• Journal of Astronomy and Space Sciences
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• 제34권4호
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• pp.289-302
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• 2017

The key risk analysis technologies for the re-entry of space objects into Earth's atmosphere are divided into four categories: cataloguing and databases of the re-entry of space objects, lifetime and re-entry trajectory predictions, break-up models after re-entry and multiple debris distribution predictions, and ground impact probability models. In this study, we focused on reentry prediction, including orbital lifetime assessments, for space situational awareness systems. Re-entry predictions are very difficult and are affected by various sources of uncertainty. In particular, during uncontrolled re-entry, large spacecraft may break into several pieces of debris, and the surviving fragments can be a significant hazard for persons and properties on the ground. In recent years, specific methods and procedures have been developed to provide clear information for predicting and analyzing the re-entry of space objects and for ground-risk assessments. Representative tools include object reentry survival analysis tool (ORSAT) and debris assessment software (DAS) developed by National Aeronautics and Space Administration (NASA), spacecraft atmospheric re-entry and aerothermal break-up (SCARAB) and debris risk assessment and mitigation analysis (DRAMA) developed by European Space Agency (ESA), and semi-analytic tool for end of life analysis (STELA) developed by Centre National d'Etudes Spatiales (CNES). In this study, various surveys of existing re-entry space objects are reviewed, and an efficient re-entry prediction technique is suggested based on STELA, the life-cycle analysis tool for satellites, and DRAMA, a re-entry analysis tool. To verify the proposed method, the re-entry of the Tiangong-1 Space Lab, which is expected to re-enter Earth's atmosphere shortly, was simulated. Eventually, these results will provide a basis for space situational awareness risk analyses of the re-entry of space objects.

• 한국항공우주학회지
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• 제30권7호
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• pp.51-60
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• 2002

통계학적 해석인 몬테-칼로 모의실험은 대기권 재진입 분산의 결과인 낙하예정지역뿐만 아니라 상태변수들의 최종조건들을 조사하는데도 사용된다. 본 논문에서 재진입 분산은 위도, 경도, 고도, 뱅크각, 비행경로각, 기수 오차, 그리고 항속거리로 생성되는 $7\times7$ 공분산 행렬로 한정된다. 감속을 목표로 하는 대기권 재진입시 이것들에 영향을 미치는 오차 원인들은 대기밀도, 온도, 초기오차, 바람, 그리고 항력계수의 추정오차 등에 관련된 불확실성들로서 이들 오차의 $3{\sigma}_n$와 공칭 비행궤적을 사용해서 상태변수의 공분산 행렬은 궤적 오차 해석을 수행함으로 결정될 수 있다. 재진입에 대한 몬테-칼로법의 적용에 있어서 주요 고려할 점은 교란궤적, 뱅크역전, 그리고 이 제적들 각각에 대한 최종 낙하지점의 결정이다. 본 논문은 불확실성에 대한 결과를 공력계수와 뱅크역전의 관점에서 해석한다.

• 한국전산유체공학회지
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• 제19권1호
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• pp.7-14
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• 2014

Aerothermodynamic characteristics of re-entry vehicles in hypersonic speed regimes are investigated by applying CFD methods based on the Navier-Stokes-Fourier equations. A special emphasis is placed on the effects of high temperature chemically reacting gases on shock stand-off distance and thermal characteristics of the flowfields. A ten species model is used for describing the kinetic mechanism for high temperature air. In particular, the hypersonic flows around a cylinder are computed with and without chemically reacting effects. It is shown that, when the chemically reacting effects are taken into account, the shock stand-off distance and temperature are significantly reduced.

• 한국항공우주학회지
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• 제49권8호
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• pp.627-636
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• 2021

본 논문에서는 재사용발사체 유도제어에 관한 연구를 다루었다. 이를 위하여 6자유도의 재사용발사체 운동방정식 모델링을 수행하였으며, 이를 이용하여 최적 재진입경로를 생성 및 해당 경로를 추종하는 유도제어 시뮬레이션을 수행하였다. 유도제어기 설계를 위하여 모델링 불확실성, 외란 및 고장에 강한 시간지연기법을 적용한 자세제어기와 비선형 유도법칙을 이용하였다. 고전적인 PD 제어기를 적용한 유도제어 시뮬레이션을 수행하여 시간지연기법을 적용한 재사용발사체의 유도제어 시뮬레이션과 비교 검증하였다.

• 국제지역연구
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• 제15권2호
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• pp.3-23
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• 2011

일본의 외국인직접투자는 90년대 후반 아시아금융위기이후로 여러모로 변화가 있다는 주장이 꾸준히 제기되어 왔으나 기존연구는 대부분 2000년대 초반까지 데이터를 중심으로 이루어졌다. 본고는 2006년 데이터를 사용하여 기존 논문에서 제기되었던 일본의 외국인직접투자 경향의 변화를 살펴본다. 전체적으로 일본의 외국인직접투자는 90년대 대미중심구조에서 탈피하여 2000년대는 아시아로 회귀하려는 경향을 보였다. 세계적으로는 아시아 집중성향이 뚜렷하였으나 아시아 지역 내에서는 고르게 분포되었다. 이와 더불어 과거 합작(조인트벤쳐)중심의 진입모드도 자회사설립 위주로 변화되는 특성이 두드러졌다. 또한 신규설립도 현저히 증가하였다. 본고는 일본 기업들이 아시아 금융위기 이후로 2000년대 중반에는 수십 년 간의 외국인직접투자의 경험을 바탕으로 가장 지역에 대한 지식이 높은 아시아 위주로 투자 전략을 바꾸고 있는 횡단면 분석 결과를 보여준다.

• International Journal of Aeronautical and Space Sciences
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• 제14권3호
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• pp.247-255
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• 2013

The flight control of re-entry vehicles poses a challenge to conventional gain-scheduled flight controllers due to the widely spread aerodynamic coefficients. In addition, a wide range of uncertainties in disturbances must be accommodated by the control system. This paper presents the design of a roll channel controller for a non-axisymmetric reentry vehicle model using the trajectory linearization control (TLC) method. The dynamic equations of a moving mass system and roll control model are established using the Lagrange method. Nonlinear tracking and decoupling control by trajectory linearization can be viewed as the ideal gain-scheduling controller designed at every point along the flight trajectory. It provides robust stability and performance at all stages of the flight without adjusting controller gains. It is this "plug-and-play" feature that is highly preferred for developing, testing and routine operating of the re-entry vehicles. Although the controller is designed only for nominal aerodynamic coefficients, excellent performance is verified by simulation for wind disturbances and variations from -30% to +30% of the aerodynamic coefficients.

• 산경연구논집
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• 제9권7호
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• pp.43-52
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• 2018

Purpose - The main purpose of this paper is to examine the effect of children's age on maternal labor supply in Korea using survival analysis. Specifically, we focus on the career re-interruption of women having children under age 12, which has rarely been studied in the existing literature. Research design, data, and methodology - We use micro data from the Korea Labor and Income Panel Study (KLIPS) surveyed from 1998 to 2016. Instead of using a pre-school child dummy or the number of young children as an explanatory variable, 9 children's age dummies are included to capture the effect of nurturing 0 to 9 years old children. This study estimates the hazard of a woman's exiting the labor market after her first experience of the career interruption, rather than the hazard of the first career interruption itself. A Cox proportional hazard model is applied to numerically capture the impact of children's age on behavioral changes in maternal labor supply. The sample used in this analysis is women between 15 and 54 years old. Most of all, we restrict the sample to women who had at least a child between 0 and 12 years old at the time of quitting their jobs. Results - The Cox proportional hazard model estimates show a strong negative effect of a 0-year-old child on maternal labor supply. Mothers with newborns have a high hazard ratio of labor force exit after the re-entry. The hazard of women with infants is three times higher than those with children aged 10 to 18. Additionally, the results show that not only newborns, but also children in the age of school-entry have a negative impact on their mother's labor supply. Conclusions - The findings reveal that children's ages need to be properly expanded and included when analyzing the effect of children and their ages on married women's labor supply, especially on women's career re-interruption. A large negative effect of 7-year-old children on maternal labor supply found here indicates that supporting mothers with school age children as well as pre-school children is necessary to prevent mothers from leaving the labor market.

• Biomolecules & Therapeutics
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• 제32권3호
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• pp.301-308
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• 2024

Alzheimer's disease (AD) is a progressive and irreversible neurodegenerative disorder characterized by extracellular amyloid plaques composed of amyloid β-peptide (Aβ). Studies have indicated that Ca²⁺ dysregulation is involved in AD pathology. It is reported that decreased capacitative Ca²⁺ entry (CCE), a refilling mechanism of intracellular Ca²⁺, resulting in increased Aβ production. In contrast, constitutive activation of CCE could decrease Aβ production. Panax ginseng Meyer is known to enhance memory and cognitive functions in healthy human subjects. We have previously reported that some ginsenosides decrease Aβ levels in cultured primary neurons and AD mouse model brains. However, mechanisms involved in the Aβ-lowering effect of ginsenosides remain unclear. In this study, we investigated the relationship between CCE and Aβ production by examining the effects of various ginsenosides on CCE levels. Aβ-lowering ginsenosides such as Rk1, Rg5, and Rg3 potentiated CCE. In contrast, ginsenosides without Aβ-lowering effects (Re and Rb2) failed to potentiate CCE. The potentiating effect of ginsenosides on CCE was inhibited by the presence of 2-aminoethoxydiphenyl borate (2APB), an inhibitor of CCE. 2APB alone increased Aβ42 production. Furthermore, the presence of 2APB prevented the effects of ginsenosides on Aβ42 production. Our results indicate that ginsenosides decrease Aβ production via potentiating CCE levels, confirming a close relationship between CCE levels and Aβ production. Since CCE levels are closely related to Aβ production, modulating CCE could be a novel target for AD therapeutics.

• Journal of Periodontal and Implant Science
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• 제26권2호
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• pp.350-355
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• 1996

The present study was performed to evaluate the amount of bony regeneration following the guided tissue regeneration(GTR). Re-entry procedure has been performed at 1 year following the GTR with Gore-tex membranes on the furcal defects and the amount of bony regeneration was measured. Sites treatedwith open flap procedures were used as controls. The results reveated that significant amount of bone could be regenerated through the GTR procedures compared with convention flap procedures.

• 한국정보통신학회논문지
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• 제22권9호
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• pp.1147-1152
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• 2018

최근 중국의 보험시장은 핀테크와 보험을 결합한 형태인 인슈어테크를 도입하였다. 이는 보험가입자가 더 이상 보험 설계자를 직접적으로 만나 계약을 체결하지 않고 자신에게 맞는 모험을 온라인에서 직접 가입할 수 있는 것이다. 이러한 인슈어테크라는 새로운 트렌드는 보험시장에서는 엄청난 발전으로 여겨진다. 특히, 인슈어테크의 성장률은 엄청난 속도를 보이고 있다. 게다가 중국 보험시장은 자국의 경제성장률의 둔화와는 상관없이 보편적으로 안정적이고 빠른 속도로 성장하는 추세이다. 예를 들면, 2016년 보험 산업의 수입 프리미엄을 전체적으로 계산하면 3조 1천 억 위안으로 그 이전 해에 비해 27.5%나 성장하였다. 더불어 중국 보험시장의 수요 규모는 전 세계에서 두 번째로 큰 것으로 밝혀졌다. 그럼에도 불구하고 중국에 진출한 한국 보험기업들은 중국 현지에 적응 하지 못하고 오히려 경영성과에서 좋지 않은 성적을 보이고 있다. 이는 중국 보험시장의 최근 트렌드를 분석함에 있어서 부족하였고, 그 환경에 적응하지 못한 것으로 보인다. 따라서 본 논 문은 최근 중국에서 인슈어테크라는 새로운 변화를 도입할 수 있었던 중국 정부 정책의 변화와 실제 인슈어테크를 도입한 중국의 보험 기업을 분석함으로써, 한국 보험회사들의 중국 시장 재진출 전략에 대한 시사점을 제고하고자 한다.