• Bulletin of the Korean Chemical Society
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• v.12 no.1
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• pp.67-70
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• 1991

A hexagonal hexamer of water cluster is optimized by ab initio method using the 4-31G basis set. At this geometry the nonadditive many-body interactions are calculated. The ab initio calculation with large basis set [T. H. Dunning, J. Chem. Phys., 53, 2823 (1970); 54, 3958 (1971)] shows that a pentagonal unit is rather stable among several kinds of clustering units of water molecules.

• Bulletin of the Korean Chemical Society
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• v.11 no.5
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• pp.422-426
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• 1990

Fully optimized MNDO molecular orbital calculations are described for N-nitroso-aziridine (I), -oxaziridine (II), and -dioxaziridine (III). The ground state geometries show the nonplanar configuration around the imino nitrogen. The nitroso group rotational energy barriers are 3.25, 0.43 and 1.18 kcal/mol for I, II and III, respectively. Also the calculated aziridine ring inversion barriers are 3.98, 15.61 and 27.46 kcal/mol for I, II and III, respectively.

• Journal of Advanced Navigation Technology
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• v.14 no.2
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• pp.161-169
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• 2010

According to the recent increase in air traffic more efficient air traffic control is required. This paper proposes the algorithm for efficient air traffic flow management. Aeronautical traffic environment is different from the common traffic environment since it needs vertical and horizontal separation deviation. In this paper used vincenty's fomula, we calculated distance of route for produced weight that was applied air traffic volume in distance of route using dijkstra algorithm. Then we let aircraft selects a course that minimize to wasting of fuel and time. As a simulation result, so unlilke simply shortest course calculation of existing course calculation algorithm, we confirmed that proposed algorithm in this paper can do air traffic control more efficiently by selecting optimized route.

• Journal of Power Electronics
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• v.14 no.2
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• pp.315-323
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• 2014

An optimized space vector pulse width modulation (SVPWM) method with common mode voltage elimination and neutral point potential balancing is proposed for an open-end winding induction motor. The motor is fed from both of the ends with two neutral point clamped (NPC) three-level inverters. In order to eliminate the common mode voltage of the motor ends and balance the neutral point potential of the DC link, only zero common mode voltage vectors are used and a balancing control factor is gained from calculation in the strategy. In order to improve the harmonic characteristics of the output voltages and currents, the balancing control factor is regulated properly and the theoretical analysis is provided. Simulation and experimental results show that by adopting the proposed method, the common mode voltage can be completely eliminated, the neutral point potential can be accurately balanced and the harmonic performance for the output voltages and currents can be effectively improved.

• Journal of Power Electronics
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• v.18 no.4
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• pp.1268-1277
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• 2018

A relatively high operating frequency is required for efficient wireless power transfer (WPT). However, the alternating current (AC) resistance of coils increases sharply with operating frequency, which possibly degrades overall efficiency. Hence, the evaluation of coil AC resistance is critical in selecting operating frequency to achieve good efficiency. For a Litz wire coil, AC resistance is attributed to the magnetic field, which leads to the skin effect, the proximity effect, and the corresponding conductive resistance and inductive resistance in the coil. A numerical calculation method based on the Biot-Savart law is proposed to calculate magnetic field strength over strands in Litz wire planar spiral coils to evaluate their AC resistance. An optimized frequency can be found to achieve the maximum efficiency of a WPT system based on the predicted resistance. Sample coils are manufactured to verify the resistance analysis method. A prototype WPT system is set up to conduct the experiments. The experiments show that the proposed method can accurately predict the AC resistance of Litz wire planar spiral coils and the optimized operating frequency for maximum efficiency.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.10
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• pp.139-145
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• 1996

The machining accuracy and performance is largely influenced by the static, dynamic and thermal characteristics of spindle systems in machine tools, because the spindle system is a intermedium for cutting force from tool and machine powef from motor. Large cutting force and power are transmitted by bearing with a point or line contact. So, the spindle system is the static and dynamic weakest point in machine structure. For improvement of static stiffness of spindle system can be changed design parameters, such as diameter of spindle, stiffness of bearing and bearing span. But for dynamic stiffness, the change of the design parameters are not useful. In this paper, the combined bearing arrangement is suggested for high damping spindle system. The combined bearing arrangement is composed of tandem double back to back arrangement type ball bearins and a high damping hydrostatic bearing. The variation of static deflection and amplitude in first natural frequency is evaluated with the location of hydrostatic bearing between front and rear ball bearing. The optimized location of hydrostatic bearing for high static and dynamic stiffness is determined rapidly and exactly using the mode shape and transfer function of spindle. The calculation of damping effect on vibration by unbalance of grinding wheel and pulley in optimized spindle system is carried out to verify the validity of the combined bearing arrangement. Finally, the simulation of grinding process show that the surface roughness of workpiece with high damping spindle system is 60% better than with ball bearing spindle system.

• Nuclear Engineering and Technology
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• v.32 no.3
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• pp.244-253
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• 2000

A Simple Large Model (SLM), which can be used to make thermal calculation for a deep geological repository with finite number of HLW canisters, was developed. In order to develop the SLM, a Simple Basic Model (SBM), which will be a unit of the SLM, was optimized first. The SBM was optimized to achieve the same maximum buffer temperature as that of the Detailed Basic Model (DBM) representing the real geometric aspects of the repository. In contrast to the models with the assumption of infinite number of canisters which cannot consider boundary effect, the SLM can model the real repository with finite number of canisters and thus consider the boundary effect. Thermal results from the SLM can be used to evaluate the reliability of the models, which do not consider boundary effect. This model can also be used to simulate the thermal layout design and to analyze the thermal safety of a deep geological repository as well as an underground laboratory.

• Environmental Engineering Research
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• v.22 no.2
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• pp.175-185
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• 2017

As the energy and environmental problems are increasingly severe, researches about carbon dioxide emissions has aroused widespread concern. The accurate prediction of carbon dioxide emissions is essential for carbon emissions controlling. In this paper, we analyze the relationship between carbon dioxide emissions and influencing factors in a comprehensive way through correlation analysis and regression analysis, achieving the effective screening of key factors from 16 preliminary selected factors including GDP, total population, total energy consumption, power generation, steel production coal consumption, private owned automobile quantity, etc. Then fruit fly algorithm is used to optimize the parameters of least squares support vector machine. And the optimized model is used for prediction, overcoming the blindness of parameter selection in least squares support vector machine and maximizing the training speed and global searching ability accordingly. The results show that the prediction accuracy of carbon dioxide emissions is improved effectively. Besides, we conclude economic and environmental policy implications on the basis of analysis and calculation.

• Bulletin of the Korean Chemical Society
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• v.24 no.9
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• pp.1333-1338
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• 2003

Hollow Fiber flow field-flow fractionation (HF-FlFFF) has been tested in polyacrylonitrile (PAN) membrane channel in order to compare it with polysulfone (PSf) membrane channel. It has been experimentally shown that the separation time of 0.05-0.304 ${mu}m$ polystyrene latex (PSL) standards in PAN membrane channel is shorter than that in PSf channel by approximately 65%. The optimized separation condition in PAN membrane is ${\dot V}_{out}/{\dot V}_{rad}=1.4/0.12\;mL/min$, which is equal to the condition in PSf membrane channel. In addition both the resolution ($R_s$) and plate height (H) in PAN membrane channel are better than that in PSf membrane channel. The membrane radius was obtained by back calculation with retention time. It shows that the PSf membrane is expanded by swelling and pressure, but the PAN membrane doesn't expand by swelling and pressure.

• Bulletin of the Korean Chemical Society
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• v.30 no.12
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• pp.2973-2978
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• 2009

The decomposition reaction mechanism of $CH_3CF_2O$ radical formed from hydroflurocarbon, $CH_3CHF_2$ (HFC-152a) in the atmosphere has been investigated using ab-initio quantum mechanical methods. The geometries of the reactant, products and transition states involved in the decomposition pathways have been optimized and characterized at DFT-B3LYP and MP2 levels of theories using 6-311++G(d,p) basis set. Calculations have been carried out to observe the effect of basis sets on the optimized geometries of species involved. Single point energy calculations have been performed at QCISD(T) and CCSD(T) level of theories. Out of the two prominent decomposition channels considered viz., C-C bond scission and F-elimination, C-C bond scission is found to be the dominant path involving a barrier height of 12.3 kcal/mol whereas the F-elimination path involves that of a 28.0 kcal/mol. Using transition-state theory, rate constant for the most dominant decomposition pathway viz., C-C bond scission is calculated at 298 K and found to be 1.3 ${\times}$ 10$^4s{-1}$. Transition states are searched on the potential energy surfaces involving both decomposition channels and each of the transition states are characterized. The existence of transition states on the corresponding potential energy surface are ascertained by performing Intrinsic Reaction Coordinate (IRC) calculation.