• Journal of Magnetics
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• 제22권1호
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• pp.133-140
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• 2017

Split magnetic fluid sealing is a combination of magnetic fluid rotary and plane sealing. Using the theory of equivalent magnetic circuit design as basis, the author theorized the pressure resistance performance of magnetic fluid plane sealing. To determine the pressure resistance of magnetic fluid plane sealing, the author adopted the method of finite element analysis to calculate the magnetic field intensity in the gap between plane sealing structures. The author also analyzed the effect of different sealing gaps, as well as different ratios between the sealing gap and tooth and solt width, on the sealing performance of split magnetic fluid. Results showed that the wider the sealing gap, the lower the sealing performance. Tooth width strongly affects sealing performance; the sealing performance is best when the ratio between tooth width and sealing gap is 2, whereas the sealing performance is poor when the ratio is over 8. The sealing performance is best when the ratio between the solt width and sealing gap is 4, indicating a slight effect on sealing performance when the ratio between the solt width and sealing gap is higher. Theoretical analysis and simulation results provide reference for the performance evaluation of different sealing equipment and estimation of critical pressure at interface failure.

• 전기학회논문지
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• 제57권3호
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• pp.429-432
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• 2008

Much studies have been concentrated to develop the fabrication technique for high critical current density but still there are a lot of gap which should be overcome for large scale application of superconducting materials at liquid nitrogen temperature. The improvement of the critical current can be achieved by forming the nano size defect working as a flux pinning center inside the superconductor. In this paper, the establishment of fabrication condition and additive effects of second elements were examined so as to improve the related properties to the practical use of superconductor.

• 중환자간호학회지
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• 제11권2호
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• pp.1-10
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• 2018

Purpose : This study aimed to develop an in-depth and comprehensive understanding of the experiences of critical care nurses caring for dying patients. Method : Eleven critical care nurses with experience in caring for dying patients were recruited from four tertiary hospitals. Semi-structured face-to-face interviews were conducted between November 2016 and March 2017. The transcribed data were analyzed using qualitative content analysis to identify major themes and sub-themes that represented the experiences of critical care nurses. Results : The following six themes, and twelve sub-themes, were identified: (1) the gap between expectation and reality, (2) a distorted meaning of death, (3) repeated emotional pain and stress, (4) finding a solution alone, (5) sublimation into mission and calling, and (6) integration into one's own life. Conclusion : This study found that critical care nurses experience various psychological difficulties while caring for dying patients, and they made efforts on their own to overcome them. These findings are expected to inform the development of specialized programs to support critical care nurses to tackle these challenges, create guidelines on caring for dying patients, and help promote death education.

• Nuclear Engineering and Technology
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• 제32권4호
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• pp.395-409
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• 2000

Parametric studies were performed to assess the sensitivity in determining the maximum in-vessel heat removal capability from the core material relocated into the lower plenum of the reactor pressure vessel (RPV）during a core melt accident. A fraction of the sensible heat can be removed during the molten jet delivery from the core to the lower plenum, while the remaining sensible heat and the decay heat can be transported by rather complex mechanisms of the counter-current flow limitation (CCFL) and the critical heat flux (CHF）through the irregular, hemispherical gap that may be formed between the freezing oxidic debris and the overheated metallic RPV wall. It is shown that under the pressurized condition of 10MPa with the sensible heat loss being 50% for the reactors considered in this study, i.e. TMI-2, KORI-2 like, YGN-3&4 like and KNGR like reactors, the heat removal through the gap cooling mechanism was capable of ensuring the RPV integrity as much as 30% to 40% of the total core mass was relocated to the lower plenum. The sensitivity analysis indicated that the cooling rate of debris coupled with the sensible heat loss was a significant factor The newly proposed heat removal capability map (HRCM) clearly displays the critical factors in estimating the maximum heat removal from the debris in the lower plenum. This map can be used as a first-principle engineering tool to assess the RPV thermal integrity during a core melt accident. The predictive model also provided ith a reasonable explanation for the non-failure of the test vessel in the LAVA experiments performed at the Korea Atomic Energy Research Institute (KAERI), which apparently indicated a cooling effect of water ingression through the debris-to-vessel gap and the intra-debris pores and crevices.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.795-800
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• 2000

A CCFL(Counter Current Flow Limit) test have been performed in narrow annular gaps with large diameter, because it has been confirmed that the CCFL phenomena affected the critical power in hemispherical narrow gap geometries from the SONATA(Simulation Of Naturally Arrested Thermal Attack)-IV (In-Vessel)/VISU(Visualization)-II experiments. The objectives of the CCFL experiments are to investigate the small gap sizes(1, 2mm) effect on CCFL under the large diameter condition and to confirm the findings of the VISU-II study that global dryout in hemispherical narrow gaps was induced by the CCFL. The test section was made of acrylic resin to allow visual observation on the two-phase flow behaviors inside annular gaps. It was observed from visualization that a part of water supplied was accumulated in the upper plenum and a significant increase in the differential pressure across the gap was occurred, which was the definition of the CCFL occurrence in this experimental study. From the experimental results in annular gap with large diameter it can be known that an increase in the differential pressure was not big at small air flow-rates. When the CCFL was occurred, the differential pressure across gaps was increased significantly and a water accumulated in the upper plenum. The occurrence of CCFL was correlated using the Wallis parameter.

• Journal of Mechanical Science and Technology
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• 제19권5호
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• pp.1169-1181
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• 2005

Experimental and numerical studies on the unsteady wake field behind a square cylinder near a wall were conducted to find out how the vortex shedding mechanism is correlated with gap flow. The computations were performed by solving unsteady 2-D Incompressible Reynolds Averaged Navier-Stokes equations with a newly developed ${\epsilon}-SST$ turbulence model for more accurate prediction of large separated flows. Through spectral analysis and the smoke wire flow visualization, it was discovered that velocity profiles in a gap region have strong influences on the formation of vortex shedding behind a square cylinder near a wall. From these results, Strouhal number distributions could be found, where the transition region of the Strouhal number was at $G/D=0.5{\sim}0.7$ above the critical gap height. The primary and minor shedding frequencies measured in this region were affected by the interaction between the upper and the lower separated shear layer, and minor shedding frequency was due to the separation bubble on the wall. It was also observed that the position (y/G) and the magnitude of maximum average velocity $(u/u_{\infty})$ in the gap region affect the regular vortex shedding as the gap height increases.

• 대한교통학회지
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• 제4권1호
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• pp.72-87
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• 1986

본 연구의 목적은 주가로상 좌회전운전자의 문격수낙특성(gap-acceptance characteristics)을 파악하는 데 있다. 이 목적을 달성하기 위하여 포켓컴퓨터를 이용한 새로 운 자료수집기법이 개발되었다. 이 기법은 적은 비용으로 정확한 자료의 수집을 가능하게 하였다. 연구교차로는 마산시의 부도심에 위치한 2차선가로 및 4차선가로상의 전형적인 신 호등 비설치교차로가 선정되었다. 정규분포 및 대수정규분포가 probit분석을 이용하여 임계 수낙문격분포(critical acceptance gap distribution)로 검정되었다. 두 분포들은 5% 우의수준 에서 기각되지 않았다. 2차선가로의 임계수낙문격은 2.9∼3.0초의 범위였으며 표준편차는 1. 2∼1.5초의 범위였고, 4차선가로는 각각3.3∼3.4초와 1.3∼1.5초의 범위였다. 2차선가로의 임 계 lag는 2.6초였으며 4차선가로의 임계lag는 3.2초이었다. 국내 좌회전운전자의 임계수낙문 격이 미국인의 것에 비하여 짧은 것으로 나타났다. 이는 도시교통류의 주구성 차량이 직업 운전자들이 운전하는 소형 택시로 이루어지는 운전자 및 차량특성에 기인한 것으로 볼 수 있다.

• Coupled systems mechanics
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• 제5권4호
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• pp.305-314
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• 2016

We utilize first-principles calculations within density-functional theory to investigate the possibility of strain engineering in the tuning of the band structure of two-dimensional $MoS_2$. We find that the band structure of $MoS_2$ monolayers transits from direct to indirect when mechanical strain is applied. In addition, we discuss the change in the band gap energy and the critical stains for the direct-to-indirect transition under various strains such as uniaxial, biaxial, and pure shear. Biaxial strain causes a larger change, and the pure shear stain causes a small change in the electronic band structure of the $MoS_2$ monolayer. We observe that the change in the interaction between molecular orbitals due to the mechanical strain alters the band gap type and energy.

• Tribology and Lubricants
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• 제15권4호
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• pp.304-313
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• 1999

High-speed rotors set a lot of high vibration and stability problems especially when the speed of rotation is going through the first or the second critical speed. The aim of this paper is to investigate the possibility of an active control of a rigid rotor with squeeze film damper which has a good configuration of easily controlled end seal clearances and/or adjustment of a feed pressure. A theoretical method is presented and some numerical results are compared with test measurements. Both results show that the vibration or bit sizes are decreased when the end seal gap decreases with constant supply pressure, and when the supply oil pressure increases with constant seal gap. The experimental results show also a pleasing similarity on both orbit sizes and their decrement ratio compared with theoretical analysis. The possibility of an active control with the squeeze film damper was verified by adjusting the seal gap and the supply pressure.

• 한국기계기술학회지
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• 제13권3호
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• pp.25-30
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• 2011

Flow control of flow field is essential to design efficient elements relating to fluid machineries. In this study, flow characteristics of rectangular prism with center gap through-flow at different aspect ratio was investigated to flow control. It was used a FLUENT 6.3 version to study flow field. It was found that the through-flow disturbs the development of vertical velocity component and decreased the vortex size and critical value of a rapid change in pressure coefficient distribution.