• Journal of the Korean Magnetics Society
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• v.15 no.6
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• pp.303-306
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• 2005

Effect of a ferromagnetic layer thickness on a narrow domain wall width is investigated. It is found that the narrow domain wall is formed in ferromagnetic/nonmagnetic/ferromagnetic multi layer structure with a loc at interlayer exchange coupling, and that the width of the narrow domain wall is affected by the ferromagnetic layer thickness. We performed micromagnetics simulations for the $Fe_1/Cr/Fe_2$ system with the local interlayer exchange coupling, with fixed thickness (20-nm) of $Fe_2$ layer and various $Fe_1$ layer thickness (1, 2, 4, and 6 nm). Consequently, we confirmed that the thinner the $Fe_1$ layer thickness, the thinner the width of the domain wall is formed, because of the surface energy nature of the interlayer exchange coupling.

• The Journal of the Acoustical Society of Korea
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• v.15 no.1
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• pp.23-33
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• 1996

In this paper we point out that if the classical principal domain for bispectra is utilized to determine a second-order Volterra model's output, such and output will be incomplete. This deficiency is associated with the periodic nature of the DFT. For this reason, the objective of this paper is to present an "extended" principal domain for Volterra kernels which leads to an improved estimate of the nonlinear system's response. In order to define the extended principal domain, we derive a new discrete frequency-domain Volterra model from a discrete time-domain Volterra model utilizing 2-dimensional DFT and the relationship between the quadratic component of the Volterra model and a square filter. The effect of the extended domain on the model output is interpreted in terms of the periodicity of DFT. Through computer simulations, we demonstrate the effects of the extended principal domain on the Volterra modeling. The simulation results indicate that the extended principal domain plays and important role in computing Volterra model outputs and estimating Volterra model coefficients.

• Proceedings of the Korean Magnetic Resonance Society Conference
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• 2002.08a
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• pp.87-87
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• 2002

• Journal of Power Electronics
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• v.12 no.4
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• pp.623-631
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• 2012

In this paper, a digital controller design procedure is presented for single-phase voltage-doubler boost rectifiers (VDBR). The model derivation of the single-phase VDBR is performed in the s-domain. After that the simplified equivalent z-domain models are derived. These z-domain models are utilized to design the input current and the output dc-link voltage controllers. For the controller design in the z-domain, the traditional K-factor method is modified by considering the nature of the digital controller. The frequency pre-warping and anti-windup techniques are adapted for the controller design. By using the proposed method, the phase margin and the control bandwidth are accurately achieved as required by controller designers in a practical frequency range. The proposed method is applied to a 2.5 kVA single-phase VDBR for Uninterruptible Power Supply (UPS) applications. From the simulation and the experimental results, the effectiveness of the proposed design method has been verified.

• ETRI Journal
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• v.35 no.5
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• pp.739-747
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• 2013

This paper investigates the multifarious nature of the long-term evolution (LTE) scheme and that of the modified LTE scheme for symbol timing synchronization (STS). This investigation allows us to propose a new replica correlation-based STS scheme to overcome the inherent weaknesses of the other two schemes. The proposed STS signal combines a gold sequence and a half sine wave in the time domain, whereas conventional STS signals specify either binary sequences or complex sequences in the time domain or in the frequency domain. In the proposed scheme, a sufficient correlation property is realized by the gold sequence, and robustness against the frequency offset (FO) is achieved through the sine wave. Compared to the existing LTE-related schemes, the proposed scheme can better achieve immunity to FO and reduction in detector complexity, as well as a low peak-to-average power ratio and a low detection error rate. Performance evaluations through analysis and simulation are provided in the paper to demonstrate these attributes.

• ETRI Journal
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• v.41 no.5
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• pp.574-584
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• 2019

A new Mirai variant found recently was equipped with a dynamic update ability, which increases the level of difficulty for DDoS mitigation. Continuous development of 5G technology and an increasing number of Internet of Things (IoT) devices connected to the network pose serious threats to cyber security. Therefore, researchers have tried to develop better DDoS mitigation systems. However, the majority of the existing models provide centralized solutions either by deploying the system with additional servers at the host site, on the cloud, or at third party locations, which may cause latency. Since Internet service providers (ISP) are links between the internet and users, deploying the defense system within the ISP domain is the panacea for delivering an efficient solution. To cope with the dynamic nature of the new DDoS attacks, we utilized an unsupervised artificial neural network to develop a hierarchical two-layered self-organizing map equipped with a twofold feature selection for DDoS mitigation within the ISP domain.

• Journal of Korean Elementary Science Education
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• v.24 no.3
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• pp.268-280
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• 2005

Teaching with laboratory activities in school science, which are distinctive characteristic, is placed from other disciplines fur teaming almost 200 hundred years ago. A number of science educators have suggested that there are rich benefits in teaming from using laboratory activities. At these time, however, some educators have begun to seriously question the effectiveness and the role of laboratory activities. There are some causes related to obscure and vague aims of laboratory activities. The purposes of this paper is to review aims of laboratory activities presented in the literatures through historical overview, and to obtain implication for school science. There are various aims of laboratory activities by a number of researchers. Overall synthesizing, there are ffur domains of aims of science teaching through laboratory activities, (a) science knowledge has two sub-domains; scientific content knowledge and procedural knowledge, (b) nature of science, (c) science attitude has two sub-domain; scientific attitude and attitude toward science, and (d) ability of scientific inquiry has two sub-domain; manipulative skills and scientific thinking. But, it is necessary to continue the following study in order to obtain the aims of laboratory activities agreed by expert community, and setting up of lists of aims of laboratory activities for students to achieve hierarchies of school science curriculums.

• Journal of Gifted/Talented Education
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• v.18 no.2
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• pp.201-237
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• 2008

The object of this research is to understand the domain-universality and domain-specificity of scientific domain and visual art domain from case studies on individuals who had made creative accomplishments in the domain of science and visual art. For case studies, 10 people who made creative accomplishments in the science and technology domain and 9 people who made creative accomplishments in the visual art domain were selected as the research participants. The conclusions for the case studies were made on the data obtained from interviewing the research participants using KES as an analytical frame. The findings of this study support as follows. Creativity on scientific domain and visual art domain is both the domain-universality and domain-Specificity. The domain-universality Of scientific domain and visual art domain is related to the nature of human beings, originality in creativity, and the natural selection. On the other hand, The domain-specificity of scientific domain and visual art domain is related to the type of knowledge and the context of applying the knowledge, will, thinking skill, direction, and social components.

• Journal of Korean Elementary Science Education
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• v.19 no.2
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• pp.29-41
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• 2000

The purpose of this study is to examine the effects of the Portfolio applied science instruction on the students' scientific affective domain and perceptions of portfolio in elementary schools. Portfolio applied science instruction of the 6th grade science unit 'Environment pollution and Nature protection' was developed for this study. Traditional instruction was implemented to the control group and portfolio applied science instruction was implemented to the experimental group. Pretests of the scientific affective domain were administered to both groups. The treatment was given for about seven weeks for both groups. Instruments about scientific affective domain were administered to both groups. A questionnaire on perception of portfolio applied science instruction was given to the experimental group after the treatment. The results were analyzed using t-test on the students' scientific affective domain. The results of this study are as follows: 1. Portfolio applied science instruction program for elementary schools was developed. Students themselves determine the portfolio learning goal in a portfolio applied science instruction. Students construct the portfolio and they evaluate themselves and other colleagues. Also teachers go on portfolio applied science instruction considering portfolio purpose, concepts, evaluation. 2. There was not a statistically meaningful difference between an experimental group and a control group o]1 the students' scientific affective domain. In three sub categories of a scientific affective domain, the science perception, the interest on science and scientific attitude, there were not statistically meaningful difference among them. 3. As the results of the questionnaire on perceptions of portfolio, they didn't understand it very well but after learning portfolio, they showed positive attitude to perceptions of portfolio. Students in portfolio applied science instruction like more the portfolio applied science instruction than general instruction. 4. Portfolio applied science instruction has an useful value as a method of teaching and evaluation. Students and teachers can produce various portfolios products in portfolio applied science instruction. As a conclusion, portfolio applied science instruction was not statistically meaningful on the students' scientific affective domain, but it gives positive effects on perceptions of portfolio in elementary schools. Therefore, portfolio has an educational value as a method of teaching and evaluation for students' growth. In the future, teachers and students must have interaction and feedback in portfolio applied science instruction.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.27 no.2
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• pp.29-42
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• 2024

As a global response to climate and biodiversity challenges, there is an emphasis on the conservation and restoration of ecosystems that can simultaneously reduce carbon emissions and enhance biodiversity. This study comprised a text analysis and keyword extraction of 1,100 research papers addressing nature restoration in Korea, aiming to provide a quantative and systematic evaluation of domestic research trends in this field. To discern the major research topics of these papers, topic modeling was applied and correlations were established through network analysis. Research on nature restoration exhibited a mainly upward trend in 2002-2022 but with a slight recent decline. The most common keywords were "species," "forest," and "water". Research topics were broadly classified into (1) predictions of habitat size and species distribution, (2) the conservation and utilization of natural resources in urban areas, (3) ecosystems and landscape managements in protected areas, (4) the planting and growth of vegetation, and (5) habitat formation methods. The number of studies on nature restoration are increasing across various domains in Korea, with each domain experiencing professional development.