• 대한수학회논문집
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• 제33권3호
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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.

• 한국재료학회지
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• 제24권11호
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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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• 한국신재생에너지학회 2011년도 춘계학술대회 초록집
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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.

• 대한수학교육학회지:학교수학
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• 제9권4호
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• pp.467-486
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• 2007

이 논문은 스프레드시트를 활용한 수학적 모델링에서 스프레드시트 환경이 수학적 모델의 정교화과정에 어떤 영향을 미치는 지를 고찰한 것이다. 좀 더 자세히 살피면 수학적 모델링에서 스프레드시트 모델의 활용은 학생이 분석 불가능한 수학적모델도 분석할 수 있도록 해줌으로써 모델을 단순화하지 않고, 대신 모델을 정교화 할 수 있는 기회를 제공하고 수학적 개념을 확장해 나갈 수 있음을 보였다. 또한 수학적 모델을 스프레드시트 모델로 변환하여, 수학적 모델로부터 수학적 결론을 얻는 단계를 거치지 않고도 실세계 상황을 해석하고 설명할 수 있는 기회를 제공할 수 있음을 보였다.

• 한국산학기술학회논문지
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• 제12권6호
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• pp.2840-2850
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• 2011

임베디드 시스템을 설계하기 위해서는 하드웨어 설계와 소프트웨어 설계를 동시에 진행하여 마지막으로 그들을 통합하여 시스템을 구축하는 하드웨어/소프트웨어 공동 설계라는 설계 방법을 사용한다. 본 연구에서는 기존의 임베디드 시스템 설계의 문제점을 분석하고 그 해결 방안으로 SpecC 기술을 이용한 시스템 레벨 설계 방법을 제안한다. 또한 시스템 레벨 설계의 단계적 상세화를 실현하기 위해 소프트웨어 공학의 리팩토링 기술을 적용하여 체계적이고, 구체적인 단계적 상세화 방법을 제시한다.

• The Korean Journal of Ceramics
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• 제5권4호
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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 $Bi_5Ti_3FeO_{15}$.

• 한국주조공학회지
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• 제18권3호
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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.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 제5회 압연심포지엄 신 시장 개척을 위한 압연기술
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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.

• 한국학교수학회논문집
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• 제17권4호
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• pp.657-677
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• 2014

본 연구의 목적은 실험수업에 참여한 세 명의 중학교 1학년 학생들의 모델 정교화 과정을 질적 사례연구를 통하여 살펴보고 모델 정교화에 영향을 미치는 요인을 분석하여 이에 관한 정보를 제공하고자 함이다. 분석 결과 학생들의 수학적 모델링의 정교화 과정은 각 단계가 단선적으로 일어나는 것이 아니라 모델 내에서 해를 구할 수 없거나 구한 해가 의미가 없는 경우 실제 문제 구성 단계로 돌아가 실제 문제를 수정하거나 수학적 모델 구성 단계로 돌아가 모델을 수정 또는 정교화하는 것을 알 수 있었으며, 모델 정교화 과정에 영향을 미치는 요인으로는 모델링 문제, 메타인지적 사고, 교사 동료와의 의사소통 및 교사의 역할 등이 복합적으로 작용함이 나타났다.

• 복식
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• 제54권5호
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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.