• Journal of Korean Society of Coastal and Ocean Engineers
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• v.10 no.4
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• pp.151-164
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• 1998

Changes in tides and tidal currents in Chonsu Bay caused by the construction of Seosan A and B reclamation regions have been investigated using a depth-integrated two-dimensional tidal model. Three water level recorders were deployed for about one month and used for the specification of the open boundary condition. The computed currents were found to be in a good agreement with the measurements at two stations within Chonsu Bay. Comparison of the absolute velocities computed with the conditions before and after the embankment clearly shows that the reduction in tidal current amplitude is evident throughout the bay and the magnitude of the reduction increases to the north. Calculation shows that the embankment has advanced the time of drying at the northern part of the bay by about 51 minutes and has increased the exposure time by about 23 minutes. The high water time has advanced by about 1 hour, lowering the high water level by about 15 cm.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.154-154
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• 2022

The frequency of natural disasters, including floods and drought events, driven by climate change has increased in recent times. Investigating the climate regimes and the roles of climate variables are indispensable to forestall future climate change-related disasters. This study compares the variability of two popular and widely used climate indices i.e., the United Nations Environment Programme (UNEP) aridity index and the Modified De-Martonne (MDM) index to assess the trend of climate change in the Chungcheong provinces of South Korea. The trend of annual and monthly climate indices was conducted using a non-parametric Mann-Kendall test and Kolmogorov-Smirnov normality test with daily climate data of 48 years (1978-2020) from 10 synoptic stations. The findings indicate that UNEP and MDM indices had a wet climate regime for the annual trend, with the UNEP index indicating a relatively humid trend of 60% humid, 20% semi-arid, and 10% sub-humid for the 48-years study period. However, the MDM index showed a high frequency of a severe wet climatic condition followed by the semi-arid condition. The months of July and August had the highest occurring frequency of the wet climatic condition (90%) for both UNEP and MDM indices. Comparing the two provinces, Chungnam showed a relatively wetter climatic condition using the UNEP index, while the MDM index indicated no significant regional difference in climate regime between the two provinces. The Kolmogorov-Smirnov normality test showed that all the 10 stations are normally distributed for monthly climate conditions at a 5% significant level in the two provinces except five stations for UNEP index and four stations for MDM index in the month of January.

• The Korean Journal of Ecology
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• v.26 no.3
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• pp.143-150
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• 2003

Korea has plentiful precipitation but rainfall events concentrate on several months of rainy season in her weather condition. Korea, therefore, experiences drought for a given period every year. Moreover the soil has usually low water holding capacity, as it is composed coarse particles originated from the granite. Response of several oaks and the Korean red pine (Pinus densiflora) on water stress showed that water budget was significant factor determining vegetation distribution. In addition, dehydration level due to cold resistance mechanism of several evergreen plants during the winter season was closely related to their distribution in natural condition. Experimental result under water stress showed that the Korean red pine was very tolerant to desiccation but the seedlings showed high mortality during the dry season. The mortality tended to proportionate to soil moisture content of each site. A comparison between soil moisture content during June when it is severe dry season and moisture content of the culture soil when the pine seedlings reached the permanent wilting point due to water withheld proved that high mortality during the dry season was due to water deficit. Water potential of sample plants measured during the exposure experiment to the air pollutant showed a probability that water related factors would dominate the occurrence of visible damage and the tolerance level of sample plants. In both field survey and laboratory experiment, plants exposed to air pollution showed more rapid transpiration than those grown in the unpolluted condition. The result would due to injury of leaf surface by air pollutants. Aluminum (Al/sup 3+/) increased in the acid soil not only inhibits root growth but also leads to abnormal distribution of root system and thereby caused water stress. The water stresses due to air pollution and soil acidification showed a possibility that they play dominating roles in inducing forest decline additionally to the existing water deficit due to weather and soil conditions in Korea. Sludge, which can contribute to improve field capacity, as it is almost composed of organic matter, showed an effect ameliorating the retarded growth of plant in the acidified soil. The effect was not less than that of dolomite known in widely as such a soil ameliorator. Litter extract contributed also to mitigate the water stress due to toxic Al/sup 3+/. We prepared a model showing the potential interaction of multiple stresses, which can cause forest decline in Korea by synthesizing those results. Furthermore, we suggested restoration plans, which can mitigate such forest decline in terms of soil amelioration and vegetation restoration.

• 한국신재생에너지학회:학술대회논문집
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• 2005.06a
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• pp.339-344
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• 2005

A PEMFC system model for FCEV was constructed and simulated numerically to examine the heat/water flow of the system and air/fuel humidification process for various operation conditions (ambient pressure /temperature/humidity, operating temperature, power load). We modeled PEMFC stack which can generate maximum electricity of about 80 kW. This stack consists of 400 unit cells and each unit cell has $250cm^2$ reacting area. Uniform current density and uniform operating voltage per each cell was assumed. The results show the flow characteristics of heat and water at each component of PEMFC system in macro-scale. The capacity shortage of the radiator occurred when the ambient was hot $(over\;40^{\circ}C)$ and power level was high (over 50 kW). In spite of some heat release by evaporation of water in stack, heat unbalance reached to 20kW approximately in such a severe operating condition. This heat unbalance could be recovered by auxiliary radiators or high speed cooling fan with additional cost. In cold environment, the capacity of radiator exceeded the net heat generation to be released, which may cause a problem to drop the operating temperature of stack. We dealt with this problem by regulating mass flow rate of coolant and radiator fan speed. Finally, water balance was not easily broken when we retrieved condensed and/or unused water.

• Aerospace Engineering and Technology
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• v.3 no.1
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• pp.197-204
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• 2004

A design of regenerative cooling system of 30 ton level thrust combustion chamber for ground test has been performed. The 1-D design code has been validated by comparing with the heat flux of the NAL calorimeter for high chamber pressure and water-cooling performance of the ECC engine of MOBIS. The present design code has been confirmed to predict accurately the heat flux and water-cooling performance for high chamber pressure condition. The maximum hot-gas-side wall temperature is predicted to be about 720 K without thermal barrier coating and the coolant-side wall temperature is less than the coking temperature of RP-1. The coolant temperature rises nearly 100 K with thermal barrier coating when Jet-A1 is used as coolant.

• PNF and Movement
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• v.15 no.3
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• pp.361-371
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• 2017

Purpose: The purpose of this study was to examine the effects of performing a dual task on gait velocity, temporospatial variables, and symmetry in subjects with subacute stroke. Methods: The study included 14 independent community ambulators with gait velocity of 0.8m/s. The Korean mini-mental state examination, the Berg balance scale, the Trunk impairment scale, and the Fugl-Meyer assessment scale were used to recruit homogeneous subjects. Subjects performed a single task (10m ambulation at a comfortable speed) and a dual task (10m ambulation at a comfortable speed while carrying a water-filled glass). Gait variables were examined with the OptoGait system. Results: The findings of this study were as follows: 1) Gait velocity decreased significantly in the dual-task condition as compared to the single task condition. 2) There were no significant differences between the paretic and non-paretic stances. 3) Paretic swing decreased significantly in the dual-task condition as compared to the single task condition. 4) The non-paretic, double-limb support phase increased significantly in the dual-task condition as compared to the single- task condition. 5) There was no significant difference in temporal symmetry. 6) Non-paretic step length decreased significantly in the dual-task condition as compared to the single-task condition. 7) There was no significant difference in spatial symmetry. Conclusion: Performing dual tasks decreases gait velocity, paretic swing phase, and non-paretic step length, while it increases non-paretic double limb support. In addition, although there is no difference in temporospatial symmetry, there is high inter-subject variability in temporospatial symmetry. Thus, dual tasks should be selected in accordance with the functional level of the hemiplegic patient, and inter-subject variability of the individual should be considered when dual tasks are considered for gait-training of hemiplegic patients.

• Journal of the Korean Institute of Rural Architecture
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• v.21 no.3
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• pp.69-75
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• 2019

The purpose of this study is to provide the conservation management direction about cultural landscape of the traditional villages in the area of Huizhou through the importance-performance analysis. The results of the survey on the importance - performance of 261 people who had many visits to various cultural landscapes of Huizhou villages such as Hongchun, Sidichun etc. are as follows. It was appeared that the item of 'good air' is the highest level of importance and satisfaction and is best condition. The item of 'historical conservation' is the high level of importance, but the level of satisfaction is low, so continuous improvement is necessary. The item of 'Old garden conservation' has high satisfaction but low importance, so it needs to improve its importance through subsequent improvement. The item of 'Keeping of old cemetary and old tower' has low importance and satisfaction but it is above average, so continuous maintenance is needed. The items of 'Preservation of stone gate' and 'Preservation of famous man's birth house' all have slightly higher satisfaction and lower importance. Both items are highly satisfied with their importance, so they should avoid excessive efforts and maintain the present status. Satisfaction with the item of 'water environment and water quality' was the lowest, and the problem of the present condition is the most serious, and a major improvement is needed. The importance and satisfaction of 'Commercial development of old villages' was the lowest among all items. This item is causing serious problems and should provide an overall improvement way to drastically improve the importance and satisfaction. Concentration is necessary to improve the environment of the whole villages, to protect the ecological plants and animals in old villages, to transfer and improve the culture of old villages, to maintain sustainability of the villages, and to protect old temple and old rock in old villages. As the level of satisfaction with sustainability is the lowest in the part of 'Concentrate here', there is a great concern about sustainability. Therefore, it is necessary to focus on sustainability and concentrate on sustainable development.

• Journal of Korean Society on Water Environment
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• v.23 no.5
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• pp.591-599
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• 2007

The quality of water released from a stratified reservoir is dependent on various factors such as the location and shape of intake facility, structure of reservoir stratification, profile of water quality constituent, and withdrawal flux. Sometimes, selective withdrawal capabilities can provide the operational flexibility to meet the water quality demands both in-reservoir and downstream. The objective of this study was to evaluate the performance of a one-dimensional reservoir selective withdrawal model (SELECT) as a tool for supporting downstream water quality management for Daecheong and Imha reservoirs. The simulated water quality variables including water temperature, dissolved oxygen (DO), conductivity, turbidity were compared with the field data measured in tailwater. The model showed fairly satisfactory results and high reliability in simulating observations. The coefficients of determinant between simulated and observed turbidity values were 0.93 and 0.95 for Daecheong and Imha reservoirs, respectively. The outflow water quality was significantly influenced by water intake level under fully stratified condition, while the effect of intake amount was minor. In conclusion, the SELECT is simple but effective tool for supporting downstream water quality prediction and management for both reservoirs.

• Journal of Ginseng Research
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• v.32 no.2
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• pp.127-134
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• 2008

This study was carried out to investigate the changes of ginsenosides composition in Korean red ginseng water extract (RGWE) after heated with high temperatures above $100^{\circ}C$. RGWEs were adjusted with pH 3.0, pH 7.0 and pH 10.0, respectively, and then heated at 100,110 and $120^{\circ}C$ for 30 minutes by using autoclave. Total ginsenosides of RGWE treated with heating showed decreasing tendency when compared with control. By TLC analysis, decreasing effect of ginsenosides in RGWE were significantly observed in the acidic condition of pH 3.0, particulary. By HPLC analysis, total ginsenoside of control showed 1.89%, while those of RGWE treated with 100, 110 and $120^{\circ}C$ showed 1.22, 1.05 and 0.97%, respectively. The ratio of protopanaxadiol (PD) to protopanaxatriol (Pr) saponins in control was 1.89, while that of PD/PT in treated RGWEs were level of 1.33 to 1.47. By the result of decreased ratio of PD/PT in RGWE, it was considered that PD type saponin such as ginsenoside$-Rb_{1}$, $-Rb_{1}$, -Rc and -Rd was more unstable than PT type saponin such as ginsenoside-Re and Rg against high temperature heating above $100^{\circ}C$.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.16 no.6
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• pp.93-107
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• 2013

Construction of an artificial wetland for the growth of Sphagnum palustre with emergent macrophytes (Phragmites australis, Typha angustifolia, and Zizania latifolia) was firstly tried and the growth of those plant components according to various environmental combinations has been monitored for three years. Above-ground dry weight of Z. latifolia ($1,500g/m^2$) was higher than T. angustifolia ($900g/m^2$) and P. australis ($500g/m^2$) under most environmental conditions. In overall, planted emergent macrophytes seemed to prefer polishing sand without moss peat as a substrate and relatively deep water-depth condition (20cm) rather than shallow water-depth (5cm). Despite of high calcium content in inflow water (> 15ppm) into the constructed wetland, S. palustre populations have survived in most experimental plots during the monitoring period. Substrate layer including moss peat with high surface-area might play a role as an ion-filter. After three years, relatively thicker litter-layer in Z. latifolia plots due to vigorous growth appeared to heavily depress S. palustre by physical compressing and complete shading processes. Most of all, for the continuous growth of S. palustre, physio-chemical characteristics of water and substrate must be carefully managed. In addition, companion emergent species should be also cautiously selected not to depress S. palustre by much litter production. We suggest P. australis and T. angustifolia as companion species rather than Z. latifolia.