• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.459-464
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• 2007

Seismic control performance of MR dampers, which have severe nonlinearity, differs with respect to the dynamic characteristics of an earthquake such as magnitude, frequency and duration. In this study, the effects of excitation characteristics on the equivalent linear system of a building structure with the MR damper are investigated through numerical analysis for artificial ground motions generated from different response spectrums. The equivalent damping ratio of the structure with the MR damper is calculated using Newmark and Hall's equations for ground motion amplification factors. It is found that the equivalent damping ratio of the structure with the MR damper is dependent on the ratio of the maximum friction force of the MR damper over excitation magnitude. Frequency contents of the earthquake ground motion affects the equivalent damping ratio of long-period structures considerably. Also, additional damping effect caused by interaction between the viscousity and friction of the MR damper is observed. Finally, response reduction factors for equivalent linear systems are proposed in order to improve accuracy in the prediction of the actual nonlinear response.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.879-885
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• 2006

Seismic control performance of MR dampers, which have severe nonlinearity, differs with respect to the dynamic characteristics of an earthquake such as magnitude, frequency and duration. In this study, the effects of excitation characteristics on the equivalent linear system of a building structure with the MR damper are investigated through numerical analysis for artificial ground motions generated from different response spectrums. The equivalent damping ratio of the structure with the MR damper is calculated using Newmark and Hall's equations for ground motion amplification factors. It is found that the equivalent damping ratio of the structure with the MR damper is dependent on the ratio of the maximum friction force of the MR damper over excitation magnitude. frequency contents of the earthquake ground motion affects the equivalent damping ratio of long-period structures considerably. Also, additional damping effect caused by interaction between the viscousity and friction of the MR damper is observed. Finally, response reduction factors for equivalent linear systems are proposed in order to improve accuracy in the prediction of the actual nonlinear response.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.1
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• pp.87-93
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• 2008

Seismic control performance of MR dampers, which have severe nonlinearity, varies with respect to the dynamic characteristics of an earthquake such as magnitude, frequency and duration. In this study, the effects of excitation characteristics on the equivalent linear system of a building structure with the MR damper are investigated through numerical analysis for artificial ground motions generated from different response spectrums. The equivalent damping ratio of the structure with the MR damper is calculated using Newmark and Hall's equations for ground motion amplification factors. It is found that the equivalent damping ratio of the structure with the MR damper is dependent on the ratio of the maximum friction force of the MR damper over excitation magnitude. Frequency contents of the earthquake ground motion affects the equivalent damping ratio of long-period structures considerably. Also, additional damping effect caused by interaction between the viscousity and friction of the MR damper is observed. Finally. response reduction factors for equivalent linear systems are proposed in order to improve accuracy in the prediction of the actual nonlinear response.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.3
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• pp.234-240
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• 2011

This study deals with progressive collapse of a structure retrofitted with MR dampers. In order to assess their effect of mitigation which prevents progressive collapse, control force ratio is defined by friction force of MR dampers divided by external force. First, simple model of a structure with MR dampers is suggested. Using the model, exact solution with the control force ratio is obtained. When and where the system is stopped is predicted by the derived solution. Through the dissipated energy by MR dampers during collapse event, equivalent damping ratio is derived. Finally, comparison of exact and equivalent solutions is presented.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2006.03a
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• pp.503-510
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• 2006

Seismic control performance of MR dampers, which have severe nonlinearity, differs with respect to the dynamic characteristics of an earthquake such as magnitude, frequency and duration. In this study, the effects of excitation characteristics on the equivalent linear system of a building structure with an MR damper are investigated through numerical analysis for artificial ground motions generated from different response spectrums. The equivalent damping ratio of the structure with an MR damper is calculated using Newmark and Hall's equations for ground motion amplification factors. It is found that the equivalent damping ratio of the structure with the MR damper is dependent on the ratio of the maximum friction force of the MR damper over excitation magnitude. Frequency contents of the earthquake ground motion affects the equivalent damping ratio of long-period structures considerably. Also, additional damping effect caused by interaction between the viscousity and friction of the MR damper is observed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.355-358
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• 2000

Magnetoresistance changes of NiFe thin films were investigated as a function of deposition temperature. DC magnetron sputtering was employed to fabricate Ta/NiFe(t)/Ta thin films on Si(001) substrates with in-situ field or with no-field. The thickness(t) of NiFe films was a range of 4 to 15nm. Substrate temperature was a range of 30 to 400$^{\circ}C$. MR measurement was carried out as a function of angle $\theta$, between external field and current direction. MR ratio increased with increasing substrate temperature, also, max. MR ratio was observed in samples deposited at 300$^{\circ}C$. With increasing upto 400$^{\circ}C$, MR ratio was rapidly decreased in the case of thinner NiFe films. In non-field deposited NiFe films, both angle $\theta$=0, 90。, there was no significant change in MR curves. However, MR curves of in-situ field deposited NiFe films were different in both angles $\theta$=0 and 90。

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.6
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• pp.748-751
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• 2012

The performance of a monopulse estimator is depend on its monopulse ratio(MR) curve. To improve its performance, a mathematical expression of the MR curve that is associated with an array the parameters is needed. In this paper, we present a novel monopulse estimator that uses the inverse function of a MR curve for the Maximum Likelihood (ML)-based monopulse estimator. It is shown that the proposed method can extend the linear region of the MR curve, which in turn improve the estimation accuracy. Moreover, it's performance is compared with the ML-based method through simulation.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.10
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• pp.960-965
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• 2011

This paper presents the mathematical derivation of a maximum likelihood(ML)-based monopulse ratio(MR) curve. The derived form is, with the linear array assumed, shown to be the function of the number of array elements and the elements' spacing. Through some simulations, the acquired form is equivalent to the expected MR curve. Furthermore, we show the form, which consists of several terms, can be simplified by one tangent function.

• Journal of Magnetics
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• v.2 no.1
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• pp.7-11
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• 1997

The dependence of magnetoresistance (MR) ratio on various variables like the thickness of the second Co layer, on the presence of cap layer, on deposition field (Hdep) and on annealing in Co/Cu/Co sandwiches was investigated. Spin-valve sandwiches were deposited on the corning glass by means of the 3-gun dcmagnetron sputtering at a 5 mTorr partial Ar pressure and room temperature. The deposition field was varied from 70 Oe to 720 Oe. The MR curve was measured by the four-terminal method with applied magnetic field up to 1000 Oe perpendicular to the direction of a current in the film plne. The MR ratio of glass/Fe(50${\AA}$)/Co(17${\AA}$)/Cu(24${\AA}$)/Cot(${\AA}$) fabricated by making 50 ${\AA}$ of Fe buffer layer has the maximum value of 8.2% when the thickness of the second Co layer was 17${\AA}$and the deposition field was 350 Oe. In the case of glass/Fe(50${\AA}$)/Co(17${\AA}$)/Cu(24${\AA}$)/Cot(${\AA}$) with Cu cap layer on top, the decrease in the MR ratio seemed to relate with the oxidation of the second Co layer. Samples prepared with deposition field showed greater MR ratios through the formation of more complete spin valve films. After annealing for 2 hours at 300$^{\circ}C$, the MR ratio of the samples prepared with deposition field decreased rapidly while the MR raito of the sample prepared without the field remained.

• Proceedings of the KSMRM Conference
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• 2002.11a
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• pp.107-107
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• 2002

목적： I-123 IPT SPECT에서 striatum에 ROI를 설정하여 Strial Binding Ratio를 측정하기 위해 사용되는 육안적인 방법과 MR Template based Coregistration 방법을 비교 평가하였다. 대상 및 방법： 파킨슨씨병 환자(IPD) 15명(남/녀：8/7, 63.3$\pm$4.8세)과 정상인 8명(남/녀：2/6, 61.4$\pm$16.5세) 에서 I-123 IPT(259MBq)를 주사한 후 2시간에 SPECT 영상을 얻었고 미상핵과 조가비핵의 전, 후부 및 후두엽에 각각 육안적인 방법과 MR Template based Coregistration방법으로 ROI를 설정하였다. MR Template based Coregistration 방법은 MNI TIMR template을 이용하여 SPECT영상을 voxel based intensity matching 방법으로 coregistration한 후midthalamic level에서 striatum의 경계를 따라 설정된 ROI를 이용하였다. 육안적인 방법은 striatal uptake가 가장 높은 level에서 3개의 ROI template를 striatum에 위치하였다. 두 방법으로 SBR과 nnterior/posterior ratio of SBR(APR)를 측정하였고 정상인과 파킨슨씨병 환자에서 두 방법을 비교하였다.