• 한국정밀공학회지
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• 제18권10호
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• pp.53-60
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• 2001

Surface roughness plays a significant role in friction, wear, and lubrication in machine components. Most engineering surfaces have the nongaussian height distribution. So, in this study, contact simulations are conducted for not only gaussian surfaces but also nongaussian surfaces. Nongaussian rough surface considering the kurtosis is generated numerically And the effects of kurtosis on real contact area fraction, average gap, and mean asperity contact pressure are studied. It will be shown that the real contact area fraction and the mean asperity contact pressure are sensitive to the characteristics of surface geometry according to kurtosis.

• 소성∙가공
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• 제18권6호
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• pp.482-487
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• 2009

A finite element based microstructural modeling for the size dependent strengthening of particle reinforced aluminum composites is presented. The model accounts explicitly for the enhanced strength in a discretely defined "punched zone" around the particle in an aluminum matrix composite as a result of geometrically necessary dislocations developed through a CTE mismatch. The density of geometrically necessary dislocations is calculated considering volume fraction of the particle. Results show that predicted flow stresses with different particle size are in good agreement with experiments. It is also shown that 0.2% offset yield stresses increases with smaller particles and larger volume fractions and this length-scale effect on the enhanced strength can be observed by explicitly including GND region around the particle. The strengths predicted with the inclusion of volume fraction in the density equation are slightly lower than those without.

• 대한기계학회논문집B
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• 제28권11호
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• pp.1398-1406
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• 2004

The nonlinear signals from an impedance meter for the area average void fraction in two-phase flow have been analyzed to construct a phase space trajectory. The pseudo phase space was constructed with the time delay and proper dimensions. The time delay and the embedding dimension were chosen by the average mutual information and by the false nearest neighborhood, respectively. The attractor-density-map of projected states was used to produce the two dimensional probability distribution functions (2D-PDF). Since the developed 2D-PDF showed clear distinction of the flow patterns, the flow regime identification was made with three rules and with the 2D-PDF. Also, the transition criteria of Mishima-Ishii agree well with the present results.

• 한국수학교육학회지시리즈D:수학교육연구
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• 제24권2호
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• pp.111-130
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• 2021

This exploratory study focuses on analyzing three mathematics textbooks in Germany, Singapore and South Korea to reveal similarities and differences in their introductions of fraction concepts. Findings reveal that all three countries' textbooks introduce fraction concepts predominantly by using pictorial representations such as area models, but the introductions of multiple fraction constructs vary. The Singaporean and South Korean textbooks predominantly used a part-whole construct to introduce fractional concepts while the German textbook introduced various constructs sequentially in the first pages using several scenarios from different real-life situations. The findings were represented using visual representations, which we called textbook signatures. The textbook signatures provided configurations of the textbook features across the three countries. At the end of paper, we share insights and limitations about the use of textbook signatures in the research on textbook analysis.

• 대한한방소아과학회지
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• 제30권3호
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• pp.1-30
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• 2016

Objectives Previous studies have found out that Forsythiae Fructus (FF) extracts have anti-atopic activities by in vitro experiment. In order to understand more about FF extracts' benefit, we subdivided FF extracts depending on systematic fractionation method by using Methylene chloride (MC), Ethyl acetate (EtOAc), n-BuOH and n-hexane (n-Hx). This study is designed to examine the effect of FF fractions on the PMA- ionomycin-induced activation of RBL-2H3 mast cell lines in vitro and on the DNCB-induced activation of NC/Nga mice in vivo. Methods For this study, we examined IL-4, IL-13 production by ELISA analysis, IL-4, IL-13, IL-31, IL-31RA and TNF-${\alpha}$ mRNA expression by real-time PCR and manifestations of AP-1 and MAPKs transcription factors by western blotting in vitro. Through in vitro experiment, we selected FF n-BuOH fraction that seems the best effective in atopic dermatitis then induced it on NC/Nga mice by DNCB. We measured mice's WBC, eosinophil and neutrophil in heart blood, IL-4, IL-5, IFN-${\gamma}$ in the spleenocyte culture supernatant, the absolute cell numbers of CD4+, CD8+, B220+CD23+, CD3+CD69+ and Gr-1+CD11b+ in the PBMCs, ALN and dorsal skin, IL-5, IL-13, IL-31, IL-31RA in the dorsal skin by real-time PCR and the distribution of immune cells by H&E on dorsal skin and ANL and toluidine blue staining on dorsal skin. Results FF n-BuOH fraction suppressed IL-4, IL-13 production and mRNA expression of IL-4, IL-13, IL-31, IL-31RA and TNF-${\alpha}$. Results from the western blot analysis showed that FF n-BuOH fraction reduced the activation of the mast cell specific transduction factors involved in AP-1 by suppressing JNK and ERK phosphorylation. In the gross, atopic dermatitis induced by DNCB in NC/Nga mice were improved by oral administration of FF n-BuOH fraction. Oral FF n-BuOH fraction also decreased the level of IgE in mice's serum and the level of IL-4 and IL-5 in the spleenocyte culture supernatant, cell numbers of CD8+, B220+CD23+ in the PBMCs, CD4+ in the ALN and CD4+, Gr-1+CD11b+ in the dorsal skin and suppressed mRNA expression of IL-5, IL-13, IL-31, IL-31RA in the dorsal skin. Histological examination showed that infiltration levels of immune cells in atopic dermatitis induced NC/Nga mice were improved by FF n-BuOH fraction. Conclusions FF n-BuOH fraction can reduce pruritus by suppressing IL-31, IL-31RA secretion and modulate molecular mediators and immune cells associated with atopic dermatitis induced in NC/Nga mice which may have played a significant role in recovering atopic dermatitis symptoms.

• 한국미생물·생명공학회지
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• 제27권1호
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• pp.8-14
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• 1999

This study was developed to evaluate the growth inhibition effects of cell wall components of Enterococcus faecalis 2B4-1 obtained from feces of neonates against tumor cell lines. Polysaccharide fraction (PS) shown sensitive growth inhibition effect in the cell wall components was isolated and characterized. In growth inhibition effects, residue fractin of whole cell was shown sensitive level of percent survival about 30% when administrated at ehe concentration of 100${\mu}$g/ml, and that was more effective than that of supernatant fraction against the tumor cell lines, SNU-1, 3LL, FARROW and HEC-1-B. Sensitive growth inhibition effects against SNU-1, FARROW and HEC-1-B were performed by whole cell (WC) fraction from Ent. faecalis 2B4-1. Cytoplasm fractin (CP) of WC was shown non-inhibition effect, however, the other part of WC, precipitate of disrupted cell (PD), was sensitive against the tumor cell line mentioned above. Followed by separation to peptidoglycan fraction (PG) and polysaccharide fraction (PS) were all sensitive which the latter was shown more sensitive percent survival than the former. Composed sugars of polysaccharide fraction were determined to D-glucose, L-rhamnose and D-glucosamine, and the rate fo composition was calculated to about 1:1:1 by the data of elemental analysis, IR, TLC and HPLC.

• Asian-Australasian Journal of Animal Sciences
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• 제18권5호
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• pp.741-746
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• 2005

To investigate the basic information and the possibility of ACE-inhibitory peptides for antihypertension materials, goat's caisin (CN) was hydrolyzed by various proteolytic enzymes and ACE-inhibitory peptides were separated and purified. ACE-inhibition ratios of enzymatic hydrolysates of goat's CN and various characteristics of ACE-inhibitory peptides were determined. ACE-inhibition ratios of goat's CN hydrolysates were shown the highest with 87.84% by pepsin for 48 h. By Sephadex G-25 gel chromatograms, Fraction 3 from goat's CN hydrolysates by pepsin for 48 h was confirmed the highest ACE-inhibition activity. Fraction 3 g and Fraction 3 gh from peptic hydrolysates by RP-HPLC to first and second purification were the highest in ACE-inhibition activity, respectively. The most abundant amino acid was leucine (18.83%) in Fraction 3 gh of ACE-inhibitory peptides after second purification. Amino acid sequence analysis of Fraction 3 gh of ACE-inhibitory peptides was shown that the Ala-Tyr-Phe-Tyr, Pro-Tyr-Tyr and Tyr-Leu. IC$_{50}$ calibrated in peptic hydrolysates at 48 h, Fraction 3, Fraction 3 g and Fraction 3 gh from goat's CN hydrolysates by pepsin for 48 h were 29.89, 3.07, 1.85 and 0.87 g/ml, respectively. Based on the results of this experiment, goat's CN hydrolysates by pepsin were shown to have ACE-inhibitory activity.

• 한국초등수학교육학회지
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• 제23권3호
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• pp.323-345
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• 2019

본 연구에서는 분수 학습에서 단위 조정 단계를 강조한 선행 연구를 중심으로 3학년 수학 교과서의 분수 도입 단원을 고찰하고, 교사가 교과서를 활용하여 분수에 대한 학생들의 이해를 자연스럽게 발달시킬 수 있도록 돕는 발문 및 추가 활동 등을 제시하였다. 연구 결과, 교과서의 분수 도입 단원은 단위 조정 단계와 관련하여 더 확장된 분수 스킴을 구성할 수 있도록 돕는 활동들이 잘 배열되어 있었다(즉, 부분-전체 분수 스킴 → 분할 단위분수 스킴 → 분할 분수 스킴). 그러나 각각의 활동들은 단위 조정의 각 단계에서 다음 단계로 발달하는 데 핵심이 되는 조작을 더욱 명시적으로 강조하여 등분할 스킴과 스플리팅 스킴을 구성하도록 도울 필요가 있었다. 또한 가분수를 이해하는 데 핵심이 되는 반복 분수 스킴을 구성하도록 돕는 활동까지 확장될 필요가 있었다. 이에 단위 조정 단계와 관련하여 교사가 각 차시에서 무엇에 초점을 두어야 하는지를 정리하였고 이를 보완할 수 있는 발문이나 활동 등을 제시하였다. 본 연구 결과를 토대로 교사 및 교과용도서 개발자에게 단위 조정 단계를 중심으로 분수를 도입하는 것과 관련된 시사점을 제공하고자 하였다.

• Composites Research
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• 제36권2호
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• pp.80-85
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• 2023

원통형 복합재 격자 구조는 필라멘트 와인딩 공법으로 제작되며 제작 공정에서 두께방향 섬유체적비 불균일이 발생할 수 있다. 섬유체적비 불균일은 구조의 강성에 영향을 미칠 수 있으며 강성 및 좌굴 특성이 변화할 수 있다. 본 연구에서는 두께방향 섬유체적비 불균일이 복합재 격자 구조의 비틀림 좌굴 하중에 미치는 영향에 대하여 분석하였다. 섬유체적비 변화에 의한 강성 변화를 유한요소 모델에 적용하였고 비틀림 하중을 가한 뒤 좌굴 해석을 수행하였다. 두께방향 섬유체적비 편차에 따른 좌굴 하중을 비교하였다. 섬유체적비 불균일에 의해 비틀림 좌굴 하중이 저하될 수 있음을 확인하였다.

• Carbon letters
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• 제26권
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• pp.11-17
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• 2018

Milled carbon fiber (mCF) was prepared by a ball milling process, and X-ray diffraction (XRD) diffractograms were obtained by a $2{\theta}$ continuous scanning analysis to study mCF crystallinity as a function of milling time. The raw material for the mCF was polyacrylonitrile-based carbon fiber (T700). As the milling time increased, the mean particle size of the mCF consistently decreased, reaching $1.826{\mu}m$ at a milling time of 18 h. The XRD analysis showed that, as the milling time increased, the fraction of the crystalline carbon decreased, while the fraction of the amorphous carbon increased. The (002) peak became asymmetric before and after milling as the left side of the peak showed an increasingly gentle slope. For analysis, the asymmetric (002) peak was deconvoluted into two peaks, less-developed crystalline carbon (LDCC) and more-developed crystalline carbon. In both peaks, Lc decreased and $d_{002}$ increased, but no significant change was observed after 6 h of milling time. In addition, the fraction of LDCC increased. As the milling continued, the mCF became more amorphous, possibly due to damage to the crystal lattices by the milling.