• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.101.1-101.1
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• 2012

Interplanetary dust particles are observable as zodiacal light, which is the sunlight scattered by the interplanetary dust particles. The origins of interplanetary dust particles are still in question because they are eroded by Poynting-Robertson photon drag and mutual collisions among dust particles. The small-scale structures in the zodiacal light provided a clue to specify their origins. Asteroidal debris were detected as band-like structures (dust bands), and the cometary large particles were detected as narrow trails (dust trails). However, little is confirmative about their detailed origins and mineralogical compositions because of the lack of observational data particularly in the optical wavelength. We made a high-resolution optical zodiacal light map based on the CCD observations at Mauna Kea, Hawaii. We analyzed data taken on November 12, 2004. After the data reduction, such as flat fielding and subtraction of airglow emissions, we succeeded in the construction of the zodiacal light map with the spatial resolution of 3' in the solar elongation between 45 degree and 180 degree. This is the highest resolution map in the visible wavelength so far. In this map, we confirmed the dust bands structures near the ecliptic plane. We will discuss about the similarities and the differences between optical and infrared dust bands.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.56.1-56.1
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• 2018

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. The theoretically expected bolometric light curve decays with time as proportional to $t^{-5/3}$. However, the light curves observed in most of the optical-UV TDEs deviate from the $t^{-5/3}$ decay rate especially at early time, while the light curves of some soft-X-ray TDEs 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 analytically and semi-analytically by taking account of the structure of the star, which is simply modeled by the polytrope. We find the relation between a polytropic index and the power law index of the mass fallback rate. We also discuss whether and how the decay curves, which we derived, fit the observed ones.

• Applied Microscopy
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• v.25 no.1
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• pp.30-47
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• 1995

The ultrastructural changes of adrenal chromaffin cells and ganglion cells in the adrenal gland of vacor-induced diabetic Mongolian gerbils were studied by electron microscopy. After one month of vacor-induced diabetes, some chromaffin cells were filled with dense bodies and large cytosomes with formy contents. Most of degenerating axon terminals were observed on chromaffin cells. A few macrophages were found among chromaffin cells at one month after induction. Several of these macrophages were filled with numerous phagosomes. After one month of vacor-induced diabetes, the ganglion cells showed increase in numbers of dense bodies and degenerating dendrites compared with the normal ganglion cells. Both electron dense and lucent types of degenerating axon terminals were found in interstitial space of the ganglion cells. Degenerating unmyelinated and myelinted axons contained dense and lamellar bodies. The satellite cells and macrophages with engulfed degenerated axon terminals were observed. After three months of vacor-induced diabetes, the unmyelinated and myelinated axons showed degenerative changes, whereas no structural changes could be demonstrated in adrenal ganglion and chromaffin cells. The satellite cells and macrophages containing partially digested debris were still commonly observed in the interstitial space of adrenal medulla. These results suggest that the degenerative changes occur in the adrenal ganglion cells as well as adrenal chromaffin cells of vacor-induced diabetic Mongolian gerbils.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.423-425
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• 2017

When many space launchers and rockets need to be separated, the pyrotechnic separators have been widely used because of their high reliability and high energy generation. However, intensive pyroshock and debris from the high-explosive type separator may cause fatal damage to the equipment inside of the space launchers or rockets. To solve this problem, a pressure-cartridge type low-impact separator has been developed. In this study, one of the low-impact separators, the split-type pyrolock, was used. We established a mathematical model for the split-type pyrolock that simulates the state of combustion gas and the separation behavior of four independent internal components and verified the mathematical model through comparing with experiment results.

• Advances in aircraft and spacecraft science
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• v.7 no.3
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• pp.271-290
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• 2020

The paper describes the analysis of deployment strategies and trajectories design suitable for executing the inspection of an operative spacecraft in orbit through re-usable CubeSats. Similar missions have been though indeed, and one mission recently flew from the International Space Station. However, it is important to underline that the inspection of an operative spacecraft in orbit features some peculiar characteristics which have not been demonstrated by any mission flown to date. The most critical aspects of the CubeSat inspection mission stem from safety issues and technology availability in the following areas: trajectory design and motion control of the inspector relative to the target, communications architecture, deployment and retrieval of the inspector, and observation needs. The objectives of the present study are 1) the identification of requirements applicable to the deployment of a nanosatellite from the mother-craft, which is also the subject of the inspection, and 2) the identification of solutions for the trajectories to be flown along the mission phases. The mission for the in-situ observation of Space Rider is proposed as reference case, but the conclusions are applicable to other targets such as the ISS, and they might also be useful for missions targeted at debris inspection.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.39.1-39.1
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• 2019

Not all stars in the Universe are gravitationally bounded to galaxies. Since first discovered in 1951, observations have revealed that a significant fraction of stars fills the space between galaxies in local (low-redshift) galaxy clusters, observed as diffuse intracluster light (ICL). Theoretical models provide mechanisms for the production of intracluster stars as tidally stripped material or debris generated through numerous galaxy interactions during the hierarchical growth of the galaxy cluster. These mechanisms predict that most intracluster stars in local galaxy clusters are long-accumulated material since z~1. However, there is no observational evidence to verify this prediction. Here we report observations of abundant ICL for a massive (above $10^{14}$ solar masses) galaxy cluster at a redshift of z=1.24, when the Universe was 5 billion years old. We found that more than 10 per cent of the total light of the cluster is contributed by the diffuse ICL out to 110 kpc from the center of the cluster, comparable to 5-20 per cent in local, massive galaxy cluster. Furthermore, we found that the colour of the brightest cluster galaxy located in the core of the cluster is consistent with that of the ICL out to 200 kpc. Our results demonstrate that the majority of the intracluster stars present in the local Universe, contrary to most previous theoretical and observational studies, were built up during a short period and early (z>1) in the history of the Virgo-like massive galaxy cluster formation, and might be concurrent with the formation of the brightest cluster galaxy.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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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.

• Journal of Korean Neurosurgical Society
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• v.59 no.6
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• pp.647-649
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• 2016

The device for intervertebral assisted motion (DIAM) is a dynamic implant that consists of a silicone bumper enveloped by a polyethylene terephthalate (PET) fiber sack. Silicone and PET were used because of their biological inertness, but repetitive motion of the spine can cause wear on the implant nonetheless. The purpose of this study is to report a case of foreign body reaction (FBR) against a DIAM. A 72-year-old female patient presented with lower back pain and both legs radiating pain. She had undergone DIAM implantation at L4-5 for spinal stenosis 5 years previously. The intervertebral disc space of L4-5, where the DIAM was inserted, had collapsed and degenerative scoliosis had developed due to left-side collapse. MRI showed L3-4 thecal sac compression and left L4-5 foraminal stenosis. The patient underwent removal of the DIAM and instrumented fusion from L3 to L5. During surgery, fluid and granulation tissue were evident around the DIAM. Histopathology showed scattered wear debris from the DIAM causing chronic inflammation due to the resulting FBR. A FBR due to wear debris of a DIAM can induce a hypersensitivity reaction and bone resorption around the implant, causing it to loosen.

• Composites Research
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• v.31 no.3
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• pp.83-87
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• 2018

An object in the Low Earth Orbit (LEO) is affected by many environmental conditions unlike earth's surface such as, Atomic oxygen (AO), Ultraviolet Radiation (UV), thermal cycling, High Vacuum and Micrometeoroids and Orbital Debris (MMOD) impacts. The effect of all these parameters have to be carefully considered when designing a space structure, as it could be very critical for a space mission. Polybenzimidazole (PBI) is a high performance thermoplastic polymer that could be a suitable material for space missions because of its excellent resistance to these environmental factors. A thin coating of PBI polymer on the carbon epoxy composite laminate (referred as CFRP) was found to improve the energy absorption capability of the laminate in event of a hypervelocity impact. However, the overall efficiency of the shield also depends on other factors like placement and orientation of the laminates, standoff distances and the number of shielding layers. This paper studies the effectiveness of using a PBI coating on the front bumper in a multi-shock shield design for enhanced hypervelocity impact resistance. A thin PBI coating of 43 micron was observed to improve the shielding efficiency of the CFRP laminate by 22.06% when exposed to LEO environment conditions in a simulation chamber. To study the effectiveness of PBI coating in a hypervelocity impact situation, experiments were conducted on the CFRP and the PBI coated CFRP laminates with projectile velocities between 2.2 to 3.2 km/s. It was observed that the mass loss of the CFRP laminates decreased 7% when coated by a thin layer of PBI. However, the study of mass loss and damage area on a witness plate showed CFRP case to have better shielding efficiency than PBI coated CFRP laminate case. Therefore, it is recommended that PBI coating on the front bumper is not so effective in improving the overall hypervelocity impact resistance of the space structure.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.9
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• pp.818-826
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• 2012

In this paper, the improvement methods of the computational efficiency of the conjunction screening algorithm, which calculates the closest distance between primary satellite and space objects are presented. First method is to use GPU(Graphics Processing Unit) that has high computing power and handles quickly large amounts of data. Second method is to use Apogee/Perigee filter which excludes non-threatening objects that have low probability of collision and/or minimum distance rather than that of thresh hold. Third method is to combine first method with second method. As a result, the computational efficiency has been improved 34 times and 3 times for the first method only and second method only, respectively. On the contrary, the computational efficiency has been dramatically improved 163 times when two kinds of methods are combined.