• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.3
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• pp.68-74
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• 2006

The evaluation of durability performance in Virtual Testing Laboratory(VTL) is a new concept of vehicle design, which can reduce the automotive design period and cost. In this study, the multibody dynamics model of a car is built with a reverse engineering design. Hard points and masses of components are measured by a surface scanning device and imported into CAD system. In order to simulate the non-linear dynamic behavior of force elements such as dampers and bushes, components and materials are tested with specialized test equipments. An optimized numerical model for the damping behavior is used and the hysteresis of bush rubber is considered in the simulation. Loads of components are calculated in VTL and used in the evaluation of durability performance. In order to verify simulation results, loads of components in the vehicle are measured and durability tests are performed.

• Proceedings of the Korean Information Science Society Conference
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• 2010.11a
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• pp.147-148
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• 2010

최근 IT 산업 전반에 걸쳐 모바일에 대한 중요도가 높아짐에 따라 인터넷 브라우저의 성능이 중요하게 되었다. 자바스크립트 언어의 수행은 인터넷 브라우저의 사용에 있어 상당히 비중이 높다. 이 논문에서는 자바스크립트 언어를 수행하는 엔진 중 하나인 TraceMonkey엔진이 트레이스를 하는 과정에서 생기는 오버헤드를 줄이는 최적화를 구현, 적용하고 이를 실험하여 평가한다.

• The Transactions of the Korean Institute of Power Electronics
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• v.23 no.5
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• pp.321-327
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• 2018

DC microgrid system composed of multiple converters has a tendency to make the system unstable due to the interaction of converters. To solve this problem, in this paper, the interaction between cascaded converters with LC input filter is analyzed with impedance modeling using g-parameter. The input impedance and the output impedance of the system can be obtained through this technique. The stability of the system can be determined by applying Middlebrook's stability criterion to the impedance. Virtual impedance is added to the controller to enhance stability. The validity of the analysis is verified by the result of several simulations and experiments.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.8
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• pp.3841-3861
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• 2017

Virtualized small cell network is a promising architecture which can realize efficient utilization of the network resource. However, conventional full duplex self-backhauls lead to residual self-interference, which limits the network performance. To handle this issue, this paper proposes a virtual resource allocation, in which the residual self-interference is fully exploited by employing a physical-layer network coding (PNC) aided self-backhaul scheme. We formulate the features of PNC as time slot and information rate constraints, and based on that, the virtual resource allocation is formulated as a mixed combinatorial optimization problem. To solve the problem efficiently, it is decomposed into two sub problems, and a two-phase iteration algorithm is developed accordingly. In the algorithm, the first sub problem is approximated and transferred into a convex problem by utilizing the upper bound of the PNC rate constraint. On the basis of that, the convexity of the second sub problem is also proved. Simulation results show the advantages of the proposed scheme over conventional solution in both the profits of self-backhauls and utility of the network resource.

• 한국HCI학회:학술대회논문집
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• 2006.02a
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• pp.118-123
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• 2006

본 논문에서는 반몰입형 가상현실 시스템인 반응형 멀티미디어 시스템(RMS: Responsive Multimedia System)을 이용한 개인화된 스토리텔링 기법을 제안한다. 인간은 글, 그림, 영상 기술 등을 이용한 다양한 스토리텔링 기법을 개발해 왔으며, 가상 현실 기술을 통하여 기존의 멀티미디어보다 한차원 높은 수준의 스토리텔링을 가능하게 하였다. 제안된 스토리텔링 기법은 테이블 형태의 다감각 사용자 인터페이스, 사용자 정보 처리와 위치기반 이벤트를 결정하는 컨텍스트 인식 응용 모델 (vr-UCAM), 그리고 가상환경 네비게이션과 변화, 캐릭터의 애니메이션을 가능케 하는 가상공간 관리기로 구성된다. 제안된 스토리텔링 기법은 다감각 사용자 인터페이스를 통하여 직관적인 상호작용을 가능하게 한다. 그리고 컨텍스트 인식 응용 모델을 활용하여 사용자 개인정보를 스토리에 적용하여 개인화된 스토리가 전개될 수 있도록 한다. 그리고 가상 환경의 네비게이션, 가상 캐릭터, 날씨 및 환경의 변화 등을 조절하여 실감있게 스토리가 전개되도록 한다. 제안된 스토리텔링 환경을 검증하기 위해 운주사에 얽힌 설화를 기반으로 가상 운주사 체험 시스템을 구현하였다. 이를 통해, 반응형 멀티미디어 시스템을 이용한 스토리텔링의 가능성을 검증하였으며, 컨텍스트 인식 응용 모형을 활용한 개인화된 스토리텔링을 선보였다. 제안된 스토리텔링 기법은 문화교육, 에듀테인먼트, 예술 분야에 활용될 것으로 기대된다.

• Proceedings of the IEEK Conference
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• 2006.06a
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• pp.685-686
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• 2006

Recently, various AR-based product design methodologies have been introduced. In this paper, we propose technologies for enhancing robust augmentation and immersive realization of virtual objects. A robust augmentation technology is developed for various lighting conditions and a partial solution is proposed for the hand occlusion problem that occurs when the virtual objects overlay the user' hands. It provides more immersive or natural images to the users. Finally, vibratory haptic cues by page motors as well as button clicking force feedback by modulating pneumatic pressures are proposed while interacting with virtual widgets. Also our system reduces gabs between modeling spaces and user spaces. An immersive game-phone model is selected to demonstrate that the users can control the direction of the car in the racing game by tilting a tangible object with the proposed augmented haptic and robust non-occluded visual feedback. The proposed methodologies will be contributed to the immersive realization of the conventional AR system.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.4
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• pp.120-127
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• 2008

A military vehicle undergoes normal to extreme driving conditions, which consequently induce the fatigue and fracture of cabin and frame. So, it is important to estimate the fatigue life of two components at an initial design stage. In this paper, Modal Superposition Method(MSM) was applied to evaluate the durability performance of a small-sized military truck. For reliable durability analysis, a Virtual Test Lab(VTL) Model was established by correlation with experimental results. These data were extracted from actual driving test, modal test, and SPMD(Suspension Parameter Measuring Device) test. This process shows that Virtual Fatigue Analysis can be a useful approach in the development of military vehicles as well as commercial vehicles.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 2004.11a
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• pp.176-176
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• 2004

• Journal of Power Electronics
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• v.19 no.2
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• pp.580-590
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• 2019

The concept of virtual synchronous generators (VSGs) is a valuable means for improving the frequency stability of microgrids (MGs). However, a great virtual inertia in a VSG's controller may cause power oscillation, thereby deteriorating system stability. In this study, a small-signal model of an MG with two paralleled VSGs is established, and a control strategy for maintaining a constant inertial time with an increasing active-frequency droop coefficient (m) is proposed on the basis of a root locus analysis. The power oscillation is suppressed by adjusting virtual synchronous reactance, damping coefficient, and load frequency coefficient under the same inertial time constant. In addition, the dynamic load distribution is sensitive to the controller parameters, especially under the parallel operation of VSGs with different capacities. Therefore, an active power increment method is introduced to improve the precision of active power sharing in dynamic response. Simulation and experimental is used to verify the theoretical analysis findings.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.12
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• pp.3133-3151
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• 2012

The optimal price strategy selection of two bounded rational cognitive mobile virtual network operators (MVNOs) in a duopoly spectrum sharing market is investigated. The bounded rational operators dynamically compete to sell the leased spectrum to secondary users in order to maximize their profits. Meanwhile, the secondary users' heterogeneous preferences to rate and price are taken into consideration. The evolutionary game theory (EGT) is employed to model the dynamic price strategy selection of the MVNOs taking into account the response of the secondary users. The behavior dynamics and the evolutionary stable strategy (ESS) of the operators are derived via replicated dynamics. Furthermore, a reward and punishment mechanism is developed to optimize the performance of the operators. Numerical results show that the proposed evolutionary algorithm is convergent to the ESS, and the incentive mechanism increases the profits of the operators. It may provide some insight about the optimal price strategy selection for MVNOs in the next generation cognitive wireless networks.