• The Bulletin of The Korean Astronomical Society
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• v.36 no.1
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• pp.36.1-36.1
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• 2011

It is generally believed that eruptive phenomena in the solar atmosphere such as solar flares and coronal mass ejections (CMEs) occur in the solar active regions with complex magnetic structures. Magnetic helicity has been recognized as a useful parameter to measure the complexity such as twists, kinks, and inter-linkages of magnetic field lines. The objective of this study is to understand a long-term (a few days) variation of magnetic helicity in active regions and its relationship with the energy buildup and instability leading to flares and CMEs. Statistical studies of flare productivity and magnetic helicity injection in about 400 active regions were carried out. The temporal variation of magnetic helicity injected through the photosphere of active regions was also examined related to 46 CMEs. The main findings in this study are as follows: (1) the study of magnetic helicity for active regions producing major flares and CMEs indicates that there is always a significant helicity injection through the active-region photosphere over a long period of 0.5 - a few days before the flares and CMEs; (2) for the 30 CMEs under investigation, it is found that there is a fairly good correlation (linear correlation coefficient of 0.71) between the average helicity injection in the CME-productive active regions and the CME speed. Beside the scientific contribution, a major impact of this study is the observational discovery of a characteristic variation pattern of magnetic helicity injection in flare/CME-productive active regions which can be used for the improvement of solar eruption forecasting.

• 제어로봇시스템학회:학술대회논문집
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• 2000.10a
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• pp.121-121
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• 2000

This paper presents a design of macro-micro system for high-speed mounting of micro-chips. A macro motion device is driven by DC servomotor and ball screw mechanism. To obtain fast response, a micro motion device utilizes a precision elector magnetic actuator In order to reduce peak impact force, We evaluate the design parameters that have an effect on it. And a characteristic of response is simulated using PID controller in velocity and force control.

• Journal of the Korean Magnetic Resonance Society
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• v.20 no.4
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• pp.114-120
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• 2016

Nitrogen vacancy-centered diamond has recently emerged as a promising material for various applications due to its special optical and magnetic properties. In particular, its applications as a fluorescent biomarker with small toxicity, magnetic field and electric field sensors have been a topic of great interest. Recent review (R. Schirhagl et al 2014) introduced those applications using single NV-center in nanodiamond. In this minireview, I introduce the rapidly emerging DNP (Dynamic Nuclear Polarization) field using optically-pumped NV center in diamonds. Additionally, the possibility of exploiting the optically-pumped NV center for polarization transfer source, which will produce a profound impact on room temperature DNP, will be discussed.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.89.2-89.2
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• 2011

The geometry of an MC (magnetic cloud) in the interplanetary space can be estimated by the magnetic flux rope model. But the single point observation in the interplanetary space near the Earth is scanty to comprehend the global configuration of MC because the MC is considered a huge loop extending from the Sun with both legs rooted on the Sun. If the MC is observed at two different locations sufficiently far away from each other, it may provide the global configuration of the MC. In this study, we model the MC which is observed two different locations using a simple straight cylinder model. The MC model fit parameters are the flux rope axis orientation (${\Theta}$, ${\phi}$), the intensity of the magnetic field at the flux rope axis ($B_0$), the radius of the MC ($R_0$), and the impact parameter (p), etc. With the MC model fit parameters we look into the difference between two observed MC geometries and also calculate the magnetic flux and helicity of the MC.

• Steel and Composite Structures
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• v.35 no.4
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• pp.545-554
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• 2020

The present paper explores nonlinear dynamical properties of piezo-magnetic beams based on a nonlocal refined higher-order beam formulation and piezoelectric phase effect. The piezoelectric phase increment may lead to improved vibrational behaviors for the smart beams subjected to magnetic fields and external harmonic excitation. Nonlinear governing equations of a nonlocal intelligent beam have been achieved based upon the refined beam model and a numerical provided has been introduced to calculate nonlinear vibrational curves. The present study indicates that variation in the volume fraction of piezoelectric ingredient has a substantial impact on vibrational behaviors of intelligent nanobeam under electrical and magnetic fields. Also, it can be seen that nonlinear free/forced vibrational behaviors of intelligent nanobeam have dependency on the magnitudes of induced electrical voltages, magnetic potential, stiffening elastic substrate and shear deformation.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.323-327
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• 2001

Electrorheological(ER) and magnetorheological(MR) fluids have a unique ability to increase the dynamic yield stress of the fluid substantially when electric or magnetic field is applied. Controllable fluids such as ER and MR fluids have received considerable attention as several components of engineering devices. One of them is a smart impact damper using ER/MR fluids. Impact damper system can be used in the joint mechanism of railroad vehicle, protection equipment of elevator's drop, and launch equipment of aircraft. This paper presents the results of an analytical study of the performance of a smart impact damper to suppress vibration during impact excitation. The damping capabilities of MR impact damper for variable applied current are analyzed using Bingham model under sudden impact load.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.5
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• pp.394-401
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• 2004

This paper presents a study on the analysis of impact responses taking into account sensor dynamics. The contact force between impacting bodies is modelled by using Hertz force-displacement law and linear damping function. Since the real impact force and acceleration at the contact surface of two colliding bodies are measured indirectly by the sensors, the measured outputs can be a little different from the real impact responses. Therefore, in this study, the importance of consideration of sensor dynamics in the impact problems of two colliding bodies is emphasized. In order to verify the appropriateness of the proposed contact force model, the drop type impact test using two kinds of sensors is carried out. Through the numerical analysis and experiment, the effect of sensor dynamics and characteristics on the contact force model is investigated.

• The KSFM Journal of Fluid Machinery
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• v.16 no.3
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• pp.32-38
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• 2013

This paper deals with the study on the rotordynamic and experimental analysis of turbine-generator system connected with a magnetic coupling. Although magnetic coupling has been used to torque transmission of chemical processing pump rotating at under 3,600rpm, magnetic coupling in this study is applied to high-speed turbine-generator system using a working fluid that is refrigerant such as ammonia or R-124a. Results of rotordynamic design analysis are as follows. The first, shaft diameter nearest to outer hub of magnetic coupling has a big effect on the $1^{st}$ critical speed of generator rotor. The second, if the $1^{st}$ critical speeds of turbine rotor and generator rotor have enough to separation margin in comparison to rated speed, the $1^{st}$ critical speed of turbine-magnetic coupling-generator rotor train has enough to separation margin regardless of connection stiffness of magnetic coupling. The analytical FE model is guaranteed by impact test on the prototype and condition monitoring such as measurements of vibration and bearing temperature is also performed.

• Journal of The Korean Astronomical Society
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• v.50 no.2
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• pp.29-39
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• 2017

We investigate two abnormal CME-Storm pairs that occurred on 2014 September 10 - 12 and 2015 March 15 - 17, respectively. The first one was a moderate geomagnetic storm ($Dst_{min}{\sim}-75nT$) driven by the X1.6 high speed flare-associated CME ($1267km\;s^{-1}$) in AR 12158 (N14E02) near solar disk center. The other was a very intense geomagnetic storm ($Dst_{min}{\sim}-223nT$) caused by a CME with moderate speed ($719km\;s^{-1}$) and associated with a filament eruption accompanied by a weak flare (C9.1) in AR 12297 (S17W38). Both CMEs have large direction parameters facing the Earth and southward magnetic field orientation in their solar source region. In this study, we inspect the structure of Interplanetary Flux Ropes (IFRs) at the Earth estimated by using the torus fitting technique assuming self-similar expansion. As results, we find that the moderate storm on 2014 September 12 was caused by small-scale southward magnetic fields in the sheath region ahead of the IFR. The Earth traversed the portion of the IFR where only the northward fields are observed. Meanwhile, in case of the 2015 March 17 storm, our IFR analysis revealed that the Earth passed the very portion where only the southward magnetic fields are observed throughout the passage. The resultant southward magnetic field with long-duration is the main cause of the intense storm. We suggest that 3D magnetic field geometry of an IFR at the IFR-Earth encounter is important and the strength of a geomagnetic storm is strongly affected by the relative location of the Earth with respect to the IFR structure.

• Imaging Science in Dentistry
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• v.49 no.2
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• pp.153-158
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• 2019

Purpose: The purpose of this study was to investigate variations in velar shape according to age, sex, and race using magnetic resonance imaging (MRI). Materials and Methods: The study sample consisted of 170 participants (85 children, 85 adults) between 4 and 34 years of age. Velar morphology was visually classified using midsagittal MRI scans for each participant by 2 independent raters. Inter- and intra-rater reliability was assessed. Statistical analyses were performed to identify correlations of velar shape with sex, age, and race. Results: The most frequent velar shape was "butt" for both adults(41%) and children (58%) in this study. The least common shapes for adults were "leaf" and "S." The children did not exhibit any "leaf" or "straight" velar shapes. A statistically significant difference was noted for age with respect to velar shape (P=0.014). Sex and race were found to have no significant impact on velar shape in this study. Conclusion: When using MRI to evaluate velar morphology, the "butt" shape was most common in both children and adults. Velar shape varied significantly with age, while race and sex did not have a significant impact.