• The Mathematical Education
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• v.52 no.1
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• pp.43-63
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• 2013

The purpose of this study is to find meaningful implications for developing curriculum and textbooks by comparison between Korean middle school mathematics textbooks and U.S.A.'s CMP textbooks. After comparing and analysing how the contents are composed focusing on the equations and functions and how the contents are presented according to 'Project 2061' mathematical textbook analytical framework, and how the contents ere different in terms of the mathematical connectivity, the research reached the following conclusions. First, compared to Korean textbooks, the CMP textbooks clearly present learners' behavior goals in a detailed way, and emphasize communication and connectivity. Second, Korean textbooks focus on explaining concepts and solving problems related to their concepts and discussion questions are briefly introduced. But all the textbooks contain a lot of problems required to be solved with algorithms. On the other hand, CMP textbooks provide students with opportunities to find the necessary concepts on their own, through problem solving processes, after presenting various real-life problem situations.

• Structural Engineering and Mechanics
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• v.77 no.4
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• pp.473-479
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• 2021

The propagation of plane waves in a linear, homogeneous and isotropic nonlocal generalized thermoelastic solid medium is considered in the framework of Lord and Shulman generalization. The governing field equations are formulated and specialized in a plane. Plane wave solutions of governing equations show that there exists three plane waves, namely, P, thermal and SV waves which propagate with distinct speeds. Reflection of P and SV waves from thermally insulated or isothermal boundary of a half-space is considered. The relevant boundary conditions are applied at stress free boundary and a non-homogeneous system of three equations in reflection coefficients is obtained. For incidence of both P and SV waves, the expressions for energy ratios of reflected P, thermal and SV waves are also obtained. The speeds and energy ratios of reflected waves are computed for relevant physical constants of a thermoelastic material. The speeds of plane waves are plotted against nonlocal parameter and frequency. The energy ratios of reflected waves are also plotted against the angle of incidence of P wave at a thermally insulated stress-free surface. The effect of nonlocal parameter is shown graphically on the speeds and energy ratios of reflected waves.

• Communications for Statistical Applications and Methods
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• v.30 no.2
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• pp.163-178
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• 2023

GARCH-X(1, 1) model specifies that conditional variance follows an AR(1) process and includes a past exogenous variable. This study proposes a new class from that model by allowing a more general (non-linear) variance function to follow an AR(1) process. The functions applied to the variance equation include exponential, Tukey's ladder, and Yeo-Johnson transformations. In the framework of normal and student-t distributions for return errors, the empirical analysis focuses on two stock indices data in developed countries (FTSE100 and SP500) over the daily period from January 2000 to December 2020. This study uses 10-minute realized volatility as the exogenous component. The parameters of considered models are estimated using the adaptive random walk metropolis method in the Monte Carlo Markov chain algorithm and implemented in the Matlab program. The 95% highest posterior density intervals show that the three transformations are significant for the GARCHX(1, 1) model. In general, based on the Akaike information criterion, the GARCH-X(1, 1) model that has return errors with student-t distribution and variance transformed by Tukey's ladder function provides the best data fit. In forecasting value-at-risk with the 95% confidence level, the Christoffersen's independence test suggest that non-linear models is the most suitable for modeling return data, especially model with the Tukey's ladder transformation.

• Journal of applied mathematics & informatics
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• v.40 no.1_2
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• pp.47-59
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• 2022

This paper concerns the problem of simultaneous fault detection and disturbance reject control(SFDDRC) for a class of linear time-invariant system. In the framework of fault detection, residual generators are required to be robust to disturbances existing in the system. Different from most of the existing simultaneous fault and control(SFDC) methods, SFDDRC rejects the influences of disturbances on residual generators by disturbance observer-based control(DOBC). This not only effectively improves the accuracy of fault detection, but also solves the problem that most of the existing SFDC methods require that the disturbance must be bounded. Finally, a numerical example is given to verify the validity of the method.

• School Mathematics
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• v.16 no.3
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• pp.585-611
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• 2014

The purpose of this study is to understand the decision-making behavior of a mathematics teacher in science academy of Korea by applying the framework of class analysis through the theory of goal-oriented decision-making. To this end, we selected as the participant a mathematics teacher in charge of the class of basic calculus of science high school for the gifted in the metropolitan area, and observed the teacher's lesson. Based on a questionnaire derived from previous studies, we analyzed goals, orientations and resources of the teacher. Research results show that there are certain teaching routines by analyzing the behavior patterns that appear repeatedly in the teacher's lesson. Also we understand that it can be used on goals, orientations and resources of the teacher to adequately explain his teaching routine. In the present study, in particular, it was found to have a similar but partially different routines to the teaching routines shown in the study of Schoenfeld. From these findings, We can derive the implications that the theory of goal-oriented decision making can be suitably used as analytical tool for understanding the behavior of the teacher who pursue a productive interaction in mathematics lesson in Korea.

• School Mathematics
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• v.17 no.3
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• pp.493-513
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• 2015

This study is based on the perspective that tasks in local and global contexts are important to raise students' ability to mathematically analyze and solve diverse phenomena and social issues as members of future civil society. Therefore, this study analyzes 880 real world tasks from 13 types of 7th grade textbook based on 2009 revised Curriculum. As a result of analyzing tasks by using 3 types of context category and 9 types of ways as analysis framework and allowing repetitive coding, personal context was most frequent in the context of Younbokhap. In level of Integrated ways of Yungbokhap, sequential model in which other subjects' topics were not directly related to mathematics problem or presented in simple description is most frequent. The result shows that the textbooks are too limited to develop learner's competencies. Through such analysis result, we discuss about the necessity and methods of developing tasks which allow learners to study further in future society and global context and which connect other subjects' knowledge and social issue with mathematics in deeper level.

• Journal of Elementary Mathematics Education in Korea
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• v.23 no.1
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• pp.19-41
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• 2019

In this study, we present an analysis framework based on the 2015 revised curriculum to analyze how mathematical contents and achievement standards for domains of numbers and computations have changed in the curriculum of elementary mathematics in Korea. Based on this, we classified the achievement standards by type and investigated their characteristics. The achievement standards for numbers and computations can be divided into the successive, the extinctive, and the additive achievement standards depending on their characteristics. The successive achievement standards are the ones that have consistently existed without being removed from the 1-st curriculum to the latest revision in 2015. The extinctive achievement standards are the ones that have been removed at some point during the revisions of nine times and do not remain in the current revision in 2015. The characteristics of the extinctive achievement standards were analyzed to be different before and after the 4-th curriculum. The additive achievement standards refer to the ones that have been newly added to the curriculum or that have been removed at a certain moment but added back in later and thus exist in the current revision in 2015. The characteristics of each type according to the changes of the achievement standards can be thought to be the results that the revision for the mathematics curriculum in Korea has been faithfully conducted. Based on the results of this study, we suggest some implications for organizing the achievement standards in the future curricular development.

• Journal of Educational Research in Mathematics
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• v.26 no.3
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• pp.403-420
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• 2016

Some of the critical changes in the revised 2015 Korean Mathematics curriculum were that direct proportion and inverse proportion were moved from elementary school to middle school and that supplementary content related to correlation was included. These decisions were based on comparative studies of international curriculum. Therefore in this study, we selected countries for comparison; United States, England, France, Finland, Australia, Japan, Singapore, China and Taiwan. We looked into the timing and scope for direct/inverse proportion and correlation in curricula of these countries. Along with this, we established four criteria; vertical sequence, horizontal sequence, external connection, and internal connection for an analysis framework. Then we compared and analysed the direct/inverse proportion and correlation in each curriculum. As a result, in most of these curricula, the direct/inverse proportions are introduced at middle school or are introduced at elementary school and then developed further at middle school. Most of curriculums on direct/inverse proportion and correlation match the four criteria. Correlation is introduced in high school mathematics in all counties except Finland and it is dealt in diverse context introducing related concepts, for example, correlation coefficient, regression straight line, and least square. We suggested that it is necessary to refer these international trends for the next revision of curriculum.

• School Mathematics
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• v.19 no.3
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• pp.423-441
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• 2017

New Zealand had reformed their national curriculum with competence and are applying the revised curriculum. As the 2015 revised national curriculum is clothed with competency-based curriculum, New Zealand may have important implications for the study of the Korean revised curriculum. In this study, we examine characteristics of the education system and the national curriculum in New Zealand. In addition, we analyze the standards into the New Zealand national curriculum in terms of 'curriculum connectivity' that is one of important curriculum criteria for improving the quality of education. For this, we look an overview of the relation between the New Zealand curriculum and NCEA, which is the core of the student-centered education system in New Zealand, and analyze the correspondence between the New Zealand curriculum and the Korean curriculum. And we establish analysis framework of curriculum connectivity based on these comparison analysis contents, and analyze Korean mathematics standards with corresponding levels from among the New Zealand mathematics curriculum. According to the results of this study, the New Zealand curriculum includes the most of standards which Korean high school students who want to enter university of natural sciences of engineering need to require. In addition, the New Zealand curriculum highlights statistical research activities for developing problem-solving ability in real life. From perspective of curriculum connectivity, 'in-depth contents' adding on to repeating mathematical concepts or contents are included in the New Zealand curriculum.

• Journal of the Korean Mathematical Society
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• v.48 no.4
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• pp.669-689
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• 2011

The notion of quasi-Einstein manifolds arose during the study of exact solutions of the Einstein field equations as well as during considerations of quasi-umbilical hypersurfaces. For instance, the Robertson-Walker spacetimes are quasi-Einstein manifolds. The object of the present paper is to study Lorentzian quasi-Einstein manifolds. Some basic geometric properties of such a manifold are obtained. The applications of Lorentzian quasi-Einstein manifolds to the general relativity and cosmology are investigated. Theories of gravitational collapse and models of Supernova explosions [5] are based on a relativistic fluid model for the star. In the theories of galaxy formation, relativistic fluid models have been used in order to describe the evolution of perturbations of the baryon and radiation components of the cosmic medium [32]. Theories of the structure and stability of neutron stars assume that the medium can be treated as a relativistic perfectly conducting magneto fluid. Theories of relativistic stars (which would be models for supermassive stars) are also based on relativistic fluid models. The problem of accretion onto a neutron star or a black hole is usually set in the framework of relativistic fluid models. Among others it is shown that a quasi-Einstein spacetime represents perfect fluid spacetime model in cosmology and consequently such a spacetime determines the final phase in the evolution of the universe. Finally the existence of such manifolds is ensured by several examples constructed from various well known geometric structures.