• Korean Journal of Fisheries and Aquatic Sciences
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• v.25 no.1
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• pp.15-28
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• 1992

Temporal variations of the path of the East Korea Warm Current(EKWC) which flows northward along the east coast of Korea were analysed to investigate whether the EKWC directly influences the existence of the so-called Warm Core in the Ulreung basin. From the 13 years(1975-1987) data of the Fisheries Research and Development Agency(FRDA), the $10^{\circ}C$ isotherm at the 100m depth and the depth of $2^{\circ}C$ isotherm and the temperature field at the 200m depth were used for identification of the path and the central position of the Warm Core. Sea surface winds computed from the surface pressure charts gave the monthly-averaged wind stress curl over the East Sea which was used for determination of the Sverdrup transport. And the mass transport stream functions were computed by use of the Sverdrup balance. The variations of the path show that the EKWC does not always have a fixed path and fluctuates with time. And the existence of the Warm Core is independent upon the presence of the EKWC even when the EKWC doesn't flow northward along the east coast of Korea. In view of the mass transport stream functions, the influences of the sea surface winds on the branching of the Tsushima Warm Currents and the presence of the EKWC were investigated. The presence of the EKWC may be hindered by the southward flow driven by the sea surface winds when the Tsushima currents are rather weak. A very weak correlation exists between the north-south component of the Sverdrup transport and the position of the Warm Core. However, a small but significant part of the southward transport across the latitudinal line of $38^{\circ}N$ indicates that cold water from the northern part of the East Sea may be driven and be forced to flow beneath the permanent thermocline in such a way that the thermal structure of the Warm Core and its position might be changed.

• Membrane and Water Treatment
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• v.2 no.3
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• pp.159-173
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• 2011

The air gap membrane distillation (AGMD) process was applied for water desalination. The main objective of the present work was to study the heat and mass transfer mechanism of the process. The experiments were performed on a flat sheet module using aqueous NaCl solutions as a feed. The membrane employed was hydrophobic PTFE of pore size 0.22 ${\mu}m$. A mathematical model is proposed to evaluate the membrane mass transfer coefficient, thermal boundary layers' heat transfer coefficients, membrane / liquid interface temperatures and the temperature polarization coefficients. The mass transfer model was validated by the experimentally and fitted well with the combined Knudsen and molecular diffusion mechanism. The mass transfer coefficient increased with an increase in feed bulk temperature. The experimental parameters such as, feed temperature, 313 to 333 K, feed velocity, 0.8 to 1.8 m/s (turbulent flow region) were analyzed. The permeation fluxes increased with feed temperature and velocity. The effect of feed bulk temperature on the boundary layers' heat transfer coefficients was shown and fairly discussed. The temperature polarization coefficient increased with feed velocity and decreased with temperature. The values obtained were 0.56 to 0.82, indicating the effective heat transfer of the system. The fouling was observed during the 90 h experimental run in the application of natural ground water and seawater. The time dependent fouling resistance can be added in the total transport resistance.

• Transactions of the Korean Society of Automotive Engineers
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• v.7 no.8
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• pp.116-122
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• 1999

According to the stringent exhaust emission regulation, precise control of air fuel ratio is one of the most important issues on gasoline engine. Although many researches have been carried out to identify the fuel transport phenomena in a port fueled gasoline engine, complexity of fuel film behavior in the intake port makes it difficult. The fuel film behavior was investigated recently by using visualization method and these gave us qualitative understanding. The purpose of this study is to estimate of wall wetting fuel in the intake port and the inducted fuel mass was predicted by using wall wetting fuel model . The model coefficient($\alpha$,$\beta$) and fuel film mass on the port wall were determined from measured in-cylinder HC concentration using FRFID after injection off. The fuel film mass was increased, but $\alpha$(ratio of directly inducted fuel mass into cylinder from injected fuel mass) was decreased with increasing load at the same engine speed. $\beta$is nearly constant value(0.8~0.9). when injected fuel mass is varied at 1500rpm , the calculated air fuel ratio using well wetting fuel model was nearly the same as measured by UEGO.

• Nuclear Engineering and Technology
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• v.53 no.9
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• pp.3044-3050
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• 2021

This study offers a Monte Carlo alternative for computing mass energy absorption coefficients of any material through calculation of photon energy deposited per mass of the sample and the energy flux obtained inside a sample volume. This approach is applied in this study to evaluate mass energy absorption coefficients of some amino acids found in human body at twenty-eight different photon energies between 10 keV and 20 MeV. The simulations involved a pencil beam source modeled to emit a parallel beam of mono-energetic photons toward a 1 mean free path thick sample of rectangular parallelepiped geometry. All the components in the problem geometry were surrounded by a 100 cm vacuum sphere to avoid any interactions in materials other than the absorber itself. The results computed using the Monte Carlo radiation transport packages MCNP6.2 and GAMOS5.1 were checked against the theoretical values available from the tables of XMUDAT database. These comparisons indicate very good agreement and support the conclusion that Monte Carlo technique utilized in this fashion may be used as a computational tool for determining the mass energy absorption coefficients of any material whose data are not available in the literature.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.5B
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• pp.475-483
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• 2008

2D finite element model for analysis of transport of accidentally released pollutants in the flow was developed by SUPG method, and the mass balance of this model was checked though two example problems: line source and point source problem in the straight channel and unidirectional 2D flow field, respectively. All the test cases were simulated with both SUPG and conventional Galerkin method to compare the accuraccy of the numerical mass balance. Test results show that the model with SUPG can adequately conserve the released mass though simulation than the model using Galerkin method, so the developed model verified to be appropriate to solve this accidental mass release problem.

• Journal of Environmental Science International
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• v.21 no.7
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• pp.855-863
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• 2012

This study analyzed mass concentrations of TSP, PM10 and PM2.5 and elemental constituents according to the isentropic backward trajectories of air parcel from Cheongwonin East Asia during the period January - October, 2011. Mass concentrations of the continental polluted airflow (CP) showed levels of TSP and PM10 mass concentrations higher than the continental background airflow (CB). Also, PM2.5 mass concentrations of anthropogenic fine particles ran higher in CP than in CB. The elemental constituents and elemental constituent ratio ended up varying depending on the origin of atmospheric aerosols generated. The average absolute content of elemental constituents reached its height in CB, the ratio of anthropogenically originating elements (PE) among the all elements (AE) analyzed marked a high in CP, and Mg+Na/AE reached its height in the oceanic airflow (OA). At the same time, TSP, PM10 and PM2.5 mass concentrations, the ratio of PM2.5/TSP and PE/AE element ratio ran higher in CP than CB. Episodes of large-scale transport of atmospheric pollutants as observed at Cheongwon were 8 cases and 22 days. The ratios of PM10, PM2.5 among TSP mass concentrations showed different results and the ratios of PM2.5 showed an increasing trend in the episodes of anthropogenic air pollution transport. Overall, dustfall episodes show a level of elemental constituents higher than those of anthropogenic air pollution.Dustfall episodes were observed to contain more of Fe, Al and Ca originating from continental soils and those of air pollution were observed to contain more of Zn, Mn, Cu and Pb. By difference in contents of absolute elemental constituents, episodes of anthropogenic air pollution showed a high PE/AE rate, and dustfall episodes a high SE/AE rate.

• Journal of the Korean Society of Groundwater Environment
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• v.3 no.2
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• pp.51-59
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• 1996

In case waste disposal site is to be constructed close to the underground facilities such as LPG storage cavern which is completely maintained by groundwater pressure, it is generally requested that the possibility on leachate contamination of cavern area be reviewed and the countermeasure, if it is estimated cavern area is severely affected by leachate, be taken into consideration. Prediction was performed and leachate control plan was made using by analytical and the numerical analysis on the leachate migration which is likely to happen at the area between the proposed waste disposal site and the underground LPG storage cavern located at the U petrochemical complex. Analytical solutions were obtained by the conservative mass advection-diffusion equation and the effect of advection and dispersion factor on the leachate migration was reviewed through peclet number calculation and the functional relationship between the factors and leachate transport velocity was established, which leads to enable us to predict the leachate transport velocity without difficulties when different parameters (factors) are used for analytical solution. Numerical solutions were obtained by FEM using AQUA2D which is for the simulation of groundwater flow and contaminant transport. 3-D discrete fracture models were simulated and fracture flow analysis was performed and feasibility study on the water-curtain system was conducted through the fracture connectivity analysis in rock mass. As results of those analyses, it was interpreted that the leachate would trespass on the LPG storage cavern area in 30 years from the proposed wate disposal site and the vertical water-curtain system was effective mathod for the prevention of leachate's migration further into the cavern area.

• Asian Journal of Atmospheric Environment
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• v.9 no.4
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• pp.237-246
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• 2015

We conducted intensive observations of ozone, CO, $NO_x$ (=NO and $NO_2$), $NO_y$ (total odd nitrogen species including particulate nitrate) and total nitrate (the sum of gaseous $HNO_3$ and particulate nitrate) at Cape Hedo, Okinawa, Japan, from 19 March to 3 April, 2009, to investigate ozone production during long-range transport from the Asian continent. Ozone production efficiency (OPE) was used to evaluate photochemical ozone production. OPE is defined as the number of molecules of ozone produced photochemically during the lifetime of a $NO_x$ molecule. OPE is calculated by the ratio of the concentration increase of ozone to that of $NO_z$ ($=NO_y-NO_x$). Average OPE during observation was estimated to be $12.6{\pm}0.5$, but concentrations of ozone increased nonlinearly with those of $NO_z$. This non-linearity suggests that OPE depends on air mass origin and $NO_z$ concentrations. There were very different values of OPE for the same air mass origin, so that only the air mass origin alone does not control OPE. OPE was low when $NO_z$ concentration was high. We examined the correlation between $NO_z$ and $CO/NO_y$ ratios, which we used instead of the ratio of non-methane hydrocarbons (NMHCs) to $NO_x$. The $CO/NO_y$ ratios decreased with increasing $NO_z$ concentrations. These results indicate that competition reactions of OH with NMHCs and $NO_2$ are the rate determining steps of photochemical ozone production during long-range transport from the Asian continent to Cape Hedo, for high concentrations of nitrogen oxides.

• Journal of the Korean Electrochemical Society
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• v.12 no.4
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• pp.329-334
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• 2009

This study is to develop a fuel cell system applicable to an in situ NMR (Nuclear magnetic resonance) diagnosis. The in situ NMR can be used in real time monitoring of various reactions occurring in the fuel cell, such as oxidation of fuel, reduction of oxygen, transport phenomena, and component degradation. The fuel cell for this purpose is, however, to be operated in a specifically designed tubular shape toroid cavity detector (TCD), which constrains the fuel cell to have a tubular shape. This may cause difficulties in effective mass transport of reactants/products and uniform distribution of assembly pressure. Therefore, a new flow field designed in a particular way is necessary to enhance the mass transport in the tubular fuel cell. In this study, a tubular-shaped close-type flow field made of non-magnetic material is developed. With this flow field, oxygen is effectively delivered to the cathode surface and the produced water is readily removed from the membrane-electrode assembly to prevent flooding. The resulting DMFC (direct methanol fuel cell) outperforms the open-type flow field and exhibits $36\;mW/cm^2$ even at room temperature.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 2000.06a
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• pp.65-86
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• 2000

Rare earth-doped ceria powders with a composition of Ce0.8R0.2O1.9(R=Yb, Y, Gd, Sm, Nd and La) were prepared by heating the oxalate coprecipitate. The green compacts began to shrink at 600$^{\circ}$-700$^{\circ}C$. The relative density after the sintering at 1200$^{\circ}$ and 1400$^{\circ}C$ became higher for the higher green density. The samples were densified above 98% relative density by the sintering ant 1600$^{\circ}C$ for 4 h and the grain sizes (4.7-7.6$\mu\textrm{m}$) showed a tendency to become larger with increasing ionic radius of doped-rare earth element. In the intial stag of sintering at 700$^{\circ}$-800$^{\circ}C$, the dominant mass transport process changed from lattice diffusion to grain boundary diffusion to grain boundary diffusion with heating time. The porosity during the intermediated and final stage of the sintering at 1200$^{\circ}$ and 1400$^{\circ}C$ decreased by the mass transport through lattice diffusion with grain growth.