• 유체기계공업학회:학술대회논문집
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• 2005.12a
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• pp.158-165
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• 2005

KOGAS(Korea Gas Corporation) has about a hundred of local stations to supply natural gas to the city gas companies and the power stations. As some severe flow fluctuation phenomena are observed in several governor stations, the investigation about the reasons and factors which are relating to flow fluctuation has been started. Some field surveys hav been carried out and experimental studies have been performed to find the fluctuation mechanism. As a result, it is found that the flow fluctuation is related with the length of straight pipe in front of the meter, the size of the header pipe and the variation of demand at the city gas company and the power station. Furthermore. it is also proved that both the length of the transmitter cable and the status of the coating of signal transmission cable do not affect flow fluctuation, but the measurement range of the differential pressure transmitter influences flow fluctuation. On the other hand, as the averaging the flow fluctuation is converged to less than 0.1 % in almost all of the cases, it is concluded that the quantity of flow fluctuation do not relates to metering accuracy directly.

• Journal of the Korean Society for Heat Treatment
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• v.11 no.1
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• pp.46-53
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• 1998

The variation of the mechanical properties, microstructures and the formation of retained austenite with heat treatment conditions in austempered ductile cast iron has been investigated. In the case of austempered ductile cast iron below 25mm diameter, it has been found that a pearlite structure are not obtained under a super cooled condition at range of $0.05^{\circ}C/sec{\sim}10^{\circ}C/sec$, and the matrix is precipitated in graphite, bainite and retained austenite. After austempering treatment the retained austenite is increased with decreasing cooling rate. The elongation increases with decreasing super cooling rate, and the optimum result has been shown to be the elongation of 15.6% at super cooling rate of $0.05^{\circ}C/sec$. The optimum result has been shown to be the tensile strength-elongation balance of $1656kgf/mm^2.%$ and it is more than doubled to as the casting state and continuous cooling condition.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.3
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• pp.174-182
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• 2007

Fuel reforming technology for the fuel cell vehicles could be applied to internal combustion engine for the reduction of engine out emissions. Since syngas which is reformed from fossil fuel has hydrogen as a major component, it has abilities to enhance the combustion characteristics with wide flammability and high speed flame propagation. In this study, syngas was added to a gasoline engine to improve combustion stability and exhaust emissions of idle state. Syngas fraction is varied to 0%, 50%, 100% with various ignition timing and excess air ratio. Combustion stability, exhaust emissions, fuel consumption and exhaust gas temperature were measured to investigate the effects of syngas addition on idle performance. Results showed that syngas has ability to widely extend lean operation limit and ignition retard range with dramatical reduction of engine out emissions.

• 보존과학연구
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• s.13
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• pp.14-36
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• 1992

The investigation has been made on the rocks consisting the pagoda(12), Buddhist Statues(9) Buldaejwa and cakra(2, rewpectively), stele(5), and Flagpole wupport and stupa(6) which are stood in Weonju city, Weonju-gun, Hwoengseong-gun and Hongcheon-gun, Kangweondo. These rock-monuments range mostly in age from late Shilla Kingdom to middle Korye Kingdom. The geology around this region is mainly composed of Precambrian metamorphic rocks and mesozoic granitic rocks. The granitic rocks are largely divided into Jurassic and cretaceous ones which are slightly different in rock phase. The main rock phase consisting the monumentsare are coarse biotite granite with minor amount of hornblende in Jurassic age. Variation in rock phase is abserved even in part of the stone used in the monuments. Inclusions composed of biotite and hornblende, porphyritic texture with microcline phenocryst, igneous lineation and exfoliation according to weathering are observable in all rocks in these monuments. In the case of stele whose a body and a capstone is remained, one is composed of black slate and the other white limestone. But the turtle shaped pedestal is constituted of coarse biotite granite. These stone-monuments are strongly weathered and exfoliated out about 1∼2mm.In case of exfoliated weathering along igneous lineation, some are taken off about 3∼5mm thick. In some monuments, the degree of weathering is somewhat different according to position, grade of sculpture, and biological activity.

• Transactions on Electrical and Electronic Materials
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• v.8 no.4
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• pp.161-165
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• 2007

In this work, Ni thin films with different thickness from $1,523{\AA}\;to\;9,827{\AA}$ were deposited for the application of micro thermal flow sensors by a magnetron sputtering and oxidized through annealing at $450^{\circ}C$ with increasing annealing time. The initial variation of resistivity decreased radically with increasing films thickness, then gradually stabilizes as the thickness increases. The resistivity of Ni thin films with $3,075{\AA}$ increased suddenly with increasing annealing time at $450{\circ}C$, then gradually stabilizes as the thickness increases after the annealing time 9 h. In case of $3,075{\AA}\;and\;9,827{\AA}$ films, the average of TCR values, measured for the operating temperature range of $0^{\circ}C\;to\;180^{\circ}C$, were $2,413.1ppm/^{\circ}C\;and\;4,438.5ppm/^{\circ}C$, respectively. Because of their high resistivity and very linear TCR, Ni oxide thin films are superior to pure Ni and Pt thin films for flow and temperature sensor applications.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.42 no.6
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• pp.159-166
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• 2005

The pulse amplitude of a search radar signal received by an ES system is not constant pulse by pulse because of the radar's scan characteristics. The variation of the pulse amplitude causes the ES detection loss in the ES system. Therefore, the ES detection range equation should consider the ES detection loss caused by the search radar's scan characteristics. In this paper, we theoretically analyze the ES detection loss for the circular scar and propose the model to evaluate it quantitatively. The experiment results for the real search radar signals demonstrate that the proposed model is suitable for the evaluation model of the ES detection loss related to the circular scan of radars.

• Journal of Korean Association for Spatial Structures
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• v.17 no.1
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• pp.77-84
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• 2017

Vortex-induced vibration and instability vibration of tall buildings are very important fluid-structure interaction phenomenon, and many fundamental questions concerning the influence of body movement on the unsteady aerodynamic force remain unanswered. For tall buildings, there are two experimental methods to investigate the characteristics of unsteady aerodynamic forces, one is forced vibration method and the other is free vibration method. In the present paper, a free vibration method was used to investigate the unsteady aerodynamic force on tall building whose aspect ratio is 9 under boundary layer simulating city area. Wind pressures on surfaces and tip displacements were measured simultaneously, and the characteristics of tip displacements and generalized forces were discussed. It was found that variation of across-wind displacements showed different trend between the case when wind speed increases and wind speed decreases, and the fluctuating generalize forces in across-wind direction of vibrating model are larger than that of static model near the resonant wind speed and approach to the static value. And for higher wind speed range, there were two peaks in across-wind power spectra of generalize forces of vibrating model, which means that two frequency components are predominant in unsteady aerodynamic forces.

• Journal of Magnetics
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• v.20 no.2
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• pp.120-128
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• 2015

Beam-quality of medical linac evaluations vary by diverse factors. Because conventional beam-quality evaluation methods yield fragmentary results, a new beam-evaluation method is suggested, and its feasibility is evaluated. The PDDs (percentage depth doses) of 6 MV (Mega-voltage) and 10 MV photon, R (Range) of a 6 MeV (Mega Electron-voltage) and 9 MeV electron were measured and compared with the conventional evaluation methods, and the improved methods $PDD^{10}{_5}$, $PDD^{20}{_{10}}$, $PDD^{30}{_{20}}$, $PDD^{20}{_5}$, $PDD^{30}{_{10}}$, and $R^{70}{_{50}}$, $R^{50}{_{30}}$, $R^{70}{_{30}}$ as the magnetic field of the bending magnet was changed to +2% to -2%, and the results were compared. The comparison showed that the improved methods exhibit a higher discrimination than the conventional methods in each energy regime. $PDD^{10}{_5}$, $PDD^{30}{_{20}}$, $PDD^{30}{_{10}}$ and $R^{70}{_{50}}$, $R^{50}{_{30}}$ should be applied. These methods exhibit a higher discrimination in each energy regime than conventional beam-quality evaluation methods; therefore, they should be used for beam-quality evaluation according to the magnetic field variation.

• Journal of Magnetics
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• v.14 no.1
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• pp.42-46
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• 2009

The measurement of external magnetic field orientation using Giant Magneto Impedance (GMI) sensors has been performed. A soft magnetic alloy of $Co_{30}Fe_{34}Ni_{36}$ was electroplated on a Si wafer with a CoFeNi seed layer. V-shaped microwire patterns were formed using a conventional photolithography process. An external magnetic field was generated by a rectangular AlNiCo permanent magnet. The reference direction was defined as the external magnetic field direction oriented in the middle of 2 GMI devices. As the orientation of the magnetic field deviated from the reference direction, variation in the field component along each device introduced voltage changes. It was found that, by taking the voltage difference between the left and right arms of the Vshaped device, the nonlinearity of each device could be significantly reduced. The fabricated angle sensor had a linear range of approximately $70^{\circ}$ and an overall sensitivity of approximately 10 mV.

• Journal of the Korean Society of Propulsion Engineers
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• v.12 no.4
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• pp.42-47
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• 2008

The power control system of Smart UAV is similar to the propeller pitch governing concept of turboprop aircraft. The pilot adjusts the engine power directly and the pitch governor controls the propeller pitch to maintain the propeller rotational speed. The electronic engine controller(EEC) of PW206C engine developed for helicopter is not fit for the power control concept of Smart UAV, and therefore the manual back-up system of PW206C engine is used for the engine power control of Smart UAV. Engine performance estimation program is used to predict the control range of power lever angle(PLA) according to the variation of engine output shaft speed, flight altitude and flight speed. These data provide a guide for the PLA control in manual mode operation.