• The Korean Journal of Zoology
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• v.26 no.1
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• pp.19-28
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• 1983

Alkaline elution profiles showed that the frequency of DNA single strand breaks associated with DNA-protein crosslinks in cells treated with both an inducing dose of MMC $(MMC_1)$ and a challenge dose of MMC $(MMC_2)$ was slightly less than that in cells treated with MMC alone. The amount of unscheduled DNA synthesisi in cells treated with both $MMC_1$ and $MMC_2$ was greater than that in cells treated with MMC alone. This enhancement of exicision repair detected by UDS autoradiography and alkaline elution, was not observed, when cells were incubated with cyclohexmide between the two treatments of $MMC_1$ and $MMC_2$. These results suggest that MMC-damaged DNA from Chinses hamster cells is repaired by excision repair mechanisms that require de novo protein synthesis for enhancement, and that an inducible repair mechanism may exist in CHO cells.

• Journal of Educational Research in Mathematics
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• v.18 no.1
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• pp.103-121
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• 2008

The primary purpose of this study was to gather knowledge about $5^{th},\;6^{th},\;and\;7^{th}$ graders' proportional reasoning ability by investigating their reactions and use of strategies when encounting proportional or nonproportional problems, and then to raise issues concerning instructional methods related to proportion. A descriptive study through pencil-and-paper tests was conducted. The tests consisted of 12 questions, which included 8 proportional questions and 4 nonproportional questions. The following conclusions were drawn from the results obtained in this study. First, for a deeper understanding of the ratio, textbooks should treat numerical comparison problems and qualitative prediction and comparison problems together with missing-value problems. Second, when solving missing-value problems, students correctly answered direct-proportion questions but failed to correctly answer inverse-proportion questions. This result highlights the need for a more intensive curriculum to handle inverse-proportion. In particular, students need to experience inverse-relationships more often. Third, qualitative reasoning tends to be a more general norm than quantitative reasoning. Moreover, the former could be the cornerstone of proportional reasoning, and for this reason, qualitative reasoning should be emphasized before proportional reasoning. Forth, when dealing with nonproportional problems about 34% of students made proportional errors because they focused on numerical structure instead of comprehending the overall relationship. In order to overcome such errors, qualitative reasoning should be emphasized. Before solving proportional problems, students must be enriched by experiences that include dealing with direct and inverse proportion problems as well as nonproportional situational problems. This will result in the ability to accurately recognize a proportional situation.

• Communications of Mathematical Education
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• v.25 no.3
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• pp.537-556
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• 2011

This paper focuses on proportional reasoning being emphasized in today's elementary math, and analyzes the way students use their proportional reasoning abilities and strategies according to their academic achievement levels in solving proportional problems. For this purpose, various types of proportional problems were presented to 173 sixth-grade elementary school students and they were asked to use a maximum of three types of proportional reasoning strategies to solve those problems. The experiment results showed that upper-ranking students had better ability to use, express and perceive more types of proportional reasoning than their lower-ranking counterparts. In addition, the proportional reasoning strategies preferred by students were shown to be independent of academic achievement. But there was a difference in the proportional reasoning strategy according to the types of the problems and the ratio of the numbers given in the problem. As a result of this study, we emphasize that there is necessity of the suitable proportional reasoning instruction which reflected on the difference of ability according to student's academic achievement.

• School Mathematics
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• v.10 no.4
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• pp.603-623
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• 2008

The purpose of this research was to gain a better understanding of the characteristics of students' mathematical representations using additive strategy in ratio and proportion tasks. The additive strategy is the erroneous one used most often among the strategies reported in solving ratio and proportion tasks. It is a problem solving strategy that preserves the difference from one ratio to another. Students' additive strategies were categorized into four parts: subtracting without considering units of quantities, comparing the numbers that represent the whole subtracted from the part and same part, adding the difference, and subtracting the difference. In order to change from additive strategy to multiplicative strategy, the researcher asked to find out the unit quantity and found the characteristics of students' mathematical notations in the following: Firstly, the students made the number which they wanted by multiplying and adding same numbers. Secondly, they represented the mid-points between natural numbers. Thirdly, they related $a{\div}b$ to decimal number, not $\frac{a}{b}$. Fourthly, they were inclined to divide the larger number with the smaller number without understanding the context of the problem. These results are interpreted as showing that lower level of performance in the dividing operation with the notations of fraction hinders the transformation from additive strategy to multiplicative strategy.

• 한국방재학회:학술대회논문집
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• 2007.02a
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• pp.551-554
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• 2007

본 연구의 목적은 현재 지반지진공학에서 가장 큰 문제점 중 하나로 대두한 동하중의 주파수에 비례하는 흙의 거동이 지반진동에 미치는 영향을 규명 하는데 있다. 이를 위해 주파수의 영향을 고려하여 지반거동을 모사할 수 있는 지반진동해석 프로그램을 제시하고자 한다. 이 프로그램은 주파수에 비례하는 흙의 전단탄성계수 및 감쇠비를 모두 고려할 수 있는 새로운 해석기법이 될 것이다. 이를 이용하여 주파수에 비례하는 흙의 거동이 지반진동에 미치는 영향을 심도 있게 연구하고자 한다.

• Proceedings of the Acoustical Society of Korea Conference
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• 1998.06e
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• pp.251-254
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• 1998

초음파 수신 신호의 공진주파수 변화를 이용한 온도 측정법에서 협대역 변환기를 사용한 초음파 온도측정이 가능함을 보여준다. 그리고 이를 위하여 공진주파수 변화와 온도변화간의 비례상수를 변화시켰다. 기존의 측정법은 온도변화와 기본주파수 변화와의 관계를 비례상수로 정의하였기 때문에, 최소한 3개 이상의 하모닉을 포함하는 광대역 변환기가 필요하였다. 하지만 협대역 변환기를 이용한 온도측정법에서는 비례상수를 주파수 변화비와 온도변화간의 관계로 나타내기 때문에 한 성분의 하모닉만을 측정하여도 온도측정이 가능하게 된다.

• Journal of Educational Research in Mathematics
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• v.27 no.4
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• pp.791-810
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• 2017

This study explored the possibility of using visual models in teaching proportional reasoning based on the review of previous studies. Many studies on proportional reasoning emphasize that students tend to simply apply formal procedures without understanding the meaning behind them and that using visual models may be an alternative to help students develop informal strategies and proportional reasoning. Given these, we re-constructed and implemented the unit of a textbook to teach sixth graders proportional reasoning with ratio table, double number line, and double tape diagram. The results of this study showed that such visual models helped students understand the meaning of proportion, explore the properties of proportion, and solve proportional problems. However, several difficulties that students experienced in using the visual models led us to suggest cautionary notes when to teach proportional reasoning with visual models. As such, this study is expected to provide empirical information for textbook developers and teachers who teach proportional reasoning with visual models.

• Journal of Industrial Technology
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• v.26 no.B
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• pp.227-231
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• 2006

This paper presents a robust speed control method of induction motors(IM) using a Non-linear PI controller(NPI). NPI is high gain controller in region of small error, and low gain controller in region of large error. So in steady state, system will be robust against variation of load torque. The simulation and experiment results confirm the validity of proposed control scheme.

• Proceedings of the KIPE Conference
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• 2014.11a
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• pp.135-136
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• 2014

본 논문은 계통연계형 인버터를 위한 비례공진제어 기반의 케스케이드전류-전압 제어기 설계에 대해 다루고있다. 인버터가 계통연계모드로 동작할 때 인버터는 계통의 보조 전력원으로서의 역할을 하기 때문에 전류원으로 정의된다. 이때 LCL 필터가 연결된 계통연계형 인버터의 출력 LC 단에 비선형 지역적 부하가 연결될 경우 기존의 단일 전류 제어기만으로는 비선형 부하로 인한 고조파 왜곡에 대처하기 힘들고 독립운전모드와의 모드절환시 매끄러운 과도 특성을 보장하기 힘들다. 따라서 본 논문에서는 비례다중공진제어기를 활용한 내부 출력 전압, 외부 출력 전류 루프로 구성된 케스케이드 전류-전압 제어기를 제안하였고 제안된 방식이 고조파 보상과 모드 절환시의 매끄러운 과도 특성에 효력을 보임을 PSIM 시뮬레이션을 통해 검증하였다.

• Education of Primary School Mathematics
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• v.15 no.2
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• pp.59-75
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• 2012

This study aims to find whether the solutions for well-structured problems learned in school can be transferred to the moderately-structured problem and ill-structured problem. For these purpose, research questions were set up as follows: First, what are the patterns of changes in strategies used in solving the mathematics problems with different level of structuredness? Second, From the group using and not using proportion algorithm strategy in solving moderately-structured problem and ill-structured problem, what features were observed when they were solving that problems? Followings are the findings from this study. First, for the lower level of structuredness, the frequency of using multiplicative strategy was increased and frequency of proportion algorithm strategy use was decreased. Second, the students who used multiplicative strategies and proportion algorithm strategies to solve structured and ill-structured problems exhibited qualitative differences in the degree of understanding concept of ratio and proportion. This study has an important meaning in that it provided new direction for transfer and analogical problem solving study in mathematics education.