• 소음진동
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• 제8권4호
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• pp.643-653
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• 1998

The sub-resonance modes can be easily excited by the assembling tolerance in the asymmetric type optical pick-up actuators, compared with the symmetric type. In this paper, we propose the novel method for reducing the vibration due to the sub-resonance modes whose amplitude can be decreased by adding the damper and increasing the flexibility of holder PCB. Using the finite element method, the change of mode shapes is investigated as the shape of holder PCB is modified. Experimental results support that the propopsed method reduces remarkably the vibration of sub-resonance modes of the optical pick-up actuator.

• 한국자기공명학회논문지
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• 제19권1호
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• pp.11-17
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• 2015

The Kubo formalism and utilizing the projection operator technique (POT) introduced by Kawabata, the electron spin resonance (ESR) line-shape formula for carbon nanotubes through the hyperfine interaction introduced earlier in terms of POT. We can see that the line-width decreases exponentially as the temperature increases. The spin relaxation time show gradual decrease as magnetic field becomes larger. The analysis reveals the peculiarities in spin relaxation inherent to one dimensional system at low temperature and weak magnetic fields. Thus, the present technique is considered to be more convenient to explain the carbon nanotubes as in the case of other optical transitions.

• Journal of Hydrospace Technology
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• 제1권1호
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• pp.57-65
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• 1995

For the mechanism of ship capsizing, we can generally consider that it\`s caused due to pure loss of stability, parametric oscillation(low cycle resonance) of ship in waves and the broaching phenomena. Among them, low cycle resonance occurs due to the dynamic change of righting arm with respect to the relative position of ship to waves. The dynamic change depends on the encounter period of a ship in following waves. This paper discusses the following items : (1) An analytical expression of GZ curve varying with respect to the relative position of ship to waves, (2) Non-linear equation of motion describing low cycle resonance, (3) The effects of righting arm, stability range and encounter period on low cycle resonance.

• 자연과학논문집
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• 제12권1호
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• pp.23-30
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• 2002

원자와 빛과의 상호작용에 의해 원자의 결맞음이 유도될 수 있는데, 이러한 원자의 결맞음은 새로운 물성 및 광학적 현상을 제공한다. 2광자 공진은 원자의 결맞음 형성에 중요한 역할을 하는데 지금까지 2광자 조건에 대한 근사적인 공식이 사용되어져 왔다. 본 논문에서는 2광자 공진 조건을 정확히 유도하고, 수치적 계산을 통하여 이를 확인하였으며, 주파수 편이 및 빛의 세기에 따른 2광자 공진 조건의 변화를 조사하였다.

• Investigative Magnetic Resonance Imaging
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• 제23권1호
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• pp.70-74
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• 2019

Cerebral air embolism (CAE) is a rare complication of various medical procedures. It manifests with symptoms similar to those of typical acute cerebral infarction, however the treatment is quite different. We present a case of arterial CAE that was associated with a disconnected central venous catheter and appeared as punctate dark signal intensities with aliasing artifacts on the susceptibility-weighted filtered phase magnetic resonance image. The susceptibility-weighted filtered phase image can be helpful for diagnosing CAE and the magnetic resonance imaging reflects the pathophysiology of CAE.

• 한국시뮬레이션학회논문지
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• 제24권3호
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• pp.45-54
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• 2015

본 논문에서는 기어감속 서보시스템의 모터입력전압 크기를 적절히 감소시키면 모터입력전압에 대한 모터각속도에서 나타나는 주파수응답특성에 미치는 백래시 영향이 매우 커지게 됨을 보여 주였다. 또한 주파수응답선도에서 나타나는 반공진 및 공진주파수 변화량을 관찰하여 기어감속 서보시스템 내 기어 백래시 변화를 감지할 수 있는 방법의 유용성을 이론적, 시뮬레이션 및 실험적으로 검증하였다. 반공진주파수 변화가 공진주파수 변화 보다 안정적으로 계측될 수 있으므로 백래시 크기 변화감지 시 반공진주파수 변화량 관찰이 좀 더 유용하며, 공진주파수는 모터입력전압을 충분히 감속시켜야 급격한 변화를 관찰할 수 있음을 보여주었다. 본 연구는 기어감속 서보시스템 내 백래시 크기 변화 감지에 대한 향후 연구에 있어서 유용하게 사용될 수 있을 것이라고 생각한다.

• Investigative Magnetic Resonance Imaging
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• 제22권1호
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• pp.61-64
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• 2018

Pancreatic lymphoepithelial cysts (LECs) are rare pancreatic cysts with squamous epithelial lining surrounded by dense lymphoid tissue. A preoperative diagnosis of LECs is difficult due to imaging diversity and inadequate documentation because of their rarity. We present a case of surgically confirmed pancreatic LEC with magnetic resonance imaging (MRI) findings as heterogeneous signal intensity on T2-weighted images with multiple septa-like structures, slightly hypo-signal intensity on T1-weighted images, and thin-wall enhancement on dynamic contrast images. LECs are benign lesions without any malignant potential. Therefore, the inclusion of LEC in the differential diagnosis of cystic pancreatic lesions may reduce unnecessary surgical procedures.

• 한국자기공명학회논문지
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• 제22권2호
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• pp.34-39
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• 2018

The Nuclear Magnetic Resonance (NMR) technique using Dynamic Nuclear Polarization (DNP) procedures is one of the promising techniques that enable overcoming low sensitivity problems in NMR spectroscopy. We constructed an ODNP-NMR system using a commercial benchtop EPR spectrometer. The $^1H$ NMR peak area of water in aqueous solutions of 4-hydroxy-TEMPO was enhanced more than 95 times in the ODNP-NMR experiments. Our signal enhancement results were about 55% of the previously reported result. This could be due to non-uniform microwave power over a sample and unwanted sample heating by microwave. However, this portable ODNP-NMR spectrometer will be eventually useful for site-specific detection with nano-scale spatial resolutions and molecular dynamics studies with significantly improved signal sensitivity.

• 소음진동
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• 제10권6호
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• pp.1041-1047
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• 2000

The main objectives of this study are to examine the random response of a vibration absorber system with autoparametric coupling in the neighborhood of internal resonance by Gaussian closure and to compare the results with those obtained by Monte Carlo simulation. The numerical simulation is found to support the main features of the nonlinear modal interaction in the neighborhood of internal resonance conditions. While the Gaussian closure exhibits regions of multiple solutions in the neighborhood of internal resonance, the numerical simulation gives only one solution depending on the assigned initial conditions. The on-off intermittency phenomena of the cantilever mode is observed in the Monte Carlo simulation over a small range of parameter.

• 대한기계학회논문집
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• 제14권5호
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• pp.1087-1095
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• 1990

본 연구에서는 슬롯을 가지는 2차원 원형 풍동에 대하여 슬롯의 갯수, 크기와 흐름의 속동에 따른 공진 특성을 2차원 8-노드 등계수(isoparametric)요소를 사용하여 해석한다.