• Journal of the Microelectronics and Packaging Society
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• v.18 no.4
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• pp.55-61
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• 2011

The n-type $Bi_2(Te_{0.9}Se_{0.1})_3$ powers were fabricated by mechanical alloying, mixed with tungsten(W) powders, and hot-pressed at $550^{\circ}C$ for 30 minutes. Thermoelectric properties of the hot-pressed $Bi_2(Te_{0.9}Se_{0.1})_3$ were characterized as a function of the volume percent of tungsten-powder addition. The power factor of the hot-pressed $Bi_2(Te_{0.9}Se_{0.1})_3$ was $21.9{\times}10^{-4}$ $W/m-K^2$, and was improved to $30.5{\times}10^{-4}$ $W/m-K^2$ by dispersion of 1 vol% W powders. While the dimensionless figure-of-merit of the $Bi_2(Te_{0.9}Se_{0.1})_3$ hot-pressed without dispersion of W powders was measured as 0.52 at room temperature, it became substantially enhanced to 0.95 with addition of 1 vol% W powders.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.3
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• pp.96-103
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• 2020

As a basic study for the application of natural zeolite as a concrete admixture, the compressive strength, activity factor, Ca(OH)₂ quantitative analysis and XRD experiments were investigated. It is thought that SiO₂, which is abundant in natural zeolite, affects the strength development by reacting with the hydration product of cement in all specimens in which natural zeolite was added according to powder level and substitution rate. As the substitution rate increases, the compressive strength decreases, which is considered to be due to the decrease in the amount of C₃S and C₂S minerals in the clinker, which affects the strength expression compared to the cement content of the reference mortar. The XRD crystal structure did not show a significant difference from the reference mortar, and it was confirmed that the Z2-10 (Blaine: 15,600㎠ / g) specimen with 10% substitution of natural zeolite was the best among the experimental levels. Substitution amount for use as concrete admixture is 10% substitution is most ideally seen.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.97-97
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• 2013

Recently, Cu2ZnSn(S,Se)4 (CZTSS), which is one of the In- and Ga- free absorber materials, has been attracted considerable attention as a new candidate for use as an absorber material in thin film solar cells. The CZTSS-based absorber material has outstanding characteristics such as band gap energy of 1.0 eV to 1.5 eV, high absorption coefficient on the order of 104 cm-1, and high theoretical conversion efficiency of 32.2% in thin film solar cells. Despite these promising characteristics, research into CZTSS based thin film solar cells is still incomprehensive and related reports are quite few compared to those for CIGS thin film solar cells, which show high efficiency of over 20%. I will briefly overview the recent technological development of CZTSS thin film solar cells and then introduce our research results mainly related to sputter based process. CZTSS thin film solar cells are prepared by sulfurization of stacked both metallic and sulfide precursors. Sulfurization process was performed in both furnace annealing system and rapid thermal processing system using S powder as well as 5% diluted H2S gas source at various annealing temperatures ranging from $520^{\circ}C$ to $580^{\circ}C$. Structural, optical, microstructural, and electrical properties of absorber layers were characterized using XRD, SEM, TEM, UV-Vis spectroscopy, Hall-measurement, TRPL, etc. The effects of processing parameters, such as composition ratio, sulfurization pressure, and sulfurization temperature on the properties of CZTSS absorber layers will be discussed in detail. CZTSS thin film solar cell fabricated using metallic precursors shows maximum cell efficiency of 6.9% with Jsc of 25.2 mA/cm2, Voc of 469 mV, and fill factor of 59.1% and CZTS thin film solar cell using sulfide precursors shows that of 4.5% with Jsc of 19.8 mA/cm2, Voc of 492 mV, and fill factor of 46.2%. In addition, other research activities in our lab related to the formation of CZTS absorber layers using solution based processes such as electro-deposition, chemical solution deposition, nano-particle formation will be introduced briefly.

• 보존과학연구
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• s.33
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• pp.33-43
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• 2012

The corrosion phenomena of the iron artifacts was studied by morphology observation and instrumental analysis(EDS, XRD, Raman) with various corrosion factors in oder to verify to confirm the danger of corrosion factors. Corrosion compounds were collected by depositing pure Fe powder(99%) into a HCl, $HNO_3$, $H_2SO_4$, and $H_2O$ solution which contained the corrosion factors. Stereoscopic-microscope observations were then conducted determine the colors and shapes of the collected corrosion compounds, and SEM-EDS analysis was conducted to confirm the corrosion factors and the growth of these compounds. X-ray diffraction (XRD), Raman analyses were conducted to examine the crystal structure and compositions of the created corrosion compounds. The results of the experiment revealed that corrosion speed was faster in an acidic environment and corrosion of HCl and $H_2SO_4$ was greater than that of $HNO_3$. The corrosion compounds of HCl grew into a needle or chestnut-like shape after being affected by Cl- ion, and XRD and Raman analyses detected goethite and lepidocrocite. The corrosion compounds of $H_2SO_4$ was affected by S ion and grew into a slender-needle-like or cylindrical shape, and the XRD and Raman analyses detected goethite and lepidocrocite. The corrosion compounds of $HNO_3$ grew into a spherical or plate-like shape after being affected by O ion and the XRD and Raman analyses detected magnetite and lepidocrocite. Although the corrosion compounds of $H_2O$ grew into a spherical or plate-like shape after being affected by O ion, most of them were observed to have had spherical shapes, and the XRD and Raman analyses failed to detect corrosion compounds in them. It was found in the study that corrosion characteristics and compounds are diversely displayed according to the corrosion factor.

• Food Science and Preservation
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• v.24 no.2
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• pp.206-214
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• 2017

The objective of this study is to investigate the quality characteristics of Yanggaeng by using the functional properties of Glechoma hederacea (GH). Sample was dried at $50^{\circ}C$ dry oven. The results of the study were as follows : The Phenolic compounds of GH was $12.99{\pm}0.3mg/g$ in water extract (GHWE), $3.14{\pm}0.07mg/g$ in 70% ethanol extract (GHEE). The antioxidant activity of GH was determined in various phenolic concentrations at $50-200{\mu}g/mL$. DPPH activities of GHWE and GHEE were 77.16-78.24% and 73.04-77.00%, respectively. The ABTS were 84.35-99.75% and 83.74-99.55%. The anti-oxidant protection factor (PF) were 1.54-1.62 PF and 1.62-2.09 PF and TBARS were 42.93-94.09% and 91.05-95.19%, respectively. Tyrosinase inhibitory activity of GHEE increased concentration dependently. Hyaluronidase inhibition activity of GHEE and GHWE, showing that there were increasing pattern depending on the increases in the phenolics concentration of GH. In texture, Hardness and springiness were significantly different in the control and 2% groups, but cohesiveness and chewiness did not show any significant difference. In color, L value decreased in proportion to concentration, and a and b values did not change. Sensory characteristics showed that the 1% group had the highest score and the 2% group had the lowest score. Thus, when the GHP Yanggaeng was prepared, in consideration of its sensory characteristics, and at appropriate concentration on below 1%.

• Journal of the Korea Concrete Institute
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• v.14 no.1
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• pp.126-135
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• 2002

Plate bonding technique has been widely used in strengthening of existing concrete structures, although it has often a serious problem of premature falure such as interface separation and rip-off. However, this premature failure problem has not been well explored yet especially in view of local failure mechanism around the interface of plate ends. The purpose of the present study is, therefore, to identify the local failure of strengthened plates and to derive a separation criterion at the interface of plates. To this end, a comprehensive experimental program has been set up. The double lap pull-out tests considering pure shear force and half beam tests considering combined flexure-shear force were performed. The main experimental parameters include plate thickness, adhesive thickness, and plate end arrangement. The strains along the longitudinal direction of steel plates have been measured and the shear stress were calculated from those measures strains. The effects of plate thickness, bonded length, and plate end treatment have been also clarified from the present test results. Nonlinear finite element analysis has been performed and compared with test results. The Interface properties are also modeled to present the separation failure behavior of strengthened members. The cracking patterns as well as maximum failure loads agree well with test data. The relation between maximum shear and normal stresses at the interface has been derived to propose a separation failure criterion of strengthened members. The present study allows more realistic analysis and design of externally strengthened flexural member with steel plates.

• Polymer(Korea)
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• v.36 no.6
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• pp.768-775
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• 2012

Alginate, obtained from the seaweeds, is a widely used biomaterial for cell transplantation, since its positive effect on viability of capsulized cells and its easier encapsulation capability of living cells. Demineralized bone powder (DBP), derived from the natural bone tissue, is widely applied for clinical trials for its low rate of reaction and antigenicity. A chondrocyte was seeded into an alginate with DBP of different contents, and a microcapsule was produced. The adhesion and proliferation of cells was observed through the MTT analysis, and the PCR was applied to estimate the content of the glycosaminoglycan (sGAG) and collagen, and confirm the specific genetic pattern of the chondrocytes. Also, the alginate microcapsule where the chondrocyte is seeded was extracted after transplantation under the skin of a nude mouse, and was immunochemically stained. The experimental result confirmed that the alginate microcapsule containing 1% of DBP not only showed the highest proliferation of cell but had a positive effect of chondrocytes by the interaction between the alginates and the growth factor in DBP. It can be expected that the microcapsule with application of the alginates and DBP might be an appropriate scaffold for tissue engineering.

• Food Science and Preservation
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• v.16 no.3
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• pp.333-341
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• 2009

The antioxidant properties of green tea leaves and powder extracts were determined using several tests including estimation of reducing power, DPPH(1,1-diphenyl-2- picrylhydrazyl) radical-scavenging activity, and FRAP(Ferric reducing/antioxidant power) assay. All tests indicated that extracts of green tea powder had higher antioxidant activities than extracts of green tea leaves, and the activities were concentration-dependent. However, each test yielded somewhat different results with respect to storage conditions. The reducing power of green tea leaves was highest at $1,000{\mu}g/mL$, storage at $4^{\circ}C$, and an Aw(water activity) value of 0.23. However, the reducing power of green tea powder, assayed at $1,000{\mu}g/mL$, was high under all storage conditions(with variations in temperature and Aw), and was about 1.5.2-fold greater than that of green tea leaves. Radical-scavenging activity, as assessed by the DPPH assay, increased in a dose-dependent manner over the range $15{\sim}125{\mu}g/mL$. At higher concentrations, activities were $80{\sim}90%$ of maximal were attained. The FRAP activity of green tea extract also increased with rising concentration. Particularly in the case of green tea leaves, antioxidant activity was most greatest with storage at $-20^{\circ}C$ and Aw values of 0.69 and 0.23 when assayed at a concentration of $1,000{\mu}g/mL$. These results indicate that the most important factor during storage of green tea is not the Aw value but rather temperature, and that use of refrigeration($4^{\circ}C$) is preferable to increase or maintain the antioxidant activities of biological components in green tea.

• Korean Journal of Food Science and Technology
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• v.38 no.3
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• pp.432-437
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• 2006

This study was carried out to investigate the effects of mulberry-leaf powder Tofu (MPT) on serum lipids profiles, Ca levels, Ca/P ratio and Pb levels in 30 middle aged obese women living in the Choongnam area. 100 g/day MPT was consumed for 4 weeks. The nutrient contents per 100 g MPT were 86.71 kcal (energy), 8.98 g protein, 0.53 mg fiber, 211.33 mg Ca and 1.59 g fat. Anthropometric measurements, 24 h recall dietary intakes, serum levels of protein, albumin, glucose, Ca and Pb, lipid profiles (cholesterol, triglyceride, HDL-cholesterol, LDL-cholesterol), and the Ca/P ratio were analyzed before and after consumption of MPT. After consumption of MPT, there were no significant differences in anthropometric measurements, the levels of serum protein, albumin, glucose, total cholesterol, HDL-cholesterol, lipase activity, HTR (HDL-cholesterol/total cholesterol), CRF (cardiac risk factor), Ca, Ca/P ratio and Pb. There were decreases in the levels of serum triglyceride, LDL-cholesterol, AI (atherogenic index) and LHR (LDL-cholesterol/HDL-cholesterol). Significantly increased dietary intakes of plant protein, total Ca, and plant Ca were observed.

• Journal of the Korean Society of Food Science and Nutrition
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• v.46 no.9
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• pp.1035-1044
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• 2017

This study was carried out to investigate the effects of freeze-dried garlic powder (FDGP) on the lipid metabolism in rats fed a high fat-cholesterol (HFC) diet for 4 weeks to induce hyperlipidemia. The rats were divided into the following four experimental groups: normal diet group (NC), HFC diet group (HFC), HFC+FDGP 5 mg/100 g body weight (BW) group (FGT-1), and HFC+FDGP 15 mg/100 g BW group (FGT-2). Body weight gains and food efficiency ratios were significantly lower in the FGT groups compared to the HFC group, and the food intake was not significantly different in all experimental groups. Serum total lipid, triglyceride, and total cholesterol levels were significantly lower in the FGT groups compared to the HFC group. Total lipid content of the FGT-2 group was reduced by about 9% and 12% compared to the FGT-1 group and HFC group, respectively. The FGT groups also showed about 10% reductions low density lipoprotein (LDL)-cholesterol, atherogenic index (AI), and cardiac risk factor (CRF) compared to the HFC group. Liver function index (alkaline phosphatase, aspartate aminotransferase, and alanine aminotransferase) and lipid components were significantly lower in the FGT groups compared to the HFC group. Thiobarbituric acid reactive substances content of serum and liver tissue was reduced in the FGT groups compared to the HFC group, and was lower in the FGT-2 group compared to the FGT-1 group in serum. Antioxidant activities in serum and liver tissue were in the order of FGT-2> FGT-1> HFC group, significantly. In conclusion, FDGP effectively reduced the lipid components of serum and liver tissue. Feeding FDGP did not increase high density lipoprotein-cholesterol, but reduced LDL-cholesterol content, AI and CRF, especially. This shows that FDGP, will be effective in preventing and improving cardiovascular diseases such as arteriosclerosis and hyperlipidemia.