• Korean Journal of Crystallography
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• v.14 no.1
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• pp.16-23
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• 2003

The electronic structure and chemical bonding of β-MnO₂ were theoretically investigated by DV-X/sub α/ (the discrete variation X/sub α/) method. which is a sort of the first principle molecular orbital method using Hatre-Fock-Slater approximation. The calculations on several cluster models having different sizes were carried out for the determination of a model suited for analyzing bulk state. The Mn/sub 15/O/sub 56/ model was selected as a sufficiently suitable model for the calculation of electronic state and chemical bonding by the comparison of the calculated XPS (X-ray photo-electron spectrum) and experimentally measured XPS. By using this model, the electron energy level, the density of state, the bond overlap population, the charge density distribution, and the net ionic transfer between cations and anions were calculated and discussed.

• Korean Journal of Materials Research
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• v.27 no.4
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• pp.229-235
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• 2017

Through density functional theory calculations, to provide insight into the origins of the catalytic activity of Au nanoparticles (NPs) toward oxidation reactions, we have scrutinized the oxygen adsorption chemistry of 9 types of small unsupported Au NPs of around 1 nm in size (Au13, Au19, Au20, Au25, Au38, and Au55) looking at several factors (size, shape, and coordination number). We found that these NPs, except for the icosahedral Au13, do not strongly bind to $O_2$ molecules. Energetically most feasible $O_2$ adsorption that potentially provides high CO oxidation activity is observed in the icosahedral Au13, our smallest Au NP. In spite of the chemical inertness of bulk Au, the structural fluxionality of such very small Au NP enables strong $O_2$ adsorption. Our results can support recent experimental findings that the exceptional catalytic activity of Au NPs comes from very small Au species consisting of around 10 atoms each.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07a
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• pp.309-312
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• 2004

The electronic structure of ZnO oxide semiconductor having high optical transparency and good electric conductivity was theoretically investigated by $DV-X_{\alpha}$(the discrete variation $X_{\alpha}$) method, which is a sort of the first principle molecular orbital method using Hatre-Fock-Slater approximation. The electrical and optical properties of ZnO are seriously affected by the addition of impurities. The imnurities are added to ZnO in order to increase the electric conductivity of an electrode without losing optical transparency. In this study, the effect of impurities of III and IV family on the band structure, impurity levels and the density of state of ZnO were investigated. The cluster model used for calculations was $[MZn_{50}O_{53}]^{-2}$(M=elements belonging to III and IV family).

• Journal of the Architectural Institute of Korea Planning & Design
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• v.35 no.10
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• pp.63-70
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• 2019

The Busan branch of the former Toyo Takushoku Co. carried out the same business as a bank at the time of construction. This required an open space of long-span, which had no pillars, on the first floor where many customers frequently visited. In addition, an office space is required in the upper part, and a column is arranged so as to place a corridor in the center. It was designed with modern complex structures for space utilization and structural adaptation. As a result, scientific structural calculations of the modern era began and various structural technologies were introduced, the rationalization and value of various spatial characteristics and their structural design were analyzed from a technical historical perspective in the structure requiring long-span space. The Busan branch of the former Toyo Takushoku Co. is a complex structure with three structures. It is highly valuable as a building that tried to design its structure in a variety of spaces through calculation and introduction of new technology based on the principle of force in modern times.

• Steel and Composite Structures
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• v.46 no.1
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• pp.15-31
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• 2023

Organic solar cells utilized natural polymers to convert solar energy to electricity. The demands for green energy production and less disposal of toxic materials make them one of the interesting candidates for replacing conventional solar cells. However, the different aspects of their properties including mechanical strength and stability are not well recognized. Therefore, in the present study, we aim to explore the chaotic responses of these organic solar cells. In doing so, a specific type of organic solar cell constructed from layers of material with different thicknesses is considered to obtain vibrational and chaotic responses under different boundaries and initial conditions. A square plate structure is examined with first-order shear deformation theory to acquire the displacement field in the laminated structure. The bounding between different layers is considered to be perfect with no sliding and separation. On the other hand, nonlocal elasticity theory is engaged in incorporating the structural effects of the organic material into calculations. Hamilton's principle is adopted to obtain governing equations with regard to boundary conditions and mechanical loadings. The extracted equations of motion were solved using the perturbation method and differential quadrature approach. The results demonstrated the significant effect of relative glass layer thickness on the chaotic behavior of the structure with higher relative thickness leading to less chaotic responses. Moreover, a comprehensive parameter study is presented to examine the effects of nonlocality and relative thicknesses on the natural frequency of square organic solar cell structure.

• Structural Engineering and Mechanics
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• v.90 no.1
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• pp.41-49
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• 2024

In recent years, China's high-speed railway (HSR) line continues to expand into seismically active regions. Analyzing the features of earthquake rail irregularity is crucial in this situation. This study first established and experimentally validated a finite element (FE) model of bridge-track. The FE model was then combined with earthquake record database to generate the earthquake rail irregularity library. The sample library was used to construct a model of desired earthquake rail irregularity based on signal processing (SFT) and hypothesis principle. Finally, the effects of random pier height and random span number on desired irregularity were analyzed. Herein, an equivalent method of calculating earthquake rail irregularities for random structures was proposed. The results of this study show that the amplitude of desired irregularity is found to increase with increasing pier height. When calculating the desired irregularity of a structure with unequal pier heights, the structure can be regarded as that with equal pier heights (taking the largest pier height). For a structure with the span number large than 9, its desired irregularity can be considered equal to that of a 9-span structure. For the structures with both random pier heights and random span number, their desired irregularities are obtained by equivalent calculations for pier height and span number, respectively.

• Journal of The Korean Association of Information Education
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• v.25 no.5
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• pp.791-801
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• 2021

In this paper, an educational case that can be applied as artificial intelligence literacy education for preservice teachers and incumbent teachers was studied. To this end, a case of educating the operating principle of an artificial neural network that recognizes images is proposed. This training case focuses on the basic principles of artificial neural network operation and implementation, and applies the method of finding parameter optimization solutions required for artificial neural network implementation in a spreadsheet. In this paper, we focused on the artificial neural network of supervised learning method. First, as an artificial neural network principle education case, an artificial neural network education case for recognizing two types of images was proposed. Second, as an artificial neural network extension education case, an artificial neural network education case for recognizing three types of images was proposed. Finally, the results of analyzing artificial neural network training cases and training satisfaction analysis results are presented. Through the proposed training case, it is possible to learn about the operation principle of artificial neural networks, the method of writing training data, the number of parameter calculations executed according to the amount of training data, and parameter optimization. The results of the education satisfaction survey for preservice teachers and incumbent teachers showed a positive response result of over 70% for each survey item, indicating high class application suitability.

• Education of Primary School Mathematics
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• v.20 no.4
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• pp.253-266
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• 2017

The purpose of the study was to investigate the perceptions of Elementary school teachers on mathematics instruction. To do this, 7 test items were developed to obtain data on teacher's perception of mathematics instruction and 73 teachers who take mathematical lesson analysis lectures were selected and conducted a survey. Since the data obtained are all qualitative data, they were analyzed through coding and similar responses were grouped into the same category. As a result of the survey, several facts were found as follow; First, When teachers thought about 'mathematics', the first words that come to mind were 'calculation', 'difficult', and 'logic'. It is necessary for the teacher to have positive thoughts on mathematics and mathematics learning, and this needs to be stressed enough in teacher education and teacher retraining. Second, the reason why mathematics is an important subject is 'because it is related to the real life', followed by 'because it gives rise to logical thinking ability' and 'because it gives rise to mathematical thinking ability'. These ideas are related to the cultivating mind value and the practical value of mathematics. In order for students to understand the various values of mathematics, teachers must understand the various values of mathematics. Third, the responses for reasons why elementary school students hate mathematics and are hard are because teachers demand 'thinking', 'because they repeat simple calculations', 'children hate complicated things', 'bother', 'Because mathematics itself is difficult', 'the level of curriculum and textbooks is high', and 'the amount of time and activity is too much'. These problems are likely to be improved by the implementation of revised 2015 national curriculum that emphasize core competence and process-based evaluation including mathematical processes. Fourth, the most common reason for failing elementary school mathematics instruction was 'because the process was difficult' and 'because of the results-based evaluation'. In addition, 'Results-oriented evaluation,' 'iterative calculation,' 'infused education,' 'failure to consider the level difference,' 'lack of conceptual and principle-centered education' were mentioned as a failure factor. Most of these factors can be changed by improving and changing teachers' teaching practice. Fifth, the responses for what does a desirable mathematics instruction look like are 'classroom related to real life', 'easy and fun mathematics lessons', 'class emphasizing understanding of principle', etc. Therefore, it is necessary to deeply deal with the related contents in the training courses for the improvement of the teachers' teaching practice, and it is necessary to support not only the one-time training but also the continuous professional development of teachers.

• Bulletin of the Korean Chemical Society
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• v.24 no.6
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• pp.864-880
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• 2003

A unified picture for magnetism, superconductivity, quantum optics and other properties of molecule-based materials has been presented on the basis of effective model Hamiltonians, where necessary parameter values have been determined by the first principle calculations of cluster models and/or band models. These properties of the matetials are qualitatively discussed on the basis of the spin and pseudo-spin Hamiltonian models, where several quantum operators are expressed by spin variables under the two level approximation. As an example, ab initio broken-symmetry DFT calculations are performed for cyclic magnetic ring constructed of 34 hydrogen atoms in order to obtain effective exchange integrals in the spin Hamiltonian model. The natural orbital analysis of the DFT solution was performed to obtain symmetry-adapted molecular orbitals and their occupation numbers. Several chemical indices such as information entropy and unpaired electron density were calculated on the basis of the occupation numbers to elucidate the spin and pair correlations, and bonding characteristic (kinetic correlation) of this mesoscopic magnetic ring. Both classical and quantum effects for spin alignments and singlet spin-pair formations are discussed on the basis of the true spin Hamiltonian model in detail. Quantum effects are also discussed in the case of superconductivity, atom optics and quantum optics based on the pseudo spin Hamiltonian models. The coherent and squeezed states of spins, atoms and quantum field are discussed to obtain a unified picture for correlation, coherence and decoherence in future materials. Implications of theoretical results are examined in relation to recent experiments on molecule-based materials and molecular design of future molecular soft materials in the intersection area between molecular and biomolecular materials.

• Korean Journal of Materials Research
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• v.28 no.6
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• pp.365-369
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• 2018

We perform density functional theory calculations to study the CO and $O_2$ adsorption chemistry of Pt@X core@shell bimetallic nanoparticles (X = Pd, Rh, Ru, Au, or Ag). To prevent CO-poisoning of Pt nanoparticles, we introduce a Pt@X core-shell nanoparticle model that is composed of exposed surface sites of Pt and facets of X alloying element. We find that Pt@Pd, Pt@Rh, Pt@Ru, and Pt@Ag nanoparticles spatially bind CO and $O_2$, separately, on Pt and X, respectively. Particularly, Pt@Ag nanoparticles show the most well-balanced CO and $O_2$ binding energy values, which are required for facile CO oxidation. On the other hand, the $O_2$ binding energies of Pt@Pd, Pt@Ru, and Pt@Rh nanoparticles are too strong to catalyze further CO oxidation because of the strong oxygen affinity of Pd, Ru, and Rh. The Au shell of Pt@Au nanoparticles preferentially bond CO rather than $O_2$. From a catalysis design perspective, we believe that Pt@Ag is a better-performing Pt-based CO-tolerant CO oxidation catalyst.