• Journal of the Korean Society for Precision Engineering
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• v.16 no.8
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• pp.9-15
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• 1999

Die-sinking electrical discharge machining(EDM) for conductive ceramic matrix composite(CMC) of Tic/$Al_2O_3$ was experienced with addition of ultrasonic emission, and the results were compared with ones obtained by the EDM only. From this experimental study, the values of material removal rate(MRR) and surface roughness($R_{max}$), scanning electron microscope(SEM) micrographs, and weibull probability distribution of bending strength for the specimens were obtained and compared. The trend of MRR was found to be increased slightly with the current and the duty factor for both EDM only and EDM with ultrasonic emission. The MRR values were found to be increased for EDM with ultrasonic emission. The SEM micrographs of EDMed surface by under various operating conditions showed less micro cracks in various places. Although smaller bending strength value was obtained by EDMed surface with ultrasonic emission by weibull probability distribution analysis of bending strength.

• Journal of the Korean Institute of Telematics and Electronics
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• v.15 no.2
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• pp.19-21
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• 1978

The electrical drift mobility of charge carrier of Cholesteryl Benzoate was measured by Polarity inversion method in the temperature range 140~ 185$^{\circ}C$. with a view to revealing the mechanism of charge carrier transport. The electrical drift mobility of charge carrier of that increased from 2.5$\times$10-7$\textrm{cm}^2$/V.sec to 2.0$\times$10-6$\textrm{cm}^2$/v.sec as the temperature increased. As a result of the experiment, the mechanism of current transport is believed to be ionic mechanism.

• Proceedings of the Membrane Society of Korea Conference
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• 1996.04a
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• pp.42-43
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• 1996

고분자 분미막을 이용한 분리기술은 기존의 분리기술에 비하여 에너지의 절약과 높은 분리효율 등의 장점이 있어 거의 모든 산업에 이용되고 있다. 분리막의 용도가 다양화됨에 따라서 내열성, 내약품성, 내유기용매성을 갖는 막소재의 개발이 필요하게 되었다. polyimide(PI)게의 고분자는 물리, 화학적 성능이 우수하고 내열성과 내유기용매성 등이 우수한 열가소성수지로서 film, sheet, tubular형으로 만들 수 있어 한외여과막이나 역삼투막, 기체분리막 등에 이용되고 있다. 그러나 투과속도를 높디고, fouling을 줄이기 위해서는 화학적 개질을 통해 친수성을 높이는 방법이 필요하다. 본 실험에서는 내열성과 내유기용매성이 우수한 polyetherimide계 고분자를 chlorosulfonic acid(CSA)를 이용하여 술폰화시킴으로써, 극성기의 도입에 의해 친수성이 향상된 sulfonated polyetherimide(SPEI)를 합성하였다.

• Applied Biological Chemistry
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• v.30 no.1
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• pp.54-59
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• 1987

Occurrence of two type brassinosteroid-like substances and less molecular weight substance than brassinosteroid were suggested in immature Vicia faba seeds extracts, which were purified using various chromatographic techniques, by Korean rice-lamina inclination test.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1996.10a
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• pp.52-57
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• 1996

Conductive Ceramic Matrix Composite(CMC) of TIC/Al2O3 and Metal Matrix Composite (MMC) of SiC/Al were experienced by the die sinking Electrical Discharge Machining(EDM) for different current and duty factor according to negative polarity. Inthis experimental study Material Removal Rate(MRR) maximum surface roughness four point bending stress distribution and Scanning Electron Microscopy(SEM) Photographs were analysed. the higher MRR was obtained for CMC than MMC but slowly decreased around duty factor of 0.67 for MMC and better surface morphology was found CMC than MMC. The SEM photographs of discharge traces for CMC showe uniform shape about 100 to 200${\mu}{\textrm}{m}$ in diameter but MMC showed irregular shape.

• Membrane Journal
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• v.14 no.3
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• pp.240-249
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• 2004

Crosslinked PVA membranes were achieved by esterification between the hydroxyl groups of PVA and carboxyl group of sulfosuccinic acid (SSA). SSA containing sulfonic group was used as a chemical crosslinking agent as well as a donor of fixed anionic group ($-SO_3$H). The crosslinking density of membranes was controlled by SSA content and calculated using polar and non-polar solvent. The crosslinking density measured by using non-polar solvent such as xylene and benzene increases with SSA content. However, using the polar solvent such as water and methanol, the crosslinking density increases up to SSA content of 20 wt% and above the content decrease due to sulfonic acid groups. The crosslinked PVA membranes were studied in relation with water diffusion coefficient and mechanical property as well as proton conductivity and methanol permeability as a function of crosslinking density. These properties were all dependent on the effect of SSA content.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.14 no.2
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• pp.38-43
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• 2015

Tungsten inert gas (TIG) welding is commonly used in industries that require airtightness, watertightness, oiltightness, and precision. It is a non-consumable welding method that is commonly used for the welding of non-ferrous metals, but it can be used to weld most metals. The methods of TIG welding can be divided into three types. The first, manual welding is done directly on the metal by a welder with a torch. The second, semi-automatic welding, gets help from a material supplying machine, but it is conducted by a welder. Lastly, automated welding is conducted fully by a machine during its process and operation. Depending on the selection of electrode, the amount of heat that is applied to the base material and the electrode rod changes and makes the shape of welded parts different. A direct-current positive electrode was used for this study. Through the change of shielding gas type on a structural steel (SS-400) that is commonly used in industry, the composition and shape changes in welded parts were detected after welding. The heat-affected area, hardness value, and tensile strength were also identified through hardness testing and tensile testing. In this study, it was found that the higher hardness value of the heat-affected is, the weaker the tensile strength becomes.

• The Journal of the Korea institute of electronic communication sciences
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• v.6 no.6
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• pp.897-902
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• 2011

This study incorporates a welder and a generator as needed while using the generator to be used as a welder is to configure the system. As such, in order to offer an integrated system to prevent the rapid charging process to manage the power state information, system configuration is the most important. Ideally, the random controls the flow of charge is ideal for that. When charging is good as long as possible, less current. However, In this study, the most ideal fusion welder and generator as required by the generator or welder can be used as a system is proposed. Specifically, the damage can be caused by carelessness, so short-circuit protection, overload protection, reverse polarity protection, automatic charging system is all about, including the ability to adjust.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.3
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• pp.582-590
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• 1994

This paper introduce a highly verstile and simple data transmission system designed for commercial power distribution lines. The system operates on the DSSS principle but utilizes two independent carrier frequencies each represents polarity of DS MODEM outiputs. At the receiving terminal, outputs of two envelope detectors are directly applied to separate DS correlators before the two components are compared. The recovered signals which represents data and line noise are then compared at comparator. With the noise power greatly rudused at the correlator, the error rate of the data observed at comparator desplays great improvement comparing to the conventional FSK-DS system in which the detector output are compared before the correlator stage. Despite its simplest structure, the prototype MODEM transmitts 2400 bps with the error rate 10 , about 10dB improved compared to conventional FSK system.

• Journal of the Korean earth science society
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• v.27 no.3
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• pp.341-347
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• 2006

Focal mechanisms were analyzed for the seven earthquakes which occurred in the southwestern part of the Korea Peninsula from 2001 to 2005. Grid searches are performed to fit distributions of P-wave first-motion polarities and SH/P amplitude ratios for each event. The focal mechanism solutions imply that most of the events have strike-slip sense including partially thrust component. The compressional axes of the solutions are predominantly ENE-WSW or NE-SW indirections. This result is similar to the directions of the principal compressional axes for major earthquakes occurred around the Korea Peninsula.