• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 한국추진공학회 2006년도 제26회 춘계학술대회논문집
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• pp.167-170
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• 2006

For a short time a pyre-starter should turn the blades of a turbine to the adequate rotational speed by a single operation. Through this process the pressures of the components of a propellant rise rapidly up to the operating point, and the components enter into a gas-generator. Combustion in the gas-generator occurs to keep the turbopumps working. In this research characteristic parameters of a pyre-starter which correspond to the required performance of the turbopump before the gas-generator starts to work were selected

• Journal of the Korean Magnetic Resonance Society
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• 제6권1호
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• pp.1-11
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• 2002

Physical properties of PVB [Poly(vinyl butyral)] polymer are strongly correlated with water contents in the polymer. Thus dynamics of PVB containing 10~50(w/w) ％ of water were studied by $^{13}$ C CP/MAS/DD over the temperature range 293K -348K. From the Peak area, line width, chemical shift, and relaxation times ( $T_{1}$ $T_{1p}$) measured at 9.4 T, it was deduced that water facilitates molecular dynamics of the PVB molecules overall including conformational exchange of the racemic and meso butyaldehyde rings in the PVB. However, the influence of water was not linear to the amount of water in the PVB samples. It is suggested that water up to 30 w/w ％ of the sample is closely bound to the PVB polymer and water relatively free from the PVB polymer starts to appear when water is added more than 30 w/w ％.％.

• Bulletin of the Korean Mathematical Society
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• 제33권2호
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• pp.259-265
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• 1996

The history of option valuation problem goes back to the year 1900 when Louis Bachelier deduced on option valuation formula under the assumption that the price process follows standard Brownian motion. More than 50 years later, the research for a mathematical theory of option valuation was taken up by Samuelson ([6]) and others. This work was brought into focus in the major paper by Black and Scholes ([1]) in which a complete option valuation model was derived on the assumption that the underlying price model is a geometric Brownian motion. THis paper starts with subjects developed mainly in Harrison and Kreps ([4]) and in Harrison and Pliska ([5]). The ideas established in these papers are essential for option valuation problem, and in particularfor the point of view that we take in this paper.

• Journal of the Korean Magnetic Resonance Society
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• 제9권1호
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• pp.21-28
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• 2005

$^{11}B$ nuclear magnetic resonance (NMR) measurements have been performed to investigate electronic structures and vortex states of $M_gB_2$ superconductor. The central transition shows a narrow peak down to 25 K at 3.15 T. Below 25 K, an extra line starts to show up and dominates. The extra line is broad and asymmetric with a long tail in the high frequency side, which confirms that this originates from vortex pinning below the irreversibility temperature. From temperature evolution of the fraction and linewidth of the broad portion, temperature dependence of coherence length and penetration depth are extracted.

• Proceedings of the KIEE Conference
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• 대한전기학회 2002년도 하계학술대회 논문집 A
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• pp.44-46
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• 2002

Service restoration following a complete or partial collapse starts with reenergize a transmission line from black-start generators. Voltage problems can arise by Ferranti effect as unloaded transmission line is reenergized. This paper presents analytical results on the primary restorative transmission system focused on the voltage problem during the early restoration process. Methodologies to handle load pick-up compensating Ferranti effect. and terminal voltage and reactive capability limitation of black-start generators about self-excitation are presented. An algorithm for static analysis about these methodologies is developed, and EMTDC simulation for verifying the efficiency of the algorithm is performed.

• Journal of the Korean Ceramic Society
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• 제26권1호
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• pp.51-58
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• 1989

Wear and wear transition mechanisms during sliding as a function of time in Al2O3 have been studied to understand the wear behaviour of brittle ceramic materials. Commercial Si3N4 ball was rotated against flat Al2O3 specimens which were hot pressed and polished using upto 1${\mu}{\textrm}{m}$ diamond paste. Paraffin oil was used as a lubricant. Experimental data show that wear of Al2O3 is separated into distinct two stages, i.e., initial stage of slow wear and final stage of rapid wear. Microstructural observations at worn surface show that wear occurs through grooving and grain pull-out in the initial and final stage respectively. TEM observations beneath the worn surfaces show that grain pull-out starts to occur by the propagation of grain boundary cracks induced by dislocation pile-up throughthe surface.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 학술대회
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• pp.268-275
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• 2008

The prediction of hydrate pellet decomposition characteristics is required to design the regasification process of GTS (gas to solid) technology, which is considered as an economic alternative for LNG technology to transport natural gas produced from small and stranded gas wells. Mathematical model based on the conservation principles, the phase equilibrium relation, equation of gas state and phase change kinetics was set up and numerical solution procedure employing volume averaged fixed grid formulation and extended enthalpy method are implemented. Initially, porous methane hydrate pellet is at uniform temperature and pressure within hydrate stable region. The pressure starts to decrease with a fixed rate down to the final pressure and is kept constant afterwards while the bounding surface of pellet is heated by convection. The predicted convective heat and mass transfer accompanied by the decomposed gas flow through hydrate/ice solid matrix is reported focused on the comparison of spherical and cylindrical pellets having the same effective radius.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년 추계학술대회논문집
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• pp.268-275
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• 2008

The prediction of hydrate pellet decomposition characteristics is required to design the regasification process of GTS (gas to solid) technology, which is considered as an economic alternative for LNG technology to transport natural gas produced from small and stranded gas wells. Mathematical model based on the conservation principles, the phase equilibrium relation, equation of gas state and phase change kinetics was set up and numerical solution procedure employing volume averaged fixed grid formulation and extended enthalpy method are implemented. Initially, porous methane hydrate pellet is at uniform temperature and pressure within hydrate stable region. The pressure starts to decrease with a fixed rate down to the final pressure and is kept constant afterwards while the bounding surface of pellet is heated by convection. The predicted convective heat and mass transfer accompanied by the decomposed gas flow through hydrate/ice solid matrix is reported focused on the comparison of spherical and cylindrical pellets having the same effective radius.

• Transactions of the Korean Society of Mechanical Engineers B
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• 제24권4호
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• pp.561-569
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• 2000

The purpose of this study is to construct a testing equipment with which several characteristics of the domestically developed swashplate type axial piston motor can be tested and to develop a software with which the data from experiment can be stored and can be applied. The results of the study are as follows; 1) The leakage flow and the torque of the motor being stopped is propotional to supply pressure and their relation can be showed by linear equations. 2) The motor movement is not smooth below 50 rpm but it moves smoothly up 170 rpm. 3) When the motor starts or stops, the pressure rise ratio effects decisively to the max. torque.

• Proceedings of the KSR Conference
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• 한국철도학회 2005년도 춘계학술대회 논문집
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• pp.291-298
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• 2005

This paper describes the characteristic feather of propulsion system adopting mass production. The train formation is composed of 4 cars by 2 Motor cars and 2 Train cars. Acceleration rate must be 3.0 km/h/s or more when the car starts up to 35km/h by 16ton of passenger load. The system information supervision is easy because the system is controlled to perfect digital circuits, all information of an action is stored in a memory and is managed. The control system is composed of a fully digital circuit and a high level software such as C language. The DSP TMS320C31 is used for main processor and has the capability of 50MHz, 32bit floating point operation and has a C compiler. Therefore, the implementation of control algorithm and the change of function are easy. VVVF inverter using IGBT conducted variable combined test, environment test using chamber, interface test and field test etc.