• Journal of Mechanical Science and Technology
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• 제18권8호
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• pp.1479-1489
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• 2004

The effect of fluctuation of Equivalence Ratio (ER) in a turbulent reactive field has been studied in order to check the global combustion characteristics induced by the local fluctuation. When the flow is premixed on a large scale, closer examination on a small scale reveals that local fluctuations of ER exist in an imperfectly premixed mixture, and that these fluctuations must be considered to correctly estimate the mean reaction rate. The fluctuation effect is analyzed with DNS by considering the joint PDF of reactive scalar and ER, followed by modeling study where an extension of stochastic mixing models accounting for the ER fluctuation is reviewed and tested. It was found that models prediction capability as well as its potential is in favor to this case accounting the local ER fluctuation. However, the effect of local fluctuation did not show any notable changes on the mean global characteristics of combustion when statistical independence between the reactive scalar and ER field is imposed, though it greatly influenced the joint PDF distribution. The importance of taking into account the statistical dependency between ER and combustible at the initial phase is demonstrated by testing the modeled reaction rate.

• 동력기계공학회지
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• 제4권1호
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• pp.39-44
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• 2000

The purpose of this study is to investigate the flame structure and combustion characteristics in the model gas turbine combustor changing equivalence ratio. For this purpose, temperature and ion current were measured and these data were analyzed by the PDF and power spectra technique. We found that the flame length is longer while increasing the equivalence ratio in experimental condition, and especially ${\psi}=0.19$, combustion reaction was active by the stable swirl flow. and these flames were governed by the random three dimensional eddy.

• 대한전자공학회논문지TC
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• 제48권8호
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• pp.1-6
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• 2011

본 논문에서는 이중 홉 증폭 후 전달(AF: Amplify-and-Forward) 릴레이 시스템에 대한 새로운 성능 분석 기법을 레일리 페이딩 채널에 대하여 제안한다. 기존의 분석 기법들에서는 S-R-D(Source-Relay-Destination) 링크의 수신 신호 대 잡음비(SNR: Signal-to-Noise Ratio)에 대한 누적 분포 함수(CDF: Cumulative Distribution Function) 혹은 확률 밀도 함수 (PDF: Probability Density Function)로부터 모멘트 발생 함수(MGF: Moment Generating Function)를 유도한 후 평균 심벌 오류율을 유도된 MGF를 이용하여 표현하였다. 본 논문에서는 기존의 분석과 다른 새로운 접근법을 제안한다. 즉, S-R(Source-Relay) 링크 및 R-D(Relay-Destination) 링크의 PDF들로부터 S-R-D 링크에 대한 MGF를 직접 유도한다. 그리고 새롭게 유도된 MGF을 기존의 연구들에서 제시한 형태와 비교 분석한다. 또한 제안된 성능분석 기법의 정확성은 모의실험을 통하여 검증한다. 이를 통하여 제안된 분석 기법이 이중 홉 증폭 후 전달 릴레이 시스템에 대한 새로운 해를 제시함을 확인한다.

• 융합신호처리학회논문지
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• 제12권3호
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• pp.188-193
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• 2011

본 논문에서는 OADF(Opportunistic Adaptive Decode-and-Forward) 릴레이 시스템에 대한 새로운 성능분석 기법을 레일리 페이딩 채널에 대하여 제안하였다. 제안된 분석 기법에서는 릴레이들의 복호 오류 사건(error-event)을 기반으로 수신된 순시 신호대 잡음비(Signal-to-Noise Ratio: SNR)를 표현한다. 또한 SNR의 확률 밀도 함수(Probability Density Function: PDF)를 기존의 분석 기법보다 일반적인 (PDF 표현에서 합 기호의 개수 및 그 영역이 구체화된)형태로 제시한다. 그리고 이를 이용하여 정확한 평균 오류율((Average Error Rate), 누락 확률(Outage Probability) 및 평균 채널용량(Average Channel Capacity)을 일반적인 형태로 유도한다. 제안된 성능분석 기법의 정확성은 모의실험을 통하여 검증한다. OADF 기법을 다른 기법들과 비교하여 평균 오류 확률, 누락 확률 및 채널 용량 측면에서 성능 향상 정도가 우수함을 확인하였다.

• Asian-Australasian Journal of Animal Sciences
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• 제12권8호
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• pp.1241-1245
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• 1999

Nine two-year old sheep fitted with rumen and duodenum cannulas were used to study the effect of controlling protozoa flora on the degradation and utilization of dietary fibre and protein in the rumen and on nitrogenous flow to the duodenum. There were three groups in this experiment: defaunation (DF); partial defaunation (PDF); faunation (F) as control. Results showed that: 1,There were no differences between treatments in dietary DM degradation in the rumen, but defaunation and partial defaunation increased the quantity of nitrogenous material in the rumen and the flow of N to duodenum. 2, partial defaunation and defaunation improved the degradabilities of dietary NDF, ADF and HC, but there were no differences between the defaunated and partially defaunated groups. 3, Partial defaunation decreased the degradability of dietary protein in the rumen. There was no difference between defaunated and faunated groups. 4, Defaunation and partial defaunation increased the quantity of total N (TN) and microbial N (MCN) in the rumen and the amounts entering the duodenum. The protozoa N (PN) flow in the faunated group was higher than that in the partially defaunated group, and the amino acid pattern in the digesta at the proximal duodenum in the defaunated group was closer to the ideal amino acid pattern. 5, There were differences in the mole percent of acetic, propionic, total-VFAs and the non-glucogenic to glucogenic VFAs ratio (NGR) value in the rumen fluids. The order was as follows: mole percent of acetate: F>PDF>DF; mole percent of propionate: DF>PDF>F; total-VFAs: PDF>F>DF; NGR: F>PDF>DF.

• 대한기계학회논문집B
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• 제32권7호
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• pp.504-512
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• 2008

The characteristics of nonpremixed oxy-fuel flame in a multi-jet burner were experimentally and numerically investigated. The overall flow rate of fuel and oxygen was fixed, and the oxygen feeding ratio (OFR) was varied by 0.25, 0.5, and 0.75. The results of numerical simulation were compared with the measured results which are temperature profile and direct flame observation. The probability density function (PDF) model was applied accounting to the description between turbulence and chemistry, and standard ${\kappa}-{\varepsilon}$ model was used for turbulent flow field. Equilibrium assumption is very reasonable due to fast chemistry of the oxy-fuel combustion. Thus, the equilibrium calculation based on Gibbs free energy minimization was guaranteed to generate the solution of the oxy-fuel combustion. The result was obtained by numerical simulation. The predicted radial temperature profiles were in good agreement with the measured results. The flame length was shorten and was intensified with the decrease of OFR because the mixture of fuel and oxidizer are fast mixed and burnt. The maximum temperature became lower as the OFR increased, as a consequence of large flame surface area.

• 대한전자공학회논문지SP
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• 제47권4호
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• pp.69-78
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• 2010

대역분할 부호화방식의 표준인 비가역 9/7 JPEG2000의 경우 0.15bpp 이하에서 양자화 손실로 배경과 에지 부분에서 급격한 화질 왜곡이 발생하는 문제점을 갖고 있다. 본 논문에서는 이러한 문제를 해결하기 위해 고주파대역들의 L-pdf(Laplace probability density function) 통계특성을 이용한 VQ(Visual Quantizer)를 제안하였다. 제안된 VQ는 재생영상의 화질왜곡을 최소화하기 위한 비주얼파라메타와 효율적인 비트율 감축을 위한 가중치 파라메타를 각각 사용하여 설계되었다. 실험결과 제안된 VQ는 0.15bpp이하에서도 재생영상의 시각적 손실을 최소화하면서 재생영상의 화질왜곡 기준척도인 MSE(Mean-Squared Error)도 최소화 할 수 있었다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 하계종합학술대회 논문집(1)
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• pp.33-36
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• 2000

In this paper, the performance of the W-CDMA system with smart antenna is investigated. The channel is assumed as wideband realistic channel mode, JTC(Joint Technique Committee), which has clustered multipaths. The beamforming-RAKE receiver structure is proposed, whose performance is analyzed on the assumption of the perfect channel estimation. In a simulation, the probability density function(pdf) of SINR(Signal to Interference and Noise Ratio) according to the number of antennas and users is presented. And based on the pdf of SINR, the BER(Bit Error Rate) is presented. According to the result of a simulation, the performance of the W-CDMA system with smart antenna over the realistic JTC channel model has been considerably improved.

• International Journal of Contents
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• 제14권1호
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• pp.18-27
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• 2018

The objective of this study was to derive approximate closed-form error rates for M-ary burst symbol transmission (MBST) of dual-hop adaptive decode-and-forward (ADF) cooperative relay systems over quasi-static Rayleigh fading channels. Within a burst, there are pilot symbols and data symbols. Pilot symbols are used for channel estimation schemes and each relay node's transmission mode selection schemes. At first, our focus was on ADF relay systems' error-events at relay nodes. Each event's occurrence probability and probability density function (PDF) were then derived. With error-event based approach, we derived a tractable form of PDF for combined signal-to-noise ratio (SNR). Averaged error rates were then derived as approximate expressions for arbitrary link SNR with different modulation orders and numbers of relays. Its accuracy was verified by comparison with simulation results.

• 한국전자파학회논문지
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• 제11권7호
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• pp.1176-1185
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• 2000

In this paper, we analyze the distribution of the envelope of the received signal over frequency-nonselective slow Rician fading channels with aadditive white Gaussian noise(AWGN). Especially, we can obtain the error rate performance of noncoherent M-ary FSK(MFSK) over slow and flat Rician fading channels and AWGN from the new probability density function(PDF) of the envelope, not PDF of the instantaneous signal-to-noise ratio(SNR) published before, of the received signal. When coherent MFSK signals experience the Rician fading channel, the performances are derived, using the union bound.