• Proceedings of the KIEE Conference
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• 1996.07b
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• pp.1212-1215
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• 1996

As usual systems, robot manipulators have also physical constraints for operating. It is a difficult problem that we operate manipulator in the minimal time under these constraints. In this pater, we solve this problem dividing it into two steps. In the first step, we find the minimal time trajectories by optimizing qubic polynomial joint trajectories using evolutionary algorithms. In the second step, we optimize controller for robot manipulator to track precisely trajectories optimized in the previous step.

• Journal of the Semiconductor & Display Technology
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• v.22 no.2
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• pp.120-127
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• 2023

Recently, metaverse has attracted great attention worldwide with the development of related technologies and the demand for on-tact systems. The ideal metaverse should constitute a virtual world more similar to the realistic society with physical interactions. However, there are many constraints when we construct a virtual world using the existing commercialized metaverse platform. In this paper, we design and implement a university campus-based metaverse which minimizes the constraints, and create a virtual environment maps very similar to the real-world using Unity engine, Photon cloud and Playfab SDK for multi-user accessible to virtual world as a personal avatar. Also, this work includes attractive interaction based on exchange between users. Lastly, we illustrate our implemented metaverse works on Android phone, and it works without difficulty in terms of performance.

• Advances in aircraft and spacecraft science
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• v.10 no.6
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• pp.521-543
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• 2023

Reynolds-averaged Navier-Stokes (RANS) models are extensively employed in industrial settings for the purpose of simulating intricate fluid flows. However, these models are subject to certain limitations. Notably, disparities persist in the Reynolds stresses when comparing the RANS model with high-fidelity data obtained from Direct Numerical Simulation (DNS) or experimental measurements. In this work we propose an approach to mitigate these discrepancies while retaining the favorable attributes of the Menter Shear Stress Transport (SST) model, such as its significantly lower computational expense compared to DNS simulations. This strategy entails incorporating an explicit algebraic model and employing a neural network to correct the turbulent characteristic time. The imposition of realizability constraints is investigated through the introduction of penalization terms. The assimilated Reynolds stress model demonstrates good predictive performance in both in-sample and out-of-sample flow configurations. This suggests that the model can effectively capture the turbulent characteristics of the flow and produce physically realistic predictions.

• Structural Engineering and Mechanics
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• v.62 no.3
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• pp.303-310
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• 2017

The model updating problems, which are to find the optimal approximation to the discrete quadratic model obtained by the finite element method, are critically important to the vibration analysis. In this paper, the structured model updating problem is considered, where the coefficient matrices are required to be symmetric and positive semidefinite, represent the interconnectivity of elements in the physical configuration and minimize the dynamics equations, and furthermore, due to the physical feasibility, the physical parameters should be positive. To the best of our knowledge, the model updating problem involving all these constraints has not been proposed in the existed literature. In this paper, based on the semidefinite programming technique, we design a general-purpose numerical algorithm for solving the structured model updating problems with incomplete measured data and present some numerical results to demonstrate the effectiveness of our method.

• ETRI Journal
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• v.37 no.5
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• pp.898-905
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• 2015

In this paper, we consider a joint beamforming and jamming design to enhance physical layer security against potential multiple eavesdroppers in a multiple-input and single-output cellular broadcast channel. With perfect channel state information at the base station, we propose various design approaches to improve the secrecy of the target user. Among the proposed approaches, the combined beamforming of maximum ratio transmission and zero-forcing transmission with a combination of maximum ratio jamming and zero-forcing jamming (MRT + ZFT with MRJ + ZFJ) shows the best security performance because it utilizes the full transmit antenna dimensions for beamforming and jamming with an efficient power allocation. The simulation results show that the secrecy rate of this particular proposed approach is better than the rates of the considered conventional approaches with quality-of-service and outage probability constraints.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.6
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• pp.2595-2618
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• 2018

In this paper, we investigate secure communication with the presence of multiple eavesdroppers (Eves) in a two-tier downlink dense heterogeneous network, wherein there is a macrocell base station (MBS) and multiple femtocell base stations (FBSs). Each base station (BS) has multiple users. And Eves attempt to wiretap a macrocell user (MU). To keep Eves ignorant of the confidential message, we propose a physical-layer security scheme based on cross-layer cooperation to exploit interference in the considered network. Under the constraints on the quality of service (QoS) of other legitimate users and transmit power, the secrecy rate of system can be maximized through jointly optimizing the beamforming vectors of MBS and cooperative FBSs. We explore the problem of maximizing secrecy rate in both non-colluding and colluding Eves scenarios, respectively. Firstly, in non-colluding Eves scenario, we approximate the original non-convex problem into a few semi-definite programs (SDPs) by employing the semi-definite relaxation (SDR) technique and conservative convex approximation under perfect channel state information (CSI) case. Furthermore, we extend the frame to imperfect CSI case and use the Lagrangian dual theory to cope with uncertain constraints on CSI. Secondly, in colluding Eves scenario, we transform the original problem into a two-tier optimization problem equivalently. Among them, the outer layer problem is a single variable optimization problem and can be solved by one-dimensional linear search. While the inner-layer optimization problem is transformed into a convex SDP problem with SDR technique and Charnes-Cooper transformation. In the perfect CSI case of both non-colluding and colluding Eves scenarios, we prove that the relaxation of SDR is tight and analyze the complexity of proposed algorithms. Finally, simulation results validate the effectiveness and robustness of proposed scheme.

• The Journal of Korean Association of Computer Education
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• v.17 no.6
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• pp.9-20
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• 2014

With the change of global awareness of Computing education and introspection about Computer education focused on ICT literacy, efforts are being made to reflect computational thinking in the new curriculum. But if computational thinking would be possible at school, it require tremendous cost to prepare computers for school. In this study, we investigate potentiality and constraints of the one board computer to teach computational thinking in school. We study fundamental performance, application of physical computing and programming education, maintenance of the computers, power consumption of the one board computers which is raspberry pi, beagle bone black, and pcduino3. The result of the study show that one board computer can substitute desktop of the school unless tasks related to require massive data storage and processing. We draw a conclusion that Pcduino3 is well-suited for computational thinking education.

• The Journal of the Korea Contents Association
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• v.11 no.1
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• pp.176-183
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• 2011

This paper is intended on providing solutions for overcoming constraints to the transmission of the Important Intangible Cultural Properties related to dance successors. For accommodating this approach, six career dancers, from the Dance Society of the Important Intangible Cultural Properties, were invited as the research participants for this study. The In-Depth Interviews and the classification analysis are used as a way of structuring and understanding my observations about these tasks. These interviews have also been verified by an expert group. In conclusion, this study identifies numerous obstacles which can restrict the transmission of the Important Intangible Cultural Properties are as follows; first, the dance successors are constrained by personal reasons such as physical strength and mutual understanding at home; second, the dance successors are affected by the structural constraint of programs such as required time for the completion of training, efficiency of the training program and the educational environment; third, the dance successors are constrained by personal relations such as the relationship between themselves, or between the dance successors and holders of Important Intangible Cultural Properties. Suggested solutions for overcoming the constraints to training programs are; building small sized training centers throughout the country; making training time realistic for individuals; and making programs to train the dancers as well as making it sociable.

• 한국체육학회지인문사회과학편
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• v.51 no.5
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• pp.559-568
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• 2012

The purpose of this study was to analyze the relationship between leisure motivation and leisure constraints negotiation of career women in city. For this study, total 300 questionnaires were distributed and 281 were collected from the selected corporate, banks, and hospitals from September to December, 2011 by using purposive sampling. After that, 12 questionnaires were excluded out of 281 due to the unreliable quality 269 were used for this study. In order to analyze the data, exploratory factor analysis, reliability analysis, correlation analysis and multiple liner regression were conducted by using SPSS 18.0. The findings of this study are as followings. First, leisure constraints negotiation of career women in city leisure and leisure motivation showed positive relationship. Second, intellectual motivation showed significant impact on sub factor of leisure constraints negotiation. Third, social motivation showed significant impact on changing interpersonal relations, improving finance and time management, controlling intensity. Fourth, competence mastery motivation showed significant impact on changing interpersonal relations, improving finance and time management, skills acquisition and relaxation motivation.

• The Journal of Korean Physical Therapy
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• v.15 no.2
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• pp.196-209
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• 2003

본 연구의 목적은 보통 보행과 장애물 보행 시작시에 accuracy constraints, 즉 발꿈치 닿기(swing limb heel-strike)의 정확도가 힘판(forceplate) 상에서 힘의 조절 (force modulation)과 EMG에 어떠한 영향을 미치는지를 분석하는 것이다. 본 실험의 대상자는 힘판(forceplate)위에서 보통 보행과 장애물 보행을 하되, 대상자 앞에 놓인 표적(target)에 정확히 발꿈치 닫기 (heel-strike)를 하도록 유도되었다. 이 때 힘판 자료와 전경골근(tibialis anterior)및 가자미근 (soleus)의 근전도 (EMG)의 활동을 양쪽 다리에서 측정하였다. 대상자 앞에 놓인 표적 (target)에 정확한 발꿈치 닫기(heel-strike)가 요구되었을 때에는 발끝밀기(swing toe-off) 시간이 증가되었으며 힘판(forceplate)상에서의 peak farce와 slope to peak force 가 감소되는 것으로 나타났다. 전경골근 (tibialis anterior)의 활동역시 큰 차이로 감소하는 것으로 나타났다. 하지만 보통 보행과 장애물 보행시의 근전도 혹은 힘판상의 자료에는 큰 차이점이 없는 것으로 나타났다. 이러한 결과는 기존의 상지(upper extremity)에서 보여준 운동제어 (motor control)의 이론들이 하지(lower extremity)에서도 동일하게 적용될 수 있음을 보여주는 것이다.