• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.05a
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• pp.303-306
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• 2008

After the successful flight test of X-43A, U.S. Airforce is developing missile-type X-51A SED (Scramjet Engine Demonstrator-Wave Rider). X-51A using PWR (Pratt and Whitney Rocketdyne) X-1 hydrocarbon fueled scramjet engine will have a ground test in 2008 and flight test in 2009. Technologies established though the X-51A program will be transferred to DARPA's Falcon program developing HTV (Hypersonic Test Vehicle)-3X and HCV (Hypersonic Cruise Vehicle). Present paper is an overview of propulsion core technologies of X-51 such as regenerative cooling of engine structures and combustion using liquid/supercritical JP-7 fuel.

• Bulletin of the Korean Mathematical Society
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• v.51 no.5
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• pp.1369-1374
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• 2014

We show that the Diophantine equation $$aQ(x_1,x_2)+bQ(x_3,x_4)+cQ(x_5,x_6)=abc$$ has integral solutions for arbitrary positive integers a, b, c when Q(x, y) is a norm form for some imaginary quadratic fields.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.314-317
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• 2008

Present review introduces the on-going or planed hypersonic vehicles by DARPA including X-51A, HTV-3X and HCV. The configuration and the R&D strategies of the hypersonic propulsion systems will be also introduced with its core technologies.

• Journal of the Korean Society of Propulsion Engineers
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• v.12 no.5
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• pp.79-91
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• 2008

The present article is intended to introduce the X-51A Scramjet Engine Demonstrator-Wave Rider (SED-WR) program and its core technologies to the korean propulsion community. The X-51A program is lead by the U.S. Air Force Research Laboratory (AFRL) and is sponsored by the U.S. Defense Advanced Research Projects Agency (DARPA). Most of the contents is taken from the paper by Hank et al.[1] with the supplemental materials from additional references. X-51A is a hypersonic experimental vehicle for the flight test of the hydrocarbon fuel-cooled scramjet engine developed by the AFRL HyTech program. The scramjet engine and the hypersonic flight technologies may enter the era of practical use by the completion of the ground tests in 2008 followed by the flight tests scheduled in 2009.

• Bulletin of the Korean Mathematical Society
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• v.51 no.1
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• pp.67-76
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• 2014

Let X be a divergence-free vector field defined on a closed, connected Riemannian manifold. In this paper, we show the equivalence between the following conditions: ${\bullet}$ X is a divergence-free vector field satisfying the shadowing property. ${\bullet}$ X is a divergence-free vector field satisfying the Lipschitz shadowing property. ${\bullet}$ X is an expansive divergence-free vector field. ${\bullet}$ X has no singularities and is Anosov.

• Journal of the Korean Mathematical Society
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• v.51 no.3
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• pp.495-507
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• 2014

Nielsen and Rege-Chhawchharia called a ring R right McCoy if given nonzero polynomials f(x), g(x) over R with f(x)g(x) = 0, there exists a nonzero element r ${\in}$ R with f(x)r = 0. Hong et al. called a ring R strongly right McCoy if given nonzero polynomials f(x), g(x) over R with f(x)g(x) = 0, f(x)r = 0 for some nonzero r in the right ideal of R generated by the coefficients of g(x). Subsequently, Kim et al. observed similar conditions on linear polynomials by finding nonzero r's in various kinds of one-sided ideals generated by coefficients. But almost all results obtained by Kim et al. are concerned with the case of products of linear polynomials. In this paper we examine the nonzero annihilators in the products of general polynomials.

• Kyungpook Mathematical Journal
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• v.51 no.3
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• pp.339-344
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• 2011

Let D be an integral domain with quotient field K, X be an indeterminate over D, and D[X] be the polynomial ring over D. A prime ideal Q of D[X] is called an upper to zero in D[X] if Q = fK[X] ${\cap}$ D[X] for some f ${\in}$ D[X]. In this paper, we study integral domains D such that every upper to zero in D[X] contains a prime element (resp., a primary element, a t-invertible primary ideal, an invertible primary ideal).

• Journal of the Korean Ceramic Society
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• v.51 no.1
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• pp.51-56
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• 2014

Mixed ionic and electronic conducting $K_2NiF_4$-type oxide, $Nd_{2-x}Sr_xNiO_{4+\delta}$ (x = 0, 0.4, 0.6) powders were synthesized by a solid-state reaction technique and solid oxide fuel cells consisting of a $Nd_{2-x}Sr_xNiO_{4+\delta}-GDC$ cathode, a Ni-YSZ anode and 8YSZ as an electrolyte were fabricated. The effect of strontium substitution for neodymium on the electrical and electrochemical properties was examined. The electrical conductivity increased with an increase in the Sr doping content, while it appears that the excess oxygen (${\delta}$) decreased. Sr doping into $Nd_2NiO_{4+\delta}$ resulted in an increase in the cathode polarization resistance and an decrease in the power density of the cell. These phenomena may be associated with the decreased amount of excess oxygen noted in the $Nd_{2-x}Sr_xNiO_{4+\delta}$ cathode.

• Journal of the Korean Mathematical Society
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• v.51 no.1
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• pp.17-53
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• 2014

Let ${\gamma}$ be a hyperbolic closed orbit of a $C^1$ vector field X on a compact boundaryless Riemannian manifold M, and let $C_X({\gamma})$ be the chain component of X which contains ${\gamma}$. We say that $C_X({\gamma})$ is $C^1$ robustly shadowable if there is a $C^1$ neighborhood $\mathcal{U}$ of X such that for any $Y{\in}\mathcal{U}$, $C_Y({\gamma}_Y)$ is shadowable for $Y_t$, where ${\gamma}_Y$ denotes the continuation of ${\gamma}$ with respect to Y. In this paper, we prove that any $C^1$ robustly shadowable chain component $C_X({\gamma})$ does not contain a hyperbolic singularity, and it is hyperbolic if $C_X({\gamma})$ has no non-hyperbolic singularity.

• Journal of Korean Society for Quality Management
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• v.51 no.4
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• pp.677-689
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• 2023

Purpose: The purpose of this study is to design a x-ray screening rating system to improve X-ray screening ability, which is a core job competency of security screener at Incheon International Airport, and to verify its effectiveness through empirical analysis to suggest ways to improve the level management system. Methods: In this study, the effectiveness of the research model was analyzed using T-test tests for effect analysis based on the empirical analysis results derived through the competency evaluation model, the screening rating system. Results: The results of this study are as follows. The average score for regular education before the implementation of the x-ray screening rating system was 94.1 points, but after the implementation of the x-ray screening rating system, the average score for regular education was 95.5 points, an average of 1.4 points increased. In addition, the proportion of those with 95 or more points classified as high scorers also increased significantly from 51.1% to 69.3%. Conclusion: The X-ray screening rating system of security inspectors will systematically manage the level of screening ability, which is a key job competency, and play a strong role in improving competency, while preventing security accidents through early identification and intensive training of level-lowers.