• Journal of The Korean Astronomical Society
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• v.39 no.4
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• pp.139-145
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• 2006

We have made a comprehensive statistical study on the coronal mass ejections(CMEs) associated with helmet streamers. A total number of 3810 CMEs observed by SOHO/LASCO coronagraph from 1996 to 2000 have been visually inspected. By comparing their LASCO images and running difference images, we picked out streamer-associated CMEs, which are classified into two sub-groups: Class-A events whose morphological shape seen in the LASCO running difference image is quite similar to that of the pre-existing streamer, and Class-B events whose ejections occurred in a part of the streamer. The former type of CME may be caused by the destabilization of the helmet streamer and the latter type of CME may be related to the eruption of a filament underlying the helmet streamer or narrow CMEs such as streamer puffs. We have examined the distributions of CME speed and acceleration for both classes as well as the correlation between their speed and acceleration. The major results from these investigations are as follows. First, about a quarter of all CMEs are streamer-associated CMEs. Second, their mean speed is 413 km $s^{-1}$ for Class-A events and 371 km $s^{-1}$ for Class-B events. And the fraction of the streamer-associated CMEs decreases with speed. Third, the speed-acceleration diagrams show that there are no correlations between two quantities for both classes and the accelerations are nearly symmetric with respect to zero acceleration line. Fourth, their mean angular width are about $60^{\circ}$, which is similar to that of normal CMEs. Fifth, the fraction of streamer-associated CMEs during the solar minimum is a little larger than that during the solar maximum. Our results show that the kinematic characteristics of streamer-associated CMEs, especially Class-A events, are quite similar to those of quiescent filament-associated CMEs.

• Journal of the Korean Magnetics Society
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• v.17 no.1
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• pp.26-29
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• 2007

Fe-based powders, Fe-M(M=Cr, Mn, Cu, Zn), were prepared in Ar gas by mechanical alloying and their crystallographic and magnetic properties were investigated. X-ray diffraction indicates that the cubic lattice parameter increases for the M substitution. The distance of closest approach around M can explained the increase of lattice constant in Fe-M powders. $M\"{o}ssbauer$ spectroscopy measurements on Fe-M samples indicates the coexistence of ferromagnetic phases and paramagnetic phase that are created by the distribution of local environment M on Fe atom. On the other hand, The spread of line-width on $M\"{o}ssbauer$ spectra can be explained by the distribution of hyperfine magnetic fields. The results of quadrupole shift and isomer shift revealed that M substitutions in Fe-M powders didn't change both structure and the local charge distribution around Fe atom severely.

• Korean Journal of Materials Research
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• v.20 no.10
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• pp.513-517
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• 2010

There have been many efforts to modify and improve the properties of functional thin films by hybridization with nano-sized materials. For the fabrication of electronic circuits, micro-patterning is a commonly used process. For photochemical metal-organic deposition, photoresist and dry etching are not necessary for microscale patterning. We obtained direct-patternable $SnO_2$ thin films using a photosensitive solution containing Ag nanoparticles and/or multi-wall carbon nanotubes (MWNTs). The optical transmittance of direct-patternable $SnO_2$ thin films decreased with introduction of nanomaterials due to optical absorption and optical scattering by Ag nanoparticles and MWNTs, respectively. The crystallinity of the $SnO_2$ thin films was not much affected by an incorporation of Ag nanoparticles and MWNTs. In the case of mixed incorporation with Ag nanoparticles and MWNTs, the sheet resistance of $SnO_2$ thin films decreased relative to incorporation of either single component. Valence band spectral analyses of the nano-hybridized $SnO_2$ thin films showed a relation between band structural change and electrical resistance. Direct-patterning of $SnO_2$ hybrid films with a line-width of 30 ${\mu}m$ was successfully performed without photoresist or dry etching. These results suggest that a micro-patterned system can be simply fabricated, and the electrical properties of $SnO_2$ films can be improved by incorporating Ag nanoparticles and MWNTs.

• The Korean Journal of Mycology
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• v.40 no.3
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• pp.177-178
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• 2012

Stem rot of perilla (Perilla frutescens var. japonica Hara) occurred sporadically in the exhibition field at Gyeongsangnam-do Agricultural Research and Extension Services in Korea. The infected stems are water-soaked, rotted, wilted and finally leads to the death of the whole plants. The sclerotia, 1-3 mm, white to brown, spherical, were formed on lesions and the surface of soil line. The optimum temperature for mycelial growth and sclerotia formation was $30^{\circ}C$ on potato dextrose agar and the hyphal width was 4-9 ${\mu}m$. The typical clamp connections were observed in the hyphae of the fungus. On the basis of mycological characteristics and pathogenicity to host plants, this fungus was identified as Sclerotium rolfsii Saccardo. This is the first report of stem rot on perilla caused by S. rolfsii in Korea.

• Polymer(Korea)
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• v.28 no.6
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• pp.445-454
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• 2004

The requirement for a much finer line width circuits on semiconductors needs new developers such as supercritical fluid to prevent the collapse of the photoresist micro-patterns. The copolymers contain t-butyl methacrylate having an acid-cleavable t-butyl group and supercritical fluid $CO_2$ soluble perfluorinated decyl methacrylate segments. The supercritical fluid $CO_2$-philic properties of the photoresist changed to supercritical fluid $CO_2$-phobic properties after the deprotection reaction by exposure, which made the exposed resist insoluble in the supercritical fluid $CO_2$ developer. The synthesized copolymers containing more than 30% of perfluorinated decyl methacrylate were found to be soluble in supercritical fluid $CO_2$. The variation of film thickness before and after exposure was largest when the mole ratio of perfluorinated decyl methacrylate in the copolymer was 30%.

• Korean Journal of Optics and Photonics
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• v.20 no.4
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• pp.249-254
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• 2009

In our study, the Hanle spectrum and nonlinear magneto-optic effect (NMOE) signals were observed as a function of magnetic field on $D_1$ line of $^{87}Rb$ atoms contained in a paraffin coated vapor cell. We observed the double structure from the Hanle and the NMOE spectrum in the paraffin coated Rb vapor cell. The narrow spectral width of the narrow resonance signal is approximately 1 kHz and the magnitude is approximately 10 percent of the total spectrum. Also, the NMOE signals corresponding to the Hanle configuration consisted of two different dispersion-like features. At the near zero magnetic field, a sharp slope signal was centered, and its value was 10 mV/${\mu}T$ with laser power was $200{\mu}W$.

• Journal of dental hygiene science
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• v.7 no.3
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• pp.201-205
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• 2007

This study was designed to compare the perception of dental hygiene students and general public with respect to minor variations in maxillary anterior tooth size, alignment and their relation to the surrounding soft tissues. Maxillary anterior teeth were intentionally diagrammed in varying degree of deviation with respect to one of three common anterior esthetic discrepancies including variations in crown length, shape of gingival margin, and length of interproximal contact. Seventeen images were generated to be preferentially selected by 2 groups consisting of dental hygiene students and lay people in Busan(total of 216). The obtained results were as follows; 1. Both group preferred gingival margin of lateral incisor to be 0.5mm lower than that of central incisor. 2. Both group preferred the gingival margin shape of central incisor has 1/9 horizontal component of the crown width. 3. Both group preferred length of the interproximal contact has 1/2 of the crown length. The results of this study may be considered to influence the decision making process by dental professionals with respect to designing the anterior esthetic gingival line.

• The Korean Journal of Mycology
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• v.39 no.2
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• pp.145-147
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• 2011

Stem rot symptoms of Convallaria keiskei occurred sporadically in the herb exhibition field at Hamyang-gun Gyeongnam province in Korea. The typical symptom is water-soaking on the main stem, rotting, wilting, and blighting, which eventually leads to death of the plant. The sclerotia, which were white to brown in color, globoid in shape with size of 1~3 mm hyphal width of which was 4~9 ${\mu}m$, were formed over lesions and surface soil line. The optimum temperature for mycelial growth and sclerotia formation was $30^{\circ}C$ on PDA. The typical clamp connections were observed in the hyphae of the fungus grown on PDA. Mycological characteristics and pathogenicity to host plants indicated that the infected fungus was Sclerotium rolfsii Saccardo. This is the first report of stem rot on Convallaria keiskei caused by S. rolfsii in Korea.

• Journal of Welding and Joining
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• v.20 no.3
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• pp.122-128
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• 2002

The laser welding in the automotive industries has been used widely for the butt joint of blank sheets rather than the lap joint of automotive body panels. But as a substitute far the spot welding of automotive body panels, the so called three dimensional laser welding will be important far the body panel engineers. Specially the laser welding of body panels with a smooth weld line is applied increasingly, for example, to the side panels. So far, some criteria of the laser weld quality was suggested by in-house regulations or national standards from experiences and/or rule of thumbs. In the manufacturing places, a go or no-go criterion is adopted because of the simplicity or a lack of rational criteria. It is true specially for the selection of the process parameters, which gives the basic causes for the good quality of laser welds. In this study, the effects of joint combination, gap and welding speed on the lap joint $CO_2$ laser welding of two mild steel sheets with different thicknesses are obtained through a $2{\times}3{\times}7$ factorial experiment. The results of the weld quality are statistically analysed using analysis of variance (ANOVA) and compared between two characteristic zones, which are separated by the type of sectional shapes and the level of input energy per volume. The thickness combinations are 0.8mm/1.2mm, 1.2mm/0.8mm of mild steel sheets. The welding speed covers from the deep penetration to the partial penetration. The gap size has three levels of no-gap, 0.16m, and 0.26mm. The bead width, penetration depth and input energy per volume are measured and used as the weld quality criteria.

• Journal of Astronomy and Space Sciences
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• v.34 no.4
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• pp.315-330
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• 2017

Halo coronal mass ejections (CMEs) originating from solar activities give rise to geomagnetic storms when they reach the Earth. Variations in the geomagnetic field during a geomagnetic storm can damage satellites, communication systems, electrical power grids, and power systems, and induce currents. Therefore, automated techniques for detecting and analyzing halo CMEs have been eliciting increasing attention for the monitoring and prediction of the space weather environment. In this study, we developed an algorithm to sense and detect halo CMEs using large angle and spectrometric coronagraph (LASCO) C3 coronagraph images from the solar and heliospheric observatory (SOHO) satellite. In addition, we developed an image processing technique to derive the morphological and dynamical characteristics of halo CMEs, namely, the source location, width, actual CME speed, and arrival time at a 21.5 solar radius. The proposed halo CME automatic analysis model was validated using a model of the past three halo CME events. As a result, a solar event that occurred at 03:38 UT on Mar. 23, 2014 was predicted to arrive at Earth at 23:00 UT on Mar. 25, whereas the actual arrival time was at 04:30 UT on Mar. 26, which is a difference of 5 hr and 30 min. In addition, a solar event that occurred at 12:55 UT on Apr. 18, 2014 was estimated to arrive at Earth at 16:00 UT on Apr. 20, which is 4 hr ahead of the actual arrival time of 20:00 UT on the same day. However, the estimation error was reduced significantly compared to the ENLIL model. As a further study, the model will be applied to many more events for validation and testing, and after such tests are completed, on-line service will be provided at the Korean Space Weather Center to detect halo CMEs and derive the model parameters.