• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.5
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• pp.531-542
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• 2011

The time-dependent temperature distribution across the section in bridges is determined on the basis of the three-dimensional finite element analyses and numerical time integration in this study. The material properties which change with time and thermal stress of concrete are taken into account to effectively trace the early-age structural responses. Since the temperature distribution is nonlinear and depends upon many material constants such as the thermal conductivity, specific heat, hydration heat of concrete, heat transfer coefficients and solar radiation, three representative influencing factors of the construction season, wind velocity and bridge pavement are considered at the parametric studies. The validity of the introduced numerical model is established by comparing the analytical predictions with results from previous analytical studies. On the basis of parametric studies for four different bridge sections, it is found that the creep deformation in concrete bridges must be considered to reach more reasonable design results and the temperature distribution proposed in the Korean bridge design specification need to be improved.

• 한국HCI학회:학술대회논문집
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• 2007.02a
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• pp.591-597
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• 2007

웨어러블 컴퓨팅의 지속적인 발전과 함께, 이들이 지원하는 기능은 점점 다양화되고 전문화되었다. 하지만 기기의 종류와 기능이 늘어나면서 각 기기의 상태를 확인하는 작업 자체가 복잡하고 불필요한 시간을 소요하기도 한다. 또한 이를 시각 디스플레이에만 의존하면, 디스플레이 크기의 한계와 더불어 시각적인 과부하가 발생할 수 있다. 본 연구에서는 이러한 문제를 극복하기 위해 웨어러블 각 기기의 상태정보 피드백으로서 소리를 이용하였다. 실험의 순서는 먼저 시각정보에 더하여 청각정보를 추가적으로 제시하는 방식의 유용성을 검증한 다음, 기기 특정적인 청각 아이콘(Auditory Icon)의 효과를 확인하였다. 청각정보의 유용성을 확인하는 단계에서는 참가자에게 특정 기기의 위치와 그 상태에 관한 정보를 시각 디스플레이를 통해 제시하면서, 조건에 따라 다양한 형태의 청각 디스플레이를 제시하고 기기 및 상태정보 확인에 소요되는 시간을 측정하였다. 시각디스플레이의 방식은 다양하지만, 본 연구에서는 사람의 몸을 나타내는 그림 위에 기기가 장착된 위치를 붉은 점으로 표시하고, 그 상태를 텍스트로 표시하는 방식(실험 1)과 텍스트를 통해 기기의 종류와 상태를 알려주는 방식(실험 2)을 적용하였다. 기기 확인에 소요되는 반응시간을 기록한 실험결과는 시각디스플레이를 통해서만 제시하는 조건보다 시각디스플레이와 청각디스플레이를 동시에 제시하는 조건에서 나은 수행을 보여주며, 정보의 내용이 일정 범위 내에서 구체적으로 제시될 수록 수행이 증가하는 경향을 보여주고 있다. 이어지는 기기 특정적인 청각 아이콘의 효과를 확인하는 단계에서는, 소리의 높낮이를 통해 기기의 위치를 표현하는 대신, 소리만 듣고 기기가 무엇인가를 알려줄 수 있도록, 참가자 평정을 통해 기기 특정적인 청각 아이콘을 선정하고, 이를 상태정보 디스플레이에 추가하였다. 기기의 수와 제시조건은 앞선 실험과 동일하였으며, 역시 기기 및 상태정보 확인에 소요되는 반응시간을 체크하였다. 실험결과는 이전의 실험과 비슷하게 시각과 청각 디스플레이의 중복제시 조건에서 높은 수행을 보였으며, 청각 아이콘의 사용으로 인한 수행의 증가도 확인할 수 있었다. 실험 2에서는 추가적으로 청각 디스플레이의 내용에 대한 주관적인 평정을 실시 하였는데, 기기 특정적인 청각 아이콘은 참가자에게 편의성, 효용성, 적합성, 확신도에서도 높은 점수를 얻었다. 이러한 결과는 청각 피드백을 이용한 정보의 디스플레이는 착용자의 시선을 자유롭게 함으로써 일상생활의 수행을 높이고, 웨어러블 컴퓨터 디스플레이 크기의 제약을 해결하는 방법이 될 수 있는 동시에 주관적인 사용성 측면에서 발전가능성이 있음을 보여준다.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.41 no.4
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• pp.9-21
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• 2004

The current paper proposes a genetic algorithm (GA)-based segmentation method that can automatically extract and track moving objects. The proposed method mainly consists of spatial and temporal segmentation; the spatial segmentation divides each frame into regions with accurate boundaries, and the temporal segmentation divides each frame into background and foreground areas. The spatial segmentation is performed using chromosomes that evolve distributed genetic algorithms (DGAs). However, unlike standard DGAs, the chromosomes are initiated from the segmentation result of the previous frame, then only unstable chromosomes corresponding to actual moving object parts are evolved by mating operators. For the temporal segmentation, adaptive thresholding is performed based on the intensity difference between two consecutive frames. The spatial and temporal segmentation results are then combined for object extraction, and tracking is performed using the natural correspondence established by the proposed spatial segmentation method. The main advantages of the proposed method are twofold: First, proposed video segmentation method does not require any a priori information second, the proposed GA-based segmentation method enhances the search efficiency and incorporates a tracking algorithm within its own architecture. These advantages were confirmed by experiments where the proposed method was success fully applied to well-known and natural video sequences.

• Journal of Advanced Navigation Technology
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• v.23 no.6
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• pp.577-583
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• 2019

A dynamic system is called positive if any trajectory of the system starting from non-negative initial states remains forever non-negative for non-negative controls. In this paper, we consider the new stability condition for the positive time-varying linear discrete interval systems with time-varying delay and unstructured uncertainty. The delay time is considered as time-varying within certain interval having minimum and maximum values and the system is subjected to nonlinear unstructured uncertainty which only gives information on uncertainty magnitude. The proposed stability condition is an improvement of the previous results which can be applied only to time-invariant systems or had no consideration of uncertainty, and they can be expressed in the form of a very simple inequality. The stability conditions are derived using the Lyapunov stability theory and have many advantages over previous results using the upper solution bound of the Lyapunov equation. Through numerical example, the proposed stability conditions are proven to be effective and can include the existing results.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.11
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• pp.889-902
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• 2020

In this study, a numerical analysis was performed to confirm the formation of supersonic flow and the stabilization time satisfying the design condition in a Direct-connect supersonic combustor. The process was examined in which the high-pressure gas of vitiation air heater propagates downstream to the supersonic combustor and forms a supersonic flow field. It was confirmed through the analysis of pressure and temperature that the supersonic flow field satisfies the design points of Mach number 2.0 and 1,000 K, and requires a minimum of 4.0 ms for stabilization. These results indicate that the time required for the supersonic flow field stabilization should be taken into account when testing for the supersonic combustion experiment.

• The Transactions of the Korea Information Processing Society
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• v.6 no.6
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• pp.1678-1685
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• 1999

In most of the existing real-time schedulers producing the total value as large as possible, the service times for all schedulable tasks are computed at each time a new task arrives. If all scheduled tasks would be executed completely before a new task arrives, the schedule may produce the greatest total value. But this is not always true in real situations. In many cases, (a) new tasks arrive(s) before all the scheduled tasks are executed completely. In this paper, we propose a unique scheduling algorithm for real-time tasks. The proposed algorithm determines the service times only for some tasks with earlier deadlines while the existing algorithms determine the service times for all tasks. This partial computation decreases the average scheduling complexity ramatically, even though, in the worst case, the complexity of the proposed algorithm becomes O(N2), which is equal to that of a previous algorithm that has been known as a less complicated one.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.9C
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• pp.712-719
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• 2008

Temporal error concealment indicates the algorithm that restores the lost video data using temporal correlation between previous frame and current frame with lost data. It can be categorized into the methods of block-based and pixel-based concealment. The proposed method in this paper is for pixel-based temporal error concealment using affine transform. It outperforms especially when the object or background in lost block has geometric transform which can be modeled using affine transform, that is, rotation, magnification, reduction, etc. Furthermore, in order to maintain good performance even though one or more motion vector represents the motion of different objects, we defines a cost function. According to cost from the cost function, the proposed method adopts affine error concealment adaptively. Simulation results show that the proposed method yields better performance up to 1.9 dB than the method embedded in reference software of H.264/AVC.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2011.11a
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• pp.251-254
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• 2011

와이브로(Wibro) 또는 WiFI 망에서 동일한 멀티캐스트 그룹에 속한 이동 단말기들은 동일한 MBS(멀티캐스트/브로드캐스트 방송 서비스) 콘텐츠를 수신한다. 동일한 MBS 존 내의 기지국(RAS: Radio Access Station) 들이 MBS 콘텐츠 소스로부터 수신된 MBS 콘텐츠에 대한 전송 시간을 동기화할 수 있도록 기지국들은 전송 동기화 정보와 신뢰성 있는 데이터 패킷 수신을 동기 시간을 결정하기 이전에 보장받을 수 있어야 한다. 만약에 동일한 MBS 존에 속하는 다수의 기지국 중에 전송 동기화 정보를 수신하지 못하거나 패킷 데이터 일부 또는 전부를 수신하지 못한다면, 동기 전송 시간을 결정하기 전에 이미 손실된 정보와 패킷 데이터를 이동 단말기로 전송하게 됨으로써 이동 단말기가 MBS 콘텐츠를 수신하면서 동일 MBS 존 내의 다른 기지국으로 핸드오버하게 되면 MBS 콘텐츠에 대한 끊김없는 수신을 보장할 수 없을 뿐만 아니라 매크로 다이버시티(macro diversity) 이득을 얻기 위한 동일한 MBS 존에서 이동 단말기들에게 전송되는 MBS 콘텐츠들의 동기를 보장 할 수 없다. 따라서, 본 논문에서는 동기 전송 시간을 결정하기 앞서서 다수의 RAS가 전송 동기화 정보와 신뢰성 있는 패킷 데이터 콘텐츠 수신을 보장받을 수 있는 장치를 보완한 멀티캐스트/브로드캐스트 서비스 데이터 전송 동기화 방법을 제안한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.6C
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• pp.523-529
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• 2010

We propose a very low complexity lattice reduction (LR) algorithm for MIMO detection in time varying channels. The proposed scheme reduces the complexity by performing LR in a block-wise manner. The proposed scheme takes advantage of the temporal correlation of the channel matrices in a block and its impact on the unimodular matrices during LR process. From this, the proposed scheme can skip a number of redundant LR processes for consecutive channel matrices and performs a single LR in a block. The simulation results investigated in this letter reveal that the proposed detection scheme requires only 43.4% multiplications and 17.3% divisions of LLL-LR and only 50.2% multiplications and 68.2% divisions of the conventional adaptive LR with almost no performance degradation.

• The Journal of the Acoustical Society of Korea
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• v.19 no.5
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• pp.79-83
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• 2000

When passband ripple α/sub p/ and stopband attenuation α/sub s/ at the w/sub s/ where the stopband begins are specified in filter design, △α/sub s/ usually exceeds the specification by △α/sub s/ due to the necessity that the order n of the filter function be an integer. In this paper, we apply a trade-off method to remove the excess stopband attenuation △α/sub s/ for reducing the value of pole-Q and improving the characteristics of the Chebyshev filter function. We also apply the trade-off method of pole-Q reduction to the modified Chebyshev function, and then the 4 types of function have been analyzed to compare in frequency and time domain characteristics. The trade-off method reduces the pole-Q which influences the filter characteristics to maximum 49.6% without increase of the order n. Thus implies that they have the improved characteristics such as the reduced passband ripple and flatter delay characteristics as compared Chebyshev filter function before trade-off. And the unit step response shows shorter delay time and settling time in time domain performance.