• The Journal of Korean Academy of Prosthodontics
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• v.59 no.2
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• pp.153-163
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• 2021

Purpose: The aim of this study was to evaluate the effects of four surface treatment methods to improve zirconia roughness and three types of resin cement on the shear bond strength (SBS). Materials and methods: A total of 120 zirconia blocks were randomly divided into four surface treatments: non-treatment (Control), airborne-particle abrasion (APA) with 50 ㎛ Al2O3 (APA50), APA with 125 ㎛ Al2O3 (APA125), and ZrO2 slurry (ZA). Three resin cements (Panavia F 2.0, Superbond C&B, and Variolink N) were applied to the surface-treated zirconia specimens. All specimens were subjected to SBS testing using a universal testing machine. The surface of the representative specimens of each group was observed by scanning electron microscope (SEM). SBS data were analyzed with oneway ANOVA, two-way ANOVA test and post-hoc Tukey HSD Test (α=.05). Results: In the surface treatment method, APA125, APA50, ZA, and Control showed high shear bond strength in order, but there was no significant difference between APA125 and APA50 (P>.05). Also, ZA showed significantly higher shear bond strength than Control (P<.05). In the resin cement type, Panavia F 2.0, Superbond C&B, and Variolink N showed significantly higher shear bond strength in order (P<.05). In SEM images, the zirconia surfaces of the APA50 and APA125 showed quite rough and irregular shapes, and the zirconia surface of the ZA was observed small irregular porosity and rough surfaces. Conclusion: APA and ZrO2 slurry were enhanced the surface roughness of zirconia, and Panavia F 2.0 containing MDP showed the highest shear bond strength with zirconia.

• Composites Research
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• v.34 no.4
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• pp.241-248
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• 2021

As the electric vehicle market grows, there is an issue of light weight vehicles to increase battery efficiency. Therefore, it is going to replace the battery module cover that protects the battery module of electric vehicles with high strength/high heat-resistant polymer composite material which has lighter weight from existing aluminum materials. It also aims to respond to the early electric vehicle market where technology changes quickly by combining 3D printing technology that is advantageous for small production of multiple varieties without restrictions on complex shapes. Based on the composite material mechanics, the critical length of glass fibers in short glass fiber (GF)/polycarbonate (PC) composite materials manufactured through extruder was derived as 453.87 ㎛, and the side feeding method was adopted to improve the residual fiber length from 365.87 ㎛ and to increase a dispersibility. Thus, the optimal properties of tensile strength 135 MPa and Young's modulus 7.8 MPa were implemented as GF/PC composite materials containing 30 wt% of GF. In addition, the filament extrusion conditions (temperature, extrusion speed) were optimized to meet the commercial filament specification of 1.75 mm thickness and 0.05 mm standard deviation. Through manufactured filaments, 3D printing process conditions (temperature, printing speed) were optimized by multi-optimization that minimize porosity, maximize tensile strength, and printing speed to increase the productivity. Through this procedure, tensile strength and elastic modulus were improved 11%, 56% respectively. Also, by post-processing, tensile strength and Young's modulus were improved 5%, 18% respectively. Lastly, using the FEA (finite element analysis) technique, the structure of the battery module cover was optimized to meet the mechanical shock test criteria of the electric vehicle battery module cover (ISO-12405), and it is satisfied the battery cover mechanical shock test while achieving 37% lighter weight compared to aluminum battery module cover. Based on this research, it is expected that 3D printing technology of polymer composite materials can be used in various fields in the future.

• Economic and Environmental Geology
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• v.54 no.4
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• pp.409-425
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• 2021

Carbon dioxide has been known to be a typical greenhouse gas causing global warming, and a number of efforts have been proposed to reduce its concentration in the atmosphere. Among them, carbon dioxide capture and storage (CCS) has been taken into great account to accomplish the target reduction of carbon dioxide. In order to commercialize the CCS, its safety should be secured. In particular, if the stored carbon dioxide is leaked in the arable land, serious problems could come up in terms of crop growth. This study was conducted to investigate the effect of carbon dioxide leaked from storage sites on soil fertility. The leakage of carbon dioxide was simulated using the facility of its artificial injection into soils in the laboratory. Several soil chemical properties, such as pH, cation exchange capacity, electrical conductivity, the concentrations of exchangeable cations, nitrogen (N) (total-N, nitrate-N, and ammonia-N), phosphorus (P) (total-P and available-P), sulfur (S) (total-S and available-S), available-boron (B), and the contents of soil organic matter, were monitored as indicators of soil fertility during the period of artificial injection of carbon dioxide. Two kinds of soils, such as non-cultivated and cultivated soils, were compared in the artificial injection tests, and the latter included maize- and soybean-cultivated soils. The non-cultivated soil (NCS) was sandy soil of 42.6% porosity, the maize-cultivated soil (MCS) and soybean-cultivated soil (SCS) were loamy sand having 46.8% and 48.0% of porosities, respectively. The artificial injection facility had six columns: one was for the control without carbon dioxide injection, and the other five columns were used for the injections tests. Total injection periods for NCS and MCS/SCS were 60 and 70 days, respectively, and artificial rainfall events were simulated using one pore volume after the 12-day injection for the NCS and the 14-day injection for the MCS/SCS. After each rainfall event, the soil fertility indicators were measured for soil and leachate solution, and they were compared before and after the injection of carbon dioxide. The results indicate that the residual concentrations of exchangeable cations, total-N, total-P, the content of soil organic matter, and electrical conductivity were not likely to be affected by the injection of carbon dioxide. However, the residual concentrations of nitrate-N, ammonia-N, available-P, available-S, and available-B tended to decrease after the carbon dioxide injection, indicating that soil fertility might be reduced. Meanwhile, soil pH did not seem to be influenced due to the buffering capacity of soils, but it is speculated that a long-term leakage of carbon dioxide might bring about soil acidification.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.6
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• pp.1092-1099
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• 2022

Research on exhaust aftertreatment devices to reduce air pollutants and greenhouse gas emissions is being actively conducted. However, in the case of the particulate matters/nitrogen oxides (PM/NOx) simultaneous reduction device for ships, the problem of back pressure on the diesel engine and replacement of the filter carrier is occurring. In this study, for the optimal design of the integrated device that can simultaneously reduce PM/NOx, an appropriate standard was presented by studying the flow inside the device and change in back pressure through the inlet/outlet pressure. Ansys Fluent was used to apply porous media conditions to a diesel particulate filter (DPF) and selective catalytic reduction (SCR) by setting porosity to 30%, 40%, 50%, 60%, and 70%. In addition, the ef ect on back pressure was analyzed by applying the inlet velocity according to the engine load to 7.4 m/s, 10.3 m/s, 13.1 m/s, and 26.2 m/s as boundary conditions. As a result of a computational fluid dynamics analysis, the rate of change for back pressure by changing the inlet velocity was greater than when inlet temperature was changed, and the maximum rate of change was 27.4 mbar. This was evaluated as a suitable device for ships of 1800kW because the back pressure in all boundary conditions did not exceed the classification standard of 68mbar.

• Economic and Environmental Geology
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• v.55 no.4
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• pp.317-338
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• 2022

Physicochemical characteristics and evaluation were studied by subdividing the concretes, bricks and earth pipes on the site of the Japanese Ministry of General Affairs in Joseon Dynasty, known as modern architecture, into three periods. Concretes showed similar specific gravity and absorption ratio, and large amounts of aggregates, quartz, feldspar, calcite and portlandite were detected. Porosity of the 1907 bricks were higher than those of 1910 and 1950 bricks. All earthen pipe is similar, but the earlier one was found to be more dense. Bricks and earthen pipes are dark red to brown in color within many cracks and pores, but the matrix of the earthen pipe is relatively homogeneous. Quartz, feldspar and hematite are detected in bricks, and mullite is confirmed with quartz and feldspar in earthen pipes, so it is interpreted that the materials have a firing temperature about 1,000 to 1,100℃. Concretes showed similar CaO content, but brick and earthen pipe had low SiO₂ and high Al₂O₃ in the 1907 specimen. However, the materials have high genetic homogeneity based on similar geochemical behaviors. Ultrasonic velocity and rebound hardness of the concrete foundation differed due to the residual state, but indicated relatively weak physical properties. Converting the unconfined compressive strength, the 1st extended area had the highest mean values of 45.30 and 46.33 kgf/cm², and the 2nd extended area showed the lowest mean values (20.05 and 24.76 kgf/cm²). In particular, the low CaO content and absorption ratio, the higher ultrasonic velocity and rebound hardness. It seems that the concrete used in the constructions of the Japanese Ministry of General Affairs in Joseon Dynasty had similar mixing characteristics and relatively constant specifications for each year. It is interpreted that the bricks and earthen pipes were through a similar manufacturing process using almost the same raw materials.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.36 no.1
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• pp.41-51
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• 1991

This study was conducted to determine the effect of 20 years long term fertilizations on the physical and chemical properties of paddy soil and the growth, yield, yield components and grain development of rice. Non-fertilized, PK, NK, NP, NPK, NPK + compost, NPK+straw and NPK+lime have been applied since 1968 after surface paddy soil was removed. NPK+compost and NPK+straw applications increased the content of organic matter, available P and CEC, and lime increased soil acidity and SiO$_2$ content. While chemical contents in non-fertilized treatment were low as compared with other treatments. Soil porosity was higher in NPK+straw (51.4%) and NPK+lime(53.1%) than in NPK application (49.8%). Soil hardness was highest in the NPK application and was lowest in the NPK + lime. Continuous application of straw with NPK markedly increased the content of aggregate with over 1mm(19.6%) as compared with NPK application (7.1%). Plant height, tiller number, root number, leaf area index and total dry weight were higher in the applications of compost, straw and lime with NPK than in any other treatments. Brown rice yield in non-fertilized, PK and NP applications was decreased 45, 55, 15 and 5% of that in NPK application, respectively, while application of compost, straw and lime with NPK increased the yield by 11, 14 and 4%, respectively, during 20 years. The number of differentiated rachis branchs in the application of compost, straw and lime was 17 to 21 and that in the other application was 13 to 15, whereas the degenerated rachis branchs was low in the application of compost, straw and lime with NPK. The applications having higher level of perfect rice grain such as non-fertilized, NPK+compost, NPK+straw and NPK+lime had high grain weight and had low level of white core rice, white belly rice. The white core and belly rice was highest in the NP application and notched belly rice kernel was markedly increased in NK and NP applications. The period of grain filling was 30 DAH at NP and NPK applications, 35 DAH at NK and NPK+lime, 40DAH at NPK+compost and NPK+ straw, and 45DAH at non-fertilized, respectively.

• Journal of the Korea Organic Resources Recycling Association
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• v.31 no.3
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• pp.73-82
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• 2023

This study was conducted to investigate the effect of soil physico-chemical properties and crop growth responses for application of biochar derived from substrate with post harvest of oyster mushroom. The biochar was produced at 450~600℃ using a top-light up draft gasifier (TLUD) production system. As a result of elemental analysis, the biochar used was C 76.2%, H 2.5%, N 3.2%, and H/C was 0.39, which met the international certification standards for biocarbons (IBI) below 0.7. The chemical properties were 10.1 for pH, 1.0% for P₂O₅, 1.8% for K₂O, and 2.5% for CaO. The application rates of biochar were 0, 100, 200, 300, and 500 kg/10a. For cultivation of chinese cabbage and welsh onion, soil organic matter (OM), total nitrogen (T-N), total carbon (T-C), Ex.cation K contents and cation exchange capacity (CEC) in the treatments were increased compared to the no treatment. In addition, the bulk density was lowered and the porosity was increased, improving the soil physical properties in the treated soil. The growth of chinese cabbage and green onion increased with the application of biochar, but the yields of chinese cabbage and green onion did not significantly different among the treatments. Soil carbon sequestration in the treatments enhanced with increasing the amount of biochar application. It is expected to apply the biochar derived from spent oyster mushroom substrate in the eco-friendly farm soil management, improving soil physico-chemical properties.

• Economic and Environmental Geology
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• v.56 no.1
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• pp.1-11
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• 2023

In this study, we explore the morphological and geochemical characteristics for 440 manganese nodules collected from two different water depths [ARA12B-St52 (150 m, n = 239) and ARA12B-St58i (73 m, n = 201)] on the continental shelf of the East Siberian Sea from the ARA12B expedition in 2021. We also discussed the variations in the characteristics of manganese nodules with varying water depths in the Arctic Sea. The sizes of the nodules are generally greater than 3 cm at both sites. However, there is an obvious difference in the morphology with water depths. For the nodules collected at 150 m, brown-black colored tabular, tube, and ellipsoidal shapes with a rough surface texture are dominant. On the other hand, yellow-brown tabular shapes with a smooth surface texture are common for the nodules collected at 73 m. Furthermore, the slope of trend line between size and weight is significantly different at both sites: particularly, the slopes of nodules at 150 and 73 m are 1.60 and 0.84, respectively. This indicates the difference in the internal structure, porosity, and constituting elements between both nodules. Micro X-ray Flourescence (µ-XRF) results clearly demonstrate that the internal textures and chemical compositions are different with water depths. The nodules at 150 m are composed of a thick Mn-layer and a thin Fe-layer centered on the nucleus, while the nodules at 73 m are alternately grown with thin Mn- and Fe- layers around the nucleus. The average chemical compositions obtained by µ-XRF are 40.6 wt% Mn, 5.2 wt% Fe, and 7.9 Mn/Fe ratio at 150 m, and 10.3 wt% Mn, 19.0 wt% Fe, and 0.6 Mn/Fe ratio at 73 m. The chemical compositions of the nodules at 150 m are similar to those of nodules from the Peru Basin in the Pacific Ocean, while the compositions of the nodules at 73 m are similar to those of nodules from the Cook Islands or the Baltic Sea. The observed morphological and geochemical characteristics of the nodules show a clear difference at the two sites, which indicates that the aqueous conditions and formation processes of the nodules in the Arctic Sea vary with the water depths.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.13 no.3
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• pp.168-177
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• 2008

Trafficablility of a miner and potential environmental impacts due to mining activities should be considered in the selection of a commercial manganese nodule mining site. These two factors can be evaluated comparatively with physical properties and shear strength of sea-bed sediments. For the qualitative comparison of potential minig sites in terms of these two factors, physical properties such as water contents, void ratios, porosities, and grain densities, and shear strengths of surface sediments were determined for the three potential manganese nodule mining sites(KR1, KR2, and KR5) in the Korean manganese nodule contract area, northeast Pacific. For the study, sediment samples were collected from 107 stations from 2004 to 2006. The physical properties of surface sediments showed more significant differences between northern(KR1, KR2) and southern(KR5) blocks than between northern blocks(KR1 vs. KR2). Water content, void ratio, and porosity of sediments from KR5 were relatively higher than those from KR1 and KR2. Grain density of sediments from KR5 was relatively lower than those from KR1 and KR2. Shear strengths of the top 10cm sediments were higher in KR1 and KR2, whereas those of the deeper part were highest in KR5 block. Generally, sediments of high water contents are less suspendible than those of the low water contents by benthic disturbances, thus less disturbance is expected in the sediments of high water content by mining activities. In terms of trafficability, the shear strength of sediment below 10 cm deep is more important than shallower part because miner will disturb at least top 10 cm interval of the surface sediments. Base on these results, we conclude that KR5 area will be the best site for commercial mining among three investigated sites in this study.

• The Korean Journal of Mycology
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• v.7 no.1
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• pp.13-73
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• 1979

These studies were conducted to investigate nutrient sources and supplementary materials of synthetic compost media for Agaricus bisporus culture. Investigation were carried out to establish the optimum composition for compost of Agaricus bisporus methods of out-door fermentation and peakheating with rice straw as the main substrate of the media. The incidence and flora of harmful organisms in rice straw compost and their control were also studied. 1. When rice straw was used as the main substrate in synthetic compost as a carbon source. yields were remarkably high. Fermentation was more rapid than that of barley straw or wheat straw, and the total nitrogen content was high in rice straw compost. 2. Since the morphological and physico-chemical nature of Japonica and Indica types of rice straw are greatly dissimilar. there were apparent differences in the process of compost fermentation. Fermentation of Indica type straw proceeded more rapidly with a shortening the compost period, reducing the water supply, and required adding of supplementary materials for producing stable physical conditions. 3. Use of barley straw compost resulted in a smaller crop compared with rice straw. but when a 50%, barley straw and 50% rice straw mixture was used, the yield was almost the same as that using only rice straw. 4. There were extremely high positive correlations between yield of Agaricus bisporus and the total nitrogen, organic nitrogen, amino acids, amides and amino sugar nitrogen content of compost. The mycerial growth and fruit body formation were severely inhibited by ammonium nitrogen. 5. When rice straw was used as the main substrate for compost media, urea was the most suitable source of nitrogen. Poor results were obtained with calcium cyanamide and ammonium sulfate. When urea was applied three separate times, nitrogen loss during composting was decreased and the total nitrogen content of compost was increased. 6. The supplementation of organic nutrient activated compost fermentation and increased yield of Agaricus bisporus. The best sources of organic nutrients were: perilla meal, sesame meal, wheat bran and poultry manure, etc. 7. Soybean meal, tobacco powder and glutamic acid fermentation by-products which were industrial wastes, could be substituted for perilla meal, sesame meal and wheat bran as organic nutrient sources for compost media. B. When gypsum and zeolite were added to rice straw. physical deterioration of compost due to excess moisture and caramelization was observed. The Indica type of straw was more remarkable in increase of yield of Agricus bisporus by addition of supplementing materials than Japonica straw. 9. For preparing rice straw compost, the best mixture was prepared by 10% poultry manure, 5% perilla meal, 1. 2 to 1. 5% urea and 1% gypsum. At spring cropping, it was good to add rice bran to accelerate heat generation of the compost heap. 10. There was significantly high positive correlation (r=0.97) between accumulated temperature and the decomposition degree of compost during outdoor composting. The yield was highest at accumulated temperatures between 900 and $1,000^{\circ}C$. 11. Prolonging the composting period brought about an increase in decomposition degree and total nitrogen content, but a decrease in ammonium nitrogen. In the spring the suitable period of composting was 20 to 25 days. and about 15 days in autumn. For those periods, the degree of decomposition was 19 to 24%. 12. Compactness of wet compost at filling caused an increase in the residual ammonium nitrogen. methane and organic acid during peak heating. There was negative correlation between methane content and yield (r=0.76)and the same was true between volatile organic acid and yield (r=0.73). 13. In compost with a moisture content range between 69 to 80% at filling. the higher the moisture content, the lower the yield (r=0.78). This result was attributed to a reduction in the porosity of compost at filling the beds. The optimum porosity for good fermentation was between 41 and 53%. 14. Peak heating of the compost was essential for the prevention of harmful microorganisms and insect pests. and for the removal of excess ammonia. It was necessary to continue fer mentatiion for four days after peak heating. 15. Ten species of fungi which are harmful or competitive to Agaricus bisporus were identified from the rice compost, including Diehliomyces microsporus, Trichoderma sp. and Stysanus stemoites. The frequency of occurrance was notably high with serious damage to Agaricus bisporus. 16. Diehliomyces microsporus could be controlled by temperature adjustment of the growing room and by fumigating the compost and the house with Basamid and Vapam. Trichoderma was prevented by the use of Bavistin and Benomyl. 17. Four species of nematodes and five species of mites occured in compost during out-door composting. These orgnanisms could be controlled through peakheating compost for 6 hours at $60^{\circ}C$.