• Communications of the Korean Mathematical Society
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• v.36 no.4
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• pp.771-782
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• 2021

In this paper we introduce generalized weakly semi-conformally symmetric manifold, a generalization of weakly symmetric manifold. We study some basic properties and obtain the forms of the scalar curvature of such manifold. In the last section an example is given to ensure the existence of such manifold.

• Korean Journal of Computational Design and Engineering
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• v.5 no.4
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• pp.293-300
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• 2000

The non-manifold geometric modeling technique is to improve design process and to Integrate design, analysis, and manufacturing by handling mixture of wireframe model, surface model, and solid model in a single data structure. For the non-manifold geometric modeling, Euler operators and other high level modeling methods are necessary. Boolean operation is one of the representative modeling method for the non-manifold geometric modeling. This thesis studies Boolean operations of non-manifold model with the data structure of selective storage. The data structure of selective storage is improved non-manifold data structure in that existing non-manifold data structures using ordered topological representation method always store non-manifold information even if edges and vortices are in the manifold situation. To implement Boolean operations for non-manifold model, intersection algorithm for topological cells of three different dimensions, merging and selection algorithm for three dimensional model, and Open Inventor(tm), a 3D toolkit from SGI, are used.

• Bulletin of the Korean Mathematical Society
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• v.49 no.4
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• pp.761-765
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• 2012

We prove that for a toric manifold (respectively, a quasitoric manifold) M, any graded ring isomorphism $H^*(M){\rightarrow}H^*({\Pi}_{i=1}^{m}\mathbb{C}P^{ni})$ can be realized by a diffeomorphism (respectively, a homeomorphism) ${\Pi}_{i=1}^{m}\mathbb{C}P^{ni}{\rightarrow}M$.

• Bulletin of the Korean Mathematical Society
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• v.53 no.1
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• pp.205-214
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• 2016

Any open Riemann surface has a conformal model in any orientable Riemannian manifold of dimension 4. Precisely, we will prove that, given any open Riemann surface, there is a conformally equivalent model in a prespecified orientable 4-dimensional Riemannian manifold. This result along with [5] now shows that an open Riemann surface admits conformal models in any Riemannian manifold of dimension ${\geq}3$.

• Honam Mathematical Journal
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• v.37 no.4
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• pp.457-468
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• 2015

The aim of present paper is to investigate 3-dimensional ${\xi}$-projectively flt and $\tilde{\varphi}$-projectively flt normal almost paracontact metric manifolds. As a first step, we proved that if the 3-dimensional normal almost paracontact metric manifold is ${\xi}$-projectively flt then ${\Delta}{\beta}=0$. If additionally ${\beta}$ is constant then the manifold is ${\beta}$-para-Sasakian. Later, we proved that a 3-dimensional normal almost paracontact metric manifold is $\tilde{\varphi}$-projectively flt if and only if it is an Einstein manifold for ${\alpha},{\beta}=const$. Finally, we constructed an example to illustrate the results obtained in previous sections.

• Bulletin of the Korean Mathematical Society
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• v.42 no.4
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• pp.713-724
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• 2005

We prove that a (k, $\mu$)-manifold with vanishing E­Bochner curvature tensor is a Sasakian manifold. Several interesting corollaries of this result are drawn. Non-Sasakian (k, $\mu$)­manifolds with C-Bochner curvature tensor B satisfying B $(\xi,\;X)\;\cdot$ S = 0, where S is the Ricci tensor, are classified. N(K)-contact metric manifolds $M^{2n+1}$, satisfying B $(\xi,\;X)\;\cdot$ R = 0 or B $(\xi,\;X)\;\cdot$ B = 0 are classified and studied.

• Korean Journal of Mathematics
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• v.13 no.1
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• pp.35-41
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• 2005

Let (M, $g$) be a compact oriented 4-dimensional Riemannian manifold whose sectional curvature $k$ satisfies $1{\geq}k{\geq}0.1714$. We show that M is topologically $S^4$ or ${\pm}\mathbb{C}\mathbb{P}^2$.

• Communications of the Korean Mathematical Society
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• v.38 no.4
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• pp.1191-1213
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• 2023

In this paper, we introduce and study two new classes of lightlike submersions, called radical transversal and transversal lightlike submersions between an indefinite Sasakian manifold and a lightlike manifold. We give examples and investigate the geometry of distributions involved in the definitions of these lightlike submersions. We also study radical transversal and transversal lightlike submersions from an indefinite Sasakian manifold onto a lightlike manifold with totally contact umbilical fibers.

• Journal of the Korean Mathematical Society
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• v.58 no.5
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• pp.1081-1107
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• 2021

In this paper, we introduce the notion of toric special weak Fano manifolds, which have only special primitive crepant contractions. We study their structure, and in particular completely classify smooth toric special weak Fano 4-folds. As a result, we can confirm that almost every smooth toric special weak Fano 4-fold is a weakened Fano manifold, that is, a weak Fano manifold which can be deformed to a Fano manifold.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.32A no.6
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• pp.787-798
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• 1995

We implement the E-plane T-juncition manifold mutiplexer having low insertion loss for output multiplexer of Ku-band satellite transponder. Manifold multiplexer implemented here is composed of 2 channel filters, T-junctions, half-wave waveguide connecting channel filters and manifold, and manifold itself.[1-4] Considering the mass and volume of the satellite transponder, the channel filters are designed to dual-mode.[5-13] And Elliptic filter function is used, which has good characteristics of suppressing the interference between 2 channels. Since the performance of manifold multiplexer depends on the manifold waveguide transmission line length, it's necessary proper analysis. In this paper, we do optimization process of T-junction and other elements by using CAD and implement the manifold multiplexer. An experiment shows that characteristic response of multiplexer matches wel its modeling result.