• 호남수학학술지
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• 제24권1호
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• pp.109-119
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• 2002

Some sufficient conditions on the existence and uniqueness of certain symmetric balanced incomplete block design are introduced. Also, a construction algorithm for the design and some examples are presented. The algorithm is developed based on the construction of subspaces of the three-dimensional vector space over a field.

• 호남수학학술지
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• 제42권4호
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• pp.811-819
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• 2020

We give characterizations of locally symmetric spaces M via the structural operator $h={\frac{1}{2}{\mathcal{L}}_{\xi}{\phi}}$ or the characteristic Jacobi operator ℓ = R(·, ξ)ξ on the unit tangent sphere bundles T1M.

• 대한수학회보
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• 제36권4호
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• pp.671-682
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• 1999

Using a base-point free version of the infinite symmetric product we define a fibrewise infinite symmetric product for any fibration $E\;\longrightarrow\;B$. The construction works for any commutative ring R with unit and is denoted by $R_f(E)\;l\ongrightarrow\;B$. For any pointed space B let $G_I(B)\;\longrightarrow\;B$ be the i-th Ganea fibration. Defining $M_R-cat(B):= inf{i\midR_f(G_i(B))\longrihghtarrow\;B$ admits a section} we obtain an approximation to the Lusternik-Schnirelmann category of B which satisfies .g.a product formula. In particular, if B is a 1-connected rational space of finite rational type, then $M_Q$-cat(B) coincides with the well-known (purely algebraically defined) M-category of B which in fact is equal to cat (B) by a result of K.Hess. All the constructions more generally apply to the Ganea category of maps.

• 대한수학회보
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• 제52권5호
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• pp.1631-1647
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• 2015

In this paper, we prove two optimal inequalities involving the intrinsic scalar curvature and extrinsic Casorati curvature of submanifolds of generalized space forms endowed with a semi-symmetric metric connection. Moreover, we also characterize those submanifolds for which the equality cases hold.

• 대한수학회논문집
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• 제32권1호
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• pp.119-133
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• 2017

In this paper, we study half lightlike submanifolds of an indefinite Kaehler manifold with a semi-symmetric non-metric connection. First, we characterize the geometry of two types of half lightlike submanifolds of such an indefinite Kaehler manifold. Next, we investigate the geometry of half lightlike submanifolds of an indefinite complex space form with a semi-symmetric non-metric connection.

• 대한수학회지
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• 제54권1호
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• pp.101-115
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• 2017

In this paper, we study three types of lightlike hypersurfaces, which are called recurrent, Lie recurrent and Hopf lightlike hypersurfaces, of an indefinite Kaehler manifold with a semi-symmetric non-metric connection. We provide several new results on such three types of lightlike hypersurfaces of an indefinite Kaehler manifold or an indefinite complex space form, with a semi-symmetric non-metric connection.

• 대한수학회논문집
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• 제35권2호
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• pp.603-611
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• 2020

The purpose of this note is to introduce a type of Riemannian manifold called an almost quasi Ricci symmetric manifold and investigate the several properties of such a manifold on which some geometric conditions are imposed. And the existence of such a manifold is ensured by a proper example.

• 대한수학회논문집
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• 제11권1호
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• pp.209-214
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• 1996

A flat space is characterized by tube volumes about geodesic balls. Similar characterizations are also given for other rank one symmetric spaces.

• 한국공간구조학회논문집
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• 제19권4호
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• pp.69-76
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• 2019

A stadium roof that uses the pin-jointed spatial truss system has to be designed by taking into account the unstable phenomenon due to the geometrical non-linearity of the long span. This phenomenon is mainly studied in the single-free-node model (SFN) or double-free-node model (DFN). Unlike the simple SFN model, the more complex DFN model has a higher order of characteristic equations, making analysis of the system's stability complicated. However, various symmetric conditions can allow limited analysis of these problems. Thus, this research looks at the stability of the DFN model which is assumed to be symmetric in shape, and its load and equilibrium state. Its governing system is expressed by nonlinear differential equations to show the double Duffing effect. To investigate the dynamic behavior and characteristics, we normalize the system of the model in terms of space and time. The equilibrium points of the system unloaded or symmetrically loaded are calculated exactly. Furthermore, the stability of these points via the roots of the characteristic equation of a Jacobian matrix are classified.

• 한국항공우주학회지
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• 제38권8호
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• pp.790-797
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• 2010

마하수 1.0~1.2 범위의 초음속 제트에서 발생되는 축대칭 스크리치 톤 소음의 모드 전이 현상이 수치적으로 분석되었다. 이를 위해 k-e 난류모델을 가진 축대칭 Navier-Stokes 방정식이 사용되었으며 수치기법으로서 공간에 대해 소산관계보존기법과 시간에 대해 최적화된 4단계 시간 적분법이 사용되었다. 특히 낮은 마하수에서 발생하는 축대칭 A1 모드의 경우, 비선형성에 기인한 부가적인 음향파 발생을 확인하였으며, 강한 와류의 발생으로 인해 스크리치 소음 주파수는 와류 통과 주파수와 일치함을 알게 되었다.