• Nuclear Engineering and Technology
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• 제41권1호
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• pp.11-20
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• 2009

Radiation effects on materials are inherently multiscale phenomena in view of the fact that various processes spanning a broad range of time and length scales are involved. A multiscale modeling approach to embrittlement of pressure vessel steels is presented here. The approach includes an investigation of the mechanisms of defect accumulation, microstructure evolution and the corresponding effects on mechanical properties. An understanding of these phenomena is required to predict the behavior of structural materials under irradiation. We used molecular dynamics (MD) simulations at an atomic scale to study the evolution of high-energy displacement cascade reactions. The MD simulations yield quantitative information on primary damage. Using a database of displacement cascades generated by the MD simulations, we can estimate the accumulation of defects over diffusional length and time scales by applying kinetic Monte Carlo simulations. The evolution of the local microstructure under irradiation is responsible for changes in the physical and mechanical properties of materials. Mechanical property changes in irradiated materials are modeled by dislocation dynamics simulations, which simulate a collective motion of dislocations that interact with the defects. In this paper, we present a multi scale modeling methodology that describes reactor pressure vessel embrittlement in a light water reactor environment.

• 한국소음진동공학회논문집
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• 제12권1호
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• pp.21-28
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• 2002

This paper intends to investigate the effects of speed fluctuation caused by the cogging torque in permanent magnetic motors on the stability of the transverse vibration for a spinning disk. Based on the Kirchhoff\`s plate theory and the assumed mode methods, a set of discretized equations of motion were derived for an annular disk rotating with a harmonically varying speed. Then, a perturbation method using the multiple time scales was employed and stability boundaries were determined explicitly in terms of the magnitude and frequency of speed fluctuation, a nominal sped and the modal characteristics of the disk. It is found that parametric resonance occurs at several speed ranges and a single mode or a combination of two modes are involved to cause instability. It is also observed that unstable regions become broadened as the spinning speed increases or two modes are combined in parametric instability. As numerical simulations, stability analysis of a conventional CD-ROM drive was performed. Results of this work can e used as guidelines for motor design and operations with low vibration.

• 폴리머
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• 제38권2호
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• pp.220-224
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• 2014

콘택트렌즈용 하이드로젤로의 단백질 흡착량을 시간에 따라 분석하여 계면으로 확산되는 단백질 흡착 반응속도를 연구하였다. HEMA(hydroxyethylmethacrylate)계열 하이드로젤과 silicone계열 하이드로젤을 단백질(알부민 또는 IgG)용액에 침지시킨 후 단백질 흡착량을 시간에 따라 측정하였다. 모든 하이드로젤로의 단백질 흡착량은 단시간(10분)에 급격히 증가한 후 90분 동안 변화 없이 일정하였다. 빠른 단백질 분자의 확산에도 불구하고 계면에너지 감소는 한 시간 이상 진행되는데 이는 계면 탈수 현상이 한 시간 이상 진행되기 때문으로 이해된다. 계면에너지와 단백질 흡착량의 상관관계를 이해하여 콘택트렌즈 재질로의 단백질 흡착 반응 속도의 메커니즘을 분석하였다.

• 벤처혁신연구
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• 제5권1호
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• pp.129-143
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• 2022

본 연구의 목적은 자기연민과 삶의 만족의 관계에서 사회에 대한 인식과 자신에 대한 평가의 매개효과를 보는 것이다. 이를 위해 자기연민척도와 삶의 만족도 척도를 사회적 안녕감과 핵심자기평가와 함께 직장인 215명에게 실시하였다. 연구결과, 사회적 안녕감과 핵심자기평가는 자기연민과 삶의 만족도 간의 관계를 완전 매개 하였고, 사회적 안녕감과 핵심자기평가의 간접효과 간의 차이는 유의하지 않았다. 이러한 결과는 자기연민이 삶의 만족도를 개선하는 효과가 사회적 안녕감과 핵심자기평가를 통해 설명될 수 있음을 보여준다. 추후 연구를 위한 본 연구의 시사점과 제한점에 대해 논의하였다.

• 천문학회지
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• 제29권spc1호
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• pp.97-98
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• 1996

Variability of active galactic nuclei is now a well-known phenomenon. This remains to be fully explained by a theoretical model of the central engine. Time scales of AGN variability seem to range continuously from hours up to months. The short time scale variability must be related to the phenomena on the event horizon of the black hole, while the long one to those in the accretion disk or surrounding matter. Based on the axisymmetric, nonstationary model of the central engine, we discuss theoretical considerations on the variability of active galactic nucleus.

• 충청수학회지
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• 제27권3호
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• pp.489-494
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• 2014

In this paper, we define the extension $f^*:[a,b]{\rightarrow}\mathbb{R}$ of a function $f:[a,b]_{\mathbb{T}}{\rightarrow}\mathbb{R}$ for a time scale $\mathbb{T}$ and investigate the properties of the Lebesgue delta integral of f on $[a,b]_{\mathbb{T}}$ by using the function $f^*$.

• International Journal of Contents
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• 제8권1호
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• pp.74-81
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• 2012

The aim is to investigate the analgesic effect of transcranial direct current stimulation(tDCS) on central neuropathic pain(CNP) in spinal cord contusive rat model. Twenty Sprague-Dawley rats($250{\pm}50$ g, male) were used. Thoracic spinal cord(T10) was contused using New York University(NYU) spinal cord impactor. The animals were randomly assigned to two groups; GroupI: Non-treatment after SCI induction(n=10), GroupII: application of tDCS(0.1 mA, 20 min/time, 2 times/day, 5 days/6week) after SCI induction(n=10). Assess the effect of tDCS using the Basso Beattie Bresnahan(BBB) locomotor rating scales, Touch $test^{TM}$ sensory evaluator(TTSE), Plantar test$^{\circledR}$after contusion at the $2^{nd}$, $3^{rd}$, $4^{th}$, $5^{th}$, $6^{th}$ week and the immunohistochemistric response of c-fos in the thalamus, cerebral cortex after contusion at the $3^{rd}$, $6^{th}$ week after SCI. The scores of BBB scales were significantly different from $3^{rd}$week. TTSE were different significantly over time, but there were no differences at each evaluation times on between-measure time effects. Plantar test were different significantly over time and there were difference at the $4^{th}$, $6^{th}$ week after SCI on between-measure time effects. Also, immunohistochemistric response of c-fos was reduced significantly from $3^{rd}$, $6^{th}$ week after SCI in tDCS group compared with control group in thalamus and cortex. These results identified that tDCS of non-invasive therapeutic method may have beneficial analgesic effect on CNP after SCI with behavioral test and immunohistochemical test.

• 한국수자원학회논문집
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• 제35권2호
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• pp.125-136
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• 2002

입력수문자료의 시간 스케일이 모형의 계산결과에 미치는 영향을 검토하였다. 동일한 강우사상에 대한 각기 다른 시간 스케일의 입력수문자료를 확보하고 이를 TOPMODEL에 적용하였다. 매개변수 보정을 위해 유전자 알고리즘을 사용하였다. 민감도 분석 결과는 상이한 시간 스케일이 TOPMODEL의 운영에 있어서 매개변수 공간에 대한 시각을 제공하였다. 입력수문자료의 시간 스케일의 변화는 모의효율과 평균 지하수위, 총유출량에 대한 지표유출과 지표하유출의 비, 그리고 매개변수 보정에 영향을 미쳤다. 시간 스케일이 커질수록 지표수유출이 많아지고 평균 지하수위가 높아지는 경향을 보였다. 이러한 결과는 TOPMODEL의 구조와 수문곡선의 형태 변화에서 비롯된 것으로 나타났다.

• 대한전자공학회논문지
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• 제24권1호
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• pp.20-27
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• 1987

The hierarchical approach method is proposed to sperate each different time scale sub-systems from linear time invariant multi-parameter singular perturbation systems. By means of this proposal, the original multi-parameter singular perturbation systems is completely separated into independent subsystems with each different time scale. It is also investigated that the controllability of the system is invariant. And this paper applies singular perturbation methods to the minimum control effort problem for linear time invariant systems with constrained controls. Also near-optimum control theory, which is based on dividing the total time interval with the time scales respectively, is proposed. As a result, the time scale separation method is show to be particularly useful in a near optimum design which can be otained through a decentralized control structure.

• 대기
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• 제28권1호
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• pp.15-24
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• 2018

Sea ice plays an important role in modulating surface conditions at high and mid-latitudes. It reacts rapidly to climate change, therefore, it is a good indicator for capturing these changes from the Arctic climate. While many models have been used to study the predictability of climate variables, their performance in predicting sea ice was not well assessed. This study examines the predictability of the Arctic sea ice extent from ensemble prediction systems. The analysis is focused on verification of predictability in each model compared to the observation and prediction in particular, on lead time in Sub-seasonal to Seasonal (S2S) scales. The S2S database now provides quasi-real time ensemble forecasts and hindcasts up to about 60 days from 11 centers: BoM, CMA, ECCC, ECMWF, HMCR, ISAC-CNR, JMA, KMA, Meteo France, NCEP and UKMO. For multi model comparison, only models coupled with sea ice model were selected. Predictability is quantified by the climatology, bias, trends and correlation skill score computed from hindcasts over the period 1999 to 2009. Most of models are able to reproduce characteristics of the sea ice, but they have bias with seasonal dependence and lead time. All models show decreasing sea ice extent trends with a maximum magnitude in warm season. The Arctic sea ice extent can be skillfully predicted up 6 weeks ahead in S2S scales. But trend-independent skill is small and statistically significant for lead time over 6 weeks only in summer.