• Journal of Advanced Marine Engineering and Technology
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• v.35 no.2
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• pp.196-203
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• 2011

Experiments to determine heat transfer coefficients and friction factors are conducted on a stationary transverse parallel wire-screen rib roughened rectangular channel. The test section consists of 198 mm (W) x 40 mm (H) x 712 mm (L). The channel has the aspect ratio of 4.95 and hydraulic diameter of $D_h$=6.66 cm. Four wire screen ribs and a solid rib are used. 0.1 mm-thick-stainless steel foil heaters and thermocouples (T type) are used to measure the heat transfer coefficients. Reynolds numbers studied range from 20,000 to 60,000. The wire-screen rib height (e) to hydraulic diameter ($D_h$) ratio ($e/D_h$) is 0.075; spacing (p) to height ratio (p/e) is 10. Results indicate that the solid rib produces the greatest Nusselt number and friction factor.

• Composites Research
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• v.17 no.5
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• pp.15-24
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• 2004

Longitudinal strains (${\varepsilon}_x$) of the core and skin layers in glass fiber reinforced plastic (GFRP) cross-ply composite laminates have been measured using the embedded optical fiber sensor of absolute extrinsic Fabry-Perot interferometer (A-EFPI). Transmission optical microscopy was used to investigate the damage behavior around the A-EFPI sensor. Foil-type strain gauges bonded on both the upper and lower surfaces were used for the measurement of the surface strains. It was shown that values of ${\varepsilon}_x$ in the interior of the skin layer and the core layer measured by embedded A-EFPI sensor were significantly higher than that of the specimen surface measured by strain gauges. The experimental results agreed well with those from finite element analysis on the basis of uniform stress model. Large strains in the core layer led to the occurrence of many transverse cracks which drastically reduced the strain at failure of optical fiber sensor embedded in the core layer.

• Journal of Sensor Science and Technology
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• v.23 no.3
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• pp.207-210
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• 2014

$TiO_2$ oxide semiconductor is being widely studied in various applications such as photocatalyst and photosensor. Pd/$TiO_2$ gas sensor is mainly used to detect $H_2$, CO and ethanol. This study focus on increasing hydrogen detection ability of Pd/$TiO_2$ in room temperature through Al-doping. Pd/$TiO_2$ was fabricated by the hydrothermal method. Contacting to Aluminum (Al) foil led to Al doping effect in Pd/$TiO_2$ by thermal diffusion and enhanced hydrogen sensing response. $TiO_2$ nanoparticles were sized at ~30 nm of diameter from scanning electron microscope (SEM) and maintained anatase crystal structure after Al doping from X-ray diffraction analysis. Presence of Al in $TiO_2$ was confirmed by X-ray photoelectron spectroscopy at 73 eV. SEM-energy dispersive spectroscopy measurement also confirmed 2 wt% Al in Pd/$TiO_2$ bulk. The gas sensing test was performed with $O_2$, $N_2$ and $H_2$ gas ambient. Pd/Al-doped $TiO_2$ did not response $O_2$ and $N_2$ gas in vacuum except $H_2$. Finally, the normalized resistance ratio ($R_{H2on}/R_{H2off}$) of Pd/Al-doped $TiO_2$ increases about 80% compared to Pd/$TiO_2$.

• Korean Journal of Materials Research
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• v.24 no.5
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• pp.243-248
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• 2014

Silicon-carbon composite was prepared by the magnesiothermic reduction of mesoporous silica and subsequent impregnation with a carbon precursor. This was applied for use as an anode material for high-performance lithium-ion batteries. Well-ordered mesoporous silica(SBA-15) was employed as a starting material for the mesoporous silicon, and sucrose was used as a carbon source. It was found that complete removal of by-products ($Mg_2Si$ and $Mg_2SiO_4$) formed by side reactions of silica and magnesium during the magnesiothermic reduction, was a crucial factor for successful formation of mesoporous silicon. Successful formation of the silicon-carbon composite was well confirmed by appropriate characterization tools (e.g., $N_2$ adsorption-desorption, small-angle X-ray scattering, X-ray diffraction, and thermogravimetric analyses). A lithium-ion battery was fabricated using the prepared silicon-carbon composite as the anode, and lithium foil as the counter-electrode. Electrochemical analysis revealed that the silicon-carbon composite showed better cycling stability than graphite, when used as the anode in the lithium-ion battery. This improvement could be due to the fact that carbon efficiently suppressed the change in volume of the silicon material caused by the charge-discharge cycle. This indicates that silicon-carbon composite, prepared via the magnesiothermic reduction and impregnation methods, could be an efficient anode material for lithium ion batteries.

• Journal of Biomedical Engineering Research
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• v.17 no.4
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• pp.449-458
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• 1996

Most of the conventional electrocardiowaphs foil to detect signals other than P-QRS-T due to the limited SNR and bandwidth. High-resolution electrocardiography(HRECG) provides better SNR and wider bandwidth for the detection of micro-potentials with higher frequency components such as vontricular late potentials(LP). We have developed a HRECG using uncorrected XYZ lead for the detection of LPs. The overall gain of the amplifier is 4000 and the bandwidth is 0.5-300Hz without using 60Hz notch filter. Three 16-bit A/D converters sample X, Y, and Z signals simultaneously with a sampling frequency of 2000Hz. Sampled data are transmitted to a PC via a DMA-controlled, optically-coupled serial communication channel. In order to further reduce the noise, we implemented a signal averaging algorithm that averaged many instances of aligned beats. The beat alignment was carried out through the use of a template matching technique that finds a location maximizing cross-correlation with a given beat tem- plate. Beat alignment error was reduced to $\pm$0.25ms. FIR high-pass filter with cut-off frequency of 40Hz was applied to remove the low frequency components of the averaged X, Y, and Z signals. QRS onset and end point were determined from the vector magnitude of the sigrlaIL and some parameters needed to detect the existence of LP were estimated. The entire system was designed for the easy application of the future research topics including the optimal lead system, filter design, new parameter extraction, etc. In the developed HRECG, without signal averaging, the noise level was less than 5$\mu$V$_rms RTI$. With signal averaging of at least 100 beats, the noise level was reduced to 0.5$\mu$V$_rms RTI$, which is low enough to detect LPs. The developed HRECG will provide a new advanced functionality to interpretive ECG analyzers.

• Korean Journal of Metals and Materials
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• v.49 no.8
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• pp.657-663
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• 2011

This study represents the results of the peel strength and surface morphology according to the preprocessing times of polyimide (PI) in a Cu/Ni/PI structure flexible copper clad laminate production process based on the polyimide. Field emission scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were used to analyze the surface morphology, crystal structure, and interface binding structure of sputtered Ni, Cu, and electrodeposited copper foil layers. The surface roughness of Ni, Cu deposition layers and the crystal structure of electrodeposited Cu layers were varied according to the preprocessing times. In the RF plasma times that were varied by 100-600 seconds in a preprocessing process, the preprocessing applied by about 300-400 seconds showed a homogeneous surface morphology in the metal layers and that also represented high peel strength for the polyimide. Considering the effect of peel strength on plastic deformation, preprocessing times can reasonably be at about 400 seconds.

• Conservation Science in Museum
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• v.30
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• pp.47-70
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• 2023

In 2019, the first excavation survey was conducted at the Temple Site No. 4 of Yaksugok Vally in Namsan Mountain, Gyeongju to determine the original location of the headless stone Buddha statue and the structure of the temple site. The survey excavated a stone Buddha head that was confirmed in a comparative analysis to be petrologically and mineralogically identical to a headless stone seated Buddha statue found derelict nearby. Traces of gold leaf and black adhesive were found on a portion of the right side of the face of the Buddha head buried in the ground. Since it is exceedingly rare for lacquer and gilding techniques to have been applied to a large stone Buddha statue without a base layer, this study examines the gilding techniques of the time by analyzing the characteristics of the materials used. In this process, the structure of the gold foil was observed through analytical microscopy and scanning electron microscopy with energy dispersive X-ray spectrometry, and the gold (Au) component was identified. As a result of analyzing the black adhesive using pyrolysis-gas chromatograph/mass spectrometry (pyrolysis-GC/MS), pyrolysis compounds such as hydrocarbons, fatty acids, catechol, and catechol oxidation products were detected. This was identical to the characteristics identified upon analyzing lacquer collected from species of lacquer tree whose main component is urushiol. Therefore, it was confirmed that the stone Buddha head excavated from the Temple Site No. 4 of Yaksugok Valley was separated from a nearby stone seated Buddha statue, and that the gold foil was attached using lacquer sap collected from lacquer trees, which grow in Korea, China, and Japan.

• Journal of Korean Academy of Oral and Maxillofacial Radiology
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• v.29 no.1
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• pp.33-42
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• 1999

Geometrically standardized dental radiographs were taken. We prepared Digital Cu-Equivalent Image Analyzing System for quantitative assessment of mandible bone. Images of radiographs were digitized by means of Quick scanner and personal Mcquintosh computer. NIH image as software was used for analyzing images. A stepwedge composed of 10 steps of 0.1mm copper foil in thickness was used for reference material. This study evaluated the effects of step numbers of copper wedge adopted for calculating equation. kVp and exposure time on the coefficient of determination(r²)of the equation for conversion to Cu-equivalent image and the coefficient of variation and Cu-Eq value(mm) measured at each copper step and alveolar bone of the mandible. The results were as follows: 1. The coefficients of determination(r²) of 10 conversion equations ranged from 0.9996 to 0.9973(mean=0.9988) under 70kVp and 0.16 sec. exposure. The equation showed the highest r was Y=4.75614612-0.06300524x +0.00032367x² -0.00000060x³. 2. The value of r² became lower when the equation was calculated from the copper stepwedge including 1.0mm step. In case of including 0mm step for calculation. the value of r showed variability. 3. The coefficient of variation showed 0.11, 0.20 respectively at each copper step of 0.2, 0.1mm in thickness. Those of the other steps to 0.9 mm ranged from 0.06 to 0.09 in mean value. 4. The mean Cu-Eq value of alveolar bone was 0.14±0.02mm under optimal exposure. The values were lower than the mean under the exposures over 0.20sec. in 60kVp and over 0.16sec. in 70kVp. 5. Under the exposure condition of 60kVp 0.16sec.. the coefficient of variation showed 0.03. 0.05 respectively at each copper-step of 0.3, 0.2mm in thickness. The value of r² showed over 0.9991 from both 9 and 10 steps of copper. The Cu-Eq value and the coefficient of variation was 0.14±0.01mm and 0.07 at alveolar bone respectively. In summary. A clinical application of this system seemed to be useful for assessment of quantitative assessment of alveolar provided high coefficient of determination is obtained by the modified adoption of copper step numbers and the low coefficient of variation for the range of Cu-Equivalent value of alveolar bone from optimal kVp and exposure time for each x-ray machine.

• Proceedings of the Korea Crystallographic Association Conference
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• 2002.11a
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• pp.22-23
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• 2002

Titanium은 높은 강도, 낮은 밀도, 부식에 대한 저항 등, 타 금속에 비해 월등히 뛰어난 성질을 가지고 있기 때문에 산업 전반에 거쳐 그 응용이 크게 증가하고 있으며, 특히 고온에서의 응용이 중요성을 띠게 됨에 따라 고온으로의 상전이 관계에 따른 구조적 규명이 필요하다. 순수한 titanium은 상온에서 조밀충진 육방정계의 α-상구조(a=2.953Å, c=4.683 Å, P6₃/mmc)를 이루고 있으나, 대략 880℃ 이상에서는 β-상의 체심입방정계 (a=3.320Å, Im3m)로 상전이가 되는 것으로 알려져 있다. 이에 대한 대부분의 연구가 kinetics와 thermodynamics에 관련되어 있으며, TEM을 이용한 직접가열실험은 거의 전무한 상태이다. 본 실험에서는 TEM 직접가열을 통하여 titanium의 고온에서의 상전이와 가열시 발생할 수 있는 산화층 형성을 연구하였다. TEM 시편은 순도 99.94％의 titanium foil(Alfa Aesar, ＃00360, 0.025mm thick)를 이용하였고, 분석 장비로는 에너지여과 기능이 있는 TEM(EM912 Omega, Carl Zeiss)과 Gatan사의 double-tilt heating holder를 사용하였다. Titanium의 상전이를 관찰하기 위해 900℃ 까지 분당 10℃ 의 속도로 가열을 하였다. 통계적 분석 오차를 줄이기 위해 서로 다른 4군데의 관찰영역을 선택하여, 상온 - 600℃ - 900℃ - 상온의 단계별로 회절패턴을 관찰 및 기록하였고, 발생 가능한 산화에 대해서는 동일한 장비를 사용하여 EDS 분석을 하였다. 상온에서의 서로 다른 영역의 회절패턴들은 결함의 존재에 상관없이, 온도가 증가함에 따라 그 결함수가 증가하게 된다. 특히 600℃ 에서는 쌍정과 관련된 회절점들이 본래의 회절점 주위에 형성되어있지만, 각 면들의 격자상수의 변화는 나타나지 않았다. 그러나 900℃ 에서는 쌍정에 의한 회절점의 수가 증가하며, 회절점 사이에 발달한 뚜렷한 막대모양의 강도분포와 격자상수의 변화를 관찰할 수 있었다. 다시 상온으로 냉각시킨 후 관찰한 각각의 회절패턴에서는 격자 상수의 감소와 함께 900℃에 보여진 막대 모양의 강도분포와 쌍정에 의한 회절점들이 여전히 남아있었다. EDS분석 결과 가열 실험을 통해 시편이 열적 산화가 되어 있음을 확인 할 수 있었다. 순수한 titanium의 α-상에서 β-상으로의 상전이를 파악할 수 있는 격자상수의 변화자체는 매우 작은 값이기 때문에 상온과 900℃ 에서 기록된 전자회절패턴 상에서의 면간거리와 면간각도의 측정만으로는 상전이 여부를 명확히 구별할 수 없었다. 그러나, 결함에 의한 상변화가 900℃ 에서 심하게 관찰되어지는 것은 상전이와 관계가 있는 것으로 볼 수 있다. 고온에서 상온으로의 가역적 반응을 관찰할 수 없었던 이유는 열적산화로 생긴 산화층의 산소원자들이 고온의 상전이 과정 중에 Ti 원자와 반응이 일어나 TiO/sub X/ 구조로 전이되었기 때문으로 추정하고 있다.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.277-277
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• 2010

The capacity of the carbonaceous materials reached ca. $350\;mAhg^{-1}$ which is close to theorestical value of the carbon intercalation composition $LiC_6$, resulting in a relatively low volumetric Li capacity. Notwithstanding the capacities of carbon, it will not adjust well to the need so future devices. Silicon shows the highest gravimetric capacities (up to $4000\;mAhg^{-1}$ for $Li_{21}Si_5$). Although Si is the most promising of the next generation anodes, it undergoes a large volume change during lithium insertion and extraction. It results in pulverization of the Si and loss of electrical contact between the Si and the current collector during the lithiation and delithiation. Thus, its capacity fades rapidly during cycling. We focused on electrode materials in the multiphase form which were composed of two metal compounds to reduce the volume change in material design. A combination of electrochemically amorphous active material in an inert matrix (Si-M) has been investigated for use as negative electrode materials in lithium ion batteries. The matrix composited of Si-M alloys system that; active material (Si)-inactive material (M) with Li; M is a transition metal that does not alloy with Li with Li such as Ti, V or Mo. We fabricated and tested a broad range of Si-M compositions. The electrodes were sputter-deposited on rough Cu foil. Electrochemical, structural, and compositional characterization was performed using various techniques. The structure of Si-M alloys was investigated using X-ray Diffractometer (XRD) and transmission electron microscopy (TEM). Surface morphologies of the electrodes are observed using a field emission scanning electron microscopy (FESEM). The electrochemical properties of the electrodes are studied using the cycling test and electrochemical impedance spectroscopy (EIS). It is found that the capacity is strongly dependent on Si content and cycle retention is also changed according to M contents. It may be beneficial to find materials with high capacity, low irreversible capacity and that do not pulverize, and that combine Si-M to improve capacity retention.