• 천문학회보
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• 제37권2호
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• pp.143.1-143.1
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• 2012

We attempt to investigate the main reason of the asymmetrical light curves of contact and near-contact eclipsing binary base on the hypothesis that cool spot was produced on late type star while hot spot was produced from transferred material from their companion star hitting surface. We select 7 eclipsing binary systems which showed asymmetric light curves and mass transfer. Period variation and mass transfer rate were obtained from O-C diagram. Radial velocity curves and light curves of those 7 eclipsing binary system were adopted from available literature in order to obtain the absolute dimension. For four contact eclipsing binary system (AD Phe, EZ Hya, AG Vir and VW Boo), their component stars belonged to spectral type G to K was fitted by cool spot model. While the other two near-contact systems (RT Scl and V1010 Oph) and one contact system (SV Cen) was fitted by cool spot model. The densities of the materials are adopted from stellar model which calculate by stellar structure code. The calculated spot temperature turns out to agree with the photometric solution but there are no correlate between period variation rate and type of spot.

• Journal of Astronomy and Space Sciences
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• 제5권2호
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• pp.97-109
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• 1988

The photometric behaviour of XY U Ma, an eclipsing binary showing photospheric and chromospheric activity, has been described by spot hypothesis. They are based on the all the available UBV light curves, which were carried out by Geyer since 1955. A "spherical rectangular" spot model shows very pronounced spot activities during the last 30 years. On the average, the spot covered about 16% of the visible hemisphere. Observational evidence for photospheric and chromospheric activities on the XY UMa and related systems are also discussed.

• 한국방송∙미디어공학회:학술대회논문집
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• 한국방송공학회 2011년도 하계학술대회
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• pp.548-551
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• 2011

본 연구에서는 방송 촬영용 LED Spot 조명기기를 두 가지 형태로 개발하여, 현재 방송용 스튜디오 조명기기가 설치되어 있는 공간에서 다수 사용되고 있는 영국의 Arri사 650W와 1000W Fresnel Spot 조명기기와 조도, 색온도, 연색성 등의 비교 데이터 측정과 피사체의 촬영 시 영상 및 연색성에 따른 색상을 비교 측정하였다. 그리고 방송 촬영용으로 LED Spot 조명기기가 대체 가능한지를 판단하기 위하여 성능평가분석 하였다.

• 한국측량학회지
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• 제18권4호
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• pp.405-414
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• 2000

IKONOS, SPOT-5, OrbView-3, 4와 같은 위성들은 기존의 위성들보다 향상된 방사영역과 기하학적으로 안정된 고해상력 위성영상을 갖게 될 것이며, 탑재된 GPS와 IMU, Star Trackers 등에 의해 고정밀의 궤도위치와 자세자료가 제공될 예정이다. 이러한 정보들은 지상기준점수를 줄일 수 있는 가능성을 보여주고 있으며, 더나가 지상기준점을 이용하지 않고 직접 위성영상을 이용하여 위치결정을 할 수 있다. 본 연구에서는 SPOT-3호와 KOMPSAT-1호 위성영상의 궤도요소계산을 위한 수학적 모델을 개발하였으며, 개발된 모델은 고해상위성영상의 활용이 현실화될 경우 이들 영상을 처리하기 위해 쉽게 확장될 것이다.

• 치과방사선
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• 제20권2호
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• pp.289-297
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• 1990

The purpose of this study was to assess the resolution and focal spot size of dental X-ray machines. Fifty dental X-ray machines were selected for measuring resolution and focal spot size. These machines were used in general dental clinics. The time of installation of the X-ray machine varies from 1 year to 10 years. The resolution of these machines was measured with the test pattern. The focal spot size of these machines was measured with the star test pattern. The following results were obtained: 1. The resolution of dental intraoral X-ray machines was not significantly changed in ten years. 2. The focal spot size of dental intraoral X-ray machines was not significantly increased in ten years. The statistical analysis between the mean focal spot size and nominal focal spot size was significant at the 0.05 level about the more than 3 years used machines.

• Journal of Astronomy and Space Sciences
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• 제30권4호
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• pp.213-221
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• 2013

We present the first BVRI CCD photometric observations of V345 Cas made on 22 nights during the observing seasons in 2007-2008. Our light curves, resembling those of EB-type binary stars, are analyzed with the 2003 version of the Wilson-Devinney binary code. The photometric study shows that V345 Cas is a typical semi-detached binary system with the primary star being about ${\Delta}T$ = 2400 K hotter, two times more massive, but only 17% larger than the secondary star being filled with it's Roche-lobe. The orbit has a relatively large inclination of about $88^{\circ}$. A cool spot on the secondary component is modeled to explain a small light curve asymmetry. Absolute dimensions and related radiometric parameters of the eclipsing pair are calculated and their evolutionary states are discussed with the HR diagrams of mass-radius and temperature-luminosity. A period analysis of all available times of minima, including our measurements, indicates that the orbital period may vary in a cyclical way, unfortunately the secondary period for the variation can not be uniquely determined because of lack of present timing data.

• Journal of Astronomy and Space Sciences
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• 제17권2호
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• pp.189-198
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• 2000

RS Cvn형 4상성 SZ Psc의 광도곡선에 나타난 뒤틀림 현상을 규명하기 위하여 자외선 영역의 방출선과 가시광선 영역의 광도곡선을 분석하였다. 자외선 영역에서 IUE 고분산 분광선 중에서 MgII 방출선의 강도를 조사하여, 채충 활동은 주로 Kl IV 별에서 일어나고 있는 것을 확인하였다. 한편, 가시광선 영역에서 나타난 광도 곡선의 뒤틀림 현상은 Kl IV별에 혹점이 존재하는 혹점 모델을 이용하여 분석한 결과 SZ Psc의 뒤틀린 광도 곡선을 잘 설명할 수 있었다. 그 결과 SZ Psc에 대한 완전한 측광학적인 해를 최초로 제시하였다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.458-461
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• 2009

Thermo-mechanical simulation of the Friction Stir Spot Welding (FSSW) processes was performed for the AA5083-H18 sheets, utilizing commercial Finite Element Method (FEM) and Finite Volume Method (FVM) which are based on Lagrangian and Eulerian formulations, respectively. The Lagrangian explicit dynamic FEM code, PAM-CRASH, and the Eulerian Computational Fluid Dynamics (CFD) FVM code, STAR-CD, were utilized to understand the effect of pin geometry on weld strength and material flow under the unsteady state condition. Using FVM code, material flow pattern near the tool boundary was analyzed to explain the weld strength difference between the weld by cylindrical pin and the weld by triangular pin, while the frictional energy concept using the FEM code had limitation to explain the weld strength difference.

• Journal of Astronomy and Space Sciences
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• 제29권1호
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• pp.47-49
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• 2012

Massive binary stars lose mass by two mechanisms: jet-driven mass loss during periods of active mass transfer and by wind-driven mass loss. Beta Lyrae is an eclipsing, semi-detached binary whose state of active mass transfer provides a unique opportunity to study how the evolution of binary systems is affected by jet-driven mass loss. Roche lobe overflow from the primary star feeds the thick accretion disk which almost completely obscures the mass-gaining star. A hot spot predicted to be on the edge of the accretion disk may be the source of beta Lyrae's bipolar outflows. I present results from spectropolarimetric data taken with the University of Wisconsin's Half-Wave Spectropolarimeter and the Flower and Cook Observatory's photoelastic modulating polarimeter instrument which have implications for our current understanding of the system's disk geometry. Using broadband polarimetric analysis, I derive new information about the structure of the disk and the presence and location of a hot spot. These results place constraints on the geometrical distribution of material in beta Lyrae and can help quantify the amount of mass lost from massive interacting binary systems during phases of mass transfer and jet-driven mass loss.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2009년도 한국우주과학회보 제18권2호
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• pp.24.2-24.2
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• 2009

We present the results of new CCD photometry for the contact binary BX Peg, made during three successive months beginning on September 2008. As do historical light curves, our observations display an O'Connell effect and the November data by themselves indicate clear evidence for very short-time brightness disturbance. For these variations, model spots are applied separately to the two data set of Group I (Sep.--Oct.) and Group II (Nov.). The former is described by a single cool spot on the secondary photosphere and the latter by a two-spot model with a cool spot on the cool star and a hot one on either star. These are generalized manifestations of the magnetic activity of the binary system. Twenty light-curve timings calculated from Wilson-Devinney code were used for a period study, together with all other minimum epochs. The complex period changes of BX Peg can be sorted into a secular period decrease caused dominantly by angular momentum loss due to magnetic stellar wind braking, a light-travel-time (LTT) effect due to the gravitational effect of a low-mass third companion, and a previously unknown short-term oscillation. This last period modulation could be produced either by a second LTT orbit with a period of about 16 yr due to the existence of a fourth body or by the effect of magnetic activity with a cycle length of about 12 yr.