• Bulletin of the Korean Mathematical Society
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• v.46 no.2
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• pp.255-261
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• 2009

In this paper, we shall prove several results concerning Ricci curvature of a Riemannian manifold (M, g) := (SU(2), g) with an arbitrary given left invariant metric g. First of all, we obtain the maximum (resp. minimum) of {r(X) := Ric(X,X) | ${||X||}_g$ = 1,X ${\in}$ X(M)}, where Ric is the Ricci tensor field on (M, g), and then get a necessary and sufficient condition for the Levi-Civita connection ${\nabla}$ on the manifold (M, g) to be projectively flat. Furthermore, we obtain a necessary and sufficient condition for the Ricci curvature r(X) to be always positive (resp. negative), independently of the choice of unit vector field X.

• 제어로봇시스템학회:학술대회논문집
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• 2002.10a
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• pp.68.5-68
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• 2002

For the performance test of rechargeable electric tools, it is necessary to test under the same condition as the actual operation condition. They are necessary to control the load torque and to acquire the test data with a computer, and it should be convenient to fix the tool on the test equipment for rechargeable electric tools. It consists of torque loading parts, sensing parts and control software. Two hysteresis brakes, connected serially with flexible coupling, were applied to control the load for the test. The sensing part consists of a torque sensor, a rpm detector and a power analyzer. The torque and the rpm were measured in order to calculate the output of the rechargeable electric...

• Honam Mathematical Journal
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• v.41 no.4
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• pp.669-682
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• 2019

The objective of this paper is to introduce and study Einstein-like para-Kenmotsu manifolds. For a para-Kenmotsu manifold to be Einstein-like, a necessary and sufficient condition in terms of its curvature tensor is obtained. We also obtain the scalar curvature of an Einstein-like para-Kenmotsu manifold. A necessary and sufficient condition for an almost para-contact metric hypersurface of a locally product Riemannian manifold to be para-Kenmotsu is derived and it is shown that the para-Kenmotsu hypersurface of a locally product Riemannian manifold of almost constant curvature is always Einstein.

• 제어로봇시스템학회:학술대회논문집
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• 1990.10b
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• pp.1150-1155
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• 1990

This paper proposes an optimal redundancy resolution of a kinematically redundant manipulator while considering homotopy classes. The necessary condition derived by minimizing an integral cost criterion results in a second-order differential equation. Also boundary conditions as well as the necessary condition are required to uniquely specify the solution. In the case of a cyclic task, we reformulate the periodic boundary value problem as a two point boundary value problem to find an initial joint velocity as many dimensions as the degrees of redundancy for given initial configuration. Initial conditions which provide desirable solutions are obtained by using the basis of the null projection operator. Finally, we show that the method can be used as a topological lifting method of nonhomotopic extremal solutions and also show the optimal solution with considering the manipulator dynamics.

• Journal of the Korean Solar Energy Society
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• v.36 no.5
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• pp.51-62
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• 2016

The purpose of this paper is to study the effectiveness of a green roof by simple mathematical model. The developed model simulates a green roof during the summer. The results explain and support the claims in the literature such that effectiveness of a green roof depends on the climate condition, and on the insulation condition of the roof. If insolation can not be reduced more than 60% by the shading effects of a green roof, more active measures than green roof seem necessary. The analysis tools like presented in the paper is necessary especially to consider climate effect, to design, and also to test green roof.

• Communications of the Korean Mathematical Society
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• v.19 no.2
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• pp.355-373
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• 2004

An extended directed triple system of order v, denoted by EDTS(v), is a pair (V, (equation omitted)) where V is a v-set and (equation omitted) is a set of transitive triples of elements of V such that every ordered pair of elements of V is contained in exactly one member of (equation omitted). We obtain a necessary and sufficient condition for the existence of cyclic EDTS(v)s, and when k=1 or 2, we also obtain a necessary and sufficient condition for the existence of k-rotational EDTS(v)s.

• 제어로봇시스템학회:학술대회논문집
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• 2000.10a
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• pp.286-286
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• 2000

We consider a negative unity feedback control system in which Che PIO, PI, PD or P controller and a transfer function having only poles are in cascade, We define the notion of the structural polynomial which means that there exists a subdomain of the coefficient space in which the polynomial is Hurwitz (left half plane stable) polynomial. We obtain the necessary and sufficient condition of the structure of the transfer function of which the characteristic polynomial is a structural polynomial, In addition, this paper present another necessary and sufficient condition for the existence of a constant gain controller with which the characteristic polynomial is structurally stable, For the structurally stabilizable P controller, it is allowed that the transfer function may not to all pole plants.

• Proceedings of the KIEE Conference
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• 1997.07e
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• pp.1804-1806
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• 1997

Route conditions, applied voltage and the condition of stringing conductors should be considered in determining standard types and skeleton diagrams of towers. In skeleton diagrams the necessary number of insulators and the air clearance have been decided by the results of studies on insulation coordination. Galloping, sleet-jumping, sag characteristics and the possibility of closeness of conductors should be considered according to the condition of stringing conductor and the span. After reviewing those factors, it is necessary to determine the minimum vertical and horizontal distance for the safety of transmission lines under any circumstances. Also it should be economical.

• Proceedings of the CALSEC Conference
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• 2003.09a
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• pp.172-177
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• 2003

As the electronic commerce in industry is spreading rapidly, the invitation and investment of e-marketplace is becoming a necessary condition for the industry's competition power insurance and existence. The successful conditions of e-marketplace are many supplier, many buyer, a globalism through the association and cooperation of a foreign marketplace. For that, the connection action inter industries and marketplaces is very necessary, In a condition of the study about the systematic connection type's classification is not exist, the paper aims at classifying the connection type that influences of e-marketplace playing a leading role. So, the connection type classifies into the list offering type, the trade mediation type, the supplementation type, the collaboration type, the information linking type. When we go ahead with a e-marketplace's plan, the paper will guide how to approach and analyze it.

• Proceedings of the KIEE Conference
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• 1998.11b
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• pp.413-416
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• 1998

We investigate the Hurwitz stability condition using the coefficient diagram. The coefficient diagram consists of a plot of logarithmic values of the coefficients of the characteristic polynomial versus the degree of the coresponding coefficients. The logarithmic value of the coefficient of the characteristic polynomials are plotted in the descending order. Using the Bhattacharyya, Chapellat and Keel's algorithm, the sufficient and necessary condition for Hurwitz stability are reconstructed using the coefficient diagram. With the coefficient diagram we also present some necessary or sufficient conditions for Hurwitz stability of polynomials. In addition we obtain a lower bound for the Manabe parameter $\tau$.