• 천문학회보
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• 제41권2호
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• pp.36.1-36.1
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• 2016

This is a presentation of the paper published as Kimm et al. 2016, ApJ, 823, 52. We investigate the formation of metal-poor globular clusters (GCs) at the center of two dark matter halos with $Mhalo{\sim}4{\times}107Msun$ at z>10 using cosmological radiation-hydrodynamics simulations. We find that very compact (${\leq}1$ pc) and massive (${\sim}6{\times}105Msun$) clusters form rapidly when pristine gas collapses isothermally with the aid of efficient $Ly{\alpha}$ emission during the transition from molecular-cooling halos to atomic-cooling halos. Because the local free-fall time of dense star-forming gas is very short (${\ll}1Myr$), a large fraction of the collapsed gas is turned into stars before stellar feedback processes blow out the gas and shut down star formation. Although the early stage of star formation is limited to a small region of the central star-forming disk, we find that the disk quickly fragments due to metal enrichment from supernovae. Sub-clusters formed in the fragmented clouds eventually merge with the main cluster at the center. The simulated clusters closely resemble the local GCs in mass and size but show a metallicity spread that is much wider than found in the local GCs. We discuss a role of pre-enrichment by Pop III and II stars as a potential solution to the latter issue. Although not without shortcomings, it is encouraging that a naive blind (not tuned) cosmological simulation presents a possible channel for the formation of at least some massive GCs.

• 한국응용약물학회:학술대회논문집
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• 한국응용약물학회 2003년도 Annual Meeting of KSAP : International Symposium on Pharmaceutical and Biomedical Sciences on Obesity
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• pp.15-23
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• 2003

Interest in the regulation of body weight and the pathological physiology of obesity has been rekindled by the cloning of the obese(ob) gene and identification of its product, leptin, in 1994. The first publication appeared in Nature and is a milestone of obesity research. The remarkable metabolic effects of leptin in rodents are: a) inhibition of food intake, b) stimulation of energy expenditure, and c) reversal of obesity. These effects, though mostly desirable, have not been fully demonstrated in humans. The central action of leptin in the regulation of body weight includes two pathways in rodents: a) When the body weight increasing, more leptin is secreted from adipose tissue, which acts on hypothalamus, probably through a POMC or MSH pathway via M4 receptor, initiates a series of response to obesity, i.e. sympathetic tone increased, energy expenditure enhanced and food intake reduced. b) When body weight reduced, leptin concentration decreased with the shrinkage of fat mass, which may also act on the hypothalamus, probably through a NPY-Y5 receptor pathway. Then a cascade of response to hungry was induced, i.e. increase of parasympathetic tone and food intake, decrease of energy expenditure and body temperature, as well as shut-down of the reproductive function.

• 한국공작기계학회논문집
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• 제17권6호
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• pp.43-48
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• 2008

This study includes contents on an effective designing of the outer-wall piece removing equipment of a hull, by applying TRIZ. To remove the piece, gas torch was used. However, the heat source must be shut down since the heat source of gas torch has a bad influence on this system. This is why TRIZ and Brainstorming were used, to solve this problem. First, we analyzed the system using TRIZ, and then presented the direction a solution is expected to follow. And the most suitable scheme was derived from brainstorming which had been conducted based on the direction of a solution. Lastly we conducted an equipment modeling based on the most suitable scheme we made before, and carried out the heat analysis to inspect its effect by comparing pre-existing mechanism with most suited scheme.

• 한국추진공학회지
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• 제14권3호
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• pp.9-15
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• 2010

과팽창 로켓노즐에서 발생하는 충격파 박리패턴의 천이 유동장을 예측하기 위해 축대칭 수치해석적연구를 수행하였다. 비정상, 압축성 N-S 방정식에 k-$\omega$ SST 난류모델을 적용하여, 유한 체적법으로 계산하였다. 종래의 실험적 연구 결과와 비교하였으며, 계산된 결과와 정성적으로 잘 일치하였다. 본 연구의 결과로부터 RSS에서 FSS로 천이할 때 가장 큰 횡력이 발생하며, 이는 비점성 제트 코어 영역에서 발생하는 Vortex ring의 발달로 기인됨을 예측하였다. 또한 엔진 시동과정과 정지과정에서 발생하는 히스테리시스 현상을 잘 모사하였다.

• Nuclear Engineering and Technology
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• 제47권4호
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• pp.434-442
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• 2015

The advanced passive pressurized water reactor (PWR) is being constructed in China and the passive residual heat removal (PRHR) system was designed to remove the decay heat. During accident scenarios with increase of heat removal from the primary coolant system, the actuation of the PRHR will enhance the cooldown of the primary coolant system. There is a risk of power excursion during the cooldown of the primary coolant system. Therefore, it is necessary to analyze the thermal hydraulic behavior of the reactor coolant system (RCS) at this condition. The advanced passive PWR model, including major components in the RCS, is built by SCDAP/RELAP5 code. The thermal hydraulic behavior of the core is studied for two typical accident sequences with PRHR actuation to investigate the core cooling capability with conservative assumptions, a main steam line break (MSLB) event and inadvertent opening of a steam generator (SG) safety valve event. The results show that the core is ultimately shut down by the boric acid solution delivered by Core Makeup Tank (CMT) injections. The effects of CMT boric acid concentration and the activation delay time on accident consequences are analyzed for MSLB, which shows that there is no consequential damage to the fuel or reactor coolant system in the selected conditions.

• Nuclear Engineering and Technology
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• 제41권1호
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• pp.91-98
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• 2009

The "3+3 Process" for safety critical software for nuclear power plants' I&C (Instrumentation and Control system) has been developed in this work. The main idea of the "3+3 Process" is both to simplify the software development and safety analysis in three steps to fulfill the requirements of a software safety plan [1]. The "3-Step" software development process consists of formal modeling and simulation, automated code generation and coverage analysis between the model and the generated source codes. The "3-Step" safety analysis consists of HAZOP (hazard and operability analysis), FTA (fault tree analysis), and DV (design validation). Put together, these steps are called the "3+3 Process". This scheme of development and safety analysis minimizes the V&V work while increasing the safety and reliability of the software product. For assessment of this process, validation has been done through prototyping of the SDS (safety shut-down system) #1 for PHWR (Pressurized Heavy Water Reactor).

• 한국가스학회지
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• 제4권4호
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• pp.6-12
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• 2000

본 연구에서는 강재 가스배관의 가스공급 중단과 가스압력의 손실이 없는 상태에서 효과적으로 분기가 가능한 분기티를 개발하였다. 본 분기티는 배관의 분기위치를 고려하여 설계하였고, 기존 분기티의 문제점인 매설배관의 심도유지가 가능해졌다 개발된 분기티는 시험결과 기밀성, 내압성, 밀폐성, 용접성, 굽힘성, 내가스성의 성능특성이 우수한 것으로 평가되었다. 본 연구결과를 통한 분기티의 적용은 비용절감과 작업시간 단축뿐만 아니라 현장 피복이 용이하다는 장점을 제공할 수 있을 것이다.

• 대한방사선방어학회:학술대회논문집
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• 대한방사선방어학회 2009년도 춘계 학술발표
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• pp.254-255
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• 2009

국내 경수로 원전의 경우, 원전의 효율적, 경제적 운영차원에서 장주기 운전으로 패턴을 바뀌면서 핵연료봉 표면상에 크러드(crud)의 침적량은 점점 증가하는 경향을 나타내고 있다. 이러한 경향은 원자로의 출력 제어와 직결되면서 이에 대한 문제 해결을 위한 대표성이 있는 시료의 채취와 재현성이 있는 부식 생성물의 측정이 요구되어져 왔다. 원자로 계통 내에서 부식생성물의 농도변화에 대한 평가, 특히 입자농도가 증가되어지면 축방향 출력편차(Axial Offset Anomaly, AOA)가 발생될 수 있는 위험에 노출되거나, 핵연료 교체를 위해 발전소 정지시(shut down) 부식생성물의 방출이 급격히 증가되는 것으로 나타났다. 특히 입자성을 띤 물질은 존재의 특성상 이들 물질에 대한 대표시료의 채취가 어려울 뿐 아니라 grab 채취로 인해, 분석결과에 대한 재현성이 낮으며 계통 선량율의 제어와 작업자 피폭관리에 많은 어려움이 뒤따르고 있어 선진 원전 운영국에서는 앞 다투어 대표시료를 채취 할 수 있는 capillary sampling 법이나 integrated sampling법을 적용해 오고 있다. 본 논문에서는 국내 경수로 원전에서 일반적으로 사용하고 있는 grab sampling 법에 대한 문제점 파악과 해외 원전에서 사용 중인 capillary sampling 법의 국내 적용 가능성에 대해 살펴보았다.

• 한국안전학회지
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• 제32권2호
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• pp.21-26
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• 2017

According to the data of Korea Occupational Safety and Health Agency, electric shock accidents during recent 11 years exceeded more than 60% in architecture/other and construction work, the countermeasures for safety are required in the harsh environment of a construction site where moving electric machines and equipments are widely used. The establishment of countermeasure for insulation degradation and defect is required, in consideration of increasing trend for accidents caused by defective insulation among low voltage electrical installation each year. The aim of this study is to propose the policy about portable electrical tool standards and/or worker's safety standards for preventing electric shock accidents on safety workings, and is to develop the technology and the safety device to prevent electric shock for accident prevention reduction through experiments. It obtained the followings through this study; statistical data analysis of late about 10 years of electric shock-related industrial accidents analysis and portable electric tools; safety device development of 'device for testing continuous grounding and power shut-down' to prevent electric shock from portable electric tools. Furthermore, developed results and proposal in this study will help to prevent the electric shock accidents from portable electric tools and will be expected the utilization of policy formulation, educational data and field supplement of the safety device, and etc.

• BMB Reports
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• 제37권5호
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• pp.597-602
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• 2004

N-terminal His-tagged recombinant $\beta$-1,4-galactosyltransferase from Neisseria meningitidis was expressed and purified to homogeneity by column chromatography using Ni-NTA resin. Mutations were introduced to investigate the roles of, Ser68, His69, Glu88, Asp90, and Tyr156, which are components of a highly conserved region in recombinant $\beta$-1,4 galactosyltransferase. Also, the functions of three other cysteine residues, Cys65, Cys139, and Cys205, were investigated using site-directed mutagenesis to determine the location of the disulfide bond and the role of the sulfhydryl groups. Purified mutant galactosyltransferases, His69Phe, Glu88Gln and Asp90Asn completely shut down wild-type galactosyltransferase activity (1-3%). Also, Ser68Ala showed much lower activity than wild-type galactosyltransferase (19%). However, only the substitution of Tyr156Phe resulted in a slight reduction in galactosyltransferase activity (90%). The enzyme was found to remain active when the cysteine residues at positions 139 and 205 were replaced separately with serine. However, enzyme reactivity was found to be markedly reduced when Cys65 was replaced with serine (27%). These results indicate that conserved amino acids such as Cys65, Ser68, His69, Glu88, and Asp90 may be involved in the binding of substrates or in the catalysis of the galactosyltransferase reaction.