• Journal of Welding and Joining
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• v.33 no.2
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• pp.56-61
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• 2015

IRW(Inverter Resistance Welding) process and DSW(Delta-spot welding) process for dissimilar materials of DP590 and Al5052 were performed to evaluate the welding quality and mechanical properties. IRW experiment was carried out with changing the welding current. The other welding parameters such as pressure force, weld time, squeezing time and holding time were fixed. On the anther hand, DSW experiment was performed using the process tape at welding current of 11.5kA. The other conditions were same as IRW conditions. The various testes such as shear tensile strength, nugget diameters, EDS, SEM and cross-sectional observation for weld zone was performed. As a result, IMC(Inter Metallic Compound) thickness at 11.5kA was thinner than those of 9.5kA and 10.5kA conditions. In addition, thined IMC layer was observed when high electric current apply to the materials(DP590 and Al5052) in a short time throught dissimilar resistance spot welding controling welding conditions. The relationship between the thickeness of IMC and current intensity was after discussed.

• Journal of Welding and Joining
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• v.30 no.2
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• pp.65-69
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• 2012

Environmental and health concerns over the lead have led to investigation of the alternative Pb-free solders to replace commonly used Pb-Sn solders in microelectronic packaging application. The leading candidates for lead-free solder alloys are presently the near eutectic Sn-Ag-Cu alloys. Therefore, extensive studies on reliability related with the composition have been reported. However, the insufficient drop property of the near eutectic Sn-Ag-Cu alloys has demanded solder compositions of low Ag content. In addition, the solder interconnections in automobile applications like a smart box require significantly improved vibration resistance. Therefore, this study investigated the effect of alloying elements (Ag, Bi, In) on the vibration fatigue strength. The vibration fatigue was conducted in 10~1000Hz frequency and 20Grms. The interface of the as-soldered cross section close to the Cu pad indicated the intermetallic compound ($Cu_6Sn_5$) regardless of solder composition. The type and thickness of IMC was not significantly changed after the vibration test. It indicates that no thermal activities occurred significantly during vibration. Furthermore, as a function of alloying composition, the vibration crack path was investigated with a focus on the IMCs. Vibration crack was initiated from the fillet surface of the heel for QFP parts and from the plating layer of chip parts. Regardless of the solder composition, the crack during a vibration test was propagated as same as that during a thermal fatigue test.

• Restorative Dentistry and Endodontics
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• v.21 no.1
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• pp.242-253
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• 1996

Penetration degree of several dyes into dentinal tubules in vivo was compared with in vitro, and experimental sensitivity of those dyes was investigated in 64 canines of 16 cats. Dentin 1mm below cusp tip was exposed by cross-sectioning with diamond disc. Pulp of 32 canines were extirpated through cervical cavities. In the presence of smear layer or after add-etching with 37% phosphoric acid to the exposed dentin surface, acrylic collar and resin cap was attached to keep dyes. 52 mmol/$\ell$ Evans' blue, 2% Methylene blue, 10 % Silver nitrate and 5% Fluorescene were then applicated on each 4 canines respectively for 30 minutes. After rinsing, the canines were ground-sectioned longitudinally and linear dye penetration was measured under microscope. The results obtained were as follows ; 1. Evans' blue and Methylene blue penetrated significantly(P<0.05) more in vitro than in vivo only in the cases that exposed dentin surfaces were not etched with acid. 2. Silver nitrate penetrated significantly(P<0.05) more in vitro than in vivo in both cases that exposed dentin surfaces remained intact and were etched with acid. 3. The penetration degree of Fluorescene did not show statistical significance between in vivo and in vitro or in acid-etched and in not acid-etched cases.

• Ocean and Polar Research
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• v.33 no.4
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• pp.409-419
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• 2011

Semi-diurnal internal tides and near-inertial waves are investigated using moored current meter measurements at four sites along the shelf break of the East China Sea during August 1987 and May-June 1988. Each mooring is equipped with four current meters spanning from near surface to near bottom. Spectral analyses of all current data reveal dominant spectra at the semi-diurnal frequency band, where the upper and lower current measurements show out-of-phase relationship between them with significant coherences. These are consistent with typical characteristics of the first-mode semi-diurnal internal tide. Strong intensification of the near-bottom baroclinic currents is observed only at one site, where the ratio of the bottom slope to the slope of the internal-wave characteristics at the semi-diurnal frequency is close to unity. An energetic near-inertial wave event is observed during the first half of May-June 1988 observation at two mooring sites. Rotary spectra reveal that the most dominant signal is clockwise rotating motion at the near-inertial frequency band. Upward phase and downward energy propagations, shown in time-depth contour plots of near-inertial bandpass filtered currents, are confirmed by cross correlations between the upper- and lower-layer current measurements. The upward-propagating phase speed is estimated to be about 0.13 cm $s^{-1}$ at both sites. Significant coherences and in-phase relationships of near-inertial currents at the same or similar depths between the two sites are observed in spite of their long distance of about 110 km.

• Journal of the korean society of oceanography
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• v.35 no.3
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• pp.129-152
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• 2000

The Cheju Current (CC), defined here as a mean eastward flow in the Cheju Strait, mostly carries water of high temperature and salinity originating from the Kuroshio in winter and spring, the Cheju Warm Current Water (CWCW). The strong core of the eastward component of the CC is found close to Cheju Island (Cheju-Do, hereafter) in winter and spring with a peak speed of about 17.0 cm/s. The eastward flow weakens towards the northern Cheju Strait, and a weak westward flow occurs occasionally close to the southern coast of Korea. The volume transport ranges from 0.37 to 0.45 Sv(1 Sv=10$^6$ m$^3$/s) in winter and spring. Seasonal thermocline and harocline are formed in summer and eroded in November. The occurrence of the CWCW is confined in the southern Cheju Strait close to Cheju-Do below the seasonal thermocline in summer and fall, and cold water occupies the lower layer north of the CWCW which is thought to be brought into the area from the area west of Cheju-Do along with the CWCW. Stratification acts to increase both the speed of the CC with a peak speed of greater than 30 cm/s and the vertical shear of the along-strait currents. The strong core of the CC detached from the coast of Cheju-Do and shifted to the north during the stratified seasons. The volume transport in summer and fall ranges 0.510.66 Sv, which is about 1.5 times larger than that in winter and spring. An annual cycle of the cross-strait sea level difference shows its maximum in summer and fall and minimum in winter and spring, whose tendency is consistent with the annual variability of the CC and its transport estimated from the ADCP measurements. Moored current measurements west of Cheju-Do indicate the clockwise turning of the CC, and the moored current measurements in the Cheju Strait for 1530 days show the low-frequency variability of the along-strait flow with a period of about 37 days.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.473-473
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• 2013

전자종이, 입을 수 있는 디스플레이, 플렉서블 터치 스크린, 투과성 면 등과 같은 차세대 플렉서블 투명 전자소자는 기계적으로 유연하고 광학적으로 투명하며 무게가 가벼운 특성을 지녀야 할 것으로 예상된다. 현재까지는Indium tin oxide (ITO), zinc tin oxide (ZTO), carbon nano tube (CNT)와 polyimide 계열의 물질들이flexible, wearable, and transparent electronics (FWTEs) 소자의 electrode, active channel, dielectric layers로 제안되어 활발히 연구되었다. 최근에는 높은 이동도(~200,000 cm2/Vs) 및 유연성(fracture strain of 30%), 투명도 (97.5% for monolayer)와 같은 특성을 갖는 그래핀에 대한 연구가 활발히 진행되고 있다. 그러나 그래핀을 차세대 플렉서블 투명 전자소자 구현에 적용하기 위해서는 플렉서블하고 투명한 절연체의 확보 및 그래핀의 진성(intrinsic) 특성 유지 등과 같은 문제점들을 해결해야 한다. 따라서, 본 연구팀에서는 그래핀 기반 플렉서블 투명 전자소자의 게이트 절연층으로 적합한 poly-4-vinylphenol/poly (melamineco-formaldehyde) (PVP/PMF) 물질을 제시하고 이에 대한 전기적 재료적 분석을 수행하였다. 특히 다양한 PVP와 PMF의 비율 및 가열(annealing 혹은 curing) 온도에서 형성된 PVP/PMF 층의 화학 및 전기적 특성을 FT-IR, I-V, 그리고 C-V 측정을 통해 확인하였다. PVP/PMF는 유기절연 물질의 하나로서 높은 유연성과 투명도를 갖고 있을 뿐만 아니라 그래핀에 적용 시 그래핀의 진성 특성을 확보할 수 있다. 이는 PVP/PMF에 존재하는 hydroxyl (-OH) 그룹과 그래핀 상에서 정공(hole)을 공급하는 것으로 알려져 있는 -OH 그룹들간의 cross-linking 메커니즘에 의한 것으로 예상된다. 마지막으로 최적화된 PVP/PMF (낮은 hysteresis 전압)를 게이트 절연층에 적용하여 polyethylene terephthalate (PET) 기판 및 연구원의 손가락 위에 95.8%의 투명도 및 0에 가까운 Dirac point를 갖는 그래핀 기반 플렉서블 투명 전자소자를 성공적으로 집적하였다.

• Journal of Conservation Science
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• v.32 no.2
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• pp.109-121
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• 2016

Mother-of-pearl turtle shell lacquerware refers to a decoration made of a mother-of-pearl, a turtle shell and metal wires. This lacquerware features bright color tone as it is produced by sprinkling metal powder over its entire surface. This study aimed to find out its material properties and characteristics by using an optical microscopy and conducting a SEM-EDS analysis on the cross section of lacquer coating. As a result, it was found that charcoal powder and soil powder were mixed for undercoating. Then a mixture of cinnabar lacquer and monoclinic arsenic sulfide mineral ($As_2S_3$) was coated on the undercoating and brass powder was sprinkled on top of it. Especially, a little amount of pigment was found on the lacquer layer, which is distinguished from the colors used for conventional lacquer patterns. In addition, it was also found that the cinnabar lacquer and monoclinic arsenic sulfide mineral were mixed together.

• Journal of Conservation Science
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• v.32 no.2
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• pp.215-221
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• 2016

This study conducted analysis of paint samples from defense industries equipments of Korean Conflict in The War Memorial of Korea to identify the characteristics of the modern paint. The samples were analyzed by microscopic observation, infrared spectroscopy and SEM-EDS. Cross-section of paint samples are made up of several layers of about 9 to 20 times, and thickness of the layer is not uniform in the $10{\sim}100{\mu}m$. The putty was used for the surface treatment before painting. Inorganic analysis showed that one type of the putty consist of minium and kaolin, talc, titanium dioxide. According to the results of infrared spectroscopy, paint samples were identified as alkyd resin. Some bands such as C-H bending, C-O and C-C stretching, C-H rocking were found in spectra.

• Journal of Biomedical Engineering Research
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• v.29 no.6
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• pp.436-442
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• 2008

Magnetic resonance electrical impedance tomography(MREIT) has been suggested to produce cross-sectional conductivity images of an electrically conducting object such as the human body. In most previous studies, recessed electrodes have been used to inject imaging currents into the object. An MRI scanner was used to capture induced magnetic flux density data inside the object and a conductivity image reconstruction algorithm was applied to the data. This paper reports the performance of a thin and flexible carbon-hydrogel electrode that replaces the bulky and rigid recessed electrode in previous studies. The new carbon-hydrogel electrode produces a negligible amount of artifacts in MR and conductivity images and significantly simplifies the experimental procedure. We can fabricate the electrode in different shapes and sizes. Adding a layer of conductive adhesive, we can easily attach the electrode on an irregular surface with an excellent contact. Using a pair of carbon-hydrogel electrodes with a large contact area, we may inject an imaging current with increased amplitude primarily due to a reduced average current density underneath the electrodes. Before we apply the new electrode to a human subject, we evaluated its performance by conducting MREIT imaging experiments of five swine legs. Reconstructed conductivity images of the swine legs show a good contrast among different muscles and bones. We suggest a future study of human experiments using the carbon-hydrogel electrode following the guideline proposed in this paper.

• Journal of Fashion Business
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• v.19 no.1
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• pp.95-105
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• 2015

This study investigated the color culture in the Japanese Medieval Age. The Japanese Medieval Age included the Kamakura period (1180-1333) and Muromachi period (1336-1573), and the leading group transitioned from the Kuge families to the Buke families. The taboos about colors from ancient times became nominal, and forbidden colors, such as purple, celadon, and red, became the colors of the samurai, leading to beautiful soldier gears that were unparalleled in history. In the Kamakura period, colors that conveyed a strong impression were created and preferred with the combination of a samurai's reasonable spirit and zen thoughts. The period was also called "the era of hari", and cross dyeing based on basic colors such as suou (red), ai (blue), and kuchinasi (yellow) was popular. In both the Kamakura and Muromachi periods, conspicuous and strong colors were sought for costumes, and embroidery was used with gold leaf, silver leaf, gold threads, silver threads, and background color. The colors of costume preferred by Buke men in the period included green, blue, and brown. In the characteristics of the kosode, the sugan and hitadare were used for men's formal dress, while kosode was used for the grooming of the working class. In these periods, additionally, the working class began to be socially engaged in actively wearing the one-layer kosode, which became popular, and the characteristics of the Japanese Medieval Age, during which functionality and practicality was valued, were also reflected in the dressing.