• ALGAE
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• 제28권3호
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• pp.281-288
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• 2013

Photosynthetic carbon fixation regulates air-sea $CO_2$ fluxes in the waters of coral reefs. However, little has been documented on the effects of solar UV radiation (UVR, 280-400 nm) upon photosynthetic behaviors of phytoplankton dwelling in these ecosystems. In order to evaluate the aforesaid, surface dwelling tropical coral reef phytoplankton assemblages collected from the South China Sea were exposed to solar radiation (i.e., photosynthetically active radiation [PAR] + UV radiation A [UVA] + UV radiation B [UVB], 280-700 nm; PAR + UVA, 320-700 nm; and PAR, 400-700 nm) under static or simulated-mixing conditions. Under the static condition, UVA and UVB significantly reduced the carbon fixation with the maximum of 22.4 and 15.3%, respectively; while lower UVR-related photosynthetic inhibition was observed in case of phytoplankton samples being subjected to mixing. At a moderate level of mixing (i.e., circulation time 80 min), the UVA and UVB caused inhibition were lowered by 52.1 and 79.6%, respectively. Based on this it could be stated that vertical mixing induced by winds and/or tides in the natural environments could reduce the inhibitory effect of solar UVR on phytoplankton productivity in the coral reefs water.

• 대한원격탐사학회지
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• 제30권6호
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• pp.703-708
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• 2014

본 연구에서는 2006년 여름철에 MAX-DOAS를 이용하여 동북아 지역의 주요 메가시티 중 하나인 북경에서 이산화질소의 고도별 분포를 산출하였다.또한 MAX-DOAS로 산출된 이산화질소 혼합비를 검증하기 위해 MAX-DOAS로 산출된 지표에서가장 가까운 0-1 km 공기층 내에서의 이산화질소 혼합비와 지점관측장비로 지표에서 측정된 이산화질소 혼합비를 상호 비교하였다. 관측기간 동안 몇 일을 제외하고는 대체적으로 지상에서의 이산화질소 혼합비가 매우 크며, 지상으로부터 3 km 정도에서는 그 혼합비가 매우 작아 지는 것을 확인 할 수 있었다. 또한, MAX-DOAS로 산출된 0-1 km 공기층 내에서의 이산화질소 혼합비와 지점관측장비로 측정된 이산화질소 혼합비를 상호 비교했을 때 두 값들 사이의 상관관계(R)는 0.7로 계산되었으며, 두 값들 사이에 있어 차이가 발생하는 주요한 이유로서는 MAX-DOAS와 지점관측장비의 관측영역에서의 차이와 여름철 북경에서는 이산화질소의 혼합비가 고도에 따라 급격하게 감소하기 때문인 것으로 판단된다.

• 한국토양환경학회지
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• 제4권2호
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• pp.163-174
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• 1999

본 논문은 매립지의 침출수 유출로 오염된 지반 및 지하수의 효과적인 처리 방법 중의 하나인 연직 차수벽의 시공사례를 다루고 있다. 연직 차수벽의 설치 목적은 오염된 지하수의 이동을 경제적이고 효과적으로 차단하고, 차단후 차수벽 내부의 오염된 지하수를 회수하여 침출수 처리장에서 처리함으로써 추가적인 지반오염을 방지하며, 매립장의 잔여 이용 기간동안 매립장의 안전 운영의 기초를 확보하는 것이다. 현장조사의 단계에서 부터, 공법의 선정과 설계, 시공. 시공품질의 확인에 까지 일련의 과정을 보고하였다. 오염원과 오염의 원인 및 범위를 파악한 후, DMW공법과 HEC고화제를 이용하여 심층 혼합 차수층을 설치하였다. 균열이 심한 암반층의 차수를 위해서는 우레탄을 주입하여 차수층을 형성하였다. 조사기간 동안의 현장 모니터링 결과에 의하면, 토사와 암반층에 걸친 심층 혼합 차수층의 설치로 본 현장의 오염 처리는 현재를 기준으로 만족스러운 것으로 판단되었다.

• 한국물환경학회지
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• 제36권1호
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• pp.1-13
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• 2020

The purpose of this study was to investigate the thermal and chemical stratification in Lake Paldang 2013-2018 weekly using Schmidt's stability index (SSI) and the index of chemical stratification (IC-i). The annual average for SSI was 19.1 g cm/㎠ with the maximum value of 45.3 g cm/㎠ in the summer and the minimum value of 4.8 g cm/㎠ in fall-winter showing seasonal differences as well as increased vertical mixing in the summer. The lake stability increased higher in 2016 as compared with the other period. The most influential factors of thermal stratification were temperature and heavy rainfall. Especially, high water temperature and a prolonged residence duration caused by reduced rainfall and inflows could result in an increase of the stratification period. While decreasing inflow and outflow at the end of the rainfall, the thermal stratification was restrengthened within 7-14 days, and then stabilized rapidly before the rainfall. IC-DO increased with high air temperature in the spring and fall-winter. However increasing sunshine duration and residence time and decreasing rate of outflow caused an increase of IC-DO in the summer. Rainfall (less than 800 mm/year) and discharge (less than 200 CMS) significantly declined in 2015 resulting in IC-DO (0.77) increased more than three times over the other years and bottom water hypoxia occurred. The SSI and IC-i used in this study could be applied to other lakes to understand changes in stratification and mixing dynamics.

• 대한기계학회논문집A
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• 제34권7호
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• pp.813-820
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• 2010

포틀랜드 시멘트용 분쇄기는 독일과 일본 등 선진국에서 도입된 고가의 대형 기계이다. 따라서 이에 대한 체계적 정비 및 보수가 원활히 진행되어야 포틀랜드 시멘트의 생산설비에 대한 안정성을 확보할 수 있다. 한편 국내에 도입된 수직형 롤러 분쇄기는 포틀랜드 시멘트의 원료인 석회석의 시간당 생산량이 5.5MN이나 되는 세계 최대 규모의 분쇄기로서 설계 수명이 $4{\times}10^{7%}$사이클 정도이나 대략 $4{\times}10^6\;{\sim}\;8{\times}10^6$ 사이클 정도에서 파괴되고 있어 계획 예방 정비에 대한 어려움이 있으며, 수직형 롤러 분쇄기의 보수비용을 절감하기 위하여 롤러 분쇄기에 대한 효과적인 재설계가 필요한 실정이다. 따라서 본 연구에서는 확률론적인 절차가 내재되어 있어 불확실성을 다룰 수 있고, 대량의 복잡한 비선형적인 관계도 단순화의 과정 없이 연관 관계를 자체 조직화할 수 있는 인간의 뇌와 가장 유사한 병렬연산모델인 신경회로망을 수직형 롤러 분쇄기에 적용하여 최적설계를 수행하였다.

• 상하수도학회지
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• 제31권1호
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• pp.13-19
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• 2017

Relatively low efficiency in anaerobic digestion process is mainly caused by unproper mixing method. In this study, tray motion type agitator was applied in actual anaerobic digestion tank in order to improve the digestion efficiency, equalize the flow velocity distribution and energy saving. The impeller of tray motion type agitator was reciprocated vertically. Gas lift type agitator and tray motion type agitator appears almost same mixing efficiency include digestion rates. However, tray motion type agitator have shown that lower energy consumption compared to the conventional gas lift type agitator. Implementation of tray motion type agitator in the anaerobic digestion tanks contributed to the stabilization of mixing environment, efficiency and energy efficiency of the tank.

• Nuclear Engineering and Technology
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• 제47권4호
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• pp.389-397
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• 2015

The effects of mixing vanes (MVs) attached to a grid spacer on the characteristics of air-water annular flows were experimentally investigated. To know the effects, a grid spacer with or without MV was inserted in a vertical circular pipe of 16-mm internal diameter. For three cases (i.e., no spacer, spacer without MV, and spacer with MV), the liquid film thickness, liquid entrainment fraction, and deposition rate were measured by the constant current method, single liquid film extraction method, and double liquid film extraction method, respectively. The MVs significantly promote the re-deposition of liquid droplets in the gas core flow into the liquid film on the channel walls. The deposition mass transfer coefficient is three times higher for the spacer with MV than for the spacer without MV, even for cases 0.3-m downstream from the spacer. The liquid film thickness becomes thicker upstream and downstream for the spacer with MV, compared with the thickness for the spacer without MV and for the case with no spacer.

• 대한금속재료학회지
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• 제50권2호
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• pp.122-128
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• 2012

Water model experiments were carried out to understand the mixing behavior of reducing agents in molten slag through vortex stirrer, which makes use of a gravitational energy to mix reducing agent in the molten slag without imparting artificial energy. At a water flow rate of 6 L/min vortex was not generated, and a stable vortex was formed when the water flow rate was 7 L/min or higher with the present experimental apparatus. Water level increased linearly with increasing the water flow rate. In the upper vortex region, the vertical and horizontal velocities slightly decreased with increasing the water flow rate, whereas those in the lower vortex region increased remarkably. Accordingly, strong mixing behavior was obtained in the lower vortex region. Owing to the strong centrifugal force, particles move downwards with approaching the funnel wall. When 40 grams of polypropylene particles added to the lower vortex, they were instantaneously mixed well.

• Nuclear Engineering and Technology
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• 제56권3호
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• pp.1052-1065
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• 2024

Advanced Pressurized Water Reactors (APWRs) and Boiling Water Reactors (BWRs) employ a suppression pool as a heat sink to prevent containment overpressure. Steam can be discharged into the pool through multi-hole spargers or blowdown pipes in both normal and accident conditions. Direct Contact Condensation (DCC) creates sources of momentum and heat. The competition between these two sources determines the development of thermal stratification or mixing of the pool. Thermal stratification is of safety concern as it reduces the cooling capability compared to a completely mixed pool condition. In this work we develop a scaling approach to prediction of the thermal stratification in a water pool induced by steam injection through spargers. Experimental data obtained from large-scale pool tests conducted in the PPOOLEX and PANDA facilities, as well as simulation results obtained using validated codes are used to develop the scaling. Two injection orientations, namely radial injection through multi-hole Sparger Head (SH) and vertical injection through Load Reduction Ring (LRR), are considered. We show that the erosion rate of the cold layer can be estimated using the Richardson number. In this work, scaling laws are proposed to estimate both the (i) transient erosion velocity and (ii) the stable position of the thermocline. These scaling laws are then implemented into a 1D model to simulate the thermal behavior of the pool during steam injection through the sparger.

• 한국농공학회지
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• 제31권4호
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• pp.111-122
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• 1989

A multiple box model which is suitable for the prediction of water quality in shallow lakes with active mixing is a water quality model expected to be used widely in estuary reservoir. In this study, a multiple box water quality model for estuary reservoirs (MBQER) was developed arid the applicability of the MBQER was tested by applying data obtained from Asan-estuary reservoir. The results of this study can be summarized as follows. 1. The MBQER, dynamic water quality model, was developed to estimate 10-day water qualities of estuary reservoirs. For the proper analysis and the application of hydraulics needed to build a model, lake hydraulics was simplified by condisering only hydrological inflow and lake mixing currents. The box division in the MBQER is longitudinal one dimension for upper and middle part, and two layers for lower part of the reservoir. 2. The methods of box division for the multiple box model were ekamined and applied to Asan-estuary reservoir. For determining the number of boxes, Pe number and Pk number were used. In case of three boxes, the error by the model simplification would be estimated about 5 % Therefore, in Asan reservoir, the proper number of boxes was three. 3. The MBQER was calibrated and verified using measured data in Asan-estuary reservoir from 1986 to 1988. The Root Mean Squares(RMS) for the differences between measured data and simulated results by the MBQER were 1.10$^{\circ}$C C for water temperature, 75.8mg/1 for salinity, 0.082mg/1 for total-phosphorus showing good estimations. 4. Through the simulation of water temperature and salinity by the MBQER, the exchange flow and the mixing coefficients for the estuary lake were determined. As a result of simulation, the horizontal mixing coefficients in Asan-estuary reservoir were in the range of 1.07X 105 to 1.12X 105 cm$^2$/sec and vertical mixing coefficient was 2.90X 10-1 cm$^2$/sec.