• Polymer(Korea)
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• v.39 no.2
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• pp.323-328
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• 2015

Poly(${\varepsilon}$-caprolactone) (PCL) nanofibers and PCL/silica membranes were synthesized by sol-gel derived electrospinning and casting, respectively. Smooth PCL nanofibers were obtained from the precursor containing N,N-dimethylformamide (DMF). PCL/silica membranes were prepared by varying the tetraethyl orthosilicate (TEOS) contents from 0 to 40 vol% to investigate the effect of silica addition on mechanical properties and cytotoxicity of the membranes. Although the strength of the membranes decreased from 12 to 8 MPa with increasing the silica content, the strength remained almost constant 7 weeks after dipping in phosphate buffered saline solution (PBS). The strength reduction was attributed to the presence of a patterned surface pores and micro-pores present in the walls between pores. The crystal structure of the membranes was orthorhombic and the crystallite size decreased from 57 to 18 nm with increasing the silica content. From the agar overlay test, the PCL/silica membranes exhibited neither deformation and discoloration nor lysis of L-929 fibroblast cells.

• Membrane Journal
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• v.27 no.1
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• pp.1-42
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• 2017

Metal-organic frameworks (MOFs) are nanoporous materials that consist of organic and inorganic moieties, with well-defined crystalline lattices and pore structures. With a judicious choice of organic linkers present in the MOFs with different sizes and chemical groups, MOFs exhibit a wide variety of pore sizes and chemical/physical properties. This makes MOFs extremely attractive as novel membrane materials for gas separation applications. However, the synthesis of high-quality MOF thin films and membranes is quite challenging due to difficulties in controlling the heterogeneous nucleation/growth and achieving strong attachment of films on porous supports. Microwave-based synthesis technology has made tremendous progress in the last two decades and has been utilized to overcome some of these challenges associated with MOF membrane fabrication. The advantages of microwaves as opposed to conventional synthesis techniques for MOFs include shorter synthesis times, ability to achieve unique and complex structures and crystal size reductions. Here, we review the recent progress on the synthesis of MOF thin films and membranes with an emphasis on how microwaves have been utilized in the synthesis, improved properties achieved and gas separation performance of these films and membranes.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.03a
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• pp.16-16
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• 2010

GaN-based light-emitting diodes (LEDs) are attracting great interest as candidates for next-generation solid-state lighting, because of their long lifetime, small size, high efficacy, and low energy consumption. However, for general illumination applications, the external quantum efficiency of LEDs, determined by the internal quantum efficiency (IQE) and the light extraction efficiency, must be further increased. The IQE is determined by crystal quality and epitaxial layer structure and high value of IQE more than 70% for blue LEDs have been already reported. However, there is much room for improvement of light extraction efficiency because most of the generated photons from active layer remain inside LEDs by total internal reflection at the interface of semiconductor with air due to the high refractive index difference between LEDs epilayer (for GaN, n=2.5) and air (n=1). The light confining in LEDs will be reabsorbed by the metal electrode or active layer, reducing the efficacy of LEDs. Here, we present the first demonstration of enhanced light extraction by forming a MgO nano-pyramids structure on the surface of vertical-LEDs. The MgO nano-pyramids structure was successfully fabricated at room temperature using conventional electron-beam evaporation without any additional process. The nano-sized pyramids of MgO are formed on the surface during growth due to anisotropic characteristics between (111) and (200) plane of MgO. The ZnO layer with quarter-wavelength in thickness is inserted between GaN and MgO layers to increase the critical angle for total internal reflection, because the refractive index of ZnO (n=1.94) could be matched between GaN (n=2.5) and MgO (n=1.73). The MgO nano-pyramids structure and ZnO refractive-index modulation layer enhanced the light extraction efficiency ofV-LEDs with by 49%, comparing with the V-LEDs with a flat n-GaN surface. The angular-dependent emission intensity shows the enhanced light extraction through the side walls of V-LEDs as well as through the top surface of the n-GaN, because of the increase in critical angle for total internal reflection as well as light scattering at the MgO nano-pyramids surface.

• Journal of the Korean Society of Food Science and Nutrition
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• v.20 no.6
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• pp.629-636
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• 1991

Yellowtail fishes(Seriola quinqueeradiata) were submitted to the storages using ice-cooling($0^{\circ}C$), partial freezing($-3^{\circ}C$) and freezing $-20^{\circ}C$) method. Changes in the structures of muscle during storage at different temperatures were investigated. The ice-cooling and partial freezing storage caused early decomposition of glycogen granules and mitochondrial inner membrane, but it was accorded to much slower manner comparing with that of ice-cooling storage. The scars of ice crystals were appeared after three days of storage. The number and size of the crystal increased as progressing of the storage. They were circular and mostly located between fibers. When using the freezing storage, glycogen granules were mostly found from the muscle cell even after fourteen days of storage. Mitochonidral inner membrane maintained their integrity. The scars of ice crystals were also found, however, different from those of partial freezing storage. Their existing sites were random and their shapes were irregular. In many cases, they located in the fiber and had keen edges. Fibers were broken mostly at the Z-lines on fourteen days of storage. From these results, it was concluded that partial freezing storage can repress autolytic enzymic action and can reduce the physical damage from ice crystals which is caused by freezing.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.40 no.4
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• pp.164-170
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• 2017

The CNC machine tool field is showing a growing trend with the recent rapid development of manufacturing industries such as semiconductors, automobiles, medical devices, various inspection and test equipment, mechanical metal processing equipment, aircraft, shipbuilding and electronic equipment. However, small and medium-sized machining companies that use CNC machine tools are experiencing difficulties in increasingly intense competition. Especially, small companies which are receiving orders from 3rd or 4th venders are very difficult in business management. In recent years, company S experienced difficulty to make product quality and delivery time due to the ignorance of the processing method when manufacturing cooling plate jig made of SUS304 material used for cell phone liquid crystal glass processing. In order to solve these problems, we redesigned the process according to the size of our company and tried to manage all processes with quantified data. In the meantime, we have found that there is a need to improve the cutter process, which accounts for most of the machining process. Therefore, we have investigated the correlation between RPM and FEED of three cutters that have been used in the past. As a result, we found that it is the most urgent problem to solve the roughing process during the cutter operation which occupies more than 70% of the total machining. In order to shorten the machining time and improve the quality in machining of SUS304 cooling plate jig, we select the main factors such as price, tool life, maintenance cost, productivity, quality, RPM, and FEED and use AHP to find the most suitable milling cutter. We also tried to solve the problem of delivery, quality and production capacity which was a big problem of S company through experiment operation with selected cutter tool. As a result, the following conclusions were drawn. First, the most efficient of the three cutters currently available in the machining center has proven to be an M-cutter. Second, although one additional facility was required, it was possible to produce the existing facilities without additional investment by supplementing the lack of production capacity due to productivity improvement. Third, the Company's difficulties in delivery and capacity shortfalls have been resolved. Fourth, annual sales increased by KRW 109 million and profits increased by KRW 32 million annually. Fifth, it can confirm the usefulness of AHP method in corporate decision making and it can be utilized in various facility investment and process improvement in the future.

• Journal of the Korean Ceramic Society
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• v.38 no.12
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• pp.1097-1103
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• 2001

TiO$_2$anchored on a porous clay ceramic support (PCS) for use in lightweight photocatalyst were synthesized by the dropping precipitant method. A PCS of macro and micro pore size of around several mm~${\mu}{\textrm}{m}$ in diameter were prepared by the rapid heat treatment at, 1,15$0^{\circ}C$ for 10 min from low grade of clay. The change in pH of reaction solution due to the different addition rate of NH$_4$HCO$_3$as a precipitant, the reaction temperature and the concentration of TiCl$_4$had a pronounced effect on the nature of precipitated TiO$_2$particles on the surface of a PCS and the crystal structure of precipitated TiO$_2$particles. At an addition rate of 0.8 ml/min of NH$_4$HCO$_3$and pH=6 of reaction solution, homogeneous precipitation of TiO$_2$particles on a PCS was achieved. TiO$_2$particles with anatase phase was precipitated on the surface of a PCS at the low concentration of TiCl$_4$, the high addition rate of NH$_4$HCO$_3$and the high reaction temperature.

• Journal of the Korean Chemical Society
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• v.53 no.5
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• pp.553-559
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• 2009

One of zeolitic imidazolate framework materials (ZIF), ZIF-8, has been synthesized with microwave irradiation and conventional electric heating at $140{\sim}180^{\circ}C}$. ZIFs are porous crystalline materials and are similar to metal organic framework (MOF) materials because both ZIFs and MOFs are composed of both organic and metallic components. ZIFs are very stable and similar to zeolites because ZIFs have tetrahedral networks. ZIF-8, with a decreased crystal size, can be synthesized rapidly with microwave irradiation. The microwave synthesis of ZIF-8 is completed in 4 h at $140{^{\circ}C}$ and the reaction time is decreased by about 5 times compared with the conventional electric heating. The ZIF-8 obtained by microwave heating has larger surface area and micropore volume compared with the ZIF-8 synthesized with conventional electric heating. It can be confirmed that ZIF-8s show type-I adsorption isotherms, explaining the microporosity of the ZIF-8s. Based on FTIR and TGA results, it can be understood that the ZIF-8s have similar bonding and thermal characteristics irrespective of heating methods such as microwave and conventional heating.

• Clean Technology
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• v.20 no.4
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• pp.383-389
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• 2014

$CO_2$ absorption processes have a good potential for large scale capture of $CO_2$ but a large amount of absorbing solution has to be regenerated, undesirably increasing the consumption of energy such as sensible heat and latent heat of vaporization. In this study, a cooling crystallization process which would separate the $CO_2$-rich potassium bicarbonate crystals from $CO_2$-lean water was developed to reduce the energy penalty. Sterically hindered alkanolamine additives were used to enhance the $CO_2$ removal efficiency and their antisolvent effect on the crystallization was found in a continuous cooling crystallizer. The production yields of crystals were increased in the sequence of 2-amino-2-methyl-1-propanol (AMP) < 2-amino-2-methyl-1,3-propanediol (AMPD) < 2-amino-2-hydroxymethyl-1,3-propanediol (AHPD), which are related to the number of hydroxyl groups in the additive molecules. Using $^{13}carbon$ nuclear magnetic resonance, the additives favored the formation of bicarbonate ions by steric hindrance effect and increased the supersaturation of $KHCO_3$. It is shown that the additives increase the mean size of crystals and crystal growth rate by increasing supersaturation. The additives are promising for enhancing the $CO_2$ removal efficiency and reducing the regeneration energy cost of $CO_2$ absorbing solution by promoting $KHCO_3$ crystallization.

• Journal of the Korean Magnetics Society
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• v.18 no.3
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• pp.120-125
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• 2008

In this study, NiCoZn ferrites with the variation of sintering temperature and chemical composition were prepared by the coprecipitation. Microstructures Crystal structure of NiCoZn ferrites were analyzed by XRD and their electric magnetic characteristics were analyzed by LCR meter and their morphology observed by SEM. We identified that these powders have a typical NiCoZn spinel structure and nanoparticles average size of 40 nm. The impurity, the initial permeability and the Q factor value are the lowest of sintered NiCoZn ferrite at $1250^{\circ}C$. Also, we measured S-parameter for $(Ni_{0.4}Co_{0.1}Zn_{0.5})Fe_2O_4$ which showed a maximum reflection loss of -3.1 dB at 6 GHz for the 2 mm thick sample. From this result, we found that the NiCoZn ferrite can be used in ferrite microwave-absorbing application at a higher frequency region (> 6 GHz).

• Journal of the Society of Cosmetic Scientists of Korea
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• v.30 no.2
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• pp.279-294
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• 2004

This study described about a liquid crystalline technology that is used in cosmetics industry. Various intermediate phases may exist between solid and liquid. At high surfactant concentration, several liquid crystalline phases can be made to have formed. Although molecular arrangement with crystallization is not regular, it is known that more relative regular state is liquid crystalline or meso-phase than liquid phase. Usually, it described in detail about manufacturing method that explained about a kind of liquid crystalline technology in cosmetics, a new liquid crystalline technology, and makes liquid crystalline. Specialty, it introduced about kind of special an emulsifier to form liquid crystalline. There were hydrogenated lecithin, ceramide, dipalmitoylhydroxyproline, DEA-cetyl phosphate, Gemini-surfactant in representative raw material to form liquid crystalline. Liquid crystalline extent that used polarization microscope to observe formation, and appears best from 400times, 600times, 1,000times well appeared. Also, droplet particle size that liquid crystal is made best 1.0-10.0$\mu\textrm{m}$ be. General emulsion more than superior result that measures the skin moisturizing effect to take advantage of liquid crystalline technology of vitamin was seen. As presence at a clinical result, wave and general emulsion more than superior result (more than 20%) that measures skin moisturizing effect about liquid crystalline of vitamin B$\_$5/ were seen (ANOMA t-test, p<0.05)