• Journal of the Korean Society of Radiology
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• v.12 no.7
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• pp.845-852
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• 2018

This study aimed to investigate the difference of X-ray exposure by comparing and analyzing absorbed dose according to changes in the number of frames in coronary angiography, also depending whether the zoom mode is FOV enlargement or Zoom Live. Moreover, for appropriate frame selection measures for examination, including the effect of frame change on the image quality, were sought by measuring the noise strength expressed by the standard deviation (SD), the signal to noise ratio (SNR) and contrast to noise ratio (CNR). The study was conducted with an anthropomorphic phantom on an angio-system. The linear relationship between the frame rate and the radiation dose was evident. On the contrary, the indices of image quality (SD, SNR, and CNR) were almost constant irrespective of the number of frames. The difference depending on the zoom mode was not statistically significant for DAP, air kerma, and SD (p > 0.05). However, SNR and CNR were statistically different between FOV enlargement and Zoom Live. In conclusion, since the image quality was not degraded significantly with the decreasing frame rate from 30, 15, to 7.5 f/s and the radiation dose evidently decreases in almost exactly linear proportion to the decreasing frame rate, the number of frames per second needs to be maintained as low as reasonably achievable. As for the dependence on the zooming mode, the Live Zoom mode showed statistically significant improvement in the image quality indices of SNR and CNR and it justifies active use of the Live Zoom mode which enables real-time image enlargment without additional radiation dose.

• Journal of the Earthquake Engineering Society of Korea
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• v.7 no.4
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• pp.81-87
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• 2003

In this paper, the feasibility of using Shannon's sampling theorem to reconstruct exact mode shapes of a structural system from a limited number of sensor points and localizing damage in that structure with reconstructed mode shapes is investigated. Shannon's sampling theorem for the time domain is reviewed. The theorem is then extended to the spatial domain. To verify the usefulness of extended theorem, mode shapes of a simple beam are reconstructed from a limited amount of data and the reconstructed mode shapes are compared to the exact mode shapes. On the basis of the results, a simple rule is proposed for the optimal placement of accelerometers in modal parameter extraction experiments. Practicality of the proposed rule and the extended Shannon's theorem is demonstrated by detecting damage in laboratory beam structure with two-span via applying to mode shapes of pre and post damage states.

• Journal of the Korea Society for Simulation
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• v.21 no.2
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• pp.51-58
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• 2012

In IEEE 802.16j MMR protocol, two modes about usage of RS are proposed; one is transparent mode to enhance data throughput and the other is non-transparent mode to extend coverage. In this paper, we focus on non-transparent mode and find that the mode can also improve data throughput. Therefore, we analyze data throughput on various RS topology and their extended coverage area by simulation in IEEE 802.16j non-transparent mode. We also compare the simulation results with the single MR-BS system of which coverage is extended by higher transmission power. From the comparisons of simulation results, we see that higher throughput can be obtained in the proposed non-transparent mode.

• 한국HCI학회:학술대회논문집
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• 2008.02a
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• pp.839-842
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• 2008

본 연구는 LCD 패널에서 시청모드별 사용자의 피로도 차이에 대한 연구이다 LCD 사용에 따른 사용자 피로도에 미치는 영향이 보고되고 있는 것을 감안하여 감성 공학적 방법을 이용하여 시청모드에 따른 사용자 피로도 차이를 분석하였다. 실험은 34명의 대학생을 두 그룹으로 나누어서 같은 동영상 조건에서 각각 영화모드와 표준모드를 60분간 시청하게 하였다. 시청 시의 피로도를 알아보기 위해 생리신호 반응(GSR, PPG, SKT), 눈 움직임(동공의 확대 축소속도, 눈 깜박임률) 및 주관적 피로도(긴장도, 쾌적도, 피로도)를 측정하였다. 그 결과 주관적인 평가와 생리 반응에서 영화모드가 표준모드보다 더 피로감을 유발시키는 것을 확인 할 수 있었다. 눈 움직임 반응에서는 통계적으로 유의한 결과를 얻지 못하였다.

• Journal of Korean Tunnelling and Underground Space Association
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• v.15 no.6
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• pp.547-557
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• 2013

The mode II fracture toughness and strength due to shear stress are important parameters in the stability of caprock and injection zone with application to geological sequestration of carbon dioxide. In this research, a short beam compression test has been used to determine the shear strength and the mode II fracture toughness for Coconino sandstone. The average value of the shear strength and mode II fracture toughness are estimated to be 23.53 MPa and 1.58 MPa${\surd}$m respectively. The stress intensity factor is suggested by finite element analysis using the displacement extrapolation method. The effect of biaxial stress and water saturation on the fracture toughness has also been investigated. The fracture toughness increases with confining stresses, but decreases by 11.4% in fully saturated condition.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.12 no.3
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• pp.485-494
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• 1999

본 연구에서는 요소를 사용하지 않고 절점들만을 이용하여 해석이 가능한 새로운 수치해석기법인 EFG(Element-Free Galerkin)법을 사용하여 임의의 균열의 성장과정을 해석할 수 있는 효율적인 알고리즘을 개발하고, 이를 바탕으로 균열의 성장방향과 경로를 정확히 추정하여 일련의 균열진전해석을 수행할 수 있는 프로그램을 개발하였다. 균열해석에 있어서는 균열선단의 특이성과 균열면의 분연속성을 수치적으로 반영할 수 있는 기법을 도입하여 균열을 모형화하였으며, 선형탄성파괴역학이론에 근거하여 균열해석과정을 정식화하였다. 또한, EFG 형상함수가 kronecker delta 조건을 만족시키지 못함으로써 발생하는 필수경계조건의 처리문제를 penalty법을 이용하여 해결하였다. 개발된 균열진전해석 알고리즘을 정지상태와 성장하는 상태에 있는 모드 Ⅰ, 모드 Ⅱ 및 혼합모드상태의 대표적인 균열문제들에 적용하여 응력확대계수와 균열성장방향 및 균열의 성장경로를 추정하고 이를 이론적·실험적 결과들과 비교함으로써 그 정확성과 효율성을 검증하였다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.8
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• pp.1163-1172
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• 2001

The two dimensional problem of a layered tribological system(TiN/Steel) containing a vertical surface breaking crack and subject to rolling contact is considered in this study. Using finite elements and stress extrapolation method, a series of preliminary models are developed. Preliminary results indicate that the extrapolation technique is valid to determine Modes I and II stress intensity factors for cracks. In the case of TiN/Steel medium, KI and KII were determined for variations in crack length, layer thickness, and load location. The results show that KII reaches maximum values when the contact is adjacent to the crack where Mode I stresses are compressive. KII values decrease with decreased crack length and significantly decrease for reduced layer thickness.

• The Korean Journal of Applied Statistics
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• v.29 no.5
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• pp.787-806
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• 2016

Mixed-mode (MM) designs in which data are collected by different modes in one design have become increasingly popular. An MM data collection has several advantages such as reductions of coverage error, non-response and cost. However, MM designs may introduce mode effects that are confounded by selection effects and measurement effects, which can make MM data quality poor. In order to investigate mode effects, SRI implemented a concurrent mixed-mode experiment in 2014 where respondents could choose between a self-administrated Web survey and a self-administrated paper survey. This paper separately estimates selection effects and measurement effects. We found that measurement effects on some items are large.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2013.06a
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• pp.296-299
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• 2013

디스플레이 기술이 발전함에 따라 다양한 크기의 디스플레이를 탑재한 장치들이 등장하게 되었고, 다양한 디스플레이 크기만큼 다양한 해상도를 사용하고 있다. 때문에 비디오 코덱과 scaler는 보편적으로 함께 사용된다. 그러나 기존의 scaler는 비디오 코덱의 복호화기와 화면 해상도 변환 모듈이 독립적으로 구성되고, 서로 간에 정보를 이용하지 않으므로 시스템의 성능 개선에 한계가 존재하였다. 즉, 비디오 코덱의 복호화기는 비트스트림으로부터 복호한 정보를 바탕으로 영상을 복원하고, 복원영상은 up/down scaler에서 확대/축소를 수행한다. 하지만 비디오 코덱의 비트스트림에 존재하는 정보는 영상의 특성을 반영하기 때문에 up/down scaler에서 비디오 코덱의 복호화기에서 복호된 정보를 이용하면 복잡도의 증가 없이 효율적인 확대/축소를 수행할 수 있다. 이에 본 논문에서는 비디오 코덱 중 차세대 비디오 코덱인 H.264/AVC 복호화기에서 생성된 복원 영상에 대해서 별도로 영상의 특성을 계산하는 모듈 없이 H.264/AVC 복호화기에서 복원된 정보 중 인트라 모드 정보를 바탕으로 영상의 특성에 맞는 up/down scaler를 구현하는 방법을 제안한다. 이 방법은 기존의 scaler들보다 물체의 경계영역을 더 선명하게 확대하는 효과를 보인다.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2001.10a
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• pp.121-126
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• 2001