• Journal of the Korean Wood Science and Technology
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• v.50 no.4
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• pp.272-282
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• 2022

The essential oil extracted from Citrus × natsudaidai (Yu. Tanaka) Hayata peels is known to have various biological properties. However, the chemical composition of essential oil is influenced by the ripening stages of fruits, which then affects related biological activities. This study investigates the antioxidant activities of essential oils extracted from Citrus × natsudaidai peels at different ripening stages (immature, mature, and overripe). The essential oils were extracted using the hydro-distillation method. As a result of gas chromatography-mass spectrometry (GC-MS) analysis, d-limonene was dominant and was increased as matured. However, 𝛄-terpinene was decreased. The antioxidant properties and their total phenolic content (TPC) were influenced by the ripening stages. The TPC was highest in the immature stage of essential oil (1,011.25 ± 57.15 mg GAE/100 g). 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity was excellent in the immature stage (EC₅₀ = 15.91 ± 0.38 mg/mL). 2,2'-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging activity was superior in overripe stage (EC₅₀ = 20.43 ± 0.37 mg/mL). The antioxidant activity measured using ferric reducing antioxidant power (FRAP) assay showed higher values for the essential oils in immaturity (1,342.37 ± 71.07 mg Fe²⁺/100 g). Comprehensively, the essential oil in the immature stage showed the best antioxidant activity. Finally, knowing the chemical composition and antioxidant activity at different ripening stages will provide data for selecting the right fruit.

• Journal of Korea Water Resources Association
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• v.54 no.11
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• pp.863-873
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• 2021

The mechanical dispersion which dominates solute transport in porous media is caused by the difference in flow velocity within pores. Longitudinal dispersion coefficient and longitudinal dispersivity that are hydro-dispersive parameters of advection-dispersion equation can only be obtained by experiment. Hydraulic mean radius that represents the amount and intensity of flowing water within pores can be obtained by the formula using the factors for physical properties. A slug injection test was conducted and a power type empirical formula for obtaining a longitudinal dispersivity using a hydraulic mean radius in rockfill porous media was derived. It is possible to obtain the longitudinal dispersivity depending on transport distance because it contains a formula for a scale constant, and expected to be applicable to waterways filled with homogeneous gravel and small flow rate.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.34 no.6
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• pp.211-221
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• 2022

The wave runup height is one of the most important parameters for affecting the design of coastal structures such as dikes, revetments, and breakwaters. In this study, SWASH (Zijlema et al., 2011), a non-hydrostatic pressure numerical model, was used to analyze the effect of reducing The wave runup height of solitary waves by submerged and floating rectangular obstacles. It was confirmed that the SWASH model reproduces the propagation, breaking, and runup of solitary waves quite well. In addition, it was confirmed that the wave deformation of the solitary wave by submerged and floating rectangular obstacles was well reproduced. Finally, we conducted an examination of the effect of reducing the runup height of submerged and floating rectangular obstacles. Reduced runup heights are calculated and the characteristics of runup height reduction according to the dimensions of the obstacle were analyzed. The energy attenuation effect of the floating obstacle is greater than the submerged obstacle, and it is shown to be more effective in reducing the runup height.

• International conference on construction engineering and project management
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• 2009.05a
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• pp.272-275
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• 2009

Carbon finance is the investment in Greenhouse Gas (GHG) emission reduction projects in developing countries and countries with economies in transition within the framework of the Kyoto Protocol's Clean Development Mechanism (CDM) or Joint Implementation (JI) and with creation of financial instruments, i.e., carbon credits, which are tradable in carbon market. The additional revenue generated from carbon credits will increase the bankability of projects by reducing the risks of commercial lending or grant finance. Meantime, it has also demonstrated numerous opportunities for collaborating across sectors, and has served as a catalyst in bringing climate issues to bear in projects relating to rural electrification, renewable energy, energy efficiency, urban infrastructure, waste management, pollution abatement, forestry, and water resource management. Establishing additionality is essential for successful CDM project development. One of the key steps is the investment analysis. As guided by UNFCCC, financial indicators such as IRR, NPV, DSCR etc are most commonly used in both Option II & Option III. However, economic indicator such as Economic Internal Rate of Return(EIRR) are often overlooked in Option III even it might be more suitable for the project. This could be due to the difficulties in economic analysis. Although Asian Development Bank(ADB) has given guidelines in evaluating EIRR, there are still large amount of works have to be carried out in estimating the economic, financial, social and environmental benefits in the host country. This paper will present a case study of a CDM development of a 18 MW hydro power plant with carbon finance option in central Vietnam. The estimation of respective factors in EIRR, such as Willingness to Pay(WTP), shadow price etc, will be addressed with the adjustment to Vietnam local provincial factors. The significance of carbon finance to Vietnam renewable energy development will also be addressed.

• International conference on construction engineering and project management
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• 2005.10a
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• pp.655-661
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• 2005

For a hydro power plant project, the headrace tunnel having a finished diameter of 3.3m was constructed in volcanic rocks with well-developed vertical joint and high groundwater table. The intake facility was located 20.3 km upstream of the powerhouse and headrace tunnel of 20 km in length and penstock of 440 m in height connected the intake and the powerhouse. The typical caldera lake, Lake Toba set the geology at the site; the caving of the ground caused tension cracks in the vertical direction to be developed and initial stresses at the ground to be released. High groundwater table(the maximum head of 20 bar) in the area of well-connected vertical joints delayed the progress of tunnel excavation severely due to the excessive inflow of groundwater. The excavation of tunnel was made using open-shield type TBM and mucking cars on the rail. High volume of water inflow raised the water level inside tunnel to 70 cm, 17% of tunnel diameter (3.9 m) and hindered the mucking of spoil under water. To improve the productivity, several adjustments such as modification of TBM and mucking cars and increase in the number of submersible pumps were made for the excavation of severe water inflow zone. Since the ground condition encountered during excavation turned out to be much worse, it was decided to adopt PC segment lining instead of RC lining. Besides, depending on the conditions of the water inflow, rock mass condition and internal water pressure, one of the invert PC segment lining with in-situ RC lining, RC lining and steel lining was applied to meet the site specific condition. With the adoption of PC segment lining, modification of TBM and other improvement, the excavation of the tunnel under severe groundwater condition was successfully completed.

• Tribology and Lubricants
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• v.39 no.4
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• pp.139-147
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• 2023

Cavitation phenomena observed during the operation of a submerged plain journal bearing (PJB) can affect bearing performance parameters such as dynamic coefficients, whirl frequency ratio, and critical mass. This study presents numerical solutions of the Reynolds equation for steadily and dynamically loaded submerged PJBs with half-Sommerfeld (HS), Reynolds, and Jakobsson-Floberg-Olsson (JFO) cavitation models when the supply pressure is larger or equal to the cavitation pressure. The loads at various eccentricity ratios are identical; however, the attitude angle is approximately 6% smaller when the eccentricity ratio is between 0.2 and 0.7 and the JFO model is used, compared to that when the Reynolds model is used. Dynamic coefficients obtained with the HS and Reynolds model show good agreement with each other, except for k_xz, which is sensitive to changes in the force normal to the rotor weight, and is attributed to the difference in the attitude angle obtained with each cavitation model. Stiffness coefficients are determined using the pressure distribution in the film, and therefore, when the JFO model is used, the direct stiffness coefficients are affected and show opposite signs for most eccentricity ratios. The mass-conservative JFO model can predict at least a 30% smaller critical mass compared to that using the HS and Reynolds models. Thus, the instability analysis results can change based on the cavitation model used in a submerged PJB. The results of this research indicate that the JFO model should be used when designing a rotor system supported by submerged PJBs.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.122-122
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• 2022

기후변화 대응 및 탄소 저감 노력의 일환으로 신재생에너지의 개발 및 활용이 전 세계적으로 활발하며, 우리나라에서도 2050년 탄소중립 달성을 위하여 친환경 에너지 시스템 구축에 많은 노력을 기울이고 있다. 전통적인 재생에너지인 수력은 발전의 효율성, 안정성과 발전 제어의 용이함 때문에 널리 사용되고 있으나, 경제성을 확보하기 위한 댐, 보의 설치 및 대규모 발전설비가 필요하여, 생태계, 환경 파괴 등의 문제점 등을 수반하여, 최근 들어 대규모 사업이 이루어지지 못하고 있다. 이러한 흐름에 따라 최근에는 유럽을 중심으로 친환경 소수력 발전으로 회전 나선형 아르키메데스 수차를 활용한 소수력 발전의 적용이 이루어지고 있으며, 특히 2000년대 이후 독일을 중심으로 활발히 개발되고 있다. 또한 휴대용 초소수력 발전은 새로운 산업분야로 민간용 초소수력 발전기의 개발 및 판매가 국내외에서 증가하고 있으며, 우리나라에서도 자연 하천 환경에 활용 가능한 초소수력 발전의 필요성이 꾸준히 제기되고 있다. 본 연구에서는 저유량 및 저낙차에 적용 가능한 '초소형 회전 나선형 아르키메데스 수차', 초소형 발전에 적합한 '발전기 및 발전시스템', 자연환경을 훼손하지 않는 친환경 '유도수로'로 구성되어, 원하는 하천이나 수로 등에 손쉽게 설치 가능한 초소형 소수력 발전시스템을 개발하였다. 회전 나선형 아르키메데스 수차는 3D프린터로 제작한 후, 강화 코팅제를 도포하여 내구성을 확보하였다. 상용 AC발전기, 소형 발전기용 '발전기 및 발전시스템'을 적용하고, 콘트롤 보드를 맞춤형으로 제작하여 경제성을 확보하였다. 이러한 발전 시스템은 개발 테스트 중에 있으며 향후 방류수로, 하수구 등 현장 적용을 준비 중에 있다.

• Economic and Environmental Geology
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• v.56 no.5
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• pp.501-514
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• 2023

Forest fires can generate numerous pollutants through the combustion of vegetation and cause serious environmental problems. The global warming and climate change will increase the frequency and scale of forest fires across the world. In Korea, many nuclear power plants (NPPs) are located in the East Coast where large-scale forest fires frequently occur. Therefore, understanding the sorption and transport characteristics of radionuclides in the forest fire areas is required against the severe accidents in NPPs. This article reviewed the physiochemical changes and contamination of groundwater and soil environments after forest fires, and discussed sorption and transport of radionuclides in the subsurface environment of burned forest area. We considered the geochemical factors of subsurface environment changed by forest fire. Moreover, we highlighted the need for studies on changes and contamination of subsurface environments caused by forest fires to understand more specific mechanisms.

• Journal of Advanced Technology Convergence
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• v.3 no.2
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• pp.9-15
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• 2024

Due to the high inflation rate of dining out, along with changes in group meals or cafeteria services, office workers are increasingly using workplace cafeterias to reduce their meal expenses even slightly. With the recent development of ICT technology, various fields are realizing that not only are smartphones becoming more popular, but they are also becoming an integration of the latest technologies. In this paper, we analyze the current status of cafeterias with a large number of customers and propose ways to improve problems or difficulties. Since most people always carry their smartphones for urgent communication or work tasks, we aim to develop a cafeteria management system that utilizes the NFC function of smartphones. By presenting the process from customer entry to menu selection, it will enable more efficient use of the cafeteria.

• Korean Journal of Remote Sensing
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• v.37 no.6_1
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• pp.1611-1623
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• 2021

Thisstudy demonstratessoil moisture and evapotranspiration performance using Korea Land Data Assimilation System (KLDAS) under Korea Land Information System (KLIS). Spin-up was repeated 8 times in 2018. In addition, low-resolution and high-resolution meteorological data were generated using meteorological data observed by Korea Meteorological Administration (KMA), Rural Development Administration (RDA), Korea Rural Community Corporation (KRC), Korea Hydro & Nuclear Power Co.,Ltd. (KHNP), Korea Water Resources Corporation (K-water), and Ministry of Environment (ME), and applied to KLDAS. And, to confirm the degree of accuracy improvement of Korea Low spatial resolution (hereafter, K-Low; 0.125°) and Korea High spatial resolution (hereafter, K-High; 0.01°), soil moisture and evapotranspiration to which Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2) and ASOS-Spatial (ASOS-S) used in the previous study were applied were evaluated together. As a result, optimization of the initial boundary condition requires 2 time (58 point), 3 time (6 point), and 6 time (3 point) spin-up for soil moisture. In the case of evapotranspiration, 1 time (58 point) and 2 time (58 point) spin-ups are required. In the case of soil moisture to which MERRA-2, ASOS-S, K-Low, and K-High were applied, the mean of R² were 0.615, 0.601, 0.594, and 0.664, respectively, and in the case of evapotranspiration, the mean of R² were 0.531, 0.495, 0.656, and 0.677, respectively, indicating the accuracy of K-High was rated as the highest. The accuracy of KLDAS can be improved by securing a large number of ground observation data through the results of this study and generating high-resolution grid-type meteorological data. However, if the meteorological condition at each point is not sufficiently taken into account when converting the point data into a grid, the accuracy is rather lowered. For a further study, it is expected that higher quality data can be produced by generating and applying grid-type meteorological data using the parameter setting of IDW or other interpolation techniques.