• 한국환경농학회지
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• 제39권3호
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• pp.197-203
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• 2020

BACKGROUND: Most lakes have increased concerns about water pollution due to the inflow of non-point sources caused by human activities. Therefore, the lake water quality survey was conducted in order to propose effective plans for water quality management by analyzing the characteristics of lakes and the change of water quality. METHODS AND RESULTS: In order to investigate the physicochemical water quality in Daedong lake, water quality analysis was undertaken from July 2018 to June 2019. Water temperature was ranged from 7.8 to 34.3℃ and pH varied from 6.9 to 10.2. The concentration of Dissolved oxygen, Suspended solid, Biochemical Oxygen Demand (BOD), and Chemical Oxygen Demand (COD) were 5.6 ~ 17.2 mg/L, 2.4 ~ 35.3 mg/L, and 4.5 ~ 15.1 mg/L, and 0.9 ~ 2.8 mg/L, respectively. The Total Nitrogen (T-N) concentration ranged from 0.974 ~ 2.126 mg/L, and Total Phosphorus (T-P) concentration ranged from 0.014 ~ 0.057 mg/L. The Chlorophyll-a (Chl-a) ranged from 2.7 ~ 37.9 mg/㎥. Through Carlson TSIm assessment using T-P and Chl-a results, evaluating trophic state, Daedong lake was evaluated as mesotrophic. CONCLUSION: Water pollution management plan needs such as nutrient removal technology and nonpoint source management for prevention of eutrophication in Daedong lake.

• 한국군사과학기술학회지
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• 제17권4호
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• pp.463-470
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• 2014

Stealth technology of combat aircraft is most significant capability in recent air battlefield. As the detector of IR missiles is being developed, IR stealth capability which is evaluated by IR signature level become more important than it was in previous generation. Among IR signature of aircraft from various sources, aerodynamic heating dominates in long-wavelength IR spectrum of $8{\sim}12{\mu}m$. Skin temperature change by aerodynamic heating which is derived by effects of Mach number and structure. The 4th and 5th generation aircraft are selected for calculation of the skin temperature, and its height and velocity in numerical conditions are 10,000 m and Ma 0.9~1.9 respectively. Aircraft skin temperature is calculated by computing convection of fluid and conduction, convection and radiation of surface. As the aircraft accelerates to higher Mach number, maximum skin temperature increases more rapidly than average temperature and temperature distribution changes in more sharp, interactive ways. The 4th generation aircraft whose shape is more complex than that of the 5th generation aircraft have complicated temperature distribution. On the other hand, the 5th generation aircraft whose shape is relatively simple shows plain temperature distribution and lower skin temperature in terms of both average and maximum value.

• 한국입자에어로졸학회지
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• 제6권2호
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• pp.91-103
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• 2010

Size-segregated number concentration and scattering coefficient of urban aerosols were measured using an SMPS (scanning mobility particle sizer) and a nephelometer, respectively in Seoul, Korea, during the winter season of 2003. The average number concentrations of ultrafine particles (20~100 nm) and accumulation mode particles (100~600 nm) were $2,170\;particles\;cm^{-3}$ and $1,521\;particles\;cm^{-3}$, respectively. The scattering coefficient at the wavelength of 550 nm ranged from $62.6Mm^{-1}$ to $330.1Mm^{-1}$ and average value was $163.4Mm^{-1}$. The peak concentrations of ultrafine particles and accumulation mode particles were simultaneously recorded between 6:00 and 9:00 A.M., indicating the effect of vehicle emissions which are major air pollution sources in the urban atmosphere. On average, the number concentration of ultrafine particles was 1.4 times higher than that of accumulation mode particles, although it was a little higher during the morning peak time. The variation of aerosol scattering coefficient was in good agreement with that of accumulation mode particle number concentration rather than that of ultrafine particle number concentration.g coefficient was in good agreement with that of accumulation mode particle number concentration rather than that of ultrafine particle number concentration.

• 한국항행학회논문지
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• 제20권2호
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• pp.134-140
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• 2016

본 연구는 항력을 고려한 탄도미사일의 비행궤적 특성에 대한 해석이다. 탄도미사일은 대부분 대기권 밖에서 초고속으로 비행하고 RCS가 작기 때문에 요격이 어렵다. 특히 부스트 및 종말단계에서는 급격한 항력의 변화에 따라 속도의 변화가 매우 커진다. 따라서 성공적인 탄도미사일 방어체계를 구축하기 위해서는 탄도미사일의 비행궤적 해석 시 항력 특성을 반드시 고려해야 한다. 이러한 관점에서 본 연구는 항력에 대한 특성을 분석하고, 이를 고려하여 스커드 B, C 및 노동미사일의 비행궤적 특성을 도출하였다. 탄도미사일의 비행궤적 모델은 지구 자전에 의한 코리올리힘과 원심력을 반영하였으며, 탄도미사일의 제원은 공개된 자료를 활용하였다.

• 청정기술
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• 제26권1호
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• pp.79-87
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• 2020

The bio-oil produced from the fast pyrolysis of lignocellulosic biomass contains a high amount of oxygenates, causing variation in the properties of bio-oil, such as instability, high acidity, and low heating value, reducing the quality of the bio-oil. Consequently, an upgrading process should be recommended ensuring that these bio-oils are widely used as fuel sources. Catalytic fast pyrolysis has attracted a great deal of attention as a promising method for producing upgraded bio-oil from biomass feedstock. In this study, the fast pyrolysis of tulip tree was performed in a bubbling fluidized-bed reactor under different reaction temperatures, with and without catalysts, to investigate the effects of pyrolysis temperature and catalysts on product yield and bio-oil quality. The system used silica sand, ferric oxides (Fe₂O₃ and Fe₃O₄), and H-ZSM-5 as the fluidized-bed material and nitrogen as the fluidizing medium. The liquid yield reached the highest value of 49.96 wt% at 450 ℃, using Fe₂O₃ catalyst, compared to 48.45 wt% for H-ZSM-5, 47.57 wt% for Fe₃O₄ and 49.03 wt% with sand. Catalysts rejected oxygen mostly as water and produced a lower amount of CO and CO₂, but a higher amount of H₂ and hydrocarbon gases. The catalytic fast pyrolysis showed a high ratio of H₂/CO than sand as a bed material.

• 한국환경과학회지
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• 제25권6호
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• pp.865-875
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• 2016

In this study, mass concentrations and chemical compositions of $PM_{2.5}$, including water-soluble ions and elements were determined at the 1,100 m-highland of Mt. Hallasan in Jeju Island across four seasons from August 2013 to August 2014. The average mass concentration of $PM_{2.5}$ was $12.5{\pm}8.41{\mu}g/m^3$ with 45.8% of the contribution from eight water-soluble ionic species. Three ionic species ($SO{_4}^{2-}$, $NH{_4}^+$, and $NO{_3}^-$) comprised 96.2% of the total concentration of ions contained in $PM_{2.5}$ and were the dominant ions, accounting for 43.5% of the $PM_{2.5}$ mass at Mt. Hallasan. On the basis of the mass concentration level, seasonal variation, enrichment factor, and relationship among elements, we can presume that Mg, K, Ca, Mn, Fe, Co, Sr, Ba, Nd, and Dy originated mainly from crust or soil and that V, Cr, Ni, Cu, Zn, As, Cd, and Pb were significantly enriched in $PM_{2.5}$ owing to the effects of the anthropogenic emissions. These results and the local distribution of emission sources and topographic characteristics near this sampling site suggest that the compositions of $PM_{2.5}$ collected at the 1100 m-highland of Mt. Hallasan were largely influenced by inflow from outside of Jeju Island.

• 천문학회보
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• 제37권1호
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• pp.31.2-31.2
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• 2012

We present the Yonsei Evolutionary Population Synthesis (YEPS) models for spectroscopic and photometric evolutions of simple and composite stellar populations. The models are based on the most up-to-date Yonsei-Yale stellar evolutionary tracks and BaSel 3.1 flux libraries, and provide integrated spectroscopic quantities of Lick/IDS system including high-order Balmer absorption-lines. Special care has been taken to incorporate the systematic variation of horizontal branch (HB) morphology as functions of metallicity, age, alpha-element mixture, and helium abundance of simple stellar populations. Our models for normal-helium stellar populations indicate that the realistic modeling of HB and alpha-element brings about 5 Gyr and 0.1 dex differences in age and metallicity estimations, respectively, compared to those without these effects. The HB effect does not depend on the specific choice of stellar libraries and alpha-element enhancements, and this effect is non-negligible even in the metal sensitive absorption indices, such as Mg2 and Mg b. Comparison of the models to observations reveals that the HB and alpha-element effects are critical in understanding otherwise inexplicable phenomena found in globular cluster systems in the Milky Way and nearby galaxies, including the observed bimodality of the line strengths of globular clusters in massive galaxies. In addition, we found that helium-enhanced stellar populations, which are the major sources of extreme HB stars, bring about increased FUV, NUV fluxes, and thus the model colors of those filters become extremely blue. Age dating based on the YEPS model with normal-helium stellar populations reveals that the evidence for 'downsizing' of elliptical galaxies is found not only in the local field but also in Coma cluster, and that the mean age of elliptical galaxies in Coma cluster is about 1.4 Gyr younger than the mean age of those in the local field. We also find that our models with helium-enhanced subpopulations can naturally reproduce the strong UV-upturns observed in giant elliptical galaxies assuming an age similar to that of old GCs in the Milky Way.

• 한국지반공학회논문집
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• 제33권2호
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• pp.35-47
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• 2017

지반의 열적 거동은 대부분 열전도에 국한되어 연구가 진행되었으며, 자연대류 현상에 대한 연구는 매우 미비한 실정이다. 지반의 온도증가는 간극수의 밀도변화에 따른 부력을 유발하여 자연대류를 발생시키게 된다. 유체역학 관점에서 다공질 재료내의 자연대류 해석의 제약조건에 대하여 논의하고, 거시적 관점에서 완전 결합된 열-수리-역학적인 지배방정식을 이용한 대류현상에 대한 수치해석 기법을 제시하였다. 실내 열전도도 측정을 위한 탐침기 실험에 대한 수치실험은 자연대류를 무시하고 평가된 열전도도의 불확실성에 대하여 논의하고, 모델식과의 오류를 최소화하기 위한 적정한 실험조건을 제시하였다. 해저 전력선의 매설은 해저면 0.2m 깊이에서의 온도상승을 $2^{\circ}C$로 제한하고 있으나, 투수성이 큰 지반재료에 대한 수치해석결과는 기준온도를 초과하는 것으로 나타났다. 해저면의 온도와 열-수리-역학적 물성은 전력선의 매설설계에 중요한 설계인자이며 자연대류의 영향을 고려하여야 한다. 특히, 큰 투수성을 갖는 지반내에 열원이 존재하는 경우, 간극수의 밀도변화에 따른 자연대류가 중요한 열전달의 인자가 되므로 이를 고려한 해석을 수행하여야 한다.

• 농촌계획
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• 제24권4호
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• pp.99-119
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• 2018

Unit load factor, which is used for the quantification of non-point pollution in watersheds, has the limitation that it does not reflect spatial characteristics of soil, topography and temporal change due to the interannual or seasonal variability of precipitation. Therefore, we developed the method to estimate a watershed-scale non-point pollutant load using seasonal forecast data that forecast changes of precipitation up to 6 months from present time for watershed-scale water quality management. To establish a preemptive countermeasure against non-point pollution sources, it is possible to consider the unstructured management plan which is possible over several months timescale. Notably, it is possible to apply various management methods such as control of sowing and irrigation timing, control of irrigation through water management, and control of fertilizer through fertilization management. In this study, APEX-Paddy model, which can consider the farming method in field scale, was applied to evaluate the applicability of seasonal forecast data. It was confirmed that the rainfall amount during the growing season is an essential factor in the non-point pollution pollutant load. The APEX-Paddy model for quantifying non-point pollution according to various farming methods in paddy fields simulated similarly the annual variation tendency of TN and TP pollutant loads in rice paddies but showed a tendency to underestimate load quantitatively.

• 한국기계가공학회지
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• 제18권3호
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• pp.33-40
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• 2019

FDM 3D printers have become widespread, and investment in the 3D printer industry is increasing. Therefore, many 3D printers are released and the functions of products are emphasized. However, to lower unit prices, open-type 3D printers are sold in kit form, and their performance is very low. If the 3D printer has many heat sources and is sealed, there is the possibility that the main accessories (the main board, power supply, and motor) will be damaged by trapped heat. At the same time, if the ambient temperature is low due to the properties of the material, the output quality deteriorates. In this study, we analyzed the temperature rise of the main accessories and the quality of the output by the heat bed when a chamber was added to an open-type 3D printer. We also compared the quality of the output due to the air flow with the temperature rise of the main accessories. Moreover, we found the optimal value. As a result of the quality analysis, it was finally confirmed that the case with the chamber at $95^{\circ}C$ was the best for the printing condition. In addition, in the absence of the chamber, the bending of the specimen was found to be large, and in the case of the chamber, the degree of bending was slightly decreased by 0.05 mm.