• Journal of The Korean Association For Science Education
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• v.27 no.4
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• pp.346-353
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• 2007

In order to be efficient in teaching, a teacher should understand the current learner's level through diagnostic evaluation. This study has examined the major issues arising from the noble diagnostic assessment tool based on the theory of knowledge space. The knowledge state analysis method is actualizing the theory of knowledge space for practical use. The knowledge state analysis method is very advantageous when a certain group or individual student's knowledge structure is analyzed especially for strong hierarchical subjects such as mathematics, physics, chemistry, etc. Students' knowledge state helps design an efficient teaching plan by referring their hierarchical knowledge structure. The knowledge state analysis method can be enhanced by computer due to fast data processing. In addition, each student's knowledge can be improved effectively through individualistic feedback depending on individualized knowledge structure. In this study, we have developed a diagnostic assessment test for measuring student's learning outcome which is unattainable from the conventional examination. The diagnostic assessment test was administered to middle school students and analyzed by the knowledge state analysis method. The analyzed results show that students' knowledge structure after learning found to be more structured and well-defined than the knowledge structure before the learning.

• Journal of The Korean Astronomical Society
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• v.35 no.4
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• pp.159-174
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• 2002

Cosmological hydrodynamic simulations of large scale structure in the universe have shown that accretion shocks and merger shocks form due to flow motions associated with the gravitational collapse of nonlinear structures. Estimated speed and curvature radius of these shocks could be as large as a few 1000 km/s and several Mpc, respectively. According to the diffusive shock acceleration theory, populations of cosmic-ray particles can be injected and accelerated to very high energy by astrophysical shocks in tenuous plasmas. In order to explore the cosmic ray acceleration at the cosmic shocks, we have performed nonlinear numerical simulations of cosmic ray (CR) modified shocks with the newly developed CRASH (Cosmic Ray Amr SHock) numerical code. We adopted the Bohm diffusion model for CRs, based on the hypothesis that strong Alfven waves are self-generated by streaming CRs. The shock formation simulation includes a plasma-physics-based 'injection' model that transfers a small proportion of the thermal proton flux through the shock into low energy CRs for acceleration there. We found that, for strong accretion shocks, CRs can absorb most of shock kinetic energy and the accretion shock speed is reduced up to $20\%$, compared to pure gas dynamic shocks. For merger shocks with small Mach numbers, however, the energy transfer to CRs is only about $10-20\%$ with an associated CR particle fraction of $10^{-3}$. Nonlinear feedback due to the CR pressure is insignificant in the latter shocks. Although detailed results depend on models for the particle diffusion and injection, these calculations show that cosmic shocks in large scale structure could provide acceleration sites of extragalactic cosmic rays of the highest energy.

• Journal of The Korean Association For Science Education
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• v.22 no.1
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• pp.122-131
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• 2002

Recently, performance assessment that makes growing use of free response items in a large scale assessment has been emphasized. This study is an empirical examination of the effectiveness of free response items in comparison with multiple choice items. Using the information function in Item Response Theory (IRT) framework, item information of free response items and multiple-choice items from the Third International Mathematics and Science Study-Repeat (TlMSS-R) were obtained. Test information of the whole science area as well as each area of science contents was computed. On average, free response items yielded more information than multiple choice items, especially in earth science, physics, chemistry, and life science. This study also showed that free response items were appropriate for students in high science ability. Also, free response items estimated students' science ability more accurately than multiple choice items with smaller number of free response items.

• Journal of the Korean Data and Information Science Society
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• v.7 no.1
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• pp.113-118
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• 1996

Principal component analysis(PCA) is an essential technique for data compression and feature extraction, and has been widely used in statistical data analysis, communication theory, pattern recognition, and image processing. Oja(1992) found that a linear neuron with constrained Hebbian learning rule can extract the principal component by using stochastic gradient ascent method. In practice real data often contain some outliers. These outliers will significantly deteriorate the performances of the PCA algorithms. In order to make PCA robust, Xu & Yuille(1995) applied statistical physics to the problem of robust principal component analysis(RPCA). Devlin et.al(1981) obtained principal components by using techniques such as M-estimation. The propose of this paper is to investigate from the statistical point of view how Xu & Yuille's(1995) RPCA works under the same simulation condition as in Devlin et.al(1981).

• Applied Microscopy
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• v.40 no.1
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• pp.21-28
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• 2010

In a simulation study of atomic resolution transmission electron microscope images of single layer and bilayer graphene, it is demonstrated that the conventional Bloch wave formulations can be used when high-order Laue zone reflections are properly taken into account in the theory. The simulated images for bilayer graphene show 3-fold rotational lattice symmetry rather than the 6-fold one under certain conditions. This result can be understood as revealed the 3-fold rotational lattice symmetry of bilayer graphene in three dimensions along [0001]. For single layer graphene the observed phase images showing 3-fold rotational lattice symmetry were particularly noted. This phenomenon has been explained by an assumption of the re-configuration of electron density on the surface of graphene. And the matching images have been obtained as simulated with up to the second order Laue zone reflections only, reflecting the re-configuration of electrons on the surface.

• Journal of the Korean Institute of Gas
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• v.14 no.2
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• pp.34-39
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• 2010

Flame propagation velocity is the one of the main mechanism of the stabilization of triple flame. To quantify the triple flame propagation velocity, Bilger presents the triple flame propagation velocity through the experiment, depending on the mixture fraction gradient, based on the laminar jet flow theory. However, in spite of these many analyses, there has not been any attempt to quantify the triple flame propagation velocity with the radius of flame curvature. In the present research, a relation of the flame propagation velocity is proposed with the radius of flame curvature for the flame stabilization mechanism. As a result, we have shown that the height of lifted flame is determined with the nozzle diameter and exit velocity of fuel and presented that the radius of flame curvature is proportion to the nozzle exit velocity of fuel and height of lifted flame. Therefore, the importance of the radius of flame curvature has to be recognized. To discribe the flame stabilization mechanism, Bilger's formula has to be modified with flame curvature effect.

• The KIPS Transactions:PartC
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• v.8C no.5
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• pp.585-596
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• 2001

In this paper, a new stream cipher algorithm based on the chaos theory is proposed and is applied to a Web security system. The Web security system is composed of three parts： certificate authority (CA), Web client, and Web server. The Web client and server system include a secure proxy client (SPC) and a secure management server (SMS), respectively, for data encryption and decryption between them. The certificate is implemented based on X.509 and the RSA public key algorithm is utilized for key creation and distribution to certify both the client and server. Once a connection is established between the client and server, outgoing and incoming data are encrypted and decrypted, respectively, using one of the three cipher algorithms： chaos, SEED, and DES. The proposed chaos algorithm outperforms the other two conventional algorithms in processing time and complexity. Thus, the developed Web security system can be widely used in electronic commerce (EC) and Internet banking.

• Journal of radiological science and technology
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• v.41 no.5
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• pp.487-491
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• 2018

The purpose of this study was to analyze questionnaires of 161 college students attending radiology departments in order to investigate the actual condition of internet use of radiology students. As a result, 95% of college students using the Internet showed 5.8% of general knowledge, 56.9% of radiation major, and 45.8% of general education. In the field of Internet use, basic medicine was 71.2%, anatomy 59.5% and physiology 51.6%. Radiation theory was 39.9% in radiation physics, 31.4% in radiation biology, and 18.3% in radiation management. The radiological applications were followed by radiography and radiography in order of 31.4% and 20.3%, respectively. The radiological imaging was 45.8%, MRI was 37.9%, CT was 37.3%, ultrasound was 24.2%, And radiation nuclear medicine 25.5%. The results of the descriptive statistics of the satisfaction of the contents using the Internet media showed that the overall satisfaction was below 2.5 Based on the results of this study, it is necessary to develop a program with high accessibility to provide various opportunities for internet-based opportunities to increase the academic achievement value of major subjects through the internet and to solve the difficulties in the major subject.

• Journal of the Korean Institute of Gas
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• v.14 no.3
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• pp.46-52
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• 2010

Flame propagation velocity is the one of the main mechanism of the stabilization of triple flame. To quantity the triple flame propagation velocity, Bilger presents the triple flame propagation velocity, depending on the mixture fraction gradient, based on the laminar jet flow theory. However, in spite of these many analyses, there has not been any attempt to quantify the triple flame propagation velocity with the flame radius of curvature and scalar dissipation rate. In the present research, there was discussion about the radius of flame curvature and scalar dissipation rate, through the numerical study. As a result, we have known that the flame propagation velocity was linear with the nozzle exit velocity and scalar dissipation rate decreases nonlinearly with the flame propagation velocity and radius of curvature of flame increases linearly. Also radius of curvature of flame decreases non-linearly with the scalar dissipation rate. Therefore, we ascertained that there was corelation among the scalar dissipation rate, radius of flame curvature and flame propagation velocity.

• Journal of Korean Physical Therapy Science
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• v.9 no.3
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• pp.179-186
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• 2002

This study addresses the need to adopt teaching-learning approaches in physical therapy education that develop links between theory and clinical practice in a meaningful way. Problem-based learning (PBL) is presented as a useful way to educate physical therapy for the future. The essential characteristics of problem-based learning include: curricular organization around problems rather than disciplines; an integrated curriculum rather than one separated into clinical and theoretical components; and an inherent emphasis on cognitive skills as well as on knowledge. PBL as implemented in the health sciences, is an educational method in which the focus of learning is a small-group tutorial in which students work through health care scenarios. The goals of the health care scenarios are to provide a context for learning, to activate prior knowledge, to motivate students, and to stimulate discussion. Learning is student-centered rather than faculty-centered, and self-directed learning is emphasized. Whereas the former focuses on critical thinking and clinical judgement, the latter's emphasis is on clinical competency. The physical therapist (PT) program at Cheju Halla college is a partial integrated problem-based curriculum. The history and process of PBL in general and in the PT program are reviewed. Long-term advocates of PBL stress that it is the only known method for preparing future professionals to be able to adapt to change, learning how to reason critically, enabling a holistic approach to health.