• The Journal of the Acoustical Society of Korea
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• 제18권2호
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• pp.40-47
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• 1999

Focusing is widely used to increase the resolution in ultrasound transmit field. It increases signal levels returning from the mainlobe direction and decreases those due to sidelobe directions. However, when the sidelobes cannot be completely canceled, the resulting image resolution is greatly deteriorated. This paper proposes a method of improving the resolution by scaling the received signal according to the difference between the mainlobe and sidelobe levels computed in the frequency domain by the use of Fourier transform. The proposed method is verified by computer simulation and experiments, and is shown to be highly effective in narrowing the mainlobe width and decreasing the sidelobe levels.

• Proceedings of the Korea Concrete Institute Conference
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• 한국콘크리트학회 1999년도 봄 학술발표회 논문집(I)
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• pp.579-584
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• 1999

In evaluating the ultimate strength of a section for a concrete flexural member, the effect of member length is not usually considered, even though the strength tends to decrease with increase of member length. In this paper the influence of specimen length on flexural compressive strength of concrete was evaluated. For this purpose, a series of C-shaped specimens subjected to axial compression and bending moment were tested using four different length-to-depth ratios(from 1, 2, 3 and 4) of specimens with compressive strength of 58 MPa. Results indicate that the reduction in flexural compressive strength with increase of length-to-width ratios was apparent. A model equation was derived using regression analyses on the experimental data. It was also founded that the effect of specimen length on ultimate strain was negligible, but its effect of the ultimate load and the displacement at center of specimen was distinct. Finally more general model equation is also suggested.

• Journal of Power Electronics
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• 제10권1호
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• pp.51-57
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• 2010

This paper proposes a new random switching strategy using a DSP TMS320F2812 to reduce the harmonics spectra of single phase switched reluctance motors. The proposed method combines the random turn-on/off angle technique and the random pulse width modulation technique. A harmonic spread factor (HSF) is used to evaluate the random modulation scheme. In order to confirm the effectiveness of the proposed method an experiment was conducted. The experimental results show that the harmonic intensity of the output voltage for the proposed method is better than that for conventional methods.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2003년도 International Meeting on Information Display
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• pp.105-108
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• 2003

A new high speed addressing method is proposed to reduce the addressing time below lus per line in AC PDP. In this method, the priming discharge is used to achieve a high speed addressing without adding an auxiliary electrode. Two different types of priming discharges were studied to achieve a high speed addressing and also reduce the inherent light output caused by the priming discharge in order to improve the contrast ratio characteristics. In the panel experiment, the addressing was successfully done with a lus address pulse width in the new method and the better contrast ratio was achieved in the Y-A priming rather than the Y-X priming case even though the reduction of the address period was smaller than that of the Y-X priming due to the extra address time for the priming discharges.

• Journal of Advanced Marine Engineering and Technology
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• 제28권3호
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• pp.413-422
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• 2004

The flow characteristic in the wake around a circular cylinder with tripping wires, which was set in constant distance, was experimentally investigated in the uniform flow, Re=2.92$\times10^4$. The measurement of velocity vector and pressure distribution are carried out various angles of tripping wires in the range of $50^(\circ)$ to $80^(\circ)$ with $10^(\circ)$ interval. The results show that velocity profiles and pressure distributions are different with angles of tripping wires. The drag of the circular cylinder was decreased about 60% maximum when tripping wires' angle was $50^(\circ)$. The lowest reduction of the velocity and wake width was occurred by coanda effect when the angle was $60^(\circ)$, and the vortex shedding periodicity become rare at the same time.

• Transactions of the Korean Society of Machine Tool Engineers
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• 제11권5호
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• pp.23-29
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• 2002

The soldering is widely used installing the electronic element on circuit board in the common electronic device. Since the flux which improves the liquidity of solder make the electronic and chemical performance worse, the circuit board need to wash clearly. At present however no-washing is required for the cost reduction, the chemical stability, and the protection of environment. In this research, the solder liquidity depending on the power density and the pulse width is comparatively analyzed by the diffusion area method for achieving the no-flux soldering.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 한국마린엔지니어링학회 2006년도 전기학술대회논문집
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• pp.61-62
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• 2006

The suppression of fluid force acting on a square prism near plane wall was studied by attaching fences on the comers of the prism. The height of the fence was 10% of the square width and the range of Reynolds number considered was $Re=2.0{\times}10^4$. The experimental parameters were the attaching position and numbers of fences, the space ratios $G/B(G/B=0.1{\sim}1.2)$ between prism and plane wall. The average drag coefficients were increased and the average hit coefficients were decreased and increased with the space ratios foulard plane wall. The drag of the prism was reduced average 7.6% with the space ratios by attaching the normal fence at the rear and upper comer and the horizontal normal fence at the rear and lower corner on the prism.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• 제16권7호
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• pp.677-682
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• 2006

In the case of aeroacoustic test in windtunnel, measurement accuracy is reduced by not only Doppler effects but also by the microphone self noise due to airflow and high turbulence in the wall boundary layer. Microphone array measurements can be easily utilized for the solutions of these problems. In this paper, geometrical optics approach and diagonal term elimination of cross spectral matrix was introduced to the de-dopplerization and self noise reduction methods for the microphone array measurement. For the validation, beamforming tests for sinusoidal point source were performed in the closed type test section of windtunnel, and their performances of beam width and sidelobe rejection were significantly improved.

• Journal of the Semiconductor & Display Technology
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• 제12권4호
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• pp.27-32
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• 2013

In this paper, the boost converter was implemented by digital control in many applications of the step-up. The PWM(pulse width modulation) control module of boost converter was digitized at power converter using the FPGA device and VHDL. The boost converter was designed to output a fixed voltage through the PI control algorithm of the PWM control module even if input voltage and output load are variable. The boost converter was digitized can be simplified by reducing the size of the module and the external control components. Thus, the digital power IC has advantageous for weight reduction and miniaturization of electronic products because it can be controlled remotely by setting the desired output voltage and PWM control module. The boost converter using the digital power IC was confirmed through experiments and the good performances were showed from experiment results.

• Proceedings of the KSR Conference
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• 한국철도학회 2007년도 추계학술대회 논문집
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• pp.129-134
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• 2007

When constructing a high-speed railroad, the reduction of the distance between track centers and the width of track bed may bring about the effect of cost savings. When, however, considering the influence that the increase of wind pressure due to the change of the distance between track centers may have on the stability of train operation, extensive technical review and overall studies need to be performed before the distance between track centers is determined. Therefore, in this study, the impact that the increase in wind pressure due to the change of aerodynamic phenomena with the change of the distance between track centers may have on two trains passing by each other was predicted, and the stability of train operation was analyzed in order to review the distance between track centers suitable to Honam HSR trains. In this study, we estimated the aerodynamical effects by the results of the real train experiments.