• Journal of the Korean Ceramic Society
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• v.39 no.6
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• pp.528-534
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• 2002

CaO ceramics were prepared by conventional sintering process and their hydration behaviors were evaluated by measuring weight increment on saturated water vapor pressure at ambient temperature. CaCO$_3$ and limestone were used as CaO source materials and $Al_2$O$_3$, MgO and SiO$_2$ were added as sintering agents. $Al_2$O$_3$ was a liquid phase sintering agent to increase densification and grain growth rates, whereas MgO and SiO$_2$, densification and grain growth inhibitors. Regardless of composition, all of the prepared CaO ceramics showed the improved hydration resistance as bulk density increased. Especially, when bulk density was more than 3.0 g/㎤, there was no weight increment after 120 h of hydration. Therefore, to decrease contact area between CaO and water vapor by increasing bulk density with the $Al_2$O$_3$ sintering additive was effective for the improvement of CaO hydration resistance.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.13 no.2
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• pp.41-48
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• 2014

Direct writing(DW) is a method of patterning materials to a substrate directly, without a mask. It can use a variety of materials and be applied to various fields. Among DW systems, the flow-based type, using a syringe pump and nozzle, is simpler than other types. Furthermore, the range of materials is exceptionally wide. In additive processes, a three dimensional structure is made of stacking layer. Each layer is made of several lines. In this regard, good surface roughness of fabricated layers is essential to three dimensional fabrication. The surface roughness of any fabricated layer tends to change with the dispensing pattern. When multiple layers fabricated by a nozzle dispensing system are stacked, control of the nozzle position from the substrate is important in order to avoid interference between the nozzle and the fabricated layer. In this study, a fluid direct writing system for three dimensional structure fabrication was developed. Experimentsto control the position of the nozzle from substrate were conducted in order to examine the characteristics of the material used in this system.

• Journal of Microbiology and Biotechnology
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• v.8 no.3
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• pp.229-236
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• 1998

6-Substituted derivatives of 1-［(2-hydroxyethoxy)methyl］-6-(phenylthio)thymine (HEPT) were synthesized by introducing alkyl groups with the aid of chlorotrimethylsilane, and then purified ranging 40 to 81 % of yield. Because of their peculiar structures, we presumed that HEPT derivatives would contain extra biological activities other than their already known anti-human immunodeficiency viral (HIV -1) activities. In this study, we investigated the possible effects of the HEPT derivatives on bacterial growth and found their selective antibiotic activities against gram-positive strains. We could not observe the corresponding activity from a disc-zone test, but confirmed the activity by liquid cultivation. Since the growth rate of cells was easily recovered, the antibiotic function was suggested to be bacteriostatic. We also suggested that the intracellular fate of HEPT derivatives would be fast. A HEPT derivative f-3 was shown to synergize unidirectionally toward chloramphenicol (Chr). With 0.1 mM f-3, the Chr-directed growth-inhibitory curve appeared 4 hours earlier than found without the additive. Interestingly, from the data of SDS-polyacrylamide gel electrophoresis (PAGE), we found that a membrane-bound protein having a molecular weight of 70-kDa was overexpressed by f-3 in S. aureus.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.11a
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• pp.7-11
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• 2012

Plasma electrolytic oxidation of magnesium alloys is a well known technique to produce corrosion and wear resistant coatings. The addition of particles to the electrolyte provides a possibility to produce coatings with an increasing range of composition by in-situ incorporation of those particles into the coating. An extensive literature review has revealed that the mode of incorporation depends mainly on the melting point of the used particles and the energy provided by the discharges of the PEO process. The spectrum ranges from inert to partly reactive incorporation, but a complete reactive incorporation and a formation of a new single phase coating was not observed so far. Thus a new approach in PEO processing is introduced using specific particles as a kind of sintering additive, changing not only the composition but lowering the melting temperature and increase the liquid phase fraction during the discharges, resulting in a new amorphous coating.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.04a
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• pp.64-67
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• 2002

The Physical and magnetic properties such as microstructure, permeability and power loss of Ni-Zn ferrite with composition of $Ni_{0.8}Zn_{0.2}Fe_2O_4$, were investigated as the function of $Bi_2O_3$ and CaO contents. The power loss increased in proportion to the amount of $Bi_2O_3$ up to 0.3 wt% but it decreased over than 0.3 wt% addition. The highest permeability of 134 was obtained to the specimen added 1.0 wt% $Bi_2O_3$ since $Bi_2O_3$ contents were strongly dominant to grain growth and size than that of CaO. $Bi_2O_3$ liquid phase created during sintering process promoted sintering and grain growth so that grain size and permeability increased compared to that of the specimens which were sintered with free-additive and CaO. Also, lots of pores existed in the specimen which was added $Bi_2O_3$ wt% with the biggest grain size.

• Journal of ILASS-Korea
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• v.20 no.4
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• pp.223-229
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• 2015

This paper was designed to investigate emission characteristics of regulated pollutants (CO, HC, NOx and PM) from 134 diesel and gasoline passenger cars based on emission standards according to fuel additives. The experiments using chassis dynamometer were conducted under NEDC and CVS-75 modes. Comparison for fuel additive management and test between Korea, USA, EU and Japan, Korea was more strict than others. The fuel additives of this study was satisfied within fuel manufacturing standards. For with/without fuel additives according to diesel emission standards, NOx of EURO 4 and EURO 5 showed a relatively similar tendency. In the case of PM reduction rate, EURO 5 was over 20% increased than EURO 4. In the case of standard deviation/average ratio for gasoline vehicles, variation interval was big for LEV 23.3~58% and ULEV 31.6~56.4%. Following the imposition of stricter regulations (EURO 5 and ULEV), difference rate for standard deviation was big. Especially, in the case of diesel vehicles, difference rate for NOx 68% and PM 48% was most big. The results of present study will be of assistance in completing the legislative process and will provide basic data to set up emission standards for fuel additives in Korea.

• Proceedings of the Korean Society of Tobacco Science Conference
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• 2000.05a
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• pp.12-21
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• 2000

The smoke from a burning cigarette is classified as mainstream, which is the smoke inhaled by the smoker during a puff, and sidestream, which is defined by ISO 10185 as all smoke which leaves a cigarette during the smoking process other than from the butt end. Most of the sidestream smoke is generated during static burn, that is, in between puffs. The amount of sidestream smoke generated by a cigarette depends on the cigarette construction, tobacco blend, and properties of the cigarette paper, The main paper properties affecting sidestream smoke generation are: porosity, basis weight, type and amount of filler, type and amount of burn additive.Sidestream smoke is composed of a visible phase (small liquid droplets) and an invisible phase (gaseous molecules). This paper focuses on the visible portion of the sidestream smoke. Optical methods, which are based on the relationship between light scattering and density of the rising plume of smoke, have been used successfully by the industry. However, the present trend is to use gravimetric methods where the particulate matter is captured on a Cambridge(R) filter pad and weighed. The gaseous portion of the sidestream smoke, which does not contribute to the visible sidestream smoke, passes through the Cambridge filter pad.Sidestream smoke reduction is achieved by modifying certain mass transport processes occurring in a smoldering cigarette. There are four main pathways for reducing sidestream smoke: A) less tobacco burned, B) slower rate of tobacco combustion, C) more efficient trapping of smoke by the cigarette paper, and D) more complete combustion of tobacco. This paper discusses how the physical properties of paper and cigarette construction affect sidestream smoke reduction via the above four mechanisms.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.160-162
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• 2017

When rubber elastomer has contact with fuel, since the component and additive having low molecular weight can flow out, the physical properties of both elastomer and fuel could be hindered. In order to predict the life of the rubber elastomer, this study is to determine the change of weight, thickness, hardness, strain, and compression set as mechanical properties of the sealant rubber O-ring, which was dependent on volume, temperature, and storage time of the contacted fuel. We also determined purity of fuel via GC analysis and measured gross heat of combution. The results could be used as a reference to evaluate the life of the rubber elastomer.

• Advances in environmental research
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• v.2 no.2
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• pp.131-141
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• 2013

Agricultural practice and improper waste disposal in developing regions have resulted in environmental degradation in land and waters, for which low-cost, proven solutions are needed. We demonstrate in the laboratory the applications of composting and trickling filter techniques to treat olive mill wastes that can be implemented in the West Bank and other regions of the world. To a pomace waste sample from a California mill, we amended with saw dust (wood carbon source) and baking soda ($NaHCO_3$ alkalinity) at weight ratios of waste/wood/$NaHCO_3$ at 70:27:1 and composted it for periods of 11 and 48 days; the compost was used as an additive to potting soil for transplanting. The pomace sample was also blended into slurry and introduced to a water-circulating pond and trickling filter system (P/TF) to examine any inhibitive effect of the pomace on biological removal of the organic waste. The results showed the compost-amended potting soil supported plant growth without noticeable stress over 34 days and the P/TF system removed BOD and COD by >90% from the waste liquid within 2 days, with a first-order rate constant of 1.9 $d^{-1}$ in the pond. An onsite treatment design is proposed that promises implementation for agricultural waste disposal in developing regions.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.547-548
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• 2006

In order to realize the commercial application of HTSC materials, it is necessary to develop the fabrication process of high Tc oxide superconductor materials with desired shape and for practical application and high critical current density as well as good mechanical strength which can withstand high lorenz force generated at high magnetic field. Much studies have been concentrated to develop the fabrication technique for high critical current density but still there are a lot of gap which should be overcome for large scale application of HTSC materials at liquid nitrogen temperature. Recently some new fabrication techniques have been developed for YBaCuO bulk superconductor with high mechanical strength and critical current density. In this project, the establishment of fabrication condition and additive effects of second elements were examined so as to improve the related properties to the practical use of YBaCuO superconductor, and we reported the production of the YBaCuO high Tc superconductor by the pyrolysis method.