• 대한수학회논문집
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• 제17권2호
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• pp.253-260
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• 2002

For an outer action $\alpha$ of a finite group G on a factor M, it was proved that H is a, normal subgroup of G if and only if there exists a finite group F and an outer action $\beta$ of F on the crossed product algebra M $\times$$_{\alpha}$ G = (M $\times$$_{\alpha}$ F. We generalize this to infinite group actions. For an outer action $\alpha$ of a discrete group, we obtain a Galois correspondence for crossed product algebras related to normal subgroups. When $\alpha$ satisfies a certain condition, we also obtain a Galois correspondence for fixed point algebras. Furthermore, for a minimal action $\alpha$ of a compact group G and a closed normal subgroup H, we prove $M^{G}$ = ( $M^{H}$)$^{{beta}(G/H)}$for a minimal action $\beta$ of G/H on $M^{H}$.f G/H on $M^{H}$.TEX> H/.

• 한국국방경영분석학회지
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• 제15권1호
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• pp.54-62
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• 1989

This paper presents a corrective maintenance model to determine either type of maintenance actions upon failure of the system. Types of maintenance actions considered are minimal repair and replacement. Minimal repair cost is assumed to be random, whereas replacement cost is fixed. A policy, B(t), which determines the type of maintenance action based on the estimated minimal repair cost when the system fails at time t is adopted. To obtain an optimal policy, an expected maintenance cost per unit time is derived and is minimized with respect to B(t).

• 한국수학교육학회지시리즈B:순수및응용수학
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• 제18권3호
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• pp.261-268
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• 2011

For a compact Hausdorff space X with its p-fold covering map ${\sigma}$, we construct its corresponding topological groupoid ${\Gamma}$, and show that there is a strong relation between the dynamical structures of (X, ${\sigma}$) and the groupoid structures of ${\Gamma}$.

• 대한수학회보
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• 제56권6호
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• pp.1539-1550
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• 2019

We classify minimal surfaces in ${\mathbb{S}}^3$ which are foliated by circles and ruled constant mean curvature (cmc) surfaces in ${\mathbb{S}}^3$. First we show that minimal surfaces in ${\mathbb{S}}^3$ which are foliated by circles are either ruled (that is, foliated by geodesics) or rotationally symmetric (that is, invariant under an isometric ${\mathbb{S}}^1$-action which fixes a geodesic). Secondly, we show that, locally, there is only one ruled cmc surface in ${\mathbb{S}}^3$ up to isometry for each nonnegative mean curvature. We give a parametrization of the ruled cmc surface in ${\mathbb{S}}^3$(cf. Theorem 3).

• 한국수학사학회지
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• 제17권1호
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• pp.43-52
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• 2004

In this paper we investigate the origin of the variational calculus with respect to the extremal principle. We also study the role the extremal principle has played in the development of the calculus of variations. We deal with Dido's isoperimetric problem, Maupertius's least action principle, brachistochrone problem, geodesics, Johann Bernoulli's principle of virtual work, Plateau's minimal surface and Dirichlet principle.

• 한국신뢰성학회지:신뢰성응용연구
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• 제18권2호
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• pp.104-113
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• 2018

Purpose: This paper proposes the non-periodic preventive maintenance policy based on the level of cumulative hazard intensity. We aim to construct a cost-effectiveness on the proposed model with relaxing the constraint on reliability. Methods: We use the level of cumulative hazard intensity as a condition variable, instead of reliability. Such a level of cumulative hazard intensity can derive the reliability which decreases as the frequency of preventive maintenance action increases. We also model the imperfect preventive maintenance action using the proportional age setback model. Conclusion: We provide a numerical example to illustrate the proposed model. We also analyze how the parameters of our model affect the optimal preventive maintenance policy. The results show that as long as high reliability is guaranteed, the inefficient preventive maintenance action is performed reducing the system operation time. Moreover, the optimal value of the proposed model is sensitive to changes in preventive maintenance cost and replacement cost.

• 대한약리학회지
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• 제10권1호
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• pp.21-39
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• 1974

Certain metabolic aspects of halothane's cardiac depressant action on the contractility of the myocardium were elucidated from a sudy of the effect of pyruvate on halothane-depressed rat atria. Approximately 6 mg% halothane was required to maintain a 50% depression of the contractility of rat atria suspended in a modified Krebs-Ringer bicarbonate glucose medium, pH 7.4, $30^{\circ}C$ for a 2 hr. period. Pyruvate was found to restore partially the contractility of halothane-depressed atria. The maximally effective concentration of pyruvate was 2.5 mM. There was minimal pyruvate effect on the force of contraction of control atria. The effect of pyruvate on halothane-depressed atria was shown to be due to the pyruvate and not the sodium ion of the sodium pyruvate. Pyruvate was found to produce no increase in the contractility of atria depressed by hypertonic medium, but caused a further depression. Selected aspects regarding the action of halothane on glucose metabolism in myocardial cells are discussed. The results are consistent with the hypothesis that at least a part of the negative inotropic action of halothane is due to an inhibition of glucose uptake or utilization in the glycolytic pathway.

• 한국화재소방학회논문지
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• 제31권6호
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• pp.67-73
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• 2017

항공기 정비 격납고는 고가의 항공기를 보관하거나 정비, 점검등을 하는 건축물로 화재발생 빈도는 낮지만 화재발생 시 인적, 물적 피해가 매우 클 수 있다. 따라서 본 연구에서는 Fault tree를 이용하여 현재 운용중인 항공기 정비 격납고 소화시스템의 화재 안전성에 대한 정성적 분석을 시행하고, 도출된 기본사상에 대한 고장률 자료를 활용하여 정량적 분석을 실시한 후 정상사상의 발생 확률에 대한 Minimal cut set의 중요도를 분석하였다. Minimal cut set에 의한 정성적 분석결과 항공기 격납고 포헤드 소화시스템의 화재제어 실패로 대형화재로 확대될 수 있는 사고경로는 14개라는 것을 알 수 있었다. 또한 정량적인 분석 결과 대형화재로 확대될 확률은 $2.08{\times}E-05/day$이며, Minimal cut set의 중요도 분석 결과 화재 발생 시 4개의 Minimal cut set 즉, 구역별 화재 감지기 및 포헤드 동작과 항공기 날개 및 Fire plume에 의한 소화약제 차단이 동일하게 24.95%로 대형화재로 확대될 가능성의 대부분을 차지하였으며, 항공기 정비 격납고의 포헤드 소화시스템은 항공기 날개 하부화재에 대한 적응성이 없어 개선이 필요한 것으로 Fault tree를 이용하여 처음 확인하였다.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 춘계학술대회 논문집
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• pp.1358-1363
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• 2011

본 연구에서는 GEC, VVVF 전동차 운전실에 취부 되어 있는 Brake Controller 점검방법 개선에 관한 연구를 수행하였다. Brake Controller내의 단동 스냅동작 스위치, 복동 스냅동작 스위치 및 단자대와 연결된 모든 부품을 개별적 점검이 아닌 현 전동차와 동일한 조건에서 전반적인 면밀한 검토 및 분석을 통하여 개선책을 강구하고, 고장을 사전에 발견해 처리함으로써 운행 장애 최소화 및 승객의 안전과 직결된 전동차 안전운행에 기여하고자 본 연구를 시작하였다.

• 대한수학회논문집
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• 제35권4호
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• pp.1299-1307
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• 2020

We show that the Liechti-Strenner's example for the closed nonorientable surface in [13] minimizes the dilatation within the class of pseudo-Anosov homeomorphisms with an orientable invariant foliation and all but the first coefficient of the characteristic polynomial of the action induced on the first cohomology nonpositive. We also show that the Liechti-Strenner's example of orientation-reversing homeomorphism for the closed orientable surface in [13] minimizes the dilatation within the class of pseudo-Anosov homeomorphisms with an orientable invariant foliation and all but the first coefficient of the characteristic polynomial p(x) of the action induced on the first cohomology nonpositive or all but the first coefficient of p(x)(x ± 1)², p(x)(x² ± 1), or p(x)(x² ± x + 1) nonpositive.