似文献
27.
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
28.
Jeongwoo Lee Chang-Sang Cho Ki-hyup Hong Jae-Hak Jeong Seungjin Kim Eui-Chan Jeon 《Environmental Earth Sciences》2013,70(4):1709-1715
Consumption of primary energy in Korea increased 5.25 % per year over a 10 years span starting in 1990. Korea ranked 8th in primary energy consumption in 2011; coal consumption increased 35 % from 87,827 million tons in 2006–119,321 tons in 2010. Heavy energy-consuming countries consistently conduct research to develop an emission factor of Tier 2 level, reflecting the characteristics of the fuel that they use. To calculate the emission factor of bituminous coal for fuel, this study developed emission factor and calculated emission amount by implementing fuel analysis on bituminous coal consumed in Korea between 2007 and 2009. CO2 emission factor calculated by fuel analysis method is 95,315 kg/TJ, which is 0.75 % higher than the default value suggested by IPCC. The emission amount calculated by using the CO2 emission factor in this study is 231.881 million tons, which has a difference of 1.739 million tons compared to the IPCC default value. 相似文献
29.
Tintinnid species as biological indicators for monitoring intrusion of the warm oceanic waters into Korean coastal waters 总被引：2，自引：0，他引：2
Young-Ok Kim Kyoungsoon Shin Pung-Guk Jang Hyun-Woo Choi Jae-Hoon Noh Eun-Jin Yang Eung Kim Dongchull Jeon 《Ocean Science Journal》2012,47(3):161-172
This study examined seasonal and annual occurrences of warm oceanic tintinnid species in southern Korea coastal waters. The indicative species of tintinnids was monitored using three approaches: monitoring from cruises traveling from the warm pool in the western North Pacific to the Korea Strait; biweekly or monthly monitoring in the Korea Strait; and daily monitoring in the nearshore water. Annual pulses of warm oceanic indicator species were regularly observed in the Korea Strait. In September 2008 recorded a maximum species number of warm water indicators, a representative species for warm oceanic waters, Climacocylis scalaroides was simultaneously detected in the nearshore water as well as the Korea Strait. The result indicates that the greater warm water extension into Korean coastal areas was in September 2008. Sharp declines in species diversity were observed in the transitional area between neritic and Kuroshio zone in East China Sea (ECS). Epiplocyloides reticulata, reported previously as a Kuroshio indicator, was considered an ECS indicator species, as it was undetected in the western North Pacific central zone but was found abundantly in the ECS. Tintinnid species can be used as biological indicators to detect the inflow of warm oceanic waters into Korean coastal waters. 相似文献
30.
From the eastern Indonesian cruise from November 14 to 23, 2007, CTD (conductivity, temperature, depth profiler) /ADCP (acoustic Doppler current profiler)casting and seawater sampling were done at 25 stations around Waigeo Island near New Guinea Island. It was found overall westward intrusion of the south Pacific waters into the Seram Sea and southward spreading of the north and south Pacific waters into the Seram Sea. There is westward residual flow along the channel between Waigeo and New Guinea within upper 200 m with the maximum speed up to 50 cm/s, and much weaker eastward flow in the lower layer (< 10 cm/s) due to blocking by the shallow sill at the west of the Dampier Strait. The abrupt change of bottom topography induces active horizontal and vertical mixing which results in a three-layered current system with a major through-flow of -0.99 Sv (Sv = 10 6 m 3 /s) into the Seram Sea; the transports in the upper and the lower layers are -1.14 Sv and -0.24 Sv (westward), respectively, and in the middle there is a return flow with the transport of +0.39 Sv (eastward). 相似文献