• Design & Manufacturing
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• 제16권3호
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• pp.9-15
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• 2022

In order to reduce the manufacturing costs of the glass lens, it is necessary to manufacture a lens using a UV curable resin or a thermosetting resin, which is a curable material, in order to replace a glass lens. In the case of forming a lens using a thermosetting material, it is necessary to form several lenses at once using the wafer-level lens manufacturing technologies due to the long curing time of the material. When a lens is manufactured using a curable material, an error in the shape of the lens due to the shrinkage of the material during the curing process is an important cause of defects. The major factors for these shape errors and deformations are the shrinkage and the change of mechanical properties in the process of changing from a liquid material during curing to a solid state after complete curing. Therefore, it is necessary to understand the curing process of the material and to examine the shrinkage rate and change of physical properties according to the degree cure. In addition, it is necessary to proceed with CAE for lens molding using these and to review problems in lens manufacturing in advance. In this study, the viscoelastic properties of the material were measured during the curing process using a rheometer. Using the results, Rheological investigation of cure kinetics was performed. At the same time, The shrinkage of the material was measured and simple mathematical models were created. And using the results, the molding process of a single lens was analyzed using Comsol, a commercial S/W. In addition, the experiment was conducted to compare and verify the CAE results. As a result, it was confirmed that the shrinkage rate of the material had a great influence on the shape precision of the final product.

• 한국포장학회지
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• 제12권1호
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• pp.35-40
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• 2006

Cushioning systems, which are cushion material and its designed configuration, are important to protect fragile items since they act as buffers between the impact force and the fragile product. As cushioning materials, several plastic foams are commonly used in industry. However, the utilization of the plastic material has been causing a solid waste problem and pollution. Thus, as an alternative cushion material to the plastic foams, a corrugated cushion, which is considered environmentally friendly and cheap material, was put into drop tests and its impact shock attenuation was investigated. Flat and free drop data were recorded and compared to the dynamic shock of EPS cushion. In addition, the mathematical model of the shock attenuation of the corrugated cushion was developed. The result showed that the corrugated cushion gave an excellent protection for items that were subjected to the limited number of drops. There was no significant difference of the shock absorbing ability between the EPS and corrugated cushions. Energy density model of cushioning material successfully explained the mechanical behavior and fatigue of the corrugated cushions.

• 대한수학교육학회지:학교수학
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• 제4권3호
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• pp.331-346
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• 2002

This study has two purposes. One is to know that it is Possible to use portfolio in the elementary math class. The other is to make a useful method for using portfolio. We got the following conclusion through the study. Portfolio gave students an opportunity that they could review their mathematical thinking. But it couldn't work very well for the low-level students. They didn't pay attention to the class. So, careful prepa-ration and training were necessary for the portfolio material. And the portfolio material must be prepared by appropriate contents. Teacher had to do math class by considering students ability. The math class could be much better for motivation, teaching-learning activity impro-vement and communication tool by using portfolio material. There are several imple-mentation processes in preparation, execution and utilization of the class. 1) Preparation: Teacher must decide if it is appropriate for portfolio by analyzing the course and textbook and set a final goal. And then teacher has to select an appropriate item and make a schedule for the class. The portfolio material must contain valuable things from which students learn mathematics and use in their life. The student level, utilization purpose and contents are considered when one prepares portfolio material. 2) Execution: Students are supposed to understand about the portfolio very well. It is important for them to get the opportunity for reviewing through math class diary, their opinion, friends opinion and teachers opinion. 3) Utilization: Parents review ameliorates the communication among teacher, student and parents about learning activity.

• Advances in nano research
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• 제13권4호
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• pp.351-368
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• 2022

Recently, promising structural technologies like multi-function, ultra-load bearing capacity and tailored structures have been put up for discussions. Finite Element (FE) modelling is probably the best-known option capable of treating these superior properties and multi-domain behavior structures. However, advanced materials such as Functionally Graded Material (FGM) and nanocomposites suffer from problems resulting from variable material properties, reinforcement aggregation and mesh generation. Motivated by these factors, this research proposes a unified shape function for FGM, nanocomposites, graded nanocomposites, in addition to traditional isotropic and orthotropic structural materials. It depends not only on element length but also on the beam's material properties and geometric characteristics. The systematic mathematical theory and FE formulations are based on the Timoshenko beam theory for beam structure. Furthermore, the introduced element achieves C1 degree of continuity. The model is proved to be convergent and free-off shear locking. Moreover, numerical results for static and free vibration analysis support the model accuracy and capabilities by validation with different references. The proposed technique overcomes the issue of continuous properties modelling of these promising materials without discarding older ones. Therefore, introduced benchmark improvements on the FE old concept could be extended to help the development of new software features to confront the rapid progress of structural materials.

• Steel and Composite Structures
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• 제45권5호
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• pp.729-747
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• 2022

The critical buckling loads and buckling modes of bi-directional functionally graded porous unified higher order shear plate with elastic foundation are investigated. A mathematical model based on neutral axis rather than midplane is developed in comprehensive way for the first time in this article. The material constituents form ceramic and metal are graded through thickness and axial direction by the power function distribution. The voids and cavities inside the material are proposed by three different porosity models through the thickness of plate. The constitutive parameters and force resultants are evaluated relative to the neutral axis. Unified higher order shear plate theories are used to satisfy the zero-shear strain/stress at the top and bottom surfaces. The governing equilibrium equations of bi-directional functionally graded porous unified plate (BDFGPUP) are derived by Hamilton's principle. The equilibrium equations in the form of coupled variable coefficients partial differential equations is solved by using numerical differential integral quadrature method (DIQM). The validation of the present model is presented and compared with previous works for bucking. Deviation in buckling loads for both mid-plane and neutral plane are developed and discussed. The numerical results prove that the shear functions, distribution indices, boundary conditions, elastic foundation and porosity type have significant influence on buckling stability of BDFGPUP. The current mathematical model may be used in design and analysis of BDFGPU used in nuclear, mechanical, aerospace, and naval application.

• 정보교육학회논문지
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• 제7권1호
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• pp.11-26
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• 2003

웹의 장점을 활용하기 위한 수학교과 교수-학습 자료들은 이미 많이 개발되어 있으나 수학교과 자료에서 사용하는 수식이 대부분 수식 자체가 아닌 그림 형태로 표현되어 있어 수식의 계산이나 검색, 재사용 등 다양한 활용이 불가능하였다. 이를 극복하기 위하여 수식 표현을 위한 마크업 언어인 MathML이 개발되었다. 본 논문에서는 수학교과 ICT 활용 교육에서의 교재 개발, 교수-학습 도구 개발, 그리고 정보교환을 위해 MathML을 활용할 수 있는 방안을 제시한다. 교재 개발에 있어서 MathML을 이용하는 것은 수식의 수정을 편리하게 하고 재사용을 가능하게 한다. 그리고 MathML을 표준으로 사용하는 교수-학습 도구들은 수식과 수학적 개념간의 연결을 강하게 해 주고, 교사들이 이와 같은 도구들을 보다 쉽게 재구성하여 수업에 활용할 수 있도록 해 준다. MathML을 이용한 수식을 사용할 수 있는 게시판은 교사와 학생간의 정보 교환을 활발하게 하고, 이를 이용한 $\ulcorner$웹토론하기$\lrcorner$와 같은 다양한 형태의 ICT활용 수업을 가능하게 한다.

• 한국수학교육학회지시리즈E:수학교육논문집
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• 제27권4호
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• pp.567-580
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• 2013

대학 입학 전형에서 통합 논술이 시행되면서 학교 교사나 학생들은 통합 논술의 중요성을 인식하고 필요하다고 생각하지만 실제 교사들은 지도 방법의 어려움을 갖고 있다. 본 연구는 예비수학교사를 대상으로 통합 논술 지도를 위한 수업의 사례를 통해 교육적 시사점을 도출해보고자 한다. 수업은 내용 지식으로서 수학에서의 원뿔곡선의 정의와 안테나 반사판의 설계에 적용된 원뿔곡선의 반사 성질을 주제로 하고, 수학사, 구체물, 종이접기, 컴퓨터 등을 이용하여 학생들이 원뿔곡선의 정의와 성질을 발견하게 하였다. 이러한 교수 학습 과정에서 학생들은 수학사를 통해 수학적 지식이 인간에 의해서 발명되었음을 이해할 수 있고, 정의나 명제를 만들고 정당화 해봄으로써 수학적 명제의 타당성을 평가할 수 있을 것이다. 또한, 발견한 성질들 사이의 관계를 논리적으로 기술할 수 있으며, 정당화 과정에서 이유나 근거를 설득력 있게 기술할 수 있다. 통합 논술을 지도함에 있어서 내용에 따라 다양한 접근의 수업 자료와 지도 방법에 대한 연구가 계속되어야 할 것이다.

• East Asian mathematical journal
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• 제31권4호
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• pp.459-481
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• 2015

In this study, we investigated whether the theorem is established even if we replace a 'square' element in the Euclidean proof of the Pythagorean theorem with different figures. At this time, we used different figures as equilateral, isosceles triangle, (mutant) a right triangle, a rectangle, a parallelogram, and any similar figures. Pythagorean theorem implies a relationship between the three sides of a right triangle. However, the procedure of Euclidean proof is discussed in relation between the areas of the square, which each edge is the length of each side of a right triangle. In this study, according to the attached figures, we found that the Pythagorean theorem appears in the following three cases, that is, the relationship between the sides, the relationship between the areas, and one case that do not appear in the previous two cases directly. In addition, we recognized the efficiency of Euclidean proof attached the square. This proving activity requires a mathematical process, and a generalization of this process is a good material that can experience the diversity and rigor at the same time.

• 한국정밀공학회지
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• 제26권11호
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• pp.70-76
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• 2009

Web tension control system recently have been applied to OLED(Organic Light-Emitting Diode), RFID of flexible material, e-Paper and PLED(Polymeric LED) and various web control algorithms have being developed for higher productivity and product quality These system need an accuracy model to design and implement controller. In this paper, the web tension control system with dancer roll is mathematically modeled. Mathematical model consists of 8 subsystems and each subsystems can be described as impedance structure which connected by velocity and tension. Mathematical model is different from the estimated model at high frequency range because of structure dynamics which is ignored on mathematical model. The estimated model is derived using ARMAX model. The controller is designed using the estimated model. The step response of the estimated model are compared with that of physical model for a validation of estimated model. The experimental results show a good match between them.

• 한국수학사학회지
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• 제22권2호
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• pp.53-68
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• 2009

고대 그리스에서 발현된 수학의 무한 개념은 헤브라이인의 유대교 전통인 카발라의 영향을 받아 중세 기독교 교부 철학자들에 의해 보다 성숙되어져 갔으며, 그 후 기독교의 무한사상이 르네상스 시대에는 화가들에 의해 원근법으로 구체화되었다. 본 논문에서는 그리스 시대부터 발전된 무한 개념의 경로를 살펴보고, 근대와 19세기 이후 무한수학이 발달될 때 당시 미술에서는 무한 개념이 어떻게 표현되었는지 그 시대정신을 고찰한다.