• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2001년도 학술대회논문집
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• pp.193-197
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• 2001

In this paper, reduction characteristics of the ac flashover voltage in the horizontal air gap of sphere-sphere and needle-needle electrode system were investigated when the combustion flame was present near the high-voltage electrodes. The reduction characteristics of ac flashover voltage were discussed with thermal ionization process, the relative air density and the deflection phenomena in the shape of flames that changed by the corona wind and coulomb's force. As the results of an experimental, It was found that the reduction of flashover voltage in sphere-sphere system, in comparison with the no-flame case, are 79.9 [%] for k=0, 82.9 [%] for k=0.5, 87.5 [%] for k=1.0, 85.0 [%] for h=0 [cm], 40.8 [%] for h=5 [cm] and 28.2 [%] for h=9 [cm] when ac voltage is applied.

• 천문학회보
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• 제37권1호
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• pp.85.1-85.1
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• 2012

In this study we use three-dimensional magnetohydrodynamic simulations of flux emergence from solar subsurface layer to corona. In order to study the twist parameter of magnetic field we compare the simulations for strongly twisted and weakly twisted cases. Based on the results, we derive a flux expansion factor of selected flux tubes which is a ratio of expanded cross section to the one measured at the footpoint of the flux tube. To understand the effect of flux expansion factor, we make a comparison between magnetic field configuration and the expansion factor. By using a fitting function of hyperbolic tangent we derive noticeable correlations among the strength of the vertical magnetic field, current density and expansion factor. We discuss what these results tell about the relationship between the twist of emerging field and the mechanism for the solar wind.

• 한국전기전자재료학회논문지
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• 제14권12호
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• pp.1041-1047
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• 2001

In this paper, reduction characteristics of the ac flashover voltage in the horizontal air gap of sphere-sphere/needle-needle electrode system were investigated when the combustion flame was present near the high-voltage electrodes. The voltage and current waveforms were measured, when the flashover is occurred, in order to examine the flashover polarity by flame. The reduction characteristics of ac flashover voltage were discussed with the thermal ionization process, the relative air density and the deflection phenomena in the shape of flames that changed by the corona wind and coulomb\`s force. As the results of an experimental investigation, It was found that the reduction of flashover voltages in sphere-sphere system, in comparison with the no-flame case, are 79.9 [%] for k=0, 82.9 [%] for k=0.5, 87.5 [%] for k=1.0, 85.0 [%] for h=0 [cm], 40.8 [%] for h=5 [cm] and 28.2 [%] for h=9 [cm] when ac voltage is applied.

• 천문학회보
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• 제37권2호
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• pp.131.1-131.1
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• 2012

We use three-dimensional magnetohydrodynamic (MHD) simulations of flux emergence from solar subsurface to corona. In our previous work, we reported the relation between magnetic-field configuration and the flux expansion factor. Following these results, we investigate where an upflow is generated in an active region and how its location is related to the flux expansion factor. We also derive physical quantities of a real active region from observation data provided by Nobeyama Radioheliograph (NoRH), X-Ray Telescope (XRT), and Extreme Ultraviolet Imaging Spectrometer (EIS) onboard Hinode. These physical quantities are plasma density, temperature and flow. By comparing the simulation result and observational one, we will discuss the properties of the location producing a solar wind.

• 천문학회보
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• 제44권1호
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• pp.51.1-51.1
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• 2019

The Korea Astronomy and Space Science Institute (KASI) has been developing a coronagraph in collaboration with the National Aeronautics and Space Administration (NASA), to install it on the International Space Station (ISS). The coronagraph will utilize spectral information to simultaneously measure electron density, temperature, and velocity. For this, we develop the coronagraph as a two-step process. First, we will perform a stratospheric balloon-borne experiment, so called BITSE, in 2019 with a new type of coronagraph. Second, the coronagraph will be installed and operate on the ISS (CODEX) in 2021 to address a number of questions (e.g., source and acceleration of solar wind, and coronal heating) that are both fundamental and practically important in the physics of the solar corona and of the heliosphere. In this presentation, we will introduce recent progresses.

• 천문학회보
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• 제44권2호
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• pp.56.4-56.4
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• 2019

The Korea Astronomy and Space Science Institute (KASI) has been collaborating with the NASA's Goddard Space Flight Center, to install a coronagraph on the International Space Station (ISS). The coronagraph will utilize spectral information to simultaneously measure electron density, temperature, and velocity. As a first step, we developed a new coronagraph and launched it on a stratospheric balloon in 2019 (BITSE) from Fort Sumner, New Mexico in USA. As the next step, the coronagraph will be be further developed, installed and operate on the ISS (CODEX) in 2022 to address a number of important questions (e.g., source and acceleration of solar wind, and coronal heating) in the physics of the solar corona and the heliosphere. Recently, BITSE has been launched at Fort Sumner, New Mexico. In this presentation, we will introduce the BITSE mission and discuss recent progress.

• 천문학회보
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• 제44권2호
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• pp.57.1-57.1
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• 2019

NASA and Korea Astronomy and Space Science Institute (KASI) have been collaborated to develop the Space solar coronagraph instrument to detect the solar wind speed and corona temperature. As an intermediate stage, BITSE is the Balloon-Borne instrument to prove our proposed technical method which uses a polarized light in 4 different bandwidth wavelengths. In the presentation, the optical design based on the requirements, tests and alignment process for integrating the system are discussed.

• 천문학회보
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• 제46권2호
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• pp.47.1-47.1
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• 2021

Transverse magnetohydrodynamic waves often called Alfvénic (or kink) waves have been often theoretically put forward to solve the outstanding problems of the solar corona like coronal heating, solar wind acceleration, and chemical abundance enhancement. Here we report the first spectroscopic detection of Alfvénic waves around a sunspot at chromospheric heights. By analyzing the spectra of the Hα line and Ca II 854.2 nm line, we determined line-of-sight velocity and temperature as functions of position and time. As a result, we identified transverse magnetohydrodynamic waves pervading the superpenumbral fibrils. These waves are characterized by the periods of 2.5 to 4.5 minutes, and the propagation direction parallel to the fibrils, the supersonic propagation speeds of 45 to 145 km s-1, and the close association with umbral oscillations and running penumbral waves in sunspots. Our results support the notion that the chromosphere around sunspots abounds with Alfvénic waves excited by the mode conversion of the upward-propagating slow magnetoacoustic waves.

• 한국위성정보통신학회논문지
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• 제6권2호
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• pp.97-101
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• 2011

태양과 지구 간 공간인 행성 간 공간 (Interplanetary space)은 태양표면에서 발생되는 X선, 플레어, 코로나 물질 등이 태양풍에 의해 지구로 이동되는 공간으로, 태양에서부터 초음속의 태양풍이 불고 있다. 이러한 태양풍은 지구 자기권 및 이온층에 직접적인 영향을 미치며, 이로 인해 방송통신 장애, 위성운용 장애, 전력선 장애 등을 야기 시키게 된다. 이러한 행성 간 공간의 태양풍 흐름은 태양풍 배경이 되는 전파원이 태양풍을 통과하면서 발생하는 신틸레이션 값을 측정함으로써 태양풍 속도, 밀도 및 방향으로 관측된다. 태양풍 관측 정확도 및 정밀도는 유효집광 면적이 넓을수록 그리고 태양 배경 관측 소스 수가 많을수록 높아진다. 본 논문에서의 성능 검증은 시제품으로 제작한 3개의 타일을 이용하였으며, 관측 타일 수량의 제한으로 관측된 빔 패턴이 요구사항을 만족하는지 여부를 검증하는 시험을 수행하였다. 본 논문은 행성 간 공간에서 이동하는 태양풍 관측을 위해 디지털 데이터 처리 기능을 갖는 태양풍 지상 관측 시스템 설계 및 규격을 제시하고 또한 설계 시 제기된 기술적 이슈와 해결방안을 제시하고 있다. 아울러 제시된 규격에 따라 제작된 시제품을 이용하여 태양풍을 관측할 수 있는 성능이 구현되었는지에 대한 검증을 수행한 결과를 제시하고 있다. 시제품으로 제작한 3개의 타일을 이용하여 수행된 성능시험 결과 관측된 빔 패턴이 요구사항을 만족하고 있어 태양풍 관측이 수행될 수 있음을 확인하였다.

• 조명전기설비학회논문지
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• 제27권8호
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• pp.83-89
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• 2013

In this paper, discharge characteristics of air in the vertical arrangement of three rods(dome-shaped, cylinder-shaped, and needle-shaped rod) and plane gap having propane flame on the plane electrode are examined under the application of a.c. and d.c. high-voltages. As the result of the experiment, flashover voltages in the presence of the flame are substantially lowered than those in the absence of flame, and relative a.c. flashover voltages in the dome-shaped, cylinder-shaped, and needle-shaped rod gaps are found 32.5%, 32.1%, and 26.4% respectively. The polarity effects with the d.c. voltages are shown, and flashover voltages in negative polarity are much lowered than those in positive one. The negative flashover voltages in the dome-shaped and cylinder-shaped gaps are found 18.3% and 18.7% respectively, but the positive ones are found 53.5% and 43.2% respectively. In the needle-shaped rod gaps, meanwhile, the flame is extinguished by corona wind, and the quenching voltages are found 28.4% under the application of a.c. voltages. The ion winds of corona and the reduction of air density are the main factors of flashover reduction owing to the flame in the case of a.c. voltages, but the electrifications of the positive ion by thermal ionization besides the above factors are remarkably found in the case of d.c. voltages.