• 한국수학교육학회지시리즈A:수학교육
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• 제38권2호
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• pp.179-187
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• 1999

Math teachers are very short of computer tools and manipulatives to use in geometry classes of middle schools for the development of spatial abilities. At most they can ask student to make regular polyhedrons for helping the students to understand by concrete experience, but this experience is not enough to develop spatial abilities in spatial figures including the regular polyhedrons. This article is to introduce instructional materials for development of spatical ability in the regular polyhedrons using computer software, Geometer's Sketchpad. In this article, students can imagine the whole figure through the parts of a plane figure and think of the parts from the solid figure by free movement from 2 dimensions to 3 dimensions, or from 3 dimensions to 2 dimensions. Also, the instructional materials devised in this article will be good to enhance spatial abilities because the relation of 1-1 correspondence in the movement of the parts can be conserved and observed precisely, which is very hard to demonstrate and visualize by paper-and-pencil. It is recommended that this kind of materials should be developed in various ways for teachers to use them directly in their geometry classes.

• 한국수학교육학회지시리즈A:수학교육
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• 제6권2호
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• pp.1-9
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• 1968

In mathematics, a definition must have authentic reasons to be defined so. On defining geometric figures, there must be adequencies in sequel and consistency in the concepts of figures, though the dimensions of them are different. So we can avoid complicated thoughts from the study of geometric property. From the texts of SMSG, UICSM and others, we can find easily that the same concepts are not kept up on defining some figures such as ray and segment on a line, angle and polygon on a plane, and polyhedral angle and polyhedron on a 3-dimensionl space. And the measure of angle is not well-defined on basis of measure theory. Moreover, the concepts for interior, exterior, and frontier of each figure used in these texts are different from those of general topology and algebraic topology. To avoid such absurdness, I myself made new terms and their definitions, such as 'gan' instead of angle, 'polygonal region' instead of polygon, and 'polyhedral solid' instead of polyhedron, where each new figure contains its interior. The scope of this work is hmited to the fundamental idea, and it merely has dealt with on the concepts of measure, dimension, and topological property. In this case, the measure of a figure is a set function of it, so the concepts of measure is coincided with that of measure theory, and we can deduce the topological property for it from abstract stage. It also presents appropriate concepts required in much clearer fashion than traditional method.

• 한국수학교육학회지시리즈A:수학교육
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• 제58권2호
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• pp.283-298
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• 2019

초등학교 교육과정에 포함된 측정 속성 가운데 둘레와 넓이, 겉넓이와 부피는 5, 6학년에서 집중적으로 다루어진다. 그러나 이 영역에서 학생들의 수행능력이 어느 정도가 되며 어떤 문제가 있는지에 대해서는 알려진 바가 많지 않다. 이 연구는 평면도형의 둘레와 넓이, 입체도형의 겉넓이와 부피에 대한 초등학교 6학년 학생들의 이해 정도를 진단하고, 각 요소별 수행 능력을 비교 분석하여 차후 수학 교과서 개발 및 측정 영역 지도를 위한 시사점을 도출하고자 하였다. 이를 위해 둘레, 넓이, 겉넓이, 부피, 둘레와 넓이의 관계, 겉넓이와 부피의 관계에 관련된 문항을 구성하여 6학년 학생 95명을 대상으로 수행 능력을 분석하였다. 분석결과 초등학교 6학년들의 수행능력이 둘레, 겉넓이, 둘레와 넓이의 관계, 겉넓이와 부피의 관계 영역에서 특히 낮은 것으로 드러났다. 이러한 연구 결과를 바탕으로 둘레와 넓이, 겉넓이와 부피 개념의 도입 순서와 지도 방법, 지도 순서 등에 대한 몇 가지 아이디어를 제안하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.1383-1388
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• 2007

Accuracy and processing time are very important factors when the desired shape is fabricated with Selective Laser Sintering (SLS), one of Solid Freeform Fabrication (SFF) systems. In a conventional SLS process, laser spot size is fixed during laser exposing on the sliced figure. Therefore, it is difficult to accurately and rapidly fabricate the desired shape. In this paper, to deal with those problems an SFF system having ability of changing spot size is developed. The system provides high accuracy and optimal processing time. Specifically, a variable beam expander is employed to adjust spot size for different figures on a sliced shape. Finally, Design and performance estimation of the SFF system employing a variable beam expander are achieved and the mechanism will be addressed to measure the real spot size generated from the variable beam expander.

• 한국분말재료학회지
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• 제3권4호
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• pp.253-259
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• 1996

The efficiency of thermoelectric devices for different applications is known to depend on the thermoelectric effectiveness of the material which tends to grow with the increase of its chemical homogeneity. Thus an important goal for thermal devices is to obtain chemically homogeneous solid solutions. In this work, the new process with rapid solidification (melt spinning method) followed by hot pressing was investigated to produce homogeneous material. Characteristics of the material were examined with HRD, SEM, EPMA-line scan and bending test. Property variations of the materials were investigated as a function of variables, such as dopant ${CdCl}_{2}$ quantity and hot pressing temperature. Quenched ribbons are very brittle and consist of homogeneous $Bi_2Te_3$, ${Bi}_{2}{Se}_{3}$ solid solutions. When the process parameters were optimized, the maximum figure of merit was 2.038$\times$$10^{-3}K^{-4}. The bending strength of the material hot pressed at 50$0^{\circ}C$ was 8.2 kgf/${mm}^2$.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.637-643
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• 2000

The shrouded corotating disk flow has a simple figure on geometric basis, but has various and complicated forms of flow. this complicated flows can be variously applied to not only information storage device, but also turbomachinery which is greatly influenced by centrifugal force. This study measured its velocity to measure inner flow field with unique flow field univluenced, using LDV and subminiature hot-wire. The result of experiment shows that distribution limits of solid body rotation region, dimensionless velocity gradient and distribution limits of disk surface boundary layer(Ekman layer) are changed by the gap of disks and rotating speed. Circulating vortex which is near the shroud is effected by the gap of disks and rotating speed.

• 한국ITS학회 논문지
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• 제5권1호
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• pp.13-19
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• 2006

본 논문에서는 7 - 11 GHz 대역에서 동작하는 광대역 Microwave Power Module (MPM)을 설계하고 제작하였다. MPM 은 TWT (Traveling Wave Tube)와 SSA (Solid State Amplifier)로 구성되며, TWT와 SSA의 이득을 최적으로 배분하여 잡음지수를 줄일 수 있도록 설계하였다. Agilent사의 ADS (Advanced Design System)을 이용하여 SSA의 컴퓨터 모델링과 시뮬레이션을 수행 하였으며, 직렬 분포형 증폭기 구조를 이용하여 설계 및 제작하였다. 제작된 광대역 MPM은 7 - 11 GHz 대역에서 8.3 - 10.02 dB의 잡음 지수, 9 GHz에서 38.12 dBm의 출력 전력이 측정되었다.

• 한국분말재료학회지
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• 제3권4호
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• pp.246-252
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• 1996

$Bi_{2}Te_{3}-Sb_{2}Te_{3}$, $Bi_{2}Te_{3}-Bi_{2}Se_{3}$ solid solutions are of great interest as materials for thermoelectric energy conversion. One of the key technologies to ensure the efficiency of thermoelectric device is to obtain chemically homogeneous solid solutions. In this work, the new process with rapid solidification followed by hot pressing was investigated to produce homogeneous thermoelectric materials. Characteristics of the materials were examined with XRD, SEM, EPMA-line scan and bending test. Property variations of the materials were investigated as a function of variables, such as excess Te quantity and hot pressing temperature. Quenched ribbons are very brittle and consisted of homogeneous $Bi_{2}Te_{3}$, $Sb_{2}Te_{3}$ solid solutions. When the process parameters were optimized, the maximum figure of merit was 3.073$\times$$10^{-3}K^{-4}$. The bending strength of the material, hot pressed at 45$0^{\circ}C$, was 5.87 kgf/${mm}^2$.

• 대한수학교육학회지:수학교육학연구
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• 제18권1호
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• pp.81-101
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• 2008

본 연구에서는 중학교의 수학 7-나 과정에서 입체도형의 부피와 겉넓이를 다루는 방식을 조사하여 그 설명방식이 도형의 종류에 따라 달라진다는 점을 지적하고, 특히 구체물을 통한 실험적 방법에 의존하는 설명이 갖는 한계에 대해 논의하였다. 이에 대해 구의 측정에 대한 Archimedes의 연구로부터 입체도형의 부피와 겉넓이에 대한 접근의 목적과 방법에 있어서의 교육적 시사점을 모색하였으며, 이를 바탕으로 현행 접근방법에 대한 보완적인 접근방법 및 그 실제 적용에 있어서의 고려사항을 논의하였다.

• 한국초등수학교육학회지
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• 제22권2호
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• pp.199-220
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• 2018

전개도는 우리나라 제 1차 교육과정부터 초등학교 수학교과서에서 꾸준히 다루어져 온 전통적인 교육내용이며, 주로 입체도형의 성질을 알아보거나 겉넓이를 구하기 위해 지도되어 왔다. 하지만 공간 감각에 대한 중요성이 점점 강조되고 있는 현 시점에서 전개도는 공간 감각을 다루기 위한 매우 적절한 학습 소재가 될 수 있다. 이에 본 연구에서는 우리나라 초등학교 수학 교육과정과 교과서에서 전개도가 어떻게 지도되어 왔는지 살펴보고, 이를 바탕으로 일본, 싱가포르, 핀란드, 홍콩의 교과서에서 다루고 있는 전개도 관련 내용을 분석하였다. 이를 통해 공간 시각화와 공간 방향화의 향상 측면에서 올바른 전개도를 찾는 활동의 강화, 다양한 각도에서 본 입체도형의 모습 제시, 무늬가 들어간 입체도형의 전개도 활용을 시사점으로 제안하였다.