• 로봇학회논문지
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• 제13권2호
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• pp.113-120
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• 2018

To fly a drone or unmanned aerial vechicle(UAV) safely, its pilot needs to maintain high situation awareness of its flight space. One of the important ways to improve the flight space awareness is to integrate both the global and the local navigation map a drone provides. However, the drone pilot often has to use the inconsistent reference frames or perspectives between the two maps. In specific, the global navigation map tends to display space information in the third-person perspective, whereas the local map tends to use the first-person perspective through the drone camera. This inconsistent perspective problem makes the pilot use mental rotation to align the different perspectives. In addition, integrating different dimensionalities (2D vs. 3D) of the two maps may aggravate the pilot's cognitive load of mental rotation. Therefore, this study aims to investigate the relation between perspective difference ($0^{\circ}$, $90^{\circ}$, $180^{\circ}$, $270^{\circ}$) and the map dimensionality matches (3D-3D vs. 3D-2D) to improve the way of integrating the two maps. The results show that the pilot's flight space awareness improves when the perspective differences are smaller and also when the dimensionalities between the two maps are matched.

• 한국정보처리학회논문지
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• 제7권7호
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• pp.2050-2059
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• 2000

In a video-on-Demand(VOD) service, a server has to return to he normal playback quickly at a certain new frame position after interactive operations such as jump or last playback. In this paper, we propose an efficient scheme to write a transmission schedule for a playback restart of a video stream at a new frame position after interactive operations. The proposed scheme is based on convergence characteristics, that is transmission schedules with different playback startup frame position in a video stream meet each other at some frame position. The scheme applies a bandwidth smoothing from a new frame position to a convergence position without considering all remaining frames of a video stream. And then the scheme transmits video dta according to the new schedule from the new frame position to the convergence position, and then transmits the remaining video data according to the reference schedule from the convergence position, and then transmits the remaining video data according to the reference schedule from the convergence position to the last frame position. In this paper, we showed that there existed the convergence position corresponding to nay frame position in a video stream through many experiments based on MPEG-1 bit trace data. With the convergence we reduced the computational overhead of a bandwidth smoothing, which was applied to find a new transmission schedule after interactive operations. Also, storage overhead is greatly reduced by storing pre-calculated schedule information up to the convergence position for each I frame position of a video stream with video data off-line. By saving information on a transmission schedule off-line along with the video data and searching the schedule corresponding to the specified restarting frame position, we expect the possibility of normal playback of a video stream with small tolerable playback startup delay.

• 대한전자공학회논문지SP
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• 제44권5호
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• pp.73-83
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• 2007

본 논문은 H.264/AVC에서 부호화 효율 개선을 위한 매크로 블록 기반의 적응 보간 필터 방법을 제안한다. 제안 방법은 다양한 방향의 움직임을 세밀하게 보상하는 9가지 분리 가능한 2차원 보간 필터들을 적용한다. 그리고 매크로 블록이 부호화되기 위한 비트율과 왜곡을 고려한 최적의 비용 함수를 정의하고 정의된 비용 함수를 최소화시키는 필터를 매크로 블록 당 적응적으로 선택한다. 실험 결과, 다양한 표준 $QCIF(176{\times}144)/CIF(352{\times}288)$ 동영상 테스트 시퀀스들에 대해서 제안 방법이 기존 방법들에 비하여 항상 우수한 부호화 효율을 지니고 있으며 H.264/AVC 보다 평균 6.25%(참조 영상 프레임: 1개), 3.46%(참조 영상 프레임: 5개)의 비트율이 절감된다.

• 한국통신학회논문지
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• 제33권4C호
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• pp.312-320
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• 2008

H.264/AVC에서 부호화 효율 개선을 위해 매크로 블록 기반 적응 보간 방법이 고려되어졌다. 이 방법에서 필터 선택 기준은 비트율과 왜곡 항들이 고려하여 좋은 성능을 발휘하지만 아직 개선의 여지를 남겨두고 있다. 따라서 본 논문에서는 기존 방법보다 높은 부호화 효율 개선을 위해 움직임 벡터와 예측 에러에 대한 두 가지 비트율과 복원 에러를 고려하여 새로운 필터 선택 기준을 제안한다. 부가적으로 선택된 필터 정보 전송을 위한 오버헤더 (overhead)를 줄이는 알고리듬을 나타낸다. 실험 결과는 제안 방법이 기존 방법에 비하여 우수한 성능을 보이고 H.264/AVC에 비해 전체 비트율이 평균 5.19% (참조 프레임: 1개)와 5.14% (참조 프레임: 5개) 절감된다.

• 항공우주산업기술동향
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• 제7권2호
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• pp.121-130
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• 2009

2010년 초 발사예정인 통신해양기상위성은 우주인증된 E3000 우주버스 기술을 근간으로 한 정지궤도 통신관측위성이다. 본 논문에서는 통신해양기상위성의 자세제어계에서 사용된 태양센서들의 운용기술을 분석함으로써 전이궤도 및 지구정지궤도 태양센서 운용기술을 분석한다. 최신 E3000 기술을 접목시킨 통신해양기상위성의 자세제어계는 전이궤도 및 임무궤도에서 기준 자세로부터 벗어난 자세오차 정보를 획득하기 위해서 또는 이상 작동 발생으로 인한 고장진단복구 과정에서 수행되는 태양획득 단계를 수행하기 위해서 저정밀 태양센서 BASS 3기와 고정밀 태양센서 LIASS 3기를 사용하는 형상을 채택하고 있다. 본 논문에서는 각각의 태양센서들에 대한 수학적 모델과 비행소프트웨어에 구현된 태양센서 운용소프트웨어에 대해서 기술한다.

• 정보처리학회논문지B
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• 제13B권5호
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• pp.499-506
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• 2006

본 논문에서는 실시간 증강현실 시스템에서의 가상 객체 삽입을 위한 빠르고 안정된 카메라 자세 추정 방법을 제안한다. 단일 프레임에서 마커의 특징점 추출을 통해 카메라의 회전행렬과 이동벡터를 추정한다. 카메라 자세 추정을 위해 정사영 투영모델에서의 분해기법을 사용한다. 정사영 투영모델에서의 분해기법은 객체의 모든 특징점의 깊이좌표가 동일하다고 가정하기 때문에 깊이좌표의 기준이 되는 참조점의 설정과 점의 분포에 따라 카메라 자세 계산의 정확도가 달라진다. 본 논문에서는 실제 환경에서 일반적으로 잘 동작하고 융통성 있는 참조점 설정 방법과 이상점 제거 방법을 제안한다. 제안된 카메라 자세추정 방법에 기반하여 탐색된 마커 위치에 가상객체를 삽입하기 위한 비디오 증강 시스템을 구현하였다. 실 환경에서의 다양한 비디오에 대한 실험 결과, 제안된 카메라 자세 추정 기법은 기존의 자세추정 기법만큼 빠르고 기존의 방법보다 안정적이고 다양한 증강현실 시스템 응용에 적용될 수 있음을 보여주었다.

• Computers and Concrete
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• 제22권5호
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• pp.461-468
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• 2018

In this paper, to access the suitability of recycled aggregate for structural applications, concrete strength i.e., compressive, tensile and flexural strength were evaluated and compared with those specimens made of natural aggregates. Test results indicated that 30 to 42% of the mentioned strength decreases. To study the performance of frame structures made of recycled aggregate concrete (RAC) two reinforced RAC frames were prepared and tested under monotonic loading. The joint regions of one of the RAC frame were casted with micro-concrete. A reference specimen was also prepared using natural aggregate concrete (NAC) and subjected to a similar loading condition. The RAC frame resulted in a brittle mode of failure as compared to NAC frame. However, the presence of a micro-concrete at the joint region of an RAC frame improved the damage tolerance and load resisting capacity. Seismic parameter such as energy dissipation, ductility and stiffness also improves. Conclusively, strengthening of joint region using micro-concrete is found to have a significant contribution in improving the seismic performance of an RAC frame.

• 대한간호학회지
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• 제42권7호
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• pp.1001-1008
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• 2012

Purpose: The purpose of this study was to identify the characteristics of anger expression in middle-aged Korean women by categorizing their patterns of expression while considering the complexity and multidimensionality of anger, and by investigating the characteristics relative to the patterns. Methods: The research design was a descriptive design using Q methodology, which is a method of measuring subjectivity. A convenience sample of 42 participants aged 40-60 years and living in the community in Korea was recruited. The PC-QUANL software program (a factor analysis program for the Q technique) was used to analyze the Q-sort data. Results: Four factors were extracted that described different expressions of anger among middle-aged Korean women; these factors explained 50.1% of the total variance. The frames of reference of the four factors were a) direct diversion, b) silent masking with remaining anger, c) self digestion, and d) controlling anger with objectification. Conclusion: In this study has identified patterns and characteristics of anger expression among middle-aged Korean women were identified, which will aid the development of effective anger-management programs for controlling anger in this population. In future studies, it would be helpful to investigate how the patterns of anger expression established herein are associated with specific health problems such as cardiovascular disorder and cancer.

• International Journal of Air-Conditioning and Refrigeration
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• 제11권3호
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• pp.132-139
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• 2003

The effects of casing shapes on the performance and the interaction between an impeller and a casing in a small-sized centrifugal compressor are investigated. Especially, numerical analyses are conducted for the centrifugal compressor with both a circular casing and a volute one. The optimum design for each element (i.e., impeller, diffuser and casing) is important to develop an efficient and compact compressor using alternative refrigerant as working fluids. Typical rotating speed of the compressor is in the range of 40,000∼45,000 rpm. The impeller has backswept blades due to tip clearance and a vane diffuser has wedge type. In order to predict the flow pattern inside an entire impeller, vaneless diffuser and casing, calculations with multiple frames of reference method between the rotating and stationery parts of the domain are carried out. For computations of compressible turbulent flow fields, the continuity and time-averaged Navier-Stokes equations are employed. To evaluate the performance of two types of casings, the static pressure recovery and loss coefficients are obtained for various flow rates. Also, static pressure distributions around casings are studied for different casing shapes, which are very important to predict the distribution of radial load. The static pressure around the casing and pressure difference between the inlet and outlet of the compressor are measured for the circular casing.

• Wind and Structures
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• 제29권6호
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• pp.405-416
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• 2019

Aerodynamic characteristic of a small scale wind turbine under the influence of an incoming uniform wind field is studied using k-ω Shear Stress Transport turbulence model. Firstly, the lift and drag characteristics of the blade section consisting of S826 airfoil is studied using 2D simulations at a Reynolds number of 1×10⁵. After that, the full turbine including the rotational effects of the blade is simulated using Multiple Reference Frames (MRF) and Sliding Mesh Interface (SMI) numerical techniques. The differences between the two techniques are quantified. It is then followed by a detailed comparison of the turbine's power/thrust output and the associated wake development at three tip speeds ratios (λ = 3, 6, 10). The phenomenon of blockage effect and spatial features of the flow are explained and linked to the turbines power output. Validation of wake profiles patterns at multiple locations downstream is also performed at each λ. The present work aims to evaluate the potential of the numerical methods in reproducing wind tunnel experimental results such that the method can be applied to full-scale turbines operating under realistic conditions in which observation data is scarce or lacking.