• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.12
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• pp.938-943
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• 2018

Thin nano-sized fibres were prepared by an electrospinning method. The spinning appratus consisted of pump for polymer injection, nozzle and nozzle rotus, and an aluminum plate collected the polymer fibers. Its surface was chemically modified for selective improved adsorption of carbon monoxide at indoor level. The chemical activation enabled to form the fibres 250-350 nm in thickness with pore sizes distributed between 0.6 and 0.7 nm and an average specific surface area of $569m^2/g$. The adsorption capacities of pure (100%) and indoor (0.3%) $CO_2$, of which level frequently appears, at the ambient condition were improved from 1.08 and 0.013 to 2.2 and 0.144 mmol/g, respectively. It was found that the adsorption amount of $CO_2$ adsorbed by the chemically activated carbon nanofiber prepared through chemical activation would vary depending on the ratio of specific surface area and micropores. In particular, chemical interaction between adsorbent surface and gas molecules could enhance the selective capture of weak acidic $CO_2$.

• Journal of Soil and Groundwater Environment
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• v.26 no.3
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• pp.25-36
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• 2021

This study evaluated monthly, seasonal and altitudinal changes of oxygen and hydrogen isotope compositions of wet precipitation samples (n = 238) that were collected for last four years from 7 altitudes (from 265 to 1,500 m above sea level) in the Jeju Samdasoo watershed at the southeastern part of Jeju island, in order to examine the recharge characteristics of groundwater that is pumped out for the production of the Samdasoo drinking mineral water. Precipitation samples showed a clear seasonal change of O-H isotopic composition as follow, due to the different air masses and relative humidity: 𝛿D = 7.3𝛿¹⁸O + 11.3 (R² = 0.76) in the wet season (June to September), while 𝛿D = 7.9𝛿¹⁸O + 9.5 (R² = 0.91) in the dry season (October to May). In contrast, the stable isotope compositions of groundwater were nearly constant throughout the year and did not show a distinct monthly or seasonal change, implying the well-mixing of infiltrated water during and after its recharge. An altitudinal effect of the oxygen isotope compositions of precipitation was also remarkable with the decrease of -0.19‰ (R² = 0.91) with the elevation increase by 100 m. Based on the observed altitudinal change, the minimum altitude of groundwater recharge was estimated as 1,200 m above the sea level in the Jeju Samdasoo watershed.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.2
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• pp.133-142
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• 2022

The purpose of this study is to develop an impact crusher with a radial rotating plate installed at the bottom, which is a shock absorber that can produce high-quality recycled coarse aggregate for concrete and to verify the effect of improving the quality performance of recycled coarse aggregate and its applicability through concrete tests. As a result, it showed improved quality in all items such as absolute dry density, absorption rate, abrasion resistance, Particle shape judgment rate, amount lost in the 0.08 mm sieve passing test, alkali aggregate reaction, clay mass, stability, and impurity content, and it was found to meet the criteria of recycled aggregate quality standards. In addition, the air volume and slump of concrete to which recycled coarse aggregate is applied meet all domestic standards. According to the test results of the compressive strength characteristics by age of concrete according to the mixing ratio of the recycled coarse aggregate, it was confirmed that the mixing ratio of the recycled coarse aggregate was applicable up to 60 %.

• Animal Bioscience
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• v.35 no.12
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• pp.1871-1880
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• 2022

Objective: The primary goal was to identify the effectiveness of chemical or biological additives in delaying the deterioration of early-harvested wilted rye silage after exposure to air. Methods: Rye harvested as a whole plant at the early heading stage was wilted for 24 h. The wilted forage was divided into treatments including sodium diacetate (SDA) at 3 (SDA3) and 6 g/kg (SDA6), Lactobacillus plantarum (LP), L. buchneri (LB), or their equal mixture (LP+LB) at 1×10⁶ colony-forming unit/g fresh matter. Results: After 60 d of conservation in 20-L silos, lactic acid was greater in LP and LP+LB silages than other treatments (102 vs 90.2 g/kg dry matter [DM]). Acetic acid was greatest in SDA6 (32.0 g/kg DM) followed by LB (26.1 g/kg DM) and was lowest in LP treatment (4.73 g/kg DM). Silage pH was lower with microbial inoculation and the lowest and highest values were observed in LP and untreated silages, respectively. After 60 d, neutral detergent fiber concentration was lowest in SDA6 silages, resulting in the greatest in vitro DM digestibility (846 g/kg DM). Aerobic stability was longest in SDA6 (176 h) followed by LB treatment (134 h). Instability after aerobiosis was greatest in LP silages (68 h), about 8 h less than untreated silages. After aerobic exposure, yeast and mold numbers were lowest in SDA6 silages, resulting in DM loss minimization. Exhaustion of acetic acid and lactic acid after aerobic exposure was lowest with SDA6 but greatest with untreated and LP silages. Conclusion: Treatment of early-cut wilted rye forage with SDA at 6 g/kg resulted in silages with higher feeding value and fermentation quality, and substantially delayed deterioration after aerobic exposure, potentially qualifying SDA at this load for promotion of silage quality and delaying aerobic spoilage of early-harvested (low DM) rye forage.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.36 no.2
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• pp.154-159
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• 1991

A field experiment was conducted to know the feasibility of direct-seeded rice. Dry seeds of a Japonica type rice variety, Donghaebyeo, was sown from May 10 to June 20 at the 10-day intervals. The number of days from seeding to emergence decreased as planting date delayed; 13, 12, 10, 9, and 7 days at May 10, May 20. May 30. and June 10 seedings, respectively. The number of maximum tillers per ㎡ was about 700-800 at all the seeding dates and effective tiller ratio ranged 40-45%. The number of days from seeding to heading decreased as seeding date delayed; from 97 days at May 10 planting to 71 days at June 20 planting. The cumulative effective temperature (mean air temperature-15$^{\circ}C$) from seeding to heading was fairly constant having 870$^{\circ}C$ with 2.3% C.V. The number of panicles per unit area at June 10 planting was higher than that of other planting dates. Panicle length and the number of spikelets per panicle tended to decrease as seeding date delayed. The number of spikelets per unit area, 1000-grain weight, and grain yield were similar among the seeding dates except June 20 seeding. At the June 20 seeding the number of spikelets and grain yield were much lower, but 1000-grain weight was higher compared with other seeding dates. Grain fertility and percent ripened grains was similar among all seeding dates.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.38 no.6
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• pp.537-544
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• 1993

Super-giant-embryo mutant line (Hwacheong-ge$^s$) with high nutritional quality was developed from Hwacheongbyeo, a Korean Japonica cultivar. Grain weight of brown rice of Hwacheong-ge$^s$ line was lighter than of Hwacheongbyeo. However, embryo dry weight of the line was 3.22 times heavier than that of Hwacheongbyeo on the single grain base. Hwacheong-ge$^s$ line showed higher protein(8.99%) than the original variety(7.39%), without changes in storage protein. In amino acid composition, lysine content was greatly increased in the mutant, while the contents of methionine, serine and tyrosine were slightly decreased as compared with the original one. Lipid content of Hwacheong-ge$^s$ line was 1.5 times higher compared with that of Hwacheongbyeo. The contents of Vitamin Bl, B2, and E(${\alpha}$-tocopherol) were also greatly increased in Hwacheong-ge$^s$line. The grain yields of the mutant lines ranged from 69.2% to 78.8% compared with that of Hwacheongbyeo, 556kg /10a. Most of the mutant lines of M4 generation were homogeneous for growth characters, and some of them seemed to be readily applicable for farmer's field.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.6C
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• pp.303-311
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• 2009

In this study, weakly cemented sand was cured at air dry condition with different periods (3, 7, 14, 21, 28 days) and its unconfined compressive strength was evaluated. As a result, the strength of specimens with low cement ratios such as 4 and 8% increases until 7 days curing but, after 7 days, their strength continuously decreases. The strength of specimens with relatively high cement ratios such as 12 and 16% increases up to 7 days curing and then stays almost constant until 21 days. After 21 days curing, their strength suddenly dropped down, which is much lower than the strength of 3 days curing specimen. A cemented sand and gravel called CSG, which is highly permeable, could be exposed to repetitive drying and wetting conditions due to rainfall or groundwater table change during curing. In this study, the weakly cemented sand is exposed to repetitive drying and wetting and then its unconfined compressive strength was evaluated. As a result, the strength of a specimen with 27 days drying condition following 1 day wetting was at maximum 35% lower than the one cured under 28 days drying. The strength degradation due to wetting decreases as a cement ratio increases. However, the strength of a specimen with repetitive drying and wetting increases as the number of wetting increases until 3 cycles. After 3 cycles of drying and wetting, the rate of strength increase decreases due to an insufficient water for hydration or stays constant. If the sufficient water supply is provided to cemented sand during curing, the target or design strength increase can be achieved. Otherwise, the strength degradation due to wetting should be considered at the design stage.

• Journal of Korean Academy of Dental Administration
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• v.6 no.1
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• pp.19-27
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• 2018

The purpose of this study was to determine the level of toothbrush bacterial growth, whether the dryness of the toothbrush head differs depending on the number of holes in the head, and to use these results as a reference for future toothbrush design. Two-millimeter holes were created on the head of the toothbrushes in groups of three, one, or zero holes. We made the solution with Streptococcus mutans, and the toothbrushes were placed in the solution and agitated. The toothbrushes were shaken to remove moisture and allowed to air-dry. The toothbrush heads were swabbed with saline and then placed in two inoculation groups. The first group was inoculated with a 102 dilution of the S. mutans culture and the second was inoculated with the original culture. After incubation, bacterial colony numbers were measured. The number of holes on the toothbrush head correlated with a decrease in number of cultured bacterial colonies. Our model of a toothbrush head with holes indicated that these holes in the toothbrush head were effective in reducing the level of microbial contamination and that a greater number of holes creates an improved toothbrush sanitation effect. The average number of colonies on the head of toothbrush by number of holes was high, followed by the number of holes 0, 1 and 3, and the average number of colony among toothbrush heads was same. The use of a toothbrush with holes between the toothbrush head indicates that it is effective in reducing the level of microbial contamination between the toothbrush head and toothbrush and the higher the number of holes, the better the effect.

• Journal of the Korean Geotechnical Society
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• v.39 no.7
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• pp.17-30
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• 2023

This study investigates the impact of water immersion and high temperature on the shear strength of cemented sand through direct shear tests. Standard Jumunjin sand was used and cemented with binders, such as ultra-rapid hardening cement and an epoxy aqueous solution. The binder was mixed at concentrations of 4%, 8%, or 12%. Subsequently, cylindrical cemented specimens with a diameter of 64 mm and height of 25 mm were produced using compaction. The curing period was three days, and the specimens were cured under dry air, immersion, and heating conditions. The heating condition involved subjecting the immersed specimens to a microwave oven three times for three minutes to achieve an internal temperature of approximately 90℃. Regardless of the binder type, the cohesion of the cemented sand increased with higher binder content, whereas the internal friction angle exhibited a slight increase or decrease. Compared with ultra-rapid hardening cemented sand, epoxy-cemented sand displayed an average cohesion that was five times higher and an internal friction angle that was 10° higher. Overall, irrespective of binder type, the shear strength decreased during water immersion and increased during heating. Notably, the epoxy-cemented sand exhibited a three-fold increase in cohesion and a more than 20° increase in the internal friction angle during heating.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.33 no.4
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• pp.517-527
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• 2023

Objectives: We examine cases of chemical poisoning that occurred in the cleaning of metal parts and the regulations on halogenated solvents in other countries and propose regulations necessary to prevent chemical poisoning from halogenated solvents. Methods: We collected cases of chemical poisoning through the website of the Korea Occupational Safety and Health Agency. A review of the literature was conducted focusing on regulations related to halogenated solvents in the United States and the European Union, particularly for cleaning metal parts. Among the Material Safety Data Sheets submitted to the government, MSDS containing eleven substances were extracted to confirm the composition and product use. We investigated cleaning methods for metal parts used in South Korea. For the hazard classification, the European Chemicals Agency or Japan's NITE's website was used. Results: In the case of poisoning, the cleaning methods involving trichloromethane were dipping and dry, which was not found in the literature. It was confirmed that many halogenated solvents and dimethyl carbonate were used for metal cleaning in South Korea. In vapor degreasing using TCE in the USA, even if the facility is strictly managed, such as by installing cooling coils in open cleaning facilities, the risk of exposure to TCE is considered to be not only carcinogenic but also a concern for acute and chronic effects. In comparison, exposure through Korean work methods such as dipping and drying operations is inevitably much higher. Conclusions: The transition to water-based cleaning with low-hazard chemicals should be a priority in the cleaning process. In the case of metal parts that require precise cleaning, if the use of a halogenated solvent is inevitable, a closed degreasing facility should be used to minimize exposure. The current regulations in the Occupational Safety and Health Act, the Chemical Substances Control Act, and the Air Environment Conservation Act do not require cleaning facilities to minimize emissions. To protect the health of workers using halogenated solvents to clean metal parts, regulations that require a fundamental reduction in exposure will be necessary.