• 한국수학교육학회지시리즈C:초등수학교육
• /
• 제26권4호
• /
• pp.219-236
• /
• 2023

본 연구는 분수의 곱셈과 나눗셈에서 예비교사의 수학적 이해와 문제 만들기 사이의 관련성을 탐색하였다. 이를 위해여 41명의 예비교사들을 대상으로 분수의 곱셈과 나눗셈에 대한 시각적 표현과 문제 만들기 과제를 수행하고 수학적 이해 정도와 문제 만들기 능력을 측정하였으며, 수학적 이해 정도와 문제 만들기 능력 사이의 관련성을 교차분석을 통해 알아보았다. 그 결과, 예비교사들의 대부분은 분수의 곱셈과 나눗셈의 개념적 이해를 나타냈으며, 다섯 가지 유형의 어려움이 나타났다. 문제 만들기에서는 대부분의 예비교사들이 풀 수 있는 수학 문제를 만들지 못했으며 이 과정에서 네 가지 유형의 어려움이 나타났다. 또한 교차분석 결과, 수학적 이해 정도는 문제 만들기 능력과 연관이 있었다. 이러한 결과를 바탕으로 예비교사의 수학적 이해와 문제 만들기에 대한 시사점을 제시하였다.

• 한국수학교육학회지시리즈C:초등수학교육
• /
• 제27권3호
• /
• pp.281-301
• /
• 2024

대수는 방정식의 풀이로 해석되는 전통적인 관점에 따라 초등 현장에서 명시적으로 다루어지지 못하는 한계가 있지만, 초등 수준의 발달 단계에 맞춰 수의 체계와 원리, 산술적 사고의 확장인 대수적 사고로서 학습되어야 한다고 주장되어왔다. 본 연구에서는 초등학교 6학년 학생들에게 분수의 나눗셈에 대한 대수적 사고 기반 수업을 실시하고 문제해결력에 미치는 영향을 분석하였다. 학생들은 11차시의 수업에서 제수와 피제수의 관계 탐구를 통해 해결 방법을 일반화하고 특정한 분수의 나눗셈 문제에서 나아가 모든 경우에 적용할 수 있는 표현을 탐색하였다. 연구 결과 대수적 사고를 기반으로 한 수학 수업이 분수의 나눗셈 문제해결력에 긍정적인 영향을 미치는 것을 확인할 수 있었다. 학생들의 해결 과정에서는 기호화, 일반화, 추론, 정당화의 대수적 사고 요소가 나타났으며 다양한 수학적 아이디어와 구조를 발견하고 이를 활용해 문제를 해결하는 특징을 보였다. 연구 결과를 바탕으로 초등학생에게 초기 대수 지도를 위한 시사점을 도출하였다.

• 한국분말재료학회지
• /
• 제17권4호
• /
• pp.270-275
• /
• 2010

Ethylene glycol-based Cu nanofluids were prepared by pulsed wire evaporation (PWE) method. The structural properties of Cu nanoparticles were studied by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). The average diameter and Brunauer Emmett Teller (BET) surface area of Cu nanoparticles were about 100 nm and $7.46\;m^2/g$, respectively. The thermal conductivity and viscosity of copper nanofluid were measured as functions of Cu concentration and temperature. As the volume fraction of Cu nanoparticles increased, both the enhanced ratios of thermal conductivity and viscosity of Cu nanofluids increased. As the temperature increased, the enhanced ratio of thermal conductivity increased, but that ratio of viscosity decreased.

• 한국자동차공학회논문집
• /
• 제15권2호
• /
• pp.15-21
• /
• 2007

The aim of this paper is controlling ignition timing and load in homogeneous charge compression ignition (HCCI) combustion with low cetane number fuel, hydrogen. Homogeneous charge compression ignition (HCCI) combustion is an advanced combustion technology that achieves higher thermal efficiency and lower $NO_x$ emissions than that of conventional combustion system. Dimethyl ether (DME), which has been researched widely as the most attractive alternative fuel of diesel, is attractive for HCCI combustion because of the easy evaporation. In this study, the single cylinder DME engine operated with a direct injection system has been used to investigate combustion processes and emissions of DME HCCI with a premixed hydrogen supply. The experiment was carried out under various engine speed and fraction rates of hydrogen. As a result, the increase of fraction rates of hydrogen retard the DME ignition timing and eliminated the knocking during high engine speed condition. IMEP was increased with increase of fraction rates of hydrogen by 30%. 40% of the fraction rates of hydrogen resulted in misfiring. The $NO_x$ emission was reduced by increasing the fraction rates of hydrogen, but HC emission was increased.

• 한국수산과학회지
• /
• 제43권5호
• /
• pp.437-444
• /
• 2010

Extracts of the marine microalgae Nannochloropsis oculata were obtained using 80% methanol (MeOH) and water. The 80% MeOH extract was further fractionated with n-hexane, chloroform, ethyl acetate (EtOAc), n-butanol (n-BuOH), and water to isolate the active fraction. Seven samples were prepared and their angiotensin converting enzyme (ACE), $\alpha$-glucosidase, and cancer cell growth inhibitory activities in vitro were determined. The most profound ACE inhibitory activity was observed in the chloroform fraction, while the others had moderate effects. By contrast, greater $\alpha$-glucosidase inhibitory activity was found in the EtOAc fraction, n-hexane fraction, and water extract of N. oculata. The antiproliferative effects of the extracts and fractions against HL-60, U937, CT-26, and SK-Hep1 cancer cells were also determined. The n-BuOH fraction had the strongest antiproliferative effects on CT-26 cells in a time-dependant manner (P<0.05). These results suggest that the extracts and fractions from N. oculata could be used as a potential functional food or as pharmaceutical ingredients.

• Archives of Pharmacal Research
• /
• 제26권12호
• /
• pp.1024-1028
• /
• 2003

A prolyl endopeptidase inhibitor was isolated from the ethyl acetate soluble fraction of Phyllanthus ussurensis. The active compound was identified as an ellagitannin, corilagin. It was shown to non-competitively inhibit prolyl endopeptidase (PEP) with the $IC_{50}$ value of $1.17 \times $10^{-6}\mu$M. The Ki value was $6.70 \times 10^{-7}$ M. Corilagin was less inhibitory to other serine proteases such as chymotrypsin, trypsin, and elastase, indicating that it was relatively a specific inhibitor of PEP. Corilagin also effectively inhibited reactive oxygen species such as hydroxide and superoxide anion radical, hydrogen peroxide, and DPPH. Especially, corilagin showed potent scavel1ging activity on the superoxide anion radical in the ESR method ($IC_{50} =3.79 \times 10^{-6}$M) as well as xanthine oxidase system.

• Journal of the Korean Wood Science and Technology
• /
• 제42권5호
• /
• pp.533-542
• /
• 2014

We extracted essential oils from four species (Pinus densiflora, Larix kaempferi, Pinus koraiensis, and Abies holophylla) in the family Pinaceae to investigate their antibacterial activities against respiratory tract bacteria (Klebsiella pneumoniae, Haemophillus influenzae, Streptococcus pyogenes, Streptococcus pneumonia, and Neisseria meningitides). Among the tested oils, that from A. holophylla was showed strong activity based on disc diffusion and broth medium dilution (minimum inhibitory concentration, MIC) assays. Qualitative analysis of A. holophylla oil was carried out by GC-MS; ${\alpha}$-pinene, camphene, ${\beta}$-pinene, 3-carene, limonene, bornyl acetate, borneol, ${\beta}$-caryophyllene, ${\alpha}$-caryophyllene, caryophyllene oxide, and ${\alpha}$-bisabolol were identified as its major constituents. Fractionation by silica gel chromatography was performed to analyze the active constituents of the crude oil. In particular, one fraction containing caryophyllene oxide as the major constituent showed stronger antibacterial activity than the crude oil of A. holophylla. Growth rates of bacterial strains exposed to fraction D were explored by optical density (OD600) measurements while morphology was examined by optical microscopy observations ( ${\times}1000$). OD600 of K. pneumoniae decreased from 0.2582 to 0.005 in response to treatment with fraction D at a MIC value of $0.31{\mu}{\ell}/m{\ell}$.

• Korean Journal of Chemical Engineering
• /
• 제35권12호
• /
• pp.2403-2412
• /
• 2018

The present study was aimed at evaluating the effect of variable sodium carbonate ($Na_2CO_3$) loading during wet air oxidation (WAO) pretreatment of rice straw in reducing biomass recalcitrance. The research study was intended to increase the cellulose recovery, hemicellulose solubilization, lignin removal in the solid fraction and limiting the generation of inhibitors in the liquid fraction while reducing the chemical input. The operating condition of $169^{\circ}C$, 4 bar, 18 min and 6.5 g/L $Na_2CO_3$ loading resulted in maximum cellulose recovery of 82.07% and hemicellulose solubilization and lignin removal of 85.43% and 65.42%, respectively, with a total phenolic content of 0.36 g/L in the liquid fraction. The crystallinity index increased from 47.69 to 51.25 along with enzymatic digestibility with an increase in $Na_2CO_3$ loading from 0 to 6.5 g/L as a result of removal of barriers for saccharification via effective cleavage of ether and ester bonds cross-linking the carbohydrates and lignin as indicated by FT-IR spectroscopy. A further increase in the $Na_2CO_3$ loading to 9.5 g/L did not significantly increase the sugar release. Thus, it was concluded that 6.5 g/L $Na_2CO_3$ during WAO is sufficient to increase the delignification and deacetylation, leading to significant changes in apparent cellulose crystallinity inter alia improvement in cellulose accessibility and digestibility of rice straw.

• 한국수산과학회지
• /
• 제35권6호
• /
• pp.578-582
• /
• 2002

양식어류 질병 세균에 대한 31종의 천연물을 $70\%$ ethanol로 추출하여 항균효과를 조사하였다. 그 중에서 망태버섯 ethanol 추출물이 비교적 높은 활성을 나타내었으며, 망태버섯을 극성이 낮은 dichlorornethane, ethyl acetate, n-buthanol, water의 순서로 분획하여 항균효과를 본 결과 ethyl acetate 추출물에서 모든 균주에대한 clear zone을 형성하여 항균효과가 보였다. 또한, 망태버섯로부터의 ethyl acetate 추출물을 Si-chromatography를 이용하여 fraction별 7개로 분획하여 항균효과를 조사한 결과 Fraction 2 (Hx :EtAOc, 3: 1)에서는 L. anguillarum에 대해 가장 항균효과가 뛰어났으며, Fraction 5 (DCM:MeOH, 5: 1)에서 5. iniae가 가장 높았다. 그 중에서 세 균주에 대해서 공통적으로 항균활성이 높은 것은 Fraction 5로 나타났다.

• Food Science and Biotechnology
• /
• 제18권4호
• /
• pp.889-894
• /
• 2009

Barley proteins are expected to have unique functional properties due to their high content of alcohol soluble protein, hordein. Since the barley proteins obtained by conventional isoelectric precipitation method cannot represent hordein fraction, barley proteins were fractionated to albumin, globulin, glutelin, and hordein with respect to extraction solvents. Functional properties and film-forming properties of solubility-fractionated barley proteins were investigated to explore their potential for human food ingredient and industrial usage. The 100 g of total barley protein comprised 5 g albumin, 23 g globulin, 45 g glutelin, and 27 g hordein. Water-binding capacities of barley protein isolates ranged from 140-183 mL water/100 g solid. Hordein showed the highest oil absorption capacity (136 mL oil/100 g), and glutelin showed the highest gelation property among the fractionated proteins. In general, the barley protein fractions formed brittle and weak films as indicated by low tensile strength (TS) and percent elongation at break (E) values. The salt-soluble globulin fraction produced film with the lowest TS value. Although films made from glutelin and hordein were dark-colored and had lower E values, they could be used as excellent barriers against water transmission.