• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.8
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• pp.749-754
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• 2008

A large number of studies on the various characteristics of epoxy-layered silicate nanocomposites, such as electric and mechanical, morphology have been conducted and contributed to improve their characteristics. However, studies on the effects of its thermal conductivities in the thermal properties are not enough, even though there are some excellent evaluations for its insulation performances. Thermal properties will cause thermal degradation and significantly affect the reliability of these epoxy-layered silicate nanocomposites. In the results of the analysis of epoxy-layered silicate nanocomposites $T_g$ for various types of organoclays (10A, 15A, 20A, 30B, and 93A), it showed an excellent thermal property of 10A. Also, it represented low values in storage modulus and mechanical Tan (Delta) at a high temperature section 140$^{\circ}C$ and excellent thermal properties due to its movement to the high temperature section in the case of the property of 10A in the measurement of DMA elastics and mechanical losses. In the results of the measurement of thermal conductivities, power ultrasonic applications represented a significant increase in thermal conductivities in the case of the applications of power ultrasonic and planetary centrifugal mixers. Based on these results, it is necessary to perform related studies because it can be applied as useful materials for future power facilities applications in mold and impregnate insulation.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.34 no.5
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• pp.314-320
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• 2021

Controlling ambient humid condition through high performance humidity sensors has become important for various fields, including industrial process, food storage, and the preservation of historic remains. Although aerosol deposited humidity sensors using ceramic BaTiO₃ (BT) material have been widely studied because of their longtime stability, there remain critical disadvantages, such as low sensitivity, low linearity, and slow response/recovery time in case of the sensors fabricated at room temperature. To achieve superior humidity sensing properties even at room temperature condition, BT-Cu composite films utilizing aerosol deposition (AD) process have been proposed based on the percolation theory. The BT-Cu composite films showed gradually improved sensing properties until the Cu concentration reached 15 wt% in the composite film. However, the excessive Cu (above 30 wt%) containing BT-Cu composite films showed a rapid decrease of the sensing properties. The results of observed surface morphology of the AD fabricated composite films, to figure out the metal filler effect, showed correlation between surface topography as well as size and the amount of open pores according to the metal filler content. Overall, it is very important not only dielectric constant of the humidity sensing films but also microstructures, because they affect either the variation range of capacitance by ambient humidity or adsorption/desorption of ambient humidity onto/from the humidity sensing films.

• Design & Manufacturing
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• v.10 no.2
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• pp.18-23
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• 2016

Injection molded thermoplastic parts may need to be coated to facilitate paint adhesion, or to satisfy other surface property requirements, such as appearance, durability, and weather resistance. In this paper, a two-component polyurethane metering system was developed for the simultaneous injection and surface coating of a plastic substrate. The system was composed of storage tanks, feed pumps, axial piston pumps, mixing head. The tank was designed to be double-jacket structured and fabricated for polyol and isocyanate, respectively. A temperature chamber was used to maintain the material temperature to be $80^{\circ}C$ during flowing from storage tank to mixing head. Inside the chamber, feed pump, low pressure filter, high pressure pump, high pressure filter, pressure sensor, flow meter were installed. A mixing head of L-type was used for homogeneous mixing of polyol and isocyanate. Inside the mixing head, a cartridge heater and a temperature sensor were installed to control the temperature of the materials. The flow rate of axial-piston pump was controlled by using closed-loop feedback control algorithm. The input flow-rates were compared with the measured values. The output error was 6.7% for open-loop control, whereas the error was below 2.2% for closed-loop control. In addition, the pressure generated through mixing-head nozzle increased with increasing flow rate. It was found that the pressure drop between metering pump and mixing-head nozzle was almost 10 bar.

• Journal of the Korean Applied Science and Technology
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• v.40 no.5
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• pp.1065-1071
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• 2023

This study compared antioxidant activity through DPPH radical scavenging activity of broccoli extract, low temperature (5℃ or less), and high temperature (50℃ or higher) storage conditions. As a result of the experiment, high DPPH radical scavenging activity of 95.5% was confirmed at 1% concentration of broccoli extract, and antioxidant power was maintained at a high level even under storage conditions due to temperature changes. Even cream containing 5% broccoli extract has been confirmed to maintain safety and stability in both preparation stability, discoloration and odor change, pH, and primary adhesion tests. Through these studies, it has been confirmed that broccoli extract is a safe and effective cosmetic material for the skin through high antioxidant activity and antioxidant power maintenance due to temperature changes.

• Journal of Pharmaceutical Investigation
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• v.6 no.1
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• pp.26-32
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• 1976

Dicalcium phosphate dihydrate (DCPD) is the most widely-used dentifrice abrasive in non-therapeutic tooth-paste requiring, low abrasive level, high stability and excellent compatibility with other formulation ingredients. One of the difficulties encountered in the use of this material in tooth-paste is that unless storage of the product is maintained at a relative low temperature there is a distinct tendency to lose water of crystallization. Another difficulty which has been encountered is that there is a tendency for the product to become lumpy. Various means have been proposed for increasing the stability and overcoming the lumping tendency, most of which means comprise the addition of stabilizing agent. But there is not any report about the relationships between the mechanism of dehydration, physical properties, structure and manufacturing condition. In this experiment, DCPD were manufactured by methods of Moss' patent, its two varied and J.P.VIII, these were studied by means of stability test, IR spectra, and DTA. According to the manufacturing conditions, DCPD has different physical properties and structures, i. e., monoclinic system of low drying temperature, triclinic system of high drying temperature. Dehydration of DCPD may be supposed one step debydration at about $100^{\circ}$ and it finaly converts to ${\gamma}-pyrophosphate$ at about $465^{\circ}$ and if the drying temperature is high it becomes DCP anhydrous. DCPD made by Moss' patent is thought of the best polishing agent of tooth-paste.

• Food Science and Preservation
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• v.13 no.1
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• pp.8-12
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• 2006

The effects of packaging treatments with either low density polyethylene (LDPE) or polypropylene (PP) films on the quality of leaf lettuce were evaluated. It was also stored within a plastic bag (LDPE and PP films) with 4 pelf orated holes (6mm diameter). Changes in weight loss, color difference, anthocyanin, chlorophyll, water content, and general appearance (shape of lettuce) ware investigated Total weight of leaf lettuce packaged within non-pelf orated films decreased slowly over the storage periods at 5 and $20^{\circ}C$. The weight loss of leaf lettuce showed no significant difference between non-pelf orated and perforated films at $20^{\circ}C$. General appearance in leaf lettuce stored at $20^{\circ}C$ was not significantly affected by packaging treatments with LDPE and PP films. The shelf life of non-packaged leaf lettuce at $5^{\circ}C$ was 8 days, whereas packaging treatments with LDPE and PP films showed freshness in leaf lettuce for 30 days of storage. Total chlorophyll and water contents of leaf lettuce packaged within pelf orated and non-pelf orated films decreased gradually during storage. However, no remarkable changes in color difference, levels of chlorophyll and anthocyanin, and water contents were observed in leaf lettuce packaged within perforated and non-pelf orated films. In this experiment, leaf lettuce packaged within LDPE or PP films without any punching holes at $5^{\circ}C$ was the most desirable for extending the quality. These results suggest that non-pelf orated packaging treatment in combination with low storage temperature could be effective in prolonging the shelf life of leaf lettuce

• Corrosion Science and Technology
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• v.11 no.6
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• pp.280-285
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• 2012

Aluminum is on active metal, but it is well known that its oxide film plays a role as protective barrier which is comparatively stable in air and neutral aqueous solution. Thus, aluminum alloys have been widely applied in architectural trim, cold & hot-water storage vessels and piping etc., furthermore, the aluminum alloy of AC8A have been widely used in mold casting material of engine piston because of its properties of temperature and wear resistance. In recent years, the oil price is getting higher and higher, thus the using of low quality oil has been significantly increased in engines of ship and vehicle. Therefore it is considered that evaluation of corrosion resistance as well as wear resistance of AC8A material is also important to improve its property and prolong its lifetime. In this study, the effect of solution and tempering heat treatment to corrosion and wear resistance is investigated with electrochemical method and measurement of hardness. The hardness decreased with solution heat treatment compared to mold casting condition, but its value increased with tempering heat treatment and exhibited the highest value of hardness with tempering heat treatment temperature at $190^{\circ}C$ for 24hrs. Furthermore, corrosion resistance increased with decreasing of the hardness, and decreased with increasing of the hardness reversely. As a result, it is suggested that the optimum heat treatment to improve both corrosion and wear resistance is tempering heat treatment temperature at $190^{\circ}C$ for 16hrs.

• Mass Spectrometry Letters
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• v.8 no.3
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• pp.59-64
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• 2017

In clinical diagnosis, it's well known that the abnormal level of uric acid (UA) in human body is implicated in diverse human diseases, for instance, chronic heart failure, gouty arthritis, diabetes, and so on. As a primary method, an isotope dilution mass spectrometry (IDMS) has been used to obtain the accurate quantity of UA in blood or serum and also develop the certificated reference material (CRM) so as to provide a SI-traceability to clinical laboratories. Due to the low solubility of UA in water, an ammonium hydroxide ($NH_4OH$) has been considered as a promising solvent to increase the solubility of UA that enables the preparation of both UA and its isotope standard solution for next IDMS-based absolute quantification. But, because of using this $NH_4OH$ solvent, it gives rise to the unwanted degradation of UA. In this study, we sought to optimize condition for the stability of UA in $NH_4OH$ solution by varying the mole ratios of UA to $NH_4OH$, followed by ID-LC-MRM analysis. In addition, we also inspected minutely the effect of the storage temperatures. Additionally, we also performed the quantitative analysis of UA in the KRISS serum certificated reference material (CRM, 111-01-02A) with diverse mixing ratios of UA to $NH_4OH$ and then compared those values to its certification value. Based on our experiments, adjusting the mole ratio of 1/2 ($UA/NH_4OH$) with the storage temperature of $-20^{\circ}C$ is an effective way to secure both the solubility and stability of UA in $NH_4OH$ solution for next IDMS-based quantification of UA in serum.

• Korean Journal of Chemical Engineering
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• v.35 no.11
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• pp.2220-2231
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• 2018

Lipase from Candida rugosa was immobilized on $MgO{\cdot}SiO_2$ hybrid grafted with amine, thiol, cyano, phenyl, epoxy and carbonyl groups. The products were analyzed using Fourier transform infrared spectroscopy, nuclear magnetic resonance, low-temperature $N_2$ sorption and elemental analysis. Additionally, the degree of coverage of the oxide material surface with different functional groups and the number of surface functional groups were estimated. The Bradford method was used to determine the quantity of immobilized enzyme. The largest quantity of enzyme (25-28 mg/g) was immobilized on the hybrid functionalized with amine and carbonyl groups. On the basis of hydrolysis reaction of p-nitrophenyl palmitate to p-nitrophenol, it was determined how the catalytic activity of the obtained biocatalysts is affected by pH, temperature, storage time, and repeated reaction cycles. The best results for catalytic activity were obtained for the lipase immobilized on $MgO{\cdot}SiO_2$ hybrids with amine and carbonyl groups. The biocatalytic system demonstrated activity above 40% in the pH range 4-10 and in the temperature range $30-70^{\circ}C$. Lipase immobilized on the $MgO{\cdot}SiO_2$ systems with amine and epoxy groups retains, respectively, around 80% and 60% of its initial activity after 30 days of storage, and approximately 60-70% after 10 reaction cycles.

• Transactions on Electrical and Electronic Materials
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• v.15 no.5
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• pp.265-269
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• 2014

Carbon nanofiber electrode has been fabricated for energy storage systems by the electrospinning of SU-8 precursor and subsequent pyrolysis. Various parameters including the applied voltage, the distance between syringe tip and target collector and the flow rate of the polymer affect the diameter of SU-8 electrospun nanofibers. Shrinkage during pyrolysis decreases the fiber diameter. As the pyrolysis temperature increases, the resistivity decreases dramatically. Low resistivity is one of the important characteristics of the electrodes of an energy storage device. Given the advantages of carbon nanofibers having high external surface area, electrical conductivity, and lithium intercalation ability, SU-8 derived carbon nanofibers were applied to the anode of a full lithium ion cell. In this paper, we studied the physical properties of carbon fiber electrode by scanning transmission microscopy, thermal gravimetric analysis, and four-point probe. The electrochemical characteristics of the electrode were investigated by cyclic voltammogram and electrochemical impedance spectroscopy plots.