• 대한전자공학회논문지TC
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• 제42권2호
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• pp.17-22
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• 2005

본 논문에서는 OFDMA 역방향 시스템에서 시간오차에 의한 사용자간 간섭을 분석하고 역방향 수신기의 성능 열화 정도를 제시한다. 이를 위해, 각 사용자의 서로 다른 시간오차를 기준 사용자 대한 상대적인 시간오차로 표현한다. 그리고 역방향 수신기의 평균 신호대 간섭잡음비를 상대적인 시간오차의 최대값을 변수로 갖는 함수로 유도한다. 분석결과는 상대적인 시간오차 증가에 의한 평균 신호대 간섭잡음비의 성능 열화로 확인하였다. 또한, 데이터 부반송파 사이의 보호 부반송파를 사용하여 상대적인 시간오차에 의한 사용자간 간섭의 영향을 감소시킬 수 있음을 확인하였다.

• 한국의류학회지
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• 제26권5호
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• pp.606-617
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• 2002

The purpose of this study is to develop a decision model that helps manufacturers and retailers determine the optimal timing of markdown in order to maximize their profit. An optimal timing decision model was developed based on three steps; conjoint measurement, scenario analysis and simulation. Data were collected from the sample of 149 out of 170 undergraduate and graduate students in Seoul in 1997. From the Jeans market, 8 brands; Levi's, lee, Guess, Calvin Klein, Pintos, Get used, MFG, and Basic, were selected as competitors for this study. In the conjoint measurement, respondents estimated the level of preference, from 1 to 100, for each item in which brand, price, style, and colors were used to explain product characteristics. Then, in order to reflect competitive situation in Jeans market, four types of scenarios were developed. In each scenario, simulations were applied to decide optimal timing of markdowns that leads to maximal profitability and sales volume. The profit was calculated based on the equation; Profit = Jean's market volume x market share of each brand - cost, where market volume was obtained by integral calculus for market utility function, and market share by logit value of part-worth from the conjoint analysis. For the purpose of the parsimony of the research, costs and the level of markdown were fixed to 30% of the regular price. In results, the optimal timing decision model identified 3 different types of brands. The brands that do not need to take markdown were Ievi's, MFG, and Basic Jeans characterized by the highest brand power and the highest price zone. The brands that needed to take early markdowns were Guess, Lee, Calvin Klein, and Get Used with the intermediate level of brand power and price. The brand that need late markdown was Pintos with the weakest brand power among the competitors and the lowest price. The optimal range of markdown remains for further research.

• Journal of Computing Science and Engineering
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• 제3권4호
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• pp.195-215
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• 2009

Worst-case execution time (WCET) analysis is critical for hard real-time systems to ensure that different tasks can meet their respective deadlines. While significant progress has been made for WCET analysis of instruction caches, the data cache timing analysis, especially for set-associative data caches, is rather limited. This paper proposes an approach to safely and tightly bounding data cache performance by computing the worst-case stack distance of data cache accesses. Our approach can not only be applied to direct-mapped caches, but also be used for set-associative or even fully-associative caches without increasing the complexity of analysis. Moreover, the proposed approach can statically categorize worst-case data cache misses into cold, conflict, and capacity misses, which can provide useful insights for designers to enhance the worst-case data cache performance. Our evaluation shows that the proposed data cache timing analysis technique can safely and accurately estimate the worst-case data cache performance, and the overestimation as compared to the observed worst-case data cache misses is within 1% on average.

• 대한물리의학회지
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• 제5권4호
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• pp.605-613
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• 2010

Purpose : The purpose of this study was to investigate the VMO/VL ratio and onset timing using EMG biofeedback training over a 5-day period. Methods : Twenty-one healthy female college students with no known right knee musculoskeletal dysfunction were recruited this study. Muscle activity was measured by surface electromyography(Myosystem 1400A, Noraxon Inc., U.S.A). Statistical analysis was used two-way repeated ANOVA to know difference between the vastus lateralis and vastus medialis oblique onset timing differences, VMO/VL ratio. Results : Biofeedback training group significantly improved VMO/VL ratio and EMG activity of the vastus medialis oblique after intervention. Conclusion : These result indicate that biofeedback training on the vastus medialis oblique has effect on the VMO/VL ratio. EMG biofeedback can be recommended for the facilitation of VMO muscular recruitment.

• 한국경영과학회지
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• 제26권4호
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• pp.83-97
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• 2001

Net Present Value (NPV) criterion has been the most widely used criterion to evaluate investment opportunities. However, the analysis based on the NPV criterion falls to consider the managerial flexibility of deferring decisions until major uncertainty is resolved. Recently, real options method attracted a lot of attention as a Powerful approach to address the problem. If investment decision is deferred, the value of the investment opportunity increases but opportunity cost increases at the same time. Therefore, it is important to decide the optimal timing how long the decision can be deferred. In this paper, we developed a model deciding the optimal decision timing. Using the real options approach, the model derived the optimal deferring time until a decision is made. Then, the model was applied to a Korean mobile telecommunications company who wants to invest on the wireless resale business. We believe that this model would be very useful to overcome the problem of NPV decision criterion. With this approach, we can make contingent decisions based on the observation of uncertainly resolutions.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2003년도 하계종합학술대회 논문집 I
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• pp.226-229
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• 2003

Under the prsence of the frequency and timing offset, we evaluate the BER performance of the FFH-MA system using noncoherent M-ary FSK modulation in the Rayleigh fading channel. The numerical resuts show that while the frequency and timing offset increases at a given SNR, the BER is severely degraded. The threshold level used in the envelope detector increases with the increase of the frequency and timing offset, and with the proper selection of the threshold level, the BER can be improved under the presence of such offsets.

• 오토저널
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• 제14권4호
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• pp.79-89
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• 1992

The behavior of belt tension in OHC drive timing belt system was investigated analytically and experimentally for (1)fixed and (2)automatic tensioner. From the numerical results it was found that the automatic tensioner makes the belt tension larger than those of the fixed tensioner. When the initial belt tension decreased due to the belt elongation, the belt tension of the fixed tensioner could decrease to near zero while the belt tension for the automatic tensioner maintained above zero by the tensioner spring. The mean valve and the difference between the maximum and the minimum belt tension for the automatic tensioner increased compared with those of the fixed tensioner. Also, the numerical results for a hydraulic tensioner showed that the hydraulic tensioner has the good parts of both tensioners; i.e., thesmaller amplitude in belt tension and the higher mean tension. Experimental results for the automatic and fixed tensioner of the OHC timing belt system were in agreement with the theoretical results.

• 대한기계학회논문집
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• 제16권4호
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• pp.649-657
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• 1992

본 연구에서는 스테핑 모터의 토크특성과 전동시스템의 미스얼라인 먼트에 의 한 플리편심을 고려하여 스페핑 모터 구동 타이밍벨트 전동시스템의 전동오차에 관한 이론 및 실험적 연구를 수행하고, 전동오차 감소를 위한 설계 개선 기초자료를 얻고자 한다.

• 한국자동차공학회논문집
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• 제22권7호
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• pp.98-106
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• 2014

Emission standards for passenger diesel engines are becoming more and more stringent. Especially, Europe started the regulation of nano-particles from 2011 with EURO 5b. The objective of this study is to investigate the effect of fuel injection strategy on combustion and nano-particle emission in a small diesel engine. In this study, we conducted combustion analysis and measured both the weight of PM and number of nano-particels. At first, the optimum injection timing was determined with fixed engine operating conditions, such as engine speed, load, and fuel injection quantity. After that, the injection timing was controlled, and the effect of pilot injection was investigated. The number of nano-particles increased as engine load decreases, and it increased up to 10 times depending on the change of injection timing. The weight of PM emissions was increased at low load, and the PM emissions increased with increasing the number of pilot injections.

• 대한산업공학회지
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• 제32권3호
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• pp.180-190
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• 2006

We evaluate the economic value and the optimal investment timing of IMT-2000 in Korea, in the perspective of a service provider who owns the business license for IMT-2000, by using the real options analysis. The result clearly shows the project value with options is positive and delaying the investment is more favorable to the provider. Binomial lattice approach, in which we try to describe American call option and sequential compound option, and sensitivity analysis present the optimal decisions according to future states and enable the management to make decision strategically and proactively.