• Journal of the korean academy of Pediatric Dentistry
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• v.33 no.4
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• pp.606-614
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• 2006

The purpose of this study was to evaluate the polymerization contraction of composite resin(Tetric $ceram^{(R)}$, Ivoclar Vivadent Liechtenstein) according to various liners(Tetric $flow^{(R)}$, Ivoclar Vivadent, Liechtenstein/$Ionosit^{(R)}$, DMG, German/ $Vitrebond,^{TM}$ 3M-ESPE, USA). The strain gauge method was used for measurement of polymerization shrinkage strain. Specimens were divided by 8 groups according to curing units and liners. Group A, E: Tetric $ceram^{(R)}$ bulk filing, Group B, F: Tetric $flow^{(R)}$ lining, Tetric $ceram^{(R)}$ filling, Group C, G: $Ionosit^{(R)}$ lining, Tetric $ceram^{(R)}$ filling, Group D, H: $Vitrebond^{TM}$ lining, Tetric $ceram^{(R)}$ filling. Group A, B, C and D were cured using the conventional halogen light($XL3000^{TM}$ 3M ESPE, USA) for 40 seconds at $400mW/cm^2$. Group E, F G and H were cured using light emitted diode(LED) light(Elipar Freelight $2^{TM}$, 3M-ESPE, USA) for 15 seconds at 800 $mW/cm^2$. Strain gauge attached to each sample was connected to a strainmeter. Measurements were recorded at each second for the total of 750 seconds including the periods of light application. Obtained data were analyzed statistically using Repeated measures ANOVA and Tukey test. The results of this were as follows : 1. Contraction stresses in flowable resin and glass ionomer lining group were lower than that in compomer lining group(p<0.05). 2, Contraction stresses in LED curing light groups were higher than that in halogen curing light groups, but there was no significant difference (p>0.05).

• Journal of Conservation Science
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• v.30 no.1
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• pp.103-109
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• 2014

This study aimed to develop materials to compensate for problems of restoration for lost parts and material problems in the conservation treatment. First, there are several problems with existing materials as follows: secondary damage due to the high shrinkage rate and low adhesive strength, sense of difference due to the severe yellowing, remelting due to irreversibility of materials, processability due to the high strength, sag due to the prolonged setting time in the work process and surface contamination of artifacts due to tools or gloves. In order to solve these problems, this study set developmental goals after understanding the types and physical properties based on epoxy resin among the currently used restoration materials of pottery and earthenware. The developed epoxy resin is epoxy putty, which is cured within 5 minutes, for earthenware restoration. In the earthenware restoration method, the epoxy putty enhanced the workability by quickly curing in paste form and compensated disadvantages such as surface contamination. In addition, the use of white micro-balloon for the epoxy stock solution made coloring easier and weight lighter, and a restoration material with low shrinkage and superior processability was developed.

• Journal of the Korean Ceramic Society
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• v.36 no.1
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• pp.43-49
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• 1999

Gas pressure sintered silicon nitride based composites with 0~5wt% $\beta$-Si3N4 whiskers were prepared. The whiskers were unidirectionally oriented by a modified tape casting technqiue and green bodies with various microstructure were formed by changing stacking sequences of sheets cut from the tape. Orientations of the large elongated grains of the sample after gas pressure sintering were the same as the those of the whiskers of green body, and the sintering shrinkage and mechanical properties of sintered sample were consistent with the microstructural characteristics. In case of unidirectional samples, the sintering shrinkage normal to whisker alignment direction was larger than that parallel to the direction. The shrinkage difference inceaed as the whiskercontent increaed. As whisker content increaed, the crack length normal to and parallel to tape casting direction became shorter and larger, respectively. Although the grain size increased by th whisker addition, the flexural strength of unidirectional samples was not lower than that of smaple without the whisker. In case of crossplied and 45$^{\circ}$rotated samples, the anisotropy of mechanical preoperties disappeared.

• Journal of Korean Society on Water Environment
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• v.34 no.4
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• pp.375-381
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• 2018

The monitoring of phytoplankton biomass and community structure is essential as a first step to control the harmful cyanobacterial blooms in freshwater systems, such as seen in rivers and lakes, due to the process of eutrophication and climate change. In order to quantify the biomass of phytoplankton with a wide range in size and shape, the measurement of cell biovolume along with cell density is required for a comprehensive review on this issue. However, most routine monitoring programs preserve the gathered phytoplankton samples before analysis using chemical additives, because of the constraint of time and the number of samples. The purpose of this study was to investigate the cell biovolume change characteristics of six cyanobacterial species, which are common bloom-causing cyanobacteria in the Nakdong River, after the preservation with Lugol's iodine solution. All species showed a statistically significant difference after the addition of Lugol's iodine solution compared to the live cell biovolume, and the cell biovolume decreased to the level of 34.0 ~ 56.3 % at maximum in each species after the preservation. The nonlinear regression models for determining the shrinkage ratio by a preservation period were derived by using the cell biovolume measured until 180 days preservation of each target species, and the equation to convert the cell biovolume measured after preservation for a certain period to the cell biovolume of viable cell was derived using that formula. The conversion equation derived from this study can be used to estimate the actual cell biovolume in the natural environment at the time of sampling, by using the measured biovolume after the preservation in the phytoplankton monitoring. Moreover this is expected to contribute to the final interpretation of the water quality and aquatic ecosystem impacts due to the cyanobacterial blooms.

• Journal of the Korea Institute of Building Construction
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• v.15 no.3
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• pp.265-271
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• 2015

This study is intended to produce a PC (Precast Concrete) member without a steam curing process in developing the high early strength concrete satisfying the condition of 10MPa in compressive strength at the age of 6 hours, and is intended to ensure economic feasibility by increasing the turnover rate of concrete form. Hence, high early strength cement with high $C_3S$ content and the hardening accelerator of powder type accelerating the hydration of $C_3S$ was used. And the properties of concrete were evaluated according to the hardening accelerator mixing ratio (0, 1.2, 1.6, 2.0). No big difference was found from the tests of both slump and air content. When 1.6 % or higher amounts of the hardening accelerator were mixed, the compressive strength of 10MPa was achieved at the age of 6 hours. From the test results of autogenous (drying) shrinkage and plastic shrinkage, it can be seen that there was a difference according to hydration reaction rate due to the addition of the hardening accelerator. However, it was shown that no problem arose with crack and durability. And it was shown that resistance to freezing-thawing, carbonation, and penetration were excellent.

• Journal of the korean academy of Pediatric Dentistry
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• v.25 no.2
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• pp.368-382
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• 1998

The purpose of this study is to evaluate and compare the results of argon laser for 5 seconds, argon laser for 10 seconds, and visible light for 40 seconds photo-polymerization in compressive strength, microhardness, curing depth, temperature rising during polymerization, and polymerization shrinkage. Hybrid type composite resin(Z-100) and compomer(Dyract) were used to be compared. The compressive strength was measured by an Instron(1mm/min cross head speed) in 60 specimens and the microhardness of the surface was expressed by Vickers Hardness Number(VHN) in 30 specimens. The curing depth was evaluated comparing the different values of upper and lower VHN according to irradiation time and thickness for the light source polymerization in 60 specimens. The temperature rising during photopolymerization was observed by the temperature change with thermocouple sensitizer beneath 40 specimens at the argon laser for 10 seconds and visible light 40 seconds irradiation. The polymerization shinkage was evaluated by calculating the decrease of % volume by using a dilatometer in 30 specimens. The results were as follows ; 1. In the case of compressive strength, the argon laser polymerization groups were higher than visible light group in Z-100 (p<0.05). In Dyract, the argon laser 5 seconds group did not show a significant difference with the visible light 40 seconds group. The argon laser 10 seconds group showed the markedly low value when compared with other groups (p<0.05) 2. In microhardness, Z-100 was better than Dyract when comparing by VHNs (p<0.05); however, there was not a significant difference between two materials in the visible light 40 seconds group and the argon laser 10 seconds group. 3. In the study of curing depth, Z-100 showed the consistent polymerization in argon laser irradiation because there was no difference in the VHN decrease according to the thickness change. Over the thickness control, the results did not show a significant difference between visible light and argon laser group in Z-100; however, in the case of Dyract, the visible light 40 seconds group was better than the argon laser groups(p<0.05). 4. There was a significant difference between the two materials in temperature rising during polymerization (p<0.05), but not a significant difference between irradiation times, 5. There was not a significant difference between the two materials in polymerization shrink age. The argon laser 5 seconds group was smaller than the other groups (p<0.05). It could be concluded that Z-100 polymerization was recommended to use the argon laser for reduction of the irradiation time while Dyract was recommended to use the visible light polymerization.

• Journal of Photoscience
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• v.9 no.2
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• pp.454-456
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• 2002

It is important to determine the action spectrum of UV-B radiation contained in the sunlight to estimate the risk of skin cancer. We have investigated action spectra for induction of apoptosis and reproductive cell death in L5178Y cells using the Okazaki Large Spectrograph at NIBB. L5178Y cells were exposed to light at different wavelengths in UV-B or UV-A region. Frequencies of apoptosis induction and reproductive cell death were determined by counting cells with chromatin condensation, and by the colony formation assay, respectively. The measured sensitivity spectra for the two end-points were in very good agreement. Sensitivity decreased steeply with increase of wavelength in UV-B region and remains nearly constant in UV-A region. The action spectra were also slightly steeper than that for the minimum erythematic dose (MED), but very similar to the light absorption spectrum of DNA in UV-B region. On the other hand, the spectra for both endpoints were similar to MED spectrum but not DNA spectrum in the UV-A region. Also different time-course and morphological difference of apoptosis were found between UV-B (long time, fragmentation) and UV-A (short time, shrinkage) region. These results suggest that DNA damage induced by UV-B light triggers apoptosis and reproductive cell death, but other damaged targets (membrane, protein and so on) trigger these effects in UV-A region.

• Journal of Korean Society of Forest Science
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• v.99 no.5
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• pp.682-685
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• 2010

Coring has been widely used to measure annual increment in temperate forest ecosystems. This method is attractive because cores can be taken in just one visit. However, the accuracy of this method has not been tested. We expected coring to be less accurate than band dendrometers because of the eccentricity of tree growth. We studied 41 trees at the Long Term Experimental Forest in Mt. Gyebang, which has been monitored with band dendrometers since 1996. We collected two tree cores from the south and north face of each tree, 10 cm below the growth band. Increment cores were measured to 0.01 mm under stereomicroscopy. Annual growth from 1997 to 2006 was 3.2 mm $yr^{-1}$ for Quercus mongolica, 3.5 mm $yr^{-1}$ for Kalopanax septemlobus, and 5.7 mm $yr^{-1}$ for Pinus densiflora. The difference between the two methods was 10% for Q. mongolica, 14% for K. septemlobus, and 4% for P. densiflora. Compaction in the corer and shrinkage during drying decreased diameter increment by 5.6% and 1.0% on P. densiflora, respectively. This study suggests that the two methods for annual increment measurement are very similar, but species specificity should be concerned for direct comparison.

• Textile Coloration and Finishing
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• v.27 no.1
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• pp.35-49
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• 2015

This paper investigated optimum process conditions of coating yarn for awning fabric. For this purpose, the simulation for processability and yarn quality using SPSS statistics package was carried out, and PP/TPO and PET/PVC coating yarns specimens were made with variation of extruder temperature and feed speed of core yarn on the yarn coating machine for examining simulation result. It was revealed that optimum coating conditions of PP/TPO 1000d coating yarn were extruder temperature $150^{\circ}C$, and core yarn feed speed 400~500m/min. Mechanical property and thermal shrinkage of PP/TPO coating yarn made at this conditions were best and core evenness rates of these coating yarns by yarn compression tester were also superior, which was certified by SEM photograph. In addition, these experimental results were coincided with simulation results. It was found that, in PET/PVC coating yarn, yarn physical properties between 1500d and 1200d coated yarns were not shown any difference, and core evenness rates of these coating yarns were superior. It revealed and concluded that these simulated coating conditions are applicable to production field.

• Textile Coloration and Finishing
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• v.6 no.2
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• pp.47-54
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• 1994

Cotton fiber, NaOH-mercerized cotton fiber, cotton fabric, and NaOH-mercerized cotton fabric have been treated by liquid ammonia at -33.4$^{\circ}C$. The fine structures, bending properties, tensile strengthes, shrinkages for laundering, and wrinkle recoveries were studied. The treatment of cottons with liquid ammonia brought about the transition of crystal lattice ; transforming cellulose I crystal of original cotton to cellulose I and III crystal, and cellulose II crystal of mercerized cotton to cellulose II and III crystals. The degree of crystallinities were decreased in the order of liquid ammonia>NaOH/liquid ammonia>NaOH-treated cotton. However moisture regain and water absorbency for liquid ammonia-treated cotton were lower than that of NaOH-treated cotton because of a difference in swelling actions of the agents. It seems caused by intermicrofibrillar pores produced in swelling processes. The bending rigidity and bending hysteresis were decreased remarkly by liquid ammonia treatment. Therefore softness and dimensional stability were improved. The liquid amminia and NaOH/liquid ammonia-treated cottons moreover show excellent properties in tensile strength, anti-shrinkage for laundering, and wrinkle recovery.