• Communications of the Korean Mathematical Society
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• v.33 no.3
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• pp.1001-1011
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• 2018

We introduce some variants of the finite Ramsey theorem. The variants are based on a refinement of homogeneity. In particular, they cover homogeneity, minimal homogeneity, end-homogeneity as special cases. We also show how to obtain upper bounds for the corresponding Ramsey numbers.

• Korean Journal of Materials Research
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• v.24 no.11
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• pp.591-598
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• 2014

In this research, magnesium powder was prepared by gas atomizing. Refinement behaviors of magnesium powder produced under different conditions were investigated using a mechanical milling (attrition milling) process. Analyses were performed to assess the characterization and comparison of milled powder with different steel ball sizes and milling times. The powders were analyzed by field emission scanning electron microscope, apparent density and powder fluidity. The particle morphology of the Mg powders changed from spherical particles of feed metals to irregular oval particles, then plate type particles, with an increasing milling time. Because of the HCP structure, deformation occurs due to the existence of the easily breakable C-axis perpendicular to the base, which results in producing plate-type powders. An increase in ball size and the impact energy of the magnesium powder maximizes the effect of refinement. Furthermore, it is possible to improve the apparent density and fluidity according to the smoothness of the surface of the initial powder.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.111.1-111.1
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• 2011

The solar energy is dramatically increasing as the alternative energy source and the silicon(Si) solar cell are used the most. In this study, the improved process and equipment for the metallurgical refinement of multicrystalline Si were evaluated for the inexpensive solar cell. The planar plane and columnar dendrite aheadof the liquid-solid interface position caused the superior segregation of impurities from the Si. The solidification rate and thermal gradient determined the shape of dendrite in solidified Si matrix solidified by the directional solidification(DS) method. To simulate this equipment, the commercial software, PROCAST, was used to solve the solidification rate and thermal gradient. Si was vertically solidified by the DS system with Stober process and up-graded metallurgical grade or metallurgical grade Si was used as the feedstock. The inductively coupled plasma mass spectrometry (ICP) was used to measure the concentration of impurities in the refined Si ingot. According to the result of ICP and simulation, the high thermal gradient between the two phases wasable to increase the solidification rate under the identical level of refinement. Also, the separating heating zone equipped with the melting and solidification zone was effective to maintain the high thermal gradient during the solidification.

• School Mathematics
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• v.9 no.4
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• pp.467-486
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• 2007

In mathematical modeling activity modeling process is usually an iterative process. When model can not be solved, the model needs to be simplified by treating some variables as constants, or by ignoring some variables. On the other hand, when the results from the model are not precise enough, the model needs to be refined by considering additional conditions. In this study we investigate the role of spreadsheet model in model refinement and modeling process. In detail, we observed that by using spreadsheet model students can solve model which can not be solved in paper-pencil environment. And so they need not go back to model simplification process but continue model refinement. By transforming mathematical model to spreadsheet model, the students can predict or explain the real word situations directly without passing the mathematical conclusions step in modeling process.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.6
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• pp.2840-2850
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• 2011

Programmers can use the Hardware-Software Co-Designing, in which they design a hardware system and software system simultaneously and then unify them, to design an embedded system. This study analyzes the problems of designing an embedded system and suggests applying the system-level design technique, which uses SpecC technology, as a solution to the problems. Also, it suggests systematic and concrete stepwise refinement by applying Refactoring technology in software engineering as a way to make the use of system-level stepwise refinement.

• The Korean Journal of Ceramics
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• v.5 no.4
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• pp.341-347
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• 1999

An ambiguity on the correct room temperature structure of $Bi_5Ti_3FeO_{15}$ was resolved using a combined Rietveld refinement of neutron and X-ray diffraction. The structure of this compound has been reported to have a space group of F2mm (adopting 2-fold rotation symmetry along the c-axis) or A21am. However, our diffraction, study reveals that some reflections would violate F-centering and confirm that the belong to $A2_1$am. Out refinement with the space group of $A2_1$am converged at $R_p=6.85%, R_wp=9.23%$ and $\chi^2$=1.66 for an isotropic temperature model with 85 variables. The lattice constants are a=5.4677(1) $\AA$, b=5.4396(1) $\AA$, and c=41.2475(8)$\AA$. In structure, Ti/Fe atoms at the oxygen octahedral sites of the perovskite unit are completely disordered, resulting in that these atoms are transparent in neutron diffraction. The octahedra of the perovskite unit are relatively displaced along the a-axis against the Bi atoms, which contribute as a major component to the spontaneous polarization of $Bi_5Ti_3FeO_{15}$.

• Journal of Korea Foundry Society
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• v.18 no.3
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• pp.283-288
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• 1998

Interest in rapid solidification of magnesium alloys stems from the fact that conventional ingot metallurgy alloys exhibit poor strength, ductility, and corrosion resistance. Such properties can be improved by microstructural refinement via rapid solidification processing. In this study, Mg-Zn alloys have been produced as continuous strips by melt overflow technique. In order to evaluate the influence of additional elements on the grain refinement and mechanical properties, Th and Zr were added in rapidly solidified Mg-5wt%Zn alloy. Then the microstructual observations were undertaken with the objective of evaluating the grain refinement as function of the cooling rate and the additional elements. The tremendous increase in hardness of Mg-Zn base alloys was mainly due to the refinement of the grain structure by the effect of rapid solidification and alloying elements. The formation of intermetallic phases on the grain boundaries may have a positive effect on the corroion resistance. Therefore, despite competition from many other developments, the rapid solidification processing of magnesium alloys emerges as a valuable method to develop superior and commercially acceptable magnesium alloys.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.08a
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• pp.11-18
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• 2004

Asymmetric rolling, in which the circumferential velocities of the upper and lower rolls are different, can give rise to intense plastic shear strains and in turn shear deformation textures through the sheet thickness. The ideal shear deformation texture of fcc metals can be approximated by the <111> // ND and $\{001\}<110>$ orientations, among which the former improves the deep drawability. The ideal shear deformation texture for bcc metals can be approximated by the Goss $\{110\}<001>\;and\;\{112\}<111>$ orientations, among which the former improves the magnetic permeability along the <100> directions and is the prime orientation in grain oriented silicon steels. The intense shear strains can result in the grain refinement and hence improve mechanical properties. Steel sheets, especially ferritic stainless steel sheets, and aluminum alloy sheets may exhibit an undesirable surface roughening known as ridging or roping, when elongated along RD and TD, respectively. The ridging or roping is caused by differently oriented colonies, which are resulted from the <100> oriented columnar structure in ingots or billets, especially for ferritic stainless steels, that is not easily destroyed by the conventional rolling. The breakdown of columnar structure and the grain refinement can be achieved by asymmetric rolling, resulting in a decrease in the ridging problem.

• Journal of the Korean School Mathematics Society
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• v.17 no.4
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• pp.657-677
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• 2014

The present qualitative case study explored the ways in which three middle school students constructed and refined their mathematical models and modeling processes, and factors that had influenced such refinement. The results suggest that students' modeling processes are non-sequential in that the participant students reformulated their initial problem from the real-world problem situation and revised the model when they could not get a satisfactory solution or the acquired solution did not make sense. Moreover, the students' model refinement processes were affected by the following four elements: the types of real-word problem situations, students' metacognitive thinking, communications between teachers and peers, and the role of teachers.

• Journal of the Korean Society of Costume
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• v.54 no.5
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• pp.95-107
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• 2004

Elegance in dress has existed as one of the important archetypes of aesthetic consciousness through the times. Nevertheless, there has generally been Ignored the Idea of analyzing it. The purpose of this study is to provide a framework for a better understanding of the beauty of dress by constructing the concept of elegance in dress as both one of aesthetic categories in dress and refined taste in the sociocultural contexts. For the purpose, the documentary study in sociocultural and aesthetic contexts has been executed. Considering from the holistic viewpoint, elegance in dress is based upon the idea of aristocratic taste cultivated by good breeding. It is expressed visually through not only the carefully contrived dress hut also a sort of aura of dressed body - a combination of appearance, behavior, attitude, manner etc.- with skillful ease. The aesthetic values of elegance consist of luxury, nobility, refinement, femininity, harmony Luxury means rarity and opulence of materials, craftsmanship for excellent qualities, genuineness. Nobility, related to the lady and the gentleman, can be explained as neatness. decency. modesty. and appropriateness for formal occasions. Refinement involves artifice, sophistication, maturity, and subtleness. Femininity reflects the characteristic of feminine attractiveness such as the dainty, the florid, the sweet. Harmony means organic unity. matching with body, moderation in opposition to exaggeration. These values has rather interactivity than exclusion. It is refinement and harmony that are centered on of all values.