• Proceedings of the KIEE Conference
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• 2003.10b
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• pp.92-94
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• 2003

The autotransformer currently used on the electric railway system is made of class A insulation material and uses the paper insulation method. As a power converter supplying power to the trolley wire, the autotransformer is one of critical equipment in the railway system. In the autotransformer, load irregularly changes and overload often occurs. These cause overheating of the autotransformer and facilitate deterioration of the autotransformer resulting in burnout accidents due to insulation breakdown. Also, the current autotransformer has poor insolation and short-circuit strength which often badly affect the service life of the transformer, and needs to improve its quality urgently. To overcome one of existing shortcomings of the mold transformer, manufacturers use epoxy resins that have superior flame retardancy to get rid of fro and explosion possibilities during accidents. Currently, new mold transformers are used in indoor distribution facilities with fire-fighting equipments. Coils molded in epoxy resins do not have their insulation performance compromised by humidity, dust, etc enabling easy inspection and maintenance. Comparing to the oil immersed transformer, the mold transformer does not have any concern about environmental pollutions by oil leak or replacement Therefore, to reduce breakdowns and improve reliability of the autotransformer, it is necessary to develop a new mold autotransformer with low loss suitable for our environment to suppress breakdowns of the autotransformer and improve the reliability. This study is about development of a low-loss mold autotransformer necessitated by reasons mentioned earlier.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.43.2-43.2
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• 2011

Single-walled carbon nanotubes (SWCNT) are transparent in the visible and show conductivity comparable to copper, and are environmentally stable. SWCNT films have high flexibility, conductivity and transparency approaching that indium tin oxide (ITO), and can be prepared inexpensively without vacuum equipment. Transparent conducting Films (TCF) of SWCNTs has the potential to replace conventional transparent conducting oxides (TCO, e.g. ITO) in a wide variety of optoelectronic devices, energy conversion and photovoltaic industry. However, the sheet resistance of SWCNT films is still higher than ITO films. A decreased in the resistivity of SWCNT-TCFs would be beneficial for such an application. We fabricated SWCNT sheet with $KAuBr_4$ on PET substrate. Arc-discharge SWCNTs were dispersed in deionized water by adding sodum dodecyl sulfate (SDS) as surfactant and sonicated, followed by the centrifugation. The dispersed SWCNT was spray-coated on PET substrate and dried on a hotplate at $100^{\circ}C$. When the spray process was terminated, the TCF was immersed into deionized water to remove the surfactant and then it was dried on hotplate. The TCF film was then treated with AuBr4-, rinsed with deionized water and dried. The surface morphology of TCF was characterized by field emission scanning electron microscopy. The sheet resistance and optical transmission properties of the TCF were measured with a four-point probe method and a UV-visible spectrometry, respectively. $HNO_3$ treated SWCNT films with Au nano-particles have the lowest 61 ${\Omega}$/< sheet resistance in the 80% transmittance. Sheet resistance was decreased due to the increase of the hole concentration at the washed SWCNT surface by p-type doping of $AuBr_4{^-}$.

• Restorative Dentistry and Endodontics
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• v.13 no.1
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• pp.103-111
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• 1988

The purpose of this study was to, examine the sealing ability of the denting bonding agent, when used with gutta percha cone, as a root canal sealer. Seventy two upper and lower extracted human teeth with single root were randomly selected and instrumented in a conventional method with K-file. After instrumentation and dry the canal with paper point, there were divided into three groups and twenty four teeth in each group were filled with the following material; In group I: Scotchbond in combination with gutta percha cone. In group II: AH 26 in combination with gutta percha cone. In group III: Tubli-Seal in combination with gutta percha cone. All specimens were immersed in Indian Ink, decalcified, and cleared. The depth of dye penetration into the canals were evaluated by caliper at the intervals of 1 day, 1 week, 2 weeks. The results were as follows; 1. Depth of dye penetration for all groups increased with time. 2. As to difference in mean dye penetration at time interval of 1 day and 14 days, Scotchbond group exhibited the smallest value as 0.53mm and Tubli-Seal group exhibited the largest value as 0.70mm. 3. There was the difference of dye penetration between each group, but its difference was not significant, statistically.

• Journal of the Korean Ceramic Society
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• v.35 no.4
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• pp.371-377
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• 1998

The effect of epoxy resin on the water stability of HAC/PVA based MDF cement composite were stu-died through the three different forming methods calendering extruding and warm pressing. In prexing step the epoxy resin was added in 5-15wt% of cement weight. The 3-point flexural strength of each dry and wet specimen which were immersed in water during 3. 7, 14 days was estmated and the mi-crostructural change of epoxy resin-added MDF cement composite due to water immersion was charac-terized by scanning electron microscopy. As the addition amount of epoxy resin the im-provement of water stability of MDF cement composite was achieved in most case. Especially through the warm press forming method the effectiveness of epoxy resin addition to the water stability was enhanced. When the epoxy resin was added by 5wt% to 7wt% the optimum flexural strength and water stability

• Journal of the Korea Institute of Information Security & Cryptology
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• v.28 no.2
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• pp.437-447
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• 2018

Virtual Reality (VR) is becoming a new standard in the game industry. PokeMon GO is a representative example of VR technology. The day after the launch of PokeMon Go in the U.S, It has achieved the highest number of iOS App Store downloads. This is an example of the power of VR. VR comprises gyroscopes, acceleration, tactile sensors, and so on. This allow users could be immersed in the game. As new technologies emerge, new and different threats are created. So we need to research the security of VR technology and game system. In this paper, we conduct a threat analysis for information assurance of VR device (Oculus Rift) and game system (Quake). We systematically analyze the threats (STRIDE, attack library, and attack tree). We propose security measures through DREAD. In addition, we use Visual Code Grepper (VCG) tool to find out logic errors and vulnerable functions in source code, and propose a method to solve them.

• Toxicological Research
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• v.17 no.2
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• pp.123-129
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• 2001

This study were carried out to investigate cytotoxicity of paraquat and bentazon that is scattering to farm products were essensial for human diet and compensatory effects of 3-methylcholanthrene (3-MC) in vitro and in vivo. In vitro, The 5.0$\times$$10^4$ cell/ml of NIH 3T3 fibroblast in each well of 24 multidish were cultured. After 24 hours, the cells were treated with solution of paraquat and bentazon (1, 25, 50, 100 pM respectively). After the NIH 3T3 fibroblast of all groups were cultured in same condition for 48 hours, Sulfohordamin B Protein (SRB) assay were performed to evaluate the cytotoxicity of cell organelles. Paraquat and bentazon $SRB_50$ were 1860.73 $\mu\textrm{M}$, 1913.38 $\mu$M respectively. In vivo, Sprague Dawley male rats divided into paraquat and bentazon only administered group and simultaneous application group of paraquat and bentazon and 3-MC. At 30 min. and 1, 3, 6, 12, 24, 48 and 96 hrs. interval after each treatment, the animals were sacrificed by decapitation and kidney were immediately removed, immersed in fixatives, and processed with routine method for light microscopic study. Paraffin sections were stained with H-E, PAM, and PAS. Under the light microscope, atrophic change of renal corpuscles were frequently observed from 3 hrs after paraquat and bentazon treatment. The increase of the mesangium was apparent from 12 hrs later after paraquat and bentazon treatment. Necrotic changes of the epithelium and loss of brush border of proximal tubules were most severe at 48 hrs after paraquat and bentazon treatment, respectively. In contrast there were no evidences of the toxic effects on renal tissues at 48hrs in paraquat and bentazon plus 3-MC treated groups.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.18 no.2
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• pp.55-62
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• 2004

In this paper, the diagnostic expert system for silicone oil-filled transformer is developed using dissolved gas analysis(DGA). There are many diagnostic methods for diagnostic oil-immersed transformer. But DGA is used to the proposed expert system since it has been verified that DGA is very efficient diagnostic method for transformer. In addition, it is resonable that fuzzy rule, degree of inclusion and fuzzy measure must be considered to handle the uncertainty nature of gas boundary and rules. The proposed expert system consists of knowledge base module, inference engine module and human-machine interface(HMI) module. The knowledge base module consists of the knowledge using the rule. The inference engine module is used to the fuzzy rule. The history of the transformer gas data is managed by the database. the effect of the proposed expert system is verified by case studies.

• The Journal of the Korea Contents Association
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• v.18 no.8
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• pp.272-286
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• 2018

VR movies form a relationship with the audience in completely different ways from general movies with their screen. In VR movies, the audience becomes the camera and also the subject of the camera viewpoint, which raises a need for a frame theory unique to VR movies to examine the first person viewpoint and replace the edition of frames to deliver a narrative. In VR movies, the frames delivering a narrative are not revealed and perform the symbolic narrative function, thus being called "implicit frames." The study discussed their related theoretical backgrounds including Russian Ark made in the one shot, one cut method by Alexander Sokurov, off-screen elements, and the Fourth Wall. In VR movies, the audience gets immersed in the narrative based on their paradoxical dilemma, which means that they exist in reality but are absent on screen at the same time, and experiences hyper-reality. In VR movies, space has a couple of attributes including the blocking of eyeline to move it and telepresence to tie up presence between reality and virtuality.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.65-65
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• 2011

Single-well carbon nanotubes (SWNT) have been proposed as a promising candidate for various applications owing to their excellent properties. In particular, their fascinating electrical and mechanical properties could provide a new area for the development of advanced engineering materials. A transparent conductive thin film (TCF) has increased for applications such as liquid crystal displays, touch panels, and flexible displays. Indium tin oxide (ITO) thin films, which have been traditionally used as the TCFs, have a serious obstacle in TCFs applications. SWNTs are the most appropriate materials for conductive films for displays due to their excellent high mechanical strength and electrical conductivity. But, a bundle of CNTs has different electrical properties than their individual counterparts. In this work, the fabrication by the spraying process of transparent SWNT films and reduction of its sheet resistance on PET substrates is researched. Arc-discharge SWNTs were dispersed in deionized water by adding sodum dodecyl sulfate (SDS) as surfactant and sonicated, followed by the centrifugation. The dispersed SWNT was spray-coated on PET substrate and dried on a hotplate at $100^{\circ}C$. When the spray process was terminated, the TCF was immersed into deionized water to remove the surfactant and then it was dried on hotplate. The TCF film was then treated with ionic doping treatment, rinsed with deionized water and dried. The surface morphology of TCF was characterized by field emission scanning electron microscopy. The sheet resistance and optical transmission properties of the TCF were measured with a four-point probe method and a UV-visible spectrometry, respectively. Results, we show that 97 ${\Omega}$/> sheet resistance can be achieved with 81% transmittance at the wavelength of 550 nm. The changes in electrical and optical conductivity of SWNT film before and after ionic doping treatments were discussed.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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• pp.116-121
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• 2006

The pressurization system in a liquid rocket propulsion system provides a controlled gas pressure in the ullage space of the vehicle propellant tanks. It is advantage to employ a hot gas heat exchanger in the pressurization system to increase the specific volume of the pressurant and thereby reduce over-all system weight. Therefore a significant improvement in pressurization system performance can be achieved, particularly in a cryogenic system. For this study air and $CN_2$ are employed as external fluid and pressurant respectively Numerical analysis on the pressurant discharging characteristics have been compared with the experimental results performed at the PTF(Propellant-feeding Test Facility). It is shown that the discrepancy of analytic and experimental results is within about ${\pm}15%$. It is estimated that the temperature drop rate of cryogenic pressurant immersed liquid oxygen can be predicted using this analytic approach method.