• East Asian mathematical journal
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• v.24 no.1
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• pp.45-55
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• 2008

We consider an M/G/1 queue with $P^M_{\lambda}$-service policy, which is a two-stage service policy. The server starts to serve with rate 1 if a job arrives to the sever in idle state. If the workload of the system upcrosses $\lambda$, then the service rate is changed to M and this rate continues until the system is empty. It costs to change the service rate to M and maintaining the rate. When the expectation of the stationary workload is supposed to be less than a given value, we derive the optimal value of M.

• Transactions of The Korea Fluid Power Systems Society
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• v.8 no.2
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• pp.17-22
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• 2011

The analysis of an air spring characteristics is necessary to design and control automotive air suspension system properly. A mathematical model of an air spring was derived in light of energy conservation first. Then static and dynamic experiments of the air spring have been fulfilled. The static stiffness with various initial pressures and effective areas were obtained from the static experimental results. Theoretical static stiffness obtained by using the mathematical model and effective area data is in close accordance with the experimental estimation. The dynamic experimental results show that the hysteresis in displacement-force cycle decreases when the frequency of the harmonic displacement excitation signal increases, but it does not change too much as the frequency is higher than 1Hz. And the dynamic stiffness goes up with increasing of the initial pressure and the excitation frequency.

• Research in Mathematical Education
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• v.13 no.1
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• pp.23-30
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• 2009

How to promote creativity for all students in mathematics education is always a hot topic for mathematics educators. Based on the theory study and practice in the project "Open-ended Questions in Mathematics" granted by Ministry of Basic Education Curriculum Study Center in China, the paper reported the effect of "Open-ended Questions in Mathematics" on the way to change the development of thinking ability, to inspire students to develop thinking flexibility, to expand their imagination, to stimulate their interest in learning, and to foster students' creativity.

• Research in Mathematical Education
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• v.17 no.4
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• pp.243-266
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• 2013

Accompanied with ongoing calls for reform in statistics curriculum, mathematics and statistics teachers purposefully have been reconsidering the curriculum and the content taught in statistics classes. Changes made are centered around statistical inference since teachers recognize that students struggle with understanding the ideas and concepts used in statistical reasoning. Despite the efforts to change the curriculum, studies are sparse on the topic of characterizing student learning and understanding of statistical inference. Moreover, there are no tools to evaluate students' statistical reasoning in a coherent way. In response to the need for a research instrument, in a series of research study, the researcher developed a reliable and valid measure to assess students' inferential reasoning in statistics (IRS). This paper describes processes of test blueprint development that has been conducted from review of the literature and expert reviews.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.13 no.3
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• pp.70-76
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• 2014

The intensity of sunlight becomes lower when weather conditions change, which affects whether a solar-electric vehicle can be driven on a shady road. The power delivered by solar cells can be vary depending on the amount of shade. As a result, the battery system is often used to compensate for variations in the power delivered by solar cells. Therefore, studies of power control systems for solar-electric vehicles are required. In this paper, mathematical models for such a power control system are studied and important variables are considered. Simulation and test results show that the mathematical model and actual designs developed here would be effective when used with solar-electric vehicles.

• Communications of the Korean Mathematical Society
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• v.22 no.2
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• pp.207-208
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• 2007

In this work, authors considered a result concerning elliptic curves $y^2=x^3+cx$ over $\mathbb{F}_p$ mod 8, given at [1]. They noticed that there should be a slight change at this result. They give counterexamples and the correct version of the result.

• Bulletin of the Korean Mathematical Society
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• v.57 no.3
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• pp.763-780
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• 2020

Let R be a commutative ring. An R-module M is said to be w-flat if Tor ^R₁ (M, N) is GV -torsion for any R-module N. It is known that every flat module is w-flat, but the converse is not true in general. The w-flat dimension of a module is defined in terms of w-flat resolutions. In this paper, we study the w-flat dimension of an injective w-module. To do so, we introduce and study the so-called w-copure (resp., strongly w-copure) flat modules and the w-copure flat dimensions for modules and rings. The relations between the introduced dimensions and other (classical) homological dimensions are discussed. We also study change of rings theorems for the w-copure flat dimension in various contexts. Finally some illustrative examples regarding the introduced concepts are given.

• Journal of the Korean Mathematical Society
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• v.57 no.4
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• pp.873-892
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• 2020

Thurston, in 1986, discovered that the Schwarzian derivative has mysterious properties similar to the curvature on a manifold. After his work, there are several approaches to develop this notion on Riemannian manifolds. Here, a tensor field is identified in the study of global conformal diffeomorphisms on Finsler manifolds as a natural generalization of the Schwarzian derivative. Then, a natural definition of a Mobius mapping on Finsler manifolds is given and its properties are studied. In particular, it is shown that Mobius mappings are mappings that preserve circles and vice versa. Therefore, if a forward geodesically complete Finsler manifold admits a Mobius mapping, then the indicatrix is conformally diffeomorphic to the Euclidean sphere S^n-1 in ℝⁿ. In addition, if a forward geodesically complete absolutely homogeneous Finsler manifold of scalar flag curvature admits a non-trivial change of Mobius mapping, then it is a Riemannian manifold of constant sectional curvature.

• Research in Mathematical Education
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• v.3 no.1
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• pp.9-21
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• 1999

In mid 1980s, open education arrived in Korea. It was influenced by the educational reforms implemented in American primary schools. Currently, the Ministry of Education is appealing to teachers for their active involvement in educational reform by using open education methodology. Often teachers in Korea complain that they do not know what to do or how to change in order to practice the open education. It is time to review the state of open education in Korea and the United States. This paper contains the following segments: 0) Introduction, 1) Beginning of open education, 2) A brief history of open education in Korea, 3) The current status of open education in the United States, 4) A glance at open mathematics classroom in Korea, 5) Lessons from the review, and 6) Conclusion.

• The Mathematical Education
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• v.25 no.1
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• pp.1-8
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• 1986

It is a common saying that markov-chain is a special case of probability course. That is to say, It means an unchangeable markov-chain process of the transition-probability of discontinuous time. There are two kinds of ways to show transition probability parade matrix theory. The first is the way by arrangement of a rightangled tetragon. The second part is a vertical measurement and direction sing by transition-circle. In this essay, I try to find out existence of procession for transition-probability applied markov-chain. And it is possible for me to know not only, what it is basic on a study of chain but also being applied to abnormal problems following a flow change and statistic facts expecting to use as a model of air expansion in physics.