• 대한수학회보
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• 제46권1호
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• pp.35-43
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• 2009

We say that an isometric immersed hypersurface x : $M^n\;{\rightarrow}\;{\mathbb{R}}^{n+1}$ is of $L_k$-finite type ($L_k$-f.t.) if $x\;=\;{\sum}^p_{i=0}x_i$ for some positive integer p < $\infty$, $x_i$ : $M{\rightarrow}{\mathbb{R}}^{n+1}$ is smooth and $L_kx_i={\lambda}_ix_i$, ${\lambda}_i\;{\in}\;{\mathbb{R}}$, $0{\leq}i{\leq}p$, $L_kf=trP_k\;{\circ}\;{\nabla}^2f$ for $f\;{\in}\'C^{\infty}(M)$, where $P_k$ is the kth Newton transformation, ${\nabla}^2f$ is the Hessian of f, $L_kx\;=\;(L_kx^1,\;{\ldots},\;L_kx^{n+1})$, $x=(x^1,\;{\ldots},\;x^{n+1})$. In this article we study the following(hyper)surfaces in ${\mathbb{R}}^{n+1}$ from the view point of $L_1$-finiteness type: totally umbilic ones, generalized cylinders $S^m(r){\times}{\mathbb{R}}^{n-m}$, ruled surfaces in ${\mathbb{R}}^{n+1}$ and some revolution surfaces in ${\mathbb{R}}^3$.

• 한국광학회:학술대회논문집
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• 한국광학회 1990년도 제5회 파동 및 레이저 학술발표회 5th Conference on Waves and lasers 논문집 - 한국광학회
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• pp.29-33
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• 1990

Efficient numerical method is developed for treating electromagnetic problems of scattering and radiation from surfaces. Special consideration is given to the treatment of edges so that rather arbitrary geometrical configurations may be handled. For the conducting body problems considered, an electric field integral formulation is used, and the method of moments is applied using pulse expantions to present currents. Numerial results indicate that the approach is free os anomalies in the behavior of current for body of revoution.

• Tribology and Lubricants
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• 제16권5호
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• pp.324-331
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• 2000

Wear characteristics of Plastic and Nylon pinions against steel gear were studied to gain a better understanding of their tribological behaviors. Wear tests were conducted with power circulating gear test rig under dry contact conditions. Specific wear rates were measured as a function of applied load and the number of revolution. The worn teeth surfaces were examined with a profile projector and a camera. Nylon pinion showed lower specific wear rates than acetal pinion, but suffered teeth breakage under high load per unit tooth width. The dominant wear mechanisms found were adhesion and abrasion.

• 한국정밀공학회지
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• 제13권6호
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• pp.59-65
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• 1996

There are many difficulties in automatic polishing for die & mold surfaces. Even though the process has been studied in the past 15 years, it has not been achieved yet, but by the process of actual hand work of well-skilled workers. A new magentic assisted polishing process, which is one of the potential methods for automation of surface finishing has been studied in the past 10 years by colleagues. The process has many merits, but on the other hand also has demerits, one being low efficiency of grindability by comparision with wheel polish. Therefore, some attempts were tried to improve the grindability by adopting electropolishing, ultra-high speed milling, 5-axis controlled machine etc... most recently by colleagues. This paper also aims to improve the efficiency of polishing by introducing the easily-polished shape surface cutting method equalizing the tool feed per revolution to the pick feed. This cutting method was experimentally confirmed to have sufficient grindability to polish milled surface (with $10{{\mu}m}$Rmax surface roughness) into mirror surface (with $0.4{{\mu}m}$Rmax surface roughness).

• 한국실내디자인학회논문집
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• 제17권3호
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• pp.139-147
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• 2008

Modern architecture's optical mechanism focused on Ocuularcentrism neglects the tactility of vision and tends to eliminate the optical and tactile dualism of traditional spaces by representing spaces and surfaces that are abstract and cold-hearted. In other words, all sensory experiences, except for visual experiences, are eliminated to make it impossible to create the substantial core of architecture that combines time, image, and surface textures. The fast-changing social trends, the emergence of new materials and technologies, and the corresponding development of various types of media since the Industrial Revolution have changed the paradigm of human perception and representation. With the development of media, other sensory experiences besides visual experience have been stressed and human perception has converted from single perspective to complex perspective. In result, new sensory items, such as visual tactility, have replaced the traditional vision-centered hierarchy. The composition of architectural surfaces has represented the functional and commercial needs of technology, structure, as well as the socio-cultural needs of the community. In contemporary times, it is being changed and developed by the new tactility and the corresponding expression of modern architecture. Based on the visual representation of tactility of architectural surface, this study used a composition of surface that combines various events, meanings, and senses to examine how architecture can mediate and reproduce viewers' visual experiences and discover the existential relationship between architecture and men.

• Korean Chemical Engineering Research
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• 제54권1호
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• pp.44-51
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• 2016

전도성 물질인 철 입자(iron particles)를 절연체로 코팅하여 제작한 압분자심(powder core)은 비저항이 작기 때문에 고주파 영역에서 와전류 손실이 크다. 이 결함을 해결하기 위해서는 압분자심의 비저항을 증가시킬 필요가 있다. 이 연구에서는 압분자심의 비저항을 증가시키기 위하여 유성볼밀을 사용하여 전기전도성 철 입자에 산화제2구리를 코팅하였다. 반응표면분석법을 사용하여 코팅변수를 최적화하였다. 최적화 시 인자는 CuO 질량분율, 밀 회전 수, 코팅시간, 볼 크기, 볼 질량, 시료 질량이며, 반응변수는 비저항이었다. 6인자-일부요인배치법에 의하면 주된 인자는 CuO 질량분율, 밀 회전 수, 코팅시간이었다. 3-인자 완전요인배치법과 최대경사법을 사용하여 3개 인자의 수준을 선정하였다. 최대경사법을 사용하여 최고의 비저항을 갖는 영역에 접근하였다. 최종적으로 Box-Behnken법을 사용하여 스크린한 인자들의 반응표면을 분석하였다. Box-Behnken법 결과에 의하면 CuO 질량분율과 밀 회전 수가 코팅공정 효율에 영향을 주는 주요 인자이었다. CuO 질량분율이 증가함에 따라 비저항은 증가하였다. 그에 반해서 밀 회전 수가 감소함에 따라 비저항은 증가하였다. 코팅공정을 최적화한 모델로부터 계산한 예측값과 실험값과는 통계적으로 유의하게 일치하였다($Adj-R^2=0.944$). 비저항의 최고값을 갖는 코팅조건은 CuO 질량분율은 0.4, 밀 회전 수는 200 rpm, 코팅시간은 15분이었다. 이 조건에서 코팅한 정제의 비저항 측정값은 $530k{\Omega}{\cdot}cm$이었다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.196-201
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• 2001

In this paper, we have described the microchannel fluid behavior in a slot between rotating curvilinear surfaces of revolution using micropolar fluid theory. ]n order to solve this problem, we have used boundary layer equations and applied non-zero values of the microrotation vector on the wall. The results are compared with the corresponding flow problems for Newtonian fluid. Results show that both the velocity distribution and the microrotation component distribution for a micropolar fluid are lower than that of a Newtonian fluid.

• 한국공작기계학회논문집
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• 제15권1호
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• pp.102-107
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• 2006

This study investigates the properties as the difference friction welding area on SM25C steel rod. The tensile and bending strength and of welded joints, the hardness distribution of welds, the microstructure of welds and the tensile fracture surfaces were mainly investigated through this experiment. The fixed friction welding conditions were revolution 2000rpm, friction pressure 70Mpa, friction time 1.5sec, upset pressure 100Mpa, upset time 2.0sec, upset length 2.8mm and changeable friction welding parameter was friction welding area.

• 한국수학교육학회지시리즈D:수학교육연구
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• 제7권2호
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• pp.101-117
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• 2003

In this paper, we give examples of models we have created for use in university mathematics courses. We explain the concept of linear transformation, investigate the roles of each component of 2 ${\times}$ 2 and 3 ${\times}$ 3 transformation matrices, consider the relation between sound and trigonometry, visualize the Riemann sum, the volume of surfaces of revolution and the area of unit circle. This paper illustrates how one can use Mathematica to visualize abstract mathematical concepts, thus enabling students to understand mathematics problems effectively in class. Development of these kinds of teaching and learning models can stimulate the students' curiosity about mathematics and increase their interest.

• 대한기계학회논문집
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• 제17권2호
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• pp.452-457
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• 1993

For the calculation of transonic laminar relative flow fields on the axisymmetric H-S and B-B stream surfaces in turbomachinery, a finite volume method developed in Part (I) is extended. Energy equation is replaced for simplicity by the condition of constant rothalpy throughout the flow fields. For axisymmetric H-S flow the circumferential componets of absolute velocity are given in advance so that this component of momentum equations can be neglected. Some numerical results show good agreement with experimental data.