• Journal of Astronomy and Space Sciences
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• v.16 no.2
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• pp.227-240
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• 1999

We performed CCD photometric observations of W UMa type contact binary BV Dra during eight nights from May 1996 to June 1999 using 61cm telescope at Sobaeksan Optical Astronomy Observatory, and completed BV R light curves of the system. From our observations, we derived nine new times of minimum lights (five timings for primary eclipse, four for secondary) and determined new light elements with the times of minima observed since 1999. Our BV R light curves and Batten & Lu(1986)'s radial-velocity ones were simultaneously analyzed with contact mode (Mode 3) of Wilson-Devinney's binary model, and the photometric and spectroscopic solutions for BV Dra were solved. In the analysis, we derived the solutions of 1999 light curves with and without spots, respectively. As the results, asymmetry of light curves may be interpreted as produced by the existence of two spots; hot spot on the secondary and cool on the primary. Combining solutions of light curves and radial-velocity ones, absolute dimensions of BV Dra are $M_1=0.40M_{odot}$, $M_2=1.01M_{odot}$, $R_1=0.72R_{odot}$, $R_2=0.40R_{odot}$. In mass-radius diagram, the less massive and hotter primary component of BV Dra is near TAMS and the secondary is near ZAMS, which is very similar to the other W-type W UMa binaries.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.3
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• pp.554-570
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• 1990

he rolling contact behaviors between a smooth ball and a flat rough surface under dynamic load are intricately affected by many factors, such as the diameter of a ball, normal load and the roughness of a flat surface etc. Accordingly, the experimental study is done to find them on the base of elastic hysteresis loss as theoretical approach is very difficult. The experimental apparatus composed of damped-free vibration system is used. This paper investigates the damping characteristics on the rolling contact area through rolling friction force and logarithmic decrement versus displacement obtained in accordance with the variations of those factors, and presents a new experimental method to find out contact width using the relations of logarithmic decrement and rolling friction force with displacement.

• Journal of Astronomy and Space Sciences
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• v.18 no.1
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• pp.43-54
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• 2001

The unpublished photoelectric observations of the contact binary W UMa in ultraviolet, blue, and yellow bandpasses made on four nights during the obsrving seasons from April, 1984 to May, 1985 were presented. From our observations new eleven times of minimum light were determined. By using the 1993 WD binary model our light curves were analyzed and new photometric solutions of W UMa were obtained.

• Proceedings of the KIEE Conference
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• 2007.11b
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• pp.40-42
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• 2007

본 논문은 전기기기에 순간전압저하를 발생 하였을 경우 응동특성에 대한 영향을 계측하였다. 실험 방법은 AVR에서 Sag 발생기인 IPC에 입력한 후, IPC에서 전압의 크기와 시간을 조정하여 실험기기에 순간전압 강하를 발생하였다 실험기기는 PLC, 전자접촉기, 400[W]고압방전램프를 시험하였다. PLC시험에서 무부하와 정격부하에 따라 특성 의 변화가 생겼으며, 정격부하에서 Voltage Sag의 영향을 더 받았다 전자접촉기의 시험은 위상을 $0^{\circ},\;30^{\circ},\;60^{\circ},\;90^{\circ}$로 변화하여 Voltage Sag 발생시켜 계측하였으며, 위상의 변화에 따라 특성곡선이 변화하였다. 고압방전램프시험은 고압나트륨램프와 수은램프, 메탈헬라이드에 Voltage Sag를 발생시켰다. 방전램프의 시험결과 고압나트륨램프의 특성곡선이 가장 안정적으로 나타났다. 본 실험을 통해 순간전압저하에 대한 저압기기의 특성을 실험적으로 입증하여 전력시스템의 설계에 영향을 미칠 것이라 기대된다.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.86.3-86.3
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• 2017

2개의 케플러 접촉쌍성인 KIC 8804824와 KIC 10229723의 초정밀 측광 자료를 가장 최신 버전의 윌슨-디비니 코드로 분석하여 정밀한 측광 해를 산출하고, 그 잔차들을 매우 자세하게 조사하였다. 두 개의 케플러 접촉 쌍성은 제2식이 편평한 광도곡선을 가지고 있어, 이 두 쌍성은 W UMa형 A sub-group에 속한다. 또한, 광도곡선의 모양이 매우 대칭이며, 시간에 따른 변화가 크지 않다. 두 별의 측광 해를 살펴 본 결과, 두 별은 모두 주성의 온도가 부성의 온도보다 높고, 0.2보다 작은 극단적인 질량비와 90도에 거의 가까운 궤도경사각을 갖고 있다. 무엇보다도, 두 별의 측광 해의 잔차에서 공통적으로 전 위상에 걸쳐 모형화 되지 않은 특이한 구조를 발견하였다. 이 구조는 phase smearing 효과를 고려하더라도 그 구조의 모습만이 약간 달라질 뿐, 구조의 진폭에는 크게 영향을 미치지 않는 것을 발견하였다. 흥미롭게도 이 현상은 두 별의 주기가 각각 다름에도 불구하고 공통적으로 나타나며, 관측된 전 쿼터에 대해 나타난다. 이 현상의 가능한 원인에 대해 논의한다.

• Journal of Astronomy and Space Sciences
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• v.23 no.3
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• pp.189-198
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• 2006

We present newly observed BVRI CCD light curves for low mass ratio contact binaries, HN UMa and II UMa. The absolute dimensions of these objects were obtained by applying the Wilson-Devinney program to previously published spectroscopic analysis and to our observed photometric data. The evolutionary status of all 21 low mass ratio contact binary system including HN UMa and II UMa was then considered. The secondaries of all low mass ratio contact binaries are located below the zero age main sequence in HR diagram. This phenomenon could be explained by mass loss from the secondary component in the low mass contact binary system because even small mass loss affects luminosity decrease in the low mass stars.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2010.10a
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• pp.154-155
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• 2010

• Proceedings of the KSR Conference
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• 2006.05b
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• pp.1128-1133
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• 2006

• Journal of Astronomy and Space Sciences
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• v.21 no.4
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• pp.275-282
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• 2004

We completed the light curves of the contact binary CK Boo for 13 nights from June to July in 2004 using the 1-m reflector and BVR filters at Mt. Lemmon Optical Astronomy Observatory, and determined four new times of minimum light (three timings for primary eclipse, one for secondary). With contact mode of the 1998-version Wilson-Devinney binary model, we analyzed our BVR light curves and Rucinski & Lu (1999)'s radial-velocity ones. As a result, we found CK boo to be A-type over-contact binary ($f=84\%$) with the low mass ratio (q=0.11) and orbital inclination ($i=65^{\circ}$). Absolute dimensions of the system are determined from our new solution; $M_1=1.42Me{\odot},\;M_2=0.15M{\odot},\;R_1=1.47R{\odot},\;R_2=0.59M{\odot}$ and the distance to it is derived as about 129pc. Our distance is well consistent with that ($157{\pm}33pc$) from the Hipparcos trigonometric parallax within the limit of the error yielded by the latter.

• Journal of Soil and Groundwater Environment
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• v.10 no.1
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• pp.26-34
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• 2005

The effects of soil-chemical contact time (aging) on sorption and desorption of atrazine were studied in soil slurries because aging is an important determinant affecting on the sorption and desorption characteristics of organic contaminants in the environment. Sorption isotherm and desorption kinetic experiments were performed, and soilwater distribution coefficients and desorption rate parameters were evaluated using linear and non-linear sorption equations and a three-site desorption model, respectively. Aging time for sorption of atrazine in sterilized soil slurries ranged from 2 days to 8 months. Atrazine sorption isotherms were nearly linear $(r^2\;>\;0.97)$ and sorption coefficients were strongly correlated to soil organic carbon content. Sorption distribution coefficients $(K_d)$ increased with increasing aging in all soils studied. Sorption non-linearity did not increase with increased aging except for the Houghton muck soil. Desorption profiles were well described by the three-site desorption model. The equilibrium site fraction $(f_{eq})$ decreased and the non-desorbable site fraction $(f_{nd})$ increased as a function of aging time in all soils. In all soils studied, it was found that when normalized to soil organic matter content the concentration of atrazine in desorbable sites was comparatively constant, whereas that in non-desorbable site increased as aging increased.