• 정보저장시스템학회논문집
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• 제1권1호
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• pp.108-114
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• 2005

The generation of fine relics of suspensions is a significant interest as it holds the key to the fabrication of electronic devices. These processes offer opportunities for miniaturization of multilayer circuits, for production of functionally graded materials, ordered composites and far small complex-shaped components. Some novel printing methods of depositing ceramic and metal droplets were suggested in recent years. In an electro-hydrodynamic printing, the metallic capillary nozzle can be raised to several kilovolts with respect to the infinite ground plate or pin-type electrode positioned a few millimeters from the nozzle tip. Depending on the electrical and physical properties of the liquid, for a given geometry, it Is possible to generate droplets in any one of three modes, dripping, cone-jet and multi-jet. In this experiment, an alumina suspension flowing through a nozzle was subjected to electro-hydrodynamic printing using pin-type electrodes in the cone-jet mode at different applied voltages. The pin-type electrodes of 1, 100, 1000${\mu}m$ in diameter were used to form fine ceramic patterns onto the substrates. Various feature sizes with applied voltages and electrode diameters were measured. The feature sizes increased with the electrode diameter and applied voltages. The feature size was as fine as $30 {\mu}m$.

• Ocean and Polar Research
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• 제37권4호
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• pp.333-340
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• 2015

The contrast (fish body to medium ratio) of density and sound speed were measured to estimate acoustic scattering from small juvenile cod (Gadus macrocephalus) with the Kirchhoff-Ray Mode backscatter model. The density contrast was measured by the density-bottle method and the sound speed contrast was estimated by the time of flight method. The results revealed that the measured density contrasts of juvenile cod varied between 1.003 and 1.029 (mean = 1.014, S.D. = 0.01). On the other hand, sound speed contrasts varied between 1.039 and 1.041 (mean = 1.041, S.D. = 0.001). The relationship between averaged target strength (TS) and total length (TL) established by the model were <$TS_{38kHz}$> = 20log(TL) - 68.8 and <$TS_{38kHz}$> = 20log(TL) - 69.4, respectively.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.195-195
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• 2010

In recent years, Anodic aluminum oxide(AAO) has become popular and attractive materials. It can be easily fabricated and self-organized pore structures. It has been widely used as a biosensor membrane, photonic crystal for optical circuit and template for nanotube growth etc. In previous papers, the theory was developed that AAO shows anisotropic optical properties, since it has anisotropic structure with numerous cylindrical pores. It gives rise to the anisotropy of the refractive index called as birefringence. It can be used as conventional polarizing elements with high efficiency and low cost. Therefore, we would like to compare the theory and experimental results in this study. One method which can measure effective refractive index of thin film is the prism coupling technique. It can give accurate results fast and simply. Furthermore, we can also measure separately the refractive index with different polarization using polarization of the laser (TE mode and TM mode). We calculated the effective refractive index with effective medium approximations (EMAs) by pore size in the SEM image. EMAs are physical models that describe the macroscopic system as the homogeneous and typical method of all mean field theories.

• 한국생산제조학회지
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• 제20권2호
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• pp.121-128
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• 2011

As high precision industries such as semiconductor, TFT-LCD manufacturing and MEMS continue to grow, the demand for higher DOF precision stages has been increasing. In general, the stages should accommodate a prescribed range of payloads in order to position various precision manufacturing/inspection instruments. Therefore a nonlinear controller using sliding motion is developed, which bears mass perturbation and makes the upper plate of the stage move in 6 DOF. For the application of the nonlinear control, an observer is also developed based on expected noise covariance. To eliminate the steady state error of step response, integral terms are inserted into the state-space model. The linear term of the controller is designed using optimization scheme in which parameters can be weighted according to their physical significance, whereas the nonlinear term of the controller is designed using trial and error method. A comprehensive simulation study proves that the designed controller is robust against mass perturbation and completely eliminates steady state errors.

• 한국강구조학회 논문집
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• 제14권4호
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• pp.519-527
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• 2002

쉘 구조물은 지붕 구조물, 굴뚝 구조물, 압력구조물, 선박구조물, 항공구조물 등에 널리 사용되는 구조물이다. 본 논문은 전단변형 효과를 고려한 비등방성 복합성층 원뿔형 쉘의 자유진동에 관하여 연구하였다. 복합재료는 2개 또는 이상의 재료들로 구성되어 구조적인 효율성을 증진시키도록 구성된 재료이다. 이러한 복합재료로 구성된 구조물의 거동은 매우 복잡하기 때문에 해석해를 구하기가 거의 불가능하다. 따라서 본 연구에서는 이러한 복합재료로 구성된 원뿔형 쉘의 자유진동을 해결하는데 유한차분법을 사용하였다. 중심각, 정점각 및 다른 기하학적 파라미터의 진동에 대한 효과를 연구하였고, 진동모드 형상을 예시함으로서 진동모드에 관한 물리적 및 공학적인 이해를 증진시키고자 하였다.

• 천문학회보
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• 제36권2호
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• pp.83.1-83.1
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• 2011

Solar flares are very spectacular, and are associated with various phenomena. Coronal shocks or disturbances are one of such flare-related phenomena. Although Moreton waves and X-ray waves are well explained with MHD first mode shocks propagating in the corona, there still remains a big problem on the nature of the waves, since they are very rare phenomena. On the other hand, EIT waves (or EUV waves) have been paid attention to as another phenomenon of coronal disturbances. However, the physical features (velocity, opening angle, and so on) are much different from those for Moreton waves and X-ray waves. We report detailed features of the coronal disturbances associated with the 2010 February 7 and the 2010 August 18 flares. For the former flare we analyzed the H-alpha images obtained by SMART at Hida Observatory, Kyoto University, Japan and by a flare telescope at National Astronomical Observatory of Japan, the X-rays images taken by Hinode/XRT, and the EUV images obtained by the both satellites of STEREO, and found the Moreton wave, X-ray wave, and EIT wave, simultaneously. In the latter flare, on the other hand, we observed a very fast EUV wave in EUV images taken by SDO/AIA. The propagating speed is comparable to the MHD first mode wave, while there is no obvious evidence of shocks for this flare. From these results, we discuss the nature of coronal disturbances.

• Nuclear Engineering and Technology
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• 제38권4호
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• pp.343-352
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• 2006

Convenient analytical tools for evaluation of the aperiodic and the fluctuating instabilities of the passive residual heat removal system (PRHRS) of an integral reactor are developed and results are discussed from the viewpoint of the system design. First, a static model for the aperiodic instability using the system hydraulic loss relation and the downcomer feedwater heating equations is developed. The calculated hydraulic relation between the pressure drop and the feedwater flow rate shows that several static states can exist with various numbers of water-mode feedwater module pipes. It is shown that the most probable state can exist by basic physical reasoning, that there is no flow rate through the steam-mode feedwater module pipes. Second, a dynamic model for the fluctuating instability due to steam generation retardation in the steam generator and the dynamic interaction of two compressible volumes, that is, the steam volume of the main steam pipe lines and the gas volume of the compensating tank is formulated and the D-decomposition method is applied after linearization of the governing equations. The results show that the PRHRS becomes stabilized with a smaller volume compensating tank, a larger volume steam space and higher hydraulic resistance of the path $a_{ct}$. Increasing the operating steam pressure has a stabilizing effect. The analytical model and the results obtained from this study will be utilized for PRHRS performance improvement.

• 대한의용생체공학회:의공학회지
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• 제32권3호
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• pp.264-269
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• 2011

To increase therapeutic efficiency and biological safety, it is important to precision control of acoustic output for therapeutic ultrasound equipment. In this paper, the electro-acoustic radiation conductance, one of electroacoustic characteristics of therapeutic ultrasound equipment, was measured by the radiation force balance method according to IEC 61161 standards and the acoustic output was estimated using the electro-acoustic radiation conductance. The estimation of acoustic output was conducted to continuous wave mode and pulse wave mode of duty cycle between 20% and 80%. The differences between prediction values and measurement results are within 5% of measurement uncertainty, which is a reasonably good agreement. The results show that acoustic output controlled by electro-acoustic radiation conductance was found to be an effective method.

• 대한전자공학회논문지TC
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• 제49권7호
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• pp.6-11
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• 2012

IEEE 802.16e는 수면 모드 작동기법을 사용하여 이동 단말기(Mobile Station: MS)의 제한된 에너지를 관리한다. MS는 수면 모드의 비가용 구간에 물리적인 작동 요소의 출력을 낮출 수 있다. 이 논문은 비가용 구간를 체계적으로 증가시켜 에너지 소모율을 감소시키기 위하여, MS에 I형과 II형의 활성화된 절전 클래스(PSC)가 존재할 때 강화된 절전 메커니즘(ePSM)을 제안한다. 성능 평가 결과, ePSM은 비가용 구간뿐 아니라 에너지 소비에 있어서도 기존 방식에 비해 성능을 향상시킨 것을 확인하였다.

• 천문학회보
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• 제39권1호
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• pp.37.2-37.2
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• 2014

Gas in disk galaxies interacts nonlinearly with a underlying stellar spiral potential to form galactic spiral shocks. Numerical simulations typically show that these shocks are unstable to the wiggle instability, forming non-axisymmetric structures with high vorticity. While previous studies suggested that the wiggle instability may arise from the Kelvin-Helmholtz instability or orbit crowding of gas elements near the shock, its physical nature remains uncertain. It was even argued that the wiggle instability is of numerical origin, caused by the inability of a numerical code to resolve a shock that is inclined to numerical grids. In this work, we perform a normal-mode linear stability analysis of galactic spiral shocks as a boundary-value problem. We find that the wiggle instability originates physically from the potential vorticity generation at a distorted shock front. As the gas follows galaxy rotation, it periodically passes through multiple shocks, successively increasing its potential vorticity. This sets up a normal-mode that grows exponentially, with a growth rate comparable to the orbital angular frequency. We show that the results of our linear stability analysis are in good agreement with the those of local hydrodynamic simulations of the wiggle instability.