• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.9
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• pp.299-305
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• 2019

As the damage factors of the three­storey stone pagoda of the Bulguksa Temple in Gyeongju could cause a reduction in the historical and artistic value and accelerate the deterioration of the stone, an appropriate solution is needed. The aim of stone conservation is to conserve the original shape and convey originality from the ancestors to their descendants. This procedure includes a record of the condition, being available in the future. In particular, the damage assessment could be used in conservational research, educational data, conservational treatment, and preventive data. As a result of quantitative damage assessment, biological damage indicated 159 %, chemical damage 114 %, and physical damage 16 %. The west direction revealed 95 % because of the amount of sunshine, moisture, and expansion of rock. Complex factors and high range damage were observed on the foundation and body of the pagoda. Since the top of pagoda was restored in the 1970s, the state presented a good condition. By doing this, the number of organisms could be reduced by cleaning and the physical damage could be minimized by bonding. On the other hand, continuous monitoring will be needed because there is a possibility of reforming the damage in the future.

• Journal of Appropriate Technology
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• v.6 no.2
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• pp.115-125
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• 2020

Housing issues such as mushrooming slums remain as chronic in most developing countries. Due to the state's restrained capacity, the housing-vulnerable's self-help approaches have been increasingly inevitable and vital for addressing the housing issues. However, there are still two challenges: securing good quality with economic efficiency, and climate change mitigation and adaptation. This study aims at doing an architectural experiment by developing and educating the production of eco-friendly interlocking stabilized soil bricks (ISSB) by employing vernacular materials and technologies for housing-vulnerable communities in Indonesia. In collaboration with a local architectural NGO, the study features a co-creation workshop in which 40 evicted households participate in the whole process. Soil analysis, mixed design, compression tests, and economic analysis are carried out. This paper illustrates that ISSB also has a high potential as an alternative to a burned brick or a cement block. The application of ISSB to self-help housing is expected to have socioeconomic and environmental effects, thereby facilitating the housing-vulnerable's self-help approaches and contributing to addressing the housing challenges in Indonesia.

• Composites Research
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• v.36 no.2
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• pp.132-139
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• 2023

A linerless composite propellant tank was designed and manufactured by using the carbon fiber-reinforced composite materials which have superior strength-to-weight ratio in order to reduce weight of the tank. In this research, we designed a sub-scale composite propellant tank with a diameter of 800 mm to withstand an MEOP of 1.7 MPa. We manufactured the boss of the tank by using the same composite materials to reduce the thermal expansion difference between the boss and the secondary-bonded composite layers of the barrel in the cryogenic environment. We used the collapsible mandrel to manufacture the tank without any liner. The mandrel was made from epoxy-based composite tooling prepregs to reduce weight of the mandrel. We manufactured the test tanks by laying up the carbon fiber fabric prepregs manually on the mandrel and then applying the autoclave cure process. We performed a proof test, a helium tightness test, a repeated pressurization test, and a burst test in room temperature. The test results demonstrate that the proposed design and manufacture process satisfies all strength requirements as well as an anti-leakage requirement.

• Tunnel and Underground Space
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• v.32 no.6
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• pp.491-501
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• 2022

Bentonite has been proposed as a buffer and backfill material for high-level radioactive waste repository. Under such repository environment conditions, bentonite is subjected to combined thermal, hydrological, mechanical, and chemical processes. This study evaluates the feasibility of applying X-ray CT technology on the characterization of bentonite under hydration conditions using a newly developed testing cell. The cylindrical cell is made of platic material, with a removable cap to place the sample, enabling to apply vertical pressure on the sample and to measure swelling pressure. The hydration test was carried out with a sample made of Gyeonju bentonite, with a dry density of 1.4 g/cm³, and a water content of 20%. The sample had a diameter of 27.5 mm and a height of 34 mm. During the test, water was injected at a constant pressure of 0.207 MPa, and lasted for 7 days. After one day of hydration, bentonite swelled and filled out the space inside the cell. Moreover, CT histograms showed how the hydration process induced an initial increase and later progressive decrease on the density of the sample. Detailed profiles of the mean CT value, CT standard deviation, and CT gradient provided more details on the hydration process of the sample and showed how the bottom and top regions exhibited a decrease on density while the middle region showed an increase, especially during the first two days of hydration. Later, the differences in CT values with respect to the initial state decreased, and were small at the end of testing. The formation and later reduction of cracks was also characterized through CT scanning.

• Journal of Science and Technology Studies
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• v.6 no.1 s.11
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• pp.119-152
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• 2006

This paper deals with the historical development of research community in Korea. As the former studies of the korean scientific community show, the government supported institutes played an important role in the formation of research community. Therefore the theme of this study is concerned with the historical development of the government supported institutes and the features of their researcher group. In this paper following questions will be answered: How the social status of these researcher group is changed, what kind of response on social problems or national politics they had, and which characteristic they showed with regards to the identity problem. After the korean liberation the government institutes, such as the Chungang Kongop Yonguso(industrial research center)and the Korean Atomic Energy Research Institute, contributed to the development of the first generation of research group. However this research group could hardly identify themselves as researcher, because they spent much time on testing, evaluation or education. The identity problem is also resulted from the deficiency of authority as research institute. The status of researcher had no difference from that of civil servant. With the establishment of KIST the korean research community came into blossom. The government supported institutes, which were founded after the model of KIST, allowed quantitative and qualitative growth of research community. Thanks to the guarantee of institutional authority and the new reward system, the researcher could get respect and improve its social status. During this period the researcher volunteered to help the government policies. We can find often the nationalistic statements in the research community. During 1990s the research group demonstrated different behaviors and attitude toward the government. The nationalistic ideology disappeared. Instead of that, the research group criticized the government policies and took actions against the government. Those changes are related with the lowered position of government supported institutes.

• Korean Journal of Food Science and Technology
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• v.27 no.1
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• pp.112-118
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• 1995

The effect of various packaging methods on kimchi quality was investigated in order to develop the packaging techniques for preventing commercial kimchi products from inflation and explosion, due to fermentative gas evolved during storage and distribution. Kimchi was packaged in different methods; 1) atmospheric packaging(AP), 2) check valve packaging(CV), 3) double packaging(DP), and 4) vacuum packaging(VP). The quality of kimchi during storage at $10^{\circ}C$ was evaluated in terms of gas composition, free volume, pH, titratable acidity color index and sensory properties. The gas composition inside packages showed different curves according to the packaging methods. Due to fermentative gas accumulation in both AP and CV, $CO_2$ concentration increased by 2 stepwise pattern, while $O_2$, concentration decreased exponentially. In DP, $O_2$ concentration remained constant, but $CO_2$ concentration increased by 2 stepwise pattern and then decreased. In contrast, VP produced low $O_2$ and high $CO_2$ concentrations only at the end of storage. The free volume in both AP and CV showed typical sigmoidal curves similar to $CO_2$ concentration changes. It remained constant in DP, but started to increase at the late stage of storage in VP. There was no significant effect of packaging methods on pH changes of kimchi. In titratable acidity, DP maintained relatively higher than others. Regarding to the color change of crushed kimchi juice in all packages, L and b values decreased exponentially but a value remained constant during storage. Color index(L b/a) of crushed kimchi juice decreased exponentially and remained constant at the end of storage. The growth of lactic acid bacteria was VP, CV, AP, DP in increasing order. In sensory test, the sourness scores of DP were fairly higher than those of others, but the texture was not significantly affected by the packaging methods. The preference for kimchi showed VP>AP, CV>DP in order of score. In this study, it could be proposed to employ DP and VP method as the effective packaging techniques for preventing commercial kimchi products from inflation.

• Clinical and Experimental Reproductive Medicine
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• v.37 no.1
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• pp.57-64
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• 2010

Objectives: Likewise fresh cycle, it is also important to select right blastocysts for transfer in purpose of improving the pregnancy and implantation rates in frozen-thawed embryo transfer (ET) cycles. To investigate the relationship between the developmental velocity at the time of cryopreservation and pregnancy rates, we compared pregnancy rates between the day 5 cryopreservation group and the day 6 cryopreservation group. Methods: Transfers of frozen-thawed blastocysts which had been cryopreserved by vitrification on day 5 or day 6 were performed between January 2006 and June 2007. Ethylene glycol, DMSO, and pull and cut straws were used for vitrification and artificial shrinkage was done in expanded blastocysts. Thawing was performed on the day before transfer and thawed blastocysts were cultured in for 15~18 hrs in Quinn's blastocyct media. Blastocyst survival was assessed before transfer and post-thaw survival was defined as >50% of cells remaining intact and blastocoele re-expansion by the time of transfer. Results: Transfers of thawed blastocyst had been cryopreserved on day 5 were 52 cycles and 41 transfer cycles were cryopreserved on day 6. Patient characteristics, the number of transferred embryos and the survival rate of thawed blastocysts were not different in each cryopreservation day. But the biochemical pregnancy, clinical pregnancy, ongoing pregnancy, and implantation rate were significantly high in transfer of frozen-thawed blastocyst which were cryopreserved on day 5. Conclusions: The clinical pregnancy and implantation rate of day-5 blastocyst showed significantly higher than those of day-6 blastocyst in frozen-ET cycles. This result indicated that developmental rate of blastocyst at cryopreservation time in frozen-thawed cycle is discriminative marker of pregnancy outcome as like in fresh cycle.

• Journal of the korean academy of Pediatric Dentistry
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• v.31 no.3
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• pp.516-526
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• 2004

Polymerization shrinkage of photoinitiation type composite resin cause several clinical problems. The purpose of this study was to evaluate the shrinkage strain stress, linear polymerization shrinkage, compressive strength and microhardness of recently developed composite resins. The composite resins were divided into four groups according to the contents of matrix and filler type. Group I : $Denfil^{TM}$(Vericom, Korea) with conventional matrix, Group II : $Charmfil^{(R)}$(Dentkist, Korea) with microfiller and nanofller mixture, Group III : $Filtek^{TM}$ Z250(3M-ESPE, USA) TEGDMA replaced by UDMA and Bis-EMA(6) in the matrix, and Group IV : $Filtek^{TM}$ Supreme(3M-ESPE, USA) using pure nanofiller. Preparation of acrylic molds were followed by filling and curing with light gun. Strain gauges were attached to each sample and the leads were connected to a strainmeter. With strainmeter shrinkage strain stress and linear polymerization shrinkage was measured for 10 minutes. The data detected at 1 minute and 10 minutes were analysed statistically with ONE-way ANOVA test. To evaluate the mechanical properties of tested materials, compressive hardness test and microhardness test were also rendered. The results can be summarized as follows : 1. Filling materials in acrylic molds showed initial temporary expansion in the early phase of polymerization. This was followed by contraction with the rapid increase in strain stress during the first 1 minute and gradually decreased during post-gel shrinkage phase. After 1 minute, there's no statistical differences of strain stress between groups. The highest strain stress was found in group IV and followed by group III, I, II at 10 minutes-measurement(p>.05). In regression analysis of strain stress, group III showed minimal inclination and followed by group II, I, IV during 1 minute. 2. In linear polymerization shrinkage test, the composite resins in every group showed initial increase of shrinkage velocity during the first 1 minute, followed by gradually decrease of shrinkage velocity. After 1 minute, group IV and group III showed statistical difference(p<.05). After 10 minutes, there were statistical differences between group IV and group I, III(p<.05) and between group II and group III(p<.05). In regression analysis of linear polymerization shrinkage, group II showed minimal inclination and followed by group IV, III, I during 1 minute. 3. In compressive strength test, group III showed the highest strength and followed by group II, IV, I. There were statistical differences between group III and group IV, I(p<.05). 4. In microhardness test, upper surfaces showed higher value than lower surfaces in every group(p<.05).

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.7
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• pp.9-15
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• 2019

The purpose of present study is to assess the maximum width of the surface cracks using the histogram analysis of image processing techniques in concrete structures. For this purpose, the concrete crack image is acquired by the camera. The image is Grayscale coded and Binary coded. After Binary coded image is Dilate and Erode coded, the image is then recognized as separated objects by applying Labeling techniques. Over time, dust and stains may occur naturally on the surface of concrete. The crack image of concrete may include shadows and reflections by lighting depending on a surrounding conditions. In general, concrete cracks occur in a continuous pattern and noise of image appears in the form of shot noises. Bilateral Blurring and Adaptive Threshold apply to the Grayscale image to eliminate these effects. The remaining noises are removed by the object area ratio to the Labeled area. The maximum numbers of pixels and its positions in the crack objects without noises are calculated in x-direction and y-direction by Histogram analysis. The widths of the crack are estimated by trigonometric ratio at the positions of the pixels maximum numbers for the Labeled objects. Finally, the maximum crack width estimated by the proposed method is compared to the crack width measured with the crack gauge. The proposed method by the present study may increase the reliability for the estimation of maximum crack width using image processing techniques in concrete surface images.

• Applied Chemistry for Engineering
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• v.27 no.4
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• pp.444-448
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• 2016

Hollow silicon/carbon (H-Si/C) composites as anode materials for lithium ion batteries were investigated to overcome the large volume expansion. H-Si/C composites were prepared as follows; hollow $SiO_2\;(H-SiO_2)$ was prepared by adding $NaBH_4$ to $SiO_2$ synthesized using $st{\ddot{o}}ber$ method followed by magnesiothermic reduction and carbonization of phenolic resin. The H-Si/C composites were analyzed by XRD, SEM, BET and EDX. To improve the capacity and cycle performance, the electrochemical characteristics of H-Si/C composites synthesized with various $NaBH_4$ contents were investigated by charge/discharge, cycle, cyclic voltammetry and impedance tests. The coin cell using H-Si/C composite ($SiO_2:NaBH_4=1:1$ in weight) in the electrolyte of $LiPF_6$ dissolved in organic solvents (EC : DMC : EMC = 1 : 1 : 1 vol%) has better capacity (1459 mAh/g) than those of other composition coin cells. It is found that the coin cell ($SiO_2:NaBH_4=1:1$ in weight) has an excellent capacity retention from 2nd cycle to 40th cycle.