• Journal of Korea Water Resources Association
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• v.34 no.4
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• pp.289-301
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• 2001

A fractional step finite difference model for the longitudinal dispersion of nonconservative pollutants is applied to the Nakdong River to simulate the phenol spill accident which occurred on March, 1971. Prior to the dispersion calculation, the flow conditions are simulated to provide inputs to the dispersion model. An unsteady flow model based on Preissmann's four-point scheme is used for this purpose. Sensitivities of the dispersion calculation to empirical equations for dispersion coefficient and to the first-order decay coefficient are analyzed. The time to peak concentration at a downstream location is significantly different depending on the formula for the dispersion coefficient. Although the decay coefficient does not affect the shape of the temporal concentration distribution, the concentration values depend on the decay coefficient verb significantly. An optimization technique is used to calibrate the dispersion model as well as the flow model. The time to the peak concentration is simulated for major positions of water intake along the Nakdong River.

• Atmosphere
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• v.29 no.1
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• pp.1-12
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• 2019

For the allergy patient who needs to know the situation about the extent of pollen risk, the National Institute of Meteorological Sciences developed a pollen forecasting system based on the Community Multiscale Air Quality Modeling (CMAQ). In the old system, pollen emission from the oak was estimated just based on the airborne concentration and meteorology factors, resulted in high uncertainty. For improving the quality of current pollen forecasting system, therefore the estimation of pollen emission is now corrected based on the observation of pollen emission at the oak forest to better reflect the real emission pattern. In this study, the performance of the previous (NIMS2014) and current (NIMS2016) model system was compared using observed oak pollen concentration. Daily pollen concentrations and emissions were simulated in pollen season 2016 and accuracy of onset and end of pollen season were evaluated. In the NIMS2014 model, pollen season was longer than actual pollen season; The simulated pollen season started 6 days earlier and finished 13.25 days later than the actual pollen season. The NIMS2016 model, however, the simulated pollen season started only 1.83 days later, and finished 0.25 days later than the actual pollen season, showing the improvement to predict the temporal range of pollen events. Also, the NIMS2016 model shows better performance for the prediction of pollen concentration, while there is a still large uncertainty to capture the maximum pollen concentration at the target site. Continuous efforts to correct these problems will be required in the future.

• Current Optics and Photonics
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• v.6 no.5
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• pp.489-496
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• 2022

Our previous study on monitoring cerebral oxygenation with a variation of isoflurane concentration in a rat model showed that near-infrared spectroscopy (NIRS) signals have potential as a new depth of anesthesia (DOA) index. However, that study obtained results from the brain in a completely invasive way, which is inappropriate for clinical application. Therefore, in this follow-up study, it was investigated whether the NIRS signals measured in a minimally invasive model including the skull and cerebrospinal fluid layer (CSFL) are similar to the previous study used as a gold standard. The experimental method was the same as the previous study, and only the subject model was different. We continuously collected NIRS signals before, during, and after isoflurane anesthesia. The isoflurane concentration started at 2.5% (v/v) and decreased to 1.0% by 0.5% every 5 min. The results showed a positive linear correlation between isoflurane concentration and ratio of reflectance intensity (RRI) increase, which is based on NIRS signals. This indicates that the quality of NIRS signals passed through the skull and CSFL in the minimally invasive model is as good as the signal obtained directly from the brain. Therefore, we believe that the results of this study can be easily applied to clinics as a potential indicator to monitor DOA.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1997.10a
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• pp.117-121
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• 1997

It is shown theoretically that uniform axial dopant concentration distribution can be made throughout the crystal by continuous Czochralski process. Numerical simulation are performed for the transient two-dimensional convection-diffusion model. A typical value of the growth and system parameters for Czochralski growth of p-type, 4 inches silicon crystal was used in the numerical calculations. Using this model with proper model parameter, the axial segregation in batchwise Czochralski growth can be described. It is studied by comparing with the experimental data. With this model parameter, the uniform axial concentration distribution of dopant is predicted in continuous Czochralski process.

• Journal of Environmental Impact Assessment
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• v.3 no.2
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• pp.47-56
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• 1994

AGNPS model is an event-based model to analyze nonpoint-source and to examine potential water quality problems from agricultural watershed. This model uses a square grid-cell system to represent the spatial variability of watershed conditions, and simulates runoff, sediment, and nutrient transport for each cell. AGNPS model was applied on Yeonwha watershed, and the test results were compared with the measured data for runoff volume, peak runoff rate, suspended solids, and phosphorus concentration. The watershed of 278.8 ha was divided into 278 cells, each of which was 1 ha in size. The coefficients of determination for runoff volume and peak flow were (0.893 and 0.801 respectively from regression of the estimated values on the measured values. The concentration of suspendid solid was increased but decreased that of phosphate with runoff volume.

• Proceedings of the KIEE Conference
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• 1988.11a
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• pp.363-367
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• 1988

A simple analytical model for the lateral channel electric field in gate - offset structured Lightly Doped Drain MOSFET has been developed. The model's results agree well with two dimensional device simulations. Due to its simplicity, our model gives a better understanding of the mechanisms involved in reducing the electric field in the LDD MOSFET. The model shows clearly the dependencies of the lateral channel electric field as function of drain and gate bias conditions and process, design parameters. Advantages of analytical model over costly 2-D device simulations is to identify the effects of various parameters, such as oxide thickness, junction depth, gate / drain bias, the length and doping concentration of the lightly doped region, on the peak electric field that causes hot - electron phenomena, individually. We are able to find the optimum doping concentration of LDD minimizing the peak electric field and hot - electron effects.

• Journal of the Korean Society of Industry Convergence
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• v.6 no.4
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• pp.277-289
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• 2003

This study proposes a mathematical model to characterize the removal of nitrogen oxides in a dielectric barrier discharge plasma process. As well as the reactions between nitrogen oxides, water vapor, oxygen and nitrogen, the model takes into account the effect of ethylene often used as a chemical additive to reduce the power consumption of the process on the removal of nitrogen oxides. Since the concentrations of the radicals concerned in the main reactions including O, OH, H and N should be calculated to predict the removal efficiency of nitrogen oxides, they were theoretically derived. The parameters affecting the removal of nitrogen oxides, such as initial concentration, discharge power, humidity, and ethylene concentration were experimentally evaluated, which were compared with the calculated results to verify the validity of the model proposed. The predicted concentrations of several byproducts formed in this process were also presented and discussed. The effects of several parameters mentioned above on the removal of nitrogen oxides were reasonable described by the proposed model.

• Biotechnology and Bioprocess Engineering:BBE
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• v.6 no.1
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• pp.42-50
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• 2001

The activity of immobilized cell-support particle aggregates is influenced by physical and biochemical elements, mass transfer, and physiology. Accordingly, the mathematical model discussed in this study is capable of predicting the steady state and transient concentration profiles of the cell mass and substrate, plus the effects of the substrate and product inhibition in an immobilized cell-support aggregate. The overall mathematical model is comprised of material balance equations for the cell mass, major carbon source, dissolved oxygen, and non-biomass products in a bulk suspension along with a single particle model. A smaller bead size and higher substrate concentration at the surface of the particle, resulted in a higher supply of the substrate into the aggregate and consequently a higher biocatalyst activity.

• 연구논문집
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• s.30
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• pp.67-77
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• 2000

This study was performed to investigate the characteristics and performance of model Decanter for separating swine wastewater to solid and liquid which is slurry state with 12.6% TS. Swine wastewater of the slurry tank was pumped into model Decanter which capacity was $2m^3$/hr in 10% TS Slurry inside of bowl was separated to solid-liquid by centrifugal acceleration. Sampling was done in the section of slurry feed pipe, supernatant outflow pipe, cake discharge pipe. After solid-liquid separation TS, $COD_cr$ and slurry volume reduction effect represented 38%, 40%, 19.6% respectively. Relation factor of model Decanter operation slurry concentration, optimum retention time of slurry, overflow velocity of supernatant, supernatant concentration, sludge removal rate etc. Optimal operation conditions can be set and evaluated efficiency based on the experimental results in the case of Decanter adopted for solid-liquid separation in highly concentrated swine wastewater.

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 2003.08a
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• pp.18-27
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• 2003

The goal of the UN Framework Convention on Climate Change (UNFCCC) is to stabilize atmospheric CO2 concentration for preventing global warming in future. However, there are many unknown factors regarding stabilization of CO2 concentration. What level of concentration should be appropriate to prevent global warming？ When should we stop the increase of CO2 concentration\ulcorner What kind of countermeasures of reducing CO2 emission will be available for CO2 stabilization？(omitted)