• Journal of applied mathematics & informatics
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• v.32 no.5_6
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• pp.585-598
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• 2014

In this paper we consider the nonlinear parabolic problems with mixed boundary condition. Under comparatively mild conditions of the coefficients related to the problem, we construct the discontinuous Galerkin approximation of the solution to the nonlinear parabolic problem. We discretize spatial variables and construct the finite element spaces consisting of discontinuous piecewise polynomials of which the semidiscrete approximations are composed. We present the proof of the convergence of the semidiscrete approximations in $L^{\infty}(H^1)$ and $L^{\infty}(L^2)$ normed spaces.

• Journal of the Korean Mathematical Society
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• v.51 no.1
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• pp.67-86
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• 2014

Based on an expanded mixed finite element method, we consider the semidiscrete approximations of the solution u of the quasilinear pseudo-parabolic equation defined on ${\Omega}{\subset}R^d$, $1{\leq}d{\leq}3$. We construct the semidiscrete approximations of ${\nabla}u$ and $a(u){\nabla}u+b(u){\nabla}u_t$ as well as u and prove the existence of the semidiscrete approximations. And also we prove the optimal convergence of ${\nabla}u$ and $a(u){\nabla}u+b(u){\nabla}u_t$ as well as u in $L^2$ normed space.

• Korean Management Science Review
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• v.25 no.1
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• pp.55-74
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• 2008

In recent warfare, the performance improvement of air weapon systems enables an aircraft to strike multiple targets on a single sortie. Further, aircrafts attacking targets may carry out an operation as a strike package that is composed of bombers, escort aircrafts, SEAD (Suppression of Enemy Air Defenses) aircrafts and etc. In this paper, we present an aircraft allocation model that allocates multiple targets to a single sortie in the form of a strike package. A mixed integer programming is developed and solved by using a commercially available software. The new model is better than existing ones because not only it allocates aircrafts to multiple targets but also it models the concept of the strike package. We perform a computational experiment to compare the result of the new model with that of existing ones, and perform sensitivity analysis by varying a couple of important parameters.

• Journal of Korean Institute of Industrial Engineers
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• v.41 no.1
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• pp.17-24
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• 2015

Mixed acceptance sampling plans for quantity of products in prepackages are widely used for compliance testing. To pass testing, random samples jointly comply with two legal requirements: (i) the average net content of an inspection lot shall be not less than the labelled quantity and (ii) the numbers of under-filled prepackages in a sample are less than or equal to permitted numbers. This paper discusses some drawbacks of the acceptance sampling plans and requirements recommended in OIML R87 (KS A 50087 translated by Korean) developed by the International Organization of Legal Metrology and evaluates the producer's and consumer's risks. In addition, problem of determining a target value in filling processes of prepackages under the OIML R87 requirements is addressed and illustrated with a numerical example.

• Bulletin of the Korean Mathematical Society
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• v.50 no.3
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• pp.993-1005
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• 2013

In this paper, to include more generalized cases, the authors present a modified concept for the tripled and quadruple fixed point of the mixed monotone mappings. Also, they investigate the existence and uniqueness of fixed point of the ordered monotone operator with the Matkowski contractive conditions in the partial ordered metric spaces. As the direct consequences, the existence of coupled fixed point, tripled fixed point and quadruple fixed point are explored at the common framework and some previous results in [T. G. Bhaskar and V. Lakshmikan-tham, Fixed point theory in partially ordered metric spaces and applications, Nonlinear Anal. 65 (2006), 1379-1393; V. Berinde and M. Borcut, Tripled fixed point theorems for contractive type mappings in partially ordered metric spaces, Nonlinear Anal. 74 (2011), no. 15, 4889-4897; E. Karapinar and N. V. Luong, Quadruple fixed point theorems for nonlinear contractions, Computers and Mathematics with Applications (2012), doi:10.1016/j.camwa.2012.02061] are improved. Finally, some fixed point theorems are proved.

• Journal of ILASS-Korea
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• v.16 no.4
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• pp.195-200
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• 2011

The pressure-swirl atomizer is widely used for the injectors in liquid rocket engines thanks to its high performance atomization and broad stability margin range. Spray mixed-interaction is an important area of study especially in cases where the propellant is mixed by spray interaction after an oxidant and a fuel are discharged separately. This interaction of sprays results in a significant modification of the spray characteristics such as the spatial evolution of the sprays. Experiments are conducted by a photographic technique to quantify the merged angle of the interaction regions of sprays from two pressure-swirl injectors. The experimental results show that the merged angle is mainly determined by the momentum flux ratios between two swirled sprays.

• International Journal of Fluid Machinery and Systems
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• v.5 no.1
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• pp.18-29
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• 2012

This paper deals with the CFD analysis of cavitating flow in the mixed-flow pump with the specific speed of 1.64 which suffers from a high level of noise and vibrations close to the optimal flow coefficient. The ANSYS CFX package has been used to solve URANS equations together with the Rayleigh-Plesset model and the SST-SAS turbulence model has been employed to capture highly unsteady phenomena inside the pump. The CFD analysis has provided a good picture of the cavitation structures inside the pump and their dynamics for a wide range of flow coefficients and NPSH values. Cavitation instabilities were detected at 70% of the optimal flow coefficient close to the NPSH3 value (NPSH3 is the net positive suction head required for the 3% drop of the total head of the pump).

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2006.06a
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• pp.77-78
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• 2006

A mixed method between $H_2\;and\;H_{\infty}$ control are widely applied to systems which has parameter perturbation and uncertain model to obtain an optimal robust controller. Brushless Direct Current (BLDC) motors are widely used for high performance control applications. Conventional PID controller only provides satisfactory performance for set-point regulation. However, with the presence of nonlinearities, uncertainties and perturbations in the system, conventional PID is not sufficient to achieve an optimal robust controller. This paper presents an approach to ease designing a Mixed $H_2/H_{\infty}$ PID controller for controlling speed of Brushless DC motors and the genetic algorithm is used to solve the optimized problems. Numerical results are shown to prove that the performance in the proposed controller is better than that in the optimal PID controller using LQR approach.

• Rapid Communication in Photoscience
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• v.5 no.1
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• pp.8-10
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• 2016

The potential curves of OH bonds of liquid water are inhomogeneous because of a variety of interactions with other molecules and this leads to a wide distribution of vibrational frequency which hampers our understanding of the structure and dynamics of water molecules. Mixed quantum/classical (QM/CM) calculation methods are powerful theoretical techniques to help us analyze experimental data of various vibrational spectroscopies to study such inhomogeneous systems. In a type of those approaches, the interaction energy between OH bonds and other molecules is approximately represented by the interaction between the charges located at the appropriate interaction sites of water molecules. For this purpose, we re-calculated the values of charges by comparing the approximate interaction energies with quantum chemical interaction energies. We determined a set of charges at the TIP4P charge sites which better represents the quantum mechanical potential curve of OH bonds of liquid water.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.52 no.10
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• pp.616-623
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• 2003

Competition among electric generation companies is a major goal of restructuring in the electricity industry, The trading system in an electricity market has been one of the most important issues in deregulated electricity market. This paper deals with comparisons of the major two types of the trading system: compulsory pool market and bilateral contract market. The two trading systems are compared quantitatively from the viewpoint of consumer's surplus and social welfare, This paper, also, proposes a unified model of Cournot and Bertrand for analyzing the mixed trading system of pool market and bilateral contract market. Nash equilibrium of the unified model is derived by criteria for participating in bilateral contract market. Numerical results from a sample case show that a mixed trading system of pool market and price-competitive bilateral market is beneficial to consumer from the view points of consumer's surplus.