• 천문학회보
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• 제41권2호
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• pp.50.3-51
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• 2016

Recent analysis on the thermophysical property of asteroids revealed that their thermal inertia decrease with their sizes at least for main belt asteroids. However, little is known about that of comet-like bodies. In this work we utilized a simple thermophysical model (TPM) to calculate the thermal inertia of a bare nucleus of the comet P/2006 HR30 (Siding Spring) and an asteroid in comet-like orbit 107P/(4015) Wilson-Harrington from AKARI observation data. From five spectroscopic observations of the targets, we find out that the former has thermal inertia of around $2,000J\;m^{-2}K^{-1}s^{-1/2}$ (using pV = 0.055) and the latter has about $1,000-2000J\;m^{-2}K^{-1}s^{-1/2}$ (using pV = 0.055 and 0.043, respectively). These are high enough for both of them to deposit water ice at few centimeters depth, and hence it is difficult to say they are cometary based on the results of this study. These values, however, dependent significantly on the errors of observation and the uncertainties of the input parameters, as well as other conditions which are ignored in simple TPM approach, such as shape model and surface roughness. Further detailed analyses on these cometary bodies will shed light on our understanding of the detailed surfacial characteristics of them.

• Asian Pacific Journal of Cancer Prevention
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• 제14권8호
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• pp.4641-4646
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• 2013

Objective: To explore clinical experience and propose new ideas for treating children diagnosed with orbital rhabdomyosarcoma (RMS). Methods: We retrospectively analyzed the clinical data for30 patients (16 males and 14 females, with a median age of 6.2 years) with primary orbital RMS who were enrolled in the Department of Eye Oncology and Pediatrics of our hospital from November 2004 to December 2012. International Rhabdomyosarcoma Organization Staging Standards indicated that among the 30 patients, 4 cases were in phase II, 20 were in phase III, and 6 were in phase IV. All patients underwent a multidisciplinary collaborative model of comprehensive treatment (surgery, chemotherapy, external radiotherapy, $^{125}I$ radioactive particle implantation, and autologous peripheral blood stem-cell transplantation). Results: Follow-up was conducted until March 2013, with a median follow-up time of 47.2 months (5 to 95 months), and 7 deaths occurred. The 2-year estimated survival rate reached 86.1%, the ${\geq}3$-year estimated survival rate was 77%, and the 5-year estimated survival rate was 70.6%. Conclusions: The multidisciplinary collaborative model can be a safe and effective approach to the comprehensive treatment of children with orbital RMS. It has clinical significance in improving the tumor remission rate.

• 한국기계가공학회지
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• 제11권4호
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• pp.104-110
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• 2012

The spindle with a built-in motor can be used to simplify the structure of machine tool system, while the rotor has unbalance mass inevitably. A high-speed spindle can be very sensitive to rotating mass unbalance which has harmful effect on many machine tools. Therefore, the balancing procedure to reduce vibration in rotating system is certainly needed for all high-speed spindles. So, it was performed with a spindle-bearing system for CNC automatic lathe by using numerical procedure. The spindle is supported by the angular contact ball bearings and the motor rotor is fixed at the middle of spindle. The spindle-bearing system has been investigated using combined methodologies of finite elements and transfer matrices. The balancing was performed through influence coefficient method and the comparison was made by whirl responses between before balancing and after balancing. As a result, balancing of simple spindle model reduced whirl orbit magnitude in case of a completely assembled spindle model.

• 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.

• 천문학회지
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• 제33권2호
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• pp.127-135
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• 2000

We investigate the effects of planetary rotation on the exospheres of the earth and Mars with simple collisionless models. We develope a numerical code that computes exospheric densities by integrating velocity functions at the exobase with a 10 point Gauss method. It is assumed in the model that atoms above the exobase altitude move collisionlessly on an orbit under the planet's gravity. Temperatures and densities at the exobase over the globe are adopted from MSIS-86 for the earth and from Bougher et al's MTGCM for Mars. For both the earth and Mars, the rotation affects the exospheric density distribution significantly in two ways: (1) the variation of the exospheric density distribution is shifted toward the rotational direction with respect to the variation at the exobase, (2) the exospheric densities in general increase over the non-rotating case. We find that the rotational effects are more significant for lower thermospheric temperatures. Both the enhancement of densities and shift of the exospheric distribution due to rotation have not been considered in previous models of Martian exosphere. Our non-spherical distribution with the rotational effects should contribute to refining the hot oxygen corona models of Mars which so far assume simple geometry. Our model will also help in analyzing exospheric data to be measured by the upcoming Nozomi mission to Mars.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.598-602
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• 2017

한국항공우주연구원에서는 1.5톤급의 실용위성을 태양동기궤도에 투입할 수 있는 3단형 발사체인 한국형발사체 KSLV-II를 개발하고 있다. 한국형발사체의 개발과정으로 2018년에는 2단과 3단으로 구성된 시험발사체(TLV)를 발사할 계획이며 여기에 사용되는 추진기관은 한국형발사체의 2단 엔진인 75톤급 엔진의 지상형 모델과 추진제 탱크, 공급 시스템이 적용되게 될 것이다. 현재 엔진시스템을 포함한 시험발사체 추진기관의 경우, 엔지니어링모델(EM)의 조립과 인증모델(QM)의 제작, 납품이 이루어지고 있다. 본 논문에서는 한국형발사체 추진기관의 개발중 수행되고 있는 제품보증 활동에 대하여 설명하고자 한다.

• Journal of Power Electronics
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• 제19권3호
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• pp.655-664
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• 2019

In order to analyze the nonlinear phenomena of the bifurcation and chaos caused by the switching of nonlinear switching devices in inductively coupled power transfer (ICPT) systems, a Jacobian matrix model, based on discrete mapping numerical modeling, is established to judge the system stability of the periodic closed orbit and to study the nonlinear behavior of Hopf bifurcation in a system under full resonance. The general flow of the parameter design, based on the stability principle for ICPT systems, is proposed to avoid the chaos and bifurcation phenomena caused by unreasonable parameter selection. Firstly, based on the state equation of SS-type compensation, a three-dimensional bifurcation diagram with the coupling coefficient as the bifurcation parameter is established with a numerical simulation to observe the nonlinear phenomena in the system. Then Filippov's method based on a Jacobian matrix model is adopted to deduce the boundary of stable operation and to judge the type of the bifurcation in the system. Then the general flow of the parameter design based on the stability principle for ICPT systems is proposed through the above analysis to realize stable operation under the conditions of weak coupling. Finally, an experimental platform is built to confirm the correctness of the numerical simulation and modeling.

• 천문학회보
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• 제44권1호
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• pp.48.2-48.2
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• 2019

Tidal disruption events (TDEs) provide evidence for quiescent supermassive black holes (SMBHs) in the centers of inactive galaxies. TDEs occur when a star on a parabolic orbit approaches close enough to a SMBH to be disrupted by the tidal force of the SMBH. The subsequent super-Eddington accretion of stellar debris falling back to the SMBH produces a characteristic flare lasting several months. It is theoretically expected that the bolometric light curve decays with time as proportional to $t^{-5/3}$. However, some of the observed X-ray light curves deviate from the $t^{-5/3}$ decay rate, while some of them are overall in good agreement with the $t^{-5/3}$ law. Therefore, it is required to construct the theoretical model for explaining these light curve variations consistently. In this paper, we revisit the mass fallback rates semi-analytically by taking account of the stellar internal structure, orbital eccentricity and penetration factor. We find that the mass fallback rate is shallower than the standard $t^{-5/3}$ decay rate independently of the polytropic index, and the orbital eccentricity only changes the magnitude of the mass fallback rate. Furthermore, the penetration factor significantly can modify the magnitude and variation of mass fallback rate. We confirm these results by performing the computational hydrodynamic simulations. We also discuss the relevance of our model by comparing these results with the observed light curves.

• 한국항공우주학회지
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• 제49권5호
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• pp.407-415
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• 2021

인공위성의 부품은 발사 전 지상에서의 우주 궤도환경 하에서의 성능검증이 필수적이다. 본 논문은 열진공시험을 위한 위성 부품 및 소형 열진공챔버 간의 전도, 복사, 열손실 및 내부 발열의 열환경을 고려한 모델식을 설계하였다. 최근 한국항공우주연구원에서 수행된 열진공시험 20건의 시험데이터를 이용한 시스템 식별을 수행하였다. 시험품 기능시험의 발열이 일정하지 않는 경우를 제외하고 시스템 식별의 정확성을 확인함으로써 개발된 모델식이 유효함을 검증하였다.

• 한국항공우주학회지
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• 제31권1호
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• pp.120-124
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• 2003

KAIST 인공위성연구센터에서는 우리별 1, 2, 3호의 개발에 이어 과학위성 1호를 개발하고 있다. 2003년에 발사 예정인 과학위성 1호는 현재 인증모델 단계의 개발 및 시험이 완료되었다. 본 인증모델 열진공 시험에서는 위성의 각 서브시스템이 예상되는 궤도 상의 온도보다 가혹한 조건에서 시험되었고, 열해석 모델의 검증 및 수정을 위한 열진공평형 시험도 수행되었다. 본 논문에서는 과학위성 1호의 인증모델 열진공 시험 과정 및 결과와 더불어 그 과정에서 알아낸 문제점 및 개선방안 등을 살펴보고, 또한 향후 유사한 소형위성 열진공 시험에 유용하게 쓰일 수 있는 고려 사항들을 검토한다.