• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.63-70
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• 2008

In this paper, we propose a bearing redundant coordinates and decoupled PD controller for 5-axes active magnetic bearing system, which consists of two bearing parts such as three-pole hybrid active magnetic bearing for stabilize the radial direction and ring-type permanent magnetic bearing stabilizing in axial and tilting motion. Based on derived system equation with decoupled control scheme, we conduct the modal analysis and measure of modal controllability and observability.

• Journal of KSNVE
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• v.5 no.1
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• pp.59-65
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• 1995

In this study, we investigated the operational limit of magnetic bearing-rotor system due to the maximum force limit and slew rjate limit of the electromagnetic actuator as a function of the time dependent control characteristics. The feedback gain of the controller varies the current of the electromagnet coil with the motion of the rotor. The distorsion of magnetic force due to the slew rate limit is not occurred jup to 30, 000 rpm in the magnetic bearing that we have a close relation with the rotational speed and vibration level of the rotor and the proportional gain of the controller. Therefore the maximum force limit determines the maximum allowable orbit radius of the magnetic bearing-rotor system. The maximum allowable vibration levels are exponentially decreased according to the increment of rotational speed and proportional gain of the controller.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.2
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• pp.184-189
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• 2002

Carbon nitride films were grown on Si (100) substrate by a laser-electric discharge method with/without a magnetic field assistance. The magnetic field leads to vapor plume plasma expending upon the ambient arc discharge plasma area. Influence of the magnetic field has resulted in increased of a crystallite size int he films due to bombardment (heating) of Si substrates by energetic carbon and nitrogen species generated during cyclotron motion of electrons in the discharge zone. The surface morphology of the films with a deposition time of 2 hours was studied using a scanning electron microscopy (SEM). In order to determine the structural crystalline parameters, X-ray diffraction (XRD) was used to analysis the grown films.

• Journal of The Korean Astronomical Society
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• v.23 no.1
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• pp.63-70
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• 1990

The original axisymmetric, stationary electrodynamic model of the central engine in an active galactic nucleus proposed by Macdonald and Thorne consists of a supermassive black hole with magnetic field lines that pass through the region just outside the event horizon of the black hole. Each magnetic field line rotates with a constant angular velocity which will exceed the speed of light at large radii. Even though the field lines are purely mathematical entities this condition sets a stringent physical constraint on the motion of the magnetic field lines and the particles on them. In this paper we will show that we can remove this auxiliary constraint in our model by allowing nonstationary processes. As a result the magnetic field lines can be twisted and wound up in a region lying outside of the quasi-stationary magnetosphere of the black hole. We conclude that astrophysical jets are formed in that region due to the twisted and wound magnetic field lines powered by the Blandford-Znajek process and the other driving forces.

• Journal of Navigation and Port Research
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• v.28 no.2
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• pp.141-148
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• 2004

The observations of rapid motion of bubbles under water for approximately 50ms or less in high . magnetic fields of 10 T have been carried out successfully for the first time. The observation system constructed is composed of a high-speed video camera, a telescope, a cryostat with a split-type superconducting magnet, a light source, a mirror and a transparent sample cell. Using this system, the influence of magnetic field on the path and shape of single bubbles of $O_2$(paramagnetism) and $N_2$ (diamagnetism) has been examined carefully. Experimental values describing the path are in good agreement with theoretical values calculated on the basis of the magneto-Archimedes effect, despite the effect of magnetism on the bubble. However, no effect of magnetism on the shape of the bubble is observed In addition, the influence of magnetic field on drag coefficient of the bubble is discussed.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.1309-1311
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• 2005

The operating speed of PWM controlled high speed magnet is affected by mass of plunger magnetic motive force inductance and return spring It is impossible to change the value of them for the purpose of increasing the speed because these factors are related with each other This paper introduces a speed increasing method using a non magnetic ring which is welded in the middle of magnetic guide tube and also presents the characteristic equations results of FEM analysis for magnetic flux distribution and computer simulation results for the dynamic characteristics of plunger motion And we proved the effect of non magnetic ring by experiments using a prototype

• Journal of The Korean Astronomical Society
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• v.47 no.6
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• pp.311-317
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• 2014

Solar chromospheric surges are often reported to contain rotational motion. However, the details of the motion and driving mechanism of the surges are not yet fully understood. Recurrent surges with rotational motion at AR 10930 on the west limb are observed by Hinode Solar Optical Telescope (SOT) continuously from 11:21 UT on December 18 to 09:58 UT on December 19, 2006, using the $Ca_{II}$ H broadband filter. We analyze details of the motion including number of turns from the rise of the surge to the fall, axial speed and acceleration. During the observation, rise and fall motion accompanying rotation appears recurrently. There occur a total of 14 surges at AR 10930 over 17 hours. The average duration is 45 minutes, and the average width, and length are 8 Mm, and 39 Mm, respectively. We speculate that the surges occurred by recurrent reconnections between the twisted prominence and large untwisted flux tube.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.12
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• pp.205-212
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• 2003

Many people are exposed to accidents by vehicles or sports. The most frequent injuries by these accidents is concerned with a knee joint. The three-dimensional surface model of a knee is needed for dynamic analysis of knee motion and knee reconstruction. three-dimensional motion data of a knee joint were obtained using X-ray and precise magnetic sensors. The surface data of a femur and a tibia were obtained using cross-sectional pictures by CT. The three-dimensional surface models of a femur and a tibia were made by the method of optimal triangular patch. Using obtained motion data, we simulated the motion of three-dimensional knee joint model.

• IEIE Transactions on Smart Processing and Computing
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• v.2 no.4
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• pp.203-207
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• 2013

The appropriate handling of motion artifacts is essential for clinical diagnosis in magnetic resonance imaging (MRI). In many cases, motion is an inherent part of MR images because it is difficult to control during MR imaging. As the motion in the human body occur in a deformable manner, they are difficult to deal with. This paper proposes a novel detection method for periodically moving regions to produce MR images with less motion artifacts. When the data is acquired by the radial trajectory, the proposed method can extract the deformable region easily using the difference in the modulated sinograms, which have different periodic phase terms. The simulation results applied to the various cases confirmed the good performance of the proposed method.

• Proceedings of the KIEE Conference
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• summer
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• pp.1061-1063
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• 2004

This paper deals with the application of cylindrical Halbach array to a PM motor capable of producing pure rotary motion, pure linear motion, or helical motion, The proposed motor consists of an exterior polar Halbach array for a rotary motion and interior cylindrical Halbach array for a linear one. The two- dimensional space harmonic method is employed for predicting the electromagnetic characteristics, with reference to the following parameters as variables: magnetic field, torque/thrust and back emf.