• 오토저널
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• 제7권2호
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• pp.45-54
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• 1985

Recently, the problem of exhaust gas pollution is increasingly being aggravated by the active use of the Diesel engine. For the fuel-injection system which affects the composition of exhaust gas from the Bosch type single-hole nozzle in the Diesel engine, a mathematical model was set up to study pressure variations in the high pressure pipe, the injection rate, and the needle lift. The fundamental equations of the mathematical model have been solved by the Newton Raphson Method applying the Finite Diffrence Method. The effective stroke of the injection pump plunger due to a change in engine rpm was calculated by the measurement of Control Rack, Pinion, and Plunger sizes and by the use of Characteristic Curve of Governor. The computed results for the pressure variations in the high pressure pipe and needle lift at 800 rpm and 1000 rpm are in good agreement with experimental ones in general. By a developed program, the effects of other various parameters will by calculated for the performance of the fuel-injection system.

• 한국수학교육학회지시리즈D:수학교육연구
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• 제16권1호
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• pp.31-50
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• 2012

The present study explored whether the implementation of focused activities (intervention programme) can enhance 22 pre-service mathematics teachers' proficiency in solid geometry thinking level as well as change for the better their feelings in this discipline. Over a period of 6 weeks the pre-service teachers participated in activities and diversified experiences with 3D shapes, using illustration aids and actual experience of building 3D shapes in relation to the various spatial thinking levels. The research objectives were to investigate whether the intervention programme, comprising task-oriented activities of solid geometry, enhance mathematics pre-service teachers' mastery of their geometric thinking levels as well as examine their feelings towards this discipline before and after the intervention programme. The findings illustrate that learners' levels of geometric thinking can be promoted, entailing control on higher thinking levels as well as a more positive attitude towards this field.

• 동력기계공학회지
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• 제16권3호
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• pp.64-68
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• 2012

Because the magnetic bearing supports levitating body without contact, wear, noise and vibration are very small comparing with mechanical bearings, it is very useful to high revolution machinery. In general, the magnetic attractive force function that is proportional to square of control current(x), and inversely proportional to square of an air gap(i) has been widely used. This paper proposed the new magnetic attractive force function that is proportional to cube of the control current, and inversely proportional to square of the air gap. The function was optimized to minimize the cost function that is the percentage of deviation about the change of a proportional constant(k), using the experimental data, ie, control currents and air gaps.

• 한국수학교육학회지시리즈D:수학교육연구
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• 제19권4호
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• pp.211-227
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• 2015

Information Technology influenced on classroom to change the teaching and learning method. Recently, flipped learning method became a hot issue in education by using Information Technology. Learning management system that is introduced in our university in the spring semester 2015, made it possible to apply flipped learning method. So, we used the flipped learning method in a calculus course. In this paper, we found that flipped learning in Calculus we was a little bit affirmative in the aspect of motivation and active learning from students' response on flipped learning method. We analyzed the reason that students were not so positive in continuing flipped learning even though they liked flipped learning a little bit better than traditional learning. We suggest what we pay attention to for applying the flipped learning method effectively.

• 호남수학학술지
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• 제39권4호
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• pp.575-590
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• 2017

A new class of functions called $R_{\theta}$-supercontinuous functions is introduced. Their basic properties are studied and their place in the hierarchy of strong variants of continuity, which already exist in the literature, is elaborated. The class of $R_{\theta}$-supercontinuous functions properly contains the class of $R_z$-supercontinuous functions [39] which in turn properly contains the class of $R_{cl}$-supercontinuous functions [43] and so includes all cl-supercontinuous (clopen continuous) functions ([38], [34]) and is properly contained in the class of $R_{\delta}$-supercontinuous functions [24].

• East Asian mathematical journal
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• 제34권4호
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• pp.487-509
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• 2018

We analyse the map of the west capital Pyongyangbu of Old Korea(AD 920) by topological method and geometrical method and compare it with the map of North Korea Pyongyang. By the analyse of the map we find the real place of the old map. The analysing and finding the real place of the old map is a very good example of geometry education. Many Koreans had learned and recognized that Old Korea(AD 920) was a small country located in the south part of Ablok river. But, after reading this paper they change their old recognitions and they take prides in Great Old Korea.

• 대한수학회지
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• 제35권3호
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• pp.659-673
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• 1998

In this paper we consider a security market whose asset price process is a vector semimartingale. The market is said to be fair if there exists an equivalent martingale measure for the price process, deflated by a numeraire asset. It is shown that the fairness of a market is invariant under the change of numeraire. As a consequence, we show that the characterization of the fairness of a market is reduced to the case where the deflated price process is bounded. In the latter case a theorem of Kreps (1981) has already solved the problem. By using a theorem of Delbaen and Schachermayer (1994) we obtain an intrinsic characterization of the fairness of a market, which is more intuitive than Kreps' theorem. It is shown that the arbitrage pricing of replicatable contingent claims is independent of the choice of numeraire and equivalent martingale measure. A sufficient condition for the fairness of a market, modeled by an Ito process, is given.

• 대한수학회지
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• 제34권4호
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• pp.973-1008
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• 1997

We reconsider the problem of calssifying all classical orthogonal polynomial sequences which are solutions to a second-order differential equation of the form $$ \ell_2(x)y"(x) + \ell_1(x)y'(x) = \lambda_n y(x). $$ We first obtain new (algebraic) necessary and sufficient conditions on the coefficients $\ell_1(x)$ and $\ell_2(x)$ for the above differential equation to have orthogonal polynomial solutions. Using this result, we then obtain a complete classification of all classical orthogonal polynomials : up to a real linear change of variable, there are the six distinct orthogonal polynomial sets of Jacobi, Bessel, Laguerre, Hermite, twisted Hermite, and twisted Jacobi.cobi.

• 한국수학교육학회지시리즈A:수학교육
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• 제39권2호
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• pp.179-186
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• 2000

Although computer technology has a great potential for improving mathematics learning practice, it rarely used in mathematics classroom. The purpose of this study is to suggest the future direction for research in mathematics computer technology. First, there has to be a research on mathematics curriculum that take computer technology into account. Second, research on teaching sequence for certain content area is needed. Because computer technology would change the order of teaching sequence. Third, how students would learn with computer technology? how do they acquire knowledge and make sense of it? Fourth, how could we assess the learning with computer technology? Most of all, because teachers play a key role to succeed in educational reform, they have to be familiar with computer technology and software to introduce it into mathematics learning and to use it properly.

• 한국수학교육학회지시리즈D:수학교육연구
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• 제19권3호
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• pp.155-174
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• 2015

The goal of this study was to examine the three components of a laboratory class cycle that empowered teachers to change their teaching practices. Six teachers and their administrator in an elementary school in the southeastern United States participated in the study. All the teachers were interviewed, and their mathematics lessons were observed at the end of each cycle of laboratory classes. The study revealed how planning, observing, and critiquing mathematics lessons as a team assisted the teachers' learning and teaching. We identified opportunities for the teachers to experiment with different teaching approaches, and we found that support from the team and from the school were key factors for the laboratory class cycle to function effectively.