• 한국항행학회논문지
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• 제6권3호
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• pp.203-210
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• 2002

본 논문에서는 IEEE 802.11a의 규격에 따라 OFDM 우선 LAN 모뎀과 프레임 포맷을 구성하여 시뮬레이션에 의해 BER 성능을 분석하고 수정된 채널 예측 알고리즘을 적용하여 채널예측성능이 개선됨을 보인다. 채널 예측에 이용되는 실내 무선채널로서는 AWGN과 TDL 모델을 적용한 지연확산채널을 고려한다. 우선 AWGN 환경에서 규격에 제시된 전송속도 및 부호율에 따른 OFDM 무선 LAN 시스템의 성능을 분석한다. 다음으로 실내 우선 채널 환경에서 채널추정이 불완전한 경우에 대해, 기존의 채널추정방식으로서 프리앰블 내의 2개의 Long 훈련심볼을 이용하여 채널을 추정하는 경우에 대한 성능을 분석하고, 수정된 채널추정기법으로는 IEEE 802.11a의 프리앰블 구조를 변경하지 않으면서 Long 훈련심볼뿐만 아니라 전체 10개의 Short 훈련심볼 중 8개의 훈련 심볼들을 채널추정에 부가적으로 사용하는 방식을 채용한 경우의 성능을 분석하여 기존의 방식과 비교한다. 시뮬레이션 결과의 분석으로부터 수정된 채널추정방식을 적용하는 경우, 규격에 정의된 프리앰블 구조의 변경 없이도 잡음을 억제하는 효과를 향상시킴으로써 채널추정오차가 감소되어 채널추정성능이 개선됨을 확인하였다.

• 유통과학연구
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• 제18권1호
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• pp.5-13
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• 2020

Purpose: The purpose of this study is to examine the growth and change process of Korean cosmetic market that has grown more than three times since 2000. It also examined how the growth and decline of the cosmetics brands are related to the change of the cosmetic distribution structure. Research methodology: This study tried to classify the change of the Korean cosmetics market into four stages based on the market sales information. It analyzed the sales information of Korean cosmetic companies and the relationship with the sales of the brands by distribution channel. Results: One-brand store channel had played a leading role in the market growth, and multi-brand stores have grown and a number of brands also grew through that channel since 2013. Since 2016, multi-brand stores have continued to grow and have dominated the market beyond one-brand store channel. Conclusions: The changes in sales of domestic cosmetics companies have been classified based on the distribution channel type in four stages: the emergence of one-brand store, the growth of one-brand store channel, the growth of multi-brand store channel, and the decline of one-brand store channel. In conclusion, multi-brand store channels have recently grown in the Korean cosmetics market, and this trend is expected to continue.

• Nuclear Engineering and Technology
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• 제20권2호
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• pp.80-87
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• 1988

소형냉각재상실사고(SBLOCA)와 대형냉각재상실사고(LBLOCA)중에 노심의 Average Channel과 Hot Channel에서의 유량분포를 예측하였다. 아울러 REALP5/MOD2 코드를 사용하여 두 채널사이의 교차류고려여부가 실제사고 분석결과에 미치는 영향을 평가하였다. 현재까지 SBLOCA계산에서는 노심을 한개의 채널로 모델하는 것이 충분하다고 판단되어 왔으나 본 계산결과에 의하면 보수적인 계산을 위해서는 Hot Channel 모델링이 필요한 것으로 밝혀졌다. 그러나 LBLOCA Blowdown Phase존에서는 교차류의 고려 여부에 상관없이 Hot Channel 이 Average Channel보다 보수적 인 결과를 가져오며, 교차류의 영향도 미세한 것으로 판명되었다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권3호
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• pp.1098-1112
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• 2018

Achievable sum rate and energy efficiency (EE) are investigated for the massive multiple-input multiple-output (Massive MIMO) downlink with channel aging in the time varying Ricean fading channel. Specifically, the expression of the achievable sum rate of the system for the maximum ratio transmission (MRT) precoder with aged channel state information (CSI) in the time varying Ricean fading channel is first presented. Based on the expression, the effect of both channel aging and the Ricean factor on the power scaling law are studied. It is found that the transmit power of base station (BS) is scaled down by $1/{\sqrt{M}}$(where M is the number of the BS antennas) when the Ricean factor K is equal to zero (i.e., time varying Rayleigh fading channel), indicating that aged CSI does not affect the power scaling law. However, the transmit power of the BS is scaled down by 1/M for the time varying Ricean fading channel (where $K{\neq}0$) indicating that the Ricean factor affects the power scaling law and sum rate, and channel aging only leads to a reduction of the sum rate. Second, the EE of the system is analyzed based on the general power consumption model. Both the theoretical analysis and the simulations show that the channel aging could degrade the sum rate and the EE of the system, and it does not affect the power scaling law.

• Korean Chemical Engineering Research
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• 제53권6호
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• pp.818-823
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• 2015

본 연구에서는 전산유체역학(CFD)을 이용하여 마이크로채널 내부의 Fischer-Tropsch(FT) 반응을 모사하였고, 나아가 반응채널의 너비와 높이, 냉각채널과의 거리 그리고 채널 사이 간격을 변수로 두고 채널 내부 온도에 대해 민감도 분석을 수행하였다. 마이크로채널 반응기는 채널 간의 열교환을 고려하기 위한 5개의 반응채널과 냉각채널을 대신한 냉각면으로 이루어져 있으며 채널의 높이와 너비를 포함한 변수들의 길이는 0.5 mm ~ 5.0 mm 범위에서 설정하였다. 반응물로는 $H_2$와 CO의 혼합기체($H_2/CO$ molar ratio=2)를 사용하였으며 반응기의 운전 조건은 $GHSV=10000h^{-1}$, 압력 20 bar와 온도 483 K($210^{\circ}C$)이다. 민감도 분석의 결과로 반응채널 내부의 최대 온도는 채널의 높이에 비례하며 너비에 대해서는 특정 길이 이상에서 영향을 받지 않는 것을 확인하였으며 이 중에 냉각채널과의 거리와 채널 사이 간격은 채널 내부 온도에 거의 영향을 미치지 않았다. 따라서 채널 레이아웃에서 반응채널의 높이는 짧을수록(약 2 mm 이하), 너비는 길수록(약 4 mm 이상) 열제거뿐만 아니라 생산량 측면에서 이득을 얻을 수 있었다.

• The Korean Journal of Physiology and Pharmacology
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• 제2권5호
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• pp.549-553
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• 1998

Using the planar lipid bilayer method, we investigated the effect of d-tubocurarine (dTC) on the extracellular side of large-conductance $Ca^{2+}-activated\;K^+$ channel from rat brain. When the initial open probability (Po) of the channel was relatively high, dTC decreased channel activity in a concentration dependent manner. In contrast, when the initial Po was lower, sub-micro molar dTC increased channel activity by destabilizing the closed states of the channel. Further addition of dTC up to micro molar range decreased channel activity. This dual effect of dTC implicates that there exist at least two different binding sites for dTC.

• 복식문화연구
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• 제26권3호
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• pp.346-359
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• 2018

Currently, dramatic change had led to the growth of the distribution environment and the retailer's distribution channel. This change had shifted the 'single channel' to 'multi channel', and from 'cross channel' to 'omni channel'. While fashion companies using omni channel are rapidly growing, few research regarding omni channel had been done in academic field. In this study, we examined the influence of omni channel characteristics on consumers' perceived risk as well as consumers' perceived risk toward attitude and intention to use omni channel. We surveyed 696 male and female respondents aged 20 to 40 who lived in Seoul and the metropolitan area. Using AMOS 20.0, factor analysis, reliability analysis, and structural equation model analysis were performed to verify the model of this study. The results were as follows. First, omni channel's instant connectivity, location-based provability, interactivity, and entertainment factors did not decrease impacts on the perceived risk related to privacy and annoyance. Second, omni channel's instant connectivity and entertainment did not increase effects on the perceived financial risk, and location-based provability and interactivity did not increase effect on perceived financial risk. Third, the perceived risk concerning omni channel did not decrease on consumer attitude toward omni channel. Fourth, consumer attitude toward omni channel influenced the intention to use omni channel significantly.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.199-200
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• 2006

It will not be an exaggeration to say that one of the most important features of RT (Rapid Tooling) technology is to easy manufacturing complex shape of cooling channel in injection mold. That is, RT technology is hardly influenced complex shape of tool, Therefore, mold designer can optimize the position and shape of cooling channel whatever they want. In this study, we optimized cooling channel through CAE analysis to solve the problem; prototype-connector-mold applied conventional cooling channel, locally warped by internal stress: The effect of three-dimensional cooling channel was supported by simulation result. But it is impossible to produce injection mold applied three-dimensional cooling channel through machining operation. Therefore, we produced the prototype-connector-mold with three-dimensional cooling channel using Direct Metal Laser Sintering (DMLS) process, and get good-quality prototype-connector without warpage.

• Journal of Mechanical Science and Technology
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• 제16권8호
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• pp.1144-1153
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• 2002

A hybrid performance prediction method is proposed in the present study. A channel diffuser is divided into four subregions: vaneless space, semi-vaneless space, channel, and channel exit region. One-dimensional compressible core flow and boundary layer calculation of each region with an incidence loss model and empirical correlation of residuary pressure recovery coefficient of a channel predict the performance of diffusers. Three channel diffusers are designed and tested for validating the developed prediction method. The pressure distributions from an impeller exit to the channel diffuser exit are measured and discussed for various operating conditions from choke to nearly surge conditions. The strong non-uniform pressure distribution which is caused by impeller-diffuser interaction is obtained over the vaneless and semi-vaneless spaces. The predicted performance shows good agreement with the measured performance of diffusers at a design condition as well as at off-design conditions.

• 음성과학
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• 제11권1호
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• pp.43-52
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• 2004

This paper concerns an effective dual-channel noise reduction method to increase the performance of speech recognition in a car environment. While various single channel methods have already been developed and dual-channel methods have been studied somewhat, their effectiveness in real environments, such as in cars, has not yet been formally proven in terms of achieving acceptable performance level. Our aim is to remedy the low performance of the single and dual-channel noise reduction methods. This paper proposes an effective dual-channel noise reduction method based on a high-pass filter and front-end processing of the eigendecomposition method. We experimented with a real multi-channel car database and compared the results with respect to the microphones arrangements. From the analysis and results, we show that the enhanced eigendecomposition method combined with high-pass filter indeed significantly improve the speech recognition performance under a dual-channel environment.