• 농촌계획
• /
• 제11권4호
• /
• pp.25-31
• /
• 2005

The present study was carried out to investigate the P fractions of surfical sediment of Dongjin sea area. Furthermore, potential released loading of adsorbed and non-apatite inorganic phosphorus were investigated in the sediment of Dongjin sea area. The contents of phosphorus fractions of the surficial sediment in Dongjin sea area were adsorbed-P 0.06%, nonapatite inorganic-P 13.02%, apatite-P 60.22%, and residual-P 26.70%. The most abundant fraction was apatite-P, residual-P, nonapatite inorganic-P, and adsorbed-P followed it. Potential released loading of adsorbed and non-apatite inorganic phosphorus surveyed 2.6 and 597ton respectively. These results show that sediment-managing and interception from external pollution are needed for water environmental maintenance of Dongjin sea area.

• Nuclear Engineering and Technology
• /
• 제31권1호
• /
• pp.29-48
• /
• 1999

Local two-phase flow parameters of subcooled flow boiling in inclined annulus were measured to investigate the effect of inclination on the internal flow structure. Two-conductivity probe technique was applied to measure local gas phasic parameters, including void fraction, vapor bubble frequency, chord length, vapor bubble velocity and interfacial area concentration. Local liquid velocity was measured by Pilot tube. Experiments were conducted for three angles of inclination; 0$^{\circ}$(vertical), 30$^{\circ}$, 60$^{\circ}$. The system pressure was maintained at atmospheric pressure. The range of average void fraction was up to 10% and the average liquid superficial velocities were less than 1.3 m/sec. The results of experiments showed that the distributions of two-phase How parameters were influenced by the angle of channel inclination. Especially, the void fraction and chord length distributions were strongly affected by the increase of inclination angle, and flow pattern transition to slug flow was observed depending on the How conditions. The profiles of vapor velocity, liquid velocity and interfacial area concentration were found to be affected by the non-symmetric bubble size distribution in inclined channel. Using the measured distributions of local phasic parameters, an analysis for predicting average void fraction was performed based on the drift flux model and flowing volumetric concentration. And it was demonstrated that the average void fraction can be more appropriately presented in terms of flowing volumetric concentration.

• 한국지하수토양환경학회지:지하수토양환경
• /
• 제15권5호
• /
• pp.16-22
• /
• 2010

Heavy metals in soils exist in various forms dependent upon surrounding conditions. As the Janghang smelter area is of concern for its high elevated heavy metal concentrations, Korean government decided to remediate the area. Main objectives of this research were; to analyze heavy metal concentrations and their existing forms in the vicinity of the smelter; and to understand differences made by analysis techniques of heavy metals. Top soils of rice field, crop field, bare field, and forestry in the area were sampled and analyzed for their physicochemical characteristics. Concentrations of Cu, Cd, Pb, and As were analyzed with two pretreatment techniques adopted using 0.1 N HCl and aqua regia. To analyze existing forms of heavy metals, Tessier's schemes for sequential extraction technique were adopted. Exchangeable fraction and carbonate bound fraction of heavy metals may pose potential threat to environment and were in the order of Pb > As > Cu > Cd. If assessing mobile fraction of heavy metals by land uses, the order was forestry > bare land > crop field > rice field. When analyzed using Tessier's scheme, high ratio of residual fractions to total arsenic concentration should be considered for remediation design of the area.

• 한국분무공학회지
• /
• 제27권3호
• /
• pp.126-133
• /
• 2022

The objective of this is to experimentally investigate the effect of mixed jet on the oxygen transfer characteristics with the primary nozzle area ratio of an annular nozzle ejector for the application of a microbial fuel cell. A direct visualization method with a high speed camera system was used to capture the horizontal mixed jet images, and a binarization technique was used to analyze the images. The clean water unsteady state technique was used for the oxygen transfer measurement. The air-water mixed jet discharging into a water tank behaved similar to a buoyancy or horizontal jet with the primary nozzle area ratio. It was found that an optimum primary nozzle area ratio was observed where the oxygen transfer performance reached its maximum value due to the decrease of air volume fraction and the increase of jet length and air bubble dispersion.

• 한국식품영양과학회지
• /
• 제26권1호
• /
• pp.54-59
• /
• 1997

토하젓의 원료인 새뱅이를 물, 에테르, 아세톤, 메탄올을 이용하여 순차적으로 추출한 다음 인체 및 식품에 유해작용을 하는 9종의 세균을 대상으로 항균성 시험을 실시한 결과는 다음과 같다. 진공동결건조한 새뱅이 분말의 용매추출 구간별 수율은 물추출구 52.0%, 에테르추출구 7.4%, 아세톤추출구 1.0%, 메탄올추출구 0.8%였다. 새뱅이의 용매추출구간별 항균성 검색 결과 시료 20$\mu\textrm{g}$/disk에 대하여 에테르추출구 8~12mm, 아세톤추출구 8~12mm, 메탄올추출구 7~9mm였으며 물 추출구는 항균성이 없었다. 새뱅이의 용매추출구간별 최저발육억제농도는 에테르추출구 250~5000$\mu\textrm{g}$/$m\ell$1, 아세톤추출구 125~500$\mu\textrm{g}$/$m\ell$, 메탄올추출구 250~500$\mu\textrm{g}$/$m\ell$ 였다. 새뱅이의 용매추출구간별 최저살균농도는 에테르추출구 2,500~10,000$\mu\textrm{g}$/$m\ell$, 아세톤추출구 1,250~10,000$\mu\textrm{g}$/$m\ell$, 메탄올추출구 5,000~10,000$\mu\textrm{g}$/$m\ell$로 나타났다.

• Environmental Analysis Health and Toxicology
• /
• 제5권3_4호
• /
• pp.19-28
• /
• 1990

Nitroarenes are ubiquitous environmental pollutants displaying potent mutagenicity in bacteria and carcinogenicity in mammal. In this study, the concentration of nitroarenes in coarse and fine particles and mutagenicity of POC$\_$N/ fraction was investigated in suspended particulates at the Shinchon and Bulkwang area of Seoul. The suspended particulates were collected bimonthly by a high volume cascade impactor air sampler from July 1987 to May 1988. Extractable organic matter was obtained by ultrasonic extraction on diethly ether/cyclohexane (8/2, v/v). Neutral fraction was obtained by liquid-liquid extraction. Polar neutral organic compounds (POC$\_$N/) was fractionated by thin-layer chromatography. Finally, the concentrations of nitroarenes in POC$\_$N/ fraction were measured and determined by capillary gas chromatography. Direct and indirect mutagenicity of POC$\_$N/ fraction were measured using Salmonella typhimurium TA 98. The result were as follows: 1) Major nitroarenes at the Shinchon area was 1-nitropyrene and at the Bulkwang area it was 2,7-dinitro-9-fluorenone during the year. 2) Average concentration of total nitroarenes measured was 67.26 ng/m$^3$in fine particles which was 1,3 folds higher that in coarse particle (52.30 ng/m$^3$). 3) Annual pattern of nitroarenes concentrations revealed that concentration during heating season (Feb., Jan., Mar.) was 2.2 folds higher than that in non heating season (May, Jul., Sep.). Concentration of each season has 157.68 ng/m$^3$and 80.39 ng/m$^3$. 4) The mutagenic activity of POC$\_$N/ fraction from fine particles was higher compared to that of coarse particles and was increased when metabolically activated, with 59 mixture. Mutagenicities, Metabolically activated, were significantly different between Shinchon and Bulkwang area, 322.8 rev/250 $\mu\textrm{g}$/plate and 286.8 rev/250 $\mu\textrm{g}$/plate, respectively. 5) Annual pattern of mutagenicity of POC$\_$N/ fraction revealed that mutagenicity during the heating season was 1.7 folds higher at Shinchon area and 1.2 folds higher at Bulkwang than during the non heating season. The variable contents and levels of nitroarenes in suspended particulates may affect human health significantly. Further studies such as risk assessment should be conducted on the basis of these kind of studies.

• 대기
• /
• 제17권4호
• /
• pp.381-391
• /
• 2007

The characteristics of flow around a single obstacle with fixed height and varied length and width are numerically investigated using a computational fluid dynamics (CFD) model. As the obstacle length increases, flow distortion near the upwind side of the obstacle increases and the size of the recirculation zone behind the obstacle also increases. As the obstacle width increases, the size of the recirculation zone decreases, despite almost invariable flow distortion near the upwind side of the obstacle. Flow passing through an obstacle is separated, one part going around the obstacle and the other crossing over the obstacle. The size of the recirculation zone is determined by the distance between the obstacle and the point (reattachment point) at which both the flows converge. When the obstacle width is relatively large, flows are reattached at the obstacle surface and their recoveries occur. Resultant shortening of the paths of flows crossing over and going around decreases the size of the recirculation zone. To support this, the extent of flow distortion defined based on the change in wind direction is analyzed. The result shows that flow distortion is largest near the ground surface and decreases with height. An increase in obstacle length increases the frontal area fraction of flow distortion around the obstacle. In the cases of increasing the width, the frontal area fraction near the upwind side of the obstacle does not change much, but near the downwind side, it becomes larger as the width increases. The frontal area fraction is in a better correlation with the size of the recirculation zone than the building aspect ratios, suggesting that the frontal area fraction is a good indicator for explaining the variation in the size of the recirculation zone with the building aspect ratios.

• 한국수학교육학회지시리즈A:수학교육
• /
• 제61권1호
• /
• pp.157-178
• /
• 2022

본 연구에서는 한국과 미국의 초등예비교사들의 분수 곱셈에 대한 이해를 살펴보기 위해서 문제제기 및 문제해결 과제의 수행 결과를 분석하였다. 연구 결과, 첫째, (분수)×(분수)의 상황에 비해서 (자연수)×(분수)에서 피승수와 승수의 위치를 혼동하여 승수를 분수가 아닌 자연수로 생각하는 경향이 더 많이 나타났다. 둘째, (분수)×(분수)에서는 집합이나 길이에 비해서 넓이 모델을 선호하는 것으로 나타났고, 대부분의 예비교사들이 주어진 수식의 계산과정이 나타나도록 모델을 연결하여 설명하였다. 이를 바탕으로 예비교사의 곱셈의미 이해에 대한 연구의 시사점을 제언하였다.

• 상하수도학회지
• /
• 제25권2호
• /
• pp.249-255
• /
• 2011

It is complicate problem to optimize removing natural organic matter (NOM) by activated carbon in drinking water treatment because the activated carbon has heterogeneous surface area and pore structure. Seven different coals based activated carbons which have different pore structures were used in the study. Sand filtered effluents which normally used as GAC adsorber influent were used. The molecular weight distribution showed that most of the NOM was bigger than 10,000Da. In this study, systematical approaches such as characteristics of surface area and pore volume were evaluated on NOM adsorption. Especially, the adsorption capacities for NOM were evaluated by effect of micro-pores and meso-pores in surface area and pore structure. The results show that the higher ratio of meso-pore compare to the micro-pore has not only the better adsorption capacities for NOM but also the higher strongly-adsorbable fraction. Therefore, the overall adsorption capacity is increased with higher meso-pore ratio with existing of reasonable micro-pore surface area and volume.

• Carbon letters
• /
• 제6권2호
• /
• pp.86-88
• /
• 2005

Mesoporous activated carbon (AC) was prepared from aged petroleum coke through chemical activation. The AC has a specific surface area of 1733 $m^2/g$ and a mean pore diameter of 2.37 nm. The volume fraction of 2 to 4nm pores is 56.74%. At a current density of 10 mA/$cm^2$, a specific capacitance of 240 F/g is achieved representing the use factor of the surface area of 69.2%. And the electrical double layer capacitor (EDLC) based on the AC shows an excellent power performance. This result suggests that the presence of high fraction of mesopores can effectively increase the adsorption efficiency of the specific surface area of the AC and enhance the power performance of EDLC based on the efficient surface area of the AC.