• Journal of Astronomy and Space Sciences
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• 제20권4호
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• pp.269-282
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• 2003

Grieve(1991), Moon et al.(2001), Earth Impact Database(2002; DB02) 등 세 가지 충돌구 DB를 이용해서 미행성 지구충돌 사건의 주기성 여부를 조사했다. 특히 DB02는 과거 사용됐던 데이터베이스들에 비해서 연령 측정오차가 크게 향상되었으며, 이를 이용한 주기분석 발표는 이번이 처음이다. DB02(나이 $t{\leq}250Myr$ 및 $t{\leq}150Myr$, 나이오차 ${\Delta}t{\leq}{\pm}10Myr$)에 대 한 Fourier 분석 결과, $D{\geq}5km$와 $D{\geq}20km$인 표본의 경우, 주기성이 검출되지 않았다. 그러나 $D{\geq}30km$인 표본인 경우 16.1Myr와 34.7Myr에서 두 개의 피크가 나타났고, $D{\geq}45km$인 표본은 16.1Myr부근에서 강한 파워를 보였다. 이로부터 우리는 $d{\geq}1.5km$인 천체의 주기적인 지구 충돌 가능성을 고려할 수 있으며, 충돌구 나이의 정밀도는 물론 t와 D의 범위, 그리고 데이터베이스의 선택이 미행성의 지구충돌의 역사를 재구성하는데 중요한 변수로 작용한다는 사실을 확인했다.

• 천문학회보
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• 제37권1호
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• pp.98.1-98.1
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• 2012

The Hayabusa mission successfully rendezvoused with its target asteroid 25143 Itokawa in 2005 and brought the asteroidal sample to the Earth in 2009. This mission enabled to connect the S-type asteroids to ordinary chondrites, the counterpart meteorites which exist in near Earth orbit. Recent finding of a fragment from 25143 Itokawa [1] suggested that the asteroid experienced an impact after the injection to the near-Earth orbit. In this presentation, we investigated the evidence of the recent impact on 25143 Itokawa using the onboard camera, AMICA. AMICA took more than 1400 images of Itokawa during the rendezvous phase. It is reported that AMICA images are highly contaminated by lights scattered inside the optics in the longer wavelength. We developed a technique to subtract the scattered light by determining the point spread functions for all available channels. As the result, we first succeeded in the determination of the surface spectra in all available bands. We consider a most fresh-looking compact crater, Kamoi, is a possible impact site.

• 천문학회보
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• 제37권2호
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• pp.138.2-138.2
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• 2012

Cave on the Moon is considered as the most appropriate place for human to live during the frontier lunar exploration. While the lava flows, the outer crust gets cooled and solidified. Then, the empty space is remained inside after lava flow stops. Such empty space is called the lava caves. Those lava tubes on the Earth are formed mostly by volcanic activity. However, the lava tubes on satellite like Moon and planet like Mars without volcanic activity are mostly formed by the lava flow inside of the crater made by large meteorite impact. Some part of lava tube with collapsed ceiling appears as the entrance of the cave. Such area looks like a deep crater so called a pit crater. Four large pit craters with diameter of > 60 m and depth of > 40 m are found without difficulty from Kaguya and LRO mission image archives. However, those are too deep to use as easily accessible human frontier base. Therefore, now we are going to identify some smaller lunar caves with accessible entrances using LRO camera images of 0.5 m/pixel resolution. Earth's lava caves and their entrances are well photographed by surface and aerial camera in immense volume. Thus, if the image data are sorted and archived well, those images can be used in comparison with the less distinct lunar cave and entrance images due to its smaller size. Then, we can identify the regions on the Moon where there exist caves with accessible entrances. The database will be also useful in modeling geomorphology for lunar and Martian caves for future artificial intelligence investigation of the caves in any size.

• Journal of Astronomy and Space Sciences
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• 제32권2호
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• pp.113-120
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• 2015

When humans explore the Moon, lunar caves will be an ideal base to provide a shelter from the hazards of radiation, meteorite impact, and extreme diurnal temperature differences. In order to ascertain the existence of caves on the Moon, it is best to visit the Moon in person. The Google Lunar X Prize(GLXP) competition started recently to attempt lunar exploration missions. Ones of those groups competing, plan to land on a pit of Lacus Mortis and determine the existence of a cave inside this pit. In this pit, there is a ramp from the entrance down to the inside of the pit, which enables a rover to approach the inner region of the pit. In this study, under the assumption of the existence of a cave in this pit, a 3D model was developed based on the optical image data. Since this model simulates the actual terrain, the rendering of the model agrees well with the image data. Furthermore, the 3D printing of this model will enable more rigorous investigations and also could be used to publicize lunar exploration missions with ease.

• Journal of Astronomy and Space Sciences
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• 제25권2호
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• pp.71-76
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• 2008

Study of terrestrial impact craters is important not only in the field of the solar system formation and evolution but also of the Galactic astronomy. The terrestrial impact cratering record recently has been examined, providing short- and intermediate-term periodicities, such as, ${\sim}26$ Myrs, ${\sim}37$ Myrs. The existence of such a periodicity has an implication in the Galactic dynamics, since the terrestrial impact cratering is usually interpreted as a result of the environmental variation during solar orbiting in the Galactic plane. The aim of this paper is to search for a long-term periodicity with a novel method since no attempt has been made so far in searching a long-term periodicity in this research field in spite of its great importance. We apply the cepstrum analysis method to the terrestrial impact cratering record for the first time. As a result of the analysis we have found noticeable peaks in the Fourier power spectrum appear ing at periods of ${\sim}300$ Myrs and ${\sim}100$ Myrs, which seem in a simple resonance with the revolution period of the Sun around the Galactic center. Finally we briefly discuss its implications and suggest theoretical study be pursued to explain such a long-term periodicity.

• Journal of Astronomy and Space Sciences
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• 제23권3호
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• pp.199-208
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• 2006

The terrestrial impact cratering record recently has been examined in the time domain by Chang & Moon (2005). It was found that the ${\sim}26$ Myr periodicity in the impact cratering rate exists over the last ${\sim}250$ Myrs. Such a periodicity can be found regardless of the lower limit of the diameter up to D ${\sim}35km$. It immediately called pros and cons. The aim of this paper is two-fold: (1) to test if reported periodicities can be obtained with an independent method, (2) to see, as attempted earlier, if the phase is modulated. To achieve these goals we employ the time/frequency analysis and for the first time apply this method to the terrestrial impact cratering records. We have confirmed that without exceptions noticeable peaks appear around ${\sim}25$ Myr, corresponding to a frequency of ${\sim}0.04(Myr)^{-1}$. We also find periodicities in the data base including small impact craters, which are longer. Though the time/frequency analysis allows us to observe directly phase variations, we cannot find any indications of such changes. Instead, modes display slow variations of power in time. The time/frequency analysis shows a nonstationary behavior of the modes. The power can grow from just above the noise level and then decrease back to its initial level in a time of order of 10 Myrs.

• 우주기술과 응용
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• 제1권2호
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• pp.217-240
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• 2021

본 논문은 다가오는 달 유인 탐사시대를 대비하여 달의 지형 및 지질학적 기초 지식을 우주과학자들에게 소개한다. 달 지형 용어에 대한 학술적 기원을 간단히 정리하였으며, 현재 통용되는 한글 용어를 확장하여 새로운 지형 용어들을 제안하였다. 특히, 일반인도 꼭 알아야 할 대표적인 달의 지형으로 1 대양(폭풍의 대양), 10대 바다(비의 바다, 평온의 바다, 고요의 바다, 감로주의 바다, 풍요의 바다, 위난의 바다, 증기의 바다, 인식의 바다, 습기의 바다, 구름의 바다), 6대 충돌구(티코, 코페르니쿠스, 케플러, 아리스타쿠스, 스테비누스, 랑그레누스)를 제안한다. 달의 지형으로 고원(highland), 바다(maria), 산맥(mountains), 충돌구(crater), 함몰 용암굴/열구(rille, rima), 지구대(graben), 돔(dome), 용암동굴(lava tube), 주름 능선(wrinkle ridge), 참호(trench), 절벽(rupes), 그리고 달의 표면 흙을 표토(regolith)로 사용할 것을 제안한다. 또한, 달의 내부 구조 표준 모델과 대표적 암석을 소개하였다. 지구의 지질 시대구분은 발견 화석과 방사성 동위원소를 이용한 절대연령 측정을 기준으로 하는 반면, 표준적인 달의 지질 시대 구분은 대표적인 충돌구 형성을 기준으로 선-넥타리스 기(Pre-Nectarian), 넥타리스 기(Nectarian), 임브리움 기(Imbrian), 에라토스네스 기(Erathostenesian), 코페르니쿠스 기(Copernican)로 나뉜다. 마지막으로 인간의 달 활용에 획기적인 계기가 되는 최근의 달 표면 물 발견에 대한 내용을 정리하였으며, 향후 한국지질자원연구원에서 개발될 물 채취 장치의 개념도 소개하였다.

• 천문학회보
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• 제43권2호
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• pp.44.3-44.3
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• 2018

수성의 대기와 자기장은 매우 희박하여 그 표면이 우주 환경에 거의 그대로 노출되어있다. 표면의 토양은 태양풍입자와 미소유성체 등에 의해 계속해서 밝기가 어두워지고 입자의 크기도 작아진다. 이러한 현상을 종합적으로 '우주풍화'(space weathering)라고 부르는데, 그 정도를 정량화하거나 상대적으로 평가하는 데에는 어려움이 따른다. 왜냐하면 우주풍화의 정도에는 원인이 되는 입자의 입사 플럭스는 물론이고, 표면의 지역 조성비와 토양의 노화도 등이 모두 섞여 영향을 미치기 때문이다. 이를 극복하는 한 가지 방법은 수성 표면을 뒤덮고 있는 수많은 충돌구(impact crater) 내의 광학적 특성 분포를 통계적으로 분석하는 것이다. 충돌구 안쪽의 토양은 충돌 시점에 동시에 형성되었고, 그 성분이 충돌구 밖 임의의 지역에 비교해 상대적으로 균질하며, 지형적으로 충돌구 안팎의 경계가 분명하게 정해져 있다. 또한, 충돌구는 수성 전구(全球)에 걸쳐 어디에서나 발견되므로 각 충돌구의 특성을 경도 위도 연대 등 여러 측면에서 조사할 수 있다. 본 연구에서는, 메신저(MESSENGER) 탐사선의 MDIS 영상기에서 얻은 관측 자료를 활용하여 수성 충돌구의 광학적 특성에 대해 알아본다.

• 대한기계학회논문집A
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• 제20권12호
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• pp.3847-3855
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• 1996

In order to study the relationship between static and cynamic behaviors of silion caride, both quasi-static indentaiton and impact experiments of spherical particle have been conducted. The difference inmaterial behavior when using the two mehtods suggests a loading rate difference in the damate pattrern and fracture strength of silicon carbide. This investigation showed some difference in damage pattern according to particla property, especially inthe case of particle impact. There was no differences in deformation behaviors according to the loading rate when the crater profiles were compared with each other at the same contact radius. From the result of residual strength evaluation, it was found that the strength degradation began at the initiation of ring crack and its behavior was colsely related to morphologies of the damage developed which was also dependent upon the extent of deformation atthe loaidng point. In the case of static indentation, there didnot exist the particle property effects onthe strength degradation behavior.

• Computers and Concrete
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• 제5권6호
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• pp.509-524
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• 2008

Containment structures not only are leak-tight barriers, but also may be subjected to impacts caused by tornado-generated projectiles, aircraft crashes or the fragments of missile warhead. This paper presents the results of an experimental study of the impact resistance of steel fiber-reinforced concrete against 45 g projectiles at velocity around 2500 m/s. An explosively formed projectile (EFP) was designed to generate an equivalent missile fragment. The formation and velocity of EFP are measured by flash x-ray. A switch made of double-layered thin copper sheets controlled the exposure time of each flash x-ray. The influence of the fiber volume fraction on the crater diameter of concrete slab and the residual velocity of the projectile were studied. The residual velocity of the projectile decreased as the fiber volume fractions increased. In this work, the residual velocity of the projectile was to 44% that of plain concrete when the fiber volume fraction exceeded 1.5%. Based on the present finding, steel fiber reinforced concrete with the fiber volume fraction exceeding 1.5% appear to be more efficient in protection against high velocity fragment impact.