• Journal of the Korea Society of Computer and Information
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• v.21 no.9
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• pp.165-176
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• 2016

This study developed the learning ability-based smart education program. The effectiveness of the developed materials was investigated using the quantitative-qualitative mixed method, and the process and results of the investigation are as follows. The quantitative investigation was conducted using the non-equivalent pretest-posttest design, in which the smart education method was applied to the experimental group, while the conventional education method was applied to the control group to analyze students' creative problem-solving potential, task concentration, and the variables required for the learning activity. The results showed significantly higher performance in the experimental group over the control group. Regarding data collection in the qualitative investigation, an analysis of the class from the instructor and class consultation logs from the class analyst were collected; the comments on the experience of each class period were collected from students. The results of the analysis of the data suggest that the perception of smart education improved for the instructor, class analyst, and learners as the course progressed.

• Journal of the Semiconductor & Display Technology
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• v.14 no.4
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• pp.72-77
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• 2015

Three-level diode clamped multilevel inverter, generally known as neutral point clamped (NPC) inverter, has an inherent problem causing neutral point (NP) potential variation. Until now, the NP potential problem of variation has been investigated and lots of solutions have also been proposed. This paper presents a neutral point voltage control technology using the anti-windup PI controller and offset technology of PWM (Pulse Width Modulation) to control the variation of NPC 3-phase three-level inverter neutral point voltage. And the proposed algorithm is tested and verified using a PLL (Phase Locked Loop) in order to synchronize the phase voltage from the line voltage of grid. It significantly improves the voltage balancing under a solar fluctuation conditions of the inverter. Experimental results show the good performance and effectiveness of the proposed method.

• Journal of the Korean Mathematical Society
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• v.56 no.6
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• pp.1529-1560
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• 2019

We are concerned with the following elliptic equations: $$(-{\Delta})^s_pu+V (x){\mid}u{\mid}^{p-2}u={\lambda}g(x,u){\text{ in }}{\mathbb{R}}^N$$, where $(-{\Delta})_p^s$ is the fractional p-Laplacian operator with 0 < s < 1 < p < $+{\infty}$, sp < N, the potential function $V:{\mathbb{R}}^N{\rightarrow}(0,{\infty})$ is a continuous potential function, and $g:{\mathbb{R}}^N{\times}{\mathbb{R}}{\rightarrow}{\mathbb{R}}$ satisfies a $Carath{\acute{e}}odory$ condition. We show the existence of at least one weak solution for the problem above without the Ambrosetti and Rabinowitz condition. Moreover, we give a positive interval of the parameter ${\lambda}$ for which the problem admits at least one nontrivial weak solution when the nonlinearity g has the subcritical growth condition.

• International Journal of Naval Architecture and Ocean Engineering
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• v.3 no.3
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• pp.159-173
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• 2011

The two different numerical approaches for solving the nonlinear ship wave problem are discussed in the present paper. One is based on a panel method, which neglects the viscous effects. The other is based on a finite volume method, which take into account the viscous effects by solving RANS equations. Focus is laid upon on the advantages and disadvantages of two methods. The developed methods are applied to calculating the flow around Series 60 hull to validate the performance of the present nonlinear methods. Although the two methods employ quite different numerical approaches, the calculated wave patterns from both methods show good agreements with the experiments. However the potential method simu-lates the global wave pattern accurately, while the viscous method shows better performance for the local wave prediction near a ship.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.10
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• pp.5062-5079
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• 2017

Malicious insider threats have increased recently, and methods of the threats are diversifying every day. These insider threats are becoming a significant problem in corporations and governments today. From a technology standpoint, detecting potential insider threats is difficult in early stage because it is unpredictable. In order to prevent insider threats in early stage, it is necessary to collect all of insiders' data which flow in network systems, and then analyze whether the data are potential threat or not. However, analyzing all of data makes us spend too much time and cost. In addition, we need a large repository in order to collect and manage these data. To resolve this problem, we develop an indicator-based behavior ontology (IB2O) that allows us to understand and interpret insiders' data packets, and then to detect potential threats in early stage in network systems including social networks and company networks. To show feasibility of the behavior ontology, we developed a prototype platform called Insider Threat Detecting Extractor (ITDE) for detecting potential insider threats in early stage based on the behavior ontology. Finally, we showed how the behavior ontology would help detect potential inside threats in network system. We expect that the behavior ontology will be able to contribute to detecting malicious insider threats in early stage.

• Journal of Korean Elementary Science Education
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• v.28 no.2
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• pp.132-141
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• 2009

The purpose of this research was to investigate the effect of using digital science textbook on the scientific problem solving of elementary school students. For this research, an instrument to measure student's problem-solving skills was developed. The pretest and posttest scores of one hundred and six 5th grade students' problem-solving skills were analyzed and also the responses of three students who were selected by their levels in the problem-solving science digital textbook class were qualitatively analyzed. The results of this study were as follows; the scores of problem solving skills of science digital textbook groups were higher than that of traditional paper textbook group(p<.05). In the qualitative analysis of the students' reponses in a digital textbook class according to their achievement level, low-achievers' problem-solving skills were much more improved than high- and mid-achievers' skills. In conclusion, science digital textbook has a potential to improve students' scientific problem solving skills, and this possibility will be much higher when science digital textbook is used with teachers' intended instructional goals and strategies like problem-solving lessons.

• Management Science and Financial Engineering
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• v.14 no.2
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• pp.45-66
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• 2008

Refuse collection, one of important elements in reverse logistics, is an activity rendering recyclables or wastes and moving them to some points where further treatment is required. Among various decisions in the collection activity, we focus on network design, which is the problem of locating collection points as well as allocating refuses at demand points to collection points while satisfying the capacity restriction at each collection point. Here, the collection point is the place where recyclables or wastes near the point are gathered, and locating the collection points is done by selecting them from a given set of potential sites. The objective is to minimize the sum of fixed costs to open collection points and transportation costs to move refuses from demand points to collection points. An integer programming model is developed to represent the problem mathematically and due to the complexity of the problem, two types of heuristics, one with simultaneous and the others with separate location and allocation, are suggested. Computational experiments were done on test problems up to 500 potential sites, and the results are reported. In particular, some heuristics gave near optimal solutions for small-size test problems, i.e., 2% gaps in average from the optimal solution values.

• Proceedings of the KIEE Conference
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• 1999.11b
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• pp.21-23
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• 1999

In this paper, the analysis of the electric field in the chamber of high voltage $SF_6$ GCB(Gas Circuit Breaker) is presented by using C-1 FEM. For this purpose, pre-processing program and post-processing program were developed for axisymmetirc 3 dimensional analysis and the electric field in cylindric chamber was analyzed. Important problem is that electric analysis must be considered coronal due to break-down of $SF_6$ when it is cutted off. To solve this problem, a procedure is needed to verify that the solution of Poisson's equation for scalar potential satisfy charge continuos condition because of using first order element os not satisfy the electric continuous condition, C-1 FEM is introduce to obtain electirc potential and electric field at the same time. Analysis of the distribution of electric field on model was done. It is confirmed that the developed program in this paper applicable to design and to analyze of characteristics in total program as electric characteristics analysis routine.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.5
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• pp.1976-1997
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• 2016

This paper investigates the problem of co-tier interference mitigation for dynamic small- cell networks, in which the load of each small-cell varies with the number of active associated small-cell users (SUs). Due to the fact that most small-cell base stations (SBSs) are deployed in an ad-hoc manner, the problem of reducing co-tier interference caused by dynamic loads in a distributed fashion is quite challenging. First, we propose a new distributed channel allocation method for small-cells with dynamic loads and define a dynamic interference graph. Based on this approach, we formulate the problem as a dynamic interference graph game and prove that the game is a potential game and has at least one pure strategy Nash equilibrium (NE) point. Moreover, we show that the best pure strategy NE point minimizes the expectation of the aggregate dynamic co-tier interference in the small-cell network. A distributed dynamic learning algorithm is then designed to achieve NE of the game, in which each SBS is unaware of the probability distributions of its own and other SBSs' dynamic loads. Simulation results show that the proposed approach can mitigate dynamic co-tier interference effectively and significantly outperform random channel selection.

• Journal of the Society of Naval Architects of Korea
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• v.30 no.2
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• pp.86-97
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• 1993

A numerical method is developed for the nonlinear motion of two-dimensional wedges and axisymmetric-forced-heaving motion using Semi-Largrangian scheme under assumption of potential flows. In two-dimensional-problem Cauchy's integral theorem is applied to calculate the complex potential and its time derivative along boundary. In three-dimensional-problem Rankine ring sources are used in a Green's theorem boundary integral formulation to salve the field equation. The solution is stepped forward numerically in time by integrating the exact kinematic and dynamic free-surface boundary condition. Numerical computations are made for the entry of a wedge with a constant velocity and for the forced harmonic heaving motion from rest. The problem of the entry of wedge compared with the calculated results of Champan[4] and Kim[11]. By Fourier transform of forces in time domain, added mass coefficient, damping coefficient, second harmonic forces are obtained and compared with Yamashita's experiment[5].