• Journal of Power Electronics
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• v.16 no.4
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• pp.1598-1611
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• 2016

In some special occasions with strict size requirements, such as mine hoists, improving the design accuracy of the forced-air cooling systems of NPC three-level inverters is a key technology for improving the power density and decreasing the volume. First, a fast power-loss calculation method was brought. Its calculation principle introduced in detail, and the computation formulas were deduced. Secondly, the average and dynamic power losses of a 1MW mine hoist acting as the research target were analyzed, and a forced-air cooling system model based on a series of theoretical analyses was designed with the average power loss as a heat source. The simulation analyses proves the accuracy and effectiveness of this cooling system during the unit lifting period. Finally, according to an analysis of the periodic working condition, the maximum power-loss range of a NPC three-level inverter under multi cycle operation was obtained and its dynamic power loss was taken into the optimized cooling system model as a heat source to solve the power device damage caused by instantaneous heat accumulation. The effectiveness and feasibility of the optimization design based on the dynamic power loss calculation of the maximum power-loss range was proved by simulation and experimental results.

• Proceedings of the KIEE Conference
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• 2001.04a
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• pp.44-46
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• 2001

This paper describes the use of the PHOENICS CFD package for the simulation of the high-current period of the arcing process in a hybrid rotating arc/auto expansion by interrupter. The operating principle of this device depends on rapid arc rotation due to the magnetic field created by the fault current through a coil which is mounted on contacts and also relies on the principle of thermal expansion created by arc energy in extinguishing chamber and finally causes pressure rise in expansion volume. This paper is divided into three main sections. The first gives a brief overview of the interrupter. The second section gives a full description of the methods used in the calculation. The final section presents some sample results for the hybrid interrupter.

• Bulletin of the Korean Chemical Society
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• v.12 no.2
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• pp.228-238
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• 1991

Generalized multichannel quantum defect theory [C. H. Greene et al. Phys. Rev., A26, 2441 (1982)] is implemented to the vibrational predissociation of triatomic van der Waals molecules. As this is the first one of such an application, the dependences of the quantum defect parameters on energy and radius are examined carefully. Calculation shows that, in the physically important region, quantum defect parameters remain smoothly varying functions of energy for this system as in atomic applications, thus allowing us very coarse energy mesh calculations for the photodissociation spectra. The choice of adiabatic or diabatic potentials as reference potentials for the calculation of quantum defect parameters as done by Mies and Julienne [J. Chem. Phys., 80, 2526 (1984)] can not be used for this system. Physically motivated reference potentials that may be generally applicable to all kinds of systems are utilized instead. In principle, implementation can be done to any other predissociation processes with the same method.

• Journal of the Korean Electrochemical Society
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• v.14 no.1
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• pp.33-37
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• 2011

$Li_4Ti_5O_{12}$ has been considered a potential material for high power lithium batteries. Since $Li_4Ti_5O_{12}$ is however an insulator having a broad band gap, various methods have been employed to improve the conductivity. In this study, we have investigated the change of fine structure and electronic structure by Cr doping using X-ray absorption spectroscopy and First Principle Calculation. Doping with Cr, we could obtain an enhanced electronic conductivity by locating the Fermi level at the center position of Cr d-band and identify the change of XANES pre-edge and white line peak due to the increase of electron density of Ti d-band.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.11a
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• pp.148-151
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• 2003

The spin density of ${\beta}-MnO_2$ structure was theoretically investigated by $DV-X_{\alpha}$ (the discrete variation $X{\alpha}$) method, which is a sort of the first principle molecular orbital method using Hatre-Fock-Slater approximation. The used cluster model was $[Mn_{14}O_{56}]^{-52}$. The ${\beta}-MnO_2$ is a paramagnetic oxide semiconductor material having the energy band gap of 0.18 eV and an 3 loan-pair electrons in the 3d orbital of an cation. This material exhibits spin-only magnetism and has the magnetic ordering temperature of 94 K. Below this temperature its magnetism appears as antiferromagnetism. The calculations of electronic state showed that if the initial spin condition of input parameters changed, the magnetic state changed from paramagnetic to antiferromagnetic. When d orbital of all Mn atoms in cluster had same initial spin state as only up spin, paramagnetic spin density distribution appeared by the calculation. On the other way, d orbital had alternately changed spin state along special direction the resulted spin distribution showed antiferromagnetism.

• Journal of the Korean Magnetics Society
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• v.15 no.6
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• pp.299-302
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• 2005

We investigated the structural md magnetic properties of Fe-Pt nanowires with linear and zigzag structures by using first-principle calculational methods. Structural degrees of freedom are optimized, the bond lengths and bond angles are determined, magnetic moments, spin density, and density of states are calculated. Results show that the zigzag structure is more stable than the linear one, and has a longer bond length and smaller magnetic moments for both Fe and Pt atoms.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.11a
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• pp.99-102
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• 2003

The electronic structure of ${\beta}-MnO_2$ having impurities in the site of Mn was theoretically investigated by $DV-X_{\alpha}$ (the discrete variation $X{\alpha}$) method, which is a sort of the first principle molecular orbital method using Hatre-Fock-Slater approximation. The used cluster model was $[Mn_{14}MO_{56}]^{-52}$ (M = transient metals). Madelung potential and spin polarization were considered for more exact calculations. As results of calculations, the energy levels of all electron included in the model were obtained. The energy band gap and positions of impurity levies were discussed in association with impurity 34 orbital that seriously affect electrical properties of $MnO_2$. It was shown that the energy band gap decreased with the increase of the atomic number of transient metal impurity.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.259-262
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• 2003

The surface electronic state of rutile $TiO_2$, which is an oxide semiconductor and has a wide band gap of 3.1 $\sim$ 3.5 eV, was calculated by DV-$X_{\alpha}$ method, which is a sort of the first principle molecular orbital method and uses Hartre-Fock-Slater approximation. The $[Ti_{15}O_{56}]^{-52}$ cluster model was used for the calculation of bulk state and the $[OTi_{11}O_{34}]^{-24}$ model for the surface state calculation. After calculations, the energy level diagrams and the deformation electron density distribution map were compared in both models. As results, it was identified that the surface energy levels are found between the valence and conduction band of bulk $TiO_2$ on the surface area. The energy values of these surface-induced levels are lower than conduction band of bulk $TiO_2$ by 0.1 $\sim$ 1 eV. From this fact, it is expected that the surface energy levels act as donar levels in n-type semiconductor.

• Journal of the Korean Magnetics Society
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• v.17 no.4
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• pp.152-155
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• 2007

We have studied electronic structures and magnetic properties of $YMnO_3,\;ScManO_3$ with hexagonal structure using Full Potential Linearized Augmented Plane Wave (FLAPW) method based on LSDA method. LSDA calculation results show that multiferroic $YMnO_3$ shows energy gap due to hexagonal symmetry and magnetic interaction. Because of insulating gap and small Y ion, $YMnO_3$ shows magnetic and ferroelectric state. However, $ScMnO_3$ does not show the energy gap because of strong hybridization of Mn-O for LSDA calculation. We confirmed the stability of multiferroic state for $YMnO_3\;and\;ScManO_3$ using total energy calculations. The antiferromagnetic and ferroelectric states have the lowest energy about 100 meV.

• Journal of Physiology & Pathology in Korean Medicine
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• v.33 no.3
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• pp.163-168
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• 2019

In order to enhance the 8 principle pattern diagnosis rate comparing with diagnostic method by self-report questionnaire on cold/heat pattern in the clinical practice, a new diagnostic method using form-color-pulse-symptom (FCPS) system is proposed. FCPS system is composed of outputs of cold/heat pattern through the calculation process of contribution degree to the cold, heat pattern and qi, blood, yin, yang deficiency patterns, based on analysis of 16 mechanisms of disease calculated by diagnostic system of oriental medicine (DSOM) first. And second component is an output of differentiated 8 principle patterns in detail through binding and calculating process with digital informations of pulse, color, form, constitution obtained by computerized measurement system. Putting together above two processes consecutively, cold-heat complex or true/false cold/heat patterns and personalized characters of cold/heat patterns of each patient can be subdivided through a computation method of determining each pattern. In conclusion, 8 principle pattern identification can be performed more accurately using FCPS system than existent self report questionnaire method. These hypothetic proposal is needed to be proven by clinical trial for the future and then the accurate numbers used in each calculational function should be revised properly.