• 대한전자공학회논문지SP
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• 제41권5호
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• pp.275-282
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• 2004

본 논문에서는 30 Hz 프레임 율의 MPEG-4 simple profile 비디오 비트스트림을 15 Hz 프레임 율을 갖는 H.264 baseline profile 비디오 비트스트림으로 변환하는 트랜스코딩을 제안한다. MPEG긱의 블록 모드(block mode)와 움직임 벡터(Motion Vector) 정보를 H.264에서 이용 가능하도록 블록 모드 변환을 수행하고, MPEG-4의 움직임 벡터 보간을 이용하여 H.264에서 움직임 예측(Motion Estimation) 없이 정수 화소 단위로 움직임 벡터를 찾는 3가지 움직임 벡터 보간 (Motion Vector Interpolation) 방법을 실험한다. 이와 같은 방법을 이용해서 움직임 예측 시 소요되는 계산량을 줄이고 낮은 대역폭에서 심각한 화질 열화가 없는 트랜스코더를 제안한다. 실험 결과 제안된 방법은 직렬 화소영역 트랜스코딩에 비해 신호 대 잡음비(PSNR: peak signal to noise ratio)는 실험 영상에 따라 높은 비트율에서는 0.2dB에서 낮은 비트율에서 0.9dB의 손실이 있으나 전체 수행 시간은 3.2배에서 4배 빨라진다.

• 한국전자파학회논문지
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• 제17권12호
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• pp.1224-1230
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• 2006

본 논문에서는 제한된 피드백 정보를 사용하는 공간 다중화 시스템을 위한 preceding 기법을 제안하였다. 제안하는 precoding 기법은 unitary 행렬로 구성된 precoder 코드북내에서 preceding 행렬의 선택 정보를 송신단에 전달하는 장구간 피드백과 선택된 unitary 행렬의 열 벡터 중 전송체 사용될 열 벡터 정보를 송신단에 전달하는 단구간 피드백을 이용한다. 또한, zero-forcing 수신기를 사용하는 $2{\times}2$ MIMO 시스템에 대해 평균 throughput을 최대화하는 precoder 코드북을 디자인하였다. 모의 실험 결과에 따르면 제안된 기법은 몇 비트의 장구간 피드백 정보를 추가함으로써 평균 SNR이 20 dB인 환경에서 멀티모드 안테나 선택 기술이나 멀티모드 기저 선택 기술에 비해 throughput 성능이 각각 11.2 %, 5.1 % 증가한다.

• 한국지진공학회논문집
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• 제2권1호
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• pp.35-46
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• 1998

대부분의 손상도 추정법들을 부재의 손상을 해당부재의 평균적인 강성감소로 표현하였다. 본 연구에서는 보다 실제적인 손상도를 추정하기 위하여, 접합부의 손상을 도입하였다. 접합부의 모형화를 위하여 보의 양단에 회전스프링을 추가하였으며, 접합부 손상을 접합부 강성의 감소로 정의하였다. 접합부의 손상도를 계측된 모드벡터를 바탕으로하여, 신경망기법을 추정하였다. 효율적인 훈련패턴을 만들기 위하여 Latin Hypercube Sampling 기법을 도입하였으며, 국부영역에서의 손상도추정을 위하여 부구조법을 도입하였다. 제안된 기법의 효율성을 검증하기 위하여 10층 프레임구조물에 대한 수치해석결과를 이용하였다. 예제해석을 통하여 추정결과가 상당히 정확함을 확인하여, 실제 적용 가능한 방법임을 알수 있었다.

• ALGAE
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• 제34권4호
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• pp.303-313
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• 2019

Floating seaweed rafts are a surface-pelagic habitat that serve as substrates for benthic flora and fauna. Since 2008, Sargassum horneri clumps have periodically invaded the Korea Strait. In this study, the polymerase chain reaction-free small-organelles enriched metagenomics method was adopted to identify the species of epibiotic eukaryotes present in floating S. horneri fronds. A total of 185 species were identified, of which about 63% were previously undetected or unreported in Korean waters. The rafts harbored a diverse assemblage of eukaryotic species, including 39 Alveolata, 4 Archaeplastida, 95 Opisthokonts, 4 Rhizaria, and 43 Stramenopiles. Of these 185 taxa, 48 species were found at both Sargassum rafts collection stations and included 24 Stramenopiles, 17 Alveolata, and 7 Opisthokonts. Among these, the highest proportion (50%) of species was photo-autotrophic in basic trophic modes, while the proportion of phagotrophic, osmo- or saprotrophic, and parasitic modes were 43.8%, 4.2%, and 2.1%, respectively. This study demonstrates the contribution of floating Sargassum rafts as dispersal vectors that facilitate the spread of alien species.

• 해양환경안전학회지
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• 제7권1호
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• pp.15-23
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• 2001

In regulation of IGC code 12.1 mechanical ventilation should be arranged to ensure sufficient air movement through the space to avoid the accumulation of flammable or toxic vapours and ensure a safe working environment, but in no case should the ventilation system have a capacity of less than 30 changes of air per hour baed upon the total volume of the space. In this study, a scaled mode chamber was constructed to investigate the ventilation characteristics and stagnation area in the hood room of LNG carrier and pump room in tanker. An experimental study was performed on the model by using visualization equipment with a laser apparatus and an image intensifier CCD camera. Twelve different kinds of measuring areas were selected as the experimental condition. Instant simultaneous velocity vectors in the whole fields were measured by a 2-D PIV system A three-dimensional numerical simulation was also carried out for three different Reynolds numbers. Then the CFD predictions were discussed with the experimental results. The results show the spiral L-shape flow that moves from the opening on the left wall diagonally to the upper right part dominates the ventilation structure. The stationary area of hood room in the velcoity distributions was located in the upper left stern part.

• 한국공간구조학회논문집
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• 제15권2호
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• pp.51-59
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• 2015

In this study, a shape design and an analysis considering structural stability were investigated to develop an icosahedron-based hemispherical modular dome. To design this modular dome, a program that can perform icosahedron shape modeling, modularization of joint connection members, and the analysis of structural stability was developed. Furthermore, based on the adopted numerical model, the eigen buckling mode, unstable behavior characteristics according to load vector, and the critical buckling load of the modular dome under uniformly distributed load and concentrated load were analyzed, and the resistance capacities of the structure according to different load vectors were compared. The analysis results for the modular dome suggest that the developed program can perform joint modeling for shape design as well as modular member design, and adequately expressed the nonlinear behaviors of structured according to load conditions. The critical buckling load results also correctly reflected the characteristics of the load conditions. The uniformly distributed load was more advantageous to the structural stability than concentrated load.

• Smart Structures and Systems
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• 제26권4호
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• pp.419-433
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• 2020

Investigation of structural integrity has been a critical issue in the field of civil engineering for years. Visual inspection is one of the most available methods to explore deteriorative components in structures. Still, this method is not applicable to invisible damage of structures. Alternatively, system identification methods are capable of tracking modal properties of structures over time. The deviation of these dynamic properties can serve as indicators to access structural integrity. In this study, a modal tracking technique using frequency-domain system identification from seismic responses of structures is proposed. The method first segments the measured signals into overlapped sequential portions and then establishes multiple Hankel matrices. Each Hankel matrix is then converted to the frequency domain, and a temporal-average frequency-domain Hankel matrix can be calculated. This study also proposes the frequency band selection that can divide the frequency-domain Hankel matrix into several portions in accordance with referenced natural frequencies. Once these referenced natural frequencies are unavailable, the first few right singular vectors by the singular value decomposition can offer these references. Finally, the frequency-domain stochastic subspace identification tracks the natural frequencies and mode shapes of structures through quick stabilization diagrams. To evaluate performance of the proposed method, a numerical study is carried out. Moreover, the long-term monitoring strong motion records at a specific site are exploited to assess the tracking performance. As seen in results, the proposed method is capable of tracking modal properties through seismic responses of structures.

• 한국통신학회논문지
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• 제33권6C호
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• pp.459-470
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• 2008

In this paper, we propose a fast ME (motion estimation) algorithm for MPEG-4 to H.264 Transcoder. Whereas 2 modes ($8{\times}8$, $16{\times}16$) are used for ME in MPEG-4 simple profile, ME using 7 modes is supported for further enhanced coding efficiency in H.264. The transcoding speed is affected dominantly by the computational complexity of encoder part in transcoder, where ME module of H.264 encoder has high complexity due to using 7 modes. In order to increase the speed of transcoding between MPEG-4 and H.264, we use 3 PMVs (predicted motion vectors) and the mode information of MBs (macroblocks) provided from the decoder part of transcoder. Since the proposed 3 PMVs are very close to an optimal motion vector, and we consider only some restricted modes according to the MB information transferred from decoder part, the proposed scheme can speed up the transcoding procedure without loss of image quality. We show experimental results which demonstrate the effectiveness of the proposed algorithm, where performance of our scheme is compared with that of the conventional fast algorithm for H.264.

• Steel and Composite Structures
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• 제19권3호
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• pp.697-711
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• 2015

It is well known the importance of considering hysteretic energy demands for the seismic assessment and design of structures. In such a way that it is necessary to establish new parameters of the earthquake ground motion potential able to predict energy demands in structures. In this paper, several alternative vector-valued ground motion intensity measures (IMs) are used to estimate hysteretic energy demands in steel framed buildings under long duration narrow-band ground motions. The vectors are based on the spectral acceleration at first mode of the structure Sa($T_1$) as first component. As the second component, IMs related to peak, integral and spectral shape parameters are selected. The aim of the study is to provide new parameters or vector-valued ground motion intensities with the capacity of predicting energy demands in structures. It is concluded that spectral-shape-based vector-valued IMs have the best relation with hysteretic energy demands in steel frames subjected to narrow-band earthquake ground motions.

• 한국전산구조공학회논문집
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• 제13권2호
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• pp.209-220
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• 2000

보강된 판 및 쉘구조의 기하학적 비선형해석을 수행하기 위하여, total lagrangian formulation에 근거한 증분 평형방정식을 적용하고, 강도행렬 산정시 회전각의 2차항을 포함시켜 기하학적 비선형 해석시 해의 수렴성을 향상시켰으며, 보강된 쉘 구조의 해석시 보강재를 쉘 요소로 모델링하고 주부재와 보강재의 연결점에서 일반적인 변환관계를 이용하였다. 등매개 쉘 유한요소의 단점인 locking 현상을 극복하기 위하여 가정 변형률장을 적용하여 감차적분 또는 선택적분시 나타날 수 있는 제로 에너지 모드를 제거하였다. 수치해석 예제를 통하여 가정 변형률장에 근거한 쉘유한요소에 대한 효율성 및 적용성을 확인하였다.