• Journal of Adhesion and Interface
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• v.24 no.4
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• pp.124-130
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• 2023

For automotive coating agents that require little change in characteristics due to changes in external temperature, changes in noise characteristics due to changes in the external environment are very important. Therefore, soft polyurethane with excellent cold resistance, weather resistance, and abrasion resistance, and polysiloxane whose -OH terminated and side chains are modified with amines, are widely used. In this study, coating agents was prepared by adding water-born polyurethane, polysiloxane, ultra high molecular weight polypropylene (UHMWPP) powder, carbon black, and a matting agent to determine the effect of each resin component on noise. To study the effect of each resin component on noise, a coating agent was prepared by adding water-born polyurethane, polysiloxane, UHMWPP powder, carbon black, and a matting agent. The hard/soft segment ratio of water-born polyurethane, the main component of the coating, was 27.1%/72.9%, and the ratio of amino siloxanes to hydroxy-terminated polysiloxane was 2:7, which produced the least noise. The difference in friction coefficient was large when the friction body moves at high speed. When UHMWPP powder replaced SiO₂, noise decreased and gloss also decreased.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.1894-1899
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• 2007

This paper presents the thermal characteristics for micro heat exchanger with different micro-channel shapes. The shapes of micro-channel has been manufactured sheet metal by chemical etching for the I shape of straight channel and V and W shapes of chevron feature and fabricated micro plated heat exchangers using the vacuum brazing of bonding technology. The experimental study has been performed on heat transfer and pressure drop characteristics with various Reynolds number for water to water at the counter flows. The average heat transfer rate of V and W shapes has been showed about 1.5${\sim}$1.6 times large than those of I shape. For the comparison of Nusselt number, it is known that the convective heat transfer of V and W shapes represent more effect than I shape. The pressure drops of V and W shapes are about 1.2${\sim}$1.7 times lager than those of I shape.

• Tribology and Lubricants
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• v.20 no.5
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• pp.237-244
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• 2004

Micro/nano tribological characteristics of PTFE coating films were experimentally studied. PTFE (polytetrafluoroethylene) modified polyethylene and low molecular weight PTFE were used as a coating materials. These films were deposited on Si-wafer (100) by IBAD (ion beam assisted deposition) method. The Ar ion beam sputtering was performed to change the surface topography of films using a hollow cathode ion gun under different Ar ion dose conditions in a vacuum chamber. Micro/nano tribological characteristics, water wetting angles and roughness were measured with a micro tribotester, SPM (scanning probe microscope), contact anglemeter and profilometer, respectively. The durability of the films were measured with macro tribotester. Results showed that the PTFE coating surfaces were converted to hydrophobic. The water contact angle of coated surfaces and surface roughness increased with the coating thickness. Adhesion and friction in micro and nano scale were governed by magnitude of normal load in soft material such as PTFE films. As the increase of sputtering time on low molecular weight PTFE films, the surface roughness was increased and nano adhesion and friction were decreased. The nano tribological characteristics of surfaces are mainly improved by chemical modification such as PTFE coating and given a synergy effect by the physical modification such as topographic modification.

• Korean Chemical Engineering Research
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• v.47 no.1
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• pp.59-64
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• 2009

This study investigated the surface characteristics of polylactic acid (PLA) film after one atmospheric pressure plasma treatment. We used de-ionized water and diiodomethane as polar and non-polar solvents, respectively, for measuring contact angles, and subsequently calculated the surface free energy of PLA film. The contact angle and free energy of PLA surface were optimized at the treatment time of 30 sec, RF-power of 70 W, Ar gas flow rate of 6 lpm and air exposure time of 5 min. We analyzed the change of chemical functional groups on the surface of PLA film through XPS and were able to observe the change of polar functional groups such as -C=O, -CO, -COO on the surface of PLA film after one atmospheric pressure plasma treatment.

• Transactions of the Korean hydrogen and new energy society
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• v.20 no.4
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• pp.323-330
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• 2009

Efficiency of a fuel cell is determined by the generated water. If water is not removed sufficiently, water will be accumulated at GDL, which causes flooding. Therefore, water control is regarded as a crucial factor to sustain fuel ell performance. In this study, PTFE coating on the surface of carbon paper was carried out to establish optimum process for hydrophobic treatment of GDL. Carbon paper was immersed at different concentrations of nano-sized PTFE coating solution. Their characteristics were analyzed systematically by FE-SEM, water contact angle, cyclic voltamogam, XRD and FT-IR. The quantitative correlation between the amount of coated-PTFE on a carbon paper and concentration of coating solution was carefully investigated. It is suggested that the amount of PTFE-coating on a carbon paper can be managed by means of controling concentration of coating solution.

• Journal of Environmental Science International
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• v.15 no.5
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• pp.447-459
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• 2006

Long-term trends and distribution patterns of water quality were investigated in the Cheonsu Bay of Korea from 1983 to 2004. Water samples were collected at 4 stations and physicochemical parameters were analyzed including water temperature, salinity, suspended solids (SS), chemical oxygen demand (COD), dissolved oxygen (DO) and nutrients. Spatial distribution patterns were not clear between stations but the seasonal variations were distinctive except COD, SS and nitrate. Twenty two year long-term trend analysis by PCA revealed the significant changes in water quality in the study area. Water quality during 1980's and early 1990's showed high SS, low nutrients and low COD which increased during the mid and late 1990's and early 2000's. Overall water duality in the Cheonsu Bay indicated the increase in nutrients and COD concentration.

• Journal of the Korean Applied Science and Technology
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• v.25 no.3
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• pp.395-403
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• 2008

In this study, the characteristics of emulsified fuel were studied. The emulsified fuel which was composed of water and diesel was manufactured by using homogenizer and ultrasonic generator. The more the percentage of water contents increases, the more the density increases to the emulsified fuel. However, the viscosity increased in the 60% of water contents and decreased in the 70% of water contents because the O/W type was formed. The 3 minutes's ultrasonic waves during the irradiation time was appropriate of 16,000 rpm. And the energy density of ultrasonic waves was 87.5J/g. The emulsion stability has improved in the lower temperature, the lower percentage of water contents, and the most stable emulsion state was obtained from 20%(w/w) of water contents. Also, the emulsion stability was related to the HLB values of emulsifiers. Especially, the HLB values of emulsifier were appropriate from 4 to 7 values.

• Korean Journal of Ecology and Environment
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• v.43 no.2
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• pp.199-211
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• 2010

The objectives for this study were to evaluate spatial and temporal characteristics of water quality, based on long-term water quality monitoring data during 1993~2008. We found that physico-chemical and ecological conditions in the Daecheong Reservoir (DR) were modified by the construction of upper dam (i.e., Yongdam Reservoir). total phosphorus (TP), Secchi depth (SD), and chlorophyll-a (CHL) in the DR showed significant longitudinal decreases along the headwater-to-the downlake, indicating a large spatial variation, and this gradient was more intensified during the high-flow season (monsoon). Nutrient-rich water containing high nitrogen and phosphorus in the monsoon season (July~August) passed through the reservoir as a density current in the metalimnetic depth, and also high suspended solids increased in the metalimnetic depth, especially during the monsoon. According to the deviation analysis of Trophic State Index (TSI), >50% of TSI (CHL)-TSI (SD) and TSI (CHL)-TSI (TP) values were negatives, so that inorganic suspended solids (non-votatile solids) influenced the underwater light regime against phytoplankton growth. Also, ratios of CHL:TP after the dam construction evidently increased, compared to the values before the upper dam constructions, indicating a greater yield of phytoplankton in the unit phosphorus. Overall data showed that ecological and functional changes in Daecheong Reservoir occurred after the construction of upper dam (Yongdam Reservoir).

• Journal of the Korean Chemical Society
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• v.34 no.4
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• pp.377-383
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• 1990

Three kinds of hydrogel membranes were prepared by the copolymerization of 2-hydroxyethylmethacrylate (HEMA) with acrylamide, N, N-dimethylamide and methylmethacrylate in the presence of solvent and crosslinker respectively. The equilibrium water content, relative permeability and partition coefficient of the membranes for alcohol solutes were measured. It has been found that the permeation of organic solute occurs through the water-filled regions in the hydrogel membrane, and that the gpermeability coefficient of organic solute depends on the molecular size. But the permeability of organic solute was controlled by the interaction of solute-membrane at the low water content. By the partition data, it has been shown that the partition of solute is only controlled by hydrophobic interaction between solute and membrane. The diffusion coefficient data were interpreted on the basis of water-solute interaction. It has been found that the diffusion of organic solute is determined by the free volume of water in the membrane, and that hardly depends on polarity-polarizability and hydrogen bonding ability between water and solute.

• Horticulture, Environment, and Biotechnology : HEB
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• v.59 no.6
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• pp.847-856
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• 2018

This research aimed to evaluate the effectiveness of hot water ($43-53^{\circ}C{\cdot}5min^{-1}$; $47^{\circ}C{\cdot}2-6min^{-1}$), 1-methylcyclopropene (1-MCP) at $50-300nL\;L^{-1}$ and a combination of hot water ($47/49^{\circ}C{\cdot}5min^{-1}$) and phosphite $40%\;P_2O_5+20%\;K_2O$;$40%\;P_2O_5+10%\;Zn$) in anthracnose control and the effect on fruit quality [fresh weight loss (FWL-%); pH, total soluble solids ($TSS-^{\circ}Brix$), and titratable acidity (TA = % citric acid (CA)] of passion fruit ( Passiflora edulis f. flavicarpa ) at the postharvest stage. When the fruits were in the stage of 0% dehydration and fully yellow peels, they were disinfested and inoculated with Colletotrichum gloeosporioides. They were then subjected to the above mentioned treatments; this was followed by incubation for 120 h. The diameter of the disease lesions was monitored daily. After the incubation, a physico-chemical analysis was performed. Hot-water treatment resulted in disease reduction at 47 and $49^{\circ}C$ for 4 and 5 min. The combination of hot-water treatment at $47^{\circ}C$ (4 or 5 min) and application of the phosphite of K or Zn significantly reduced disease severity in fruits. The 1-MCP treatment reduced anthracnose severity in passion fruit mainly at $200nL\;L^{-1}{\cdot} 24h^{-1} $. None of the treatments significantly changed the physico-chemical characteristics of the fruit [FWL (2.6-4.1%); pH (3.2-3.5), TSS ($8.9-10.9^{\circ}Brix$), and TA (1.8-2.5% CA)].