• Bulletin of the Korean Chemical Society
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• v.35 no.10
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• pp.2906-2910
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• 2014

This report introduces Gaussian electrostatic models (GEMs) to account for charge penetration effects in water-water interactions, allowing electrostatic interactions to be accurately described. Three different Gaussian electrostatic models, GEM-3S, GEM-5S, and GEM-6S are designed with s-type Gaussian functions. The coefficients and exponents of the Gaussian functions are optimized using the electrostatic potential (ESP) fitting procedure based on that of the MP2/aug-cc-pVTZ method. The electrostatic energies of ten different water dimers that were calculated with GEM-6S agree well with the results of symmetry-adapted perturbation theory (SAPT), indicating that this designed model can be effectively applied to future water models.

• 전기의세계
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• v.29 no.10
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• pp.667-677
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• 1980

A new approach for optimal decentralized load-frequency control in a multi-area interconnected power system is presented, which includes the optimal determination of decentralized load-frequency controller, observer for unmeasurable local states and load disturbances, quadratic estimator for tie-line power flow information transmitted at intervals. The optimal design of the decentralized controller is based on a modified application of the singular perturbation theory, and the decentralized Luenberger obeserver uses techniques of state augmentation for exponential disturbance functions and the representation of tie-line power flow states as non-directly-controlled inputs. The approach presented herein is numerically tested through Elgerd's two-area load-frequency system model, and the results demonstrate remarkable advantages over the conventional ones.

• Journal of Advanced Marine Engineering and Technology
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• v.20 no.3
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• pp.144-153
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• 1996

The magnetic levitation system has many advantages, such as little friction, no lubrication, no noise and so on. For this reason, the magnetic levitation system is utilized in the magnetic bearing of high-speed rotor. The method to obtain magnetic force is both the repulsive suspension method and the attraction suspension method need a stabilizing controller because it is a unstable system in natural. This paper presents the design of robust stabilizing servo controller in spite of being the model uncertainties in the magnetic levitation system by $\textit{H}_{\infty}$ control theory using the free parameter. And we investigated the validity of a designed controller through results of the simulation and the actual experiment.

• Bulletin of the Korean Chemical Society
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• v.34 no.1
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• pp.179-187
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• 2013

We describe newly developed software named KPACK for relativistic electronic structure computation of molecules containing heavy elements that enables the two-component ab initio calculations in Kramers restricted and unrestricted formalisms in the framework of the relativistic effective core potential (RECP). The spin-orbit coupling as relativistic effect enters into the calculation at the Hartree-Fock (HF) stage and hence, is treated in a variational manner to generate two-component molecular spinors as one-electron wavefunctions for use in the correlated methods. As correlated methods, KPACK currently provides the two-component second-order M${\o}$ller-Plesset perturbation theory (MP2), configuration interaction (CI) and complete-active-space self-consistent field (CASSCF) methods. Test calculations were performed for the ground states of group-14 elements, for which the spin-orbit coupling greatly influences the determination of term symbols. A categorization of three procedures is suggested for the two-component methods on the basis of spin-orbit coupling manifested in the HF level.

• Journal of Ocean Engineering and Technology
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• v.26 no.5
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• pp.40-46
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• 2012

This paper considers a two-dimensional hydrofoil that is fully submerged and oscillating with forward speed. The flow field is assumed to be a propagating vertical velocity field. Using the perturbation theory, the problem is linearized, and the leading-order lift force is surveyed. The thrust force is analytically derived as the second-order horizontal force. As an example, the lift and thrust for a flapping flat plate in heaving and pitching modes are analyzed. The parameters affecting the thrust are listed. The thrust is expressed in terms of the quadratic transfer functions in relation to the disturbances. The quadratic transfer functions are studied parametrically to assess the most favorable thrust.

• Journal of Electrical Engineering and Technology
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• v.13 no.1
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• pp.418-429
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• 2018

This paper studies the decentralized position/force control problem for constrained reconfigurable manipulator without torque sensing. A novel joint torque estimation scheme that exploits the existing structural elasticity of the manipulator joint with harmonic drive model is applied for each joint module. Based on the estimated joint torque and dynamic output feedback technique, a decentralized position/force control strategy is presented. In order to solve the problem of controller parameter perturbation, the non-fragile robust technique is introduced into the dynamic output feedback controller. Subsequently, the stability of the closed-loop system is proved using the Lyapunov theory and linear matrix inequality (LMI) technique. Finally, two 2-DOF constrained reconfigurable manipulators with different configurations are applied to verify the effectiveness of the proposed control scheme in numerical simulation.

• Transactions on Electrical and Electronic Materials
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• v.17 no.1
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• pp.29-32
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• 2016

Using the various exchange-correlation functionals, such as LDA, GGA-PBE, GGA-PBEsol and GGA-AM05 functionals, first principle studies were conducted to determine the structures of paraelectric and ferroelectric PbTiO₃. Based on the structures determined by the various functionals, the piezoelectric properties of PbTiO₃ are predicted under the density-functional perturbation theory (DFPT). The present prediction with the various GGA functionals are closer to the experimental findings compared to the LDA values. The present DFT calculations using the GGA-PBEsol functional estimate the experimental data more reasonably than the conventional LDA and GGA fucntionals. The GGA-AM05 functional also predicts the experimental data as well as the GGA-PBEsol. The piezoelectric tensor calculated with PBEsol is relatively insensitive to pressure.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.9
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• pp.33-42
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• 1998

If a ship diesel engine is operated by consolidated control with Controllable Pitch Propeller(CPP), the minimum fuel consumption is achieved together with the demanded ship speed. For this, it is necessary that the ship is operated on the ideal operating line which satisfies the minimum fuel consumption and that the pitch angle of CPP and throtle valve angle are controlled simultaneously. In this point of view, this paper presents a controller design method for a ship propulsion system with CPP based on the decoupling control theory. To do this, Linear Matrix Inequality(LMI) approach is introduced for the control system to satisfy the given $H_\infty$ control performance and robust stability in the presence of physical parameter perturbations. The validity and applicability of this approach are illustrated by simulation in the all operating ranges.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.10a
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• pp.138-144
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• 1997

The analysis of lateral hydrodynamic forces from the compressor labyrinth seals is presented. The basic equations are derived using a two-control-volume model for compressible flow. Blasius' wall friction-factor formula and jet flow theory are used for the calculation of the wall shear stresses and the recirculation velocity in the cavity. Linearized zeroth-order and first-order perturbation equations are developed for small motion about a centered position by an expansion in the eccentricity ratio. Integration of the resultant first-order pressure distribution along and around the seal defines the rotordynamic coefficients of the labyrinth seal. The rotordynamic analysis for the balance drum labyrinth seal of an ethylene refrigeration compressor is carried out. The results of rotordynamic characteristic of the labyrinth seal and comparisons with other types of seal, honeycomb seal and smooth seal, are presented.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.16 no.3
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• pp.151-167
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• 2012

In this paper, we investigate the dynamic behaviors of a one-prey and two-predator system with Holling-type II functional response and defensive ability by introducing a proportion that is periodic impulsive harvesting for all species and a constant periodic releasing, or immigrating, for predators at different fixed time. We establish conditions for the local stability and global asymptotic stability of prey-free periodic solutions by using Floquet theory for the impulsive equation, small amplitude perturbation skills. Also, we prove that the system is uniformly bounded and is permanent under some conditions via comparison techniques. By displaying bifurcation diagrams, we show that the system has complex dynamical aspects.