• Applied Chemistry for Engineering
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• v.31 no.6
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• pp.639-645
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• 2020

Among the components of redox flow battery (RFB), the electrode serves as a diffusion layer of an electrolyte and a path for electrons and also is a major component that directly affects the RFB performance. In this paper, chloric/sulfuric mixed acidwas used as a supporting electrolyte in RFB system with Fe2+/Fe3+ and V2+/V3+ as redox couple. The optimum electrode and activation temperature were suggested by comparing the capacity, coulombic efficiency and energy efficiency according to the electrode type and activation temperature. In the RFB single cell evaluation using 5 types of carbon electrodes used in the experiments, all of them showed close to the theoretical capacity to retain the reliability of the evaluation results. GFD4EA showed relatively excellent energy efficiency and charge/discharge capacity. In order to investigate the electrochemical performance according to the activation temperature, GFD4EA electrode was activated by heat treatment at different temperatures of 400, 450, 500, 600 and 700 ℃ under an air atmosphere. Changes in physical properties before and after the activation were observed using electrode mass retention, scanning electron microscope (SEM), XPS analysis, and electrochemical performance was compared by conducting RFB single evaluation using electrodes activated at each temperature given above.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.32 no.6
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• pp.373-383
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• 2020

In this study we established an operational storm-surge system for the northwestern pacific ocean, based on the NEMO (Nucleus for European Modeling of the Ocean). The system consists of the tide and the surge models. For more accurate storm surge prediction, it can be completed not only by applying more precise depth data, but also by optimal parameterization at the boundaries of the atmosphere and ocean. To this end, we conducted several sensitivity experiments related to the application of available bathymetry data, ocean bottom friction coefficient, and wind stress and air pressure on the ocean surface during August~September 2018 and the case of typhoon SOULIK. The results of comparison and verification are presented here, and they are compared with POM (Princeton Ocean Model) based Regional Tide Surge forecasting Model (RTSM). The results showed that the RTSM_NEMO model had a 29% and 20% decrease in Bias and RMSE respectively compared to the RTSM_POM model, and that the RTSM_NEMO model had a lower overall error than the RTSM_POM model for the case of typhoon SOULIK.

• Korean Journal of Agricultural and Forest Meteorology
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• v.23 no.4
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• pp.415-423
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• 2021

Recently, an R-based point time series data validation system has been established for the statistical post processing and improvement of the National Center for AgroMeteorology-Land Atmosphere Modeling Package (NCAM-LAMP) medium-range prediction data. The time series verification system was used to compare the NCAM-LAMP with the AWS observations and GDAPS medium-range prediction model data operated by Korea Meteorological Administration. For this comparison, the model latitude and longitude data closest to the observation station were extracted and a total of nine points were selected. For each point, the characteristics of the model prediction error were obtained by comparing the daily average of the previous prediction data of air temperature, wind speed, and hourly precipitation, and then we tried to improve the next prediction data using Support Vector Machine( SVM) method. For three months from August to October 2017, the SVM method was used to calibrate the predicted time series data for each run. It was found that The SVM-based correction was promising and encouraging for wind speed and precipitation variables than for temperature variable. The correction effect was small in August but considerably increased in September and October. These results indicate that the SVM method can contribute to mitigate the gradual degradation of medium-range predictability as the model boundary data flows into the model interior.

• Atmosphere
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• v.32 no.2
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• pp.103-118
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• 2022

This study evaluates the simulated meteorological fields with a particular focus on the low-level wind, which plays an important role in air pollutants dispersion, under the varying synoptic environment. Additionally, the effects of subgrid-scale orography parameterization and improved topography/land-use data on the simulated low-level wind is investigated. The WRF model version 4.1.3 is utilized to simulate two cases that were affected by different synoptic environments. One case from 2 to 6 April 2012 presents the substantial low-level wind speed over the Korean peninsula where the synoptic environment is characterized by the baroclinic instability. The other case from 14 to 18 April 2012 presents the relatively weak low-level wind speed and distinct diurnal cycle of low-level meteorological fields. The control simulations of both cases represent the systematic overestimation of the low-level wind speed. The positive bias for the case under the baroclinic instability is considerably alleviated by applying the subgrid-scale orography parameterization. However, the improvement of wind speed for the other case showing relatively weak low-level wind speed is not significant. Applying the high-resolution topography and land-use data also improves the simulated wind speed by reducing the positive bias. Our analysis shows that the increased roughness length in the high-resolution topography and land-use data is the key contributor that reduces the simulated wind speed. The simulated wind direction is also improved with the high-resolution data for both cases. Overall, our study indicates that wind forecasts can be improved through the application of the subgrid-scale orography parameterization and high-resolution topography/land-use data.

• Clean Technology
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• v.28 no.3
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• pp.210-217
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• 2022

Boron(B) is a rare resource used for various purposes such as glass, semiconductor materials, gunpowder, rocket fuel, etc. However, Korea depends entirely on imports for boron. Considering the global boron reserves and its current production rate, boron will be depleted on earth in 50 years. Thus, a process including proper adsorbent materials recovering boron from seawater is demanded. This research proposed carbonized nanofibers prepared from electrospun PAN(polyacrylonitrile) mats as promising materials to adsorb boron in aqueous solution. First, the mechanism of boron adsorption on carbonized nanofibers was investigated by DFT(density functional method)-based molecular modeling and the calculated energetics demonstrated that the boron chemisorption on the nitrogen-doped graphene surface by a two-step dehydration is possible with viable activation energies. Then, the electrospun PAN mats were stabilized in air and then carbonized in an argon atmosphere before being immersed in the boric acid aqueous solution. Analytically, SEM(scanning electron microscopy) and Raman measurements were employed to confirm whether the electrospinning and carbonization of PAN mats proceeded successfully. Then, XPS(X-ray photoelectron spectroscopy) peak analysis showed whether the intended nitrogen-doped carbon nanofiber surface was formed and boron was properly adsorbed on nanofibers. Those results demonstrated that the carbonized nanofibers prepared from electrospun PAN mats could be feasible adsorbents for boron recovery in seawater.

• Atmosphere
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• v.31 no.5
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• pp.625-635
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• 2021

South Korea established the 2050 Carbon Neutral Plan in response to the climate crisis, and to achieve this policy, it is very important to monitor domestic carbon emissions and atmospheric carbon concentration. Both CO₂ and CO are emitted from fossil fuel combustion processes, but the relative ratios depend on the combustion efficiency and the strength of local emission regulations. In this study, the relationship between CO₂ and CO was analyzed using ground observation data for the period of 2018~2020 at Anmyeon-do site and the CO/CO₂ ratio according to regional origin during high CO₂ cases was investigated based on the footprint simulated from Stochastic Time-Inverted Lagrangian Transport (STILT) model. CO₂ and CO showed a positive correlation with correlation coefficient of 0.66 (p < 0.01), and averaged footprints during high CO₂ cases confirmed that air particles mainly originated from eastern and north-eastern China, and inland of Korean Peninsula. In addition, it was revealed that among the cases of high CO₂ concentration, when the CO/CO₂ ratio is high, the industrial area of eastern China is greatly affected, and when the ratio is low, the contribution of the domestic region is relatively high. The ratio of CO₂ and CO in this study is significant in that it can be used as a useful factor in determining the possibility of domestic and foreign origins of climate pollutants.

• Journal of Environmental Health Sciences
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• v.49 no.2
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• pp.108-117
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• 2023

Background: When particles are absorbed into the human body, they penetrate deep into the lungs and interact with the tissues of the body. Heavy metals in PM_2.5 can cause various diseases. The main source of PM_2.5 emissions in South Korea's atmosphere has been surveyed to be places of business. Objectives: The concentration of heavy metals in PM_2.5 near the Ulsan Industrial Complex was measured and a health risk assessment was performed for residents near the industrial complex for exposure to heavy metals in PM_2.5. Methods: Concentrations of heavy metals in PM_2.5 were measured at four measurement sites (Ulsan, Mipo, Onsan, Maegok) near the industrial complexes. Heavy metals were analyzed according to the Air Pollution Monitoring Network Installation and Operation Guidelines presented by the National Institute of Environmental Research. Among them, only five substances (Mn, Ni, As, Cd, Cr⁶⁺) were targeted. The risk assessment was conducted on inhalation exposure for five age groups, and the excess cancer risk and hazard quotient were calculated. Results: In the risk assessment of exposure to heavy metals in PM_2.5, As, Cd, and Cr⁶⁺ exceeded the risk tolerance standard of 10^-6 for carcinogenic hazards. The highest hazard levels were observed in Onsan and Mipo industrial complexes. In the case of non-carcinogenic hazards, Mn was identified as exceeding the hazard tolerance of 1, and it showed the highest hazard in the Ulsan Industrial Complex. Conclusions: This study presented a detailed health risk from exposure to heavy metals in PM_2.5 by industrial complexes located in Ulsan among five age groups. It is expected to be utilized as the basis for preparing damage control and industrial emission reduction measures against PM_2.5 exposure at the Ulsan Industrial Complex.

• Proceedings of the Korean Society of Embryo Transfer Conference
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• 2002.11a
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• pp.80-80
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• 2002

This study was carried out that to investigate the effects of amino acids supplemented with culture medium on development of porcine embryos cultured in vitro. Cumulus oocyte complexes (COCs) were cultured in the maturation medium containing hormones (0.5$\mu\textrm{g}$/$m\ell$ LH, 0.5$\mu\textrm{g}$/$m\ell$ FSH and 1$\mu\textrm{g}$/$m\ell$ estradiol-17${\beta}$) for 20-22 h at 39$^{\circ}C$ in an atmosphere of 5% CO$_2$in air. Subsequently, COCs were cultured in hormone-free maturation medium for 20-22 h. After maturation for 40-44h, oocytes were removed cumulus cells by pipetting and cultured with epididymal sperm for 5 h in the mTBM. Embryos obtained were divided in 4 groups (1) cultured in NCSU 23 containing 0.4% BSA to blastocyst stage(Control), (2) essential amino acids (EA), (3) non-essential amino acids (NA), (4) mixture of essential and non essential amino acid (EA+NA). All treated groups(2-4) were used a glucose free NCSU 23 medium supplemented with pyruvate (0.33 mM), lactate (4.5 mM) to morula stage. From morula to blastocyst stage embryos of all treated groups were cultured in NCSU 23 containing 0.4% BSA. The rates of cleaved oocytes at 48 h after IVF were from 82% to 88% in the groups of control, EA, NA and EA+NA, respectively. The in vitro developmental rates into blastocysts in the groups of EA and EA+NA were significantly (P<0.05) higher than those of group of control (35.1, 35.4 vs. 19.4%, respectively), however, no significant (P<0.05) between control and NA. In conclusion, supplemented with essential amino acid or mixture of essential and non essential amino acid in the culture medium at morula stage increased the rate of development to blastocyst on in vitro produced porcine embryos.

• Nuclear Engineering and Technology
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• v.54 no.11
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• pp.4348-4358
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• 2022

The thermal-hydraulics phenomena in a containment during an accident will necessarily include radiative heat transfer (i) within the gas mixture due to the high radiative absorption and emission of steam and (ii) between the gas mixture and the surrounding structures. The analysis of some previous PANDA experiments (PSI, Switzerland) demonstrated the importance of the proper modelling of radiation for the benefit of numerical simulations. These results together with dedicated scoping calculations conducted for the present experiments indicated that the radiative heat transfer is considerable, even for a very low amount of steam (≈2%). The H2P2 series conducted in the large-scale PANDA facility at the Paul-Scherrer-Institut (PSI) in the framework of the OECD/NEA HYMERES-2 project is intended to enhance the understanding of thermal radiation phenomena and to provide a benchmark for corresponding numerical simulations. Thus, the test matrix was tailored around the two opposite extremes: either gas compositions with small steam content such that radiative heat transfer phenomena can be neglected. Or gas mixtures containing larger amounts of steam, so that radiative heat transfer is expected to play a dominant role. The H2P2 series consists of 5 experiments designed to isolate the radiation phenomena from convective and diffusive effects as much as possible. One vessel with a diameter of 4 m and a height of 8 m was preconditioned with different mixtures of air / steam at room and elevated temperatures. This was followed by the build-up of a stable helium stratification at constant pressure in the upper part of the vessel. After that, helium was injected from the top into the vessel which leads to an increase of the vessel pressure and a corresponding elevation-dependent and transient rise of the gas temperature. It is shown that even the addition of small amounts of steam in the initial gas atmosphere considerably impacts the radiative heat transport throughout all phases of the experiments and markedly influences i) the monitored gas peak temperature, ii) the temperature history during the compression and iii) the following relaxation phase after the compression was stopped. These PANDA experiments are the first of its kind conducted in a large scale thermal-hydraulic facility.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.18 no.6
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• pp.253-257
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• 2008

To enhance the luminescence properties, the red phosphor composed of $(Y,\;Zn)_2O_3$:$Eu^{3+}$ as doping concentration of Zn ion is synthesized at $1200^{\circ}C$ for 6 hrs in air atmosphere by conventional solid reaction method. As a result of the red phosphor $(Y,\;Zn)_2O_3$:$Eu^{3+}$ is measured X-ray diffraction (XRD), The main peak is nearly corresponded to the same as JCPDS card (No. 41-1105). When the doping concentration of Zn ion is more than 5 mol%, However, the ZnO peak is showed by XRD analysis. Therefore, when the doping concentration of Zn ion is less than 5 mol%, the Zn ion is well mixed in $Y_2O_3$ structure without the impurity phases. The photoluminescence (PL) properties is shown as this phosphor is excited in 254 nm region and the highest emission spectra of $(Y,\;Zn)_2O_3$:$Eu^{3+}$ has shown in 612 nm region because of a typical energy transition ($^5D_0{\rightarrow}^7F_2$) of $Eu^{3+}$ ion. As the doping concentration of Zn ion is more than 10 mol%, the emission peak is suddenly decreased. when the highest emission peak as doping concentration of Zn ion is shown, the composition of this phosphor is $(Y_{0.95},\;Zn_{0.05})_2O_3$:$Eu^{3+}_{0.075}$ and the particle size analyzed by FE-SEM is confirmed from 0.4 to $3{\mu}m$.