• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.130.1-130.1
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• 2011

인류의 우주공간에 대한 영향력이 확대됨에 따라, 우주공간에서의 인위적인 활동에 영향을 미칠 수 있는 모든 종류의 상황들에 대한 이해가 최근 전 세계적으로 매우 중요한 이슈로 부상하고 있다. 이를 Space Situational Awareness (SSA)라고 하는데, 특히 근지구공간에서의 인위적, 자연적 우주물체는, 우주발사체의 지속적인 증가와 이리듐-코스모스 위성의 상호 충돌 및 중국 폐기위성 파괴 등과 같은 사건으로 기하급수적으로 증가된 우주물체의 개체수로 인해 대한민국 국적의 모든 위성에도 실제적인 위협 요인으로 대두되고 있다. 이에 기초 기술연구회와 한국천문연구원은 이러한 위협을 국가적으로 해결해야할 과제(National Agenda Project) 중의 하나로 정의하고, 이를 해결하기 위해 우주물체 전자광학 감시체계 기술개발(OWL; Optical Wide-field patroL) 사업을 시작하였다. 이 사업의 목표는 자국위성에 대한 궤도력을 독자적으로 유지할 수 있는 시스템을 개발하는 것이며, 이를 위하여 2011년부터 6년 동안 총 5개소의 해외 관측소에 50cm급 광시야 망원경을 각각 설치하여 자국위성을 자동으로 상시관측하고, 관측된 자료를 이용한 궤도계산을 통하여 독자적으로 궤도력을 유지할 계획이다. 또한, 우주잔해물 감시는 하나의 국가에서 단독으로 할 수 없기 때문에 2m급 우주물체 감시망원경을 개발하여 국제공동으로 진행할 계획이다. 사업 첫해인 2011년 4월 시스템 요구사항 분석을 완료하였고 10월말 시스템 기본설계를 완료할 예정이다. 최종 완성될 소구경 광시야 망원경과 우주물체 감시망원경의 주요 임무는 우주물체 관측이지만, 향후 광시야를 이용한 다양한 탐사천문학에도 기여할 수 있을 것으로 기대한다. 한편, 자국위성에 대한 충돌 위험도 분석 및 회피기동에 관한 연구는 한국항공우주연구원이 이 사업의 협동연구로 참여하고 있다.

• Geophysics and Geophysical Exploration
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• v.15 no.4
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• pp.219-226
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• 2012

This study provides an analysis on results of neutron logging for various borehole environments through numerical simulation based on a Monte Carlo N-Particle (MCNP) code developed and maintained by Los Alamos National Laboratory. MCNP is suitable for the simulation of neutron logging since the algorithm can simulate transport of nuclear particles in three-dimensional geometry. Rather than simulating a specific tool of a particular service company between many commercial neutron tools, we have constructed a generic thermal neutron tool characterizing commercial tools. This study makes calibration chart of the neutron logging tool for materials (e.g., limestone, sandstone and dolomite) with various porosities. Further, we provides correction charts for the generic neutron logging tool to analyze responses of the tool under various borehole conditions by considering brine-filled borehole fluid and void water, and presence of borehole fluid.

• Journal of Ocean Engineering and Technology
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• v.29 no.3
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• pp.241-248
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• 2015

A subsea pipeline for oil/gas transportation or gas injection is subjected to extreme variations in internal pressure and temperature, which can involve a strain rate effect on the pipeline material. This paper describes the flow stress characteristics of a pipeline material called API 5L X52N PSL2, using and experimental approach. High-speed tensile tests were carried out for two metal samples taken from the base and weld parts. The target temperature was 100℃, but two other temperature levels of –20℃and 0℃ were taken into account. Three strain rates were also considered for each temperature level: quasi static, 1/s, and 10/s. Flow stress data were proposed for each temperature level according to these strain rates. The dynamic hardening behaviors of the base and weld metals appeared to be nonlinear on the log-scale strain rate axis. A very high material constant value was required for the Cowper-Symonds constitutive equation to support the experimental results.

• Journal of Korean Tunnelling and Underground Space Association
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• v.14 no.2
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• pp.131-139
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• 2012

In this study, the numerical analysis has been conducted in order to check behavior characteristics of liner plate made of corrugated steel from urban small sized tunnel excavation. The analysis was conducted with five kinds of conditions like 5 m, 10 m, 15 m, 20 m and 25 m to examine the behavior characteristics of liner plate according to the depth of cover. Analysis results showed that the maximum axial stress and the maximum displacement occurs in the lower end of the member, and the maximum shear stress occurs in the upper part of the member. Also, change of displacement, stress shearing stress of liner plate based on various depth of cover are existed, but the difference is slight, and by increasing depth of cover, structural stability is gradually ensured.

• Journal of the Korean Geotechnical Society
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• v.37 no.10
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• pp.55-63
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• 2021

The construction of shield tunnels is being expanded from the small-bore tunnels such as power, telecommunications, water supply, and sewerage pipes to the large bore tunnels such as road and railway tunnels with the advancement of the shield TBM (Tunnel Boring Machine) manufacturing technology. Accordingly, the construction of twin shield tunnels is increasing. Peck (1969) reported that the surface settlement trough is well described by a Gaussian distribution on a single shield tunnel. Hereafter, many studies about the surface settlement trough were performed by the field measurement, laboratory model test, and numerical analysis. This study confirmed that the additional surface settlement trough induced by the 2^nd tunneling were well described by using each Gaussian curve for the right and left sides of the settlement trough.

• Journal of Dental Rehabilitation and Applied Science
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• v.37 no.4
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• pp.268-273
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• 2021

Paramolar tubercle is a rare developmental dental anomaly defined as an additional cusp occurring on the buccal or lingual surfaces of the molar. Permanent molar fused with paramolar tubercles can be a cause of difficulty in root canal treatment. Therefore, proper understanding of these variations is important in order to ensure successful endodontic treatment. Cone beam computed tomography (CBCT) can be helpful to understand anatomy of complicated cases. This case report describes nonsurgical endodontic treatment of maxillary second premolar fused with paramolar tubercle.

• Journal of the Korean Geotechnical Society
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• v.38 no.9
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• pp.53-67
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• 2022

Micropiles are cast-in-place-type piles with small diameters. They are widely used for the foundation reinforcement of existing buildings and structures because this technique is easy to construct and economic. A base expansion structure is developed following the mechanism of radial expansion at the pile tip under compression. Numerical analysis, durability tests, and centrifuge tests have been conducted using the base expansion structure. In this study, three-dimensional numerical modeling was performed to describe the behavioral mechanism of the base expansion structure using steel bar penetration under compressive loading, and numerical analyses using centrifuge test conditions were performed for the comparative studies. Additionally, the base structure was modified based on the results of lab-scale analyses, and the bearing capacities of micropiles were compared using field-scale numerical analyses under various ground conditions.

• Journal of the Korean Geotechnical Society
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• v.22 no.5
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• pp.69-81
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• 2006

The micropile, which is a kind of the in-situ manufactured pile with small diameter of $150\sim300mm$, is constructed by installing a steel bar or pipe and injecting grout into a borehole. The application fields of micropile are being gradually expanded in a limited space of down-town area, because the micropile has various advantages with low vibration and noise in method and compact size in machine, etc. Mostly, the micropile has been applied to secure the safety of structures, depending on the increment of bearing capacity and the restraint of displacement. The micropile is expected to be used in various fields due to its effectiveness and potentiality in the future. The model test, focused on the interaction between micropile and soil in this study, was carried out. The micropile is installed in a soil adjacent to footing (concept of 'soil reinforcement'). With the test results and soil deformation analysis, the reinforcement effect (relating to bearing capacity and settlement) was analysed in a qualitative and quantitative manner, respectively. Consequently, it is expected that we nay demonstrate the improvement of an efficiency and application in the design and construction of micropile.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3C
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• pp.191-200
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• 2006

The micropile, which is a kind of the in-situ manufactured pile with small diameter of 100~300mm, is constructed by installing a steel bar or pipe and injecting grout into a borehole. The application fields of micropile are being gradually expanded in a limited space of down-town area, because the micropile has various advantages with low vibration and noise in method and compact size in machine, etc. Mostly, the micropile has been applied to secure the safety of structures, depending on the increment of bearing capacity and the restraint of displacement. The micropile is expected to be used in various fields due to its effectiveness and potentiality in the future. The model test, focused on the interaction between micropile and soil in this study, was carried out. The micropile is installed under footing(concept of "structure supporting"). With the test results and soil deformation analysis, the reinforcement effect(relating to bearing capacity and settlement) was analysed in a qualitative and quantitative manner, respectively. Consequently, it is hoped to demonstrate the improvement of an efficiency and application in the design and construction of micropile.

• Journal of the Korean Geotechnical Society
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• v.40 no.2
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• pp.41-53
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• 2024

Micropiles are small, cast-in-place piles with a diameter of 300 mm or less, primarily used to reinforce existing structures and support new constructions. As the application of these piles has expanded, extensive research has been conducted on their bearing characteristics, particularly in micropiled rafts. These studies have consistently demonstrated the positive impact of micropiles on foundation reinforcement. However, previous research often overlooked the potential variations in behavior between micropiled and conventional piled rafts based on different pile conditions. Furthermore, the influence of the cohesive characteristics of the soil layer beneath the foundation on the reinforcing effect of the micropiles has not been adequately addressed. This study, therefore, undertook 3D numerical analysis to assess the reinforcing effect of micropiles, considering both pile conditions and the cohesive characteristics of the soil layer beneath the foundation. The findings revealed that micropiles are significantly more effective in non-cohesive soil layers compared to cohesive ones, with the potential to increase the bearing capacity of the raft by up to 3.7 times.