• Communications of the Korean Mathematical Society
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• v.25 no.2
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• pp.225-234
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• 2010

In this paper, we study the geometry of lightlike hypersurfaces of a semi-Riemannian manifold. We prove a classification theorem for Einstein lightlike hypersurfaces M of a Lorentzian space form subject such that the second fundamental forms of M and its screen distribution S(TM) are conformally related by some non-vanishing smooth function.

• Bulletin of the Korean Mathematical Society
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• v.40 no.1
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• pp.63-76
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• 2003

In this article, we establish relations between the sectional curvature and the shape operator and also between the k-Ricci curvature and the shape operator for a slant submanifold in a Sasakian space form of constant $\varphi-sectional$ curvature with arbitrary codimension.

• Bulletin of the Korean Mathematical Society
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• v.36 no.2
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• pp.315-336
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• 1999

In the paper [12] we have introduced the new kind of pseudo-einstein ruled real hypersurfaces in complex space forms $M_n(c), c\neq0$, which are foliated by pseudo-Einstein leaves. The purpose of this paper is to give a geometric condition for non-proper pseudo-Einstein ruled real hypersurfaces to be totally geodesic in the sense of Kimura [8] for c> and Ahn, Lee and the present author [1] for c<0.

• Bulletin of the Korean Mathematical Society
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• v.59 no.4
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• pp.897-904
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• 2022

In this paper, we obtain an inequality involving the squared norm of the covariant differentiation of the shape operator for a real hypersurface in nonflat complex space forms. It is proved that the equality holds for non-Hopf case if and only if the hypersurface is ruled and the equality holds for Hopf case if and only if the hypersurface is of type (A).

• Proceeding of Spring/Autumn Annual Conference of KHA
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• 2008.11a
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• pp.397-402
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• 2008

For the past years, Korean Housing policy have been focused on quantity rather then quality, when they provide housing. Focusing great quantity on housing led monolithic and standardized house forms in limited area. Most of our traditional residental environment, which made Koreans to communicate with neighbors, disappeared from the result of providing great quantity on housing. However, the increase of the income and standard of living, changed people's view. People start to demand for the place which is commodious and comfortable to live. Moreover, more leisure time caused people to communicate with their neighbors. To meet the demands of new forms of housing, they started to provide a community space to increase sense of belonging and community spirit for the residents in apartment house. The forms of past house which is defined by uniformity is delivered from rational thoughts. People can get emotional satisfaction from Community space because it provides opportunity of communicating and increase community spirit. This research is to classify the emotional expression in Community space and analyze the elements that is expressed in community space of apartment house.

• Kyungpook Mathematical Journal
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• v.31 no.2
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• pp.131-141
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• 1991

• Journal of the Korean Mathematical Society
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• v.55 no.3
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• pp.735-747
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• 2018

Let M be a real hypersurface of a complex space form with constant curvature c. In this paper, we study the hypersurface M admitting Miao-Tam critical metric, i.e., the induced metric g on M satisfies the equation: $-({\Delta}_g{\lambda})g+{\nabla}^2_g{\lambda}-{\lambda}Ric=g$, where ${\lambda}$ is a smooth function on M. At first, for the case where M is Hopf, c = 0 and $c{\neq}0$ are considered respectively. For the non-Hopf case, we prove that the ruled real hypersurfaces of non-flat complex space forms do not admit Miao-Tam critical metrics. Finally, it is proved that a compact hypersurface of a complex Euclidean space admitting Miao-Tam critical metric with ${\lambda}$ > 0 or ${\lambda}$ < 0 is a sphere and a compact hypersurface of a non-flat complex space form does not exist such a critical metric.

• Bulletin of the Korean Mathematical Society
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• v.54 no.2
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• pp.417-428
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• 2017

We classify the extreme bilinear forms of the unit ball of the space of bilinear forms on ${\mathbb{R}}^2$ with hexagonal norms.

• Kyungpook Mathematical Journal
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• v.58 no.1
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• pp.47-54
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• 2018

We classify the extreme, exposed and smooth bilinear forms of the unit ball of the space of bilinear forms on $l^2_{\infty}$.

• Kyungpook Mathematical Journal
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• v.54 no.3
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• pp.341-347
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• 2014

We classify the exposed symmetric bilinear forms of the unit ball of $\mathcal{L}_s(^2d_*(1,{\omega})^2)$.