• Title/Summary/Keyword: Euler Characteristic

### A Study on Learning Environments for Euler's formula with activities ('오일러 공식과 오일러 표수' 탐구 활동을 위한 학습 환경 연구)

• Song, Min Ho
• Journal for History of Mathematics
• /
• v.26 no.2_3
• /
• pp.131-148
• /
• 2013
• Euler's formula provides the topological characteristics of geometrical objects including polyhedra, and so an important mathematical concept. Descriptions on Euler's formula had been in the textbooks according to the 3rd through 7th National Mathematics Curriculum. However, they are gone after that. In this study, we focus on Euler characteristic and Euler's formula as an educational material for educations for the gifted or after-school educations. We first look at the mathematical history and the applications of Euler's formula and national curriculums to search for its mathematical and educational meaning. We further make a suggestion for a learning environment which provides a better education relying on search activities, not just depending on memorization, illuminated from the education of Euler's formula.

### A Paper on the Pedagogy Focused in the Mathematical Thinking Mathematicians used (수학자가 수학을 탐구하듯이 학습자도 수학을 탐구할 수 있는 방안 모색)

• Kim, Jin-Ho
• The Mathematical Education
• /
• v.44 no.1 s.108
• /
• pp.87-101
• /
• 2005
• The purpose of this paper is to propose a teaching method which is focused on the mathematical thinking skills such as the use of induction, counter example, analogy, and so on mathematicians use when they explore their research fields. Many have indicated that students have learned mathematics exploring to use very different methods mathematicians have done and suggested students explore as they do. In the first part of the paper, the plausible whole processes from the beginning time they get a rough idea to a refined mathematical truth. In the second part, an example with Euler characteristic of 1. In the third, explaining the same processes with ${\pi}$, a model modified from the processes is designed. It is hoped that the suggested model, focused on a variety of mathematical thinking, helps students learn mathematics with understanding and with the association of exploring entertainment.

### SIGNED A-POLYNOMIALS OF GRAPHS AND POINCARÉ POLYNOMIALS OF REAL TORIC MANIFOLDS

• Seo, Seunghyun;Shin, Heesung
• Bulletin of the Korean Mathematical Society
• /
• v.52 no.2
• /
• pp.467-481
• /
• 2015
• Choi and Park introduced an invariant of a finite simple graph, called signed a-number, arising from computing certain topological invariants of some specific kinds of real toric manifolds. They also found the signed a-numbers of path graphs, cycle graphs, complete graphs, and star graphs. We introduce a signed a-polynomial which is a generalization of the signed a-number and gives a-, b-, and c-numbers. The signed a-polynomial of a graph G is related to the $Poincar\acute{e}$ polynomial $P_{M(G)}(z)$, which is the generating function for the Betti numbers of the real toric manifold M(G). We give the generating functions for the signed a-polynomials of not only path graphs, cycle graphs, complete graphs, and star graphs, but also complete bipartite graphs and complete multipartite graphs. As a consequence, we find the Euler characteristic number and the Betti numbers of the real toric manifold M(G) for complete multipartite graphs G.

### (1,λ)-EMBEDDED GRAPHS AND THE ACYCLIC EDGE CHOOSABILITY

• Zhang, Xin;Liu, Guizhen;Wu, Jian-Liang
• Bulletin of the Korean Mathematical Society
• /
• v.49 no.3
• /
• pp.573-580
• /
• 2012
• A (1, ${\lambda}$)-embedded graph is a graph that can be embedded on a surface with Euler characteristic ${\lambda}$ so that each edge is crossed by at most one other edge. A graph $G$ is called ${\alpha}$-linear if there exists an integral constant ${\beta}$ such that $e(G^{\prime}){\leq}{\alpha}v(G^{\prime})+{\beta}$ for each $G^{\prime}{\subseteq}G$. In this paper, it is shown that every (1, ${\lambda}$)-embedded graph $G$ is 4-linear for all possible ${\lambda}$, and is acyclicly edge-($3{\Delta}(G)+70$)-choosable for ${\lambda}$ = 1, 2.

### Numerical Analysis of Nonlinear Combustion Instability Using Pressure-Sensitive Time Lag Hypothesis (시간지연 모델을 이용한 비선형 연소불안정 해석기법 연구)

• Park Tae-Seon;Kim Seong-Ku
• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.30 no.7 s.250
• /
• pp.671-681
• /
• 2006
• This study focuses on the development of numerical procedure to analyze the nonlinear combustion instabilities in liquid rocket engine. Nonlinear behaviors of acoustic instabilities are characterized by the existence of limit cycle in linearly unstable engines and nonlinear or triggering instability in linearly stable engines. To discretize convective fluxes with high accuracy and robustness, approximated Riemann solver based on characteristics and Euler-characteristic boundary conditions are employed. The present procedure predicts well the transition processes from initial harmonic pressure disturbance to N-like steep-fronted shock wave in a resonant pipe. Longitudinal pressure oscillations within the SSME(Space Shuttle Main Engine) engine have been analyzed using the pressure-sensitive time lag model to account for unsteady combustion response. It is observed that the pressure oscillations reach a limit cycle which is independent of the characteristics of the initial disturbances and depends only on combustion parameters and operating conditions.

### ON THE ADJOINT LINEAR SYSTEM

• Kwan, Shin-Dong
• Bulletin of the Korean Mathematical Society
• /
• v.31 no.1
• /
• pp.15-23
• /
• 1994
• Throughout this paper, we are working on the complex number field C. The aim of this paper is to explain the applications of Theorem 2 in .cint. 1. In the surface theory, the adjoint linear system has played important roles and many tools have been developed to understand it. In the cases of higher dimensional varieties, we don't have any useful tools so far. Theorem 2 implies that it is enough to compute the dimension of the adjoint linear system to check the birationality. We can compute, somehow, the dimension of the adjoint linear system. For example, we can get an information about $h^{0}$ (X, $O_{x}$( $K_{x}$ + D)) from Euler characteristic of vertical bar $K_{X}$ + D vertical bar and some vanishing theorems. We are going to show the applications of Theorem 2 to smooth three-folds and smooth fourfold, specially, of general type with a nef canonical divisor, smooth Fano variety, and Calabi-Yau manifold. Our main results are Theorem A and Theorem B. Most of birationality problems in Theorem A and Theorem B have been studied. (see Ando [1] and Matsuki [4] for the detail matters.) But Theorem 2 gives short and easy proofs in the cases of dimension 3 and improves the previously known results in the cases of dimension 4.4. 4.4.