• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.8
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• pp.583-593
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• 2018

Lightning causes physical damage to aircraft, such as melting, burning and arcing, and magnetic field that occurs on the aircraft's outer body during the penetration of a lightning stroke causes voltage and current transients in the electronics and wiring within the aircraft. This effect will cause induced lightning strikes in the aircraft's internal airborne electronic systems, preventing safe flight. This paper introduces protection circuit design techniques, and the test results that meet the requirements for certification of criteria.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.193-195
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• 2015

The Palomar Transient Factory is a project making use of a Schmidt 48 inch telescope located on the Palomar Mountain, which is surveying the sky with dynamical cadences. It was deployed in 2009 and the observed sky region is over 1200 square degrees. We have studied the long-term periodic variabilities of the known galactic cataclysmic variables (CVs). More than 20 of the sources had been found to have long term periodic signals, ranging from several tens of days to several hundreds of days. Some possible scenarios are proposed to explain the results, such as a magnetic field change of the companion star, precession of the accretion disk, triple systems and superoutburst cycles. Some preliminary discussion will be presented in this article.

• Korean Journal of Radiology
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• v.22 no.10
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• pp.1680-1689
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• 2021

Objective: To investigate the diagnostic yield of diffusion-weighted imaging (DWI) in patients with transient global amnesia (TGA) and identify significant parameters affecting diagnostic yield. Materials and Methods: A systematic literature search of the MEDLINE and EMBASE databases was conducted to identify studies that assessed the diagnostic yield of DWI in patients with TGA. The pooled diagnostic yield of DWI in patients with TGA was calculated using the DerSimonian-Laird random-effects model. Subgroup analyses were also performed of slice thickness, magnetic field strength, and interval between symptom onset and DWI. Results: Twenty-two original articles (1732 patients) were included. The pooled incidence of right, left, and bilateral hippocampal lesions was 37% (95% confidence interval [CI], 30-44%), 42% (95% CI, 39-46%), and 25% (95% CI, 20-30%) of all lesions, respectively. The pooled diagnostic yield of DWI in patients with TGA was 39% (95% CI, 27-52%). The Higgins I² statistic showed significant heterogeneity (I² = 95%). DWI with a slice thickness ≤ 3 mm showed a higher diagnostic yield than DWI with a slice thickness > 3 mm (pooled diagnostic yield: 63% [95% CI, 53-72%] vs. 26% [95% CI, 16-40%], p < 0.01). DWI performed at an interval between 24 and 96 hours after symptom onset showed a higher diagnostic yield (68% [95% CI, 57-78%], p < 0.01) than DWI performed within 24 hours (16% [95% CI, 7-34%]) or later than 96 hours (15% [95% CI, 8-26%]). There was no difference in the diagnostic yield between DWI performed using 3T vs. 1.5T (pooled diagnostic yield, 31% [95% CI, 25-38%] vs. 24% [95% CI, 14-37%], p = 0.31). Conclusion: The pooled diagnostic yield of DWI in TGA patients was 39%. DWI obtained with a slice thickness ≤ 3 mm or an interval between symptom onset and DWI of > 24 to 96 hours could increase the diagnostic yield.

• Journal of Astronomy and Space Sciences
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• v.29 no.4
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• pp.337-342
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• 2012

In this study, the transient second or third layer on the topside of the Martian ionosphere were investigated with the most recently released Mars advanced radar for subsurface and ionospheric sounding/Mars Express data obtained from January 2010 to September 2011 to study the correlation between these topside additional layers and surface magnetic fields, solar zenith angle and solar activities. When examining the zones where the topside layer appeared, the occurrence rate of the topside layer was low at the areas with a strong Martian crustal magnetic field as observed by the Mars global surveyor. The occurrence rate of additional layers on the Martian topside ionosphere decreases as the solar zenith angle increases. However, these layers appeared significantly near the terminator of which solar zenith angle is $90^{\circ}$. In comparison between F10.7 which is the index of solar activities and the occurrence rate of the topside layer by date, its occurrence rate was higher in 2011 than in 2010 with less solar activities. The result of this study will contribute to better understanding of the environments in the topside of the ionosphere through the correlation between the various conditions regarding the Martian ionosphere and the transient layer.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.10
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• pp.84-88
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• 2008

This paper deals with the part of the surge protection method of the underground distribution system in Korea using arrestors by simulating with ATP-EMTP(Electro-Magnetic Transient Program) based on the "A Study on the Surge Propagation Property of Underground Distribution Cables by Field Tests" which was published in 2007. Although domestic underground distribution system is protected by arrester which installed at a riser pole, we need to additional protection method because lightning surge can be doubled and affect underground distribution facilities when it is injected into the mixed distribution line of overhead and underground through a riser pole. In this paper, it is proposed that scout method that arresters are attached to the sides of a riser pole is better than developing of a elbow arrester on a viewpoint of economics and maintenance, because of the situation of the domestic underground distribution system.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.5
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• pp.1043-1058
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• 1990

The Strain rate effect in electro-magnetic forming, which is one of the high velocity forming methods, is studied by the finite element method in this paper. The forming process is simplified by neglecting the coupling between magnetic field and work-piece deformation, and the impulsive magnetic pressure is regarded as inner pressure load. A rate-dependent elasto-plastic material model, of which tangential modulus depends of effective strain rate, is proposed. The model is shown to well describe the transient increase of yield stresses, the decreases of the final displacement and yield stress, the decrease of the difference in the distribution of deformation along the axial direction, and the change of deformation mechanism due to strain rate effect. As a result, displacement, final deformed shape, radial velocity, deformation energy, and the changes of effective stress, effective strain and effective strain rate through plastic working are given. Based on the results, the effectiveness of this model and the strain rate effect of the deformation process of the work-piece are discussed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.9 no.3
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• pp.359-368
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• 1998

One of the topics concerning the electromagnetic compatibility of modern electronic circuits is to take protection from transient overvoltages caused by not only cloud-to-ground lightnings but also induced lightning discharges. In this paper, the vertical electric and horizontal magnetic fields from cloud-to-ground lightnings were measured and analyzed. The electric and magnetic fields waveforms associated with cloud-to-ground lightnings have several subsidiary peaks which decrease with time. There were not much differences between the electric and magnetic field due to long distance cloud-to-ground discharges. Average values of 10~90% rise times of electric fields are $4.65mutextrm{s}$ for the positive cloud-to-ground lightning and $3.29mutextrm{s}$ for the negative cloud-to-ground lightning, respectively. Also, in the positive and negative cloud-to-ground lightning discharges, the zero-to-zero crossing times in the wave tail of magnetic fields are significantly longer than those of the electric fields.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.3
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• pp.437-444
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• 2000

In this paper, we propose a method that directly converts 3D CAD files for handheld phones designed by a commercial CAD S/W, PATRAN, to FDTD modeling with 1mm resolution. To qualify the accuracy of this method, we compared the calculation of radiation pattern using 3D transient far zone transformation with the measured results by gain comparison method in anechoic chamber and the difference is less than 0.5 dB. The calculation of magnetic field distributions on the front of handheld phones has been done to find a factor contributes to SAR. The result showed up the H-field in the width direction of the phone gives more dominant effect than the field in the length or inside to the front direction.

• Journal of Power Electronics
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• v.18 no.5
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• pp.1577-1584
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• 2018

The content of harmonic current increases with an increase in the number of power electronic devices in power grid. When a generator is directly connected to the power grid through a step-up transformer, the influence of the harmonic currents on the generator is inevitable. To study the influences of harmonics on generators, a 24-MW bulb tubular turbine generator is taken as an example in this paper. A 2-D transient electromagnetic field model is established. Through a comparative analysis of the data of experiments and simulations, the correctness of the model is verified. The values of the air gap magnetic density, torque and losses of the generator under various conditions are calculated using the finite element method. Taking the rated condition as a reference, the influence of the harmonic currents on the magnetic flux density is analyzed. It is confirmed that the time harmonic is a key factor affecting the generator performance. At the same time, the effects of harmonic currents on the torque ripple, average torque and eddy current loss of the generator are studied, and the mechanism of the variation of the eddy current loss is also discussed.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.61.2-61.2
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• 2017

We report a fine scale transient brightening event near a pore boundary with the Fast Imaging Solar Spectrograph (FISS) of the 1.6m Goode Solar Telescope (GST), the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory (SDO), and Helioseismic and Magnetic Imager (HMI) aboard SDO. The event appears in all AIA extreme ultraviolet bands, also in the two FISS lines, $H{\alpha}$ and Ca II $8542{\AA}$, and lasted for a minute. The brightening occurred at a footpoint of a loop. The conjugate brightening occurred at the other foot point outside the FISS field of view. The brightening near the pore exhibit a redshift of 4.3 km s-1 in the $H{\alpha}$ and about 2.3 km s-1 in Ca II line. Differential emission measure derived from 6 AIA EUV passbands and cloud model fitting of the two FISS lines indicate the temperature increase of between 10,000 and 20 MK at the main event. After the brightening, the upward mass motion appears in the AIA images. We discuss the physical implication of this brightening in the context of magnetic reconnection and coronal heating.