• 천문학논총
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• 제30권2호
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• pp.447-449
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• 2015

Although the link between activity in the nuclei of galaxy and galactic mergers has been under scrutiny for several years, it is still unclear to what extent and for which populations of active galaxies merger-triggered activity is relevant. The environments of AGN allow an indirect probe of the past merger history and future merger probability of these systems, suffering less from sensitivity issues when extended to higher redshifts than traditional morphological studies of AGN host galaxies. Here we present results from our investigation of the environment of radio selected sources out to a redshift z=2. We employ the first data release J-band catalog of the new near-IR Infrared Medium-Deep Survey (IMS), 1.4 GHz radio data from the Faint Images of the Radio Sky at Twenty-cm (FIRST) survey and a deep dedicated VLA survey of the VIMOS field, covering a combined total of 20 sq. degrees. At a flux limit of the combined radio catalog of 0.1 mJy, we probe over 8 orders of magnitude of radio luminosity. Using the second closest neighbor density parameters, we test whether active galaxies inhabit denser environments. We find evidence for a sub-population of radio-selected AGN that reside in significantly overdense environments at small scales, although we do not find significant overdensities for the bulk of our sample. We show that radio-AGN in the most underdense environments have vigorous ongoing star formation. We interpret these results in terms of the triggering and fuelling mechanism of radio-AGN.

• 조명전기설비학회논문지
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• 제21권2호
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• pp.20-27
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• 2007

정보화 시대로 변화함에 따라 고품질 전력의 중요성이 강조되고 있으며 이를 보장하기 위한 전력기기 운전의 신뢰성 향상이 선결과제로 대두되었다. 특히 대용량 전력기기 중 개폐기와 차단기의 성능을 일정 수준 이상으로 유지하기 위한 예방진단기술이 발달되어 왔다. 개폐기와 차단기에서 많이 사용되는 $SF_6$ 가스의 절연성능을 검출하여 유지보수 여부를 결정하는 것이 매우 중요하다. 본 연구에서는 이러한 $SF_6$ 가스의 절연성능을 검출하기 위해 사용되는 여러 가지 방법 중에 전기방전에 의해 나타나는 여러 현상을 검출하는 센서들의 기초특성을 확인하고 파악된 특성을 통해 복수의 검출센서를 사용할 것을 제안하였다. 즉 코로나 방전이나 아크방전 시에도 사용할 수 있는 UHF 센서와 방전전류 검출기를 병용하는 것이 $SF_6$ 가스의 절연성능 확인에 유리할 것으로 판단되었다. 이외에도 가스센서를 이용한 $SF_6$ 가스의 절연상태 검출을 시도해 그 가능성을 시험해 보았다.

• Nuclear Engineering and Technology
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• 제52권1호
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• pp.59-68
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• 2020

ECCMIX component was introduced in RELAP5/MOD3 for calculating the interfacial condensation. Compared to other existing components in RELAP5, user experience of ECCMIX component is restricted to developmental assessment applications. To evaluate the capability of the ECCMIX component, ECCS experiment was conducted which included single-phase and two-phase thermal mixing. The experiment was carried out with test sections containing a main pipe (70 mm inner diameter) and a branch pipe (21 mm inner diameter) under the atmospheric pressure. The steam mass flow in the main pipe ranged from 0 to 0.0347 kg/s, and the subcooled water mass flow in the branch pipe ranged from 0.0278 to 0.1389 kg/s. The comparison of the experimental data with the calculation results illuminated that although the ECCMIX component was more difficult to converge than Branch component, it was a more appropriate manner to simulate interfacial condensation under two-phase thermal mixing circumstance, while the two components had no differences under single-phase circumstance.

• 한국포장학회지
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• 제9권1호
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• pp.33-54
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• 2003

The aim of this study was to develop a model that could be used in the design of modified atmosphere packaging (MAP) for peaches. Respiratory data at 5, 10, $20^{\circ}C$ for peaches were gathered and altered for create useful respiration model. Packaging materials were conventional low density polyethylene and polypropylene with anti-fog, and anti-fungi treatments, and thickness was $30{\mu}m$ and $50{\mu}m$ each. Permeability tests were performed to find their oxygen, carbon dioxide, water vapor transmission rate as increases in temperature. Test results were then converted to logarithm format for MAP modeling. The maximum rate of oxygen uptake increased with increasing temperature. Optimum gas composition in the package system for fruits were set according to literature and upper or lower limits of oxygen and dioxide established. To predict gas composition at certain storage time, weight of fruits, film thickness, film type, and other variables, respiration rate was studied at various storage conditions. The results of tests were used to calculate Cameron's model and converted to a cubic estimation equation. The validity of the model was tested experimentally by observing actual atmospheric changes inside packages. This result of study may be useful for designing dynamic gas exchange MAP systems for similar agricultural products.

• Journal of Welding and Joining
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• 제27권6호
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• pp.68-73
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• 2009

Recently, as titanium and titanium alloys are being increasingly used in wide areas, there are on-going researches to obtain high quality weld zone. In particular, growing interest is being drawn to laser welding, which involves low heat input and large aspect ratio in various welding processes and can facilitate shield in atmospheric condition compared with electron beam welding. The first report covered the analysis of embrittlement by the bead color of weld zone through quantitative analysis of oxygen and nitrogen and measurement of hardness as basic experiment to apply laser welding to titanium. Results indicated that the element that affect embrittlement the most was nitrogen, and as embrittlement and oxygenation go on, bead color changed to silver, gold, brown, blue and gray. This study performed butt welding of pure titanium and STS304 by using 1kW CW Nd:YAG laser, and to find out basic physical properties, evaluated welding performance by laser output, welding speed, root gap and misalignment etc, and examined mechanical properties through tensile stress and Erichsen test. The reason particles of pure titanium welded metal and HAZ are greater than STS304 is because they are pure metal and do not include many impure elements that work as nuclei in case of resolidification, thus becoming coarse columnar crystals eventually. In addition, the reason STS304 requires more energy during welding than pure titanium is because the particle size of base metal is smaller.

• 한국정밀공학회지
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• 제21권9호
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• pp.167-173
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• 2004

The heterodyne He-Ne laser interferometer is the most widely used sensing unit to measure the position error. It measures the positioning error from the displacement of a moving reflector in terms of the wave length. But, the wave length is affected by the variation of atmospheric temperature. Temperature variation of 1$^\circ C$ results in the measuring error of 1ppm. In this paper, for measuring more accurately the position error of the ultra precision stage, the refractive index compensation method is introduced. The wave length of the laser interferometer is compensated using the simultaneously measured room temperature variations in the method. In order to investigate the limit of compensation, the stationary test against two fixed reflectors mounted on the zerodur$\circledR$ plate is performed firstly. From the experiment, it is confirmed that the measuring error of the laser interferometer can be improved from 0.34${\mu}m$ to 0.11${\mu}m$ by the application of the method. Secondly, for the verification of the compensating effect, it is applied to estimate the positioning accuracy of an ultra precision aerostatic stage. Two times of the refractive index compensation are performed to acquire the positioning error of the stage from the initially measured data, that is, to the initially measured positioning error and to the measured positioning error profile after the NC compensation. Although the positioning error of an aerostatic stage cannot be clarified perfectly, it is known that by the compensation method, the measuring error by the laser interferometer can be improved to within 0.1${\mu}m$.

• 한국해양공학회지
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• 제27권5호
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• pp.10-15
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• 2013

The crack-healing behavior and corrosion resistance of SiC ceramics were investigated. Heat treatments were carried out from $900^{\circ}C$ to $1300^{\circ}C$. A corrosion test of SiC was carried out in acid and alkaline solutions under KSL1607. The results showed that heat treatment in air could significantly increase the strength. The heat-treatment temperature has a profound influence on the extent of crack healing and the degree of strength recovery. The optimum heat-treatment temperature was $1100^{\circ}C$ for one hour at an atmospheric level. In the two kinds of solutions, the cracks in a specimen were reduced with increasing time, and the surface of the crack healed specimen had a greater number of black and white spots. The strength of the corroded cracked specimen was similar to that of the cracked specimen. The strength of the corroded crack healed specimen decreased 47% and 75% compared to that of the crack healed specimen in the acid and alkaline solutions, respectively. Therefore, the corrosion of SiC ceramics is faster in an alkaline solution than in an acid solution.

• Journal of Ginseng Research
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• 제43권3호
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• pp.368-376
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• 2019

Background: In the current phytochemical research on ginseng, the differentiation and structural identification of ginsenosides isomers remain challenging. In this paper, a two-dimensional mass spectrometry (2D-MS) method was developed and combined with statistical analysis for the direct differentiation, identification, and relative quantification of protopanaxadiol (PPD)-type ginsenoside isomers. Methods: Collision-induced dissociation was performed at successive collision energy values to produce distinct profiles of the intensity fraction (IF) and ratio of intensity (RI) of the fragment ions. To amplify the differences in tandem mass spectra between isomers, IF and RI were plotted against collision energy. The resulting data distributions were then used to obtain the parameters of the fitted curves, which were used to evaluate the statistical significance of the differences between these distributions via the unpaired t test. Results: A triplet and two pairs of PPD-type ginsenoside isomers were differentiated and identified by their distinct IF and RI distributions. In addition, the fragmentation preference of PPD-type ginsenosides was determined on the basis of the activation energy. The developed 2D-MS method was also extended to quantitatively determine the molar composition of ginsenoside isomers in mixtures of biotransformation products. Conclusion: In comparison with conventional mass spectrometry methods, 2D-MS provides more direct insights into the subtle structural differences between isomers and can be used as an alternative approach for the differentiation of isomeric ginsenosides and natural products.

• Journal of Electrochemical Science and Technology
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• 제10권2호
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• pp.223-230
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• 2019

A facile method for surface coating with $Li_2TiF_6$ which has a high lithium-ion conductivity, on $LiMn_2O_4$ spinel cathode material for high performance lithium ion batteries. The surface coating is performed by using a co-precipitation method with $Li_2CO_3$ powder and $H_2TiF_6$ solution under room temperature and atmospheric pressure without special equipment. Total coating amount of $Li_2TiF_6$ is carefully controlled from 0 to 10 wt.% based on the active material of $LiMn_2O_4$. They are evaluated by a systematic combination of analyses comprising with XRD, SEM, TEM and ICP. It is found that the surface modification of $Li_2TiF_6$ is very beneficial to high cycle life and excellent rate capability by reducing surface failure and supporting lithium ions transportation on the surface. The best coating condition is found to have a high cycle life of $103mAh\;g^{-1}$ at the 100th cycle and a rate capability of $102.9mAh\;g^{-1}$ under 20 C. The detail electrochemical behaviors are investigated by AC impedance and galvanostatic charge and discharge test.

• 대기
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• 제31권2호
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• pp.157-170
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• 2021

To investigate the effect of snowfall on the traffic of general roads in Gangwon-do, case analysis was performed in Gangneung, Pyeongchang, and Chuncheon using ASOS (Automated Synoptic Observing System) snowfall data and VDS (Vehicle Detector System) traffic data. First, we analyzed how much the traffic volume and speed decrease in snowfall cases on regional roads compared to non-snow cases, and the characteristics of monthly reduction due to snowfall were investigated. In addition, Pearson correlation analysis and regression analysis were performed to quantitatively grasp the effect of snowfall on traffic volume and speed, and sensitivity tests for snowfall intensity and cumulative snowfall were performed. The results showed that the amount of snowfall caused decrease both in the traffic volume and speed from usual (non-snowfall) condition. However, the trend was different by region: The decrease rate in traffic volume was in the order of Gangneung (17~22%), Chuncheon (14~17%), and Pyeongchang (11~14%). The decrease rate in traffic speed was in the order of Chuncheon (9~10%), Gangneung (8~9%), Pyeongchang (5~6%). No significant results were found in the monthly decrease rate analysis. In all regions, traffic volume and speed showed a negative correlation with snowfall. It was confirmed that the greater the amount of traffic entering the road, the greater the slope of the trend line indicating the change in snowfall due to the traffic volume. As a result of the sensitivity test for snowfall intensity and cumulative snowfall, the snowfall information at intervals of 6-hours was the most significant.