• 한국가스학회지
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• 제22권4호
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• pp.32-38
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• 2018

본 연구는 불화 수소 탱크 컨테이너 하역장에서 불화수소 누출 시 누출량 및 확산 정도를 정량적으로 평가하여 동종사고의 재발을 방지하고 안전성 향상방안을 제시하는데 목적이 있다. 2012년 H사에서는 최대 저장량이 18 Ton인 탱크컨테이너에서 누출사고가 발생하여 인근 지역으로 8 Ton이 누출되었고, 그로인해 사회적 이슈가 되었다. 가우시안 플럼(Gaussian plume) 모델을 이용하여 계산한 결과 누출지점으로부터 반경 1,321m까지의 농도가 20ppm 이상으로 예측되었다. 2014년 R사에서 발생한 불화수소 누출사고에서는 누출량이 11.02kg으로 추정되었고, 그 중 2.9kg이 세정기로 회수되었다. 가우시안 플럼 모델을 사용하여 계산 한 결과, 누출 원으로 부터 20ppm 이상의 농도를 갖는 피해 범위가 반경 69m로 예상되었다. 위의 두 가지 사고를 비교 한 결과, 누출량은 약 987배 차이가 발생했고, 피해 지역은 19 배 이상 차이가 나는 것으로 나타났다. 따라서 보호구의 착용, 하역 장소의 밀폐 및 세정기 설치, 그리고 비상훈련을 실시하여 하역장에서 불화수소가 대량으로 누출되는 사고가 발생하지 않도록 관리해야 한다는 결론을 얻었다.

• 폴리머
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• 제30권1호
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• pp.90-94
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• 2006

다중벽 탄소 나노튜브(multi-walled carbon nanotubes, MWNTs)를 포함하고 있는 poly(methyl methacrylate)(PMMA) 나노섬유를 전기 방사법에 의해 제작하였다. 주사 전자 현미경을 통하여 용매의 종류(dimethyl formamide, chloroform and toluene)와 탄소 나노튜브의 함량(0.5 and $3.0\;wt\%$)에 의해 나노섬유 표면의 형상과 탄소 나노튜브와 나노섬유의 구조가 영향을 받았다. 집적판의 전극 모양을 조절함으로써 나노섬유의 정렬이 가능하였다. 고분자 사슬의 회전 반경과 탄소 나노튜브의 크기의 비교를 통하여 PMMA 나노섬유와 탄소 나노튜브의 관계를 정리하였다. 탄소 나노튜브 투입량이 증가함에 따라 고분자 비드가 증가하였다.

• 천문학회지
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• 제49권5호
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• pp.193-198
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• 2016

Early-type galaxies (ETGs) are supposed to follow the virial relation $M=k_e{\sigma}^2R_e/G$, with M being the mass, σ_* being the stellar velocity dispersion, R_e being the effective radius, G being Newton's constant, and k_e being the virial factor, a geometry factor of order unity. Applying this relation to (a) the ATLAS^3D sample of Cappellari et al. (2013) and (b) the sample of Saglia et al. (2016) gives ensemble-averaged factors 〈k_e〉 = 5.15 ± 0.09 and 〈k_e〉 = 4.01 ± 0.18, respectively, with the difference arising from different definitions of effective velocity dispersions. The two datasets reveal a statistically significant tilt of the empirical relation relative to the theoretical virial relation such that $M{\propto}({\sigma}^2_*R_e)^{0.92}$. This tilt disappears when replacing R_e with the semi-major axis of the projected half-light ellipse, a. All best-fit scaling relations show zero intrinsic scatter, implying that the mass plane of ETGs is fully determined by the virial relation. Whenever a comparison is possible, my results are consistent with, and confirm, the results by Cappellari et al. (2013). The difference between the relations using either a or R_e arises from a known lack of highly elliptical high-mass galaxies; this leads to a scaling (1 - ϵ ) ∝ M^0.12, with ϵ being the ellipticity and $R_e=a\sqrt[]{1-{\epsilon}}$. Accordingly, a, not R_e, is the correct proxy for the scale radius of ETGs. By geometry, this implies that early-type galaxies are axisymmetric and oblate in general, in agreement with published results from modeling based on kinematics and light distributions.

• 한국음향학회지
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• 제22권7호
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• pp.545-553
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• 2003

압전 변환기를 사용하는 초음파유량계에서 고온의 유체로부터 압전 변환기를 보호하기 위하여 도파관을 사용하면서 종진동 초음파 전파성능을 향상시키기 위한 연구를 하였다. 도파관을 따라 전달되는 열을 효율적으로 차단하는 도파관 재질을 선정하였고, 압전 변환기를 보호할 수 있는 도파관의 최소 길이를 파악하였다. 균일한 원형 봉의 종진동 가진 응답을 구하여 진폭을 최대로 하는 도파관 길이를 선정하였다. 원추형 테이퍼 봉의 가진 응답을 구하여 도파관의 단면 크기가 길이방향으로 작은 쪽에서 파동이 증폭됨을 확인하였다. 균일한 도파관에서 단면 반지름이 작을수록 펄스 파 분산이 줄어듬을 파악하고, 단일 봉 도파관을 사용한 실험으로 이를 입증하였다. 실용적 도파관으로서 철심 조합형 도파관을 제시하고 제작과 평가를 통하여 파동 전파의 우수성을 확인하였다.

• 천문학회보
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• 제35권1호
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• pp.75.2-75.2
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• 2010

We investigate the dependence of occurrence of bar in galaxies on galaxy properties and environment. The environmental conditions considered include the large-scale background density and distance to the nearest neighbor galaxy. We use a volume-limited sample of 33,296 galaxies brighter than $M_r$=-19.5+5logh at $0.02{\leqq}z{\leqq}0.05489$, drawn from the Sloan Digital Sky Survey Data Release 7. We classify the galaxies into early and late types, and identify bars by visual inspection. We find that the fraction of barred galaxies ($f_{bar}$) is 18.2% on average in the case of late-type galaxies, and depends on both u-r color and central velocity dispersion $(\sigma);f_{bar}$ is a monotonically increasing function of u-r color, and has a maximum value at intermediate velocity dispersion (${\sigma}{\simeq}170km\;s^{-1}$). This trend suggests that bars are dominantly hosted by systems having intermediate-mass with no recent interaction or merger history. We also find that $f_{bar}$ does not directly depend on the large-scale background density as its dependence disappears when other physical parameters are fixed. We discover the bar fraction decreases as the separation to the nearest neighbor galaxy becomes smaller than 0.1 times the virial radius of the neighbor regardless of neighbor's morphology. These results imply that it is difficult for bars to be maintained during strong tidal interactions, and that the source for this phenomenon is gravitational and not hydrodynamical.

• 천문학회보
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• 제35권1호
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• pp.74.1-74.1
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• 2010

We have investigated the radial g-r color gradients of early-type galaxies in the Sloan Digital Sky Survey (SDSS) DR6 in the redshift range 0.00$H{\beta}$ absorption-line strengths and/or emission-line ratios that are indicative of the presence of young stellar populations. This implies that most of the residual star formation in early-type galaxies is centrally concentrated. Blue-cored galaxies are predominantly low-velocity dispersion systems. A simple model shows that the observed positive color gradients are visible only for a billion years after a star formation episode for the typical strength of recent star formation. The observed effective radius decreases and the mean surface brightness increases due to this centrally concentrated star formation episode. As a result, the majority of blue-cored galaxies may lie on different regions in the fundamental plane (FP) from red-cored ellipticals. However, the position of the blue-cored galaxies on the FP cannot be solely attributed to recent star formation but requires substantially lower velocity dispersion. We conclude that a low-level of residual star formation persists at the centers of most of low-mass early-type galaxies, whereas massive ones are mostly quiescent systems with metallicity-driven red cores.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2009년도 한국우주과학회보 제18권2호
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• pp.34.4-35
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• 2009

We have studied the radial g-r color gradients of early-type galaxies in the Sloan Digital Sky Survey (SDSS) DR6 in the redshift range 0.00 < z < 0.06. The color profiles of ~30 per cent of the galaxies in this sample show positive color gradients (centers being bluer). These positive gradient galaxies often show strong $H\beta$ absorption line strengths or emission line ratios that are consistent with star-forming populations. Combining the optical data with Galaxy Evolution Explorer (GALEX) UV photometry, we find that all positive gradient galaxies show blue UV-optical colors. They also exhibit a tendency of having a lower stellar velocity dispersion. Positive gradient galaxies tend to live in lower density regions than negative gradient galaxies and are likely to have a late-type companion galaxy. On the other hand, massive early-type galaxies show negative color gradients. A simplistic population analysis shows that these positive color gradients are visible only for half a billion years after a star burst. Although the effective radius decreases and mean surface brightness increases due to this centrally concentrated star formation, the positions of the positive gradient galaxies on the fundamental plane cannot be reproduced by any amount of recent star formation. Instead it required a lower velocity dispersion.

• 천문학회보
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• 제40권1호
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• pp.48.1-48.1
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• 2015

We investigate the role of small-scale and large-scale environments in triggering nuclear activity of the local galaxies using a volume-limited sample with $M_r$ < -19.5 and 0.02 < z < 0.0685 from the Sloan Digital Sky Survey Data Release 7. To fix the mass of the supermassive black hole in its host galaxy, we limit the central velocity dispersion of the sample galaxies. The active galactic nuclei (AGN) host sample is composed of Type II AGNs identified with flux ratios of narrow emission lines with S/N > 6. In this study, we find that the AGN fraction of late-type host galaxies are commonly larger than of early type galaxies. The AGN fraction of host galaxy with late-type nearest neighbor starts to increase as the host galaxy approaches the virial radius of the nearest neighbor (about a few hundred kpc scale). Our result may support the idea that the hydrodynamic interaction with the nearest neighbor plays an important role in triggering the nuclear activity of galaxy. The early-type galaxies in high density regions show decline of AGN activity compared to ones in lower density regions, whereas the direction of the environmental dependence of AGN activity for late-type galaxies is rather opposite. We also find that the environmental dependence of star formation rate is analogous to one of AGN activity except in the high density region.

• 한국전자파학회지:전자파기술
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• 제2권1호
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• pp.46-54
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• 1991

排列 素子간의 급전 位相差에 의하여 放射 빔의 방향을 조정할 수 있고 指向性과 利得을 높일 수 있는 마이크 로스트립 슬로트 素子가 圓形으로 排列된 位相 排列 안테나 시스템을 提案 設計하였다. 排列된 슬로트의 수와 圓의 반경을 변화시켜 요구되는 指向性과 利得을 얻을 수 있으나, 본 연구에서는 4개의 마이크로스트립 슬로트를 원주의 接線방향으로 排列시키고 바렉터 다이오드릎 사용한 아나로그 移相器로 안테 나 소자에 급전시켜 40。까지 放射 빔을 조정시킬 수 있는 位相排列 안테나시스템을 분산과 불연속 특성을 고려 하여 10 GHz에서 마이크로스트립 선로로 製作하였다. 측정 결과는 이론과 잘 일치하였으며, 64개의 마이크로스트립 디스크 패치를 短形排列시킨 경우(1)와 비교하였을 때 배열 소자의 수를 고려한 안테나의 性能이 전반적으로 향상되었음을 알 수 있었다.

• 천문학회지
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• 제46권4호
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• pp.173-181
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• 2013

We trace the dynamical evolution of dark matter (DM) content in NGC 6397, one of the native Galactic globular clusters (GCs). The relatively strong tidal field (Galactocentric radius of ~ 6 kpc) and short relaxation timescale (~0.3 Gyr) of the cluster can cause a significant amount of DM particles to evaporate from the cluster in the Hubble time. Thus, the cluster can initially contain a non-negligible amount of DM. Using the most advanced Fokker-Planck (FP) method, we calculate the dynamical evolution of GCs for numerous initial conditions to determine the maximum initial DM content in NGC 6397 that matches the present-day brightness and velocity dispersion profiles of the cluster. We find that the maximum allowed initial DM mass is slightly less than the initial stellar mass in the cluster. Our findings imply that NGC 6397 did not initially contain a significant amount of DM, and is similar to that of NGC 2419, the remotest and the most massive Galactic GC.