• 한국수학교육학회지시리즈E:수학교육논문집
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• 제25권4호
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• pp.693-734
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• 2011

연구의 목적은 자연수 개념에 대한 초등 교사들의 교수학적 내용지식을 분석하는 것이다. Shulman(1986b)은 교사의 지식을 이해하기 위한 도구를 개발하면서, 가르치는데 필요한 내용지식을 교과내용지식, 교육과정지식, 교수학적 내용지식의 세 가지로 구분하였고, 방정숙(2002)은 교사의 교수 방법에 포함되는 요소를 개인 요소와 사회 문화 요소로 구분하였다. 연구 문제는 (1) 초등 교사들은 자연수 개념에 대하여 어떤 교수학적 내용지식을 가지고 있는가, (2) 초등 교사들이 가지고 있는 자연수 개념에 대한 교수학적 내용지식에는 어떤 요소들이 포함되어 있는가의 두 가지이다. 연구 결과 (1) 초등 교사들은 자연수 개념에 대한 교수학적 내용지식의 세 가지 유형을 적절히 갖추고 있고, (2) 초등 교사들이 가지고 있는 자연수 개념에 대한 교수학적 내용지식에는 사회문화적 요소 보다는 개인 요소가 더 많이 포함되어 있다. 연구의 제안점으로는 (1) 보통의 현장 교사와 수학교육을 전공한 교사간의 비교 연구와 (2)자연수 개념에 대한 교실 활동에 대한 연구가 수행되기를 바란다.

• 한국전산유체공학회지
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• 제21권3호
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• pp.64-70
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• 2016

Multiple solutions in natural convection of water with Pr=7 between two horizontal plates with small magnitude non-uniform temperature distribution in the upper plate is numerically investigated. The dimensionless temperature of upper plate is ${\theta}={\epsilon}sinkx$. Two upright cells are formed over one wave length in the conduction-dominated regime of small Rayleigh number. However, multicellular convection occurs above a critical Rayleigh number for small wave number. When k = 1.5, dual solutions are found and a transition of $6{\rightarrow}4$ eddy flow occurs with decrease of Rayleigh number. When k = 0.75, two, three, four and five multiple solutions are observed. Transitions of $14{\rightarrow}12$, $12{\rightarrow}10$, $10{\rightarrow}8$ and $6{\rightarrow}8$ eddy flow occur with decrease of Rayleigh number.

• 대한기계학회논문집B
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• 제28권11호
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• pp.1440-1448
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• 2004

Multiple solutions in natural convection of air (Pr=0.7) between two horizontal walls with mean temperature difference and the same periodic nob-uniformities are investigated. An analytical solution is found for small Rayleigh number, and the general solution is investigated by using a numerical method. In the conduction-dominated regime, two upright cells are formed between two walls over one wave length. When the wave number is small, the flow becomes unstable with increase of the Rayleigh number, and multicellular convection occurs above a critical Rayleigh number. The multicellular flows at high Rayleigh numbers consist of approximately square-shape cells. And several kinds of multiple flows classified by the number of cells are found.

• Nuclear Engineering and Technology
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• 제44권3호
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• pp.283-296
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• 2012

The natural convection in a horizontal enclosure heated from the bottom wall, cooled at the top wall, and having a square adiabatic body in the center is studied. Three different Prandtl numbers (0.01, 0.7 and 7) are considered for the investigation of the effect of the Prandtl number on natural convection. Adiabatic boundary conditions are employed for the side walls. A two-dimensional solution for unsteady natural convection is obtained, using an accurate and efficient Chebyshev spectral methodology for different Rayleigh numbers varying over the range of $10_3$ to $10_6$. It had been experimentally reported that the heat transfer mode becomes oscillatory when Pr is out of a specific Pr band beyond the critical Ra. In this study, we reproduced this phenomenon numerically. It was found that when Ra=$10_6$, only the case for intermediate Pr (=0.7) reached a non-changing steady state and the low and high Pr number cases (Pr=0.01 and 7) showed a periodically oscillatory fashion hydrodynamically and thermally. The variation of time- and surface-averaged Nusselt numbers on the hot and cold walls for different Rayleigh numbers and Prandtl numbers are presented to show the overall heat transfer characteristics in the system. Further, the isotherms and streamline distributions are presented in detail to compare the physics related to their thermal behavior.

• 설비공학논문집
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• 제30권2호
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• pp.58-67
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• 2018

This study investigated the effect of variation in the angle of the elliptic cylinder as well as the presence of circular cylinder on natural convection inside a square enclosure. The Rayleigh number was varied between $10^3$ and $10^6$, and the Prandtl number was fixed to 0.7. In the present study, the angle of the elliptic cylinder was changed from $0^{\circ}$ to $90^{\circ}$, and the perimeter of the elliptic cylinder was same as that of the circular cylinder. The immersed boundary method was used to capture the virtual wall boundary of the inner cylinder. With the increasing angle of the elliptic cylinder, the surface-averaged Nusselt numbers on the cylinder and the enclosure increased. In the Rayleigh number range considered in the present study, the surface-averaged Nusselt number on the elliptic cylinder over = $45^{\circ}$ was higher than that of the circular cylinder. The effect of elliptic cylinder's angle on natural convection in the enclosure was analyzed according to the flow and thermal fields, and the distributions of the Nusselt number.

• 한국발생생물학회지:발생과생식
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• 제25권4호
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• pp.213-223
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• 2021

Controlled ovarian hyperstimulation (COH) is routinely used in the in vitro fertilization and embryo transfer (IVF-ET) cycles to increase the number of retrieved mature oocytes. However, the relationship between repeated COH and ovarian function is still controversial. Therefore, we investigated whether repeated ovarian stimulation affects ovarian aging and function, including follicular development, autophagy, and apoptosis in follicles. Ovarian hyperstimulation in mice was induced by intraperitoneal injection with pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG). Mice subjected to ovarian stimulation once were used as a control group and 10 times as an experimental group. Repeated injections with PMSG and hCG significantly reduced the number of primary follicles compared to a single injection. The number of secondary and antral follicles increased slightly, while the number of corpus luteum increased significantly with repeated injections. On the other hand, repeated injections did not affect apoptosis in follicles associated with follicular atresia. The expression of autophagy-related genes Atg5, Atg12, LC3B, and Beclin1, cell proliferation-related genes mTOR, apoptosis-related genes Fas, and FasL was not significantly different between the two groups. In addition, the expression of the aging-related genes Dnmt1, Dnmt3a, and AMH were also not significantly different. In this study, we demonstrated that repeated ovarian stimulation in mice affects follicular development, but not autophagy, apoptosis, aging in ovary. These results suggest that repetition of COH in the IVF-ET cycle may not result in ovarian aging, such as a decrease in ovarian reserve in adult women.

• 한국양식학회지
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• 제16권2호
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• pp.69-75
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• 2003

Genetic variability and population structure of 11 natural ayu, Plecoglossus altivelis populations and one hatchery stock were assessed by starch gel electrophoretic analysis with 10 enzyme coding loci. Three loci were polymorphic (lower than 0.95 in major allele frequency) in natural populations,2 loci in hatchery stock. The average number of alleles per locus was 1.38. Observed heterozygosities ranged from 0.0235 to 0.088 (0.055 on the average) in natural population while 0.0925 in hatchery stock. The genetic distance among natural populations measured 0.000047-0.005407 and no significant differentiation was observed among them. On the other hand, a signifcant genetic distance was found between natural populations and the hatchery stock with measuring 0.002032-0.O08605. The results in this study suggest that the hatchery stock has diverged from natural populations, and also that careful to maintain sustainable and effective population size (parents number) should be made.

• 대한기계학회논문집B
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• 제23권2호
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• pp.226-233
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• 1999

An experimental study has been performed on natural convection heat transfer with a rapid crust formation in the molten metal pool of a low Prandtl number fluid. Two types of steady state tests, a low and high geometric aspect ratio cases in the molten metal pool, were performed. The crust thickness by solidification was measured 88 a function of boundary surface temperatures. The experimental results on the relationship between the Nusselt number and Rayleigh number In the molten metal pool with a crust formation were compared with existing correlations. The experimental study has shown that the bottom surface temperature of the molten metal layer, in all experiments. is the major influential parameter in the crust formation, duo to the natural convection flow. The Nusselt number of the case without a crust formation in the molten metal pool is greater than that of the case with the crust formation at the same Rayleigh number. The present experimental results on the relationship between the Nusselt number and Rayleigh number In the molten metal pool match well with Globe and Dropkin's correlation. From the experimental results, a now correlation between the Nusslet number and Rayleigh number in the molten metal pool with the crust formation was developed as $Nu=0.0923(Ra)^{0.302}$ ($2{\times}10^4< Ra<2{\times}10^7$).

• 대한수학교육학회지:학교수학
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• 제12권3호
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• pp.371-388
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• 2010

이 논문의 목적은 소수(素數, prime number) 개념을 처음 배우는 학생들이 소수와 그 관련 개념들을 어떻게 이해하고 있는지를 탐구하기 위한 것이다. 이를 위하여 소수와 합성수 개념을 학습한 직후의 중학교 1학년 학생들에게 설문조사를 중심으로 자료를 수집하고 분석하였다. 연구 결과, 학생들은 주어진 자연수의 소수성을 판정하기 위한 소수의 기능적인 정의를 선호하며, 주어진 자연수의 약수를 찾는 것에만 주목하여 소수와 합성수를 곱셈적 관계로 이해하는데 어려움을 나타내었다. 이러한 결과는 학생들이 자연수의 곱셈적 기본 단위로서 소수 개념의 본질적인 중요성을 인식하고 산술의 기본 정리가 보장하는 자연수의 곱셈적 구조를 이해할 수 있도록 하는 교수학적 전략의 필요성을 제안한다.

• 한국수학교육학회지시리즈E:수학교육논문집
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• 제29권3호
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• pp.353-372
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• 2015

본 연구에서는 초등학교 수학 교과서에서 수 개념 학습과 관련하여 수직선이 어떻게 활용되고 있는지 살펴보고, 현재 교과서의 수직선 활용과 관련된 문제점을 자연수와 유리수(분수, 소수)의 개념 학습을 중심으로 분석하였다. 초등학교 수학 교과서에서 수직선의 도입 시기, 도입 내용, 활용 방법에 대한 분석을 바탕으로 수직선 활용 방안과 관련한 시사점을 도출하고자 하였다.