• Journal of Elementary Mathematics Education in Korea
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• v.24 no.1
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• pp.53-87
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• 2020

The purpose of this study was to find a future direction for improving computational estimation instruction through examining the contents of computational estimation included in the 2015 revised elementary school mathematics curriculum and elementary school mathematics textbook and teacher's guide. Through this, several suggestions was made as follow. Firs, it is necessary to emphasize the computational estimation across all grade groups. Second, it is necessary to teach the computational estimation strategies systematically. It was found that it is necessary to reinforce the activities related to computational estimation in the computation related units.

• Communications of Mathematical Education
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• v.9
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• pp.177-186
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• 1999

본고에서는 먼저 어림과 근사값의 의미를 고찰한다. 그리고 근사값과 어림수 사이의 관계를 살펴보고 1940년대 초등학교 5학년에서의 어림수의 곱셈과 나눗셈에 대한 지도 방법과 현행 중학교 교육과정에서의 근사값의 곱셈과 나눗셈의 지도 방법을 살펴본다. 이들을 살펴봄으로써 어림과 근사값을 지도하는 의의를 강조하고 어림셈과 근사값 계산에 대한 교수 ${\cdot}$ 학습 자료로서 제시하고자 한다.

• Education of Primary School Mathematics
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• v.1 no.2
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• pp.149-161
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• 1997

기술 공학 및 수학 학문 자체의 발전으로 인하여 논리성 개발뿐만 아니라 사고력을 개발하고, 일상 생활에 유용한 학습 내용들이 학교 수학에 도입되고 있다 수학 학습의 이러한 변화의 측면에서 보면, 어림은 사고력 개발이나 일상생활에서의 유용성에 많은 도움이 될 수 있는 수학 학습의 한 영역이다. 그러나 하나의 정확한 답을 구하는데 익숙해 있는 아동들은 오차를 포함하는 어림 값을 문제에 대한 답으로 수용하는 것을 어려워하며, 어림을 사용해서 문제를 해결할 때 문제에 대한 답이 여러 개 있을 수 있음을 인정하지 못한다. 또 어떤 경우에는 정확한 계산을 한 후 그 결과를 반올림해서 어림 값을 구한다. 이러한 형태의 어림 학습은 어림의 유용성을 충분히 인식시키거나 효율적으로 어림하는 감각이나 융통성 있는 사고를 개발하지 못해 아동들로 하여금 어림을 귀찮고 성가신 것으로 생각하게 한다.

• Journal of The Korean Association For Science Education
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• v.24 no.5
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• pp.814-824
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• 2004

This article presents the effects of estimation activities related to speed and density on students' concept-understanding, answer-prediction, and answer-calculation in problem solving procedure with quantitative and qualitative methods. Participants were one hundred and ninety two seventh graders from one coeducational school in Seoul. Half of them participated in the estimation activities and the other half did in the measurement activities. Discussions of three students during estimation activities on density and their post-interviews were tape-recorded. Pre- and post-assessment scores were analyzed for the whole classes, and students' discussions and interviews served this research as evidences for the case analysis. Results of scores indicated that students in the estimation activities were significantly better than those in the measurement activities for predicting answers, but not for understanding concepts. Analysis of the cases revealed that estimation activity helped them to understand the relations of mass, volume and density, empirically, which enhanced their prediction ability. Furthermore, the ability could help a student with low calculation ability to comprehend the calculation problems. Thus, it is concluded that estimation activities could influence students' empirical learning on quantitative concepts, which enhanced their prediction ability.

• Journal of Elementary Mathematics Education in Korea
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• v.15 no.1
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• pp.1-18
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• 2011

The purpose of this study was to investigate the effects of estimation strategy on placing decimal point in multiplication and division of decimals. To examine the effects of improving calculation ability and reducing decimal point errors with this estimation strategy, the experimental research on operation with decimal was conducted. The operation group conducted the decimal point estimation strategy for operating decimal fractions, whereas the control group used the traditional method with the same test paper. The results obtained in this research are as follows; First, the estimation strategy with understanding a basic meaning of decimals was much more effective in calculation improvement than the algorithm study with repeated calculations. Second, the mathematical problem solving ability - including the whole procedure for solving the mathematical question - had no effects since the decimal point estimation strategy is normally performed after finishing problem solving strategy. Third, the estimation strategy showed positive effects on the calculation ability. Th Memorizing algorithm doesn't last long to the students, but the estimation strategy based on the concept and the position of decimal fraction affects continually to the students. Finally, the estimation strategy assisted the students in understanding the connection of the position of decimal points in the product with that in the multiplicand or the multiplier. Moreover, this strategy suggested to the students that there was relation between the placing decimal point of the quotient and that of the dividend.

• Composites Research
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• v.25 no.4
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• pp.117-125
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• 2012

Warpage of the film insert molded (FIM) part is caused by an asymmetric residual stress distribution. Asymmetric residual stress and temperature distribution is generated by the retarded heat transfer in the perpendicular direction to the attached film surface. Since warpage was not prevented by controlling injection molding conditions, glass fiber (GF) filled composites were employed as substrates for film insert molding to minimize the warpage. Distribution of short GFs was evaluated by using micro-CT equipment. Proper models for micro mechanics, anisotropic thermal expansion coefficients, and closure approximation should be selected in order to calculate fiber orientation tensor and warpage of the FIM part with the composite substrate. After six kinds of micro mechanics models, three models of the thermal expansion coefficient and five models of the closure approximation had been considered, the Mori-Tanaka model, the Rosen and Hashin model, and the third orthotropic closure approximation were selected in this study. The numerically predicted results on fiber orientation tensor and warpage were in good agreement with experimental results and effects of GF reinforcement on warpage of the FIM composite specimen were identified by the numerical results.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.1
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• pp.97-107
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• 2015

An analytical model was developed to estimate the viscous and squeeze-film damping ratios of heat exchanger tubes subjected to a two-phase cross-flow. Damping information is required to analyze the flow-induced vibration problem for heat exchange tubes. In heat exchange tubes, the most important energy dissipation mechanisms are related to the dynamic interaction between structures such as the tube and support and the liquid. The present model was formulated considering the added mass coefficient, based on an approximate model by Sim (1997). An approximate analytical method was developed to estimate the hydrodynamic forces acting on an oscillating inner cylinder with a concentric annulus. The forces, including the damping force, were calculated using two models developed for relatively high and low oscillatory Reynolds numbers, respectively. The equivalent diameters for the tube bundles and tube support, and the penetration depth, are important parameters to calculate the viscous damping force acting on tube bundles and the squeeze-film damping forces on the tube support, respectively. To calculate the void fraction of a two-phase flow, a homogeneous model was used. To verify the present model, the analytical results were compared to the results given by existing theories. It was found that the present model was applicable to estimate the viscous damping ratio and squeeze-film damping ratio.

• Journal of Educational Research in Mathematics
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• v.19 no.4
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• pp.513-530
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• 2009

In this paper, We analyse the contents of the national mathematical curriculum, the handbook of the curriculum, and elementary school mathematics textbook for the elementary school grade 1-2 focusing on 'number sense'. At first, we identify the meaning and the elements of number sense through analysing studies which are related to number sense. Number sense includes understanding the meaning of number, operation, and estimation, and the ability of applying numbers, operation and estimation on the context. Number sense consists of the elements of the contents and the elements of the processes. Secondly, with the elements of number sense which we have identified, we analyse the contents of the national mathematical curriculum, the handbook of the curriculum, and elementary school mathematics textbooks, and then criticize the contents. We find some problems as a result of the analysis : the range of number sense is unclear, the word 'number sense' is not used consistently, the elements used are limited, and the contents of the textbook are materialized inconsistently and poorly.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.26 no.5
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• pp.285-291
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• 2014

The statistical information of the coastal water temperature monitoring data can be biased because of outliers and missing intervals. Though a number of outlier detection methods have been developed, their applications are very limited to the in-situ monitoring data because of the assumptions of the a prior information of the outliers and no-missing condition, and the excessive computational time for some methods. In this study, the practical robust method is developed that can be efficiently and effectively detect the outliers in case of the big-data. This model is composed of these two parts, one part is the construction part of the approximate components of the monitoring data using the robust smoothing and data re-sampling method, and the other part is the main iterative outlier detection part using the detailed components of the data estimated by the approximate components. This model is tested using the two-years 5-minute interval water temperature data in Lake Saemangeum. It can be estimated that the outlier proportion of the data is about 1.6-3.7%. It shows that most of the outliers in the data are detected and removed with satisfaction by the model. In order to effectively detect and remove the outliers, the outlier detection using the long-span smoothing should be applied earlier than that using the short-span smoothing.

• Progress in Medical Physics
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• v.9 no.4
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• pp.195-200
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• 1998

Purpose: When an elongated x-ray field is used for treating a patient, the equivalent- field method is commonly used for the output calculation. This study is intended for investigating potential factors such as, beam quality, field elongation ratio, and depth of measurement, which might effect on the applicability of the equivalent square technique for output calculation. The derivation of a 'rule of thumb' for the application criteria of the equivalent-field method is also aimed. Materials and Methods: Three x-ray beams, 4-, 6- and 10-MV, were employed for this study. Width of the rectangular field was ranged from 5-40 cm and the elongation ratio (length/width) 1:0 to 10:0. An elongation effect was measured in a water phantom at three different depths, dmax, 5-cm, and 10-cm. For an elongated field and its equivalent square field, the output factor was measured and the difference in the output factor were examined between two fields. Results and Discussions: As the elongation ratio increases, a larger discrepancy in outputs is observed between the elongated rectangular field and its corresponding equivalent square field. Output was measured larger for an elongated field than for its corresponding equivalent square field and the maximal difference over 10 % was found. The difference was found larger for the smaller field with the same elongation ratio. The effect of the beam quality and the depth of measurement on the output difference was minimal. Conclusion: Based on the study, there is criteria for the application of the method for output calculation. For the combination of long axis and elongation ratio whose relationship satisfies Elongation ratio < (0.48) (Long axis) - 0.5, the equivalent-field method is valid for output calculation within 2 % for the field whose long axis < 25-cm. For other combinations, instead of using the equivalent-field method, direct output measurement is recommended. This criteria can be applied for 4-10 MV x-ray beams up to 10-cm depth.