• Progress in Superconductivity and Cryogenics
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• v.23 no.3
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• pp.5-9
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• 2021

Comprehensive utilization of sulfur-containing iron tailings (SIT) not only solves environmental problems but also creates certain economic value. The iron element from SIT was enriched by the superconducting high gradient magnetic separation (S-HGMS) technology in this study. In the experiments, the total iron content (TFe) was increased from 26.3% to 60.5% with the total sulfur content (TS) of 5.9% under the optimal parameters, i.e., a magnetic flux density of 0.4 T, a slurry flow rate of 1500 mL/min. The high-quality sulfur-containing material with TFe of more than 60% was obtained, which can be used for preparing high-sulfur free cutting steel. The S-HGMS technology can realize the resource utilization of iron tailings with high added value.

• Steel and Composite Structures
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• v.38 no.2
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• pp.189-211
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• 2021

An analytical solution is presented to analyze the thermoelastoplastic response of a rotating thick-walled cylindrical pressure vessel made of functionally graded material (FGM). The analysis is based on Tresca's yield condition, its associated flow rule and linear strain hardening material behaviour. The uncoupled theory of thermoelasticity is used, and the plane strain condition is assumed. The material properties except for Poisson's ratio, are assumed to vary nonlinearly in the radial direction. Elastic, partially plastic, fully plastic, and residual stress states are investigated. The heat conduction equation for the one-dimensional problem in cylindrical coordinates is used to obtain temperature distribution in the vessel. It is assumed that the inner surface is exposed to an airstream and that the outer surface is exposed to a uniform heat flux. Tresca's yield criterion and its associated flow rule are used to formulate six different plastic regions for a linearly hardening condition. All these stages are studied in detail. It is shown that the thermoelastoplastic stress response of a rotating FGM pressure vessel is affected significantly by the nonhomogeneity of the material and temperature gradient. The results are validated with those of other researchers for appropriate values of the system parameters and excellent agreement is observed.

• Korean Journal of Ecology and Environment
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• v.36 no.3 s.104
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• pp.277-285
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• 2003

Temperature profiles were observed to understand seasonal variation of thermal structures in the Juam reservoir from March 2000 to May 2001. Heat flux which affects thermal structures was calculated by observed water temperature and meteorological data. Temperature became homogeneous vertically by convection due to the surface cooling in winter. Maximum heat loss through the surface (109.45W/$m^2$) occurred in December. There was a horizontal gradient of water temperature in winter. The temperature was $3^{\circ}C$ at upstream and $5^{\circ}C$ near the dam. The surface temperature increased by the increase of solar radiation in spring and summer. Maximum heat gained through the surface was 101.95 W/$m^2$ in July. Maximum surface temperature was $29^{\circ}C$ in August, whereas the bottom water was $7^{\circ}C.$ Surface mixed layer became thicker and its temperature decreased by surface heat loss in fall and winter.

• Nuclear Engineering and Technology
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• v.28 no.2
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• pp.175-184
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• 1996

A nuclide transfer by utilizing mass transfer coefficient and barrier response function defined for each barrier is proposed, by which the final nuclide transfer rate into the sea water can be evaluated. When simple and immediate quantification of the nuclide release is necessary in the conservative aspect, using this kind of approach may be advantageous since each layered barrier can be treated separately from other media in series in the repository system, making it possible to apply separate solutions in succession to other various media. Although one disadvantage is that while flux continuity can be maintained at the interface by using the exit nuclide flux from the first medium as the source flux for the next one, there may be no guarantee for concentration continuity, this problem could be eliminated assuming that there is no boundary resistance to mass transfer across the interface. Mass transfer coefficient can be determined by the assumption that the nuclide concentration gradient at the interface between adjacent barriers remains constant and barrier response function is obtained from an analytical expression for nuclide flow rate out of each barrier in response to a unit impulse into the barrier multiplied by mass transfer coefficient. Total time-dependent nuclide transfer rate from the barrier can then be obtained by convoluting the response function for the barrier with a previously calculated set of time-varying input of nuclide flow rate for the previous barrier.

• Journal of Environmental Science International
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• v.13 no.12
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• pp.1089-1102
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• 2004

Seasonal variation of biogeochemical characteristics was determined in Lake Shihwa from October 2002 to August 2003. When the lake was artificially constructed for the freshwater reservoir in 1988, the development of the strong haline density stratification resulted in two-layered system in water column and hypoxic/anoxic environment prevailed in the bottom layer due to oxidation of accumulated organic matters in the lake. Recently, seawater flux to the lake through the sluice has been increased to improve water quality in the lake since 2000, but seasonal stratification and hypoxic bottom layer of the lake still developed in the summer due to the nature of artificially enclosed lake system. As the lake is still receiving tremendous amount of organic matters and other pollutants from neighboring streams during the rainy summer season, limited seawater flux sluicing into the lake may not be enough for the physical and biogeochemical mass balance especially in the summer. The excess of accumulated organic matters in the bottom layer apparently exhausted dissolved oxygen and affected biogeochemical distributions and processes of organic and inorganic compounds in the stratified two-layered environment in the summer. During the summer, ammonia and dissolved organic carbon remarkably increased in the bottom layer due to the hypoxic/anoxic condition in the bottom layer. Phosphate also increased as the result of benthic flux from the bottom sediment. Meanwhile, dissolved organic carbon showed the highest value at the upstream area and decreased along the salinity gradient in the lake. In addition to the sources from the upstream, autochthonous origin of particulate organic carbon from algal bloom in the lake might be more important for sustaining aggravated water quality and development of deteriorated bottom environment in the summer. The removal of trace metals could be attributed to scavenging by strong insoluble metal-sulfide compounds in the hypoxic/anoxic bottom layer in the summer.

• Korean Journal of Soil Science and Fertilizer
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• v.28 no.2
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• pp.183-190
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• 1995

Various factors such as sampling height in the chamber, sampling interval, sampling time at daytime and the effects of pedoturbation on methane emission during chamber installation were evaluated using a simplified closed static chamber method to measure methane flux in paddy soils. Sampling height of the chamber for representative samples was 65cm. An additional DC fan was required to attain an even methane gradient in the chamber. Considering the change of methane concentration and air temperature in the chamber, sampling is recommended to finish within 30 minutes after starting sampling. The aim of setting DC fan in the chamber was to get the thermal equilibrium in the chamber as well as the representative samples. Suitable time to collect the gas samples representing the day's methane flux was 0900~1200 hours. Gas sampling was possible even after installation of small chambers if the elapsed time was more than 6 hours and supporting stand would be to be added to minimize pedoturbation.

• Atmosphere
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• v.15 no.2
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• pp.75-90
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• 2005

This study examines the impacts of land cover changes on the East Asia summer monsoon with the National Center for Atmospheric Research Regional Climate Model (NCAR RegCM2), coupled with Biosphere Atmosphere Transfer Scheme (BATS). To assess the goals, two types of land cover maps were used in the simulation of summer climate. One type was NCAR land cover map (CTL) and the other was current land cover map derived from satellite data (land cover: LCV). Warm and cold surface temperature biases of $1-3^{\circ}C$ occurred over central China and Mongolia in CTL. The model produced excessive precipitation over northern land area but less over southern ocean of the model domain. Changes of biophysical parameters, such as albedo, minimum stomatal resistance and roughness length, due to the land cover changes resulted in the alteration of land-atmosphere interactions. Latent heat flux and wind speed in LCV increased noticeably over central China where deciduous broad leaf trees have been replaced by mixed farm and irrigated crop. As a result, the systematic warm biases over central China were greatly reduced in LCV. Strong cooling of central China decreased pressure gradient between East Asian continent and Pacific Ocean. The decreased pressure gradient suppressed the northward transport of moisture from south China and South China Sea. These changes reduced not only the excessive precipitation over north China and Mongolia but also less precipitation over south China. However, the land cover changes increased the precipitation over the Korean Peninsula and the Japan Islands, especially in July and August.

• Journal of Korean Society for Atmospheric Environment
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• v.14 no.4
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• pp.369-377
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• 1998

To examine various aspects of Hg exchange processes, we measured Hg$^{\circ}$concentration gradients over soil surfaces in a residential area of Seoul during Sept. 1997. From these measurements, we found that Hg$^{\circ}$concentrations in lower(20 cm) and upper(200 cm) levels varied in the range of 3.15~14.38 (5.30$\pm$1.88: N=236) and 2.07~15.10ng/m$^3$(4.06$\pm$1.69: N=236), respectively. When our data were divided into emission and dry deposition, emission of Hg$^{\circ}$was overwhelmingly dominant (up to 98% in frequency) over dry deposition. The concentration gradients for emission and deposition events were 1.29$\pm$0.86(N=231) and -1.0$\pm$1.27ng/m$^3$(N=5), respectively. The observation of excessively high concentrations in both levels and development of strong gradients suggest that our study site be greatly affected by certain pollution sources of mercury. In face, those data were quite comparable to that had previously been observed from highly contaminated soil environs of Tennessee, USA. To provide some insights into the processes governing the Hg$^{\circ}$exchange processes, we have conducted correlation analyses between Hg$^{\circ}$data and other concurrently determined meteorological plus chemical data. In general, Hg$^{\circ}$concentrations of both levels exhibited similarly the existence of strong correlations with parameters like windspeed, temperature, and relative humidity. Although its concentration gradient data showed similarly strong correlations with meteorological parameters, they showed somewhat unique patterns in that their correlations with Hg$^{\circ}$concentration were noticeably stronger for the lower level than the upper level. To provide rough estimates of Hg$^{\circ}$fluxes in this study, we computed its flux using our gradient data and the predicted K values from previous studies. According to this approach, Hg$^{\circ}$emissions were generally in the range of 103$\pm$80(N=231), while its depositions, being scarcely found, were on the similar magnitude of -92$\pm$128ng/m$^2$/hr(N=5). The findings of excessive emission of Hg$^{\circ}$in residential area of Korea suggests that contamination of mercury be a significant process and hence be dealt more seriously.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.4
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• pp.632-640
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• 2017

In order to understand the seasonal and geographical characteristics of environmental factors and distribution of Escherichia coli by salinity gradient due to precipitation, we investigated abiotic and biotic factors during four seasons from February 2013 to November 2015. The study area was divided into three different zones based on salinity gradient and geo-oceanographic characteristics. During the study period, water temperature, salinity, Chlorophyll a, and secchi-depth varied in the range of $8.5-26.1^{\circ}C$, 13.5-34.4 psu, $0.4-74.0{\mu}g\;L^{-1}$, and 0.5-10.0 m, respectively. Salinity was low at Zone I, which was influenced by water flux from Tae-hwa River, especially in 2014. Salinity was gradually increased (one-way ANOVA; p < 0.05) toward Zone III located offshore of the bay. The highest colony form of E. coli was detected at Zone I. E. coli maintained a relatively low level at Zone III during all seasons. E. coli was correlated with transparency (r = -0.36; p < 0.05) and salinity (r = -0.53; p < 0.01), implying that those parameters might play important roles in the proliferation of E. coli. These results indicated that E. coli were strongly affected by frequent rain (< 50 mm) around inner stations in Ulsan Bay of Korea.

• Journal of the Korean Society of Marine Environment & Safety
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• v.20 no.1
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• pp.1-10
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• 2014

The effects of temperature, salinity and irradiance on the growth of the dinoflagellate Akashiwo sanguinea isolated from Jaran Bay were examined in the laboratory. Maximum specific growth rate($0.28day^{-1}$) was observed with combination of $25^{\circ}C$ and 30 psu. Optimal growth (${\geq}80%$ of maximum specific growth rate) was obtained at $25^{\circ}C$ with salinities of 15~35 psu. This results indicated that A. sanguinea is a stenothermal of the high water temperature and euryhaline species. The irradiance-growth curve was described as ${\mu}=0.31(I-16.87)/(I+51.19)$. The compensation photon flux density ($I_0$) and half-saturation photon flux density ($K_I$) were $16.87{\mu}mol\;m^{-2}s^{-1}$ and $84.93{\mu}mol\;m^{-2}s^{-1}$, respectively. In conclustion, A. sanguinea has advantage physiological characteristics for the species succession at the coastal areas in summer with sufficient irradiance, high water temperature and large salinity gradient.