• Korea-Australia Rheology Journal
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• 제13권3호
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• pp.141-148
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• 2001

In this research, experimental studies leave been performed on the hydrodynamic interaction between a spherical particle and a plane wall by measuring the force between the particle and wall. To approach the system as a resistance problem, a servo-driving system was set-up by assembling a microstepping motor, a ball screw and a linear motion guide for the particle motion. Glycerin and dilute solution of polyacrylamide in glycerin were used as Newtonian and non-Newtonian fluids, respectively. The polymer solution behaves like a Boger fluid when the concentration is 1,000 ppm or less. The experimental results were compared with the asymptotic solution of Stokes equation. The result shows that fluid inertia plays all important role in the particle-wall interaction in Newtonian fluid. This implies that the motion of two particles in suspension is not reversible even in Newtonian fluid. In non-Newtonian fluid, normal stress difference and viscoelasticity play important roles as expected. In the dilute solution weak shear thinning and the migration of polymer molecules in the inhomogeneous flow field also affect the physic of the problem.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2489-2494
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• 2008

The two-dimensional circular cylinder freely falling in a channel has been simulated by using Immersed boundary - lattice Boltzmann method in order to analyze the characteristics of motion originated by the interaction between the fluid and the solid. The wide range of the solid/fluid density ratio has been considered to identify the effect of the solid/fluid density ratio on the motion characteristics such as the falling time, the terminal velocity and the trajectory in the vertical and horizontal directions. In addition, the effect of the gap between the cylinder and the wall on the motion of two-dimensional circular cylinder freely falling has been revealed by taking into account a various range of the gap size. The Reynolds number in terms of the terminal velocity is diminished as the cylinder becomes close to the wall at the initial dropping position, since the repulsive force induced between the cylinder and wall constrains the vertical motion. Quantitative information about the flow variables such as the pressure coefficient and vorticity on the cylinders is highlighted.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2006년도 동계학술연구발표회 및 자성 스핀트로닉스 국제학술대회
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• pp.137-137
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• 2006

• 한국지진공학회논문집
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• 제20권1호
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• pp.1-8
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• 2016

Permanent deformation plays a key role in performance based earthquake resistant design. In order to estimate permanent deformation after earthquake, it is essential to secure reliable response history analysis(RHA) as well as earthquake scenario. This study focuses on permanent deformation of an inverted T-type wall under earthquake. The study is composed of two separate parts. The first one is on the verification of RHA and the second one is on an effect of input earthquake motion. The former is discussed in this paper and the latter in the companion paper. The verification is conducted via geotechnical dynamic centrifuge test in prototype scale. Response of wall stem, ground motions behind the wall obtained from RHA matched pretty well with physical test performed under centrifugal acceleration of 50g. The rigorously verified RHA is used for parametric study to investigate an effect of input earthquake motion selection in the companion paper.

• 대한설비공학회지:설비저널
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• 제16권1호
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• pp.103-108
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• 1987

The heat transfer processes taking place in the side wall of a thermocline enclosure have been analyzed for idealized conditions based on the assumption that, at any instant time, side wall heat transfer processses are independent of the thermocline bulk motion. However, the axial tempera-ture distribution in the thermocline core provides the means for specifying the liquid medium-side boundary condition to the enclosure side wall. A picture is drawn which reflects the side wan response to thermocline bulk motion within the frame work of a quasi-steady analytic approach. For valves of the parameters typical of systems of engineering interest, the analysis shows that a significant amount of heat transfer short - circuiting can take place along the side wall enclosure. This phenomenon is favored by high values of $H_l$ and low values of P and $H_g$ respec-tively. The location of the point of zero normal heat flux on the side wan can be expected to mark, approximately, the region of confluence of two sidewall boundary flows respectively driven by the buoyant effects.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2000년도 International Symposium on Magnetics The 2000 Fall Conference
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• pp.279-286
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• 2000

Magnetic field dependence of magnetization reversal in Co/Pt multilayers has been quantitatively investigated. Serial samples of Co/Pt multilayers have been prepared by dc-magnetron sputtering under various Ar pressure. Magnetization reversal was monitored by magnetization viscosity measurement and direct domain observation using a magneto-optical microscope system, and the wall-motion speed and the nucleation rate R were determined using a domain reversal model based on time-resolved domain reversal patterns. Both and R were found to be exponentially dependent on the reversing applied field. From the exponential dependencies, the activation volumes of the wall motion and nucleation could be determined based on a thermally activated relaxation model, and the wall-motion activation volume was revealed to be slightly larger than the nucleation activation volume.

• 대한방사선기술학회지:방사선기술과학
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• 제45권4호
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• pp.321-330
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• 2022

Echocardiography and cardiac enzymes test are the tests to assess ischemic heart disease. The purpose of this study was to verify the accuracy by comparing and analyzing two tests for the diagnosis of ischemic heart disease. A retrospective study was conducted on 393 study subjects who underwent echocardiography and cardiac enzymes test. As a result of the study, regional wall motion abnormality (RWMA) increased as the age of the study subjects increased. As a result of ROC analysis, RWMA showed a larger area under the curve (AUC) than cardiac enzymes. RWMA showed the highest accuracy with 81.1% of all cardiac enzymes. Among cardiac enzymes, cTnI showed the highest accuracy. Thus, It was confirmed that RWMA of echocardiography is more accurate than cardiac enzyme is in diagnosing ischemic heart disease.

• 대한기계학회논문집B
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• 제24권9호
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• pp.1255-1263
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• 2000

In this study, the modification of turbulent boundary layer flow by local wall vibration is investigated. The wall is locally vibrated using a wall deformation actuator, which moves up and down at the frequencies of 100Hz and 50Hz. Simultaneous measurements of the streamwise velocities in the spanwise direction are performed at several wall-normal and streamwise locations using an in-house multi-channel hot wire anemometer and a spanwise hot-wire-probe rake. The mean velocity is reduced in most places due to the wall vibration and its reduced amount becomes small as flow goes downstream. Interestingly, the mean velocity is found to increase very near the wall and near the actuator. This is due to the motion induced by the streamwise vortices which are generated by the downward motion of the actuator. In case of the streamwise velocity fluctuations, their magnitude increases as compared to the unperturbed turbulent boundary layer, and the increased amount becomes small as the flow moves downstream. The modified flow field at the forcing frequency of 50Hz is not much different from that of 100Hz, except the reduced amount of modification.

• Journal of Magnetics
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• 제8권3호
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• pp.108-112
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• 2003

We report the experimental finding that there exists a transition of magnetization reversal process with varying the applied field in Co/Pd multilayer. We have measured the wall-motion speed V and the nucleation rate R during magnetization reversal via time-resolved direct domain observation, where the magnetization reversal process of Co/Pd multilayer is found to take a transition from thermal activation process to viscous process at the critical field of about 1.87 H$\_$C/ (coercivity). In the thermal activation regime, we find that the field dependences of two activation volumes for the wall-motion process and the nucleation process are different with each other, which reveals that the wall-motion and nucleation experience completely different interactions. In the viscous regime, we find that the wall-mobility is much smaller than a typical value for the sandwiched Co films, which implies that the Co/Pd interfaces in multilayer substantially contribute to the dynamic dissipation.

• 대한핵의학회지
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• 제32권3호
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• pp.259-265
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• 1998

목적: 심근의 T1-201 섭취는 심근 조직의 관류를 반영한다. 급성 심근 경색 환자에서 재관류 후에 T1-201 심근 SPECT로 구조된 심근을 찾아내어 심근벽 운동 회복을 예측할 수 있다. 대상 및 방법: 급성 심근 경색 환자에서 조기 재관류 또는 경색 연관동맥에 대한 지연 재관류를 시행하고 6 시간 이내에 휴식, 다음날 지연 심근 T1-201 심근 SPECT를 촬영하여 휴식기 T1-201의 섭취 정도와 지연 재분포 여부를 관찰하여 재관류 후 조기에 시행한 T1-201 심근 SPECT의 심근벽 운동 호전 예측능을 평가하였다. 결과 휴식기 T1-201 섭취와 지연 재분포를 같이 고려하여 판정한 심근벽 운동 호전 예측능은 양성 예측율 99% (70/71), 음성 예측율 54% (14/27)이었다. 휴식기 T1-201 섭취 정도로 판정한 심근벽운동 호전 예측능은 양성 예측율 100% (69/69),음성 예측율 52% (15/29)로, 지연 재분포의 관찰이 휴식기 T1-201 섭취로만 판가한 심근벽 운동 호전 예측능을 유의하게 향상시키지 않았다. 심근벽 운동감소 정도에 따라 분류한 T1-201 심근 SPECT의 심근벽 운동 호전 예측능은 심근벽 운동이 저하된 46 분절에서 양성 예측율 100%, 음성 예측능 14%이었고, 심근벽 운동이 전혀 없거나 이상 운동이 있었던 52 분절에서 양성 예측을 97%, 음성 예측율 60%이었다. 음성 예측율은 심근벽 운동이 저하된 분절보다 전혀 없거나 이상 운동이 있는 분절에서 유의하게 높았다. 결론: 급성 심근 경색 환자에 대한 재관류 후 조기에 검사한 T1-201 심근 SPECT에서 심근생존능이 있으면 심근벽 운동은 호전되어 좋은 양성예측율을 보였으나 음성 예측율은 비교적 낮았다. 음성 예측율을 올리기 위해서 심근벽 운동을 고려하여 심근 관류를 판정할 필요성이 있었다.