• 천문학회지
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• 제50권6호
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• pp.157-165
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• 2017

$H_2O$ maser emission at 22 GHz in the circumstellar envelope is one of the good tracers of detailed physics and kinematics in the mass loss process of asymptotic giant branch stars. Long-term monitoring of an $H_2O$ maser spectrum with high time resolution enables us to clarify acceleration processes of the expanding shell in the stellar atmosphere. We monitored the $H_2O$ maser emission of the semi-regular variable R Crt with the Kagoshima 6-m telescope, and obtained a large data set of over 180 maser spectra over a period of 1.3 years with an observational span of a few days. Using an automatic peak detection method based on least-squares fitting, we exhaustively detected peaks as significant velocity components with the radial velocity on a $0.1kms^{-1}$ scale. This analysis result shows that the radial velocity of red-shifted and blue-shifted components exhibits a change between acceleration and deceleration on the time scale of a few hundred days. These velocity variations are likely to correlate with intensity variations, in particular during flaring state of $H_2O$ masers. It seems reasonable to consider that the velocity variation of the maser source is caused by shock propagation in the envelope due to stellar pulsation. However, it is difficult to explain the relationship between the velocity variation and the intensity variation only from shock propagation effects. We found that a time delay of the integrated maser intensity with respect to the optical light curve is about 150 days.

• 지구물리와물리탐사
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• 제20권1호
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• pp.25-32
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• 2017

이 연구는 동아시아 지역의 지각과 상부맨틀의 3차원 SH파 속도구조 및 지진파 속도 방사 이방성을 알아보기 위하여 수행되었다. SH파 속도모델은 한국과 일본, 중국에 설치되어 있는 광대역 지진관측소에 기록된 지진자료로부터 러브파 군속도 분산 자료를 획득한 후 이를 역산하여 구하였다. 군속도 분산곡선은 총 3,369개의 파선경로에 대하여 다중필터기법을 사용하여, 접선 성분에 기록된 주기 3 ~ 150 초 범위의 러브파 군속도를 획득하였다. 획득한 군속도자료를 역산하여 깊이 100 km까지의 SH파 속도구조를 계산하였다. 10 ~ 40 km 깊이에서 동해지역은 일본지역보다 SH파 속도가 빠르게 나타난다. 고속도 이상이 나타나는 깊이로 판단할 때, 모호면의 깊이는 동해의 경우 10 ~ 20 km 사이, 한반도의 경우에는 35 km 부근에서 모호면이 존재한다고 생각된다. 50 km 깊이에서 동해지역은 강한 저속도 이상이 관측이 되고, 저속도 이상이 나타나는 깊이로 판단할 때, 50 km 부근에 암석권과 연약권의 경계가 존재한다고 생각된다. 연구지역 아래 50 ~ 100 km 깊이에서는 저속도 이상이 광범위하게 관측된다. 지진파 속도 이방성은 35 km 깊이 까지는 평균적으로 SH파의 속도가 빠른 양의 이방성을 보이며, 그보다 더 깊은 깊이에서는 평균적으로 SV파의 속도가 빠른 음의 이방성이 관측된다.

• 천문학회지
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• 제45권1호
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• pp.1-6
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• 2012

We use a Probabilistic Neural Network (PNN) technique to derive the orbital parameters of spectroscopic binary stars. Using measured radial velocity data of five double-lined spectroscopic binary systems (i.e., EQ Tau, V376 And, V776 Cas, V2377 Oph and EE Cet), we find the corresponding orbital and spectroscopic elements. Our numerical results are in good agreement with those obtained by other groups via more traditional methods.

• 지구물리와물리탐사
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• 제22권1호
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• pp.21-28
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• 2019

이 연구에서는 사우디 아라비아 지역의 S파 속도구조와 이방성을 알아보기 위해 표면파 분산 곡선을 사용하여 3차원 토모그래피를 수행하였다. 아라비아 반도는 지질학적 및 지형적으로 순상지(shield)와 플랫폼(platform)의 지형으로 나뉜다. 본 연구에서는 사우디 지질조사소(Saudi Geological Survey)에서 받은 2008 ~ 2014년 기간의 규모 5.5 이상, 진앙거리 $40^{\circ}$ 이내인 지진 자료들을 사용하였다. 획득한 자료들은 전처리를 거쳐 다중 필터 기법(multiple filter technique)을 적용하여 분산 곡선을 구하였다. 주기 5 ~ 140초에 해당하는 러브파와 레일리파의 군속도 분산 곡선을 역산하여 10 ~ 60 km에서의 SH파와 SV파 속도모델 그리고 이방성을 계산하였다. 그 결과 SV파의 속도모델에서는 순상지 하부 10 ~ 30 km 깊이에서 고속도 이상대를 보이며, 플랫폼 하부에서는 10 km 깊이에서 저속도 이상대를 보인다. 이는 순상지가 원생누대 기원의 오래되고 차가운 육괴로 되어있으며, 플랫폼이 고생대, 중생대, 신생대의 퇴적물로 덮여 있기 때문에 이와 같은 결과가 나왔다고 판단된다. SV파와 SH파의 속도 차이를 이용하여 구한 이방성의 결과는 전반적으로 양의 이방성이 나타나며, 이는 자그로스 조산대에서의 섭입으로 인한 아라비아 판의 당김에 의해 인장력이 수평 방향으로 발생하여 SH파의 속도가 빠르게 나타난다고 판단된다.

• 천문학회보
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• 제40권1호
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• pp.78.4-79
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• 2015

We present the spatially resolved kinematics of ionized gas and stars along the major axis of 9 pseudo bulge galaxies. Using the high quality long-slit spectra obtained with the FOCAS at the Subaru telescope, we measured the flux, velocity, and velocity dispersion of the [OIII] and $H{\beta}$ lines to determine the size of the narrow-line region, rotation curve, and the radial profile of velocity dispersions. We compare ionized gas kinematics and stellar kinematics to investigate whether ionized gas shows any signs of outflows and whether stars and ionized gas show the same sigma-dip feature (i.e., decrease of velocity dispersion) at the very center.

• 천문학회보
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• 제39권2호
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• pp.69.1-69.1
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• 2014

We present the spatially resolved kinematics of ionized gas and stars along the major axis of 9 pseudo bulge galaxies. Using the high quality long-slit spectra obtained with the FOCAS at the Subaru telescope, we measured the flux, velocity, and velocity dispersion of the [OIII] and $H{\beta}$ lines to determine the size of the narrow-line region, rotation curve, and the radial profile of velocity dispersions. We compare ionized gas kinematics and stellar kinematics to investigate whether ionized gas shows any signs of outflows and whether stars and ionized gas show the same sigma-dip feature (i.e., decrease of velocity dispersion) at the very center.

• 천문학회보
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• 제36권2호
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• pp.141.2-141.2
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• 2011

We present physical parameters of the detached eclipsing binary KIC3858884, which has a d-Scuti type pulsating secondary component. To derive orbital elements from radial-velocity curve, high-resolution Echelle spectra were obtained at the Bohyunsan Optical Astronomy Observatory in Korea. The BOES spectra and Kepler photometric data were analyzed with JKTEBOP and Wilson-Devinney model for eclipsing light-curve synthesis and Period04 for pulsation frequency analysis. After the iterative curve fitting, we determined physical parameters of KIC3858884 as $M_1=2.02{\pm}0.23M_{\odot}$, $M_2=2.02{\pm}0.16M_{\odot}$, $R_1=3.61{\pm}0.12R_{\odot}$, $R_2=2.84{\pm}0.10R_{\odot}$, respectively.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.22-23
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• 2006

High velocity compaction (HVC) is a production technique with capacity to significantly improve the mechanical properties of powder metallurgy (PM) parts. Investigated here are green body data such as density, tensile strength, radial springback, ejection force and surface flatness. Comparisons are performed with conventional compaction using the same pressing conditions. Cylindrical samples of a pre-alloyed water atomized iron powder are used in this experimental investigation. The HVC process in this study resulted in a better compressibility curve and lower ejection force compared to conventional quasi static pressing. Vertical scanning interferometry measurements show that the HVC process gives flatter sample surfaces.

• Wind and Structures
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• 제32권4호
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• pp.371-391
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• 2021

Tornadoes are the most devastating meteorological natural hazards. Many empirical and theoretical numerical models of tornado vortex have been proposed, because it is difficult to carry out direct measurements of tornado velocity components. However, most of existing numerical models fail to explain the physical structure of tornado vortices. The present paper proposes a new empirical numerical model for a tornado vortex, and its load effects on a low-rise and a tall building are calculated and compared with those for existing numerical models. The velocity components of the proposed model show clear variations with radius and height, showing good agreement with the results of field measurements, wind tunnel experiments and computational fluid dynamics. Normal stresses in the columns of a low-rise building obtained from the proposed model show intermediate values when compared with those obtained from existing numerical models. Local forces on a tall building show clear variation with height and the largest local forces show similar values to most existing numerical models. Local forces increase with increasing turbulence intensity and are found to depend mainly on reference velocity Uref and moving velocity Umov. However, they collapse to one curve for the same normalized velocity Uref / Umov. The effects of reference radius and reference height are found to be small. Resultant fluctuating force of generalized forces obtained from the modified Rankine model is considered to be larger than those obtained from the proposed model. Fluctuating force increases as the integral length scale increases for the modified Rankine model, while they remain almost constant regardless of the integral length scale for the proposed model.

• Journal of Astronomy and Space Sciences
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• 제29권2호
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• pp.115-121
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• 2012

Existing but largely unused binary star model capabilities are examined. An easily implemented scheme is parameterization of starspot growth and decay that can stimulate work on outer convection zones and their dynamos. Improved precision in spot computation now enhances analysis of very precise data. An existing computational model for blended spectral line profiles is accurate for binary system effects but needs to include damping, thermal Doppler, and other intrinsic broadening effects. Binary star ephemerides had been found exclusively from eclipse timings until recently, but now come also from whole light and radial velocity curves. A logical further development will be to expand these whole curve solutions to include eclipse timings. An attenuation model for circumstellar clouds, with several absorption and scattering mechanisms, has been applied only once, perhaps because the model clouds have fixed locations. However the clouds could be made to move dynamically and be combined into moving streams and disks. An area of potential interest is polarization curve analysis, where incentive for modeling could follow from publication of observed polarization curves. Other recent advances include direct single step solutions for temperatures of both stars of an eclipsing binary and third body kinematics from combined light and velocity curves.