• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.1C
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• pp.48-56
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• 2011

Cognitive radio (CR) systems have received significant interest as a promising solution to the spectral shortage problem through efficient use of the frequency spectrum by opportunistically exploiting unlicensed frequency bands. Orthogonal frequency division multiplexing (OFDM) is widely regarded as a highly promising candidate for CR systems. However, the frequency bands used by CR systems are expected to suffer from non-Gaussian noise, which considerably degrades the performance of the conventional OFDM carrier frequency offset (CFO) estimation schemes. In this paper, robust CFO estimation schemes for OFDM-based CR systems in non-Gaussian channels are proposed. Simulation results demonstrate that the proposed estimators offer robustness and substantial performance improvement over the conventional estimator.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.10
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• pp.905-913
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• 2017

In this work, a method of size optimization is proposed to maximize the natural frequency of a rod that consists of a hidden shape in one part and an exposed shape in the other. The frequency response function of a rod composed of two parts is predicted by using the frequency response functions of each of the parts instead of the shapes of the parts. The mass and stiffness matrices of the rod are obtained by using the mass and stiffness matrices of the equivalent vibration systems, which are obtained by applying the experimental modal analysis method to the frequency response functions of the parts. Through several numerical examples, the frequency response function obtained by using the proposed method is compared with that of a rod to validate the prediction method based on equivalent vibration systems. A size optimization problem is formulated for maximizing the first natural frequency of a combined rod, which is replaced with an equivalent vibration system, and a rod structure is optimized by using an optimization algorithm.

• Journal of Positioning, Navigation, and Timing
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• v.10 no.4
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• pp.315-333
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• 2021

Due to the Global Navigation Satellite System (GNSS) modernization, recently launched GNSS satellites transmit signals at various frequency bands such as L1, L2 and L5. Considering the Korean Positioning System (KPS) signal and other GNSS augmentation signals in the future, there is a high probability of applying more complex communication techniques to the new GNSS signals. For the reason, GNSS receivers based on flexible Software Defined Radio (SDR) concept needs to be developed to evaluate various experimental communication techniques by accessing each signal processing module in detail. This paper proposes a novel SDR-based A-GNSS receiver capable of processing multi-GNSS/RNSS signals at multi-frequency bands. Due to the modular structure, the proposed receiver has high flexibility and expandability. For real-time implementation, A-GNSS server software is designed to provide immediate delivery of satellite ephemeris data on demand. Due to the sampling bandwidth limitation of RF front-ends, multiple SDRs are considered to process the multi-GNSS/RNSS multi-frequency signals simultaneously. To avoid the overflow problem of sampled RF data, an efficient memory buffer management strategy was considered. To collect and process the multi-GNSS/RNSS multi-frequency signals in real-time, the proposed SDR A-GNSS receiver utilizes multiple threads implemented on a CPU and multiple NVIDIA CUDA GPGPUs for parallel processing. To evaluate the performance of the proposed SDR A-GNSS receiver, several experiments were performed with field collected data. By the experiments, it was shown that A-GNSS requirements can be satisfied sufficiently utilizing only milliseconds samples. The continuous signal tracking performance was also confirmed with the hundreds of milliseconds data for multi-GNSS/RNSS multi-frequency signals and with the ten-seconds data for multi-GNSS/RNSS single-frequency signals.

• Journal of Korean Institute of Industrial Engineers
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• v.20 no.4
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• pp.85-97
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• 1994

An interactive and iterative control panel layout method based on the constraint satisfaction problem (CSP) technique was developed to generate an ergonomically sound panel design. This control panel layout method attempts to incorporate a variety of relevant ergonomic principles and design constraints, and generate an optimal or, at least, a "satisfactory" solution through an efficient search algorithm. The problem of seeking an ergonomically sound panel design should be viewed as a multi-criteria design problem and most of the design objectives should be understood as constraints. Hence, a CSP technique was employed in this study for dealing with the multi-constraints layout problem. The efficient search algorithm using "preprocess" and "look_ahead" procedures was developed to handle vast amount of computation. In order to apply the CSP technique to the panel layout procedure, the ergonomic principles such as spatial compatibility, frequency-of-use, importance, functional grouping, and sequence-of-use were formalized as CSP terms. The effectiveness of the proposed panel layout method was evaluated by example problems and the results clearly showed that the generated layouts properly considered various ergonomic design principles.

• Journal of Korean Home Economics Education Association
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• v.7 no.2
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• pp.91-101
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• 1995

The purposes of the study were to: (1) develop instructional method for consumer education of home economics in the middle school. (2) test the effectiveness of the developing instructional method focusing on the problem solving. In the method of the research, literature review related to the consumer education. models of teaching and characteristics of problem solving method were studied. Also, on the basis of theoretical evidence. the teaching plan focusing on problem solving method was developed. In addition, experimental research was done to find out the learning effectiveness on the developing instructional method of the study. This experimental research were made in the six classes of the three middle school in Seoul. For the statistical analysis of the study, frequency, mean and two way ANOVA(factorial design) were used. The results of this study were summarized as follows; (1) The developed instructional method of the study was more effective than the traditional lecture method. (2) The effects of the teaching-learning method were depended on the sex. The learning effects on the female students were higher than the male students. (3) The learning effects on the students were influenced by the sex and teaching method.

• The Journal of Korean Association of Computer Education
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• v.13 no.2
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• pp.45-57
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• 2010

In this paper, we propose a C_PBS(C Program Bank System) which can support effective learning of C language. C_PBS allows a variety of problem uses and provides 3 types of search method for user convenience. It also shows many useful facilities: a variety of answers to a problem, display of problems according to reference frequency, interesting problem list, and problem carts. Especially, with the addition of comments and reference to the problems and answers, it implements collective intelligence via mutual collaborative learning by supporting the philosophy of web 2.0: participation, sharing, and open.

• Korean Journal of Human Ecology
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• v.13 no.4
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• pp.507-519
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• 2004

The purpose of this study is to explore the general trends and the correlations of parent-child conflicts, copings, and psychological well-being of single mothers and their children, and to analyze the variables explaining relationships between single mothers and their children. The subjects were 196 dyads of single mothers and their children who reside in Gwangju city and Jeonnam area. The data were analyzed with frequency, t-Test, Pearsons' r, and multiple regression by SPSS. The major findings are as follows: 1. Scores of single mothers and their children had conflicts and emotion-focused copings lower than median. Another scores of single mothers and their children had significantly higher problem solving focused copings and emotion-focused copings than their children except life satisfaction; 2. Conflicts, copings, life satisfaction, and depression of a single mother were positively related to those of children; 3. Life satisfaction of single mothers depends on the reason for spouse-loss, their own education background, and problem solving-focused copings. Also, that of children depends on problem solving-focused copings, mother-child conflicts, and the mothers' education. Depression of single mothers is dependent upon mother-child conflicts, emotion-focused copings, and mothers' education. Also, that of children is upon mother-child conflicts, emotion-focused copings, mothers' education, and problem solving-focused copings.

• Journal of the Society of Naval Architects of Korea
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• v.44 no.4
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• pp.398-407
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• 2007

A smoothed particle hydrodynamics (SPH) method is applied for simulating two-dimensional free-surface problems. The SPH method based on the Lagrangian formulation provides realistic flow motions with violent surface deformation, fragmentation and reunification. In this study, the effect of computational parameters in SPH simulation is explored through two-dimensional dam-breaking and sloshing problem. The parameters to be considered are the speed of sound, the frequency of density re-initialization, the number of particle and smoothing length. Through a series of numerical test. detailed information was obtained about how SPH solution can be more stabilized and improved by adjusting computational parameters. Finally, some numerical simulations for various fluid flow problem were carried out based on the parameters chosen through the sensitivity study.

• Smart Structures and Systems
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• v.25 no.3
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• pp.345-368
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• 2020

The present work proposes a self-controlled multi-stage optimization method for damage identification of structures utilizing standard particle swarm optimization (PSO) algorithm. Damage identification problem is formulated as an inverse optimization problem where damage severity in each element of the structure is considered as optimization variables. An efficient objective function is formed using the first few frequencies and mode shapes of the structure. This objective function is minimized by a self-controlled multi-stage strategy to identify and quantify the damage extent of the structural members. In the first stage, standard PSO is utilized to get an initial solution to the problem. Subsequently, the algorithm identifies the most damage-prone elements of the structure using an adaptable threshold value of damage severity. These identified elements are included in the search space of the standard PSO at the next stage. Thus, the algorithm reduces the dimension of the search space and subsequently increases the accuracy of damage prediction with a considerable reduction in computational cost. The efficiency of the proposed method is investigated and compared with available results through three numerical examples considering both with and without noise. The obtained results demonstrate the accuracy of the present method can accurately estimate the location and severity of multi-damage cases in the structural systems with less computational cost.

• Journal of the Korea Safety Management & Science
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• v.14 no.4
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• pp.281-289
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• 2012

Recently, creative innovation has become a major topic in management innovation and due to this, various researches on its need and methodologies are being performed. According to previous studies on ambidexterity, explorative innovation is closer to divergent and right-sided brain, while exploitative innovation is closer to convergent and left-sided brain. Five attributes of the questionnaires were developed based on right-sided and left-sided brain theory. Also, 25 problem solving tools were selected according to previous studies. QC 7 Tools and new QC 7 Tools were frequently used in Six Sigma projects. Other 11 problem solving tools were selected with consideration on its usage frequency. Survey questionnaires were distributed to 25 Six Sigma consultants and 22 were retrieved for this study's use. As a result, 14 tools were identified to hold exploitative attribute while 11 tools were identified to hold explorative attributes.