• Journal of the Korean Mathematical Society
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• v.44 no.3
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• pp.647-659
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• 2007

Relationships between the Ricci curvature and the squared mean curvature and between the shape operator associated with the mean curvature vector and the sectional curvature function for slant submanifolds of an S-space-form are proved, particularizing them to invariant and anti-invariant submanifolds tangent to the structure vector fields.

• Proceedings of the KIPE Conference
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• 1998.07a
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• pp.280-286
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• 1998

In this paper, space voltage vector pulsewidth modulation for 2-phase inverter is proposed. When this method is appled to 2-phase induction motor, the phase difference of voltage between phase A and B is fixed at $90^{\circ}$and amplitude of voltage of phase Ais same with that of phase B. This method have advantages over low-power servo system because this is simple method comparing to 3-phase space vector method which requires d-q transform.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.9 no.1
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• pp.16-19
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• 2009

In this paper, we study the existence and uniqueness of solutions for the fuzzy differential equations in n-dimension fuzzy vector space $(E_N)^n$ using by Banach fixed point theorem.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 2008.04a
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• pp.23-25
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• 2008

In this paper, we study the existence and uniqueness of solutions for the fuzzy differential equations in ${(E_N)^n}$ using by Banach fixed point theorem. ${(E_N)^n}$ is n-dimension fuzzy vector space.

• Honam Mathematical Journal
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• v.43 no.1
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• pp.78-87
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• 2021

In this study, we firstly compute the energies and the angles of Frenet vector fields in Lorentz 5-space ��5. Then we obtain the bienergies and biangels of Frenet vector fields in ��5 by using the values of energies and angles. Finally, we present the relations among energies, angles, bienergies, and biangles with graphics.

• Communications of the Korean Mathematical Society
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• v.37 no.4
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• pp.1199-1207
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• 2022

In the present paper, a Riemannian submersion 𝜋 between Riemannian manifolds such that the total space of 𝜋 endowed with a torse-forming vector field 𝜈 is studied. Some remarkable results of such a submersion whose total space is Ricci soliton are given. Moreover, some characterizations about any fiber of 𝜋 or the base manifold B to be an almost quasi-Einstein are obtained.

• Journal of Astronomy and Space Sciences
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• v.29 no.3
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• pp.287-293
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• 2012

Satellite operating agencies are constantly monitoring conjunctions between satellites and space objects. Two line element (TLE) data, published by the Joint Space Operations Center of the United States Strategic Command, are available as raw data for a preliminary analysis of initial conjunction with a space object without any orbital information. However, there exist several sorts of uncertainties in the TLE data. In this paper, we suggest and analyze a method for estimating the uncertainties in the TLE data through mean, standard deviation of state vector residuals and covariance matrix. Also the estimation results are compared with actual results of orbit determination to validate the estimation method. Characteristics of the state vector residuals depending on the orbital elements are examined by applying the analysis to several satellites in various orbits. Main source of difference between the covariance matrices are also analyzed by comparing the matrices. Particularly, for the Korea Multi-Purpose Satellite-2, we examine the characteristics of the residual variation of state vector and covariance matrix depending on the orbital elements. It is confirmed that a realistic consideration on the space situation of space objects is possible using information from the analysis of mean, standard deviation of the state vector residuals of TLE and covariance matrix.

• The Transactions of the Korean Institute of Power Electronics
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• v.3 no.2
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• pp.118-124
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• 1998

This paper describes a relationship of a space vector PWM and a sinusoidal PWM and presents that the space vector PWM can produce linearly the output voltage to the unity MI(modulation index). At first, reference angles and holding angles are derived from expanding a Fourier series of the reference voltage waveform and then the angles are used for the inverter switching to linearize transfer characteristics of the inverter. In addition, the harmonic components of the output voltage are analyzed and on-line control is shown to be feasible by approximating in piecewise-linearization the reference and holding angles versus the MI. In V/f control of the induction motor, it is verified by the experiment that the motor current is changed smoothly for the variation of the inverter input voltage and the change of the reference voltage.

• Journal of Power Electronics
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• v.16 no.4
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• pp.1336-1345
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• 2016

A modified space vector pulse width modulation (SVPWM) strategy based on vector space decomposition and its equivalent carrier-based PWM realization are proposed in this paper, which is suitable for six-phase asymmetrical dual stator induction machines (DSIMs). A DSIM is composed of two sets of symmetrical three-phase stator windings spatially shifted by 30 electrical degrees and a squirrel-cage type rotor. The proposed SVPWM technique can reduce torque ripples and suppress the harmonic currents flowing in the stator windings. Above all, the equivalent relationship between the proposed SVPWM technique and the carrier-based PWM technique has been demonstrated, which allows for easy implementation by a digital signal processor (DSP). Simulation and experimental results, carried out separately on a simulation system and a 3.0 kW DSIM prototype test bench, are presented and discussed.

• Journal of Institute of Control, Robotics and Systems
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• v.5 no.7
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• pp.821-826
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• 1999

This paper proposes a face recognition method using feature spaces and image vectors in the image plane. We obtain the 2-D feature space using the self-organizing map which has two inputs from the axis of the given image. The image vector consists of its weights and the average gray levels in the feature space. Also, we can reconstruct an normalized face by using the image vector having no connection with the size of the given face image. In the proposed method, each face is recognized with the best match of the feature spaces and the maximum match of the normally retrieval face images, respectively. For enhancing recognition rates, our method combines the two recognition methods by the feature spaces and the retrieval images. Simulations are conducted on the ORL(Olivetti Research laboratory) images of 40 persons, in which each person has 10 facial images, and the result shows 100% recognition and 14.5% rejection rates for the 20$\times$20 feature sizes and the 24$\times$28 retrieval image size.