• Korean Journal of Ecology and Environment
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• v.43 no.1
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• pp.55-68
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• 2010

The seasonal variation of microbial community, based on the bacteria, heterotrophic nanoflagellates (HNF), phytoplankton and ciliates, was investigated at three sites in the eutrophic brackish water of Lake Shihwa and its adjacent areas from May 2007 through May 2008. At the upstream-region site St. 1, compared to the other two sites, significantly lower salinities and higher concentrations of nutrients and chlorophyll $\alpha$ (Chl. $\alpha$) were recorded. The annual average abundances of bacteria at St. 1, St. 2 and St. 3 were $6.8{\times}10^6$, $7.4{\times}10^6$ and $4.6{\times}10^6\;cells\;mL^{-1}$, respectively. As for the annual average concentrations of HNF, $19{\times}10^2$, $6.7{\times}10^2$ and $5.9{\times}10^2\;cells\;mL^{-1}$, were recorded in St. 1, St. 2 and St. 3 respectively. The highest ciliate abundance appeared at St. 1 on 29 April, 2008 and in which, 99% were autotrophic ciliate Mesodinium rubrum (Myrionecta rubra). Significant linear correlations between the biomass of bacteria and Chl. $\alpha$ were found, however, no significant relationships between ciliates abudance/biomass and their prey organisms were detected in all three sites, implying relatively low energy transfer efficiencies between them. These results indicated that the trophic relationship between ciliates and their prey organisms in the microbial community might be influenced by indirect route since higher trophic level organisms did not directly correlate to those of lower trophic level, although high primary productions were detected in the eutrophic brackish water of Lake Shihwa and its adjacent areas.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.10 no.1
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• pp.100-112
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• 2005

Soil temperature was measured from the surface to 40 cm depth at three stations with different heights in tidal flat of Gomso Bay, west coast of Korea, for one month in every season 2004 to examine the thermal structure and the variation. Mean temperature in surface layer was higher in summer and lower in winter than in lower layer, reflecting the seasonal variation of vertically propagating structure of temperature by heating and cooling from the tidal flat surface. Standard deviation of temperature decreased from the surface to lower layer. Periodic variations of solar radiation energy and tide mainly caused short term variation of soil temperature, which was also intermittently influenced by precipitation and wind. Time series analysis showed the power spectral energy peaks at the periods of 24, 12 and 8 hours, and the strongest peak appeared at 24 hour period. These peaks can be interpreted as temperature waves forced by variations of solar radiation, diurnal tide and interaction of both variations, respectively. EOF analysis showed that the first and the second modes resolved 96% of variation of vertical temperature structure. The first mode was interpreted as the heating antl cooling from tidal flat surface and the second mode as the effect of phase lag produced by temperature wave propagation in the soil. The phase of heat transfer by 24 hour period wave, analyzed by cross spectrum, showed that mean phase difference of the temperature wave increased almost linearly with the soil depth. The time lags by the phase difference from surface to 10, 20 and 40cm were 3.2,6.5 and 9.8 hours, respectively. Vertical thermal diffusivity of temperature wave of 24 hour period was estimated using one dimensional thermal diffusion model. Average diffusivity over the soil depths and seasons resulted in $0.70{\times}10^{-6}m^2/s$ at the middle station and $0.57{\times}10^{-6}m^2/s$ at the lowest station. The depth-averaged diffusivity was large in spring and small in summer and the seasonal mean diffusivity vertically increased from 2 cm to 10 cm and decreased from 10 cm to 40 cm. Thermal propagation speeds were estimated by $8.75{\times}10^{-4}cm/s,\;3.8{\times}10{-4}cm/s,\;and\;1.7{\times}10^{-4}cm/s$ from 2 cm to 10 cm, 20 cm and 40 cm, respectively, indicating the speed reduction with depth increasing from the surface.

• Journal of Soil and Groundwater Environment
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• v.10 no.4
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• pp.54-61
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• 2005

An aquifer thermal energy storage (ATES) system can be very cost-effective and renewable energy sources, depending on site-specific parameters and load characteristics. In order to develop the ATES system which has certain hydrogeological characteristics, understanding the thermohydraulic process of an aquifer is necessary for a proper design of an aquifer heat storage system under given conditions. The thermohydraulic transfer for heat storage was simulated according to two sets of simple pumping and waste water reinjection scenarios of groundwater heat pump system operation in a two-layered aquifer model. In the first set of the scenarios, the movement of the thermal front and groundwater level was simulated by changing the locations of injection and pumping wells in a seasonal cycle. However, in the second set the simulation was performed in the state of fixing the locations of pumping and injection wells. After 365 days simulation period, the shape of temperature distribution was highly dependent on the injected water temperature and the distance from the injection well. A small temperature change appeared on the surface compared to other simulated temperature distributions of 30 and 50 m depths. The porosity and groundwater flow characteristics of each layer sensitively affected the heat transfer. The groundwater levels and temperature changes in injection and pumping wells were monitored and the thermal interference between the wells was analyzed to test the effectiveness of the heat pump operation method applied.

• Korean Journal of Agricultural and Forest Meteorology
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• v.18 no.4
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• pp.348-356
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• 2016

Carbon dioxide ($CO_2$) gases concentration in atmosphere has been growing since preindustrial times. By sequestering a large amount of atmospheric carbon (C), terrestrial ecosystems are thought to offer a mitigation strategy for reducing global warming. Woody agro-ecosystems such as fruit tree are among the least quantified and most uncertain elements in the terrestrial carbon cycle. $CO_2$ and energy fluxes were measured by the eddy covariance method on a 15-year old apple orchard of South Korea in 2006. Environmental parameters (net radiation, precipitation, etc.) were measured along with fluxes. The results showed that during late June, the ability to sequestrate C was significant at an apple orchard ecosystem and it reached on the peak of $-6.5g\;C\;m^{-2}\;d^{-1}$. We found that in the apple orchard, the daily average of net ecosystem exchange of $CO_2$ (NEE) and cumulative NEE on a yearly basis were $-1.1g\;C\;m^{-2}$ and $-396.9g\;C\;m^{-2}$, respectively. These results reveal that there is high carbon sequestration in the apple orchard of South Korea, which is the same magnitude with repect to that of a natural forested ecosystem of the same biome rank (temperate-humid deciduous forest).

• The Korean Journal of Applied Statistics
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• v.31 no.1
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• pp.139-153
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• 2018

This paper investigates solar power forecasting based on several time series models. First, we consider weather variables that influence forecasting procedures as well as compare forecasting accuracies between time series models such as ARIMAX, Holt-Winters and Artificial Neural Network (ANN) models. The results show that ten models forecasting 24hour data have better performance than single models for 24 hours.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.44 no.4
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• pp.366-371
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• 2011

The sea squirt Halocynthia roretzi is mainly cultured in Tongyeong, Southern coastal area of Korea. This study presents the physiological rates of respiration, excretion, feeding and assimilation efficiency of the sea squirt Halocynthia roretzi to analyze the SFG(scope for growth) and net growth efficiency, determined during 2007. Oxygen consumption and nitrogen excretion rates increased with a rise in temperature during the summer period whereas feeding rates decreased. The O:N ratio was high during winter(October to February). Assimilation efficiency showed an annual average of 75.4% during the experimental period, except during a period of elevated temperature in July to September(average $25^{\circ}C$). Net growth efficiency($K_2$) was 8.7 to 64.2% except for May to September, when temperature increased at the aquaculture farm. SFG was negative from May to September, reflecting high temperatures and low feeding rates during this period; its highest positive values occurred during winter.

• Journal of the Institute of Convergence Signal Processing
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• v.24 no.3
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• pp.140-146
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• 2023

A lot of research is being done to develop a high-efficiency heat pump to save energy. Among them, research to reduce or eliminate the phenomenon of frost occurring in the outdoor unit coil are being conducted at the same time. A constant temperature chamber that can be tested under the same conditions as natural conditions was constructed to conduct research that does not cause frost on the outdoor unit of the heat pump regardless of the season. The outdoor unit of the heat pump installed in the constant temperature chamber was simulated under the same natural conditions. As a result, it was confirmed that the mass flow rate of the refrigerant decreased as the outdoor temperature decreased, and the dryness of the refrigerant also increased linearly with the outdoor temperature.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2022.06a
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• pp.161-164
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• 2022

부유식 라이다는 해상풍력단지 조성시 필수적으로 수행하고 있는 풍황관측 업무에 새로운 패러다임을 제공하고 있는 시스템으로, 전통적으로 풍황관측을 수행하고 있던 해상기상관측탑을 대체하여 사업 초기의 대규모 공사를 획기적으로 축소하여 시간과 비용을 절약하고, 환경적 영향을 최소화 하며, 지역사회의 반발 요소까지 줄일 수 있어 해당 업계의 표준으로 자리잡고 있는 중이다. 다만 부표식의 동요에 따른 외란적 요소가 관측자료의 신뢰성에 영향을 미치는 만큼 안정적인 플랫폼의 설계 및 검증이 매우 중요한 상황이며, 국내에서는 해당기술에 대한 늦은 진입으로 인해 다수의 외산장비 제조사들이 국내시장까지 선점하고 있는 상황이다. 한국의 서해안은 천해 환경으로 조석차가 매우 커 지역에 따라 강한 조류가 반복적으로 나타나며, 계절별로 상이한 강한 에너지의 파랑이 형성되는 등 플랫폼에 안정도에 많은 영향을 미치는 바다 환경을 갖고 있다. 본 논문에서는 이러한 복잡한 환경적 특성을 갖고 있는 우리나라의 해역에 라이다 운영에 적합한 부표식에 대한 연구를 수행하며, 우선적으로 적용하였던 선박형 부표식의 최적화 설계 및 검증 사례를 소개하고, 향후 다양한 플랫폼 개발에 토대가 되는 중요 개념을 도출하고자 한다.

• Journal of Energy Engineering
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• v.5 no.1
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• pp.87-92
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• 1996

This paper formulates dynamic optimization model for Time-Of-Use Rates when a electric power system consists of three generators and a rating period is divided into three sub-periods. We use Pontryagin's Maximum Principle to derive optimal price and investment policy. Particularly the cross-price elasticities of demand are considered in the objective function. We get the following results. First, the price is equal to short-run marginal cost when the capacity is sufficient. However, if the capacity constraint is active, the capacity cost is included in the price. Therefore it is equal to the long-run marginal cost. Second, The length of rating period affects allocation of capacity cost for each price. Third, the capacity investment in dynamic optimization is proportional to the demand growth rate of electricity. However the scale of investment is affected by not only its own demand growth rate but also that of other rating period.

• Journal of the Korean Society for Marine Environment & Energy
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• v.18 no.2
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• pp.74-80
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• 2015

To assess environmental characteristics of the aquaculture area in Tongyeong, pH, dissolved oxygen (DO), dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorous (DIP) and chemical oxygen demand (COD), and acid volatile sulfur (AVS) were measured in seawater and sediment samples collected from 10 locations of Tongyeong coastal area from July to December in 2013. The quality of the seawater may be affected by seasonal variation rather than the distance from fish farm. However, sediment was contrary to seawater; the distance from fish farm may be a main factor to affect COD and AVS in sediment than season and other parameters. It is expected that contaminated organic sediments of fishery located in semi-closed bay are rapidly dispersed into surrounding waters due to fast current.