• Journal of the Korean Institute of Gas
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• v.25 no.5
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• pp.11-18
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• 2021

Since hydrogen has the lower minimum ignition energy than that of gasoline, hydrogen could be also appropriate for the IC engine systems. However, due to the low ignition energy, there might be a 'back-fire' and 'pre-ignition' problems with hydrogen SI(Spark-ignition) combustion. In this research, cooling effects of intake gas mixture on the improvement of the maximum power output were evaluated in a 2.4 L SI engine. There were two ways to cool intake gas mixtures. The first one was cooling intake fresh air by adjusting inter-cooler system after turbocharger. The other one was cooling hydrogen fuel before supplying by using heat ex-changer. Cooling hydrogen was performed under natural aspired condition. The result showed that cooling fresh air from 40 ℃ to 20~30 ℃ improved the maximum brake power up to 6.5~8.6 % and cooling hydrogen fuel as -6 ℃ enhanced the maximum brake power likewise.

• Journal of Conservation Science
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• v.35 no.3
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• pp.227-235
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• 2019

In Korea, various methods are applied to prevent wooden structures from being damaged by termites. However, since there is no way to quickly bring toxic substances in contact with the termites inside the timber, it leads to the damage of wooden cultural property due to the prolonged period of controlling the termites. Accordingly, an indoor evaluation criteria study was conducted for the introduction of powder-type termiticides in Korea, which produced rapid control effects by drilling wood and directly contacting and transferring toxic substances inside the timber. First, contact toxicity and transfer ability of termite dusts were evaluated to establish the criteria for evaluation of effectiveness against Reticulitermes speratus. The contact toxicity confirmed 100% mortality of fipronil, deltamethrin and cyfluthrin termite dusts within 24 h of contact; however, differences occurred in the active ingredient transfer time to the sublethal. In addition, in the case of transfer ability evaluation, the rate of mortality gradually decreased under 1:9 and 1:25 ratio conditions; however, the difference in the reduction rate was identified depending on the type of termite dust. the results of the evaluation of compressive strength of the wood showed that the difference in the measured values between the control group and the conditions of perforation 1 to 3 times, which does not significantly affect the compressive strength of wood. In this study, the criteria of termite dust selection and evaluation method of dust-type termiticides were presented and the applicability of the method was identified.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.12
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• pp.258-264
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• 2018

In this study, the improved performance of sprayed green soil was evaluated by incorporating functional additives. The optimal mixing ratio of the thickener and super-absorbent polymer, as an additive for moisture supply to the growth of plants within the range of mixing ratios that gives sufficient strength of green soil, was 5% and 1%, respectively. Using Portland cement as a main binder, the pH of the green soil was 9.1. To solve this alkali problem, the mixing proportion was improved so that the pH of the green soil was approximately 7.2 by mixing more than 10% of the chelate resin. The soil conductivity was measured to be 280 ~ 350mS/m under all the mixing conditions. This satisfied the criterion of less than 1000mS/m on the slope surface. As a result of measuring the soil hardness of the green soil prepared under the optimal mixing conditions of functional additives, it satisfied the criteria of 18 ~ 23mm when sprayed under a 1 bar pressure. The rebound rate was less than 15% when spraying green soil on a 75 % slope, and the hardness of the sprayed green soil was more than 18 mm.

• Journal of the Korea Organic Resources Recycling Association
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• v.31 no.3
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• pp.35-41
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• 2023

In this study, silicon sludge generated in semiconductor manufacturing process is recycled and applied as materials for pigments and paints. In detail, metallic impurities are removed from silicon sludge to obtain plate-like silicon sludge powder (SW-sludge), which is then coated with titanium dioxide via sol-gel method (TCS-sludge). SW-sludge and TCS-sludge are dispersed in hydrophilic transparent varnish and sprayed onto glass substrates to observe the possibility for the application as materials for pigments and paints. Notably, the applicability of TCS-sludge-based paint is improved compared to SW-sludge-based paint after the titanium dioxide coating. Moreover, the color of TCS-sludge-based paint turns into white. Accordingly, it is confirmed that the applicability and hydrophilicity are improved by the presence of outer titanium dioxide layer. In this regard, it is expected that the recycled TCS-sludge may be a future material for the application as pigments and paints.

• Korean Journal of Ecology and Environment
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• v.36 no.3 s.104
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• pp.356-368
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• 2003

Water quality of effluent from wastewater treatment plants (WWTPS) was reviewed to examine the feasibility of agricultural reuse using USEPA and WHO guidelines. It might meet the guidelines for BOD and SS, however, the most critical microbiological concentration was too high and further treatment is required. The pilot study of three treatments were performed to reduce microbiological concentrations. The UV irradiation was proved to be very effective in disinfection of secondary level effluent, and about 30 mW ${\cdot}$ s/$cm^2$ of dose was suggested to meet the even most stringent USEPA guidelines. Slow sand filter demonstrated effective removal of bacteria, and effluent concentration of total coliform (TC), fecal coliform (FC), and E. coli. dropped from about 10,000/100 mL to 300, 200, and 150 MPN/100 mL, respectively, showing over 95% removal. These level of bacterial concentration sufficiently meet the WHO guidelines ($10^3\;{\sim}\;10^5$ FC/100 mL), and could meet the more stringent USEPA guidelines (200 FC/100 mL) if properly applied. Slow sand filter also provided about 50% removal of SS, turbidity, and BOD in addition to bacterial removal. The removal efficiency of pond system was relatively poor, but still showed over 85% removal and effluent concentration of TC, FC, and E. coli was all below 10,000/100 mL. The pond system alone could meet the WHO guidelines, but hardly meet the USEPA guidelines and further treatment might be necessary. Overall, three methods evaluated in the study treat the effluent to meet the WHO microbiological guidelines for agricultural reuse. The UV disinfection and slow sand filter might also could the USEPA guidelines, while the pond system can hardly meet the USEPA guidelines if applied alone. The WHO and USEPA guidelines were made based on data from upland field agricultural system and may not be directly applicable to the paddy field agricultural system. Therefore, national standards for agricultural reuse of reclaimed water should be made considering domestic agricultural systems as well as international guidelines. Also, further investigation is recommended to develop optimum and feasible treatment measures for agricultural reuse of effluent from WWTPs.

• The Journal of Korean Academy of Prosthodontics
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• v.51 no.3
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• pp.167-174
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• 2013

Purpose: This study was conducted to evaluate the roughness and surface alternations of three differently blasted titanium discs treated by $Nd:YVO_4$ Laser irradiation in different conditions. Materials and methods: Thirty commercially pure titanium discs were prepared and divided into three groups. Each group was consisted of 10 samples and blasted by $ZrO_2$ (zirconium dioxide), $Al_2O_3$ (aluminum oxide), and RBM (resorbable blasted media). All the samples were degreased by ultrasonic cleaner afterward. Nine different conditions were established by changing scanning speed (100, 300, 500 mm/s) and repetition rate (5, 15, 35 kHz) of $Nd:YVO_4$ Laser (Laser Pro D-20, Laserval $Korea^{(R)}$, Seoul, South Korea). After laser irradiation, a scanning electron microscope, X-ray diffraction analysis, energy dispersive X-ray spectroscopic analysis, and surface roughness analysis were used to assess the roughness and surface alternations of the samples. Results: According to a scanning electron microscope (SEM), titanium discs treated with laser irradiation showed characteristic patterns in contrast to the control which showed irregular patterns. According to the X-ray diffraction analysis, only $Al_2O_3$ group showed its own peak. The oxidation tendency and surface roughness of titanium were similar to the control in the energy dispersive X-ray spectroscopic analysis. The surface roughness was inversely proportional to the scanning speed, whereas proportional to the repetition rate of $Nd:YVO_4$. Conclusion: The surface microstructures and roughness of the test discs were modified by the radiation of $Nd:YVO_4$ laser. Therefore, laser irradiation could be considered one of the methods to modify implant surfaces for the enhancement of osseointegration.

• Korean Journal of Environmental Agriculture
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• v.34 no.2
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• pp.134-138
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• 2015

BACKGROUND: In recent years, several researchers have focused on odour control methods to remove the harmful chemicals from chemical accidents and incidents. The present work deals with the system development of the hazardous. METHODS AND RESULTS: For on-site removal of hazardous gaseous materials from chemical accidents, mobile vortex wet scrubber was designed with water vortex process to absorb the gas into the water. The efficiency of the mobile vortex wet scrubber was evaluated using water spray and 25% ammonia solution. The inlet air velocity (gas flow rate) was according to the damper angle installed within the hood and with increase of gas flow rate, consequently the absorption efficiency was markedly decreased. In particular, when 25% ammonia solution was exposed to the hood inlet for 30 min, the water pH within the scrubber was changed from 7 to 12. Interestingly, although the removal efficiency of ammonia gas exhibited approximately 80% for 5 min, its efficiency in 10 min showed the greatest decrease with 18%. Therefore, our results suggest that the ammonia gas may be absorbed with the driving force of scrubbing water in water vortex process of this scrubber. CONCLUSION: When chemical accidents are occurred, the designed compact scrubber may be utilized as effective tool regarding removal of ammonia gas and other volatile organic compounds in the scene of an accident.

• The Journal of Korean Academy of Prosthodontics
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• v.53 no.4
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• pp.295-300
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• 2015

Purpose: The aim of this study was to evaluate the shear bond strength between Ni-Cr alloy and composite resin using universal adhesive systems coMPared to conventional method using metal primers. Materials and methods: For this study, a total of 120 cast commercial Ni-Cr alloy (Vera Bond 2V) disks were embedded in acrylic resin, and their surfaces were smoothed with silicon carbide papers and airborne-particle abrasion. Specimens of each metal were divided into 6 groups based on the combination of metal primers (Metal primer II, Alloy primer, Metal & Zirconia primer, MKZ primer) and universal adhesive systems (Single Bond Universal, All Bond Universal). All specimens were stored in distilled water at $37^{\circ}C$ for 24 hours. Shear bond strength testing was performed with a universal testing machine at a cross head speed of 1 m/min. Data (MPa) were analyzed using one-way ANOVA and the post hoc Tukey's multiple comparison test (${\alpha}$=.05). Results: There were significant differences between Single Bond Universal, All Bond Universal, Metal Primer II and Alloy Primer, MKZ Primer, Metal & Zirconia Primer (P<.001). Conclusion: Universal Adhesive system groups indicated high shear bond strength value bonded to Ni-Cr alloy than that of conventional system groups using primers except Metal Primer II. Within the limitations of this study, improvement of universal adhesive systems which can be applied to all types of restorations is recommended especially non-precious metal alloy. More research is needed to evaluate the effect of silane inclusion or exclusion in universal adhesive systems.