• Proceedings of the IEEK Conference
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• 2005.11a
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• pp.97-100
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• 2005

우리는 페이딩 환경에서 비동기 블록 수신 CPFSK에 적용되는 TCM의 성능을 분석하였다. 여기서 비동기 블록 수신기는 N개의 심볼을 하나의 블록으로 취급하여 비동기 복조를 수행한다. 일반적으로 이러한 블록 수신 방식은 관찰 블록의 길이가 길어질수록 더 좋은 성능을 나타낸다. 그러나 페이딩의 응집 시간이 수신기의 관찰 블록 길이 보다 작아지면, 블록 수신기의 오류 성능은 매우 나빠지게 된다. 본 논문에서는 페이딩의 응집 시간이 수신기의 관찰 블록 시간 NT(여기서, T는 심볼 시간)보다 큰 환경을 저속 페이딩 환경 이라고 하고, 그렇지 않은 환경을 고속 페이딩 환경이라고 정의하여, 각각의 환경에서 시스템의 성능을 분석하였다. 그 결과 고속 페이딩 환경에서 비동기 블록 수신기의 사용은 오류 층(error floor) 현상을 초래한다는 사실을 알 수 있었다. 따라서 고속 페이딩 환경에서는 수신기의 관찰 블록 길이를 짧게 하는 것이 더 좋다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.1000-1002
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• 2017

Here, the unsteady Navier-Stokes solver has been developed using implicit dual time stepping method. The implicit dual time stepping method introduced the pseudo time step for solving the new residual including the steady state residual and real time derivative. For the validation of code, Stokes 2nd problem, the laminar flow on the oscillating flat plate was selected and compare the calculating results with analytic solutions. The calculating velocity profile and skin friction has a good agreement with analytic solutions.

• Proceedings of the Korean Environmental Sciences Society Conference
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• 2002.05b
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• pp.185-186
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• 2002

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.26-26
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• 2015

기후변화나 인위적인 요인 등에 의해 수문 자료에 비정상성(nonstationarity)이 나타나면서 정상성 가정 하에서 수행되는 빈도해석으로는 정확한 확률수문량 산정이 어려운 실정이다. 최근 이를 보완하기 위한 비정상성 빈도해석에 대한 연구가 진행되고 있고, 이와 더불어 비정상성 지역빈도 해석에 대한 관심도 높아지고 있다. 비정상성 지역빈도해석은 대개 홍수지수법(index flood method)을 기반으로 진행되고 있는데, 홍수지수와 성장곡선(growth curve)에 시간에 따른 변화를 고려하느냐의 여부에 따라 다양한 형태의 홍수지수모형이 적용되고 있다. 본 연구는 다양한 형태의 홍수지수모형의 성능을 평가하여 비정상성 자료에 적합한 형태를 선정하는 것을 목적으로 한다. 이를 위해 위치 매개변수가 시간에 따라 변화하는 비정상성 GEV 분포(GEV100)를 모분포로 하는 지점들로 지역들을 구성하고, Monte Carlo 모의를 통해 발생시킨 자료에 여러 형태의 홍수지수모형을 적용하여 각 모형의 성능을 평가하였다. 모의실험 결과 홍수 지수는 시간에 따른 변화가 없고, 성장곡선은 시간에 따라 변화하는 형태인 홍수지수모형이 다른 형태의 모형에 비해 대체로 더 정확한 확률수문량을 산정할 수 있는 것으로 나타났다. 또한 우리나라 기상청 관할 강우 관측 지점들 중 GEV100 분포가 적합한 것으로 선정된 지점들을 하나의 지역으로 구성하여 모의실험에서 적용한 것과 동일한, 여러 형태의 홍수지수모형을 적용한 결과 모의실험 결과와 일치하게 성장곡선에만 비정상성 고려된 홍수지수모형이 상대적으로 정확한 확률강우량을 산정하는 것으로 나타났다. 따라서 GEV100 모형 기반의 비정상성 지역빈도해석을 수행하기 위해서는 성장곡선만 시간에 따라 변화하는 홍수지수모형이 적합할 것으로 판단된다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.1A
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• pp.237-246
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• 2006

In order to evaluate the seismic performance of damaged reinforced concrete members, particularly bridge piers, an inelastic time-dependent element is proposed. The proposed element enables increased characteristics due to structural intervention(i.e., repair or retrofitting) to be accurately reflected to the degraded strength and stiffness of the members. The inelastic time-dependent element having both birth and death time can freely be activated within the user-defined time intervals during static and dynamic time-history analysis. Comparative studies are carried out for reinforced concrete bridge piers that are repaired and retrofitted. Analytical predictions using the developed element show reasonable correlation with experimental results. Also conducted is a nonlinear time-history analysis of a reinforced concrete bridge under multiple earthquakes. The comparative analytical results prove the validation of current development. In all, it is concluded that the present element is capable of providing salient features for the healthy evaluation of seismic performance and hence seismic stability assessment of RC bridge piers being repaired and retrofitted.

• The Journal of the Korea Contents Association
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• v.22 no.2
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• pp.593-604
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• 2022

This study examines how auditors respond to labor investment inefficiency, specifically its impact on audit fees and audit hours. Using a sample of Korean firms listed on the Korea Stock Exchange from 2003 to 2018, our empirical results indicate that firms involved in inefficient investment in labor incur higher audit fees and audit hours. This implies that auditors consider inefficient labor investment to cause considerable business risk, thus requesting higher external audit fees to compensate for higher audit risk. Furthermore, auditors expend more time and effort while auditing those firms by expanding the audit procedures to reduce the audit risk to an acceptable level. Finally, this study provides empirical evidence on whether the investment inefficiency in labor, an important factor in firms' competitiveness, incur higher audit fees as well as audit hours.

• Journal of the East Asian Society of Dietary Life
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• v.12 no.1
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• pp.38-46
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• 2002

This study was carried out in order to investigate dextran formation and internal structure during fermentation of the oligosaccharide Jeung-Pyun. The dextran and sugar reducing contents of Jeung-Pyun batter and the specific volume and the internal structure of Jeung-Pyun were analyzed as a function of fermentation time. The specific volume of Jeung-Pyun peaked at the 7th hour of fermentation. The dextran content of Jeung-Pyun batters peaked at the 7~13th hour of fermentation, and Fructooligosaccharide Jeung-Pyun had the least peak value. Reducing sugar content of Jeung-Pyun batters slowly decreased as fermentation progressed. From the air pore size and distribution of Jeung-Pyun observed by SEM, the sucrose Jeung-Pyun fermented for 3~7 hours and oligosaccharide one fermented for 7 hours were judged as the best. It was concluded that dextran may be formed by fermentation of oligosaccharides as well as sucrose and dextran has a significant role on the volume expansion of Jeung-Pyun.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.1
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• pp.97-107
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• 2020

In this study, finite element analysis was carried out through the finite element analysis program (ANSYS) to investigate the fire resistance of composite columns in fire. Transient heat transfer analysis and static structural analysis were performed according to ASTM E 119 heating curve and axial force ratio 0.7, 0.6, 0.5 by applying stress-strain curves according to temperature, and loading heating experiments were carried out under the same conditions. In addition, the nominal compressive strength of the composite column according to the heating time according to the standard(Eurocode 4) was calculated and expressed as the axial force ratio and compared with the analytical and experimental values. Through the analysis, As a result of finite element analysis, the fire resistance time was 180 minutes and similar value to the experimental value was obtained, whereas the fire resistance time 150 minutes and 60 minutes were derived from the axial force ratios 0.6 and 0.7. In addition, it was confirmed that the fire resistance time according to the axial force ratio calculated according to the reference equation (Eurocode 4) was lower than the actual experimental value. However, it was confirmed that the standard(Eurocode 4) was higher than the experimental value at the axial force ratio of 0.7. Accordingly, it is possible to confirm the fire resistance characteristics(time-axial force ratio relationship) of the SRC column at high axial force, and to use the experimental and anaylsis data of the SRC column as the data for verification based on Eurocode.

• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.4
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• pp.367-381
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• 2020

This paper presents the seal material mixing ratio of tunnel umbrella arch reinforcement method. Currently, there is no clear standard for the proper gelation time and curing time of the Seal material in Korea, and the quality control is also difficult because it cannot be verified. In response, the ratio of the mixture of the seal material was composed of four types of indoor experiments, and the amount of gelation time and bleed was checked. In addition, a non-cart penetration test confirmed the curing time and compared the ratio of each combination. Further experiments on W/C 120% identified the effect of mixing speed and time on the seal material. A total of three field experiments were conducted based on indoor experiments, and the size and strength of bulb formation were compared by checking the curing time of the specimen and main injection. Comparisons show that the lower W/C, the stronger the strength, the larger the size of the bulb, and the faster the hardening time appears. Based on the results of the gelation time and curing time, it was deemed that the mixing ratio of W/C 120% is most appropriate when applied to the actual site.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.7B
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• pp.1021-1033
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• 2001

본 논문에서는 초광대역 시간 도약 임펄스 무선 전송 (ultra wideband time hopping impulse radio) 다원 접속 시스템을 위한 잡음 부호 기반의 새로운 시간 도약 시퀀스를 제안한다. 임펄스 무선 전송 시스템에 대한 지금까지의 연구에서는 대부분 이상적인 랜덤 시간 도약 시퀀스를 사용하여 여러 사용자가 다원 접속한다고 가정하였다. 본 논문에서는 동일 차수의 다수 m-시퀀스와 십진화기를 이용하여 구현 가능한 시간 도약 시퀀스를 제안하고, 여러 사용자의 동기식 및 비동기식 접속 상황에 대한 모의 실험을 통해 이상적인 랜덤 시퀀스와 유사한 우수한 비트오율 성능을 얻을 수 있음을 확인하였다. 또한 제안된 시간 도약 시퀀스를 사용하는 경우 좀 더 일반적인 상황인 비동기식 다원 접속이 동기식 다원 접속에 비해 우수한 성능을 얻을 수 있음을 분석한다.