• 한국연소학회:학술대회논문집
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• 한국연소학회 2000년도 제21회 KOSCO SYMPOSIUM 논문집
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• pp.183-193
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• 2000

Soot formation and oxidation is closely related to the combustion phenomena inside a diesel engine. Laser-based diagnostics provide a means for improving our understanding of diesel combustion, because they have highly temporal and spatial ability. To understand the soot behavior we did preliminary study by taking flame luminosity photographs and 2-D images of soot distribution using Laser Elastic Scattering(LIS) and Laser-Induced Incandescence(LII). From the data we found that soot concentration was high in the bowl and disappeared from the central region in the late combustion stage and that soot exists in the flame using luminosity, LIS and LII.

• 천문학논총
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• 제9권1호
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• pp.69-84
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• 1994

The spectral types of stars can be classified by using Balmer discontinuity($D_B$) and wavelength(${\lambda}_B$) expressed in terms of effective temperatures appeared in Balmer discontinuity. In this research, in order to classify stars, we used the well established observational data of high dispersion spectrophotometry for the spectral types and luminosity classes of stars in the Breger(1976) catalogue. Balmer discontinuity by effective temperatures of stars was accurately measured, and the ${\lambda}_B$ was replaced to luminosity classes of MK system, because of the close relationship between the As and luminosity classes. We measured the energy gradients(${\phi}_R$) of stars which were expressed as a function of spectral types in the interval of ${\lambda}{\lambda}4,000{\sim}4600{\AA}$, and then obtained a new physical parameter(${\phi}$) from the $D_B$ and ${\phi}_B$. The new parameter, ${\phi}$ can be used instead of HD classifications of stars and can be used widely for spectrophotometrical classifications of stars.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집B
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• pp.162-167
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• 2000

Soot formation and oxidation is closely related to the combustion phenomena inside a diesel engine. Laser-based diagnostics provide a means for improving our understanding of diesel combustion, because they have highly temporal and spatial ability. To understand the soot behavior we did preliminary study by taking flame luminosity photographs and 2-D imaging soot distribution using Laser Elastic Scattering(LIS) and Laser-Induced Incandescence(LII). From the data we found that soot concentration was high in the bowl and disappeared from the central region in the late combustion stage.

• 천문학회보
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• 제42권1호
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• pp.49.3-50
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• 2017

Metallicity is one of the most important properties in understanding galaxy evolution. However, measuring metallicity is limited to low redshift (z<3.5) due to the faintness of the metallicity indicators in normal galaxies. For high redshift universe, active galactic nuclei (AGN) can be used to constrain the host galaxy metallicity. Previous studies investigated AGN metallicity using emission line flux ratios (i.e., NV/CIV and FeII/MgII), finding no evolution up to z~6. Those results might be due to selection effect since previous studies are based on very luminous AGNs. The observed luminosity-metallicity relation of AGNs (e.g., Nagao et al. 2006) suggests that luminous AGNs may be already matured at the observed epoch. Considering the luminosity-metallicty relation, we focused on low luminosity AGNs to find young AGNs (i.e., low metallicity). Through the Gemini/GNIRS observation in 2012A and 2015A (K-GMT GN-2015A-Q-203 PI: Shin, J.), we obtained the Gemini/GNIRS data for 7 high redshift AGNs (3.0

• 천문학회보
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• 제36권2호
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• pp.77.1-77.1
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• 2011

The sizes of galaxies are correlated with their masses or luminosities, which is known as the 'mass-size relation' or 'luminosity-size relation'. Those relations show scatters in the sense that the sizes of galaxies range somewhat widely at given mass or luminosity, which is largely affected by the morphologies or colors of the sample galaxies. However, the scatters of the relations are still large even when the galaxy sample is limited to red early-type galaxies: at fixed mass or luminosity, the largest red early-type galaxies are larger than the smallest red early-type galaxies by a factor of 4 - 5. This is a progress report of a study on what determines the sizes of red early-type galaxies. We investigate how the sizes of red early-type galaxies depend on several quantities of them, such as color, color gradient, axis ratio, local number density and mass-to-light ratio. The physical implication of those preliminary results is discussed.

• 천문학회지
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• 제22권2호
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• pp.101-111
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• 1989

We have analysed the proper motion data of LHS catalog, to derive the faint end of the luminosity function more precise than ever before, by mean absolute method, and by making use of the reudced proper motion diagram. It is found that the relations between the mean absolute magnitude and the reduced proper motion for main sequence stars, subdwarfs, and white dwarfs are so different that the proper application of an appropriate relation to each group is much more important. The derived luminosity function shows the broad maximum peak from $M_B{\sim}14$ to $M_B{\sim}17$ and declines after $M_B{\sim}17$ up to $M_B{\sim}22$.

• 천문학논총
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• 제30권2호
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• pp.363-365
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• 2015

We study galaxies drawn from the semi-analytic models of Guo et al. (2011) based on the Millennium Simulation. We establish a set of four observationally measurable parameters which can be used in combination to identify a subset of galaxy groups which are old, with a very high probability. We therefore argue that a sample of fossil groups selected based on the luminosity gap will result in a contaminated sample of old galaxy groups. By adding constraints on the luminosity of the brightest galaxy, and its offset from the group luminosity centroid, we can considerably improve the age-dating.

• 천문학회보
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• 제37권2호
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• pp.88.1-88.1
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• 2012

We utilize Sloan Digital Sky Survey DR7 spectroscopic data of ~340 star forming galaxies in the Virgo cluster to investigate their chemical properties depending on the environments. The chemical evolution of galaxies is linked to their star formation histories (SFHs), as well as to the gas interchange in different environments. In this sense, galaxy metallicity could be an observable parameter providing information on the impact of the environment on the galaxy SFH and/or the galaxy gas content. Thus, we derived gaseous metallicity (e.g., oxygen abundance) of star forming galaxies located in different regions of the Virgo cluster using well-known empirical calibrations. We also estimated their star formation rate (SFR) using H alpha luminosity. Inorder to investigate the chemical properties of these galaxies, we examined relations between various parameters: metallicity vs. luminosity, SFR vs. luminosity, and metallicity vs. cluster-centric radius. From our results, we discuss environmental effects of cluster to the chemical properties of star forming galaxies.

• 천문학회보
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• 제45권1호
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• pp.53.2-53.2
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• 2020

We measure X-ray timing and spectral properties of the pulsar PSR J0205+6449. Pulsar's rotation frequency ν = 15.20102357(9) s-1 and its derivative ${\dot{\nu}}=-4.5(1){\times}10^{-11}s^{-2}$ are measured, and the pulsed spectrum of 2-30 keV is model of power law with photon index ��psr = 1.07(16) and F2-30 keV = 7.3(6) × 10-13 erg cm-2 s-1. We use thermal emission models and non-thermal model to fit the pulsar spectrum and measure the surface temperature and luminosity of the pulsar. The surface temperature T∞ = 0.5-0.8 MK and luminosity Lth = 1-5 × 1032 erg s-1 are measure, and this result verifies the previous results known to have low surface temperature and luminosity for the age range of

• 조명전기설비학회논문지
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• 제19권3호
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• pp.44-50
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• 2005

본 논문에서는 산화아연(이하 ZnO) 피뢰기 열화진행의 한 요인으로 예측되는 전극과 ZnO소자 사이에서 발생하는 방전광 현상에 관한 연구를 수행하였다. 이를 위해 $8/20[{\mu}s]$, 최대 10[kA]의 뇌임펄스전류를 발생시키는 뇌임펄스전류 발생장치를 설계${\cdot} $제작하였다. 실험결과, 상${\cdot}$하부의 전극 부근에서 발생하는 방전광의 형상은 인가되는 뇌임펄스의 극성에 따라 다르게 나타났으며 상대적으로 (-)극의 전극부근에서 방전광이 더 강하고 활발하게 발생하는 것으로 관찰되었다. 또한 전극의 면적에 따른 방전광의 세기는 전극의 면적이 증가할수록 감소하는 것으로 관측되었다. 동시에 전극과 소자의 접촉상태도 방전광의 발생과 매우 밀접한 관계가 있는 것으로 확인되었다. 따라서 배전급 ZnO피뢰기의 기존 전극구조는 보완이 필요하며 ZnO피뢰기 제품의 성능향상 및 지속적인 성능유지를 위해서는 환형구조 대신 내부면적이 있는 원판구조로 교체하는 것이 바람직하다고 판단된다.