• Bulletin of the Korean Mathematical Society
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• v.25 no.2
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• pp.171-174
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• 1988

Let M be an n-dimensional compact connected and oriented Riemannian manifold isometrically immersed in an (n+2)-dimensional Euclidean space $R^{n+2}$. Moore [5] proved that if M is of positive curvature, then M is a homotopy sphere. This result is generalized by Baldin and Mercuri [2], Baik and Shin [1] to the case of non-negative curvature, which is stated as follows: If M of non-negative curvature, then M is either a homotopy sphere or diffeomorphic to a product of two spheres. In particular, if there is a point at which the curvature operator is positive, then M is homeomorphic to a sphere.e.

• Journal of the Society of Disaster Information
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• v.14 no.4
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• pp.466-473
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• 2018

Purpose: Nowadays, it is the trend that seismic isolation method and combined method are used for seismic retrofitting, if concrete sphere foundation(CSF) system is applied to mid and low rise RC structure for the seismic isolation, the characteristics of concrete sphere, etc split tensile strength will be need. Method: The various experiments are carried out to know the split strength of high strength concrete sphere(60Mpa) and the ratio of split strength of concrete sphere to standard cylinder specimen, the size effect of concrete sphere with diameter. Results: It was purposed that the split strength of concrete sphere with diameter 150mm will be lower than that of cylinder specimen but, the average value is 4.39 Mpa and the ratio is higher than that of cylinder specimens, each 3.8% and 13.7%, the reason of this result is thought that the internal stress action of spot load and line load are different. Conclusion: There is a standard method for split tensile strength of cylinder type specimen, but there are few studies for the tensile split of concrete sphere. And therefore, in this study, theoretical and experimental details of concrete sphere will be served for the concrete sphere foundation or other sequent studies.

• Korean journal of communication and information
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• v.27
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• pp.153-181
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• 2004

This study tries 'interdisciplinary research' regarding the formation process of public sphere and the modern media on the Korean society. From the process where the civil society of modern ages is formed, the public sphere was condition that pulls down the feudal system of medieval Europe and appears the civil society. The modern newspaper collected the public opinion from lower part and did play a leading role which forms public sphere in Europe. Even from Korea the literary public sphere and political public sphere were developing inside the Chosun Dynasty period from lower part since 18th century. However the opening of a port became accomplished before making the printing media which is newspaper. As a result the public sphere in Korea was accomplished a conflict-structure. This study cleared where the crisis of Korean journalism is originated by presenting a conflict-structure differently with a transplantation theory or a graft hybrid hypothesis.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.3
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• pp.280-285
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• 2023

A breakdown voltage and breakdown electric field of the transformer insulating oil of liquid dielectric were studied in uniform electric field and non-uniform electric field and the transformer insulating oil was observed by the process reached breakdown. Insulation performance evaluation of the liquid dielectric was evaluated at the electrode spacing of 2.5 mm under the conditions of domestic and international standards (KS C IEC 60156), so a comparative review was conducted at the electrode spacing of 2.5 mm. When the electrode spacing is 2.5 mm, the average breakdown voltage is 38.5 kV for sphere-sphere electrodes, 26.6 kV for plate-plate electrodes, 22.9 kV for needle-needle electrodes, and 24.3 kV for sphere-needle electrodes. 23.7 kV for the sphere-plate electrode, and 20.7 kV for the needle-plate electrode. From these results, it can be seen that the average value of the breakdown voltage at the electrode spacing of 2.5 mm, in ascending order, is sphere-sphere, plate-plate, sphere-needle, sphere-plate, needle-needle and needle-plate. It was found that the breakdown voltage of the unequal field was lower than that of the equal field.

• Journal of the Korean Mathematical Society
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• v.41 no.4
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• pp.755-772
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• 2004

We show that the Fourier-Laplace series of a distribution on the sphere is uniformly Cesaro-summable to zero on a neighborhood of a point if and only if this point does not belong to the support of the distribution. Similar results on the ball and on the real projective space are also proved.

• The Pure and Applied Mathematics
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• v.3 no.2
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• pp.173-179
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• 1996

M be an ($n\geq3$)-dimensional compact connected and oriented Riemannian manifold isometrically immersed on an (n ＋ 2)-dimensional sphere $S^{n＋2}$(c). If all sectional curvatures of M are not less than a positive constant c, show that M is a real homology sphere.

• The Pure and Applied Mathematics
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• v.5 no.1
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• pp.79-86
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• 1998

In this paper, we study an (n ＋ 1)-dimensional compact, orientable, minimal contact CR-submanifold of (n - 1) ontact CR-dimension in a (2m ＋ 1)-dimensional unit sphere $S^{2m＋1}$ in terms of integral formula.

• Honam Mathematical Journal
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• v.41 no.3
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• pp.609-617
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• 2019

We characterize two-point homogeneous spaces M by means of the structural operator $h={\frac{1}{2}}{\mathcal{L}}_{\xi}{\phi}$ or the characteristic Jacobi operator ${\ell}=R({\cdot},{\xi}){\xi}$ on the unit tangent sphere bundles $T_1M$.

• Honam Mathematical Journal
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• v.42 no.4
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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.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2753-2756
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• 2007

In the present study, we reduce the drag and lift fluctuations of the sphere by providing a linear proportional control. For this purpose, we measure the radial velocity along the centerline in the wake and provide blowing and suction at a part of sphere surface based on the measured velocity. Zero-net mass flow rate is satisfied during the control. This control is applied to the flow over a sphere at Re=300 and 425. We vary the sensing location at $0.8d{\leq}X_s{\leq}1.3d$ and find that the most effective sensing region coincides with the location at which minimum correlation between the lift and sensing-velocity directions occurs. As a result, the lift and drag fluctuations are significantly reduced.