• The Journal of Korean Institute of Communications and Information Sciences
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• v.16 no.10
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• pp.914-924
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• 1991

It has been generally used for PLL(Phase Locked Loop) to be synthesized randomly chosen frequency state, but the PLL locking time was inevitable element. A direct digital synthesizer. Which makes output frequency directly in sine wave by a phase accumulating method, could be leiminate the defect, although a phase distortion in frequency spectrum. In order to improve this disadvantage, the phase accumulating method is reconsidered in the side of he output wave formula expression. A new mechanism is proposed, and it is constructed by a most suitable logic elements. The spectrum of synthesized sine waveform is simulated and compared with a measured value, and it’s the coherence frequency hoppong state with the PN(Pseudo Noise) code sequence is confirmed. In this results, the power levels of phase distortion harmonics are decreased to 10~25dB and bandwidths are increased to 420kHz.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.6 no.2
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• pp.67-75
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• 1986

This paper introduces the nonlinear Stream Function Wave Theory for design waves efficiently to compute the wave energy and energy transport quantities and to analyze the effects of nonlinearities on them. The Stream Function Wave Theory was developed by Dean for case of the observed waves with assymmetric wave profiles and of the design waves with symmetric theoretical wave profiles. Dalrymple later improved the computational procedure by adding two Lagrangian constraints so that more efficient convergence of the iterative numerical method to a specified wave height and to a zero mean free surface displacement resulted. And the Stream Function coefficients are computed numerically by the improved Marquardt algorithm developed for this study. As the result of this study the effects of nonlinearities on the wave quantities of the average potential energy density, the average kinetic energy density result in overestimation by linear wave theory compared to the Stream Function Wave Theory and increase monotonically with decreasing $L^*/L_O$ and with increasing $H/H_B$. The effects of nonlinearities on the group velocity and the wavelength quantities result in underestimation by linear wave theory and increase monotonically with increasing $H/H_B$. Finally the effect of nonlinearity on the average total energy flux results in overestimation for shallow water waves and underestimation for deep water waves by linear wave theory.

• Korean Journal of Acupuncture
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• v.24 no.2
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• pp.185-191
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• 2007

목 적 : 전침 자극은 최근에 임상연구와 더불어 기초연구에서 자주 사용하는 방법으로 경락이론에 의거하여 신체에 분포되어 있는 경락상의 각종경혈부위에 인위적인 전기 자극을 통하여 질병을 치료, 예방 혹은 완화하는 방법이다. 이에 본 연구에서는 정상적인 쥐의 상태에서 일정한 전침 자극을 주었을 때, 심박변이도의 변화를 측정 하였다. 방 법 : 쥐의 정상적인 마취상태에서 태충혈에 4 Hz와 80 Hz의 5 V 크기로 10 mA 강도의 사각파 파형으로 자극을 주었으며 대조조로 비경혈 부위에 4 Hz의 동일한 파형으로 자극을 주어 심박 변이도의 변화정도를 측정하였다. 결 과 : 본 실험에서 RR Interval의 경우 태충혈 4 Hz 보다 80 Hz일때 RR Interval의 파형이 더 크게 나타났으며, PSD의 분석에서도 자극 전후를 비교하였을 때 $1{\sim}3$ Hz 사이에 높은 피크가 보였으며 4 Hz의 비경혈 부위에서는 큰 변화를 보이지 않았다. 결 론 : 이번 실험연구를 통하여 정상적인 쥐의 상태에서 일정한 전침 자극을 주었을 때, 심박 변이도 변화를 도출할 수 있었으며, 이번 실험을 통해 비수술적인 방법으로 치료효과와 심박 변이도를 측정할 수 있었고, 이를 통해 전침자극의 기전 연구에 있어 과학적 근거를 제시할 수 있다고 사료된다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.1
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• pp.46-50
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• 1993

The sensitivity study to evaluate the effects of parameters on the fatigue crack propagation life under the constant loadings is executed in the previous study of the authors. It is shown that the effect of the crack opening ratio is large comparatively. The purpose of this paper is to evaluate the effects of parameters on the fatigue crack propagation life under the random loadings. A new method of evaluation of the effective stress under the random loadings is developed. The sensitivity study of parameters on the fatigue crack propagation life under the random loadings is executed by using it.

• The Transactions of the Korean Institute of Power Electronics
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• v.8 no.5
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• pp.435-441
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• 2003

Dynamic Voltage Restorers (DVR)s are known as the best effective and economic means to compensate for voltage sags and swells. This paper proposes a novel method to generate reference voltages synchronized with the grid whether the line voltages are distorted by a fault or not. The proposed reference wave generator (RWG) looks for the original wave forms from the corrupted line voltages and synthesizes the expected positive sequence reference waves for DVRs. There is no transient problem on the generated reference waves when the line voltages are distorted by the fault.

• Journal of the Korean Institute of Telematics and Electronics
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• v.7 no.2
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• pp.13-20
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• 1970

The dispersion characteristics of tape meander line were analyzed by electromagnetic field theory. The several different tape meander lines were photoetched on copper printed-bakelit substrate, and these tape meander line structures were inserted into the X-band waveguide. Phase bridge method was used for the dispersion characteristics measurement of meanderline. The measured. results were plotted on diagram(Brillouin diagram) and compared with theoretical values. Measured results were consistent with theoretical Values. But, on the measured diagram, passband midfrequency was lower than theoretical value. It was believed that the discrepancy was due to the backelite loading. The group velocity of stagger tuned meander line was higher than that of uniform meander live, and the freqnency band of constant group velocity of stagger tuned meanderline was sider than that of uniform meander line.

• The Journal of the Acoustical Society of Korea
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• v.17 no.8
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• pp.103-109
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• 1998

디지털신호의 변조에는 기본적으로 진폭 편이 변조(ASK: Amplitude-Shift Keying), 주파수 편이 변조(FSK: Frequency-Shift Keying), 위상 편이 변조(PSK: Phase-Shift Keying) 등의 세 가지 방법이 있다. 본 논문에서는 표본클록 합성계수 방식에 관한 이론을 고찰하고, 클록초기치 누적방식의 DDFS를 이용하여 위에서 언급한 변조방법을 실현할 수 있는 주파수 도약 대역 확산 통신에 적합한 변조기를 구현하였다. 또한, 합성된 출력주파수 의 정현파형에 대한 스펙트럼 분석과 PN(Pseudo Noise) 부호를 사용한 순시적인 주파수 도 약 상태, 위상제어의 가능성 등을 확인한 결과 실험으로부터 다음과 같은 결과를 얻었다. 첫 째, 합성된 출력주파수는 주파수 Index에 따라 기준주파수에 정확히 정수배가 되며, 둘째, 합성된 정현파형의 스펙트럼으로 기본파와 여러 고조파의 크기를 비교하여 본 결과 50[dB] 이상의 차이가 남으로서 고조파 성분들이 상당히 감소되었음을 확인하였고, 셋째, PN 코드 를 사용하여 순시적인 주파수 도약 상태를 확인하여 본 결과 스위칭 시간이 빠르기 때문에 주파수 도약 특성이 뛰어남을 알 수 있었으며 또한, 누산기의 set/reset 상태를 변화시킴에 따라 위상이 제어됨을 입증하였다.

• Korean Journal of Optics and Photonics
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• v.1 no.2
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• pp.162-168
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• 1990

Two ZnSe loss plates were installed in the resonator of waveguide CO2 laser which consisted of Pyrex capillary tube in order to change the internal loss. By rotating the loss plates, the output variations with the internalloss was measured on various discharge conditions. The variations could be explained by the Rigrod theory. and the saturation power and the unsaturated gain coefficient were determined by fitting of the experimental results. It was found that the saturation power increased while the unsaturated gain coefficient reduced as the discharge current or the gas flow rate increased.reased.

• The Journal of Natural Sciences
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• v.1
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• pp.21-31
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• 1987

A pulse shape of a pulsed TEA $CO_2$ laser in analyzed theoretically by the use of Computer simulation. Since the laser operates $10.6\mum$ P-20 line, regular band, the pulse shape is obtained by adding the hot band R-23 effect to the regular band $10.6\mum$ P-20. The results are well agreed to the experimental results.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.5
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• pp.1683-1696
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• 1991

본 연구에서는 정4각단면덕트 입구영역에서 층류맥동유동(laminar pulsating flows)의 유동특성을 이론 및 실험적으로 규명하기 위하여, 이론적 방법으로 덕트 입 구영역에서의 층류맥동유동에 대한 운동량방정식을 유도한 후 비선형인 대류항을 선형 화 시켜서 라플라스변환으로 속도분포식의 해를 구하였고, 실험적인 방법으로는 시험 덕트 크기는 횡단면의 가로*세로가 40mm*40mm이고, 길이가 4000mm인 정4각단면덕트 입구영역에서 송풍기에 의한 공기흡입유동으로 층류진동유동을 발생하며 이들 두유동 을 합성시켜 발생한 층류맥동유동에 대하여 열선유속계의 열선신호로부터 얻어진 속도 파형을 고찰하여 덕트내의 맥동유동에 대한 임계레이놀즈수를 결정하고 속도분포를 측 정하였다. 그리고 이론적으로 얻어진 속도분포식과 열선유속계로 측정한 속도분포를 비교검토하여 정확성을 검증하고, 이들 해석결과로 부터 층류맥동유동의 입구길이(en- trance lenght)식을 결정하여 제안하였다.