• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1997년도 춘계학술발표회논문집(1)
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• pp.542-547
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• 1997

In the SSC(Super System Code), the reactivity feedback models of the Doppler effect and fuel axial expansion were modified to evaluate the safety performance of the metal-fueled core. The core radial expansion model was developed and implemented into the code as well. The transient analyses have been performed by the modified SSC for UTOP, ULOHS, ULOF/LOHS, and UTOP/LOF/LOHS events for one of the core design options being considered. Analysis results shows that the reactivity feedbacks can provide an inherent shutdown capability in response to key anticipated events without scram. Development of other reactivity feedback models and validation of these models against experimental data would make the SSC suitable for the assessment of the metal-fueled core safety performance.

• 한국전산유체공학회지
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• 제6권4호
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• pp.8-14
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• 2001

The phenomena of two-phase suspension flows appear widely in nature and industrial processes. Hence, it is of great importance to understand the mechanism of the gas-solid two-phase flows. In the present study, the numerical simulation has been approached by utilizing the Eulerian-Lagrangian methodology for describing the characteristics of the fluid and particulate phases in a vertical pipe and a 90°square-sectioned bend. The continuous phase(gas phase) is described by the Eulerian formulation and a κ-ε turbulence model is employed to find mean and turbulent properties of the gas phase. The particle properties(velocity and trajectory) are then described by a Lagrangian approach and computed using the mean velocity and turbulent fluctuating velocity of the gas phase. The predictions are compared with measurements by laser-Doppler velocimeter for the validation. As a result, the calculated results show good agreements.

• 한국항행학회논문지
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• 제13권4호
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• pp.544-550
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• 2009

본 논문은 밀리미터파 페이딩 채널에서 차세대 초고속 무선통신 시스템의 전파 전파 특성에 대해 제안한다. 도플러 천이와 레일리 페이딩을 동시에 고려하기 위해서 Jakes 모델의 페이딩 시뮬레이터를 구현하고 차세대 무선통신 시스템의 성능을 분석하였다. 또한 밀리미터파 페이딩 채널에서 DS-CDMA 시스템의 오율 특성을 분석하고 부호화 기법과 다이버시티기법에 의해 시스템의 성능이 향상됨을 확인 하였다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2002년도 ITC-CSCC -2
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• pp.1086-1089
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• 2002

In this paper, an adaptive packet acquisition performance of a CDMA/TDD packet radio system is analyzed and simulated in a frequency-selective Rayleigh fading channel. The frequency-selective fading process is assumed to be WSSUS model which is typical for a satellite and a mobile radio communications. The performance is evaluated in terms of packet error probability. In this adaptive packet acquisition scheme, an auxiliary training sequence is placed within data packet to estimate time-varying channel state. From the simulation results, it is confirmed that the proposed acquisition scheme significantly improves packet error performance compared to the conventional fixed acquisition scheme, especially, for the case of low Doppler frequency. The analysis in this paper can be applied to the design of a CDMA/TDD packet radio system.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.287-290
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• 2002

'Backhole' is an extra empty volume where is located behind the tangential entries at the rear par of the vortex chamber in the swirl coaxial injector. With the backhole, there are three major hydraulic characteristics. First, mass flow rate is increased about $15{\%}$ compared with the case without the backhole. Second, with the backhole, the center region of the injected flow has more large volume than that of without the backhole. The last, some range of the cone angle can be controlled by the backhole Experiments are conducted by using a PDPA apparatus, a mechanical patternator, stroboscopic photography and etc. With the backhole, based on cold-flow tests, the model swirl injector has some Improvement in its performance.

• The Journal of the Acoustical Society of Korea
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• 제16권3E호
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• pp.24-31
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• 1997

A mobile propagation characteristics for wideband DS-SS (Direct Sequence-Spectrum) signal is presented. Existing narrowband model is extended for the wideband pulse with an arbitrary shape. The received DS-SS signal in the frequency domain is the transfer function of the propagation channel weighted by the inverse Fourier transform. In this proposed method, received signal spectral density, instantaneous waveform, and Doppler spectrum of DS-SS signal via either Rayleigh of Rician channel can be obtained easily. Simulation results match well with both simulated theoretical fading statistics and classical theory. As expected, the extraction of chip timing in Rician fading shown to be more tractable than Rayleigh fading.

• Archives of Reconstructive Microsurgery
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• 제4권1호
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• pp.1-8
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• 1995

장시간 허혈상태의 토끼 이개를 실험대상으로 하여 유로키나제와 헤파린을 병용 또는 단독으로 사용시와 또한 약물을 사용하지 않았을 때, 이들이 모세혈관의 개존성과 아울러 미세수술후의 조직 생존율에 미칠 수 있는 효과를 보기 위하여 허혈상태의 토끼 이개를 미세수술로 접합한 후 모세혈관으로의 혈류를 측정하기 위하여 레이저 초음파 혈류측정기(Laser doppler flowmetry)를 이용하였으며 방사선 구슬들(Cobalt-57 with plastic material with average diameter 15 micron)을 주입한 결과 유로키나제 조합에서 통계적으로 유효한 성적을 얻었다. 광학현미경 소견은 유로키나제와 헤파린을 병용한 조합에서 모세혈관내 내피세포의 배열이 유지되어 있었으며 헤파린을 사용한 조합에서도 유사한 소견을 보였으나 약물을 사용하지 않은 조합에서는 국소적인 내피세포의 배열이 결핍되어 있었다. 전자현미경 소견에서 유로키나제와 헤파린을 병용한 조합에서 내피세포가 혈관내벽에 배열되어 있었고 또 불규칙한 세포질이 돌출되어 있었다.

• Journal of electromagnetic engineering and science
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• 제7권4호
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• pp.195-200
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• 2007

Doubly-selective channel estimator for orthogonal frequency division multiplexing(OFDM) systems is proposed in this paper. Based on the generalized complex exponential basis expansion model(GCE-BEM), we describe the time-variant channel with time-invariant coefficients over multiple OFDM blocks. The time variation of the channel destroys the orthogonality between subcarriers, and the resulting channel matrix in the frequency domain is no longer diagonal, but the main interference comes from the near subcarriers. Based on this, we propose a channel estimator with low pilot ratio. We first develop a least-square(LS) estimator under the assumption that only the maximum Doppler frequency and the channel order are known at the receiver, and then verify that the correlation matrix of inter-channel interference(ICI) is a scaled identity matrix based on which we derive an optimal pilot insertion scheme for the LS estimator in the sense of minimum mean square error. The proposed estimator has the advantages of low pilot ratio and robustness against inter-carrier interference.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.392-395
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• 2006

The configuration of coaxial co-rotating contained in shroud provides a useful model for investigating the characteristics of flow in the HDD. Reynolds number is defined as $Re_R={\Omega}{R_o}^2/{\upsilon},\;Re_H={\Omega}R_oH/{\upsilon}$ in present study. An experimental investigation was performed for turbulence profiles and PSD distribution and vortices frequency behavior for various range of $Re_R=2.43{\times}10^4{\sim}3.61{\times}10^5$. A laser Doppler anemometry (LDA) is used to obtain the velocity field of unobstructed co-rotating disks flow. Airflow pattern visualization between inner and outer region was compared with turbulence profiles measured from LDA. Outer detached shear layer and dead-zone without oscillating velocity fluctuation to circumferential mean were quantitively traced.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 추계학술대회논문집
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• pp.720-725
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• 2000

A new ultrasonic pulse-echo technique was developed and described for vibration measurement of the suspension assembly in hard disk drives. The method is based upon the difference in magnitude of two consecutive reflection waves from a moving object(suspension), while the traditional ultrasonic vibrometer uses the phase shift of the reference wave and the reflection wave. A cone-shape delay line is designed to access the small structure. A simple mathematical model is presented and analyzed with experimental results to show the feasibility of the method. The advantages of this ultrasonic vibration measurement method are relatively high resolution, low cost, and ease of implementation comparing with the Laser Doppler vibrometer.