• Bulletin of the Korean Mathematical Society
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• v.37 no.3
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• pp.641-648
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• 2000

It has been conjectured that, on a compact 3-dimensional manifold, a critical point of the total scalar curvature functional restricted to the space of constant scalar curvature metrics of volume 1 is Einstein. In this paper we find a sufficient condition that a critical point is Einstein. This condition is equivalent for a critical point ot be conformally flat. Its relationship with the Fisher-Marsden conjecture is also discussed.

• Bulletin of the Korean Mathematical Society
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• v.52 no.1
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• pp.335-344
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• 2015

We characterize a homogeneous real hypersurface of type (A) or a ruled real hypersurface in a non-flat complex space form, respectively.

• Journal of the Korean Mathematical Society
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• v.41 no.2
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• pp.379-396
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• 2004

In this article, we study rotation surfaces in the 4-dimensional pseudo-Euclidean space E$_2$$^4$. Also, we obtain the complete classification theorems for the flat rotation surfaces with finite type Gauss map, pointwise 1-type Gauss map and an equation in terms of the mean curvature vector. In fact, we characterize the flat rotation surfaces of finite type immersion with the Gauss map and the mean curvature vector field, namely the Gauss map of finite type, pointwise 1-type Gauss map and some algebraic equations in terms of the Gauss map and the mean curvature vector field related to the Laplacian of the surfaces with respect to the induced metric.

• Communications of the Korean Mathematical Society
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• v.18 no.1
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• pp.95-104
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• 2003

The deformation spaces of the six orientable 3-dimensional flat Riemannian manifolds are studies. It is proved that the Teichmuller spaces are homeomorphic to the Euclidean spaces. To state more precisely, let $\Phi$ denote the holonomy group of the manifold. Then the Teichmuller space is homeomorphic to (1) ${\mathbb{R}}^6\;if\;\Phi$ is trivial, (2) ${\mathbb{R}}^4\;if\;\Phi$ is cyclic with order two, (3) ${\mathbb{R}}^2\;if\;\Phi$ is cyclic of order 3, 4 or 6, and (4) ${\mathbb{R}}^3\;if\;\Phi\;\cong\;{\mathbb{Z}_2}\;\times\;{\mathbb{Z}_2}$.

• Journal of the Optical Society of Korea
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• v.19 no.6
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• pp.658-664
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• 2015

Lens designers generally refer to flat image fields and attempt to minimize the field curvature. Present-day CMOS image sensors for mobile phone cameras, however, are not flat, but curved. Sometimes it is necessary to generate an intentional field curvature according to the degree and direction of the CMOS image-sensor’s curvature. This paper presents the degree of curvature of a CMOS image sensor measured using an interferometer, and proposes an effective compensation method that minimizes the net field curvature through optimizing the air gap between lens elements, which is demonstrated using simulations and experiments.

• Computers and Concrete
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• v.20 no.6
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• pp.731-738
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• 2017

Reinforced concrete flat plates consist of slabs supported directly on columns. The absence of beams makes these systems attractive due to advantages such as economical formwork, shorter construction time, less total building height with more clear space and architectural flexibility. Punching shear failure is usually the governing failure mode of flat plate structures. Punching failure is brittle in nature which induces more vulnerability to this type of structure. To analyze the flat plate behavior under punching shear, twelve finite element models of flat plate on a column with different parameters have been developed and verified with experimental results. The maximum range of variation of punching stress, obtained numerically, is within 10% of the experimental results. Additional finite element models have been developed to analyze the influence of integrity reinforcement, clear cover and column reinforcement. Variation of clear cover influences the punching capacity of flat plate. Proposed finite element model can be a substitute to mechanical model to understand the influence of clear cover. Variation of slab thickness along with column reinforcement has noteworthy impact on punching capacity. From the study it has been noted that integrity reinforcement can increase the punching capacity as much as 19 percent in terms of force and 101 percent in terms of deformation.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.828-836
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• 2008

To develop an engineering-model of hydrogen-fueled ultra-micro combustor for Ultra Micro Gas Turbine(UMGT), we reviewed and summarized the problems in downsizing combustors, and determined a suitable burning method. The key issue to actualize practical ultra-micro combustors is reducing heat loss from the combustor to compressor and turbine. The reduction of heat loss was discussed from 3 different viewpoints; heat-insulation material, high-space-heating-rate combustion, and combustor-insolated gas turbine structure. Use of heat-insulation material induced the heat loss reduction to the surroundings. The heat loss ratio decreased substantially in reverse proportion to space heating rate, leading the idea that it could be reduced by burning at a high space heating rate. By settling the combustor insolated from the compressor and turbine, the heat transfer from the combustor to the compressor and turbine becomes smaller. For a selection of the suitable burning method, comparison between 2 burning methods, flat-flame and swirling-flamer types, was conducted. Synthetically the flat-flame burning method was confirmed to be more suitable for ultra-micro combustors than latter one. Base on them, an engineering-model of hydrogen-fueled flat-flame ultra-micro combustor was developed. To obtain high overall heat-insulation, heat-resistant and strength, the engineering-model combustor had triple layer structure with an advanced ceramic, a heat insulation material and a stainless steel. To simplify heat transfer issue in the combustor, it was isolated from the other components. Furthermore it was designed by considering structure, size, material, velocity, pressure loss and prevention of flashback.

• Fashion & Textile Research Journal
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• v.2 no.4
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• pp.360-365
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• 2000

This research is the trial for the computation of the ease-rate for the bodice pattern. The result of the analysis about the cross section figures of garment space by using a 3-D measuring instrument is that: The garment space of each bodice by each body size is definite. In the figure of cross section of the basic lines, an area of cross section of garment space and length of cross section of garment space are not increased in proportion to an area of cross section of the body. The ease rate is the same no matter that flat-rate of the body is same or different. The ease-rate is computed by length of cross section of garment space that is in proportion to the radius of the body.

• Korean Institute of Interior Design Journal
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• v.18 no.5
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• pp.175-182
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• 2009

Korea Protestant slower growth and social church's changes in the environment of the traditional worship center for the sermon to a variety of changes was required, because of this period reflects the availability of a new type of worship was to appear. These changes in the type of worship in the form of the worship space, and space configuration is affecting many more. This study was the type of church korea today, the type is classified as a traditional worship and contemporary worship, and to characterize the category by a change in the type of church worship space in the configuration that affects cases throughout the analysis was to investigate, study follows. Traditional worship the center of the altar, the altar placed platform form, a vertical elevation of the platform sheet form, the installation of the cross, place the side of the choir seats, church chair type attribute appears tradition and in part compressed pulpit appears symbolism. Contemporary worship to the exclusion of the symbolic elements of the platform open, flat sheet form and the platform was the preferred form of minor elevations of the flat, multi-purpose space used for worship to sermon platform placed around the altar of the adjustable type, the choir seats placed in scheelite, preferred form of scheelite was an individual chair. However, the characteristics of traditional and contemporary worship space features a mix of worship space, quite a lot of cases that have been found. Integrated and consistent element of the worship space, the worship of the discrepancy in the form of systematic theological depth analysis did not come true without lust about contemporary culture is changing rapidly to accommodate sprawl is judged. Therefore, the characteristics of the type of worship and prayer to understand the changes in the church building is a prerequisite to be a very important aspect.

• Journal of the Korean Mathematical Society
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• v.11 no.2
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• pp.121-133
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• 1974