• Bulletin of the Korean Mathematical Society
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• v.34 no.1
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• pp.51-61
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• 1997

• Bulletin of the Korean Mathematical Society
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• v.52 no.4
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• pp.1113-1122
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• 2015

This paper is concerned with the pattern formation of a diffusive predator-prey model with two time delays. Based upon an analysis of Hopf bifurcation, we demonstrate that time delays can induce spatial patterns under some conditions. Moreover, by use of a series of numerical simulations, we show that the type of spatial patterns is the spiral wave. Finally, we demonstrate that the spiral wave is asymptotically stable.

• Honam Mathematical Journal
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• v.30 no.4
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• pp.659-670
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• 2008

We denote by $\mathcal{Q}$(A) the set of all real matrices with the same sign pattern as a real matrix A. A matrix A is an SN-matrix provided there exists a set S of sign pattern such that the set of sign patterns of vectors in the -space of $\tilde{A}$ is S, for each ${\tilde{A}}{\in}\mathcal{Q}(A)$. Some properties of SN-matrices arc investigated.

• Journal of the Korean Mathematical Society
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• v.36 no.3
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• pp.469-487
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• 1999

Sign patterns of idempotent matrices, especially symmetric idempotent matrices, are investigated. A number of fundamental results are given and various constructions are presented. The sign patterns of symmetric idempotent matrices through order 5 are determined. Some open questions are also given.

• Honam Mathematical Journal
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• v.28 no.3
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• pp.333-342
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• 2006

We denote by Q(A) the set of all matrices with the same sign pattern as A. A matrix A is an SN-matrix provided there exists a set S of sign patterns such that the set of sign patterns of vectors in the null-space of A is S, for each A ${\in}$ Q(A). We have a characterization of an SN-matrix related with L-matrix and we analyze the structure of an SN-matrix.

• Education of Primary School Mathematics
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• v.7 no.1
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• pp.15-29
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• 2003

The present study examined the 7th national elementary school mathematics curriculum from a perspective of mathematical creativity. The study investigated to what extent the activities in the Pattern and Function lessons in the national elementary school mathematics textbooks promoted the development of mathematical creativity. The results indicated that the current elementary school mathematics curriculum was limited in many ways to promote the development of mathematical creativity. Regarding the activities in Pattern lessons, for example, most activities presented closed tasks involving finding and extending patterns. The lesson provided little opportunities to explore the relationships among various patterns, apply patterns to different situations, or create ones own patterns. In regard to the Function lessons, the majority of activities were about computing the rate. This showed that the function was taught from an operational perspective, not a relational perspective. It was unlikely that students would develop the basic understanding of function through the activities involving the computing the rate. Further, the lessons had students use exclusively the numbers in representing the function. Students were provided little opportunities to use various representation methods involving pictures or graphs, explore the strengths and limitations of various representation methods, or to choose more effective representation methods in particular contexts. In conclusion, the lesson activities in the current elementary school mathematics textbooks were unlikely to promote the development of mathematical creativity.

• The Mathematical Education
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• v.46 no.2 s.117
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• pp.227-237
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• 2007

This research analyzes students' response types in the creativity assessment by using pattern block, geoboard, and pantomino. 74 students from third grade to sixth grade participated in this research. 15 minutes were given to pattern block and geoboard questions. 74 students showed 393 answers in pattern block question and 590 answers in geoboard question. In pantomino, 20 minutes were given and 54 students showed 443 types of answers. The results are as follows: First, in the students' responses, tendency of using particular piece or figure, which presents conjoining in a piece selection and positioning, showed strongly. For example, usage of hexagon and trapezoid pieces were higer in pattern block and usage of L, P, and I pieces were higer in pentomino. Second, it is confirmed that creativity's subordinate factors, fluency, flexibility, and originality, are separate from each other. To illustrate, in pattern block, three students', who showed 11 types of responses in fluency, flexibility responses were each 5, 6, and 8 types. Specially, among those studenys, only one could achieve a point in originality. Third, students' response types categorized in this research could be used for a bae-data to mark grades on originality.

• School Mathematics
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• v.5 no.4
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• pp.459-476
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• 2003

Internet was introduced to this study for making mathematics class the surroundings where students can solve the mathematics problems and communicate mathematically in a free way without restriction of time and place. With the intention of investigating mathematical communication and problem solving in mathematics education using internet, the objects of this study were determined as follows: First, how does a student express mathematical idea in problem solving using internet\ulcorner Second, is there any difference in the degree of participation of mathematical communication according to schoolwork accomplishment and characteristics of the student\ulcorner Third, what's the effect of class using internet on problem solving of mathematics class\ulcorner A case study was executed for the solution and the subjects were all students(44 persons) of a class in the fourth grade of elementary school in D city got into web-site of internet and had class with it and 8 students out of them were deeply analyzed. Their results were shown on internet, and eight of them had interview for deep research after survey with questionnaires for all of the students after class. The results and the conclusions of this study were as follows: First, it showed that there was various types(simple statement, fact enumerating, logical thinking, using letters and formula, insufficiency of explanation) of the mathematical idea expression in internet according to students and study using internet seems to be helpful to the improvement of logical his own expression through other students' expression. Second, it showed that there was difference in mathematical communication participation according to the student's characteristics and it helped students of poor schoolwork be interested and confident in mathematics. Third, it showed that pattern study using internet had effect on forming a habit of reason and verification in problem solving in mathematics class. Accordingly, pattern study using internet seems to have a positive effect on increasing mathematical interests and solving problems in mathematics class.

• The Transactions of the Korean Institute of Power Electronics
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• v.17 no.4
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• pp.337-344
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• 2012

A matrix converter is used for converting AC/AC power directly. In order to generate sinusoidal input/output waveform in matrix converter, it uses nine bidirectional switches and PWM modulation. This paper presents an analytical averaged loss model of matrix converter with DDPWM(direct duty ratio PWM) and proposes a new switching method for reducing switching losses. A Mathematical loss models with average magnitude of voltage/current are classed as conduction and switching loss. The proposed switching pattern is improved with existing DDPWM. To prove improved efficiency with proposed DDPWM, this paper compares losses between suggested switching pattern and conventional switching pattern using mathematical and simulation method. Each loss types are influenced by environmental factors such as temperature, switching frequency, output current and modulation method.

• Communications of the Korean Mathematical Society
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• v.25 no.1
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• pp.11-18
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• 2010

The work in this paper was motivated by [3], where Eschenbach and Li listed four 4 by 4 sign patterns, conjectured to be nilpotent sign patterns of nilpotence index at least 3. These sign patterns with no zero entries, called full sign patterns, are shown to be potentially nilpotent of nilpotence index 3. We also generalize these sign patterns of order 4 so that we provide classes of n by n sign patterns of nilpotence indices at least 3, if they are potentially nilpotent. Furthermore it is shown that if a full sign pattern A of order n has nilpotence index k with $2{\leq}k{\leq}n-1$, then sign pattern A has nilpotent realizations of nilpotence indices k, k + 1, $\ldots$, n. Hence, the four 4 by 4 sign patterns in [3, page 91] also allow nilpotent realizations of nilpotence index 4.