• Physical Therapy Korea
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• v.9 no.4
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• pp.61-68
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• 2002

본 연구는 하퇴의지 착용자와 정상 성인간의 시간-거리, 운동형상학 변수를 조사하고 비교하기 위하여 실시하였다. 연구 대상자는 외상으로 인한 하퇴 절단자로서 내골격식 하퇴의지를 착용하고 독립적으로 보행이 가능한 20명과 연령, 신장으로 짝짓기한 대조군(matched control group) 20명이 참여하였다. 보행분석은 Vicon Clinical Manager Software (VCM)를 내장한 PC에 5개의 카메라가 연결되어 있는 Vicon 512 Motion Analysis System (MAS, Oxford Metrics Inc.)을 이용하였다. 하퇴의지 착용군의 단하지 지지시간이 정상 성인군에 비해 유의하게 짧았으며(p<.05), 하퇴의지 착용군에서 슬관절의 선전이 증가되었으며 족관절의 저측굴곡이 감소되었다(p<.05). 하퇴절단자들의 보행개선을 위해서는 하퇴절단자 개인의 보행능력에 알맞은 부품의 선택, 체계적인 보행훈련 및 평가, 보행능력 향상을 위한 근력강화 프로그램 등 체계적인 재활훈련 프로그램이 필요한 것으로 사료된다. 본 연구는 연구대상자의 수가 제한되어 있으므로 연구의 결과를 일반화하기에는 제한점이 있으나, 향후 편측 하퇴절단자의 보행연구에 대한 기초 자료로 사용될 수 있을 것이라고 생각된다.

• Journal of the Korean Society for Marine Environment & Energy
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• v.18 no.4
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• pp.254-262
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• 2015

Parametric study on submerged body shape of an oscillating hemisphere point absorber was conducted to predict the optimal relation between radius and draft of the body. As an additional damping due to power takeoff system, the optimal damping same as wave radiation damping was applied to the PTO system to produce the maximum wave power. Body response spectrum and power spectrum were obtained for various peak frequencies on wave spectra. It was found that the maximum power can be generated when the peak frequency of available wave power was 20% greater than that of wave spectrum.

• Journal of Navigation and Port Research
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• v.37 no.4
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• pp.345-350
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• 2013

It is well known that the hydrodynamic forces and moments induced by the proximity of bank in confined waters, such as in a harbour or narrow channel affect ship's maneuvering motion. In this paper, the calculation method based on the slender body theory for estimation of the hydrodynamic force between ship and breakwater is applied, and also, the characteristic features of hydrodynamic force acting on a large vessel in the proximity of a breakwater are described and illustrated. Furthermore, the effects of water depth and the lateral spacing between ship and breakwater are summarized and discussed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.4
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• pp.341-348
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• 2015

This paper addresses Monte-Carlo simulation analyses for the stage separation of the general launch vehicle. The stage separation event of the launch vehicle occurs during a very short time and is related with many dynamic parameters. The stage separation is a critical event in that the launch fails if there is a collision during the stage separation. The stage separation analyses was conducted for the general launch vehicle to confirm the separation without collision within the designed clearance in case of the random input parameters. This paper presents the stochastic results of the stage separation of the launch vehicle using the Monte-Carlo simulation.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.9
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• pp.56-65
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• 2005

A dynamic analysis method that freezes a time domain by discretization and solves the spatial propagation equation has a unique feature that provides a degree of freedom on spatial domain compared with the space discretization or space-time discretization finite element method. Using this feature, the time finite element analysis can be effectively applied to optimize the spatial characteristics of distributed type actuators. In this research, the time domain finite element method was used to discretize the model. A state variable vector was used in the discretization to include arbitrary initial conditions. A performance index was proposed on spatial domain to consider both potential and vibrational energy, so that the resulting shape of the distributed actuator was optimized for dynamic control of the structure. It is assumed that the structure satisfies the final rest condition using the realizable control scheme although the initial disturbance can affect the system response. Both equations on states and costates were derived based on the selected performance index and structural model. Ricatti matrix differential equations on state and costate variables were derived by the reconfiguration of the sub-matrices and application of time/space boundary conditions, and finally optimal actuator distribution was obtained. Numerical simulation results validated the proposed actuator shape optimization scheme.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.11
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• pp.948-956
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• 2012

This paper presents the computations of the longitudinal and directional stability derivatives for the SDM(Standard Dynamic Model). The static and dynamic derivatives are evaluated at once using forced harmonic oscillations in the pitch and yaw directions. For the numerical simulations, a 3-D Euler solver that uses a dual time stepping method for unsteady time accurate simulations is applied. This work investigates the variation of the derivatives in terms of the Mach number and the several motion parameters. Good agreement of the pitch and yaw stability derivatives with previously published numerical results and experimental results are observed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.4
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• pp.82-91
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• 2003

Experiments to investigate the mixing performance of unlike doublet impinging jets are conducted. Reynolds number of simulants used in this study rages from 1.0 to 1.5 Cold flow test is performed to investigate the hydrodynamic effect and spray of the impinging jets are collected locally and calculated by using Rupe's mixing efficiency equation. Momentum exchanges and relative velocity ratio between two jets are taken as the main parameter to represent the effect of enlargement of the orifice diameter. As diameter ratio increases, the corresponding momentum ratio where maximum mixing efficiency occurs and relative velocity at the maximum mixing efficiency ranges 0.6 to 0.7, respectively. Penetration depth can be taken as a prominent parameter to estimate the mixing efficiency.

• Journal of the Korean Society for Marine Environment & Energy
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• v.5 no.3
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• pp.35-44
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• 2002

In this paper, the analytic studies on the wave control performance of moored pontoon-type floating breakwater are presented. A two-dimensional eigenfunction expansion method is adopted to study the motion responses and the transmission coefficients of pontoon-type floating breakwater in beam waves. The stiffness coefficients of mooring line are idealized as linear elastic spring. Comparison of the analytical results with a numerical results (FEM) shows good agreement over a wide range of frequencies. The performance of mooed pontoon-type floating breakwater is tested with various design parameters such as sectional geometry, mooring line characteristics and wave frequencies. It is found that the properly designed floating breakwater can be an effective wave control structure.

• Journal of Korean Ophthalmic Optics Society
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• v.6 no.2
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• pp.85-97
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• 2001

A mathematical model was proposed to analyze the damped motion of contact lens which is initially displaced from the equilibrium position. The model incorporates the differential equations and their numerical solution program, based on the formulations of restoring force arising from the capillary action in the tear-film layer between the lens and cornea. The model predicts the capillary action induced surface tension, time dependence of displacement of lens when it is released from the equilibrium position. It seems that the motion of lens is similar to the typical over-damped oscillation caused by the large viscous friction in the liquid layer between the cornea and lens. The effect of variables such as base curves, lens diameters and thickness of tear film layer were illustrated by the computer simulation of the derived program. The time required for the lens to return to the original position increases as the liquid layer thickness increases and it decreases as the diameter of lens increases. With the certain value of base curve the time interval is found to be minimum. The free vibrations of lenses were also simulated varying the parameters such as base curve, diameter, layer thickness. The resonant frequencies are inversely proportional to the liquid layer thickness and it increases as the lens diameter increases. The resonant frequency of lens has a maximum when the diameter is of certain value. If the external impulse or force of the same frequency as the natural frequency of contact lens acted on the cornea in vivo it may cause an excessive movement and thus it might cause the distortion 10 the lens or be pulled off the eye.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.655-655
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• 2013

그래핀은 높은 전자 이동도, 열전도도, 기계적 강도, 유연성 등의 고유한 특성으로 다양한 분야에 응용하기 위한 연구가 수행되고 있으며, 특히 전자 소자에의 적용에 관한 연구가 활발히 이루어지고 있다. 전자 소자에 적용하기 위해서는 성장 및 물성에 관한 규명, 응용 소자에 따른 특성 평가가 필요하다. 이러한 소자 특성은 그래핀 물성에 의한 영향이 기본적이지만 에칭, 전사 등의 공정 중 발생하는 오염, 표면 특성, 잔여물 등에 의한 물성 변화 또한 분석 및 제어에 관한 연구가 필요하다. 열화학증착법(thermal chemical vapor deposition)을 이용한 그래핀 합성은 구리 기판을 사용하며, 합성된 그래핀의 에칭, 박리 및 전사 공정이 있다. 이러한 공정 중 발생하는 오염 입자가 그래핀 표면에 흡착되거나, 제거되지 않은 PMMA 잔여물이 그래핀의 특성에 영향을 미치게 된다. 따라서 본 연구에서는 $CO_2$ 클러스터의 표면 충돌을 이용하여 이러한 오염 물질 및 잔여물을 제거하고 그래핀 표면을 평탄화하는 것에 관한 연구를 수행하였다. 가스 클러스터란 작동기체의 분자가 수십에서 수백 개 뭉쳐 있는 형태를 뜻하며 이렇게 형성된 클러스터는 수 nm 크기를 형성하게 된다. 그리고 짧은 시간의 응축에 의해 수십 nm 크기 까지 성장 하게 된다. 클러스터를 이용한 표면 처리는 충돌에 의한 제거에 기반 한다. 따라서 생성 및 가속되는 클러스터로부터 대상으로 전달되는 운동량의 정도가 세정 특성에 영향을 미치며 이는 생성되는 클러스터의 크기에 종속적이다. 생성 클러스터의 크기 분포는 분사거리, 유량, 분사 각도, 노즐 냉각 온도 등의 변수에 관한 함수이다. 본 연구에서는 이러한 변수들을 제어하여 클러스터를 이용한 그래핀 표면 처리 실험을 수행하였다. 평가는 클러스터 표면 처리 전과 후의 특성 비교에 기반 하였으며, 광학 현미경을 이용한 표면 형상 측정, 라만분광 분석, AFM을 이용한 표면 조도 측정, 그래핀 면저항 측정 결과를 비교하였다. 평가 결과를 통하여 표면 처리를 하지 않은 그래핀에 비하여 면저항과 표면 조도가 낮아지는 것을 확인 할 수 있었다. 또한 클러스터 세정은 300 mm 웨이퍼 크기 이상의 대면적을 짧은 시간에 건식으로 세정할 수 있다는 장점이 있어 향후 최적화를 통해 그래핀 양산 시 특성 향상을 위한 후처리 방법으로 사용될 수 있음을 확인하였다.