• 천문학회보
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• 제30권1호
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• pp.75.1-75.1
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• 2005

• 항공우주기술
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• 제12권2호
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• pp.91-98
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• 2013

LEO (Low Earth Orbit), GEO (Geosynchronous Earth Orbit) 위성을 비롯한 우주 탐사선의 컴퓨팅 환경은 지상의 내장형 시스템(Embedded System)과 동일한 범주로 간주될 수 있으며 개인용, 산업/서버용 컴퓨터와 비교했을 때 비교적 원시적이고 발전 속도도 더뎠다. 특히 개인 컴퓨터 및 서버/워크스테이션에서 필수적으로 사용되고 있는 파일 시스템도 우주 탐사선에는 최근까지 거의 사용되지 않았다. 본 논문에서는 최근에 우주 탐사선에 파일 시스템을 적용하기 위한 유럽 PUS (Packet Utilization Standard)와 CCSDS (Consultative Committee for Space Data Systems) 커뮤니티의 관련 규격 제정 등 국제적 연구 개발 동향 및 우주 탐사선에 적용가능한 응용 기술 분야에 대한 연구 결과를 기술한다.

• Journal of Astronomy and Space Sciences
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• 제22권3호
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• pp.249-262
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• 2005

순간적인 속도변화에 의한 ECO(Earth-Crossing Object)의 케도변경을 최적화하는 알고리즘을 개발하였다. 이를 통해, ECO의 궤도변경을 위한 속도변위를 계산할 때, 기존연구에서 간과되었던 궤도평면에 수직인 방향의 속도 변화를 살펴보았다. 이러한 3차원의 최적화 문제를 풀기위해서 순간적인 속도변화를 계산하기 위한 순간추력 근사법이 적용되었으며, ECO의 지구 접근 시에는 지구중력 효과를 고려한 부분적 궤도근사법을 사용하였다. 지구와 충돌천체의 상대적인 위치와 속도에 따라 ECO의 궤도변경을 위한 최적해가 달라지며, 그러한 최적해는 순간추력시간에 대한 최적속도변화나 최적비행각으로 표현될 수 있다. 순간추력시간이 작을 때, 궤도평면에 수직인 방향의 속도 변화를 무시할 수 없는 경우도 발견되었다. ECO의 궤도가 지구의 궤도와 비슷할수록 더 많은 최적속도변화가 필요로 하였으며, 순간추력시간이 충돌 순간에 가까워질수록 궤도변경에 필요한 최적속도변화의 크기가 지수함수적으로 증가하였다. 이러한 연구결과는 실제 ECO의 우주임무를 설계하는데 중요한 지침이 될 것이다.

• 천문학회보
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• 제37권2호
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• pp.108.1-108.1
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• 2012

Previously we introduced ray-tracing based 3D optical earth system model for specular and scattering properties of all components of the system (i.e. clear-sky atmosphere, land surfaces and an ocean surface). In this study, we enhanced 3-dimensional atmospheric structure with vertical atmospheric profiles for multiple layer and cloud layers using Lambertian and Mie theory. Then the phase dependent disk averaged spectra are calculated. The main results, simulated phase dependent disk averaged spectra and light curves, are compared with the 7 bands(300~1000nm) light curves data of the Earth obtained from High Resolution Instrument(HRI) in Deep Impact spacecraft during Earth flyby in 2008. We note that the results are comparable with the observation.

• 천문학회보
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• 제38권2호
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• pp.92.2-92.2
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• 2013

We revisit the 1.3-year (yr) signals observed on the Sun, in the interplanetary space, and in the Earth's magnetosphere to study the coupling among signals from the three regions for about forty years (1970--2007) covering three solar cycles 21, 22, and 23. For this, we make dynamic spectra of datasets including three different regions. From this, we estimate the peak frequency around 1.3 yr for each region and the corresponding band power. We found that coherent power only appears during 1987-1995 and the coherent behavior is found only in the interplanetary space and Earth, not in the Sun. Although the solar surface magnetic field shows significant power around 1.3 yr, their peak frequencies are statistically different from those of the outer regions, which make us to dismiss the existence of coherence among the three regions. But it is notable that the peaks in band power corresponding to the 1.3-yr period are clearly simultaneous in the interplanetary space and Earth.

• 지구물리와물리탐사
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• 제26권4호
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• pp.238-267
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• 2023

지구자전과 조석현상에 관하여 19세기 이후 현재까지 알려진 주요 내용들을 소개하였다. 지구자전속도의 영년적/주기적 변화, 세차운동과 장동, 극운동에 관하여 기술하였으며, 또한 지구의 공전/자전 상태와 빙하기도래의 관련설 - Milankovitch 이론에 대하여 돌아보고, 자전과 긴히 연관된 현상으로서 지구조석에 대하여도 기술하였다. 그리고 몇몇 이론적 상세를 부록에 두었다.

• Journal of Photoscience
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• 제9권2호
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• pp.41-43
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• 2002

In photoreceptor cells, light activates visual pigments consisting of a chromophore (retinal) and a protein moiety (opsin). Activated visual pigments trigger an enzymatic cascade, called phototransduction cascade, in which more than ten phototransduction proteins are participating. Two types of vertebrate photoreceptor cells, rods and cones, play roles in twilight and daylight vision, respectively. Cones are further classified into several subtypes based on their morphology and spectral sensitivity. Though the diversities of vertebrate photoreceptor cells are crucial for color discrimination and detection of light over a wider range of intensities, the molecular mechanism to characterize the photoreceptor types remains unclear. We investigated the amino acid sequences of about 50 vertebrate opsins, and found that these sequences can be classified into five fundamental subfamilies. Clear relationships were found between these subfamilies and their characteristic spectral sensitivities. In addition to opsins, we studied other phototransduction proteins. The amino acid sequences of phototransduction proteins can be classified into a few subfamilies. Even though their spectral sensitivity is considerably different, cones fundamentally share the phototransduction protein isoforms which are different from those found in rods. It is suggested that the difference in phototransduction proteins between rods and cones is responsible for their sensitivity to light. Isoforms and their selective expression may characterize individual photoreceptor cells, thus providing us with physiological functions such as color vision and daylight/twilight visions.

• Journal of Astronomy and Space Sciences
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• 제31권1호
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• pp.7-13
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• 2014

Variabilities in the solar wind cause disturbances throughout the heliosphere on all temporal and spatial scales, which leads to changeable space weather. As a view of space weather forecasting, in particular, it is important to know direct and indirect causes modulating the space environment near the Earth in advance. Recently, there are discussions on a role of the interaction of the solar wind with Mercury in affecting the solar wind velocity in the Earth's neighborhood during its inferior conjunctions. In this study we investigate a question of whether other parameters describing the space environment near the Earth are modulated by the inner planets' wake, by examining whether the interplanetary magnetic field and the proton density in the solar wind observed by the Advanced Composition Explorer (ACE) spacecraft, and the geomagnetic field via the Dst index and Auroral Electrojet index (AE index) are dependent upon the relative position of the inner planets. We find there are indeed apparent variations. For example, the mean variations of the geomagnetic fields measured in the Earth's neighborhood apparently have varied with a timescale of about 10 to 25 days. Those variations in the parameters we have studied, however, turn out to be a part of random fluctuations and have nothing to do with the relative position of inner planets. Moreover, it is found that variations of the proton density in the solar wind, the Dst index, and the AE index are distributed with the Gaussian distribution. Finally, we point out that some of properties in the behavior of the random fluctuation are to be studied.

• International Journal of Aeronautical and Space Sciences
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• 제14권2호
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• pp.193-199
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• 2013

This work investigates the orbital perturbations of the cubesats that lie on LEO due to Earth albedo. The motivation for this paper originated in the investigation of the orbital perturbations for closed- Earth pico-satellites due to the sunlight reflected by the Earth (the albedo). Having assumed that the Sun lies on the equator, the albedo irradiance is calculated using a numerical model in which irradiance depends on the geographical latitude, longitude and altitude of the satellite. However, in the present work the longitude dependency is disregarded. Albedo force and acceleration components are formulated using a detailed model in a geocentric equatorial system in which the Earth is an oblate spheroid. Lagrange planetary equations in its Gaussian form are used to analyze the orbital changes when $e{\neq}0$ and $i{\neq}0$. Based on the Earth's reflectivity data measured by NASA Total Ozone Mapping Spectrometer (TOMS project), the orbital perturbations are calculated for some cubesats. The outcome of the numerical test shows that the albedo force has a significant contribution on the orbital perturbations of the pico-satellite which can affect the satellite life time.

• 천문학회보
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• 제36권2호
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• pp.94.1-94.1
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• 2011

Recurrent substorms occur when high-speed solar wind streamers pass by Earth's magnetosphere. Most of the previous researches have been done using the observations obtained at the geosynchronous orbit focusing on the relationship between the solar wind disturbances and the occurrence of substorms. However, it is important to investigate the dynamics of the magnetotail because the magnetotail is the place where substorms develop. In this study we investigated the observations of recurrent dipolarizations in the near-Earth magnetotail that occurred during high-speed solar wind streamers. The dipolarizations and subsequent stretchings have occurred for more than three days with the average period of ~2 - 3 hours. The average period of ~2 - 3 hours is consistent with the average occurrence period of recurrent substorms. Also, the observed signatures on the geosynchronous orbit and the ground show recurrent substorms have occurred during the event. These suggest that the recurrent dipolarizations in the near-Earth magnetotail should be closely related to the recurrent substorms. On the other hand, there was no clear flow activities directly associated with the dipolarizations, except for some intermittent bursty flow activities. We will discuss the detailed characteristics of the dipolarizations and the relationship with recurrent substorms.