• 한국수학사학회지
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• 제18권2호
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• pp.9-22
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• 2005

본 연구는 자연수 개념이 역사적으로 전개된 방식을 이해하는 것이 수학적$\cdot$ 교육적으로 매우 중요함에도 불구하고, 그 역사적 고찰이 미진한 상태에 있다는 데에 문제 의식을 갖고 출발하였다. 그리하여 자연수 개념이 역사적으로 어떻게 논의되어 왔는지 살펴보고자 하였다. 수학의 발달 과정에서 수가 어떤 의미를 지녔는지, 문화적$\cdot$사회적 요소가 수 개념을 이해하는 방식과 수 개념의 발달에 어떤 영향을 주었는지 밝힘으로써 자연수 개념에 대한 이해를 풍부하게 하고자 하였다. 그리고 자연수 개념의 역사에 나타난 특징을 드러내고자 하였다.

• 대한기계학회논문집
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• 제15권2호
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• pp.654-660
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• 1991

Natural convection heat transfer in a horizontal annulus from an inner tube with two vertical fins has been studied for the effects of dimensionless fin length and Rayleigh number. The maximum local Nusselt number of inner tube was obtained at .theta. = 145.deg. and that of outer cylinder at .theta. = 0.deg. for the case of $l_{F}$=0.3 Local Nusselt number distributions for the lower fins show higher values than that of the upper fins. The mean Nusselt number of inner tube was increased with the values of dimensionless fin length. The mean Nusselt number can be represented in an exponential function of Grashof number at various fin lengths. As compared with experimental and numerical results, isotherms and local Nusselt number show good agreement.t.

• 한국수학교육학회지시리즈A:수학교육
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• 제44권4호
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• pp.587-602
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• 2005

The primary purpose of this study was to investigate how number sense performance of sixth graders was and what every character of five components of number sense possessed by sixth graders was. For the this purpose, Two kinds of studies were conducted : a descriptive study by pencil-and-paper tests(Basic Test, Number Sense Test) and a clinical study by interviews. The conclusions drawn from the results obtained in the this study were as follows : First, students were highly scored in Basic Test but not highly scored equally in Number Sense Test. Second, students hardly used the benchmarks and lacked consideration of the reasonableness about computation results. Interview results were that students' notion about the meaning, and the greater - than and less - than relations for fractions was weak and students tended to not use number sense but apply standard algorithm and compute numbers in the question without thinking.

• 한국안전학회지
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• 제18권1호
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• pp.33-37
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• 2003

The objective of the present work is to examine the variation of cooling characteristics due to the Weber number of droplet on a heated surface. The surface temperatures varied from 72.5 - $106.1^{\circ}C$ on steel and Teflon, when Weber number was 60, 180, 300. The results are as follows; In the case of the same droplet size, the initial temperature of solid increases the indepth temperature of solid more drop. In the case of the same surface temperature, Weber number increases with increasing the cooling effect of droplet. The time-average heat flux increases with increasing the initial temperature of solid and Weber number. The evaporation time decreases with increasing the initial temperature of solid and Weber number.

• 대한수학회지
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• 제44권6호
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• pp.1213-1231
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• 2007

The domination number ${\gamma}(G)$ of a graph G=(V,E) is the minimum cardinality of a subset of V such that every vertex is either in the set or is adjacent to some vertex in the set. The bondage number of b(G) of a graph G is the cardinality of a smallest set of edges whose removal from G results in a graph with domination number greater than ${\gamma}(G)$. In this paper, we calculate the bondage number of the Cartesian product of cycles $C_3\;and\;C_n$ for all n.

• 동력기계공학회지
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• 제12권3호
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• pp.26-31
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• 2008

This experimental study investigates the local heat transfer enhancement characteristics and the associated frictional head loss in the rectangular channel with a single inclined baffle. Four different types of the baffle are used. The inclined baffles have the width of 19.8 cm, the square diamond of $2.55cm{\times}2.55cm$, and the inclination angle of 5o, and number of holes of up to 9. Reynolds number is varied between 23,000 and 57,000. Results show that the heat transfer and friction factor depend significantly on the number of baffle holes and Reynolds number. The friction factor decreases with increasing Reynolds number and the number of holes on the baffle. It is found that the heat transfer performance of baffle type II(3 hole baffle) has the best values.

• 한국콘텐츠학회논문지
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• 제2권1호
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• pp.98-103
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• 2002

단일화된 번호체계가 없는 VoIP 문제점으로 인해 현재 VoIP 서비스 관련 사업자마다 각기 다른 전화번호 체계를 사용하고 있으며 전화번호의 자리수, 단축버튼 등 번호체계를 제각각 개빌 사용하고 있는 실정이다. 본 논문에서는 이를 해결하기 위해 ITU-T와 IETF의 표준화 동향을 파악하고, 국내의 VoIP 번호체계 표준화 동향과 VoIP서비스외 국내외 번호체계 사용 현황 등을 살펴본다. 이를 토대로 VoIP 서비스 사업자 실정에 적합하면서 번호 할당이 용이하고 세계적인 추세에 부응하는 번호 할당 방안 세 가지를 제안한다.

• 설비공학논문집
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• 제13권3호
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• pp.145-152
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• 2001

Low Rayleigh number thermal convection in a fluid layer confined between two-infinite horizontal walls kept at spatially sinusoidal temperature distributions, T_L=T_m+\Delta T\sin \kappax,\;T_U=T_m+\Delta T\sin(\kappax-\beta)$, is theoretically investigated by a regular perturbation expansion method. For small wave numbers, an upright cell is formed between the two walls at $\beta$=0. The cell is tilted, as the phase difference increases, and a flow with tow counter-rotating eddies occurs at $\beta=\pi$. when the wave number is large, isolated eddies are formed near the lower and upper walls, for all the phase differences. There exists a wave number at which maximum heat transfer rate at the walls occurs, at each of the phase differences. And the wave number increases with increase of the phase difference. for a fixed wave number, the heat transfer rate decrease with increase of the phase difference.

• Kyungpook Mathematical Journal
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• 제45권1호
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• pp.67-71
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• 2005

We call K a (1, 1)-knot in M if M is a union of two solid tori $V_1\;and\;V_2$ glued along their boundary tori ${\partial}V_1\;and\;{\partial}V_2$ and if K intersects each solid torus $V_i$ in a trivial arc $t_i$ for i = 1 and 2. Note that every (1, 1)-knot is a tunnel number one knot. In this article, we determine when a tunnel number one knot is a (1, 1)-knot. In other words, we show that any tunnel number one knot with bridge number 3 is a (1, 1)-knot.

• International Journal of Fluid Machinery and Systems
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• 제4권2호
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• pp.229-234
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• 2011

For Lift-type Vertical Axis Wind Turbine (VAWT), it is difficult to evaluate the performance through the scale-model wind tunnel tests, because of the scale effect relating to Reynolds number. However, it is beneficial to figure out the critical value of Reynolds number or minimum size of the Lift-type VAWT, when designing this type of micro wind turbine. Therefore, in this study, the performance of several scale-models of Lift-type VAWT (Reynolds number : $1.5{\times}10^4$ to $4.6{\times}10^4$) was investigated. As a result, the Reynolds number effect depends on the blade chord rather than the inlet velocity. In addition, there was a transition point of the Reynolds number to change the dominant driving force from Drag to Lift.